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.