Bench–scale evaluation of calcium sorbents for acid gas emission control

Abstract

AbstractCalcium sorbents for acid gas emission control were evaluated for effectiveness in removing SO2/HCl and SO2/NO from simulated incinerator and boiler flue gases. All tests were conducted in a bench‐scale reactor (fixed‐bed) simulating fabric filter conditions in an acid gas removal process. Reagent grade Ca(OH)2 was used to establish baseline sorbent performance. The reactivity of reagent grade Ca(OH)2 with HCl from SO2/HCl mixtures gradually increased with decreasing approach to saturation temperature. SO2 reactivity toward Ca(OH)2 was very sensitive to approach to saturation. Novel calcium silicate sorbents were tested for reactivity with both SO2 and HCl. A “thermal window” for optimum NO removal was found at 90°C (194°F) when Ca(OH)2 was used at SO2/NO ratios of 1:1. Reactivity of Ca(OH)2 toward SO2 from SO2/NO mixtures was very sensitive to approach to saturation, while reactivity with NO was insensitive. Several additives were subsequently tested to determine optimum sorbent combinations for SO2/NO control. To date the most promising additives are Mg(OH)2 and Na2HPO4 at 10 mol percent concentrations. As with SO2/HCl, calcium silicate has been shown to be superior for SO2/NO capture. Some implications for larger‐scale process configurations and sorbent selection for HCl/SO2/NO control are discussed. Future activities and limited larger–scale pilot plant results are also discussed.