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Process for separating ammonia and acid gases from waste waters containing fixed ammonia salts

  • US 4,111,759 A
  • Filed: 07/08/1976
  • Issued: 09/05/1978
  • Est. Priority Date: 07/08/1976
  • Status: Expired due to Term
First Claim
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1. A process for separating acid gases and ammonia from a dilute aqueous solution thereof, said solution being derived from a coal conversion process and also containing free and fixed ammonia salts but containing sulfate ion in a concentration of less than about 1500 ppm, said process comprising:

  • (a) subjecting said solution to a first counter-current multi-stage continuous distillation, said distillation being conducted 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 8,(i) withdrawing an overhead vapor stream containing a major proportion of stripping vapor, a major proportion of said acid gases in said solution, and a major proportion of the ammonia from said free ammonia salts,(ii) withdrawing an aqueous bottom stream which contains a major proportion of water and substantially all of said fixed ammonia salts;

    (b) adding lime to said withdrawn bottom stream, said lime being added in an amount sufficient to form an insoluble precipitate and evolve ammonia contained in the fixed ammonia salts during a second distillation of said mixture;

    (c) adding a threshold amount of at least one scale inhibitor compound of the general formula ##STR4## R'"'"' is selected from the group consisting of R and --CH2 CH2 OH, and R" is selected from the group consisting of R, --CH2 CH2 OH, and ##STR5## where each M is independently selected from the group consisting of H, NH4, and alkali metal, "n" is a whole number from 1 to 3, to said dilute aqueous solutions to thereby inhibit the deposition of scale on the trays of the distillation towers; and

    (d) subjecting said withdrawn bottom stream to a second countercurrent multi-stage continuous distillation,(i) withdrawing an overhead vapor stream, said vapor stream containing a major proportion of stripping vapor and a portion of the ammonia from the fixed ammonia salts, and(ii) withdrawing an aqueous bottom stream, said stream having a substantially reduced concentration of acid gases and ammonia are compared to said aqueous solution.

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