EP1144724A2

EP1144724A2 - Heat exchanger with a reduced tendency to produce deposits and method for producing same

Info

Publication number: EP1144724A2
Application number: EP99964672A
Authority: EP
Inventors: Stephan Hüffer; Axel Franke; Stephan Scholl; Hans Mueller-Steinhagen; Qi Zhao; Bernd Diebold; Peter Dillmann
Original assignee: BASF SE
Current assignee: BASF SE
Priority date: 1998-12-30
Filing date: 1999-12-24
Publication date: 2001-10-17
Anticipated expiration: 2019-12-24
Also published as: DE59903362D1; KR20010100009A; EP1144723B1; EP1144723A2; ATE237006T1; KR20010103724A; CN1338008A; ATE245210T1; DE59905005D1; WO2000040774A2; WO2000040775A2; EP1144725A2; US6617047B1; EP1144723A3; DE59906313D1; EP1144725B1; WO2000040775A3; ES2197710T3; CA2358099A1; EP1144724B1

Abstract

The present invention relates to a process for coating apparatuses and apparatus parts for chemical plant construction-which are taken to mean, for example, apparatus, tank and reactor walls, discharge devices, valves, pumps, filters, compressors, centrifuges, columns, dryers, comminution machines, internals, packing elements and mixing elements-wherein a metal layer or a metal/polymer dispersion layer is deposited in an electroless manner on the apparatus(es) or apparatus part(s) to be coated by bringing the parts into contact with a metal electrolyte solution which, in addition to the metal electrolyte, comprises a reducing agent and optionally the polymer or polymer mixture to be deposited in dispersed form, where at least one polymer is halogenated.

Description

Heat exchangers with reduced tendency to form deposits and processes for their production

The invention relates to a method for producing heat exchangers, which comprises the electroless chemical deposition of a metal-polymer dispersion layer. The invention further relates to heat exchangers according to the invention. The invention further relates to the use of a metal-polymer dispersion layer as a permanent incrustation inhibitor.

Over the past few decades, all industries have suffered from deposition in heat exchangers (Steinhagen et al. (1982), Problems and Costs Due to Heat Exchanger Fouling in New Zealand Industries, Heat Transfer Eng., 14 (1), pages 19-30). When calculating heat exchangers, an increasing friction pressure loss and heat transfer resistance due to deposits (fouling) must be included. This leads to the oversizing of heat exchangers by 10 to 200%.

The development of anti-fouling processes is therefore very high

Played a role. Mechanical solutions have the disadvantage that they are relatively large

Heat exchangers are limited and also cause considerable additional costs.

Chemical additives can lead to undesirable contamination of the

Products drive and pollute the environment.

For these reasons, possibilities have recently been sought to reduce the tendency to fouling by modifying the heat transfer surfaces.

Surface coatings with organic polymers such as polytetrafluoroethylene (PTFE) reduces the tendency to form deposits, but the known coatings themselves lead to a remarkable additional thermal resistance. At the same time, a lower limit is set for reasons of durability of the layer thickness. Similar problems are also observed in processes which involve the application of monolayer silane layers to the surface to be protected (Polym. Mater. Sei. And Engineering, Proceedings of the ACS Division of Polymeric Materials Science and Engineering (1990), volume 62, pages 259 to 263).

The problems associated with the use of polymer coatings do not arise in a process described in WO 97/16692. In this method, the surface's hydrophobicity is increased by ion implantation or by sputtering techniques. Although this leads to a reduction in the tendency to foul, the use of these methods, which always require vacuum techniques, is very expensive. In addition, the methods described are not suitable for coating difficult-to-access or complexly shaped surfaces or components with a uniform layer.

The deposits whose formation is to be prevented are inorganic salts such as calcium and barium sulfate, calcium and magnesium carbonate, inorganic phosphates, silicas and silicates, corrosion products, particulate deposits, for example alluvial sand (river and sea water), as well as organic deposits such as bacteria, algae, proteins, mussels or mussel larvae, polymers, oils and resins as well as the biomineralized composites, which consist of the aforementioned substances.

The object of the present invention is to provide a method for producing a heat exchanger which, on the one hand, reduces the tendency of the heat-transferring surfaces to deposit solids with the formation of deposits and, on the other hand, is negligible with high resistance (for example to heat, corrosion and undermining) Thermal resistance leads. The surfaces treated according to the process should have a satisfactory durability. The method should also be cost-effective to use on hard-to-reach areas.

The object of the invention is achieved by a method for producing a heat exchanger, characterized by the electroless chemical deposition of a metal-polymer dispersion layer, in which the polymer is halogenated, on a heat transfer surface.

In the context of the invention, a heat exchanger is a device which has surfaces designed for heat exchange (heat transfer surfaces). Heat exchangers which exchange heat with fluids, in particular with liquids, are preferred.

Heating elements and heat exchangers, in particular plate heat exchangers and

Spiral heat exchangers are preferred versions of heat exchangers. A halogenated polymer is a fluorinated or a chlorinated polymer; fluorinated polymers, in particular perfluorinated, are preferred. Examples of perfluorinated polymers are polytetrafluoroethylene (PTFE) and perfluoro-alkoxy

Polymers (PFA, according to DIN 7728, Part 1, January 1988).

This inventive solution to the problem is based on a method for electroless chemical deposition of metal-polymer dispersion phases, which is known per se (W. Riedel: Functional nickel plating, Verlag Eugen Leize, Saulgau, 1989 pages 231 to 236, ISBN 3-750480- 044-x). A metal-polymer dispersion phase comprises a polymer, in the context of the invention a halogenated polymer which is dispersed in a metal alloy. The metal alloy is preferably a metal-phosphor alloy.

The methods previously used to reduce the tendency towards incrustation led to surfaces which had greater roughness than electropolished steel (see Table 1). It has now been found that a coating associated with a reduction in roughness serves the same purpose. In addition, it was found that the influence of the polymer fraction is decisive in reducing the tendency towards incrustation, although the polymer fraction in the dispersion layer is rather low at 5 to 30% by volume.

It was also found that the surfaces treated according to the invention enable good heat transfer, although the coatings can have a not inconsiderable thickness of 1 to 100 μm. The surfaces treated according to the invention also have a satisfactory durability, which also makes layer thicknesses of 1 to 100 μm appear reasonable; 3 to 20 μm, in particular 5 to 16 μm, are preferred. The polymer content of the dispersion coating is 5 to 30% by volume, preferably 15 to 25% by volume, especially 19 to 21% by volume. Furthermore, the coatings used according to the invention are relatively inexpensive due to the process and can also be applied to hard-to-reach areas. These surfaces can be any heat transfer surfaces, such as inner pipe surfaces, surfaces of electrical heating elements and surfaces of plate heat exchangers, etc., which are used for heating or cooling fluids in industrial plants, in private households, in food processing or in plants for power production or water treatment become.

"Heat transfer" refers to the heat transfer from the interior of the heat exchanger to an optionally present coating facing the fluid, the heat conduction within the coating layer and the heat transfer from the coating layer to a fluid (e.g. a saline solution).

In a preferred embodiment of the method according to the invention, the metal-phosphorus alloy of the metal-polymer dispersion layer is copper-phosphorus or nickel-phosphorus; nickel phosphorus is preferred. In a further embodiment of the method according to the invention, the nickel polymer dispersion layer is a dispersion layer made of nickel-phosphorus-polytetrafluoroethylene. However, other fluorinated polymers are also suitable, such as perfluoroalkoxy polymers (PFA, copolymers of tetrafluoroethylene and perfluoroalkoxy vinyl ether, for example perfluorovinyl propyl ether). If the heat exchanger is to be operated at a comparatively low temperature, the use of chlorinated polymers is also conceivable.

In a further embodiment of the method according to the invention, the metal-polymer dispersion layer has spherical polymer particles with an average diameter (number average) of 0.1 μm to 1.0 μm, in particular of 0.1 μm to 0.3 μm.

In contrast to electrodeposition, chemical or autocatalytic deposition of nickel phosphorus does not provide the electrons required for this through an external power source, but rather through chemical conversion in the electrolyte itself (oxidation of a reducing agent). The coating is done by immersing the workpiece in a metal electrolyte solution that has been mixed with a stabilized polymer dispersion beforehand. An annealing at 200 to 400 ° C., especially at 315 to 325 ° C., is preferably carried out after the dipping process. The tempering period is generally 5 minutes to 3 hours, preferably 35 to 45 minutes. For example, commercially available nickel electrolyte solutions which contain Ni ¹¹ , hypophosphite, carboxylic acids and fluoride and optionally deposition moderators such as Pb ²⁺ can be used as metal solutions. Such solutions are sold, for example, by Riedel, Galvano- und Filtertechnik GmbH, Halle, Westphalia and Atotech Deutschland GmbH, Berlin. For example, commercially available polytetrafluoroethylene dispersions (PTFE dispersions) can be used as the polymer. PTFE dispersions with a solids content of 35 to 60% by weight and an average are preferred Particle diameter (number average) from 0.1 μm to 1 μm, in particular from 0.1 μm to 0.3 μm, is used, the particles of which have a spherical morphology and which have a neutral detergent (for example polyglycols, alkylphenol ethoxylate or, if appropriate, mixtures of the substances mentioned, 80 to 120 g of neutral detergent per liter) and an ionic detergent (for example alkyl and haloalkyl sulfonates, alkylbenzenesulfonates, alkylphenol ether sulfates,

Tetraalkylammoniumsalze or mixtures of the substances mentioned, 15 to 60 g of ionic detergent per liter). Dip baths with a pH of around 5 and about 27 g / 1 NiSO ₄ x 6 HO and about 21 g / 1 NaH ₂ PO ₂ x H ₂ O with a PTFE content of 1 to 25 g / 1 are typical contain.

The polymer content of the dispersion coating is mainly influenced by the amount of polymer dispersion added and the choice of detergents.

Another object of the invention is a method for producing a heat exchanger which has a particularly adhesive, durable and heat-resistant coating and therefore solves the problem according to the invention in a special way. This method is based on a method for producing a heat exchanger, characterized by the electroless chemical deposition of a metal-polymer dispersion coating, in which the polymer is halogenated, on a heat transfer surface.

This method is additionally characterized in that a 1 to 15 μm thick metal-phosphor layer is applied by electroless chemical deposition before the metal-polymer dispersion layer is applied

The electroless chemical application of a 1 to 15 μm thick metal-phosphor layer to improve adhesion takes place through the metal electrolyte baths already described, to which, however, no stabilized polymer dispersion is added in this case. Tempering is preferably dispensed with at this point in time, since this affects the adherence of the subsequent metal Polymer dispersion layer generally adversely affected. After the metal-phosphor layer has been deposited, the workpiece is placed in the immersion bath described above, which in addition to the metal electrolyte also comprises a stabilized polymer dispersion. This forms the metal-polymer dispersion layer. Annealing is then preferably carried out at 200 to 400 ° C., in particular at 315 to 325 ° C. The tempering period is generally 5 minutes to 3 hours, preferably 35 to 45 minutes.

In a further embodiment of the method according to the invention, the metal-phosphor layer has a thickness of 1 to 5 μm.

In a further embodiment of the method according to the invention, the metal-phosphorus alloy of the metal-polymer dispersion layer and the metal-phosphorus layer is nickel-phosphorus or copper-phosphorus.

In a further embodiment of the method according to the invention, the metal-polymer dispersion layer is a dispersion layer made of nickel-phosphorus-polytetrafluoroethylene.

Another object of the invention is a heat exchanger that can be produced by a method according to the invention. The heat exchanger according to the invention is preferably produced by using a method according to the invention.

In a further embodiment, the aforementioned heat exchanger according to the invention is designed to transfer heat to fluids, in particular to liquids. All heating elements that transfer heat to fluids can be used. Furthermore, heat exchangers, in particular plate heat exchangers and spiral heat exchangers, are preferred examples of such heat exchangers. Another object of the invention is the use of a coating, produced by the electroless chemical deposition of a metal-polymer dispersion layer, in which the polymer is halogenated, to reduce the tendency of the coated surfaces to deposit solids from fluids with the formation of deposits. The fluids are preferably liquids. The deposits, the formation of which is prevented according to the invention, have already been described.

Some advantages of the heat exchangers according to the invention or their coatings are shown by the attached drawing. It shows

Fig. 1 shows the change over time in the heat transfer coefficient through the boundary layer, including any existing

Coating layer on contact of different

Heat exchanger surfaces with a boiling salt solution.

Fig. 2 shows the change over time in the heat transfer coefficient by

Boundary layer including a possibly existing coating layer when different ones come into contact

Heat exchanger surfaces with a warm salt solution flowing past.

1 shows the decrease in the heat transfer coefficient (α [W / m ² K]) as a result of CaSO ₄ deposits as a function of time (t [min], abscissa) for different heat exchangers which differ in the nature of their surfaces. The reference number 1 refers to the measured values of the coating according to the invention of example (* 7). The reference number 2 designates the measured values for an electropolished steel surface. The area-related power is 200 kW / m ² , the concentration of the CaSO - Solution is 1.6 g / 1 and has a temperature that corresponds to the boiling point.

2 shows the measured decrease in the heat transfer coefficient (α [W / m ² K]) as a result of CaSO ₄ deposits as a function of time (t [min], abscissa) for different heat exchangers which differ in the nature of their surfaces. Reference number 1 is the coating according to the invention of example (* 7). The reference number 3 indicates an untreated steel surface. The power related to the surface of the heat exchanger is 100 kW / m. A CaSO ₄ solution with a concentration of 2.5 g / 1 flows past the heat exchanger at a speed of 80 cm / s and a temperature of 80 ° C.

example

The advantages of the heating surfaces coated according to the invention over correspondingly uncoated heating surfaces, electropolished surfaces and ion-implanted or sputtered surfaces were determined in laboratory tests. Table 1 contains a comparison of the measured values of surface roughness, surface energy and wetting angle of the heating surfaces examined, as well as the relative decrease in the measured heat transfer coefficients within the first 100 hours of the test. It can be seen that the heat exchangers according to the invention provide a very low surface energy, a very large contact angle and very good heat transfer behavior. Table 1:

Table 2 compares surface energy, contact angle and bacteria deposited per surface (Streptococcus Thermophilus) of the heat exchangers according to the invention with the heat exchangers of the prior art.

^ Table 2:

* Determination according to A. J. Kinloch, Adhesion and Adhesives, Chapman

& Hall, University Press, Cambridge 1994

** Determination according to D.K. Owens, J. of Appl. Polym. Be. 13 (1969) 1741-1747

*** Relative heat transfer coefficient after 100 hours of operation

(according to Müller-Steinhagen et al., Heat Transfer Engineering 17 (1998), 46-63)

**** Surface roughness, Ra according to DIN ISO 1302

* 5 Method according to J. W. Mayer, "Ion Implantation in Semiconductors, Silicon and Germanium", Academic Press 1970 (ISSBN 75107563)

* 6 Process for applying Diamond-Like-Carbon DLC according to GB-A 90 06073

First, a 5 μm chemically electroless nickel layer, which contains 8% phosphorus, was applied to improve the adhesion by immersing it in a electroless nickel electrolytic solution. The Ni-phosphor-PTFE dispersion coating was then produced in an immersion bath, consisting of a mixture of a chemically electroless nickel electrolyte solution and a detergent-stabilized PTFE Dispersion. The deposition of nickel-phosphorus-polytetrafluoroethylene was carried out at 87 to 89 ° C, that is below 90 ° C and at a pH of the electrolyte solution of 4.6 to 5.0. The deposition rate was 10 μm h, the layer thickness 15 μm. The composition of the electroless nickel electrolyte PTFE solution is shown in Table 3.

Table 3:

Electroless nickel electrolyte solutions are commercially available (Riedel, Galvano- und Filtertechnik GmbH, Halle, Westphalia and Atotech Deutschland GmbH, Berlin). After the nickel-phosphorus-PTFE layer had been applied, the workpiece was annealed at 300 ° C. for 20 minutes. The proportion of polymer and phosphorus in the dispersion layer was 20% by volume of PTFE, corresponding to 6% by weight of PTFE and 7% of phosphorus.

The PTFE dispersions are commercially available. The solids content and average particle size were 50% by weight and 0.2 μm, respectively. The dispersion was made using a neutral detergent (50 g / 1 alkylphenol ethoxylate from the Lutensol® brand, 50 g / 1 alkylphenol ethoxylate from the Emulan® brand, both detergents are manufactured by BASF AG, Ludwigshafen) and an ionic detergent (15 g / 1 alkylsulfonate from the brand) Lutensit®, BASF AG, Ludwigshafen, 8 g / 1 perfluoro-C ₃ -C ₈ -alkyl sulfonate of the brand Zonyl®, DuPont, Wilmington, USA) stabilized. The concentration specification 2-50 g / 1 refers to the amount of dispersion solution added.

The determination was made according to H. Müller-Steinhagen, Q. Zao and M. Reiss "A novel low fouling metal heat transfer surface", 5 ^Λ UK National Conference on Heat Transfer, London 17-18 Sept. 1997. Acting in cell culture Streptococcus thermophilus.

Claims

claims

1. A method for producing a heat exchanger, characterized by the electroless chemical deposition of a metal-polymer dispersion layer, in which the polymer is halogenated, on a heat transfer surface.

2. The method according to claim 1, characterized in that it is copper-phosphorus or nickel-phosphorus in the metal-phosphorus alloy of the metal-polymer dispersion layer.

3. The method according to claim 2, characterized in that it is in the nickel polymer dispersion layer is a dispersion layer made of nickel-phosphorus-polytetrafluoroethylene.

4. The method according to any one of claims 1 to 3, characterized in that the metal-polymer dispersion layer has spherical polymer particles with an average diameter of 0.1 microns to 1.0 microns.

5. The method according to any one of claims 1 to 3, characterized in that the metal-polymer dispersion layer has spherical polymer particles with an average diameter of 0.1 microns to 0.3 microns.

6. The method according to any one of claims 1 to 5, characterized in that before the application of the metal-polymer dispersion layer a 1 to 15 microns thick metal-phosphor layer is applied by electroless chemical deposition.

7. The method according to claim 6, characterized in that the metal-phosphor layer has a thickness of 1 to 5 microns.

8. The method according to claim 6 or 7, characterized in that it is nickel-phosphorus or copper-phosphorus in the metal-phosphorus alloy of the metal-polymer dispersion layer and the metal-phosphorus layer.

9. The method according to claim 8, characterized in that it is in the metal-polymer dispersion layer is a dispersion layer made of nickel-phosphorus-polytetrafluoroethylene.

10. Heat exchanger, producible by the method according to one of claims 1 to 9.

11. The heat exchanger according to claim 10, which is designed to exchange heat with fluids.

12. Use of a coating made by electrolessly chemical depositing a metal-polymer dispersion layer in which the polymer is halogenated to reduce the tendency of the coated surfaces to deposit solids from fluids to form deposits.