Fundamentals of Coal Gasification

The gasification process may be described by three laws of nature  

These three factors make it possible to compute the course of gasification theoretically. To this end, numerous equations have to be introduced in an iterative process. However, the way in which gasification is to proceed in practice, and thus the exact compositions, cannot be derived until the kinetic processes, too, are known with sufficient accuracy. 

The complex reaction of coal gasification may be described by the heterogeneous and homogeneous reactions listed in Table 1.3 and by its pyrolysis [1.4]. It will generally be sufficient to have a look at these reactions, since the reaction enthalpies of all other equations can be derived from them by simple arithmetic manipulation. The course of the individual reaction has no influence on the total heat input/output of a reaction sequence as long as the same feedstocks lead to the same products (Hess s law). 

To compute the distribution of the main coal components in the product gas, i.e. carbon, hydrogen and oxygen, the simultaneous side reactions are normally neglected in the first run. If the distribution of secondary components such as sulfur in H2S, COS, mercaptanes etc. or of nitrogen in NH3 or HCN needs to be known, it can be derived by secondary computations using the distribution of main components computed before. 

Thermodynamic equilibrium makes it possible to compute how far a chemical reaction can proceed under the given conditions of pressure and temperature. For such reversible reactions, the velocity of forward and backward reactions is the same, although thermodynamic considerations provide no clue as to how fast this equilibrium is reached. 

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Johnson J.L, Fundamentals of coal gasification, in chemistry of coal utilization (1981), editor Elliott M.A... 

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