FI82550B - FOERFARANDE FOER TILLVERKNING AV EN SKIVVAERMEVAEXLARE. - Google Patents

Description

1 82550

Method for manufacturing a plate heat exchanger

The invention relates to a plate heat exchanger consisting of at least three spaced apart plate elements made of parallel graphite and fluoro-5 polymer, consisting of a plate and a surrounding frame, and a heat exchanger fluid supply and outlet The plate heat exchangers described heretofore according to the invention consist of at least three or generally more plate parts with gutters and joined together to form a stack in which the plates are separated from each other. The stack and each plate section are provided with means for supplying and discharging heat exchange fluids flowing through the space between the plates. The distance between adjacent plates is determined by the spacers placed between the two plates in each case. It is advantageous to stretch the tip of the spacers at the edges 20 of the plate parts, e.g. by deep drawing (German model 82 08 878) and it is also known to place corrugations in the planes of the plate parts which increase stability and improve fluid distribution, honeycomb structures and other surface structures. The corrugations can be formed so deep in the material that they apply to the 25 adjacent plate portions and thus carry it. In this way, very thin plate parts can be used, which are mainly metal plate and sheets and also thermoplastic. Thermoplastic sheet metal parts are made simply and generally withstand corrosive media better than metals. This applies in particular to fluoropolymers, e.g. polyvinylidene fluoride (PVDF). The disadvantages of this material are the relatively low temperature resistance, limited stiffness and deformation caused by the creep. It is known to improve the properties of PVDF by mixing carbon fibers with plastic, where the fiber ratios are more than 30%, but this impairs the flowability of the 2,82550 mixture, so that normal mold casting methods can no longer be used (Pat. No. 6B 1,324,424). Finally, a method of making bodies is known in which mixtures containing cellugra-5 phytate and corrosion-resistant resins such as PVDF are compressed (U.S. Pat. No. 4,199,628). The graphite particles are arranged in planes which are at right angles to the compression direction, which is the direction of the heat flow determined by the manufacture of the plate heat exchangers. Due to the anisotropy of the graphite flakes 10, this inevitably gives plates with high thermal resistance in this direction and heat exchangers with poor transfer capacity, respectively. These moldings are therefore used exclusively as corrosion-resistant coatings and the like.

It is therefore an object of the invention to provide a method of manufacturing a heat exchanger of the type mentioned at the beginning, the plate parts of which are manufactured simply and have the same corrosion resistance as fluoropolymers, higher mechanical stability than these plastics and low thermal resistance.

The object is achieved by the process according to the invention, characterized in that the plate heat exchanger is manufactured in the following steps: a) a graphite powder with a particle size of less than 25 0.5 mm is mixed with a powdered fluoropolymer having a particle size of less than 0.001 mm in a ratio of 95: 5; 70:30 at a temperature between 200 and 350 eC, b) the mixture is cooled to room temperature, after which it is ground to a particle size of less than 0.3 mm, and c) the ground material is compressed into sheet elements at a pressure of at least 200 bar at a temperature of at least 200 eC , and d) the plate elements are assembled into a heat exchanger and flexible planar seals are provided between the adjacent frames.

Other preferred embodiments of the invention are characterized by what is set out in the claims below.

In a preferred embodiment, the plate parts forming the plate heat exchanger contain at least 70% graphite powder and at most 30% fluoropolymer. Plate sections having this composition can be made with a very small thickness; their brittleness is substantially less than that of sheets composed exclusively of graphite, and the reversible and final deformations are much smaller than the changes in length and volume in sheet parts made of plastics and filled plastics. The material properties suitable for plate heat exchangers are apparently due to the fluoropolymer which surrounds the individual graphite particles as a thin film and binds them together, whereby this bond has a high shear strength. A suitable binder is, in particular, a thermoplastically processable fluoropolymer such as a copolymer of tetrafluoroethylene or trifluorochloroethylene, polyvinyl fluoride and polyvinylidene fluoride, which is considered to be the best binder because it is easy to process in a mixture with graphite powder.

The mechanical and thermal properties of the plate parts made of graphite powder and the fluoropolymer group binder can be adjusted over a wide range according to different operating conditions, possibly by changing the amount of binder or some other manufacturing parameter. Particularly preferred are plate sections with a bulk density of 2.0-2.1 30 g / cm 3, a thermal conductivity of 15-20 W / m.K and a tensile strength of 20-40 MPa. The range of use of such plate parts is wide and even parts with a large surface area have sufficient rigidity. Under special operating conditions, e.g. when the solid load of the heat exchange fluid is high, the wear of the plate parts may increase under certain conditions due to the low size of the graphite. In order to reduce wear, it is advantageous under certain conditions to use plate parts in which wear-resistant particles are dispersed. The number of particles is determined by the wear stress of the plate parts and the suitable size of the particles is less than 5 times the half thickness of the heat exchange plates. Particularly suitable and preferred are silicon carbide particles which have a higher hardness and a more suitable thermal conductivity and which have little effect on the corrosion resistance of the plate parts and which can therefore be present in an amount of up to 50% by weight. If the corrosive effect is particularly high, it is most preferable to add coke particles. For heat exchangers which are operated at higher pressures or which have a higher mechanical load, plate parts which contain carbon fibers as reinforcement are preferred, preferably in the form of short, cut fibers in an amount of 2-20%. Since fiber reinforcement is particularly effective on flat surface areas of sheets, the fibers should be collected at the boundary, feed and discharge areas of the sheet sections.

One more important parameter for the efficiency of the heat exchanger exchanger-20 is the rate of liquid distribution inside the heat exchanger. For controlling the flow of liquid, the plate parts are preferably provided with knobs placed in a kind of sieve and centered in the liquid supply area. They extend, for example, in rows transversely to the flow direction of the liquid. The frustoconical knobs preferably contact the proximal plate portions, resulting in additional stiffening of the plate stack. In another embodiment, the reinforcing members may be reinforced with laminar carbon fiber shapes, such as strips or pre-30 layer plate layers in which the carbon fibers are arranged in one or two directions. The laminar fiber forms are attached to the surface of the sheet parts, e.g. with molten polyvinyl chloride, or pressed into it during the manufacture of the parts. Flat areas of the plate part, of which. . The 35 spaced apart knobs begin, are preferably stiffened.

Gaskets made of a flexible and corrosion-resistant material, e.g. a fluoropolymer, are placed between the boundary regions of the two plate parts. Gra-5 fillet leaf seals with very low cold flow are preferred. Gaskets made of cellular graphite having a bulk density of about 0.8-1.2 g / cm 3 are compressed together, preferably to a thickness of 0.1-0.3 mm, by compressing the plate stack. The release of these seals from the boundaries of the plate parts is facilitated by coating them with a fluoropolymer, e.g. dispersions containing tetrafluoroethylene copolymers. Alternatively, at low operating pressures, sufficient sealing can be achieved by coating the sealing surfaces of the boundary region with such a dispersion. In this embodiment, the sealing surfaces 15 are roughened or grooved or the like are made in them.

The plate heat exchangers according to the invention have the same resistance to corrosive substances as graphite, but they do not have this brittleness, which makes the manufacture and use of thin-walled graphite parts impossible in practice. The creep strength of the plate parts is higher than that of heat exchangers made exclusively of polymers. Other advantages are higher thermal conductivity and easy adaptation of shape and properties to the intended use by adding particulate or fibrous materials.

To prepare the sheet sections, the graphite is already mixed with the fluoropolymer in a ratio of 95: 5 to 70:30. The graphite in the mixture is natural graphite, such as flake graphite or natural graphite or electrical graphite, obtained by graphitizing petroleum coke, needle coke or bituminous tar pitch coke. The particle size of the graphite is less than 0.5 mm. In a known manner, several particle fractions are also mixed together, e.g. 0-0.063, 0.063-0.1 and 0.1-0.3 mm fractions to obtain a suitable adjustment to a given packing density. The fluoropolymer is likewise used as a powder or added to the mixture in the form of a dispersion. Mixtures containing exclusively powder are mixed at a temperature of 200-350 ° C and mixtures containing dispersions at room temperature or less at elevated temperature. After cooling or evaporation of the dispersing medium, the mixtures formed from the mixtures are ground. Preferably, after the addition of a compression additive such as stearic acid or metal soap, the compression mold with the core is then filled with the powdered substance. The core is in the shape of a compression matrix and the distance between the mold surface and the core at different points is proportional to the thickness of the compressed plate portion 10. The ratio of the thickness of the frame or boundary to the thickness of the heat exchange surface is e.g. 4: 1, so that the mold and the core are separated from each other at positions where the corresponding ratio is 4: 1. The powder layer filled between the mold and the core is correspondingly four times thicker in the edge region than in the middle, so that when compressed to the final value, the powder becomes compressed at the same size at each point. The molding pressure is at least 200 bar and the molding temperature is at least 200 eC. When pressing, the boundary areas, heat exchange surfaces and possibly 20 knobs etc. for controlling the fluid flow are connected to each other.

The invention is explained in more detail below by means of examples and drawings, in which: Fig. 1 shows a schematic view of a plate heat exchanger; Fig. 2 shows a plan view of the plate part; and Figure 3 shows a cross-sectional view of a stack containing a plurality of plate portions.

In Fig. 1, the plate parts 1 are movably arranged in a frame 2. Each plate part has openings extending therethrough through which heat exchange fluids are fed to the corrugated part 4 of the plate part. Several plate parts are fastened together to form a plate heat exchanger 5 closed by a front plate 6 and a back plate 7. Protrusions 8 are placed on the front plate 6 in line with the openings 3, 7 82550 through which the heat exchange fluids F1 # F2 are fed and removed. The plate sections, front plates and back plates, are supported together by tie rods, which are not shown in the drawings. According to Fig. 2, each plate part consists of a frame or boundary area 9 and a corrugated part 4 surrounded by a frame. In the boundary areas grooves 10 are placed for control in frame 2 (Fig. 1) and knobs 11 for fluid flow control are placed through protruding openings 3 and corrugated between part 4. The edges 12 also act to divide the nes-10. According to Figure 3, the flat seal 13 is placed between the adjacent frames or boundary areas 9 and is made of a flexible, corrosion-resistant material, mainly a graphite sheet.

Example 1 80 parts of electrographite powder - 60% 60-200 micrometers, 40% <60 micrometers - were mixed with 20 parts of polyvinylidene fluoride powder in a mixing tray with Sigma mixing means, whereby the particle size of the polyvinylidene fluoride was less than 1 micrometer. The stirring temperature was 20,220 ° C and the stirring time was one hour. After cooling to room temperature, the mixed product was ground in a pin mill to a particle size of <0.3 mm and filled into a compression mold as described above and compressed into a unitary plate section; the compression pressure was 400 bar, the temperature 25 ° C 270 ° C and the residence time 10 minutes. The following quantities of substances were measured:

Bulk density 2.02 g / cm 3

Flexural strength 50 MPa

Tensile strength 30 MPa

30 Thermal conductivity 25 W / m.K

Permeability coefficient 3.10'6cm2 / s

Seventeen plate portions were supported together with the front plate and the back plate as shown in Fig. 1, and a flat seal having a thickness of 0.3 mm was placed between the adjacent frames. The plate heat exchanger was cooled with dilute β 82550 hydrochloric acid (about 20% HCl), which was impure with organic solvents. The liquid temperatures were: acid inlet temperature 116 ° C and acid outlet temperature 52 ° C, cooling water inlet temperature 7 eC, cooling water 5 outlet temperature 40 eC. The heat transfer coefficient was 2000-3000 W / m.K and no corrosion damage or leakage occurred at an operating pressure of 3.5 bar.

Example 2

Half of the 60-200 micrometer graphite fraction described in Example 1 was replaced with silicon carbide powder having a particle size of 50-300 μm, and the mixture was processed as described and compressed into plate parts. The wear resistance of silicon carbide-containing parts and some silicon carbide-free parts were compared. For this purpose, corundum particles with a particle size of 150-200 micrometers were blown into the sections, with a nozzle diameter of 8 mm and a throughput of 30 g / min. The substance was removed as follows:

Shower angle Samples containing SiC Samples not containing SiC 20 30 ° 0.08 0.12 90 ° 0.12 0.18

Example 3 60 g of natural graphite powder with a maximum particle size of 0.5 mm were mixed with 40 parts of a commercially available dispersion of tetrafluoroethylene-perfluoroalkoxyethylene copolymers. The average particle size of the dispersant was about 0.3 micrometers and the amount of dispersing medium was 50%. To evaporate the dispersing medium, the mixture was heated to about 350 ° C, the resulting flowable material was ground and the waste fraction <0.3 mm was compressed into plate sections at 380 ° C and 400 bar. Bulk density 2.03 g / cm 3

Bending strength 25 MPa Thermal conductivity 25 W / m.K 35 Permeability coefficient 5.10'6cm2 / s.

Claims (5)

A method of manufacturing a disk heat exchanger (5) consisting of at least three parallel discs (1) of graphite and fluoropolymer spaced apart elements (1) consisting of a disk (4) and a frame (9). ) surrounding it, and of the inlet and outlet means for the heat exchange fluid flowing through the space between the disk heat exchanger (1) each pair of disks, characterized in that a) graphite powder, whose particle size is less than 0.5 mm, mixed with a powdery fluoropolymer, whose particle size is less than 0.001 mm, in a ratio between 95: 5 and 70:30, at a temperature between 200 and 350 ° C; b) the mixture is cooled to room temperature, after which it is ground to a particle size below 0.3 mm, and c) the ground blank is pressed into disk element (1) under a pressure of at least 200 bar at a temperature of at least 200 ° C, and d) the disk elements (1 ) is mounted to a heat exchanger (5) and h Flexible flat seals (13) are arranged between wide-adjacent frames (9). 2. A process according to claim 1, characterized in that the element (1) consisting of sheets (4) and frames (9) of heat exchanger (5) is pressed by a mixture containing graphite powder and powdered polyvinyl diene fluoride. 3. A method according to claim 1 or 2, characterized in that the sheets (4) are at least partially reinforced with planar coil fiber structures. Method according to Claim 1, 2 or 3, characterized in that seals of graphite foil are sealed between the frames (9) of adjacent sheets (4), the thickness of which is 0.1-0.3 mm. 12 82550 5. A method according to claim 4, characterized in that the seals (13) are coated with fluoropolymer. 5 11