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Margaret K. Mann National Renewable Energy Laboratory Golden, Colorado USA

A Comparison of the Environmental. Consequences of Power from Biomass,. Coal, and Natural Gas. Margaret K. Mann National Renewable Energy Laboratory Golden, Colorado USA. Outline of Presentation. Purpose of LCAs conducted System descriptions Biomass IGCC Average coal

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Margaret K. Mann National Renewable Energy Laboratory Golden, Colorado USA

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  1. A Comparison of the Environmental Consequences of Power from Biomass, Coal, and Natural Gas Margaret K. Mann National Renewable Energy Laboratory Golden, Colorado USA

  2. Outline of Presentation Purpose of LCAs conducted System descriptions • Biomass IGCC • Average coal • Coal/biomass cofiring • Natural gas combined cycle Comparative Results • Energy • Greenhouse gases • Other air emissions • Resource consumption

  3. Life Cycle Assessment: Definition LCA, in the context of novel systems, 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 so that research can be focused on mitigating them (no show-stopping surprises)

  4. 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.

  5. Biomass / coal 15% cofiring by heat input cofiring Biomass residue (urban, mostly) into PC boiler 0.9 percentage point efficiency derating Credit taken for avoided operations including decomposition (i.e., no biomass growth) Direct-fired biomass Biomass residue Avoided emissions credit as with cofiring Natural gas Combined cycle Upstream natural gas losses = 1.4% of gross Systems Examined Biomass IGCC Indirectly-heated gasification Dedicated hybrid poplar feedstock Zero carbon sequestration in base case Average coal Pulverized coal / steam cycle Illinois #6 coal - moderate sulfur, bituminous Surface mining

  6. Energy Balance Oddities Key question: why are the energy results so poor for the fossil systems? Answer: Upstream Energy Consumption is High % o f n o n - f e e d s t o c k e n e r g y r N o n - f e e d s t o c k e n e r g y ( k J / k W h ) e l a t e d t o : F l u e - g a s T r a n s p o r t a t i o n N a t u r a l g a s c l e a n u p p r o d u c t i o n o r c o a l m i n i n g B i o m a s s I G C C 2 3 1 0 % 1 6 % N / A D i r e c t b i o m a s s 1 2 5 0 % 4 9 % N / A C o a l 7 0 2 3 5 % 3 2 % 2 5 % 1,718 N a t u r a l g a s 0 . 5 % N / A 9 8 . 3 %

  7. Example flows: Biomass energy crop - photosynthesis, carbon sequestration in soil Biomass residue - avoided decomposition emissions Coal - coal mine methane, coal mine waste Natural gas- fugitive emissions, leaks General - incomplete combustion, upstream fossil fuel consumption Carbon Cycle (GHG Emissions) Key question: On a life cycle basis, what are the net greenhouse gas emissions of these systems?

  8. Other Air Emissions Biomass IGCC also emits isoprene at 21 g/kWh 15 5 CH4 Particulates SOx NOx CO NMHCs -5 -15 Average PC coal 15% Coal / biomass cofiring Direct biomass residue Dedicated biomass IGCC NGCC -41 g/kWh

  9. Resource Consumption h W k / g 50 - 500 450 Average PC coal 400 15% cofiring 350 Direct-fired residue biomass 300 Dedicated biomass IGCC NGCC 250 200 150 100 Coal Limestone Oil Natural Gas

  10. Summary • 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 • Energy: • Coal and natural gas: negative system energy balance • Even neglecting the energy content of coal and natural gas, biomass systems are more energy efficient • NGCC: natural gas extraction and losses account for 21% of total energy • Air emissions: • Biomass: few particulates, SO2, NOx, and methane • Coal: upstream CO and NMHC emissions lower • NGCC: system methane emissions high • Resource consumption: Biomass systems << fossil systems • Cofiring: • 15% cofiring reduces GWP of coal system by 18% • Reduction in emissions, resource consumption, and energy use

  11. Credits Co-author: Pamela L. Spath, NREL Funding from the U.S. Department of Energy Biomass Power Program

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