Effect of re-carbonation on CO2 capture by carbide slag and energy consumption in the calciner

The re-carbonation was proposed to improve the CO2 capture performance of the carbide slag, an industrial solid waste, calcined under high concentration of steam during the calcium looping process. The effects of re-carbonation conditions, including duration and CO2 concentration on CO2 capture by the cycled carbide slag were studied. The results show that the re-carbonation significantly improves the CO2 capture capacity of the carbide slag. Notably, the re-carbonation dramatically reactivates the carbide slag which has experienced 11 cycles, increasing its carbonation conversion from 0.19 to about 0.6. In addition, the carbide slag shows higher re-carbonation conversions than the limestones reported by other researchers. A porous structure of the carbide slag is formed after the calcination from the extra CaCO3 generated in the re-carbonation step, which improves its CO2 capture capacity. In addition, the impacts of the re-carbonation on the CO2 capture ratio of the calcium looping system and the energy consumption in the calciner were discussed. The re-carbonation improves the CO2 capture ratio from 0.46 to 0.88 and reduces the energy consumption in the calciner from 321 kjimol CO2 to 261 kJ/mol CO2, when the molar ratio of sorbent to CO2 is 2 and the make-up ratio of the sorbent is 0.16 in the calcium looping system using the carbide slag. Thus, the re-carbonation and high concentration of steam in the calcination is an effective way to improve the CO2 capture capacity of the carbide slag and reduce the energy consumption in the calciner during the calcium looping process. (c) 2017 Elsevier Ltd. All rights reserved.