Process for separating ammonia and acid gases from waste waters containing fixed ammonia salts
First Claim
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 and sulfate ion in a concentration of less than about 1500 ppm, said process comprising:
- (a) subjecting said solution to a first countercurrent 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 more than 9,(i) withdrawing an overhead vapor stream containing a major proportion of stripping vapor, some of said acid gases from said solution, and some of the ammonia from said free ammonia salts,(ii) withdrawing an aqueous bottom stream which contains a major proportion of water, acid gases, free ammonia salts 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(b) adding lime to said withdrawn bottom stream, said lime being added in an amount sufficient to form an insoluble precipitate and evolve ammonia contained in the fixed ammonia salts during a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 ##STR5## where R is ##STR6## R'"'"' is selected from the group consisting of R and --CH2 CH2 OH, andR" is selected from the group consisting of R, --CH2 CH2 OH, and ##STR7## 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(d) subjecting said withdrawn bottom stream to a second countercurrent multi-stage continuous distillation,(i) withdrawing an overhead vapor stream, said vapor stream containing a major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 reusing this overhead vapor stream as a stripping vapor in the first distillation, and(ii) withdrawing an aqueous bottom stream, said stream having a substantially reduced concentration of acid gases and ammonia as compared to said aqueous solution.
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Abstract
A water purification process is described for the removal of ammonia and optionally one or more acid gases from waste waters such as coke-plant or coal conversion waste waters. The process involves adding lime to these waste waters in amounts sufficient to react with fixed ammonia salts present in the waste water and to enable substantial amounts of the ammonia to be evolved upon distillation, adding a threshold amount of a scale inhibitor compound chosen from the class of certain organic phosphonates and subjecting the thus treated waste water to distillation to remove substantial amounts of the ammonia and acid gases present from the waste water. Preferably, this process is achieved by two separate and successive distillations. In this preferred process, the first distillation substantially reduces the amount of the acid gases and free ammonia and is conducted at a pH of more than 9. In the second distillation, the amount of fixed ammonia is substantially reduced. To conserve energy, the stripping vapors from the second distillation are reused as stripping vapors for the first distillation.
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Citations
38 Claims
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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 and sulfate ion in a concentration of less than about 1500 ppm, said process comprising:
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(a) subjecting said solution to a first countercurrent 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 more than 9, (i) withdrawing an overhead vapor stream containing a major proportion of stripping vapor, some of said acid gases from said solution, and some of the ammonia from said free ammonia salts, (ii) withdrawing an aqueous bottom stream which contains a major proportion of water, acid gases, free ammonia salts 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 ##STR5## where R is ##STR6## 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 ##STR7## 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 reusing this overhead vapor stream as a stripping vapor in the first distillation, and (ii) withdrawing an aqueous bottom stream, said stream having a substantially reduced concentration of acid gases and ammonia as compared to said aqueous solution. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27)
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28. A process of purifying a waste water of a composition comprising:
- (a) free ammonia of a concentration above about 3000 ppm, (b) fixed ammonia in a concentration of between about 50 and about 50,000 ppm, (c) acid gases in a concentration of between about 250 and about 50,000 ppm, and (d) sulfate ion in a concentration of less than about 1500 ppm, said process comprising (a) adding lime to said waste water, said lime and fixed ammonia salts being present in amounts sufficient to form an insoluble precipitate and evolve ammonia contained in the fixed ammonia salts during a distillation of said mixture;
(b) adding a threshold amount of at least one scale inhibitor compound of the general formula ##STR9## where R is ##STR10## 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 ##STR11## 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 tower in which the distillation is conducted;
(c) subjecting the thus treated waste water to a 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, (ii) withdrawing an aqueous bottom stream. - View Dependent Claims (29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
- (a) free ammonia of a concentration above about 3000 ppm, (b) fixed ammonia in a concentration of between about 50 and about 50,000 ppm, (c) acid gases in a concentration of between about 250 and about 50,000 ppm, and (d) sulfate ion in a concentration of less than about 1500 ppm, said process comprising (a) adding lime to said waste water, said lime and fixed ammonia salts being present in amounts sufficient to form an insoluble precipitate and evolve ammonia contained in the fixed ammonia salts during a distillation of said mixture;
Specification