Study on Chemical Kinetics Modeling and Thermodynamics Characteristics of Entrained Flow Coal Gasification

Abstract

Current simulations of coal gasification are mostly based on equilibrium reactions, which cannot reflect the residence time and carbon conversion rate. In this paper, a simplified chemical kinetics model is proposed to avoid the reliance on experimental data in the chemical kinetics modeling for entrained flow coal gasification. In this model, the chemical kinetics simulation of the coal gasification process is carried out based on some assumptions that conforms to the characteristics of gas-solid reaction. The reliability of the model is verified by comparisons with the carbon conversion rate xc and the main syngas composition from the results of other models or experiments. Then, the impacts of primary parameters (e.g., gasifier size, coal particle size, O2/coal ratio, H2O/coal ratio and gasification pressure) on the performance of gasification process (e.g., carbon conversion rate xc, cold gas efficiency η, solid residence time t, syngas temperature and main syngas composition) were simulated and detailly analyzed, providing data and suggestions for gasifier design and operation. The results show that the height has a great influence on the properties of the syngas. The carbon conversion rate xc, the solid residence time t, and the cold gas efficiency η all increase with the height of the gasifier. As the gasification coal particle size increases, the reaction takes longer to complete, and the carbon conversion rate xc reduces and the gasification temperature increases sharply. Thus, particle size is a very important parameter for gasifier design and operation. The higher the O2/coal ratio, the higher the carbon conversion rate xc until it reaches 100%. However, an excessively high O2/coal ratio will reduce the cold gas efficiency η. The carbon conversion rate xc and cold gas efficiency η both increase first and then decrease with the increase of H2O/coal ratio. Further considering coal that has not been gasified, the ideal cold gas efficiency η* is proposed. It is found that the ideal cold gas efficiency η* is high despite insufficient the carbon conversion rate xc and the cold gas efficiency η. That is, the energy utilization efficiency can be improved if the ungasified coal can be properly reused.

Keywords: entrained gasification, Chemical kinetics, carbon conversion rate, cold gas efficiency, residence time