Open AccessRemoval of H{sub 2}S and SO{sub 2} by CaCO{sub 3}-based sorbents at high pressures. Semiannual report, August 1995--January 1996
Author(s) -
Stratis V. Sotirchos
Publication year - 1996
Language(s) - English
Resource type - Reports
DOI - 10.2172/415351
Subject(s) - flue gas desulfurization , dolomite , calcination , sulfur dioxide , combustion , zeolite , mineralogy , porosity , flue gas , chemical engineering , coal , fluidized bed , coal combustion products , materials science , chemistry , inorganic chemistry , composite material , organic chemistry , catalysis , engineering
In a fluidized-bed combustor, a bed of combustible (coal) and noncombustible material is fluidized using air blown upward. Using dolomite or limestone as the noncombustible material, it is possible to have fuel combustion and flue gas desulfurization taking place simultaneously in the combustion vessel. If operation occurs under atmospheric pressure, the average partial pressure of carbon dioxide in the combustor (typically, 10-15% of the total pressure) is considerably lower than the equilibrium CO, pressure for decomposition of limestone (CaCO{sub 3})or dolomite (CaCO{sub 3}{circ}MgCO{sub 3}) at the temperatures usually encountered in FBC units (800-950 {degrees}C). In the high temperature environment of the AFBC unit, the limestone or dolomite particles undergo calcination, yielding a highly porous product (CaO or MgO), which reacts with the sulfur dioxide produced during coal combustion forming, mainly, calcium or magnesium sulfate. The sulfates occupy more space than the oxides they replace, and as a result, the pores of the calcine are completely plugged with solid product before complete conversion takes place. (The conversion for complete with pore plugging is about 50% for the calcine of a stone consisting of CaCO{sub 3} only.) Pores of different size are plugged at different conversion levels, and it is thus possible to have formation of inaccessible pore space in the interior of the particles when the small feeder pores of clusters of large pore are filled with solid product. Moreover, under conditions of strong internal diffusional limitations, complete pore closure may first take place at the external surface of the particles while there is still open pore space left in the interior. For these reasons, ultimate conversions much lower than those predicted by the stoichiometry of the reaction for complete plugging of the internal pore space (less than 30-40%) are seen in AFBC units