A comparison of prediction and experiment in the gasification of anthracite in air and oxygen-enriched steam mixtures

Abstract

Gas composition and temperature profiles for anthracite gasified in a combustion pot have been measured and shown to be in good agreement with prediction. The pot was refractory of 6.5″×15.5″ and bed depths were up to 4′ deep. Gasification was in air, and in steam up to 38.5% with oxygen enrichment up to 31%. Measurements confirmed that the initial temperature rise at the bottom of the bed was very steep, at about 1000°C/cm. Comparison with model predictions showed that: the gas-solid reaction in the combustion region was mainly endothermic reduction of CO 2 in a double film, with the main heat release in the ambient gas by reaction of CO to CO 2 ; and that the bed temperature in this region was maintained by radiation as the principal heat transfer mechanism in the bed. This double film mechanism replaces the single film assumption that is common to essentially all past theories of solid bed combustion. The model is otherwise similar to a prior construct (2) but with an improved solution procedure in which computation for the two parabolic differential equations starts at the boundary between the combustion and gasification regions. In other experimental results with computational agreement it is shown: that with sufficiently high or low velocity, the reaction zone exhibits classical blow-off and flashback; that bed depth has no significant effect on the reaction zone width; that the main effect of a deep bed is to act as a heat exchanger; and that the model presented is able to predict with good accuracy the temperature and composition profiles for a wide range of air rates and reactive gas compositions of air with steam and oxygen enrichment.