A cost-effective approach to realization of the efficient methane chemical-looping combustion by using coal fly ash as a support for oxygen carrier

Abstract

Developing highly reactive, durable and low-cost oxygen carrier (OC) is the key to the advancement of the chemical looping combustion (CLC) technology that is regarded as the most energy-efficient way for the capture of CO2 emitted from fossil fuel combustion. In this study, the byproduct from coal power plant, coal fly ash (FA) was utilized as the support for Cu-based OC in methane CLC. Its performance was investigated with a thermogravimetric analyzer and a lab-scale fixed bed reactor. The results showed the FA is better as a support of OC than the most commonly used Al2O3 in anti-carbon deposition and thus beneficial to the importance of the stability of FA supported OCs. Among all the tested OCs, the Cu-based OC synthesized with FA support and impregnation method demonstrated the best performance, with CH4 conversion of 94–100% and CO2 selectivity of 91–94% in ten cycles at 800–850 °C, and minor deactivation. The characterization of the fresh and spent OCs revealed that the FA support itself could provide 1.0–2.9 wt% active oxygen for fuel combustion, which is enabled by the iron oxide in FA. In addition, the distribution of Cu on the FA support became more uniform on spent OC than on the fresh one. Also, the partially irreversible CuO decomposition into Cu2O during cyclic tests was the main reason for the deactivation of OC. Thus, Use of FA as an OC support is conducive to both development of cost-effective CLC and an environmental-friendly utilization of waste FA.