Investigation on Steam Gasification of High-metamorphous Anthracite Using Mixed Black Liquor and Calcium Catalyst

Abstract

The catalytic effects of single and mixed catalysts, i.e. single 3%Ca and 5%Na-BL(black liquor) catalysts and mixed 3%Ca+5%Na-BL catalyst, on carbon conversion, gasification reaction rate constant and activation energy, relative amount of harmful pollutant like sulphur containing gases have been investigated by thermogravimetry in steam gasification under temperature 750°C to 950°C at ambient pressure for three high-metamorphous anthracites (Longyan, Fenghai and Youxia coals in Fujian Province). The mixed catalyst of 3%Ca+5%Na-BL increases greatly the carbon conversion and gasification rate constant by accelerating the gasification reaction C+H 2O → CO+H 2 due to presence of alkali surface compounds [COM], [CO 2M] and exchanged calcium phenolate and calcium carboxylate (—COO) 2. By adding CaCO 3 into BL catalyst in gasification, in addition to improving the catalyst function and enhancing the carbon conversion, the effective desulphurization is also achieved, but the better operating temperature should be below 900°C. The homogenous and shrinking core models can be successfully employed to correlate the relations between the conversion and the gasification time and to estimate the reaction rate constant. The reaction activation energy and pre-exponential factor are estimated and the activation energy for mixed catalyst is in a range of 98.72-166.92 kJ·mol −1, much less than 177.50-196.46 kJ·mol −1 for non-catalytic steam gasification for three experimental coals.