WO2000036355A1

WO2000036355A1 - A rotating tube heat exchanger

Info

Publication number: WO2000036355A1
Application number: PCT/NO1999/000369
Authority: WO
Inventors: Hans Jørgen BRØNLUND
Original assignee: Kvaerner Technology And Research Limited
Priority date: 1998-12-14
Filing date: 1999-12-07
Publication date: 2000-06-22
Also published as: NO985862L; NO985862D0; AU1699300A; NO309743B1

Abstract

A rotating shell and tube heat exchanger for use as a reactor, or for heating, cooling of or evaporation from a processing medium comprises a shell (3) with an inlet (4) and an outlet (5) for the processing medium; rotatable heat exchanger tubes (8) which are provided inside the shell (3) for transferring energy between an energy medium flowing in the heat exchanger tubes (8) and the processing medium; and connecting pipes (85, 86) for connection between the heat exchanger tubes (8) and an external pipe system (31, 32). The heat exchanger tubes (8) form at least two at least partly separated circuits (87, 87') for the energy medium.

Description

A rotating tube heat exchanger

The invention relates to a rotating shell and tube heat exchanger for use as a reactor, or for heating, cooling of or evaporation from a processing medium in the form of bulk materials, granules or pellets, comprising a shell with an inlet and an outlet for the processing medium; rotatable heat exchanger tubes which are provided inside the shell for transferring energy between an energy medium flowing inside the heat exchanger tubes and the processing medium; and connecting pipes for connection between the heat exchanger tubes and an external pipe system.

The shell may be stationary or may rotate together with the heat exchanger tubes. When the shell is stationary the heat exchanger tubes can be connected to a central supporting shaft which is rotatably mounted in or outside end plates in the drum. In the case of a rotating shell the heat exchanger tubes and the shell may be interconnected and thus rotate at the same speed.

International patent application PCT/NO98/00214 describes a rotating shell and tube heat exchanger without a central supporting shaft. The shell and tube heat exchanger comprises a drum with an inlet and an outlet for the processing medium, and relative to the drum internal, parallel coaxial tube discs which constitute energy transfer surfaces. The outside of the drum is provided in the circumferential direction with at least two external circular paths or flanges for mounting on rollers arranged under the drum.

Rotating shell and tube heat exchangers are used in various types of processing plant, for example in the mineral industry, chemical industry or sludge treatment plants. The processing medium may be composed of any kind of moist or dry bulk material, such as sludge, powder, granules or pellets. The energy medium which is employed in shell and tube heat exchangers may be any fluid which has a different temperature from the processing medium. A common energy medium is steam, which is advantageous since it can be given a high temperature and is normally available in processing plants.

Apart from the properties of the processing medium, the heat transfer capacity of a rotating shell and tube heat exchanger is principally determined by the size of the energy-transferring surface and the temperature of the energy medium. If the heat transfer requires to be regulated, this is normally done by changing the temperature of the energy medium. When steam is used as energy medium, the temperature is normally regulated by regulating the steam pressure.

On account of the risk of a reduction or stoppage in the through-flow of the processing medium, when using rotating shell and tube heat exchangers it is always desirable for the processing medium to have low viscosity and to flow through the heat exchanger without developing lumps or forming bridges. A non-viscous processing medium has the additional advantage that the power requirement for rotation of the heat exchanger becomes less than in the case of a viscous processing medium.

A high degree of heat transfer is normally desirable in a heat exchanger, thus demanding good, even contact between the processing medium and the heat exchanger tubes. It is known that the contact between the processing medium and the tubes is better and more even with a processing medium of low viscosity than with a viscous one, and consequently this is another reason for the desirability of a non-viscous processing medium. The convection is also better in a processing medium of low viscosity than in a viscous one, which is naturally also an advantage with regard to heating of the processing medium. In the processing of abrasive media, such as mineral concentrates, wear on the shell and tube heat exchanger may be a problem. It is known that the wear on the heat exchanger tubes is less when there is good, even contact between the processing medium and the tubes than when there is poor and uneven contact, and in the processing of abrasive media this is a further reason for the desirability of a non-viscous processing medium.

Most processing media are of a less viscous nature and thereby achieve better and more even contact with the heat exchanger tubes at high temperature. In order to ensure that the processing medium becomes non-viscous as rapidly as possible, it is advantageous to transfer as much heat as possible to the processing medium as soon as it has entered the shell. In order to achieve this substantial and rapid heat transfer an energy medium is employed with a high temperature.

However, the use of an energy medium with a high temperature also leads to substantial heat transfer from the energy medium to the processing medium during the rest of the course of the processing. If the amount of processing medium flowing through is lower than the nominal amount, this will cause the processing medium to become warmer than required, which is normally undesirable.

When using a rotating heat exchanger for evaporation of, for example, water, in addition to the need to reduce the moisture content, there is also usually a need to be able to control the temperature in the outgoing processing medium. An excessively high temperature in the outgoing processing medium is uneconomical, and may result in thermal or processing problems for following processing equipment. Consequently, in this case a high degree of heat transfer during the last part of the processing is undesirable.

In general, therefore, when using rotating tube and shell heat exchangers, it is desirable to transfer a great deal of heat to the processing medium as soon as it enters the shell and tube heat exchanger, while at the same time in a number of applications of shell and tube heat exchangers it is desirable to be able to control the heat transfer during the course of processing, particularly the last part of the processing. In known rotating shell and tube heat exchangers, however, these two wishes are difficult to fulfil.

The object of the invention is to provide a rotating shell and tube heat exchanger where it is possible to control the heat transfer during the course of processing. A particular object is to provide a rotating shell and tube heat exchanger where it is possible to transfer a great deal of heat to the processing medium as soon as it enters the shell and tube heat exchanger, and less heat during the rest of the processing, particularly the last part of the processing.

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

The invention therefore consists in a rotating tube and shell heat exchanger which can be used as a reactor, or for heating, cooling of or evaporation from a processing medium in the form of bulk materials, granules or pellets, comprising a shell with an inlet and an outlet for the processing medium; rotatable heat exchanger tubes which are provided inside the shell for transferring energy between an energy medium flowing in the heat exchanger tubes and the processing medium; and connecting pipes and couplings for connection between the heat exchanger tubes and an external pipe system. The heat exchanger tubes form at least two at least partly separated circuits for the energy medium. By supplying these two circuits with different amounts of an energy medium or an energy medium with different temperature it is possible to control the heat transfer during the course of processing.

One circuit of heat exchanger tubes is preferably provided in an area at the inlet for the processing medium and a second circuit of heat exchanger tubes in an area at the outlet for the processing medium. It is thereby possible to transfer a great deal of heat to the processing medium as soon as it enters the shell and tube heat exchanger, and a smaller amount of heat during the rest of the course of processing, especially the last part of the processing.

The invention will now be explained in more detail in connection with a description of specific embodiments, and with reference to the drawings, in which: fig. 1 is an elevational view/longitudinal sectional view of a rotating shell and tube heat exchanger according to the invention,

fig. 2 illustrates a sectional elevation taken along the intersecting line II-II through the shell and tube heat exchanger in fig. 1.

fig. 3 is an elevational view/longitudinal sectional view of an alternative embodiment of the shell and tube heat exchanger according to the invention, and fig. 4 is an elevational view/longitudinal sectional view of yet another embodiment of the shell and tube heat exchanger according to the invention.

Fig. 1 is an elevational view of a rotating shell and tube heat exchanger according to the invention, which is used amongst other things for evaporation from a processing medium. The shell and tube heat exchanger comprises a shell in the form of a rotatable drum 3 which is illustrated substantially cut away, and a stationary end plate 28 at each end of the drum. Rotatable heat exchanger tubes 8 are arranged inside the drum as concentric tube rings in parallel, coaxial tube discs 6, 6' which during operation rotate together with the drum 3. The drum is rotatably mounted about a longitudinal axis 7, the outside 15 in the circumferential direction being provided with two external circular paths or flanges 17, each of which runs over two rollers 18 which are arranged under the drum 3. In the embodiment in fig. 1 the drum's rotation is provided by a drive unit in the form of an electrical gear motor 20, which via a drive gear 39 drives a gear rim 40 which is installed on the outside 15 of the drum. Axial forces are absorbed by wheels 52 which roll against the side of one of the paths 17.

During the operation of the shell and tube heat exchanger the processing medium is fed in through an inlet 4 in an end plate 28 in one end of the drum, as illustrated by the arrow P I . Due to gravity and the rotation of the drum and the tube discs the processing medium is moved towards the opposite end of the shell and tube heat exchanger, where it leaves the shell and tube heat exchanger through an outlet 5 in the second end plate 28, as illustrated by the arrow P2. During the processing medium's movement through the shell and tube heat exchanger heat is transferred from an energy medium flowing in the heat exchanger tubes 8. As a result of the heat transfer the processing medium gives off steam and moist gases, which flow out through an outlet 75, as illustrated by the arrow P3. The rotatable heat exchanger tubes 8 are connected via connecting pipes to an external pipe system for the supply and discharge of energy medium. These connecting pipes may be designed in several ways. In the version of the shell and tube heat exchanger illustrated in fig. 1 steam is employed as energy medium, and the connecting pipes are designed with due regard to this. In order to avoid overloading fig. 1 with too many details, however, the connecting pipes are illustrated in a simplified manner in this figure. The connecting pipes are shown in greater detail in fig. 2, which is a cross sectional view through the shell and tube heat exchanger taken along intersecting line II-II in fig. 1.

Fig. 2 illustrates how a rotation of the shell and tube heat exchanger in a direction R is made possible by the path 17 arranged on the outside 15 of the shell 3 running over the rollers 18.

Fig. 2 further illustrates a tube disc 6 comprising 6 concentric tube rings 8 which are interconnected by a manifold 9 in order to lead steam to and from each tube ring. Reference numeral 9' indicates manifolds in tube discs located at the back. The tube rings 8 are kept in place relative to one another in the tube disc 6 by distance pieces 36 and 37. The tube disc 6 in turn is connected via releasable, supporting connections 21 to attachment elements 22 on the inside of the drum.

The steam is supplied through an inlet 31 (see fig. 1 ) which is connected via a connection 13 to a supply pipe 85 which leads the steam into a distribution chamber 10 in the centre of the tube discs 6. From the distribution chamber 10 the steam flows via short pipes 51 into the manifolds 9, and on into the tube rings 8 (see fig. 2). Here the steam gives off heat and condenses into water. Gravity and the rotation of the tube discs lead the water back to the manifolds, and on back to the distribution chamber 10. The speed of rotation of the shell and tube heat exchanger is relatively low, and thus the water will settle on the bottom of the distribution chamber 10.

The steam pressure forces the water located in the distribution chamber 10 out through a syphon 53 which is connected to an outlet pipe 86. The outlet pipe 86 is arranged inside the supply pipe 85, and is passed via the connection 13 to an external outlet 32.

In the illustrated embodiment where steam is the energy medium the distribution chamber 10 and the supply pipe 85 are rotating, while the syphon 53 and the outlet pipe 86 are stationary. The connection 13 is designed as a rotating coupling or seal between the inlet 31 and the supply pipe 85, and the stationary outlet pipe 86 is passed centrally through this rotating coupling. In other embodiments of the connecting pipes which connect the heat exchanger tubes with the external pipe system the connection 13 may be designed in other ways.

The connection 13 is provided in the heat exchanger's longitudinal axis 7 in one end area of the shell 3. outside the end plate 28, but if it is expedient, it may instead be located inside or in the end plate 28. In the illustrated embodiment the tube discs 6, 6' are grouped in tube disc sections 26 and 26' respectively which are interconnected by couplings 38.

As mentioned in the general part of the description the heat exchanger tubes 8 form at least two at least partly separated circuits for the energy medium. In the embodiment in fig. 1 this is achieved by one circuit 87 of heat exchanger tubes in an area at or closest to the inlet 4 for the processing medium and a second circuit 87' of heat exchanger tubes in an area at or closest to the outlet 5 for the processing medium. It can be seen in fig. 1 that the circuit 87 closest to the inlet 4 is composed of three tube disc sections 26 which are supplied with steam from the distribution chamber 10, and that the circuit 87' closest to the outlet 5 is composed of two tube disc sections 26' which are supplied with steam from a distribution chamber 10' as an extension of the distribution chamber 10. Beside the coupling 38 which is located between the two distribution chambers 10, 10' there is provided a plate with a valve opening 62. The valve opening 62 can be closed and opened by an axially movable valve element 61 which is controlled by a valve rod 63 which is connected via a radial guide 64 and a seal 65 which forms a seal against a lead-through portion 90 to a valve rod actuator 66 which is external relative to the shell 3 to provide the axial movement. The valve rod actuator 66 is connected via a cable 67 to a not-illustrated control unit for the heat exchanger. It is thereby possible by means of electrical signals from this control unit to open and close the valve opening 62, in order to open or close the supply of steam to the circuit 87' of heat exchanger tubes.

The valve element 61 and the valve rod 63 with the lead-through portion 90 are non-rotating. The valve element 61 may have a rotatable contact surface for contact with the rotating valve opening 62. A syphon 53' is provided as part of the lead-through portion 90, extending via an outlet pipe 86' inside the lead-through portion 90 to an external outlet 32'. The steam pressure forces water which is located in the distribution chamber 10' out through the syphon 53', and on out through the external outlet 32'.

Fig. 1 thus illustrates an embodiment of the heat exchanger according to the invention where both supply and discharge of energy medium are common for the circuits of heat exchanger tubes, and where the heat transfer during the course of processing is controlled by a valve device which is located inside the shell, or more precisely in the distribution chamber.

Fig. 3 illustrates a second embodiment of the heat exchanger according to the invention, which is also used for evaporation. As in the embodiment in fig. 1 concentric rings of heat exchanger tubes 8 are by means of distance pieces 36, 37 held in place in tube discs 6, 6', which are connected via releasable, supporting connections 21 to attachment elements 22 on the inside of the drum 3. The distribution chamber 10 is composed of a centrally located pipe 83 which supports the tube discs 6, 6'. The pipe 83 is provided with central connecting pipes 89 which extend through seals 76 to the outside of the stationary end plates 28. The end plates 28 are supported by brackets 69.

In the same way as in the embodiment in fig. 1 the drum 3 is rotatingly mounted about an axis 7 by means of external paths 17 which rest on rollers 18, and the rotation is provided in a similar manner by a drive unit 20 which via a drive gear 39 drives a gear rim 40 on the outside 15 of the drum. Seals 68 ensure sealing between the drum 3 and the end plates 28.

As explained with reference to fig. 1 , during operation of the heat exchanger, as the processing medium moves from the inlet 4 to the outlet 5 steam is given off, which leaves the shell and tube heat exchanger through the outlet

75.

In the embodiment in fig. 3 the energy medium is also steam, and the details described with reference to fig. 1 concerning the steam inlet 31 , the connection 13, the supply pipe 85, the distribution chamber 10, the short pipes 51 , the syphon 53, the outlet pipe 86 and the water outlet 32 also apply to the shell and tube heat exchanger in fig. 3. The circulation of steam in the tube rings, the condensation of the steam into water and the movement of the water back to the distribution chamber 10 are also conducted in the same manner. The water in the bottom of the distribution chamber 10 is indicated by reference numeral 74.

As in the embodiment in fig. 1 a circuit 87 of heat exchanger tubes is arranged closest to the inlet 4, and a circuit 87' is arranged closest to the outlet 5. It can be seen that the circuit 87 is composed of four tube discs 6, while the circuit 87' is composed of three tube discs 6'. Inside the pipe 83 a valve 70 with associated valve actuator 71 is mounted on each of the short pipes 51 ' which pass steam into the three tube discs 6' which form the circuit 87'. In the illustrated embodiment pneumatic valve actuators 71 are employed. From the valve actuators 71 pneumatic pipes 72 lead via a rotating coupling to a stationary unit 73 on the outside of the heat exchanger. The unit 73 contains a solenoid valve for controlling the supply of pneumatic pressure from a supply line 88 to the pneumatic pipes 72. The solenoid valve is controlled in turn by electrical signals which are supplied via a cable 67 from a not-illustrated control unit. Thus by means of signals from this control unit it is possible to open and close the valves 70, in order to open or close the supply of steam to the circuit 87' of heat exchanger tubes closest to the outlet 5.

As an alternative to pneumatic valve actuators hydraulic valve actuators with hydraulic supply pipes may be used which are connected via a rotating coupling with the unit 73 on the outside of the heat exchanger. It is also possible to employ electromechanical valve actuators which via electric cables and collector rings or wireless transfer are supplied with electric current from the outside of the heat exchanger.

Fig. 4 illustrates a further embodiment of the shell and tube heat exchanger, which in the same way as the preceding embodiments is also used for evaporation, and where the energy medium is also steam. In this embodiment, however, the drum or the shell 3 is stationary, and the tube discs 6, 6' are consequently not connected to the shell 3. Otherwise the tube discs correspond to the tube discs previously described. The tube discs 6, 6' are attached in a centrally located pipe 83 which in turn is attached in shafts 82. The shafts 82 extend through seals 76 to the outside of the end plates 28, where they are rotatably mounted about the axis 7 in bearings 78. Bearing brackets 77 support the bearings 78, and also support the end plates 28, which form part of the shell 3. Since the shell is stationary, the inlet 4 and the outlet 5 for the processing medium and the outlet 75 for steam and moist gases are arranged in the actual shell.

The rotation of the pipe 83 with the tube discs is provided by a drive unit 20 which via a belt drive 80 drives a transmission 79 which in turn rotates the shaft 82. The drive unit 20 is supported by the transmission 79. which in turn is supported by a bracket 81.

It can be seen in figure 4 that the pipe 83 is divided internally by a partition 84, thus providing two separated distribution chambers 10, 10'. In each of the distribution chambers 10, 10' short pipes 51 , 51 ' are provided to pass steam into the tube discs 6, 6' and to prevent the water from running back to the tube discs. Syphons 53, 53' pass water 74, 74' out of the distribution chambers 10, 10', and the circulation of the steam and the water is thus the same as in the embodiments in figs. 1 and 3. The partition 84 thereby forms a division between two circuits 87, 87' of heat exchanger tubes. A supply pipe 85 for supplying steam to the circuit 87 of heat exchanger tubes 8 is connected to the steam inlet 31 via a connection 13 provided in the axis 7 on one side of the heat exchanger tubes 8, and a supply pipe 85' for supplying steam to the circuit 87' of heat exchanger tubes 8 is connected to the steam inlet 31 ' via a connection 13' provided in the axis 7 on the other side of the heat exchanger tubes 8. An outlet pipe 86 for discharging water from the circuit 87 of heat exchanger tubes 8 is connected to the water outlet 32 via the connection 13 provided in the axis 7 on one side of the heat exchanger tubes 8, and an outlet pipe 86' for discharging water from the circuit 87' of heat exchanger tubes 8 is connected to the water outlet 32' via the connection 13' provided in the axis 7 on the other side of the heat exchanger tubes 8. The heat supply to the two circuits of heat exchanger tubes can be regulated by not-illustrated valves on the two steam inlets 31 , 31 '.

In the above the invention has been explained with reference to one embodiment where the drum or the shell is stationary and the heat exchanger tubes are connected to a rotatably mounted shaft, and two embodiments where the drum is mounted on external rollers and is rotatable together with the heat exchanger tubes. It should be understood that the drum may also be rotatable by being connected to a rotatably mounted shaft.

The invention is particularly suited to embodiments where the energy medium is steam, and has been described in the above with reference to such embodiments. However, the invention is not dependent on the type of energy medium, and it should be understood that the invention can be employed together with any energy medium, such as a water/glycol mixture or hot oil. The heat exchanger tubes may be arranged in a number of different ways; in parallel, in series or in a combination of series and parallel.

Furthermore, the valves may be located in other ways than those described above; inside or outside the shell, in the supply pipe or the outlet pipe for the energy medium. An example of an alternative is to arrange a plurality of heat exchanger tubes in series in a section, and arrange a plurality of sections of heat exchanger tubes in parallel. The supply of energy medium to each of these sections can be implemented through coaxial pipes arranged in the shell and tube heat exchanger's axis, and can be controlled by valves mounted inside or outside the shell.

In conclusion it should be pointed out that instead of being pure shut-off valves the valves may be stepless control valves.

Claims

PATENT CLAIMS

1. A rotating shell and tube heat exchanger for use as a reactor, or for heating, cooling of or evaporation from a processing medium in the form of bulk materials, granules or pellets, comprising a shell (3) with an inlet (4) and an outlet (5) for the processing medium; rotatable heat exchanger tubes (8) which are provided inside the shell (3) for transferring energy between an energy medium flowing inside the heat exchanger tubes (8) and the processing medium; and connecting pipes (85, 86) for connection between the heat exchanger tubes (8) and an external pipe system (31 , 32), characterized in that the heat exchanger tubes (8) form at least two at least partly separated circuits (87, 87') for the energy medium.

2. A rotating shell and tube heat exchanger according to claim 1 , characterized by one circuit (87) of heat exchanger tubes (8) in an area at the inlet (4) for the processing medium and a second circuit (87') of heat exchanger tubes in an area at the outlet (5) for the processing medium.

3. A rotating shell and tube heat exchanger according to claim 1 or 2, characterized by a common supply (85) of energy medium to the circuits (87, 87') of heat exchanger tubes (8).

4. A rotating shell and tube heat exchanger according to one of the preceding claims, characterized by a common discharge (86) of energy medium from the circuits (87, 87') of heat exchanger tubes (8).

5. A rotating shell and tube heat exchanger according to one of the preceding claims, characterized by at least one valve device (61 , 62, 70) for regulating the flow of energy medium in at least one of the circuits (87').

6. A rotating shell and tube heat exchanger according to claim 5, characterized in that the at least one valve device (61 , 62, 70) is located inside the shell (3).

7. A rotating shell and tube heat exchanger according to one of the preceding claims, characterized in that the heat exchanger tubes (8) are arranged for rotation about a common axis (7), that a supply pipe (85) for supplying energy medium to a circuit (87) of heat exchanger tubes (8) is connected to the external pipe system (31 ) via a connection (13) located in the axis (7) on one side of the heat exchanger tubes (8), and that a supply pipe (85') for supplying energy medium to another circuit (87') of heat exchanger tubes (8) is connected to the external pipe system (31 ') via a connection ( 13') located in the axis (7) on the other side of the heat exchanger tubes (8).

8. A rotating shell and tube heat exchanger according to one of the preceding claims, characterized in that the heat exchanger tubes (8) are arranged for rotation about a common axis (7), that an outlet pipe (86) for discharge of energy medium from one circuit (87) of heat exchanger tubes (8) is connected to the external pipe system (32) via a connection ( 13) located in the axis (7) on one side of the heat exchanger tubes (8), and that an outlet pipe (86') for discharge of energy medium from another circuit (87') of heat exchanger tubes (8) is connected to the external pipe system (32') via a connection ( 13') located in the axis (7) on the other side of the heat exchanger tubes (8).

9. A rotating shell and tube heat exchanger according to one of the preceding claims, characterized in that each circuit (87, 87') of heat exchanger tubes (8) comprises one or more parallel, coaxial tube discs (6, 6') which are arranged for rotation about a common longitudinal axis (7), the heat exchanger tubes (8) being arranged as concentric tube rings (8) in the tube discs (6) and interconnected by at least one manifold (9) in order to guide energy medium to and from each tube ring (8).

10. A rotating shell and tube heat exchanger according to claims 7, 8 and 9, characterized in that the energy medium is steam which condenses into water on the emission of heat, that the supply pipes (85, 85') for steam each lead to their own distribution chamber ( 10, 10') in the centre of the tube discs (6, 6') which form the associated circuit (87, 87'), for distribution (51 , 51 ') of steam to the tube discs, and that the outlet pipes (86, 86') are arranged inside the supply pipes (85, 85') and lead from syphons (53, 53') for collecting water (74, 74') inside the distribution chambers ( 10, 10').