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How can coal be converted into liquid fuels?
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coal utilization
Cross-regenerative coke oven. (A) Cross section, showing the alternating arrangement of flue walls and ovens; (B) longitudinal section, showing (left) a series of combustion flues in a single flue wall and (right) part of a long, slotlike oven.
Coal is a hydrogen-deficient hydrocarbon, meaning that converting it into liquid fuels requires increasing its hydrogen-to-carbon ratio. This is achieved through coal liquefaction, which generally follows four methods:1
- Pyrolysis and hydrocarbonization: Coal is heated in the absence of air or within a hydrogen stream.1
- Solvent extraction: Coal hydrocarbons are selectively dissolved, and hydrogen is added to produce liquid products.1
- Catalytic liquefaction: Hydrogenation occurs in the presence of a catalyst, such as zinc chloride.1
- Indirect liquefaction: Coal is first converted into synthesis gas (a mixture of carbon monoxide and hydrogen) via gasification. This gas is then combined over a catalyst, a process known as the Fischer-Tropsch reaction.123
Additionally, pulverized coal can be mixed with water and chemicals to create a coal-water slurry fuel. While this mixture can be handled and burned similarly to liquid fuel, it is a physical suspension rather than a chemical conversion into synthetic crude oil.14