DE102008011341A1 - Heat exchanger for heating temperature and residence time sensitive products - Google Patents

Abstract

The invention describes a tube bundle heat exchanger which is capable of gently and rapidly cooling or heating temperature-sensitive and / or polymerizable products.

Description

Field of the invention

The The invention relates to a heat exchanger for temperature-sensitive and / or polymerizable products.

State of the art

Out The literature is many different embodiments known from heat exchangers. So are for yourself short residence times z. B. Heat exchanger of the plate heat exchanger type or micro heat exchanger. These heat exchangers However, they have the disadvantage of being due to the narrow flow gaps only suitable for low viscosity products. At higher Viscous products can reduce the pressure drop across these heat exchangers be very high. For polymer prone products such as monomers or polymer syrup which still contains monomers, is the Risk that the monomers in the heat exchanger during to polymerize during operation or at standstill. The distance of polymerized syrup from the plate heat exchangers and micro heat exchangers is very expensive, though not impossible. For high viscosities, especially for several pas, and high pressures, greater than 10 bar, are due to the manufacturing process and the forces occurring no plate heat exchanger offered.

U.S. Patent No. 1,961,907 describes a shell-and-tube heat exchanger with helically grooved displacers in the tubes. Due to the helical flow, a particularly effective heat transfer is achieved. However, by the flow of the medium to be tempered within the displacement tube, an additional pressure loss and an additional residence time is generated, which can be detrimental to the product. Moreover, the complex construction also entails high costs, poor disassembly, and difficult drainability.

DE-G 8712815 (VIA Gesellschaft für Verfahrenstechnik) describes a tube bundle heat exchanger for compressed air dryers. The inserted into the tube displacement body consists of material saving reasons in turn from a tube which is closed at the inlet side. The displacer tube may have a corrugated surface. However, the design, which is not designed for temperature-sensitive products, has a large product-filled volume since no very low hold-up trays are used and the displacer bars are not sealed at the bottom. In addition, the displacer pipes are not removable, which is a major disadvantage in temperature-sensitive polymers.

DE-G 89 03 349 (VIA Gesellschaft für Verfahrenstechnik) describes a tube bundle heat exchanger, especially for compressed air dryers. In order to allow the heat transfer medium as uniformly as possible to flow through the apparatus, a screen plate is arranged in the apparatus, which ensures a uniform flow of the tubes. A gentle heat transfer is not necessary in this tube bundle heat exchanger, so that no special requirements for the cross section of the displacer exist and no Verdrängerhauben or flat bottoms with minimal hold-up are necessary. In addition, the displacer rods are not removable.

Heat exchanger, even with more viscous products a low pressure drop show, are often z. B. of the tube bundle type. at In this embodiment, the product flows through several parallel tubes. The disadvantage here, however, is that the shell and tube heat exchangers usually a low specific heat exchange area have. The specific heat exchange surface is defined here as the ratio of the heat exchange surface to the volume in the tubes filling the product. By The low heat exchange surface will usually large heat exchanger with thereby large Hold-up in the pipes needed. The residence time is therefore quite high in the tube bundle heat exchangers.

task

in view of The object of the discussed prior art was to provide a To develop a heat exchanger, the residence time for that in the heat exchanger to be heated or cooled Keep the product as short as possible. The heat exchanger should continue to be designed so that both low viscous than even higher viscous products heated or cooled can be.

• • eine kurze Verweilzeit bei gleichzeitig geringem Druckabfall ermöglicht,
• • leicht zu reinigen ist,
• • leicht zu fertigen ist,
• • leicht abzudichten ist,
• • für ein breites Temperatur-, Druck- und Viskositätsspektrum einsetzbar ist, und
• • Temperaturdifferenzen zwischen Produktraum und Heiz- bzw. Kühlraum gut abfängt.

What was sought after an embodiment of a heat exchanger, the

• • allows a short residence time with low pressure drop,
• • easy to clean,
• • easy to manufacture,
• • easy to seal,
• • can be used for a wide range of temperature, pressure and viscosity, and
• • Cuts temperature differences between product room and heating or cooling room well.

These Task was solved by a tube bundle heat exchanger with specially designed displacement rods in the product-filled pipes. The displacer rods are designed so that they exceed 40% of the pipes occupy the volume, preferably more than 50% of the in the Take tubes located volume and very particularly preferred more than 60% of the volume in the tubes. To keep the product-filled volume in the apparatus low, are expediently one or more displacer arranged in the heat exchanger hoods of the apparatus or at least one flat bottom used.

Implementation of the invention

1. Execution of the Tube bundle heat exchanger description

The tube bundle heat exchanger consists of a housing ( 4 ) and a tube bundle, which is formed from one or more of the product to be tempered flowed through, substantially parallel tubes. The tubes can be aligned, offset or arranged on concentric hole circles to each other. Preference is given to a minimum and substantially equal pipe spacing, whereby a small product-filled volume ( 6 ) results. Particularly preferred is an arrangement of the tubes on concentric circles in order to obtain a uniform flow of the tubes and little dead zones in the bottom region.

The product flows through the pipes and is heated or cooled by the pipe jacket. The heating or cooling medium ( 5 ) flows through the outer jacket of the tubes. The tubes may be in cross-flow, countercurrent or cocurrent to the product flow of the heating or cooling medium ( 5 ) are flown. Preferably, the temperature is essentially in the cross-countercurrent, since so lower driving temperature gradient between tempering ( 5 ) and product space ( 6 ) suffice. So that the emptying can be easily made, the heat exchanger is preferably flowed through by the product from top to bottom. So that the venting of the heating or cooling medium ( 5 ) can be done easily, the heat exchanger from the temperature control ( 5 ) preferably flows through from bottom to top.

At least one end of the tube bundle is enclosed by a bottom through which the product enters or exits. This floor can be used as a heat exchanger hood ( 2 ) with a small wall thickness or as a thick-walled but compact flat bottom ( 17 ). The bottom preferably has an apparatus flange so that it can be flanged or disassembled to the heat exchanger body. The floor may have a preferably on-axis nozzle, through which the product can enter or exit. Also conceivable are several nozzles near the axis through which product can escape. The floor is preferably designed so that it can be heated or cooled with a temperature control medium. But also conceivable is an electric heating.

It is also conceivable that the heat exchanger directly to a other apparatus is connected, so on this page a corresponding floor can be dispensed with.

To the Strain compensation can, if necessary, a compensator in the outer Cloak be used to the different thermal expansion balance between tube bundle and outer jacket.

advantage

Of the Pressure drop in the heat exchanger tubes is for higher viscous products by choosing suitable pipe diameters manageable.

2nd execution of Displacer rods Description

To the volume of the product ( 6 ) in the heat exchanger tubes and to increase the heat transfer, are Verdrängerstäbe ( 7 . 10 . 12 . 15 ) introduced into the tubes. The displacer rods ( 7 . 10 . 12 . 15 ) can partially into the heat exchanger hoods ( 2 protrude). The displacer rods ( 7 . 10 . 12 . 15 ) are designed to displace more than 40% of the volume in the heat exchanger tubes. virtue example, more than 60% of the void volume of the tubes by the Verdrängerstäbe ( 7 . 10 . 12 . 15 ) repressed. Preferably, less than 95% of the volume is displaced to obtain both a compact heat exchanger design and a low pressure drop. The outer contour of the displacement rods ( 7 . 10 . 12 . 15 ) is designed so that the axis of the displacement rods ( 7 . 10 . 12 . 15 ) is centered in the tubes to avoid dead zones and to achieve a homogeneous over the cross section of the heat exchanger tube flow. The product stream flows in the gap ( 11 ) between displacer rod ( 7 . 10 . 12 . 15 ) and inner wall of the heat exchanger tube.

• • Beidseitig verschlossene Rohre, geschlossene Hohlkörper oder Massivkörper (15), dessen Querschnitte entlang seiner Achse in zumindest zwei Teilbereichen (14, 16) zur Zentrierung im Rohr (9) verformt sind (siehe 2 und 5–6),
• • Beidseitig verschlossene Rohre, geschlossene Hohlkörper oder Massivkörper (12) mit zumindest an zwei axialen Positionen außen angebrachten Elementen (13) zur Zentrierung im Rohr (siehe 3–4),
• • Entlang der Rohrachse versetzte Platten mit der Eigenschaft, Volumen zu verdrängen

To the Verdrängerstäbe ( 7 . 10 . 12 . 15 ) center in the tube with a defined gap, the displacement rods ( 7 . 10 . 12 . 15 ) z. B. be constructed as follows:

• • Tubes closed on both sides, closed hollow bodies or solid bodies ( 15 ) whose cross-sections along its axis in at least two sub-areas ( 14 . 16 ) for centering in the tube ( 9 ) are deformed (see 2 and 5 - 6 )
• • Tubes closed on both sides, closed hollow bodies or solid bodies ( 12 ) with elements attached at least at two axial positions ( 13 ) for centering in the tube (see 3 - 4 )
• • Plates offset along the tube axis with the capacity to displace volume

The displacer rods ( 7 . 10 . 12 . 15 ) are preferably in the tubes ( 9 ) are pushed in so that they can be taken out for cleaning and testing purposes if necessary. The displacer rods ( 7 . 10 . 12 . 15 ) can also consist of several individual bars connected in series. It is also conceivable to use hollow displacer rods which are filled with a medium which improves the heat transport. For example, water may be contained which evaporates in the hot region and condenses in the cool region, so that heat is transported in the axial direction. It is also conceivable to additionally transfer heat with the aid of a heat transfer medium flowing through the displacer tubes. Another possibility is the use of electrically heated displacement rods, which further increases the specific heat transfer area and further reduces the residence time. It is also conceivable that combinations of the above Verdrängerstäbe be used.

The Verdrängerstäbe produce preferably in the heated Part of the tubes can have a narrow cross-section, in the entry area a cross-sectional expansion to reduce the pressure loss be provided in the tube plate area.

advantage

By the displacement rods ( 7 . 10 . 12 . 15 ), the hold-up of the product in the pipelines ( 6 ) and increases the specific heat exchange area. The pressure drop across the tube bundle heat exchanger with displacement rods ( 7 . 10 . 12 . 15 ) is lower than in micro heat exchangers and plate heat exchangers the same thermal performance and number of tubes. The pressure drop can be reduced in micro heat exchangers and plate heat exchangers only by a significant increase in the number of tubes in these heat exchanger types to the level of the tube bundle heat exchanger with Verdrängerstäben. The small pipe diameter and the large number of pipes makes it much more difficult to clean these heat exchangers.

The Residence time in the tube bundle heat exchanger with Verdrängerstäben is naturally lower as in tube bundle heat exchangers without displacer rods of the same diameter. Just for conduits with significantly smaller diameter, the but then are significantly longer, the residence time can the same level as the shell and tube heat exchanger be adjusted with Verdrängerstäben.

3. displacer in the heat exchanger hoods description

To hold-up in the heat exchanger hoods ( 2 ), displacers ( 3 ) in the hoods ( 2 ) built-in. The hoods ( 2 ) may also be heated or cooled. For centering these z. B. plates or pins on the outer sides. To uniformly charge the heat exchanger tubes with liquid, the heat exchanger tubes facing side is preferably made conical; please refer 7 ,

advantage

Reduced residence time in the heat exchanger hoods ( 2 ) and thus lower thermal stress on the products.

4. flat bottom

The zones for product entry ( 1 ) and product leakage ( 8th ) can also be used as a flat bottom ( 17 ) with recesses (low volume head) (see 8th ). The recesses are dimensioned so that the residence time of the product in the soil at full load between 0.5 s and 20 s, preferably between 1.5 s and 15 s, or at part load between 1 s and 40 s, preferably between 1.5 s and 30 s. The recesses can be made for example by turning or milling. The recess of the flat bottom can be made conical.

5. Operating parameters

description

• Operating temperatures T = -20 ° C to + 400 ° C;
• Pressure in the product space of the pipes ( 6 ) and the hoods ( 2 ) P = -0.95 barg to +100 barg.

The pressure in the space of the heat transfer medium ( 5 ) can be between P = -0.95 barg to +50 barg. The temperature of the heat transfer medium ( 5 ) T = -20 ° C to + 400 ° C.

The heat transfer medium ( 5 ) can be supplied in liquid or vapor form. The heat exchanger described according to the invention is suitable for heating or cooling products having a viscosity of n = 0.1 mPas to 500 Pas. The residence time of the products in the heat exchanger can be 1 s to 300 s.

advantage

Of the Heat diver allows the setting of a wide range at temperatures, pressures and viscosities.

Comparison between conventional Heat exchangers of the prior art and heat exchangers with annular gap

The following table summarizes results of mass and energy balances as well as calculations of flow and heat transfer in pipes and annular gaps. The pressure loss calculations are based on the analytical solution of the conservation of momentum equation for the laminar flow-through pipe (Hagen-Poiselle flow) or for the laminar flow-through annular gap. The heat transfer calculations are based on semiempirical Nusselt number relationships for hydrodynamically and thermally unformed laminar flow. Unless otherwise stated, a mass flow of 1,000 kg / h, a residence time in the tubes of 60 seconds, a temperature increase of the medium to be heated of 100 K and a logarithmic temperature difference between the heat transfer medium ( 5 ) and 30 K medium to be warmed up. The latter two numerical values can be combined to a quotient of 3.33. Also used as physical properties are a thermal conductivity of 0.15 W / mK, a density of 1,000 kg / m ³ , a specific heat capacity of 2,200 J / kgK and a constant dynamic viscosity of 1 Pas, ie a newtonian medium is used. Furthermore, it is assumed that the heat transfer-side heat transfer resistance and the line resistance through the pipe wall are negligible. Pipe, case A Pipe, case B Pipe, case C Pipe, case D Pipe, case E Tube, case F Pipe, case G Pipe, case H Annular gap, case I Dwell / s 60 25 60 580 60 5 60 60 60 Quotient of T increase and log. T-difference 3.33 3.33 12.7 3.33 0.80 3.33 23.7 3.33 3.33 Pressure drop / bar 4.4 4.4 4.4 4.4 4.4 4.4 4.4 0,069 4.4 tube number 170 408 2120 18 6 2041 6610 1360 40 Pipe length / m 4.7 2.0 2.0 45.5 14.6 0.4 1.4 0.6 3.0 Pipe diameter / mm 5.2 3.3 2.2 16 16 1.5 1.5 5.2 24/20

example A shows that conventional tube bundle heat exchangers very tight, long pipes are necessary to the given conditions to reach. These are difficult to produce and can be practically not clean.

Examples B and C show that shorter tubes with less residence time (Case B) or changed thermal conditions (case C) are possible. However, at the same time, the pipe diameters sink even more and the number of tubes increases sharply, so that there is no Alternative to case A can be seen.

Examples D and E demonstrate that a larger pipe diameter although with the help of longer residence time (case D) or higher Wall temperatures (by larger logarithmic Temperature differences; Case E) can be achieved. The advantage the better cleanability due to the larger Diameter is however due to the extremely increased tube length, which makes the fertility very difficult, as well as deterioration in the Product quality due to increased residence times and wall temperatures overcompensated. Furthermore, the space requirement such long apparatus in buildings is problematic.

Examples F and G show that a smaller pipe diameter due to shorter Residence time (case F) or changed thermal conditions (Case G) results in an extremely large number of tubes. Such a high number of filigree tubes is in view of the high pressures and temperatures to which the tube bundle apparatus should be designed, not manufacturable.

The not negligible pipe length also allows not yet a cleaning of the interior of the apparatus.

example H states that a reduced pressure drop is due to an increased pressure drop Number of tubes and a shortened length no small Pipe diameter has the consequence. Because of the high number of thin ones Pipes with non-disappearing length is also here Cleanability, as well as the manufacturability, practically not possible.

Comparison of an inventive Design (Example I) with those for conventional shell-and-tube heat exchangers (Examples A-H):

example I shows an example of a design for an inventive Heat exchanger with displacement rods. Taking into account residence time, thermal conditions and pressure drop has this in comparison to the examples of conventional Heat exchanger (Examples A-H) a very large pipe diameter, which is a good cleaning option guaranteed. In addition, holds in comparison to Examples A, D and E, the tube length in limits, which a good manufacturability and cleanability is possible and little space is required. Compared to Examples A-C and F-H is also the number of tubes low, so that a simple and cost-effective production is possible.

Of the Tube bundle heat exchanger according to the invention can be used particularly advantageously in the synthesis of polymers because the low residence time while effective Heat transfer the product little thermally loaded and thus prevents unwanted polymerizations.

Calculating method

lässt sich bei Vorgabe von zwei der drei Geometriegrößen (Spalt-Außendurchmesser d_a, Spalt-Innendurchmesser d_i, Rohrlänge L) die dritte berechnen.From the heat balance at the pipe wall:

can be calculated by specifying two of the three geometry sizes (gap outer diameter d _a , gap inner diameter d _i , tube length L) the third.

Here, L are the tube or annular gap length, τ the residence time, d _a the outer diameter of the gap or tube diameter, d _i the inner diameter of the annular gap (tube: d _i = 0), ρ the density, c _p the specific heat capacity, ΔT _s the temperature increase of the syrup, d _h the hydraulic diameter, λ the thermal conductivity, ΔT _lg the logarithmic temperature difference between the heating medium ( 5 ) and syrup.

The average Nusselt number Nu _{m is} calculated for a pipe after Baehr / Stefan (heat and mass transfer, Springer-Verlag Berlin, 1994, p. 381-382) taking into account the hydrodynamic and thermal start-up via:

Where Pr is the Prandtl number and X is a dimensionless length:

With K = d _i / d _a , the average Nusselt number in the externally heated annular gap also applies: Nu m, RS = 3.657 + 1.2 · K 1.2 + (Nu m, tube - 3.657) · (1 + 0.14 · K 3.1 )

For pressure loss in annular gaps or pipes (K = 0), according to Martin ( Heat exchanger, Georg Thieme Verlag Stuttgart, 1988, p. 24 ):

1

product entry

2

heat exchanger cover

3

displacement

4

Heat exchanger housing

5

heating and / or cooling medium around the heat exchanger tubes

6

product space in the heat exchanger tubes

7

displacement rods in the tubes of the tube bundle

8th

product outlet

9

heat exchanger tube (Schematically)

10

displacer

11

free Volume between displacement rod and heat exchanger tube

12

displacer

13

spacer for centering the displacer rod in the heat exchanger tube

14

centering in a partial area of the displacer bar

15

displacer

16

centering in a partial area of the displacer bar

17

flat bottom (low volume head)

QUOTES INCLUDE IN THE DESCRIPTION

This list The documents listed by the applicant have been automated generated and is solely for better information recorded by the reader. The list is not part of the German Patent or utility model application. The DPMA takes over no liability for any errors or omissions.

Cited patent literature

• - US 1961907 [0003]
• - DE 8712815 G [0004]
• - DE 8903349 G [0005]

Cited non-patent literature

• Baehr / Stefan (heat and mass transfer, Springer-Verlag Berlin, 1994, pp. 381-382) [0039]
• Heat exchanger, Georg Thieme Verlag Stuttgart, 1988, p. 24 [0042]

Claims (10)

Tube bundle heat exchanger for heat transfer in temperature-sensitive and / or polymerizable media, characterized in that in a housing ( 4 ) with one or more product exits ( 8th ) and one or more product entries ( 1 ) a tube bundle is arranged in the tubes of the tube bundle displacers ( 7 . 10 . 12 . 15 ) are arranged and at least one heat exchanger hood of the tube bundle heat exchanger for the reduction of product-filled volume with displacers ( 3 ) is filled. Tube bundle heat exchanger according to claim 1, characterized in that the displacer rods ( 7 . 10 . 12 . 15 ) are designed removable for cleaning purposes. Tube bundle heat exchanger according to claim 1, characterized in that the displacer rods ( 7 . 10 . 12 . 15 ) have self-centering cross-sections. Tube bundle heat exchanger according to claim 1, characterized in that the displacer rods ( 7 . 10 . 12 . 15 ) fill more than 40% of the volume of the tube. Tube bundle heat exchanger according to claim 1, characterized in that the displacer rods ( 7 . 10 . 12 . 15 ) fill more than 50% of the volume of the tube. Tube bundle heat exchanger according to claim 1, characterized in that the displacer rods ( 7 . 10 . 12 . 15 ) fill more than 60% of the volume of the tube. Tube bundle heat exchanger according to claim 1, characterized in that the displacer rods ( 7 . 10 . 12 . 15 ) fill at most 95% of the volume of the tube. Use of the tube bundle heat exchanger according to any one of the preceding claims in the synthesis of polymers. Tube bundle heat exchanger for heat transfer in temperature-sensitive and / or polymerizable media, characterized in that in a substantially cylindrical housing ( 4 ) with one or more product exits ( 8th ) and one or more product entries ( 1 ) a tube bundle is arranged in the tubes of the tube bundle displacers ( 7 . 10 . 12 . 15 ) are arranged and at least one bottom of the tube bundle heat exchanger as a flat bottom ( 17 ) for reducing the product-filled volume. Tubular heat exchanger for heat transfer in temperature-sensitive and / or polymerizable media according to claim 9, characterized in that the residence time of the product in the recesses of the flat bottom ( 17 ) is between 0.5 s and 40 s.