Exergy analysis of methane cracking thermally coupled with chemical looping combustion for hydrogen production

Abstract

This paper proposes a novel hydrogen production process by Methane Cracking thermally coupled with Chemical Looping Combustion (MC–CLC) which provides an advantage of inherent capture of CO2. The energy utilisation performance of the MC–CLC process is compared with that of conventional Methane Cracking with combusting CH4 (MC-CH4) and Methane Cracking with combusting H2 (MC-H2) using exergy analysis, with focus on exergy flows, destruction and efficiency. The three MC processes are simulated using Aspen Plus software with detailed heat integration. In these processes, the majority of the exergy destruction occurs in the combustors or CLC mostly due to the high irreversibility of combustion. The CO2 capture unit has the lowest exergy efficiency in the MC-CH4 process, leading to a lower overall exergy efficiency of the process. The combustor in the MC-H2 process has a much higher energy efficiency than that in the MC-CH4 process or the CLC in the MC–CLC process. Although the use of H2 as fuel decreases the H2 production rate, the MC-H2 process provides the advantage of an absence of CO2 generation, and stores more chemical exergy in the solid carbon which can be utilised appropriately. The MC–CLC process obtains the highest exergy efficiency among the three models and this is primarily due to the absence of a CO2 capture penalty and the CLC’s higher fuel utilization efficiency than the conventional combustion process.