Zero emission urea process and plant

Patent metadata

Field	Value
Publication number	US-9776957-B2
Application number	US-201214007637-A
Country	US
Kind code	B2
Filing date	Mar 30, 2012
Priority date	Mar 31, 2011
Publication date	Oct 3, 2017
Grant date	Oct 3, 2017

Abstract

Disclosed is a method for the production of urea allowing a substantial reduction, even down to zero, of the continuous emission of ammonia conventionally resulting from such a process. According to a preferred embodiment of the invention, the urea-forming reaction from carbon dioxide and ammonia is conducted in a synthesis section that does not require passivation by oxygen. As a result of the absence of oxygen, a hydrogen-rich gas stream results from the synthesis section, that can be used as a fuel in an incinerator. In the incinerator, ammonia-comprising gas streams from the urea production process are combusted.

First claim

The invention claimed is:

1. A method for the production of urea in a plant for the production of urea, the plant comprising a urea synthesis section, wherein the urea synthesis section has an outlet for urea solution and an outlet for gas, and wherein the plant further comprises an incinerator and downstream of said outlet for urea solution one or more downstream processing units, the method comprising
subjecting ammonia and a feed comprising carbon dioxide and hydrogen to reaction under urea-forming conditions in said urea synthesis section in the absence of oxygen, so as to form an aqueous urea solution,
supplying gas comprising hydrogen from said outlet for gas of said urea synthesis section to said incinerator, and
subjecting said aqueous urea solution to concentration so as to form concentrated urea in said one or more downstream processing units, wherein in at least one of said one or more downstream processing units, inert vapor that contains ammonia is released,
supplying said inert vapor that contains ammonia from one or more of said downstream processing units to said incinerator, and
subjecting in said incinerator said gas comprising hydrogen to combustion, together with said inert vapor that contains ammonia from one or more of said downstream processing units in the presence of oxygen.

2. A method according to claim 1 , wherein said gas stream is directed to the combustion chamber of an incinerator and are used for the combustion of the gas stream comprising hydrogen.

3. A method according to claim 2 , wherein air is added to the combustion chamber of the incinerator.

4. A method according to claim 3 , wherein the generated heat of combustion is used to produce steam at a pressure between 0.3 and 3 MPa.

5. A method according to claim 2 , wherein vapor generated in the incinerator is subjected to an SCR catalyst in order to reduce the formed NOx.

6. A method according to claim 5 , wherein, prior to SCR, the vapor is subjected to a selective non-catalytic reduction (SNCR).

7. A method according to claim 1 , wherein the reaction between ammonia and carbon dioxide is conducted in a synthesis section made from a duplex ferritic-austenitic stainless steel having a content of Cr of at least 28 wt % and N of at least 0.2 wt %, and a content of Ni of no more than 10 wt %.

8. A method according to claim 7 , wherein the synthesis section is made from a duplex, stainless steel alloy, containing, in percent by weight:
C maximally 0.05%;
Si maximally 0.8%;
Mn 0.3-4%;
Cr 28-35%;
Ni 3-10%;
Mo 1.0-4.0%;
N 0.2-0.6%;
Cu maximally 1.0%;
W maximally 2.0%;
S maximally 0.01%;
Ce 0-0.2%;
the remainder being Fe and normally occurring impurities and additives, the ferrite content being 30-70% by volume.

9. A method according to claim 1 , wherein the feed comprising hydrogen gas also comprises methane gas.

10. A method for reducing the continuous emission of ammonia from a plant for the production of a urea melt, wherein the plant comprises a urea synthesis section, wherein the urea synthesis section has an outlet for urea solution and an outlet for gas, and
wherein the plant further comprises an incinerator and downstream of said outlet for urea solution one or more downstream processing units in which said urea solution is subjected to concentration so as to form concentrated urea and inert vapor that contains ammonia is released,
wherein in said plant urea is produced by subjecting, in said urea synthesis section, ammonia and a feed containing carbon dioxide and hydrogen to reaction under urea-forming conditions so as to form an aqueous urea solution without substantial combustion of said hydrogen contained in said carbon dioxide feed;
said method comprising supplying hydrogen-containing gas from said outlet for gas to said incinerator,
supplying said inert vapor that contains ammonia to said incinerator, and
subjecting said hydrogen-containing gas and inert vapor that contains ammonia to combustion in said incinerator together with oxygen or air.

11. A method according to claim 10 , wherein the synthesis section is made of a duplex ferritic-austenitic stainless steel having a content of Cr of at least 28 wt % and N of at least 0.2 wt %, and a content of Ni of no more than 10 wt %.

12. A method according to claim 10 , wherein the carbon dioxide feed and the effluent contain methane.

13. A method according to claim 1 , wherein said gas comprising hydrogen is obtained from a urea reactor in said urea synthesis section, wherein urea is formed in said urea reactor.

14. A method according to claim 1 , wherein said ammonia is obtained from one or more of said downstream processing units, wherein said units are selected from the group consisting of an atmospheric absorber, a breathing system of urea storage and a breathing system of a process condensate storage.

15. A method according to claim 1 , wherein the urea synthesis is conducted at 12-40 MPa and 150°-250° C. in a total recycle process.

Assignees

• Mennen Johannes Henricus
• Cucchiella Barbara
• Stamicarbon

Inventors

• Mennen Johannes Henricus
• Cucchiella Barbara

Classifications

• B01J19/24

  Stationary reactors without moving elements inside (B01J19/08, B01J19/26 take precedence; with stationary particles B01J8/02) · CPC title

• C07C273/04 Primary

  from carbon dioxide and ammonia · CPC title