CMI ANNUAL MEETING A CHALLENGE TO ETHANOL. Robert H. Williams Princeton Environmental Institute Princeton University Princeton, New Jersey

Transcription

1 CMI ANNUAL MEETING A CHALLENGE TO ETHANOL Robert H. Williams Princeton Environmental Institute Princeton University Princeton, New Jersey 21 February 2007

2 DILEMMA FOR CONVENTIONAL BIOFUELS Advantages: Carbon neutrality via photosynthetic CO 2 removal from atmosphere Renewability Downside: Limited availability of high-quality land for dedicated energy crops arising from low efficiency of photosynthesis (competition with food production) conventional biofuels can satisfy only part of liquid fuel demand even with improved conversion technologies Biodiversity loss concerns about high levels of development of monoculture crops grown for energy

3 DILEMMA FOR CONVENTIONAL BIOFUELS Advantages: Carbon neutrality via photosynthetic CO 2 removal from atmosphere Renewability Downside: Limited availability of high-quality land for dedicated energy crops arising from low efficiency of photosynthesis (competition with food production) conventional biofuels can satisfy only part of liquid fuel demand even with improved conversion technologies Biodiversity loss concerns about high levels of development of monoculture crops grown for energy Challenges can be addressed by exploiting negative emissions potential of biomass + biomass/coal coprocessing for energy

4 PHOTOSYNTHETIC CO 2 STORAGE: BIOMASS IN IGCC w/ccs Biomass Input Coal Input Coal - Upstream GHG Coal - CO2 in Fuel Biomass - Upstream GHG Biomass - CO2 in Fuel Coal/biomass IGCC, CCS Coal IGCC, CO2 vented Coal IGCC, CCS Coal/biomass IGCC, CCS - Coal - Biomass Coal IGCC, CCS Coal IGCC, CO2 vented (Fuel input)/(electricity output) GHG emissions, kgco2equiv/mwh IGCC (dry-feed) for coal & coal/biomass w/enough biomass to to reduce net GHG emissions to zero 85% of feed C captured in CCS cases

5 TWO PART C-STORAGE STRATEGY FOR ADDRESSING DILEMMA Biomass, C-neutral C-negative via two-part strategy: First part, based on biomass conversion via gasification, involves separating out/storing underground (in geological formations) as CO 2 most C in biomass not needed in final energy products. This part of strategy is made economically feasible by coprocessing biomass with coal to make synfuels with CO 2 capture and storage (CCS) in large conversion plants. Negative CO 2 emissions from photosynthetic CO 2 storage offset coal CO 2 emissions from conversion facility and from eventual release of CO 2 from coal as result of synfuel combustion (Princeton U research) Second part, growing biomass as mixed grasses on C-depleted soils, leads to substantial additional storage of photosynthetic CO 2 as soil C and root C (U of Minn research) Second part of strategy also addresses effectively biodiversity challenge posed by conventional biofuels

6 F-T FUELS + ELECTRICITY FROM COAL + PRAIRIE GRASSES WITH TWO C-STORAGE MECHANISMS Coal Pressurized gasification Gas cooling & cleaning Water gas shift H 2 S, CO 2 removal F T synthesis Upgrading, refining F-T FUELS Mixed prairie grasses farms biomass oxygen Air separation unit oxygen Pressurized gasification air Gas cooling & cleaning 2 stage water gas shift H 2 S + CO 2 Underground storage unconverted + recovered gas process electricity GTCC power island air EXPORT ELECTRICITY carbon Soil and root C storage Growing mixed prairie grasses on C-depleted soils substantial build-up of C in roots/soils up to 0.6 tc per tc in harvested biomass H 2 is made from biomass via gasification to compensate for H 2 deficit in coal syngas; photosynthetic CO 2 coproduct of biomass H 2 (~ 90% of C in harvested biomass) is stored along with coal-derived CO 2 in in deep geological formations Deep reductions in GHG emissions with modest biomass inputs

7 RELATIVE GHG EMISSION RATE & BIOMASS INPUT FRACTION VS (PRAIRIE GRASSES INPUT)/(FTL OUTPUT) FOR COAL/BIOMASS F-T POLYGEN PLANT w/ccs GJ of biomass input per GJ of synfuel GHG gas emission rate relative to rate for crude-oilderived fuels displaced Biomass fraction of input fuel Assumptions: 90% of C in harvested prairie grasses is stored as CO 2 soil/root C storage rate = 60% of C in harvested prairie grasses

8 GHG Emission Rates for Fuel Production and Use kg Cequiv per GJ (LHV) Gasoline Diesel Coal FTL, CO2 vented Coal FTL, CCS Coal/biomass FTL, CCS, 21% biomass for FTL + electricity, switchgrass Coal/biomass FTL, CCS, 21% biomass for FTL + electricity, 16 prairie grasses Penultimate case w/switchgrass (45% of emission rate for gasoline) exploits negative CO 2 emissions potential of photosynthetic CO 2 storage in geological media Final case shows what can be realized by exploiting both CO 2 storage and soil/root C storage by growing mixed prairie grasses on C-depleted soils

9 Biomass Required to Make 1 GJ of Liquid Fuel FTL with zero GHG emissions from coal + grasses with CO 2 capture/storage Cellulosic Ethanol GJ biomass per GJ liquid fuel, LHV (coal) 0.50 F 0.00 Coal/biomass FTL, CCS, 21% biomass for FTL + electricity, 16 prairie grasses Ethanol, vintage 2000, 72 gallons/ton Ethanol, vintage 2015, 90 gallons/ton Ethanol, vintage 2030, 105 gallons/ton

10 THOUGHT EXPERIMENT: BIOMASS/COAL FOR SMP TRANSPORT ENERGY SCENARIO (2050) # LDVs, LDV fuel economy (mpg) Transportation Fuel Use, EJ/y LDVs Total GHG emissions w/oil, GtC/y Biomass in 2050 with alternative coal/biomass FTL fueling, EJ/y 0.89 GJ/GJ FTL (no soil/root C storage) Mixed 0.67 GJ/GJ FTL (soil/root C storage) Coal in 2050 with coal/biomass FTL fueling, EJ/y GHG emissions with coal/biomass FTL fueling, GtC/y CO 2 storage rate in 2050, GtC/y Soil/root C storage rate in 2050, GtC/y

11 ALTERNATIVE THOUGHT EXPERIMENT: NO SOIL/ROOT C STORAGE # LDVs, LDV fuel economy (mpg) Transportation Fuel Use, EJ/y LDVs Total GHG emissions w/oil, GtC/y Biomass in 2050 with alternative coal/biomass FTL fueling, EJ/y 0.89 GJ/GJ FTL (no soil/root C storage) Mixed 0.67 GJ/GJ FTL (no soil/root C storage) Coal in 2050 with coal/biomass FTL fueling, EJ/y GHG emissions with coal/biomass FTL fueling, GtC/y CO 2 storage rate in 2050, GtC/y Soil/root C storage rate in 2050, GtC/y

12 LAND REQUIREMENTS FOR GROWING PRAIRIE GRASSES IN THOUGHT EXPERIMENT Energy crops (53 EJ/y) Energy crops (53 EJ/y) Global Cropland Global Grasslands Average Yield (t/ha/y) Land Area (10 6 hectares)

13 ECONOMICS OF SHIFTING IOWA CORN TO MIXED PRAIRIE GRASSES FOR MAKING FTL WITH COAL Assumed carbon price, $ per tonne of C Breakeven oil price for coal FTL, $ per barrel FTL price, $/gallon of gasoline equivalent Assumed prairie grasses yield, dry tonnes per hectare per year Prairie grasses price, $ per short dry tonne Willingness to pay for prairie grasses at FTL plant Cost of harvesting, grinding, storing grasses Biomass transport cost Income to farmer Income per unit of land area for Kossuth, Winnebago, Hancock counties, $/ha/y To farmer for sale of grasses to FTL plant Average CRP rental rate Corn returns including loan deficiency/counter-cyclical payments Corn returns (loan deficiency/counter-cyclical payments)

14 PULP MILL-INTEGRATED BIOREFINING > 1.2 EJ/yr black liquor (BL) energy used in USA. Tough global competition in pulp production can integrated biorefinery be helpful? Way to get started with biofuels via thermochemical conversion? Pulp industry interest in gasification Swedish BL gasifier technology near commercial demonstration. Aging black liquor boiler fleet provides economic window of opportunity for gasification North American Black Liquor Boilers, START-UPS Year Built / Rebuilt RE-BUILDS FTL biorefinery at pulpmill in Southeast USA: 4,800 bbl/day oil equiv. 78 MW e (for pulp mill) $330 million incremental capital investment ~ 18% IRR for $50/bbl crude oil and $53/MWh electricity black liquor air Dryer biomass (50% mc) Pressurized, hightemp gasifier oxygen Air separation unit oxygen Fluidized bed gasifier Syngas cooling & cleaning condensed phase to causticizing clean biomass syngas Syngas quench w/ heat recovery process steam to mill Rectisol for H 2 S and CO 2 removal unconverted syngas sulfur to polysulfide liquor preparation Gas Turbine CC (Frame 6FA GT) Once thru LP FT synthesis CRUDE F-T LIQUIDS (to existing refinery) recovered process heat ELECTRICITY Much better economics than for stand-alone biofuels (which need high C price) Integration with pulpmill capital cost-sharing, low bio feedstock cost But pulp industry is technology risk-averse. How about integration with coal gasification and CCS for FTL + electricity?

15 COMPARING MARKET & EFFECTIVE PRICES FOR COAL & PRAIRIE GRASSES WHEN GHG EMISSIONS PRICE = $100/tC equiv for C/B-FT-CoC plants with soil/root C storage, in $/GJ, HHV (and $/dry tonne for mixed prairie grasses) Net profit for farmers Harvesting, grinding, storage, and transport Plantgate market price Upstream GHG emissions Net CO 2 emissions from plant + FTL use Soil and root C storage Effective price coal prairie grasses 3.48 ($65) 1.88 ($35) 5.36 ($100) ~ 1/2 of payment to farmer would be for C storage in soil and roots