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How does coal gasification produce synthesis gas?

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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 gasification is the process of converting coal into a mixture of gases, primarily hydrogen and carbon monoxide, known as synthesis gas or syngas.12

This conversion occurs at high temperatures through the thermal treatment of coal in the presence of steam and oxygen (or air), without the need for full combustion. Because coal is hydrogen-deficient compared to liquid hydrocarbons, these processes effectively add hydrogen—often derived from water—to the coal's chemical structure.312

Specific methods include:
* Pulverization and reaction: Coal is pulverized and mixed with oxygen and steam at high temperatures.3
* In situ gasification: Controlled, incomplete burning of underground coal beds while injecting air and steam, with the resulting gases withdrawn for use.2
* Catalytic exposure: Exposing coal to hydrogen at high temperatures in the presence of a catalyst.3

Once produced, the syngas must be cleansed of impurities like coal tar before it can be utilized for electricity generation or as a feedstock for chemical production.12