Coal gasification characteristics in a thermobalance and a cyclone reactor

Abstract

The kinetic parameters of heterogeneous catalytic and/or non-catalytic char-gas reactions (C-$H_2O$, C-$CO_2$ and C-$O_2$) are determined using a thermobalance. The effects of key experimental variables such as coal rank, particle size, temperature, heating rate, reactant gas concentration, catalyst type and the amount of catalyst loading on these rate processes are investigated. The generalized equilibrium prediction model is developed to calculate the equilibrium composition of complex gasification products with the variation of temperature, pressure and feed condition. The cyclone gasifier model is developed to estimate the product gas composition and the carbon conversion with the variation of operating conditions. Basic calculated values of concentration and conversion of the char-$H_2O$-$O_2$ reaction in a cyclone gasifier are provided with the variation of operating conditions such as temperature and mole ratio of the reactant materials, with which to evaluate its potential application to industrial needs. Reaction kinetics of char-$CO_2$ gasification at atmospheric pressure are investigated in a 5.5 cm-ID thermobalance reactor using four ranks of coals. Effects of coal ranks (lignite-semianthracite), particle size (0.18-1.00 mm), reaction temperature (700-900℃), and concentration (30-100 %) of the reactant gas ($CO_2$) on the conversion rate of char gasification are determined. The gasification reaction order and the reaction rate constant are determined from the conversion data, and the activation energy of the reaction is determined from the Arrhenius plot. Chemical reactivity of the char is correlated with the carbon content of the parent coals, particle size, partial pressure of $CO_2$ and reaction temperature. The experimental conversion data are well represented by the unreacted shrinking core model in which chemical reaction is the rate controlling step. Three different catalysts ($K_2CO_3$, $Na_2CO_3$, $Li_2CO_3$) and its mixture [$(Na,K)_...