Patent Application
20100282450
The present invention relates to a heat exchanger shell assembly and a method of assembling a heat exchanger shell structure.
A shell-and-tube heat exchanger is an indirect heat exchanger. Heat is transferred between a fluid passing through the tubes of a tube bundle (the tube side) extending in a heat exchanger shell, and a fluid passing through the space outside the tubes (the shell side). Details of shell-and-tube heat exchangers can for example be found in Perry's Chemical Engineers' Handbook, 7th edition, 1997, McGraw-Hill Inc., page 11-33 to 11-46.
Shell-and-tube heat exchangers can be distinguished according to the number of passes for fluid in the shell side and in the tube side. In each pass, the respective fluid flows substantially along the entire length of the heat exchanger, which is typically horizontally elongated. In multiple shell passes, the fluid flow meanders a plurality of times back and forth the length of the shell.
The heat exchanger shell has inlet and outlet nozzles for the shell-side fluid. For a single shell-side pass heat exchanger, an inlet nozzle is typically arranged at one end of the shell, in particular on top of the shell, and an outlet nozzle is arranged at the opposite end, in particular at the bottom. The same is true for an uneven number of passes. In case of two shell-passes (or in fact an even number), the inlet and outlet nozzles are suitably arranged at the same end.
When retrofitting a heat exchanger such as for modified use or improved performance, it can be desired to adapt the number of passes. For example, if a tube bundle with transverse supports comprising expanded metal baffles is to be installed, a higher number of shell-side passes can be preferred for optimum performance. Expanded metal is produced from sheet metal that is slit and expanded. Expanded-metal baffles are for example known from International patent applications with publication Nos. WO 2003/067170, WO2005/015107 and WO2005/061982, incorporated herein by reference, and turn out to have significant advantages in practice, such as less fouling tendency, lower pressure drop, and improved heat transfer due to turbulence created in the shell fluid. In expanded metal baffles spanning the cross-section of the available shell pass, the flow of shell fluid is longitudinal. In a conventional heat exchanger using segmental baffles, the flow meanders even with one shell side pass along the main flow path in the shell, so that the effective length of the shell-side flow is longer than the longitudinal extension of the shell. When expanded metal baffles are used, it is preferred to use a higher number shell-side passes to optimise the shell flow path length, and this can particularly be done in view of the low pressure drop caused by the expanded metal baffles.
A problem is encountered when the number of shell-side passes is to change between even and uneven, since then one of the nozzles is unsuitably located. In principle, it can be envisaged to arrange an internal flow path for shell-side fluid from one end of the shell to the other. It is an object of the invention to provide a heat exchanger shell arrangement that allows to modify the number of shell-side passes.
To this end the present invention provides a heat exchanger shell arrangement comprising
an outer shell having a nozzle at its lower side;
an inner shell member within the outer shell and forming an intermediate space with the outer shell, the inner shell member having an opening at its lower side;
wherein the arrangement further comprises a seal member arranged to fit in the intermediate space, the seal member providing a sealed passageway for fluid between the opening and the nozzle.
By arranging an inner shell member, it is possible to direct shell side fluid from one shell end to the other, using the intermediate space. The inner shell space, in which the actual heat exchange with a tube bundle is to take place, needs to be sealed against the intermediate space, otherwise shell side fluid could flow along a shortcut route, lowering heat transfer efficiency. A seal member between inner shell member and outer shell is provided for this purpose. Preferably, the seal member is a gravity seal member, wherein sealing force is provided by the gravity force exerted on the seal member by the inner shell member. In particular, the seal member is not connected to at least one of the outer shell and the inner shell member, preferably it is not connected to both the outer shell and the inner shell member. This allows particularly easy installation of the shell arrangement, since the sealing member can be pushed into the intermediate space after the inner shell member is arranged in the outer shell, and sealing is simply accomplished lowering the inner shell so that its weight, suitably together with the weight of the tube bundle, exerts the sealing force for the sealing member. Moreover, by not connecting the inner and outer shells via the seal member, different temperature expansion between the outer shell and inner shell member can be accommodated.
In a suitable embodiment, the seal member is a plate having upper and lower surfaces that are arranged to conform to the outer shell and inner shell member surrounding the nozzle and the opening, preferably comprising a gasket at the upper and/or lower surface.
In a particular embodiment, the nozzle forms a first nozzle of the outer shell and the opening forms a first opening of the inner shell member, the outer shell further comprises a second nozzle and the inner shell member comprises a second opening, and the second nozzle and the second opening are arranged to be fluid communication via the intermediate space.
The invention further provides a method of assembling a heat exchanger, comprising
providing an outer shell having a nozzle at its lower side and an inner shell member having an opening;
sliding the inner shell member into the outer shell to form an intermediate space with the outer shell and to reach a position in which the opening is above the nozzle;
arranging the inner shell member in a lifted position in the outer shell;
sliding a seal member into the intermediate space, the seal member providing a passageway for fluid between the opening and the nozzle; and
lowering the inner shell member so that the gravity force exerted on the seal member acts as sealing force.
The method is particularly useful for revamping a heat exchanger, wherein the outer shell is maintained and a new tube bundle is arranged within an inner shell member.
The invention will now be described in more detail and with reference to the accompanying drawings, wherein
Where the same reference numerals are used in different Figures, they refer to the same or similar objects.
Reference is made to
A seal member 25 is placed in the intermediate space 16, the seal member providing a sealed passageway 26 for fluid between the outlet opening 23 and the outlet nozzle 9.
The seal member 25 is only very schematically shown in
For optimum sealing the seal member is provided with top and bottom gasket rings 32,33, suitably arranged in a circular groove seating machined into plate 28 of the seal member. A suitable gasket material is polytetrafluoroethylene (PTFE) for temperature resistance up to 250 degree C. Good results have been obtained with 100% expanded PTFE (e-PTFE), multidirectional orientated fibre structure, type Gore-Tex Series 300. The temperature range of this material is between −240° C. and +250° C., with allowable peak temperatures up to 315° C. A PTFE tape of 3 mm thickness was used. For the sealing of the floating head and baffle sealing tape with a thickness 2 mm was used. Before placement of the gasket rings, the seating was cleaned with alcohol and the gasket was glued into the seating.
Thus, the seal member 25 is arranged to seal by gravity. It can be introduced loosely into the intermediate space 16 while the inner shell is lifted. Sealing force is provided by the gravity force exerted on the seal member by the inner shell member, and sealing is achieved without the seal member being fastened to either one of the shells 4,5. After installation of the seal member, the inner shell member does not rest on the sliding strips 24 in the vicinity of the outlet opening 23.
The inner shell member houses the tubes 35,36 extending from the tube sheet 12 to floating head 16, and the tubes contribute to the weight pressing on the seal member. The weight can for example be more than 1000 kg such as 5000 kg. A longitudinal baffle 38 with an opening 39 serves to provide a two-pass configuration of the shell side. For mechanically mounting the longitudinal baffle, the inner shell member can be constructed of upper and lower half shells, between which the longitudinal baffle is clamped.
Turning now to the tube side of the heat exchanger 1, only few tubes 35,36 are shown for the sake of clarity. The tube side of the heat exchanger 31 is indicated with dots. In this embodiment the tube side has a two-tube-pass arrangement. The tube side has an inlet 41 to a tube inlet header 43. The tube inlet header is in fluid communication with the lower part of the tube bundle, tubes 36 which extend to the tube end sheet 44 connected to the floating head 14 which in turn is in fluid communication with the upper part of the tube bundle, tubes 35 extending into the tube outlet header 47 where the outlet 49 from the tube side is arranged. The inlet and outlet tube heads 43,47 are separated by a horizontal plate 51 extending horizontally along in the centre of the outer shell 4 from the shell end to the tube sheet 12 in which the tubes are fixed. The tube sheet is secured to the shell by flanges (not shown), through which the inlet end of the shell can be opened for inserting or removing the internals. Flanges through which the end part of the shell can be removed are also arranged at the rear end near floating head 14.
The tube end sheet 44 at the opposite end also fixes the tubes, but unlike the tube sheet 12, the tube end sheet 44 and the floating head 14 to which it is connected, are not connected to the shell 34, i.e. the end header is floating. This allows thermal expansion of the tubes within the shell. Instead of an end header, which receives and distributes all tube fluid, also separate U-tubes could be applied.
The tubes are supported by a plurality of transverse baffles 65. They can in particular be expanded metal baffles, but rod baffles or other baffles can also be applied. In
Normal operation of the assembled heat exchanger 1 will now be discussed. When the heat exchanger is used in a crude preheat train of a crude distilling unit, tube-side fluid can be (cold) crude oil and shell-side fluid can be (hot) long residue from the crude distillation unit. For such an application with considerable fouling risk, expanded metal baffles in the shell side are advantageous because they suppress fouling. Tube-side fluid is passed via inlet 41 and tube inlet header 43 along the tubes 36, and further via the floating head 14 to along the upper part of the tube bundle to outlet header 47 and outlet 49. During that passage, it is heated by exchanging heat with the shell side fluid.
Hot shell-side fluid is introduced via inlet nozzle 8 into the outer shell, where it flows along the intermediate space towards the inlet 21 of the inner shell member. This inlet is formed of a plurality of holes spread around the upper part of the inner shell member. In this way an optimum distribution of shell fluid around the tubes 35 is achieved. The shell-side fluid flows towards the tube sheet 12, turns via the opening 39 and continues towards the outlet 23. From outlet 23 it passes through the passageway 26 formed by the seal member to the outlet nozzle 9, with a lower temperature than at the inlet nozzle 8.
The lower half of the intermediate space (annulus) between outer shell 4 and inner shell member 5 is filled with non- or slow flowing shell fluid. This fluid will adopt a temperature somewhere near the tube side inlet temperature. Since the seal member does not interconnect outer shell 4 and inner shell member 5, they can thermally expand differently in response to different temperatures they will have in the course of operation.
Now a method of assembling the heat exchanger shell structure 2 of
If cleaning of the heat exchanger is required, it can be disassembled in reverse order, cleaned, and assembled again.
| Number | Date | Country | Kind |
|---|---|---|---|
| 07109296.9 | May 2007 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP2008/056487 | 5/27/2008 | WO | 00 | 5/4/2010 |
