Method of sulfur dioxide removal from gaseous streams with .alpha.-hemihydrate gypsum product formation
AssigneeDravo Lime Company
InventorJohn W. College
Life of this patent
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Abstract
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.
Claims12
A method of removing sulfur dioxide from a sulfur dioxide-containing hot gaseous stream and producing .alpha.-hemidydrate gypsum, comprising:
- contacting said sulfur dioxide-containing hot gaseous stream with an aqueous scrubbing medium containing calcium and magnesium scrubbing components in a scrubbing unit, wherein said sulfur dioxide is converted to calcium and magnesium sulfites in an aqueous medium;
- continuously removing at least a portion of said aqueous medium containing calcium sulfite and magnesium sulfite from said scrubbing unit;
- continuously passing at least a portion of said removed aqueous medium containing calcium sulfite and magnesium sulfite, having a solids content of between about 5-35 percent by weight, to a pressurized oxidation vessel;
- contacting said aqueous medium containing calcium sulfite and magnesium sulfite in said pressurized oxidation vessel with an oxidizing gas at an elevated temperature and super-atmospheric pressure to convert said calcium sulfite to .alpha.-hemihydrate gypsum, which precipitates from said aqueous medium, and said magnesium sulfite to magnesium sulfate, which dissolves in said aqueous medium, with heat of reaction resulting from said conversion used to maintain said elevated temperature and provide a portion of the pressure within said pressurized oxidation vessel, and the presence of magnesium ions from said magnesium sulfite and magnesium sulfate enhancing said conversion of calcium sulfite to .alpha.-hemihydrate gypsum;
- continuously removing aqueous medium containing precipitated .alpha.-hemihydrate gypsum and dissolved magnesium sulfate from said pressurized oxidation vessel;
- and
- separating said .alpha.-hemihydrate gypsum from said aqueous medium.
A method of removing sulfur dioxide from a sulfur dioxide-containing hot gaseous stream and producing .alpha.-hemihydrate gypsum, comprising:
- contacting said sulfur dioxide-containing hot gaseous stream with an aqueous scrubbing medium containing calcium and magnesium scrubbing components in a scrubbing unit, wherein said sulfur dioxide is converted to calcium and magnesium sulfites in an aqueous medium;
- continuously removing at least a portion of said aqueous medium containing calcium sulfite and magnesium sulfite, having solids content of between about 5-35 percent by weight, from said scrubbing unit;
- continuously passing at least a portion of said removed aqueous medium containing calcium sulfite and magnesium sulfite to a pressurized oxidation vessel;
- contacting said aqueous medium containing calcium sulfite and magnesium sulfite in said pressurized oxidation vessel with an oxidizing gas at an elevated temperature of between about and 100-145.degree. C. and superatmospheric pressure of between about 20-60 pounds per square inch, while maintaining the pH of said aqueous medium at between 2.5-5.5, to convert said calcium sulfite to .alpha.-hemihydrate gypsum, which precipitates from said aqueous medium, and said magnesium sulfite to magnesium sulfate, which dissolves in said aqueous medium, with heat of reaction resulting from said conversion used to maintain said elevated temperature and provide a portion of the pressure within said pressurized oxidation vessel, and the presence of magnesium ions from said magnesium sulfite and magnesium sulfate enhancing said conversion of calcium sulfite to .alpha.-hemihydrate gypsum;
- continuously removing aqueous medium containing precipitated .alpha.-hemihydrate gypsum and dissolved magnesium sulfate from said pressurized oxidation vessel;
- and
- separating said .alpha.-hemihydrate gypsum from said aqueous medium.
Dependencies are inferred from the claim text.