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Solid Fuels 6-A
- 2. Liquefaction The term liquefaction refers to the conversion of the coal to a product that is primarily a liquid (CTL) Several very old processes… since WWII Same general theme: increase H/C ratio Can make a wide variety of hydrocarbon products (e.g. synthetic crude or synfuel) Two basic methods: direct and indirect
- 3. 3 Advantages of Coal To Liquid (CTL) Fuels • CTL Improves national and economic security • Lessens dependence on foreign oil • Uses domestic resources • Provides environmental benefits - Cleaner fuels that reduce NOx and particulate emissions - Enables use of higher efficiency engines • Is capable of capturing CO2 emissions • Provides geographic diversity as energy source
- 4. 4 Direct Liquefaction of Coal Attractive Because of Low transportation cost Less chemical transformation required Higher efficiency than high Btu gas production Easy to store Less water required for manufacture However, processing slurries at high temperature and pressure presents difficulties with equipment life and solid/liquid separation (still not commercial)
- 5. 5 Coal Liquefaction Very expensive Liquefaction attractive for transportation fuel Indirect liquefaction commercially proven (>50 yrs) Acid gas removal by amines (CO2, H2S) S removal by Claus Process H2S + O2 = H2O + SO2 H2S + SO2 = S + H2O
- 6. 6 Two Basic Approaches To Convert Coal To A Liquid Fuel 1. Direct Liquefaction: • Dissolves coal in a solvent at elevated temperature and pressure • Combine with hydrogen gas and a catalyst 2. Indirect Liquefaction: • Involves first gasifying coal, followed by reacting carbon monoxide and hydrogen together nCO + (2n+1)H2 = CnH2n+2 + nH2O
- 7. 7 Adds hydrogen to break down the coal Dissolves in a solvent followed by hydrocracking Operates at 450 C and 170 bars Light products are distilled Medium and heavy distillates obtained from vacuum distillation Liquid yields of 70% of the dry weight of coal feed Further upgrade is needed for use as transportation fuels Complete breakdown of coal with steam and oxygen Sulfur is removed from the syngas Syngas reacted over catalyst at 300 C and 20 bars Produces a lighter suite of products; high quality gasoline and petrochemicals Oxygenated chemicals Comparison of Processes DIRECT LIQUEFACTION INDIRECT LIQUEFACTION
- 8. 8 SASOL in South Africa • South Africa’s SASOL Co. developed a commercial coal liquids industry (fuel plus chemicals) • The plant produces about 150,000 barrels daily Indirect Coal liquefaction is proven technology
- 9. 9 Concerned about increasing dependence on oil imports and its impact on economic growth and national security, China is making a massive $6 billion investment in new coal liquefaction plants. Planned $2 billion Shenhua facility will eventually produce 50,000 barrels daily of diesel fuel and gasoline. Coal To Liquids in China
- 10. Light Gases Gasoline Jet Fuel Diesel Catalyst N2 Air Recycle Solvent Residue O2 H2 Coal Prep Slurry Mixing Liquefaction Separation Upgrading Fractionation Air Separation Gasification Purification First Train: 1 MT/a Liquefaction Oil Coal Shenhua DCL Process
- 11. Coal Raw ICL Products Raw DCL Products H2 H2 F-T Tail Gas Final Products Coal Gasification Indirect Coal Liquefaction (F-T) Product Blending and Refining Hydrogen Recovery Direct Coal Liquefaction Hybrid DCL/ICL Plant Concept
- 12. 12 Indirect Liquefaction • Fischer-Tropsch Indirect Liquefaction Process - Yields high quality transportation fuels plus other products
- 13. Indirect Coal Liquefaction Overview Natural Gas Coal Pet Coke Biomass Wastes Synthesis Gas Production • Gasification • Reforming • Steam • POX • ATR Oxygen Plant Air O2 F-T Liquid Synthesis Slurry/Fixed/ Fluid-Bed Liquid Fuels Product Storage Naphtha/ Diesel Tail Gas Power Generation H2 Hydrogen Recovery Wax Hydrocracking Liquids Wax Product Recovery
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- 17. 17 • Coal-based liquid fuel becomes viable when the per-barrel price of oil is expected to exceed the $70-100 range for 20+ years • CTL has high front-end capital cost - A 50,000 barrel-a-day plant would cost over $3 billion to construct • The product refinement process is three to four times more expensive than refining an equivalent amount of oil • The cost of sequestering the captured CO2 would increase the price of the end product by $10-20 a barrel. • The imposition of a carbon cap and trade policy would also raise the cost of fuel produced with CTL technology CTL Costs
- 18. 18 CTL is Very Water-Intensive CTL requires ~7:1 water to fuel ratio ~7 gallons of water per gallon of fuel produced Water scarcity can be a limiting factor for CTL plant permitting Conventional gasoline 1-2.5 gallons of water per gallon of fuel produced Irrigated Biofuels 1000 gallons of water per gallon of fuel
- 19. 19 Liquids Fuels Summary…. Proven technologies All processes require adding hydrogen All processes remove sulfur and ash Product include liquid, gas, and combustible solid(char) Several long-standing commercial processes (e.g., S. Africa - SASOL) So far no large-scale use without government support
- 20. 20 Coal to Liquids Summary…. Good promise because of very large coal deposits in the world Numerous processes that can generate a wide variety of products Environmental issues include some hazardous wastes and byproducts Does not yet effectively compete with natural gas or oil production … requires some form of subsidy
- 21. Carbonization Carbonization is the process by which coal is heated and volatile products—gaseous and liquid—are driven off, leaving a solid reside called char or coke. The coke produced by carbonization of coal is used in the iron and steel industry and as a domestic smokeless fuel Only a limited range of coals produces acceptable metallurgical cokes. These coals are in the bituminous rank range but not all bituminous coals are caking coals.
- 22. Carbonization Coal carbonization processes are classified into i. high-temperature ii. low-temperature High-temperature Carbonization processes performed at temperatures in the range of 900 − 1200°C. The main purpose of high-temperature carbonization is the production of metallurgical coke for use in blast furnaces and foundries.
- 23. Carbonization Low-temperature In low temperature carbonization heating is carried out at 500-700°C. Coke produced is not mechanically strong so it is not used as metallurgical coke. Low-temperature carbonization was originally developed to provide town gas for residential and street lighting and to manufacture a smokeless fuel for domestic and industrial heating
- 24. Carbonization Characteristics Low temperature carbonization High temperature carbonization 1 Heating temperature 500-7000C 900-1200°C 2 Yield of coke 75−80% 65−75% 3 Volatile matter content 5−15% 1−3% 4 Mechanical strength Poor Good 5 Calorific value 6500−9500 kcal/m3 5400−6000 kcal/m3 6 Quantity of by-product gases 130−150 m3/tone 300−390 m3/tone 7 Coke produced Soft Hard 8 In gas, percentage of (a) Aromatic hydrocarbons (b) Aliphatic hydrocarbons Lower Higher Higher Lower 9 Uses Domestic Metallurgy
- 25. Coal Properties for Coke Production The ability of a coal to melt upon heating and to form a coherent residue on cooling is termed caking; caking is an essential prerequisite for a coking coal that it should cake or fuse when heated. Coals that are low in rank, such as lignites, or high in rank, such as anthracites, do not cake and therefore are not capable of forming coke. Several properties of coals are measured to identify appropriate coking coals, including swelling, fluidity, composition etc.