Gasification: Thermochemical Conversion

Transcription

1 Technologies for Treating Dairy Manure Gasification Developing Projects and Partners to Comprehensively Treat Dairy Manure in the San Joaquin Valley 11 January 2006 Modesto, California Bryan M. Jenkins, University of California Gasification: Thermochemical Conversion Pyrolysis thermal decomposition of organic material through heating Gasification conversion of solids or liquids to fuel- or synthesis-gases through gas-forming reactions Combustion (solids) exothermic oxidation involving pyrolysis, gasification, and heterogeneous and homogeneous oxidation reactions 1

2 Pyrolysis and Gasification as Integral Processes in Combustion Z916 Gasifier 2

3 Thermal Gasification Fuel + Oxidant/Heat Partial Oxidation/Air or Oxygen Steam/Carbon Dioxide/Hydrogen Indirect Heating CO + H 2 + HC + CO 2 + N 2 + H 2 O + Char + Tar + PM + H 2 S + NH 3 + Other + Heat Classification by Reactor Type: Fixed/Moving Beds Updraft Countercurrent High moisture fuel (<60% wet basis) High tar production except with post-reactor catalytic cracking or dual stage air injection Low carbon ash Downdraft Cocurrent Moisture < 30% Lower tar than uncontrolled updraft Carbonaceous char Crossdraft Adaptation for high temperature charcoal gasification 3

4 Swedish design downdraft gasifier for mobile applications Small Power Systems: CPC Fuel handling incorporating dryer Downdraft gasifier with dry scrubbing to produce low-btu producer gas Engine-generator sets rated 5-50 kwe Can operate in CHP mode 50 kwe unit designed for 144 hour continuous operation before shut down for cleanout Capital cost $700-3,500/kWe (not fully demonstrated) 4

5 Small Power Systems: Chiptec Crossdraft gasifier to produce low-btu producer gas Principally used in heat applications without gas cleaning (effectively 2-stage burners) Cogeneration systems 35 kwe to 5 MWe (steam turbine) Fixed-bed indirect gasifier BGP Gasifier 5

6 Classification by Reactor Type: Fluidized Beds Bubbling beds Lower velocity Low entrainment/elutriation Simple design Lower capacity and potentially less uniform reactor temperature distribution than circulating beds Circulating beds Higher velocity Solids separation/recirculation More complex design Higher conversion rates and efficiencies Demonstration Biomass IGCC Varnamo, Sweden FW-Sydkraft 6 MW electric Pressurized fluidized bed Burlington, Vermont FERCO dual-fluidized bed Not tested in IGCC mode 6

7 Classification by Reactor Type: Entrained Beds Solids or slurry entrained on gas flow Small particle size Entrained flow used as component in some developmental pyrolytic biomass reactor systems ChevronTexaco Gasifier Classification by Oxidation Medium Air gasification (partial oxidation in air) Generates Producer Gas with low heating value (~150 Btu ft -3 ) and high N 2 dilution. Oxygen gasification (partial oxidation using pure O 2 ) Generates synthesis gas (Syngas) with medium heating value (~350 Btu ft -3 ) and low N 2 in gas. Steam gasification Generates high H 2 concentration, medium heating value, low N 2 in gas. Can also use catalytic steam gasification with alkali carbonate or hydroxide Carbon dioxide Hydrogen Indirect heated--pyrolysis 7

8 Gasification Reactions and Products Simplified Reaction System for Carbon C + O2 = CO 2 C + CO 2 = 2CO C + 2H2 = CH4 C + H2O = CO + H 2 C + 2H2O = CO 2 + 2H2 CO + H2O = CO 2 + H2 CO + 3H2 = CH4 + H2O Oxidation Boudard Reaction Hydrogasification Water-gas reaction s Water-gas shift Methanation Typical Clean, Dry Gas Composition from air-blown gasifier % by volume CO 22 H2 14 CH4 5 H2O 2 CO2 11 N2 46 Composition of Raw Gas from Steam Gasification % by volume dry (excep t as n oted) H 2 O (wet) CH C 2 H C3 fraction CO CO H N H 2 S ppmv NH ppmv Tar 2 5 g Nm -3 Particulate Matter g Nm -3 Lower Heating Value ~350 Btu ft -3 Advantages of Gasification Produces fuel gas for more versatile application in power generation and chemical synthesis. Potential for higher efficiency conversion using integrated gasifier combined cycles compared with conventional Rankine steam cycle power systems. Typically lower temperatures than direct combustion thus decreases potential alkali volatilization, fouling, slagging, and bed agglomeration (fluidized beds) although for high alkali, high ash fuels such as manure, slagging and bed agglomeration can be problems. Can also reduce heavy metal volatilization. Lower volume of gas requiring treatment to reduce NOx and SOx emissions compared to combustion flue gas. Fuel nitrogen evolved principally as NH 3 and sulfur as H 2 S, more readily removed than NOx and SO 2 in combustion systems. Applications for power generation at smaller scales than direct combustion systems although gas cleaning is primary concern and expense 8

9 Gasification Constraints Gas cleaning required for use of fuel gas in engines, turbines, and fuel cells For reciprocating engines, tar and particulate matter removal are primary concerns, tar removal difficult to achieve. Reactor designs influence tar production, some newer two stage gasifiers reduce tar but cleaning is still an issue. Need for cool gas to maintain engine volumetric efficiency leads to tar condensation and waste water production for wet scrubbing systems. Engine derating for gas from air-blown reactors. For gas turbines, alkali concentration in gas must be kept low (typically less than 1 ppmv), need for hot gas cleaning to maintain high efficiency. Alkali typically removed by condensing on particles and hot filtering at temperatures ~1,300 F. Fuel cells require clean gas and alkaline, phosphoric acid, and PEM types intolerant of high CO. Molten carbonate and solid oxide fuel cells internally reforming and developmental for gasification systems. Gasification Constraints Generates carbonaceous solid (char) Low grade carbon, can be activated to improve value. Dual-reactor and similar systems burn char to provide additional heat to process (e.g. FERCO dual fluidized bed tested in Vermont). Individual reactors limited in scale, multi-reactor systems needed for large power or refinery systems Advanced IGCC systems using pressurized reactors need pressure feeding systems For lower tar reactors, moisture content limited (<30%), requires feedstock drying for wet manure solids. Particle size distribution important for proper fuel handling and material flow 9

10 Manure Composition Fresh cattle manure Proximate Analysis Ultimate Analysis Ash Analysis Ash 15.9 C SiO Volatiles 70.3 H 5.35 Al 2 O Fixed Carbon 13.8 O TiO Total N 0.96 Fe 2 O S 0.29 CaO Cl 1.16 MgO 3.18 Total (with ash): Na 2 O 4.26 K 2 O 6.4 P 2 O SO Total Undetermined 2.65 Concentrations vary depending on feed, management, age of manure, collection technique. Fate of N, S, Cl in gasification Fuel N principally converted to NH 3 and N 2 20 to 70% conversion to NH 3 Concentrations from 600 to 6,000 ppmv depending on fuel N HCN, other species present at lower concentrations Need to remove to avoid high NOx emissions during gas combustion At sufficiently low NH 3 concentrations, gas can be used in reburning applications to reduce NOx from solid-fuel direct combustion systems Options to produce ammonia as gasification product Fuel S principally converted to H 2 S, can be scrubbed. Fuel Cl mostly evolved as HCl, can interfere with sulfur removal (e.g. reaction with zinc and iron based sorbents). 10

11 Gasifier Applications Close-coupled Gasification Fuel Gasifier Boiler Gas Fuel Ash Char Gasifier to supply fuel gas to solid fueled boiler Gasifier operates at lower temperatures/ lower volatilization of alkali, lower fouling Potential for lower emissions Reburning/Staged combustion /NOx 11

12 Thermochemical Processing/Conversion FEEDSTOCK BIOMASS Cat: Ni, Fe, Cu-Zn SELECTED SYNTHESIS GAS OPTIONS Cat: Cu-Zn, Cu-Co HYDROGEN ETHANOL, MIXED ALCOHOLS Cat: Cu-ZnO METHANOL, DME FEED PREP Cat: H3PO4, Cr2O3 OLEFINS GASIFICATION CLEANUP Cat: Ni SYNGAS Cat: Fe Cat: Co/K Cat: Cu-ZnO FTL MeOH UPGRADE Cat: Zeolite LPG NAPHTHA KEROSENE/DIESEL LUBES WAXES GASOLINE Cat: Mixed Bases Na, Ca OXOCHEMICALS e.g., KETONES CaCN AMMONIA Cat: Ni/Mg SNG Cat = Catalytic Conversion Process Combined Cycle CHP Cofiring/ Reburn CHP + Others Source: NREL Gasifier Boiler Application CONDENSATE option 12

13 CFB with gas conditioning Engine Gensets (Carbona Skive Project, Denmark) PRODUCT GAS FILTER GAS COOLER TAR CRACKER TO STACK BOILER BIOMASS Cyclone Separator FLY ASH PRODUCT GAS COOLING (Heat Recovery) Bed media and char return PRODUCT GAS SCRUBBING GASIFIER (Heat Recovery) DISTRICT HEATING 11.5 MW th PRODUCT GAS BUFFER TANK FLUE GAS HEAT RECOVERY AIR STEAM ASH WATER TREATMENT POWER 5.4 MW e GAS ENGINES Courtesy Carbona Corporation BIGCC Power Generation 3 MWe and up 13

14 BTL: Biomass To Liquids Fischer-Tropsch Synthesis Air/O 2 Gas Cleaning Wet/Cold Dry/Hot Gasification Water, Tar, PM Recycle Gas Processing Methane Reforming CH 4 + H 2 O = 3H 2 + CO Shift H 2 /CO adjust CO 2 removal Fe, Co CO + 2H 2 = -(CH 2 )- + H 2 O H 500K = kj/mol C/0.5-4 MPa CO 2 + 3H 2 = -(CH 2 )- + 2H 2 O H 500K = kj/mol (Kölbel reaction) Ash, Char Pretreatment Drying Comminution Extraction Biomass FT Synthesis Off-gas Power Generation Liquid/Wax Products Refining Products (80 gals/ton) Power Heat/Steam =33-50% LHV Overall Biomass To Hydrogen: Gasification Gas Cleaning Wet/Cold Dry/Hot Reformer CH 4 + H 2 O = 3H 2 + CO Air/O 2 Gasification Water, Tar, PM Water Gas Shift H 2 O + CO =H 2 + CO 2 (Methanol production) Ash, Char Pretreatment Gas Purification Hydrogen Drying Comminution Extraction Power Generation/ Power Biomass (can also use bio-oil through steam reforming) Carbon Capture and Storage Heat/Steam =52-61% LHV Overall 14

15 Biomass Power Levelized cost of electricity (COE)/solid-fuel thermal systems COE ($/kwh) % Efficiency = 10% 20% 30% 40% Zero fuel cost Benchmark comparison for California: Natural gas combined cycle with heat rate of 7,000 Btu/kWh (49% efficiency) at $9/MMBtu gas price COE=$0.074/kWh (fuel cost = $0.063/kWh or 85% of COE) Current natural gas price $10-13/MMBtu 0.02 Fuel cost = $20/ton except as noted Installed Capital Cost ($/kw) Levelized Cost of Energy: Sensitivity to Economic Factors/solid-fuel thermal systems without CHP COE ($/kwh, Constant) Capital Cost Fuel Cost Debt Ratio Debt Interest Rate Cost of Equity Net Efficiency Capacity Factor Impact of Economic Life: Base COE = 20 Year: $0.067/kWh 5 Year: $0.124/kWh (no salvage) small modular/portable systems? 0.02 Sensitivity of COE (2004 constant $/kwh) to technical and financial factors for stand-alone power generation from biomass Capital cost = $2,800/kW e Relati e Change (%) Fuel cost = $20/ton Base-case assumptions (20 year life): Net Efficiency = 20% Capacity factor = 85% Debt ratio = 75% Debt interest = 5%/year Cost of equity = 15%/year Capacity payment = $166/kW-y PTC = $0.009/kWh Straight line depreciation General inflation = 2.1%/year One year debt reserve 15

16 Cost of Electricity: Biomass Combined Heat and Power (CHP) COE (constant $/kwh) Current California Natural Gas Price Range (12/2005) Value of Heat ($/MMBtu) CHP provides opportunities for low cost power 16