KR20080065289A - Tube bundle heat exchanger and method for removing dissolved substances from a polymer solution by means of degassing in a tube bundle heat exchanger - Google Patents

Abstract

The invention proposes a tube bundle heat exchanger (R) for removing dissolved substances from a polymer solution (4) by means of degassing, having a bundle of tubes (1) which are arranged parallel to one another and vertically and are fastened at both ends in each case in a tube base (2), having a fixture (3) in each tube (1) which narrows the free passage cross section through the tube (1), wherein the tubes (1) are traversed by the polymer solution (4), and having a casing space (5) around the tubes (1) which is traversed by a liquid heat carrier (6), having deflecting plates (7) in the casing space (5) which are each arranged in cross-sectional planes of the tube bundle heat exchanger (R) and in each case form a deflecting region (8) for the heat carrier (6), which tube bundle heat exchanger (R) is characterized in that no tubes (1) are arranged in the deflecting regions (8), and in that all the fixtures (3) are of identical design.

Description

 TUBE BUNDLE HEAT EXCHANGER AND METHOD FOR REMOVING DISSOLVED SUBSTANCES FROM A POLYMER SOLUTION BY MEANS OF DEGASSING IN A TUBE BUNDLE HEAT EXCHANGER}

The present invention relates to a shell-and-tube heat exchanger for removing dissolved material from a polymer solution by degassing, a continuous method for removing dissolved material from a polymer solution by degassing in a tubular heat exchanger, and also for use. It is about.

A significant process step in the preparation of the polymer is the removal of dissolved substances, in particular unreacted monomers, low molecular weight reaction products (oligomers), degradation products, auxiliaries and solvents from the solutions obtained in the polymerization to produce concentrated polymers in industrially useful conditions. will be.

The dissolved material is often isolated from the polymer solution by degassing, where the dissolved material becomes gaseous by separating heat and, if appropriate, reducing the pressure, and is removed from the liquid polymer in this state.

From the point of view of the device, the degassing of the polymer solution is often carried out in a tube bundle heat exchanger with parallel vertical tube bundles, each end of which is fixed to a tube plate, where the heat transfer medium creates a space in the cylinder between the tubes. Pass through to heat the polymer solution and the reduced pressure product of the polymer solution.

Known tubular heat exchangers for degassing polymer solutions often cannot meet stringent quality requirements for the acceptable residual content of dissolved material in the degassed polymer solution.

To ensure a very uniform heat transfer coefficient of the heat transfer medium from the device to the liquid polymer solution through the tube wall, a deflection plate is installed to achieve transverse flow over the tube by controlling the flow direction of the heat transfer medium in the cylinder space. Try to do it.

They take the form of circle segments which, for example, alternately freely maintain an open cross section on opposite inner walls of the tube.

A further type of structure that can be used is an alternating arrangement of annular and disc shaped deflection plates which alternately freely maintain an open cross section for the heat transfer medium in the center of the reactor and in the inner wall of the reactor.

While the heat transfer medium flows transversely over the tubes arranged in the region of the deflection plate, the longitudinal flow of the heat transfer medium is predominantly for tubes in the deflection region without the deflection plate. Correspondingly, the heat transfer in the tubes in the longitudinal flow zone is poor, with the result that the product quality in the individual tubes is not uniform across the reactor cross section.

It is known that it is possible to provide an internal insert which reduces the free open cross section in individual tubes to create a pressure drop and achieve an improved heat transfer effect from the heat transfer medium to the polymer solution to be degassed.

Because of the non-uniform heat transfer as a result of the different flow of heat transfer medium over the tube, a non-uniform internal insert, especially above the reactor cross section, is essential to compensate for this effect. This leads to an increase in costs in manufacturing and in particular in the installation of internal inserts.

It is therefore an object of the present invention to provide an improved method for degassing a liquid polymer solution in a tubular heat exchanger which ensures a lower residual content of dissolved material in combination with a simpler design and assembly of the device.

This purpose is to provide a bundle of parallel vertical tubes, each end of which is fixed to the tube plate, an internal insert in each tube that reduces the free-opening cross section through the tube (polymer solution passes through the tube), around the tube through which the liquid heat transfer medium flows. A deflection plate in the cylindrical space of the cylinder, and in the cylindrical space each arranged in the cross section of the tubular heat exchanger, each freely retaining the deflection zone of the heat transfer medium, wherein the tube is not located in the deflection zone and all internal inserts are One having the same structure is achieved by a tubular heat exchanger for removing dissolved material from the polymer solution by degassing.

The internal inserts result in a large pressure drop of the inlet pressure below 50 bar absolute to very low vacuum, often 4 to 200 mbar, in particular 4 to 30 mbar.

The internal inserts arranged in the tubes and reducing their free open cross section can be secured to the tube plates, preferably by threaded connections, in which the welds of the tubes are located below the threaded connections to the internal inserts. In this way, the internal insert is easily installed and can be removed for the purpose of cleaning the device.

The inner insert is secured to the tube plate using a polygonal key, preferably a hexagonal key. The recess for the polygon key preferably runs to the right through the center of the inner insert. As a result, it can be advantageously used to supply the polymer solution after the internal insert is fixed and the key removed.

The invention is not limited to the specific arrangement of the deflection plates, whereby the deflection zones remain free. The deflection zone freely held relative to the heat transfer medium by the deflection plate is preferably formed in the space in the cylinder of the tubular heat exchanger. Preferably the deflection plate may be a deflection plate in the form of a circle segment which alternately maintains a deflection zone for the heat transfer medium freely on the inner wall of the tubular heat exchanger, or alternatively the deflection plate having an annular or disc shape has an annular bundle. The disc-shaped deflection plate may be a deflection plate that freely maintains the deflection region located in the center of the heat exchanger and freely maintains the deflection region located on the inner wall of the tubular heat exchanger.

In a further structural variant, the outer wall of the tubular heat exchanger is provided with one or more chambers for circulating the heat transfer medium through the perforations in the outer wall of the tubular heat exchanger, the deflection plate being freely held against the heat transfer medium. The area is located in the chamber, and the perforations serve to make the flow uniform.

The heat transfer medium is preferably introduced into or exits the space in the cylinder in each case via the ring channel or the partial ring channel, which ring channel or the partial ring channel is preferably free open area in the flow direction of the heat transfer medium. It has a decreasing opening.

The tubular heat exchanger is preferably designed such that the heat transfer coefficient on the heat transfer medium side is 500 to 2000 W / m ² / K, preferably 800 to 1200 W / m ² / K.

Preference is given to using liquid heat transfer media, in particular heat transfer oils.

The tubular heat exchanger is preferably 100 to 1000 tubes, preferably 450, in particular having a length of 1.0 to 6.0 m, preferably 1.2 to 2.0 m and an inner diameter of 10 to 25 mm, preferably 13 to 18 mm. To 3500 tubes. The deflection plate preferably has a thickness of 6 to 30 mm, in particular 8 to 16 mm.

The tube bundle heat exchanger is preferably configured such that the upper tube plate is significantly thicker, in particular about five times thicker than the lower tube plate, preferably the upper tube plate is 150 mm thick and the lower tube plate is 30 mm thick.

The outlet for the heat transfer medium may preferably be provided at or just below the upper tube plate, with the pipes coming out of these openings leading to the equilibration reservoir or collection vessel.

A system for emptying the heat transfer medium through the holes in the wall of the tubular heat exchanger or through the lower tube plate can be advantageously provided.

Without rolling the deflection plate onto the tube, it is advantageous to ensure that the gap between the tube and the deflection plate during manufacture is as small as possible, in particular 0.1 to 0.4 mm, preferably 0.14 to 0.25 mm, as the manufacturing technique allows.

The deflection plate is preferably sealed against the wall of the tubular heat exchanger.

Without arranging the deflection plates equidistantly, it may be advantageous for the distance between the deflection plates to be higher in the tube area required for the process technology area, in particular in accordance with the degassing process in the tube.

Advantageously a compensator for thermal expansion is provided in the cylinder of the tubular heat exchanger.

Especially for the degassing of multicomponent products, for example ABS solutions, the tubular exchanger may have two or more zones such that two or more separate circuits are provided in the heat transfer medium to achieve different temperatures and consequently different degassing levels.

The invention also includes passing a polymer solution from top to bottom through a tube of a tubular heat exchanger and delivering the heat transfer medium to the polymer solution in cross-counterflow or cross-cocurrent flow, as described above. Provided is a continuous process for removing dissolved material from a polymer solution by degassing in a type heat exchanger.

In each case the mode of operation in which the polymer solution and the heat transfer medium flow co-currently from the top to the bottom is particularly useful when overheating is desired in the inlet region of the polymer solution, for example in the device upon degassing of polystyrene.

The present invention also provides the use of said tubular heat exchanger for the degassing of polystyrene or ABS.

The invention is illustrated by the following figures and examples.

1 shows a longitudinal cross section of a preferred embodiment of a tubular heat exchanger according to the invention with a cross-counterflow flow of a polymer solution and a heat transfer medium, showing the cross section of the B-B plane in FIG. 1A,

FIG. 2 shows a longitudinal cross section of a further preferred embodiment of a tubular heat exchanger according to the invention with a radial flow of heat transfer medium, showing the cross section of the E-E face in FIG. 2A,

FIG. 3 shows a longitudinal cross section of a reactor with transverse co-current flow of a heat transfer medium according to the prior art and shows the cross section of the A-A plane in FIG. 3A,

FIG. 4 shows a longitudinal cross section of a tubular heat exchanger according to the prior art with a radial flow of heat transfer medium and shows a cross section of the E-E plane in FIG. 4A, and FIG.

5 shows a longitudinal cross section of a further preferred embodiment of a tubular heat exchanger according to the invention, shows a cross section of the C-C plane in FIG. 5A and a cross section of the D-D plane in FIG. 5B,

6 shows a longitudinal cross section of a further preferred embodiment of a tubular heat exchanger according to the invention with a cocurrent flow of polymer solution and heat transfer medium,

7 shows a longitudinal section of a further preferred embodiment of a tubular heat exchanger according to the invention having a plurality of zones,

8 shows a longitudinal cross section of a further preferred embodiment of a tubular heat exchanger according to the invention having a radial flow of heat transfer medium and a cocurrent flow of polymer solution and heat transfer medium,

9A-9C show preferred embodiments of a cap for a tubular heat exchanger,

10 shows a longitudinal cross section of a preferred embodiment of a tubular heat exchanger according to the invention with a body of machining in the cap of the device,

11A and 11B show preferred embodiments of openings in ring channels for introduction and release of heat transfer media.

Reference number

R tube bundle heat exchanger

1 tube

2 tube plates

3 internal insert

4 polymer solution

5 In-cylinder space around the tube

6 heat transfer medium

7 deflection plate

8 deflection zones

9 Chamber on outer wall

10 Perforation in the outer wall

11 ring channel

Opening in the 12-ring channel

S1-S4 gap

In the drawings, the same reference numerals in each case represent the same or corresponding features.

The tubular heat exchanger (R) shown in FIG. 1 has a bundle of tubes (1) through which the polymer solution (4) passes from top to bottom. Each end of the pipe 1 is fixed and sealed to the pipe plate 2. An inner insert 3 is provided in the tube 1 which reduces the open cross section for the liquid polymer solution 4. All internal inserts 3 have the same structure.

The deflection plate 7 is arranged in the cylindrical space 5 between the tubes 1. They have the form of circular segments and alternately freely hold the deflection zone 8 relative to the heat transfer medium 6 at the inner wall of the tubular heat exchanger R.

The illustration of the cross section in FIG. 1A clearly shows that there is no tube 1 in the deflection region 8.

2 shows a further preferred variant of the tubular heat exchanger according to the invention with a radial flow of heat transfer medium 6. This is caused by the geometry of the deflection plates 7 which are alternately annular or disc shaped. In the figure, the lowermost deflection plate is, for example, an annular shape having a disk shape located above, and the uppermost deflection plate 7 is again annular.

As can be clearly seen, especially in the cross sectional view of FIG. 2A, the central deflection region 8 preferably does not have a tube 1.

In contrast, FIG. 3 shows a tubular heat exchanger according to the prior art with a cross-counter flow of heat transfer medium 6 as a result of a deflection plate 7 having a circular segment shape. The tube is present throughout the device. As a result, the unrestricted flow prevails in the deflection zone 8 and, most undesirable, the heat transfer medium flows purely longitudinally along the outside of the tube, significantly lower heat transfer compared to the purely transverse flow over the tube. Results in a factor. To compensate for this, for example, internal inserts 3 of different geometries are required, which is expensive to manufacture and assemble.

The illustration of the cross section in FIG. 3A clearly shows that the tube is present throughout the device.

4 shows a further embodiment of the device according to the prior art with a radial flow of heat transfer medium 6 generated by deflection plates 7 having an alternating annular and disc shape. As can be clearly seen from the figure, for example, reduced heat corresponding to the longitudinal flow of the heat transfer medium 6, compensated by a different arrangement of internal inserts 3 for a correspondingly high production and assembly cost. A propagation zone and a recycle band occur in the deflection zone 8.

The illustration of the cross section in FIG. 4A indicates that the tube is present throughout the device. The area between the two dashed lines corresponds to the overlapping area of the deflection plate which ensures purely transverse flow over the pipe.

FIG. 5 shows a preferred embodiment with a chamber 9 located on the outer wall of the tube bundle heat exchanger R. FIG. The deflection zone 8 is located in the chamber 9. The arrangement of the chamber 9 on the outer wall of the tubular heat exchanger R is particularly apparent in the illustration of the cross section of FIGS. 5A and 5B.

FIG. 6 shows a further variant of the device shown in FIG. 5, with a cocurrent flow of polymer solution 4 and heat transfer medium 6.

FIG. 7 shows a further variant of the device shown in FIGS. 5 and 6, with two circuits for a plurality of bands, preferably two bands, ie heat transfer medium 6.

FIG. 8 shows a further variant of the radial flow device shown in FIG. 2 with the cocurrent flow of the polymer solution 4 and the heat transfer medium 6.

9A-9B show preferred structural embodiments of a cap that couples to both ends of the tubular heat exchanger R, in which a central replacement body is provided in FIG. 9A, and in the variant shown in FIG. 9B the cap has a plate shape. In the variant shown in Figure 9C, it has a pipe shape.

A further preferred embodiment of the cap space for coupling to the tubular heat exchanger (R) is shown in FIG. 10, where the processing body is provided in a poorly flown cap area.

FIG. 11A schematically shows the shape of the opening 12 in the annular channel 11 (open size decreases in the flow direction), which is rectangular in the variant shown.

A further variant of the opening 12 in the ring channel 11 is shown in FIG. 11B. In this embodiment, the opening 12 is circular.

Good heat transfer operating conditions corresponding to the transverse flow of the heat transfer medium above the tube, ie heat transfer of about 1000 W / m ² / K compared to longitudinal flow with poor heat transfer coefficient of about 200 W / m ² / K Regeneration was achieved in double wall tubes with an outer diameter of 17.8 mm and a wall thickness of 1.5 mm by the amount of heat transfer medium circulating the count (Marlotherm® heat transfer oil). An internal insert with a length of 300 mm was placed in the double wall tube. The introduction temperature of the Malosum® heat transfer oil was 300 ° C. upon introduction into the jacket of the tube, and the introduction temperature of the polystyrene solution in which residual monomer styrene and ethylbenzene were separated off by reduced pressure was 160 ° C.

The experimental results are summarized in the table below.

As can be seen in the table below, the residual concentrations of monomeric styrene and ethylbenzene (comparative experiment No. C1) at a heat transfer coefficient of 200 W / m ² / K corresponding to a longitudinal flow along the tube are either transverse or predominantly transverse Higher than in the experiments with good heat transfer coefficients corresponding to (experiments I1 and I2 according to the invention).

Experiment number Heat transfer coefficient [W / m ² / K] Temperature at reduced pressure site [℃] Styrene Content [ppm] Ethylbenzene content [ppm] C1 200 203.5 442 499 I1 600 211.3 377 423 I2 1000 213.1 363 407

Claims (25)

Bundle of parallel vertical tubes (1), each end of which is fixed to the tube plate (2), an internal insert (3) (polymer solution (4)) in each tube (1) that reduces the free-opening cross section through the tube (1) Through the tube (1), the in-cylinder space (5) around the tube (1) through which the liquid heat transfer medium (6) flows, and in the cross section of the tube bundle type heat exchanger (R), respectively; A deflection plate 7 in the cylindrical in-cylinder space 5 which freely holds the deflection region 8 relative to 6), the tube 1 being not located in the deflection region 8 and having all internal inserts 3 Is a shell-and-tube heat exchanger (R) for removing dissolved material from the polymer solution (4) by degassing. The tube bundle row according to claim 1, wherein the inner insert (3) is fixed to the tube plate (2) by threaded connection, and the weld of the tube (1) is located below the threaded connection to the internal insert (3). Exchanger (R). 3. The insert according to claim 2, wherein the inner insert (3) proceeds to the right through the center of the inner insert (3) and inserts a polygon key and removes the polygon key to secure the inner insert to the tube plate (2) by means of the polygon key. A tubular heat exchanger (R) having an opening that can then be used to introduce the polymer solution (4). 4. The cylindrical inner space of the tubular heat exchanger R according to claim 1, wherein the deflection zone 8 freely held by the deflection plate 7 with respect to the heat transfer medium 6. Tube bundle type heat exchanger (R) as formed in 5). 5. The tube bundle type according to claim 4, wherein the deflection plate 7 has a circular segment shape which alternately maintains the deflection zone 8 relative to the heat transfer medium 6 at the inner wall of the tube bundle heat exchanger R. 6. Heat exchanger (R). 5. The deflection plate (7) according to claim 4, wherein the deflection plates (7) alternately have an annular or disc shape so that an annular deflection plate (7) freely holds the deflection region (8) located in the center of the tubular heat exchanger (R). A tube bundle heat exchanger (R) in which the disc-shaped deflection plate (7) freely holds the deflection region (8) located on the inner wall of the tube bundle heat exchanger (R). 7. The deflection zone 8 according to claim 1, which is freely held in each case by the deflection plate 7, preferably 5 to 20% of the total cross sectional area of the tubular heat exchanger R. 8. Tubular heat exchanger (R). The heat transfer medium (6) according to any one of claims 1 to 3 and 7, wherein the outer wall of the tubular heat exchanger (R) is through a perforation (10) in the outer wall of the tubular heat exchanger (R). ) Is a tubular bundle having one or more chambers (9) circulating therein, wherein a deflection zone (8) freely held relative to the heat transfer medium (6) by means of a deflection plate (7) is located in the chamber (9). Heat exchanger (R). 9. The heat transfer medium (6) according to any one of the preceding claims, wherein the heat transfer medium (6) is introduced into or discharged from the in-cylinder space (5) in each case via the ring channel or the partial ring channel (11). Or the partial ring channel 11 has an opening in which the free open area decreases in the flow direction of the heat transfer medium 6. The tubular heat exchanger according to any one of claims 1 to 9, wherein the heat transfer coefficient on the heat transfer medium side is 500 to 2000 W / m ² / K, preferably 800 to 1200 W / m ² / K. (R). Tube tubular heat exchanger (R) according to any of the preceding claims, wherein the heat transfer medium (6) is a liquid, preferably a heat transfer oil. 12. Tube bundle row according to any of the preceding claims, wherein the bundle of parallel vertical tubes (1) comprises from 100 to 10000 tubes (1), preferably from 450 to 3500 tubes (1). Exchanger (R). 13. Tube bundle type heat exchanger (R) according to any of the preceding claims, wherein the length of the tube (1) is 1.0 to 6.0 m, preferably 1.2 to 2.0 m. 14. Tube bundle type heat exchanger (R) according to any of the preceding claims, wherein the inner diameter of the tube (1) is 10 to 25 mm, preferably 13 to 18 mm. The tubular heat exchanger (R) according to any one of the preceding claims, wherein the deflection plate (7) has a thickness of 6 to 30 mm, preferably 8 to 16 mm. The process according to claim 1, wherein the upper tube plate 2 is significantly thicker, in particular about five times thicker, preferably the upper tube plate 2 is 150 than the lower tube plate 2. Tube bundle type heat exchanger (R) having a thickness of mm and a lower tube plate (2) of 30 mm thickness. 17. The outlet according to any one of the preceding claims, wherein an outlet for the heat transfer medium (6) is provided at or immediately below the upper tube plate (2), and pipes emerge from these holes and into the equilibrium reservoir or collection vessel. Tube bundle type heat exchanger (R). 18. A system according to any one of the preceding claims, wherein a system is provided for emptying the heat transfer medium (6) through holes in the wall of the tubular heat exchanger (R) or through the lower tube plate (2). Phosphorus tube type heat exchanger (R). 19. Tubular bundle according to any one of the preceding claims, wherein a gap with a gap width of 0.1 to 0.4 mm, preferably 0.14 to 0.25 mm is present between the tube (1) and the deflection plate (7). Heat exchanger (R). The tube bundle heat exchanger (R) according to any one of the preceding claims, wherein the deflection plate (7) is sealed against the wall of the tube bundle heat exchanger. 21. A tubular heat exchanger (R) according to any of the preceding claims, wherein a compensator for thermal expansion is provided in the cylinder of the tubular heat exchanger. The tube bundle heat exchanger (1) according to any one of the preceding claims, wherein the tube bundle heat exchanger (R) has at least two zones such that at least two separate circuits are provided for the heat transfer medium (6). (R). 23. Tube bundle type heat exchanger (R) according to any one of claims 1 to 22, wherein the distance between the deflection plates (7) is suitable for the degassing process in the tube. Passing the polymer solution (4) from top to bottom through the tube (1) of the tubular heat exchanger (R) and the heat transfer medium (6) in a cross-counterflow or cross-cocurrent flow to the polymer solution (4). A continuous process for removing dissolved material from a polymer solution (4) by degassing in a tubular heat exchanger (R) according to any one of claims 1 to 23, comprising the step of delivering. Use of the tubular heat exchanger (R) according to any one of claims 1 to 23 or the method according to claim 24 for degassing polystyrene or ABS.

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