WO2016193093A1

WO2016193093A1 - A heat exchanger

Info

Publication number: WO2016193093A1
Application number: PCT/EP2016/061792
Authority: WO
Inventors: Mike Dahl GIVERSEN
Original assignee: Alfa Laval Corporate AB
Current assignee: Alfa Laval Corporate AB
Priority date: 2015-05-29
Filing date: 2016-05-25
Publication date: 2016-12-08
Anticipated expiration: 2017-11-29
Also published as: KR20160004195U

Abstract

A heat exchanger comprises an inner casing (1) enclosing at least partly a channel (2) for a high temperature fluid. An outer shell (5) encloses at least partly the inner casing. An interspace (6) is provided around the inner casing between the inner casing and the outer shell. An insulation is provided in the interspace. The insulation is formed by porous balls, which at least partly fill out the interspace.

Description

A heat exchanger

TECHN ICAL FI ELD OF TH E I NVENTION The present invention refers to a heat exchanger, especially a heat exchanger for heati ng a fluid by a high temperature fluid, such as flue gases. Such heat exchangers comprise apparatuses frequently referred to as boilers , economizers, superheaters , etc. More specifically, the present invention refers to a heat exchanger comprising an i nner casing at least partly enclosing a channel for a high temperature fluid, an outer shell at least partly enclosing the inner casing , an i nterspace provided around the inner casi ng between the inner casing and the outer shell , and an insulation provided in the interspace .

BACKG ROU ND OF TH E I NVENTION AN D P RIOR ART

I n such heat exchangers, the temperature of the inner casi ng may reach a high temperature during the operation of the heat exchanger. The temperature could be in the order of 50-700°C, or even higher. The temperature of the outer shell has to be significantly lower to permit an operator to touch the outer shell .

I n order to solve this problem , it is known to provide an insulation layer in the interspace between the inner casing and the outer shell of the heat exchanger. Normally, the i nsulation layer is formed by a fiber or mineral material , such as

Rockwool® and/or similar boards of insulation materials.

However, the adaptation and alig nment of such an insulation layer on the inner casing of the heat exchanger is rather time consu ming , which contributes to high costs for the manufacturing of the heat exchanger.

US-4,351 ,277 discloses an economizer of the type having a vertically extendi ng cyli ndrical casi ng in which is mounted a plurality of spiral coils arranged in parallel to each other in concentric relation with respect to the central vertical axis of the cylindrical casing . The spiral coils are in the form of finned tubes. A heat exchange fluid is conducted through the spiral coils whereby the coils can extract heat from exhaust gases passi ng upwardly throug h the economizer from a boiler. The economizer comprises an interior lini ng and an outer casing separated from the interior lining . An insulation of mineral wool is provided between the interior lining and the outer casing . SUMMARY OF TH E I NVENTION

The object of the present invention is to overcome the problem s discussed above. Especially, it is aimed at an insulation material which may be applied to the heat exchanger within a shorter time period and in a more cost efficient manner. Furthermore, it is aimed at an easier application of the insulation when the heat exchanger offers small and inaccessible spaces.

This object is achieved by the heat exchanger i nitially defi ned, which is characterized in that the insulation comprises porous balls, which at least partly fill out the interspace.

The porous balls may be supplied to the i nterspace in an easy and quick manner. For instance, the supply of the porous balls may be performed by pouri ng the porous balls to the interspace via a pipe or a hose. The porous balls permit a supply through pouri ng or spraying , or i n other words through the same supply techniques as are used for the supply of a fluid. The time saving in comparison with the application of the prior art insulation is considerable. The insulation of porous balls is also easy to apply when the heat exchanger offers small and inaccessible spaces, for i nstance in connection with replacement of the insulation on an existing heat exchanger. According to an embodi ment of the invention, the porous balls are made of clay. The porous balls then comprises or consists of porous clay balls. The porous balls may be made through heating of formed clay balls containing a fuel , wherei n the fuel during the heating is burned thereby creating the porosity of the porous balls with small gas or air pockets. Porous clay balls are com mercially available as LECA^® balls. LECA^® stands for Lightweight Expanded Clay Aggregates.

The porous balls have a porosity with a plurality of gas or air pockets. The porosity is advantageous for the insulation capability. Thus, the porous balls may have a low weight and a high porosity, making them su itable as an insulation material , which thus may be supplied i n an easy man ner to the i nterspace of the heat exchanger. According to a further embodi ment of the invention , the interspace surrou nds the inner casing . The i nner casing may thus be surrounded , or enclosed, by the porous balls.

According to a further embodiment of the invention, the heat exchanger comprises an aperture which gives access to the interspace. By means of such an aperture, the porous balls may be supplied into the interspace.

According to a further embodi ment of the invention, the aperture is closable, for instance by means of a closing element. The aperture may be permanently closed , for instance through weldi ng , after the supply of the porous balls, or openably closed .

According to a further embodi ment of the invention, the aperture extends through, or at least partly through, the outer shell. According to a further embodi ment of the invention, the outer shell is removable. Advantageously, the outer shell may be removably attached to the inner casing . The outer shell may be attached by means of threaded elements.

According to a further embodiment of the invention, the interspace has a thickness of 50-300 mm , or even more. The thickness may be the distance, or average distance, between the inner casing and the outer shell . The distance depends on the size of the heat exchanger.

According to a further embodiment of the invention, each porous ball has a maximu m outer measure of 2-25 mm , or larger. The porous balls comprised in the i nsulation may have different maximum outer measures. Advantageously, the maximum outer measure may be 4- 1 5 m m .

According to a further embodi ment of the invention, the porous balls have an irregular shape. Such an irregular shape deviates from a spherical shape or outer contour. More precisely, the porous balls may have any outer shape, for instance not only rounded shapes but also edgy shapes.

According to a further embodiment of the i nvention, an adhesive is provided in the interspace and permits the porous balls to adhere to each other. I n such a way, the porous balls are prevented from falling out of the i nterspace , even if the outer shell is removed . According to a further embodiment of the invention, the adhesive comprises concrete. Concrete is suitable since it is heat resistance and may solidify to secure the position of the porous balls in the interspace. According to a further embodi ment of the invention, the porous balls and the adhesive are mixed with each other before the supply of the porous balls into the interspace. The mixture, which is flowing , may be supplied by being poured into the interspace to fill out the i nterspace, and then solidify, to create a solid , or substantially solid , insulation. This is advantageous, especially for large heat exchangers and when it is necessary to remove the outer shell for maintenance.

According to a further embodi ment of the invention, the porous balls and the adhesive are mixed with each other duri ng the supply of the porous balls to the i nterspace. Advantageously, the porous balls may be sprayed with concrete when fed from the pipe or hose. The porous balls may thus be discharged from the pipe or hose, and the concrete may be discharged from a pipe or hose arranged beside the pipe or hose for the porous balls to coat the porous balls with concrete.

According to a further embodiment of the i nvention, the i nner casing comprises an inlet to the channel and an outlet from the channel , thereby permitting the high temperature fluid, such as flue gases, to flow through the channel .

According to a further embodiment of the invention, the inlet and the outlet extend throug h the outer shell . According to a further embodiment of the invention, the heat exchanger comprises a tube arrangement comprising at least one tube provided in the channel and configured to convey a fluid to be heated . The tube arrangement may thus comprise 1 , 2, 3, 4, 5, 6, 7, 8 or even more tubes.

According to a further embodiment of the invention , the tube, or tubes, is formed as a helical coil having a plurality of turns, wherein the tube arrangement comprises a fluid inlet member connected to a first end of the tube, and a fluid outlet member connected to a second end of the tube. According to a further embodi ment, a central casing is provided inside the helical coil of the tube or tubes . The central casi ng may extend in parallel with the longitudinal axis. The central casing encloses a bypass channel for the high temperature fluid.

According to a further embodiment of the i nvention, the fluid inlet member and the fluid outlet member both extend throug h the i nner casing , the interspace and the outer shell . BRI EF DESCRI PTION OF TH E DRAWI NGS

The present i nvention is now to be expl ained more closely through a description of different embodiments and with reference to the drawings attached hereto.

Fig 1 discloses a partly sectional view through a heat exchanger according to a first embodiment of the invention.

Fig 2 discloses a partly sectional view of the heat exchanger in Fig 1 duri ng manufacturi ng of the heat exchanger.

DETAI LED DESCRI PTION OF D I FFERENT EMBODI M ENTS Fig . 1 discloses a heat exchanger according to a first embodiment of the invention. The heat exchanger comprises an inner casing 1 . The inner casing 1 encloses a channel 2 which is configured to convey a hig h temperature fluid, having a temperature in the order of 50-700°C or even higher.

I n the first embodiment, the heat exchanger is a boiler, economizer, superheater or the like. It is to be noted that the invention is not limited to these two kinds of heat exchangers, but the invention may also be applied to other kind of heat exchangers. I n the embodiment disclosed, the high temperature fluid is flue gases from a burner (not disclosed) .

The inner casing 1 comprises an inlet 3 to the channel 2, and an outlet 4 from the channel 2. The channel 2 extends i n parallel with a longitudinal axis x, which extends through the inlet 3 and the outlet 4. The flue gases may thus pass through the channel 2 via the inlet 3 and out throug h the outlet 4. The heat exchanger also comprises an outer shell 5 enclosi ng the inner casing 1 . An i nterspace 6 is provided around the inner casing 1 between the i nner casing 1 and the outer shell 5. The interspace 6 thus surrounds the inner casi ng 1 . The interspace 6 is closed in the state disclosed in Fig . 1 . An insulation 7 is provided in the i nterspace 6.

The insulation 7 comprises porous balls 8, see Fig 2, which fill out, or at least partly fill out the interspace 6. The porous balls 8 may be made of clay, concrete or any similar material , for instance plastic foam material . Plastic foam material may be suitable when the temperature of the hig h temperature gases is relatively low, i .e. in the lower region of the above mentioned range .

The porous balls 8 of clay may be made through heating of formed clay balls containi ng a fuel . Duri ng heating of the formed clay balls, the fuel is burnt, thereby creati ng the porosity of the porous balls 8.

Porous balls 8 of concrete may be made in a similar manner.

Each porous ball 8 may have a maximu m outer measure of 2-25 mm , or even more. For instance, the maximum outer measure may be 4- 1 5 mm . It is to be noted that the maxi mum outer measure of the porous balls 8 contai ned in the interspace 6 may vary within the limits mentioned. It is also to be noted that the porous balls 8 may have any irregular shape deviating from a spherical shape. The interspace 6 may have a thickness of 50-300 mm , or even more, depending on the size of the heat exchanger, and also on the temperature of the flue gases. The thickness is measured i n a radial direction with respect to the longitudinal axis x. The heat exchanger also comprises a first connection element 9 at the inlet 3 to permit attachment to further equipment, and a second connecting element 1 0 at the outlet 4 for connection to further equipment. I n the embodiments disclosed, the first and second connecting elements 9 and 1 0 comprise a respective flange.

The heat exchanger comprises a tube arrangement for a fluid to be heated by the high temperature fluid, in the embodiments, disclosed by the flue gases.

I n the embodi ments disclosed, the tube arrangement comprises four tubes 1 1 , 1 2, 13, 1 4 provided in the channel 2. The tubes 1 1 - 1 4 are formed as helical coils each having a plurality of turns. The tubes 1 1 - 1 4 are concentrically provided with respect to the longitudi nal axis x. The tubes 1 1 - 1 4 may be provided with fins (not disclosed) .

It should be noted that the tube arrangement may comprise another number of tubes, for i nstance 1 , 2, 3, 4, 5, 6, 7, 8 or even more tubes.

Furthermore, the heat exchanger may comprise a central casing provided inside the helical coil of the tubes 1 1 - 1 4. The central casing may extend i n parallel with the longitudinal axis x. The central casing encloses a bypass channel for the flue gases. A valve may be provided for closing and opening the bypass channel.

The tube arrangement also comprises a fluid inlet member 15 and a fluid outlet member 16. Each tube 11-14 is connected to the fluid inlet member 15 at a first end of the respective tube 11- 14. Each tube 11-14 is also connected to the fluid outlet member 16 at a second end of the respective tube 11-14. The fluid is fed through the fluid inlet member 15, through the tubes 11-14 an out through the fluid outlet member 16 to be heated.

As can be seen in Fig. 1, both the fluid inlet member 15 and the fluid outlet member 16 extend through the inner casing 1, the interspace 6 and the outer shell 5.

The heat exchanger comprises an aperture 17, see Fig.2, which gives access to the interspace 6. In the first embodiment, the aperture 17 extends through the outer shell 5. The aperture 17 is closable, for instance by means of a closing element. In the embodiments disclosed in the figures, the aperture 17 is closable by means of the second connecting element 10. It is to be noted, that the aperture 17 may be provided at other positions of the heat exchanger and may be closable through welding, to be permanently closed, or by means of other elements than the second connecting element 10.

Furthermore, the outer shell 5 may be removable, and for instance removably attached to the inner casing 1. The outer shell 5 may be attached by means of threaded elements, schematically indicated by reference sign 18, such as screws and nuts in order to permit removal of the outer shell 5.

In Fig 2 a pipe 20, or hose, is disclosed. The porous balls 8 may be supplied to the interspace 6 by means of the pipe 20 in an easy and convenient manner. The porous balls 8 are poured into the i nterspace 6 via the pipe 20 to fill up at least partly the interspace 6.

I n the first embodiment, the porous balls 8 are supplied to the interspace 6 without any further substances or material . The porous balls 8 are thus loosely contained i n the i nterspace 6.

A second embodi ment differs from the first embodi ment only in that an adhesive is provided in the i nterspace 6. The adhesive permits the porous balls 8 to adhere to each other. The porous balls 8 will thus not be loosely contai ned i n the i nterspace 6 , but more or less fixed to each other so that they may not fall out of the interspace 6, for instance in case of any opening or loosening of the outer shell 5 from the heat exchanger.

The adhesive may comprise or consist of concrete. I n the second embodiment, the porous balls 8 and the adhesive are mixed with each other before the supply of the porous balls 8 into the i nterspace 6, for i nstance via the pipe 20.

A third embodiment differs from the second embodiment only in that the porous balls 8 and the adhesive are mixed with each other during the supply of the porous balls 8 into the interspace 6. I n this embodiment, a further pipe 21 may be provided, for instance beside the pipe 20. Each of the pipe 20 and the further pipe 21 has an outlet, or nozzle, through which the porous balls 8 and the adhesive, respectively, passes into the interspace 6. The outlets, or nozzles, may be arranged so that the porous balls 8 and the adhesive are mixed during the supply of the porous balls 8 and the adhesive.

The present invention is not limited to the embodiments disclosed but may be varied and modified withi n the scope of the following clai ms.

Claims

1. A heat exchanger comprising

an inner casing (1) at least partly enclosing a channel (2) for a high temperature fluid,

an outer shell (5) at least partly enclosing the inner casing (1), an interspace (6) provided around the inner casing (1) between the inner casing (1) and the outer shell (5), and

an insulation (7) provided in the interspace (6),

characterized in that the insulation comprises porous balls (8), which at least partly fill out the interspace (6).

2. A heat exchanger according to claim 1, wherein the porous balls (8) are made of clay.

3. A heat exchanger according to any one of claims 1 and 2, wherein the heat exchanger comprises an aperture (17) which gives access to the interspace (6).

4. A heat exchanger according to claim 3, wherein the aperture (17) is closable.

5. A heat exchanger according to any one of the preceding claims, wherein the outer shell (5) is removable.

6. A heat exchanger according to any one of the preceding claims, wherein the interspace (6) has a thickness of 50-300 mm, or even more.

7. A heat exchanger according to any one of the preceding claims, wherein each porous ball (8) has a maximum outer measure-of 2-25 mm, or even larger.

8. A heat exchanger according to any one of the preceding claims, wherein the porous balls (8) have an irregular shape.

9. A heat exchanger according to any one of the preceding claims, wherein an adhesive is provided in the interspace (6) and permits the porous balls (8) to adhere to each other.

10. A heat exchanger according to claim 9, wherein the adhesive comprises concrete.

11. A heat exchanger according to any one of claims 9 and 10, wherein the porous balls (8) and the adhesive are mixed with each other before the supply of the porous balls (8) into the interspace (6).

12. A heat exchanger according to any one of claims 9 to 11 , wherein the porous balls (8) and the adhesive are mixed with each other during the supply of the porous balls (8) to the interspace (6).

13. A heat exchanger according to any one of the preceding claims, wherein the inner casing (1) comprises an inlet (3) to the channel (2) and an outlet (4) from the channel (2), thereby permitting the high temperature fluid to flow through the channel (2).

14. A heat exchanger according to claim 14, wherein the inlet (3) and the outlet (4) extend through the outer shell (5).

15. A heat exchanger according to claim 15, wherein the heat exchanger comprises a tube arrangement comprising at least one tube (11-14) provided in the channel (2) and configured to convey a fluid to be heated.

16. A heat exchanger according to claim 15, wherein the tube (11-14) forms a helical coil having a plurality of turns, and wherein the tube arrangement comprises a fluid inlet member (15) connected to a first end of the tube (11-14), and a fluid outlet member (16) connected to a second end of the tube (11- 14).

17. A heat exchanger according to claim 16, wherein the fluid inlet member (15) and the fluid outlet member (16) both extend through the inner casing (1), the interspace (6) and the outer shell (5).