CURRENT STATUS OF THE ADVOCATE PROCESS FOR FLUE-GAS DESULFURIZATION

The following report discusses current bench- and pilot-plant advances in preparation of ADVAnced siliCATE (ADVACATE) calcium silicate sorbents for flue gas desulfurization. It also discusses current bench- and pilot-plant advances in sorbent preparation. Fly ash was ground in a laboratory scale grinder prior to slurrying in order to decrease the slurrying time needed for the sorbent to be reactive with SO2. Reactivity of ADVACATE sorbents with SO2 in the bench-scale reactor correlated with their surface area. ADVACATE sorbents produced with ground fly ash were evaluated in the 50 cfm (85 m3/h) pilot plant providing 2 s duct residence time. ADVACATE sorbent was produced by slurrying ground fly ash (median particle size of 4.3-mu-m) with Ca(OH)2 at the weight ratio of 3.1 at 90-degrees-C (194-degrees-F) for 3 h to yield solids with 30 weight percent of initial free moisture. When this sorbent was injected into the duct with 1500 ppm SO2 and at 11-degrees-C (20-degrees-F) approach to saturation, the measured SO2 removal was approximately 60 percent at a Ca/S stoichiometric ratio of 2. Previously, when ADVACATE sorbent was produced at 90-degrees-C (194-degrees-F) and at the same fly-ash-to-Ca(OH)2 weight ratio using unground fly ash, removal under the same conditions in the duct was approximately 50 percent following 12 h slurrying. The report presents the results of pilot-scale recycle tests at the recycle ratio of 2. Finally, the report discusses future U.S. Environmental Protection Agency plans for commercialization of ADVACATE.