Shell-and-tube heat exchanger

Abstract

The present disclosure provides a vertical top-down shell-and-tube heat exchanger and a method for condensing a gas stream comprising water, ammonia, and carbon dioxide.

Description

Technical Field

[0001] This disclosure relates to shell-and-tube heat exchangers. Background Technology

[0002] In chemical plants, a heat exchanger is a device that allows a fluid (i.e., a liquid or gas) to be heated or cooled without direct contact with a cooling or heating medium.

[0003] Such devices come in different designs, one of which is the falling film shell-and-tube heat exchanger, hereinafter referred to as the falling film heat exchanger.

[0004] A shell-and-tube heat exchanger is a device comprising three sections: a distribution section, in which the fluid to be cooled or heated is introduced into the device and divided into sub-flows; a heat exchange section, which includes a main body and multiple vertical tubes, wherein the vertical tubes guide the fluid to be cooled or heated from the distribution section to a collection section, where the cooled or heated fluid is recovered. The distribution section and the heat exchange section are separated by a top tube sheet including orifices for accommodating the vertical tubes. The heat exchange section comprises two spaces: a shell space, a continuous space between the main body and the multiple vertical tubes, in which the heating or cooling medium is circulated; and a tube space, a discontinuous space formed by the interior of each tube. Typically, in a shell-and-tube heat exchanger, the cross-sectional area of ​​the tubes across the shell is uniformly distributed.

[0005] Shell-and-tube heat exchangers are widely used in various industries, such as the fertilizer industry. In some cases, the fluid to be cooled or heated can be a single-phase fluid (liquid or gas) or a two-phase fluid (a mixture of liquid and gas). This fluid may contain liquid components (such as ammonia, carbon dioxide, water, and urea) and gaseous components (such as ammonia, carbon dioxide, and water). The fluid to be cooled or heated may contain corrosive compounds that can react with the heat exchanger. To protect the device, a passivating agent (such as oxygen-containing air or hydrogen peroxide) can be injected into the exchanger or in an upstream section of the device: oxygen always moves downstream and thus remains in the liquid solution being treated. For effective protection of the device, it is important to uniformly distribute the liquid solution containing the passivating agent into the vertical tubes of the heat exchanger: proper distribution of the liquid solution ensures uniform distribution of the passivating agent on exposed surfaces (including the top tube sheet). It has been found that it can be difficult to uniformly distribute the liquid containing the passivating agent into the multiple vertical tubes and top tube sheet of the heat exchanger: in such cases, vapor may condense on unpassivated surfaces, leading to corrosion. Summary of the Invention

[0006] A novel shell-and-tube heat exchanger has been designed to improve the distribution of liquids containing passivating agents. The heat exchanger includes a distribution plate located above the top tube sheet of the heat exchanger, wherein the distribution plate is configured to uniformly distribute the liquid across the tube sheet, ensuring that each tube of the exchanger receives a portion of the liquid containing the passivating agent, and that the area of ​​the top tube sheet between the orifices accommodating the vertical tubes is properly and uniformly wetted.

[0007] In a first aspect, this disclosure provides a vertical, top-down shell-and-tube heat exchanger for a condensate gas flow, the heat exchanger comprising a body, a distribution section, a heat exchange section including a set of vertical tubes, a cooling medium inlet, a cooling medium outlet, and a collection section including a cooling fluid outlet, wherein:

[0008] - The distribution section and the heat exchange section are separated by a top tube sheet, which includes multiple openings configured to accommodate vertical tubes;

[0009] - The distribution section includes a gas inlet for the gas flow to be condensed, a liquid inlet for the liquid containing a passivating agent, and a distribution tray located below the liquid inlet, wherein the distribution tray (14) is adapted to distribute both the gas flow and the liquid containing the passivating agent, wherein the distribution tray (14) includes two sets of through holes perforated in the distribution tray, the first set of through holes being configured to distribute the liquid containing the passivating agent across the top of the top tube sheet, and the second set of through holes being configured to allow the gas flow to reach the vertical tube;

[0010] - The axis of each through hole in the second group is located directly above the axis of the vertical pipe of the distribution section;

[0011] - The dispensing tray includes multiple hollow tubes fastened to the dispensing tray, wherein the hollow tubes are configured to prevent liquid from reaching the through holes in the second set of through holes.

[0012] In an embodiment, this disclosure provides a vertical, top-down shell-and-tube heat exchanger (1) for a condensate gas flow, the heat exchanger comprising a body (5), a distribution section (2), a heat exchange section (3) including a set of vertical tubes (10), a cooling medium inlet (9), a cooling medium outlet (12), and a collection section (4) including a cooling fluid outlet (13), wherein:

[0013] - The distribution section (2) and the heat exchange section (3) are separated by a top tube sheet (8) which includes a plurality of openings configured to accommodate vertical tubes (10);

[0014] - The distribution section (2) includes a gas inlet (7) for the gas flow to be condensed, a liquid inlet (6) for the liquid containing a passivating agent, and a distribution tray (14) located below the liquid inlet (6), wherein the distribution tray (14) is adapted to distribute both the gas flow and the liquid containing the passivating agent, the distribution tray (14) including two sets of through holes (15, 16) perforated in the distribution tray (14), the first set of through holes (15) being configured to distribute the liquid containing the passivating agent across the top of the top tube sheet (8), and the second set of through holes (16) being configured to allow the gas flow to reach the vertical tube (10);

[0015] - The axis of each through hole in the second set of through holes (16) is located directly above the axis of the vertical pipe of the distribution section (2);

[0016] - The dispensing tray (14) includes a plurality of hollow tubes (17) fastened to the dispensing tray (14), wherein the hollow tubes (17) are configured to prevent liquid from reaching the through holes in the second set of through holes (16).

[0017] In the implementation, the vertical top-down shell-and-tube heat exchanger (1) is configured such that the axis of at least one of the first set of through holes (15) is located directly above the axis of the center of the equilateral triangular arrangement of the tubes (10).

[0018] In the implementation, the vertical top-down shell-and-tube heat exchanger (1) further includes a distribution tube (21), particularly an L-shaped distribution tube, wherein one end of the distribution tube (21) is connected to the liquid inlet (6), and the other end is located above the non-perforated portion of the distribution tray (14).

[0019] In the implementation, the vertical top-down shell-and-tube heat exchanger (1) is configured such that the end of the distribution tube (21) is located above the non-perforated portion of the distribution tray (14) and at a distance of 10.0 mm to 100.0 mm from the distribution tray (14).

[0020] In the implementation, the vertical top-down shell-and-tube heat exchanger (1) is configured such that the end of the distribution tube (21) is located above the non-perforated portion of the distribution tray (14) and is surrounded by a perforated wall (19) extending from the distribution tray (14), wherein the wall (19) is cylindrical.

[0021] In the implementation, the vertical top-down shell-and-tube heat exchanger (1) is configured such that the wall (19) has a height of 100.0 mm to 300.0 mm.

[0022] In the implementation, the vertical top-down shell-and-tube heat exchanger (1) is configured such that the wall (19) is cylindrical and the distance between the center of the wall (19) and the center of the distribution tray (14) is 0.0 mm to 25% of the diameter of the distribution tray (14).

[0023] In the implementation scheme, the vertical top-down shell-and-tube heat exchanger (1) is configured such that the height of the hollow tube (17) is 200.0 mm to 500.0 mm.

[0024] In the implementation scheme, the vertical top-down shell-and-tube heat exchanger (1) is configured such that the diameter of the through holes in the first set of through holes (15) is smaller than the diameter of the through holes in the second set of through holes (16).

[0025] In the implementation, the vertical top-down shell-and-tube heat exchanger (1) is configured such that hollow tubes (17) are secured to the top (41) of the distribution tray (14).

[0026] In the implementation scheme, the vertical top-down shell-and-tube heat exchanger (1) is configured such that a hollow tube (17) is fastened inside the through hole (51) in the second set of through holes (16).

[0027] In a second aspect, this disclosure provides a method for condensing a gas stream containing water, ammonium, and carbon dioxide in a heat exchanger according to this disclosure:

[0028] a) A liquid containing a passivating agent is directed to the liquid inlet of the heat exchanger, wherein the passivating agent is oxygen or oxygen peroxide;

[0029] b) Directing a cooling liquid stream, such as water or steam condensate, to the inlet of the heat exchanger for the cooling medium;

[0030] c) Direct a gas stream containing water, ammonium, and carbon dioxide to the gas inlet of the heat exchanger;

[0031] d) Collect the fluid containing liquid condensate from the first outlet of the heat exchanger.

[0032] The preferred embodiment of the first aspect of the present invention is also the preferred embodiment of the second aspect of the present invention, and vice versa.

[0033] In an embodiment, this disclosure provides a method for condensing a gas stream containing water, ammonium, and carbon dioxide in a heat exchanger according to this disclosure:

[0034] a) A liquid containing a passivating agent is directed to the liquid inlet (6) of the heat exchanger, wherein the passivating agent is oxygen or oxygen peroxide;

[0035] b) Directing a cooling liquid flow, such as water, to the inlet (9) of the heat exchanger for the cooling medium;

[0036] c) Guide the gas stream containing water, ammonium and carbon dioxide to the gas inlet (7) of the heat exchanger;

[0037] d) Collect the fluid containing liquid condensate from the cooling fluid outlet (13) of the heat exchanger.

[0038] In a third aspect, this disclosure provides the use of a vertical, top-down shell-and-tube heat exchanger according to a first aspect of the invention or a (preferred) embodiment thereof for condensing a gas stream, particularly wherein the gas stream comprises water, ammonia, and carbon dioxide. Attached Figure Description

[0039] The following description of 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.

[0040] Figure 1 is a diagram of an embodiment of a vertical top-down shell-and-tube heat exchanger according to the present disclosure.

[0041] Figure 2 is a partial diagram of another embodiment of a vertical top-down shell-and-tube heat exchanger.

[0042] Figure 3 is a diagram of an implementation scheme for the staggered arrangement of vertical tubes in a vertical top-down shell-and-tube heat exchanger.

[0043] Figures 4 and 5 are diagrams of an embodiment of a portion of the distribution section of a vertical, top-down shell-and-tube heat exchanger. Detailed Implementation

[0044] Unless otherwise defined, all terms used in disclosing this invention, including technical and scientific terms, have the meaning commonly understood by one of ordinary skill in the art to which this invention pertains. Further guidance is provided, including terminology definitions, to better understand the teachings of this invention.

[0045] The different aspects or embodiments of the invention will be defined in more detail in the following paragraphs. Unless otherwise expressly indicated to the contrary, each aspect or embodiment so defined may be combined with any other one or more aspects or embodiments. In particular, any feature indicated as preferred or advantageous may be combined with any other one or more features indicated as preferred or advantageous.

[0046] All references cited in this specification are hereby considered as incorporated herein by reference in their entirety.

[0047] As used herein, the following terms have the following meanings:

[0048] Unless the context clearly specifies otherwise, the terms “a,” “an,” and “the” as used herein refer to the singular and plural referents, respectively. For example, “compartment” refers to one or more compartments.

[0049] As used herein, “about” refers to a measurable value, such as a parameter, quantity, duration, etc., meaning a variation covering the specified value and a variation of + / - 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, provided that such variation is suitable for implementation in the disclosed invention. However, it should be understood that the value referred to by the modifier “about” is itself specifically disclosed.

[0050] As used herein, “comprise”, “comprising”, and “comprises” and “comprised of” are synonymous with “include”, “including”, “includes”, or “contain” and are inclusive or open-ended terms that specify the presence of the following content and do not exclude or preclude the presence of any additional, unlisted parts, features, elements, components, or steps known in the art or disclosed herein.

[0051] The range of values ​​represented by the endpoints includes all numbers and fractions contained within that range, as well as the endpoints themselves.

[0052] Unless otherwise defined, the expressions “percentage by weight,” “%wt,” or “weight %” herein and throughout the specification mean the relative weight of the corresponding component based on the total weight of the formulation.

[0053] In a first aspect, this disclosure provides a shell-and-tube heat exchanger, preferably a vertical, top-down shell-and-tube heat exchanger for condensing gas flows, the heat exchanger comprising a body, a distribution section, a heat exchange section including a set of vertical tubes, an inlet for a cooling medium, an outlet for a cooling medium, and a collection section including a cooling fluid outlet for a fluid comprising liquid and optionally gas, wherein:

[0054] - The distribution section and the heat exchange section are separated by a top tube sheet, which includes multiple openings configured to accommodate vertical tubes;

[0055] - The distribution section includes a gas inlet for the gas flow to be condensed, a liquid inlet for a liquid containing a passivating agent, and a distribution tray located below the liquid inlet, wherein the distribution tray (14) is adapted to distribute both the gas flow and the liquid containing the passivating agent, wherein the distribution tray includes two sets of through holes perforated in the distribution tray, the first set of through holes being configured to distribute the liquid containing the passivating agent across the top of the top tube sheet, and the second set of through holes being configured to allow the gas flow to reach the vertical tube;

[0056] - The axis of each through hole in the second group is located directly above the axis of the vertical pipe of the distribution section;

[0057] - The dispensing tray includes multiple hollow tubes fastened to the dispensing tray, wherein the hollow tubes are configured to prevent liquid from reaching the through holes in the second set of through holes.

[0058] In a preferred embodiment, the shell-and-tube heat exchanger according to this disclosure is a vertical, top-down device. This means that the fluid to be cooled or heated is introduced at the top of the device, and the cooled or heated fluid is obtained at the bottom of the device. This design is particularly interesting when the device is used to condense a gas stream containing water, because gravity ensures that the condensed liquid reaches the cooling fluid outlet of the device without any additional energy input.

[0059] The heat exchanger comprises a distribution section, a heat exchange section, and a collection section, all three sections being enclosed within a main body. The distribution section is located at the top of the unit, the heat exchange section is located between the distribution section and the collection section, and the collection section is located at the bottom of the unit.

[0060] The heat exchange section and the distribution section are separated by a top tube sheet comprising multiple openings configured to accommodate a set of vertical tubes. The vertical tubes are configured to guide a liquid-gas flow containing a passivating agent and the condensate of that gas flow from the distribution section to the collection section. The heat exchange section comprises two spaces: a continuous space outside the vertical tubes, also known as the shell space; and a discontinuous collection of spaces inside the vertical tubes, also known as the tube space. In this heat exchanger, the shell space is configured to receive cooling fluids, particularly cooling water or steam condensate. Cooling water used in industrial plants (such as urea production plants) primarily consists of water. Cooling water may also contain additives, such as inorganic salts and small organic molecules. In this heat exchanger, the tube space is configured to receive a gas flow to be condensed and a liquid containing a passivating agent. The liquid containing the passivating agent accumulates on the top tube sheet and enters the tubes, thereby forming a falling film on the inner wall of the vertical tubes. The gas flow containing water, ammonia, and carbon dioxide condenses as it travels through the tubes, increasing the thickness of the falling film. The condensate obtained from the gas stream flows downward to the collection section.

[0061] In some embodiments, the liquid containing the passivating agent contains ammonia and / or carbon dioxide and / or ammonium carbamate and / or ammonium carbonate.

[0062] The heat exchange section includes an inlet for the cooling medium and a second outlet for the cooling medium. The inlet and the second outlet for the cooling medium are located on the wall of this section.

[0063] In some embodiments, the inlet for the cooling medium is located above the second outlet for the cooling medium. In some embodiments, the inlet for the cooling medium is located below the second outlet for the cooling medium.

[0064] The collection section includes a first outlet for removing the fluid generated by the condenser. The removed fluid may contain only liquid components, such as condensate from the gas stream and liquid containing a passivating agent, but may also contain gas, i.e., uncondensed vapor.

[0065] The distribution section includes a gas inlet for the gas stream to be condensed, a liquid inlet for a liquid containing a passivating agent, and a distribution tray located below the liquid inlet. The distribution tray includes two sets of through-holes: a first set of through-holes is configured to distribute the liquid containing the passivating agent across the top of the top tube sheet, and a second set of through-holes is configured to allow the gas stream to reach the vertical tubes. The distribution tray serves a dual purpose: ensuring that the gas stream to be condensed can flow from the gas inlet to the vertical tubes, and uniformly distributing the liquid entering the heat exchanger from the liquid inlet across the top tube sheet.

[0066] The role of the liquid containing the passivating agent is to bring the passivating agent (e.g., oxygen) into contact with or near the inner surface of the walls of the vertical tubes of the heat exchanger and onto the surface of the top tube sheet. The passivating agent is carefully selected so that it reacts with the materials of the vertical tubes and the top tube sheet to form a material layer that is more corrosion-resistant than the materials of the vertical tubes and the top tube sheet.

[0067] The top tube sheet is a perforated plate, which includes openings for accommodating vertical tubes of the condenser.

[0068] In some embodiments, the axis of at least one of the through-holes in the first set of through-holes in the distribution tray may be equidistant from the nearest opening in the top tube sheet. For good distribution of the liquid containing the passivating agent, equidistant alignment of the axis of at least one of the through-holes in the first set of through-holes in the distribution tray with the nearest opening in the top tube sheet can be advantageous. This means that the liquid containing the passivating agent can fall onto the top tube sheet at equidistant points from several openings in the top tube sheet and can diffuse uniformly in all directions, thereby ensuring good coverage of the top tube sheet and more uniform film formation within the vertical tube.

[0069] In some embodiments, the axis of at least one of the through holes in the first set can be located directly above the axis of the center of the equilateral triangle arrangement of the openings in the top tube sheet. For shell-and-tube heat exchangers (such as condensers), the vertical tubes are typically positioned in a staggered arrangement, particularly in a 60º staggered arrangement as shown in Figure 3. In such a configuration, the axis of at least one of the through holes in the first set of through holes in the distribution tray can pass through the center of the triangle formed by the centers of the three openings.

[0070] In some implementations, the axis of the through-hole in the first set of through-holes may be located directly above the axis of the center of the equilateral triangle arrangement of the openings in the top tube sheet.

[0071] In some implementations, the gas stream and / or condensate from it contains corrosive compounds that may react with the vertical pipe and slowly corrode it. This can ultimately lead to porosity in the vertical pipe, which disrupts the impermeable barrier between the shell space and the pipe space. Such damage requires plugging the top and bottom ends of the pipe or replacing it. For example, a urea production plant includes one or more condensers configured to condense a gas stream containing water, carbon dioxide, and ammonia. The condensate from such gas streams contains compounds selected from the group consisting of ammonium carbamate, ammonium carbonate, ammonium bicarbonate, and mixtures thereof. These compounds are corrosive to stainless steel, and the condenser needs to be protected against their corrosive effects.

[0072] A gas stream containing oxygen can be injected into the condenser to provide passivation. However, since the vertical tubes are covered by a liquid film during operation, gaseous oxygen needs to dissolve in the liquid film to passivate the tubes. Therefore, it is generally preferred to use a liquid containing a passivating agent (such as oxygen or oxygen peroxide). The passivating agent is present in the liquid film falling inside the tubes and can react with the tubes to form a passivation layer.

[0073] The conventional method for introducing a passivating agent-containing liquid into a shell-and-tube heat exchanger is to spray the liquid over the top tube sheet using a spraying device. However, it has been found that when the pressure or velocity of the liquid flow changes during operation, the spraying method (e.g., a full cone) cannot cover the entire top tube sheet. Consequently, some tubes and portions of the top tube sheet do not receive the required amount of passivating agent-containing liquid, leading to accelerated corrosion and a shortened service life of the vertical tubes and the top tube sheet (particularly the weld joints between the tube sheet and the vertical tubes). Therefore, a new system for distributing the passivating agent-containing liquid to the top tube sheet has been designed.

[0074] It has been found that the distribution tray, comprising two sets of through-holes, ensures uniform distribution of the passivating agent-containing liquid to the top tube sheet. The distribution tray is located below the liquid inlet and above the top tube sheet. The distribution tray includes two sets of through-holes: the first set of through-holes is configured to distribute the passivating agent-containing liquid across the top of the top tube sheet, and the second set of through-holes is configured to allow gas flow to reach the vertical pipe.

[0075] Each of the first set of through-holes is located above the solid section of the top tube sheet, meaning that the passivating agent-containing liquid falling from the first set of through-holes will fall onto the top tube sheet and be distributed across it. The top of each vertical tube connecting the distribution section to the collection section is above the top tube sheet, ensuring that a certain volume of passivating agent-containing liquid is always present on the top tube sheet during operation.

[0076] The axis of each through-hole in the second group is located directly above the axis of the vertical pipe of the distribution section, so that the gas to be condensed can reach the vertical pipe in a near-laminar manner.

[0077] The heat exchanger includes multiple hollow tubes fastened to a distribution tray, wherein the hollow tubes are configured to prevent liquid from reaching the through-holes in a second set of through-holes. The hollow tubes prevent liquid containing a passivating agent from falling directly into the vertical tubes, which could interfere with gas distribution within the tubes and allow the gas to be condensed to flow through the distribution plate.

[0078] In some implementations, the hollow tube is secured to the top of the dispensing tray.

[0079] In some implementations, the hollow tube is secured inside the through-hole in the second set of through-holes.

[0080] At least two methods are envisioned for attaching the hollow tube to the dispensing tray. First, the hollow tube can be secured to the top of the dispensing tray. In this case, it is preferable that the inner diameter of the hollow tube is equal to the diameter of the through-hole in the second set of through-holes. Second, the hollow tube can be secured inside the through-hole in the second set of through-holes. In this case, it is preferable that the outer diameter of the hollow tube is equal to or 0.1 mm to 2.0 mm smaller than the diameter of the through-hole in the second set of through-holes, such that the hollow tube is inserted inside the through-hole.

[0081] In some implementations, the bottom end of the hollow tube is flush with the bottom surface of the dispensing tray.

[0082] In some embodiments, the dispensing section includes a dispensing tube, particularly an L-shaped dispensing tube, wherein one end of the dispensing tube is connected to a liquid inlet, and the other end (i.e., the outlet) of the dispensing tube is located above the non-perforated portion of the dispensing tray. A dispensing tube connected to a liquid inlet at one end, with its other end located above the non-perforated portion of the dispensing tray, can provide more controlled dispensing of the passivating agent-containing liquid to the dispensing tray, thereby providing a more stable liquid level and ensuring uniform liquid flow through the first set of through-holes.

[0083] In some implementations, the outlet of the dispensing tube is located 10.0 mm to 100.0 mm above the non-perforated portion of the dispensing tray.

[0084] In some embodiments, the outlet of the dispensing tube is located above the non-perforated portion of the dispensing tray and is surrounded by a wall extending from the dispensing tray, specifically, where this wall is cylindrical and / or perforated. Depending on the pressure and velocity of the liquid flow containing the passivating agent and the height difference between the inlet and the dispensing tray, the impact of the passivating agent-containing liquid on the dispensing tray can create a highly turbulent region, including droplets that may enter the hollow tube and cause an unstable stable liquid level above the dispensing tray. It has been found that the wall extending from the dispensing tray and surrounding the outlet of the dispensing tube reduces the turbulent region generated by the impact of the liquid on the dispensing tray. The turbulent region is limited to the internal volume of the wall. The passivating agent-containing liquid reaches the entire dispensing tray in a more controlled manner and at a lower velocity by flowing through the wall or through the perforations (if any) than at the outlet of the dispensing tube.

[0085] In some embodiments, the wall surrounding the outlet of the distribution pipe includes perforations, particularly perforations with a diameter ranging from 2.0 mm to 8.0 mm or from 2.0 mm to 5.0 mm.

[0086] In some embodiments, the wall surrounding the outlet of the dispensing pipe has a height of 100.0 mm to 300.0 mm. In some embodiments, the wall surrounding the outlet of the dispensing pipe has a height of 100.0 mm to 200.0 mm.

[0087] In some implementations, the walls are cylindrical, and the distance between the center of the wall and the center of the dispensing tray ranges from 0.0 mm to 25% of the diameter of the dispensing tray. The cylindrical walls ensure uniform distribution of the liquid containing the passivating agent from the walls in all directions. Walls located around the center of the dispensing tray also provide more uniform distribution of the liquid across the dispensing plate. Due to the location of through-holes or hollow tubes, the walls may not be perfectly centered on the dispensing tray, but it has been observed that walls can be at a distance from the center, such as less than 20% of the diameter of the dispensing tray, and still provide very good distribution of the liquid containing the passivating agent.

[0088] In some embodiments, the height of the hollow tube is 200.0 mm to 500.0 mm. In some embodiments, the height of the hollow tube is 200.0 mm to 400.0 mm. In some embodiments, the height of the hollow tube is 300.0 mm to 400.0 mm. The main function of the hollow tube is to prevent liquid containing passivating agent from falling through the second set of through-holes. Their height determines how much liquid can accumulate on the dispensing tray.

[0089] In some implementations, the diameter of the through-holes in the first set of through-holes is smaller than the diameter of the through-holes in the second set of through-holes. In such heat exchangers, the volume of the liquid containing the passivating agent is typically much smaller than the volume of the gas stream to be condensed per unit time; therefore, the amount of gas that needs to pass through the second set of through-holes is greater than the amount of liquid that needs to pass through the first set of through-holes. Thus, the larger diameter of the second set of through-holes allows for a reduction in the pressure drop caused by the distribution tray.

[0090] In some implementations, the diameter of the through holes in the first set of through holes ranges from 2.0 mm to 8.0 mm or from 2.0 mm to 6.0 mm.

[0091] In some embodiments, the diameter of the through holes in the second set of through holes ranges from 10.0 mm to 25.0 mm or from 15.0 mm to 25.0 mm.

[0092] On the other hand, this disclosure provides a method for condensing a gas stream comprising water, ammonium, and carbon dioxide in a heat exchanger according to this disclosure:

[0093] a) A liquid containing a passivating agent is directed to the liquid inlet of the heat exchanger, wherein the passivating agent is oxygen or oxygen peroxide;

[0094] b) Directing a cooling liquid stream, such as water or steam condensate, to the inlet of the heat exchanger for the cooling medium;

[0095] c) Direct a gas stream containing water, ammonium, and carbon dioxide to the gas inlet of the heat exchanger;

[0096] d) Collect the fluid containing liquid condensate from the cooling fluid outlet of the heat exchanger.

[0097] The aforementioned heat exchanger can be used in methods for condensing gas streams containing water, ammonium, and carbon dioxide. For example, a urea production plant has several units that generate gas streams containing water, ammonia, and carbon dioxide. Ammonia and carbon dioxide are feedstocks for urea production, and it is desirable to recover these components as aqueous solutions rather than gas streams to the synthesis section, medium-pressure section, or low-pressure section.

[0098] A carbamate condenser is a heat exchanger configured to condense a gas stream containing water, ammonia, and carbon dioxide into an aqueous solution containing ammonium ions, such as ammonium carbamate, ammonium carbonate, and ammonium bicarbonate. This type of heat exchanger can be used as a carbamate condenser in urea production plants.

[0099] A liquid containing a passivating agent is directed to the liquid inlet of the heat exchanger. In some embodiments, the liquid is an aqueous solution containing oxygen or oxygen peroxide. The liquid containing the passivating agent may contain other components. In some embodiments, the liquid containing the passivating agent contains ammonia and / or carbon dioxide and / or urea.

[0100] A coolant (such as water or steam condensate) is directed to the inlet of the heat exchanger for use as a cooling medium. If the coolant is primarily water, it may contain some inorganic salts or organic molecules. For example, in urea production plants, calcium salts are typically added to the cooling water. In some embodiments, the coolant has a pH higher than 7.0. In some embodiments, the coolant contains alkaline additives to maintain a pH higher than 7.0.

[0101] A gas stream containing water, ammonium, and carbon dioxide is directed to the gas inlet of a heat exchanger. The gas stream can originate from any unit in a urea production plant, such as a carbamate decomposer or desorption tower. When the gas stream reaches the vertical tube of the heat exchanger, the water contained in the gas stream condenses into liquid water. The ammonia and carbon dioxide contained in the gas stream dissolve in the water and react together to form ammonium carbamate, ammonium carbonate, or ammonium bicarbonate, depending on the specific conditions within the vertical tube, such as pressure, temperature, and the composition of the gas stream. The reaction of ammonia and carbon dioxide causes the gas to dissolve into the liquid phase.

[0102] In some embodiments, the gas stream containing water, ammonium, and carbon dioxide has a pressure ranging from 0.1 MPa to 4.0 MPa. In some embodiments, the gas stream containing water, ammonium, and carbon dioxide has a pressure ranging from 3.0 MPa to 4.0 MPa.

[0103] Liquid condensate is recovered from the cooling fluid outlet of the heat exchanger. In some embodiments, the liquid condensate comprises one or more components selected from the group consisting of ammonium carbamate, ammonium carbonate, and ammonium bicarbonate. In some embodiments, complete condensation of vapor is not achieved, and a mixed stream of liquid and vapor is recovered from the cooling fluid outlet.

[0104] In some implementations, the liquid containing the passivating agent and directed to the liquid inlet of the distribution section includes a portion of the condensate collected from the cooling fluid outlet. It has been found that the liquid condensate obtained in the collection section of the heat exchanger can be used as part of the liquid containing the passivating agent in the same unit. This has the advantage of allowing for reduced plant water consumption without altering the chemical composition of the condensate.

[0105] Figure 1 is a schematic diagram of an embodiment of a vertical, top-down shell-and-tube heat exchanger 1 according to the present disclosure. The device 1 includes a main body 5, a distribution section 2, a heat exchange section 3, and a collection section 4. The collection section 4 includes a cooling fluid outlet 13 for removing condensate from the device 1. The heat exchange section 3 includes a vertical pipe 10 fluidly connecting the distribution section 2 and the collection section 4. The heat exchange section 3 includes an inlet 9 for a cooling medium and an outlet 12 for a cooling medium. The space 11 between the main body 5 and the exterior of the vertical pipe 11 is called the shell space.

[0106] Distribution section 2 and heat exchange section 3 are separated by top tube sheet 8. Collection section 4 and heat exchange section 3 are separated by bottom tube sheet 18. Tube sheets 8 and 18 each independently include openings configured to accommodate vertical tubes 10.

[0107] Distribution section 2 includes a gas inlet 7 for a flow of gas to be condensed, a liquid inlet 6 for a liquid containing a passivating agent, and a distribution tray 14 located below the liquid inlet 6 and above the top tube sheet 8, wherein the distribution tray 14 includes two sets of through-holes 15 and 16. The first set of through-holes 15 is configured to distribute the passivating agent-containing liquid across the top of the top tube sheet 8, and the second set of through-holes 16 is configured to allow gas flow to reach the vertical tube 10. The axis of each through-hole in the second set of through-holes 16 is located directly above the axis of the vertical tube of distribution section 2. The distribution tray 14 includes a plurality of hollow tubes 17 fastened to the distribution tray 14, wherein the hollow tubes 17 are configured to prevent liquid from reaching the through-holes in the second set of through-holes 16.

[0108] Figure 2 is a schematic diagram of a portion of another embodiment of the vertical top-down shell-and-tube heat exchanger 20 according to the present disclosure. The heat exchange section and collection section of the device 20 are the same as those of device 1, and are not reproduced in Figure 2 for simplicity. The distribution section 2 includes a gas inlet 7, a liquid inlet 6, and a distribution tray 14 including two sets of through-holes 15 and 16. The first set of through-holes 15 is configured to distribute liquid containing a passivating agent across the top of the top tube sheet 8, and the second set of through-holes 16 is configured to allow gas flow to reach the vertical tube 10. The distribution tray 14 includes a plurality of hollow tubes 17 fastened to the distribution tray 14. The distribution section 2 includes an L-shaped distribution pipe 21 connected at one end to the liquid inlet 6. The outlet of the distribution pipe 21 is located above the solid section of the distribution tray 14 and is surrounded by a circular wall 19 configured to minimize turbulence caused by the impact of the passivating agent-containing liquid on the distribution tray 14. The distance between the center of wall 19 and the center of distribution tray 14 is approximately between 0 and 25% of the diameter of distribution tray 14.

[0109] Figure 3 illustrates an embodiment of a portion of a tube sheet in a heat exchanger according to the present disclosure. The tube sheet includes openings 22 for accommodating vertical tubes. The openings 22 are arranged in a 60º staggered pattern, wherein the centers of three openings form an equilateral triangle, and point A is the center of this equilateral triangle.

[0110] Figure 4 is a schematic diagram of a portion of the distribution section of another embodiment of the vertical top-down shell-and-tube heat exchanger 40 according to the present disclosure. The heat exchange section and collection section of the device 40 are the same as those of device 1, and are not reproduced in Figure 4 for simplicity. The distribution tray 14 includes a plurality of hollow tubes 17 fastened to the top 41 of the distribution tray 14. Therefore, the diameter of the second set of through holes 16 is substantially equal to the diameter of the hollow tubes.

[0111] Figure 5 is a schematic diagram of a portion of the distribution section of another embodiment of the vertical top-down shell-and-tube heat exchanger 50 according to the present disclosure. The heat exchange section and collection section of the device 50 are the same as those of device 1, and are not reproduced in Figure 5 for simplicity. The distribution tray 14 includes a plurality of hollow tubes 17 fastened to the interior 51 of the through holes in the second set of through holes 16. Therefore, the diameter of the second set of through holes 16 is larger than the diameter of the hollow tubes.

Claims

1. A vertical, top-down shell-and-tube heat exchanger for a condensate gas flow, the heat exchanger comprising a main body, a distribution section, a heat exchange section including a set of vertical tubes, a cooling medium inlet, a cooling medium outlet, and a collection section including a cooling fluid outlet, wherein: - The distribution section and the heat exchange section are separated by a top tube sheet, the top tube sheet including a plurality of openings configured to receive the vertical tube; - The distribution section includes a gas inlet for a gas flow to be condensed, a liquid inlet for a liquid containing a passivating agent, and a distribution tray located below the liquid inlet, wherein the distribution tray is adapted to distribute both the gas flow and the liquid containing the passivating agent, the distribution tray including two sets of through holes perforated in the distribution tray, a first set of through holes configured to distribute the liquid containing the passivating agent across the top of the top tube sheet, and a second set of through holes configured to allow the gas flow to reach the vertical tube; - The axis of each through hole in the second group is located directly above the axis of the vertical pipe of the distribution section; - The dispensing tray includes a plurality of hollow tubes fastened to the dispensing tray, wherein the hollow tubes are configured to prevent liquid from reaching the through holes in the second set of through holes.

2. The heat exchanger according to claim 1, wherein the axis of at least one of the first set of through holes is located directly above the axis of the center of the equilateral triangular arrangement of the tubes.

3. The heat exchanger according to claim 1 or 2, further comprising a distribution pipe, particularly an L-shaped distribution pipe, wherein one end of the distribution pipe is connected to the liquid inlet and the other end is located above the non-perforated portion of the distribution tray.

4. The heat exchanger according to claim 3, wherein the end of the distribution tube is located above the non-perforated portion of the distribution tray at a distance of 10.0 mm to 100.0 mm from the distribution tray.

5. The heat exchanger according to claim 3 or 4, wherein the end of the distribution tube is located above the non-perforated portion of the distribution tray and is surrounded by a perforated wall extending from the distribution tray, particularly wherein the wall is cylindrical.

6. The heat exchanger of claim 5, wherein the wall has a height of 100.0 mm to 300.0 mm.

7. The heat exchanger according to claim 5 or 6, wherein the wall is cylindrical and the distance between the center of the wall and the center of the distribution tray is from 0.0 mm to 25% of the diameter of the distribution tray.

8. The heat exchanger according to any one of claims 1 to 7, wherein the height of the hollow tube is 200.0 mm to 500.0 mm.

9. The heat exchanger according to any one of claims 1 to 8, wherein the diameter of the through holes in the first group of through holes is smaller than the diameter of the through holes in the second group of through holes.

10. The heat exchanger according to any one of claims 1 to 9, wherein the hollow tube is secured to the top of the distribution tray.

11. The heat exchanger according to any one of claims 1 to 9, wherein the hollow tube is secured inside the through-hole in the second set of through-holes.

12. A method for condensing a gas stream comprising water, ammonium, and carbon dioxide in a heat exchanger according to any one of claims 1 to 11: a) A liquid containing a passivating agent is directed to the liquid inlet of the heat exchanger, wherein the passivating agent is oxygen or oxygen peroxide; b) Directing a cooling liquid stream, such as water, to the cooling medium inlet of the heat exchanger; c) Directing a gas stream containing water, ammonium, and carbon dioxide to the gas inlet of the heat exchanger; d) Collect the fluid containing liquid condensate from the cooling fluid outlet of the heat exchanger.

13. The use of the vertical top-down shell-and-tube heat exchanger according to any one of claims 1 to 11 for a condensate gas stream, particularly wherein the gas stream comprises water, ammonia, and carbon dioxide.

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