Trace Na_2CO_3 Addition to Limestone Inducing High-Capacity SO_2 Capture

摘要

Although the literature has reported enhanced indirect sulfation of limestone by adding Na_2CO_3, the amount of Na_2CO_3 additive required to achieve high CaO conversion is typically high (~4.0 mol 96), which commonly results in adverse effects in fluidized-bed combustion boiler systems and increased cost of sorbents. In this work, we demonstrate for the first time that trace Na_2CO_3 (0.1 mol %) can significantly enhance the sulfate conversion of limestone. This enhanced sulfation is attributed to the increased surface area and optimized pore size distribution. The trace Na_2CO_3 additive splits the pores of the original sorbents peaking at ~70 nm into pores peaking at ~4 nm and ~140 nm due to the slight promotion of sintering. This well-developed pore structure results in a relatively high reactivity for sulfation. Thus, the Na_2CO_3 additive influences the sorbent reactivity in two ways: (1) at less than 0.5 mol %, tuning its pore structure; (2) at more than 0.5 mol %, promoting the product layer diffusion. We also find that trace amount of other metal salts, such as CaCl_2 and NaCl, clearly enhance the sulfation of limestone. The strategy of enhancing limestone sulfation by the addition of trace amount of metal salts offers evident engineering and economic advantage.