GB2065859A - Shell and tube heat exchanger for use with at least three fluid streams - Google Patents

Abstract

A shell and tube heat exchanger (10) comprises a plurality of tube and/or tube bundles (25, 26) communicating with headers (13, 14) at both ends of the tubes or tube bundles. Both headers (13, 14) are divided in a similar manner by partitions (15, 22) into at least two chambers (16, 17 and 23, 24) per header so that fluid passes through one tube bundle (25) between a header chamber (16) of one header (13) and a header chamber (23) of the other header (14) independently of fluid passing through another tube bundle (26) from a different header chamber (17) of the said one header (13) to a different header chamber (24) of the said other header (14). The heat exchanger enables heat exchange to take place between at least two heat source fluids and a heat sink fluid (or vice-versa) in a space which is of a similar size to that of a shell and tube heat exchanger designed for effecting heat exchange between two fluids only. <IMAGE>

Description

SPECIFICATION Shell and tube heat exchanger for use with at least three fluid streams The present invention relates to a shell and tube heat exchanger for use with at least three fluid streams.

At many industrial sites, there are fluid streams whose heat content is relatively low and/or which are of variable and/or intermittent availability. The exploitation of heat from such fluid streams has heretofore been considered generally uneconomic due to the relatively high cost of providing suitable heat exchangers and their ancillary equipment and also due to the high demand for siting space for such additional heat exchangers at convenient locations.

The present invention provides a heat exchanger comprising a shell for containing a fluid, a plurality of heat exchanger tubes and/or tube bundles within the shell, and two headers, one header being at one end of the tubes and/or tube bundles and communicating therewith, and the other header being at the other end of the tubes and/or tube bundles and communicating therewith, both headers being partitioned into an equal number of header sections in such a way that each tube or tube bundle communicates at each end with only one header section whereby a fluid passing from a header section at one end of a tube or tube bundle to a header section at the other end of the tube or tube bundle cannot mix with fluid in another header section, each header section at one end of a tube or tube bundle having an opening for the entry of fluid, and there being an opening for the exit of fluid either at the header section at the said one end or at the header section at the other end of the tube or tube bundle.

Preferably, one header is fixed relative to the shell and the other header is a floating header, and preferably, the said openings for the entry of fluid and the exit of fluid are all at the same end of the tubes and/or tube bundles.

For ease of maintenance, each header section may have a respective cover plate which is removable independently of the cover plate(s) of the other header section(s).

The invention also provides the combination comprising apparatus which operates to provide a heat source fluid or a heat sink fluid and at least one heat exchanger, as described above, connected for receiving on the shell side at least some heat source fluid or heat sink fluid from the said apparatus and arranged for passing a plurality of discrete fluid streams separately via respective tubes and/or tube bundles in heat transfer relationship with the heat source fluid or heat sink fluid for the separate transfer of heat between each of the said discrete fluids and the heat source fluid or heat sink fluid.

The said apparatus may comprise a distillation column and the heat exchanger may serve as a vapourizer (e.g. a kettle reboiler or a thermosyphon reboiler) or a condenser or a cooler of a preheater.

The distillation column and heat exchanger may be so connected that a fluid stream passing out of the distillation column will pass through the shell side of the heat exchanger in indirect heat exchange relationship with different fluid streams passing through the respective tubes and/or tube bundles.

The invention is now further described with reference to some non-limitative embodiments thereof given by way of example only, and with reference to the accompanying diagrammatic drawings, in which: Figure 1 is a vertical cross sectional elevation of a heat exchanger of the invention, with some parts omitted; Figure 2 is a view of the left-hand end cover of the heat exchanger of Figure 1; Figure 3 is a schematic illustration of a heat exchanger of the invention in use in one type of service; Figure 4 is a radial cross-section through a fixed header of the heat exchanger of Figure 3; Figure 5 is a schematic illustration of a heat exchanger of the invention in use in another type of service; and Figure 6 illustrates the use of a heat exchanger of the invention in service as a condenser for overheads from a distillation tower.

Referring first to Fig. 1 , the heat exchanger is generally designated by reference 10 and comprises a shell 11 closed at one end by a dished cover 1 2 and closed at the opposite end by a fixed header 13. Within the volume enclosed by the shell 11 and dished cover 12 is a floating header 14. The fixed header 13 is divided by a partition 1 5 into two non-communicating header sections or chambers 16 and 17. Chamber 16 is provided with a fluid inlet port 18 and a fluid exit port 19, and chamber 17 is similarly provided with a fluid inlet port 20 and a fluid exit port 21.

Floating header 14 is divided by a partition 22 into two non-communicating header sections or chambers 23 and 24, and chamber 16 of the fixed header 13 communicates with the chamber 23 of the floating header 14 via a plurality of heat exchange tubes 25. In a similar manner, the chamber 1 7 of the fixed header 1 3 communicates with the chamber 24 of the floating header 14 via a plurality of heat exchange tubes 26. The chambers 16 and 17 of the fixed header 13 are provided with vertical partitions (not shown) on the well-known manner to ensure that fluid circulates between the headers through each of the respective sets of communicating tubes 25, 26 in the desired directions.

The shell 11 may be provided with an inlet (not shown) and an outlet (not shown) for the passage of a fluid through the shell in indirect heat exchange relationship with fluids in the tubes 25 and 26. Alternatively, the shell 11 may be adapted for containing a heat transfer fluid under suitable pressure such that the lower tubes 26 are immersed in liquid and the upper tubes 25 are in contact with the vapour of the heat transfer fluid.

In this arrangements, the heat transfer fluid may be employed to transfer heat from a hot fluid (e.g.

a hydrocarbon stream) in tubes 26 to a cool fluid (e.g. water) in the tubes 25.

As will be appreciated from Figure 2, the outer end of the fixed header 13 is closed by an end cover comprising an upper cover plate 27 and lower cover plate 28, both of which cover plates are independently removable. In a corresponding manner, the outer end of the floating header is closed by an upper cover plate 29 and a lower cover plate 30, both of which cover plates are independently removable. The provision of separate, independently removable upper and lower cover plates would not usually be necessary where leakage of fluid(s) between the chambers 1 6 and 1 7 is acceptable.

Reference is now made to Figures 3 and 4 which show a floating head shell-and-tube heat exchanger in accordance with the invention. The fixed header 30 is divided by a partition 36 into two non-communicating chambers 31 and 32 and the floating header 33 is similarly divided by a partition 37 into two non-communicating chambers 34 and 35. The chambers 31 and 34 communicate via heat exchange tubes 38 and the chambers 32 and 35 communicate via heat exchange tubes 39.As will be seen from Figure 4, the chambers 31 and 32 of the fixed header 30 are divided by vertical pass partitions 40, 41 so that fluid passed into the inlet side of the chamber 31 from inlet line 42 circulates along the tubes 38 which communicate with the inlet side of the chamber 31 to the floating header 33 and returns to the outlet side of the chamber 31 on the opposite side of the vertical pass partition 40 and exit therefrom into outlet line 43. In a similar manner, the pass partition 41 ensures that fluid entering the inlet side of the chamber 32 from inlet line 44 circulates along some of the tubes 39 to the floating header 33 and returns along the other tubes 39 to the outlet side of the chamber 32 and passes therefrom into an outlet line 45.

The shell 46 is provided with three openings 47, 48 and 49. Openings 47 and 48 may both be employed for the entrance of shell side fluid and opening 49 for the exit of shell side fluid. The interior of the shell 46 may be furnished with baffles, in the conventional manner, to promote the desired type of flow of the shell side fluid.

Apart from instances wherein the heat exchanger of the invention is employed as a kettle reboiler, the heat exchanger will usually have a horizontal shell-side baffle.

When the heat exchanger of Figures 3 and 4 is in use, the shell-side fluid may be a heat sink for heat available from the tube-side fluids. For example, a heavy stream from a distillation tower (not shown) may be passed along a line 50 to the shell-side inlets 47 and 48, and recovered, after being heated in the heat exchanger, in return line 51 from outlet 49 for recirculation (at least in part) to the distillation tower. The source of heat for heating the heavy stream supplied via line 50 may be the fluid circulated via the upper tubes 38 or the lower tubes 39 or both sets of tubes 38 and 39. Thus, if the upper tubes 38 are supplied with a heat source fluid such a stream or hydrocarbons at a relatively high temperature from a source of heat, additional steam or hydrocarbons, as available, can be circulated via the lower tubes 39 so that the heat requirement in tubes 38 is reduced.Suitable controls (not shown) which are well-known in the art may be provided to ensure that when heat is furnished to the shell-side fluid from the lower tubes 39, the temperature of the heated steam in return line 51 is maintained at its set point by reducing the amount of fuel which must be burned to provide the heat recovered in the heat exchanger, thereby economizing on the use of fuel when circumstances permit.

A feature worth noting is that with good design, the heat exchanger, of the invention may occupy the same plot space (approximately) as, and only slightly more volume than, a heat exchanger which is not capable of utilizing heat from an additional hot fluid stream. Using known heat exchangers, not in accordance with this invention, an additional plot space would be required to accommodate an additional heat exchanger to recover heat from the additional hot fluid stream, and such additional plot spaces are not usually conveniently available. Thus, even in the relatively crowded surroundings of a distillation tower, it is relatively easy to accommodate a heat exchanger in accordance with the invention and to increase the efficiency of primary fuel utilization.

Figure 5 shows a heat exchanger according to the invention arranged for use as a thermosyphon reboiler in a manner somewhat similar to that described in relation to Figures 3 and 4, but in an arrangement more suited to use two sources of heat of which the upper one is always hotter than the lower one.

As depicted, the shell-side opening 48 on the lower side of the shell 46 is utilized bs the inlet for reboilerfeed from line 50 and the shell-side opening 47 on the upper side of the shell 46 is utilized as the outlet for heated reboiler feed into reboilerreturn line 51.

Heat supplying fluids are circulated to the upper section 31 and lower section 32 of the fixed header 30. The fluid supplied to the upper header section 31 via line 42 and exiting therefrom via line 43 after passage through the upper tube bundle 38 is supplied at a higher temperature than the fluid passed to the lower header section 32 from line 44 and exiting therefrom via line 45 after circulating through the lower tube bundle 39.

It will be appreciated from the foregoing that the heat exchanger of the invention may be employed to recover heat which is in addition to that which has heretofore been recovered or used, and which additional heat is available from heat sources of varying or variable heat content -- e.g., from constantly-available or intermittent-available sources of heat and/or at relatively low temperatures, and that such additional recovery of heat may be achieved by the provision of suitable additional fluid-conveying pipework to the site of the heat exchanger of the invention, thereby avoiding the usual drawback of employing additional heat recovery equipment which occupies additional sites.

Reference is now made to Figure 6 wherein a floating head heat exchanger 60 in accordance with the invention and having its fixed header 61 and its floating header 62 divided into upper and lower sections by respective horizontal partitions 63,64 is employed as a condenser for overheads from a distillation tower 65.

The said overheads pass via line 66 to an opening 67 on the upper side of the shell 68 of the heat exchanger 60 and after passage through the shell, the cooled and partially or totally condensed overheads are recovered from an opening 69 on the lower side of the shell 68 and pass therefrom via line 70 to a reflux drum 71.

A relatively warm heat recovery fluid is passed from an inlet line 75 to the upper bank or bundle 74 of heat exchange tubes via the upper section 72 of the fixed header 61 and, after recovering heat from the hotter overheads stream on the shell side, is recovered from the upper section 72 at an increased temperature and passed via an outlet line 76 to wherever its heat content may be best utilized.

A relatively cooler heat recovery fluid is passed from an inlet line 77 to the lower bank or bundle 78 of heat exchange tubes via the lower section 73 of the fixed header 61, and is recovered in an outlet line 79 at an increased temperature after removing heat from the shell-side stream passing in heat exchange relationship with the lower tube bundle 78.

Depending upon the conditions of operation, the heat exchanger 60 may be supplied with only one of the two heat recovery fluids, or alternatively, the flow rate of one or both heat recovery fluids may be automatically regulated.

In the embodiments described, the heat exchanger is adapted for use with three fluid streams. However, it will be appreciated that by the provision of additional partitions in the headers, more than two tube-side streams could be circulated through the heat exchanger. In addition or alternatively, the shell side may be provided with suitable partitions so that more than one shell-side fluid may be passed in heat exchange relationship with the heat exchange tubes.

Claims (9)

1. A heat exchanger comprising a shell for containing a fluid, a plurality of heat exchange tubes and/or tube bundles within the shell, and two headers, one header being at one end of the tubes, and/or tube bundles and communicating therewith, and the other header being at the other end of the tubes and/or tube bundles and communicating therewith, both headers being partitioned into an equal number of header sections in such a way that each tube or tube bundle communicates at each end with only one header section whereby a fluid passing from a header section at one end of a tube or tube bundle to a header section at the other end of the tube or tube bundle cannot mix with fluid in another header section, each header section at one end of a tube or tube bundle having an opening for the entry of fluid, and there being an opening for the exit of fluid either at the header section at the said one end or at the header section at the other end of the tube or tube bundle.

2. A heat exchanger as in claim 1 in which one header is fixed relative to the shell and the other header is a floating header.

3. A heat exchanger according to claim 1 or claim 2 in which the said openings for the entry of fluid and the exit of fluid are all at the same end of the tubes and/or tube bundles.

4. A heat exchanger according to any one of claims 1 to 3 in which each header section has a respective cover plate which is removable independently of the cover plate(s) of the other header section(s).

5. A heat exchanger substantially as hereinbefore described with reference to the accompanying drawings.

6. The combination comprising apparatus which operates to provide a heat source fluid or a heat sink fluid and at least one heat exchanger according to any one of claims 1 to 5 connected for receiving on the shell side at least some heat source fluid or heat sink fluid from the said apparatus and arranged for passing a plurality of discrete fluid streams separately, via respective tubes and/or tube bundles, in heat transfer relationship with the heat source fluid or heat sink fluid for the separate transfer of heat between each of the said discrete fluids and the heat source fluid or heat sink fluid.

7. The combination according to claim 6 in which the apparatus comprises a distillation column and the heat exchanger serves as a vapourizer or a condenser or a cooler qr a preheater.

8. The combination of claim 7 in which the distillation column and heat exchanger are so connected that a fluid stream passing out of the distillation column will pass through the shell side of the heat exchanger in indirect heat exchange relationship with different fluid streams passing through the respective tubes and/or tube bundles.

9. The combination of any one of claims 6 to 8 substantially as hereinbefore described with reference to the accompanying drawings.