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Process for separating ammonia and acid gases from streams containing fixed ammonia salts

  • US 4,323,430 A
  • Filed: 03/16/1981
  • Issued: 04/06/1982
  • Est. Priority Date: 03/16/1981
  • Status: Expired due to Fees
First Claim
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1. In a process for achieving substantially complete removal of acid gases and ammonia from a dilute aqueous solution thereof, said solution also containing free and fixed ammonia salts, said process comprising:

  • (a) subjecting said solution to a first countercurrent multi-stage continuous distillation, said distillation being conducted by heating said solution, at least in part by means of a stripping vapor, and by having a gradient of ammonia concentration decreasing towards the region of bottom liquid withdrawal which results in said bottom liquid having a pH of less than about 8.0,(i) withdrawing from this first distillation an overhead vapor stream containing a major proportion of stripping vapor, substantially all of said acid gases in said solution, and substantially all of the ammonia from said free ammonia salts,(ii) withdrawing from this distillation an aqueous bottom stream which contains substantially all of said fixed ammonia salts;

    (b) adding alkali to said withdrawn bottom stream, said alkali being added in an amount sufficient to evolve ammonia contained in said fixed ammonia salts during subsequent distillation of said mixture;

    (c) subjecting said withdrawn bottom stream to a second counter-current multi-stage continuous distillation,(i) withdrawing from this second distillation an overhead vapor stream said vapor stream containing a portion of the ammonia from said fixed ammonia salts,(ii) withdrawing from this second distillation an aqueous bottom stream;

    (d) vaporizing the aqueous bottom stream of step (a), at least in part (1) by heating said bottom stream by means of indirect heat exchange with at least a portion of the overhead vapor stream being withdrawn in step (c) and (2) by conducting said first distillation at a pressure substantially less than the pressure of the second distillation;

    (e) passing said vapor stream from said first distillation through a condenser to concentrate the ammonia in the vapor stream leaving the condenser, the improvement comprising adding ammonia to said vapor stream from said first distillation to reduce corrosion of said condenser.

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