Method and system for the integrated production of urea and melamine

Patent metadata

Field	Value
Publication number	US-10358413-B2
Application number	US-201615568795-A
Country	US
Kind code	B2
Filing date	Apr 25, 2016
Priority date	Apr 23, 2015
Publication date	Jul 23, 2019
Grant date	Jul 23, 2019

Abstract

Disclosed is an integrated process for the production of urea and melamine, as well as a system for carrying out the process. The invention thereby pertains to an integrated process of the type wherein off-gas obtained from the production of melamine is entered into the process for the production of melamine, by condensation in the presence of water. A typical embodiment thereof is the condensation in the presence of an aqueous carbamate solution obtained from urea recovery. In accordance with the invention, said condensation takes place at a substantially lower pressure than the pressure at which the melamine off-gas is obtained. To this end, the pressure of the off-gas is reduced typically by 2-10 bar. In connection herewith, the system of the invention comprises a pressure reducing unit downstream of an outlet for the melamine off-gas, and upstream of a section for the condensation of the off-gas. The invention also includes a method for the modernization of an integrated system for the production of melamine and urea. This is accomplished by adding the aforementioned pressure reducing unit to a pre-existing system.

First claim

The invention claimed is:

1. An integrated process for the production of urea and melamine, the process comprising:
(a) subjecting ammonia and carbon dioxide to urea forming conditions so as to obtain an aqueous urea synthesis solution;
(b) subjecting said urea synthesis solution to recovery of unreacted ammonia and carbon dioxide, thereby obtaining aqueous carbamate solution and urea;
(c) producing melamine in a melamine plant, whereby off-gas resulting from the melamine synthesis is obtained at a pressure of 15 to 35 bar;
(d) feeding obtained urea to the melamine plant as a starting material for producing the melamine;
(e) condensing said off-gas in the presence of water so as to form an aqueous carbamate solution;
(f) recycling carbamate obtained from said off-gas and carbamate obtained from said urea recovery section to the urea synthesis section as a starting material in producing urea;
wherein prior to condensation the pressure of the off-gas is reduced so as to be controlled at a pressure in a range of from 2 bar to 10 bar lower than the pressure at which the off-gas is obtained.

2. The process of claim 1 , wherein the reduction of pressure is conducted downstream of the melamine plant.

3. The process of claim 1 , wherein the reduction of pressure is in a range of from 2 bar to 5 bar lower than the pressure at which the off-gas is obtained.

4. The process of claim 1 , wherein the reduced pressure is controlled so as to be rectified with a margin of 2-5 bar.

5. The process of claim 1 , wherein the pressure of the gas subjected to condensation is in a range of from 18 bar to 24 bar.

6. The process of claim 1 , wherein the water in the presence of which the off-gas is condensed, comprises water vapor contained in the off-gas.

7. The process of claim 1 , wherein the water in the presence of which the off-gas is condensed, comprises water contained in the aqueous carbamate solution obtained by recovery from the urea synthesis solution.

8. The process of claim 1 , wherein the water in the presence of which the off-gas is condensed comprises water obtained from adiabatic expansion of the aqueous urea synthesis solution.

9. A system for the production of urea and melamine, said system comprising:
(a) a urea production zone; said urea production zone comprising a high pressure urea synthesis section and, downstream thereof and in fluid communication therewith, a low pressure urea recovery section adapted to separately obtain a urea solution and an aqueous carbamate solution;
(b) a melamine production zone; said melamine production zone comprising a high pressure melamine synthesis section and, downstream thereof and in fluid communication therewith, a melamine off-gas treatment section for obtaining melamine off-gas;
said urea production zone and melamine zone being connected with each other so as to allow transport of urea solution obtained from the urea recovery section to the melamine synthesis section and to allow transport of melamine off-gas from the melamine off-gas treatment section to the urea production zone, wherein the urea production zone comprises a medium pressure condensation section adapted to receive said melamine off-gas, said condensation section having an outlet for condensed carbamate which is in fluid communication with an inlet of the urea synthesis section and in fluid communication therewith, and
(c) a pressure control device between the melamine off-gas treatment section and the medium pressure condensation section.

10. The system of claim 9 , comprising a connection from the urea recovery section to the medium pressure condensation section, said connection provided with a pressure control device, so as to allow feeding the aqueous carbamate solution from the recovery section to the medium pressure condensation section.

11. The system of claim 9 , comprising, downstream of the urea synthesis section and upstream of the urea recovery section, and in fluid communication with both sections, a unit for subjecting a synthesis solution obtained from the urea synthesis section to adiabatic expansion, whereby the unit for adiabatic expansion has a gas outlet adapted to transport vapor released by adiabatic expansion to the medium pressure condensation section.

12. The system of claim 9 , wherein the urea and melamine production zones are separate plants.

13. A method for the modernization of a urea plant comprising a high pressure urea synthesis section and, downstream thereof and in fluid communication therewith, a low pressure urea recovery section adapted to separately obtain a urea solution and an aqueous carbamate solution, the method comprising
connecting the urea plant with a melamine plant comprising a high pressure melamine synthesis section and, downstream thereof and in fluid communication therewith, a melamine off-gas treatment section for obtaining melamine off-gas;
said plants being connected with each other so as to allow transport of urea solution obtained from the urea recovery section to the melamine synthesis section and to allow transport of melamine off-gas from the melamine off-gas treatment section to the urea plant,
the method further comprising adding a medium pressure condensation section adapted to receive said melamine off-gas, said condensation section having an outlet for condensed carbamate which is in fluid communication with an inlet of the urea synthesis section, and providing a pressure reducing device between the melamine off-gas treatment section and said medium pressure condensation section.

14. A method for the modernization of a pre-existing system for the production of urea and melamine, said pre-existing system comprising a urea production zone and a melamine production zone;
said urea production zone comprising a high pressure urea synthesis section in fluid communication with a low pressure urea recovery section adapted to separately obtain urea and an aqueous carbamate solution, and, downstream thereof and in fluid communication therewith via a pressure increasing unit, a medium pressure condensation section;
said melamine production zone comprising a high pressure melamine synthesis section and, downstream thereof and in fluid communication therewith, a melamine off-gas treatment section for obtaining melamine off-gas;
said production zones being connected with each other so as to allow transport of urea solution obtained from the urea recovery section to the melamine synthesis section and to allow transport of melamine off-gas from the melamine off-gas treatment section to the medium pressure condensation section;
the method comprising providing a pressure control device, adapted to be used as a pressure reducing unit, between the melamine off-gas treatment section and the medium pressure condensation section.

15. The process of claim 3 , wherein the reduction of pressure is in a range of from 3 bar to 4 bar.

16. The process of claim 4 , wherein the reduced pressure is controlled so as to be rectified with a margin of 3-4 bar.

17. The process of claim 5 , wherein the pressure of the gas subjected to condensation is in a range of from 20 bar to 22 bar.

18. The system of claim 9 , wherein the transport of urea solution obtained from the recovery section is via an evaporation section.

19. The method of claim 13 , wherein transport of the urea solution obtained from the urea recovery section is via an evaporation section.

20. The method of claim 14 , wherein the pressure increasing unit is a pump.

21. The method of claim 14 , w

Assignees

• Stamicarbon

Inventors

• Mennen Johannes Henricus

Classifications

• C07D251/62

  Purification of melamine · CPC title

• C07D251/60

  from urea or from carbon dioxide and ammonia · CPC title

• C07C273/12 Primary

  combined with the synthesis of melamine · CPC title

• B01J2219/24

  Stationary reactors without moving elements inside · CPC title

• B01J2219/00024

  Revamping, retrofitting or modernisation of existing plants · CPC title