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

Abstract

Abstract Calcium sorbents for acid gas emission control were evaluated for effectiveness in removing SO 2 /HCl and SO 2 /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 SO 2 /HCl mixtures gradually increased with decreasing approach to saturation temperature. SO 2 reactivity toward Ca(OH) 2 was very sensitive to approach to saturation. Novel calcium silicate sorbents were tested for reactivity with both SO 2 and HCl. A “thermal window” for optimum NO removal was found at 90°C (194°F) when Ca(OH) 2 was used at SO 2 /NO ratios of 1:1. Reactivity of Ca(OH) 2 toward SO 2 from SO 2 /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 SO 2 /NO control. To date the most promising additives are Mg(OH) 2 and Na 2 HPO 4 at 10 mol percent concentrations. As with SO 2 /HCl, calcium silicate has been shown to be superior for SO 2 /NO capture. Some implications for larger‐scale process configurations and sorbent selection for HCl/SO 2 /NO control are discussed. Future activities and limited larger–scale pilot plant results are also discussed.