EP1938036A1 - 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 solutes from a polymer solution by degassing in a shell and tube heat exchanger

The invention relates to a tube bundle heat exchanger for the removal of dissolved substances from a polymer solution by degassing, a continuous process for the removal of solutes from a polymer solution by degassing in a shell and tube heat exchanger, and a use.

An essential process step in the preparation of polymers is the removal of solutes from the solution obtained in the polymerization, in particular unreacted monomers, low molecular weight reaction products (oligomers), decomposition products, excipients and solvents to represent the concentrated polymers in a technically utilizable state ,

The isolation of the solutes from polymer solutions is often carried out by degassing, the dissolved substances are converted by heat and optionally pressure reduction in the vapor state and separated in this from the liquid polymers.

Apparatively, the degassing of polymer solutions is often performed in Rohrbündelwärmeübertragern, with a bundle of parallel and vertically arranged tubes which are fixed at their ends in each case a tube plate and wherein a heat carrier is passed through the shell space between the tubes, the polymer solution and the Relaxation product of the polymer solution heated.

Known tube bundle heat exchangers for degassing of polymer solutions can often not meet strict quality requirements regarding permissible residual contents of dissolved substances in the degassed polymer solution.

In order to ensure the most uniform heat transfer coefficient in the apparatus of the heat transfer medium through the pipe wall in the liquid polymer solution, a transverse flow of the pipes is sought by the flow direction of the heat carrier in the shell space is controlled by the installation of baffles.

These may be formed, for example, in the form of circular segments, which leave passage cross sections alternately at the mutually opposite inner tube walls.

Another common design consists in the alternating arrangement of annular and disc-shaped baffles, which leave open alternately passage cross-sections for the heat transfer medium in the reactor center or on the reactor inner jacket. While the tubes arranged in the region of the baffles are flowed transversely by the heat carrier, there is a predominant longitudinal flow through the heat carrier for the tubes in the deflection regions which are free of baffle plates. Accordingly, the heat transfer in the tubes with longitudinal flow is worse and consequently the product quality in the individual tubes over the reactor cross-section is unequal.

It is known to provide internals in the individual tubes, which narrow the free passage cross-section in order to build up a pressure drop and to effect an improved heat transfer from the heat transfer medium to the polymer solution to be degassed.

Due to the above-described uneven heat transfer due to the different flow of the tubes through the heat carrier in particular unequal internals over the reactor cross section are required to compensate for this effect. This requires an increased effort in the production and in particular in the assembly of the internals.

It was accordingly an object of the invention to provide an improved process for the degassing of a liquid polymer solution in a shell-and-tube heat exchanger, which ensures lower residual contents of dissolved substances with at the same time simpler structural design and installation of the apparatus.

The solution consists in a shell and tube heat exchanger for removing solutes from a polymer solution by degassing, with a bundle of parallel and vertically arranged tubes, which are fixed at both ends in a tube plate, with an installation in each tube, the free passage cross-section Narrowed through the tube and wherein the tubes are flowed through by the polymer solution, as well as with a jacket space around the tubes, which is flowed through by a liquid heat carrier, with baffles in the shell space, which are each arranged in cross-sectional planes of the tube bundle heat transfer and each a deflection for the Wärmeträ - leave ger, which is characterized in that in the deflection no pipes are arranged and that all internals are identical.

By installing a strong pressure drop from an inlet pressure of up to 50 bar absolute on a very low vacuum, often in the range between 4 and 200 mbar, in particular between 4 and 30 mbar, causes.

The internals, which are arranged in the tubes and narrow the free passage cross section of the same, can preferably be fixed by a threaded connection in the tube plate, wherein the welds of the tubes in the tube plate below the thread screw connection for the internals. As a result, the internals for cleaning the apparatus can be easily installed and removed. The internals are preferably screwed into the tubesheet with a Vielzahnschlüssel, preferably a hexagonal Allen key. The insert opening for the multi-tooth key is preferably arranged centrally and continuously in the installation. As a result, it can be advantageously used after screwing in the installation and removing the key for the supply of the polymer solution.

The invention is not limited with regard to the specific design of the baffles and the deflection areas released from them. Preferably, the deflection regions, which are released from the baffles for the heat carrier, formed within the shell space of the tube bundle heat exchanger. This may preferably be baffles in the form of circular segments, which leave the deflector for the heat transfer medium alternately on the inner shell of Rohrbündelwärmeübertragers or even around baffles, which are formed alternately in ring or disc shape, such that the baffles release in the ring form deflection , which are arranged centrally in the tube bundle heat exchanger and the disc-shaped baffles release deflection areas, which are arranged on the inner shell of the tube bundle heat exchanger.

In a further constructive variant, one or more chambers may be provided on the outer jacket of the shell-and-tube heat exchanger, through which the heat transfer medium circulates via perforations in the outer jacket of the tube bundle heat exchanger and wherein the deflection regions which are released by the deflection plates for the heat transfer medium are arranged in the chambers , wherein the perforations serve to equalize the flow.

The heat carrier is preferably in each case via a ring channel or partial ring channel in the mantle space or removed, wherein the annular channel or partial ring channel has openings, preferably such that their free passage area decreases in the flow direction of the heat carrier.

The shell-and-tube heat exchanger is preferably designed in such a way that the heat carrier-side heat transfer coefficient is between 500 and 2000 W / m ² / K, preferably 800 to 1200 W / m ² / K.

Preferably, a liquid heat transfer medium, in particular a heat transfer oil, is used.

The tube bundle heat exchanger preferably comprises 100 to 10,000, preferably 450 to 3,500 tubes, in particular a length between 1, 0 and 6.0 m, preferably between 1, 2 and 2.0 m and an inner diameter between 10 and 25 mm, preferably between 13 and 18 mm. The baffles are preferably formed with a thickness between 6 and 30 mm, in particular between 8 and 16 mm. Preferably, the tube bundle heat exchanger is designed in such a way that the upper tube sheet is substantially thicker compared to the lower tube plate, in particular five times thicker, preferably that the upper tube plate 150 mm thick and the lower tube plate is 30 mm thick.

Preference may be provided in the upper tube sheet or shortly below the same vent holes for the heat transfer medium, via which a pipeline leads to a surge tank or a collecting container.

Advantageously, an emptying system for the heat transfer medium can be provided via the lower tube plate or via a bore in the wall of the tube bundle heat exchanger.

It is advantageous not to roll the tubes in the baffles, but to make sure during manufacture that the gaps between the tubes and the baffles are as small as it is possible in terms of manufacturing technology, in particular in the range between 0.1 to 0.4 mm, preferably in the range between 0.14 and 0.25 mm.

The baffles are preferably designed to be sealing to the wall of the tube bundle heat exchanger.

It may be advantageous not to equidistantly arrange the deflecting plates, but to specifically adapt the spacing of the deflecting plates from one another to the degassing process in the tubes, in such a way that the heat transfer coefficients in the tube regions are higher, where this is required for procedural reasons.

Advantageously, a compensator for the thermal expansion in the shell of the shell and tube heat exchanger is provided.

In particular, for the degassing of multi-component products, such as ABS solutions, the tube bundle heat exchanger may be formed two or more zonig, such that two or more separate circuits are provided for the heat carrier to achieve a different temperature and thus different Entgasungsstadien.

The invention also provides a continuous process for the removal of solutes from a polymer solution by degassing in a shell and tube heat exchanger as described above, wherein the polymer solution is passed from top to bottom through the tubes of Rohrbündelwärmeübertragers and the heat transfer in cross-countercurrent or cross-flow to the polymer solution. The procedure with direct conduction of polymer solution and heat carrier, respectively from top to bottom through the apparatus, is particularly suitable when overheating is desired already in the inlet region of the polymer solution in the apparatus, for example in the degassing of polystyrene.

The invention also relates to the use of the above-described Rohrbündelwärmeübertragers for degassing of polystyrene or ABS.

The invention will be explained in more detail below with reference to a drawing and an embodiment.

They show in detail:

1 shows a longitudinal section through a preferred embodiment of a tube bundle heat exchanger according to the invention with cross-countercurrent flow of polymer solution and heat carrier, showing a cross-section in the plane B-B in FIG. 1A, FIG.

FIG. 2 shows a longitudinal section through a further preferred embodiment of a tube bundle heat exchanger according to the invention under radial flow guidance of the invention

Heat carrier, with a cross-sectional view in the plane E-E in Figure 2A,

3 shows a longitudinal section through a reactor with cross-flow guidance of the heat carrier according to the prior art, with a cross-sectional view in the plane A-A in Figure 3A,

4 shows a longitudinal section through a tube bundle heat exchanger according to the prior art, with radial flow guidance of the heat carrier, with a cross-sectional view in the plane E-E in Figure 4A,

5 shows a longitudinal section through a further preferred embodiment of a tube bundle heat exchanger according to the invention, with a cross-sectional view in the plane C-C in FIG. 5A and a cross-sectional view in the plane D-D in FIG. 5B,

FIG. 6 shows a longitudinal section through a further preferred embodiment of a shell-and-tube heat exchanger according to the invention with DC guidance of polymer solution and heat transfer medium, FIG. 7 shows a longitudinal section through a further preferred embodiment of a shell-and-tube heat exchanger according to the invention, which is designed in a multi-zone configuration,

8 shows a longitudinal section through a further preferred embodiment of a tube bundle heat exchanger according to the invention with radial flow guidance of the heat carrier and DC flow of polymer solution and heat transfer medium,

FIGS. 9A to 9C show preferred embodiments of hoods for the tube bundle heat exchanger,

Figure 10 is a longitudinal section through a preferred embodiment of a Rohrbündelwärmeübertragers invention with dummy bodies in the hoods of the apparatus and

Figures 11A and 11B preferred embodiments for the openings in the annular channels for the

Supply and discharge of the heat carrier.

In the figures, like reference numerals designate like or corresponding features.

The tube bundle heat exchanger R shown in FIG. 1 has a bundle of tubes 1 through which a polymer solution 4 is passed from top to bottom. The tubes 1 are attached sealingly at their two ends in a tube plate 2. In the tubes 1 internals 3 are provided, which narrow the passage cross-section for the liquid polymer solution 4. All fittings 3 are identical.

In the mantle space 5 between the tubes 1 baffles 7 are arranged, which are kreisseg- ment-shaped and the alternately on the inner wall of the Rohrbündelwärmeübertragers R deflection 8 for the heat transfer medium 6 released.

The cross-sectional illustration in FIG. 1A clarifies that the deflection regions 8 are free of tubes 1.

FIG. 2 shows a further preferred embodiment of an inventive device

Rohrbündelwärmeübertragers, with radial flow guidance of the heat carrier 6. This is effected by the geometry of the baffles 7, which are formed alternately in ring or disc shape. In the figure, by way of example, the lowermost deflection plate is annular, the disc-shaped and the uppermost deflecting plate 7, which is arranged above it, again has a ring shape.

As illustrated in particular in the cross-sectional illustration in FIG. 2A, the centrally arranged deflecting region 8 is preferably free of tubes 1.

In contrast, the illustration in Figure 3 shows a tube bundle heat exchanger according to the prior art with cross-countercurrent flow of the heat carrier 6 by circular segment-shaped baffles 7. The apparatus is fully drilled. As a result, an undefined flow prevails in the deflection regions 8, in the worst case a pure longitudinal flow of the heat carrier outside the tubes and thus significantly lower heat transfer coefficients compared to a pure transverse flow of the tubes. For example, internals 3 different geometry are required to compensate, with a correspondingly high effort in the design and installation.

The cross-sectional view in Figure 3A illustrates that the apparatus is fully drilled.

FIG. 4 shows a further embodiment of an apparatus according to the prior art, with radial flow guidance of the heat carrier 6, which is effected by deflecting disks 7, which are formed alternately in ring or disk form. As illustrated in the figure, it comes in the deflection 8 to recirculation zones and areas of longitudinal flow for the heat transfer 7 according to deteriorated heat transfer, which is compensated for example by an adapted, different design of the fixtures 3, with a correspondingly high design and installation effort.

The cross-sectional view in Figure 4A illustrates that the apparatus is fully drilled. The area between the two dashed lines corresponds to the overlapping area of the baffles by a pure cross-flow of the tubes is guaranteed safe.

Figure 5 shows a preferred embodiment with chambers 9, which are arranged on the outer jacket of the tube bundle heat exchanger R. The deflection regions 8 are located in the chambers 9. The arrangement of the chambers 9 on the outer shell of the tube bundle heat exchanger R is particularly illustrated in the cross-sectional views in Figures 5A and 5B.

FIG. 6 shows a further variant of the apparatus shown in FIG. 5, but with DC guidance of polymer solution 4 and heat transfer medium 6.

FIG. 7 shows a further variant of the apparatus shown in FIGS. 5 and 6, which, however, is provided with a multi-zone, by way of example two-zone, ie with two circuits for the heat carrier 6. FIG. 8 shows a further variant of the radial flow apparatus shown in FIG. 2, but with direct current control of polymer solution 4 and heat carrier 6.

FIGS. 9A to 9B show preferred constructional designs for hoods which delimit the tube bundle heat exchanger R at both ends. According to FIG. 9A, a central displacer body is provided, the variant shown in FIG. 9B is plate-shaped or in the form shown in FIG 9C illustrated variant in a pipe shape.

A further preferred embodiment of the hood spaces delimiting the shell-and-tube heat exchanger R is shown in FIG. 10: Dummy bodies are provided in the hoods in the hoods, which flow through poorly.

Figure 1A shows schematically the design of openings 12 in the annular channels 11, which are rectangular in the illustrated variant, with decreasing size of the openings in the flow direction.

Another variant of openings 12 in the annular channels 1 1 is shown in Figure 1 1 B. In this embodiment, the openings 12 are circular.

embodiment

In a double jacket test tube with an outer diameter of 17.8 mm and a wall thickness of 1.5 mm, the operating conditions of a good heat transfer, corresponding to a transverse inflow of the tubes with the heat carrier, were varied by varying the heat transfer medium circulation rate (Marothermo thermal oil). that is a heat transfer coefficient of about 1000 WIm ² IK and in comparison for a longitudinal flow, with a poor heat transfer coefficient, of about 200 WIm ² IK, readjusted. The jacketed test tube had an installation length of 300 mm. The temperature of the MarlothermO heat transfer oil was 300 ° C when entering the jacket and the inlet temperature of the polystyrene solution from which the residual monomers styrene and ethylbenzene should be separated by relaxation, 160 ° C.

The test results are summarized in the table below.

As can be seen from the table below, with a heat transfer coefficient of 200 WIm ² IK, corresponding to a longitudinal flow of the pipe (Run No. V1, for comparison) higher residual concentrations of the monomers styrene and ethylbenzene were compared to the tests with good heat transfer coefficient, obtained according to a transverse flow or predominant transverse flow (experiments E1 or E2 or according to the invention).

LIST OF REFERENCE NUMBERS

R tube bundle heat exchanger

1 tubes

2 tubesheet

3 installation

4 polymer solution

5 jacket space around the pipes

6 heat transfer medium

7 baffles

8 deflection area

9 chambers on the outer jacket

10 perforations in the outer jacket

1 1 ring channel

12 openings in the annular channel

S1-S4 column

Claims

claims 1. tube bundle heat exchanger (R) for the removal of solutes from a polymer solution (4) by degassing, with a bundle of parallel and vertically arranged tubes (1) which are fixed at both ends in a tube plate (2), with an installation (3) in each tube (1), which narrows the free passage cross-section through the tube (1) and through which the tubes (1) are flowed through by the polymer solution (4) and with a jacket space (5) around the tubes (1), which is traversed by a liquid heat transfer medium (6), with baffles (7) in the shell cavities (5), which are each arranged in cross-sectional planes of the tube bundle heat transfer (R) and in each case a deflection region (8) for the heat transfer medium ( 6) leave empty, characterized in that in the deflection areas (8) no tubes (1) are arranged and that all internals (3) are identical. 2. tube bundle heat exchanger (R) according to claim 1, characterized in that the internals (3) are fixed by a threaded connection in the tube sheet (2) and that the welds of the tubes (1) below the threaded connection for the internals (3). 3. tube bundle heat exchanger (R) according to claim 2, characterized in that the internals (3) have a central, through the internals (3) through opening, for the insertion of a multi-tooth key for the recess of the internals in the tube sheet (2) with a Vielzahnschlüssel and after removal of the multi-tooth key for the supply of the polymer solution (4) can be used. 4. tube bundle heat exchanger (R) according to one of claims 1 to 3, characterized in that the baffles (8), which are released from the baffles (7) for the heat carrier (6), within the jacket space (5) of the Rohrbündelwärmeübertragers (R. ) are formed. 5. tube bundle heat exchanger (R) according to claim 4, characterized in that the baffles (6) are formed in the form of circular segments, the alternately on the inner shell of the Rohrbündelwärmeübertragers (R) deflection areas (8) for the heat carrier (6). 6. tube bundle heat exchanger (R) according to claim 4, characterized in that the baffles (7) are formed alternately in ring form or in disk form, such that the baffles (7) in the form of a ring release deflection areas (8), the centrally in the tube bundle heat exchanger ( R) are arranged and the plate-shaped baffles (7) release deflection regions (8), which are arranged on the inner shell of the tube bundle heat exchanger (R). 7. tube bundle heat exchanger (R) according to one of claims 1 to 6, characterized in that the deflection regions (8), which are released from the baffles (7), respectively 5 to 20%, preferably 8 to 14%, of the entire cross-sectional area of Take the tube bundle heat exchanger (R). 8. tube bundle heat exchanger (R) according to one of claims 1 to 3 or 7, characterized in that on the outer jacket of the Rohrbündelwärmeübertragers (R) one or more chambers (9) are provided, through which the heat carrier (6) via perforations (10) in Outer jacket of Rohrbündelwärmeübertragers (R) circulates and that the deflection regions (8), which are released from the baffles (7) for the heat transfer medium (6), are arranged in the chambers (9). 9. tube bundle heat exchanger (R) according to one of claims 1 to 8, characterized in that the heat transfer medium (6) each via an annular channel or partial ring channel (1 1) in the jacket space (4) is supplied or removed, wherein the Ring channel or Partial ring channel (1 1) has openings (12) whose free passage area decreases in the flow direction of the heat carrier (6). 10. tube bundle heat exchanger (R) according to one of claims 1 to 9, character- ized in that the heat transfer coefficient heat transfer coefficient 500 to 2000th W / m ² / K, preferably 800 to 1200 W / m ² / K. 1 1. tube bundle heat exchanger (R) according to one of claims 1 to 10, characterized in that the heat transfer medium (6) is liquid, preferably a heat transfer oil. 12. tube bundle heat exchanger (R) according to one of claims 1 to 1 1, characterized in that the bundle of parallel to each other and vertically arranged tubes (1) 100 to 10,000, preferably 450 to 3,500 tubes (1). 13. tube bundle heat exchanger (R) according to one of claims 1 to 12, characterized in that the tubes (1) have a length of 1, 0 to 6.0 m, preferably from 1, 2 to 2.0 m. 14. tube bundle heat exchanger (R) according to one of claims 1 to 13, character- ized in that the inner diameter of the tubes (1) is 10 to 25 mm, preferably 13 to 18 mm. 15. tube bundle heat exchanger (R) according to one of claims 1 to 14, characterized in that the thickness of the baffles (7) 6 to 30 mm, preferably 8 to 16 mm. 16. tube bundle heat exchanger (R) according to one of claims 1 to 15, characterized in that the upper tube sheet (2) relative to the lower tube sheet (2) is substantially thicker, in particular is five times thicker, preferably that the upper tube sheet (2) 150 mm thick and the bottom tube sheet (2) is 30 mm thick. 17 shell and tube heat exchanger (R) according to one of claims 1 to 16, characterized in that in the upper tube plate (2) or shortly below the same vent holes for the heat transfer medium (6) are provided, via the pipeline to a surge tank or reservoir leads. 18 shell and tube heat exchanger (R) according to one of claims 1 to 17, characterized in that an emptying system for the heat transfer medium (6) via the lower tube sheet (2) or via a bore in the wall of the Rohrbündelwärmeübertragers (R) is provided. 19. tube bundle heat exchanger (R) according to one of claims 1 to 18, characterized in that between the tubes (1) and the baffles (7) column with a gap width in the range of 0.1 to 0.4 mm, preferably in the range between 0.14 and 0.25 mm, are present. 20. tube bundle heat exchanger (R) according to one of claims 1 to 19, characterized in that the baffles (7) are sealingly carried out to the wall thereof. 21. tube bundle heat exchanger (R) according to one of claims 1 to 20, characterized in that a compensator for the thermal expansion in the same is provided. 22. tube bundle heat exchanger (R) according to one of claims 1 to 21, character- ized in that the tube bundle heat exchanger (R) is formed two or more zonig, such that two or more separate circuits for the heat carrier (6) are provided. 23. tube bundle heat exchanger (R) according to one of claims 1 to 22, character- ized in that the distance of the baffles (7) to each other is adapted to the degassing process in the tubes. 24. A continuous process for the removal of solutes from a polymer solution (4) by degassing in a shell and tube heat exchanger (R) according to one of claims 1 to 23, characterized in that the polymer solution (4) from top to bottom through the tubes (1) of the shell and tube heat exchanger (R) and the mega carrier (6) in cross-countercurrent or cross-flow to the polymer solution (4) is passed. 25. Use of the tube bundle heat exchanger (R) according to any one of claims 1 to 23 or of the method according to claim 24 for degassing of polystyrene or ABS.