Gasification, coal heating values

Coal can be converted to gas by several routes (2,6—11), but often a particular process is a combination of options chosen on the basis of the product desired, ie, low, medium, or high heat-value gas. In a very general sense, coal gas is the term appHed to the mixture of gaseous constituents that are produced during the thermal decomposition of coal at temperatures in excess of 500°C (>930°F), often in the absence of oxygen (air) (see Coal CONVERSION PROCESSES, gasification) (3). A soHd residue (coke, char), tars, and other Hquids are also produced in the process ... 

Gasification technologies for the production of high heat-value gas do not all depend entirely on catalytic methanation, that is, the direct addition of hydrogen to coal under pressure to form methane. 

Air-blown gasifiers benefit from a low-cost (free) source of oxidant, but produce a gasifier product gas that has a very low heating value (approximately 5MJ/m3 for air-blown gasification of coal, compared to 38MJ/m3 for a typical natural gas) and which is too dilute to use for liquid fuel synthesis. 

In ordar to determine the effect of coal rank (at established by reflectance measurement of vitrinite in coal) on the reactions of coal as related to carbonization, gasification, combustion, and other processes, a wide range of bituminous coals were studied. The results show that reflectance measurements can be used effectively (1) to determine accurately yields of coal carbonization products such as coke, tar, gas, light oil, and liquor from pilot and commercial coke oven (2) to obtain the heating value and specific gravity properties of gases from these processes (3) to determine the free swelling index and B.t.u. content of coals ... 

High sulfur coal would be the optimum feed stock for coal gasification plants since the sulfur content of the feed stock has little effect on manufacturing costs and high sulfur coal probably will be priced substantially below low sulfur coals of equivalent heating value. 

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