a comparison of the environmental consequences of power ...biomass igcc average coal 15% cofiring by...

Margaret K. MannCo-author: Pamela L. Spath

National Renewable Energy LaboratoryGolden, Colorado USA

A Comparison of the Environmental Consequences of Power from Biomass,

Coal, and Natural Gas

Short discussion of life cycle assessment (LCA)

Purpose of LCAs conducted

System descriptions• Biomass IGCC• Average coal• Coal/biomass cofiring• Natural gas combined cycle

Comparative Results• Air emissions• Greenhouse gases• Energy

Outline of Presentation

Life Cycle Assessment: Definition

LCA is:• a systematic analytical method• used to quantify the environmental benefits and drawbacks

of a process• performed on all processes, cradle-to-grave, resource

extraction to final disposal• ideal for comparing new technologies to the status quo• helps to pinpoint areas that deserve special attention• reveals unexpected environmental impacts

(no show-stopping surprises)

Systems Examined

Indirectly-heated gasificationDedicated hybrid poplar feedstockZero carbon sequestration in base case

Pulverized coal / steam cycleIllinois #6 coal - moderate sulfur, bituminousSurface mining

Biomass IGCC

Average coal

15% cofiring by heat inputBiomass residue (urban, mostly) into PC boiler0.9 percentage point efficiency deratingCredit taken for avoided operations including decomposition (i.e., no biomass growth)

Biomass / coal cofiring

Biomass residueAvoided emissions credit as with cofiring

Direct-fired biomass

Combined cycleUpstream natural gas losses = 1.4% of gross

Natural gas

Purpose of Studies

Biomass LCA was conducted to answer common questions:• What are the net CO2 emissions?• What is the net energy production?• Which substances are emitted at the highest rate?• What parts of the system are responsible for the greatest impacts?• What should biomass R&D focus on?

Coal and natural gas LCAs the foundation for quantifying the benefits of biomass power.

Direct-fired biomass system describes current biomass power industry.

Cofiring LCA examined near-term option for biomass utilization.

Each assessment conducted separately - common systems not excluded.

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Dedicated BiomassIGCC

Average PC Coal Coal/biomass cofiring(15%)

Direct-f ired biomassresidue

Natural gas combinedcycle

g/kW

h

Operating plantTotal system

Life Cycle & Plant CO Emissions

Life Cycle & Plant Particulate Emissions

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Dedicated BiomassIGCC

Average PC Coal Coal/biomass cofiring(15%)

Direct-fired biomassresidue

Natural gas combinedcycle

g/kW

h

Operating plantTotal system

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Dedicated BiomassIGCC

Average PC Coal Coal/biomass cofiring(15%)

Direct-fired biomassresidue

Natural gas combinedcycle

g/kW

h Operating plantTotal system

Life Cycle & Plant SO2 Emissions

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Dedicated BiomassIGCC

Average PC Coal Coal/biomass cofiring(15%)

Direct-fired biomassresidue

Natural gas combinedcycle

g/kW

h

Operating plantTotal system

Life Cycle & Plant NOx Emissions

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Dedicated BiomassIGCC

Average PC Coal Coal/biomass cofiring(15%)

Direct-fired biomassresidue

Natural gas combinedcycle

g/kW

h Operating plantTotal system

Life Cycle & Plant NMHC Emissions

Life Cycle Air Emissions

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CO Particulates SO2 NOx NMHCs

g/kW

h

Average PC CoalCoal/biomass cofiring (5%)Coal/biomass cofiring (15%)Natural gas combined cycleDirect-fired biomass residueDedicated Biomass IGCC

100 kg biomass (bone dry)(50.6 kg carbon)

46%landfilled

54%mulched

90.0 kg CO2(24.6 kg carbon)

90%aerobic

54 kg biomass(27.3 kg carbon)

14.8 kg CO2(4.05 kg carbon)

5.4 kg CH4(4.05 kg carbon)

46 kg biomass(23.3 kg carbon)

anaerobicdecomposition

50% to CO2

50% to CH4

40.5% capturedand combusted 59.5% released

as CH4

5.4 kg CO2(1.5 kg carbon)

2.9 kg CH4(2.2 kg carbon)

of the non-ligninlignin and 50%

resistant to degradation

15.2 kg carbon

degradation of50% of cellulose& hemicellulose

8.1 kg carbon

10% oxidizedby soil

microbes 1.5 kg CO2(0.4 kg carbon)

90% notoxidized by

soil microbes

4.9 kg CH4(3.65 kg carbon)

10%anaerobic

decomposition

3.6 kg CH4(2.7 kg carbon)

Avoided Biomass Decomposition

Avoided per 100 kg of biomass:111.7 kg CO2 + 6.5 kg CH4

= 248.2 kg CO2-equiv

If 100 kg biomass were to completely decompose aerobically: 185.4 kg CO2

Life Cycle Greenhouse Gas Emissions

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Dedicatedbiomass

IGCC

AveragePC coal

Coal/biomassCofiring

NGCCGW

P( g

CO

- equ

ival

ent/

kWh)

2

Direct-firedbiomassresidue

Summary

Air emissions:• Biomass: few particulates, SO2, NOx, and methane• Coal: upstream CO and NMHC emissions lower• NGCC: system methane, NMHC, CO emissions high

Greenhouse Gases:• Biomass IGCC nearly zero net GHGs• Average coal system: ~1,000 g CO2-equiv/kWh• NGCC system: ~500 g CO2-equiv/kWh• Today’s biomass systems remove GHGs from

atmosphere• Cofiring: greater reduction than rate of biomass input