WO1995030866A1

WO1995030866A1 - Heat exchanger

Info

Publication number: WO1995030866A1
Application number: PCT/FI1995/000160
Authority: WO
Inventors: Tapio Kordelin
Original assignee: Oy Shippax Ltd.
Priority date: 1994-05-05
Filing date: 1995-03-27
Publication date: 1995-11-16
Also published as: FI942068A0; FI942068A; AU2074695A

Abstract

The invention relates to a heat exchanger (10) comprising hoses (11) to be positioned vertically. The hoses (11) are mounted to a transverse perforated upper mounting plate (21) at their upper ends and the hoses are mounted to a transverse perforated lower mounting plate (31) at their lower ends. The hoses are made of thin flexible material like plastic sheet. The upper mounting plate (21) forms a cover of the feed tank (20) of the liquid to be evaporated. The bottom (22) of the feed tank is provided with lead-through holes (24) for the hoses, and the diameter of the lead-through holes (24) is larger than the outer diameter of the hoses (11) so as to allow liquid to flow down through the gap (25) formed between the outer surface of the hose and the plate. According to the invention, one or more redistributing tanks (50) provided with a perforated bottom plate (51) are fitted between the feed tank (20) of the liquid to be evaporated and the condensate receiver (30).

Description

HEAT EXCHANGER

The invention relates to a hose heat exchanger wherein the hoses are made of thin flexible material like plastic sheet.

Conventional tubular heat exchangers comprise a package of tubes fitted inside a closed pressure vessel wherein one substance, normally the liquid to be heated, runs in the tubes, and another substance, normally the condensing vapour, flows between the tubes and condenses when it meets the tube surface. Normally the heat exchanger is mounted so that the package of tubes lies in horizontal direction.

The prior art tube heat exchangers are made of steel or some other metal. Manufacturing costs are high and, owing to its structure, servicing of the apparatus like cleaning of the heat surfaces is time consuming. Therefore, these heat exchangers are not suitable for use in situations wherein the heat surfaces easily get dirty like e.g. in the production of fresh water from sea water. Neither are they suitable for treating such solutions in which the problem is strong corrosion of metallic surfaces.

The heat exchanger of this invention is suitable for use particularly in such situations which involve heavy fouling of the heat surfaces or corrosive liquids.

This kind of heat exchanging situations are normally such that the condensing of the vapour phase into liquid takes place on the first side of the heat exchanging surface and the evaporation of the liquid phase into vapour takes place on the second side of the heat exchanging surface. This kind of heat exchangers can be used e.g. in thermo- compressor evaporators and in conventional evaporator plants in which live steam is used as the source of energy. Their purpose of use may be to obtain a distillation product of desired quality like production of fresh water from sea water or purification of industrial process water before leading back to the process or to drain. Another purpose may be evaporation of excess solvent from various dilute solutions or suspensions to obtain a desired concentrate.

Such film heat exchangers are previously known which are suitable for use in a film evaporator or distillation apparatus operating in the thermo-compressor principle. In known apparatuses the heat exchanger unit is formed of flat bag-like elements of thin sheet material like plastic sheet placed against each other. Heat transfer takes place from the vapour condensing inside the elements through the sheet to the evaporating liquid falling on the outer surfaces of the elements. The vapour, which is introduced into the elements and which releases heat upon condensing, is generated outside the elements and its pressure and temperature has been raised by a compressor before it is introduced into the elements. In patent publications FI 79948 and FI 86961 is described a heat exchanger suitable for a film distillation apparatus wherein the heat surfaces are thin plastic sheet. The plastic sheets are formed into vertical bag structures arranged adjacently. The liquid to be evaporated is led to fall from the top downwards along the outer surfaces of the bags whereupon part of it is evaporated. The pressure of the evaporated vapour and accordingly the condensation temperature is raised by a compressor after which it is introduced into the bag structures. Condensing of the vapour takes place there and the distillate or condensate obtained is discharged from the bottom of the bag. Inside the bag structure there are gorges obtained by welding the sheets together by point welds or by welding the sheets together by broken zigzag seams. At the top of the bag structure, there is an end lath with a honeycomb structure from which the liquid to be evaporated is introduced onto the outer surface of the bag structure. The end lath also comprises channels through which the vapour going into the bag structure is introduced.

These bag structures, however, involve some points of risk. The plastic sheets may break at the welding points or at the seams since welding may have changed the composition of the plastic material at these points . During operation the bags flutter due to formation of vapour and the sheets of two adjacent bags often stick together over a considerable area. When the bags come loose from each other, they readily stick at another point. This kind of continuous fluttering and sticking may lead to breaking of the plastic sheet and above all to lowering of the efficiency of the apparatus because a significant part of the heat surface is continuously out of use due to sticking. Furthermore, distribution of the liquid to be evaporated onto the outer surface of the bag is uneven because the liquid streams from the top tend to unite leaving part of the surface dry and the united liquid streams on the other hand are too fast-flowing to effect maximum evaporation. This uneven distribution of liquid may lead to lowering of efficiency.

For the reasons mentioned above heat transfer is fairly low with respect to the area of the heat surfaces because part of the heat surface is continuously out of use. To ensure a certain heat transfer efficiency an excessively large heat surface must be constructed and this often leads to very large and expensive apparatuses .

The objective of this invention is to remove the above problems and obtain an improved heat exchanger which has a structure of a hose heat exchanger. Tube exchangers which would suit to the evaporators described above and which, consequently, would have the tubes made of plastic or the like material are not previously known.

Consequently, the invention relates to a heat exchanger comprising a bundle of hoses to be positioned vertically. At their upper ends, the hoses are mounted to a transverse perforated upper mounting plate and, at their lower ends, the hoses are mounted to a transverse perforated lower mounting plate. The heat exchanger also comprises means for introducing vapour into the hoses and distributing the liquid to be evaporated onto the outer surface of the hoses. The hoses are made of thin flexible material like plastic sheet. The upper mounting plate forms a cover of the feed tank of the liquid to be evaporated. The bottom of the feed tank is provided with lead-through holes for the hoses . The diameter of the lead-through holes is larger than the outer diameter of the hoses so as to allow liquid to flow down through the gap formed between the outer surface of the hose and the plate. According to the invention, one or more redistributing tanks provided with a perforated bottom plate are fitted between the feed tank of the liquid to be evaporated and the condensate receiver.

The heat exchanger of the invention has a much better heat transfer efficiency than the conventional solutions. Owing to the structure a large heat surface is obtained with respect to the volume of the apparatus . Said heat surface is always fully utilized because the hoses cannot stick together during operation. The heat exchanger is quite beneficial in terms of manufacturing, service, storage, and transportation costs. It is particularly suitable for use in such plants which nowadays employ heat exchangers comprising of bag-like plastic sheet elements.

The invention will be described in the following referring to the enclosed drawings in which

Fig. 1 shows the structure of a heat exchanger as a partly cross-sectional perspective view, Fig. 2 shows the leading-through of the heat exchanger hoses at the bottom of the feed and redistribution tank, Fig. 3 shows the attachment of the heat exchanger hoses of Fig. 1 to the mounting plate, Fig. 4 shows the perforation of the plates.

Fig. 1 shows one embodiment of the heat exchanger 10. The apparatus has a bundle of vertically positioned hoses 11. At their upper ends, the hoses are attached to a transverse perforated upper mounting plate 21 and, at their lower ends, they are attached to a transverse perforated lower mounting plate 31. The figure shows only a few hoses but in practice there are as many as the area of the plates 21 and 31 accommodates. The vapour is introduced into the hoses from above with means which are not shown in the figure except the sleeves 12. The hoses 11 are made of thin and flexible plastic sheet. In order to spread the liquid to be evaporated onto the outer surface of the hoses there is formed a feed tank 20 in which said upper mounting plate 21 forms the cover. The bottom 22 of the feed tank is provided with lead-through holes 24 for the hoses 11. It is seen in Fig. 2 that the diameter of the lead-through holes 24 is larger than the outer diameter of the hoses 11. Thus the liquid collected in the feed tank 20 can flow down through the gap 25 formed between the outer surface of the hose and the plate as indicated by the arrow. The gap 25 must be dimensioned so that the liquid in question flows down at a suitable velocity.

The feed tank 20 presented in Fig. 1 has a shape of a prism. It is closed at two of its opposite sides 28, 29 and open at two of its opposite sides 26, 27 communicating with the distribution tank 40 of the liquid to be evaporated into which the liquid to be evaporated is pumped. Liquid flows from the distribution tank 40 into the feed tank 20 through its open sides 26, 27. The bottom 41 of the distribution tank 40 is suitably located at a lower level than the bottom 22 of the feed tank. The reference number 42 is a seal in the joint between the tank 40 and the tank 20. The lower mounting plate 31 forms the cover of the receiver

30 of the condensate that has condensed inside the hose.

The condensate is removed from the receiver though a hose 32.

In order to make the liquid to be evaporated distribute as evenly as possible over the length of the tubes, one or more redistribution tanks 50, 50' provided with a perforated bottom plate 51, 51' may be fitted between the feed tank 20 of the liquid to be evaporated and the condensate receiver 30 as shown in Fig. 1. If the length of the hoses is 1200 mm, it is presumably the most suitable way to employ 1-2 redistribution tanks. The holes in the bottom of the redistribution tank are larger than the external diameter of the hoses so that the liquid can flow through the gaps thus formed at a suitable velocity along the external surface of the hoses until evaporation has taken place. According to the figure, the condensate receiver 30 and both redistribution tanks 50, 50' are suspended by chains 60 from the bottom of the redistribution tank or the liquid feed tank 20, respectively, next above. By using this kind of flexible and collapsible attachment means 60, a heat exchanger is obtained which is collapsible and takes very little space during storage and transportation.

Fig. 3 shows the attachment of the hose 11 to the upper mounting plate 21. The hose is tightened fast to the hole by means of a sleeve 12 fitting into the hose, the sleeve being pressed down until a sufficient tightness is obtained. The sleeve 12, which is preferably made of plastic, may be slightly conical as shown in the figure. This kind of attachment is rapid and easy needing no adhesive, filling compound or any other adhesive compound of non-foodstuffs quality which would restrict the use of the heat exchanger. The hoses are attached to the lower mounting plate in the corresponding way. The perforation of all plates is such that the holes are placed at intervals as shown in Fig. 4 to make the available plate area accommodate a maximum number-of hoses. This solution accomplishes a very large heat surface per unit volume of the heat exchanger.

Larger combinations can be readily assembled from the above heat exchanger modules by placing the modules adjacently so that the sides 28, 29 of the module are fitted face to face with the corresponding sides of the subsequent modules.

It is obvious to a specialist in the field that different embodiments of the invention may vary within the limits of the claims presented hereinafter.

Claims

1. Heat exchanger (10) comprising a bundle of hoses (11) to be positioned vertically, the hoses being attached at their upper ends to a transverse perforated upper mounting plate

(21) and the hoses being attached at their lower ends to a transverse perforated lower mounting plate (31), and means for introducing vapour into the hoses and distributing the liquid to be evaporated onto the outer surface of the hoses, wherein the hoses are made of thin flexible material like plastic sheet, and wherein the upper mounting plate (21) forms a cover of the feed tank (20) of the liquid to be evaporated, and the bottom (22) of the feed tank is provided with lead-through holes (24) for the hoses, and the diameter of the lead-through holes (24) is larger than the outer diameter of the hoses (11) so as to allow liquid to flow down through the gap (25) formed between the outer surface of the hose and the plate, characterized in that one or more redistributing tanks (50) provided with a perforated bottom plate (51) are fitted between the feed tank (20) of the liquid to be evaporated and the condensate receiver (30).

2. Heat exchanger according to claim 1 characterized in that the feed tank (20) is prismatic or round and that, at two of its opposite sides (26, 27), it is joined to a distribution tank (40) of the liquid to be evaporated.

3. Heat exchanger according to claim 1 or 2 characterized in that the lower mounting plate (31) forms a cover of the receiver (30) for the condensate formed inside the hoses and that the receiver is provided with means (32) for removing the condensate.

4. Heat exchanger according to claim 1, 2 or 3 characterized in that the condensate receiver (30) and each redistribution tank (50, 50') are suspended from the bottom of the redistribution tank (50, 50') or the liquid feed tank (20) next above by flexible and collapsible means (60) like chains.

5. Heat exchanger according to any of the above claims characterized in that the hoses (11) are, at their upper and lower ends, tightened fast to the upper and the lower mounting plate, respectively, by means of sleeves (12), preferably made of plastic, fitting into the hoses.

6. Heat exchanger according to any of the above claims characterized in that the holes of the upper mounting plate (21), the lower mounting plate (31), the bottom plates (51, 51') of the redistribution tanks possibly fitted between them, and the bottom plate (22) are placed at intervals to maximize the heat surface with respect to the plate area.

7. Heat exchanger combination characterized in that it comprises several adjacently fitted heat exchanger modules according to any of the claims 1 - 6.