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ACTIVATION AND REACTIVITY OF NOVEL CALCIUM-BASED SORBENTS FOR DRY SO2 CONTROL IN BOILERS
Jozewicz, W. AND D A. Kirchgessner*. ACTIVATION AND REACTIVITY OF NOVEL CALCIUM-BASED SORBENTS FOR DRY SO2 CONTROL IN BOILERS. POWDER TECHNOLOGY 58(3):221-229, (1989).
Chemically modified calcium hydroxide (Ca(OH)2) sorbents developed in the U.S. Environmental Protection Agency's Air and Energy Engineering Research Laboratory (AEERL) for sulfur dioxide (SO2) control in utility boilers were tested in an electrically heated, bench-scale isothermal flow reactor. Novel surfactant-modified Ca(OH)2 (SM-Ca(OH)2) sorbents were compared with conventional Ca(OH)2 produced by dry hydration (DH-Ca(OH)2) to determine why modified sorbents have a higher reactivity with SO2. Sorbents were activated in the flow reactor. Activated sorbents (SM-CaO and DH-CaO) were size classified with an inertial cascade impactor downstream of the flow reactor. The structure of each separated fraction (six trays plus preimpactor, D50 from 0.74 to> 11.9 μm) was characterized by nitrogen adsorption. For each size fraction measured, the surface area was higher for SM-CaO than for DH-CaO. It was concluded, therefore, that retardation of the sintering process was the primary advantage of the modified sorbent. The effect of thermal sintering was to increase median pore size by eliminating fine pores (below 100 Å). Changes in the pore structure of Ca(OH)2 sorbents reacting with SO2 were also investigated. Small amounts Of SO2 (below 100 ppm) in the combustion gas present during calcination at 900 °C modified the structure of sorbents. These sorbents typically had higher surface areas and porosities than sorbents calcined in the absence of SO2, suggesting that small amounts of calcium sulfate product are capable of slowing the solid state diffusion process of sintering.
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