Energy quality factor and exergy destruction processes analysis for chemical looping hydrogen generation by coal

Chemical looping hydrogen generation (CLHG) is a hydrogen production process with broad prospects for its advantages of not requiring H-2 purification process and direct CO2 capture. Presently, the research on the integrated system of CLHG focuses on the impact of integrated processes and operating variables on the overall energy efficiency and exergy efficiency of the system. However, the research on the matching relationship between quantity and quality in the process of energy conversion is insufficient, and the flow direction of exergy and the specific exergy destruction process for equipment are not clear. The integrated system of coal gasification (CG) and three reactors CLHG was established in this paper with a hydrogen production efficiency of 42.55% and system exergy efficiency of 52.98%. This paper studied the exergy flow direction and efficiency of the equipment in the system, providing the improved direction for the amelioration of the system; a detailed description was present on the change process of energy quality in each equipment with energy quality factor, and the concept of energy quality factor ratio was proposed as an evaluation tool for matching the quantity and quality of energy in the system. It is calculated that the ratio of energy quality factor of the integrated system of CG and CLHG is 0.944. By comparing with the energy quality ratio of the traditional CG hydrogen production system (0.896), it can be concluded that the integrated system of CG and CLHG has a better energy matching relationship.

Automated summary

CLHG is a hydrogen production process with great prospects, focusing on overall energy efficiency and exergy efficiency; this study proposes a new evaluation tool and provides guidance for system improvement by studying the relationship between quantity and quality during energy conversion, also establishing a better energy matching relationship in the integrated system of CG and CLHG.