Novel Binders-Promoted Extrusion-Spheronized CaO-Based Pellets for High-Temperature CO2 Capture

Abstract

Calcium looping (CaL) is a well-acknowledged approach in CO2 removal via the circulation of CaO-based sorbents between a carbonator and a calciner. During circulation, there is usually a quick decrease in CO2 sorption capacity and sorbent pellets experience severe attrition in fluidized-bed reactors, which are the two major challenges in CaL application. To develop sorbent pellets with high and stable sorption capacity and sufficient mechanical strength simultaneously, in this work, three kinds of novel phosphates were screened and utilized as binders in producing sorbent pellets via extrusion and spheronization, and their mechanical and chemical properties were tested and analyzed systematically. It was found that Mg3(PO4)2·4H2O was a good binder candidate in preparing CaO-based sorbent pellets with promoted mechanical and chemical performance. Under the optimum conditions of 10 wt % loading and 900 °C precalcination temperature, pellets of Ca8Mg1 (80 wt % Ca(OH)2 + 10 wt % Mg3(PO4)2·4H2O) demonstrated a compressive stress of 12.14 MPa and a CO2 uptake of 0.23 g-CO2/g-sorbent after 25 cycles, which were almost three times larger and 64% improved, respectively, compared to the typical Ca10 (pure Ca(OH)2). Additionally, the main reasons for performance enhancement were confirmed to be the production of Ca5(PO4)3(OH) with good hardness and the “spacer” effect of MgxCa1–xCO3.