RU2815492C2 - High-pressure stripping columns for use in installations for manufacture of carbamide - Google Patents

Abstract

FIELD: chemistry.

SUBSTANCE: present inventions relate to production of carbamide, specifically to a high-pressure stripping column for decomposing carbamate and stripping ammonia in carbamide-carbamate mixtures (CCM), a system for producing carbamide, a stripping method and use of a heat carrier distributor and a stripping column. Shell-tubular stripping column (STSC) (100) for stripping of CCM has upper end (110) in connection with possibility of fluid medium transfer with lower end (120) through multiple pipes (150) located inside shell (160). Upper end (110) comprises inlet (111) for CCM and outlet (112) for gas mixture containing stripping gas and one or more stripped compounds. Lower end (120) comprises outlet (122) for carbamide-concentrated CCM, wherein lower end (120), optionally comprising stripping gas inlet (121). STSC additionally comprises heating fluid (HF) inlet (131) and outlet (133) of HF in connection, with possibility of transfer of fluid medium with space (130) on shell side, located between plurality of pipes (150) and shell (160). STSC has a longitudinal direction and side cross-sections, wherein the longitudinal direction is parallel to the pipes, and lateral cross-sections are perpendicular to the longitudinal direction, wherein the STSC comprises distributor (170) of the HF near inlet (131) of the HF for homogenizing the flow of HF in the STSC, wherein distributor (170) of the LF comprises edge wall (171) and distribution plate (175) for HF, wherein the angle between the longitudinal direction and distribution plate (175) for HF is from 85.0° up to 90.0°, and accordingly the angle between the longitudinal direction and edge wall (171) is from 0.0° up to 5.0°. Edge wall (171) defines band-like space (179) between shell (160) and edge wall (171), and wherein edge wall (171) comprises two or more holes and/or a plurality of perforated holes configured to uniformly feed the heating fluid into the inner space for distributing the heating fluid. HF inlet (131) is made with possibility of direct introduction of HF into band-like space (179), wherein band-like space (179) is made with possibility of the HF introduction into the inner space for the HF distribution and distributing plate (175) for HF is made with possibility of introduction of HF from inner space (178) for HF distribution into space (130) on shell side between HF distributor (170) and lower end (120), wherein between distribution plate (175) for HF and edge wall (171) there is space for thermal expansion in terms of thermal expansion. Distributor plate (175) for HF comprises a plurality of perforated holes, a plurality of perforated holes comprises a plurality of pipe openings (176) and a plurality of openings (177) for HF, wherein size and/or density of holes (177) for HF varies in radial direction of distribution plate (175) for HF.

EFFECT: reduced corrosion of pipes and increased efficiency of stripping.

15 cl, 10 dwg, 9 ex

Description

Field of the present invention

The present invention relates to the field of urea production, in particular to the field of high pressure stripping columns for decomposing urea and stripping ammonia in urea-urea mixtures from urea reactors in urea production plants.

BACKGROUND OF THE INVENTION

High pressure strippers are used in urea production plants to concentrate urea by removing carbamate from a liquid urea-urea mixture. The urea-urea mixture is a solution that contains urea, ammonium carbamate, free ammonia and water and exits a reactor in which urea is formed by the reaction of ammonia and CO ₂ to form ammonium carbamate (also called "carbamate") and subsequent dehydration carbamate to form urea. The conversion of carbamate to urea is in practice never complete, and the solution leaving the urea reactor always contains some carbamate and free ammonia.

The conventional method of removing carbamate and concentrating the solution is carried out using a tubular heat exchanger, termed a "high pressure stripper", which operates at the same pressure as the urea reactor. Under the influence of heat provided by a heating medium such as steam, the ammonium carbamate in the urea-urea mixture decomposes to form NH ₃ and CO ₂ gases. Said NH ₃ and CO ₂ gases are removed from the stripping column. Accordingly, a urea-urea solution is formed, concentrated in terms of urea, which is collected from the bottom of the stripping column.

Currently, there are two categories of high pressure stripping columns, which are carbon dioxide stripping columns and self-stripping columns.

In carbon dioxide stripping columns, CO ₂ is used as stripping gas. It enters the bottom of the high pressure stripper column, and the NH ₂ and CO ₂ that are formed from the decomposition of ammonium carbamate are entrained in the stripping gas, which is CO ₂ .

In self-stripping columns, no stripping gas is introduced into the stripping column, but NH ₂ and CO ₂ , which are formed from the decomposition of ammonium carbamate, serve as stripping gas.

Stripping columns contain tubes and casing, an upper end and a lower end. During normal operation, the upper end is located at the top of the stripping column, and the lower end is located at the bottom of the stripping column. At the upper end, the urea-urea mixture is distributed through the pipes, and the gas mixture containing the stripping gas, also entrained with NH ₃ and CO ₂ , which are formed as a result of the decomposition of the carbamate, leaves the stripping column. A solution of stripped urea is collected at the lower end. In the case of carbon dioxide stripping columns, stripping gas, which is CO ₂ , is introduced into the lower end of the stripping column.

During normal operation, the pipes are installed almost vertically. They limit the space on the pipe side. The space on the shell side is located between the pipes and the shell. The stripping gas and urea-urea mixture flow counter-currently through the tube side space, and the urea-urea mixture is heated by the shell side space using a heating medium, which is typically steam. The urea-urea mixture moves through the pipes in falling film mode, while the gases rise in the inside of the pipes.

US 5,653,282 discloses a shell-and-tube heat exchanger comprising a reflector distributor, the reflector distributor comprising a cylindrical distributor plate with uniformly spaced rows of longitudinal perforations and a plurality of impact beams longitudinally aligned with the perforations. In this way, the hot fluid reaches the impact beams and direct impact on the pipes is prevented.

EP 0002298 discloses a method and apparatus for removing ammonium carbamate from a urea synthesis solution, wherein an aqueous urea solution is introduced into a stripping zone and is forced to flow down a heat exchange wall in the form of a thin film by heating and contacting countercurrently with a gaseous stripping agent.

It would be desirable to scale up such stripping columns to produce large volumes of urea in a cost-effective manner. Unfortunately, scaling up these stripping columns is not always an easy task, and numerous unforeseen problems tend to arise during the scaling process.

Brief Disclosure of the Present Invention

The present inventors have identified two problems in the process of scaling up shell-tubular stripping columns, which are severe tube corrosion and inefficient stripping. These problems are solved using stripping columns, systems and methods that are described herein.

In particular, the present document provides a shell-tubular stripping column for stripping a urea-urea mixture, the stripping column having an upper end in fluid communication with the lower end through a plurality of pipes disposed within the shell; wherein the upper end contains an inlet for a urea-urea mixture and an outlet for a gas mixture containing stripping gas and one or more stripped compounds; the lower end contains an outlet for a urea-urea stream concentrated in relation to urea; wherein the lower end optionally includes an inlet for boil-off gas; the shell-tube stripping column further comprises a heating fluid inlet and a heating fluid outlet in fluid transfer communication with a shell-side space located between the plurality of tubes and the shell; wherein the shell-tubular stripping column has a longitudinal direction and lateral cross sections, the longitudinal direction being parallel to the pipes, and the lateral cross sections being perpendicular to the longitudinal direction; wherein the shell-tubular stripping column comprises a heating fluid distributor near a heating fluid inlet for homogenizing the heating fluid flow in the stripping column, wherein the heating fluid distributor comprises an edge wall and a heating fluid distribution plate that is arranged parallel to the sides cross sections; wherein the edge wall contains two or more holes and/or a plurality of perforated holes, and the edge wall defines a ribbon-like space between the shell and the edge wall; wherein the heating fluid inlet is configured to introduce the heating fluid into the ribbon-like space; the belt-shaped space is configured to introduce heating fluid into the internal space to distribute the heating fluid; wherein the heating fluid distribution plate is configured to introduce heating fluid from the inner space for distributing the heating fluid into a space on the shell side between the heating fluid distributor and the lower end; wherein the heating fluid distribution plate comprises a plurality of perforated holes, the plurality of perforations including a plurality of pipe holes and a plurality of heating fluid holes, wherein the size and/or density of the heating fluid holes varies in a radial direction of the heating fluid distribution plate .

In some embodiments, the size of the heating fluid openings varies from the center of the heating fluid distribution plate to the outer rim of the heating fluid distribution plate.

In some embodiments, pipe vibration limiting devices are provided between the heating fluid distribution plate and the lower end, wherein the pipe vibration limiting devices optionally include a plurality of baffle disks.

In some embodiments, the angle between the longitudinal direction and the heating fluid distribution plate is 85.0° to 90.0°, or 87.5° to 90.0°, or 88.0° to 90.0°, preferably from 89.0° to 90.0°, more preferably from 89.5° to 90.0°, even more preferably 90.0°; and/or wherein the angle between the longitudinal direction and the edge wall is from 0.0° to 5.0°, or from 0.0° to 2.5°, or from 0.0° to 2.0°, preferably from 0.0° to 1.0°, preferably 0.0° to 0.5°, even more preferably 0.0°.

According to some embodiments, the size of the heating fluid openings increases from the outer rim to the center of the heating fluid distribution plate, while optionally the size of the heating fluid openings strictly increases from the outer rim to the center of the heating fluid distribution plate; or wherein the size of the heating fluid openings decreases from the outer rim toward the center of the heating fluid distribution plate, wherein optionally the size of the heating fluid openings strictly decreases from the outer rim toward the center of the heating fluid distribution plate.

According to some embodiments, the heating fluid distribution plate includes one or more regions in which the size of the heating fluid openings strictly decreases from an outer rim toward the center of the heating fluid distribution plate, and wherein the heating fluid distribution plate contains one or more several regions in which the size of the heating fluid openings strictly increases from the outer rim to the center of the heating fluid distribution plate.

In some embodiments, the diameter of the heating fluid openings is from at least 1 mm to no more than 16 mm, preferably from at least 2 mm to no more than 13 mm, more preferably from at least 3 mm to no more than 10 mm, even more preferably from at least 5 mm to not more than 7 mm.

In some embodiments, the ratio of the diameter of the largest heating fluid openings, on the one hand, to the diameter of the smallest heating fluid openings, on the other hand, is from at least 1.1 to no more than 16, preferably from at least 1 ,4 to no more than 3.5.

In some embodiments, heating fluid openings in the heating fluid distribution plate are spaced at equal intervals on concentric circles around the center of the heating fluid distribution plate.

According to some embodiments, the density of heating fluid openings is constant in the heating fluid distribution plate, wherein the size of the heating fluid openings varies from the center of the heating fluid distribution plate to the outer rim of the heating fluid distribution plate, wherein the tube openings arranged in a triangular geometric configuration, with each heating fluid opening occupying a central position between three adjacent tube openings.

According to some embodiments, the density of heating fluid holes is constant in the heating fluid distribution plate, the size of the heating fluid holes varies from the center of the heating fluid distribution plate to the outer rim of the heating fluid distribution plate, the tube holes are arranged in a square geometric pattern configuration, with each heating fluid opening occupying a central position between four adjacent pipe openings.

In some embodiments, the stripping column contains more than 3,000 pipes, or more than 4,000 pipes, or more than 5,000 pipes, or more than 6,000 pipes, or more than 7,000 pipes, or from 3,000 to 7,000 pipes, or from 4,000 to 6,000 pipes, or from 5000 to 7000 pipes, or from 5000 to 10000 pipes.

In addition, a system for producing urea is provided, comprising a urea condenser, a urea reactor and a shell-tubular stripper, which are described herein.

In addition, it is proposed to use a shell-tubular stripping column, which is described herein, for stripping a urea-urea mixture.

In addition, a method for stripping a urea-urea mixture is provided, the method comprising the following steps: providing a shell-tubular stripping column as described herein; introducing the urea-urea mixture into the inlet for the urea-urea mixture; introducing a heating fluid into the space on the shell side by injecting a heating fluid, the heating fluid being saturated steam; optionally introducing stripping gas into the stripping gas inlet at the lower end; contacting the urea-urea mixture and the boil-off gas in a pipe-side space that is located in the pipes, heating the urea-urea mixture by means of a heating fluid, and thereby obtaining a urea-urea concentrated stream; withdrawing the urea-urea concentrated urea stream to an outlet for the urea-concentrated urea stream; removing a gas mixture containing one or more stripped compounds at the gas mixture outlet, one or more stripped compounds including NH ₃ , CO ₂ and water; discharging the heating fluid at the outlet of the heating fluid.

In addition, the use of a heating fluid distributor for homogenizing a steam flow near the heating fluid inlet of a shell-tubular stripper column for stripping a urea-urea mixture is proposed, the heating fluid distributor comprising an edge wall and a heating fluid distribution plate, which is located parallel to in relation to the lateral cross sections; wherein the edge wall contains two or more holes and/or a plurality of perforated holes, the distribution plate for the heating fluid contains an outer rim and a center, the distribution plate for the heating fluid contains a plurality of perforated holes, a plurality of perforated holes, including a plurality of pipe holes and a plurality of heating fluid holes, wherein the size and/or density of the heating fluid holes varies from the center of the heating fluid distribution plate to the outer rim of the heating fluid distribution plate.

Brief description of the figures

The following description of the figures for specific embodiments of the present invention is presented by way of example only and is not intended to limit the present invention, application or use thereof. In the figures, the same conventional numbers mean the same or similar parts and features.

In fig. 1 shows an embodiment of a carbon dioxide stripping column (100).

In fig. 2 shows an embodiment of a self-stripping column (100).

In fig. 3 shows a heating fluid distributor (170) comprising an edge wall (171) and a heating fluid distribution plate (175).

In fig. 4 represents the vibration modes of pipes.

In fig. 5 shows possible types of flow of heating fluid between pipes (150).

In fig. 6 shows an example of a high pressure section of a particular type of urea plant in which the technology described herein may be used.

In fig. 7 shows two pictures of corrosion that are simultaneously observed in the pipes of shell-tubular stripping columns for stripping a urea-urea mixture of the prior art. In some operating modes, the corrosion pattern, which is presented in Fig. 7a is observed in carbon dioxide stripping columns, and the corrosion pattern shown in FIG. 7b is observed in self-stripping columns.

In fig. 8 shows the gas densities and corrosion rates that are simultaneously observed in the tubes of shell-tubular stripping columns for stripping a urea-urea mixture of the prior art.

In fig. 9 is a schematic illustration of gas density as a function of position in cooler pipes and in hotter pipes.

In fig. 10 shows an example of a bushing (700).

For the description and figures, the following symbols are used: 100 - stripping column; 101 - stripping gas pipeline; 102 - pipe for urea-urea flow; 103 - pipe for a stream containing stripping gas and one or more stripped compounds; 104 - pipe for urea-urea flow concentrated in relation to urea; 110 - upper end (on top of the stripping column during normal operation); 111 - inlet for urea-urea mixture; 112 - outlet for gas mixture; 120 - lower end (from the bottom of the stripping column during normal operation); 121 - inlet for boil-off gas; 122 release for urea-urea solution concentrated in relation to urea; 130 - space on the shell side; 131 - inlet of heating fluid; 133 - release of heating fluid; 134 - fender discs; 140 - space on the pipe side; 150 - pipe; 151 - upper tube sheet; 152 - lower tube sheet; 153 - corrosion area; 154 - deposit area; 155 - flow lines (transverse steam flow); 156 - flow lines (longitudinal steam flow); 157 - flow lines (flow in the heating fluid distributor) 160 - shell; 170 - heating fluid distributor; 171 - edge wall; 172 - space for thermal expansion; 174 - hole in the edge wall; 175 - distribution plate for heating fluid; 176 - pipe hole; 177 - steam hole; 178 - internal space for distribution of heating fluid; 179 - ribbon-shaped space; 200 - reactor; 201 - pipe for NH ₃ , CO ₂ vapors, water and inert substances; 300 - carbamate capacitor; 301 - pipe for gaseous flow; 302 - pipe for the flow of carbamate solution; 400 - gas purifier; 40 -1 pipe for supplying carbamate solution from the downstream section; 402 - pipe for the flow of inert gases; 500 - supply of heating fluid; 501 - steam generator; 502 - connection to an external supply of heating fluid; 503 - pipe for flow of heating fluid; 504 - pipe for a cooled flow of heating fluid; 600 - high pressure injector; 601 - ammonia supply; 700 - bushing; 710 - hole for urea-urea mixture; 720 - gas hole; 800 - blocked area; 810 - unclogged area; 1000 - high pressure section of the urea production plant.

Detailed Disclosure of the Present Invention

As used herein, grammatical forms of the singular include both the singular and the plural unless the context clearly dictates otherwise.

The terms “comprise”, “comprises”, as used below, are synonymous with the terms “include”, “includes” or “cover”, “spans” and are non-limiting or open-ended terms that do not exclude additional unspecified parts, elements or technological steps . Where this specification describes a product or method that "includes" specific features, parts or steps, this means that it is possible that other features, parts or steps may also be present, but this may also refer to embodiments in which only the listed characteristics, parts or stages are present.

Representing numeric values using numeric ranges covers all whole and fractional numbers within the specified ranges, as well as the given endpoints.

All documents cited herein are deemed to be incorporated herein in their entirety by reference.

Unless otherwise defined, all terms used herein, including technical and scientific terms, have the meanings commonly assigned to them by one skilled in the art. As further guidance, definitions are provided to further clarify the terms that are used in the description of the present invention.

During the scaling up of high-pressure shell-tubular stripping columns for the decomposition of urea-urea mixtures, a characteristic corrosion pattern was observed. In particular, it has been discovered that some pipes in high-pressure strippers for urea-urea mixtures are subject to more severe corrosion than other pipes. Without binding the present invention to any particular theories or operating conditions, the inventors believe that corrosion problems are caused by pipe corrosion induced by ammonium carbamate at high temperature. In addition, it was discovered that corrosion problems could be caused by non-uniform heating of the pipes; Because ammonium carbamate is more corrosive at elevated temperatures, the resulting non-uniform heating of the pipes causes non-uniform corrosion. During normal operation, the methods and devices that are described herein improve temperature uniformity in the liquid phase of the ammonium carbamate phase, and as a result, transverse temperature changes are reduced. In turn, this improves the uniformity during the heating process of pipes, reduces pipe corrosion, and also increases the useful life of stripping columns.

In addition, the present inventors have discovered that corrosion problems can be solved by using a stripper column of the type described herein. In this way, it can be ensured that the pipes in the stripping columns according to the present invention have an expected service life of approximately 20 to 30 years.

Although the present invention has been disclosed in the context of scaling up stripping columns, we do not believe that the benefits provided by the present invention can be in any way limited to stripping columns having any particular dimensions.

The term "carbamate" as used herein means ammonium carbamate. The term "urea-urea mixture" as used herein means a mixture containing urea, ammonium carbamate, ammonia and water. In some embodiments, the urea-urea mixture contains from 31 to 34 wt. % urea, from 32 to 35 wt. % ammonium carbamate, from 16 to 18 wt. % ammonia, from 0.1 to 0.3 wt. % biuret, and the remaining mass is water. Here the abbreviation “wt. %" means the mass percentages of the components relative to the mass of the urea-urea mixture.

The expression "urea-urea mixture stripping" as used herein means the process of decomposing the ammonium carbamate contained in the mixture to form ammonia and carbon dioxide. The resulting ammonia and carbon dioxide are carried away by the stripping gas. In addition, the water contained in the urea-urea mixture is also at least partially entrained in the stripping gas.

The terms "upstream" and "downstream" as used herein have the following meanings: the upstream direction is the direction towards the inlet of the heating fluid, and the downstream direction is the direction towards the outlet of the heating fluid

The term "vertical" as used herein is explained as follows: when objects are specified as vertically oriented, this means the orientation of their longitudinal axis. It should be understood that this orientation may have a certain deviation from the vertical axis. Preferably this deviation is less than 1.0° or less than 0.5°. Preferably, this deviation is less than 0.1°.

The expression “near the heating fluid inlet” as used herein to describe the position of the heating fluid distributor means that the heating fluid distributor occupies the same or substantially the same longitudinal position in the stripping column.

The stripper finds some application as a high pressure stripper in a urea production plant which also contains a urea reactor. Such strippers typically operate at a pressure that is approximately the same as the pressure in the urea reactor, for example equal to it with a deviation not exceeding 5.0%.

The present document provides a stripping column, in particular a shell-tubular stripping column, for stripping a urea-urea mixture. The present invention is applicable to any type of stripping columns for stripping urea-urea mixtures. In particular, it is applicable to both self-stripping columns and carbon dioxide stripping columns. In carbon dioxide stripping columns, CO ₂ is used as stripping gas. It enters the bottom of the high pressure stripping column, and the NH ₃ and CO ₂ that are formed during the decomposition of ammonium carbamate are entrained in the stripping gas, which is CO ₂ . In the case of self-stripping columns, no stripping gas is introduced into the stripping column, but the NH ₃ and CO ₂ that are formed during the decomposition of ammonium carbamate themselves serve as stripping gas.

Accordingly, in some embodiments, the stripping column is a carbon dioxide stripping column and the stripping gas is CO ₂ .

Alternatively, in some embodiments, the stripping column is a self-stripping column and the stripping gas is NH ₃ and CO ₂ that are formed during the decomposition of ammonium carbamate. When the stripping column is a self-stripping column, its lower end does not include a stripping gas inlet. Despite this, the lower end of the self-stripping columns still preferably contains an inlet for the passivation gas stream. Preferably, air is used as the passivating gas stream. It should be noted that the passivation air flow rates are so low that they cannot make any significant contribution to the said steaming process. Typical passivation air flow rates are 50 to 250 kg air per hour or 50 to 500 kg air per hour.

The stripping column has a longitudinal direction and a lateral cross-section. The longitudinal direction is parallel to the pipes. The lateral cross section is perpendicular to the longitudinal direction. In other words, the longitudinal direction is the direction that connects the upper end and the lower end. The lateral cross sections are perpendicular to the longitudinal direction. In other words, the term "lateral cross-section through the stripper" means a cross-section through the stripper in a plane that is perpendicular to the pipes. Preferably the stripping column is cylindrical. In other words, the stripping column preferably has a circular side cross-section.

The stripping column has an upper end and a lower end. The upper and lower ends are in connection with the possibility of transferring fluid through a plurality of pipes. The pipes are located inside the shell. During normal operation, the upper end of the stripping column is located on top of the stripping column, and the lower end is located at the bottom of the stripping column.

In other words, the upper end is in fluid transfer communication with the lower end through a plurality of pipes located within the shell. The space on the shell side is not in fluid transfer communication with the upper end and the lower end. The space on the shell side is separated from the upper end, for example, by means of an upper tube sheet. The space on the shell side is separated from the lower end, for example by means of a lower tube sheet. When the upper end is separated from the space on the shell side by the upper tube sheet, a fluid transfer connection between the pipes at the upper end is provided by the perforated holes in the upper tube sheet. When the lower end is separated from the space on the shell side by the lower tube sheet, a fluid transfer connection between the pipes and the lower end is provided by the perforated holes in the lower tube sheet. Preferably, the perforated holes in the upper tube sheet and the lower tube sheet are circular, the pipes are cylindrical, and the perforated holes have a diameter that is equal to the diameter of the pipes within a permissible error of less than 10.0%, 5.0%, 2.0 % or 1.0%.

The upper end contains an inlet for the urea-urea mixture and an outlet for a gas mixture containing stripping gas and one or more stripped compounds.

The lower end contains an outlet for a urea-urea stream concentrated in terms of urea. In some embodiments, the urea-concentrated urea-urea stream contains unreacted ammonium carbamate in an amount of, for example, 0.0 to 30.0 wt. %, or from 10.0 to 20.0 wt. %, or from 10.0 to 15.0 wt. %, or from 15.0 to 25.0 wt. % ammonium carbamate.

In some embodiments, the urea-urea concentrated urea stream contains free ammonia in an amount of, for example, 0.0 to 20.0 wt. %, or from 0.5 to 1.0 wt. %, or from 0.5 to 20.0 wt. %, or from 10.0 and 15.0 wt. % free ammonia.

Here the abbreviation “wt. %" means the mass percentages of the components relative to the mass of the urea-urea stream.

In some embodiments, the urea-concentrated urea stream simultaneously contains free ammonia and ammonium carbamate, for example, in the concentrations described above.

Optionally, the lower end includes an inlet for boil-off gas. Particularly in the case of a carbon dioxide stripper, the lower end contains an inlet for CO ₂ used as stripping gas. In the case of a self-stripping column, the bottom end does not contain a stripping gas inlet.

The stripping column further includes a heating fluid inlet and a heating fluid outlet, both of which are in fluid transfer communication with a shell-side space located between the tubes and the shell.

Preferably, the heating fluid inlet is located near the upper end of the stripping column, and the heating fluid outlet is located near the lower end of the stripping column.

The shell-tubular stripping column contains a heating fluid distributor near the heating fluid inlet. The heating fluid distributor ensures homogenization of the heating fluid flow in the stripping column.

The heating fluid distributor contains an edge wall and a distribution plate for the heating fluid, which occupies a transverse position in the stripping column. It should be understood that the expression "lateral position" as used herein in relation to the heating fluid distribution plate means that the heating fluid distribution plate is parallel with respect to the lateral cross sections, or in other words, that the distribution plate for the heating fluid is located perpendicular to the longitudinal direction.

The edge wall contains two or more holes and/or a plurality of perforated holes, and the edge wall defines a band-like space between the shell and the edge wall. In some embodiments, the perforated holes are circular. This edge wall reduces the velocity of the steam flow that impacts the tubes in the stripping column and, as a result, reduces tube erosion.

The heating fluid inlet is configured to introduce the heating fluid into the ribbon-like space. Preferably, this is accomplished by directly introducing heating fluid into the belt-like space through the heating fluid inlet.

The belt-shaped space is configured to introduce a heating fluid into the internal space to distribute the heating fluid. In particular, two or more holes and/or a plurality of perforated holes in the edge wall ensure uniform introduction of heating fluid into the interior space for distributing the heating fluid.

The heating fluid distribution plate is configured to introduce heating fluid from the inner space for distributing the heating fluid into the space on the shell side between the heating fluid distributor and the lower end. Specifically, the heating fluid enters into the space on the shell side through a plurality of perforated holes contained in the heating fluid distribution plate. The plurality of perforated holes includes a plurality of pipe holes and a plurality of heating fluid holes. The size and/or density of the heating fluid holes varies in the radial direction of the heating fluid distribution plate.

The term "radial direction" as used herein means a direction in a transverse plane that is oriented away from the center of the stripping column. Each radial direction corresponds to a tangential direction, which is in the transverse plane, and which is perpendicular to the radial direction. In some embodiments, the size of the tube opening varies in radial directions and is constant in tangential directions. As a result, a rotationally symmetrical configuration of the dimensions of the pipe openings appears.

In some embodiments, the space between any pipe and the pipe opening through which it passes is less than 1.0%, 2.0%, 3.0%, 5.0%, or 10.0% of the diameter of the pipe. In some embodiments, the space between any pipe and the pipe opening through which it passes through the heating fluid distribution plate is 0.0% to 1.0%, or 1.0% to 2.0%, or 2.0% to 3.0%, or from 3.0% to 5.0%, or from 5.0% to 10.0%, or from 0.5% to 1.5%, or from 1, 5% to 2.5%, or from 2.5% to 3.5%, or from 3.5% to 5.5%, or from 5.5% to 10.5% of the pipe diameter.

Accordingly, the shape of the perforated holes is in close correspondence with the edge of the pipes that pass through the distribution plate. If necessary, the allowable dimension between the pipe and the edge of the perforated hole allows for thermal deformation in the stripping column.

In some embodiments, the shell is cylindrical and the shell has an outer diameter of 2.0 to 6.0 m or 3.0 to 5.0 m.

In some embodiments, the upper end of the stripping column is connected to the tubes via bushings in the top tube sheet. Each sleeve is a liquid separation device and is connected to pipes. The bushings are made with the possibility of uniform distribution of the urea-urea mixture over all pipes through the holes in the bushing. Preferably, these holes are located at the bottom of the sleeve. In addition, the bushings contain one or more holes, preferably in their upper part, which allow the release of a gas stream into the upper end of the stripping column.

Preferably, the edge wall of the heating fluid distributor is made of sheet metal, for example sheet steel.

In some embodiments, the edge wall includes three openings on its surface, including a central opening and two side openings.

The holes can be, for example, rectangular or circular. For example, the heating fluid distributor contains from 2 to 1000 holes, for example from 5 to 500 holes, or from 10 to 250 holes, or from 50 to 225 holes, or from 100 to 200 holes, or from 150 to 175 holes.

In some embodiments, the total area of the holes or perforations in the heating fluid distributor is 2 to 8 times, or 3 to 6 times, or 4 times the total area of the corresponding heating fluid inlet.

Preferably, the height of the edge wall of the heating fluid distributor is less than the height of the inlet and the height of the belt-like space. In other words, in these embodiments, a void space through which a limited amount of steam can flow is left at the top of the belt-shaped space between the edge wall and the shell of the stripping column. An exemplary embodiment of this configuration is shown in FIG. 3(b).

Preferably, the edge wall does not contain an opening immediately before the inlet of the heating fluid.

According to some embodiments, the edge wall of the heating fluid distributor includes a perforated area and a non-perforated area. In the non-perforated area, the edge wall is closed.

In some embodiments, the perforated area is located near the heating fluid inlet. Therefore, the non-perforated area is located at a distance from the inlet of the heating fluid.

In some embodiments, the perforated area is located at a distance from the heating fluid inlet. Therefore, the non-perforated region is located near the inlet of the heating fluid.

In some embodiments, the edge wall includes a plurality of perforated holes whose density and/or size varies across its surface. Preferably, the edge wall contains perforated holes which are distributed uniformly over its surface and whose size varies with increasing distance from the heating fluid inlet.

In some embodiments, the edge wall includes perforated holes that are distributed uniformly over its surface and the size of the perforated holes increases, for example, strictly increases as the distance from the heating fluid inlet increases.

In some embodiments, the edge wall includes perforated holes that are distributed uniformly across its surface and the size of the perforated holes decreases, for example, strictly decreases as the distance from the heating fluid inlet increases.

According to some embodiments, the edge wall contains perforated holes that are distributed uniformly over its surface, and also contains regions where the size of the perforated holes increases, for example, strictly increases with increasing distance from the heating fluid inlet; and it contains regions in which the size of the perforated holes decreases, for example, strictly decreases as the distance from the heating fluid inlet increases.

In some embodiments, the size of the heating fluid openings varies from the center of the heating fluid distribution plate to the outer rim of the heating fluid distribution plate. In other words, in some embodiments, the size of the heating fluid openings is different at the center of the heating fluid distribution plate compared to the outer rim of the heating fluid distribution plate.

In other words, preferably only the size of the heating fluid holes is changed and not the distance between the heating fluid holes. Changing the size of the heating fluid holes is of greater practical importance than changing the distance between the holes: changing this distance can lead to the formation of dead zones if the distance between the heating fluid holes is too large. In addition, for the purpose of mechanical stability, the heating fluid openings are preferably located at a certain distance, for example at least 1.0 mm or at least 10.0 mm, from the pipe openings. Thus, the arrangement of the heating fluid holes with variable spacing becomes more complex, while the variable sized heating fluid holes provide a significantly simplified configuration.

In some embodiments, pipe vibration limiting devices are provided between the heating fluid distribution plate and the lower end. Preferably, the pipe vibration limiting devices comprise a plurality of baffle discs.

The use of baffle discs instead of standard baffles ensures a minimum pressure drop and at the same time ensures minimal distortion of the heating flow. Reducing the pressure drop allows for increased tube density and thus increases stripper capacity while maintaining stripper size.

In some embodiments, the angle between the longitudinal direction and the heating fluid distribution plate is 85.0° to 90.0°, or 87.5° to 90.0°, or 88.0° to 90.0°, preferably 89.0° to 90.0°, more preferably 89.5° to 90.0°, even more preferably 90.0°.

In some embodiments, the angle between the longitudinal direction and the edge wall is from 0.0° to 5.0°, or from 0.0° to 2.5°, or from 0.0° to 2.0°, preferably from 0 .0° to 1.0°, preferably 0.0° to 0.5°, even more preferably 0.0°.

The term "increase" as used herein means that the parameter to which it refers increases or remains constant and does not decrease in a specified direction and within a specified range.

The term "strict increase" as used herein means that the parameter to which it refers increases and does not decrease or remains constant in a specified direction and within a specified range.

The term "decrease" as used herein means that the parameter to which it refers decreases or remains constant and does not increase in a specified direction and within a specified range.

The term "strict reduction" as used herein means that the parameter to which it refers decreases and does not increase or remains constant in a specified direction and within a specified range.

In some embodiments, the size, eg, diameter, of the heating fluid openings increases from the outer rim toward the center of the heating fluid distribution plate.

According to some embodiments, the size of the heating fluid openings strictly increases from the outer rim to the center of the heating fluid distribution plate.

In some embodiments, the size of the heating fluid openings decreases from the outer rim toward the center of the heating fluid distribution plate. According to some embodiments, the size of the heating fluid openings strictly decreases from the outer rim toward the center of the heating fluid distribution plate.

According to some embodiments, the heating fluid distribution plate contains one or more regions in which the size of the heating fluid openings strictly decreases from the outer rim to the center of the heating fluid distribution plate, and the heating fluid distribution plate contains one or more regions , in which the size of the heating fluid openings strictly increases from the outer rim to the center of the heating fluid distribution plate.

Preferably, holes are drilled into the distribution plate for the heating fluid.

Preferably, the size of the holes is selected such that, during normal operation, the same amount of heating fluid flows through each heating fluid hole, for example, within a tolerance of 10.0%, or 5.0%, or 1.0% .

In some embodiments, the diameter of the heating fluid openings is from at least 1 mm to no more than 16 mm, preferably from at least 2 mm to no more than 13 mm, more preferably from at least 3 mm to no more than 10 mm, even more preferably from at least 5 mm to not more than 7 mm.

In some embodiments, the ratio of the diameter of the largest of the heating fluid orifices on the one hand to the diameter of the smallest of the heating fluid orifices on the other hand is from at least 1.1 to no more than 16, preferably from at least at least 1.4 to no more than 3.5.

In some embodiments, heating fluid openings in the heating fluid distribution plate are spaced at equal intervals on concentric circles around the center of the heating fluid distribution plate.

According to some embodiments, the density of heating fluid holes is constant in the heating fluid distribution plate, and the size of the heating fluid holes varies from the center of the heating fluid distribution plate to the outer rim of the heating fluid distribution plate, and the tube holes are located in a triangular geometric configuration. A triangular geometric tube hole configuration is a configuration in which the tube holes occupy positions at the corners of equilateral triangles. The steam hole is located in the center of each equilateral triangle. In other words, each heating fluid opening occupies a central position between three adjacent pipe openings.

Preferably, six equilateral triangles form a hexagonal unit cell configuration.

Preferably, the one and only one heating fluid opening occupies a central position between three adjacent pipe openings. Accordingly, the openings for the heating fluid also occupy positions in a triangular geometric configuration. Preferably, the heating fluid openings and pipe openings are arranged in a hexagonal grid.

Preferably, the geometric configuration of the pipe holes and steam holes is constant throughout the heating fluid distribution plate, and only the size of the heating fluid holes varies between the center and the rim of the heating fluid distribution plate.

According to some embodiments, the density of heating fluid holes is constant in the heating fluid distribution plate, and the size of the heating fluid holes varies from the center of the heating fluid distribution plate to the outer rim of the heating fluid distribution plate, and the tube holes are located in a square geometric configuration. A simple square geometric tube hole configuration is a configuration in which the tube holes occupy positions at the corners of a square. The steam hole is located in the center of each square. In other words, each heating fluid hole occupies a central position between four adjacent pipe holes. In other words, in a square geometric configuration, four tube holes and centrally positioned steam holes are arranged to form a square unit cell.

Preferably, the one and only one heating fluid opening occupies a central position between four adjacent pipe openings. Accordingly, the openings for the heating fluid also occupy positions in a square geometric configuration. Preferably, the heating fluid openings and pipe openings are arranged to form interconnected square grids.

Preferably, also for the case of a square geometric configuration, the geometric configuration of the pipe holes and steam holes is constant throughout the heating fluid distribution plate, and only the size of the heating fluid holes changes between the center and the rim of the heating fluid distribution plate.

The terms "triangular geometric configuration" and "square geometric configuration" are equivalent to the terms "triangular lattice" and "square lattice", respectively.

In some embodiments, the stripping column contains more than 3,000 pipes, or more than 4,000 pipes, or more than 5,000 pipes, or more than 6,000 pipes, or more than 7,000 pipes. In some embodiments, the stripping column contains 3,000 to 7,000 tubes, or 4,000 to 6,000 tubes, or 5,000 to 7,000 tubes, or 5,000 to 10,000 tubes.

In some embodiments, the shell is cylindrical, and the shell has an outer diameter of 2.0 to 6.0 m or 3.0 to 5.0 m.

As mentioned above, the stripping column contains a shell and a plurality of pipes that are located within the shell. In some embodiments, the pipes are arranged vertically within the shell. In some embodiments, the pipes have a length of greater than 3.0 m, greater than 4.0 m, or greater than 5.0 m. In some embodiments, the pipes have a length of from 4.0 to 8.0 m, or a length of from 5.0 to 7.0 m. Preferably, the pipes have a length of from 5.0 to 6.0 m.

The pipes preferably have an outer diameter ranging from 20.0 to 40.0 mm.

In the case of a carbon dioxide stripper, the pipes preferably have an outer diameter of 20.0 to 40.0 mm or 25.0 to 35.0 mm.

In the case of a self-stripping column, the pipes preferably have an outer diameter of from 20.0 to 30.0 mm. In the case of a carbon dioxide stripper, the pipes preferably have an outer diameter of 30.0 to 35.0 mm.

In some embodiments, the pipes have a diameter of up to 32.0 mm or up to 31.0 mm.

Preferably, the pipes are made of stainless steel.

Furthermore, the present invention provides a system for producing urea comprising a urea condenser, a urea reactor and a shell-tubular stripper, which is described herein.

The stripping column may be, for example, a carbon dioxide stripping column or a self-stripping column, as described above.

In some embodiments, the urea reactor and the urea condenser are separate reaction vessels. Alternatively, the urea reactor and urea condenser is an integrated urea reactor and urea condenser. These two embodiments are discussed separately.

When the urea condenser and the urea reactor are separate reaction vessels, the urea condenser is configured to partially and exothermically convert ammonia and carbon dioxide into ammonium carbamate, and the urea condenser partially converts the ammonium carbamate thus obtained into urea. Thus, the output flow from the condenser is obtained. The urea reactor is configured to adiabatically convert at least a portion of the ammonium carbamate contained in the condenser effluent into urea. Thus, a urea-urea mixture is obtained. The system is configured to introduce a urea-urea mixture into the stripping column. The stripping column is configured to convert the urea-urea mixture into a urea-urea stream concentrated in terms of urea and a gaseous stream containing carbon dioxide and ammonia.

When the system contains an integrated reactor that simultaneously serves as a carbamate condenser and a urea reactor, the integrated reactor is configured to partially and exothermically convert ammonia and carbon dioxide to ammonium carbamate. In addition, the combined reactor is designed with the additional possibility of partially converting ammonium carbamate into urea.

Thus, a urea-urea mixture is obtained. The system is configured to introduce a urea-urea mixture into a stripping column, and the stripping column is configured to convert the urea-urea mixture into a urea-urea concentrated urea stream and a gaseous stream containing carbon dioxide and ammonia.

In addition, according to the present invention, the use of a shell-tubular stripping column, which is described herein, for stripping a urea-urea mixture is proposed.

In addition, it is proposed to use a stripping column, which is described above, to increase the stripping efficiency and/or to reduce pipe corrosion in the process of stripping urea-urea mixtures.

In addition, a method for steaming a urea-urea mixture has been proposed. In addition or alternatively, this method can be defined as a method of reducing corrosion in the tubes of stripping columns for decomposing urea-urea mixtures and/or increasing stripping efficiency in the process of stripping urea-urea mixtures.

The method includes the step of providing a shell-tubular stripping column. The stripping column is a stripping column as described above. Preferably, the stripping column is configured in which the tubes are arranged vertically within the shell. In addition, the stripping column is preferably arranged such that an upper end is at the top of the stripping column and a lower end is at the bottom of the stripping column. The urea-urea mixture enters the urea-urea mixture inlet.

When a carbon dioxide stripper is used, the stripping gas, which is CO ₂ , enters the stripping gas inlet. When a self-stripping column is used, the CO ₂ and NH ₃ that are generated from the decomposition of ammonium carbamate serve as stripping gas. It should be noted that, as mentioned above, self-stripping columns typically still include a passivation air inlet for the purpose of reducing corrosion, but the passivation air flow rate is not sufficient to make a significant contribution to the stripping process.

The heating fluid enters the space on the shell side through the heating fluid inlet. The heating fluid is preferably steam, more preferably saturated steam. The urea-urea mixture and the stripping gas come into contact in the pipes. In particular, the urea-urea mixture moves in the falling film mode along the inner walls of the pipes. The stripping gas moves upward in the space on the pipe side.

The urea-urea mixture is heated by a heating fluid. Under the influence of heat provided by the heating fluid, the ammonium carbamate in the urea-urea mixture decomposes to form ammonia gas and carbon dioxide. When ammonium carbamate in a urea-urea mixture decomposes, a urea-urea stream concentrated in terms of urea is obtained. The urea-concentrated urea stream exits through the outlet for the urea-concentrated urea stream.

The gas mixture containing one or more stripped compounds exits through the gas mixture outlet. When a carbon dioxide stripper is used, this gas mixture also contains stripping gas. The heating fluid exits the space on the shell side by releasing the heating fluid.

These methods effectively provide improved stripping of urea-urea mixtures and at the same time reduce corrosion of stripping columns.

In some embodiments, the temperature of the tubes is constant along any lateral cross-section through the stripper column. In some embodiments, the temperature of the tubes is constant along any lateral cross-section through the stripping column, within a tolerance of less than 10°C, less than 5°C, less than 2°C, or less than 1°C. Constant temperature along the side cross sections through the stripping column ensures uniform heat transfer to the pipes. Constant temperature in the radial direction provides improved distribution of the heating fluid, and in turn, constant temperature in the radial direction reduces corrosion of the stripper tubes.

In some embodiments, the shell side space gauge pressure is from 10.0 to 30.0 bar, and preferably from 16.0 to 24.0 bar.

The mass flow rate of the heating fluid depends on the capacity of the stripping column. In some embodiments, the mass flow rate of the heating fluid is between 10.0 and 60.0 kg/s, between 20.0 and 50.0 kg/s, or between 30.0 and 40.0 kg/s.

In some embodiments, the heating fluid contains steam. Preferably, the heating fluid consists mainly of steam. In other words, the heating fluid preferably contains at least 99.0 wt. % steam or at least 99.9 wt. % pair. Here the abbreviation “wt. %" means that the composition of the heating fluid is expressed as a mass percentage, i.e. as a percentage of the mass flow rate of the steam contained in the heating fluid and the mass flow rate of the entire heating fluid.

In some embodiments, the heating fluid has a density ranging from 7.0 to 13.0 kg/m ³ or from 8.5 to 12.0 kg/m ³ .

In addition, the present invention provides the use of a heating fluid distributor for homogenizing a steam stream near the heating fluid inlet of a shell-tubular stripping column for stripping a urea-urea mixture. The heating fluid distributor contains an edge wall and a transversely located distribution plate for the heating fluid. The edge wall contains two or more holes and/or a plurality of perforated holes. The heating fluid distribution plate has an outer rim and a center and contains a plurality of perforated holes. The plurality of perforated holes includes a plurality of pipe holes and a plurality of heating fluid holes. The size and/or density of the heating fluid openings varies from the center of the heating fluid distribution plate to the outer rim of the heating fluid distribution plate. Preferably, the heating fluid distributor is a heating fluid distributor as described herein.

Examples

Example 1

In the first example, consider FIG. 1, wherein image (a) shows the stripping column (100) that is described herein. In particular, the stripping column (100) is a carbon dioxide stripping column. The stripping column (100) includes a shell (160) and a plurality of pipes (150) that are located inside the shell (160). In addition, the stripping column (100) includes an upper end (110) and a lower end (120). The pipes (150) are located between the upper end (110) and the lower end (120). The pipe side space (140) is the space that is located in the pipes (150). The space (130) on the shell side is located between the pipes (150) and the shell (160). A space (130) on the shell side is separated from the upper end (110) and the lower end (120). The upper end (110) and the lower end (120) are in fluid transfer communication with the space on the pipe side (140).

The lower end (120) includes an outlet (122) for the urea-concentrated urea stream and an inlet (121) for the stripping gas.

The upper end (110) contains an inlet (111) for the urea-urea mixture and an outlet (112) for the gas mixture, which contains stripping gas and one or more stripped compounds.

The stripping column (100) further includes a heating fluid inlet (131) and a heating fluid outlet (133). The heating fluid inlet (131) and the heating fluid outlet (133) are in fluid transfer communication with the space (130) on the shell side. In addition, the heating fluid inlet (131) is located near the upper end (110) of the stripping column (100). The heating fluid outlet (133) is located near the lower end (120) of the stripping column (100).

The pipes (150) have a length of 6.0 m and an outer diameter of 31.0 mm. The stripping column contains a cylindrical shell with a diameter of 3.1 m.

The fender discs (134) are located at regular intervals in the space (130) on the shell side. Two specific baffle disc configurations are shown in FIG. 1, image (b). Such fender discs are known in the art.

The stripping column in FIG. 1 includes a heating fluid distributor comprising a heating fluid distribution plate (175) and an edge wall. The heating fluid distributor ensures that the flow of the heating fluid is substantially parallel with respect to the pipes (150) in the portion of the stripping column between the heating fluid distribution plate (175) and the lower end (120) of the stripping column.

A detailed description of the heating fluid distributor is presented in Example 3.

Example 2

In the second example, consider FIG. 2, which shows the stripping column (100) that is described herein. In particular, the stripping column (100) is a self-stripping column. The design of the stripping column (100) is similar to that of Example 1 with some differences.

In particular, the self-stripping column does not include a stripping gas inlet at its lower end; NH ₃ and CO ₂ , which are generated from the decomposition of ammonium carbamate, serve as stripping gas in self-stripping columns, and thus there is no need for a stripping gas inlet.

In addition, the tubes of the self-stripping column have a smaller thickness than the tubes of the carbon dioxide stripper column in Example 1. In particular, the tubes of the self-stripping column have an outer diameter of 25 mm.

The stripping column in FIG. 2 includes a heating fluid distributor comprising a heating fluid distribution plate (175) and an edge wall (171) as described in Example 3. The heating fluid distributor uniformly distributes the heating fluid from the inlet (131) into the belt-like space.

Example 3

In the third example, consider FIG. 3 which presents some details of the exemplary heating fluid distributor described herein. This heating fluid distributor is particularly suitable for introducing steam into the shell side space in a urea stripping column.

In fig. 3 shows six images (a)-(f).

Image (a) is a top view of a heating fluid distributor (170), which includes a heating fluid distribution plate (175) and an edge wall (171). The shell (160) and rim wall (171) of the stripping column define a belt-like space (179) into which heating fluid enters from the heating fluid inlet (131). The edge wall (171) contains seven holes (174) through which a flow of heating fluid enters the inner space (178) to distribute the heating fluid over the heating fluid distribution plate (175) as indicated by the flow lines (156). The number and type of holes (174) depend on the operating conditions of the stripping column and may vary.

The heating fluid distribution plate (175) includes a plurality of steam holes that uniformly distribute the heating fluid from the inner space (178) to distribute the heating fluid to the space below on the shell side. The steam hole configurations are shown in detail in images (d)-(g).

Image (b) is a side view of the heating fluid distributor (170). This image clearly shows the heating fluid inlet (131), edge wall (171), top tube sheet (151) and heating fluid distribution plate (175).

Image (c) shows that the heating fluid distribution plate (175) does not contact the edge wall (171). Instead, space is left for thermal expansion between the heating fluid distribution plate (175) and the edge wall in anticipation of thermal expansion. It should be noted that during normal operation, a small amount of heating fluid may pass through the thermal expansion space (172) without adversely affecting the supply of heating fluid to the space on the shell side.

Image (d) shows a distribution plate (175) for heating fluid.

Image (e) is a detailed illustration of the configuration of the tube openings (176) and heating fluid (177) near the edge of the heating fluid distribution plate. The pipe openings (176) in particular occupy positions at the corners of equilateral triangles. At the center of each equilateral triangle is an opening (177) for heating fluid. Six equilateral triangles form a hexagonal unit cell.

Image (f) is a detailed illustration of the configuration of the pipe openings (176) and heating fluid openings (177) near the center of the heating fluid distribution plate. This configuration is similar to that shown in (e), with the only difference being that the sizes of the heating fluid holes (176) are different.

Image (g) provides a detailed illustration of an alternative configuration of tube openings (176) and heating fluid openings (177). Pipe holes (176) occupy positions at the corners of the squares. At the center of each square is an opening (177) for heating fluid. Thus, the heating fluid openings (177) and the pipe openings (176) are arranged to form interconnected square grids. This configuration of tube openings (176) and heating fluid openings (177) may occur at either the edge or the center of the heating fluid distribution plate, the only difference being that the dimensions of the heating fluid openings (177) are different. heating fluid.

Example 4

In the fourth example, consider FIG. 4, which presents the beneficial effects associated with the use of baffle discs as devices for limiting pipe vibrations in a shell-tubular stripping column. In particular, images (a)-(c) schematically illustrate the mechanism by which vibration of pipes occurs in cases where there are no breaker disks (image (a)), one breaker disk is present (image (b)), and two breaker disks are present. disk (image (c)). Each additional set of baffles introduces an additional unit into the pipe vibration mode, and as a result, the amplitude at which the pipes vibrate occurs is limited.

Example 5

In the fifth example, consider FIG. 5, which shows images (a) and (b). Image (a) represents the flow of heating fluid, which is shown by flow lines (155) in the transverse direction, i.e. in a direction perpendicular to the pipes (150). This flow of heating fluid is reduced to a minimum by using a heating fluid distribution plate (175) as described herein. Image (b) shows heating fluid flows parallel to the pipes (150) as indicated by flow lines 156. This is the predominant type of flow that the distribution plate (175) induces for the heating fluid.

Example 6

The following example discusses an exemplary method of operating the stripping column (100) shown in Example 1. According to this method, the stripping column (100) is arranged vertically, and the upper end (110) is located on top of the stripping column, and the lower end (120) is located at the bottom of the stripping column (100). The stripping column contains a heating fluid distributor containing a heating fluid distribution plate (175) and an edge wall that is located at the heating fluid inlet (131).

The method includes introducing a mixture containing urea and ammonium carbamate into the urea-urea mixture inlet (111) and introducing CO ₂ , which is a stripping gas, into the stripping gas inlet (121).

The stripping gas and urea-urea mixture move in countercurrent mode through pipes (150). At the same time, the urea-urea mixture is heated, and the ammonium carbamate contained in the urea-urea mixture decomposes to form gaseous NH ₃ and CO ₂ , which are carried away by the stripping gas. Thus, a urea-urea stream, concentrated in terms of urea, is formed in the pipes (150). This stream moves down to the lower end (120) where it is discharged through the outlet (122) for a urea-concentrated urea stream.

The steam, which is used as the heating fluid, enters the space (130) on the shell side through the heating fluid inlet (131).

A heating fluid distributor is used to homogenize the steam flow in the space on the shell side. The steam has an operating pressure (absolute pressure) of approximately 18 bar and also has a mass flow rate of 36 kg/s and a steam density of 9 kg/m ³ .

The condensed steam exits the space (130) on the shell side through the heating fluid outlet (133). On the way from the heating fluid inlet (131) to the heating fluid outlet (133), steam passes through the space (130) on the shell side and heats the pipes (150) and their contents, which ensures the above-mentioned decomposition of ammonium carbamate to form NH ₃ and CO ₂ .

The presence of a heating fluid distributor ensures uniform heating of the tubes (150) and their contents, which in turn results in increased stripper efficiency and reduced corrosion in the tubes.

Example 7

The following example discusses an exemplary method of operating the stripper column (100) shown in Example 2. Specifically, its operation is similar to that of the stripper shown in Examples 1 and 6, except that no stripping gas is supplied to the bottom end. Instead, NH ₃ and CO ₂ , which are formed from the decomposition of ammonium carbamate, serve as stripping gas. Such a stripping column is called a “self-stripping column”.

Example 8

In the next example, consider FIG. 6, which shows selected parts of a plant (1000) for the production of urea. The installation for the production of urea contains a stripping column (100), which is described in example 1, a reactor (200) for converting ammonium carbamate into urea, a urea condenser (300) for the formation of ammonium carbamate, and a gas purifier (400) for condensing NH ₃ and CO ₂ , which come from the reactor, and a carbamate condenser. The gas cleaning fluid is a carbamate solution that is supplied through pipe (401) from the downstream section.

The stripper gas line (101) is in fluid transfer communication with the stripper gas inlet (121) of the stripper column (100). A pipe (104) for the urea-concentrated urea stream is in fluid transfer communication with an outlet (122) of the urea-concentrated urea stream of the stripping column (100).

The stripping column (100) contains a space on the shell side (see FIG. 1 (130)) where there is a heating fluid inlet and a heating fluid outlet (see FIG. 1) (131, 133).

The heating fluid inlet is in fluid transfer communication with the heating fluid flow pipe (503). The heating fluid outlet is in fluid transfer communication with a pipe for cooled heating fluid flow (504). A heating fluid flow pipe (503) and a cooled heating fluid flow pipe (504) are in fluid transfer connection with a heating fluid supply (500), which in turn is in fluid transfer connection environment with a connection (502) with an external supply of heating fluid.

In addition, the stripping column (100) is in fluid transfer communication with a pipe (102) for the urea-urea stream. This pipe (102) supplies the urea-urea stream from the reactor (200), in which ammonium carbamate is converted to urea. This reactor in turn receives ammonium carbamate from the carbamate condenser (300) through a pipe (302), as well as NH ₃ and CO ₃ gases, water and inerts through another pipe (301). The heat that is produced in the carbamate formation reaction in the carbamate condenser (300) is removed by steam and steam supply (501).

Example 9

In the next example, consider FIG. 7, 8, 9 and 10, which illustrate some of the problems that can be overcome using the systems and methods of the present invention. In particular, the systems and methods of the present invention provide increased stripper operating time and increased stripper efficiency. This example illustrates these indicators for a specific carbon dioxide stripper column. However, it is expected that similar corrosion problems may also occur in other types of stripper columns when uneven heating occurs, although the exact corrosion pattern is expected to depend on the specific morphology of the stripper column. The self-stripping column is one example of another type of stripping column that is expected to have similar corrosion problems.

In fig. 7 shows two patterns of corrosion that occur simultaneously in fairly large prior art carbon dioxide strippers that contain stainless steel pipes and in which CO ₂ is used as stripping gas to strip the urea-urea solution. More specifically, this corrosion pattern has been observed in shell-and-tubular strippers that contain 6 m high pipes, have a shell diameter of approximately 3 m, contain disc-ring baffles mounted in space on the shell side, and contain approximately 5000 pipes (150).

The type of corrosion also depends on whether the stripper is a carbon dioxide stripper or a self-stripper.

As such, it was found that the corrosion pattern shown in FIG. 7(a) typically occurs in small diameter carbon dioxide strippers, and it has been found that the corrosion pattern shown in FIG. 7(b) typically occurs in small diameter self-stripping columns. In the context of the present invention, both carbon dioxide strippers and self-strippers are specific configurations of shell-tubular strippers.

Said shell-tubular stripping columns comprise an upper tube sheet (151) which is located above and at the upper end of the tubes. It separates a space on the shell side containing disc-ring partitions from the upper end of the stripping column. The upper tube sheet (151) also allows the urea-urea mixture to flow down in the form of a liquid film along the inner wall of the tubes (150). It also allows the gas mixture containing CO ₂ and NH ₃ to exit the pipes (150).

Shell-tube strippers also include a bottom tubesheet (152) that is located below and at the lower end of the tubes. It separates the space on the shell side from the bottom end of the stripping column. The bottom tubesheet (152) also allows the urea-concentrated urea stream to exit the tubes (150), and in a carbon dioxide stripper it allows the stripping gas, which is CO ₂ , to enter the tubes (150).

These strippers exhibit different corrosion patterns in the outer and inner tubes of the stripper. The inner tubes approximately cover the cross-section of the disc baffles, and the outer tubes approximately cover the cross-section of the annular baffles. The picture of corrosion in the outer pipes is shown in Fig. 7 (see image (a)). The picture of corrosion in the internal pipes is shown in Fig. 7 (see image (b)). The corrosion rate in the outer pipes is schematically shown in Fig. 8 (see image (a), right graph). The corrosion rate in internal pipes is shown schematically in FIG. 8 (see image (b), right graph).

In the outer pipes there is simultaneously an area (153) of corrosion and an area (154) of deposits. On the other hand, in the inner pipes, only the area (153) of corrosion is present. In areas of corrosion, pipe corrosion occurs. In the area (154) of deposits, corrosion does not occur, but deposits containing iron are formed. Although the area of corrosion in the outer pipes extends only along a portion of the length of the pipes, the corrosion appears to be significantly more severe in the corrosion area (153) of the outer pipes. The useful life of stripping columns is limited by the corrosion rate of the pipes. Thus, if the rate of corrosion that occurs in the outer tubes (150) could be reduced, the degree of corrosion after a certain period of operation would also be reduced, and therefore the useful life of the stripping columns could be increased.

Without limiting the present invention to any particular operating mode, the inventors believe that the occurrence of uneven corrosion in prior art carbon dioxide strippers for stripping ammonium carbamate from urea-urea streams can be explained as follows. During normal operation of prior art strippers, the urea-urea mixture flows down the inner wall of the tubes (150) in the form of a falling film and is heated by steam that enters the space on the shell side. Under the influence of heat, ammonium carbamate in the urea-urea mixture decomposes to form gaseous NH ₃ and CO ₂ , which move upward along with the stripping gas flow. Thus, ammonium carbamate gradually decomposes.

During the making of the present invention, it was discovered that the presence of iron deposits in the lower part of the outer pipes, i.e. in the region (154) of deposits means that in this region of deposits the liquid phase contains mainly urea, residual urea, free NH ₃ and water. In other words, a significant portion of the ammonium carbamate is decomposed, leaving behind a liquid phase which consists mainly of urea, residual carbamate, free NH ₃ and water, and which flows down the pipe walls in the deposit area (154). Iron (Fe) appears to be significantly less soluble in urea than in ammonium carbamate. On the other hand, in the central pipes there is no deposit area, which means that the ammonium carbamate is not completely decomposed.

In addition, it was found that the rate at which ammonium carbamate decomposes increases with the amount of heat introduced into the pipes (150). Accordingly, the observation that ammonium carbamate decomposes toward the upper end of the stripping column in the outer tubes indicates greater heating in the outer tubes compared to the inner tubes. Since heat is provided by the steam flow in the space on the shell side of the stripping column, the amount of heat is determined by this steam flow. Therefore, the introduction of more heat into the outer tubes compared to the inner tubes is due to the steam flow in the space on the shell side of the stripping column. Thus, the inventors of the present invention have discovered that the uneven flow of steam in the space on the shell side of the stripping column is the cause of the observed increase in corrosion rates in the outer tubes compared to the inner tubes.

In addition, it has been discovered that uneven heating of the tubes leads to inefficient operation of the stripping columns due to uneven distribution of the stripping gas, which is CO ₂ , throughout the tubes. In particular, it has been found that under typical operating conditions of prior art shell-and-tube strippers containing a steam inlet and a disk-ring partition in the space on the shell side, the gas flow rate through the less heated inner tubes is significantly higher. than the speed of gas flow through the more heated outer pipes. Uneven stripping gas flow causes symptoms of process inefficiency such as uneven stripping of carbamate in the tubes and therefore ineffective decomposition of ammonium carbamate in the stripping column.

Liquid separating devices (called bushings, an example of which is shown in Fig. 10) are installed in the front head of the stripping column and are connected to pipes in the upper tube sheet in order to ensure uniform distribution of the urea-urea mixture throughout each pipe through holes (710) in the lower bushing parts. In addition, one or more holes (720) at the top of the liquid separation device are configured to release a gas stream to the top end of the stripping column. The stripping gas flow is determined by a combination of hydrodynamic and hydrostatic effects. Hydrodynamic effects correspond to the pressure drop across one or more openings (720) at the top of the fluid separating devices (called bushings) and can be expressed as Δp=0.5ρ⋅v ² where Δp is the pressure drop, ρ is the density fluid, and v represents the velocity of the fluid.

For typical operating conditions, the hydrodynamic pressure drop across the pipes is approximately 250 Pa. The hydrostatic effect corresponds to the pressure effect due to the gas density along the height of the pipes and for a given pressure can be expressed as Δр=Δр⋅g⋅h. The hydrostatic pressure drop in the stripper column, which was described above, is estimated to be approximately 5500 Pa. Accordingly, the hydrostatic effect is predominant and thus is primarily responsible for the distribution of the stripping gas flow through the pipes. Thus, any possible disequilibrium of the stripping gas flow between the pipes caused by differences in the hydrostatic pressure drop across the pipes cannot be compensated by changing the hydrodynamic pressure drop across the hole in the top of the sleeve. The pressure drop across the orifice can be changed by changing the size of the orifice in the bushing. As the hole size decreases, the pressure drop increases and vice versa.

It was found that in the case of pipes that are heated to a greater extent, the decomposition of carbamate and the accompanying release of CO ₂ and NH ₃ occur in the upper part of the pipes, i.e. near the top end, for example in the top half of pipes. Thus, the partial pressure of NH ₃ at the top of the pipes is high, while the partial pressure of NH ₃ at the bottom of the pipes is low. The stripping gas is CO ₂ , and under the same conditions NH ₃ has a lower density than CO ₂ . As the gas moves upward, the concentration of NH ₃ is highest at the top of the pipes. Thus, the gas at the top of the pipes has a lower density than the gas at the bottom of the pipes. This is illustrated in FIG. 8 (see image (a)). This image shows that there are three regions in the pipes: a lower region, which is characterized by higher gas density and lower corrosion rates, a transition region, in which gas density and corrosion rates change sharply, and an upper region, which is characterized by higher corrosion rates and lower gas density. Particularly in the upward direction of the pipes, the first region into which the gas enters is the downstream region. In the lower region, the gas density gradually decreases as the gas heats up as it moves up the pipes. In the transition region, the gas density decreases sharply due to the decomposition of ammonium carbamate and the resulting release of ammonia gas. In the upper region, the gas density gradually decreases as the gas is further heated, and the corrosion rate is high because the pipe walls are in contact with the intensely heated urea-urea solution. Essentially, the depth of pipe corrosion increases in a downward direction within the upper region as the solution heats up as it moves downward.

In addition, the present inventors have discovered that in less heated pipes, carbamate decomposition occurs from the top of the pipe all the way to the bottom of the pipes, such that in all less heated pipes the gas has a lower density compared to the gas density in more heated pipes. pipes, and this, in turn, leads to the fact that the hydrostatic pressure in the less heated pipes is lower than the hydrostatic pressure in the more heated pipes.

The gas density profile in the hotter outer tubes is shown in FIG. 8 (see image (a), left graph). The gas density profile in the less heated inner tubes is shown in Fig. 8 (see image (b), left graph). Gas density profiles in less heated pipes and in more heated pipes are also presented for comparison in Fig. 9. In FIG. Figure 9 clearly shows that in less heated tubes the carbamate decomposes near the bottom of the stripping column compared to more heated tubes. This results in a different gas density profile, which in turn creates a difference in hydrostatic pressure. Less high hydrostatic pressure in the inner tubes causes the stripping gas flow rate in the cooler tubes to be higher than in the hotter tubes, resulting in reduced stripping efficiency.

This is slightly compensated for when boil-off gas, which is CO ₂ and has a lower temperature than the pipes, is used, because the lower temperature CO ₂ gas reduces the density of the gas phase in the pipes, and as a result the hydrostatic pressure increases and the compensating effect of increased heating . However, this effect is not sufficiently pronounced to eliminate the steaming inefficiency associated with uneven heating.

Essentially, simulations (results not shown) demonstrated that even small differences in density profiles lead to significant effects on flow distribution. In particular, the area-weighted average fluid velocity in the cooler inner tubes was estimated to be approximately five times greater than the area-weighted average fluid velocity in the hotter outer tubes. This large discrepancy between fluid velocities results in significant stripping inefficiencies in prior art stripping columns.

Consequently, as a result of uneven heating in the large carbon dioxide stripping columns of the prior art, problems of corrosion and stripping inefficiency arise. These problems can be solved by installing a heating fluid distributor as described herein, which will result in uniform heating so that all tubes of the stripper can be heated moderately and evenly, and this will result in a low corrosion rate throughout the stripper. column. In addition, uniform heating results in a uniform gas density profile, which in turn provides a uniform stripping gas flow rate and increased stripping efficiency.

Claims (41)

1. Shell-tubular stripping column (100) for stripping the urea-urea mixture, wherein the stripping column (100) has an upper end (110) in fluid transfer communication with a lower end (120) through a plurality of pipes (150) located within the shell (160); an upper end (110) containing an inlet (111) for a urea-urea mixture and an outlet (112) for a gas mixture containing a stripping gas and one or more stripped compounds; a lower end (120) containing an outlet (122) for a urea-urea concentrated urea stream; a lower end (120) optionally containing a boil-off gas inlet (121); wherein the shell-tube stripper (100) further comprises a heating fluid inlet (131) and a heating fluid outlet (133) in fluid transfer communication with a shell-side space (130) located between the plurality of tubes (150) and shell (160); wherein the shell-tubular stripping column (100) has a longitudinal direction and lateral cross sections, wherein the longitudinal direction is parallel to the pipes, and the lateral cross sections are perpendicular to the longitudinal direction; wherein the shell-tubular stripping column includes a heating fluid distributor (170) adjacent a heating fluid inlet (131) to homogenize the heating fluid flow in the stripping column (100), wherein the heating fluid distributor (170) includes an edge wall (171) and a distribution plate (175) for heating fluid, wherein the angle between the longitudinal direction and the distribution plate (175) for heating fluid is from 85.0° to 90.0°, and the angle between the longitudinal direction and the edge wall (171) is from 0.0° to 5.0°; wherein the edge wall (171) defines a band-shaped space (179) between the shell (160) and the edge wall (171), and wherein the edge wall (171) contains two or more holes and/or a plurality of perforated holes configured to uniformly introduce heating fluid into the interior space to distribute the heating fluid; wherein the heating fluid inlet (131) is configured to directly introduce the heating fluid into the band-shaped space (179); wherein the belt-shaped space (179) is configured to introduce heating fluid into the inner space to distribute the heating fluid; wherein the heating fluid distribution plate (175) is configured to introduce heating fluid from the inner space (178) to distribute the heating fluid into the space (130) on the shell side between the heating fluid distributor (170) and the lower end (120) wherein between the distribution plate (175) for the heating fluid and the edge wall (171) there is space for thermal expansion based on thermal expansion; And wherein the heating fluid distribution plate (175) includes a plurality of perforated holes, the plurality of perforated holes contains a plurality of pipe holes (176) and a plurality of heating fluid holes (177), and wherein the size and/or density of the heating fluid holes (177) the fluid changes in the radial direction of the distribution plate (175) for the heating fluid. 2. The shell-tubular stripping column (100) according to claim 1, wherein the size of the heating fluid openings (177) varies from the center of the heating fluid distribution plate (175) to the outer rim of the heating fluid distribution plate. 3. The shell-tubular stripping column (100) according to claim 1 or 2, wherein pipe vibration limiting means are provided between the heating fluid distribution plate and the lower end (120), wherein the pipe vibration limiting means optionally comprise a plurality of baffle disks (134). 4. Shell-tubular stripping column (100) according to any one of paragraphs. 1-3, in which the angle between the longitudinal direction and the distribution plate (175) for the heating fluid is from 87.5° to 90.0°, or from 88.0° to 90.0°, preferably from 89.0° up to 90.0°, more preferably from 89.5° to 90.0°, even more preferably 90.0°; and/or in which the angle between the longitudinal direction and the edge wall (171) is from 0.0° to 2.5°, or from 0.0° to 2.0°, preferably from 0.0° to 1.0°, more preferably from 0.0° to 0.5°, even more preferably 0.0°. 5. Shell-tubular stripping column (100) according to any one of paragraphs. 1-4, in which the size of the heating fluid holes (177) increases from the outer rim to the center of the heating fluid distribution plate (175), and optionally the size of the heating fluid holes (177) strictly increases from the outer rim to the center of the distribution plate plates (175) for heating fluid; or wherein the size of the heating fluid holes (177) decreases from the outer rim to the center of the heating fluid distribution plate (175), wherein optionally the size of the heating fluid holes (177) strictly decreases from the outer rim to the center of the distribution plate (175 ) for heating fluid. 6. Shell-tubular stripping column (100) according to any one of paragraphs. 1-4, in which the heating fluid distribution plate (175) includes one or more regions in which the size of the heating fluid openings (177) strictly decreases from the outer rim to the center of the heating fluid distribution plate (175), and wherein the heating fluid distribution plate (175) comprises one or more regions in which the size of the heating fluid openings (177) strictly increases from the outer rim to the center of the heating fluid distribution plate (175). 7. Shell-tubular stripping column (100) according to any one of paragraphs. 1-6, in which the diameter of the heating fluid holes (177) is from at least 1 mm to not more than 16 mm, preferably from at least 2 mm to not more than 13 mm, more preferably from at least 3 mm up to no more than 10 mm, even more preferably from at least 5 mm to no more than 7 mm; and/or wherein the ratio of the diameter of the largest of the heating fluid holes (177), on the one hand, and the diameter of the smallest of the heating fluid holes (177), on the other hand, is from at least 1.1 to no more than 16, preferably from at least 1.4 to at most 3.5. 8. Shell-tubular stripping column (100) according to any one of paragraphs. 1-7, in which the heating fluid openings (177) in the heating fluid distribution plate (175) are located at equal intervals on concentric circles around the center of the heating fluid distribution plate (175). 9. Shell-tubular stripping column (100) according to any one of paragraphs. 1-8, in which the density of the heating fluid holes (177) is constant in the heating fluid distribution plate (175), and the size of the heating fluid holes (177) varies from the center of the heating fluid distribution plate (175) to the outer rim of the heating fluid distribution plate (175), wherein the pipe openings (176) are arranged in a triangular geometric configuration, and wherein each heating fluid opening (177) occupies a central position between three adjacent pipe openings (176). 10. Shell-tubular stripping column (100) according to any one of paragraphs. 1-8, in which the density of the heating fluid holes (177) is constant in the heating fluid distribution plate (175), and the size of the heating fluid holes (177) varies from the center of the heating fluid distribution plate (175) to the outer rim of the heating fluid distribution plate (175), the pipe openings (176) being arranged in a square geometric configuration, and each heating fluid opening (177) occupying a central position between four adjacent pipe openings (176). 11. Shell-tubular stripping column (100) according to any one of paragraphs. 1-10, in which the stripping column contains more than 3000 pipes (150), or more than 4000 pipes (150), or more than 5000 pipes (150), or more than 6000 pipes (150), or more than 7000 pipes ( 150), or from 3000 to 7000 pipes (150), or from 4000 to 6000 pipes (150), or from 5000 to 7000 pipes (150), or from 5000 to 10000 pipes (150). 12. A system for the production of urea, containing a urea condenser (300), a urea reactor (200) and a shell-tubular stripping column (100) according to any one of paragraphs. 1-11. 13. The use of a shell-tubular stripping column according to any one of paragraphs. 1-11 for steaming the urea-urea mixture. 14. A method for stripping a urea-urea mixture, the method including the following stages: - providing a shell-tubular stripping column (100) according to any one of claims. 1-11; - introducing the urea-urea mixture into the inlet (111) for the urea-urea mixture; - introducing a heating fluid into the space (130) on the shell side through a heating fluid inlet (131), the heating fluid being saturated steam; - optionally introducing boil-off gas into the boil-off gas inlet at the lower end (120); - contacting the urea-urea mixture and the boil-off gas in the space on the pipe side (140), which is located in the pipes (150), heating the urea-urea mixture by means of a heating fluid and as a result obtaining a urea-urea stream concentrated in the ratio urea; - removing the urea-urea stream concentrated in relation to urea at the outlet (122) for the urea-urea stream concentrated in relation to urea; - removing a gas mixture containing one or more stripped compounds at the outlet (112) for the gas mixture, wherein one or more stripped compounds contain NH ₃ , CO ₂ and water; - removing the heating fluid at the outlet (133) of the heating fluid. 15. Using a heating fluid distributor (170) to homogenize a steam stream near the heating fluid inlet (131) of a shell-tubular stripping column (100) for stripping a urea-urea mixture; wherein the heating fluid distributor (170) comprises an edge wall (171) and a heating fluid distribution plate (175), wherein the angle between the longitudinal direction and the heating fluid distribution plate (175) is from 85.0° to 90.0 °, and the angle between the longitudinal direction and the edge wall (171) is from 0.0° to 5.0°; wherein the edge wall (171) defines an internal space (178) for distributing heating fluid above the heating fluid distribution plate (175), and wherein the edge wall (171) contains two or more holes and/or a plurality of perforated holes made with allowing heating fluid to be uniformly introduced into the interior space (178) to distribute the heating fluid; wherein the heating fluid distribution plate (175) is configured to introduce heating fluid from the inner space (178) to distribute the heating fluid into the space (130) on the shell side between the heating fluid distributor (170) and the lower end (120) wherein between the distribution plate (175) for the heating fluid and the edge wall (171) there is space for thermal expansion based on thermal expansion; and wherein the heating fluid distribution plate (175) comprises a plurality of perforated holes, the plurality of perforated holes comprises a plurality of pipe holes (176) and a plurality of heating fluid holes (177), and wherein the size and/or density of the holes (177) for heating fluid changes in the radial direction of the heating fluid distribution plate (175).