Process for separating ammonia and acid gases from streams containing fixed ammonia salts
First Claim
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(b) adding alkali to said withdrawn bottom stream, said alkali being added in an amount sufficient to evolve ammonia contained in said fixed ammonia salts during subsequent distillation of said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(c) subjecting said withdrawn bottom stream to a second counter-current multi-stage continuous distillation,(i) withdrawing from this second distillation an overhead vapor stream said vapor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said bottom stream by means of indirect heat exchange with at least a portion of the overhead vapor stream being withdrawn in step (c) and (2) by conducting said first distillation at a pressure substantially less than the pressure of the second distillation;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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Accused Products
Abstract
A process for the substantially complete removal of acid gases and ammonia from aqueous solutions is disclosed, which comprises a two stage distillation operation wherein the pressure in the first distillation stage is substantially less than the pressure in the second stage, the ammonia concentration in this stage decreases downwardly so that an aqueous bottoms stream has a pH less than 8, this aqueous bottoms stream is treated with alkali and then distilled in the second stage. A portion of the aqueous bottoms can be vaporized by indirect heat exchange with vapors evolving from the second stage. The improvement lies in adding ammonia to the overhead vapor from the first stage to reduce corrosion of the condenser and preferably, the amount of vapor condensed is controlled to further minimize corrosion.
20 Citations
34 Claims
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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:
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(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. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. 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:
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(a) subjecting said solution to a first counter-current 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 being in the acid range and wherein said distillation is conducted at a pressure in the range of about 0.3 to about 3 atmospheres absolute, (i) withdrawing from this first distillation an overhead vapor stream containing a major proportion of stripping vapor comprising steam having a temperature in the range of about 140°
to 265°
F., substantially all of said acid gases in said solution and substantially all of the ammonia from said free ammonia salts,(ii) withdrawing from this first distillation an aqueous bottom stream which contains substantially all of said fixed ammonia salts and has a temperature in the range of about 160°
to about 275°
F.;(b) adding alkali to said withdrawn bottom stream and cooling said bottom stream to a temperature in the range of about 155°
to about 270°
F., said alkali being added in an amount sufficient to evolve ammonia contained in the 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 having a temperature in the range of about 140°
to about 295°
F., said vapor stream comprising steam and a portion of the ammonia from the fixed ammonia salts,(ii) withdrawing from this second distillation an aqueous bottom stream, said bottom stream being substantially free of acid gases and ammonia, and having a temperature in the range of about 160°
to 315°
F.;(d) vaporizing at least a portion of the aqueous bottom stream of step (a) to form a stripping vapor for use in step (a) by indirect heat exchange with at least a portion of the streams being withdrawn in step (c) to thereby achieve substantially complete removal of the free ammonia and acid gases from the liquid that is to be treated in the second distillation of step (c), and wherein the ratio of solution flow to vapor flow within the columns is in the range of about 10/1 to 2/1 and wherein the first distillation is conducted at a pressure sufficiently less than the pressure of the second distillation to permit the overhead vapors of step (c) to provide sufficient heat by indirect heat exchange to vaporize the aqueous bottom stream of step (a); (e) combining at least part of said ammonia from said ammonia containing vapor stream from said second distillation with said vapor stream from said second distillation; and (f) passing the combined stream from step (e) through a steel condenser, and wherein the amount of ammonia added in step (e) and said condenser is adjusted to produce a condensed liquid having a concentration of ammonia and acid gases which is substantially non-corrosive to said condenser. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34)
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Specification