Thermodynamic analysis of chemical looping gasification coupled with lignite pyrolysis

Abstract

A poly-generation system integrating coal pyrolysis and chemical looping gasification (CLG) is proposed to realize the multi-generation of value-added chemicals, synthetic gas fuels and heat/electricity. In this system, the models including coal pyrolysis, coal drying, air reactor (AR) and fuel reactor (FR) are employed to simulate the coupled system using Aspen Plus software. Especially, the FR model is used to produce syngas, which is the main target product, on the basis of Gibbs free energy minimization approach. According to the thermodynamic data obtained from the simulation, chemical exergy and physical exergy are determined for process streams and thermal efficiency is discussed as well. The overall energy efficiency of the new system can achieve values of 43.12%, with the drying unit causing the highest energy destruction. The results indicate that the coupled system shows a better performance compared with its original individual processes in consideration of the thermodynamic efficiency and effects on the environment, though the additional mechanical energy consumption occurs in the new system. Moreover, being used as the gasification agent in the FR, phenol wastewater has been greatly reduced, which reduces levels of environmental pollution. Hence, this new system will be of great potential in industrial application due to its high energy utilization efficiency and low pollution.