Urea plant with valve, urea production process, use and method

Abstract

The present disclosure, in one particular embodiment, relates to a plant and the production of urea in the plant, the plant comprising a valve body comprising an inner body portion and an outer body portion.

Description

[Technical field]

[0001] The present invention, in some embodiments, relates to a urea production plant including a valve. [Background technology]

[0002] An exemplary urea production plant is illustrated in Ullmann's Encyclopaedia of Industrial Chemistry, Chapter Urea, 2010.

[0003] In urea plants, the equipment used must have an adequate resistance to the process media. Materials such as duplex stainless steels are used to obtain adequate life span and resistance to corrosion due to the aggressive nature of the media involved in the urea production process. In particular, carbamate-containing process streams are highly corrosive, especially at the relatively high temperatures encountered in the high pressure synthesis section.

[0004] It is generally desirable to have better valves for urea plants, particularly those with better corrosion resistance and good mechanical properties, as well as relatively low capital expenditures. This desire is even more important for high pressure valves, and particularly for high pressure control valves.

[0005] Valves in urea plants are typically made from urea grade steel, for example duplex stainless steel.

[0006] The brochure "BHDT High Pressure Products for a Safe and Reliable Urea Industry", http: / / www.ureaknowhow.com, discusses various valves for urea plants.

[0007] An exemplary method for producing a one-piece duplex stainless steel unit is to prepare a sufficiently large block of duplex stainless steel, followed by shaping, e.g., forging, the material and modifying the microstructure in the solid state by additional heat treatment, which can be difficult for large sized devices due to possible non-uniform heating and cooling.

[0008] At the end of the life of the valve, or at least the end of the life of the valve body, the entire valve is conventionally replaced. Summary of the Invention [Problem to be solved by the invention]

[0009] There remains a need for better valves for urea plants, urea plants with better valves, urea production processes using such valves, and uses of such valves. [Means for solving the problem]

[0010] The present invention relates in a first aspect to a fertiliser production plant and / or a urea production plant comprising a valve comprising a valve body, an inlet for a fluid, an outlet for a fluid, a flow control member, a chamber for receiving a fluid arranged in the valve body, and a valve seat, the valve body comprising an outer body part and an inner body part mated with each other and / or mechanically connected with each other, whereby the outer body part is preferably made of a first material and whereby the inner body part is made of a second material, preferably the first and second materials being different from each other, the inner body part preferably comprising a surface exposed to said chamber and in direct contact with said fluid in the chamber during operation.

[0011] The invention also provides for the use of the valve in a carbamate environment, said use comprising exposing the inner body portion to a liquid comprising a carbamate and / or a gas stream comprising CO2 and NH3.

[0012] The present invention also relates to a process for the production of urea, comprising forming urea from NH3 and CO2 in a urea production plant according to the present invention.

[0013] The present invention also relates to a method of retrofitting an existing urea production plant equipped with a first valve by replacing the first valve with a valve as described herein. [Brief description of the drawings]

[0014] [Figure 1] 1 illustrates diagrammatically an exemplary valve for use in the present invention; [Diagram 2] 1A-1D show various views of an exemplary valve for use in the present invention. [Diagram 3] 1A-1D show various views of an exemplary valve for use in the present invention. [Figure 4] 1A-1D show various views of an exemplary valve for use in the present invention. [Diagram 5] 1A-1D show various views of an exemplary valve for use in the present invention. [Figure 6] 1A-1D show various views of an exemplary valve for use in the present invention. [Figure 7] 1 illustrates an exemplary urea production plant according to the present invention. [Figure 8] 1 illustrates an exemplary urea production plant according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Any illustrated embodiments are merely examples and are not intended to be limiting of the present invention.

[0016] The inner body part of the valve used in the present invention can be advantageously made from duplex stainless steel, having a relatively small size, especially a thin wall thickness compared to a single-body valve of equal flow rate, and therefore with suitable mechanical properties throughout the thickness, as well as corrosion resistance. In particular, the correct microstructure of duplex stainless steel can be more easily obtained. In particular, the maximum depth of the inner body part (depth being the smallest distance from an inner point of the inner body part to the surface of the inner body part) is small compared to a reference valve body forged from a single piece of metal, which is advantageous for the final heat treatment of the inner body part, especially the inner body part of duplex stainless steel.

[0017] The outer body portion of the valve does not come into direct contact with the carbamate-containing liquid during operation and therefore can be made from less corrosion resistant materials, which advantageously reduces capital expenditures.

[0018] The use of mating and / or mechanically connected inner and outer body portions provides the advantage that relatively complex shapes can be achieved for the chamber that receives the fluid during operation, which provides an advantage over, for example, a lining.

[0019] The lining process involves applying a thin layer of a suitable material, typically a polymeric material, such as PTFE, to the inner fitting surfaces in contact with the medium (surfaces to be protected against corrosion). The lining process generally cannot be applied to valves in chemical plants, such as the high pressure (HP) section of a urea plant, due to several limitations, including the maximum allowable temperature being too close to the operating temperature. The lining material is a soft thermoplastic material that cannot guarantee an adequate life against erosion, corrosion, and / or cavitation. Soft thermoplastic materials furthermore cannot guarantee an adequate life against the high pressures involved (e.g., at least 100 bar).

[0020] Welded duplex stainless steel cladding is not an attractive option for valve bodies due to the complex internal geometry of the valve body, and the inevitable microporosity of the cladding can compromise valve functionality.

[0021] The inner body portion of the valve used in the present invention may be made from a highly corrosion resistant steel, such as, for example, duplex stainless steel.

[0022] The present invention relates to a plant (system), in particular a fertilizer production plant (system) and / or a urea production plant (system). The plant is preferably suitable for making a product comprising urea. The product comprises, for example, urea ammonium nitrate, urea ammonium sulfate, e.g., urea-containing fertilizer. The product can also be, for example, diesel exhaust fluid (DEF) or a urea feed stream for a melamine plant, or urea for other uses, or a combination thereof.

[0023] The plant preferably comprises a high pressure (HP) synthesis section for the synthesis of urea. The HP synthesis section comprises a reaction zone, e.g. a high pressure (HP) stripper and also a high pressure (HP) carbamate enrichment zone. The HP stripper is e.g. of the CO2 stripping type or e.g. of the autostripping or NH3 stripping type. In the HP synthesis section, NH3 and CO2 feed react to form urea. The reaction zone is for example provided by at least partly a trayed vertical urea reactor, with one or more inlets at the bottom and one or more outlets at the top.

[0024] The HP stripper is, for example, a vertical shell-and-tube heat exchanger with a falling film of urea solution in the tubes, which has, for example, an inlet for a strip gas, for example CO2 gas stream, at the bottom, and an outlet for the stripped urea solution at the bottom and an outlet for a gas stream at the top connected to the inlet of the HP carbamate condensation zone.

[0025] The HP condensation zone is, for example, a shell-and-tube heat exchanger, e.g., a vertical or horizontal shell-and-tube heat exchanger, comprising at least one tube bundle, e.g., including straight or U-shaped tubes. In some embodiments, the reaction zone and the condensation zone are combined in a single vessel, e.g., in a pool reactor. The HP carbamate condensation zone has a fluid connection to the HP reaction zone, e.g., the HP carbamate condenser has an outlet connected to the inlet of the reactor.

[0026] In an exemplary embodiment, the urea plant is of the CO2 stripping type, the HP stripper has an inlet for CO2 at the bottom, and preferably the stripper tube is made of duplex stainless steel, preferably the same steel alloy as is preferred for the inner body portion of the valve. In this embodiment, the HP carbamate condenser is a horizontal shell-and-tube heat exchanger, e.g., with a U-shaped tube bundle, receiving cooling fluid in the tubes and gases from the stripper in the shell.

[0027] In an exemplary embodiment, the urea plant is of the self-stripping type, and the HP stripper comprises, for example, bimetallic stripper tubes. In this embodiment, the HP carbamate condenser is of the kettle type, for example, with a U-shaped tube bundle, receiving cooling fluid in the shell and gases from the stripper in the tubes.

[0028] The urea plant includes a recovery section. In this specification, the recovery section refers to a section for purifying the urea synthesis solution from the HP synthesis section to increase the urea content. The urea synthesis solution from the HP synthesis section includes urea, water, NH3, and carbamate.

[0029] The stripping section preferably includes a low pressure (LP) stripping section and, optionally, a medium pressure (MP) stripping section. The stripping section preferably comprises a low pressure (LP) and / or medium pressure (MP) decomposer with a gas outlet for removing carbamates from the urea solution. The gas stream is preferably partially or totally condensed in a carbamate condenser and the resulting carbamate solution is preferably recycled to the HP synthesis section. The urea plant is, for example, of full recycle design. Alternatively, the urea plant is of partial recycle design.

[0030] The urea plants may be, for example, but not limited to, CO2 stripping, self-stripping, or NH3 stripping, with non-limiting examples being Stamicarbon CO2 stripping designs, Saipem self-stripping designs, and Toyo CO2 stripping designs.

[0031] Optionally, the urea production plant is part of a melamine production plant.

[0032] The valve may be provided, for example, in the HP synthesis section, the MP recovery section, or, optionally, in the LP recovery section. The valve of the present invention is particularly useful in the HP synthesis section.

[0033] The valve preferably receives a fluid flow comprising or consisting of a liquid at at least 100 bar, more preferably at least 140 bar, e.g. less than 200 bar. The fluid flow may for example be a urea solution, e.g. a stripped urea solution comprising at least 10% by weight, or at least 15% by weight, of ammonium carbamate. The fluid flow, e.g. the urea solution, may for example have a temperature of at least 150°C, e.g. in the range of 160-220°C.

[0034] The valves may be designed, for example but not limited to, as regulating valves (control valves) or as on-off valves or as manually operated valves.

[0035] The valves can be used for fluids such as gases or liquids. For example, but not limited to, the valves can be used for urea solutions or for off-gas from the HP synthesis section. The valves can be used, for example, as control valves, e.g., reactor pressure reducing valves, or as isolated on-off valves. The off-gas streams from urea plants contain NH3 and CO2, which pose a risk of condensation corrosion.

[0036] The invention also relates to a process for the production of urea, comprising reacting NH3 with CO2 under urea-forming conditions in a urea production plant, the plant comprising at least one valve according to the invention, the plant being preferably a urea production plant according to the invention, for example pressures above 100 bar, for example in the range 100-400 bar, and temperatures above 120°C, for example in the range 150-250°C.

[0037] Preferably, the process includes forming ammonium carbamate and dehydrating the ammonium carbamate to provide urea and water.

[0038] The process is preferably of the CO2 stripping, NH3 stripping or self-stripping type and is preferably the same as that for the plant.

[0039] All valve preferences discussed in relation to the plant also apply to the process. All plant preferences, e.g., plant type and synthesis type, also apply to the plant in which the process is carried out. All process preferences also apply to the plant.

[0040] The invention also relates to the use of a valve according to the invention (or a valve for use in a plant according to the invention) in a carbamate environment, said use comprising exposing the inner body part to a liquid comprising carbamate and / or a gas stream comprising CO2 and NH3. This particularly relates to concentrated carbamate solutions, for example ammonium carbamate solutions having an ammonium carbamate concentration of 15% to 95% by weight. The inner body part is preferably in direct contact with such a carbamate solution during use or during the process. All the preferences of the valve discussed in relation to the plant and the process also apply to the valve according to the use.

[0041] The present invention also provides a method of retrofitting an existing urea production plant comprising a first valve by replacing the first valve with a valve comprising a valve body comprising an inner body portion and an outer body portion as described herein. All valve preferences discussed in relation to the urea plant apply equally to the method of retrofitting an existing urea production plant. The method preferably results in a plant of the present invention comprising a valve. The replaced valve is, for example, a high pressure (HP) control valve.

[0042] All of the valve features, preferences, and details discussed in the following paragraphs apply equally to all aspects of the present invention, including the urea production plants, processes, uses, and methods of retrofitting existing urea production plants.

[0043] Valves generally can be used to stop or start a fluid flow, or to vary the amount of a fluid flow, or to control the direction of a fluid flow, for example, or to relieve excess pressure, for example. A valve can also be referred to as a device for controlling the passage of a fluid or a device for controlling a fluid flow.

[0044] The valve body, which may also be called the valve shell, is the primary pressure boundary of the valve. The valve body holds the valve's elements together. During operation, the valve body resists fluid pressure loads from the connecting pipes. The valve body receives the inlet and outlet piping through joints. The valve body typically contains openings for assembly of the valve, particularly the flow-controlling internal elements, with the valve body.

[0045] The valve comprises a first opening and a second opening in the valve body for fluid to enter / exit the valve body. The openings are configured, inter alia, to allow fluid to enter / exit a chamber for holding the fluid, said chamber being provided within the valve body. Thus, the valve comprises an inlet and an outlet. The valve may comprise two or more inlets and may comprise two or more outlets.

[0046] The valve also comprises a flow control member, i.e. a flow control internal element, e.g. a control stem or disk. The flow control member can be moved between at least two different positions in the chamber to control the fluid flow. The flow control member is located in the chamber. The valve usually comprises a stem that connects the flow control member to a control device, such as an actuator or a handle. The flow control member is, for example, a plug, e.g. a pressure retaining component. The flow control member is typically a movable obstruction in the valve body that regulates and restricts the fluid flow through the valve. The flow control member can typically be moved to a position where a passage or port of the valve is blocked to control the fluid flow. The flow control member is also known as a disk, and the flow control member may have various shapes.

[0047] The valve may, for example, comprise a valve seat, providing a seating surface for the flow control member. The seat may be a surface of the valve body, but is preferably a separate element of the valve from the valve body. The valve seat may, for example, provide an inner surface of the valve body, which contacts the flow control member to form a leak-proof seal at least at one location of the flow control member.

[0048] The flow control member is connected to a control device, such as an actuator, for example, by a stem. The actuator is, for example, located outside the valve body. The stem transmits motion, for example, from a handle or actuator, to the flow control member. The actuator is, for example, the control device of the valve, and comprises, for example, a motor.

[0049] The valve typically comprises a removable part, allowing assembly of the valve, in particular of the inner body part in a recess in the outer body part. In some embodiments this part is provided by the valve seat and the seat connection piece. The removable part is connected to the valve body, for example by bolts. The removable part may comprise openings for fluid flow and may be connected to a pipe.

[0050] The valve may have a valve body size of, for example, 4 inches (10.2 cm) or greater, such as 8 inches (20.3 cm) or greater. The valve may have a nominal inside diameter of, for example, 2.75 inches (70 mm) or greater, such as 5.60 inches (142 mm) or greater, and / or the valve may have a seat diameter of, for example, 0.39 inches (10 mm) or greater, or 3.94 inches (100 mm) or greater, such as 6.70 inches (170 mm) or greater.

[0051] The valve body includes a chamber for receiving a fluid. In the valve of the present disclosure, the inner body portion provides the chamber. The walls of the chamber are provided by the inner body portion. In particular, the walls of the chamber are not provided by the outer body portion, but only by the inner body portion. The chamber is contained in the inner body portion.

[0052] The valve may be, for example, but is not limited to, an angle globe valve, a straight globe valve, a butterfly valve, or a check valve. The angle globe valve may be, for example, a control valve or an on-off valve. The straight globe valve may be, for example, a control valve or an on-off valve. The butterfly valve may be, for example, a control valve or an on-off valve.

[0053] The valve may, for example, comprise a movable plug or disk element and a fixed valve seat. The plug is typically movable within a chamber configured to receive a fluid within the body.

[0054] The valve seat provides a stable, uniform and typically replaceable shutoff surface. The valve seat may be, for example, a ring seat.

[0055] The valve may be designed, for example and without limitation, to withstand at least 50 bar gauge, or at least 100 bar gauge pressure, or at least 240 bar gauge with high pressure fluid therein.

[0056] The valve body comprises an inner body part and an outer body part. The inner body part and the outer body part are fitted together and / or mechanically connected to each other. The inner body part is for example mechanically held in the outer body part, in particular in a recess in the outer body part. The inner body part is for example fitted into a recess in the outer body part. In this way, the inner and outer body parts can be fitted together. For example, an interference fit or a friction fit is used. The inner body part and the outer body part are for example mechanically attached to each other. The inner body part is typically mechanically held in place in the outer body part, for example by a seat connection piece. The above provides an example of the inner and outer body parts mechanically connected to each other. The inner body part and the outer body part are therefore separate and disjoint parts. An interference fit and a friction fit are suitable for releasably holding the inner body part in place in the recess in the outer body part.

[0057] Typically, the inner body part is releasably held in place on the outer body part. The outer body part typically includes a recess that receives the inner body part, among other things, for assembly of the valve. In embodiments in which the inner body part is releasable from the outer body part, advantageously only the inner body part is replaceable for maintenance purposes and to mitigate any wear, corrosion or erosion caused by process fluids in the chamber.

[0058] Thus, it is preferred that the outer body portion has a recess for receiving, and more particularly for receiving and releasably retaining, the inner body portion, in such an embodiment, the inner body portion can be moved, e.g., slidable, from the outer body portion.

[0059] The valve body may include a gap between the inner body portion and the outer body portion and may also include a sealing element for said gap.

[0060] Preferably, the outer body portion is made of a first material and the inner body portion is made of a second material, the first material and the second material being different from each other, which may advantageously allow for lower manufacturing costs.

[0061] The inner body portion comprises a surface exposed to the chamber, i.e. which provides a boundary for the chamber and which is in direct contact with the fluid therein during operation. Preferably, the inner body portion is partly exposed to the chamber and partly in direct contact with the fluid during operation.

[0062] The outer body portion is made of, for example, but not limited to, carbon steel, duplex stainless steel, or austenitic stainless steel. In an interesting embodiment, the outer body portion is made of carbon steel. Other materials, such as duplex stainless steel, are also possible. However, the outer body portion is made of a material other than duplex stainless steel in some embodiments. The use of a material other than duplex stainless steel may be advantageous, firstly, due to the high content of expensive alloying elements in highly corrosion resistant duplex stainless steels, and secondly, due to the need to control the microstructure of duplex stainless steels, which may optionally be a challenge for larger equipment parts.

[0063] The outer body portion is made of, for example, carbon steel, austenitic stainless steel, and / or stainless steel containing up to 27.0 wt.% Cr, for example, 10.0-27.0 wt.% Cr, for example, 10.0-25.0 wt.% Cr, or for example, 17.0-25.0 wt.% Cr.

[0064] The outer body portion may for example have a wall thickness of at least 10 mm, or at least 20 mm, or at least 100 mm, or at least 300 mm, whereby the outer body portion typically contributes to the mechanical strength of the valve.

[0065] The valve is configured to ensure that the outer body portion does not come into contact with the corrosive process fluid during operation.

[0066] The outer body portion may be, for example, a single piece of metal.

[0067] The outer body part comprises, for example, a recess for holding the inner body part and at least two openings providing a passage for the fluid. Typically, the valve comprises a hollow element extending through each of said openings, allowing the fluid to flow from the chamber to said openings without direct contact with the outer body part. Typically, the outer body part also comprises an opening through which the stem of the flow control member extends. For example, the outer body part comprises an opening through which a portion of the inner body part extends, said portion of the inner body part comprising a stem packing. Preferably, the valve body comprises two separate fluid passages or ports from and to the chamber, said passages extending through both the inner body part and the outer body part.

[0068] The inner body part is operated in direct contact with the process fluid. It comprises a chamber and has a surface directly exposed to said chamber, said chamber receiving the process fluid during operation. The chamber may have, for example, a concavely curved inner surface. The parts of the inner body part which provide the walls of the chamber preferably fit entirely within recesses in the outer body part in the assembled valve body.

[0069] The inner body portion is, for example, made of a corrosion resistant material, for example duplex stainless steel.

[0070] The inner body portion may, for example, be a sleeve that fits over the outer body portion, for example through an opening in the outer body portion. The outer body portion may, for example, comprise a recess for receiving the inner body portion. Preferably, in this embodiment, the inner body portion is releasably held in place on the outer body portion.

[0071] The inner body portion is, for example, a sleeve provided in one piece, in two pieces, or, for example, in three or more pieces, preferably provided in one or more pieces. Optionally, the inner body portion is a single integral piece. Optionally, the inner body portion is a monolithic piece.

[0072] The inner body part is provided as a single integral part, more preferably made of duplex stainless steel, and the risk of corrosion of the crevice is avoided compared to an inner body part made as two or more parts. Furthermore, in this embodiment, compared to an inner body part provided as two or more parts with a crevice between them, which crevice gives the fluid in the chamber access to the outer body part, the crevice between the inner body parts can be completely shielded by the single integral inner body part, so that the crevice between the inner body parts and the outer body part is less exposed to the process fluid compared to an embodiment with an inner body part provided as two or more parts. This is particularly advantageous when the outer body part is made of carbon steel, which is susceptible to corrosion by the fluid in the chamber.

[0073] The inner and outer body parts are preferably fitted together. The inner and outer body parts are for example connected to each other by mechanical connecting elements, such as for example pin or bolt components. The inner body part is held in place on the outer body part. The inner and outer body parts can also be mechanically connected by an interference fit. For example, a sheet connecting piece can fix the inner body part in place. It can be observed that the above mentioned connecting means are suitable for releasably connecting the inner and outer body parts.

[0074] The inner body portion and the outer body portion together form a valve body. The inner body portion includes a chamber and includes at least two openings for fluids, and typically an opening for a stem.

[0075] The valve optionally comprises an O-ring and / or a sealing element between the inner and outer body portions, e.g., to prevent external fluids from entering a gap between the inner and outer body portions.

[0076] The valve typically comprises a sealing element, for example between the inner body part and the valve seat. A sealing element can also be simultaneously arranged between the protective element and the inner body part.

[0077] In embodiments where the inner body portion is made of two or more parts, the valve optionally comprises O-rings and / or sealing elements between the parts of the inner body portion. The one or more sealing elements are, for example, sealing rings or metal-to-metal seals. The sealing elements are, for example, made of PTFE, PEEK or are, for example, metal seals. Other types of non-metallic seals are also possible.

[0078] The valve may also comprise, for example, a leak detection element. The leak detection element is optional and is provided to detect any leakage of fluid, particularly process fluid, from the inner body portion to the outer body portion.

[0079] The valve seat is preferably releasably connected to the valve body. The valve seat is preferably replaceable for maintenance. The valve seat is preferably mechanically and releasably connected to the inner body part. In an exemplary embodiment, the valve seat is supported by the inner body part. The valve seat is, for example, in direct contact with the inner body part. The valve seat and the inner body part are preferably separate device parts, preferably separate components. This provides the advantage that the valve seat is independently replaceable.

[0080] The valve seat is made of, for example, duplex stainless steel, including the same suitable alloy as the inner body portion. The valve seat is typically configured to contact a flow control member, for example, a plug, when the valve is in a closed position to seal the valve.

[0081] The valve seat optionally includes a notch extension, which advantageously contributes to a proper fit with the plug, for example, the valve seat includes an extension with a mating surface for engaging the plug.

[0082] The valve comprises, for example, a seat connection piece. The seat connection piece is arranged, for example, to hold the valve seat in place in the valve body. The seat connection piece is also arranged, for example, to attach a tube or a pipe to the valve. The seat connection piece is attached or connected to the outer body part, for example, preferably by releasable, for example removable, connection means, such as a stud. The inner body part is preferably in direct contact with the seat connection piece, for example by a threaded flange. The seat connection piece can be removed from the valve body to allow replacement of the valve seat and / or the flow control member, such as a plugged stem. The seat connection piece is, for example, made of duplex stainless steel. The same material as the inner body part is preferred. The seat connection piece is, for example, a tubular piece, provided at one end with means for connection with a pipe, such as a flange, and at the other end, fitted into an opening in the inner body part and in direct contact with the valve seat. The seat connection piece is arranged, for example, to hold the inner body part in place in a recess in the outer body part. The seat connection piece is typically configured to hold the valve seat in place in the valve body, e.g. the inner body part and the seat connection piece together provide a recess into which the valve seat fits, thereby holding the valve seat in place, and therefore the seat connection piece is usually a pressure bearing component.

[0083] In embodiments where the inner body portion is releasably retained within the outer body portion, removal of the seat connection piece from the valve body allows the inner body portion to be removed from the outer body portion, which may be used, for example, for replacement or inspection of the inner body portion.

[0084] The valve, in some embodiments, comprises a control stem and / or a stem and a plug as the flow control member. The control stem may include a stem and a plug. The plug may be moved through the chamber by the stem.

[0085] The valve comprises, for example, a control stem or stems and a plug arranged to move the chamber between at least an open position and a closed position. The plug, for example, in the closed position, contacts the valve seat. The stem at one end extends through an opening in the wall of the valve. The stem is preferably provided with a plug at one end of the stem and at the other end the stem extends through an opening in the wall of the valve. For example, the stem and plug are one piece, or for example, the stem and plug are welded together. The stem and plug are both preferably made of duplex stainless steel or other corrosion resistant stainless steel.

[0086] Optionally, the stem extends through an opening in only the inner body portion, preferably said opening being provided with a stem packing. Optionally, the inner body portion comprises a surface exposed to the exterior of the valve and having an opening through which the stem extends. This embodiment provides an example of an embodiment in which some, but not all, of the exterior surface of the inner body portion is covered by the outer body portion.

[0087] The stem and plug operate in contact with the process fluid and are preferably made from a highly corrosion resistant steel, such as duplex stainless steel, preferably the same material as the inner body portion.

[0088] In embodiments in which the valve includes a stem opening, the valve typically includes a stem packing to provide a seal, for example a self-energizing stem packing is used.

[0089] Exemplary materials for the self-energizing stem packing include PTFE, PEEK, and a spring. The self-energizing stem packing, for example, includes a soft sealing ring, a support ring, and a spring. The spring is preferably made of stainless steel or other corrosion resistant material.

[0090] The stem packing may, for example, include a bushing and a seal.

[0091] The boosting is beneficial for the sealing functionality. In comparison to the standard seals used, pre-compression and regular checking of this pre-compression is not required with self-energizing stem packings. This means that self-energizing stem packings require no or less regular maintenance and the risk of leakage during valve operation is minimised.

[0092] In a preferred embodiment, the valve comprises a first opening in the inner body portion and a second opening in the outer body portion. The first and second openings are aligned with one another to allow fluid to flow between the second opening and the chamber. The openings in the inner and outer body portions together comprise the opening of the valve body.

[0093] The valve preferably comprises a protective element arranged in the second opening and protecting the outer body part from exposure to the fluid at the second opening. The protective element may also be called a pipe connection piece. The protective element is, for example, a tubular element, preferably having a radially extending end. The tubular element is inserted through the opening of the outer body part and preferably also through an opening of the inner body part aligned with said opening of the outer body part. The preferred radially extending end of the tubular element can be used to releasably attach the tubular element to the outer body part. The preferred radially extending end is, for example, provided on the outside of the valve body. The end of the tubular element arranged on the outside of the valve body, for example the radially extending end, can also provide a flange for a pipe.

[0094] The protective element is preferably releasably, e.g. removably, attached or connected to the valve body, in particular to the outer body part, thereby allowing easy replacement of the protective element. It may also be possible to detach the inner body part from the outer body part by removing the protective element or the pipe connection piece.

[0095] The protective element is made, for example, of duplex stainless steel, including the same preferred alloy as the inner body portion.

[0096] The valve comprises connection means for a pipe for connecting to the valve, e.g. a screw, etc. The protective element comprises an opening for fluid flow between the pipe and the valve chamber.

[0097] The valve may comprise a sealing system for sealing the protective element to the inner body part, for example a sealing ring, which may be a soft sealing, for example a PTFE sealing ring, or a metal-to-metal sealing.

[0098] The protective element is, for example, screwed onto the outer body part. The valve, for example, comprises a locking element which holds the protective element in place and which is attached or connected to the outer body part, for example by a screw.

[0099] The inner body portion is made from the bar by, for example, but not limited to, hot working and / or cold working and optional additional heat treatment. Hot working is a process where steel is plastically deformed above its recrystallization temperature and new strain-free grains are formed by the combined action of load and heat. Examples of hot working processes are forging, rolling, and extrusion. Cold working refers to plastically deforming steel below its recrystallization temperature. This causes permanent changes in the steel by introducing dislocations in its structure. The steel is then work hardened. Some methods of cold working include cold rolling, cold pilger rolling, and cold drawing. Steels are typically heat treated to produce a wide variety of microstructures and properties. Annealing, normalizing, tempering, and quenching are different types of well-known heat treatments.

[0100] The heat treatment can be used to obtain the desired mechanical properties in the inner body part, as well as the desired corrosion resistance. The relatively small size, especially the wall thickness (mid-wall distance) of the inner body part compared to the one-piece valve body (single valve body) of the equivalent valve, contributes to achieving suitable mechanical properties and corrosion resistance by heat treatment. This applies especially to the embodiment in which the inner body part is made of duplex stainless steel. Heat treating the inner body part of duplex stainless steel can also be performed on bar elements with pre-drilled holes. Also, for such a manufacturing method, the relatively small size (mid-wall distance) of the inner body part contributes to achieving suitable mechanical properties and corrosion resistance by heat treatment.

[0101] Aspects of the invention also relate to methods of making such inner body parts, for example, a method is provided for making an inner body part, preferably made of duplex stainless steel, comprising shaping a steel body into a shaped body, heat treating, and optionally further shaping, the shaped body including, for example, a drilled hole prior to heat treatment.

[0102] Suitable stainless steels for the inner body portion of the valve and for all other components of the valve that come into contact with fluids during operation (eg, stem, plug, valve seat, protective elements) include, for example, duplex stainless steels.

[0103] As used herein, the term "typical" denotes a feature that is frequently used, but not required.

[0104] The term "duplex stainless steel" refers to austenitic-ferritic duplex stainless steels.

[0105] The term "fluid" is used to include gases and liquids, as well as two-phase fluid flows. A fluid flow can include gases and / or liquids. A fluid flow can also be, for example, a suspension.

[0106] In some embodiments, the inner body portion of the valve and all other components that come into contact with the process fluid during operation (e.g., stem, plug, valve seat, protective elements) are made of duplex stainless steel, suitable duplex stainless steels include, for example, steel available as Safurex® steel and having a composition of 29Cr-6.5Ni-2Mo-N (which steel is also designated by ASME Code 2295-3 and UNS S32906) or, for example, steel available as DP28W™ steel and having a composition of 27Cr-7.6Ni-1Mo-2.3WN, which is also designated by ASME Code 2496-1 and UNS S32808. A dual-phase steel for these components has, for example, the composition (in mass%): C: max 0.05, Si: max 0.8, Mn: 0.3-4.0, Cr: 28-35, Ni: 3-10, Mo: 1.0-4.0, N: 0.2-0.6, Cu: max 1.0, W: max 2.0, S: max 0.01, Ce: 0-0.2, balance Fe and (unavoidable) impurities. Preferably, the ferritic composition is 30-70% by volume, more preferably 30-55%. More preferably, the steel contains (in weight%) C max 0.02, max 0.5, Si, Cr 29-33, Mo 1.0-2.0, N 0.36-0.55, Mn 0.3-1.0, balance Fe and impurities. Also suitable are duplex stainless steels having the following composition weight percent (wt%): C max 0.030, Si max 0.8, Mn max 2.0, Cr 29.0-31.0, Ni 5.0-9.0, Mo less than 4.0, W less than 4.0, N 0.25-0.45, Cu max 2.0, S max 0.02, P max 0.03, balance Fe and unavoidable impurities, where the Mo+W content is greater than 3.0 but less than 5.0 or less than 4.0 (wt%), more preferably having the steel composition as described in US20180195158A1, which is incorporated herein by reference. Duplex stainless steels having the following composition are also suitable: C max 0.03; Mn 0.80-1.50; P max 0.03; S max 0.03; Si max 0.80; Ni 5.8-7.5; Cr 28.0-30.0; Mo 1.50-2.60; N 0.30-0.40; Cu max 0.80, balance Fe.

[0107] Other urea grade duplex stainless steels may also be used for the inner body portion of the valve and for all other components that come into contact with process fluids during operation (eg, stem, plug, valve seat, protective elements).

[0108] As used herein, "highly corrosion resistant steel" refers inter alia to urea grade steels, and more specifically to urea grade duplex steels.

[0109] In one embodiment, the inner body portion is made of duplex stainless steel and preferably the outer body portion is made of carbon steel. Preferably, in these embodiments, the stem, plug, valve seat, protective element and inner body portion are made of duplex stainless steel.

[0110] In a preferred feature, the inner body portion is a sleeve that fits over and through an opening in the outer body portion, the outer body portion including a recess for receiving the inner body portion and for releasably retaining the inner body portion thereon. In a preferred feature, the outer body portion is a single piece of metal and the inner body portion is a single integral part.

[0111] In conclusion, the present invention relates to a plant and / or a urea production process in a plant, comprising a valve body comprising an inner body part and an outer body part, as well as a method for retrofitting an existing urea production plant.

[0112] As used herein, the term "plant" refers to a facility and may also be referred to as a system. The term "carbamate" refers to ammonium carbamate as the term is used in the art of urea production.

[0113] As used herein, HP (high pressure) refers to a pressure of at least 100 bara, e.g., 120-250 bara, or e.g., 110-160 bara, MP (medium pressure) refers to a pressure of, e.g., 15-80 bara, 20-80 bara, and LP (low pressure) refers to a pressure of, e.g., 1-10 bara, e.g., 4-10 bara, these pressure ranges being for the process streams of a urea plant and are not necessarily the same for the steam and heating fluids. The abbreviation "bara" refers to the absolute unit of bar. Pressures are absolute unless otherwise indicated.

[0114] FIG. 1 shows a schematic diagram of an exemplary valve (1) according to and / or for use in the present invention. The valve (1) comprises a valve body (2) according to the present invention, comprising an inner body portion (3) and an outer body portion (4). The valve (1) further comprises a first opening (5) and a second opening (6) for fluid to enter and leave the valve body (2), inter alia, a chamber (7) for holding the fluid in the valve body (2). The valve (1) also comprises a flow control member (8), e.g., a control stem or disk. The flow control member (8) can be moved between at least two different positions to control the fluid flow. The flow control member (8) is at least partially located within the chamber (7). The flow control member (8) can extend partially through the opening in the valve body (2).

[0115] 2 shows an exemplary valve (1) according to and / or for use in the present invention. Valve (1) comprises a valve body (2) comprising an inner body portion (3) and an outer body portion (4). The inner body portion (3) sits within a recess (28) in the outer body portion (4). As shown, both the inner body portion (3) and the outer body portion (4) are, for example, a single integral piece, for example, of two different types of steel. The recess (28) and the outer surface of the inner body portion (3) have interlocking shapes, with no gap between them, as shown.

[0116] The valve (1) further comprises a first opening (5) and a second opening (6) for fluid to enter and exit the valve body (2), particularly a chamber (7) for holding the fluid in the valve body (2). A flow control member (8) is provided as a plug (24) on the stem (25). A stem packing (9) is provided between the stem (25) and the inner body portion (3). The stem (25) extends through an opening (30) in the inner body portion (3). The stem (25) is movable within the chamber (7) to control the fluid flow.

[0117] The inner body portion (3) and the outer body portion (4) are held in place using an optional pin (10).

[0118] An O-ring (11) is located between the inner body portion (3) and the outer body portion (4) and provides a seal against, for example, external fluids.

[0119] Fluid flow openings (5) are provided through both the inner and outer body parts (26, 27). The pipe connection piece (12) provides an exemplary protection element located at the opening (27) in the outer body part (4) and, optionally, at the opening (26) in the inner body part (3). This protects the outer body part (4) from corrosive fluids in the openings (5). A sealing ring (13) is provided between the pipe connection piece (12) and the inner body part (3). The pipe connection piece (12) is connected at its radially extending end to the outer body part (4) by means of an optional plate (14) and screws (15). A pipe can be connected to the outer end of the pipe connection piece (12). The openings (26, 27) in the inner and outer body parts (3, 4), respectively, are aligned with each other to provide the fluid flow openings (5) through the valve body (2).

[0120] A seat connection piece (16) is provided to hold the inner body part (3) in place within the outer body part (4). The seat connection piece (16) is attached or connected to the valve outer body part (4) using a seat flange (17) and bolts and nuts (18, 19). The seat connection piece (16) includes a flange (20) for connection to a pipe.

[0121] In the exemplary embodiment, the seat connection piece (16) and the seat flange (17) are removable, and in the exemplary embodiment in which the pipe connection piece (12) protrudes from an opening (26) in the inner body part, the inner body part (3), which is a one-piece metal piece, can exit the recess (28) of the outer body part (4) through an opening in the outer body part on the side where the seat flange (17) is located (the right-hand side in the figure) after removal of the pipe connection piece (12) and after appropriate removal of the stem (25).

[0122] The valve (1) includes a valve seat (21) configured for sealing contact with a control stem, and in particular for sealing contact with a plug. The valve seat (21) includes a notch extension (23) for engaging the plug.

[0123] The control stem is attached at one end to an actuator, in this embodiment for example by means of a screw 22. Alternatively, the valve 1 can be operated manually.

[0124] The valve (1) may also comprise a leak detection element (29), which is optional and is a provision for detecting any leakage of fluid, particularly a process fluid, from the inner body portion (3) to the outer body portion (4).

[0125] FIG. 3 shows a view U of the valve (1) of FIG.

[0126] FIG. 4 shows a view V of the valve (1) of FIG.

[0127] FIG. 5 shows a view of the valve (1) of FIG. 2 along the line AA (see FIG. 4).

[0128] FIG. 6 shows an isometric view of the valve (1) of FIG.

[0129] 7 shows a schematic diagram of an exemplary urea plant (100) according to the invention. The urea plant (100) comprises a synthesis section (101) and a stripping section (102) which receives a urea solution from the synthesis section (101) and has an outlet for the purified urea solution. The urea plant comprises valves (103A; 103B) in the synthesis section (101) and / or in the stripping section (102) which comprise inner and outer body parts.

[0130] FIG. 8 shows a schematic diagram of an exemplary high pressure (HP) synthesis section of an exemplary urea production plant (100) according to the present invention. The HP synthesis section (101) comprises a reaction zone (104) comprising a reactor (104). The HP synthesis section (101) further comprises a high pressure (HP) stripper (105) and a high pressure (HP) carbamate condensation zone (106) comprising a carbamate condenser (106). In particular, the HP stripper (105) is shown as a CO2 stripping type stripper having an inlet for a CO2 feed at the bottom and an outlet for a stripped urea solution at the bottom connected to the stripping section (102). The HP carbamate condenser (106) is shown as a horizontal condenser containing condensed gases from the stripper (105) in a shell, which also receives an NH3 feed, and contains a cooling fluid in a U-shaped tube bundle. The carbamate solution from the HP carbamate condenser (106) is fed to the lower inlet of the reactor (104). By way of example only, the flow line for the stripped urea solution from the HP stripper (105) to the stripping section (102) can preferably be equipped with a valve (103) according to the present invention for reducing the pressure of the stripped urea solution from high pressure (HP) to medium pressure (MP) or low pressure (LP).

Claims

1. A fertilizer and / or urea production plant (100) comprising a valve (1, 103), the valve comprising a valve body (2), an inlet (5) for a fluid, an outlet (6) for a fluid, a flow control member (8), a chamber (7) for receiving a fluid in the valve body (2), and a valve seat (21), the valve body (2) comprising an outer body part (4) and an inner body part (3) mated with each other and / or mechanically connected with each other, whereby the outer body part (4) is made of a first material and whereby the inner body part (3) is made of a second material, the first material and the second material being different from each other, the inner body part (3) comprising a surface exposed to the chamber (7) and in direct contact with the fluid in the chamber (7) during operation.

2. 2. The plant according to claim 1, wherein the plant is a urea production plant (100) and the valves (1, 103) are comprised in a high pressure (HP) synthesis section (101) of the plant (100), the HP synthesis section (101) comprising a reaction zone (104) and preferably an HP stripper and an HP carbamate condensation zone (106).

3. 3. The plant according to claim 1 or 2, wherein the second material is a duplex stainless steel.

4. 4. The plant according to claim 1, wherein the flow control member (8) comprises a control stem, or a stem (25) and a plug (24), arranged for movement within the chamber (7) between at least two different positions to control the fluid flow, the stem (25) extending through an opening (30) in the inner body portion (3) provided with a stem packing (9).

5. 5. A plant according to any one of the preceding claims, wherein the valve seat (21) is supported by and in direct contact with the inner body part (3).

6. 6. The plant according to claim 1, wherein the valve (1, 103) comprises an opening (26) in the inner body part and an opening (27) in the outer body part (4), the openings (26, 27) being aligned with each other and allowing a fluid flow between the opening (26) in the inner body part (3) and the chamber (7), the valve (1, 103) comprising a protective element (12) arranged inside the opening (27) in the outer body part (4) and protecting the outer body part (4) from exposure to a fluid present at the opening (27) in the outer body part (4), the protective element (12) also optionally extending through the opening (26) in the inner body (3).

7. 7. The plant according to claim 6, wherein the protective element (12) is a tubular element inserted both in the opening (26) in the inner body part (3) and in the opening (27) in the outer body part (4).

8. 8. The plant according to any one of claims 1 to 7, wherein the valve (1, 103) comprises a seat connection piece (16) attached to the outer body part (4) by releasable connection means and holding the inner body part (3) in a predetermined position in a recess (28) of the outer body part (4), preferably also holding the valve seat (21) in a predetermined position in the valve body (2).

9. 9. The plant of claim 1, wherein the outer body portion includes a recess for receiving the inner body portion, the inner body portion being releasably held in position on the outer body portion.

10. 10. The plant of claim 1, wherein the inner body part is a sleeve that fits into a recess in the outer body part and through an opening in the outer body part.

11. 11. The plant of claim 1, wherein the inner body portion is mechanically retained in a recess in the outer body portion with an interference or friction fit.

12. Use of a valve in a carbamate environment, said valve comprising a valve body (2), an inlet for a fluid (5), an outlet for a fluid (6), a flow control member (8), a chamber (7) for receiving a fluid in said valve body (2), and a valve seat (21), said valve body (2) comprising an outer body part (4) and an inner body part (3) mated with each other and / or mechanically connected to each other, whereby said outer body part (4) is made of a first material and whereby said inner body part (3) is made of a second material, said first material and said second material being different from each other, said inner body part (3) comprising a surface exposed to said chamber (7) and in direct contact with said fluid in said chamber (7) during operation, said use comprising: exposing said inner body part (3) to a liquid comprising a carbamate and / or a CO ２ and N.H. ３ The use of the present invention includes exposing the material to a gas flow comprising:

13. The use according to claim 12, wherein said exposure is under high pressure of at least 100 bara, preferably in the range of 120 to 250 bara.

14. Use according to claim 12 or 13, wherein the valve has the characteristics defined in any one of claims 3 to 11.

15. In the plant according to any one of claims 1 to 11, NH ３ and CO ２ forming urea from

16. The process comprises CO ２ Stripping, NH ３ 16. The process for producing urea according to claim 15, which is of the stripping or self-stripping type.

17. 1. A method for upgrading an existing urea production plant comprising a first valve by replacing said first valve with a replacement valve, said replacement valve comprising a valve body (2), an inlet for a fluid (5), an outlet for a fluid (6), a flow control member (8), a chamber for receiving a fluid in said valve body (2) and a valve seat (21), said valve body (2) comprising an outer body part (4) and an inner body part (3) mated with each other and / or mechanically connected with each other, whereby said outer body part (4) is made of a first material and whereby said inner body part (3) is made of a second material, said first material and said second material being different from each other, said inner body part (3) comprising a surface exposed to said chamber (7) and in direct contact with said fluid in said chamber (7) during operation, said replacement valve preferably having the features defined in any one of claims 3 to 11.

Images