Method for treating process condensate

• US 5,779,861 A
• Filed: 03/18/1996
• Issued: 07/14/1998
• Est. Priority Date: 09/03/1993
• Status: Expired due to Fees

• Current Assignee: Farmland Industries Incorporated
• Original Assignee: Farmland Industries Incorporated
• Inventors: Scott, Ralph A., Holiday, Allan
• Primary Examiner(s): TRAN, HIEN THI
• Application Number:
  US08/617,324
• Time in Patent Office: 848 Days
• Field of Search: 203/10, 203/11, 203/12, 203/14, 203/75-76, 203/92-94, 203/98, 203/DIG. 6, 203/77, 203/49, 203/95, 203/96, 423/352, 423/359, 568/913, 518/705, 518/704, 422/187, 159/16.3, 202/203
• US Class Current: 203/11
• CPC Class Codes: B01D 3/322 Reboiler specifications
• CPC Class Codes: B01D 3/38 Steam distillation

Abstract

An apparatus and method for treating chemical production plant process condensate and low pressure purge gas such that a contaminant-rich stream is recoverable from the condensate and purge gas, wherein the contaminants are substantially removed from the condensate by steam stripping and subsequent rectification in a relatively low pressure stripping/rectification tower. The tower overhead is then condensed, and any non-condensed gases are subjected to water scrubbing, along with the low pressure purge gas to further recover contaminates from the non-condensed gas. A portion of the condensed overhead and scrubbing water containing contaminates is returned to the top of the rectification section of the tower as reflux and the balance being withdrawn as a concentrated stream for reuse in the plant. The apparatus may be used in conjunction with existing low pressure equipment, avoiding costly major modifications, and is particularly adapted to use in conjunction with ammonia and methanol plants.

Claims

1. A method for treating an ammonia production plant process effluent stream of dilute ammonia contaminants and an ammonia production plant low pressure purge gas stream of dilute ammonia contaminants, said method comprising the following steps:

stripping at least a portion of ammonia contaminants from a process effluent obtained from an ammonia production plant, wherein said stripping is conducted in a stripping section to obtain an ammonia contaminant-rich vapor stream and an aqueous bottom stream of reduced ammonia contaminant content;

rectifying said ammonia contaminant-rich vapor stream in a rectification section to obtain a concentrated overhead stream;

condensing said concentrated overhead stream to obtain ammonia contaminant-rich overhead condensate and non-condensed gases comprising trace amounts of the ammonia contaminates;

scrubbing said non-condensed gases and a purge gas stream of dilute ammonia contaminates with water so as to recover a portion of said trace amounts of the ammonia contaminates from the non-condensed gases and said dilute ammonia contaminates from the purge gas stream into said ammonia contaminant-rich overhead condensate;

recycling said overhead condensate to said rectifying step to form a closed loop so as to build up the concentration of ammonia contaminants in said overhead condensate;

separating and withdrawing from said closed loop a fraction of said overhead condensate; and

reusing said fraction of the overhead condensate in the ammonia production plant.

2. A method according to claim 1, wherein said method additionally comprises collecting said aqueous bottom stream of reduced ammonia contaminant content and reusing said bottom stream in said ammonia production plant.

3. A method according to claim 2, wherein said aqueous bottom stream is used as scrubbing water for said scrubbing step.

4. A method according to claim 1, wherein said stripping section and said rectification section are housed one above another respectively in a common upright tower permitting vapor from said stripping section to pass upwardly within the common tower to the rectification section above and condensate from each section to pass downwardly within the common tower.

5. A method according to claim 1, wherein said stripping section and said rectification section are provided in separate columns in series.

6. A method according to claim 5, wherein said rectification step is conducted in a rectification section to obtain the concentrated overhead stream and a second aqueous bottom stream of reduced ammonia contaminant content, said second aqueous stream being returned to said stripping step.

7. A method according to claim 1, wherein said reusing step comprises injecting said fraction of overhead condensate withdrawn from said closed loop back into said ammonia production plant.

8. A method according to claim 7, wherein said reusing step comprises pumping said fraction of overhead condensate under pressure for entry into said ammonia production plant.

9. A method according to claim 1, wherein said separating and withdrawing step comprises separating and withdrawing from said closed loop a fraction of said overhead condensate in an amount ranging from 3 to 50% by volume of the overhead condensate in said loop.

10. A method according to claim 9, wherein said separating and withdrawing step comprises separating and withdrawing from said closed loop a fraction of said overhead condensate in an amount ranging from 5 to 20% by volume of the overhead condensate in said loop.

11. A method according to claim 1 wherein said stripping section is operable at pressures ranging from 0 psia to 300 psig.

12. A method according to claim 1, wherein said fraction of the overhead condensate is delivered to the ammonia production plant by delivering said fraction to a mixed feed coil of a primary reformer of said ammonia production plant.

13. A method according to claim 1, wherein said fraction of the overhead condensate is delivered to the ammonia production plant by delivering said fraction to an air preheat coil of a secondary reformer of said ammonia production plant.

14. A method according to claim 1, wherein said purge gas stream comprises purge gas recovered from a processing unit of the ammonia production plant, said processing unit selected from the group consisting of an ammonia separator, a combined product refrigerant receiver, or combinations thereof.

15. A method according to claim 14, wherein said fraction of the overhead condensate is delivered to the ammonia production plant by delivering said fraction to a mixed feed coil of a primary reformer of said ammonia production plant.

16. A method according to claim 14, wherein said fraction of the overhead condensate is delivered to the ammonia production plant by delivering said fraction to an air preheat coil of a secondary reformer of said ammonia production plant.

17. A method for treating a methanol production plant process effluent stream of dilute methanol contaminants and a methanol production plant low pressure purge gas stream of dilute methanol contaminants, said method comprising the following steps:

stripping at least a portion of methanol contaminants from a process effluent obtained from a methanol production plant, wherein said stripping is conducted in a stripping section to obtain a methanol contaminant-rich vapor stream and an aqueous bottom stream of reduced methanol contaminant content;

rectifying said methanol contaminant-rich vapor stream in a rectification section to obtain a concentrated overhead stream;

condensing said concentrated overhead stream to obtain methanol contaminant-rich overhead condensate and non-condensed gases comprising trace amounts of the methanol contaminates;

scrubbing said non-condensed gases and a purge gas stream of dilute methanol contaminates with water so as to recover a portion of said trace amounts of the methanol contaminates from the non-condensed gases and said dilute methanol contaminates from the purge gas stream into said methanol contaminant-rich overhead condensate and a scrubbed purge gas;

recycling said overhead condensate to said rectifying step to form a closed loop so as to build up the concentration of methanol contaminants in said overhead condensate;

separating and withdrawing from said closed loop a fraction of said overhead condensate; and

reusing said fraction of the overhead condensate in the methanol production plant.

18. A method according to claim 17, wherein said method additionally comprises collecting said aqueous bottom stream of reduced methanol contaminant content and reusing said bottom stream in said methanol production plant.

19. A method according to claim 18, wherein said aqueous bottom stream is used as scrubbing water for said scrubbing step.

20. A method according to claim 17, wherein said purge gas stream comprises purge gas recovered from a processing unit of the methanol production plant, said processing unit selected from the group consisting of a methanol separator, a combined product refrigerant receiver, or combinations thereof.

21. A method according to claim 17 further comprising disposing of the scrubbed purge gas.

22. A method according to claim 21 wherein disposing of scrubbed purge gas comprises delivering the scrubbed purge gas to a furnace firebox.

23. A method according to claim 21 wherein disposing of scrubbed purge gas comprises delivering the scrubbed purge gas to a vent.