Process and system to capture ammonia from a purge gas of a urea plant

Patent metadata

Field	Value
Publication number	US-10927012-B2
Application number	US-201816485276-A
Country	US
Kind code	B2
Filing date	Feb 1, 2018
Priority date	Feb 27, 2017
Publication date	Feb 23, 2021
Grant date	Feb 23, 2021

Abstract

A process and system for removing ammonia from ammonia-containing purge gas of a urea plant, the process comprising: contacting said ammonia-containing purge gas with carbon dioxide at a low temperature, reaction of ammonia to form crystals of ammonium salts in a multiphase stream, and removal of the solid ammonium salts from the multiphase stream.

First claim

What is claimed is:

1. A process for removing ammonia from ammonia-containing purge gas of a urea plant, the process comprising:
a) said ammonia-containing purge gas is contacted with a stream of carbon dioxide;
b) at least one of:
said ammonia-containing purge gas prior to contacting said stream of carbon dioxide,
said stream of carbon dioxide prior to contacting the ammonia purge-gas,
the mixture of purge gas and carbon dioxide resulting from the contacting step a),
is refrigerated;
c) in the so obtained refrigerated mixture of purge gas and carbon dioxide, at least some of the ammonia contained in the purge gas reacts to form one or more ammonium salts and a multiphase mixed stream containing the ammonium salts is obtained, and
d) said ammonium salts are removed from said mixed stream.

2. The process according to claim 1 , wherein said at least one of purge gas, carbon dioxide and mixture of purge gas and carbon dioxide is refrigerated to a temperature lower than the temperature of the input ammonia-containing purge gas.

3. The process according to claim 1 , wherein said mixed stream has a temperature equal to or less than 10° C.

4. The process according to claim 3 , wherein the ammonia-containing purge gas is contacted with said carbon dioxide at a pressure of 1 to 10 bar abs.

5. The process according to claim 4 , wherein the ammonia-containing purge gas and the refrigerated carbon dioxide are contacted in a mixer or in a gas ejector.

6. The process according to claim 4 , wherein the ammonia-containing purge gas is contacted with said carbon dioxide at a pressure of 1 to 2 bar abs.

7. The process according to claim 3 , wherein said mixed stream has a temperature in the range of 10° C. to −30° C.

8. The process according to claim 1 , comprising refrigeration of said carbon dioxide, wherein the temperature of refrigerated carbon dioxide is equal to or less than −10° C.

9. The process according to claim 8 , wherein refrigerated carbon dioxide is obtained by: separating a secondary gaseous stream of carbon dioxide from an inter-refrigeration stage of a carbon dioxide feed compressor of said urea plant, and expanding said secondary stream of carbon dioxide to a lower pressure in order to lower its temperature.

10. The process according to claim 9 , wherein said secondary stream of carbon dioxide has a pressure of 65 to 85 bar and a temperature after inter-refrigeration of 40 to 80° C., and is expanded to atmospheric pressure.

11. The process according to claim 8 , comprising refrigeration of said carbon dioxide, wherein the temperature of refrigerated carbon dioxide is in the range −25 to −65° C.

12. The process according to claim 1 , wherein during or after the contacting of ammonia-containing purge gas and carbon dioxide, a further refrigerant medium is added.

13. The process according to claim 12 , comprising the steps of: contacting the ammonia-containing purge gas and the carbon dioxide in an absorber, and injecting said refrigerant medium into said absorber, so that the refrigerant medium comes into direct contact with the purge gas and carbon dioxide.

14. The process according to claim 12 , wherein the refrigerant medium is at a temperature equal to or less than −10° C.

15. The process according to claim 1 , wherein said ammonia-containing purge gas comprises a plurality of purge streams taken from different sections of said urea plant.

16. The process according to claim 1 , wherein said ammonium salts include ammonium bicarbonate NH 4 HCO 3 and ammonium carbamate NH 4 COONH 2 .

17. The process according to claim 1 , wherein ammonium salts are removed from said mixed stream in a filter or by a scrubbing process.

18. The process according to claim 17 , wherein said scrubbing process comprises water as a scrubbing medium.

19. The process according to claim 1 , wherein the ammonia-containing purge gas is a purge gas as vented from the urea plant, or the process comprise at least one step of removing ammonia from the purge gas prior to said contacting with cold carbon dioxide.

20. The process according to claim 1 , wherein said mixed stream contains a residual amount of free gaseous ammonia of less than 10 ppm.

21. An ammonia capture system for removing ammonia contained in a purge gas of a urea plant, comprising:
a mixing device wherein said ammonia-containing purge gas and a stream of carbon dioxide are introduced,
at least one of a refrigerator for the ammonia-containing purge gas, a refrigerator for said stream of carbon dioxide, means to add a refrigerant medium to said mixing device,
the mixing device delivering a multiphase mixed stream containing solid ammonium salts, as a result of mixing and refrigeration of the purge gas and carbon dioxide, and
a phase-separation device disposed to receive said mixed stream from the mixing device and adapted to remove said ammonium salts from said mixed stream.

Assignees

• Casale Sa

Inventors

• Rugnone Luca

Classifications

• Y02P20/141

  Feedstock · CPC title

• C01C1/12 Primary

  Separation of ammonia from gases and vapours {(as part of the ammonia synthesis process C01C1/04)} · CPC title

• C07C273/16 Primary

  Separation; Purification · CPC title

• C01C1/26

  Carbonates or bicarbonates of ammonium · CPC title

• B01D2252/103

  Water · CPC title