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Abstract

A model is developed for the countercurrent char gasifier of Lurgi form. Char particles are fed to the top and oxygen, inert, and steam in the bottom. The combustion zone is defined as the zone in which there is a nonzero molfraction of oxygen. In the gasification zone, the particles are assumed to be a lumped system in which the Johnson reaction kinetic expressions are assumed to be valid with the water gas shift reaction at equilibrium. All of the reactions between oxygen and carbon and water and carbon are assumed to take place in the combustion zone but with the carbon-oxygen reaction predominating to form a shell progressive system within the particles. Radiation is taken into account, and parametric computations are made on temperatures, compositions, flow rates, and char reactivity. The maximum temperature is strongly influenced by radiation and its position is a sensitive function of the solid flow rate producing an ash layer at the bottom of varying thickness.