Characterization of a process for the in-furnace reduction of NOx, SO2, and HCl by carboxylic salts of calcium

Calcium magnesium acetate has been assessed as an agent for the reduction of NOx, SO2, and HCl, at the pilot scale, in a down-fired combustor operating at 80 kWth. In addition to this, the chemical and physical processes that occur during heating have been investigated. Benchmarking of calcium magnesium acetate with a suite of five other carboxylic salts (calcium magnesium acetate, calcium propionate, calcium acetate, calcium benzoate, magnesium acetate, and calcium formate) has been performed. NOx reduction involves the volatile organic content of the carboxylic salt being released at temperatures of >1000 °C, where the reaction of CHi radicals with NO under fuel-rich conditions can result in some of the NO forming N2 in a “reburning” process. Thermogravimetry-Fourier transform infrared (TG-FTIR) studies identified the nature of the decomposition products from the low- and high-temperature decompositions. In addition, the rate of weight losses were studied to investigate the influence of the organic decomposition on NOx reduction by reburning. In-furnace reductions of SO2 and HCl are aided by the highly porous, particulate residue, which results from the in situ drying, pyrolysis, and calcination processes. Simultaneous reduction of all three pollutants was obtained, and a synergy between SO2 and HCl capture was identified. A mechanism for this inter-relationship has been proposed. Sorbent particle characterization has been performed by collecting the calcined powder from a spray pyrolysis reactor and compared with those produced from a suite of pure carboxylic salts. Physical properties (including porosity, surface area, and decomposition behavior) have been discussed, relative to reductions in NOx and acid gas emissions.