US-20260124595-A1 - UREA PLANT WITH MODIFIED CONDENSER AND MODIFIED REACTOR INTERNALS

US20260124595A1US 20260124595 A1US20260124595 A1US 20260124595A1US-20260124595-A1

Abstract

The disclosure pertains to a modification of a stripping-type urea plant by replacing the falling-film type HP carbamate condenser with a horizontal submerged condenser in combination with modification of the reactor internals, thereby permitting to maintain gravity flow in the modified plant.

Inventors

Wilhelmus Hubertus GEURTS
Paul Wilhelmus Maria MEIJBOOM

Assignees

STAMICARBON B.V.

Dates

Publication Date: 20260507
Application Date: 20250320
Priority Date: 20240320

Claims (20)

1 . A method of modifying an existing urea plant, wherein the existing urea plant comprises a high-pressure (HP) synthesis section comprising: a vertical urea reactor; a stripper having an inlet for gaseous CO 2 feed; a falling-film high-pressure carbamate condenser configured to receive gas from the stripper, wherein the falling-film high-pressure carbamate condenser is a falling-film shell-and-tube heat exchanger having a bottom outlet from the tubes connected to a bottom inlet of the reactor, wherein the reactor comprises one or more feed pipes for fluid from the condenser, the one or more feed pipes having an outlet at a first vertical level in the reactor; wherein the method involves: replacing the high-pressure carbamate condenser by a replacement carbamate condenser that is a horizontal submerged condenser which is a shell-and-tube heat exchanger with a tube bundle and with a shell side space, configured for condensation in the shell side space, preferably wherein the replacement condenser is a pool condenser; and modifying at least one of the one or more feed pipes of the reactor to have an outlet at a second vertical level that is higher than the first vertical level, preferably modifying the one or more feed pipes of the reactor to have an outlet at a second vertical level that is higher than the first vertical level.
2 . The method according to claim 1 , wherein modified plant has a liquid flow line for condensate from the condenser to a first feed pipe of the reactor and a separate gas flow line from the condenser to a second feed pipe of the reactor, and the method involves modifying the second feed pipe to have an outlet at the second vertical level that is higher than the first vertical level.
3 . The method according to claim 1 , wherein the replacement carbamate condenser has a horizontal tube bundle, preferably a U-shaped tube bundle, and wherein the distance from the second vertical level to the bottom of the reactor is at least equal to (equal to or larger than) the height of said tube bundle.
4 . The method according to claim 1 , wherein the method involves providing the reactor with an inlet for an oxygen-containing fluid in a bottom reactor compartment that is provided between the reactor bottom and the second vertical level.
5 . The method according to claim 4 , wherein the method involves providing the reactor with a vertical divider in the bottom reactor compartment, wherein the vertical divider separates a first compartment from a second compartment between the vertical divider and the reactor wall, and wherein the vertical divider is arranged for receiving said oxygen-containing fluid and liquid from said second compartment into said first compartment at a bottom of said vertical divider.
6 . The method according to claim 5 , wherein said vertical divider is a vertical tubular divider.
7 . The method according to claim 5 , wherein a feed pipe extends through said first compartment, preferably wherein said second feed pipe extends through the vertical tubular divider.
8 . The method according to claim 1 , wherein the first vertical level is the same as the vertical level of the bottom outlet of the falling-film HP carbamate condenser.
9 . The method according to claim 1 , wherein the first vertical level is the same as the bottom of the shell side space of the replacement carbamate condenser.
10 . The method according to claim 1 , wherein the second vertical level is at a higher elevation than the upper tubes of the tube bundle of the horizontal submerged condenser.
11 . A urea plant comprising a high-pressure synthesis section comprising: a vertical urea reactor comprising a first and a second feed pipe; a stripper having an inlet for gaseous CO 2 feed; a high-pressure carbamate condenser configured to receive gas from the stripper, wherein the high-pressure carbamate condenser is a horizontal submerged shell-and-tube heat exchanger with condensation of gas from the stripper in the shell, having a horizontal tube bundle, preferably wherein the high-pressure carbamate condenser is a pool condenser, and a liquid flow line for condensate from the condenser to a first feed pipe of the reactor and a separate gas flow line from the condenser to a second feed pipe of the reactor; wherein the vertical distance between the outlet of the second feed pipe for gas to the bottom of the reactor is at least equal to (equal to or larger than) the height or diameter of said tube bundle.
12 . A urea plant according to claim 11 , wherein the outlet of the second feed pipe is located vertically at the same height, or higher than, the liquid outlet of the high-pressure carbamate condenser; and preferably the outlet of the first feed pipe as well.
13 . A urea plant according to claim 11 , wherein the bottom of the high-pressure carbamate condenser and the bottom of the reactor are at the same vertical level of the urea plant.
14 . A urea plant according to claim 11 , wherein the reactor comprises an inlet for an oxygen-containing fluid in a bottom reactor compartment that is provided between the reactor bottom and the second vertical level.
15 . A urea plant according to claim 11 , wherein the reactor comprises internal supply means for introducing additional fluid into the reactor vertically between the bottom of the reactor and the point of introduction of the gas and liquid from the pool condenser.
16 . A urea plant according to claim 11 , wherein the reactor comprises a vertical divider in the bottom reactor compartment, wherein the vertical divider separates a first compartment from a second compartment between the vertical divider and the reactor wall, and wherein the vertical divider is arranged for receiving said oxygen-containing fluid and liquid from said second compartment into said first compartment at a bottom of said vertical divider; preferably wherein said vertical divider is a vertical tubular divider.
17 . A urea plant according to claim 16 , wherein a feed pipe extends through said first compartment, preferably wherein said second feed pipe extends through said first compartment, preferably wherein said first compartment is provided by the inner space of the vertical tubular divider.
18 . A urea production plant according to claim 11 , wherein the horizontal submerged shell-and-tube heat exchanger comprises a capped horizontal cylindrical vessel holding the horizontal tube bundle, and the vertical distance between the outlet of the second feed pipe for gas to the bottom of the reactor is equal to or larger than the diameter of said horizontal cylindrical vessel.
19 . A urea production process carried out in a plant according to claim 11 , comprising supplying CO 2 feed to said stripper and NH 3 to said high-pressure carbamate condenser, and operating the high-pressure synthesis section under a pressure of at least 100 bar to form urea.
20 . A urea production process according to claim 19 , wherein the flow of liquid from the condenser to the reactor and from the reactor to the stripper is gravity flow.

Description

FIELD The invention pertains to the production of urea. INTRODUCTION A frequently used type of urea production process is the so-called stripping process, wherein the high-pressure urea synthesis section comprises a reaction zone, a stripper, and a condenser. A background reference for such processes is Ullmann's Encyclopaedia of Industrial Chemistry, chapter Urea, 2010. This document mentions that some processes use a recycle flow purely based on gravity, i.e. to maintain the main recycle flow in the high-pressure (HP) loop of the synthesis section, formed by the flow from the stripper to the condenser, from the condenser to the reactor, and from the reactor to the stripper. The invention is particularly directed to the CO2 stripping type urea production process, wherein the urea solution from the reactor is stripped with feed CO2 gas in the stripper comprised in the high-pressure section. An early embodiment of the CO2 stripping type urea production process and plant is described in Kaasenbrood and Chermin, “The Urea Stripping Process”, Fertiliser Society, 1977. In the embodiment described therein, gas from the top of HP stripper flows to the head of the carbamate condenser. In the condenser tube the gas is partly condensed. The liquid-gas mixture leaving the condenser is introduced into the bottom of the reactor. Reactor, stripper, and condenser have a spatial arrangement such that the driving flow through these vessels is provided by variations in phase and hence fluid density, brought about by the supply of heat in the stripper and the withdrawal of heat in the condenser. The top of the stripper is about 10 m below the bottom of the reactor and the condenser. The reactor is operated adiabatically, which is realised by the condensation of the gas mixture from the condenser. FIG. 7 of Kaasenbrood 1977 shows that the condenser in that embodiment is a vertical shell-and-tube heat exchanger with steam raised in the shell and with gas from the stripper supplied to the top of the tube bundle and with an outlet at the bottom for supplying fluid to the bottom of the vertical reactor. The bottom of the reactor and of the condenser are at equal height. Liquid is withdrawn from the top of the reactor and supplied to the liquid inlet of the upper chamber of the stripper. An improved type of high-pressure condenser is described in EP0155735A1. Herein gas to be condensed is introduced to the shell-side of a shell-and-tube heat exchanger with a horizontal tube bundle, in particular with a U-shaped tube bundle, wherein in operation continuous liquid phase is maintained in the shell side compartment. Thereby the condenser operates as a horizontal submerged condenser. The bottom of the vertical reactor is shown as substantially the same height as the fluid outlet of the pool condenser, which is located in a top part of the pool condenser. It is often desired to increase the capacity of existing urea plants, making maximum use of the existing equipment and with minimum modifications. Such projects are known as ‘revamps’ in the art. Furthermore, a number of existing urea plants of the CO2 stripping type with a falling-film high-pressure carbamate condenser are still operating. The present invention in an aspect aims to provide a revamp method for such urea plants. EP1036787A1 discusses a revamping method wherein a falling-film type condenser of the HP synthesis section is modified into a vertical submerged condenser. A further reference for such a method is US20080242890A1. US2015343409A1 mentions as a known way of increasing the reactor volume of an existing plant, to replace “the HPCC” (high-pressure carbamate condenser) with a pool condenser. It is said that this requires a complicated equipment design. The document proposes to increase by installing an additional reactor. US20030088126A1 FIG. 4B shows a plant with a pool condenser, with fluid from the condenser being supplied to the bottom of an upper compartment of a vertical combination reactor. Gas from the bottom compartment of the vertical combination reactor is released into the upper compartment. An ejector is used to supply a part of the gas from the stripper to the bottom compartment of the vertical combination reactor. EP0329215A1 shows a urea process with a HP CO2 stripper, a vertical reactor, and a condenser. Liquid from the condenser is supplied to the bottom of the reactor, gas from the condenser is supplied to a HP scrubber. A part of the gas from the stripper is supplied to the bottom of the reactor using an ejector driven by a part of the ammonia feed. Gas from the reactor top is supplied to the condenser. The document explains that if the line connecting the condenser with the reactor as well as the line from the rector to the stripper are filled with liquid, these equipment items function as communicating vessels, enabling liquid transport by gravity from the condensation zone through the reaction zone to the stripping zone. Non-condensed gas from th