Abstract: A process for desulfurizing an exhaust gas which comprises desulfurizing an exhaust gas containing SO.sub.2 by bringing it into contact with a slurry containing calcium compounds and aluminum compounds, characterized in that the concentration of the dissolved aluminum ion in said slurry is detected and a manganese compound is supplied into said slurry in such a manner that the ratio of the concentration of manganese (including both solid and liquid) to said concentration of the dissolved aluminum ion may be maintained in a molar ratio of less than 1 in said slurry.

Abstract: A wet process for stack gas treatment wherein the stack gas is scrubbed with a suspension containing calcium hydroxide and/or calcium carbonate to remove sulfur oxides from the gas, characterized in that(1) air or oxygen-containing gas is supplied to the gas scrubber so as to oxidize at least 18% of the sulfur oxides absorbed by the scrub liquid to gypsum, and then part of the gypsum from the gypsum-containing scrub liquid partly taken out is recycled to the scrubber, or(2) part or whole of the scrub liquid is taken out from the scrubber into an oxidizer, where it is oxidized with the supply of air or oxygen-containing gas, and, after the oxidation, part of the scrub liquid from the oxidizer is recycled to the scrubber, whereby at least 18% of the sulfur oxides absorbed from the gas by the scrub liquid is oxidized to gypsum.

Abstract: A process for treating an exhaust gas discharged from a coal combustion apparatus, in which the exhaust gas is first led to a dry type dust collecting device, and after fly ash in said exhaust gas is removed, said exhaust gas is treated by a wet type exhaust gas cleaning device; a part of said fly ash collected in said dry type dust collecting device is added to a discharge liquid or a discharge sludge discharged from said wet type exhaust gas cleaning device. The amount of the fly ash to be added to the discharge sludge should be at least three times (in weight) as much as the amount of water contained in said discharge sludge. Preferably fly ash of approximately the same weight as that of said discharge sludge should be added to the discharge sludge discharged from said wet type exhaust gas cleaning device, and subsequently calcium hydroxide of about one-tenth in weight of said discharge sludge should be added to the mixture for solidifying said discharge sludge.

Abstract: A process for exhaust gas desulfurization by the wet lime-gypsum process comprises an absorption step for scrubbing the exhaust gases with a calcium hydroxide slurry as an absorbent; an oxidizing step for oxidizing a slurry composed chiefly of calcium sulfite from the absorption step; and a solids-liquid separation step for separating a slurry composed mainly of gypsum from the oxidizing step, characterized in that the liquid from said solids-liquid separation step is passed into a sulfate impurity reaction step where said liquid reacts with added calcium hydroxide and is thereby freed from water-soluble sulfate impurities; and the so purified liquid is supplied to the absorbent preparation step where it is mixed with calcium hydroxide to form said absorbent. Also, precipitates formed in said sulfate impurity reaction step are supplied to said absorbent preparation step.

Abstract: A process for treating a waste gas containing SO.sub.2 and HCl which comprises determining the amount of HCl in said waste gas and supplying at least one magnesium salt selected from the group consisting of MgSO.sub.4, MgSO.sub.3, MgO, MgCO.sub.3 and Mg(HSO.sub.3).sub.2 in an amount corresponding to the amount of HCl additionally supplying CaCO.sub.3 or Ca(OH).sub.2 as an absorbent for SO.sub.2 to a column for treating said waste gas.

Abstract: A method of desulfurizing exhaust gases by a wet lime-gypsum process comprises the steps of neutralizing a suitable amount of liquid containing impurities separating the neutralized material into solid and liquid phases, heating the separated solid phase to dryness while concentrating the separated liquid phase, mixing the concentrated liquid and dried solid phase in such a manner that the resulting mixture exists as a solid mass containing the impurities, thus making it unnecessary to dispose of any waste liquid.

Abstract: A spray type wet scrubber includes a plurality of spray nozzles installed in parallel banks across the path of gas stream within the scrubber body, and partition walls held upright in grating fashion to divide the path of gas stream into a plurality of passages, each of which accommodates one of the spray nozzles.