Method and apparatus for regeneration of flue gas scrubber caustic solutions
First Claim
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1. A method for regeneration of caustic soda from a flue gas purge liquid containing sodium sulfate, said method comprising the steps of:
- receiving an influent flow of said purge liquid from a flue gas scrubber that removes sulfur dioxide from a waste gas stream;
adding lime to said influent flow of said purge liquid so as to react a portion of said sodium sulfate therein to gypsum and caustic soda;
collecting said gypsum as a solid from said purge liquid;
extracting said caustic soda as a solution from said purge liquid;
returning a remainder portion of said purge liquid from which said gypsum and caustic soda have been removed to said influent flow of said purge; and
supplying said caustic soda solution to said flue gas scrubber for use in removing sulfur dioxide from said waste gas stream.
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Abstract
A process to regenerate wet flue gas scrubber purge liquid into NaOH caustic suitable for make-up caustic for the scrubber is disclosed. Further, sulfur is removed from waste effluent in the form of gypsum with the process described herein. Lime is added to the spent, sodium sulfate-containing purge liquid to result in the formation of gypsum and sodium hydroxide.
15 Citations
17 Claims
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1. A method for regeneration of caustic soda from a flue gas purge liquid containing sodium sulfate, said method comprising the steps of:
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receiving an influent flow of said purge liquid from a flue gas scrubber that removes sulfur dioxide from a waste gas stream; adding lime to said influent flow of said purge liquid so as to react a portion of said sodium sulfate therein to gypsum and caustic soda; collecting said gypsum as a solid from said purge liquid; extracting said caustic soda as a solution from said purge liquid; returning a remainder portion of said purge liquid from which said gypsum and caustic soda have been removed to said influent flow of said purge; and supplying said caustic soda solution to said flue gas scrubber for use in removing sulfur dioxide from said waste gas stream. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method for regeneration of caustic soda from a flue gas purge liquid containing sodium sulfate, said method comprising the steps of:
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receiving an influent flow of said purge liquid from a flue gas scrubber that removes sulfur dioxide from a waste gas stream; passing said influent flow over a reverse osmosis membrane so as to increase a concentration of sodium sulfate in said purge liquid; adding an aqueous lime slurry to said purge liquid having said increased concentration of sodium sulfate therein, in an amount sufficient to yield from about 5% to about 30% by weight of said sodium sulfate as gypsum; crystallizing said gypsum in a reactor vessel so as to form particulate gypsum that precipitates from said purge liquid; thickening said particulate gypsum so as to separate said particulate gypsum from a substantially clear component of said purge liquid; filtering said separated particulate gypsum so as to form a solid gypsum product; passing said substantially clear component of said purge liquid over a sulfate membrane that permits caustic soda from said clear component to pass therethrough so as to be extracted from said purge liquid, leaving a remainder component of said purge liquid that contains unreacted sodium sulfate; returning said remainder component of said purge liquid to said influent flow of said purge liquid; passing said caustic soda solution extracted from said purge liquid over a reverse osmosis membrane so as to concentrate said caustic soda in said solution by removing water therefrom; and providing said concentrated caustic soda solution back to said flue gas scrubber for use in removing sulfur dioxide from said waste gas flow. - View Dependent Claims (15, 16, 17)
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Specification