The effect of SO 2 on CO 2 capture by CaO-based pellets prepared with a kaolin derived Al(OH) 3 binder

Abstract

High-temperature CO 2 capture by Ca looping cycles was investigated in the presence of SO 2. The sorbents tested included natural limestone (HV-P), pellets formed from powdered limestone with a binder (HV-AH) and pellets formed from powdered acetified limestone with a binder (HV10-AH). The binder used in pellet preparation was Al(OH) 3 obtained from acid leaching of kaolin. Simulated flue gas with a composition of 15% CO 2, 3% O 2, 0.45% SO 2, and N 2 balance was used during the CO 2 capture step. Two calcination conditions were employed for sorbent regeneration: pure CO 2 at 920 °C and pure N 2 at 850 °C. By five reaction cycles, the well-developed porous texture of HV10-AH acetified by 10 vol.% acetic acid did not offer better CO 2 capture than that for natural limestone at 650 °C for calcination in CO 2; instead it promoted a higher SO 2 retention than that for the limestone. Unfortunately, the CO 2 capture capacity for all sorbents calcined in CO 2 in the presence of SO 2 was effectively eliminated after 2–3 cycles. Calcination in N 2 did not significantly enhance CO 2 sorbent capture capacity; but instead it improved the SO 2 retention ability of HV10-AH, for which the sulphation level was over twice that of the natural limestone. Increasing the carbonation temperature to 700 °C enhanced sulphation rather than carbonation with HV10-AH, but produced the opposite effect with natural limestone. In general, it appears that SO 2 impedes CO 2 capture, leading to a negligible CO 2 capture capacity after only few cycles regardless of how the sorbent morphology is modified, which suggests any method designed to improve sorbent performance for CO 2 capture will not be proof against significant SO 2 concentrations in flue gas. These results suggest that despite the fact that sorbent performance can be influenced to some extent by altering carbonation and calcination conditions; the presence of SO 2 must be avoided if the objective is CO 2 capture from flue gas.