GB2049151A - Heat exchanger headers and tube end plates - Google Patents

Abstract

A fluid tight joint between a container (1) (e.g. a header) of or including fibre reinforced plastics material and the edges of a metallic plate (8) (for example the tubeplate of a condenser for a multi-stage flash desalination plant) comprises a bent reduced thickness peripheral lip portion (3) of the container made closely to follow the edges of the metallic plate (8) which are arcuately curved, the lip portion being held in engagement with said edges by a tightenable band (13). <IMAGE>

Description

SPECIFICATION Fluid tight joints This invention relates to fluid tight joints, particularly but not exclusively for multi-stage flash desalination.

In a typical plant for multi-stage flash desalination, there are condensers in each stage which look like and function as tube and tubeplate heat exchangers, and each condenser has water headers, often termed water boxes, for supplying brine from a preceding stage to the tubes of the condenser and passing on to the succeeding stage. Hitherto such water boxes have been made of mild steel and are liable to much corrosion by the brine. As a water box for a typical commercial plant can be 2 meters square and weigh half a ton, replacement presents considerable problems. Linings for the water boxes have been tried but are expensive and so far have met with only limited success.

One of the type of materials which has been suggested as a replacement for mild steel for water boxes is fibre reinforced plastics. Glass fibre reinforced plastics are not ideal for contact with brine because the glass can leach out over a period, but such material can be employed for the outside skin of the box where a composite construction is contemplated. The material employed for contact with the brine is preferably a carbon fibre reinforced plastics skin, because carbon fibres do not leak in brine but do have great strength in tension and therefore impart a good resistance to tensile loading to the material in which they are employed as reinforcement. Where a composite structure is contemplated, the glass fibre reinforced plastics and the carbon fibre reinforced plastics skin are preferably separated by a filler such as polyurethane foam.

Whether fibre reinforced plastics type of material is employed, whether composite or entirely of carbon reinforced plastics, there remains the problem of making an effective and durable joint between such material and the metallic tubeplate of the condenser. It is an object of the present invention to provide such a joint.

According to the present invention, a fluid tight joint between a container of or including fibre reinforced plastics material and the edges of a metallic plate comprises a peripheral lip portion of said container,. which portion is of reduced thickness compared with the normal thickness of the container material, arcuately curved edges of metallic plate, the portion engaging the upper surface of the plate and being bent inwardly so as to follow closely the arcuate edges of the plate and a band having tightening means, said band being disposable at the outer edge region of the lip portion to encircle it and the part of the plate which has a reduced periphery compared with that of the upper surface of the plate due to the arcuately shaped edges.

To assist in providing this reduction in periphery, it is preferable to provide gashes at regular intervals in the surface of the lip to avoid buckling and provide a good surface fit.

In order to guard against the band disengaging from said lip portion, the extremity of the lip portion may be bent outwardly. The bent extremity advantageously may seat against the part of a casing to which the tubeplate is secured, for example, the casing of a condenser for multi-stage flash desalination plant.

In the further variation, the lip portion of the water box may comprise a rib for engagement in a corresponding groove in the upper surface of the tubeplate. This serves to help the upper part of the lip portion to resist creeping away from the plate over a period of time due to the action of the said band and the fluid pressure in the container.

Two embodiments of the present invention will now be described by way of example only with reference to the accompanying drawings in which: Figure 1 is a fragmentary side view in section of the first embodiment, and Figure 2 is a similar view but of the second embodiment.

Reference is directed firstly to Fig. 1, which shows a water box for one stage of a multi flash desalination plant, a lower portion only of the water box, which forms a container, being illustrated and designated by 1. Full thickness of the container 1 is shown at the portion 2, and the lower edge of the container is reduced in thickness to provide the lip portion 3 with the step 4 at the change of thickness. At its extremity the lip portion is bent outwardly to provide a curled part 5. The lip portion 3 has transverse gashes (not shown) produced in its surface from the commencement of the preformed curled part 5 up to the level indicated by the dot and dash line 6.The state of the container 1 before a joint is made between it and the condenser 7 of the said plant (a fragment only-part of the tubeplate 8 carrying tubes 9 parts of which are shown), is illustrated in dot and dash lines in Fig. 1. The tubeplate 8 is shaped so that its peripheral edge 10 is arcuately curved in a direction such that the upper surface 11 is of greater area than the lower surface 12, or, to put it another way, the peripheral boundary of the upper surface 11 is of greater length than that of the lower surface 1 2.

In assembling the container 1 and a condenser 7, the lip portion 3 is fitted to the tubeplate 6 so that the step 4 engages the upper surface of the tubeplate 6. A band 1 3 which has tightening means in known manner (not shown, but a clip whose peripheral length can be reduced by a mechanical operation is one example) is disposed within the curled part 5 and is tightened until the lip portion 3 is bent and constraint to follow and to lie closely against the arcuately curved edge 10 of the tubeplate 8, thus forming a seal for the contents of the container. The gashes in the lip portion 3 allow the latter to conform to and fit closely against the edge 10 of the tubeplate 8 without buckling.In this position, the curled part 5 may also be in contact with a part of the wall 14 of the casing 1 5 of the condenser, a fragment only of which is illustrated.

The container is formed from fibre reinforced plastics, either alone (in which case the fibres are all carbon fibres) or, as shown in Fig. 1, as a composite, referred to herein before, incorporating a filler F of expanded foam such as polyurethane foam. The fibres shown in Fig. 1 are glass and carbon fibre longitudinals, shown in dot and dash lines disposed with the glass fibres adjacent to the water box external surface and the carbon fibres adjacent to the water box surface exposed to the brine. It is preferably so arranged, in manufacturing the container, that the reinforcing fibres lie close to the surface in those parts of the container which is of normal thickness, and that in the lip portion, the fibres are concentrated to occupy the plane of the neutral axis of the lip as far as can be managed, see Fig. 1.This maintains tensile strength in the lip portion, which is desirable for a good joint, and also assists in giving a measure of bendability as required in this region, said gashes also assisting in this respect. The crosses in Fig. 1 indicate circumferentially disclosed carbon fibres.

In a variant, illustrated in Fig. 2 to which reference is now directed, the construction is similar to that described with reference to Fig.

1 except that the lower end of the container has an intermediate part 1 6 of increased thickness and so shaped as to provide an inner peripheral rib 1 7 extending in the same direction as the lip portion 3 and situated at the end of a step 4t from greater depth than that of the step 4 of Fig. 1. The rib 17 engages a corresponding groove 1 8 in the upper surface 11 of the tubeplate 8, and this engagement serves to prevent creep of the lip portion 3 away from the tubeplate 8 which might otherwise take place over an extended period of operation.

From the above description, it can be seen that an improved fluid tight joint is provided by the present invention.

Claims (6)

1. A fluid tight joint between a container of or including fibre reinforced plastics material and the edges of a metallic plate comprising a peripheral lip portion of the said container, which portion is of reduced thickness compared with the normal thickness of the container material, arcuately curved edge of the metallic plate, the portion engaging the upper surface of the plate and being bent inwardly so as to follow closely the arcuate edges of the plate and a band having tightening means, said band being disposable at the outer edge region of the lip portion to encircle it and a part of the plate which has reduced periphery compared with that of the upper surface of the plate due to the arcuately shaped edges.

2. A fluid tight joint as claimed in claim 1, in which the surface of the lip comprises gashes at regular intervals there along.

3. A fluid tight joint as claimed in claim 1 or 2, in which the extremity of the lip portion is bent outwardly.

4. A fluid tight joint as claimed in claim 3, in which the bent extremity seats against the part of the casing to which a tubeplate is secured.

5. A fluid tight joint as claimed in any preceding claim, in which the lip portion of the water box comprises a rib for engagement in corresponding groove in the upper surface of the tubeplate.

6. A fluid tight joint substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.