Process modelling of two-stage entrained-bed gasification composed of rapid pyrolysis and gasification processes

A novel two-stage entrained-bed gasification system composed of the rapid pyrolysis of pulverized coal and the gasification of char is proposed to obtain high-quality synthetic gas with low tar content and high methane content. A new framework containing a modified multi-step kinetic pyrolysis model and a non-linear programming (NLP) process is developed to simulate the rapid pyrolysis process of pulverized coal. The method can be used to simulate the volatile composition, which includes only the high-weight hydrocarbons/distillable liquids (benzene, toluene, xylene, naphthalene, pyrene, phenol) based on the proximate and ultimate analysis data of coal. The framework for coal rapid pyrolysis and the simulation of the two-stage entrained-bed gasification are validated by experimental data and semi-industrial data, respectively. This paper analyses the effects of the final pyrolysis temperature, the gas residence time, and the steam/coal ratio on the performance of the two-stage entrained-bed gasification system. The results indicate that by adjusting the gas residence time to 15.5 s at the final pyrolysis temperature of 1000 degrees C, the tar yield can be reduced to less than 500 mg/Nm(3), the molar fraction of methane in the syngas can be approximately 5.84%, the exit temperature can be approximately 943 degrees C, and the higher heating value (HHV) of syngas and the cold gas efficiency (CGE) will be 11.41 MJ/(Nm(3)) and 91.23%, respectively.