stripper bottom chamber

Abstract

This disclosure provides a bottom chamber of a stripper (or bottom reservoir) including an anti-vortex device, a baffle, and a guide vane. This disclosure further provides a stripper, a urea HP stripper, a urea unit, a method of operating the stripper, and a method of producing a composition based on solid particulate urea.

Description

Technical Field

[0001] This disclosure relates to the field of chemical manufacturing, and more particularly to the field of stripping equipment. Background Technology

[0002] A stripper is a device used in the manufacture of chemicals to remove gases or compounds that may decompose into gases when heated from a liquid solution. A typical stripper includes: a top or top chamber, which includes an inlet for the liquid solution to be stripped and a gas outlet for recovering any gases evaporated from the liquid solution, the top being fluidly connected to a middle or intermediate chamber; a middle or intermediate chamber, which includes multiple tubes in which the liquid solution forms a falling film; and a bottom or base chamber, which is where the liquid solution with the gases removed is collected.

[0003] Urea production plants typically include strippers. Urea is one of the most important industrial chemicals produced today, with approximately 200 million tons produced worldwide annually. The majority of this (over 90% of total production) is used as an agricultural fertilizer, serving as a nitrogen source. Urea is produced from ammonia (NH3) and carbon dioxide (CO2) through a two-step reaction: first, two molecules of ammonia react with one molecule of carbon dioxide to form ammonium carbamate (H2N-COONH4); then, the ammonium carbamate (referred to as carbamate ester in the remainder of this document) decomposes into urea and water. In a vessel (called a urea reactor), carbon dioxide and ammonia are mixed under high pressure and high temperature.

[0004] However, due to the thermodynamics and kinetics of the reaction, ammonium carbamate does not completely decompose into urea and water, resulting in a urea solution containing urea, ammonium carbamate, free ammonia, and water. The urea solution undergoes several purification steps to remove ammonium carbamate, unreacted ammonia, and water, yielding a concentrated urea melt. In some of these steps, ammonium carbamate (referred to herein as carbamate) is forced to decompose back into ammonia and carbon dioxide. Since ammonia and carbon dioxide are gases, they are readily removed from the urea solution. A crucial step in removing significant amounts of carbamate and free ammonia is carried out in a so-called high-pressure (HP) urea stripper, operating at pressures very close to the urea reactor. This allows for easy recirculation of ammonia and carbon dioxide gases back to the reactor. HP strippers are commonly operated at pressures between 80 and 150 bar. Strippers can also be operated at low pressures (less than 5 bar) or medium pressures (10 to 60 bar). The overall design of low-pressure or medium-pressure strippers is the same as that of HP strippers, but some details (such as the choice of manufacturing materials) may differ slightly due to the different operating conditions.

[0005] Based on the process technology, HP strippers can be classified into several categories: In all strippers, the HP urea stripper comprises three parts: a top or top chamber, where a urea solution rich in carbamates from the urea reactor is injected; a middle or intermediate chamber, where the urea solution diffuses into multiple bundled tubes and forms a downward-flowing falling film; and a bottom or bottom chamber. Heat is supplied to the middle section of the HP stripper via condensed steam and heats the outer surfaces of the tubes. The urea solution is heated from a temperature ranging from 160°C to 190°C (according to the technology) to a temperature between 165°C and 210°C (according to the technology) and maintained at a pressure typically between 130 bar and 180 bar (according to the technology). Within the multiple tubes of the HP stripper, some of the ammonium carbamate is converted back to its feedstock (ammonia and carbon dioxide) and evaporates from the urea solution along with some free ammonia. The gas rises in the center of the tube and is collected through the gas outlet located in the top chamber of the urea HP stripper, while the urea solution, from which carbamate and free ammonia have been removed, is collected at the bottom of the HP stripper in a container (often called a bottom reservoir). In some techniques, stripping gas containing carbon dioxide and / or ammonia is introduced into the container to aid in ammonia stripping within the tube. In some techniques, due to the highly corrosive nature of carbamates, a small amount of air is introduced into the container to provide oxygen for passivating the stainless steel.

[0006] The urea solution is sent downstream from the container for further purification steps, operating at a pressure lower than that of the HP stripper. It is important to control the residual carbamate and free ammonia levels in the urea solution leaving the HP stripper, and to prevent any ammonia and carbon dioxide gases produced by carbamate decomposition from escaping from the bottom with the urea solution. Any ammonia and carbon dioxide gases present in the urea solution leaving the HP stripper must be removed in the downstream steps. Therefore, a certain liquid level should be maintained in the bottom chamber of the HP stripper (container). Furthermore, the liquid level in the bottom chamber of the HP stripper should be kept as low as possible so that:

[0007] • Reduce residence time and avoid urea hydrolysis reactions that decompose urea back into carbamate and further into ammonia and carbon dioxide; and / or

[0008] • Reduce the formation of biuret from urea; high temperature and residence time can enhance this reaction.

[0009] However, it has been observed that even when a high liquid level is maintained in the lower cylindrical section of the bottom reservoir, the urea solution collected at the bottom of the HP stripper may still contain some gases, particularly ammonia and / or carbon dioxide. As mentioned above, this is highly undesirable. Therefore, there is a need to develop a new type of stripper to prevent this phenomenon. Summary of the Invention

[0010] In one aspect, this disclosure provides a stripper apparatus including a bottom chamber and the bottom chamber of the stripper apparatus, the bottom chamber comprising: a container including a lower cylindrical section, a middle section, and an upper cylindrical section; a plurality of openings located on the top wall of the upper cylindrical section; a liquid outlet located at the bottom of the lower cylindrical section of the container and concentric with the lower cylindrical section of the container; wherein the bottom chamber includes an anti-vortex device, the anti-vortex device including a top circular plate parallel to the bottom of the lower cylindrical section, concentric with the liquid outlet, and connected to the bottom of the lower cylindrical section of the container by one or more vertical plates, wherein the diameter of the top plate is larger than the diameter of the liquid outlet to prevent fluid from falling directly into the liquid outlet from one or more of the plurality of openings; a baffle for preventing air bubbles carried by the fluid falling from the plurality of openings from reaching the liquid outlet, the baffle including baffles concentric with the liquid outlet. A first cylindrical section with a diameter greater than that of the anti-vortex device and a height greater than that of the anti-vortex device, wherein the first cylindrical section is connected to the bottom of a lower cylindrical section, and a second section is connected to the top of the first cylindrical section and has an upwardly pointing frustoconical shape, wherein the diameter of the bottom of the second section is equal to the diameter of the first cylindrical section, the first cylindrical section includes one or more openings to allow fluid to flow from the wall of the lower cylindrical section to the anti-vortex device, a baffle overlaps with the anti-vortex device, a guide plate is used to guide fluid falling from the wall of the middle outward section to the side wall of the lower cylindrical section, the guide plate is concentric with the liquid outlet, wherein the diameter of the guide plate is equal to or greater than the diameter of the baffle, but less than the diameter of the lower cylindrical section of the container, wherein the guide plate is located at the junction of the lower cylindrical section and the middle section, partially extending into the lower cylindrical section of the container and partially extending into the middle section of the container.

[0011] Another aspect of this disclosure provides a stripper apparatus, particularly a urea HP stripper apparatus, which includes a bottom chamber according to this disclosure.

[0012] In another aspect, this disclosure provides a method for operating a stripper apparatus according to this disclosure as a urea HP stripper apparatus, comprising the steps of: directing a urea solution containing urea, carbamate, ammonia and water to a liquid inlet of the urea HP stripper apparatus; and recovering the urea solution containing urea and water and removing carbamate, ammonia and optionally carbon dioxide from a liquid outlet.

[0013] In another aspect, this disclosure provides the use of a urea stripper according to this disclosure for removing carbamates from an aqueous solution containing urea and carbamates.

[0014] In another aspect, this disclosure provides the use of the bottom chamber of the urea HP stripper according to this disclosure for reducing the content of ammonia and carbon dioxide in the liquid drawn from the bottom chamber of the stripper via the liquid outlet. Attached Figure Description

[0015] The following description of the accompanying drawings, which illustrate specific embodiments of the system according to this disclosure, is given by way of example only and is not intended to limit this description, its application, or use. In the drawings, the same reference numerals denote the same or similar parts and features.

[0016] Figure 1 This image shows a cross-section of the bottom chamber of an embodiment of the urea HP stripper according to the present disclosure. Detailed Implementation

[0017] Unless otherwise defined, all terms (including technical and scientific terms) used in disclosing this invention have the meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. Further guidance includes the inclusion of terminology definitions to better understand the teachings of this invention.

[0018] All references cited in this specification are hereby deemed to be incorporated herein by reference in their entirety.

[0019] As used herein, the following terms have the following meanings:

[0020] Unless the context clearly specifies otherwise, as used herein, “a,” “an,” and “the” refer to both the singular and plural referents. For example, “section” refers to one or more sections.

[0021] As used herein, the term "about" to refer to measurable values ​​such as parameters, quantities, and durations means a variation that covers or deviates from the specified value by + / -20% or less, particularly + / -10% or less, more particularly + / -5% or less, even more particularly + / -1% or less, and still more particularly + / -0.1% or less, such variations being suitable for implementation in the disclosed invention. However, it should be understood that the values ​​referred to by the modifier "about" are themselves specifically disclosed.

[0022] As used herein, “comprise,” “comprising,” “comprises,” and “comprised of” are synonymous with “include,” “including,” “includes,” or “contain,” “containing,” and are inclusive or open-ended terms that specify the presence of the following thing (e.g., a component) and do not exclude or preclude the presence of additional, unlisted components, features, elements, components, or steps known in the art or disclosed herein.

[0023] "Carbamate" refers to ammonium carbamate, which is a compound obtained by reacting two moles of ammonia with one mole of carbon dioxide.

[0024] The enumeration of a range of values ​​by endpoints includes all numbers and fractions contained within that range, as well as the endpoints of the enumeration.

[0025] Unless otherwise defined, expressions such as “percentage by weight,” “%wt,” or “% by weight” throughout this specification refer to the relative weight of each component based on the total weight of the formulation.

[0026] In the context of this application, the terms "stripper" and "stripper apparatus" are used interchangeably. Also in the context of this application, a stripper apparatus refers to a top-to-bottom stripper apparatus in which the liquid solution to be stripped is guided to the top chamber of the stripper apparatus and falls under gravity through multiple tubes. The liquid solution is collected in the bottom chamber of the stripper apparatus. Therefore, when referring to different features of the apparatus or subsections thereof according to this disclosure, the terms "top," "upper," "bottom," and "lower" refer to the location of the features within the apparatus under normal operating conditions.

[0027] In one aspect, this disclosure provides a stripper apparatus including a bottom chamber and the bottom chamber of such a stripper apparatus, the bottom chamber comprising: a container including a lower cylindrical section, an intermediate section, and an upper cylindrical section; a plurality of openings located on the top wall of the upper cylindrical section; a liquid outlet located at the bottom of the lower cylindrical section of the container and concentric with the lower cylindrical section of the container; wherein the bottom chamber includes an anti-vortex device including a top circular plate parallel to the bottom of the lower cylindrical section and concentric with the liquid outlet and connected to the bottom of the lower cylindrical section of the container via one or more vertical plates, wherein the diameter of the top plate is larger than the diameter of the liquid outlet to prevent fluid from falling directly into the liquid outlet from one or more of the plurality of openings; and a baffle for preventing air bubbles carried by the fluid falling from the plurality of openings from reaching the liquid outlet, the baffle including openings connected to the liquid outlet. A first cylindrical section, concentric with a diameter greater than that of the anti-vortex device, and a height greater than that of the anti-vortex device, is connected to the bottom of a lower cylindrical section. A second section, connected to the top of the first cylindrical section and having an upwardly pointing frustoconical shape, is provided, wherein the diameter of the bottom of the second section is equal to the diameter of the first cylindrical section. The first cylindrical section includes one or more openings to allow fluid to flow from the wall of the lower cylindrical section to the anti-vortex device. A baffle overlaps with the anti-vortex device. A guide vane is used to guide fluid falling from the wall of the middle outward section to the side wall of the lower cylindrical section. The guide vane is concentric with the liquid outlet. The diameter of the guide vane is equal to or greater than that of the baffle, but less than that of the lower cylindrical section of the container. The guide vane is located at the junction of the lower cylindrical section and the middle section, extending partially into the lower cylindrical section of the container and partially into the middle section of the container.

[0028] The stripper's bottom chamber comprises three sections: an upper cylindrical section connected to a scrubber chamber containing tubes in which the solution is heated and the gaseous components are stripped; a middle section, which does not have a constant diameter, connecting the upper cylindrical section to the lower cylindrical section; and the lower cylindrical section where the solution is collected from multiple tubes and exits the stripper through a liquid outlet.

[0029] Under typical operating conditions, the stripper contains a certain amount of liquid solution located in its bottom section. It is generally believed that when liquid flowing from multiple tubes into the intermediate section and overflowing into the lower cylindrical section collides with the surface of the liquid solution in the lower cylindrical section, some of the gas present in the bottom chamber of the stripper is entrained by the solution in the form of bubbles. After entering the solution, the gas can be collected through the liquid outlet, especially when the residence time of the liquid in the stripper is relatively short, typically 10 to 20 seconds in a urea HP stripper. It is generally believed that a large amount of entrained gas reaches the liquid outlet due to the momentum of the liquid solution overflowing from the intermediate section to the central region of the lower cylindrical section. The presence of gases, such as ammonia and / or carbon dioxide, in the liquid solution at the liquid outlet is highly undesirable, as these gases can cause downstream overload and system chaos. Furthermore, the gas can often be recycled, for example in the urea reactor, to increase the yield of the production process.

[0030] A first cylindrical plate or baffle is installed in the lower cylindrical section of the stripper to prevent the liquid solution (overflowing from the middle section and reaching the bottom of the lower cylindrical section due to momentum) from contacting the inlet of the anti-vortex device, thus forcing any entrained gas to rise and move away from the inlet and liquid outlet of the anti-vortex device. The baffle is inclined at the top to prevent any bubbles from diffusing into the central region of the lower cylindrical section as the liquid solution overflows downwards. Secondly, a guide plate is located at the junction of the lower cylindrical section and the middle section of the stripper, causing the overflowing liquid solution to remain within the same annular area formed by the baffle.

[0031] The standard stripper unit has a funnel-shaped chamber comprising: a lower cylindrical section, a middle section, and an upper cylindrical section; multiple openings located on the top wall of the upper cylindrical section; and a liquid outlet located at the bottom of the lower cylindrical section and concentric with it. A vortex deflector is installed at the liquid outlet. The vortex deflector consists of a plate with a diameter larger than the liquid outlet, fixed to the bottom by a vertical plate and maintained at a certain distance from the liquid outlet.

[0032] To reduce the amount of gas present in the liquid solution collected at the liquid outlet, several improvements were made to the standard stripper. First, an anti-vortex device is located at the bottom of the lower cylindrical section of the vessel. The anti-vortex device includes a top circular plate parallel to the bottom of the lower cylindrical section and concentric with the liquid outlet, wherein the diameter of the top plate is larger than the diameter of the liquid outlet, and the top circular plate is fixed to the bottom of the lower cylindrical section by a vertical plate. The anti-vortex device prevents vortex formation as the liquid solution leaves the stripper. The anti-vortex device also prevents solution falling from the tube located at the center of the stripper from directly entering the liquid outlet of the vessel. The top circular plate prevents any gas entrained by the falling solution at the center of the vessel from flowing directly to the liquid outlet.

[0033] In one embodiment, the anti-vortex device is fixed to the bottom of the lower cylindrical section by cross-arranged vertical plates. The anti-vortex device includes a top circular plate and is fixed to the bottom of the lower cylindrical section of the container. The anti-vortex device can be connected to the bottom of the lower cylindrical section by one or more vertical plates that allow the liquid solution to flow to the liquid outlet. For example, the anti-vortex device can be fixed by cross-arranged vertical plates, i.e., the vertical plates are connected at the central axis of the liquid outlet and positioned at 90° to each other, which is a typical design for anti-vortex devices.

[0034] In one embodiment, the diameter of the top circular plate of the anti-vortex device is between 400 mm and 600 mm, particularly between 500 mm and 600 mm.

[0035] In one embodiment, the diameter of the top circular plate of the anti-vortex device is between 100% and 150% of the diameter of the liquid outlet.

[0036] Furthermore, the base of the HP urea stripper includes a baffle comprising: a first cylindrical section concentric with the liquid outlet and having a diameter larger than that of the anti-vortex device, the height of the first cylindrical section being greater than that of the anti-vortex device; and a second section connected to the top of the first cylindrical section and having an upward-pointing truncated cone shape, i.e., pointing towards the middle section, wherein the diameter of the bottom of the second section is equal to the diameter of the first cylindrical section. The first cylindrical section includes one or more openings, thereby allowing fluid to flow from the wall of the lower cylindrical section to the anti-vortex device, and the baffle overlaps with the anti-vortex device, meaning that there exists a cross-section of the base comprising the first cylindrical section of the baffle and the vertical plate of the anti-vortex device. The primary function of the baffle is to block the flow directly from the outer region of the lower cylindrical plate to the liquid outlet. By blocking this flow, the liquid solution and the air bubbles entrained in the solution must move upward to the top of the baffle before flowing past it. This movement increases the chance of air bubbles leaving the liquid solution without being recovered at the liquid outlet.

[0037] The first cylindrical section of the baffle is concentric with the liquid outlet, meaning the first cylindrical section of the baffle and the liquid outlet share a common central axis and are connected to the bottom of the lower cylindrical section. The first cylindrical section of the baffle includes one or more openings or slots near the bottom of the lower cylindrical section to allow the liquid solution to circulate within a very small area between the wall of the lower cylindrical section of the container and the liquid outlet. This circulation prevents liquid stagnation, which can be problematic if the liquid contains corrosive compounds, such as carbamates in a urea stripper. There may be one, two, three, four, five, six, seven, eight, nine, ten, or more slots or openings. The openings may be evenly distributed along the circumference of the first cylindrical section of the baffle, and in particular, the openings may contact or be adjacent to the bottom of the lower cylindrical section of the container. The openings may have any kind of shape, such as regular polygonal shapes, such as square, triangular, or pentagonal shapes; or circular or irregular shapes. In one embodiment, the openings are square in shape. The diameter of the opening can be between 1.0 mm and 5.0 mm, particularly between 1.0 mm and 4.0 mm, and even more particularly between 1.0 mm and 3.0 mm, that is, the diameter is small enough to allow the urea solution to flow, but not to allow air bubbles to flow.

[0038] In one embodiment, one or more openings included in the first cylindrical segment of the baffle have a polygonal shape, particularly a square shape, especially a square shape in which the sides of the square are between 1 mm and 10 mm.

[0039] In one embodiment, one or more openings occupy 0.1% to 90% of the circumference of the first cylindrical segment of the baffle, i.e., 0.1% to 50% of the circumference is empty, allowing fluid to move from the side of the lower cylindrical segment to the vortex deflector. The larger the area occupied by the one or more openings, the more fluid will be allowed to move to the deflector, reducing the risk of fluid stagnation. However, this also increases the risk that some bubbles will pass through the one or more openings and reach the vortex deflector. In one embodiment, the one or more openings occupy less than 10% of the circumference of the first cylindrical segment of the baffle, particularly less than 5.0%, more particularly less than 2.0%, and even more particularly less than 1.0%. In one embodiment, the combined area of ​​the one or more openings includes 10 to 100 mm². 2 Between 10 and 80mm 2 Between 10 and 70mm, and more specifically... 2 Between, and even more specifically between 10 and 50mm 2 between.

[0040] The second section of the first plate is a truncated cone pointing upwards, towards the middle of the container. The purpose of this second section is to prevent air bubbles carried by the urea solution falling from the top from spreading further to the bottom, ensuring they reach the inlet of the anti-vortex device. The truncated cone prevents the bubbles from flowing towards the center of the lower cylindrical section of the container, thus reducing the momentum of the urea solution. Consequently, the bubbles will rise because they are lighter than the liquid urea solution.

[0041] The bottom chamber of the stripper apparatus according to this disclosure further includes a guide plate concentric with the liquid outlet, wherein the diameter of the guide plate is equal to or greater than the diameter of the baffle, but smaller than the diameter of the lower cylindrical section of the container, wherein the guide plate is partially located in the lower cylindrical section of the container and partially located in the middle section of the container. That is, the guide plate is a cylindrical plate that extends partially into the lower cylindrical section and partially into the middle section of the container. The function of the guide plate is to prevent the liquid solution from the middle section from overflowing into the center of the lower cylindrical section and to carry the entrained gas into the center. The guide plate guides the liquid solution and the entrained gas along the wall of the lower cylindrical section of the container to increase the distance traveled by the solution and gas, and guides the liquid solution and the entrained gas to the annular portion formed by the first cylindrical plate. The guide plate is coaxial with the first cylindrical plate and the liquid outlet.

[0042] In one embodiment, the bottom chamber of the stripper is the bottom chamber of a urea stripper, and the liquid solution flowing in the tube is a urea solution containing urea, carbamate, ammonia, and water. In another embodiment, the bottom chamber of the stripper is the bottom chamber of a urea HP stripper, and the liquid solution flowing in the tube is a urea solution containing urea, carbamate, ammonia, and water.

[0043] In one embodiment, the height of the cylindrical section of the baffle is between 30% and 70% of the height of the lower cylindrical section of the container, particularly between 30% and 65%, and even more particularly between 30% and 60%. The higher the first cylindrical plate, the longer the distance the fluid must travel to reach the liquid outlet, and the higher the area of ​​gas release entrained in the solution after the fluid changes direction. Increasing the fluid travel distance may increase the chance of gas escape, but it may also increase the residence time of the liquid solution in the stripper. In some cases, increasing the residence time of the liquid solution in the stripper may not be recommended: for example, in a urea stripper, increasing the residence time of the urea-containing liquid solution increases the formation of biuret, a byproduct of the decomposition of urea under high pressure and high temperature conditions and the decomposition of urea in feedstocks ammonia and carbon dioxide. Biuret is not an ideal product, and its formation should be limited as much as possible because partial decomposition of urea reduces the efficiency of the urea unit. Therefore, it may be necessary to find a balance between the amount of gas collected at the liquid outlet, the amount of biuret present in the composition at the liquid outlet, and the amount of urea present in the liquid solution.

[0044] In one embodiment, the second section of the baffle (i.e., the truncated cone) has an angle between 15° and 60° deviating from the vertical axis and an upper diameter equal to or less than the diameter of the top circular plate of the anti-vortex device. As described above, the inclined portion serves to prevent air bubbles entrained from the urea solution below the middle section of the container from diffusing into the anti-vortex device. The inclined portion will impede the flow of air bubbles, thereby reducing their momentum, and the air bubbles will rise because they are lighter than the liquid.

[0045] In one embodiment, the portion of the baffle extending into the middle section is between 100 mm and 400 mm. The greater this overlap, the less likely the urea solution is to overflow from this portion into the central portion of the lower cylindrical section of the container.

[0046] The second plate can be attached to the lower cylindrical section or the middle section using various attachment devices, such as clips or brackets.

[0047] In one embodiment, the portion of the guide plate extending into the lower cylindrical section is between 100 mm and 400 mm. The greater the overlap, the less likely entrained air bubbles are to diffuse extensively into the lower cylindrical section. The overlap between the guide plate and the lower cylindrical section guides the liquid solution to the outside of the annular portion formed by the first cylindrical plate.

[0048] In one embodiment, the bottom chamber of the stripper includes a conduit extending through the wall of the intermediate or upper cylindrical section of the container, the conduit being adapted to receive means for determining the level of the liquid solution in the stripper, particularly a radioactive source. During operation of the stripper, a key parameter is the level of liquid present in the lower cylindrical section of the container. Numerous methods exist for determining this level. One method uses a combination of a radioactive source enclosed in a conduit located within the intermediate or upper cylindrical section of the container and a detector located below the lower cylindrical section of the container.

[0049] In one embodiment, the bottom chamber of the stripper includes an injection pipe extending through the wall of the container into a middle or upper cylindrical section for injecting stripping gas into the container. The stripping gas may contain ammonia and / or carbon dioxide. The stripping gas is injected into the base of the stripper and flows into multiple tubes in which it contacts a urea solution. The stripping gas increases the evaporation of gases (i.e., ammonia and carbon dioxide) contained in the urea solution falling into the multiple tubes by reducing the partial pressure of ammonia and / or carbon dioxide in the aqueous solution and accelerating their vaporization.

[0050] In one embodiment, the diameter of the first cylindrical segment of the baffle is between 400 mm and 900 mm.

[0051] In one embodiment, the diameter of the lower cylindrical section of the container is between 0.5m and 1.5m, particularly between 0.6m and 1.4m, more particularly between 0.7m and 1.3m, and even more particularly between 0.7m and 1.1m.

[0052] In one embodiment, the height of the lower cylindrical section of the container is between 0.5m and 1.5m, particularly between 0.7m and 1.4m, more particularly between 0.8m and 1.3m, and even more particularly between 0.9m and 1.3m.

[0053] In one embodiment, the diameter of the liquid outlet is between 150 mm and 600 mm, particularly between 170 mm and 550 mm, more particularly between 180 mm and 500 mm, even more particularly between 200 mm and 450 mm, and even more particularly between 250 mm and 400 mm.

[0054] In one embodiment, the diameter of the second plate is between 450 mm and 1100 mm, particularly between 470 mm and 1050 mm, more particularly between 480 mm and 1000 mm, even more particularly between 500 mm and 950 mm, and even more particularly between 400 mm and 900 mm.

[0055] In one embodiment, the height of the deflector is between 200 mm and 600 mm, particularly between 250 mm and 550 mm.

[0056] In one embodiment, the middle section is curved outwards. In another embodiment, the middle section is a truncated cone pointing downwards (i.e. towards the lower cylindrical section).

[0057] In another aspect, this disclosure provides a stripper comprising a top chamber or distribution chamber, a middle chamber, and a bottom chamber as described herein, wherein the top chamber and the middle chamber are connected to each other, and the middle chamber and the bottom chamber are also connected to each other. The top chamber of the stripper includes: a liquid inlet for a liquid solution to be stripped; a gas outlet for collecting gas; and a plurality of openings for receiving a plurality of tubes contained in the middle chamber of the stripper. The middle chamber includes: a plurality of tubes for guiding a liquid solution from the top chamber of the stripper to the bottom chamber; and means for heating the plurality of tubes. The means for heating the plurality of tubes may include: a housing surrounding the plurality of tubes; an inlet for heating a fluid (e.g., steam); and an outlet for heating the fluid. The plurality of openings in the bottom chamber are configured to receive the plurality of tubes of the middle chamber of the stripper means.

[0058] In another aspect, the stripper apparatus according to this disclosure is a urea HP stripper. Accordingly, in another aspect, this disclosure provides a urea HP stripper comprising a top chamber or distribution chamber, a middle chamber, and a bottom chamber as described herein, wherein the top chamber and the middle chamber are connected to each other, and the middle chamber and the bottom chamber are also connected to each other. The top chamber of the urea HP stripper includes: a liquid inlet for a urea solution comprising urea, carbamate, ammonia, and water; a gas outlet for collecting gases generated by the decomposition of carbamate and heating of the urea solution; and a plurality of openings for receiving a plurality of tubes contained in the middle chamber of the stripper. The middle chamber includes: a plurality of tubes for guiding a liquid solution from the top chamber of the stripper to the bottom chamber; and means for heating the plurality of tubes. The means for heating the plurality of tubes may include: a shell surrounding the plurality of tubes; an inlet for heating a fluid (e.g., steam); and an outlet for heating the fluid. The plurality of openings in the bottom chamber are configured to receive the plurality of tubes of the middle chamber of the stripper apparatus.

[0059] The collected gases may include ammonia, carbon dioxide, and / or water. The top chamber of the urea HP stripper may include other devices, such as a distribution device, to uniformly distribute the urea solution over multiple tubes in the middle section. The middle chamber includes multiple tubes for guiding the urea solution from the top chamber to the bottom chamber. The middle chamber may include a shell for containing a heating fluid that heats the multiple tubes and catalyzes the conversion of carbamate back to ammonia and carbon dioxide. The middle chamber may also include baffles or rods to reduce vibration of the multiple tubes. The bottom chamber of the urea HP stripper is the bottom chamber according to this disclosure.

[0060] The top, middle, and bottom chambers of the HP stripper have the same diameter.

[0061] In one embodiment, the urea HP stripper has a diameter between 2.0 m and 4.0 m, particularly between 2.1 m and 3.9 m, more particularly between 2.3 m and 3.7 m, and even more particularly between 2.5 m and 3.3 m. The larger the diameter of the urea HP stripper, the more tubes it contains, thus allowing more urea solution to be processed per unit time.

[0062] In another aspect, this disclosure provides a urea apparatus for producing urea, the apparatus including a urea HP stripper according to this disclosure. The urea apparatus includes multiple devices for converting feedstock, ammonia, and carbon dioxide into a composition based on solid particulate urea. The urea apparatus consistently includes a urea reactor in which ammonia and carbon dioxide are mixed under high pressure and high temperature to produce a urea solution comprising urea, carbamate, ammonia, and water. Specifically, the urea apparatus for producing urea includes: a synthesis section comprising the urea HP stripper according to this disclosure; a low-pressure section; and optionally a refining section.

[0063] In another aspect, this disclosure provides a method for operating a stripper apparatus according to this disclosure, the method comprising the steps of: a) introducing a liquid composition into a stripper according to this disclosure, particularly into a liquid inlet of a urea HP stripper; and b) collecting the gas-removed liquid composition from a liquid outlet of the stripper.

[0064] In another aspect, this disclosure provides a method for operating a urea HP stripper apparatus according to this disclosure, the method comprising the steps of: a) introducing a obtained liquid composition comprising urea, carbamate, ammonia and water into a liquid inlet of the urea HP stripper according to the disclosure; b) collecting a liquid composition comprising urea and water, from a liquid outlet of the urea HP stripper, from which ammonia and carbamate have been removed.

[0065] It is necessary to obtain a high-quality aqueous urea solution, i.e., one with very low levels of contaminants, in order to produce compositions based on solid particulate urea. Due to the thermodynamics of the reaction that produces urea, it is not possible to obtain a urea solution with high purity at the outlet of the urea reactor. The urea solution always contains urea, carbamates, ammonia, and water. It is known that in units such as urea HP strippers, it is possible to force the carbamates back to their feedstocks (ammonia and carbon dioxide). Once the stripper is installed on the production line, the urea solution obtained from the urea reactor can be injected into the stripper. The pressure and temperature conditions within the stripper cause the carbamates to decompose back into ammonia and carbon dioxide, while urea exhibits a very low reaction rate. Ammonia and carbon dioxide are recovered from the gas outlet included in the HP stripper and can be recycled, for example, to the urea reactor. The aqueous urea solution obtained at the liquid outlet of the urea HP stripper may still contain some carbamates, although in much smaller amounts than the solution injected into the stripper.

[0066] In another aspect, this disclosure provides the use of the urea HP stripper according to this disclosure for removing carbamates from an aqueous solution containing urea and carbamates.

[0067] In another aspect, this disclosure provides the use of the bottom chamber of the urea HP stripper according to this disclosure for reducing the content of ammonia and carbon dioxide in the liquid drawn from the bottom chamber of the stripper via the liquid outlet.

[0068] In another aspect, this disclosure provides a method for producing a composition based on solid particulate urea, comprising the steps of: a) reacting a mixture of ammonia and carbon dioxide in a urea reactor to produce a urea solution comprising urea, carbamate, ammonia, water, and optionally carbon dioxide; b) guiding the urea solution comprising urea, carbamate, ammonia, water, and optionally carbon dioxide obtained in step a) into a urea HP stripper according to this disclosure; c) collecting the urea solution comprising urea and water and removing ammonia and carbamate from the liquid outlet of the urea HP stripper; d) concentrating the urea solution comprising urea and water obtained in step c) to obtain a concentrated aqueous urea solution; and e) converting the concentrated aqueous urea solution obtained in step d) into a composition based on solid particulate urea.

[0069] Steps a), b), d) and e) of the above-described method for producing a composition based on solid particulate urea are well known in the field of urea production.

[0070] Under typical operating conditions, the mixture of ammonia and carbon dioxide in the urea reactor is heated at high temperature and pressure, as described above. Ammonia and carbon dioxide are added to the reactor in such a manner that an excess of ammonia is always present compared to carbon dioxide.

[0071] Concentration step d) typically provides a urea melt containing 1.0 to 5.0% by weight of water. The water content can be adjusted depending on the conversion step.

[0072] The conversion step can be carried out in a variety of devices known in the art, such as fluidized beds, disc granulators, drum granulators, granulation towers, pelletizers, mixers, and tablet machines.

[0073] If necessary, the method may include further steps, such as additional steps to remove any of ammonia, carbamate, or carbon dioxide still present in the urea solution obtained in step c) before concentrating the urea solution.

[0074] In one embodiment, it may be necessary to add other components to the urea solution or concentrated urea solution. These other components may be process additives that improve the production process, such as viscosity reducers, or additives that improve the properties of the composition based on solid particulate urea, such as granulation additives, for example, additives containing urea-formaldehyde.

[0075] In another aspect, this disclosure provides strippers according to this disclosure, and in particular, the urea HP stripper according to this disclosure, for use in reducing the content of urethane, ammonia, and carbon dioxide in a solution containing urea, urethane, ammonia, and water.

[0076] Example 1

[0077] Figure 1 The schematic diagram depicts a cross-section of the bottom chamber of the urea high-pressure stripper according to the present invention. The stripper includes a container 1 comprising three parts: an upper cylindrical section 4, a middle section 3, and a lower cylindrical section 2. The upper cylindrical section has a diameter of 3.1 m, and the lower cylindrical section 2 has a diameter of 1.0 m and a height of 1.1 m. The stripper may include 3500 to 6000 tubes connected to a plurality of openings 6 located on the top wall of the upper cylindrical section. The tubes are arranged in a bundle, with the outlet located in the top chamber of the container: a urea solution containing urea, carbamate, ammonia, and water enters the container via a falling film, while gas exits the container through the same tubes. The stripper includes a liquid outlet 7 located at the bottom of the lower cylindrical section 2 and concentric with it. The diameter of the liquid outlet is 320 mm.

[0078] The container comprises two plates: a guide plate and a baffle. The first cylindrical baffle 12 includes a first cylindrical section 8 concentric with the liquid outlet 7, having a diameter between 650 mm and 900 mm, particularly between 650 mm and 850 mm, and a height between 250 mm and 500 mm, particularly between 300 mm and 450 mm. The first cylindrical baffle 12 includes a second section 10 connected to the top of the first cylindrical section 8, and having a frustoconical shape pointing towards the middle section 3, wherein the diameter of the bottom of the second section 10 is equal to the diameter of the first cylindrical section 8. The angle of the frustoconical 10 deviating from the vertical direction is between 15° and 60°, particularly between 30° and 45°. The upper diameter of the second section 10 is between 400 mm and 600 mm, particularly between 500 mm and 600 mm. The first cylindrical section 8 includes 2 to 10 openings or holes (not shown here) on its circumference, thereby allowing fluid to flow from the wall of the lower cylindrical section to the anti-vortex device. Each hole is square and contacts the bottom of the lower cylindrical section 2 of the container, wherein the side dimensions of the square are between 1 mm and 5.0 mm.

[0079] The second plate is a cylindrical guide plate 9. The guide plate 9 is concentric with the first cylindrical section 8 of the baffle 12 and with the liquid outlet 7, and also overlaps with the intermediate section 3, meaning that a portion of the guide plate enters the intermediate section. The diameter of the guide plate 9 can be between 650 mm and 950 mm, but is always at least equal to the diameter of the first cylindrical section 8 of the baffle 12, but smaller than the diameter of the lower cylindrical section 2 of the container. The guide plate 9 is located between the end of the intermediate section 3 of the container and the top of the lower cylindrical section 2. The height of the second plate 9 includes between 200 mm and 600 mm, particularly between 250 mm and 550 mm. The second plate 9 is attached to the lower cylindrical section 2 by a bracket 14.

[0080] The container 1 also includes a vortex deflector 11 concentric with the liquid outlet 7. The vortex deflector includes a top circular plate 13 having a diameter between 400 mm and 600 mm, particularly between 500 mm and 600 mm. The diameter of the top plate 13 of the vortex deflector 11 should be smaller than the diameter of the first cylindrical section 8 of the baffle 12 to allow urea solution to reach the liquid outlet. The vortex deflector is fixed to the bottom of the lower cylindrical section by cross-arranged vertical plates 15.

Claims

1. A stripping device, comprising: The stripper includes a top chamber with a liquid inlet and a gas outlet, an intermediate chamber with multiple tubes, and a bottom chamber, wherein the bottom chamber includes: a container (1) comprising a lower cylindrical section (2), an intermediate section (3), and an upper cylindrical section (4); multiple openings (6) located on the top wall of the upper cylindrical section; a liquid outlet (7) located at the bottom of the lower cylindrical section (2) of the container and concentric with the lower cylindrical section (2) of the container; and the multiple openings (6) are configured to receive the multiple tubes of the stripper, wherein the multiple tubes are configured to guide a fluid containing dissolved gas from the top chamber of the stripper to the bottom chamber; The bottom chamber is characterized in that it comprises: (i) A vortex deflector (11) connected to the bottom of the lower cylindrical section (2) of the container, the vortex deflector (11) comprising a top circular plate (13) parallel to the bottom of the lower cylindrical section and concentric with the liquid outlet, the top circular plate (13) being fixed to the bottom of the lower cylindrical section by cross-arranged vertical plates (15), wherein the diameter of the top circular plate is larger than the diameter of the liquid outlet (7) to prevent fluid from falling directly into the liquid outlet (7) from one or more of the plurality of openings; (ii) A baffle (12) for preventing air bubbles carried by fluid falling from the plurality of openings from reaching the liquid outlet (7), the baffle (12) comprising a first cylindrical section (8) and a second section (10), the first cylindrical section being concentric with the liquid outlet (7) and having a diameter greater than that of the anti-vortex device (11), and the height of the first cylindrical section (8) being greater than that of the anti-vortex device (11), the first cylindrical section (8) being connected to the bottom of the lower cylindrical section (2); the second section being connected to the top of the first cylindrical section (8) and having an upwardly pointing truncated cone shape, wherein the diameter of the bottom of the second section (10) is equal to the diameter of the first cylindrical section (8), wherein the first cylindrical section (8) includes one or more openings thereby allowing fluid to flow from the wall of the lower cylindrical section (2) to the liquid outlet (7); (iii) A guide plate (9) for guiding fluid falling from the wall of the intermediate section (3) toward the side wall of the lower cylindrical section (2), the guide plate (9) being concentric with the liquid outlet (7), wherein the diameter of the guide plate (9) is equal to or greater than the diameter of the baffle (12), but less than the diameter of the lower cylindrical section (2) of the container, wherein the guide plate (9) is located at the junction of the lower cylindrical section (2) and the intermediate section (3), extending partially into the lower cylindrical section (2) of the container (1) and partially into the intermediate section (3) of the container.

2. The stripper according to claim 1, wherein the height of the first cylindrical section (8) of the baffle (12) is between 10% and 50% of the height of the lower cylindrical section (2) of the container.

3. The stripper according to claim 1 or 2, wherein the diameter of the top circular plate (13) of the anti-vortex device (11) is between 400 mm and 600 mm.

4. The stripper according to claim 3, wherein, The diameter of the top circular plate (13) of the anti-vortex device (11) is between 500 mm and 600 mm.

5. The stripper according to claim 1 or 2, wherein the diameter of the first cylindrical section (8) of the baffle (12) is between 400 mm and 900 mm.

6. The stripper according to claim 1 or 2, wherein the height of the guide plate (9) is between 200 mm and 600 mm.

7. The stripper according to claim 6, wherein, The height of the guide plate (9) is between 250 mm and 550 mm.

8. The stripper according to claim 1 or 2, further comprising a conduit extending through the wall of the intermediate section (3) or the upper cylindrical section (4) of the container, the conduit being adapted to receive means for determining the liquid level in the bottom chamber of the stripper.

9. The stripper according to claim 8, wherein, The apparatus for determining the liquid level in the bottom chamber of the stripper includes a radiation source.

10. The stripper according to claim 1 or 2, further comprising an injection pipe extending through the wall of the container (1) into the intermediate section (3) or the upper cylindrical section (4) for injecting stripping gas into the bottom chamber.

11. The stripper according to claim 10, wherein, The stripping gas contains carbon dioxide and / or ammonia.

12. The stripper according to claim 1 or 2, wherein the one or more openings included in the first cylindrical segment (8) of the baffle (12) have a polygonal shape.

13. The stripper according to claim 12, wherein, The one or more openings contained in the first cylindrical segment (8) of the baffle (12) have a square shape.

14. The stripper according to claim 13, wherein, The side length of the square shape is between 1 mm and 10 mm.

15. A urea apparatus for producing urea, comprising a synthesis section, a low-pressure section, and optionally a refining section, said synthesis section comprising a stripper according to any one of claims 1 to 14, said stripper being a high-pressure urea stripper.

16. A method for operating a stripper according to any one of claims 1 to 14, said stripper being a urea high-pressure stripper, the method comprising the steps of: a) guiding a urea solution containing urea, carbamate, ammonia, and water to the liquid inlet of the urea high-pressure stripper, and b) recovering a urea solution containing urea and water and removing carbamate, ammonia, and optionally carbon dioxide from the liquid outlet of the bottom chamber of the urea high-pressure stripper.

17. The method of claim 16, used to produce a composition based on solid particulate urea, the method comprising the steps of: a0) React a mixture of ammonia and carbon dioxide in a urea reactor to produce a urea solution containing urea, carbamate, ammonia, water and optionally carbon dioxide. a) The urea solution containing urea, carbamate, ammonia, water and optionally carbon dioxide obtained in step a0) is introduced into a urea high-pressure stripper. b) Collect a urea solution containing urea and water and removing ammonia and carbamate from the liquid outlet of the urea high-pressure stripper; c) Concentrate the urea solution containing urea and water obtained in step c) to obtain a concentrated urea aqueous solution; d) The concentrated urea aqueous solution obtained in step d) is converted into a composition based on solid particulate urea.

18. Use of the stripper according to any one of claims 1 to 14 for reducing the content of carbamate, ammonia and carbon dioxide in a solution containing urea, carbamate, ammonia and water.

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