Preparation of fly ash-Ca(OH)₂ sorbents by pressure hydration for so₂ removal

Reactive sorbents for SO₂ removal from humidified flue gas were prepared from fly ash-Ca(OH)₂ mixtures using the pressure hydration technique. The fly ash samples were taken from three different coal-fired power plants in Turkey. The fly ash/Ca(OH)₂ weight ratio, hydration time, and temperature were varied during the sorbent preparation step. Effects of these variations on the physical properties of activated sorbents were investigated. A statistical design technique was applied by use of a two-level factorial design matrix to interpret experimental results. It was found that increasing the temperature and fly ash/Ca(OH)₂ weight ratio caused a decrease in the total surface area of sorbents. However, surface area values of sorbents were not generally affected by the hydration time variation. Finally, fly ash-Ca(OH)₂ sorbents prepared at the optimum hydration conditions were sulphated at 338 K with a synthetic gaseous mixture containing 5000 ppm SO₂ and 55% relative humidity.