Simultaneous CO2 capture and thermochemical heat storage by modified carbide slag in coupled calcium looping and CaO/Ca(OH)2 cycles

Abstract

• A process coupled calcium looping and CaO/Ca(OH) 2 heat storage is proposed. • Modified carbide slag with by-product of biodiesel is employed in coupled process. • Treatment of by-product of biodiesel improves heat storage capacity of carbide slag. • Heat storage capacity of modified carbide slag rises by introducing calcium looping. • CO 2 uptake of modified carbide slag is activated by introducing heat storage cycles. The simultaneous CO 2 capture and heat storage performances of the modified carbide slag with by-product of biodiesel were investigated in the process coupled calcium looping and CaO/Ca(OH) 2 thermochemical heat storage using air as the heat transfer fluid. The modified carbide slag with by-product of biodiesel exhibits superior CO 2 capture and heat storage capacities in the coupled calcium looping and heat storage cycles. The hydration conversion and heat storage density of the modified carbide slag after 30 heat storage cycles are 0.65 mol·mol −1 and 1.14 GJ·t −1 , respectively, which are 1.6 times as high as those of calcined carbide slag. The negative effect of CO 2 in air as the heat storage fluid on the heat storage capacity of the modified carbide slag is overcome by introducing CO 2 capture cycles. In addition, the CO 2 capture reactivity of the modified carbide slag after the multiple calcium looping cycles is enhanced by the introduction of heat storage cycles. By introducing 10 heat storage cycles after the 10th and 15th CO 2 capture cycles, the CO 2 capture capacities of the modified carbide slag are subsequently improved by 32% and 43%, respectively. The porous and loose structure of modified carbide slag reduces the diffusion resistances of CO 2 and steam in the material in the coupled process. The formed CaCO 3 in the modified carbide slag as a result of air as the heat transfer fluid in heat storage cycles decomposes to regenerate CaO in calcium looping cycles, which improves heat storage capacity. Therefore, the modified carbide slag with by-product of biodiesel seems promising in the coupled calcium looping and CaO/Ca(OH) 2 heat storage cycles.