Highly Cyclic Stability and Absorbent Activity of Carbide Slag Doped with MgO and ZnO for Thermochemical Energy Storage.

ABSTRACT

Carbide slag is a solid waste with a high content of reactive CaO, which can be used as an active material for the chemical absorption of CO2 and calcium looping. Calcium looping of CaO-based absorbents is one of the most promising methods of thermochemical energy storage. However, the sintering of pores and a reduction in the CO2 diffusion rates as the carbonization/calcination cyclic reaction progresses have posed challenges to the practical application of CaO-based absorbents. This study proposes a method for alleviating the sintering of the pore structure by improving the activity and cycling stability of such absorbents by doping carbide slag with MgO and ZnO powders. Results showed that the raw material ratio, reaction temperature, and reaction time have a considerable influence on the CO2 absorption rate. Furthermore, the specific surface area and pore volume of the absorbents increased with increasing ZnO and MgO doping levels in the carbide slag. Thus, the problems of sintering and clogging of pores in CaO-based absorbents were effectively alleviated, and the MgO and ZnO-doped absorbents CMZ85 and CMZ90 maintained 41-42% CO2 absorption after 10 cycles. These results confirmed that the cyclic stability and absorbent activity improved significantly with the MgO and ZnO doping of carbide slag for the calcium looping process.