cheap, plentiful coal is expected to fuel power plants forthe …ceweb/courses/che119/... · 2009....
TRANSCRIPT
OVERV IEW
-- Coal is widely
burned for power but produces large quan t ities of climateshychanging carbon Dioxide_
ii Compared with conventiona l power plan ts new gasificashyshytion fac il ities can more effectivel~ and affordably extract C02 so it can be safe ly stored underground _
ii The world must begin implementing carbon captu re and storage soon to stave off global warming
Cheap plentiful coal is expected to fuel power plants forthe
foreseeable future but can we keep it from devastating the environment
BY DAVID G HAWKINS DANIEL A LASHOF AND ROBERT H WILLIAMS
68 SCIENTIFIC AMERI CAN
More than most people realize dealing with climate change means addressing the problems posed by emissions from coal-fired power plants Unless humanity takes prompt action to strictly
limit the amount of carbon dioxide (C02) released into the atmosphere when con suming coal to make electricity we have little chance of gaining control over global warming
Coal-the fuel that powered the Industrial Revolution-is a particularly worrisome source of energy in part because burning it produces considerably more carbon diox ide
per unit of electricity generated than burning either oil or natural gas does In addishytion coal is cheap and will remain abundant long a fter oil and natural gas have
become very sca rce With coal plentiful and inexpensive its use is burgeoning in the US and elsewhere and is expected to continue rising in areas with
abundant coal resources Indeed US power providers are expected to
build the equivalent of nearly 280 SOO-megawatt coal-fired electricshyity plants between 2003 and 2030 Meanwhile China is already
constructing the equivalent of one large coal-fueled power station a week Over their roughly 60-year life spans the
new genera ting facilities in operation by 2030 could collectively introduce into the atmosphere about as
much ca rbon dioxide as was re leased by all the
SCIENTIFIC AMERICAN 69 I r
coal burned since the dawn of the Indusshytrial Revolution
Coals projected popularity is disturbshying not only for those concerned about climate change but also for those worried about other aspects of the environmen t and abo ut huma n hea lth and safe ty Coals market price may be low but the true costs of its extraction processing and consumption are high Coal use can lead to a range of harmful consequences including decapitated mountains air polshylution from acidic and toxic emissions and water fouled with COol I wastes Exshytraction also endangers and ca n kill minshyers Together such effects make coal pro- duction and conversion to useful energy one of the most destructive activities on the planet [see box on page 73 ]
In keeping with Scientific Amerishycans focus on climate concerns in this is sue we will concentrate below o n methods that can help prevent C02genshyerated during coal conversion from reaching the atmosphere It goes withshyout saying that the env ironmental safeshyty and health effects of coal production and use must be reduced as well Fortushynately affordable techniques for adshydressing C02 emissions and these other problems a lready exist although the will to implement them quickly still lags significantly
Geologic Storage Strategy TI-IE TEC HNIQU ES that powcrprovidshyers could apply to keep most of the carshybon diox ide they produce from entering the air are co llec tively called C02 capshyture and storage (CCS) or geologic carshybon sequ es trati on These procedures involve se parat ing out much of the C02 that is created when coa l is converted to useful energy a nd tra nsporting it to sites where it can be stored deep underground in porous media-mainly in depleted oil or gas field s or in sa line form ations (pershymeable geologic strata filled with salty water) [see Can We Bur y Global Warming by Robert H Socolow SCIshyENT FIC AM ERICAN July 2005]
All the technological components needed for CCS at coal conversion plants are commercially ready-having been proved in applications unrelated to clishy
70 SCIENTIFiC AMERICAN
mate change mitigation although inte shygrated systems have not yet been conshystructed at the necessary scales Captu re technologies have been deployed extenshysively throughout the world both in the manufacture of chemicals (s uch as fertilshyizer) and in the purification of natural gas supplies contaminated with carbon dioxshyide and hydrogen sulfide (so ur gas) Industry has gained considerable experishyence with C02 storage in operations that purify natural gas (mainly in Canad a) as well as with C02 injection to boost oil production (primarily in the US) Enshyhanced oil recovery processes account for most of the C02 that has been sent into
Affordable methods that prevent CO2
from reaching the atmosphere exist the will to implement them
quickly lags r
I
underground reservoirs Currently about 35 million metric tons are injected annushyally to coax more petroleum out of mashyture fields accounting for about 4 pershycent of US crude oil output
Implementing CCS at coa l-consu mshying plants is imperative if the carbon dishyoxide concentration in the atmosphere is to be kept at an acceptable level The 1992 United N ations Framework Conshyvention on Climate Change calJs for stashybilizing the atmospheric C02 concentrashytion at a safe level but it does not specshyify what the ma ximum value should be The current view of man y scientists is that atmospheric C0 2 level s must be kept below 450 parts per million by volume (ppmv) to avoid unaccepta ble climate changes Rea lization of this aggressive goa l requires that the power industry start commercial- sca le C CS p roj ec ts
within the next fe w years and expand them rapidly thereafter Thi s stabilizashytion benchmark cannot be real ized by CCS a lone but can plausibly be achieved if it is combined with other eco-friend ly measures such as wide improvements in energy efficiency a nd much expanded use of renewable energy sources
The Intergovernmenta l Panel on C lishymate Change (IPCC) estimated in 2005 that it is highly probable that geolog ic media worldwide are capa ble of sequesshytering at leas t two trillion metric tons of C02-more than is likely to be produced by fossil-fuel-con suming plants during the 21st century Society will want to be sure however that potential sequestrashytion sites are evaluated carefully for their ability to retain C02 before they are alshylowed to operate Two classes of risks are of concern sudd en escape and gradshyualleakage
Rapid outflow of large amounts of C02 could be lethal to those in the vi shycinity Da ngero us sudden releases-such as that which occurred in 1986 at Lake Nyos in Cameroon when C02 of volcashynic origin asphyxiated 1700 nearby vilshylagers and thousands of cattle-are imshyprobable for engi neered C02 storage proj ects in carefully selected deep poshyrous geologic formations accord ing to the IPCe
Gradual seepage of carbon dioxide into the ai r is also an issue because over time it could defeat the goa l of CCS The 2005 IPCC report estimated that the fraction re tained in appropriately selectshyed and managed geo logic reservoirs is very likely to exceed 99 percent over 100 years and likely to exceed 99 percent over 1000 years What remains to be demonshystrated is whether in practice operators can routinely keep C02 leaks to levels that avoid unacceptable environmental and public heal th risks
Technology Choices DES IG N 5 TU DIE S indicate that existing power generation tech nologies could capshyture fro m 85 to 95 percent of the carbon in coal as C02 with the rest released to the atmosphere
The coal convers ion technologies that come to dominate w ilJ be those that
SEPTEMBER 2006
To slow climate change the authors urge power providers to build
integrated gasifi cation combined cycle [IGCC] coal power plants
with carbon dioxide capture and storage [CCS] capabilities
[below] rather than conventional steam -elect ric facilities
Conventional coal plants burn the fuel to transform water into
steam to turn a turbine-generator If CCS technology were applied
to a steam plant C02 would be extracted from the flue exhaust
An IGCC plant in contrast employs a partial oxidation reaction
using limited oxygen to convert the co al into a so-ca lled
synthesis gas or syngas [mostly hydrogen and carbon
mono xide] lt is much easier and less costly to remove CO 2 from
syngas than from the flue gases of a steam plant The hydrogenshy
rich syngas remainingafterC02 extraction is then burned to run
both gas and steam turbine-generators The wor ld s first
commerciallGCC project that will sequester C02 underground is
being planned near Long Beach Calif
C02 EXTRACTION 2 The syngas is reacte d with steam to produce a gaseous mixture of mostly carbon dioxide and hydrogen [H 2 ] from which CO 2 is extracted for burial [yellow pathways at bottom]
GASIFICATION 1 Coal water and oxygen are fed into a high-pressure gasifier in which the coal is partially oxmiddotidized and converted into syngas
CO 2 is compressed and middotsent via pipeline systems to permanent underground storage sites
3 Hydrogen-rich syngas is burned and the combustion products drive a gas turb ine-generator
4 The hot gas turbine exhaust passes to a heat-recovery steam generator which converts water to steam that turns a steam turbine-generator
C02 can be sent into saline formations-saltwatermiddot filled strata capped with impermeable rock
wwwsciam_com SCIENTIFIC AMERICAN 71
can meet the objectives of climate change mitigation at the least cost Funshydamenta lIy different approaches to ees would be pursued for power plants usshying the conventional pulverized-coal steam cycle and the newer integrated gasification combined cycle (IGee) Alshythough todays coal IGee power (with C02 venting) is slightly more expensive than coal steam-electric power it looks like IGee is the most effective and least expensive option for ees
Standard plants burn coal in a boiler at atmospheric pressure The heat genshyerated in coal combustion transforms water into steam which turns a steam turbine whose mechanica I energy is converted to electricity by a generator In modern plants the gases produced by combustion (flue gases) then pass through devices that remove particushylates and oxides of sulfur and nitrogen before being exhausted via smokestacks into the air
Carbon dioxide could be extracted from the flue gases of such steam-elecshytric plants after the removal of convenshytional pollutants Because the flue gases contain substantial amounts of nitrogen (the result of burning coal in air which is about 80 percent nitrogen) the carshybon dioxide would be recovered at low concentration and pressure-which imshyplies that the C02 would have to be reshymoved from large volumes of gas using processes that are both energy-intensive and expensive The captured C02 would then be compressed and piped to an apshypropriate storage site
In an IGee system coal is not burned but rather partially oxidized (reacted with limited quantities of oxygen from
DAVID G HAWKI NS DANIEL A LASH OF and ROBERT H WILLIAMS have endeavored to help
stave off climate change problems for decades Hawkins is director of the Climate Center
at the Natural Resources Defense Council (NRDCJ where he has worked on air energy
and climate issues for 35 years Hawkins serves on the boards of many bodies that advise
government on environmental and energy subjects Lashof is science director and depmiddot
uty director of the NRDCs Climate Center at which he has focused on national energy
policy climate science and solutions to global warming since 1989 Before arriving at the
NRDC Lashof developed policy options for stabilizing global climate at the US Environmiddot
mental Protection Agency Williams is a se nior research scientist at Princeton Un iversity
which he joined in 1975At the universitys Princeton Environmentallnstitute he heads
the Energy Systems Policy Analysis Group and the Carbon Capture Group under the inmiddot
stitutes Carbon Mitigation Initiative (which is supported by BP and Ford)
72 SCIENTIFIC AMERICAN
Commercial power plants using IGCC technology such as this one in Italy have been operating since 1994 Togetherthey generate 3600 megawatts of electricity
an air separation plant and with steam) at high pressure in a gasifier The prodshyuct of gasification is so-called synthesis gas or syngas which is composed mostshyly of carbon monoxide and hydrogen undiluted with nitrogen In current practice IGee operations remove most conventional pollutants from the syngas and then burn it to turn both gas and steam turbine-generators in what is called a combined cycle
In an IGee plant designed to capshyture C02 the syngas exiting the gasifier after being cooled and cleaned of parshyticles would be reacted with steam to produce a gaseous mixture made up mainly of carbon dioxide and hydrogen The C02 would then be extracted
dried compressed and transported to a storage site The remaining hydrogenshyrich gas wou ld be bu rned in a combined cycle plant to generate power [see box on preceding page]
Analyses indicate that carbon dioxshyide capture at Ieee plants consuming high-quality bituminous coals would entai I significantly sma ller energy and cost penalties and lower total generashytion costs than what could be achieved in conventional coal plants that capshytured and stored C02 Gasification sysshytems recover CO2 from a gaseous stream at high concentration and pressure a feature that makes the process much easier than it would be in conventional steam facilities (The extent of the ben shyefits is less clear for lower-grade subbishytuminous coals and lignites which have received much less study) Precombusshytion remova I of conventional pollutants including mercury makes it feasible to realize very low levels of emissions at much reduced costs and with much smaller energy penalties than with cleanup systems for flue gases in convenshytional plants
Captured carbon dioxide can be transported by pipeline up to several hundred kilometers to suitable geologic storage sites and subsequent subterrashynean storage with the pressure produced during capture Longer distances may however require recompression to comshypensate for friction losses during pipe shyline transfer
Overall pursuing ees for coa I powshyer facilities requires the consumption of more coal to generate a kilowatt-hour of electricity than when C02 is ventedshyabout 30 percent extra in the case of coal steam-electric plants and less than 20 percent more for IGee plants But overall coal use would not necessarily increase because the higher price of coal-based electricity resulting from adding ees equipment would dampen demand for coal-based electricity rna kshying renewable energy sources and enershygy-efficient products more desirable to consumers
The cost of ees will depend on the type of power plant the distance to the storage site the properties of the storage
SEPTEMBER 2006
II reservoir and the availability of opporshy cost would occur as long as the oil price ed policies for climate change mitigation tunities (such as enhanced oil recovery) is at least $35 per barrel which is much that would make CCS cost-effective for for selling the captured C02 A recent lower than current prices uses not associated with enhanced oil study co-authored by one of us (Wilshy recovery Absent revenues from sales to
liams) estimated the incremental electric CCS Now or Later oil field operators applying CCS to new generation costs of two alternative CCS MANY ELECTR1CITY producers in coal plants using current technology options for coal IeCC plants under typshy the industria I world recognize that enshy would be the least-cost path only if the ical production transport and storage vironmental concerns will at some point cost of emitting C02 were at least $25 conditions For C02 sequestration in a force them to implement CCS if they are to $30 per metric ton Many current saline formation 100 kilometers from a to continue to employ coal But rather policy proposals for climate change mitshypower plant the study calculated that than building plants that actually capshy igation in the US envision significantly the incremental cost of CCS would be ture and store carbon dioxide most lower cost penalties to power providers 19 cents per kilowatt-hour (beyond the plan to construct conventional steam for releasing C02 (or similarly payshygeneration cost of 47 cents per kilowattshy facilities they claim will be C02 capshy ments for C02 emissions-reduction hour for a coal IeCC plant that vents ture ready-convertible when CCS is credits) C02-a 40 percent premium) For CCS mandated Yet delaying CCS at coal power pursued in conjunction with enhanced Power providers often defend those plants until economy-wide carbon dioxshyoil recovery at a distance of 100 kilomeshy decisions by noting that the US and ide control costs are greater than CCS ters from the conversion plant the analshy most other countries with coal-intensive costs is shortsighted For several reashyysis finds no increase in net generation energy economies have not yet institut- sons the coal and power industries and
- I I I e I i L I
Despitethe current popularity of the term clean coal coal is in factdirty Although carbon capture and storage could prevent much carbon dioxide fromentering the atmosphere coal production and consumption is still oneaf the most destructive industrial processes As long as
thewbrld copsumescoal more must be done to mitigate the harm it causes
MINING DANGERS Underground mining can cause serious problems on the
Coal mining is among the most dangerous occupations Official surface Mines collapse and cause land subsidence
reports for 2005 indicate that roughly 6000 people died damaging homes and roads Acidic mine drainage caused by
(16 a day) in China from coal mine floods iave~ins fires and slJlfur compounds leaching from coal waste into surface
explosions Unofficial estimates are waters has tainted thousands of
closer to 10000 Some 600000 streams The acid leachate releases
Chinese toal minegtrsslJfferfrom heavy metals that foul groundwater
black lung disease The Us has better safety TOXIC EMISSIONS
Coalmiddotfired power plants account for
all-time low of 22 domestic fatalities practices thanChina and achieved an
more than two thirds of sulfur dioxide
in 2005 US mines are far from middot andabout one fifth of nitrogen oxide
perfect however as evidenced by a middot emissions in the US Sulfur dioxide
series offatalities inearly 2006 reacts in the atmosphere to form middot sulfate particles which in addition to
ENVIRONME~TAL EFFECTS middot causing acid rain contribute to fine
Conventiona-l coal mining proces~ing particulate pollution a contaminant
and transportation practices scar linked to thousands of premature
the landscape and pollute the water which harms people and deaths from lung disease nationwide Nitrogen oxides combine
eCosystems The most destructive mining teChniques Clear with hydrocarbons to form smog-causingground-Ievel ozone
forests and blast away mountaintops The overburden Coalmiddotburning plants ltllso emit approximately 48 metric
removed when a coal seam is uncovered middotis typically dumped tons of mercury a year in America Thishighly toxic element
into nearby valleyswhere it often buries rivers andstreams persists in the ecosystem Aftertransforming into methyl
Stripmiddotmining operations rip apart ecosystems and reshape mercury it accum ulates in the tissues offishes Ingested
the landscape Although regulations require landreclamatipn mercury is particularly detrimental to fetuses andyoung
in principle it is often left incomplete Asforests are replaced infants exposed during periods of rapid brain growth causing
with nonnative grasslands soils become compacted and developmental and neurOlogical damage
streams contaminated -DGH DAL and RHW
wwwsciamcom SCIENTIFIC AMERICAN 73
pound Acid runoff from a Pennsylvania coal mine stains this creek bed orange
--_bull 1
THE PATH TO C02MITIGATION Our calculations indicate that a prompt commitment to carbon capture and storage
[eeS) would make it possible to meet global energy demands while limiting the
atmospheric carbon dioxide concentration to 450 parts per million by volume [ppmv)
This goal could be attained if by midcentury sequestration is applied for all coal use
and about a quarter of natural gas use while energy efficiency increases rapidly and
carbon-free energy sources expand sevenfold Under these conditions overall fossilshy
fuel consumption could expand modestly from today by midcentury coal use could be
somewhat higher than at present oil use would be down by a fifth and natural gas use
would expand by half
To realize this pathway growth rates for fossil-fuel use would have to be reduced
now and ee Smust begin for coal early in the next decade and for natural gas early in
the next quarter of a century The top graph below depicts the energy provided by the
various sources if this mitigation path were followed The bottom graph shows total
quantities of carbon extracted from the earth [emissions plus storage)
-DGH DAL and RHW
FOSSIL AND CARBON-FREE ENEmiddotRGY MIX FOR C02 STABILIZATION
35 Additional carbon-free energ~ needed to satisfy demand
30 Oil
~ bull Natural gas with CCS cu ~ 25 Natural gas with C02 vented ~ bull Coal with CCS ~ 20 Coal with C02 vented ~ eo c
IJJ 15 ~ cu
sect Q
10
5
0 2010 2030 2050 2070 2090
FATE OF CARBON FROM FOSSIL ENERGY SYSTEMS
cu 10 ~
n cu
c 8B cu on On
c 0 5 -e cu u ~ 4e IJJ
0 ~
tgt 2 0 Vi
0 I i i 2010 2030 2050 2070 2090
Year
74 SCIENTIFIC AMERICAN
bull Natural gas C stored
NalUral gas C emitted
Coal C emitted
Emissions level needed to stabilize C02at 450 ppmv
bull Coal carbon [C) stored
society would ultimately benefit if deshyployment of plants fitted with CCS equipment were begun now
First the fastest way to reduce CCS costs is via learning by doing-the acshycumulation of experience in building and running such plants The faster the understanding is accumulated the quicker the know-how with the new technology will grow and the more rapshyidly the costs will drop
Second installing CCS equipment as soon as possible should save money in the long run Most power stations curshyrently under construction will still be opshyerating decades from now when it is likely that CCS efforts will be obligatory Retrofitting generating faciliti es for CCS is inherently more expensive than deshyploying CCS in new plants Moreover in the absence of C02 emission limits fashymiliar conventional coal steam-electric technologies will tend to be favored for most new plant construction over newer gasification technologies for which CCS is more cost-effective
Finally rapid implementation would allow for continued use of fossil fuels in the near term (until more environmenshytally friendly sources become prevalent) without pushing atmospheric carbon dioxide beyond tolerable levels Our studies indicate that it is feasible to stashybilize atmospheric C02 levels at 450 ppmv over the next half a century if coal-based energy is completely decarshybonized and other measures described in the box at the left are implemented This effort would involve decarbonizing 36 gigawatts of new coal generating cashypacity by 2020 (corresponding to 7 pershycent of the new coal capacity expected to be built worldwide during the decade beginning in 2011 under business-asshyusual conditions) In the 35 years after 2020 C02 capture would need to rise at an average rate of about 12 percent a year Such a sustained pace is high compared with typical market growth rates for energy but is not unprecedentshyed It is much less than the expansion rate for nuclear generating capacity in its heyd ay-1956 to 1980-during which global capacity rose at an average rate of 40 percent annually Further the
SEPTEMBER 2005
expansion rates for bo th wind a nd sola r photovoltaic power capaci ties worldshywide have hovered around 30 percent a year since the ea rly 1990s In a ll three cases such growth would not have been practical without public policy mea shysures to suppor t them
Our calculations indica te that the costs of CCS deployment would be manshyageable as well Using conservative assumptions-such as that technology will not improve over time-we estimate that th e present worth of the cost of capturing and storing all C02produced by coal-based electricity generation pla nts du ring the next 200 years will be $18 triiJion (in 2002 dollars) That might seem like a high price tag but it is equivalent to just 007 percent of the curren t value of gross world prod uc t over the same interva l Thus it is plaushyslble that a rapid decarbonization path for coal is both phys ica lly and economshyically feasible although deta iled regionshya l analyses are needed to confirm thi s conclusion
Policy Push Is Nee d THO SE GOO D R EASO N S for comshymencing concerted CCS efforts soon will probably not move the industry unshyless it is a lso prodded by new public polshyicies Such initiatives would be part of a broader d rive to control carbon dioxide emissions from a ll sou rces
In the US a nat ional program to limit C02 emissions mu st be enac ted soon to introduce the government regshyu lat ions a nd market incentives necshyessary to shift investment to the leastshypolluting energy technologies promptly and on a w ide scale Leaders in the American business and policy commushynities increasi ngly agree that quantifi shyable a nd enforceable rest r ictions on global warming emissions are imperashytive and inev ita ble To ensure that powshyer companies put into practice the reshyductions in a cost-effective fashion a market for trading C02emissions credshyits shou ld be created-one similar to that for the sulfur emissions that cause acid rain In such a plan organizations that intend to exceed designated emisshysion limits may buy cred its from others
www s ciamcom
that are able to stay below these va lues Enhancing energy efficienc y efforts
and raising renewable energy producshyti on are cri tical to achieving carbon dishyox ide limits at the lowes t possible cost A po rtion of the emission a llowances created by a carbon cap-and-trade proshygram shou Id be a llocated to the es tabshylishment of a fund to help overcome inshystitutional ba rriers and technica l r isks that obstruct widespread deployment of otherwise cost-effective C02 mitigation technologies
=
Delaying carbon capturemiddot
and storage at coal power
plants is shortsighted
Even if a carbon dioxide cap-andshytrade program were enacted in the next few yea rs the econom ic value of C02 emissions reduction may not be enough initially to convince power providers to invest in power systems with CCS To avoid the construction of another genshyeration of conventional coa l plants it is essential that the fed eral government esshytablish incentives that promote CCS
One ap proach would be to insist that an increasing share of total coal-based
MORE TO EXPLORE
electricity generation comes from faci lishyties that meet a low C02 emissions stanshydard-perhaps a maximum of 30 grams of carbon per k ilowatt-hour (a n achievshyable goal using todays coal CCS techshynologies) Such a goa l might be ach ieved by obliging electricity producers that use coal to include a growing fraction of decarbon ized coal power in thei r supply portfolios Each covered electricity proshyducer could either generate the required amount of decarbonized coal power or purchase decarbonized-generation credshyits Th is sys tem would share the increshym en tal costs of CCS for coal power among all US coal-based electricity producers and consumers
If the surge of conventional coa lshyfired power plants currently on drawing boa rds is built as planned atmospheric carbon dioxide levels will almost cershytainly exceed 450 ppmv Vle can meet global energy needs while st ill stabili zshying C02 at450 ppmv however through a combination of improved efficiency in energy use greater reliance on renewshyable energy resources and for the new coal investments that are made the inshystallation of C02 capture and geolog ic storage technologies Even though there is no such thing as clean coal more can and must be done to reduce the danshygers and environmental degradations associated with coal production and use An integrated low-carbon energy strategy that incorporates C02 capture and storage can reconcile substantia I use of coa l in the coming decades with the imperatlve to prevent catastro phic changes to the earths climate m
_
How to Clean Coal C Can ine in OnEarth Nat ural Resollrces Defense Council 200 5 Avail able at wwwnrdcorgonearth OSfallcoallasp
IPCC Special Report on Carbon Capture and Storage 2005 Avqilable at http archrrvm n I env Ii ntipcc pages_medi alSRC CS-fi n a II IPCC Spec ial Reporton Carbon d i oxideC apt urea ndSt 0 rage htm
Avoiding Dangerous Climate Change ~ditec1 by H J Sch ellnhuber W Cramer N Nallicenovic T Wigley and G Yoh e Cambridge University Press 2006
Big Clal The Dirty Secret behind America s Energy Future J Goodell Houghton Mifflin 20 06
Carbo~ Dioxide Capture andG~ologic Storage J J Doniey RTGahowski C L David so n M A Wise N Gupt a S H Kim and E L Malone Tec hnology Report from the Second Phase of the Global Energy Technology Strategy Program 2006
Natural Resou rces Defense Council Web si te wwwnrdcor~globalwarming
PrincetonEnvironmentallnstitute Web site wwwprincet on edu-cmi
SCIENTIFIC AMERICAN 75
More than most people realize dealing with climate change means addressing the problems posed by emissions from coal-fired power plants Unless humanity takes prompt action to strictly
limit the amount of carbon dioxide (C02) released into the atmosphere when con suming coal to make electricity we have little chance of gaining control over global warming
Coal-the fuel that powered the Industrial Revolution-is a particularly worrisome source of energy in part because burning it produces considerably more carbon diox ide
per unit of electricity generated than burning either oil or natural gas does In addishytion coal is cheap and will remain abundant long a fter oil and natural gas have
become very sca rce With coal plentiful and inexpensive its use is burgeoning in the US and elsewhere and is expected to continue rising in areas with
abundant coal resources Indeed US power providers are expected to
build the equivalent of nearly 280 SOO-megawatt coal-fired electricshyity plants between 2003 and 2030 Meanwhile China is already
constructing the equivalent of one large coal-fueled power station a week Over their roughly 60-year life spans the
new genera ting facilities in operation by 2030 could collectively introduce into the atmosphere about as
much ca rbon dioxide as was re leased by all the
SCIENTIFIC AMERICAN 69 I r
coal burned since the dawn of the Indusshytrial Revolution
Coals projected popularity is disturbshying not only for those concerned about climate change but also for those worried about other aspects of the environmen t and abo ut huma n hea lth and safe ty Coals market price may be low but the true costs of its extraction processing and consumption are high Coal use can lead to a range of harmful consequences including decapitated mountains air polshylution from acidic and toxic emissions and water fouled with COol I wastes Exshytraction also endangers and ca n kill minshyers Together such effects make coal pro- duction and conversion to useful energy one of the most destructive activities on the planet [see box on page 73 ]
In keeping with Scientific Amerishycans focus on climate concerns in this is sue we will concentrate below o n methods that can help prevent C02genshyerated during coal conversion from reaching the atmosphere It goes withshyout saying that the env ironmental safeshyty and health effects of coal production and use must be reduced as well Fortushynately affordable techniques for adshydressing C02 emissions and these other problems a lready exist although the will to implement them quickly still lags significantly
Geologic Storage Strategy TI-IE TEC HNIQU ES that powcrprovidshyers could apply to keep most of the carshybon diox ide they produce from entering the air are co llec tively called C02 capshyture and storage (CCS) or geologic carshybon sequ es trati on These procedures involve se parat ing out much of the C02 that is created when coa l is converted to useful energy a nd tra nsporting it to sites where it can be stored deep underground in porous media-mainly in depleted oil or gas field s or in sa line form ations (pershymeable geologic strata filled with salty water) [see Can We Bur y Global Warming by Robert H Socolow SCIshyENT FIC AM ERICAN July 2005]
All the technological components needed for CCS at coal conversion plants are commercially ready-having been proved in applications unrelated to clishy
70 SCIENTIFiC AMERICAN
mate change mitigation although inte shygrated systems have not yet been conshystructed at the necessary scales Captu re technologies have been deployed extenshysively throughout the world both in the manufacture of chemicals (s uch as fertilshyizer) and in the purification of natural gas supplies contaminated with carbon dioxshyide and hydrogen sulfide (so ur gas) Industry has gained considerable experishyence with C02 storage in operations that purify natural gas (mainly in Canad a) as well as with C02 injection to boost oil production (primarily in the US) Enshyhanced oil recovery processes account for most of the C02 that has been sent into
Affordable methods that prevent CO2
from reaching the atmosphere exist the will to implement them
quickly lags r
I
underground reservoirs Currently about 35 million metric tons are injected annushyally to coax more petroleum out of mashyture fields accounting for about 4 pershycent of US crude oil output
Implementing CCS at coa l-consu mshying plants is imperative if the carbon dishyoxide concentration in the atmosphere is to be kept at an acceptable level The 1992 United N ations Framework Conshyvention on Climate Change calJs for stashybilizing the atmospheric C02 concentrashytion at a safe level but it does not specshyify what the ma ximum value should be The current view of man y scientists is that atmospheric C0 2 level s must be kept below 450 parts per million by volume (ppmv) to avoid unaccepta ble climate changes Rea lization of this aggressive goa l requires that the power industry start commercial- sca le C CS p roj ec ts
within the next fe w years and expand them rapidly thereafter Thi s stabilizashytion benchmark cannot be real ized by CCS a lone but can plausibly be achieved if it is combined with other eco-friend ly measures such as wide improvements in energy efficiency a nd much expanded use of renewable energy sources
The Intergovernmenta l Panel on C lishymate Change (IPCC) estimated in 2005 that it is highly probable that geolog ic media worldwide are capa ble of sequesshytering at leas t two trillion metric tons of C02-more than is likely to be produced by fossil-fuel-con suming plants during the 21st century Society will want to be sure however that potential sequestrashytion sites are evaluated carefully for their ability to retain C02 before they are alshylowed to operate Two classes of risks are of concern sudd en escape and gradshyualleakage
Rapid outflow of large amounts of C02 could be lethal to those in the vi shycinity Da ngero us sudden releases-such as that which occurred in 1986 at Lake Nyos in Cameroon when C02 of volcashynic origin asphyxiated 1700 nearby vilshylagers and thousands of cattle-are imshyprobable for engi neered C02 storage proj ects in carefully selected deep poshyrous geologic formations accord ing to the IPCe
Gradual seepage of carbon dioxide into the ai r is also an issue because over time it could defeat the goa l of CCS The 2005 IPCC report estimated that the fraction re tained in appropriately selectshyed and managed geo logic reservoirs is very likely to exceed 99 percent over 100 years and likely to exceed 99 percent over 1000 years What remains to be demonshystrated is whether in practice operators can routinely keep C02 leaks to levels that avoid unacceptable environmental and public heal th risks
Technology Choices DES IG N 5 TU DIE S indicate that existing power generation tech nologies could capshyture fro m 85 to 95 percent of the carbon in coal as C02 with the rest released to the atmosphere
The coal convers ion technologies that come to dominate w ilJ be those that
SEPTEMBER 2006
To slow climate change the authors urge power providers to build
integrated gasifi cation combined cycle [IGCC] coal power plants
with carbon dioxide capture and storage [CCS] capabilities
[below] rather than conventional steam -elect ric facilities
Conventional coal plants burn the fuel to transform water into
steam to turn a turbine-generator If CCS technology were applied
to a steam plant C02 would be extracted from the flue exhaust
An IGCC plant in contrast employs a partial oxidation reaction
using limited oxygen to convert the co al into a so-ca lled
synthesis gas or syngas [mostly hydrogen and carbon
mono xide] lt is much easier and less costly to remove CO 2 from
syngas than from the flue gases of a steam plant The hydrogenshy
rich syngas remainingafterC02 extraction is then burned to run
both gas and steam turbine-generators The wor ld s first
commerciallGCC project that will sequester C02 underground is
being planned near Long Beach Calif
C02 EXTRACTION 2 The syngas is reacte d with steam to produce a gaseous mixture of mostly carbon dioxide and hydrogen [H 2 ] from which CO 2 is extracted for burial [yellow pathways at bottom]
GASIFICATION 1 Coal water and oxygen are fed into a high-pressure gasifier in which the coal is partially oxmiddotidized and converted into syngas
CO 2 is compressed and middotsent via pipeline systems to permanent underground storage sites
3 Hydrogen-rich syngas is burned and the combustion products drive a gas turb ine-generator
4 The hot gas turbine exhaust passes to a heat-recovery steam generator which converts water to steam that turns a steam turbine-generator
C02 can be sent into saline formations-saltwatermiddot filled strata capped with impermeable rock
wwwsciam_com SCIENTIFIC AMERICAN 71
can meet the objectives of climate change mitigation at the least cost Funshydamenta lIy different approaches to ees would be pursued for power plants usshying the conventional pulverized-coal steam cycle and the newer integrated gasification combined cycle (IGee) Alshythough todays coal IGee power (with C02 venting) is slightly more expensive than coal steam-electric power it looks like IGee is the most effective and least expensive option for ees
Standard plants burn coal in a boiler at atmospheric pressure The heat genshyerated in coal combustion transforms water into steam which turns a steam turbine whose mechanica I energy is converted to electricity by a generator In modern plants the gases produced by combustion (flue gases) then pass through devices that remove particushylates and oxides of sulfur and nitrogen before being exhausted via smokestacks into the air
Carbon dioxide could be extracted from the flue gases of such steam-elecshytric plants after the removal of convenshytional pollutants Because the flue gases contain substantial amounts of nitrogen (the result of burning coal in air which is about 80 percent nitrogen) the carshybon dioxide would be recovered at low concentration and pressure-which imshyplies that the C02 would have to be reshymoved from large volumes of gas using processes that are both energy-intensive and expensive The captured C02 would then be compressed and piped to an apshypropriate storage site
In an IGee system coal is not burned but rather partially oxidized (reacted with limited quantities of oxygen from
DAVID G HAWKI NS DANIEL A LASH OF and ROBERT H WILLIAMS have endeavored to help
stave off climate change problems for decades Hawkins is director of the Climate Center
at the Natural Resources Defense Council (NRDCJ where he has worked on air energy
and climate issues for 35 years Hawkins serves on the boards of many bodies that advise
government on environmental and energy subjects Lashof is science director and depmiddot
uty director of the NRDCs Climate Center at which he has focused on national energy
policy climate science and solutions to global warming since 1989 Before arriving at the
NRDC Lashof developed policy options for stabilizing global climate at the US Environmiddot
mental Protection Agency Williams is a se nior research scientist at Princeton Un iversity
which he joined in 1975At the universitys Princeton Environmentallnstitute he heads
the Energy Systems Policy Analysis Group and the Carbon Capture Group under the inmiddot
stitutes Carbon Mitigation Initiative (which is supported by BP and Ford)
72 SCIENTIFIC AMERICAN
Commercial power plants using IGCC technology such as this one in Italy have been operating since 1994 Togetherthey generate 3600 megawatts of electricity
an air separation plant and with steam) at high pressure in a gasifier The prodshyuct of gasification is so-called synthesis gas or syngas which is composed mostshyly of carbon monoxide and hydrogen undiluted with nitrogen In current practice IGee operations remove most conventional pollutants from the syngas and then burn it to turn both gas and steam turbine-generators in what is called a combined cycle
In an IGee plant designed to capshyture C02 the syngas exiting the gasifier after being cooled and cleaned of parshyticles would be reacted with steam to produce a gaseous mixture made up mainly of carbon dioxide and hydrogen The C02 would then be extracted
dried compressed and transported to a storage site The remaining hydrogenshyrich gas wou ld be bu rned in a combined cycle plant to generate power [see box on preceding page]
Analyses indicate that carbon dioxshyide capture at Ieee plants consuming high-quality bituminous coals would entai I significantly sma ller energy and cost penalties and lower total generashytion costs than what could be achieved in conventional coal plants that capshytured and stored C02 Gasification sysshytems recover CO2 from a gaseous stream at high concentration and pressure a feature that makes the process much easier than it would be in conventional steam facilities (The extent of the ben shyefits is less clear for lower-grade subbishytuminous coals and lignites which have received much less study) Precombusshytion remova I of conventional pollutants including mercury makes it feasible to realize very low levels of emissions at much reduced costs and with much smaller energy penalties than with cleanup systems for flue gases in convenshytional plants
Captured carbon dioxide can be transported by pipeline up to several hundred kilometers to suitable geologic storage sites and subsequent subterrashynean storage with the pressure produced during capture Longer distances may however require recompression to comshypensate for friction losses during pipe shyline transfer
Overall pursuing ees for coa I powshyer facilities requires the consumption of more coal to generate a kilowatt-hour of electricity than when C02 is ventedshyabout 30 percent extra in the case of coal steam-electric plants and less than 20 percent more for IGee plants But overall coal use would not necessarily increase because the higher price of coal-based electricity resulting from adding ees equipment would dampen demand for coal-based electricity rna kshying renewable energy sources and enershygy-efficient products more desirable to consumers
The cost of ees will depend on the type of power plant the distance to the storage site the properties of the storage
SEPTEMBER 2006
II reservoir and the availability of opporshy cost would occur as long as the oil price ed policies for climate change mitigation tunities (such as enhanced oil recovery) is at least $35 per barrel which is much that would make CCS cost-effective for for selling the captured C02 A recent lower than current prices uses not associated with enhanced oil study co-authored by one of us (Wilshy recovery Absent revenues from sales to
liams) estimated the incremental electric CCS Now or Later oil field operators applying CCS to new generation costs of two alternative CCS MANY ELECTR1CITY producers in coal plants using current technology options for coal IeCC plants under typshy the industria I world recognize that enshy would be the least-cost path only if the ical production transport and storage vironmental concerns will at some point cost of emitting C02 were at least $25 conditions For C02 sequestration in a force them to implement CCS if they are to $30 per metric ton Many current saline formation 100 kilometers from a to continue to employ coal But rather policy proposals for climate change mitshypower plant the study calculated that than building plants that actually capshy igation in the US envision significantly the incremental cost of CCS would be ture and store carbon dioxide most lower cost penalties to power providers 19 cents per kilowatt-hour (beyond the plan to construct conventional steam for releasing C02 (or similarly payshygeneration cost of 47 cents per kilowattshy facilities they claim will be C02 capshy ments for C02 emissions-reduction hour for a coal IeCC plant that vents ture ready-convertible when CCS is credits) C02-a 40 percent premium) For CCS mandated Yet delaying CCS at coal power pursued in conjunction with enhanced Power providers often defend those plants until economy-wide carbon dioxshyoil recovery at a distance of 100 kilomeshy decisions by noting that the US and ide control costs are greater than CCS ters from the conversion plant the analshy most other countries with coal-intensive costs is shortsighted For several reashyysis finds no increase in net generation energy economies have not yet institut- sons the coal and power industries and
- I I I e I i L I
Despitethe current popularity of the term clean coal coal is in factdirty Although carbon capture and storage could prevent much carbon dioxide fromentering the atmosphere coal production and consumption is still oneaf the most destructive industrial processes As long as
thewbrld copsumescoal more must be done to mitigate the harm it causes
MINING DANGERS Underground mining can cause serious problems on the
Coal mining is among the most dangerous occupations Official surface Mines collapse and cause land subsidence
reports for 2005 indicate that roughly 6000 people died damaging homes and roads Acidic mine drainage caused by
(16 a day) in China from coal mine floods iave~ins fires and slJlfur compounds leaching from coal waste into surface
explosions Unofficial estimates are waters has tainted thousands of
closer to 10000 Some 600000 streams The acid leachate releases
Chinese toal minegtrsslJfferfrom heavy metals that foul groundwater
black lung disease The Us has better safety TOXIC EMISSIONS
Coalmiddotfired power plants account for
all-time low of 22 domestic fatalities practices thanChina and achieved an
more than two thirds of sulfur dioxide
in 2005 US mines are far from middot andabout one fifth of nitrogen oxide
perfect however as evidenced by a middot emissions in the US Sulfur dioxide
series offatalities inearly 2006 reacts in the atmosphere to form middot sulfate particles which in addition to
ENVIRONME~TAL EFFECTS middot causing acid rain contribute to fine
Conventiona-l coal mining proces~ing particulate pollution a contaminant
and transportation practices scar linked to thousands of premature
the landscape and pollute the water which harms people and deaths from lung disease nationwide Nitrogen oxides combine
eCosystems The most destructive mining teChniques Clear with hydrocarbons to form smog-causingground-Ievel ozone
forests and blast away mountaintops The overburden Coalmiddotburning plants ltllso emit approximately 48 metric
removed when a coal seam is uncovered middotis typically dumped tons of mercury a year in America Thishighly toxic element
into nearby valleyswhere it often buries rivers andstreams persists in the ecosystem Aftertransforming into methyl
Stripmiddotmining operations rip apart ecosystems and reshape mercury it accum ulates in the tissues offishes Ingested
the landscape Although regulations require landreclamatipn mercury is particularly detrimental to fetuses andyoung
in principle it is often left incomplete Asforests are replaced infants exposed during periods of rapid brain growth causing
with nonnative grasslands soils become compacted and developmental and neurOlogical damage
streams contaminated -DGH DAL and RHW
wwwsciamcom SCIENTIFIC AMERICAN 73
pound Acid runoff from a Pennsylvania coal mine stains this creek bed orange
--_bull 1
THE PATH TO C02MITIGATION Our calculations indicate that a prompt commitment to carbon capture and storage
[eeS) would make it possible to meet global energy demands while limiting the
atmospheric carbon dioxide concentration to 450 parts per million by volume [ppmv)
This goal could be attained if by midcentury sequestration is applied for all coal use
and about a quarter of natural gas use while energy efficiency increases rapidly and
carbon-free energy sources expand sevenfold Under these conditions overall fossilshy
fuel consumption could expand modestly from today by midcentury coal use could be
somewhat higher than at present oil use would be down by a fifth and natural gas use
would expand by half
To realize this pathway growth rates for fossil-fuel use would have to be reduced
now and ee Smust begin for coal early in the next decade and for natural gas early in
the next quarter of a century The top graph below depicts the energy provided by the
various sources if this mitigation path were followed The bottom graph shows total
quantities of carbon extracted from the earth [emissions plus storage)
-DGH DAL and RHW
FOSSIL AND CARBON-FREE ENEmiddotRGY MIX FOR C02 STABILIZATION
35 Additional carbon-free energ~ needed to satisfy demand
30 Oil
~ bull Natural gas with CCS cu ~ 25 Natural gas with C02 vented ~ bull Coal with CCS ~ 20 Coal with C02 vented ~ eo c
IJJ 15 ~ cu
sect Q
10
5
0 2010 2030 2050 2070 2090
FATE OF CARBON FROM FOSSIL ENERGY SYSTEMS
cu 10 ~
n cu
c 8B cu on On
c 0 5 -e cu u ~ 4e IJJ
0 ~
tgt 2 0 Vi
0 I i i 2010 2030 2050 2070 2090
Year
74 SCIENTIFIC AMERICAN
bull Natural gas C stored
NalUral gas C emitted
Coal C emitted
Emissions level needed to stabilize C02at 450 ppmv
bull Coal carbon [C) stored
society would ultimately benefit if deshyployment of plants fitted with CCS equipment were begun now
First the fastest way to reduce CCS costs is via learning by doing-the acshycumulation of experience in building and running such plants The faster the understanding is accumulated the quicker the know-how with the new technology will grow and the more rapshyidly the costs will drop
Second installing CCS equipment as soon as possible should save money in the long run Most power stations curshyrently under construction will still be opshyerating decades from now when it is likely that CCS efforts will be obligatory Retrofitting generating faciliti es for CCS is inherently more expensive than deshyploying CCS in new plants Moreover in the absence of C02 emission limits fashymiliar conventional coal steam-electric technologies will tend to be favored for most new plant construction over newer gasification technologies for which CCS is more cost-effective
Finally rapid implementation would allow for continued use of fossil fuels in the near term (until more environmenshytally friendly sources become prevalent) without pushing atmospheric carbon dioxide beyond tolerable levels Our studies indicate that it is feasible to stashybilize atmospheric C02 levels at 450 ppmv over the next half a century if coal-based energy is completely decarshybonized and other measures described in the box at the left are implemented This effort would involve decarbonizing 36 gigawatts of new coal generating cashypacity by 2020 (corresponding to 7 pershycent of the new coal capacity expected to be built worldwide during the decade beginning in 2011 under business-asshyusual conditions) In the 35 years after 2020 C02 capture would need to rise at an average rate of about 12 percent a year Such a sustained pace is high compared with typical market growth rates for energy but is not unprecedentshyed It is much less than the expansion rate for nuclear generating capacity in its heyd ay-1956 to 1980-during which global capacity rose at an average rate of 40 percent annually Further the
SEPTEMBER 2005
expansion rates for bo th wind a nd sola r photovoltaic power capaci ties worldshywide have hovered around 30 percent a year since the ea rly 1990s In a ll three cases such growth would not have been practical without public policy mea shysures to suppor t them
Our calculations indica te that the costs of CCS deployment would be manshyageable as well Using conservative assumptions-such as that technology will not improve over time-we estimate that th e present worth of the cost of capturing and storing all C02produced by coal-based electricity generation pla nts du ring the next 200 years will be $18 triiJion (in 2002 dollars) That might seem like a high price tag but it is equivalent to just 007 percent of the curren t value of gross world prod uc t over the same interva l Thus it is plaushyslble that a rapid decarbonization path for coal is both phys ica lly and economshyically feasible although deta iled regionshya l analyses are needed to confirm thi s conclusion
Policy Push Is Nee d THO SE GOO D R EASO N S for comshymencing concerted CCS efforts soon will probably not move the industry unshyless it is a lso prodded by new public polshyicies Such initiatives would be part of a broader d rive to control carbon dioxide emissions from a ll sou rces
In the US a nat ional program to limit C02 emissions mu st be enac ted soon to introduce the government regshyu lat ions a nd market incentives necshyessary to shift investment to the leastshypolluting energy technologies promptly and on a w ide scale Leaders in the American business and policy commushynities increasi ngly agree that quantifi shyable a nd enforceable rest r ictions on global warming emissions are imperashytive and inev ita ble To ensure that powshyer companies put into practice the reshyductions in a cost-effective fashion a market for trading C02emissions credshyits shou ld be created-one similar to that for the sulfur emissions that cause acid rain In such a plan organizations that intend to exceed designated emisshysion limits may buy cred its from others
www s ciamcom
that are able to stay below these va lues Enhancing energy efficienc y efforts
and raising renewable energy producshyti on are cri tical to achieving carbon dishyox ide limits at the lowes t possible cost A po rtion of the emission a llowances created by a carbon cap-and-trade proshygram shou Id be a llocated to the es tabshylishment of a fund to help overcome inshystitutional ba rriers and technica l r isks that obstruct widespread deployment of otherwise cost-effective C02 mitigation technologies
=
Delaying carbon capturemiddot
and storage at coal power
plants is shortsighted
Even if a carbon dioxide cap-andshytrade program were enacted in the next few yea rs the econom ic value of C02 emissions reduction may not be enough initially to convince power providers to invest in power systems with CCS To avoid the construction of another genshyeration of conventional coa l plants it is essential that the fed eral government esshytablish incentives that promote CCS
One ap proach would be to insist that an increasing share of total coal-based
MORE TO EXPLORE
electricity generation comes from faci lishyties that meet a low C02 emissions stanshydard-perhaps a maximum of 30 grams of carbon per k ilowatt-hour (a n achievshyable goal using todays coal CCS techshynologies) Such a goa l might be ach ieved by obliging electricity producers that use coal to include a growing fraction of decarbon ized coal power in thei r supply portfolios Each covered electricity proshyducer could either generate the required amount of decarbonized coal power or purchase decarbonized-generation credshyits Th is sys tem would share the increshym en tal costs of CCS for coal power among all US coal-based electricity producers and consumers
If the surge of conventional coa lshyfired power plants currently on drawing boa rds is built as planned atmospheric carbon dioxide levels will almost cershytainly exceed 450 ppmv Vle can meet global energy needs while st ill stabili zshying C02 at450 ppmv however through a combination of improved efficiency in energy use greater reliance on renewshyable energy resources and for the new coal investments that are made the inshystallation of C02 capture and geolog ic storage technologies Even though there is no such thing as clean coal more can and must be done to reduce the danshygers and environmental degradations associated with coal production and use An integrated low-carbon energy strategy that incorporates C02 capture and storage can reconcile substantia I use of coa l in the coming decades with the imperatlve to prevent catastro phic changes to the earths climate m
_
How to Clean Coal C Can ine in OnEarth Nat ural Resollrces Defense Council 200 5 Avail able at wwwnrdcorgonearth OSfallcoallasp
IPCC Special Report on Carbon Capture and Storage 2005 Avqilable at http archrrvm n I env Ii ntipcc pages_medi alSRC CS-fi n a II IPCC Spec ial Reporton Carbon d i oxideC apt urea ndSt 0 rage htm
Avoiding Dangerous Climate Change ~ditec1 by H J Sch ellnhuber W Cramer N Nallicenovic T Wigley and G Yoh e Cambridge University Press 2006
Big Clal The Dirty Secret behind America s Energy Future J Goodell Houghton Mifflin 20 06
Carbo~ Dioxide Capture andG~ologic Storage J J Doniey RTGahowski C L David so n M A Wise N Gupt a S H Kim and E L Malone Tec hnology Report from the Second Phase of the Global Energy Technology Strategy Program 2006
Natural Resou rces Defense Council Web si te wwwnrdcor~globalwarming
PrincetonEnvironmentallnstitute Web site wwwprincet on edu-cmi
SCIENTIFIC AMERICAN 75
coal burned since the dawn of the Indusshytrial Revolution
Coals projected popularity is disturbshying not only for those concerned about climate change but also for those worried about other aspects of the environmen t and abo ut huma n hea lth and safe ty Coals market price may be low but the true costs of its extraction processing and consumption are high Coal use can lead to a range of harmful consequences including decapitated mountains air polshylution from acidic and toxic emissions and water fouled with COol I wastes Exshytraction also endangers and ca n kill minshyers Together such effects make coal pro- duction and conversion to useful energy one of the most destructive activities on the planet [see box on page 73 ]
In keeping with Scientific Amerishycans focus on climate concerns in this is sue we will concentrate below o n methods that can help prevent C02genshyerated during coal conversion from reaching the atmosphere It goes withshyout saying that the env ironmental safeshyty and health effects of coal production and use must be reduced as well Fortushynately affordable techniques for adshydressing C02 emissions and these other problems a lready exist although the will to implement them quickly still lags significantly
Geologic Storage Strategy TI-IE TEC HNIQU ES that powcrprovidshyers could apply to keep most of the carshybon diox ide they produce from entering the air are co llec tively called C02 capshyture and storage (CCS) or geologic carshybon sequ es trati on These procedures involve se parat ing out much of the C02 that is created when coa l is converted to useful energy a nd tra nsporting it to sites where it can be stored deep underground in porous media-mainly in depleted oil or gas field s or in sa line form ations (pershymeable geologic strata filled with salty water) [see Can We Bur y Global Warming by Robert H Socolow SCIshyENT FIC AM ERICAN July 2005]
All the technological components needed for CCS at coal conversion plants are commercially ready-having been proved in applications unrelated to clishy
70 SCIENTIFiC AMERICAN
mate change mitigation although inte shygrated systems have not yet been conshystructed at the necessary scales Captu re technologies have been deployed extenshysively throughout the world both in the manufacture of chemicals (s uch as fertilshyizer) and in the purification of natural gas supplies contaminated with carbon dioxshyide and hydrogen sulfide (so ur gas) Industry has gained considerable experishyence with C02 storage in operations that purify natural gas (mainly in Canad a) as well as with C02 injection to boost oil production (primarily in the US) Enshyhanced oil recovery processes account for most of the C02 that has been sent into
Affordable methods that prevent CO2
from reaching the atmosphere exist the will to implement them
quickly lags r
I
underground reservoirs Currently about 35 million metric tons are injected annushyally to coax more petroleum out of mashyture fields accounting for about 4 pershycent of US crude oil output
Implementing CCS at coa l-consu mshying plants is imperative if the carbon dishyoxide concentration in the atmosphere is to be kept at an acceptable level The 1992 United N ations Framework Conshyvention on Climate Change calJs for stashybilizing the atmospheric C02 concentrashytion at a safe level but it does not specshyify what the ma ximum value should be The current view of man y scientists is that atmospheric C0 2 level s must be kept below 450 parts per million by volume (ppmv) to avoid unaccepta ble climate changes Rea lization of this aggressive goa l requires that the power industry start commercial- sca le C CS p roj ec ts
within the next fe w years and expand them rapidly thereafter Thi s stabilizashytion benchmark cannot be real ized by CCS a lone but can plausibly be achieved if it is combined with other eco-friend ly measures such as wide improvements in energy efficiency a nd much expanded use of renewable energy sources
The Intergovernmenta l Panel on C lishymate Change (IPCC) estimated in 2005 that it is highly probable that geolog ic media worldwide are capa ble of sequesshytering at leas t two trillion metric tons of C02-more than is likely to be produced by fossil-fuel-con suming plants during the 21st century Society will want to be sure however that potential sequestrashytion sites are evaluated carefully for their ability to retain C02 before they are alshylowed to operate Two classes of risks are of concern sudd en escape and gradshyualleakage
Rapid outflow of large amounts of C02 could be lethal to those in the vi shycinity Da ngero us sudden releases-such as that which occurred in 1986 at Lake Nyos in Cameroon when C02 of volcashynic origin asphyxiated 1700 nearby vilshylagers and thousands of cattle-are imshyprobable for engi neered C02 storage proj ects in carefully selected deep poshyrous geologic formations accord ing to the IPCe
Gradual seepage of carbon dioxide into the ai r is also an issue because over time it could defeat the goa l of CCS The 2005 IPCC report estimated that the fraction re tained in appropriately selectshyed and managed geo logic reservoirs is very likely to exceed 99 percent over 100 years and likely to exceed 99 percent over 1000 years What remains to be demonshystrated is whether in practice operators can routinely keep C02 leaks to levels that avoid unacceptable environmental and public heal th risks
Technology Choices DES IG N 5 TU DIE S indicate that existing power generation tech nologies could capshyture fro m 85 to 95 percent of the carbon in coal as C02 with the rest released to the atmosphere
The coal convers ion technologies that come to dominate w ilJ be those that
SEPTEMBER 2006
To slow climate change the authors urge power providers to build
integrated gasifi cation combined cycle [IGCC] coal power plants
with carbon dioxide capture and storage [CCS] capabilities
[below] rather than conventional steam -elect ric facilities
Conventional coal plants burn the fuel to transform water into
steam to turn a turbine-generator If CCS technology were applied
to a steam plant C02 would be extracted from the flue exhaust
An IGCC plant in contrast employs a partial oxidation reaction
using limited oxygen to convert the co al into a so-ca lled
synthesis gas or syngas [mostly hydrogen and carbon
mono xide] lt is much easier and less costly to remove CO 2 from
syngas than from the flue gases of a steam plant The hydrogenshy
rich syngas remainingafterC02 extraction is then burned to run
both gas and steam turbine-generators The wor ld s first
commerciallGCC project that will sequester C02 underground is
being planned near Long Beach Calif
C02 EXTRACTION 2 The syngas is reacte d with steam to produce a gaseous mixture of mostly carbon dioxide and hydrogen [H 2 ] from which CO 2 is extracted for burial [yellow pathways at bottom]
GASIFICATION 1 Coal water and oxygen are fed into a high-pressure gasifier in which the coal is partially oxmiddotidized and converted into syngas
CO 2 is compressed and middotsent via pipeline systems to permanent underground storage sites
3 Hydrogen-rich syngas is burned and the combustion products drive a gas turb ine-generator
4 The hot gas turbine exhaust passes to a heat-recovery steam generator which converts water to steam that turns a steam turbine-generator
C02 can be sent into saline formations-saltwatermiddot filled strata capped with impermeable rock
wwwsciam_com SCIENTIFIC AMERICAN 71
can meet the objectives of climate change mitigation at the least cost Funshydamenta lIy different approaches to ees would be pursued for power plants usshying the conventional pulverized-coal steam cycle and the newer integrated gasification combined cycle (IGee) Alshythough todays coal IGee power (with C02 venting) is slightly more expensive than coal steam-electric power it looks like IGee is the most effective and least expensive option for ees
Standard plants burn coal in a boiler at atmospheric pressure The heat genshyerated in coal combustion transforms water into steam which turns a steam turbine whose mechanica I energy is converted to electricity by a generator In modern plants the gases produced by combustion (flue gases) then pass through devices that remove particushylates and oxides of sulfur and nitrogen before being exhausted via smokestacks into the air
Carbon dioxide could be extracted from the flue gases of such steam-elecshytric plants after the removal of convenshytional pollutants Because the flue gases contain substantial amounts of nitrogen (the result of burning coal in air which is about 80 percent nitrogen) the carshybon dioxide would be recovered at low concentration and pressure-which imshyplies that the C02 would have to be reshymoved from large volumes of gas using processes that are both energy-intensive and expensive The captured C02 would then be compressed and piped to an apshypropriate storage site
In an IGee system coal is not burned but rather partially oxidized (reacted with limited quantities of oxygen from
DAVID G HAWKI NS DANIEL A LASH OF and ROBERT H WILLIAMS have endeavored to help
stave off climate change problems for decades Hawkins is director of the Climate Center
at the Natural Resources Defense Council (NRDCJ where he has worked on air energy
and climate issues for 35 years Hawkins serves on the boards of many bodies that advise
government on environmental and energy subjects Lashof is science director and depmiddot
uty director of the NRDCs Climate Center at which he has focused on national energy
policy climate science and solutions to global warming since 1989 Before arriving at the
NRDC Lashof developed policy options for stabilizing global climate at the US Environmiddot
mental Protection Agency Williams is a se nior research scientist at Princeton Un iversity
which he joined in 1975At the universitys Princeton Environmentallnstitute he heads
the Energy Systems Policy Analysis Group and the Carbon Capture Group under the inmiddot
stitutes Carbon Mitigation Initiative (which is supported by BP and Ford)
72 SCIENTIFIC AMERICAN
Commercial power plants using IGCC technology such as this one in Italy have been operating since 1994 Togetherthey generate 3600 megawatts of electricity
an air separation plant and with steam) at high pressure in a gasifier The prodshyuct of gasification is so-called synthesis gas or syngas which is composed mostshyly of carbon monoxide and hydrogen undiluted with nitrogen In current practice IGee operations remove most conventional pollutants from the syngas and then burn it to turn both gas and steam turbine-generators in what is called a combined cycle
In an IGee plant designed to capshyture C02 the syngas exiting the gasifier after being cooled and cleaned of parshyticles would be reacted with steam to produce a gaseous mixture made up mainly of carbon dioxide and hydrogen The C02 would then be extracted
dried compressed and transported to a storage site The remaining hydrogenshyrich gas wou ld be bu rned in a combined cycle plant to generate power [see box on preceding page]
Analyses indicate that carbon dioxshyide capture at Ieee plants consuming high-quality bituminous coals would entai I significantly sma ller energy and cost penalties and lower total generashytion costs than what could be achieved in conventional coal plants that capshytured and stored C02 Gasification sysshytems recover CO2 from a gaseous stream at high concentration and pressure a feature that makes the process much easier than it would be in conventional steam facilities (The extent of the ben shyefits is less clear for lower-grade subbishytuminous coals and lignites which have received much less study) Precombusshytion remova I of conventional pollutants including mercury makes it feasible to realize very low levels of emissions at much reduced costs and with much smaller energy penalties than with cleanup systems for flue gases in convenshytional plants
Captured carbon dioxide can be transported by pipeline up to several hundred kilometers to suitable geologic storage sites and subsequent subterrashynean storage with the pressure produced during capture Longer distances may however require recompression to comshypensate for friction losses during pipe shyline transfer
Overall pursuing ees for coa I powshyer facilities requires the consumption of more coal to generate a kilowatt-hour of electricity than when C02 is ventedshyabout 30 percent extra in the case of coal steam-electric plants and less than 20 percent more for IGee plants But overall coal use would not necessarily increase because the higher price of coal-based electricity resulting from adding ees equipment would dampen demand for coal-based electricity rna kshying renewable energy sources and enershygy-efficient products more desirable to consumers
The cost of ees will depend on the type of power plant the distance to the storage site the properties of the storage
SEPTEMBER 2006
II reservoir and the availability of opporshy cost would occur as long as the oil price ed policies for climate change mitigation tunities (such as enhanced oil recovery) is at least $35 per barrel which is much that would make CCS cost-effective for for selling the captured C02 A recent lower than current prices uses not associated with enhanced oil study co-authored by one of us (Wilshy recovery Absent revenues from sales to
liams) estimated the incremental electric CCS Now or Later oil field operators applying CCS to new generation costs of two alternative CCS MANY ELECTR1CITY producers in coal plants using current technology options for coal IeCC plants under typshy the industria I world recognize that enshy would be the least-cost path only if the ical production transport and storage vironmental concerns will at some point cost of emitting C02 were at least $25 conditions For C02 sequestration in a force them to implement CCS if they are to $30 per metric ton Many current saline formation 100 kilometers from a to continue to employ coal But rather policy proposals for climate change mitshypower plant the study calculated that than building plants that actually capshy igation in the US envision significantly the incremental cost of CCS would be ture and store carbon dioxide most lower cost penalties to power providers 19 cents per kilowatt-hour (beyond the plan to construct conventional steam for releasing C02 (or similarly payshygeneration cost of 47 cents per kilowattshy facilities they claim will be C02 capshy ments for C02 emissions-reduction hour for a coal IeCC plant that vents ture ready-convertible when CCS is credits) C02-a 40 percent premium) For CCS mandated Yet delaying CCS at coal power pursued in conjunction with enhanced Power providers often defend those plants until economy-wide carbon dioxshyoil recovery at a distance of 100 kilomeshy decisions by noting that the US and ide control costs are greater than CCS ters from the conversion plant the analshy most other countries with coal-intensive costs is shortsighted For several reashyysis finds no increase in net generation energy economies have not yet institut- sons the coal and power industries and
- I I I e I i L I
Despitethe current popularity of the term clean coal coal is in factdirty Although carbon capture and storage could prevent much carbon dioxide fromentering the atmosphere coal production and consumption is still oneaf the most destructive industrial processes As long as
thewbrld copsumescoal more must be done to mitigate the harm it causes
MINING DANGERS Underground mining can cause serious problems on the
Coal mining is among the most dangerous occupations Official surface Mines collapse and cause land subsidence
reports for 2005 indicate that roughly 6000 people died damaging homes and roads Acidic mine drainage caused by
(16 a day) in China from coal mine floods iave~ins fires and slJlfur compounds leaching from coal waste into surface
explosions Unofficial estimates are waters has tainted thousands of
closer to 10000 Some 600000 streams The acid leachate releases
Chinese toal minegtrsslJfferfrom heavy metals that foul groundwater
black lung disease The Us has better safety TOXIC EMISSIONS
Coalmiddotfired power plants account for
all-time low of 22 domestic fatalities practices thanChina and achieved an
more than two thirds of sulfur dioxide
in 2005 US mines are far from middot andabout one fifth of nitrogen oxide
perfect however as evidenced by a middot emissions in the US Sulfur dioxide
series offatalities inearly 2006 reacts in the atmosphere to form middot sulfate particles which in addition to
ENVIRONME~TAL EFFECTS middot causing acid rain contribute to fine
Conventiona-l coal mining proces~ing particulate pollution a contaminant
and transportation practices scar linked to thousands of premature
the landscape and pollute the water which harms people and deaths from lung disease nationwide Nitrogen oxides combine
eCosystems The most destructive mining teChniques Clear with hydrocarbons to form smog-causingground-Ievel ozone
forests and blast away mountaintops The overburden Coalmiddotburning plants ltllso emit approximately 48 metric
removed when a coal seam is uncovered middotis typically dumped tons of mercury a year in America Thishighly toxic element
into nearby valleyswhere it often buries rivers andstreams persists in the ecosystem Aftertransforming into methyl
Stripmiddotmining operations rip apart ecosystems and reshape mercury it accum ulates in the tissues offishes Ingested
the landscape Although regulations require landreclamatipn mercury is particularly detrimental to fetuses andyoung
in principle it is often left incomplete Asforests are replaced infants exposed during periods of rapid brain growth causing
with nonnative grasslands soils become compacted and developmental and neurOlogical damage
streams contaminated -DGH DAL and RHW
wwwsciamcom SCIENTIFIC AMERICAN 73
pound Acid runoff from a Pennsylvania coal mine stains this creek bed orange
--_bull 1
THE PATH TO C02MITIGATION Our calculations indicate that a prompt commitment to carbon capture and storage
[eeS) would make it possible to meet global energy demands while limiting the
atmospheric carbon dioxide concentration to 450 parts per million by volume [ppmv)
This goal could be attained if by midcentury sequestration is applied for all coal use
and about a quarter of natural gas use while energy efficiency increases rapidly and
carbon-free energy sources expand sevenfold Under these conditions overall fossilshy
fuel consumption could expand modestly from today by midcentury coal use could be
somewhat higher than at present oil use would be down by a fifth and natural gas use
would expand by half
To realize this pathway growth rates for fossil-fuel use would have to be reduced
now and ee Smust begin for coal early in the next decade and for natural gas early in
the next quarter of a century The top graph below depicts the energy provided by the
various sources if this mitigation path were followed The bottom graph shows total
quantities of carbon extracted from the earth [emissions plus storage)
-DGH DAL and RHW
FOSSIL AND CARBON-FREE ENEmiddotRGY MIX FOR C02 STABILIZATION
35 Additional carbon-free energ~ needed to satisfy demand
30 Oil
~ bull Natural gas with CCS cu ~ 25 Natural gas with C02 vented ~ bull Coal with CCS ~ 20 Coal with C02 vented ~ eo c
IJJ 15 ~ cu
sect Q
10
5
0 2010 2030 2050 2070 2090
FATE OF CARBON FROM FOSSIL ENERGY SYSTEMS
cu 10 ~
n cu
c 8B cu on On
c 0 5 -e cu u ~ 4e IJJ
0 ~
tgt 2 0 Vi
0 I i i 2010 2030 2050 2070 2090
Year
74 SCIENTIFIC AMERICAN
bull Natural gas C stored
NalUral gas C emitted
Coal C emitted
Emissions level needed to stabilize C02at 450 ppmv
bull Coal carbon [C) stored
society would ultimately benefit if deshyployment of plants fitted with CCS equipment were begun now
First the fastest way to reduce CCS costs is via learning by doing-the acshycumulation of experience in building and running such plants The faster the understanding is accumulated the quicker the know-how with the new technology will grow and the more rapshyidly the costs will drop
Second installing CCS equipment as soon as possible should save money in the long run Most power stations curshyrently under construction will still be opshyerating decades from now when it is likely that CCS efforts will be obligatory Retrofitting generating faciliti es for CCS is inherently more expensive than deshyploying CCS in new plants Moreover in the absence of C02 emission limits fashymiliar conventional coal steam-electric technologies will tend to be favored for most new plant construction over newer gasification technologies for which CCS is more cost-effective
Finally rapid implementation would allow for continued use of fossil fuels in the near term (until more environmenshytally friendly sources become prevalent) without pushing atmospheric carbon dioxide beyond tolerable levels Our studies indicate that it is feasible to stashybilize atmospheric C02 levels at 450 ppmv over the next half a century if coal-based energy is completely decarshybonized and other measures described in the box at the left are implemented This effort would involve decarbonizing 36 gigawatts of new coal generating cashypacity by 2020 (corresponding to 7 pershycent of the new coal capacity expected to be built worldwide during the decade beginning in 2011 under business-asshyusual conditions) In the 35 years after 2020 C02 capture would need to rise at an average rate of about 12 percent a year Such a sustained pace is high compared with typical market growth rates for energy but is not unprecedentshyed It is much less than the expansion rate for nuclear generating capacity in its heyd ay-1956 to 1980-during which global capacity rose at an average rate of 40 percent annually Further the
SEPTEMBER 2005
expansion rates for bo th wind a nd sola r photovoltaic power capaci ties worldshywide have hovered around 30 percent a year since the ea rly 1990s In a ll three cases such growth would not have been practical without public policy mea shysures to suppor t them
Our calculations indica te that the costs of CCS deployment would be manshyageable as well Using conservative assumptions-such as that technology will not improve over time-we estimate that th e present worth of the cost of capturing and storing all C02produced by coal-based electricity generation pla nts du ring the next 200 years will be $18 triiJion (in 2002 dollars) That might seem like a high price tag but it is equivalent to just 007 percent of the curren t value of gross world prod uc t over the same interva l Thus it is plaushyslble that a rapid decarbonization path for coal is both phys ica lly and economshyically feasible although deta iled regionshya l analyses are needed to confirm thi s conclusion
Policy Push Is Nee d THO SE GOO D R EASO N S for comshymencing concerted CCS efforts soon will probably not move the industry unshyless it is a lso prodded by new public polshyicies Such initiatives would be part of a broader d rive to control carbon dioxide emissions from a ll sou rces
In the US a nat ional program to limit C02 emissions mu st be enac ted soon to introduce the government regshyu lat ions a nd market incentives necshyessary to shift investment to the leastshypolluting energy technologies promptly and on a w ide scale Leaders in the American business and policy commushynities increasi ngly agree that quantifi shyable a nd enforceable rest r ictions on global warming emissions are imperashytive and inev ita ble To ensure that powshyer companies put into practice the reshyductions in a cost-effective fashion a market for trading C02emissions credshyits shou ld be created-one similar to that for the sulfur emissions that cause acid rain In such a plan organizations that intend to exceed designated emisshysion limits may buy cred its from others
www s ciamcom
that are able to stay below these va lues Enhancing energy efficienc y efforts
and raising renewable energy producshyti on are cri tical to achieving carbon dishyox ide limits at the lowes t possible cost A po rtion of the emission a llowances created by a carbon cap-and-trade proshygram shou Id be a llocated to the es tabshylishment of a fund to help overcome inshystitutional ba rriers and technica l r isks that obstruct widespread deployment of otherwise cost-effective C02 mitigation technologies
=
Delaying carbon capturemiddot
and storage at coal power
plants is shortsighted
Even if a carbon dioxide cap-andshytrade program were enacted in the next few yea rs the econom ic value of C02 emissions reduction may not be enough initially to convince power providers to invest in power systems with CCS To avoid the construction of another genshyeration of conventional coa l plants it is essential that the fed eral government esshytablish incentives that promote CCS
One ap proach would be to insist that an increasing share of total coal-based
MORE TO EXPLORE
electricity generation comes from faci lishyties that meet a low C02 emissions stanshydard-perhaps a maximum of 30 grams of carbon per k ilowatt-hour (a n achievshyable goal using todays coal CCS techshynologies) Such a goa l might be ach ieved by obliging electricity producers that use coal to include a growing fraction of decarbon ized coal power in thei r supply portfolios Each covered electricity proshyducer could either generate the required amount of decarbonized coal power or purchase decarbonized-generation credshyits Th is sys tem would share the increshym en tal costs of CCS for coal power among all US coal-based electricity producers and consumers
If the surge of conventional coa lshyfired power plants currently on drawing boa rds is built as planned atmospheric carbon dioxide levels will almost cershytainly exceed 450 ppmv Vle can meet global energy needs while st ill stabili zshying C02 at450 ppmv however through a combination of improved efficiency in energy use greater reliance on renewshyable energy resources and for the new coal investments that are made the inshystallation of C02 capture and geolog ic storage technologies Even though there is no such thing as clean coal more can and must be done to reduce the danshygers and environmental degradations associated with coal production and use An integrated low-carbon energy strategy that incorporates C02 capture and storage can reconcile substantia I use of coa l in the coming decades with the imperatlve to prevent catastro phic changes to the earths climate m
_
How to Clean Coal C Can ine in OnEarth Nat ural Resollrces Defense Council 200 5 Avail able at wwwnrdcorgonearth OSfallcoallasp
IPCC Special Report on Carbon Capture and Storage 2005 Avqilable at http archrrvm n I env Ii ntipcc pages_medi alSRC CS-fi n a II IPCC Spec ial Reporton Carbon d i oxideC apt urea ndSt 0 rage htm
Avoiding Dangerous Climate Change ~ditec1 by H J Sch ellnhuber W Cramer N Nallicenovic T Wigley and G Yoh e Cambridge University Press 2006
Big Clal The Dirty Secret behind America s Energy Future J Goodell Houghton Mifflin 20 06
Carbo~ Dioxide Capture andG~ologic Storage J J Doniey RTGahowski C L David so n M A Wise N Gupt a S H Kim and E L Malone Tec hnology Report from the Second Phase of the Global Energy Technology Strategy Program 2006
Natural Resou rces Defense Council Web si te wwwnrdcor~globalwarming
PrincetonEnvironmentallnstitute Web site wwwprincet on edu-cmi
SCIENTIFIC AMERICAN 75
To slow climate change the authors urge power providers to build
integrated gasifi cation combined cycle [IGCC] coal power plants
with carbon dioxide capture and storage [CCS] capabilities
[below] rather than conventional steam -elect ric facilities
Conventional coal plants burn the fuel to transform water into
steam to turn a turbine-generator If CCS technology were applied
to a steam plant C02 would be extracted from the flue exhaust
An IGCC plant in contrast employs a partial oxidation reaction
using limited oxygen to convert the co al into a so-ca lled
synthesis gas or syngas [mostly hydrogen and carbon
mono xide] lt is much easier and less costly to remove CO 2 from
syngas than from the flue gases of a steam plant The hydrogenshy
rich syngas remainingafterC02 extraction is then burned to run
both gas and steam turbine-generators The wor ld s first
commerciallGCC project that will sequester C02 underground is
being planned near Long Beach Calif
C02 EXTRACTION 2 The syngas is reacte d with steam to produce a gaseous mixture of mostly carbon dioxide and hydrogen [H 2 ] from which CO 2 is extracted for burial [yellow pathways at bottom]
GASIFICATION 1 Coal water and oxygen are fed into a high-pressure gasifier in which the coal is partially oxmiddotidized and converted into syngas
CO 2 is compressed and middotsent via pipeline systems to permanent underground storage sites
3 Hydrogen-rich syngas is burned and the combustion products drive a gas turb ine-generator
4 The hot gas turbine exhaust passes to a heat-recovery steam generator which converts water to steam that turns a steam turbine-generator
C02 can be sent into saline formations-saltwatermiddot filled strata capped with impermeable rock
wwwsciam_com SCIENTIFIC AMERICAN 71
can meet the objectives of climate change mitigation at the least cost Funshydamenta lIy different approaches to ees would be pursued for power plants usshying the conventional pulverized-coal steam cycle and the newer integrated gasification combined cycle (IGee) Alshythough todays coal IGee power (with C02 venting) is slightly more expensive than coal steam-electric power it looks like IGee is the most effective and least expensive option for ees
Standard plants burn coal in a boiler at atmospheric pressure The heat genshyerated in coal combustion transforms water into steam which turns a steam turbine whose mechanica I energy is converted to electricity by a generator In modern plants the gases produced by combustion (flue gases) then pass through devices that remove particushylates and oxides of sulfur and nitrogen before being exhausted via smokestacks into the air
Carbon dioxide could be extracted from the flue gases of such steam-elecshytric plants after the removal of convenshytional pollutants Because the flue gases contain substantial amounts of nitrogen (the result of burning coal in air which is about 80 percent nitrogen) the carshybon dioxide would be recovered at low concentration and pressure-which imshyplies that the C02 would have to be reshymoved from large volumes of gas using processes that are both energy-intensive and expensive The captured C02 would then be compressed and piped to an apshypropriate storage site
In an IGee system coal is not burned but rather partially oxidized (reacted with limited quantities of oxygen from
DAVID G HAWKI NS DANIEL A LASH OF and ROBERT H WILLIAMS have endeavored to help
stave off climate change problems for decades Hawkins is director of the Climate Center
at the Natural Resources Defense Council (NRDCJ where he has worked on air energy
and climate issues for 35 years Hawkins serves on the boards of many bodies that advise
government on environmental and energy subjects Lashof is science director and depmiddot
uty director of the NRDCs Climate Center at which he has focused on national energy
policy climate science and solutions to global warming since 1989 Before arriving at the
NRDC Lashof developed policy options for stabilizing global climate at the US Environmiddot
mental Protection Agency Williams is a se nior research scientist at Princeton Un iversity
which he joined in 1975At the universitys Princeton Environmentallnstitute he heads
the Energy Systems Policy Analysis Group and the Carbon Capture Group under the inmiddot
stitutes Carbon Mitigation Initiative (which is supported by BP and Ford)
72 SCIENTIFIC AMERICAN
Commercial power plants using IGCC technology such as this one in Italy have been operating since 1994 Togetherthey generate 3600 megawatts of electricity
an air separation plant and with steam) at high pressure in a gasifier The prodshyuct of gasification is so-called synthesis gas or syngas which is composed mostshyly of carbon monoxide and hydrogen undiluted with nitrogen In current practice IGee operations remove most conventional pollutants from the syngas and then burn it to turn both gas and steam turbine-generators in what is called a combined cycle
In an IGee plant designed to capshyture C02 the syngas exiting the gasifier after being cooled and cleaned of parshyticles would be reacted with steam to produce a gaseous mixture made up mainly of carbon dioxide and hydrogen The C02 would then be extracted
dried compressed and transported to a storage site The remaining hydrogenshyrich gas wou ld be bu rned in a combined cycle plant to generate power [see box on preceding page]
Analyses indicate that carbon dioxshyide capture at Ieee plants consuming high-quality bituminous coals would entai I significantly sma ller energy and cost penalties and lower total generashytion costs than what could be achieved in conventional coal plants that capshytured and stored C02 Gasification sysshytems recover CO2 from a gaseous stream at high concentration and pressure a feature that makes the process much easier than it would be in conventional steam facilities (The extent of the ben shyefits is less clear for lower-grade subbishytuminous coals and lignites which have received much less study) Precombusshytion remova I of conventional pollutants including mercury makes it feasible to realize very low levels of emissions at much reduced costs and with much smaller energy penalties than with cleanup systems for flue gases in convenshytional plants
Captured carbon dioxide can be transported by pipeline up to several hundred kilometers to suitable geologic storage sites and subsequent subterrashynean storage with the pressure produced during capture Longer distances may however require recompression to comshypensate for friction losses during pipe shyline transfer
Overall pursuing ees for coa I powshyer facilities requires the consumption of more coal to generate a kilowatt-hour of electricity than when C02 is ventedshyabout 30 percent extra in the case of coal steam-electric plants and less than 20 percent more for IGee plants But overall coal use would not necessarily increase because the higher price of coal-based electricity resulting from adding ees equipment would dampen demand for coal-based electricity rna kshying renewable energy sources and enershygy-efficient products more desirable to consumers
The cost of ees will depend on the type of power plant the distance to the storage site the properties of the storage
SEPTEMBER 2006
II reservoir and the availability of opporshy cost would occur as long as the oil price ed policies for climate change mitigation tunities (such as enhanced oil recovery) is at least $35 per barrel which is much that would make CCS cost-effective for for selling the captured C02 A recent lower than current prices uses not associated with enhanced oil study co-authored by one of us (Wilshy recovery Absent revenues from sales to
liams) estimated the incremental electric CCS Now or Later oil field operators applying CCS to new generation costs of two alternative CCS MANY ELECTR1CITY producers in coal plants using current technology options for coal IeCC plants under typshy the industria I world recognize that enshy would be the least-cost path only if the ical production transport and storage vironmental concerns will at some point cost of emitting C02 were at least $25 conditions For C02 sequestration in a force them to implement CCS if they are to $30 per metric ton Many current saline formation 100 kilometers from a to continue to employ coal But rather policy proposals for climate change mitshypower plant the study calculated that than building plants that actually capshy igation in the US envision significantly the incremental cost of CCS would be ture and store carbon dioxide most lower cost penalties to power providers 19 cents per kilowatt-hour (beyond the plan to construct conventional steam for releasing C02 (or similarly payshygeneration cost of 47 cents per kilowattshy facilities they claim will be C02 capshy ments for C02 emissions-reduction hour for a coal IeCC plant that vents ture ready-convertible when CCS is credits) C02-a 40 percent premium) For CCS mandated Yet delaying CCS at coal power pursued in conjunction with enhanced Power providers often defend those plants until economy-wide carbon dioxshyoil recovery at a distance of 100 kilomeshy decisions by noting that the US and ide control costs are greater than CCS ters from the conversion plant the analshy most other countries with coal-intensive costs is shortsighted For several reashyysis finds no increase in net generation energy economies have not yet institut- sons the coal and power industries and
- I I I e I i L I
Despitethe current popularity of the term clean coal coal is in factdirty Although carbon capture and storage could prevent much carbon dioxide fromentering the atmosphere coal production and consumption is still oneaf the most destructive industrial processes As long as
thewbrld copsumescoal more must be done to mitigate the harm it causes
MINING DANGERS Underground mining can cause serious problems on the
Coal mining is among the most dangerous occupations Official surface Mines collapse and cause land subsidence
reports for 2005 indicate that roughly 6000 people died damaging homes and roads Acidic mine drainage caused by
(16 a day) in China from coal mine floods iave~ins fires and slJlfur compounds leaching from coal waste into surface
explosions Unofficial estimates are waters has tainted thousands of
closer to 10000 Some 600000 streams The acid leachate releases
Chinese toal minegtrsslJfferfrom heavy metals that foul groundwater
black lung disease The Us has better safety TOXIC EMISSIONS
Coalmiddotfired power plants account for
all-time low of 22 domestic fatalities practices thanChina and achieved an
more than two thirds of sulfur dioxide
in 2005 US mines are far from middot andabout one fifth of nitrogen oxide
perfect however as evidenced by a middot emissions in the US Sulfur dioxide
series offatalities inearly 2006 reacts in the atmosphere to form middot sulfate particles which in addition to
ENVIRONME~TAL EFFECTS middot causing acid rain contribute to fine
Conventiona-l coal mining proces~ing particulate pollution a contaminant
and transportation practices scar linked to thousands of premature
the landscape and pollute the water which harms people and deaths from lung disease nationwide Nitrogen oxides combine
eCosystems The most destructive mining teChniques Clear with hydrocarbons to form smog-causingground-Ievel ozone
forests and blast away mountaintops The overburden Coalmiddotburning plants ltllso emit approximately 48 metric
removed when a coal seam is uncovered middotis typically dumped tons of mercury a year in America Thishighly toxic element
into nearby valleyswhere it often buries rivers andstreams persists in the ecosystem Aftertransforming into methyl
Stripmiddotmining operations rip apart ecosystems and reshape mercury it accum ulates in the tissues offishes Ingested
the landscape Although regulations require landreclamatipn mercury is particularly detrimental to fetuses andyoung
in principle it is often left incomplete Asforests are replaced infants exposed during periods of rapid brain growth causing
with nonnative grasslands soils become compacted and developmental and neurOlogical damage
streams contaminated -DGH DAL and RHW
wwwsciamcom SCIENTIFIC AMERICAN 73
pound Acid runoff from a Pennsylvania coal mine stains this creek bed orange
--_bull 1
THE PATH TO C02MITIGATION Our calculations indicate that a prompt commitment to carbon capture and storage
[eeS) would make it possible to meet global energy demands while limiting the
atmospheric carbon dioxide concentration to 450 parts per million by volume [ppmv)
This goal could be attained if by midcentury sequestration is applied for all coal use
and about a quarter of natural gas use while energy efficiency increases rapidly and
carbon-free energy sources expand sevenfold Under these conditions overall fossilshy
fuel consumption could expand modestly from today by midcentury coal use could be
somewhat higher than at present oil use would be down by a fifth and natural gas use
would expand by half
To realize this pathway growth rates for fossil-fuel use would have to be reduced
now and ee Smust begin for coal early in the next decade and for natural gas early in
the next quarter of a century The top graph below depicts the energy provided by the
various sources if this mitigation path were followed The bottom graph shows total
quantities of carbon extracted from the earth [emissions plus storage)
-DGH DAL and RHW
FOSSIL AND CARBON-FREE ENEmiddotRGY MIX FOR C02 STABILIZATION
35 Additional carbon-free energ~ needed to satisfy demand
30 Oil
~ bull Natural gas with CCS cu ~ 25 Natural gas with C02 vented ~ bull Coal with CCS ~ 20 Coal with C02 vented ~ eo c
IJJ 15 ~ cu
sect Q
10
5
0 2010 2030 2050 2070 2090
FATE OF CARBON FROM FOSSIL ENERGY SYSTEMS
cu 10 ~
n cu
c 8B cu on On
c 0 5 -e cu u ~ 4e IJJ
0 ~
tgt 2 0 Vi
0 I i i 2010 2030 2050 2070 2090
Year
74 SCIENTIFIC AMERICAN
bull Natural gas C stored
NalUral gas C emitted
Coal C emitted
Emissions level needed to stabilize C02at 450 ppmv
bull Coal carbon [C) stored
society would ultimately benefit if deshyployment of plants fitted with CCS equipment were begun now
First the fastest way to reduce CCS costs is via learning by doing-the acshycumulation of experience in building and running such plants The faster the understanding is accumulated the quicker the know-how with the new technology will grow and the more rapshyidly the costs will drop
Second installing CCS equipment as soon as possible should save money in the long run Most power stations curshyrently under construction will still be opshyerating decades from now when it is likely that CCS efforts will be obligatory Retrofitting generating faciliti es for CCS is inherently more expensive than deshyploying CCS in new plants Moreover in the absence of C02 emission limits fashymiliar conventional coal steam-electric technologies will tend to be favored for most new plant construction over newer gasification technologies for which CCS is more cost-effective
Finally rapid implementation would allow for continued use of fossil fuels in the near term (until more environmenshytally friendly sources become prevalent) without pushing atmospheric carbon dioxide beyond tolerable levels Our studies indicate that it is feasible to stashybilize atmospheric C02 levels at 450 ppmv over the next half a century if coal-based energy is completely decarshybonized and other measures described in the box at the left are implemented This effort would involve decarbonizing 36 gigawatts of new coal generating cashypacity by 2020 (corresponding to 7 pershycent of the new coal capacity expected to be built worldwide during the decade beginning in 2011 under business-asshyusual conditions) In the 35 years after 2020 C02 capture would need to rise at an average rate of about 12 percent a year Such a sustained pace is high compared with typical market growth rates for energy but is not unprecedentshyed It is much less than the expansion rate for nuclear generating capacity in its heyd ay-1956 to 1980-during which global capacity rose at an average rate of 40 percent annually Further the
SEPTEMBER 2005
expansion rates for bo th wind a nd sola r photovoltaic power capaci ties worldshywide have hovered around 30 percent a year since the ea rly 1990s In a ll three cases such growth would not have been practical without public policy mea shysures to suppor t them
Our calculations indica te that the costs of CCS deployment would be manshyageable as well Using conservative assumptions-such as that technology will not improve over time-we estimate that th e present worth of the cost of capturing and storing all C02produced by coal-based electricity generation pla nts du ring the next 200 years will be $18 triiJion (in 2002 dollars) That might seem like a high price tag but it is equivalent to just 007 percent of the curren t value of gross world prod uc t over the same interva l Thus it is plaushyslble that a rapid decarbonization path for coal is both phys ica lly and economshyically feasible although deta iled regionshya l analyses are needed to confirm thi s conclusion
Policy Push Is Nee d THO SE GOO D R EASO N S for comshymencing concerted CCS efforts soon will probably not move the industry unshyless it is a lso prodded by new public polshyicies Such initiatives would be part of a broader d rive to control carbon dioxide emissions from a ll sou rces
In the US a nat ional program to limit C02 emissions mu st be enac ted soon to introduce the government regshyu lat ions a nd market incentives necshyessary to shift investment to the leastshypolluting energy technologies promptly and on a w ide scale Leaders in the American business and policy commushynities increasi ngly agree that quantifi shyable a nd enforceable rest r ictions on global warming emissions are imperashytive and inev ita ble To ensure that powshyer companies put into practice the reshyductions in a cost-effective fashion a market for trading C02emissions credshyits shou ld be created-one similar to that for the sulfur emissions that cause acid rain In such a plan organizations that intend to exceed designated emisshysion limits may buy cred its from others
www s ciamcom
that are able to stay below these va lues Enhancing energy efficienc y efforts
and raising renewable energy producshyti on are cri tical to achieving carbon dishyox ide limits at the lowes t possible cost A po rtion of the emission a llowances created by a carbon cap-and-trade proshygram shou Id be a llocated to the es tabshylishment of a fund to help overcome inshystitutional ba rriers and technica l r isks that obstruct widespread deployment of otherwise cost-effective C02 mitigation technologies
=
Delaying carbon capturemiddot
and storage at coal power
plants is shortsighted
Even if a carbon dioxide cap-andshytrade program were enacted in the next few yea rs the econom ic value of C02 emissions reduction may not be enough initially to convince power providers to invest in power systems with CCS To avoid the construction of another genshyeration of conventional coa l plants it is essential that the fed eral government esshytablish incentives that promote CCS
One ap proach would be to insist that an increasing share of total coal-based
MORE TO EXPLORE
electricity generation comes from faci lishyties that meet a low C02 emissions stanshydard-perhaps a maximum of 30 grams of carbon per k ilowatt-hour (a n achievshyable goal using todays coal CCS techshynologies) Such a goa l might be ach ieved by obliging electricity producers that use coal to include a growing fraction of decarbon ized coal power in thei r supply portfolios Each covered electricity proshyducer could either generate the required amount of decarbonized coal power or purchase decarbonized-generation credshyits Th is sys tem would share the increshym en tal costs of CCS for coal power among all US coal-based electricity producers and consumers
If the surge of conventional coa lshyfired power plants currently on drawing boa rds is built as planned atmospheric carbon dioxide levels will almost cershytainly exceed 450 ppmv Vle can meet global energy needs while st ill stabili zshying C02 at450 ppmv however through a combination of improved efficiency in energy use greater reliance on renewshyable energy resources and for the new coal investments that are made the inshystallation of C02 capture and geolog ic storage technologies Even though there is no such thing as clean coal more can and must be done to reduce the danshygers and environmental degradations associated with coal production and use An integrated low-carbon energy strategy that incorporates C02 capture and storage can reconcile substantia I use of coa l in the coming decades with the imperatlve to prevent catastro phic changes to the earths climate m
_
How to Clean Coal C Can ine in OnEarth Nat ural Resollrces Defense Council 200 5 Avail able at wwwnrdcorgonearth OSfallcoallasp
IPCC Special Report on Carbon Capture and Storage 2005 Avqilable at http archrrvm n I env Ii ntipcc pages_medi alSRC CS-fi n a II IPCC Spec ial Reporton Carbon d i oxideC apt urea ndSt 0 rage htm
Avoiding Dangerous Climate Change ~ditec1 by H J Sch ellnhuber W Cramer N Nallicenovic T Wigley and G Yoh e Cambridge University Press 2006
Big Clal The Dirty Secret behind America s Energy Future J Goodell Houghton Mifflin 20 06
Carbo~ Dioxide Capture andG~ologic Storage J J Doniey RTGahowski C L David so n M A Wise N Gupt a S H Kim and E L Malone Tec hnology Report from the Second Phase of the Global Energy Technology Strategy Program 2006
Natural Resou rces Defense Council Web si te wwwnrdcor~globalwarming
PrincetonEnvironmentallnstitute Web site wwwprincet on edu-cmi
SCIENTIFIC AMERICAN 75
can meet the objectives of climate change mitigation at the least cost Funshydamenta lIy different approaches to ees would be pursued for power plants usshying the conventional pulverized-coal steam cycle and the newer integrated gasification combined cycle (IGee) Alshythough todays coal IGee power (with C02 venting) is slightly more expensive than coal steam-electric power it looks like IGee is the most effective and least expensive option for ees
Standard plants burn coal in a boiler at atmospheric pressure The heat genshyerated in coal combustion transforms water into steam which turns a steam turbine whose mechanica I energy is converted to electricity by a generator In modern plants the gases produced by combustion (flue gases) then pass through devices that remove particushylates and oxides of sulfur and nitrogen before being exhausted via smokestacks into the air
Carbon dioxide could be extracted from the flue gases of such steam-elecshytric plants after the removal of convenshytional pollutants Because the flue gases contain substantial amounts of nitrogen (the result of burning coal in air which is about 80 percent nitrogen) the carshybon dioxide would be recovered at low concentration and pressure-which imshyplies that the C02 would have to be reshymoved from large volumes of gas using processes that are both energy-intensive and expensive The captured C02 would then be compressed and piped to an apshypropriate storage site
In an IGee system coal is not burned but rather partially oxidized (reacted with limited quantities of oxygen from
DAVID G HAWKI NS DANIEL A LASH OF and ROBERT H WILLIAMS have endeavored to help
stave off climate change problems for decades Hawkins is director of the Climate Center
at the Natural Resources Defense Council (NRDCJ where he has worked on air energy
and climate issues for 35 years Hawkins serves on the boards of many bodies that advise
government on environmental and energy subjects Lashof is science director and depmiddot
uty director of the NRDCs Climate Center at which he has focused on national energy
policy climate science and solutions to global warming since 1989 Before arriving at the
NRDC Lashof developed policy options for stabilizing global climate at the US Environmiddot
mental Protection Agency Williams is a se nior research scientist at Princeton Un iversity
which he joined in 1975At the universitys Princeton Environmentallnstitute he heads
the Energy Systems Policy Analysis Group and the Carbon Capture Group under the inmiddot
stitutes Carbon Mitigation Initiative (which is supported by BP and Ford)
72 SCIENTIFIC AMERICAN
Commercial power plants using IGCC technology such as this one in Italy have been operating since 1994 Togetherthey generate 3600 megawatts of electricity
an air separation plant and with steam) at high pressure in a gasifier The prodshyuct of gasification is so-called synthesis gas or syngas which is composed mostshyly of carbon monoxide and hydrogen undiluted with nitrogen In current practice IGee operations remove most conventional pollutants from the syngas and then burn it to turn both gas and steam turbine-generators in what is called a combined cycle
In an IGee plant designed to capshyture C02 the syngas exiting the gasifier after being cooled and cleaned of parshyticles would be reacted with steam to produce a gaseous mixture made up mainly of carbon dioxide and hydrogen The C02 would then be extracted
dried compressed and transported to a storage site The remaining hydrogenshyrich gas wou ld be bu rned in a combined cycle plant to generate power [see box on preceding page]
Analyses indicate that carbon dioxshyide capture at Ieee plants consuming high-quality bituminous coals would entai I significantly sma ller energy and cost penalties and lower total generashytion costs than what could be achieved in conventional coal plants that capshytured and stored C02 Gasification sysshytems recover CO2 from a gaseous stream at high concentration and pressure a feature that makes the process much easier than it would be in conventional steam facilities (The extent of the ben shyefits is less clear for lower-grade subbishytuminous coals and lignites which have received much less study) Precombusshytion remova I of conventional pollutants including mercury makes it feasible to realize very low levels of emissions at much reduced costs and with much smaller energy penalties than with cleanup systems for flue gases in convenshytional plants
Captured carbon dioxide can be transported by pipeline up to several hundred kilometers to suitable geologic storage sites and subsequent subterrashynean storage with the pressure produced during capture Longer distances may however require recompression to comshypensate for friction losses during pipe shyline transfer
Overall pursuing ees for coa I powshyer facilities requires the consumption of more coal to generate a kilowatt-hour of electricity than when C02 is ventedshyabout 30 percent extra in the case of coal steam-electric plants and less than 20 percent more for IGee plants But overall coal use would not necessarily increase because the higher price of coal-based electricity resulting from adding ees equipment would dampen demand for coal-based electricity rna kshying renewable energy sources and enershygy-efficient products more desirable to consumers
The cost of ees will depend on the type of power plant the distance to the storage site the properties of the storage
SEPTEMBER 2006
II reservoir and the availability of opporshy cost would occur as long as the oil price ed policies for climate change mitigation tunities (such as enhanced oil recovery) is at least $35 per barrel which is much that would make CCS cost-effective for for selling the captured C02 A recent lower than current prices uses not associated with enhanced oil study co-authored by one of us (Wilshy recovery Absent revenues from sales to
liams) estimated the incremental electric CCS Now or Later oil field operators applying CCS to new generation costs of two alternative CCS MANY ELECTR1CITY producers in coal plants using current technology options for coal IeCC plants under typshy the industria I world recognize that enshy would be the least-cost path only if the ical production transport and storage vironmental concerns will at some point cost of emitting C02 were at least $25 conditions For C02 sequestration in a force them to implement CCS if they are to $30 per metric ton Many current saline formation 100 kilometers from a to continue to employ coal But rather policy proposals for climate change mitshypower plant the study calculated that than building plants that actually capshy igation in the US envision significantly the incremental cost of CCS would be ture and store carbon dioxide most lower cost penalties to power providers 19 cents per kilowatt-hour (beyond the plan to construct conventional steam for releasing C02 (or similarly payshygeneration cost of 47 cents per kilowattshy facilities they claim will be C02 capshy ments for C02 emissions-reduction hour for a coal IeCC plant that vents ture ready-convertible when CCS is credits) C02-a 40 percent premium) For CCS mandated Yet delaying CCS at coal power pursued in conjunction with enhanced Power providers often defend those plants until economy-wide carbon dioxshyoil recovery at a distance of 100 kilomeshy decisions by noting that the US and ide control costs are greater than CCS ters from the conversion plant the analshy most other countries with coal-intensive costs is shortsighted For several reashyysis finds no increase in net generation energy economies have not yet institut- sons the coal and power industries and
- I I I e I i L I
Despitethe current popularity of the term clean coal coal is in factdirty Although carbon capture and storage could prevent much carbon dioxide fromentering the atmosphere coal production and consumption is still oneaf the most destructive industrial processes As long as
thewbrld copsumescoal more must be done to mitigate the harm it causes
MINING DANGERS Underground mining can cause serious problems on the
Coal mining is among the most dangerous occupations Official surface Mines collapse and cause land subsidence
reports for 2005 indicate that roughly 6000 people died damaging homes and roads Acidic mine drainage caused by
(16 a day) in China from coal mine floods iave~ins fires and slJlfur compounds leaching from coal waste into surface
explosions Unofficial estimates are waters has tainted thousands of
closer to 10000 Some 600000 streams The acid leachate releases
Chinese toal minegtrsslJfferfrom heavy metals that foul groundwater
black lung disease The Us has better safety TOXIC EMISSIONS
Coalmiddotfired power plants account for
all-time low of 22 domestic fatalities practices thanChina and achieved an
more than two thirds of sulfur dioxide
in 2005 US mines are far from middot andabout one fifth of nitrogen oxide
perfect however as evidenced by a middot emissions in the US Sulfur dioxide
series offatalities inearly 2006 reacts in the atmosphere to form middot sulfate particles which in addition to
ENVIRONME~TAL EFFECTS middot causing acid rain contribute to fine
Conventiona-l coal mining proces~ing particulate pollution a contaminant
and transportation practices scar linked to thousands of premature
the landscape and pollute the water which harms people and deaths from lung disease nationwide Nitrogen oxides combine
eCosystems The most destructive mining teChniques Clear with hydrocarbons to form smog-causingground-Ievel ozone
forests and blast away mountaintops The overburden Coalmiddotburning plants ltllso emit approximately 48 metric
removed when a coal seam is uncovered middotis typically dumped tons of mercury a year in America Thishighly toxic element
into nearby valleyswhere it often buries rivers andstreams persists in the ecosystem Aftertransforming into methyl
Stripmiddotmining operations rip apart ecosystems and reshape mercury it accum ulates in the tissues offishes Ingested
the landscape Although regulations require landreclamatipn mercury is particularly detrimental to fetuses andyoung
in principle it is often left incomplete Asforests are replaced infants exposed during periods of rapid brain growth causing
with nonnative grasslands soils become compacted and developmental and neurOlogical damage
streams contaminated -DGH DAL and RHW
wwwsciamcom SCIENTIFIC AMERICAN 73
pound Acid runoff from a Pennsylvania coal mine stains this creek bed orange
--_bull 1
THE PATH TO C02MITIGATION Our calculations indicate that a prompt commitment to carbon capture and storage
[eeS) would make it possible to meet global energy demands while limiting the
atmospheric carbon dioxide concentration to 450 parts per million by volume [ppmv)
This goal could be attained if by midcentury sequestration is applied for all coal use
and about a quarter of natural gas use while energy efficiency increases rapidly and
carbon-free energy sources expand sevenfold Under these conditions overall fossilshy
fuel consumption could expand modestly from today by midcentury coal use could be
somewhat higher than at present oil use would be down by a fifth and natural gas use
would expand by half
To realize this pathway growth rates for fossil-fuel use would have to be reduced
now and ee Smust begin for coal early in the next decade and for natural gas early in
the next quarter of a century The top graph below depicts the energy provided by the
various sources if this mitigation path were followed The bottom graph shows total
quantities of carbon extracted from the earth [emissions plus storage)
-DGH DAL and RHW
FOSSIL AND CARBON-FREE ENEmiddotRGY MIX FOR C02 STABILIZATION
35 Additional carbon-free energ~ needed to satisfy demand
30 Oil
~ bull Natural gas with CCS cu ~ 25 Natural gas with C02 vented ~ bull Coal with CCS ~ 20 Coal with C02 vented ~ eo c
IJJ 15 ~ cu
sect Q
10
5
0 2010 2030 2050 2070 2090
FATE OF CARBON FROM FOSSIL ENERGY SYSTEMS
cu 10 ~
n cu
c 8B cu on On
c 0 5 -e cu u ~ 4e IJJ
0 ~
tgt 2 0 Vi
0 I i i 2010 2030 2050 2070 2090
Year
74 SCIENTIFIC AMERICAN
bull Natural gas C stored
NalUral gas C emitted
Coal C emitted
Emissions level needed to stabilize C02at 450 ppmv
bull Coal carbon [C) stored
society would ultimately benefit if deshyployment of plants fitted with CCS equipment were begun now
First the fastest way to reduce CCS costs is via learning by doing-the acshycumulation of experience in building and running such plants The faster the understanding is accumulated the quicker the know-how with the new technology will grow and the more rapshyidly the costs will drop
Second installing CCS equipment as soon as possible should save money in the long run Most power stations curshyrently under construction will still be opshyerating decades from now when it is likely that CCS efforts will be obligatory Retrofitting generating faciliti es for CCS is inherently more expensive than deshyploying CCS in new plants Moreover in the absence of C02 emission limits fashymiliar conventional coal steam-electric technologies will tend to be favored for most new plant construction over newer gasification technologies for which CCS is more cost-effective
Finally rapid implementation would allow for continued use of fossil fuels in the near term (until more environmenshytally friendly sources become prevalent) without pushing atmospheric carbon dioxide beyond tolerable levels Our studies indicate that it is feasible to stashybilize atmospheric C02 levels at 450 ppmv over the next half a century if coal-based energy is completely decarshybonized and other measures described in the box at the left are implemented This effort would involve decarbonizing 36 gigawatts of new coal generating cashypacity by 2020 (corresponding to 7 pershycent of the new coal capacity expected to be built worldwide during the decade beginning in 2011 under business-asshyusual conditions) In the 35 years after 2020 C02 capture would need to rise at an average rate of about 12 percent a year Such a sustained pace is high compared with typical market growth rates for energy but is not unprecedentshyed It is much less than the expansion rate for nuclear generating capacity in its heyd ay-1956 to 1980-during which global capacity rose at an average rate of 40 percent annually Further the
SEPTEMBER 2005
expansion rates for bo th wind a nd sola r photovoltaic power capaci ties worldshywide have hovered around 30 percent a year since the ea rly 1990s In a ll three cases such growth would not have been practical without public policy mea shysures to suppor t them
Our calculations indica te that the costs of CCS deployment would be manshyageable as well Using conservative assumptions-such as that technology will not improve over time-we estimate that th e present worth of the cost of capturing and storing all C02produced by coal-based electricity generation pla nts du ring the next 200 years will be $18 triiJion (in 2002 dollars) That might seem like a high price tag but it is equivalent to just 007 percent of the curren t value of gross world prod uc t over the same interva l Thus it is plaushyslble that a rapid decarbonization path for coal is both phys ica lly and economshyically feasible although deta iled regionshya l analyses are needed to confirm thi s conclusion
Policy Push Is Nee d THO SE GOO D R EASO N S for comshymencing concerted CCS efforts soon will probably not move the industry unshyless it is a lso prodded by new public polshyicies Such initiatives would be part of a broader d rive to control carbon dioxide emissions from a ll sou rces
In the US a nat ional program to limit C02 emissions mu st be enac ted soon to introduce the government regshyu lat ions a nd market incentives necshyessary to shift investment to the leastshypolluting energy technologies promptly and on a w ide scale Leaders in the American business and policy commushynities increasi ngly agree that quantifi shyable a nd enforceable rest r ictions on global warming emissions are imperashytive and inev ita ble To ensure that powshyer companies put into practice the reshyductions in a cost-effective fashion a market for trading C02emissions credshyits shou ld be created-one similar to that for the sulfur emissions that cause acid rain In such a plan organizations that intend to exceed designated emisshysion limits may buy cred its from others
www s ciamcom
that are able to stay below these va lues Enhancing energy efficienc y efforts
and raising renewable energy producshyti on are cri tical to achieving carbon dishyox ide limits at the lowes t possible cost A po rtion of the emission a llowances created by a carbon cap-and-trade proshygram shou Id be a llocated to the es tabshylishment of a fund to help overcome inshystitutional ba rriers and technica l r isks that obstruct widespread deployment of otherwise cost-effective C02 mitigation technologies
=
Delaying carbon capturemiddot
and storage at coal power
plants is shortsighted
Even if a carbon dioxide cap-andshytrade program were enacted in the next few yea rs the econom ic value of C02 emissions reduction may not be enough initially to convince power providers to invest in power systems with CCS To avoid the construction of another genshyeration of conventional coa l plants it is essential that the fed eral government esshytablish incentives that promote CCS
One ap proach would be to insist that an increasing share of total coal-based
MORE TO EXPLORE
electricity generation comes from faci lishyties that meet a low C02 emissions stanshydard-perhaps a maximum of 30 grams of carbon per k ilowatt-hour (a n achievshyable goal using todays coal CCS techshynologies) Such a goa l might be ach ieved by obliging electricity producers that use coal to include a growing fraction of decarbon ized coal power in thei r supply portfolios Each covered electricity proshyducer could either generate the required amount of decarbonized coal power or purchase decarbonized-generation credshyits Th is sys tem would share the increshym en tal costs of CCS for coal power among all US coal-based electricity producers and consumers
If the surge of conventional coa lshyfired power plants currently on drawing boa rds is built as planned atmospheric carbon dioxide levels will almost cershytainly exceed 450 ppmv Vle can meet global energy needs while st ill stabili zshying C02 at450 ppmv however through a combination of improved efficiency in energy use greater reliance on renewshyable energy resources and for the new coal investments that are made the inshystallation of C02 capture and geolog ic storage technologies Even though there is no such thing as clean coal more can and must be done to reduce the danshygers and environmental degradations associated with coal production and use An integrated low-carbon energy strategy that incorporates C02 capture and storage can reconcile substantia I use of coa l in the coming decades with the imperatlve to prevent catastro phic changes to the earths climate m
_
How to Clean Coal C Can ine in OnEarth Nat ural Resollrces Defense Council 200 5 Avail able at wwwnrdcorgonearth OSfallcoallasp
IPCC Special Report on Carbon Capture and Storage 2005 Avqilable at http archrrvm n I env Ii ntipcc pages_medi alSRC CS-fi n a II IPCC Spec ial Reporton Carbon d i oxideC apt urea ndSt 0 rage htm
Avoiding Dangerous Climate Change ~ditec1 by H J Sch ellnhuber W Cramer N Nallicenovic T Wigley and G Yoh e Cambridge University Press 2006
Big Clal The Dirty Secret behind America s Energy Future J Goodell Houghton Mifflin 20 06
Carbo~ Dioxide Capture andG~ologic Storage J J Doniey RTGahowski C L David so n M A Wise N Gupt a S H Kim and E L Malone Tec hnology Report from the Second Phase of the Global Energy Technology Strategy Program 2006
Natural Resou rces Defense Council Web si te wwwnrdcor~globalwarming
PrincetonEnvironmentallnstitute Web site wwwprincet on edu-cmi
SCIENTIFIC AMERICAN 75
II reservoir and the availability of opporshy cost would occur as long as the oil price ed policies for climate change mitigation tunities (such as enhanced oil recovery) is at least $35 per barrel which is much that would make CCS cost-effective for for selling the captured C02 A recent lower than current prices uses not associated with enhanced oil study co-authored by one of us (Wilshy recovery Absent revenues from sales to
liams) estimated the incremental electric CCS Now or Later oil field operators applying CCS to new generation costs of two alternative CCS MANY ELECTR1CITY producers in coal plants using current technology options for coal IeCC plants under typshy the industria I world recognize that enshy would be the least-cost path only if the ical production transport and storage vironmental concerns will at some point cost of emitting C02 were at least $25 conditions For C02 sequestration in a force them to implement CCS if they are to $30 per metric ton Many current saline formation 100 kilometers from a to continue to employ coal But rather policy proposals for climate change mitshypower plant the study calculated that than building plants that actually capshy igation in the US envision significantly the incremental cost of CCS would be ture and store carbon dioxide most lower cost penalties to power providers 19 cents per kilowatt-hour (beyond the plan to construct conventional steam for releasing C02 (or similarly payshygeneration cost of 47 cents per kilowattshy facilities they claim will be C02 capshy ments for C02 emissions-reduction hour for a coal IeCC plant that vents ture ready-convertible when CCS is credits) C02-a 40 percent premium) For CCS mandated Yet delaying CCS at coal power pursued in conjunction with enhanced Power providers often defend those plants until economy-wide carbon dioxshyoil recovery at a distance of 100 kilomeshy decisions by noting that the US and ide control costs are greater than CCS ters from the conversion plant the analshy most other countries with coal-intensive costs is shortsighted For several reashyysis finds no increase in net generation energy economies have not yet institut- sons the coal and power industries and
- I I I e I i L I
Despitethe current popularity of the term clean coal coal is in factdirty Although carbon capture and storage could prevent much carbon dioxide fromentering the atmosphere coal production and consumption is still oneaf the most destructive industrial processes As long as
thewbrld copsumescoal more must be done to mitigate the harm it causes
MINING DANGERS Underground mining can cause serious problems on the
Coal mining is among the most dangerous occupations Official surface Mines collapse and cause land subsidence
reports for 2005 indicate that roughly 6000 people died damaging homes and roads Acidic mine drainage caused by
(16 a day) in China from coal mine floods iave~ins fires and slJlfur compounds leaching from coal waste into surface
explosions Unofficial estimates are waters has tainted thousands of
closer to 10000 Some 600000 streams The acid leachate releases
Chinese toal minegtrsslJfferfrom heavy metals that foul groundwater
black lung disease The Us has better safety TOXIC EMISSIONS
Coalmiddotfired power plants account for
all-time low of 22 domestic fatalities practices thanChina and achieved an
more than two thirds of sulfur dioxide
in 2005 US mines are far from middot andabout one fifth of nitrogen oxide
perfect however as evidenced by a middot emissions in the US Sulfur dioxide
series offatalities inearly 2006 reacts in the atmosphere to form middot sulfate particles which in addition to
ENVIRONME~TAL EFFECTS middot causing acid rain contribute to fine
Conventiona-l coal mining proces~ing particulate pollution a contaminant
and transportation practices scar linked to thousands of premature
the landscape and pollute the water which harms people and deaths from lung disease nationwide Nitrogen oxides combine
eCosystems The most destructive mining teChniques Clear with hydrocarbons to form smog-causingground-Ievel ozone
forests and blast away mountaintops The overburden Coalmiddotburning plants ltllso emit approximately 48 metric
removed when a coal seam is uncovered middotis typically dumped tons of mercury a year in America Thishighly toxic element
into nearby valleyswhere it often buries rivers andstreams persists in the ecosystem Aftertransforming into methyl
Stripmiddotmining operations rip apart ecosystems and reshape mercury it accum ulates in the tissues offishes Ingested
the landscape Although regulations require landreclamatipn mercury is particularly detrimental to fetuses andyoung
in principle it is often left incomplete Asforests are replaced infants exposed during periods of rapid brain growth causing
with nonnative grasslands soils become compacted and developmental and neurOlogical damage
streams contaminated -DGH DAL and RHW
wwwsciamcom SCIENTIFIC AMERICAN 73
pound Acid runoff from a Pennsylvania coal mine stains this creek bed orange
--_bull 1
THE PATH TO C02MITIGATION Our calculations indicate that a prompt commitment to carbon capture and storage
[eeS) would make it possible to meet global energy demands while limiting the
atmospheric carbon dioxide concentration to 450 parts per million by volume [ppmv)
This goal could be attained if by midcentury sequestration is applied for all coal use
and about a quarter of natural gas use while energy efficiency increases rapidly and
carbon-free energy sources expand sevenfold Under these conditions overall fossilshy
fuel consumption could expand modestly from today by midcentury coal use could be
somewhat higher than at present oil use would be down by a fifth and natural gas use
would expand by half
To realize this pathway growth rates for fossil-fuel use would have to be reduced
now and ee Smust begin for coal early in the next decade and for natural gas early in
the next quarter of a century The top graph below depicts the energy provided by the
various sources if this mitigation path were followed The bottom graph shows total
quantities of carbon extracted from the earth [emissions plus storage)
-DGH DAL and RHW
FOSSIL AND CARBON-FREE ENEmiddotRGY MIX FOR C02 STABILIZATION
35 Additional carbon-free energ~ needed to satisfy demand
30 Oil
~ bull Natural gas with CCS cu ~ 25 Natural gas with C02 vented ~ bull Coal with CCS ~ 20 Coal with C02 vented ~ eo c
IJJ 15 ~ cu
sect Q
10
5
0 2010 2030 2050 2070 2090
FATE OF CARBON FROM FOSSIL ENERGY SYSTEMS
cu 10 ~
n cu
c 8B cu on On
c 0 5 -e cu u ~ 4e IJJ
0 ~
tgt 2 0 Vi
0 I i i 2010 2030 2050 2070 2090
Year
74 SCIENTIFIC AMERICAN
bull Natural gas C stored
NalUral gas C emitted
Coal C emitted
Emissions level needed to stabilize C02at 450 ppmv
bull Coal carbon [C) stored
society would ultimately benefit if deshyployment of plants fitted with CCS equipment were begun now
First the fastest way to reduce CCS costs is via learning by doing-the acshycumulation of experience in building and running such plants The faster the understanding is accumulated the quicker the know-how with the new technology will grow and the more rapshyidly the costs will drop
Second installing CCS equipment as soon as possible should save money in the long run Most power stations curshyrently under construction will still be opshyerating decades from now when it is likely that CCS efforts will be obligatory Retrofitting generating faciliti es for CCS is inherently more expensive than deshyploying CCS in new plants Moreover in the absence of C02 emission limits fashymiliar conventional coal steam-electric technologies will tend to be favored for most new plant construction over newer gasification technologies for which CCS is more cost-effective
Finally rapid implementation would allow for continued use of fossil fuels in the near term (until more environmenshytally friendly sources become prevalent) without pushing atmospheric carbon dioxide beyond tolerable levels Our studies indicate that it is feasible to stashybilize atmospheric C02 levels at 450 ppmv over the next half a century if coal-based energy is completely decarshybonized and other measures described in the box at the left are implemented This effort would involve decarbonizing 36 gigawatts of new coal generating cashypacity by 2020 (corresponding to 7 pershycent of the new coal capacity expected to be built worldwide during the decade beginning in 2011 under business-asshyusual conditions) In the 35 years after 2020 C02 capture would need to rise at an average rate of about 12 percent a year Such a sustained pace is high compared with typical market growth rates for energy but is not unprecedentshyed It is much less than the expansion rate for nuclear generating capacity in its heyd ay-1956 to 1980-during which global capacity rose at an average rate of 40 percent annually Further the
SEPTEMBER 2005
expansion rates for bo th wind a nd sola r photovoltaic power capaci ties worldshywide have hovered around 30 percent a year since the ea rly 1990s In a ll three cases such growth would not have been practical without public policy mea shysures to suppor t them
Our calculations indica te that the costs of CCS deployment would be manshyageable as well Using conservative assumptions-such as that technology will not improve over time-we estimate that th e present worth of the cost of capturing and storing all C02produced by coal-based electricity generation pla nts du ring the next 200 years will be $18 triiJion (in 2002 dollars) That might seem like a high price tag but it is equivalent to just 007 percent of the curren t value of gross world prod uc t over the same interva l Thus it is plaushyslble that a rapid decarbonization path for coal is both phys ica lly and economshyically feasible although deta iled regionshya l analyses are needed to confirm thi s conclusion
Policy Push Is Nee d THO SE GOO D R EASO N S for comshymencing concerted CCS efforts soon will probably not move the industry unshyless it is a lso prodded by new public polshyicies Such initiatives would be part of a broader d rive to control carbon dioxide emissions from a ll sou rces
In the US a nat ional program to limit C02 emissions mu st be enac ted soon to introduce the government regshyu lat ions a nd market incentives necshyessary to shift investment to the leastshypolluting energy technologies promptly and on a w ide scale Leaders in the American business and policy commushynities increasi ngly agree that quantifi shyable a nd enforceable rest r ictions on global warming emissions are imperashytive and inev ita ble To ensure that powshyer companies put into practice the reshyductions in a cost-effective fashion a market for trading C02emissions credshyits shou ld be created-one similar to that for the sulfur emissions that cause acid rain In such a plan organizations that intend to exceed designated emisshysion limits may buy cred its from others
www s ciamcom
that are able to stay below these va lues Enhancing energy efficienc y efforts
and raising renewable energy producshyti on are cri tical to achieving carbon dishyox ide limits at the lowes t possible cost A po rtion of the emission a llowances created by a carbon cap-and-trade proshygram shou Id be a llocated to the es tabshylishment of a fund to help overcome inshystitutional ba rriers and technica l r isks that obstruct widespread deployment of otherwise cost-effective C02 mitigation technologies
=
Delaying carbon capturemiddot
and storage at coal power
plants is shortsighted
Even if a carbon dioxide cap-andshytrade program were enacted in the next few yea rs the econom ic value of C02 emissions reduction may not be enough initially to convince power providers to invest in power systems with CCS To avoid the construction of another genshyeration of conventional coa l plants it is essential that the fed eral government esshytablish incentives that promote CCS
One ap proach would be to insist that an increasing share of total coal-based
MORE TO EXPLORE
electricity generation comes from faci lishyties that meet a low C02 emissions stanshydard-perhaps a maximum of 30 grams of carbon per k ilowatt-hour (a n achievshyable goal using todays coal CCS techshynologies) Such a goa l might be ach ieved by obliging electricity producers that use coal to include a growing fraction of decarbon ized coal power in thei r supply portfolios Each covered electricity proshyducer could either generate the required amount of decarbonized coal power or purchase decarbonized-generation credshyits Th is sys tem would share the increshym en tal costs of CCS for coal power among all US coal-based electricity producers and consumers
If the surge of conventional coa lshyfired power plants currently on drawing boa rds is built as planned atmospheric carbon dioxide levels will almost cershytainly exceed 450 ppmv Vle can meet global energy needs while st ill stabili zshying C02 at450 ppmv however through a combination of improved efficiency in energy use greater reliance on renewshyable energy resources and for the new coal investments that are made the inshystallation of C02 capture and geolog ic storage technologies Even though there is no such thing as clean coal more can and must be done to reduce the danshygers and environmental degradations associated with coal production and use An integrated low-carbon energy strategy that incorporates C02 capture and storage can reconcile substantia I use of coa l in the coming decades with the imperatlve to prevent catastro phic changes to the earths climate m
_
How to Clean Coal C Can ine in OnEarth Nat ural Resollrces Defense Council 200 5 Avail able at wwwnrdcorgonearth OSfallcoallasp
IPCC Special Report on Carbon Capture and Storage 2005 Avqilable at http archrrvm n I env Ii ntipcc pages_medi alSRC CS-fi n a II IPCC Spec ial Reporton Carbon d i oxideC apt urea ndSt 0 rage htm
Avoiding Dangerous Climate Change ~ditec1 by H J Sch ellnhuber W Cramer N Nallicenovic T Wigley and G Yoh e Cambridge University Press 2006
Big Clal The Dirty Secret behind America s Energy Future J Goodell Houghton Mifflin 20 06
Carbo~ Dioxide Capture andG~ologic Storage J J Doniey RTGahowski C L David so n M A Wise N Gupt a S H Kim and E L Malone Tec hnology Report from the Second Phase of the Global Energy Technology Strategy Program 2006
Natural Resou rces Defense Council Web si te wwwnrdcor~globalwarming
PrincetonEnvironmentallnstitute Web site wwwprincet on edu-cmi
SCIENTIFIC AMERICAN 75
THE PATH TO C02MITIGATION Our calculations indicate that a prompt commitment to carbon capture and storage
[eeS) would make it possible to meet global energy demands while limiting the
atmospheric carbon dioxide concentration to 450 parts per million by volume [ppmv)
This goal could be attained if by midcentury sequestration is applied for all coal use
and about a quarter of natural gas use while energy efficiency increases rapidly and
carbon-free energy sources expand sevenfold Under these conditions overall fossilshy
fuel consumption could expand modestly from today by midcentury coal use could be
somewhat higher than at present oil use would be down by a fifth and natural gas use
would expand by half
To realize this pathway growth rates for fossil-fuel use would have to be reduced
now and ee Smust begin for coal early in the next decade and for natural gas early in
the next quarter of a century The top graph below depicts the energy provided by the
various sources if this mitigation path were followed The bottom graph shows total
quantities of carbon extracted from the earth [emissions plus storage)
-DGH DAL and RHW
FOSSIL AND CARBON-FREE ENEmiddotRGY MIX FOR C02 STABILIZATION
35 Additional carbon-free energ~ needed to satisfy demand
30 Oil
~ bull Natural gas with CCS cu ~ 25 Natural gas with C02 vented ~ bull Coal with CCS ~ 20 Coal with C02 vented ~ eo c
IJJ 15 ~ cu
sect Q
10
5
0 2010 2030 2050 2070 2090
FATE OF CARBON FROM FOSSIL ENERGY SYSTEMS
cu 10 ~
n cu
c 8B cu on On
c 0 5 -e cu u ~ 4e IJJ
0 ~
tgt 2 0 Vi
0 I i i 2010 2030 2050 2070 2090
Year
74 SCIENTIFIC AMERICAN
bull Natural gas C stored
NalUral gas C emitted
Coal C emitted
Emissions level needed to stabilize C02at 450 ppmv
bull Coal carbon [C) stored
society would ultimately benefit if deshyployment of plants fitted with CCS equipment were begun now
First the fastest way to reduce CCS costs is via learning by doing-the acshycumulation of experience in building and running such plants The faster the understanding is accumulated the quicker the know-how with the new technology will grow and the more rapshyidly the costs will drop
Second installing CCS equipment as soon as possible should save money in the long run Most power stations curshyrently under construction will still be opshyerating decades from now when it is likely that CCS efforts will be obligatory Retrofitting generating faciliti es for CCS is inherently more expensive than deshyploying CCS in new plants Moreover in the absence of C02 emission limits fashymiliar conventional coal steam-electric technologies will tend to be favored for most new plant construction over newer gasification technologies for which CCS is more cost-effective
Finally rapid implementation would allow for continued use of fossil fuels in the near term (until more environmenshytally friendly sources become prevalent) without pushing atmospheric carbon dioxide beyond tolerable levels Our studies indicate that it is feasible to stashybilize atmospheric C02 levels at 450 ppmv over the next half a century if coal-based energy is completely decarshybonized and other measures described in the box at the left are implemented This effort would involve decarbonizing 36 gigawatts of new coal generating cashypacity by 2020 (corresponding to 7 pershycent of the new coal capacity expected to be built worldwide during the decade beginning in 2011 under business-asshyusual conditions) In the 35 years after 2020 C02 capture would need to rise at an average rate of about 12 percent a year Such a sustained pace is high compared with typical market growth rates for energy but is not unprecedentshyed It is much less than the expansion rate for nuclear generating capacity in its heyd ay-1956 to 1980-during which global capacity rose at an average rate of 40 percent annually Further the
SEPTEMBER 2005
expansion rates for bo th wind a nd sola r photovoltaic power capaci ties worldshywide have hovered around 30 percent a year since the ea rly 1990s In a ll three cases such growth would not have been practical without public policy mea shysures to suppor t them
Our calculations indica te that the costs of CCS deployment would be manshyageable as well Using conservative assumptions-such as that technology will not improve over time-we estimate that th e present worth of the cost of capturing and storing all C02produced by coal-based electricity generation pla nts du ring the next 200 years will be $18 triiJion (in 2002 dollars) That might seem like a high price tag but it is equivalent to just 007 percent of the curren t value of gross world prod uc t over the same interva l Thus it is plaushyslble that a rapid decarbonization path for coal is both phys ica lly and economshyically feasible although deta iled regionshya l analyses are needed to confirm thi s conclusion
Policy Push Is Nee d THO SE GOO D R EASO N S for comshymencing concerted CCS efforts soon will probably not move the industry unshyless it is a lso prodded by new public polshyicies Such initiatives would be part of a broader d rive to control carbon dioxide emissions from a ll sou rces
In the US a nat ional program to limit C02 emissions mu st be enac ted soon to introduce the government regshyu lat ions a nd market incentives necshyessary to shift investment to the leastshypolluting energy technologies promptly and on a w ide scale Leaders in the American business and policy commushynities increasi ngly agree that quantifi shyable a nd enforceable rest r ictions on global warming emissions are imperashytive and inev ita ble To ensure that powshyer companies put into practice the reshyductions in a cost-effective fashion a market for trading C02emissions credshyits shou ld be created-one similar to that for the sulfur emissions that cause acid rain In such a plan organizations that intend to exceed designated emisshysion limits may buy cred its from others
www s ciamcom
that are able to stay below these va lues Enhancing energy efficienc y efforts
and raising renewable energy producshyti on are cri tical to achieving carbon dishyox ide limits at the lowes t possible cost A po rtion of the emission a llowances created by a carbon cap-and-trade proshygram shou Id be a llocated to the es tabshylishment of a fund to help overcome inshystitutional ba rriers and technica l r isks that obstruct widespread deployment of otherwise cost-effective C02 mitigation technologies
=
Delaying carbon capturemiddot
and storage at coal power
plants is shortsighted
Even if a carbon dioxide cap-andshytrade program were enacted in the next few yea rs the econom ic value of C02 emissions reduction may not be enough initially to convince power providers to invest in power systems with CCS To avoid the construction of another genshyeration of conventional coa l plants it is essential that the fed eral government esshytablish incentives that promote CCS
One ap proach would be to insist that an increasing share of total coal-based
MORE TO EXPLORE
electricity generation comes from faci lishyties that meet a low C02 emissions stanshydard-perhaps a maximum of 30 grams of carbon per k ilowatt-hour (a n achievshyable goal using todays coal CCS techshynologies) Such a goa l might be ach ieved by obliging electricity producers that use coal to include a growing fraction of decarbon ized coal power in thei r supply portfolios Each covered electricity proshyducer could either generate the required amount of decarbonized coal power or purchase decarbonized-generation credshyits Th is sys tem would share the increshym en tal costs of CCS for coal power among all US coal-based electricity producers and consumers
If the surge of conventional coa lshyfired power plants currently on drawing boa rds is built as planned atmospheric carbon dioxide levels will almost cershytainly exceed 450 ppmv Vle can meet global energy needs while st ill stabili zshying C02 at450 ppmv however through a combination of improved efficiency in energy use greater reliance on renewshyable energy resources and for the new coal investments that are made the inshystallation of C02 capture and geolog ic storage technologies Even though there is no such thing as clean coal more can and must be done to reduce the danshygers and environmental degradations associated with coal production and use An integrated low-carbon energy strategy that incorporates C02 capture and storage can reconcile substantia I use of coa l in the coming decades with the imperatlve to prevent catastro phic changes to the earths climate m
_
How to Clean Coal C Can ine in OnEarth Nat ural Resollrces Defense Council 200 5 Avail able at wwwnrdcorgonearth OSfallcoallasp
IPCC Special Report on Carbon Capture and Storage 2005 Avqilable at http archrrvm n I env Ii ntipcc pages_medi alSRC CS-fi n a II IPCC Spec ial Reporton Carbon d i oxideC apt urea ndSt 0 rage htm
Avoiding Dangerous Climate Change ~ditec1 by H J Sch ellnhuber W Cramer N Nallicenovic T Wigley and G Yoh e Cambridge University Press 2006
Big Clal The Dirty Secret behind America s Energy Future J Goodell Houghton Mifflin 20 06
Carbo~ Dioxide Capture andG~ologic Storage J J Doniey RTGahowski C L David so n M A Wise N Gupt a S H Kim and E L Malone Tec hnology Report from the Second Phase of the Global Energy Technology Strategy Program 2006
Natural Resou rces Defense Council Web si te wwwnrdcor~globalwarming
PrincetonEnvironmentallnstitute Web site wwwprincet on edu-cmi
SCIENTIFIC AMERICAN 75
expansion rates for bo th wind a nd sola r photovoltaic power capaci ties worldshywide have hovered around 30 percent a year since the ea rly 1990s In a ll three cases such growth would not have been practical without public policy mea shysures to suppor t them
Our calculations indica te that the costs of CCS deployment would be manshyageable as well Using conservative assumptions-such as that technology will not improve over time-we estimate that th e present worth of the cost of capturing and storing all C02produced by coal-based electricity generation pla nts du ring the next 200 years will be $18 triiJion (in 2002 dollars) That might seem like a high price tag but it is equivalent to just 007 percent of the curren t value of gross world prod uc t over the same interva l Thus it is plaushyslble that a rapid decarbonization path for coal is both phys ica lly and economshyically feasible although deta iled regionshya l analyses are needed to confirm thi s conclusion
Policy Push Is Nee d THO SE GOO D R EASO N S for comshymencing concerted CCS efforts soon will probably not move the industry unshyless it is a lso prodded by new public polshyicies Such initiatives would be part of a broader d rive to control carbon dioxide emissions from a ll sou rces
In the US a nat ional program to limit C02 emissions mu st be enac ted soon to introduce the government regshyu lat ions a nd market incentives necshyessary to shift investment to the leastshypolluting energy technologies promptly and on a w ide scale Leaders in the American business and policy commushynities increasi ngly agree that quantifi shyable a nd enforceable rest r ictions on global warming emissions are imperashytive and inev ita ble To ensure that powshyer companies put into practice the reshyductions in a cost-effective fashion a market for trading C02emissions credshyits shou ld be created-one similar to that for the sulfur emissions that cause acid rain In such a plan organizations that intend to exceed designated emisshysion limits may buy cred its from others
www s ciamcom
that are able to stay below these va lues Enhancing energy efficienc y efforts
and raising renewable energy producshyti on are cri tical to achieving carbon dishyox ide limits at the lowes t possible cost A po rtion of the emission a llowances created by a carbon cap-and-trade proshygram shou Id be a llocated to the es tabshylishment of a fund to help overcome inshystitutional ba rriers and technica l r isks that obstruct widespread deployment of otherwise cost-effective C02 mitigation technologies
=
Delaying carbon capturemiddot
and storage at coal power
plants is shortsighted
Even if a carbon dioxide cap-andshytrade program were enacted in the next few yea rs the econom ic value of C02 emissions reduction may not be enough initially to convince power providers to invest in power systems with CCS To avoid the construction of another genshyeration of conventional coa l plants it is essential that the fed eral government esshytablish incentives that promote CCS
One ap proach would be to insist that an increasing share of total coal-based
MORE TO EXPLORE
electricity generation comes from faci lishyties that meet a low C02 emissions stanshydard-perhaps a maximum of 30 grams of carbon per k ilowatt-hour (a n achievshyable goal using todays coal CCS techshynologies) Such a goa l might be ach ieved by obliging electricity producers that use coal to include a growing fraction of decarbon ized coal power in thei r supply portfolios Each covered electricity proshyducer could either generate the required amount of decarbonized coal power or purchase decarbonized-generation credshyits Th is sys tem would share the increshym en tal costs of CCS for coal power among all US coal-based electricity producers and consumers
If the surge of conventional coa lshyfired power plants currently on drawing boa rds is built as planned atmospheric carbon dioxide levels will almost cershytainly exceed 450 ppmv Vle can meet global energy needs while st ill stabili zshying C02 at450 ppmv however through a combination of improved efficiency in energy use greater reliance on renewshyable energy resources and for the new coal investments that are made the inshystallation of C02 capture and geolog ic storage technologies Even though there is no such thing as clean coal more can and must be done to reduce the danshygers and environmental degradations associated with coal production and use An integrated low-carbon energy strategy that incorporates C02 capture and storage can reconcile substantia I use of coa l in the coming decades with the imperatlve to prevent catastro phic changes to the earths climate m
_
How to Clean Coal C Can ine in OnEarth Nat ural Resollrces Defense Council 200 5 Avail able at wwwnrdcorgonearth OSfallcoallasp
IPCC Special Report on Carbon Capture and Storage 2005 Avqilable at http archrrvm n I env Ii ntipcc pages_medi alSRC CS-fi n a II IPCC Spec ial Reporton Carbon d i oxideC apt urea ndSt 0 rage htm
Avoiding Dangerous Climate Change ~ditec1 by H J Sch ellnhuber W Cramer N Nallicenovic T Wigley and G Yoh e Cambridge University Press 2006
Big Clal The Dirty Secret behind America s Energy Future J Goodell Houghton Mifflin 20 06
Carbo~ Dioxide Capture andG~ologic Storage J J Doniey RTGahowski C L David so n M A Wise N Gupt a S H Kim and E L Malone Tec hnology Report from the Second Phase of the Global Energy Technology Strategy Program 2006
Natural Resou rces Defense Council Web si te wwwnrdcor~globalwarming
PrincetonEnvironmentallnstitute Web site wwwprincet on edu-cmi
SCIENTIFIC AMERICAN 75