In bed and downstream hot gas desulphurization during solid fuel gasification: A review

Reaction of arsenic vapor species with fly ash compounds: kinetics and speciation of the reaction with calcium silicates

Thermogravimetric analysis of the reaction between carbon and CaSO4·2H2O, gypsum and phosphogypsum in an inert atmosphere

Investigation of the SO2 adsorption properties of Ca(OH)2-fly ash systems

Coal fly ashes have been slurried with quicklime at elevated temperatures to determine their reactivity with SO[sub 2] in a minipilot spray dryer. Bench-scale experimental results indicate that this hydration process greatly increases the total surface area of the solids. Minipilot-scale spray dryer tests reveal that the slurry reaction step can significantly increase calcium utilization and SO[sub 2] removal of these fly ash/quicklime sorbents, depending on the type of fly ash used. One type of fly ash showed considerably better reactivity in the spray dryer tests. This enhancement is considered due to the presence of calcium silica hydrate material formed from the reaction between calcium and the alumina silicate found in the fly ashes and the difference in reactivity due to the type of calcium silica hydrate material formed. The benefit, however, decreases with the calcium feed rate. Pozzolanic strength tests were performed on the fly ashes used, and the measured unconfined compressive strengths followed the reactivity results in the spray dryer; the most reactive fly ash possessed the highest pozzolanic activity.

Heated Fly Ash/Hydrated Lime Slurries for SO2 Removal in Spray Dryer Absorbers

A thermodynamic and kinetic study on the use of calcium silicates and silica-supported lime as regenerative sorbents for desulfurization of hot combustion gases showed that, except for ..gamma..-Ca/sub 2/SiO/sub 4/ and Ca/sub 3/SiO/sub 5/, all the calcium silicates and the silica-supported calcium oxide were as reactive as, or more reactive than, calcium oxide. The regeneration rates of these sorbents were substantially higher than that of calcium oxide, the rate of thermal decomposition of the sulfated mono- and dicalcium silicates being about 15 times higher than that of calcium sulfate. Sulfation rates of CaSiO/sub 3/ and Ca/sub 2/SiO/sub 4/ were first order with respect to sulfur dioxide only for partial pressure of sulfur dioxide Vertical Bar3; 3000 ppm. The silica-supported calcium oxide after heat treatment at 1075/sup 0/C had ..beta..-CaSiO/sub 3/ on its surface.

Calcium silicates: A new class of highly regenerative sorbents for hot gas desulfurization

Results of studies of the mechanism and kinetics of the reaction, CaS + 3CaSO/sub 4/ ..-->.. 4CaO + 4SO/sub 2/, of importance to the development of advanced regenerative processes for fluidized-bed combustion of coal are presented. Rates were measured of the thermal decomposition of CaSO/sub 4/ with and without physically separating the CaS. Gas evolved from heating at 900/sup 0/ and 1100/sup 0/C was measured thermogravimetrically. The data indicate that gaseous intermediates exist in the reaction. Analysis of the solid reaction products showed that the gaseous intermediates likely arise form the CaSO/sub 4/ decomposition. A complete kinetic analysis of six thermodynamically feasible side reactions indicate that the decomposition of CaSO/sub 4/ to CaO and SO/sub 3/ is the rate limiting step in the reaction, and that SO/sub 3/, rather than SO/sub 2/, is the gaseous intermediate. (BLM)

Ming‐Shing ‐S Shen

Papers

Calcium silicates: A new class of highly regenerative sorbents for hot gas desulfurization

Direct evidence for the existence of gaseous intermediates in the calcium sulfide‐calcium sulfate reaction