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Method for simultaneous absorption of sulfur dioxide and nitric oxide from flue gas

  • US 5,433,934 A
  • Filed: 01/11/1994
  • Issued: 07/18/1995
  • Est. Priority Date: 08/13/1991
  • Status: Expired due to Fees
First Claim
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1. A process for abating nitric oxide and sulfur dioxide from a flue gas, comprising the steps of:

  • (a) contacting flue gas with an aqueous absorbent solution, in an absorption stream comprising a reduced metal chelate and sulfites to absorb nitric oxide from said flue gas, and a piperazinone SO2 absorbent of the formula;

    ##STR13## wherein R is hydrogen, an alkyl group having one to six carbon atoms or aryl or aralkyl group having from six to twelve carbon atoms, R1 is hydrogen, an alkyl or hydroxyalkyl group having from one to six carbon atoms, or an aryl or aralkyl group having from six to twelve carbon atoms, and R2 is R1 or a 2-hydroxyethyl group of the formula;

    ##STR14## wherein R3 is hydrogen or an alkyl group having one or two carbon atoms to reversibly absorb sulfur dioxide from said flue gas, at a pH between 3 and 8 effective to maintain compatibility between the chelate, sulfites and SO2 absorbent to form an SO2 -rich absorbent solution containing oxidized metal chelate and heat stable piperazinone salts;

    (b) thermally stripping a major portion of the sulfur dioxide from said SO2 -rich absorbent solution to obtain an SO2 -lean absorbent solution containing only a minor portion of the SO2 absorbed in step (a);

    (c) passing said SO2 -lean absorbent solution through an electrochemical cell to reduce said oxidized metal chelates, and to convert the heat stable piperazinone salts into free piperazinone SO2 absorbent, to regenerate said absorbent solution; and

    (d) recycling said regenerated absorbent solution to said contacting step.

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