REDUCTION OF GREENHOUSE GAS EMISSIONS USING VARIOUS THERMAL SYSTEMS IN A LANDFILL SITE
Global Conference on Global Warming6-10 July, 2008 - Istanbul, Turkey
CAN OZGUR COLPAN
IBRAHIM DINCER
FERIDUN HAMDULLAHPUR
OUTLINE• Introduction
• Global warming• Municipal solid waste (MSW)• Energy from MSW
• Literature Survey• Landfill Processes
• Landfill gas generation• Landfill gas collection
• Analysis• Flaring• Internal combustion engine• Gas turbine system• SOFC
• Case study• Conclusions
Introduction – Global Warming• Drivers of climate change:
• Changes in the atmospheric concentrations of GHGs and aerosols
• land cover • solar radiation
• Long-lived GHGs which are released due to human activities: • CO2, CH4, N2O, halocarbons
• Global Warming Potential (GWP) for 100-year time horizon (IPCC, 2007):• CO2 1• CH4 25• N2O 298
Introduction – MSW• Uncontrolled MSW may have significant
effects in global warming as well as other environmental problems and human health.
• Decomposition of MSW:• Waste is decomposed by aerobic bacteria
until all the oxygen is consumed. • Organic acids are produced in the
absence of oxygen. • Organic materials are decomposed into
CH4 and CO2.
• These sites should be properly designed: Groundwater may be protected by using liners and leachate collection systems; and gas collection, treatment and processing systems may be used to reduce the GHG effect.
Introduction – Energy from MSW• Energy from MSW:
• Incineration• Gasification• Generation of biogas (landfill gas) and its utilization.
• Electricity generation from landfill gas (LFG): • Internal combustion engine• Gas turbine• Stirling engine• Fuel cells.
Literature Survey• Murphy and McKeogh (2004): Generation of biogas and its
conversion to transport fuel requires the least gate fee among different alternatives.
• Qin et al. (2001): Analysis of the LFG combustion through experimental studies: the determination of laminar flame speeds, extinction strain rates, stable species and NOx concentrations, and thermal flame structures.
• Bove and Ubertini (2006): ICE presents the poorest environmental performance.
• Lombardi et al. (2006): LFG reforming to vehicle FC has the lowest specific greenhouse effect emission.
• Duerr et al. (2007): Biogas fueled alkaline fuel cell • Spiegel et al. (1999): Operation of a phosphoric acid fuel cell
(PAFC) with landfill gas• Lunghi et al. (2004): Life cycle assessment analysis of a molten
carbonate fuel cell (MCFC) system for LFG recovery
ObjectiveObjective of this study:
• Conventional energy recovery technologies from LFG such as flaring, internal combustion engine and gas turbine are compared with an emerging technology, Solid Oxide Fuel Cell (SOFC), in terms of their effect to global warming.
Landfill Processes - I• Landfill Gas Generation
• LandGEM is used to calculate the generation rate.• The model is based on a 1st order decomposition rate equation for
quantifying emissions from the decomposition of landfilled waste
• It is generally assumed that landfill gas has a composition of 50% CH4 and 50% CO2. Hence, total landfill gas generation may be found by doubling the result from above equation.
• Methane generation rate, k is a function of• moisture content, availability of nutrients for methane-generating
bacteria, pH, and temperature of the waste mass • Potential methane generation capacity, Lo, depends on
• type and composition of waste placed in the landfill • Clean Air Act (CAA) default values:
• k and Lo are, 0.05 year-1 and 170 m3/ton, respectively.
∑∑= =
⋅−
=
n
1i
1
1.0j
tkioCH
ij4
e10MkLQ
Landfill Processes - II• Landfill Gas Collection
• collected gas quantity is estimated by multiplying the generated landfill gas by the collection efficiency
• According to the EPA (1998), collection efficiencies at such landfills typically range from 60% to 85%, with an average of 75%.
LFGGenerated
CollectedGas
CH4 oxidation
GHG emissionVented
GHG emission
Flared On-site electricity/heat production
Sent to natural gas grid
UncollectedGas
ANALYSIS – Uncontrolled Site• Landfill site without an active collection system
• The oxidation of methane
• The fraction of methane oxidized is generally taken as 10%OH2COO2CH 2224 +→+
∑=
××++×−×=
finalt
1y 4CHρ2COρ
gen.4CHmOXCO2.genmCH4GWPOX)(1gen.4CHmGHG.uncollm
ANALYSIS - Flaring• Flaring
• Economical approach • It reduces the risk of explosion of uncontrolled LFG emission
• In today’s market, open and closed flare types are available
( ) ( )∑=
×+×−=
finalt
1yycollycoll GHG.flaremηGHG.uncollm)η1(GHG.collm
( )
××−++××=
4CH
2COρρ
gen.4CHmvent1CO2.genmCH4GWPventgen.4CHmGHG.flarem
ANALYSIS – I.C.E.• The most employed technology for electricity
generation from LFG• economical feasibility • compact and easy to transport• but high amounts of NOx and CO emissions
• Lean-burn spark ignition engines are the most common type of I.C.E. used in the market in landfill sites.
( ) ( )
( )∑
∑
=
=
×+×−
+
×+×−=
finalt
downty ycollycoll
downt
1yycollycoll
GHG.flaremηGHG.uncollm)η1(
GHG.ICEmηGHG.uncollm)η1(GHG.collm
( ) ( ) ( ) GHG.flarem365/τ13600/εηhhvm365/τGHG.ICEm ICEICEgen.LFG ×−+××××=
ANALYSIS – Gas Turbine• The majority of gas turbines presently operating at
landfills are simple cycle, single shaft type. • Lower NOx and CO emissions, and also few
moving parts. • But it has a lower electrical efficiency, higher
capital cost, sensitive to LFG supply loads and ambient air temperature variations.
• For small size landfills, microturbines are used.
o,co,ci,ci,cfff hnhnhnLHVn02.00 ⋅−⋅+⋅+⋅⋅−=
( ) ( ) GHG.flarem365/τ1MM
λ0003.0λm365/τGHG.GTm
LFG
COgen.LFG
2 ×−+
×
+××=
ANALYSIS – SOFC• High temperature fuel cell (500-1000°C)• Application areas:
• Stationary power and heat generation• Transportation applications• Portable applications
• Advantages:• No need for precious metal electrocatalysts • Fuel flexibility (Hydrogen, carbon monoxide, methane, higher
hydrocarbons, methanol, ethanol, landfill and biomass-produced gases, ammonia, hydrogen sulfide)
• Internal reforming• Good thermal integration with other systems
• Disadvantages: • Degradation due to carbon deposition and sulphur poisoning• Challenges with construction and durability
• Model developed by Colpan et al. (2008) is used.
ANALYSIS – SOFC
Load
H2 H2
O2- O2-
H2O H2O e- e- e- e-
O2 O2
e- e- e- e-
Anode
ElectrolyteCathode
Comparison of LFG utilization technologies• GHG reduction ratio: It quantifies the GHG emission reduction
when an active collection system is used
• Specific lifetime GHG emission: It is the ratio of the total GHG emission from the landfill site in its lifetime to the total amount of useful energy produced from LFG.
( ) GHG.uncollm/GHG.collmGHG.uncollmΓ −=
( ) elcoll η6.3/hhv365/τηgen.2COmgen.4CHmGHG.collm
σ××××+
=
Case Study• We consider that the landfill site, which is filled with municipal solid
waste, is opened in 2008 and it accepts waste for 20 years. The annual waste acceptance rate is taken as 200,000 ton/year.
Fraction of oxidized methane 10%Fraction of vented gas in flare 1%Collection efficiency 75%The year that the electricity production ends 2088Number of days that electricity producing technology operates per year 320Higher heating value of LFG 14829 MJ/tonnesSpecific GHG emission ratio of ICE 0.551 tonnes.eq.CO2/MWh (Lombardi et al., 2006)Electrical efficiency of ICE 35%Combustion chamber inlet temperature of GT 850 KGas turbine inlet temperature 1520 KGas turbine electrical efficiency 28%Operating cell voltage of SOFC 0.65 VFuel utilization ratio of SOFC 85%Inlet gas temperature of SOFC 850 CExit gas temperature of SOFC 950 CActive surface area of a single cell 100 cm2
RESULTS-I
0
10000
20000
30000
40000
50000
60000
2008 2028 2048 2068 2088 2108 2128 2148
Year
Ann
ual g
as g
ener
atio
n [to
nnes
/yea
r] Methane generated CO2 generated
NMOC generated LFG generated
0
10000
20000
30000
40000
50000
60000
2008 2028 2048 2068 2088 2108 2128 2148
Year
Ann
ual g
as g
ener
atio
n [t
onne
s/ye
ar]
Collected methane Uncollected methaneCollected CO2 Uncollected CO2Collected NMOC Uncollected NMOCCollected LFG Uncollected LFG
RESULTS-II
0
50000
100000
150000
200000
250000
300000
350000
400000
2008 2028 2048 2068 2088 2108 2128 2148
Year
Tota
l GH
G e
mis
sion
[tonn
es-C
O2.e
q/ye
ar]
Without Collection FlaringICE GTSOFC
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 1.8
Current Density [A/cm2]
Cell
Volta
ge [V
], El
ectri
cal E
ffici
ency
0
0.05
0.1
0.15
0.2
0.25
0.3
0.35
Powe
r Den
sity
[W/c
m2 ]
SOFC-VoltageSOFC-EfficiencySOFC-Pow er
RESULTS-III
0.54
0.56
0.58
0.6
0.62
0.64
0.66
Flaring ICE GT SOFC
GH
G re
duct
ion
ratio
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
ICE GT SOFC SOFC-Cogeneration
Spec
ific
lifet
ime
GH
G e
mis
sion
[to
nnes
CO
2.eq/
MW
h]
CONCLUSIONS• Uncontrolled site and control site with flaring, ICE, gas
turbine and SOFC are compared in terms of GHG emission.• Even with the simplest solution which is flaring, total GHG
emissions in the lifetime of the site can be reduced by 58% compared to the uncontrolled case.
• SOFC seems the best option, which reduces the GHG emissions by 63%, and has a specific lifetime GHG emission of 2.3836 tonnes CO2.eq/MWh when it only produces electricity and 1.1217 tonnes CO2.eq/MWh when it is used in a cogeneration application.
• SOFCs are very effective in combating global warming in landfill sites.