Numerical Simulation Of Yanzhou Coal Gasification

With the rapid development of Chinese economy, the consumption of energy is increasing. The structure of energy consumption, which coal is used as the main energy in China, will last for a long time. In order to improve the efficiency of coal utilization and decrease the environmental pollution from coal combustion, it is required to develop clean coal technology. The research and application of coal gasification technology have become the consensus in the field of the energy technology and the business community.The study of coal gasification and gas clean up system by thermodynamics and kinetics process was researched based on the previous experimental work in this paper. The major works and research results were shown following:(1) The thermodynamic model of coal gasification process was set up, and the simulation of the coal gasification process was carried out using Aspen Plus. The entrained-flow pulverized coal gasification process was simulated by Gibbs free energy minimization and equilibrium constant method. The flow arithmetic was also improved. Simulation results were in excellent agreement with experimental data, so this model might be useful for analyzing thermodynamic characteristics of coal gasification process.(2) Major operating parameters affecting the coal gasification process performance were analyzed with Aspen Plus. Oxygen-coal ratio is one of the most important conditions for gasification process, which is more significant than the other conditions, and the best oxygen-coal ratio is 0.70~0.80kg/kg for simulated coal. The best parameters corresponding gasification process were CO+H2 volume fraction of 96.48% (dry base), cold gas efficiency of 83.56% and CO+H2 yield of 1.74m3/kg coal. The gasification temperature is elevated about 40oC when the oxygen-coal ratio is increased by 0.1kg/kg and reduced about 8℃when the stream-coal ratio is increased by 0.1kg/kg. Gasification agent added in an appropriate amount of steam can increase the H2 volume fraction in gas, and reduce oxygen consumption. But the amount of inappropriate steam will reduce the furnace temperature and affect the gasification process.(3) The gas purification process in coal gasification was summed up and analyzed. The desulfurization process is designed based on the model of the middle temperature dry desulfurization system as the simulation object. The results show that the efficiency of limestone desulfurization in furnace can come theoretically up to 86%, in which the Ca amount of 1.0 ~ 1.2 Ca/S ratio is optimum. Increasing pressure is not disadvantage for the desulfurization in the furance. The desulfurization eficiency for hot coal gas based on the specially designed desulfurizing processes could reach 99%. It is sure to meet the basic needs of follow-up industrial production 1mg/m3.(4) Effect of heating rate on coal pyrolysis is mainly dominated by the coal pyrolysis activation energy and frequency factor. As the heating rate increases, the maximum weight loss temperature is delayed. This is mainly because the reverse polymerization activation energy was slightly lower than that of depolymerization during coal pyrolysis.(5) The kinetics of coal pyrolysis process is studied at different heating rate. It is found that the activation energy in different stages vary widely and there is the basic regularity of increasing at first and then decreasing.(6) With the increase of coal gasification temperature and heating rate increases, the conversion of carbon increases significantly and the time coal gasification reaction is shortened. For the reaction at constant temperature, the change of coal-CO2 gasification rate with time was peak-like trend.(7) The dynamic model of coal gasification process is set up using multiple linear regression. The coal gasification kinetic equations under different temperature are obtained. The total kinetic expression is dx 2712.5exp( 158.457) (1 x)2dt = ? RT? ? . The form of dynamics control is the shrinking core model between 900~1000℃, the expression is dx 5811.857exp( 176.107)(1 x)2/3dt RT= ?? . The reaction order and temperature presents a linear relationship between 1000~1100℃, the expression is n=9.926-0.006T. The form of dynamics control is the corrected random pore model, the expression is amended as ddxt = 11062exp by the nonlinear least squares regression parameters for this interval.