阅读说明：本技术 高压氨基甲酸盐冷凝器 (High pressure carbamate condenser ) 是由 D·波帕 于 2018-10-26 设计创作，主要内容包括：本发明描述了高压氨基甲酸盐冷凝器、尿素装置和尿素生产方法。如所述的高压氨基甲酸盐冷凝器为具有管束的管壳式换热器类型,并且具有连接到所述管束的管和管道的再分配室。管道在所述再分配室和所述壳体之间延伸。(The invention describes a high-pressure carbamate condenser, a urea plant and a urea production process. The high-pressure carbamate condenser as described is of the shell-and-tube heat exchanger type with a tube bundle and has a redistribution chamber of tubes and pipes connected to said tube bundle. A conduit extends between the redistribution chamber and the housing.)

1. A high-pressure carbamate condenser (100) comprising a shell-and-tube heat exchanger (101) comprising a vessel (102) comprising a shell (1) and at least one tube bundle (103), wherein the shell (1) encloses a vessel space (104), wherein the tube bundle (103) comprises tubes (2) having ends (3), and wherein a shell space (105) is arranged between the tubes (2) and the shell (1),

wherein the heat exchanger further comprises a redistribution chamber (7) in the container space (104), wherein the redistribution chamber comprises a wall (8) for separating a first fluid in the housing space (105) from a second fluid inside the redistribution chamber (7),

wherein a plurality of said tubes (2a,2b) are connected to a single redistribution chamber (7) such that said second fluid is flowable between said tubes (2a,2b) and said redistribution chamber (7),

wherein the condenser (100) further comprises a conduit (9) extending from an opening (10) of the second fluid in the housing (1) through the container space (104) to the redistribution chamber (7) such that the second fluid can flow between a tube end (3) and the opening (10) of the second fluid in the housing through the redistribution chamber (7) and the conduit (9).

2. The high-pressure carbamate condenser according to claim 1,

configured for condensing carbamate in said shell space (105),

wherein the container comprises a gas inlet (4) to the housing space (105) and an outlet (5) for liquid from the housing space (105),

wherein the vessel further comprises a gas distributor (6) connected to the gas inlet (5) for distributing gas to be condensed in the shell space.

3. The high-pressure carbamate condenser according to claim 2,

wherein the condenser comprises at least two of said conduits including an inlet conduit and an outlet conduit, and at least two of said redistribution chambers including an inlet redistribution chamber for distributing a cooling fluid feed from said inlet conduit to a plurality of tubes and an outlet redistribution chamber for combining heated cooling fluid from a plurality of tubes to said outlet conduit.

4. The high-pressure carbamate condenser according to claim 3, wherein said condenser is configured for horizontal positioning in operation, wherein said tube comprises or consists of straight tube portions, and wherein said gas distributor and said straight tube portions are arranged in parallel, and wherein preferably said tube bundle comprises U-shaped tubes, wherein each tube has a bend and two legs.

5. The high-pressure carbamate condenser of any one of claims 2-4, wherein the shell comprises a substantially cylindrical middle portion and two cap portions closing the middle portion at opposite ends,

and wherein the housing space is a single housing space defined by the middle portion and the cap portions such that fluid can flow from the gas distributor to both of the cap portions.

6. The high-pressure carbamate condenser according to any one of the preceding claims, wherein said redistribution chamber comprises a plurality of elements providing walls of said redistribution chamber, and wherein at least one of said elements is openable and closable for providing access to an interior of said redistribution chamber.

7. The high-pressure carbamate condenser according to any one of the preceding claims,

-wherein a plurality of redistribution chambers are stacked on top of each other,

-and wherein the plate member having a bore is common to the plurality of redistribution chambers.

8. The high-pressure carbamate condenser according to claim 7,

wherein the tube bundle comprises U-shaped tubes, wherein each tube has a bend and two legs, and wherein the plurality of redistribution chambers comprises inlet and outlet redistribution chambers of the same U-shaped tube bundle, arranged in the same stack of redistribution chambers.

9. A urea production plant comprising a high pressure urea synthesis section comprising a reactor, a stripper and a high pressure carbamate condenser, wherein the high pressure carbamate condenser is according to any one of the preceding claims, and wherein optionally the reactor and the high pressure carbamate condenser are combined in a single vessel, wherein a vessel has a liquid outlet connected to the stripper.

10. Urea production plant according to claim 9, wherein the high pressure carbamate condenser comprises a tube bundle connected by redistribution chambers and piping to a feed line for a urea solution further comprising carbamate, wherein the feed line is connected to the stripper for receiving stripped urea solution from the stripper and/or wherein the feed line is connected to the reactor for receiving a portion of the urea solution from the reactor.

11. Urea production plant according to claim 10, wherein the feed line comprises an expansion device and a gas/liquid separator for separating gas from the expanded urea solution, and wherein the feed line is configured for supplying at least a part of the expanded urea solution to the piping.

12. Urea production plant according to claim 10 or 11, wherein the tube bundle is connected by means of a redistribution chamber and a conduit to a gas/liquid separator having a liquid flow connection to the recovery section and a gas flow connection to the second condenser,

preferably wherein said second condenser is operated at medium pressure, and preferably wherein said second condenser is in heat exchange contact with an evaporation section of said urea plant, and preferably wherein said second condenser preferably has a liquid stream connection for recycling carbamate to said high pressure carbamate condenser.

13. A process for urea production, wherein urea is formed in a reactor to produce a urea synthesis solution, at least part of which is stripped in a stripper to produce a stripped urea solution, and wherein gases from the stripper are condensed in a high pressure carbamate condenser, wherein the process is carried out in an apparatus according to any one of claims 9-12, and/or wherein the high pressure carbamate condenser is according to any one of claims 1-8.

14. Process for urea production according to claim 13, wherein at least one of said tubes is contacted with a solution comprising carbamate on both the inside and the outside of said tube, and wherein said tubes of at least one tube bundle are contacted with a solution comprising carbamate on both the inside and the outside.

15. Process for urea production according to claim 14, wherein the gases from the stripper are supplied to the shell space of the condenser, wherein at least a part of the stripped urea solution and/or a part of the urea synthesis solution not sent to the stripper are expanded while also containing carbamate, and wherein at least a part of the expanded urea solution is supplied, optionally after gas/liquid separation, to tube bundles of the high pressure carbamate condenser through ducts and redistribution chambers as defined in claim 1, and is heated in the tube bundles by heat exchange with a condensing process medium in the shell space, such that carbamate in the urea solution is decomposed in the tube bundles.

Background

A common type of carbamate condenser is the pool condenser described in "a lower cost design for urea", Nitrogen, No. 222, 1996, months 7-8, pages 29-31. Such pool condensers comprise tube sheets. The tube sheet is more generally a typical component of a high pressure carbamate condenser of the shell and tube heat exchanger type. The tube sheet is typically a planar metal plate that defines the shell space in the condenser from the header. In addition, the tubesheet seals one end of the typically cylindrical shell. The tube sheet is provided with a plurality of bores. The tubes are inserted or joined through the bores to the tubesheet aligned with the apertures so that fluid can flow between the headers and the tubes. The tube bundle typically has a large number of tubes, for example more than 100 tubes or even more than 1000 tubes. The header is used to distribute fluid from the inlet to the plurality of tubes or to collect fluid from the plurality of tubes to the outlet.

In known carbamate condensers, the tube sheets generally need to be able to withstand high pressures. Furthermore, preventing corrosion is a challenge because carbamates are highly corrosive, especially at the high temperatures of high pressure carbamate condensation. In order to achieve high mechanical strength and high corrosion resistance, known tube sheets are typically made of carbon steel lined on the side (or sides) exposed to the corrosive medium with a layer of highly corrosion resistant steel, such as a duplex stainless steel alloy. This increases construction costs, for example, due to the difficulty in welding the tubes to the tubesheet.

Known tube sheets for kettle carbamate condensers used in urea plants are shown in EP 0464307 and US 4082797.

The construction of tubesheets is generally challenging and expensive. The present invention generally addresses the disadvantages of known high pressure carbamate condensers with tube sheets, such as the high construction costs associated with the tube sheets.

Disclosure of Invention

Accordingly, the present invention relates in a first aspect to a high pressure carbamate condenser comprising a shell-and-tube heat exchanger, the shell-and-tube heat exchanger comprising a vessel, the vessel comprising a shell and at least one tube bundle, wherein the shell encloses a vessel space, wherein the tube bundle comprises tubes having ends, and wherein a shell space is provided between the tubes and the shell, wherein the heat exchanger further comprises a redistribution chamber located in the vessel space, wherein the redistribution chamber comprises walls for separating a first fluid in the shell space from a second fluid inside the redistribution chamber, wherein a plurality of the tubes are connected to a single redistribution chamber such that the second fluid can flow between the tubes and the redistribution chamber, wherein the condenser further comprises a tube extending from an opening of the second fluid in the shell through the vessel space to the redistribution chamber, enabling the second fluid to flow between a tube end and the opening of the second fluid in the housing through the redistribution chamber and the conduit.

The invention also relates to a urea production plant comprising a high pressure urea synthesis section comprising a reactor, a stripper and a high pressure carbamate condenser, wherein the high pressure carbamate condenser is as described and wherein optionally the reactor and the high pressure carbamate condenser are combined in a single vessel, wherein the vessel has a liquid outlet connected to the stripper.

The invention also relates to a process for urea production, wherein urea is formed in a reactor to produce a urea synthesis solution, at least a part of which is stripped in a stripper to produce a stripped urea solution, and wherein gases from said stripper are condensed in a high pressure carbamate condenser, wherein said process is carried out in said plant, and/or wherein said high pressure carbamate condenser is as described.

More generally, the invention also relates to a shell-and-tube heat exchanger comprising such a vessel and comprising such a shell, a tube bundle, a redistribution chamber and a tube. The shell-and-tube heat exchanger is for example configured for the condensation of compounds other than carbamate and/or for operating at a pressure lower than 100 bar and/or for heat exchange processes other than condensation. The heat exchanger can be used in urea production as well as other plants and processes.

Drawings

Figure 1 shows a reference carbamate condenser with a tube sheet not according to the invention.

Figure 2 shows an example of a high-pressure carbamate condenser according to the invention.

Fig. 3 schematically shows an example of a urea plant according to the invention.

Detailed Description

In the present application, the High Pressure (HP) is higher than 100 bar, for example 120 bar to 300 bar, typically 150 bar to 200 bar, for the process stream (i.e. not for the steam line). The Medium Pressure (MP) is, for example, 10 to 70 bar (including medium pressures of 30 to 70 bar), in particular 15 to 25 bar, and the Low Pressure (LP) is, for example, 0 to 10 bar, in particular 1 to 8 bar or 2 to 5 bar. As used herein, "carbamate" refers to ammonium carbamate.

In contrast to falling film condensers, high pressure carbamate condensers are preferably submerged condensers. In the operation of a submerged condenser, condensation takes place in a space where liquid is the continuous phase and the gas to be condensed is dispersed in the liquid. The liquid level is thus present in the condensation space. For example, the tubes are covered (on the inside or outside of the tubes) with condensed liquid when in operation, and the tubes are preferably immersed in the condensed liquid. A submerged condenser, including a shell-and-tube heat exchanger, is configured for condensation within the interior of the tubes or shell space. Suitably, the condensation takes place in the shell space. The housing space is an empty space to which the outer surface of the tube is exposed. The housing space is defined by the housing. Condensation in the shell space is an option for providing a relatively simple construction, wherein the condensate has a sufficient residence time in the condenser. This advantageously allows a portion of the urea to already be formed in the condenser. In case of condensation in the tubes, it is also possible to provide a longer residence time by using more tubes and/or tubes with a larger diameter.

The condenser is for example a high-pressure carbamate condenser, which is configured as a submerged condenser, wherein the condensation takes place in the shell space, for example based on a pool condenser design, but is modified to have one or more such redistribution chambers and pipes. An exemplary pool condenser design is shown in Nitrogen, No. 222, 7-8 months 1996, pages 29-31. Preferably, the cooling fluid is provided in a tube. In the present invention, the cooling fluid is, for example, a process stream, such as a solution comprising urea and carbamate, which is heated while passing through the tubes, and, in addition, optionally, water (process condensate) is also used as cooling fluid.

The high-pressure carbamate condenser has, for example, a vertical configuration, wherein (the straight portion of) the tubes are arranged vertically with respect to gravity when installed in a urea plant. Generally, the upright carbamate condenser is configured for condensation in a shell space or tube, preferably in a shell space. The condenser has, for example, a U-shaped or straight tube bundle, preferably a U-shaped tube bundle. For example, a vertical carbamate condenser of the type described in US 6518457 and/or with a tube bundle having tube ends at the bottom can be improved with the redistribution chamber and the tubes according to the invention. Furthermore, a vertical condenser with a tube bundle having a tube end at the top can be provided with redistribution chambers and tubes according to the invention, which are placed, for example, at the top of the condenser.

The high-pressure carbamate condenser preferably has a horizontal configuration, wherein (the straight portion of) the tubes are arranged horizontally with respect to gravity when installed in a urea plant. For example, a high-pressure carbamate condenser with a horizontal orientation can be configured for condensation in the tubes and for receiving the cooling fluid in the shell space. For example, a kettle carbamate condenser (e.g., as described in EP 0464307 or US 4899813) can be modified using redistribution chambers and piping as described herein.

In one embodiment, the condenser is configured as a horizontal submerged condenser. This advantageously allows the height of the device to be reduced. In a preferred embodiment, the condenser is configured as a horizontal immersion condenser, which operates with condensation taking place on the shell side (i.e. in the shell space). This provides the further advantage that the condenser volume can easily be designed for longer condensate residence times. This can also be used to form a pool reactor. The condensation on the shell side also results in a high pressure medium on the shell side, which makes the condenser easier to manufacture and in particular allows for a simpler design of the redistribution chamber.

Thus, in a preferred embodiment, the vessel comprises a gas inlet to the shell space for the gas to be condensed. The gas inlet comprises an opening in the housing. The gas inlet allows condensation to take place in the shell space and the cooling fluid to operate with the tubes. Furthermore, the vessel comprises an outlet for a flow of liquid, such as carbamate-containing liquid, from the shell space. The outlet includes an opening in the housing. The vessel preferably comprises a gas distributor connected to the gas inlet. The gas distributor preferably comprises a plurality of channels for gas to enter the housing space from the gas inlet. The gas distributor can be used for distributing the gas to be condensed above and into the housing space, in particular into the liquid when in operation. In operation, the gas distributor is preferably arranged below the liquid level. The gas distributor for example comprises a sparger having one or more tubes extending over the length of the container, said tubes being provided with arms extending over the width of the container at both sides of the tubes, wherein the arms have a number of openings for the gas at the upper side of the arms (e.g. more than 50 openings per arm). The gas to be condensed is, for example, CO-containing from a high-pressure stripper₂And NH₃A mixture of (a). Furthermore, the vessel preferably comprises a liquid inlet to the shell space for introducing a liquid stream comprising ammonia and/or a carbamate recycle stream into the shell space. In an exemplary embodiment, will be derived, for example, fromThe carbamate recycle stream of the medium-pressure section of the urea plant is introduced into the shell space at the top of the shell through an opening in the shell. This can provide improved mixing because the carbamate recycle liquid has a higher density than the condensed mixture in the shell space. The opening in the housing for carbamate recirculation is preferably spaced less than 1m in the length direction from the redistribution chamber. This provides good fluid mixing in the housing space near the redistribution chamber.

The carbamate condenser has for example a horizontal or vertical arrangement. In the case of horizontal carbamate condensers with gas distributors which are spaced apart in the horizontal direction, the gas distributors extend horizontally and parallel to (the straight parts of) the tubes in order to introduce the gas to be condensed into the shell space at the respective outlets of the gas distributors. In this embodiment, the length direction is also horizontal. The tube is preferably U-shaped.

The condenser preferably comprises a liquid distributor for distributing liquid into the shell space at a plurality of openings. The openings are preferably spaced apart in the length direction of the condenser. The liquid distributor is for example connected to an ammonia supply means, such as a liquid flow connection with a compressor leading to the ammonia feed. Typically, a liquid distributor (e.g. an ammonia distributor) is connected to an opening in the housing and, in operation, is for example immersed in the liquid present in the housing space.

The tube bundle generally comprises a plurality of tubes, wherein the tubes comprise or consist of straight tube portions. Typically, the straight portions of the tubes are arranged in parallel and spaced apart from each other. As used in this application, the tubes of a single tube bundle contain the same cooling fluid if condensation is performed in the shell. The redistribution chamber is therefore preferably connected to the tubes of the single tube bundle. In another embodiment, two or more cooling fluids are used in the tubes (with separate supply means), and the condenser comprises a plurality of tube bundles. The tube bundles can be combined into a combined tube bundle. The straight portions of all the tubes in the combined tube bundle are preferably parallel to each other.

In order to have a sufficient heat exchange surface, the high-pressure carbamate condenser has one or more tube bundles, wherein for example at least 300 tubes in total, usually 1000 to 4000 tubes in total, such as 1500 to 3000 tubes, in total, wherein for example at least 100 tubes in each tube bundle. The tube has, for example, a constant inner diameter over its length. Preferably, each redistribution chamber is connected to only the inlet end or the outlet end of a single tube bundle.

In some embodiments, the tube bundle comprises straight tubes having tube ends at opposite sides of the tube bundle in the length direction. A redistribution chamber can be provided at each end of the tube bundle. In principle, it is also possible to use a tube sheet at one end and a redistribution chamber at the opposite end. The tube bundle can be located anywhere along the length of the vessel, such as at the ends or center of the vessel. The length of the straight portion of the tube is for example 20-90% of the length of the container, such as preferably at least 30%, at least 40%, at least 50%, or at least 60%, and/or for example up to 90%, up to 80%, or up to 70% of the length of the container. In some embodiments, the length of the straight portion of the tube is 60% to 90% of the length of the vessel, and the condensate obtained by condensation in the condenser is preferably supplied to the high pressure reactor. In some embodiments, the length of the straight portion of the tube is 20% to 60% of the length of the vessel, and the condensate obtained by condensation in the condenser is preferably supplied to the high pressure stripper. For example, the condensate is supplied directly to the stripper, so that the high-pressure stripper receives condensate having the same composition as the liquid at the condenser outlet. In a urea plant according to such embodiments, the reactor and condenser are combined in a single vessel.

In some embodiments, the redistribution chamber is disposed at both ends of the tubes (preferably the tubes of a straight tube bundle) and the redistribution chamber is spaced apart from the vessel in the length direction at one or both ends of the tube bundle by a distance of at least 1%, at least 5%, at least 10% or at least 20% of the length of the vessel. At one or both ends of the tube bundle, the larger spacing between the redistribution chamber and the vessel creates a relatively larger shell space for condensate, and can contribute to a longer residence time of condensate in the shell space. This may allow urea formation to occur and, for example, allow operation in the form of a pool reactor. The condensed carbamate is typically sent to the urea reactor, and in some embodiments directly to the stripper when in operation. Especially for larger tube lengths (based on straight tube portions), such as 5m or more, 10m or more, 20m or more, or 30m or more, the manufacture of straight tubes can be simpler than U-tubes.

In another embodiment, the tube bundle is a bundle of U-shaped tubes, wherein each tube comprises a curved portion and two leg portions, the leg portions being straight tube portions. The carbamate condenser optionally includes a reactor section between the bends of the U-shaped tube bundle and the shell (as opposed to the tube legs), such as, but not limited to, in the case of a pool reactor. An exemplary pool reactor is described in US 5767313. The straight portions of the tubes of the U-tube bundle are arranged in the length direction of the shell. In some embodiments, the housing includes a substantially cylindrical middle portion having a diameter and a length, and having cap portions at both ends. In the case of a U-shaped tube bundle, a substantially hemispherical top cover (optionally with manholes), for example, is joined to the end of the middle portion near the tube bundle bend of the tube bundle and to the other end of the middle portion. In the prior art, for example as in US 5767313, tube sheets are provided at the ends remote from the bends of the U-shaped tube bundle to connect the tube ends with the feed and discharge lines via headers.

The present invention is broadly based on the insight that placing the redistribution chamber inside the shell and connecting the tubes of the tube bundle to the redistribution chamber and providing a conduit connecting the redistribution chamber with the feed or discharge line through an opening in the shell. The conduit is disposed inside the housing and spaces the redistribution chamber from the housing. The pipe is in operation in contact on one side with the cooling fluid and on the other side with the gas to be condensed and/or the condensate formed in the condenser. The same applies to the walls of the redistribution chamber. In embodiments where condensation is carried out on the shell side (outside the tubes), the shell is the part of the apparatus that contains the high pressure condensation medium and is in contact with this medium internally. On the outside, the housing is typically exposed to the environment.

In a typical embodiment, each tube of the tube bundle has two tube ends, and for each tube, one tube end is connected to the inlet redistribution chamber (for distributing fluid to the plurality of tubes) and the other tube end is connected to the outlet redistribution chamber (for collecting fluid from the plurality of tubes).

In a preferred embodiment, the vessel comprises two tube bundles of, for example, two different cooling fluids, each tube bundle having an inlet redistribution chamber and an outlet redistribution chamber, such that the vessel accommodates four redistribution chambers.

The redistribution chamber comprises a wall. The wall includes a wall portion having a bore. In operation, fluid flows between the redistribution chamber and the tubing connected thereto through the bore. Unlike conventional tube sheets, however, this wall portion, and more particularly the entire redistribution chamber, is spaced from the shell. Thus, no part of the redistribution chamber is normally in direct contact with (the inner surface of) the housing.

The redistribution chamber is connected to the tube end. In particular, the wall portion having the bore is connected to the pipe end, for example, using a crack-free joint.

Thus, at least some of the tube ends are located inside the space enclosed by the housing (container space) and are connected (for fluid flow) to the opening in the housing by the redistribution chamber and a conduit extending between the redistribution chamber and the housing. The redistribution chamber is spaced apart from the housing opening by, for example, at least 5cm, at least 10cm, or at least 40 cm. The redistribution chamber is also preferably completely spaced apart from the housing, preferably at least 5cm, at least 10cm or at least 40cm apart. These spacings are preferably provided by empty spaces which, in operation, can be filled with a cooling fluid or a condensing medium. A support element can be present between the redistribution chamber and the housing and the conduit.

Advantageously, in a preferred embodiment with cooling fluid in the tubes, the high pressure is outside the redistribution chamber, rather than inside.

Advantageously, the walls of the redistribution chamber can be thinner than in known tube sheets due to the smaller dimensions of the redistribution chamber compared to the tube sheets. In particular, the redistribution chamber has a smaller surface area in a cross-section perpendicular to the length of the vessel than the shell and the tube sheet sealing the shell. This results in the need to design significantly less force (stress) for the redistribution chamber walls.

In a preferred embodiment, the (plate) element having a bore of the redistribution chamber (or common to the stack of redistribution chambers) has, for example, only a relatively small flange surrounding the tube bundle, such as a relatively small flange surrounding each tube bundle at each side less than 40cm, less than 20cm, or less than 10cm from the outer tube of each tube bundle.

The redistribution chamber can for example be provided with internal load bearing structures, such as spacers. The walls of the redistribution chamber can be made of or consist of a single piece of corrosion resistant material, such as duplex stainless steel. For the preferred embodiment with a monolithic wall, the welded connection of the tube to the redistribution chamber is easier to manufacture, especially since there is no risk of carbon steel exposure.

Furthermore, it is advantageous that the walls of the redistribution chamber also contribute to the heat exchange surface, since in operation it can be in contact with the cooling fluid at one side and the condensing medium at the other side.

The invention also relates to a urea production plant comprising a high-pressure urea synthesis section comprising a high-pressure carbamate condenser, a reactor and a stripper according to the invention. The reactor, condenser and stripper are each operated at high pressure. The stripper has a gas flow line leading to a condenser having a liquid flow line leading to the reactor, and the reactor has a liquid flow line leading to the stripper for at least a part of the urea solution. The reactor and the condenser are optionally combined in a single vessel, which is for example placed horizontally, and the condensate is supplied directly from said vessel to the stripper. Such a single vessel comprises, for example, a condenser section and a reactor section. In addition, in case the condenser and the reactor (usually with a vertical reactor vessel) are provided as separate vessels, optionally some urea is already formed in the condenser. The plant for example comprises a gas flow line leading from the stripper to the shell space and a liquid flow line leading from the stripper to the tube bundle of the carbamate condenser; or the plant for example comprises a gas flow line leading from the stripper to the tube bundle and a liquid flow line leading from the stripper to the shell space of the carbamate condenser; wherein said flow line to the tube bundle passes through the conduit and the redistribution chamber as described in the present invention.

In operation, the reactor is supplied with a feed stream comprising urea, water and CO₂And NH₃The urea synthesis stream (partly in the form of carbamate) is at least partly supplied to the stripper. Carbamate dissociation into CO in the stripper₂And NH₃And a portion of the unreacted components are removed from the solution as a gas. Dissociation of the carbamate is promoted in the stripper by heating and countercurrent contact with a stripping gas to promote dissociation. The stripper uses heat and feeds, for example, high-pressure CO₂Is used as stripping agent, so-called thermal stripping is also possible. The heating in the stripper is usually indirect heat exchange with steam, usually with steam on the shell side and the urea synthesis stream inside the tubes of a shell-and-tube heat exchanger used as stripper. Will generally still contain some carbamate and NH₃Is expanded to a lower pressure and fed to a recovery section, wherein more carbamate is removed from the urea solution; the recovery section comprises, for example, MP recovery in series with the downstream LP recovery section, or LP only recovery. Containing NH from the stripper₃And CO₂Is supplied to the high-pressure condenser, to the tubes or to the shell space.

In a preferred embodiment, the mixed gas stream is supplied to the housing space through an opening in the housing. One or more cooling fluids are supplied to the tubes through the conduits and redistribution chambers as described (different cooling fluids have separate conduits and redistribution chambers). A liquid condensate is formed and in the preferred embodiment, the liquid condensate is present in the shell space and optionally gas is at a top portion of the shell space. The condensed liquid is in contact with the tubes so that the condensate is typically subcooled.

In this preferred embodiment, the gas to be condensed is distributed in the shell space, in particular in the length direction of the condenser, using a gas distributor such as a sparger. The sparger is, for example, a tube having an inlet connected to the inlet opening of the housing, optionally having an arm, and having a plurality of outlet openings for the gas, wherein the outlet openings are spaced apart in the length direction. The arm extends over the width of the container and has an opening for the gas. Preferred carbamate condensers include such spargers. For a horizontal condenser, both the gas distributor and the straight portion of the tube extend in parallel in the length direction; preferably, at least a portion of the gas distributor is arranged below the straight portion. This advantageously provides an improved distribution of condensation heat in the shell.

In some embodiments, ammonia is also introduced into the shell space, for example using a liquid distributor, particularly when using CO₂The stripper.

In some embodiments, the heat of condensation is at least partially extracted by generating steam (water evaporation) in at least some of the tubes in the case of condensation in the shell space, and in the case of condensation in the tubes, said steam being formed, for example, from the process condensate.

Especially at higher temperatures, the parts of the carbamate condenser that are in contact with the process medium (e.g. the process medium that condenses at high pressure in the condenser) are usually made of corrosion resistant materials, in particular urea grade steel, such as austenitic-ferritic duplex stainless steel (duplex steel). For example, the shell is typically provided internally with weld overlays (i.e., weld overlays) or linings made of urea grade steel or other corrosion resistant metals (e.g., duplex austenitic-ferritic stainless steel, AISI 316L steel, or INOX 25/22/2Cr/Ni/Mo steel). Such liners are typically used in the shell of high pressure carbamate condensers. The outer casing is, for example, a carbon steel casing and is, for example, at least 30mm or at least 40mm thick.

In some embodiments, the HP carbamate condenser comprises two tube bundles. This can be used to implement a process in which two different cooling fluids are used, for example a first tube bank for generating steam from water and a second tube bank in which an aqueous solution comprising urea and carbamate is heated to cause dissociation of the carbamate.

Such condensers can for example be used in the apparatus and method as described in US 2015/0119603.

In one embodiment, an HP condenser having two tube bundles is used in a urea production process, wherein a first tube bundle of steam is produced from water (also referred to as condensate). In the second tube bundle, the carbamate-containing (and usually also urea-containing) solution is heated by the heat of condensation received from the high-pressure process medium on the shell side, so that at least part of the carbamate in the solution in the second tube bundle dissociates into NH₃And CO₂. The solution is obtained, for example, as a stripped urea solution from a HP stripper or as a part of a urea synthesis solution from a reactor that is not stripped in a HP stripper. For example, the urea solution as part of the liquid from the reactor (optionally from a combined vessel comprising the condenser and the reactor) and/or the urea solution as at least part of the liquid from the stripper is supplied to the second tube bank, in particular through the inlet redistribution chamber and the inlet conduit, optionally with intermediate steps such as expansion and gas/liquid separation (flash). For example, all or a portion of the urea solution leaving the stripper is expanded, optionally flashed, and optionally further expanded and supplied to the second tube bank at an intermediate pressure (e.g., 10-35 bar).

In some embodiments, the second tube bank receives the carbamate-containing solution, for example in a urea production process involving supplying the urea solution directly or indirectly to the second tube bank from the reactor (or reactor section), e.g. from the reactor, the stripper or from the recovery section, preferably through the inlet conduit and the inlet redistribution chamber. In such embodiments, thermal dissociation of carbamate (to CO)₂And NH₃Gas) can occur in the second tube bundle.

The high-pressure condenser can be used, for example, in a stripping-type urea production process, in which a portion of the urea solution coming from the reactor is sent to a high-pressure stripper and another portion of the solution bypasses the stripper and is sent to a medium-pressure treatment step involving dissociation of the carbamate by heating the solution at medium pressure. The invention also relates to such a method. An example of such a method using a different type of high pressure condenser is described in US 2004/0116743. In the operation of the high-pressure carbamate condenser of the invention, and in the preferred process of the invention, the medium-pressure treatment step is carried out, for example, by bringing the urea solution into indirect heat-exchange contact with the condensation gases received in the condenser from the stripper, through the (second) tube bundle of the high-pressure carbamate condenser. In another embodiment, the carbamate condenser is used to generate steam (e.g. in the tube bundle) for supplying heat to the medium-pressure dissociation step of the urea solution obtained from the stripper or of the non-stripped urea solution from the reactor.

With conventional HP carbamate condensers, the challenges are the risk of corrosion in operation with one or more carbamate-containing liquids in at least some of the tubes and in the shell space, and the way the tubes are connected to tube plates, for example for a pool condenser with tube plates, as shown in US 2015/0119603. The present invention provides the important advantage that in one embodiment the redistribution chamber, in particular the wall portion with a bore hole exposed on both sides to the corrosive carbamate-containing solution, can be made of (and consist of) a single piece of corrosion resistant steel, such as a single piece of duplex stainless steel. This is especially true when condensation is performed on the shell side. Multiple walls of the chamber are also possible, especially if all layers are of corrosion resistant material. In some embodiments, the wall portion having a bore for the tube has a thickness 0.5 to 2 times the thickness of any other portion of the redistribution chamber wall, and the wall portion having a bore is a flat plate. For example, if the other portion of the redistribution chamber has a wall with a thickness of 1-2cm, the wall portion having a bore for the tube has a thickness of 0.5-4 cm. In some embodiments, the thickness of the wall portion having the bore for the tube is 0.9 to 1.1 times the thickness of the other portion of the redistribution chamber wall. An advantage of the invention is that the wall portion having the bore for the tube need not be a very thick plate, such as in the case of a tube sheet.

In an exemplary embodiment, the condenser comprises two U-shaped tube bundles arranged in a vertical direction with ABBA, wherein a is the straight portion of the first tube bundle and B is the straight portion of the second tube bundle, or wherein a is the straight portion of the second tube bundle (in operations such as for carbamate dissociation) and B is the straight portion of the first tube bundle (in operations such as for steam generation), and preferably has a vertical stack of four redistribution chambers connected to the two tube bundles. In such embodiments, the bends of the U-tube bundle can be arranged in a concentric manner (in particular, in cross-section in the length-height plane). Alternatively, the arrangement can be an AABB that will produce, for example, two sets of concentric bends within each tube bundle, and the two sets are arranged overlapping each other.

In a preferred embodiment of the urea production plant according to the invention, the high-pressure carbamate condenser comprises a tube bundle connected to the feed line by means of a redistribution chamber and of tubes. The feed line is used to feed the urea solution, which also comprises carbamate, to the tubes of the tube bundle. The feed line is connected to the stripper for receiving stripped urea solution from the stripper and/or to the reactor for receiving a portion of urea solution from the reactor. In a preferred embodiment, the feed line comprises an expansion device, and preferably a gas/liquid separator for separating gas from the expanded urea solution. Preferably, the feed line is configured for supplying at least a portion of the expanded urea solution to the conduit.

In a preferred embodiment, the tube bundle (receiving the urea solution also comprising carbamate) is connected to the gas/liquid separator through the outlet redistribution chamber and the conduit. The gas/liquid separator preferably has a liquid stream connection to the recovery section and a gas stream connection to the second condenser. Ammonia and CO obtained by thermal dissociation of carbamate in tubes₂At least partially condensed in a second condenser. Preferably, the second condenser is operated at medium pressure. Preferably, the condensation is performed in heat exchanging contact with an evaporation section of the urea plant, such that the heat of condensation is used for evaporation of water from the urea solution. Preferably, the second condenser has an opening to the high-pressure carbamate condenser, and more preferably to the shell spaceIs connected to the liquid stream of the carbamate recycle stream.

Furthermore, the HP condenser may also comprise a second tube bundle connected to a feed line for the process condensate (i.e. water) and to a discharge line for the steam.

In a preferred embodiment, the condenser comprises one or more pairs of tubes, each pair comprising an inlet tube and an outlet tube. The condenser preferably comprises one or more pairs of redistribution chambers, each pair comprising an inlet redistribution chamber for distributing the cooling fluid feed from the inlet conduit to the plurality of tubes and an outlet redistribution chamber for combining the heated cooling fluid from the plurality of tubes to the outlet conduit. For each pair, the redistribution chambers are typically arranged at the same side of the straight tube portion in the case of a U-shaped tube bundle, or at opposite sides (in the length direction) of the tubes in the case of a straight tube bundle.

In a preferred embodiment, the redistribution chamber comprises a plurality of elements (such as plate elements) and is therefore not completely unitary. These elements together provide the walls of the redistribution chamber. At least one of the elements is provided with a bore for a pipe and the same or another element (e.g. other plate) is provided with a hole for a pipe. Preferably, at least one other element is openable and closable, e.g. removable, to provide access to the interior of the redistribution chamber. Such as a cover plate. This element can be used to make the interior of the redistribution chamber accessible, for example for a person and/or a device. In this way, the interior of the redistribution chamber (i.e. the space for receiving the fluid) may be used for maintenance and inspection of the interior redistribution chamber and the tubes, in particular for inspection of the interior tubes and for plugging of the tubes. Plugging of the tube can involve placing a plug in the tube at the end of the tube connected to the redistribution chamber. In a preferred embodiment, the redistribution chamber comprises a fastener for fastening the openable element to at least one other element (such as a bolt). For example, a box-shaped redistribution chamber having an openable front plate may include a front plate having an opening and a side plate having a recess (e.g., threaded hole) aligned with the opening. The openings and recesses can receive fasteners such as bolts.

In addition, the redistribution chamber may further comprise spacers for spacing the wall portions (e.g., plate members) from each other, e.g., to provide resistance to compressive forces.

The container preferably comprises a support for the redistribution chamber, which is arranged, for example, below the redistribution chamber and on the housing. For example, the support element can be provided below the wall portion provided with the bore (and e.g. at the same position in the length direction of the container). The support may comprise grooves for receiving ears of the redistribution chamber for locking the redistribution chamber in position. The redistribution chamber or e.g. the stack of redistribution chambers is for example provided with fixing means for holding the chambers in place in the housing.

Preferably, the surface area of a transverse cross-section (cross-section perpendicular to the longitudinal axis of the container) of the redistribution chamber is less than 90% or less than 80% or less than 40% of the surface area of the cross-section of the container (in particular, the surface area enclosed by the shell in this cross-section).

In the case of a (vertical) stacking of the redistribution chambers, the surface area of the cross-section of the stack in the width-height plane (perpendicular to the central longitudinal axis of the container) is, for example, less than 90% or less than 80% or less than 70% of the surface area of the cross-section of the container (in particular, the surface area enclosed by the shell in this cross-section).

Preferably, the housing space is a single undivided space, wherein all parts of the space are in fluid communication with each other; additionally, in such embodiments, the shell space can include baffles to divide the shell space in compartments that are not completely sealed from each other. Preferably, the housing is in contact with the housing space, and preferably, the entire inner surface of the housing is in contact with the housing space. Preferably, each conduit extends through the housing space. Preferably, each conduit comprises a length section, wherein the entire outer wall of the conduit is exposed to the housing space. Preferably, the front plate of the box-shaped redistribution chamber, which has holes for connection with the tubes in the opposite rear plate, is on the outer side exposed to the housing space.

In some embodiments, the at least one redistribution chamber is at least partially submerged in the condensed liquid when in operation, preferably each redistribution chamber is at least partially submerged in the condensed liquid, and preferably the at least one redistribution chamber is completely submerged in the condensed liquid, wherein the condensed liquid condenses in the shell space.

In a preferred embodiment, the housing comprises a substantially cylindrical middle portion and two cap portions. Each cap portion may comprise a plurality of housing portions. The roof part is for example a substantially hemispherical part, optionally with a manhole and a plate. The two roof parts close the intermediate part at opposite ends, in particular at opposite ends in the length direction. Preferably, the housing space is a single housing space defined by the intermediate portion and the cap portion. Preferably, the housing space is not divided by, for example, a partition wall; but can include baffles. Preferably, the fluid is able to flow from the gas distributor to both roof parts.

The high-pressure carbamate condenser differs from other types of heat exchangers, in particular hot gas coolers, in many features, which are preferred for the carbamate condenser of the present invention. A horizontal carbamate condenser configured for condensation in the shell may for example comprise a baffle (or partition) dividing the shell space in the chamber lengthwise and extending from the bottom of the vessel, but not completely to the top, leaving a gas discharge zone at the top of the shell; the top of the baffle defines the level of condensate in operation. Some of the baffles can have openings, for example, at the vertical height of the tube bundle. Typically, the most downstream baffle has no openings therein so that liquid condensate flows over the top of the baffle to the liquid outlet in the housing. Thus, the shell section comprises a weir. This allows to control the level of condensate in the condenser, especially in a fully submerged tube bundle. Furthermore, the tube bundles, in particular the U-shaped tube bundles, usually have a straight-flow configuration or each cooling fluid (urea solution and/or process condensate).

The carbamate condenser, which condenses in, for example, a horizontal still tube, comprises, for example, an ejector at the inlet of the carbamate solution and, for example, a mixing zone comprising the inlets of the gas to be condensed and the carbamate solution. The carbamate condenser has, for example, a conduit for recirculating the carbamate solution from the outlet end of the tube to the inlet of the gas to be condensed.

In the case of a vertical carbamate condenser configured for condensation in the shell space, the condenser comprises a packing section, e.g. at the top, e.g. with packing, for scrubbing the off-gases with a solution supplied through the shell inlet above the packing section, in particular the inlet for the carbamate solution, and a downcomer arranged below the packing section but above the U-bend of the tube bundle to a portion of the condenser below said bend. The vertical carbamate condenser preferably has an outlet for the liquid of the shell, optionally with downcomers, so that in operation the liquid level is maintained above the U-bend of the tube bundle, with the tube ends at the bottom of the vessel.

The pipe preferably comprises or is made of corrosion resistant steel, such as duplex stainless steel. For example, the pipe is made entirely of such steel. The wall portions of the redistribution chamber, as well as any internal structures that come into contact with the carbamate during operation, such as spacers, are preferably made of corrosion resistant steel, such as duplex stainless steel. The preferred lining of the tube and the shell is preferably made of corrosion resistant steel, such as duplex stainless steel.

Suitable duplex stainless steels for the section of the carbamate condenser include, for example, those under the trade nameSteels are commercially available and have the composition 29Cr-6.5Ni-2Mo-N, also designated by ASME number 2295-3 and UNS S32906, or steels are commercially available, for example, under the trade name DP28W (TM) steel and have the composition 27Cr-7.6Ni-1 Mo-2.3W-N, also designated by ASME number 2496-1 and UNS S32808. The Safurex (R) steel has, for example, a composition (mass%) C: at most 0.05, Si: at most 0.8, 0.3-4.0 Mn, 28-35 Cr, 3-10 Ni, 1.0-4.0 Mo, 0.2-0.6N, Cu: at most 1.0W: at most 2.0S: 0-0.2, at most 0.01Ce, with the remainder Fe and (unavoidable) impurities. Preferably, the ferrite content is 30-70 vol%, and more preferably 30-55%. More preferably, the steel comprises (in weight%): c up to 0.02, up to 0.5Si, Cr 29 to 33, Mo 1.0 to 2.0, N0.36 to 0.55, Mn 0.3 to 1.0, and the balance Fe and impurities. Also suitable is a duplex stainless steel having the following composition in weight percent (wt%): c is at most 0.030; si is at most 0.8; mn is at most 2.0; cr 29.0 to 31.0; ni 5.0 to 9.0; mo is less than 4.0; w is less than 4.0; n0.25-0.45; cu is at most 2.0; s is at most 0.02; p is at most 0.03; residual Fe and inevitable impurities; and wherein the content of Mo + W is more than 3.0 but less than 5.0 (wt%), furthermore preferably having a steel composition as described in WO 2017/014632, which patent document is hereby incorporated by reference. In some embodiments, the shell comprises an inner liner made of such steel.

Each conduit has a first conduit end connected to the wall of the redistribution chamber and a second end connected to the housing. The first conduit end is aligned with the opening in the wall and the second conduit end is aligned with the opening in the housing such that fluid can flow from outside the housing through the conduit to the redistribution chamber. The conduit is at least partially located in the vessel. The first conduit end is located in the container. The conduit extends through the container space. Further, the outer surface of the pipe is exposed to the housing space.

The conduit may consist of one or more conduit portions, for example conduit portions arranged in series and connected to each other.

The first tube end is connected to the redistribution chamber, for example with a weld. The first conduit end is for example placed radially outside the tube end connected to the redistribution chamber, i.e. further removed from the central longitudinal axis of the vessel in a direction perpendicular to the length. In an exemplary embodiment having a box-shaped redistribution chamber with a bottom plate, a top plate, a front plate, a back plate and two side plates, the pipe ends are for example attached to the side plates, top plate or bottom plate and the pipe ends are attached to the back plate, and the front plate is for example a cover plate that can be opened for maintenance and inspection. In principle, the duct can also be connected to a rear plate or a front plate. In an exemplary embodiment of the redistribution chamber having a box shape, the conduit is connected to the front plate and the side plates can be opened.

In a preferred embodiment, a plurality of redistribution chambers are stacked on top of each other to create a stack, preferably a box-shaped stack, of redistribution chambers, and preferably vertically stacked. Preferably, the plate member is common to the stacked redistribution chambers, preferably the floor member has a bore. Preferably, the tube bundle comprises U-shaped tubes, wherein each tube has a bend and two legs. Preferably, the stack of redistribution chambers comprises an inlet redistribution chamber and an outlet redistribution chamber connected to the same U-shaped tube bundle.

In the case of a (vertical) stacking of the preferably box-shaped redistribution chambers, the various plates can be common to the stacked redistribution chambers, as may be the case, for example, for the rear plate (e.g. with bores for connection to the tube bundle) and the side plates. The horizontal plate can be common to two adjacent chambers, providing a top plate and a bottom plate, in particular when the chambers receive fluid at the same pressure when in operation. In the case of a vertical stack of four or more redistribution chambers, the tubes can be connected to the top plate for the top redistribution chamber, to the bottom plate for the bottom redistribution chamber, and to the side plates for the redistribution chambers in the middle tubes. In a preferred embodiment, the redistribution chamber is provided with conduits at two opposite side plates, and these conduits are for example both used as inlets or both used as outlets when in operation. This may advantageously facilitate good distribution of the fluid within the tube and efficient removal of the fluid from the tube. In particular, because in some embodiments the box-shaped redistribution chamber has a width (from side to side) that is longer than the height of the redistribution chamber, and wherein this applies equally to the area of the back plate provided with holes.

In an exemplary embodiment of a stack with redistribution chambers, all of the conduits connected to the stack extend to the top of the housing. In combination with a support structure for the tube bundle, for example in a vessel between the bottom of the shell and the tube bundle, this may allow for expansion and/or contraction of the apparatus. In the case of a stack of redistribution chambers, the chambers may have, for example, a shared back plate, and also shared side plates for a vertical stack.

In some exemplary embodiments, the spacing in the length direction between the first and second ends of the tubes is less than 20% or less than 10% of the length of the vessel, or less than 20% or less than 10% of the length of the straight portion of the tube, for one or more tubes (or even for all tubes).

In another embodiment, one or more conduits extend in the length direction, e.g., wherein the conduits are arranged substantially parallel (e.g., with a deviation of less than 5 °) to the (straight portion of the tube. In some exemplary embodiments, the spacing in the length direction between the first and second ends of the tubes is greater than 10% or greater than 20% of the length of the straight portion of the tube for one or more or even all of the tubes.

Generally, for the redistribution chamber, the number of tubes connected to the redistribution chamber is at least 10 times higher, such as at least 50 times higher or at least 100 times higher, than the number of tubes connected to the redistribution chamber. Thus, the surface area of the pipe in a transverse cross-section (perpendicular to the flow direction) of the inner flow space of the pipe is typically at least 10 times or at least 20 times larger than this surface area of the pipe.

Each pipe has at least two pipe ends, wherein pipe ends are referred to as end portions and not only as side edges. In the case of a Y-shaped pipe, the pipe may also have, for example, three pipe ends. The end of the conduit is connected to the redistribution chamber. For example, the pipe edge may abut the (planar) side of the redistribution chamber wall with a crack-free joint. The tube end may also be inserted through an opening in the redistribution chamber wall, for example, wherein a crack between the wall and the tube portion is sealed by a weld.

In the same way, the pipe end (end portion) is connected with the housing, e.g. the pipe end may abut the housing, e.g. with a crack-free joint. In case the housing wall comprises carbon steel elements and the fluid to be transported through the pipe comprises carbamate, the pipe end or a portion of the pipe can be inserted through an opening in the housing. The crevice between the inserted pipe section and the bore surface of the housing (including any exposed carbon steel) can also be closed by welding at the inside of the housing, as will the bore site be accessible. Optionally, a pipe section such as a sleeve (e.g. a sleeve of duplex stainless steel) is first inserted through the hole, the split is sealed, e.g. by welding, and the inserted pipe section (e.g. sleeve) is connected to another pipe section, e.g. by bore welding. For example, the condenser includes a pipe end portion inserted through an opening in the housing and having a sealed split between the inserted pipe portion and the housing.

In embodiments where the redistribution chamber is provided with a plurality of tubes, these tubes are optionally connected to a header (or junction section) which can be placed inside or outside the vessel. In some embodiments, the pipe comprises a joint section (e.g., a T-joint) connecting at least three pipe sections. With such a conduit, two conduit ends can for example be connected to the redistribution chamber and one conduit end is connected to the housing. In an exemplary embodiment, the inlet conduit is connected to the floor of the bottom redistribution chamber of the vertical stack of redistribution chambers by two or more conduit sections each connected to the floor, at least one conduit section connected to the shell, and a fitting section inside the vessel space engaging the conduit section. At least two pipe sections connected to the redistribution chamber can be spaced apart from each other to optimize the distribution of the fluid over the pipes.

The condenser can be constructed, for example, using a method that includes mounting a tube bundle in a shell (having at least one open end), such as on a support baffle. The invention also relates to such a construction method. The method can include attaching the redistribution chamber to the tube end, for example using an internal bore weld, either before or after installing the tube bundle. For example, a stacked tube bundle connected to a redistribution chamber is mounted in a housing. The method may involve connecting the conduit to the redistribution chamber after installation of the tube bundle. The conduit can be inserted through the housing before or after installation. The method can involve closing the container by, for example, engaging a closure cap (e.g., a half-head) to a substantially cylindrical middle portion of the container having at least one open end (e.g., at an end of the middle portion in which the redistribution chamber is located).

Exemplary embodiments of the present invention are illustrated and discussed in conjunction with the accompanying drawings, which do not limit the invention or the claims.

Figure 1 shows a reference high-pressure carbamate condenser not according to the invention. The condenser (100) is arranged as a shell-and-tube heat exchanger (101) and is configured as a horizontal submerged condenser having a U-shaped tube bundle (103) for cooling a fluid and in operation condensing a gas in the shell space (105). A portion of the lower half of the condenser (100) is shown in fig. 1. The heat exchanger (101) comprises a vessel (102) comprising a shell (1) and a tube bundle (103). The housing is designed to withstand high pressure and enclose a container space (104). The vessel (102) also includes a manifold (107). The manifold (107) is not enclosed by the housing (1) and is outside the container space (104). The tubes (2) of the tube bundle (103) are arranged in the vessel space (104). The space between the tube (2) and the housing (1) is a housing space (105) for receiving the gas to be condensed. The vessel thus comprises a gas inlet (4) to the housing space (105), and an outlet (5) for liquid from the housing space (104), and a corresponding opening for the process medium in the housing (1). Furthermore, the vessel comprises a carbamate recirculation inlet (13) comprising an opening in said shell (1). The vessel further comprises a gas distributor (6) connected to the gas inlet (4). The gas distributor (6) is configured for distributing a gas to be condensed (e.g. a mixed gas from a high-pressure stripper of a urea plant) in the shell space (105).

The vessel (102) further comprises a tube sheet (108). The tube sheet separates the shell space (105) from the header (107) and therefore needs to withstand large pressure differences. One open end of the substantially cylindrical shell (1) is sealed by a tube sheet (108). The tube sheet contains a bore (110) for a cooling fluid. The ends (3) of the tubes (2) are connected to a tube sheet (108) so that fluid can flow between the tubes and a header (107). The header is provided with openings (109) that serve as inlets or outlets, so that the cooling fluid flows between the openings (109) of a large number of tubes (2), for example more than 100 tubes. The tube sheet (108) is, for example, a substantially circular metal plate, and is typically a thick carbon steel plate (e.g., about 30cm to 60cm carbon steel) lined on the side exposed to the shell space (105) with a corrosion resistant steel, such as with a duplex stainless steel alloy lining (which includes, for example, weld overlay).

For the reference carbamate condenser of fig. 1 (not according to the invention), the construction of the tube sheet (108) is challenging and expensive in view of the need to withstand high pressures, at least one side exposed to the extremely corrosive process media, and the very large number of tubes. Furthermore, any crevices between the tubes and the tubesheet introduce a high risk of crevice corrosion, since they are in contact with the carbamate-containing medium. For example, there are cracks where the tube legs extend through bores, for example with a bore diameter (slightly) larger than the outer diameter of the tube. Crevice corrosion is particularly severe for metal parts in contact with carbamate. Crevice corrosion can refer to the difficulty in maintaining a passivation layer on the steel with a passivating agent (such as oxygen) in the crevice due to restricted flow in the crevice. If carbon steel is exposed to such cracks, corrosion also occurs in the cracks. Thus, in known pool condensers, the tubes are often not inserted into the holes, but are joined to the tube sheet in a crack-free manner using, for example, female welding. Exposing the carbon steel portion of the tubesheet to the process condensate and steam in the holes is not problematic.

In case a urea solution further comprising carbamate is provided as cooling fluid into the header (107), such as when used in a method as described in US 2015/0119603, a corrosion protection layer is necessary for the side of the tube sheet (108) exposed to the header (107) and the carbon steel surface of the bore (110) should not be exposed to the cooling fluid. An alternative to a single piece duplex stainless steel alloy tubesheet is not practically feasible because it is not feasible to manufacture a uniform duplex stainless steel plate with a thickness sufficient to accommodate high pressure media (e.g., 30cm to 60cm), at least in a practically acceptable manner.

In US 2015/0086440, a construction method is described in which a sleeve is inserted into a bore through a tubesheet such that the sleeve extends through the tubesheet. The sleeve is much shorter than the tube. The thimble tubes can be welded (externally) on both sides of the tube sheet so that the carbon steel layer of the tube shield is sealed from the fluid in the shell space (105) and the fluid in the header (107). At one side of the tube sheet, the thimble tubes are then connected with the legs of the U-tube bundle with female welds. Therefore, after the shell pipe is welded to the tube plate, the tube end is connected to the shell pipe by welding from the inside by inserting a welding probe into the shell pipe from the low pressure side (header side) and forming an inner hole welding portion.

Thus, the welding of the sleeve to the exterior of the tubesheet is performed before the sleeve is attached to the tube bundle, since otherwise the tube bundle (with a large number of closely spaced tubes) would obstruct access at one side of the tubesheet. However, a disadvantage is that three welds are required for each tube, resulting in high construction costs.

If in the method of US 2015/0086440 the sleeve could be omitted and the tubes connected directly to the tubesheet by means of female welding, the carbon steel plate inside the tubesheet would be exposed at the bore to the carbamate present in the urea solution used as cooling fluid inside the tubes. This will cause corrosion. If the tube is inserted into the bore, there will be a crack between the end of the tube inserted into the bore and the tubesheet, i.e., a gap between the exterior of the tube and the interior of the tubesheet bore, such that the process media contacts the carbon steel portion of the tubesheet. In the present invention, the walls of the redistribution chamber (including the wall portions with the bore holes as in conventional tube sheets) can advantageously be made of a single piece of duplex stainless steel, so that the urea solution containing carbamate used as cooling fluid can come into contact with the surface of the bore holes, without causing an excessive risk of corrosion.

In order to have a longer residence time of the condensate in the shell space in the condenser of fig. 1, one option is to increase the diameter of the shell such that the shell has a much larger cross-sectional surface area than the tube bundle, as shown for example in US 5767313. The disadvantage is that the diameter of the tubesheet also increases, as the tubesheet is used to seal one end of the shell, and therefore the stresses caused by the pressure differential also increase.

Fig. 2A shows an example of a carbamate condenser (100) according to the invention. Fig. 2B shows an enlarged portion. Instead of the header (107) and the tube plate (108) as shown in fig. 1, the carbamate condenser (100) comprises a redistribution chamber (7) with walls (8). The wall (8) is configured for separating the fluid in the redistribution chamber (7) from the fluid in the housing space (105). The two fluids generally have different compositions when in operation. The redistribution chamber (7) is arranged inside the container space (104) and is thus enclosed by the housing (1). The housing (1) is configured for holding a fluid in fluid contact with the outer surface of the tube (2). A plurality of tubes (2a,2b) are connected to each individual redistribution chamber (7) such that fluid can flow between the tubes (2) and the redistribution chamber (7) through openings (12) (e.g. bores) in the wall (8) provided in a portion (11) of the wall (8). The end (3) of the tube (2) is attached to the wall (8) such that the opening of the tube end is aligned with the opening (12) of the wall (8). This is schematically illustrated in fig. 2C, where the diameter of the tubes (2a,2b) is increased compared to the redistribution chamber (7). The pipe end (3) is attached, for example, with a bore weld. The redistribution chamber (7) is connected to an opening (10) in the housing (1) by a conduit (9) for (cooling) the fluid. The conduit (9) is placed in the container space (104) and is preferably exposed to the housing space (105). The conduit (9) extends between the opening (10) of the housing (1) and the redistribution chamber (7), more particularly to the opening (14) of the redistribution chamber (7). In this way, the cooling fluid can be conveyed between the opening (10) in the housing (1) and the pipe (2) via the redistribution chamber (7) and the conduit (9), while separating the cooling fluid from the process medium fluid in the housing space (105). In operation, the conduit (9) is in contact internally with the cooling fluid and externally with the process medium in the shell space (105). As shown in fig. 2A and 2B, the carbamate condenser (100) also includes a manhole (106) and a baffle (15).

Fig. 2D schematically shows a cross-sectional view perpendicular to the length of the exemplary embodiment. The carbamate condenser (100) comprises a vertical stack of 4 box-shaped redistribution chambers (7) each having a pipe (9), in each redistribution chamber (7) a portion (11) with a bore is shown. The arrangement of the conduit (9) in fig. 2D is schematic and many variations are possible. The conduit (9) extends generally outwardly from the redistribution chamber to an opening (1) in the housing (1). The same reference numerals of fig. 1 and 2 preferably have the same features in fig. 2 as described in connection with fig. 1.

Fig. 3 shows an exemplary urea plant according to the present invention. The plant comprises a high-pressure synthesis section comprising a urea reactor R,Stripper S and HP carbamate condenser HPCC. The reactor R has a liquid flow connection of the urea synthesis solution USS to a stripper S which, in addition to being heated by indirect heat exchange with steam, also uses CO₂The feed is stripped. Optionally, reactor R is combined with condenser HPCC in a single vessel with a liquid flow connection to stripper S. The urea synthesis solution USS further comprises carbamate, ammonia and water, which is (at least partly) removed from the final urea product using a stripper S and a recovery section REC, which comprises and for example consists of a low pressure section but does not have an intermediate pressure section. Downstream of the REC, an evaporation section EVAP is optionally provided for removing water to produce a urea melt UM, which is optionally solidified in the finishing section completion to produce a solid urea product SU. The stripper S has a gas connection for the mixed gas SG to the condenser HPCC. The condenser HPCC comprises two U-shaped tube bundles T1 and T2. Each tube bundle (T1, T2) includes a plurality of tubes (e.g., over 100 tubes). One end of each tube is connected to the inlet redistribution chambers RC1A, RC2A, and the other end is connected to the outlet redistribution chambers RC1B, RC 2B. The inlet redistribution chambers (RC1A, RC2A) are connected to the inlet conduits D1a, D2 a. The outlet redistribution chamber (RC1B, RC2B) is connected to the outlet conduit (D1b, D2 b).

Condensation is performed on the shell side of the HPCC, to which NH is also supplied₃Feeding. The stripper S has a liquid flow connection for stripping the urea solution SUSS through an expansion device (e.g., expansion valve) V1 into a flash vessel F1 for gas/liquid separation. Flash vessel F1 has a liquid connection to the medium pressure urea solution MPUS of tube bundle T2, which still contains carbamate. In tube bundle T2, the MPUS solution is heated and the carbamate in MPUS decomposes accordingly. The MPUS solution is sent from the outlet of tube bundle T2 to a gas/liquid separator, such as a flash vessel (F2). The gas G1 is sent to a condenser MPC, which is typically operated at Medium Pressure (MP) and heat exchanged, for example, with the evaporation section EVAP. The liquid US1 from separator F2 is sent, for example, to a low pressure recovery section (REC) to further remove carbamate and water, and then it is sentSent as urea solution US2 to the evaporation section EVAP. In the recovery section REC, the urea solution is subjected to carbamate dissociation by heating, typically at low pressure, the removed gases being condensed into a liquid carbamate recycle stream CR 2. The condenser MPC may also receive gas G2 from flash vessel F1 and uncondensed gas G3 from the HPCC and off-gas from R (not shown). The condensate from the MPC is sent as liquid carbamate recycle CR1 to the synthesis section, in particular to the shell space of the HPCC condenser, using a pump (not shown), which is usually combined with the liquid carbamate recycle (CR2) from the recovery section REC. The condenser HPCC has a liquid flow connection to the condensate C of the reactor. Alternatively or in addition, a portion of USS can be sent from R to tube bundle T2, for example to F, bypassing stripper S. In tube bundle T1, water (typically condensate) is converted to steam (not shown).

As used herein, "a" and "an" include one or more. The term "comprising" allows the presence of other elements than those described. Various exemplary embodiments have been described above, in part, in connection with the accompanying drawings, but the present invention is not limited to these embodiments. The features of the embodiments described separately can generally be combined with each other, as will be apparent to the skilled person. The steps of the production method can be realized with corresponding units and fluid flow connections of the inventive device. The process of the invention is preferably carried out in an apparatus as described and using a high-pressure carbamate condenser as described, wherein all preferred apparatus features apply equally to the process. Reference numerals in the figures in the claims only provide an illustrative illustration and do not limit the claims.