ROTATING TUBE HEAT EXCHANGER The invention concerns a rotating shell and tube heat exchanger for use as a reactor, or for heating, cooling or evaporation, alone or in combination, of bulk materials, granules or pellets, comprising a drum with intake and outlet for the bulk material, and relative to the drum internal, parallel, coaxial tubular discs which form energy transfer surfaces, where the energy medium flows into the tubes, and the bulk material is located on the outside of the tubular discs, where the tubular discs are arranged for rotation about a longitudinal axis which is common for the drum and the tubular discs, where each tubular disc comprises concentric tubular rings and at least one manifold to conduct the energy medium to and from each tubular ring, where the shell and tube heat exchanger further comprises distribution pipes and collecting pipes to conduct the energy medium between the tubular discs' manifolds and between the manifolds and rotating couplings which are connected to an external pipe system.

Rotating shell and tube heat exchangers of the above-mentioned type are employed in various types of processing plants, for example within the mineral industry, the food industry, the petrochemical industry or sludge treatment plants. Apart from being used for heating or cooling, rotating shell and tube heat exchangers of the above type may also be employed for evaporation, especially of water, but also of other volatile liquids. Rotating shell and tube heat exchangers of the above type may also be employed as reactors during chemical reactions at approximately atmospheric pressure, such as the calcination of soda, where amongst other processes a reaction and a degassing of carbon dioxide take place. By means of this type of rotating shell and tube heat exchanger it is also possible to perform a simultaneous combination of these processes, such as evaporation and after-cooling. The processing medium may be composed of any kind of liquid or dry bulk material, for example sludge, powder, granules or pellets, hereinafter designated bulk material.

In known rotating shell and tube heat exchangers of this type the drum may either be stationary or rotate together with the tubular discs. In the former case the tubular discs are securely connected to a central shaft which is rotatably mounted in the centre of the stationary drum's gable ends. In the latter case the drum is also securely connected to this shaft, and this shaft is

externally supported. In both cases this entails practical limitations to the size of the rotating shell and tube heat exchanger, since bending moments in the drum and the shaft and stresses on the bearings become excessive in large rotating shell and tube heat exchangers.

Naturally enough, a known phenomenon with rotating shell and tube heat exchangers is thermal expansions during the operation of the shell and tube heat exchanger. In known rotating shell and tube heat exchangers, and particularly if the drum is securely connected to the shaft, these thermal expansions give rise to material stresses which can be excessive, and which, if they are not taken into consideration during the design of the shell and tube heat exchanger, can cause material fracture. This problem increases with increasing dimensions of the shell and tube heat exchanger, and is consequently a factor which limits the size of the shell and tube heat exchanger.

Rotating shell and tube heat exchangers are often used for processing of abrasive media, such as mineral concentrates from the mineral industry, with the result that the tubular discs can be highly subject to wear. In operations of this kind it is therefore necessary to be able to remove the tubular discs for maintenance and possibly welding in of new tube pieces. Problems related to handling of large tubular discs, which may be securely connected to one another, is a further reason for keeping the dimensions of the heat exchanger below a certain size.

An additional problem with known rotating shell and tube heat exchangers is so-called bridge-formation and accumulation of the bulk material, leading to reduced heat transfer, which may result in clogging up of the heat exchanger.

This problem is particularly connected with treatment of powdered material, with a moisture content within certain material-dependent critical limit values.

Yet another problem connected with rotating shell and tube heat exchangers is uneven rotation caused by rhythmic movements in the bulk material. The greater the content of bulk material in the shell and tube heat exchanger, the greater this problem is, and consequently also increases with increasing dimensions of the shell and tube heat exchanger.

The object of the invention is to provide a rotating shell and tube heat exchanger which can be built on a large scale without being encumbered by the above-mentioned problems or limitations.

This object is achieved according to the invention with a rotating shell and tube heat exchanger of the type mentioned in the introduction, characterized by the features which are stated in the claims.

The invention therefore consists in a rotating shell and tube heat exchanger of the type mentioned in the introduction where the outside of the drum in the circumferential direction is provided with at least two external circular paths or flanges, where the drum is rotatably mounted via each of the paths or flanges on two rollers or bogies arranged under the drum on each side of the longitudinal axis's horizontal projection, where the drum is connected to a drive unit for rotation of the drum, and where the shell and tube heat exchanger includes means for rotation of the tubular discs together with the drum.

Thus the rotating shell and tube heat exchanger according to the invention has no load-bearing central shaft, thereby providing a rotating shell and tube heat exchanger which can be built on a large scale without being encumbered with the said problem connected with bending moments in the drum and the shaft and stresses on the bearings which affects large rotating shell and tube heat exchangers which have a load-bearing central shaft.

Moreover, thermal expansions do not cause such great material stresses in the shell and tube heat exchanger according to the invention as in the rotating shell and tube heat exchangers where the drum is securely connected to both the shaft and the drum. A rotating shell and tube heat exchanger is thereby provided which can be built on a larger scale than known rotating shell and tube heat exchangers, and calculations show that it will be possible to build without difficulty the shell and tube heat exchanger according to the invention with a capacity of 250 tons of mineral concentrate per hour, which at present is considered to be an upper practical capacity limit for those processing plants where installation of the shell and tube heat exchanger may be envisaged. A lower practical capacity limit for the shell and tube heat exchanger according to the invention appears to be 50 tons per hour for

mineral concentrate, since the shell and tube heat exchanger will be too expensive to design for a lower capacity.

The rotating shell and tube heat exchanger's means for rotation of the tubular discs together with the drum can be composed of welded or bolted connections, or of different types of fit connections. In a preferred embodiment the means for rotation of the tubular discs comprise releasable, load-bearing connections between the drum and the tubular discs for transferring the tubular discs'weight to the drum and transferring the drum's rotary motion to the tubular discs.

The invention will now be explained in more detail in connection with a description of a specific embodiment, and with reference to the drawings, in which: fig. 1 is an elevational view of a rotating shell and tube heat exchanger according to the invention, where the drum is shown substantially cut away, fig. 2 is a cross section through the shell and tube heat exchanger in fig. 1, viewed along the intersecting line II-II, fig. 3 illustrates an alternative embodiment of the shell and tube heat exchanger's distribution pipes and collecting pipes, fig. 4 illustrates a second alternative embodiment of the shell and tube heat exchanger's distribution pipes and collecting pipes, fig. 5 illustrates releasable, load-bearing connections between the drum and the tubular discs, and fig. 6 is a cross section viewed along the intersecting line VI-VI in fig. 5.

Figs. 1 and 2 illustrate a rotating shell and tube heat exchanger 1 according to the invention, and fig. 2 illustrates a cross section through the shell and tube heat exchanger viewed along the intersecting line II-II in fig. 1. The shell and tube heat exchanger 1 comprises a drum 3 which in fig. 1 is shown substantially cut away. An intake 4 and an outlet 5 for the bulk material is provided in gable ends 28. Parallel, coaxial tubular discs 6 for energy transfer to or from the bulk material are located inside the drum and in the illustrated embodiment are releasably connected thereto in a manner which will be explained further below.

During operation the tubular discs 6 rotate together with the drum 3 about a common longitudinal axis 7, as illustrated by the arrow R, while the drum's gable ends 28 with the intake 4 and the outlet 5 are stationary. The bulk material is fed in through the intake 4, as illustrated by the arrow PI, and is transferred by means of gravity and the drum's and the tubular discs'rotation towards the outlet 5, where it leaves the shell and tube heat exchanger, as illustrated by the arrow P2. During the movement through the shell and tube heat exchanger the tubular discs 6 rotate through the bulk material, with the result that it is stirred and energy is transferred to or from the energy medium which flows through the tubes in the tubular discs.

The outside 15 of the drum is provided in the circumferential direction with two external circular paths or flanges 17, each of which runs over two rollers 18 which are provided under the drum 3 on each side of the longitudinal axis's 7 horizontal projection, which is best illustrated in fig. 2. In this manner a rotatable mounting of the drum 3 is obtained. In a not shown alternative embodiment, especially when the drums are large and heavy, instead of rollers 18, bogies may be employed for mounting of the drum.

The drum's rotation is generated by a drive unit 20, for example an electric gear motor, which via a drive 39 drives a gear rim 40 which is provided on the outside 15 of the drum. The drum's axial forces are absorbed by a wheel 52 which rolls against the side of one of the paths 17.

Each tubular disc 6 includes concentric tubular rings 8 and a manifold 9 to guide the energy medium to and from each tubular ring 8, which is most clearly illustrated in figs. 2-4, which illustrate tubular discs each consisting of 6 tubular rings.

During operation of the rotating shell and tube heat exchanger the energy medium is led from an external pipe system, through a rotating coupling 13 and into distribution pipes 10. From here the energy medium flows into the manifolds 9 in each individual tubular disc 6, and on into each individual tubular ring 8. From the tubular ring the energy medium flows back to the manifold and on into collecting pipes 11, whereupon the energy medium leaves the shell and tube heat exchanger through the rotating coupling 13.

Depending on what kind of energy medium is employed different designs of the distribution pipes and the collecting pipes may be used.

Fig. 2, which corresponds to fig. 1, illustrates an embodiment of the distribution pipes and the collecting pipes which is well-suited to heating with steam, where the steam is condensed into water in the tubular rings. The steam flows in through an inlet 31, and on into the centrally located distribution pipe 10, where the steam flows in the space above the water which flows in the opposite direction. Short pipes 51 extend from each manifold 9 into the centrally located distribution pipe 10, passing the steam into the manifold. In this case the manifolds 9 are composed of pipes which have a common through-flow space for the steam and the water. The steam's circulation is generated by condensation of the steam, resulting in a weak underpressure inside the tubular rings, while the water's circulation is generated by gravity, which causes the water to run out of the tubular ring 8 into the manifold 9. From here the water runs into the distribution pipe 10, which in this embodiment therefore also acts as a collecting pipe. By means of the steam pressure the water is forced via a syphon 53 out through the rotating coupling 13 and out through an outlet 32.

Fig. 3 illustrates an embodiment of the rotating shell and tube heat exchanger where the distribution pipes 10 and the collecting pipes 11 are located on the outside of the drum 3 and connected to the manifolds 9 with releasable couplings 16, while fig. 4 illustrates an embodiment where the distribution pipes 10 and the collecting pipes 11 are located immediately inside the innermost tubular ring 8. In both of these embodiments the distribution pipes and the collecting pipes constitute separate pipe systems for supply and removal of the energy medium. These embodiments are suitable when using liquid energy media, for example hot oil or a cooling mixture of water and glycol. It should also be noted that in the embodiment illustrated in fig. 1 the steam flows through the tubular discs in parallel, while the energy medium which is employed in the embodiments in figs. 2 and 3 flows through the tubular discs in series, since parallel connection when using liquid would give too low flow rates in the different tubular discs. In some operating conditions the distribution pipes and the collecting pipes can be provided in such a manner that the energy medium flows through the tubular discs in a combination of series and parallel connection, since the energy medium, for example, can be distributed in parallel to groups of tubular discs, whereupon it flows in series through the tubular discs in each group. The distribution pipes 10 and the collecting pipes 11 also include couplings and fittings and

may be held in place by pipe clamps. These elements are only partly illustrated in the figures, and are of a known type.

Compared with the embodiment illustrated in figs. 1 and 2 the embodiments illustrated in figs. 3 and 4 have the advantage that the tubular discs 6 have an opening 27 in their central areas, thus providing in the shell and tube heat exchanger's central area an access area for maintenance.

The illustrated embodiment of the rotating shell and tube heat exchanger according to the invention also includes releasable, load-bearing connections 21 between the drum 3 and the tubular discs 6 for transferring the tubular discs'weight to the drum and transferring the drum's rotary motion to the tubular discs.

Figs. 5 and 6 illustrate the releasable, load-bearing connections 21 in more detail, and also illustrate in more detail how the tubular discs 6 are constructed. Fig. 5 is an enlarged view of the area of the releasable, load- bearing connections 21 which are shown in the bottom part of fig. 2, viewed in the drum's longitudinal direction, while fig. 6 is a cross section viewed along the intersecting line VI-VI in fig. 5, showing the outer section of three tubular discs 6. It can be seen how the releasable, load-bearing connection 21 includes longitudinal guide elements 22 on the inside of the drum 3, and corresponding longitudinal guide elements 23 on the tubular discs. By means of these longitudinal guide elements it is possible, after dismantling one of the gable ends 28, to withdraw the tubular discs 6 from the drum 3 in the drum's longitudinal direction, which enables maintenance of the tubular discs to be carried out outside the drum.

The drum's and the tubular discs'guide elements 22 and 23 respectively have opposite, co-operating, radially directed surfaces or sections indicated by reference numerals 24 and 25 respectively, permitting radial movement relative to one another between the drum's and the tubular discs'guide elements.

The drum's longitudinal guide elements 22 are welded into the inside of the drum 3, while the tubular discs'guide elements 23 are welded to a number of spacers 33, one for each tubular disc 6, which in turn are each welded to a doubling plate 34 which is welded to the outermost tubular ring 8 in each tubular disc 6. The outermost tubular ring 8 is welded to a spacer 37 in the

form of a flattened tube, which is located with its longitudinal direction in the tubular rings'circumferential direction. The spacer 37 is welded in turn to the second outermost tubular ring 8, which in turn is welded to a spacer 36 which is composed of a short radial tube. The spacer 36 is welded in turn to the tubular ring inside, with the result that between the four innermost and the second outermost tubular ring 8 in each tubular disc 6 spacers 36 are employed in the form of radial tubes, while between the second outermost and the outermost tubular ring 8 in the illustrated embodiment a spacer 37 is employed in the form of a flattened tube which is located with its longitudinal direction in the tubular rings'circumferential direction. The reason for this difference is that the bulk material, which on account of the force of gravity collects at the outermost tubular ring, would be apt to accumulate at the circular tubular spacers if they were also employed between the second outermost and the outermost tubular ring. The manifold 9, which is composed of a flattened tube, is in itself capable of keeping the tubular rings 8 in place, thus fulfilling in its position the function of the spacers.

Since the drum's and the tubular discs'guide elements 22 and 23 respectively are permitted to move radially relative to one another, a self-centring of the tubular discs in relation to the drum is achieved. This is highly advantageous with regard to the fact that the manufacturing tolerances can be greater than would have been necessary without this self-centring. The further advantage is achieved that the tubular discs'centre of gravity coincides with the rotating shell and tube heat exchanger's centre axis 7, thus providing an even rotation.

A further advantage which is obtained with the possibility of relative radial movement between the drum's and the tubular discs'guide elements is that due to the temperature difference between the tubular discs and the drum, as well as different diameters, thermal expansions are absorbed in the guide elements without causing material stresses or displacements.

The longitudinal guide elements 22 are preferably evenly distributed along the drum's 3 circumference, as illustrated in figs. 2-4, where the longitudinal guide elements 22 are located at three points along the drum's circumference, thus having an angular distance of 120°. By means of this even distribution of the guide elements 22 an even distribution is obtained of the forces which are transferred between the tubular discs and the drum.

A plurality of tubular discs 6 may preferably be combined to form a tubular disc section, as illustrated in fig. 1, where a tubular disc section is indicated by reference numeral 26 and is composed of a number of tubular discs which are located between two tubular disc section connections 38. This is advantageous for maintenance, since it means that several tubular discs can be removed from the drum together. The tubular discs in a tubular disc section may be interconnected, for example with spacers and bolts. The tubular disc section connections 38 preferably comprise bolted connections, and may, for example, be composed of flanges.

During the tubular discs'rotation, due to their large dimensions, the manifolds will carry along more bulk material than the rest of the tubular discs. In order to prevent all the manifolds from being simultaneously passed down into the bulk material, which could result in uneven stirring of the bulk material and erratic running of the shell and tube heat exchanger, the manifolds 9 in adjacent tubular discs 6 or tubular disc sections 26 respectively are preferably displaced relative to one another in the direction of rotation. Viewed in the shell and tube heat exchanger's longitudinal direction the manifolds 9 will thereby form a helix or be in the form of a spoked wheel, as illustrated in figs. 2-4.

In a specially preferred embodiment this displacement between the manifolds 9 constitutes a relative angular distance which, calculated about the longitudinal axis, corresponds to a fraction or a multiple of the angular distance between the drum's longitudinal guide elements 22. An embodiment is thereby obtained which is advantageous to manufacture, since the different elements in the tubular discs are easily adapted to one another. With reference to figs. 2-4 these figures illustrate embodiments in which the longitudinal guide elements 22 are arranged with a relative angular distance of 120°, and in which the manifolds 9 in the different tubular discs are arranged, i. e. displaced, with an angular distance of 60°. Embodiments are thereby obtainted where the relative displacement between the manifolds corresponds to a fraction, viz. a half, of the angular distance between the drum's longitudinal guide elements.

In a further preferred embodiment the rotating shell and tube heat exchanger comprises arms which are pivotably attached to the inside of the drum 3 for free movement between the tubular discs 6, in order to eradicate bridge

formation and accumulation of the bulk material. In order to avoid complicating the figures unnecessarily, only one such arm is illustrated in fig. 1 with reference numeral 29, but in a practical embodiment there will, of course, be several arms, the number varying from only a few arms located, for example, in the vicinity of the drum's intake and outlet, to an embodiment in which there may be several arms, for example three, placed between each tubular disc. Instead of arms, chains may be employed which are pivotably attached to the inside of the drum 3 for free movement between the tubular discs 6, as illustrated in fig. 1 with reference numeral 30.

In the above the invention has been explained with reference to individual specific embodiments. It is obvious, however, that a number of different variants are possible within the scope of the invention, for example associated with the number of arms or chains and their size, the design of the rotating shell and tube heat exchanger being selected on the basis of the bulk material concerned in the individual operating situation.