GB1601726A

GB1601726A - Heat exchanger for liquids mixed with solids

Info

Publication number: GB1601726A
Application number: GB7071/78A
Authority: GB
Original assignee: Sulzer AG; Gebrueder Sulzer AG
Current assignee: Sulzer AG
Priority date: 1977-04-18
Filing date: 1978-02-22
Publication date: 1981-11-04
Also published as: IT1095104B; FR2388234B3; DK15978A; DE2804431A1; NL7801936A; FR2388234A1; IT7822028A0

Description

(54) HEAT EXCHANGER FOR LIQUIDS MIXED WITH SOLIDS (71) We, SULZER BROTHERS LIMITED, a Company organised under the laws of Switzerland of Winterthur, Switzerland, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement: This invention relates to a heat exchanger for heat exchange between liquids mixed with solids, more particularly clarified sludges, having up to 15% of solids by weight.

Direct heat exchange between two liquids which are mixed with solids, particularly sewage or sludges containing up to 15% solids content, that is to say heat exchange without intermediate transfer from a first liquid-solid mixture to an intermediate liquid heat exchange medium, e.g. water, and then from the latter to the second liquid-solid mixture often gives rise to difficulties. On the one hand an effective heat transfer coefficient requires relatively high speeds of flow through a heat exchanger, leading to relatively narrow flow cross-sections in the heat exchanger, while on the other hand the danger of the system being clogged by coarse impurities, e.g.

stones, hair, pieces of cloth and paper, rags, fibres, pieces of rubber and plastics and other coarse materials, requires the maximum possible sizes for the flow paths.

In known devices for heat exchange, one medium generally flows through a pipe and the other through an annular duct enclosed by a second pipe surrounding the first pipe.

The risk of clogging is high in such devices, particularly in the outer annular chambers and in the connections to them.

Heat exchangers with an indirect heat exchange via an intermediate medium are of poor thermal efficiency and require relatively complex and expensive devices.

The object of the invention is therefore to provide a heat exchanger for the heat exchange, between the said mixtures of substances, in which the risk of clogging is avoided while good heat transfer coefficients are nevertheless obtained.

Accordingly the present invention provides a heat exchanger for heat exchange via a heat conducting partition between materials comprising liquids mixed with solids, comprising a primary chamber which has primary inlet and outlet means for a first said material to be passed through it and means comprising at least one pump for causing a forced flow of said first material in the primary chamber; and a secondary chamber defined by a continuous heat conducting partition to be within and peripherally surrounded by the primary chamber, said secondary chamber having secondary inlet and outlet means for a second said heat exchange material to be passed through it and means comprising an agitator for causing a forced flow of said second material in the secondary chamber.

This arrangement, in which the chambers accommodating the material may have large dimensions, avoids the need for narrow flow cross-sections in pipes or annular chambers and also looped bypass pipes, and good heat transfer coefficients are achieved by a forced movement of the mixtures in the chambers.

To ensure the necessary heat transfer as the throughputs increase per unit of time, a number of secondary chambers which are connected in parallel to one another with respect to the material flowing through them, may be provided in the primary chamber.

Other advantages of the invention are realised in the simple construction of the heat exchanger and its simple and rapidly performed cleaning whereby incrustation can be avoided, particularly on the partitions effecting the heat transfer, so that deterioration of the heat transfer is also avoided. The partitions advantageously consist of a material which on the one hand is a good thermal conductor and yet on the other hand is as corrosion-resistant as possible. Any deposition of solids from the liquid is in any event reduced by the forced flow of material in the chambers.

Agitators and/or pumps, for example, are the preferred means for producing the forced flow in the chambers which are preferably rotationally symmetrical. Varying the running times of the agitators makes it a simple matter to control the amount of heat to be transferred from one material to the other. An additional advantage of the heat exchanger is that it can be used both for continuous and intermittent operation.

To impart a circular flow to the material in the individual chambers of the tank it may be advantageous if agitators in the secondary chambers are disposed eccentrically to the central axis of the chambers and the agitators in the primary chamber are disposed with their axis at an angle to the vertical.

Assuming equal quantities, single-stage devices of the invention will give a theoretical maximum for the mixing temperature between the heat-yielding and heat-absorbing materials. It is possible to heat the heat-absorbing material beyond this temperature if at least two of the new devices are disposed in series successively and the two materials flow through them in countercurrent.

In addition to the use for heat-recovery, the heat exchanger can also be used for maximum cooling of the treated sludge of a pasturization plant; the improved cooling achieved in turn reduces environmental pollution.

Where the tanks have a number of secondary chambers, good utilization of the heat exchange surfaces formed by the partitions can be achieved if the total volume of the secondary chambers, through which the material flows in parallel, is in such a ratio to the volume of the primary chambers that the levels of liquid in the chambers, for predetermined set-value flows, are at least approximately equal. In the simplest case, this condition is satisfied if the total volume of the secondary chambers, through which the material flows in parallel, is substantially equal to the volume of the primary chamber. Given a number of secondary chambers, the flow in the primary chamber and hence the heat transfer can be intensified if the primary chamber has its own drive means for the forced flow for each of the secondary chambers.

In order to promote a fuller understanding of the above and other aspects of the present invention, some embodiments will now be described by way of example only, with reference to the accompanying drawings in which: Fig. 1 is a diagrammatic longitudinal section through a first embodiment of the invention.

Fig. 2 is a similar section to Figure 1 of a further embodiment, taken on the line II-II in Figs. 3 and 4.

Fig. 3 is a section on the line III-III in Fig. 2.

Fig. 4 shows a third embodiment of the invention in plan view, a number of secondary chambers being provided in one tank.

Fig. 5 is a section on the line V-V in Fig.

4 while Figs. 6 and 7 show two further embodiments in similar views to that of Fig. 4.

Like parts in the various Figures have been given like references in the following description.

Referring first to the embodiment of Figure 1, there is shown a cylindrical tank 1 which is of circular cross-section, is formed, for example, of metal and is covered with insulation 2, such as mineral or glass wool, to reduce heat loses to the surroundings.

The tank 1 is provided with a closed circular cylindrical cross-section partition 3 made of a material which is a good thermal conductor, the partition separating and defining a secondary chamber 4 and a primary chamber 5. The two chambers 4 and 5 preferably have approximately the same volumetric capacity.

At their top edges, the side wall of the tank 1 and the partition 3 have flanges indicated at 6 to 8 on which lids 9 and 10 for the chambers 5 and 4 rest respectively, the lids being secured on the tank 1 by a suitable means such as threaded studs and nuts.

Agitators 11 and 12 are fitted into the lids 9 and 10 respectively as a means of producing a circulating flow of liquid in the chambers 4 and 5 being driven by the motors 13 and 14. As will be seen from Fig. 1, agitator 12 is disposed eccentrically from the central axis in the secondary chamber 4 and may be set at an angle to the vertical in order to bring about a circular flow guided around the inside of the wall 3. In addition, the agitator 11 may be disposed at an angle to the vertical in the primary chamber 5 to improve the formation of a circular flow in that chamber 5. The generation and maintenance of the forced flow, the movement of which may be made substantially horizontal or vertical or may have components in both directions, can also be effected by other suitable means. It is also possible to provide a number of agitators in each of the chambers 4 and 5, and in addition the agitator for chamber 5 may be disposed in the side wall of the tank 1.

The two chambers 4 and 5 of the tank 1 has inlet and outlet connections indicated by arrows at the pipes 15 to 18 for the supply and discharge of the materials between which heat is to be exchanged, the higher temperature material preferably being fed to the secondary chamber 4 and the lower temperature material to the primary chamber 5 because of the centrifugal forces produced by the circular flow.

In order to avoid a direct short-circuit flow in the secondary chamber 4, particularly in continuous operation, the feed connection pipe 16 for the material is extended some way into the secondary chamber 4.

Alternatively, other suitable means may be provided for preventing a short-circuit flow.

Since the agitators may tend to become clogged in some cases, it is possible to use non-clogging pumps, such as sludge pumps, of known construction per se. These may be disposed in the chambers 4, 5 mounted, for example, in the lids 9, 10, or alternatively just one such pump may be provided in the chamber 5 and the agitator 12 be retained in the secondary chamber 4. The primary chamber 5 is then preferably charged with the material to be heated, such material in practice generally containing coarser impurities than the material from which heat is to be taken.

An arrangement of this last kind is shown in Figs. 2 and 3. Instead of the agitator 11 being driven by the motor 13, a pump 20 is provided in communication with the chamber 5 to maintain the flow of material for the heat transfer. The pump 20 is a nonclogging sludge pump which for space reasons, is preferably disposed outside the chamber 5. It is driven by a motor 21 mounted in the lid 22 of a separate pump housing 23. The housing 23 includes an axial-intake for the pump 20, and is also enclosed by the insulation 2. The axial intake is connected to the primary chamber 5 via a suction pipe 24 leading from the side wall of the tank 1. The material delivered by the pump 20 flows back to the chamber 5 via a pressure pipe 25 (Figure 3), which in turn leads tangentially back to the side wall of the tank 1, so that the inflow of material produces the required circular flow in chamber 5.

In the example shown in Figs. 4 and 5, the tank 1 contains a plurality of closed partitions 3, by means of which the three secondary chambers 4 are defined in a primary chamber 5 surrounding them. The total volume of the chambers 4 and the volume of the chamber 5 are again preferably substantially equal.

The construction of the heat exchanger shown in Fig. 4 corresponds in detail to that shown in Figs. 2 and 3, e.g. in respect of the agitators and pumps.

However, as a modification of the previous example, each of the secondary chambers 4 has a connection 16 and 18 for the supply and discharge of heat exchange material, the supply line 16 for the material again being extended into the respective chamber 4.

In order that the flow may pass through the secondary chambers 4 in parallel, the feed pipes to the connections 16 radiate from a common feed pipe 30 while the discharge connections 18 similarly lead into a common header or pipe 31. The feed of heat exchange material, preferably that which is to take up heat, to the primary chamber 5 is by way of a connection 15 and the heated material leaves the tank 1 via a connection 17 (Fig. 2).

Circular flow is ensured in the primary chamber 5 as previously described by means of one or more pumps 20, to maintain a good circular flow in the relatively extensive primary chamber 5, each of the secondary chambers 4 being provided with its own means for circulation.

All the pumps 20 jointly produce the required circular flows in the primary chamber 5 as indicated by arrows 11 in Fig.

4. Since pumps 20 are of a type which do not clog, it may be that under certain conditions, depending upon the direction of heat transfer, it is preferable to charge the primary chamber 5 with the material which is to take up heat, which generally contains coarser impurities than the material which is to give up heat.

The flow in the chamber 5 can be guided, with the arrangement shown in Fig. 4, if the pumps 20 are mounted alternately in opposite walls of the tank 1, as shown, giving a sinusoidal main flow surrounding the secondary chambers 4 in chamber 5.

In Fig. 6 the tank 1 has a circular cylindrical shape in which three secondary chambers 4 are illustrated positioned at the apices of an equilateral triangle. This construction of the heat exchanger may be used if one of the flows of material for treatment is greater than the other, since with this form there is generally a larger volume for the primary chamber 5 than for the secondary chambers 4.

Another arrangement of the secondary chambers for very large throughputs is shown in Fig. 7, which corresponds substantially to Fig. 4 in its presentation. If required, in this arrangement a number of feed and discharge pipes may be provided for the primary chamber, although these are not shown in the Figure.

As already stated, only a relatively moderate heat exchange between the materials can be obtained with the singlestage heat exchangers illustrated, in which substantially equal quantities of hot and cool materials participate in the heat exchange. Higher output temperatures of the material receiving heat can be obtained if two or more units, of the examples illus trated, are arranged in series and the two materials flow through them consecutively, the two flows being in countercurrent to one another; a multi-stage plant of this kind is not shown in detail because its construction does not differ in principle from the heat exchangers illustrated.

WHAT WE CLAIM IS: - 1. A heat exchanger for heat exchange via a heat conducting partition between materials comprising liquids mixed with solids, comprising a primary chamber which has primary inlet and outlet means for a first said material to be passed through it and means comprising at least one pump for causing a forced flow of said first material in the primary chamber; and a secondary chamber defined by a continuous heat conducting partition to be within and peripherally surrounded by the primary chamber, said secondary chamber having secondary inlet and outlet means for a second said heat exchange material to be passed through it and means comprising an agitator for causing a forced flow of said second material in the secondary chamber.

2. A heat exchanger as claimed in Claim 1, in which a plurality of such secondary chambers are so defined within said primary chamber, each being provided with means for causing forced flow of material therein, the inlet and outlet means of the secondary chambers being connected in parallel.

3. A heat exchanger as claimed in Claim 1 or 2, in which the primary chamber is symmetric about an axis.

4. A heat exchanger as claimed in Claim 1 or 2, in which each secondary chamber is symmetric about an axis.

5. A heat exchanger as claimed in any preceding Claim in which the primary chamber pump is disposed outside the chamber and is connected thereto by a suction and a delivery pipe each extending through the side of the chamber.

6. A heat exchanger as claimed in any preceding Claim in which the primary chamber is provided with respective means for causing a forced flow therein associated with each secondary chamber defined therein.

7. A heat exchanger as claimed in any preceding Claim in which the primary chamber is provided with external thermal insulation.

8. A heat exchanger as claimed in any preceding Claim in which the total volume of the secondary chamber or chambers is related to the volume of the primary chamber so that the level of material in the primary and secondary chambers for a predetermined flow through them is substantially equal.

9. A combination of two or more heat exchangers as claimed in any preceding Claim connected with their primary and secondary chambers in series for flow of material therethrough, the flow of material through the primary chambers being arranged in the opposite direction to the flow in the secondary chambers.

10. A heat exchanger as claimed in any one of the preceding Claims in which the total volume of the secondary chamber or chambers is substantially equal to the volume of the primary chamber.

11. A method of operating a heat exchanger as claimed in any preceding Claim, in which heat transfer between material in the primary and secondary chambers is controlled by varying the time for which the means for causing forced flow in the chambers is operated.

12. A heat exchanger substantially as herein described with reference to the accompanying drawings.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. trated, are arranged in series and the two materials flow through them consecutively, the two flows being in countercurrent to one another; a multi-stage plant of this kind is not shown in detail because its construction does not differ in principle from the heat exchangers illustrated. WHAT WE CLAIM IS: -

1. A heat exchanger for heat exchange via a heat conducting partition between materials comprising liquids mixed with solids, comprising a primary chamber which has primary inlet and outlet means for a first said material to be passed through it and means comprising at least one pump for causing a forced flow of said first material in the primary chamber; and a secondary chamber defined by a continuous heat conducting partition to be within and peripherally surrounded by the primary chamber, said secondary chamber having secondary inlet and outlet means for a second said heat exchange material to be passed through it and means comprising an agitator for causing a forced flow of said second material in the secondary chamber.