Continuous process for recovering pure, concentrated ammonia
AssigneesMetallgesellschaft Aktiengesellschaft, Chemie Linz Aktiengesellschaft
InventorsAlfred Garber, Hans-Martin Stonner, Paul Wiesner, Alan Sinclair, Alfred Schmidt
Life of this patent
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Abstract
Pure, concentrated ammonia is recovered from aqueous liquors by stripping off gas water, de-acidifications, scrubbing and withdrawing ammonia from the top of a scrubbing column.
Claims17
In a continuous process of recovering pure, concentrated ammonia, which contains not more than 0.2% H.sub.2 O, 0.1% CO.sub.2, 10 ppm H.sub.2 S, and 10 ppm HCN, from aqueous liquors from which dust, tar, oil, and phenols have been removed, said aqueous liquors being condensates formed during the gasification or degasification of coal, or from aqueous liquors of similar compositions which contain free and/or combined ammonia in concentrations between 0.1 and 12 n carbon dioxide in concentrations between 0.1 and 12 n, hydrogen sulfide in concentrations between 0.003 and 3 n hydrocyanic acid in concentrations between 0.001 to 1 g/l, and residual organic substances introduced during a preceding dephenolation, which process includes the steps of stripping off gas water, de-acidification, scrubbing, and withdrawing ammonia from the top of a scrubbing column, the improvement which comprises the following steps:
- a. stripping ammonia from the aqueous liquor in a stripping column having 15-80 actual plates or equivalent packing columns operated under a pressure of 1-2 bars with an inlet temperature of 30.degree.-90.degree. C, the ammonia and the acid constituents being jointly withdrawn overhead and waste water being withdrawn from the sump of the column,
- b. scrubbing the overhead product from (a) with an aqueous solution containing surplus ammonia from which the acid constituents have been substantially removed under a pressure of 1-2 bars and at temperatures of 30.degree.-70.degree. C withdrawing pure ammonia overhead and subjecting it to a fine purification by liquification and treatment to remove inert constituents;
- c. stripping most of the residual ammonia from the spent scrubbing liquor from (b) in a stripping column having 3-25 plates, or equivalent packing columns, operated under 1-2 bars, top temperatures of 50.degree.-80.degree. C, and sump temperatures of 60.degree.-90.degree. C, and withdrawing ammonia overhead and recycling it to (b);
- and
- d. de-acidifying aqueous solutions having a (CO.sub.2 + H.sub.2 S) ;
- NH ratio .gtoreq. 1 under superatmospheric pressure by stripping the acid constituents in a pressure de-acidification column operated under a pressure of 3-25 bars, and sump temperatures of 110.degree.-180.degree. C, and withdrawing same from the top of said column;
- said steps being carried out in the sequence a), b), c), d), with the sump product of step c) being subjected to step d) in the processing of solutions in which the (CO.sub.2 + H.sub.2 S) :
- NH.sub.3 weight ratio .ltoreq. 1 whereas the feed solution is subjected to the pressure de-acidification step d) and this is succeeded by steps a), b), c) in the processing of solutions having a (CO.sub.2 + H.sub.2 S) :
- NH.sub.3 weight ratio >
- 1.
In a continuous process of recovering pure, concentrated ammonia, which contains not more than 0.2% H.sub.2 O, 0.1% CO.sub.2, 10 ppm H.sub.2 S, and 10 ppm HCN, from aqueous liquors from which dust, tar, oil, and phenols have been removed, said aqueous liquors being condensates formed during the gasification or degasification of coal, or from aqueous liquors of similar compositions which contain free and/or combined ammonia in concentrations between 0.1 and 12 n, carbon dioxide in concentrations between 0.1 and 12 n, hydrogen sulfide in concentrations between 0.003 and 3 n, hydrocyanic acid in concentrations between 0.001 to 1 g/l, and residual organic substances introduced during a preceding dephenolation, which process includes the steps of stripping off gas water, de-acidification, scrubbing, and withdrawing ammonia from the top of a scrubbing column, the improvement which comprises the following steps:
- a. stripping ammonia from the aqueous liquor in a stripping column having 15-80 actual plates or equivalent packing columns operated under a pressure of 1-2 bars with an inlet temperature of 30.degree.-90.degree. C, the ammonia and the acid constituents being jointly withdrawn overhead and waste water being withdrawn from the sump of the column,
- b. scrubbing the overhead product from (a) with an aqueous solution containing surplus ammonia from which the acid constituents have been substantially removed under a pressure of 1-2 bars and at temperatures of 30.degree.-70.degree. C withdrawing pure ammonia overhead and
- c. stripping most of the residual ammonia from the spent scrubbing liquor from (b) in a stripping column having 3-25 plates, or equivalent packing columns, operated under 1-2 bars, top temperatures of 50.degree.-80.degree. C, and sump temperatures of 60.degree.-90.degree. C, and withdrawing ammonia overhead and recycling it to (b);
- and
- d. de-acidifying aqueous solutions having a (CO.sub.2 + H.sub.2 S);
- NH ratio .gtoreq. 1 under superatmospheric pressure by stripping the acid constituents in a pressure de-acidification column operated under a pressure of 3-25 bars, and sump temperatures of 110.degree.-180.degree. C, and withdrawing same from the top of said column;
- said steps being carried out in the sequence a), b), c), d), with the sump product of step c) being subjected to step d) in the processing of solutions in which the (CO.sub.2 + H.sub.2 S) :
- NH.sub.3 weight ratio .ltoreq. 1 whereas the feed solution is subjected to the pressure de-acidification step d) and this is succeeded by steps a), b), c) in the processing of solutions having a (CO.sub.2 + H.sub.2 S) :
- NH.sub.3 weight ratio >
- 1.
Dependencies are inferred from the claim text.