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AssigneeInstitut Francais du Petrole
InventorsPhilippe Renault, Andre Deschamps, Sigismond Franckowiak, Claude Dezael
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This process for purifying a sulfur dioxide containing gas, for example stack gas, comprises the steps of washing the gas with aqueous ammonia or ammonium sulfite, vaporizing sulfur dioxide and ammonia therefrom, reacting vaporized sulfur dioxide with hydrogen sulfide and recycling an ammonia containing stream. To avoid the drawbacks resulting from the presence of hydrogen sulfide in the recycle stream, a further oxidation step is provided to convert hydrogen sulfide to sulfur dioxide.
In a process for purifying a sulfur dioxide containing gas, which comprises the steps of (a) washing the gas with an aqueous solution of ammonia and/or ammonium sulfite and then separating the gas from the resulting aqueous solution of increased ammonium sulfites content, (b) heating the aqueous solution obtained in step (a) to decompose at least a portion of the sulfites and produce a stream of gas containing sulfur dioxide, ammonia and steam, (c) reacting hydrogen sulfide with the gas stream obtained in step (b), thereby producing elemental sulfur and a gas containing ammonia, steam and unconverted hydrogen sulfide, and separating the elemental sulfur from said gas, and (d) recycling to step (a) the ammonia obtained in step (c), the improvement which comprises subjecting the ammonia-containing gas separated in step (c) to controlled oxidation to selectively convert residual hydrogen sulfide to sulfur dioxide, and conducting step (d) by recycling ammonia and at least one member of the group consisting of sulfur dioxide and ammonium sulfite to step (a).
Dependencies are inferred from the claim text.
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Sulfur oxides: by treating the gases with a solution or a suspension of an alkali or earth-alkali or ammonium compound
Removing sulfur compounds: hydrogen sulfide
From gaseous sulfur compounds including gaseous sulfides: by wet processes
Separation
Term ended 13 Sep 1994 (estimated)
USPTO file history isn’t available for this patent, so only indexed dates are shown.
Many industrial gases, for example stack-gas from power plants, are known to contain sulfur dioxide; their discharge to the atmosphere generates pollution which cannot be prevented at low cost. Sulfur trioxide is also often present, although in relatively lower proportion. it is however essential to eliminate these two gases, in order to reduce the sulfur content of industrial waste-gases to acceptable values.
According to a known purification process, the SO.sub.2 and SO.sub.3 contents of industrial waste-gases can be reduced by converting them to sulfur, which is non-polluting, easily storable and marketable. This applies particularly to stack-gas from power plants and certain waste-gases from chemical works.
This process comprises the following steps:
The invention is non-limitatively illustrated by the accompanying drawing.
The gas to be purified contains SO.sub.2 and a low proportion of SO.sub.3. It is conveyed through pipe 1 to the washing column 2, while the aqueous absorption solution enters through line 3. The purified gas is discharged through line 4. It may be subjected to additional washing, in order to recover any ammonia carried along therewith, for example a washing with a solution of sulfuric acid or ammonium hydrogen sulfate; the latter solution may be fed back to one of the units of the plant. The absorption solution may be recirculated through line 15. At least a portion of the aqueous ammonium sulfite solution is conveyed through pipe 5 to the vaporizer 6. The vaporized phase is passed through pipe 7 and delivered to the reactor 8 also fed with H.sub.2 S delivered through pipe 9. This reactor preferably contains an organic liquid, for example polyethylene glycol. Sulfur as formed is discharged through line 10.
The unvaporized liquid phase from 6 is passed through line 12 to the reactor 13 where ammonium sulfate reacts with a reducing agent, for example ammonium thiosulfate, hydrogen sulfide and/or sulfur. The resulting gas is supplied to column 8 through pipe 14. The gas discharged from the reactor 8 through line 11 contains NH.sub.3, H.sub.2 O, traces of SO.sub.2 and H.sub.2 S which has been used in excess over the stoichiometrical amount necessary to form sulfur. This gas is supplied to an incinerator 16 also fed with a gas containing hydrocarbons and air (pipes 17 and 18); it is discharged through line 19, passes through the cooler 20 and the condenser 21. The condensate is conveyed to line 3 through line 22. An additional amount may be supplied through line 23 to compensate for possible losses.