Preparation of active absorbent for dry-type flue gas desulfurization from calcium oxide, coal fly ash, and gypsum

As compared to a commercial absorbent prepared from Ca(OH)(2), gypsum (CaSO4) and coal fly ash, an absorbent prepared by use of CaO in place of Ca(OH)(2), exhibited a higher activity for dry-type flue gas desulfurization. The order of the addition of the raw materials in the slaking procedure has much effect on the activity of the resulting absorbent. The activity of the absorbent increased further upon hydrothermal treatment following the kneading procedure. The period of hydrothermal treatment was reduced to 3 h to attain the activity which exceeds 20% of the activity of the commercial absorbent which requires an optimum hydrothermal treatment period of 10 h. The activity enhancement by use of CaO is considered to result from exothermic heat of slaking CaO. At a high temperature, the reaction of CaO with a SiO2 component included in the coal fly ash facilitates the formation of calcium silicate. The formation of calcium silicate was suppressed by the existence of CaSO4 in the slaking procedure.