High pressure carbamate condensing device

Abstract

The present disclosure relates to a high pressure carbamate condensing device for a urea plant, a urea plant and a urea production method. The device comprises a first U-shaped tube bundle arranged around a second U-shaped tube bundle.

Description

Technical Field

[0001] This invention relates to the production of urea from CO2 and NH3. Background Technology

[0002] The chapter on urea in the Ullman Encyclopedia of Industrial Chemistry (2010) describes an example urea production facility.

[0003] US2015 / 0119603A1 describes a urea production facility with a high-pressure synthesis section having a horizontal pool-type condenser configured to receive a high-pressure process medium at its shell side. The pool-type condenser includes a first tube bundle receiving a medium-pressure urea solution and a second tube bundle receiving steam condensate. The two tube bundles are shown as vertically stacked horizontal U-shaped tube bundles. As shown, the urea solution is supplied to the bottom straight tube portion of the lower tube bundle.

[0004] US2020 / 0306663A1 describes a high-pressure urethane condenser of the shell-and-tube heat exchanger type with a tube bundle, having tubes connected to the tube bundle and a redistribution chamber connected to a conduit extending between the redistribution chamber and the shell. Figure 3 of US'663 shows a high-pressure urethane condenser with two U-shaped tube bundles, wherein the lower tube bundle receives urea solution at the lower leg portion.

[0005] The brochure “Staminkabon’s Ultra-Low Energy Design; Technical Paper” (September 2018) shows a pool-type condenser / reactor with two stacked U-shaped tube bundles, through which urea solution is supplied to the bottom tube bundle.

[0006] There is still a need for an improved high-pressure (HP) carbamate condenser for urea facilities, particularly one with improved heat exchange performance. Summary of the Invention

[0007] The invention relates in a first aspect to a high-pressure carbamate condenser comprising: a shell-and-tube heat exchanger including a shell and first and second horizontal U-tube bundles, each horizontal U-tube bundle having an upper leg portion and a lower leg portion connected by an elbow portion; a shell-side space defined by the shell; a first fluid distributor disposed in the shell-side space at a bottom section of the condenser for distributing a first high-pressure gas flow into the shell-side space; and an inlet and an outlet for a medium-pressure (MP) urea-containing flow, wherein the first U-tube bundle is arranged around a second U-tube bundle and the upper leg portion of the outer first U-tube bundle is proximally connected to the inlet for the MP urea-containing flow and the lower leg portion of the outer first U-tube bundle is proximally connected to the outlet for the MP urea-containing flow, and wherein the inner second U-tube bundle is configured to generate steam.

[0008] The present invention also relates to a urea production facility comprising a high-pressure synthesis section, which includes an HP stripper, a reaction zone, and a high-pressure carbamate condenser according to the invention. The high-pressure synthesis section has a liquid flow connection for a urea solution to reach, via an expansion device, the inlet for an MP urea-containing flow and to the upper leg portion of an external first U-shaped tube bundle. The HP stripper has a gas flow line connected to a gas inlet on the shell side of the condenser.

[0009] The present invention also relates to a urea production process for producing urea from ammonia and carbon dioxide in a urea production facility according to the invention, the process comprising supplying gas from an HP stripper to the shell side of an HP carbamate condenser and at least partially condensing the gas into carbamate in the shell side and at least partially converting the carbamate into urea in the shell side, and supplying an MP urea solution further comprising carbamate to the inlet for the MP urea-containing stream.

[0010] Various aspects of the present invention therefore relate to a high-pressure carbamate condensation apparatus for a urea facility, a urea facility, and a method for producing urea. The apparatus includes a first U-shaped tube bundle arranged around a second U-shaped tube bundle. Attached Figure Description

[0011] Figure 1 An example urea production facility according to the present invention is illustrated schematically.

[0012] Figure 2 A cross-section of an example of an HP carbamate condenser according to the present invention is shown schematically.

[0013] Any embodiments shown in the accompanying drawings are merely examples and do not limit the invention. Detailed Implementation

[0014] One aspect of the invention relates to a shell-and-tube heat exchange type HP horizontal carbamate condenser. This device is particularly a horizontally submerged condenser. Two examples of such horizontally submerged condensers that can be used in, but are not limiting of, the invention are pool condensers and pool reactors.

[0015] A submerged condenser is a condenser in which the tube bundle is submerged in a liquid process medium present in the shell-side space during operation. The apparatus of the present invention includes a shell-side space between the shell (wall) and the tubes. The shell-side space is filled with HP process medium during operation. Gases containing NH3 and CO2 from the HP stripper condense in the shell-side space into a solution containing carbamates, and a cooling fluid flows through the tubes during operation. The gas to be condensed is supplied and distributed by one or more gas distributors at the bottom of the shell-side space.

[0016] In one aspect, the present invention is based on the insightful understanding that the heat exchange performance of an HP carbamate condenser can be improved by benefiting from the cross-flow effect between the medium-pressure (MP) urea solution in the tubes of the U-shaped tube bundle and the condensing process medium in the shell-side space. The process medium in the shell-side space flows upward between the tubes of the tube bundle, and the carbamate-containing MP urea solution, used as the cooling fluid, flows from the upper leg portion of the horizontal tube bundle to the lower leg portion within the tubes, and its temperature increases, causing the relatively cooler urea solution in the upper leg portion to exchange heat with the relatively cooler process medium in the upper portion of the shell-side space. This contributes to optimal heat exchange and thus advantageously allows for a smaller heat exchange surface.

[0017] In particular, since the urethane condensation reaction is rapid and exothermic, and the urea formation reaction has already occurred at least partially in the condensation unit and is endothermic and relatively slow, the configuration of the first and second tube bundles according to the invention allows for good heat exchange between the cooling fluid in the tubes and the process medium (in the shell-side space), while taking into account the vertical temperature distribution of the process medium in the shell side and the temperature distribution of the urea solution flowing through the first U-shaped tube bundle.

[0018] One aspect of the invention relates to an HP carbamate condensation apparatus, particularly for urea plants. The apparatus can be a submerged condenser, such as a pool condenser or a pool reactor. Reference is made to this apparatus. Figure 1 The discussion is to be conducted, however, the figure does not limit the invention or the claims.

[0019] The HP carbamate condenser includes a shell-and-tube heat exchanger comprising a shell and a first horizontal U-tube bundle (4) and a second horizontal U-tube bundle. Thus, the heat exchanger has a tube side and a shell side.

[0020] For the HP carbamate condenser, the horizontal direction is defined by the legs of the tube bundle, which are arranged horizontally. Additionally, the length direction is defined by the legs of the tube bundle arranged in the length direction. The bottom section of the HP carbamate condenser is defined by a first fluid distributor (11). For urea facilities, verticality is defined relative to gravity, and the HP carbamate condenser is arranged accordingly.

[0021] The shell defines the shell-side space (18). The shell is, for example, a container having a horizontal length direction; preferably, a cylindrical container. The shell is, for example, sealed at one end with a cap, such as a substantially hemispherical cap portion, and closed at the other end by a tube sheet, or, for example, sealed at both ends with caps. The cap and tube sheet, or both caps, define the shell-side space (18) and expose the HP process media in the shell-side space (18) on the inside.

[0022] The parts of a carbamate condenser that come into contact with the process medium, especially at higher temperatures (e.g., when the process medium condenses under high pressure in the condenser), are typically made of corrosion-resistant materials, particularly urea-grade steel, such as austenitic-ferritic duplex stainless steel (duplex steel). For example, the shell is internally lined with a weld overlay (i.e., a weld cover) or a lining made of urea-grade steel or other corrosion-resistant metals, such as duplex austenitic-ferritic stainless steel, AISI 316L steel, or INOX 25 / 22 / 2Cr / Ni / Mo steel. Such linings are typical for the shell of an HP carbamate condenser. The outer shell is, for example, a carbon steel shell and is, for example, at least 30 mm or at least 40 mm thick.

[0023] The HP carbamate condenser further includes a first fluid distributor (11). The first fluid distributor (11) is arranged in the shell at the bottom section of the condenser. The first fluid distributor (11) is used to distribute a first high-pressure gas flow, particularly from the HP stripper, in the shell side, i.e., in the shell side space (18). The first HP gas flow may be supercritical. The first fluid distributor is particularly horizontally arranged for horizontally distributing the gas flow.

[0024] The first fluid distributor (11) is, for example, a distributor. A distributor includes, for example, a tube extending along the length of a housing, wherein the tube is provided with arms extending in the width direction on both sides of the tube. The arms are spaced apart in the length direction. Each arm has a plurality of gas outlets (e.g., more than 50 openings per arm) on its upper side. A distributor may include two or more such tubes with arms. Typically, the first fluid distributor is provided with an upper surface containing a large number (e.g., more than 50) of outlet openings for gas distributed in both the length and width directions.

[0025] A first fluid distributor (11) is connected to a gas inlet (22) contained in the housing; the gas inlet is configured to supply the gas to be condensed into the shell-side space (18).

[0026] The first fluid distributor (11) and the straight portion (leg) of the tube bundle extend parallel to the length of the housing. The arm extends horizontally in the width direction, i.e., perpendicular to the length direction.

[0027] The first fluid distributor (11) is typically configured to distribute gas across the width of the tube bundle and at least along its length; preferably, the tube bundles have the same width and the leg portions of the first U-shaped tube bundle (4) and the second U-shaped tube bundle have the same length. The housing is wider than the tube bundle and allows fluid to flow downward in the shell-side space surrounding the tube bundle.

[0028] The shell side (18) of the HP carbamate condenser typically includes a carbamate inlet for receiving recirculated carbamate solution from one or more recovery sections for purifying urea solution from the HP synthesis section.

[0029] The shell also includes an outlet for process fluid, which is used to extract supply fluid from the shell-side space (18). The process fluid includes a solution containing urea and carbamate.

[0030] In some embodiments, the shell-side space (18) is completely filled with process fluid during operation, and the process fluid at the outlet comprises both gas and liquid. The process fluid is, for example, a gas / liquid separation unit supplied to the outside of a condenser. In such embodiments, the outlet is located on the top side of the shell.

[0031] In some embodiments, the liquid level is maintained in the shell-side space (18) during operation and the condensation device includes a liquid overflow element in the shell-side space (18), such as a baffle or downcomer. The overflow element may act as a weir.

[0032] During operation, the entire first tube bundle (4) and the second tube bundle are immersed in and contained within the liquid phase in the shell-side space (18). Therefore, the HP carbamate condenser provides a horizontally immersed carbamate condenser.

[0033] The HP carbamate condenser includes an inlet (13) and an outlet (14) for an MP urea-containing flow (i.e., for a fluid flow comprising a liquid phase containing urea). The liquid phase also contains carbamate at least at the inlet (13) and typically also contains carbamate at the outlet (14), but less frequently. The fluid flow also contains gas at least at the outlet (14) because at least a portion of the carbamate decomposes during the flow through the first U-tube bundle (4). The fluid is at a pressure in the medium pressure (MP) range at both the inlet and outlet.

[0034] The MP contains a urea inlet (13) and an outlet (14), both of which are connected to the first U-shaped tube bundle (4).

[0035] The MP urea inlet (13) and outlet (14) are located within the outer wall of the HP carbamate condenser. The outer wall is typically exposed to the external environment of the urea facility. The outer wall may be provided, for example, by the housing or by additional components of the facility, such as manifolds located outside the housing.

[0036] Both the inlet (13) and the outlet (14) are provided with connecting devices, such as flanges, for connection to fluid flow lines, such as pipes, for the facilities for MP urea flow.

[0037] Both the inlet (13) and the outlet (14) are connected to the first U-shaped tube bundle (4) via corresponding connecting chambers that connect the inlet and outlet to a number of tubes in the bundle, respectively. The connecting chamber is, for example, a manifold partially formed by the tube sheet, or a redistribution chamber located within the shell-side space, such as the redistribution chamber described in more detail in US2020 / 0306663A1.

[0038] An example embodiment of the condenser includes a tube sheet and the connection chamber is configured as a manifold. In such embodiments with a tube sheet, the tube sheet is preferably also provided with a corrosion-resistant layer, such as a duplex stainless steel layer, for example, provided with a weld overlay on the side exposed to the manifold, especially since the manifold includes an MP urea solution containing carbamates during operation.

[0039] Typically, if used, the tube sheet has an opening at each end of each U-shaped tube in the tube bundle, such as an opening (drill hole) through which the tube end extends from the tube or a sleeve extends from the tube through the opening. An example of a sleeve extending through a drill hole in a tube sheet is described in US2015 / 0086440.

[0040] Generally, if used, the tube sheet comprises, for example, a carbon steel plate and a layer of corrosion-resistant material, particularly urea-grade steel, on the side exposed to the shell space. The preferred material for this layer is the same as that for the shell liner. This layer is, for example, provided with weld overlay.

[0041] Therefore, preferably, the condenser includes a tube sheet, wherein the tube bundle is arranged on a first side of the tube sheet and the inlet (13) and outlet (14) for the MP urea-containing flow are provided by manifolds arranged on a second side of the tube sheet. The first side faces the shell-side space (18) and is therefore exposed to the shell-side space (18). The second side of the tube sheet is external and not exposed to the shell-side space (18). The tube sheet seals the shell and the shell-side space (18).

[0042] Generally, the first U-shaped tube bundle (4) has an inlet end and an outlet end. Typically, all tube ends at the inlet end are directly connected to a single inlet connection chamber, which in turn is connected to an inlet (13) for the MP urea flow. Typically, all tube ends at the outlet end are directly connected to a single outlet connection chamber, which in turn is connected to an outlet (14) for the MP urea flow.

[0043] Each tube bundle has an upper support leg portion and a lower support leg portion connected by elbows. Each tube in the tube bundle includes two horizontal supports connected by elbows. The supports of the tubes are arranged parallel to each other in the length direction of the shell within the tube bundle. The upper and lower supports of the tubes are vertically spaced apart and connected by elbow portions of U-shaped tubes.

[0044] The total number of tubes in the tube bundle is, for example, at least 50, at least 100, or at least 500. The first tube bundle (4) and the second tube bundle each include, for example, at least 100 tubes. The number of tubes depends on the facility's capacity.

[0045] In this invention, a first U-shaped tube bundle (4) is arranged around a second U-shaped tube bundle, for example, forming a ring, i.e., the first U-shaped tube bundle (4) is arranged concentrically around the second U-shaped tube bundle. The bends of the first tube bundle are therefore preferably concentric with the bends of the second U-shaped tube bundle. The first U-shaped tube bundle (4) is the outer tube bundle and is arranged closest to the housing. The second U-shaped tube bundle is typically at least partially surrounded by the outer first U-shaped tube bundle.

[0046] The upper leg portion (6) of the outer first U-shaped tube bundle (4) is connected proximally to the inlet (13) for the MP urea-containing flow. The lower leg portion of the outer first U-shaped tube bundle (4) is connected proximally to the outlet (14) for the MP urea-containing flow.

[0047] In this document, "proximal connection" specifically refers to a connection used for fluid to flow between the leg portion and the inlet or outlet without flowing through the pipe.

[0048] Specifically, the condenser includes a connection chamber that is directly connected to the upper leg portion (6) of the external first U-tube bundle (4) and optionally connected via piping to an inlet (13) for the MP urea-containing flow. The connection chamber is, for example, a manifold used in conjunction with a tube sheet. (US2020 / 0306663A1) Figure 1 Such a manifold is also shown in the diagram. The connection chamber can also be provided by a redistribution chamber and piping, as in US2020 / 0306663A1. Figure 2 As shown in A.

[0049] Preferably, the lower leg portion of the outer first U-shaped tube bundle (4) is directly connected to the connection chamber, which is optionally connected via a pipe to the outlet (14) for the MP urea-containing flow.

[0050] Preferably, the upper leg portion of the inner second U-shaped tube bundle is connected proximally to the steam outlet and the lower leg portion of the inner second U-shaped tube bundle is connected proximally to the boiler feedwater inlet; even more preferably, this is done through a connecting chamber.

[0051] The internal second U-shaped tube bundle is configured to generate steam, specifically connected to an inlet for boiler feedwater and an outlet for steam. The outlet is connected, for example, to a steam drum. The inlet for boiler feedwater is connected, for example, to a steam condensate tank, which includes, for example, a condensation unit. The boiler feedwater is, for example, steam condensate. The boiler feedwater at the inlet is, for example, at a gauge pressure of 4 to 5 bar. The fluid at the outlet includes steam and optionally condensate (wet steam). The fluid at the outlet is, for example, steam at a gauge pressure of 3.5 to 4.5 bar.

[0052] The outlet (14) for the MP urea-containing flow preferably has a larger flow area than the inlet (13) for the MP urea-containing flow, preferably at least 1.1 times or at least 1.2 times larger. Therefore, the condenser is suitable for the decomposition of carbamate in the first U-shaped tube bundle, thereby generating a two-phase fluid flow at the outlet (14).

[0053] Optionally, the outlet (14) for the urea-containing flow in MP is provided by two or more outlet nozzles and the total flow area of ​​these outlet nozzles is greater than the flow area of ​​the inlet. The flow area of ​​each nozzle may be smaller than the flow area of ​​the inlet.

[0054] Optionally, the inlet (13) for the MP urea-containing flow is provided by two or more inlet nozzles.

[0055] Preferably, the condensation device, more preferably the container, includes a reaction zone within the shell (i.e., in the shell-side space (18) between the bend of the first U-shaped tube bundle (4) and the shell). The reaction zone extends beyond, for example, at least 10% or at least 20% and / or up to 60% of the length of the container and shell. The dimension of the reaction zone in the longitudinal direction of the shell is, for example, at least 20% or at least 50% or, for example, at least 60% and / or up to 150% of the length of, the straight portion (single leg) of the outer first U-shaped tube bundle (4).

[0056] This reaction zone allows for the dehydration of carbamates. Preferably, the first fluid distributor (11) extends to the bottom of the reaction zone. This helps maintain thermal equilibrium within the reaction zone. Therefore, in a preferred embodiment, the condensation device is a pool reactor.

[0057] Specifically, preferably, the U-shaped horizontal tube bundle extends less than 80% or less than 70% of the horizontal length of the shell or shell-side space (18), and the remaining portion of the shell-side space (18) provides the reaction zone within the shell-side space (18). Thus, the carbamate condenser and the reaction zone are provided by a single vessel, which may be referred to as a pool reactor. The pool reactor preferably includes baffles in the shell. Preferably, one of the baffles is configured as an overflow weir, which provides gas / liquid separation in the shell-side space (18). Preferably, the shell-side space (18) has a liquid outlet and a separate outlet for gas. In operation, urea formation has already occurred in the shell-side space (18); in particular, the reaction zone can provide sufficient liquid residence time for the urea formation reaction. The urea solution from the shell-side space (18) of the pool reactor is supplied, for example, directly to an HP stripper.

[0058] Preferably, the condenser, more preferably the container, includes a second fluid distributor, particularly a distributor, arranged at the bottom section of the condenser for distributing a second high-pressure gas flow, particularly NH3, more particularly the NH3 feed, in the shell side, especially into the shell-side space (18). Preferably, the second fluid distributor extends horizontally below the first tube bundle (4) and is preferably connected to an elbow of the first tube bundle (4). If a reaction zone exists, the second fluid distributor, particularly the NH3 distributor, preferably does not extend into the reaction zone. The NH3 distributor is connected to an inlet for NH3 in the shell.

[0059] In a preferred embodiment, the apparatus includes a redistribution chamber preferably located in the shell-side space (18), wherein the redistribution chamber includes a wall for separating the HP process medium in the shell-side from the MP urea flow inside the redistribution chamber, wherein an end of a first U-tube bundle (4) is connected to the redistribution chamber such that the MP urea flow can flow between the first U-tube bundle (4) and the redistribution chamber. Preferably, the condensation device further includes a conduit extending from an inlet (13) or outlet (14) for the MP urea flow to the redistribution chamber, such that the MP urea flow can flow between the first tube bundle (4) and the inlet (13) or outlet (14) through the redistribution chamber and the conduit. Preferably, the apparatus includes four redistribution chambers, one at each end of the first U-tube bundle (4) and the second U-tube bundle; each redistribution chamber has a corresponding conduit leading to an inlet or outlet in the shell. In this embodiment, the tube sheet may be omitted. The redistribution chambers are spaced apart from the shell. The conduit is surrounded by the HP process medium in the shell-side space (18) during operation.

[0060] Preferably, the pipes directly connected to the redistribution chamber of the upper leg portion (6) of the external first U-shaped tube bundle (4) are arranged vertically upwards, i.e., the vertical pipe portion extending through the housing is further from the horizontal first fluid distributor (11) than the joint between the pipe and the redistribution chamber. This vertical arrangement of the pipes facilitates good distribution of the MP urea solution from the inlet (13) to the large number of tubes of the first U-shaped tube bundle (4).

[0061] The redistribution chamber is preferably made of duplex stainless steel, more preferably of a single-piece plate element of duplex stainless steel. The pipe end can be welded into the chamber through a drilled hole in the redistribution chamber wall (e.g., a plate) at the inside of the chamber. Using duplex stainless steel as the construction material for the redistribution chamber wall can prevent or mitigate crevice corrosion.

[0062] Further details and preferences for piping and redistribution chambers are given in US2020 / 0306663A1.

[0063] For all components preferably made of duplex stainless steel, particularly preferred duplex stainless steel alloys are available as... The steel is obtained and has the composition 29Cr-6.5Ni-2Mo-N, which is also specified by ASME Case 2295-3 and UNSS 32906. Duplex stainless steel has, for example, a composition (wt%) of: C: maximum 0.05, Si: maximum 0.8, Mn: 0.3 to 4.0, Cr: 28 to 35, Ni: 3 to 10, Mo: 1.0 to 4.0, N: 0.2 to 0.6, Cu: maximum 1.0, W: maximum 2.0, S: maximum 0.01, Ce: 0 to 0.2, balance Fe and (unavoidable) impurities. Preferably, the ferrite content is 30 to 70% by volume, more preferably 30 to 55%. More preferably, the steel comprises (wt%): C maximum 0.02, Si maximum 0.5, Cr 29 to 33, Mo 1.0 to 2.0, N 0.36 to 0.55, Mn 0.3 to 1.0, balance Fe and unavoidable impurities. Example steels are specified as described in WO 95 / 000674, which is incorporated herein by reference. Also suitable are duplex stainless steels having the following composition, by weight percent (wt.%): C maximum 0.030; Si maximum 0.8; Mn maximum 2.0; Cr 29.0 to 31.0; Ni 5.0 to 9.0; Mo less than 4.0; W less than 4.0; N 0.25 to 0.45; Cu maximum 2.0; S maximum 0.02; P maximum 0.03; balance Fe and unavoidable impurities; and wherein the content of Mo+W is greater than 3.0 but less than 5.0 (wt.%), and preferably a steel composition as described in WO 2017 / 014632, which is incorporated herein by reference. DP28W is also suitable. TMThe steel is a steel with the composition 27Cr-7.6Ni-1Mo-2.3WN, which is also specified by ASME Case 2496-1 and UNS S32808.

[0064] The present invention also relates to a urea production facility including an HP carbamate condenser according to the present invention.

[0065] refer to Figure 1 In a non-limiting example embodiment, the urea production facility (100) specifically includes an HP synthesis section (101), which includes an HP stripper (preferably a CO2 HP stripper (102)), a reaction zone (103), and an HP carbamate condenser (104) according to the invention. The HP synthesis section (101), such as the HP stripper (102), has a liquid flow connection (105) for the urea solution to reach the inlet (13) for the MP urea-containing flow through the expansion device (106) and, in particular, to the upper leg portion (6) of the outer first U-shaped tube bundle (4). A two-phase fluid flow (gas / liquid) is formed by expanding from HP to MP in the expansion device (106). A gas / liquid separation unit (106A) is disposed downstream of the expansion device (106) and has a liquid outlet connected to the gas inlet (13) and the outlet (111).

[0066] The stripper (102) receives urea synthesis solution (109) from the reaction zone (103) and has a gas outlet at the top. If the HP stripper (102) is a CO2 stripper, it has a CO2 inlet (not shown) at the bottom.

[0067] Preferably, the shell-side space (18) of the HP carbamate condenser (104) has a liquid outlet (109) for urea solution and a separate outlet (112) for gas.

[0068] The HP synthesis section (101) also has an inlet (not shown) for NH3 feed, such as to the HP carbamate condenser (104).

[0069] The facility includes a gas flow line (107) from the gas outlet of the HP stripper to the gas inlet (22) on the shell side of the condenser (104).

[0070] The HP stripper (102) is preferably of the CO2 stripping type. Alternatively, the HP stripper (102) may be of the hot stripping type.

[0071] The HP stripper (102) is a vertical shell-and-tube heat exchanger in operation, in which a falling film of urea solution to be stripped exists within the tubes, a heating medium (particularly steam) exists within the shell, a liquid inlet and a gas outlet are located at the top of the stripper, and a liquid outlet for stripping the urea solution is located at the bottom. Preferably, an inlet for CO2 feed, used as stripping gas, is also located at the bottom. The gas outlet of the stripper is connected to the shell-side gas inlet of the HP carbamate condenser (104). The liquid inlet is connected to the reaction zone (103) to receive all or part of the liquid from the reaction zone.

[0072] In embodiments with a CO2 HP stripper (102), the N / C ratio of the urea solution at the outlet of the reaction zone (103) (or reactor) is, for example, 2.8 to 3.8, or 2.9 to 3.2. Preferably, the synthesis pressure is in the range of 140 bar to 150 bar in the synthesis section. Preferably, the reaction zone (103) (e.g., reactor), condenser (104), and stripper (102) form a substantially isobaric loop.

[0073] The N / C ratio (NH3:CO2 ratio) of the reaction zone (103) reflects the composition of the initial mixture prior to urea production, which consists only of NH3, CO2 and H2O, as used in the urea plant field, and is a molar ratio, and is measured at the outlet of the reaction zone (103) of the urea synthesis solution.

[0074] The HP synthesis section (101), particularly the reaction zone (103) and / or the HP stripper (102), has a liquid flow connection for the HP urea solution to reach the inlet (13) for the MP urea-containing flow via an expansion device (106) (e.g., a control valve) and to the external first U-tube bundle (4), and in the present invention, particularly to the upper leg portion (6) of the external first U-tube bundle (4).

[0075] The urea production facility (100) preferably also includes a gas / liquid separation unit (106A) located directly downstream of the expansion unit (106), which is, for example, a flash evaporator, more preferably an MP adiabatic flash evaporator.

[0076] The HP synthesis section (101) includes a reaction zone (103). The reaction zone (103) is typically configured as a vertical urea reactor or as part of the HP carbamate condenser (100). Two or more reaction zones may be configured in parallel or in series.

[0077] The HP synthesis section (101) includes one or more inlets for CO2 feed and NH3 feed; wherein at least a portion of the CO2 feed is used as stripping gas in the HP stripper (102).

[0078] In one embodiment, the HP synthesis section (101) includes a pool reactor and a stripper (102). In another embodiment, the HP synthesis section (101) includes a pool condenser, a vertical urea reactor, and a stripper (102). In yet another embodiment, the HP synthesis section (101) includes a pool reactor, a vertical reactor as a downstream reactor, and a stripper (102). The vertical urea reactor typically has an inlet at the bottom, an outlet for removing urea solution from the top section, optionally uses a downcomer, and includes trays.

[0079] In a preferred embodiment, the urea production facility (100) includes a gas / liquid separator (106A), such as a flash evaporator, connected to receive a urea solution from the expansion unit (106), particularly a two-phase fluid containing the urea solution. The gas / liquid separator (106A) is arranged at a level vertically higher than the inlet (13) for the MP urea-containing flow and the upper leg portion (6) of the external first U-shaped tube bundle (4), preferably at least 2 m or at least 4 m higher. For the vertical level of the facility, vertical is defined relative to gravity. The gas / liquid separator (106A) has a liquid outlet connected to the inlet (13) for the MP urea-containing flow; a separate gas outlet (111); and a separate inlet connected to the expansion unit (106).

[0080] Preferably, a urea solution column of at least 3 m or at least 6 m height is maintained at the inlet (13) for the urea-containing flow in the MP. Preferably, in the urea production process, the urea solution column, for example, at least 2 m or at least 4 m height, and / or for example, up to 12 m or up to 10 m height, is maintained between the liquid outlet of the gas / liquid separator (106) and the inlet (13) (particularly the upper support leg (6)). This column height and the corresponding pressure head at the inlet (13) provide gravity flow of the urea solution through the pipe. The pressure head also improves the liquid distribution on the pipe.

[0081] Preferably, the expansion device (106) for expanding the urea synthesis solution from HP to MP is located at ground level of the urea production facility (100). Preferably, the solution is a urea solution stripped from an HP stripper (102) located at ground level. In this document, "ground level" of the facility means a maximum of 7m above ground level. Preferably, the expansion device (106) (e.g., an HP control valve) is placed directly at ground level.

[0082] Therefore, it is advantageous to release mechanical energy by expanding the urea solution from HP to MP, i.e., a pressure reduction of at least 50 bar or at least 70 bar can be used to transport the liquid to a higher level, particularly to the inlet of the gas / liquid separator (106), which is arranged, for example, 25 m to 50 m above the HP control valve.

[0083] In another embodiment, the HP carbamate condenser (104) includes a redistribution chamber located in and spaced apart from the shell side space (18). The walls of the redistribution chamber are in contact with the HP process medium on the outside and with the MP urea solution on the inside. The redistribution chamber is connected via piping to an inlet (13) of the MP urea-containing stream located in the shell. The HP carbamate condenser (104) comprises four redistribution chambers, each connected via piping to an inlet or outlet in the shell.

[0084] As a separate feature, the urea production facility (100) may include a gas / liquid separator (106A), such as a flash evaporator, which receives urea solution from the expansion unit (106). The flash evaporator (106A) is arranged at a height vertically higher than the inlet (13) for the MP urea-containing stream and the upper leg portion (6) of the external first U-tube bundle (4), for example, 4 m to 8 m above the upper leg portion (6). The flash evaporator has a liquid outlet at the bottom, which is connected to the inlet (13) for the MP urea-containing stream; and a separate gas outlet (111) at the top. This arrangement of the flash evaporator (106A) can also be used in conjunction with a tube sheet.

[0085] In one embodiment, the liquid outlet of the flash evaporator is directly connected to the inlet (13). Specifically, there is no pressure-reducing element, such as a control valve, between the liquid outlet and the inlet (13) of the outer first U-shaped tube bundle (4). The static pressure at the inlet (13) is substantially the same, for example, at most 1 bar lower than at the liquid outlet. In this way, the formation of a two-phase flow between the liquid outlet and the inlet (13) is avoided, which facilitates good delivery of the urea solution to the tube bundle and its distribution along the tube bundle's pipes.

[0086] The pool reactor preferably includes vertical baffles in the shell. Preferably, one of the baffles is configured as an overflow weir, which provides gas / liquid separation in the shell-side space (18).

[0087] Generally, in all embodiments of the urea production facility (100), the lower leg portion of the external first U-shaped tube bundle is preferably connected directly or indirectly (for urea solution) to a low-pressure (LP) dissociator via a (second MP) gas / liquid separator (106). The LP dissociator is typically contained within an LP recovery section. The LP urea solution from the LP dissociator is supplied, for example, to an evaporation section. The urea melt from the evaporation section is supplied, for example, to a finishing section, where it is solidified into a solid urea product using, for example, fluidized bed granulation or pelletizing. The urea melt can also be supplied partly or entirely as feedstock for a melamine plant. The MP or LP urea solution can also be purified and used to manufacture diesel exhaust fluid (DEF).

[0088] The gas from the second MP gas / liquid separation is condensed into an MP carbamate solution, for example, in an MP carbamate condenser, and typically comes into heat exchange contact with the urea solution to be heated. The MP carbamate condenser is, for example, a shell-and-tube heat exchanger, in which the MP gas is condensed in the shell side and the urea solution is heated in the tubes, typically having a vertical tube bundle. The urea solution to be heated is typically a urea solution obtained directly or indirectly from the LP dissociator, which is expanded to a subatmospheric pressure, typically 0.2 bara to 0.5 bara, preferably 0.25 bara to 0.35 bara. The heated urea solution is supplied, for example, to an evaporation section. The heat exchanger thus provides a combined MP carbamate condenser and a pre-evaporator. Heat is thus effectively used three times: first for HP stripping, then for MP carbamate dissociation in the HP carbamate condenser, and finally for heating the urea solution and / or removing water in the pre-evaporator; this advantageously provides two heat recovery heat exchanges through the walls without using steam as the heat transfer fluid. Pre-evaporation and evaporation sections are typically used to reduce the water content of urea solutions to obtain a urea melt having at least 90 wt.% or at least 95 wt.% urea and less than 10 wt.% or less than 5 wt.% or less than 2 wt.% water. This molten urea is then suitable for refining methods such as granulation or pelletizing.

[0089] The evaporation section includes, for example, a vacuum evaporator operating at below 0.30 bara or below 0.10 bara.

[0090] The gas from the LP dissociator is typically condensed into an LP carbamate solution. These carbamate solutions are then typically recycled to the HP carbamate condenser.

[0091] Generally, the MP urea solution from the HP carbamate condenser according to the present invention can be, for example, in a manner such as US20150119603A1. Figure 1 The MP segment is processed in the MP recirculation section shown, and the MP recirculation section includes an MP separator, an MP distillation column, and an MP condenser / evaporator.

[0092] The present invention also provides a urea production process for producing urea from ammonia and carbon dioxide in a urea production facility (100) according to the invention, the process comprising supplying gas from an HP stripper (102) to the shell side of an HP carbamate condenser (104) and at least partially condensing the gas into carbamate in the shell side and at least partially converting the carbamate into urea in the shell side, and supplying an MP urea solution further comprising carbamate to an inlet for an MP urea-containing stream.

[0093] The process involves heat exchange between a high-pressure process medium received in the shell-side space (18) and an MP urea-containing solution received in the first U-tube bundle (4), the solution also containing carbamate, thereby decomposing at least a portion of the carbamate into NH3 and CO2.

[0094] The process also involves supplying boiler feedwater to the inlet of the second U-tube bundle. Suitable boiler feedwater is, for example, steam condensate. Typically, steam is generated in the second tube bundle.

[0095] Urea solution from a stripper, particularly from an HP CO2 stripper (102), is flashed in a flash tank, for example, at a medium pressure, such as 20 to 30 bar, to produce flash vapor and flash urea solution. More preferably, the flash pressure is 23 to 28 bar, and even more preferably 25 to 28 bar. Flashing refers to the adiabatic expansion of the urea solution and the separation of the released liquid. The flash tank, for example, has an inlet for liquid at the top, an outlet for gas, and an outlet for liquid at the bottom.

[0096] Flash vapor is relatively rich in CO2 and is supplied directly or indirectly to the MP carbamate condenser to adjust (reduce) the NH3:CO2 molar ratio in the condenser.

[0097] The flash-evaporated urea solution is optionally further depressurized to within the MP pressure range and supplied to the first U-tube bundle. Preferably, the flash-evaporated urea solution is maintained at the same pressure and supplied to the first U-tube bundle. The flash evaporation step allows liquid to be delivered only to the first U-tube bundle, thereby contributing to good liquid distribution on the tubes. This applies to embodiments using a redistribution chamber (25) and embodiments using a tube sheet.

[0098] The flash gas, for example, is optionally condensed in an MP urethane condenser after countercurrent contact with the MP urea solution from a second gas / liquid separation step downstream of the first U-tube bundle, to advantageously provide a lower NH3:CO2 molar ratio in an LP urethane condenser.

[0099] Preferably, the MP urea solution supplied to the first U-shaped tube bundle is obtained by adiabatic expansion and gas / liquid separation of the urea solution from the HP synthesis section, and the temperature of the urea solution at the inlet is at least 10°C or at least 20°C lower than the temperature at the outlet of the HP carbamate condenser.

[0100] The urea solution at the inlet of the first tube bundle contains, for example, 40 to 60 wt.% urea, 20 to 30 wt.% water, 10 to 20 wt.% NH3, and 10 to 20 wt.% CO2, wherein the amounts of NH3 and CO2 include the corresponding amounts present in the solution as carbamates. The pressure is, for example, 20 to 30 bar. The temperature is, for example, 130°C to 150°C.

[0101] The liquid phase at the outlet of the first tube bundle, i.e. after gas / liquid separation, contains, for example, 50 to 70 wt.% urea, at least 5 wt.% more than at the inlet, and typically contains 2 to 7 wt.% CO2 (including CO2 present as carbamates), at least 5 wt.% less than at the inlet.

[0102] The amount of gas phase at the outlet of the first tube bundle corresponds to, for example, 10 to 20 wt. of the urea solution at the inlet of the first tube bundle.

[0103] Generally, the HP carbamate condenser (104) of the present invention can be used in urea facilities (100) and processes as shown in US20150119603A1.

[0104] Figure 2 An example HP condenser (104) according to the invention is schematically shown, with a more specific vertical cross-section shown. Unless otherwise stated, reference numerals are consistent with... Figure 1 The same applies to the HP carbamate condenser (104). It includes a redistribution chamber (25) and piping (26) as discussed above. During operation, the tube bundle is immersed in liquid in the shell-side space (18), as shown by the liquid level (27). The flow of the condensation process medium in the shell-side space (18) at the vertical section (i.e., through the reaction zone (103)) is indicated by the dashed arrow (28). Gas from the first fluid distributor (11) (as shown in the vertical section) causes upward flow and circulation at the center of the container. As shown, the outlet (14) for the MP urea-containing flow has a larger flow area (diameter) than the inlet (13) for the MP urea-containing flow. In fact, the outlet (15) for steam also has a larger flow area (diameter difference not shown) than the inlet (16) for boiler feedwater.

[0105] As used in this article, the term "carbamate" refers to the term ammonium carbamate used in the urea production industry.

[0106] As used herein, the term "usually" indicates a feature that is frequently used but not required. The phrase "in particular" indicates a feature that is exemplary but not required.

[0107] As used herein, for process flows (i.e., not for steam lines), high pressure (HP) is above 100 bar, for example, 120 bar to 300 bar, typically 150 bar to 200 bar. Medium pressure (MP) is for example, 10 bar to 70 bar (including intermediate pressures of 30 bar to 70 bar), particularly 15 bar to 30 bar, and low pressure (LP) is for example, 0 bar to 10 bar, particularly 1 bar to 8 bar or 2 bar to 5 bar. All pressures are in bar absolute pressure (bara).

[0108] The condensation in a carbamate condenser refers to the so-called carbamate condensation, which involves the reaction of NH3 and CO2 to form carbamate solutions. Carbamate decomposition refers to the dissociation reaction of carbamate into NH3 and CO2.

[0109] As used in this article, the gases used in HP process media include supercritical fluids.

[0110] Preferably, the urea production process is carried out in the urea facility of the present invention. All the preferences for the urea production process also apply to the urea facility. All the preferences and details for the equipment components related to the urea production process also apply to the urea facility.

[0111] Example 1

[0112] In the example process, the urea solution containing carbamate at the inlet at the top of the HP carbamate condenser of the present invention is about 143°C and about 25 bar, and the urea solution containing carbamate at the outlet at the bottom of the HP carbamate condenser is about 165°C and about 24.5 bar.

[0113] The process medium at the shell side, i.e., the HP process fluid, has a bottom temperature of approximately 173°C and a top temperature of approximately 171°C (i.e., at the liquid level, approximately at the height of the upper leg of the first outer U-shaped tube bundle). These points are... Figure 2 The tubes are denoted as X1 and X2, respectively. The first U-shaped tube bundle receives MP urea solution at the upper leg. In the second U-shaped tube bundle, steam condensate is supplied at approximately 148°C and 4.9 bar at the lower leg, and steam is released along with unevaporated boiler feedwater at 4.4 bar and 148°C. The flow configuration in the shell and in the two tube bundles facilitates good heat exchange in the HP urethane condenser.

[0114] The urea solution at the inlet of the first tube bundle contains 40 to 60 wt.% urea, 20 to 30 wt.% water, 10 to 20 wt.% NH3, and 10 to 20 wt.% CO2, wherein the amounts of NH3 and CO2 include the corresponding amounts present in the solution as carbamates. The pressure is 20 to 30 bar. The temperature is 130°C to 150°C.

[0115] The liquid phase at the outlet of the first tube bundle, i.e. after gas / liquid separation, contains, for example, 50 to 70 wt.% urea, which is at least 5 wt.% more than at the inlet, and contains 2 to 7 wt.% CO2 (including CO2 present as carbamate), which is, for example, at least 5 wt.% less than at the inlet.

Claims

1. A high pressure carbamate condensing device, comprising: A shell and tube heat exchanger comprising a shell and a first and a second horizontal U-tube bundle, each horizontal U-tube bundle having an upper leg portion and a lower leg portion connected by an elbow portion; a shell side space (18) defined by the shell; a first fluid distributor (11) arranged in the shell side space (18) at a bottom section of the high pressure carbamate condensation device for distributing a first high pressure gas stream into the shell side space (18); and an inlet (13) and an outlet (14) for an MP urea containing stream, wherein the first horizontal U-tube bundle (4) is arranged around the second horizontal U-tube bundle and the upper leg portion (6) of the outer first horizontal U-tube bundle (4) is proximally connected to the inlet (13) for the MP urea containing stream and the lower leg portion of the outer first horizontal U-tube bundle (4) is proximally connected to the outlet (14) for the MP urea containing stream; wherein the upper leg portion of the second horizontal U-tube bundle is proximally connected to a steam outlet and the lower leg portion of the second horizontal U-tube bundle is proximally connected to a boiler feed water inlet; and wherein the inner second horizontal U-tube bundle is configured to produce steam; wherein the outlet (14) for the MP urea containing stream has a larger flow area than the inlet (13) for the MP urea containing stream.

2. The high pressure carbamate condensation device according to claim 1, wherein the outlet (14) for the MP urea containing stream is provided by two or more outlet nozzles.

3. The high pressure carbamate condensation device according to claim 1 or 2, comprising a reaction zone in the shell side space (18) between the elbows of the first horizontal U-tube bundle (4) and the shell.

4. The high pressure carbamate condensation device according to claim 1 or 2, further comprising a second fluid distributor arranged at a bottom section of the high pressure carbamate condensation device for distributing a second high pressure gas stream into the shell side space (18).

5. The high pressure carbamate condensation device according to claim 4, wherein the second fluid distributor extends horizontally below the first horizontal U-tube bundle.

6. The high pressure carbamate condensation device according to claim 1 or 2, wherein the high pressure carbamate condensation device comprises a tube sheet, wherein the horizontal U-tube bundles are arranged at a first side of the tube sheet and the inlet and outlet are provided by headers arranged at a second side of the tube sheet.

7. The high pressure carbamate condenser according to claim 1 or 2, wherein the condenser comprises a redistribution chamber (25), wherein the redistribution chamber (25) comprises a wall separating the HP process medium in the shell side space from the MP urea stream inside the redistribution chamber (25), wherein the end of the first horizontal U-tube bundle is connected to the redistribution chamber (25) such that the MP urea stream can flow between the first horizontal U-tube bundle (4) and the redistribution chamber (25), wherein the high pressure carbamate condenser further comprises a pipe (26) extending from the inlet (13) or outlet (14) for the MP urea stream to the redistribution chamber (25) such that the MP urea stream can flow between the first horizontal U-tube bundle and the inlet (13) or outlet (14) through the redistribution chamber (25) and the pipe (26).

8. The high pressure carbamate condenser according to claim 7, wherein the redistribution chamber (25) is located in the shell side space (18).

9. The high pressure carbamate condenser according to claim 7, wherein the pipe (26) extending to the redistribution chamber (25) directly connected to the upper leg portion (6) of the outer first horizontal U-tube bundle (4) is arranged vertically upwards.

10. A urea production plant (100) comprising a high pressure synthesis section (101) comprising a HP stripper (102), a reaction zone (103) and a high pressure carbamate condenser (104), wherein the high pressure carbamate condenser comprises a shell and tube heat exchanger comprising a shell and a first horizontal U-tube bundle (4) and a second horizontal U-tube bundle, each horizontal U-tube bundle having an upper leg portion and a lower leg portion connected by an elbow portion; a shell side space (18) defined by the shell; a first fluid distributor (11) arranged in the shell side space (18) at a bottom section of the high pressure carbamate condenser for distributing a first high pressure gas stream into the shell side space (18); and an inlet (13) and an outlet (14) for an MP urea containing stream, wherein the first horizontal U-tube bundle (4) is arranged around the second horizontal U-tube bundle and the upper leg portion (6) of the outer first horizontal U-tube bundle (4) is proximally connected to the inlet (13) for the MP urea containing stream and the lower leg portion of the outer first horizontal U-tube bundle (4) is proximally connected to the outlet (14) for the MP urea containing stream, wherein the upper leg portion of the second horizontal U-tube bundle is proximally connected to a steam outlet and the lower leg portion of the second horizontal U-tube bundle is proximally connected to a boiler feed water inlet, and wherein the inner second horizontal U-tube bundle is configured to produce steam, wherein the high pressure synthesis section (101) has a liquid flow connection (105) for urea solution through an expansion device (106) to the inlet (13) for MP urea containing stream and to the upper leg portion (6) of the external first horizontal U-tube bundle (4), wherein the HP stripper (102) has a gas flow line (107) connected to the gas inlet (22) of the shell side space of the high pressure carbamate condensation device (104).

11. The urea production plant (100) according to claim 10, wherein the reaction zone (103) and / or the HP stripper (102) has the liquid flow connection (105).

12. The urea production plant (100) according to claim 10, wherein the urea production plant comprises a gas / liquid separator (106A) for urea solution from the expansion device (106), which is arranged at a higher vertical level of the urea production plant than the inlet (13) for MP urea containing stream and the upper leg portion (6) of the external first horizontal U-tube bundle (4), and which has a liquid outlet connected to the inlet (13) for MP urea containing stream.

13. The urea production plant (100) according to claim 12, wherein the gas / liquid separator (106A) is a flash vessel.

14. The urea production plant (100) according to claim 12, wherein the high pressure carbamate condensation device (104) comprises a redistribution chamber (25), wherein the redistribution chamber (25) comprises a wall separating the HP process medium in the shell side space from the MP urea stream inside the redistribution chamber (25), wherein the end of the first horizontal U-tube bundle is connected to the redistribution chamber (25) such that the MP urea stream can flow between the first horizontal U-tube bundle (4) and the redistribution chamber (25), wherein the high pressure carbamate condensation device further comprises a pipe (26) extending from the inlet (13) or the outlet (14) for the MP urea stream to the redistribution chamber (25) such that the MP urea stream can flow between the first horizontal U-tube bundle and the inlet (13) or outlet (14) through the redistribution chamber (25) and the pipe (26), wherein the pipe (26) extends vertically between the redistribution chamber (25) and the inlet (13) for MP urea containing stream.

15. The urea production plant (100) according to claim 14, wherein the redistribution chamber (25) is located in the shell side space (18).

16. The urea production plant (100) according to any one of claims 10 to 14, wherein the reaction zone (103) is provided as a vertical urea reactor or as part of the high pressure carbamate condensation device (104).

17. A urea production process producing urea from ammonia and carbon dioxide in a urea production plant (100) according to any one of claims 10 to 14, comprising supplying gas from the HP stripper (102) to the shell side space of the high pressure carbamate condensing device (104) and at least partially condensing the gas into carbamate at the shell side space and at least partially converting the carbamate into urea at the shell side space, and supplying MP urea solution also containing carbamate to the inlet (13) for MP urea containing stream.

18. The urea production process according to claim 17, wherein the MP urea solution is obtained by adiabatic expansion of urea solution from the high pressure synthesis section (101) and gas / liquid separation into MP urea solution and has a temperature at the inlet (13) at least 10 °C lower than at the outlet (14).

19. The urea production process according to claim 18, wherein at least a 3 m height of urea solution liquid column is maintained at the inlet (13) for the MP urea containing stream.

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