Low-energy-consumption CO2 recovery by combining H2 sweeping and methanation with the conventional VTSA approach

Abstract

To achieve carbon capture and utilization, low-energy-consumption CO2 recovery and conversion technologies are required. However, the majority of previous studies on CO2 capture and conversion have been conducted independently. Therefore, we developed a local carbon recycling system that links these two technologies. In this system, CO2 is recovered from combustion exhaust gases by physical adsorption, the recovered CO2 is converted to CH4 by methanation, and the produced CH4 is used as a fuel. During conversion of the recovered CO2 into CH4, the recovered gas can contain a mixture of CO2 and H2; thus, H2 can be supplied during the desorption process to lower the CO2 partial pressure in the CO2 adsorber (hereafter referred to as H2 sweep). In addition, methanation is an exothermic reaction that can supply heat to the CO2 adsorber. In this study, focusing on the energy consumption of the CO2 adsorber, the effect of combining these two approaches with the conventional vacuum temperature swing adsorption process was investigated. Since this system requires the effective use of the methanation reaction heat, a shell-and-tube CO2 adsorber containing zeolite 13X was constructed. By combining these two approaches for an exhaust gas with a CO2 concentration of 9.6%, a CO2 recovery ratio of 90% was achieved with an energy consumption of 0.9 GJ/t-CO2. Moreover, a superior CO2 recovery ratio of 99% was achieved with an energy consumption of 1.4 GJ/t-CO2, thereby constituting a higher CO2 recovery ratio with a lower energy consumption compared with conventional CO2 adsorption systems.