A system and process is described for treating the effluent chemicals from an air pollution control system for fossil fuel fired equipment. The air pollution control system involves the addition of magnesium-containing additives such as dolomite to the equipment followed by the wet scrubbing of the flue gases resulting in the reaction of the sulfur oxides with the additive. The treatment involves the addition of ammonium hydroxide to the solution removed from the scrubber to convert the soluble magnesium sulfate to soluble ammonium sulfate and precipitate magnesium hydroxide. The ammonium sulfate solution is removed from the magnesium hydroxide and either used for fertilizer or further reacted with calcium oxide to precipitate calcium sulfate and form ammonium hydroxide which is recycled for reaction with the scrubber effluent.
In the method for the humid treatment of effluents containing a compound selected from the group consisting of H.sub.2 SO.sub.4, free SO.sub.2, SO.sub.3.sup.-, or SO.sub.4.sup.= and having a pH lower than 5, the effluents are reacted with a basic compound. Particles selected from the group consisting of CaCO.sub.3.MgCO.sub.3, MgCO.sub.3 and a mixture of these, are used for treating the said effluents, the said particles having a particle size such that at least 95% of the particles selected from the group consisting of CaCO.sub.3.MgCO.sub.3 and MgCO.sub.3 have a particle size smaller than 75 .mu.m. After treatment magnesium sulfate in the form of a solution or brine is recovered.
A reagent for treating flue gases constituted by an intimate mixture, in the solid state, of a main component selected from the group comprising alkaline-earth, oxides, hydroxides, carbonates, bicarbonates, and mixtures thereof, and an additive selected from the group comprising hydrogen halide acids, salts of such acids of alkaline metals, ammonium, and alkaline-earth metals, sulphuric acid, and mixtures thereof, said additive being present in an amount of from 0.1 to 15% by mole respect to said main component.
A desulphurization reagent comprising an intimate mixture, in the solid state, of a main component selected from the group consisting of alkaline-earth, oxides, hydroxides, carbonates, bicarbonates, and mixtures, thereof, and an additive selected from the group consisting of hydrogen halide acids, salts of such acids of alkaline metals, ammonium, and alkaline-earth metals, sulphuric acid, and mixtures thereof, said additive being present in an amount of from 0.1 to 15% by mole respect to said main component.
A method is provided for removing sulfur dioxide from a hot gaseous stream while directly producing .alpha.-hemihydrate gypsum from a scrubber effluent. A portion of an aqueous scrubbing medium containing calcium and magnesium sulfite is removed from a scrubbing unit and passed to a pressurized oxidation vessel where the sulfites are contacted with an oxidizing gas at an elevated temperature to convert calcium sulfite directly to .alpha.-hemihydrate gypsum and magnesium sulfite to magnesium sulfate. The .alpha.-hemihydrate is separated from the aqueous medium removed from the pressurized oxidation vessel.
Magnesium hydroxide of high purity, having a fine particle size suitable for use in flame retardants and other high-end uses, is produced by utilizing flue gas desulfurization system process slurry as feedstock; the production process is absent energy-intensive steps as well as high-cost chemical usage.
