Effectiveness of calcium magnesium acetate as an SOX sorbent in coal combustion

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Abstract
A fundamental study was conducted on the effectiveness of the chemical calcium magnesium acetate (CMA) as a sulfur capture agent during combustion of pulverized coal. It was based on high‐temperature laboratory‐bench experiments with the scope of exploring the use of CMA as a “dry scrubbing” medium for in‐boiler injection. Two methods of CMA introduction in the furnace were considered: dry‐spraying fine powders of the chemical and wet‐spraying aqueous solutions to generate fine aerosols. It considered conditions pertinent to post‐flame in‐boiler injection of CMA to identify optimum temperatures and residence times. In addition to the versatility of the water‐soluble CMA to enable spray drying injection and therefore eliminate grinding costs, there are other attractive features. Mainly, its ability to form highly cenospheric, “popcorn” ‐like, oxide particles on heating to high temperatures. These cenospheres possess thin, porous walls with blowholes that enable penetration of the SO2 in the interior of the particle which promotes high sorbent utilization. SO2 captures in the order of 90% were achieved with dry‐injection of the chemical at furnace gas temperatures of about 1,000° C, a Ca/S ratio of 2, and particle size of ≈ 50 μm. Moreover, CMA was superior(by over 40%) to either CaCO3 or Ca(OH)2 in sulfur capture effectiveness per unit mass of calcium. This commercially obtained CMA was even superior to reagent‐grade calcium acetate (by as much as 30%), again per unit mass of calcium. The utilization of CMA and calcium acetate depended on the cenosphere wall thickness, rather than the particle size and, thus, outperformed other sorbents regardless of the size of the resulting oxide particles.

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