The Effectiveness of Calcium (Magnesium) Acetate and Calcium Benzoate as NOxReduction Agents in Coal Combustion

Abstract

Abstract A laboratory study was conducted to assess the effectiveness of the chemicals calcium magnesium acetate (CMA), calcium acetate (CA), and calcium benzoate (CB) in reducing NOx emission from coal-fired furnaces. CMA, which is currently being used as a non-corrosive road deicing salt, has demonstrated exceptional effectiveness in our laboratory as an in-boiler S02 removal agent (Levendis et al., 1993). This is due to the affinity of the calcium and magnesium components of CM A for sulfur; the reaction results in solid sulfate salts. The current investigation explored the role of the organic component of CMA, as well as that in CA and CB, in removing NOx emissions that are typically found in post-flame regions of furnaces burning pulverized coal or residual oil. Bench-scale experiments were conducted at gas temperatures ranging from 450 to 1450°C and oxygen concentrations between 0 to 5%. The residence time was in the order of 4 s, Injection of the CMA reagent at a mass ratio of CMA/NO of 41 (or an equivalent acetate/NO molar ratio of 18) reduced NO, by more than 90% (at 0% O2 and temperatures above 850°C) to 50% (at 5% O2 and 650 to 850°C). At an oxygen concentration of 2%, NOx reduction seemed to be most effective between 1000 and 1350°C with NOx reductions of 70 to 80%. The efficacy of calcium acetate (CA) and calcium benzoate (CB) as NO, reducers was also explored, with CA (CA/NO mass ratio of 41 and acetate/NO molar ratio of 15) being less efficient than CMA at a similar φ with oxygen present but as efficient in 0% oxygen. CB (CB/NO mass ratio of 41 with benzoic acid/NO molar ratio of 9) was as efficient as CMA, regardless of O2 concentration, but at temperatures higher by 200°C