Experiment Study And Modelling On Coal Gasification In Atmosphere Circulating Fluidized Bed

Being an efficient, bubble free and high production capacity reactor, circulating fluidized bed has been successfully used in many fields. However, coal gasification in circulating fluidized bed has not been widely studied and developed. The research on coal gasification in a circulating fluidized bed is made and described in detail in the thesis.Based on the cold experiment results from a cold model, a circulating fluidized bed gasification test rig with a lift tube of 100 mm in diameter and 3000 mm in height was built. Some preliminary gasification experiments on Shenhua coal with the agents of oxygen and steam at atmospheric pressure were made. The tests were run stably and gasification efficiency and carbon conversion conuld be 60.5% and 96.9%, respectively. But there were problems, e.g. clinker and high carbon losses in fly ash.Experiments on gasification of Shenhua, Longkou and Datong coals in the rig with the agents of air and steam at atmospheric pressure and different operation conditions were carried out. The effects of operation condition, such as type of coal, coal feed rate, steam/coal ratio and air/coal ratio on gas composition, calorific value, carbon conversion and gasification efficiency are analyzed. In the investigate range, the maximum gasification efficiency is 53.96% and the highest coal conversion is 92.31% for Longkou coal, 45.64% and 83.84% for Shenhua coal, 34.71%and 61.99% for Datong coal, respectively. Considerable carbon was lost in fly ash after the cyclone. Experiments of injecting steam in U-valve, feeding coal at the standpipe and the upper part of the lift were made, but no satisfactory results were obtained.A kinetic modified equilibrium model of coal gasification in the circulating fluidized bed is proposed. The model is based on mass balance, heat balance, chemical equilibrium as well as the kinetically empirical correlations of the carbon conversion and the yield of CH₄ obtained from experimental data. Predictions of the model compare reasonably well with the obtained experimental data in the same conditions. The effects of the feed rate of air, steam and coal on bed temperature, gas composition, calorific value, carbon conversion and gasification efficiency are predicted and analyzed with the model.