Introduction
The manufacture of combustible gases from solid fuels is an ancient art but by no means a forgotten one. In its widest sense the term gasification covers the conversion of any carbonaceous fuel to a gaseous product with a useable heating value. This definition excludes combustion, because the product flue gas has no residual heating value. It does include the technologies of pyrolysis, partial oxidation, and hydrogenation. Early technologies depended heavily on pyrolysis (i. e., the application of heat to the feedstock in the absence of oxygen), but this is of less importance in gas production today. The dominant technology is partial oxidation, which produces from the fuel a synthesis gas (otherwise known as syngas) consisting of hydrogen and carbon monoxide in varying ratios, whereby the oxidant may be pure oxygen, air, and/or steam. Partial oxidation can be applied to solid, liquid, and gaseous feedstocks, such as coals, residual oils, and natural gas, and despite the tautology involved in “gas gasification,” the latter also finds an important place in this book. We do not, however, attempt to extend the meaning of gasification to include catalytic processes such as steam reforming or catalytic partial oxidation. These technologies form a specialist field in their own right. Although we recognize that pyrolysis does take place as a fast intermediate step in most modern processes, it is in the sense of partial oxidation that we will interpret the word gasification, and the two terms will be used interchangeably. Hydrogenation has only found an intermittent interest in the development of gasification technologies, and where we discuss it, we will always use the specific terms hydro-gasification or hydrogenating gasification.
