Integrated production of urea and melamine

Patent metadata

Field	Value
Publication number	US-9981924-B2
Application number	US-201715692715-A
Country	US
Kind code	B2
Filing date	Aug 31, 2017
Priority date	Dec 17, 2013
Publication date	May 29, 2018
Grant date	May 29, 2018

Abstract

Disclosed is a process for the integrated production of urea and melamine. A urea production zone produces a urea synthesis stream comprising urea, water and ammonium carbamate. This stream is subjected to processing, preferably involving stripping, so as to separate an aqueous urea stream from residual dissociated carbamate vapor comprising ammonia, carbon dioxide, and water. The urea is fed to a melamine synthesis zone and subjected to melamine forming conditions so as to form melamine and off-gas comprising carbon dioxide and ammonia. The dissociated carbamate vapor and the melamine off-gas are subjected to combined condensation so as to form a dilute melamine off-gas condensate.

First claim

The invention claimed is:

1. A process for the integrated production of urea and melamine, the process comprising:
(i) subjecting carbon dioxide and ammonia to urea forming conditions in a urea production zone, so as to form a urea synthesis stream comprising urea, water and ammonium carbamate; wherein the urea production zone comprises a urea synthesis section that comprises a reactor and a stripper,
(ii) subjecting the urea synthesis stream to processing so as to obtain an aqueous urea stream and a vapor comprising ammonia, carbon dioxide, and water; wherein said processing comprises stripping in said stripper,
(iii) feeding urea to a melamine production zone;
(iv) subjecting the urea fed to the melamine production zone to melamine forming conditions so as to form melamine and melamine off-gas comprising carbon dioxide and ammonia;
(v) feeding the off-gas to the urea production zone;
(vi) subjecting the vapor and the melamine off-gas to combined condensation in indirect heat exchange with the aqueous urea stream thus forming a combined stream of the condensate of the vapor from said processing of (ii) and the condensate of the off-gas, so as to provide a dilute melamine off-gas condensate; and
(vii) thus using said dilute melamine off-gas condensate as a fluid in said indirect heat-exchange.

2. The process of claim 1 , wherein in said indirect heat exchange the aqueous urea stream is concentrated by heat-induced evaporation.

3. The process of claim 2 , wherein the indirect heat exchange is carried out in a shell and tube heat exchanger, the vapor and the melamine off-gas being fed to the shell side of the heat exchanger, and the aqueous urea solution to the tube side thereof.

4. The process of claim 1 , wherein the vapor is set to have a pressure sufficiently equal to the pressure of the melamine off-gas to allow combination in the gas phase.

5. The process of claim 1 , wherein the dilute melamine off-gas condensate is recirculated to the urea synthesis section.

6. The process of claim 1 , wherein the urea synthesis section further comprises a condenser and a scrubber, wherein the operating pressure in the urea synthesis section is between 12 and 20 MPa.

7. The process of claim 1 , wherein the dilute condensate contains of from 20 wt. % to 35 wt. % of water.

8. The process of claim 1 , wherein the processing so as to obtain an aqueous urea stream and a vapor comprising ammonia, carbon dioxide, and water, further comprises subjecting the stripped urea synthesis stream to adiabatic flashing, wherein gas from the adiabatic flashing is sent to the combined condensation, wherein liquid from the adiabatic flash is sent to a carbamate recirculation section comprising an inlet for stripped and flashed aqueous urea solution and a liquid/gas separation section, and wherein the process further comprises supplying the dilute melamine off-gas condensate comprising carbamate to said reactor.

9. A method for reducing the energy consumption of a urea production zone of a pre-existing facility for the integrated production of urea and melamine, said facility comprising a urea production zone and a melamine production zone; the urea production zone comprising a urea synthesis section and a carbamate recirculation section, wherein the urea synthesis section comprises a reactor and a stripper, and wherein the carbamate recirculation section comprises an inlet for stripped aqueous urea solution and a liquid/gas separation section; the melamine production zone comprising a melamine synthesis section and an off-gas separation section,
the method comprising
(i) adding a concentrator to the urea production zone, said concentrator comprising an evaporation chamber for liquid to be heated and evaporated, said evaporation chamber comprising a gas outlet for evaporated liquid and being in heat-exchanging communication with a chamber for indirect heat exchange;
(ii) providing a transport line for liquid feed from the liquid/gas separation section of the urea plant to said evaporation chamber; providing a gas flow-line from the liquid/gas separation section of the urea plant to a condensation system, said condensation system comprising a liquid outlet in fluid communication with the chamber for indirect heat exchange; and
(iii) providing a gas flow-line from the off-gas separation section of the melamine production zone to the condensation system, wherein said condensation system is configured for subjecting the vapor from the liquid/gas separation and the melamine off-gas to combined condensation in indirect heat exchange with the aqueous urea stream.

10. A method of increasing the plant capacity of the melamine production zone of a pre-existing facility for the integrated production of urea and melamine, said facility comprising a urea production zone and a melamine production zone; the urea production zone comprising a urea synthesis section and a carbamate recirculation section, wherein the urea synthesis section comprises a reactor and a stripper, and wherein the carbamate recirculation section comprises an inlet for stripped aqueous urea solution and a liquid/gas separation section; the melamine production zone comprising a melamine synthesis section and an off-gas separation section,
the method comprising
(i) expanding the melamine synthesis capacity of the melamine synthesis section;
(ii) adding a concentrator to the urea production zone, said concentrator comprising an evaporation chamber for liquid to be heated and evaporated, said evaporation chamber comprising a gas outlet for evaporated liquid and being in heat-exchanging communication with a chamber for indirect heat exchange;
(iii) providing a transport line for liquid feed from the liquid/gas separation section of the urea plant to said evaporation chamber; providing a gas flow-line from the liquid/gas separation section of the urea plant to a condensation system, said condensation system comprising a liquid outlet in fluid communication with the chamber for indirect heat exchange; and
(iv) providing a gas flow-line from the off-gas separation section of the melamine production zone to the condensation system, wherein said condensation system is configured for subjecting the vapor from the liquid/gas separation and the melamine off-gas to combined condensation in indirect heat exchange with the aqueous urea stream.

Assignees

• Stamicarbon

Inventors

• Mennen Johannes Henricus

Classifications

• C07C273/12

  combined with the synthesis of melamine · CPC title

• C07D251/62

  Purification of melamine · CPC title

• B01J19/245 Primary

  placed in series · CPC title

• B01J2219/24

  Stationary reactors without moving elements inside · CPC title

• B01J2219/00103

  in a heat exchanger separate from the reactor · CPC title