Process optimization and thermodynamic analysis of autothermal coal chemical looping gasification industrial demonstration system

Abstract

Chemical looping gasification (CLG) is an innovative clean coal conversion technology with industrial application prospects. The technical reliability of coal CLG (CCLG) in an autothermal state remains to be investigated. To clarify the process characteristics of an autothermal CCLG process, a CCLG autothermal operation system was established based on a CLG industrial demonstration unit. Process modeling of the CCLG reactor system and economizer, air preheater, and other heat exchange units was performed, to ensure autothermal operation of the global CCLG process. The optimal operating parameters of the system were established, the optimal heat exchange network was designed, and the source and distribution of thermodynamic irreversibility were clarified. The results showed that the optimal coal feed flow rate, air feed temperature and flue gas circulation temperature were 437.07 kg/h, 550 °C and 450 °C, respectively. The fuel reactor (FR) flue gas circulation was not conducive to system autothermal, resulting in weakened gasification performance. The optimal heat exchange plan allowed the system to operate without an external heat source. The thermodynamic irreversibility mainly originated from the redox process. The system heat efficiency was 81.63 %, the product exergy efficiency was 78.06 %, the total exergy efficiency was 41.10 %, and the total exergy destruction rate was 55.40 %. Additionally, the FR flue gas circulation caused high exergy loss, resulting in reduced system thermodynamic efficiency.