"HEAT EXCHANGER"

D e s c r i p t i o n

The present invention relates to a tube-bundle heat exchanger intended for use in industrial plants, for example .

It is known that in industrial applications producing gas flows or fumes to high temperatures, use of heat exchangers is provided which on the one hand, can enable cutting down of the gas temperature ^' and, on the other hand, are able to obtain an energy and/or heat regeneration.

Generally it is known to make a holding structure or casing within which the high-temperature gas is conveyed, which casing in this region has a suitable pipe coil consisting of pipes welded together within which a cooling/heat-regeneration fluid such as water runs .

In the casing, during passage of the gas, heat exchange occurs and the water within the pipes is converted to steam and/or overheats the existing high-temperature steam thereby enabling a subsequent energy regeneration .

While the system described above fulfils the intended functions, it however has some drawbacks and/or operating limits.

First of all the exchangers of known type have a number of problems during the building and assembling steps.

It is in fact to be noted that generally the pipe coil is made up of several pipe portions connected and joined' to each other by welds that can generate stresses in the tube bundle and in the materials, which stresses in turn can give rise to cracks or in any case cause damage to the circuit. Obviously, the construction time too is adversely affected by the working operations required for joining the pipes.

In addition, once the pipe coil is provided, it is placed within the casing and rigidly secured to the structure at different parts and in an irremovable manner.

In this way, should repairs or even particular inspections of the device be required, the necessary intervention will involve cutting or unwelding operations on the different components of the structure, so that much time is required (also for subsequent re-assembling) , material and pieces are wasted and many parts are to be replaced even if they were in working conditions before servicing, since they have been damaged for access.

It is also to be pointed out that heat exchangers of known type are not generally able to withstand possible sudden thermal shocks that can be generated either on starting of the heat exchanger, or in case of malfunction or wrong use of same.

In fact, under this condition of non-optimal exchange, mechanical deformations due to heat are generated, which can impair the structural soundness of the exchanger giving rise to the other already mentioned problems.

Under this situation, the present invention aims at obviating the above listed drawbacks.

Accordingly, it is an aim of the invention to provide a heat exchanger that can withstand possible thermal shocks or deformations without being substantially damaged.

It is a further aim of the invention to make available a heat exchanger that can work with rather forced operating parameters (high temperatures of the gas or high pressures of the exchange fluid) without requiring particular design modifications and without being damaged.

It is also an aim of the invention to enable an easier assembling and dismantling of the apparatus, so that during these operations there is a reduction in the required time, costs and material waste.

The foregoing and still further aims that will become more apparent during the following specification, are achieved by a heat exchanger in accordance with the present invention and as claimed in the appended claims.

Further features and advantages of the invention will be best understood from the description of a preferred but not exclusive embodiment of the device illustrated by way of non-limiting example in the accompanying drawings, in which:

- Fig. 1 shows a partly sectioned side view of a heat exchanger in a preferred embodiment;

- Fig. 2 is a top view of the apparatus seen in Fig. 1; - Fig. 3 is a front view of two supporting plates used

in the heat exchanger seen in Figs. 1 and 2;

Fig. 4 is a diagrammatic view of a tube-bundle support with a cooling circuit for the plates seen in Fig. 3 and adopted in the exchanger in Fig. 1.

With reference to the drawings, a tube-bundle heat exchanger has been generally identified in ..the accompanying drawings with reference numeral 1.

This apparatus 1 first of all comprises a holding structure 2, also called !'envelope", that in the accompanying drawings takes the form of a parallelepipedic casing. Into this casing adapted to define a passage region 3, a first fluid is conveyed, which fluid 4 is generally a high-temperature gas (or also fumes) . By way of example, the gas can have an entry temperature of about 500-800 degrees depending on the type of plant.

As can be viewed from Figs. 1 and 2, use of a plurality of tubes 5 is provided which define a tube bundle 6, (at least partly) disposed within the gas passage region 3 to enable heat exchange between the gas itself (first fluid 4) and a second fluid 9, generally water, running in the tubes 5.

The tube bundle preferably made of stainless steel, is in engagement with the holding structure 2 at an attachment body 10 diagrammatically shown also in Fig. 4 and having corresponding attachment holes for each end portion of the tubes 5 (only partly shown in Fig. 4) -

As clearly shown in Fig. 1, the tubes 5 substantially have a U-shaped configuration being defined by suitably

bent single elements. In this way, welding operations on the tubes are avoided except at the end portions (to the attachment plate 10) .

Generally, under use conditions of the exchanger, the free end lengths of the tubes are disposed above each other.

In addition, each section of the tube bundle 6 taken along a plane containing the "U" extensions has at least two and preferably three U-shaped tubes 5 disposed inside each other as in the configuration shown in Fig. 1.

In this way the bundle spacing can be optimised, which spacing is also accompanied by a certain construction simplicity.

In addition, should one tube be damaged, only this tube will be replaced since the others are not adversely affected.

In addition, as can be seen still in Fig. 1, the heat exchanger is characterised by the presence of free lengths of the tubes 5 in a tapered configuration with respect to each other, close to the attachment body 10. In other words, the distance between the tubes 5 in the region of attachment to the plate 10 is smaller than that at the opposite end.

This solution enables all sizes of the entrance region,

• and in particular the thickness of the attachment plate

10, to be reduced. In fact, the surface acted upon by the pressure of the second fluid is reduced and conseguently the forces acting on these areas are

greatly reduced as well.

The water (or second fluid) 9 is conveyed into the tube bundle by an inlet 7 that through a header (or cap) 16 brings the fluid to all the inlet portions of tubes 5.

Generally the inlets 7 are at a lower position while the outlets 8 are at a higher position; if necessary however, a similar system can be used for a steam overheating device (inlet at a high position/outlet at a low position) or it is also possible to combine several tube bundles on the same plate.

Therefore, once the water has covered its travel within the heat exchange region, it emerges from the other end portions of the tubes and flows into a second header 17 in turn connected to one or more outlets 8.

Therefrom, the steam reaches a tank and regeneration of heat (energy) occurs following standard processes that therefore are not further described.

Looking at the figures, it is possible to notice the presence of at least one and preferably several supporting plates 11 of the type highlighted in Fig. 3.

These plates are formed with through holes 22 adapted to enable the tubes 5 to pass through the plate itself; the supporting plate 11 rests on the holding structure 2 as better clarified in the following, and carries the tube bundle 6 in an intermediate region of the tube 5 extension.

Obviously, depending on the length of the tubes and on requirements, use of two, three or more plates at

different positions and spaced apart along the tube axis is provided. The embodiment shown refers to the presence of these supports in a single region.

The through holes 22 of the supporting plate 11 shown in Fig. 3 have such sizes that a relative-movement freedom between the plate and tubes 5 passing therethrough is allowed; the tubes 5 have a circular section; on the contrary the holes 22 can, just as an indication, have an elongated shape to enable sliding of the tubes 5 relative to plate 11 in a predetermined direction. In the embodiment shown this direction is coincident with the vertical, under use conditions of the exchanger.

The described configuration offers a possibility of movement in the vertical plane of tubes 5 during all the operating steps of the exchanger; in this connection it is to be pointed out that each tube is provided with a free movement independent of the other tubes and that therefore the _. pipe coil can also deal, at the inside thereof, with unhomogeneous heat distributions involving variable deformations on the tubes .

In the described embodiment use of two supporting plates 11 is provided which are disposed in the same plane and superposed. This enables the lower plate to independently support all the tube portions with an inner flow in a first direction (delivery) and lower fluid temperatures also homogeneous with each other; vice versa the upper plate 11 co-operates with the tube portions with an inner flow in the opposite direction

(return lines) in which the fluid has been already heated due to heat exchange.

The supporting plates 11 rest on a base 20 of the holding structure 2 by use of two support elements 12, one for each side of the plate; the two supporting plates 11 shown in Fig. 3 are inserted into vertical grooves 21 present in the support elements 12 and bear thereon due to the presence of tongues 18. This enables the tubes 5 to have further margins of movement freedom in a vertical plane.

In turn the support elements rest (by means of rollers or similar elements) on the base of the holding structure 2; in the example shown in the drawings there is the presence of a roller 19 for each side of plates 11 so that a two-way movement along the extension axis of tubes 5 is allowed without too much friction. In other words, a tube elongation due to thermal expansion is accompanied by the plates 11 without any element being submitted to dangerous deformations.

Obviously, since resting on a base surface 20 takes place by means of rollers 19, possible movements transverse to the above mentioned direction 23 are also allowed. In fact, if the deformations in the tube bundle 6 are of such a nature that the average sliding friction is overcome, movements in a direction 13 substantially parallel to the rotation axis of rollers 19 are allowed.

Briefly, due to the particular links, the tube bundle 6 is suitably supported but it can be submitted to deformations in all the three Cartesian axes without creating damages in the exchanger.

Advantageously, should the working temperatures of the plant be particularly high, the exchanger 1 will also

comprise a cooling circuit 14 acting on at least the supporting plate/s 11 to avoid the temperature of same rising too much.

The cooling circuit 14 is diagrammatically shown in Fig. 4 and it is made up of at least one first straight length 14a linked to the attachment body 10 and connected to the header or cap 16 to receive the second fluid 9 (water) thereinto; it is to be pointed out in fact that cooling is obtained through exploitation of the same process fluid 9 suitably running around plates 11.

The first length 14a is directed towards the supporting plate 11 and it simultaneously also acts as a structural support element for said plate, thus making the exchanger simpler.

Therefore the circuit 14 comes close to plates 11 (tubes substantially in contact with the surface thereof - Fig. 1) and can be disposed so as to cross them along the whole transverse extension of same by at least one second length 14b in the extension of the first one, which second length is adapted to take the desired (also non rectilinear) geometry, depending on the design requirements.

Then a third straight length 14c in the extension of the second one is directed from the supporting plate 11 to the attachment body 10 bringing the heated fluid back to the cap 16.

For construction purposes and in order to obtain a better and more homogeneous cooling, use of two cooling circuits 14 disposed as shown in Fig. 4 is

provided .

The different innovative aspects of the invention (supporting plates 11, cooling circuit 14, elongated holes 22 and tapering tube portions 5) can be also used individually in the heat exchanger and not necessarily in combination with each other, although their synergistic function is well apparent.

In particular, should it be allowed by the design requirements, the cooling circuit 14 could also be optional .

The assembling steps of the above described heat exchanger are greatly simplified. In fact, once the U- shaped tubes 5 have been bent, their ends are passed through the holes 22 of the respective plates 11 and then welded to the attachment body 10.

Once the support elements 12 have been assembled, the whole structure thus made can be inserted into and linked to the holding structure 2, so that the assembling/disassembling operations are minimised and the exchanger inspection steps are simplified.

The invention achieves important advantages.

First of all, the exchanger being the object of the invention enables the assembling, repair and servicing costs and times to be reduced.

The device is suitable to work also with very forced operating parameters without being submitted to important structural decay. The deformation freedom allowed to the different tubes also in an independent

manner, and the possibility of displacement offered to the supporting plates can enable easy overcoming of the starting transients, arising of problems or errors on inputting of the use parameters of the exchanger being also eliminated.

Cooling of the supporting plates allows very high working temperatures to be reached, and use of the same fluid running in the pipe coil for carrying out cooling avoids dedicated circuits and auxiliary pumps being required, which happens in known plants.

Due to the U-shaped configuration of the tubes, the welding operations on the components are minimised and the risks of breakage of the tube bundle are .reduced.

Finally, the tapered arrangement of the tubes in the entrance region enables thickness of the attachment body, and consequently weight and cost of same to be reduced, by virtue of a reduction in the forces acting in these regions.

A further advantage resides in that the apparatus of the invention enables the overall costs of the exchanger to be reduced, the same performance (and even higher performance than the standard one) being ensured, and the operating reliability of the structure to be certainly increased.