Method to Control Fluid Flow Variations Among Fluid Tubes of Heat Exchangers in Transfer Line Exchangers and Like Applications

Abstract

Tube-bundle heat exchangers are commonly used to quench reacting fluids to drop the temperature of the reacting fluid below a specific temperature which cuts off undesirable chemical reactions in a minimal time as practical. A common commercial application is production of olefins. Shell and tube type and bundles of tube in tube exchanges are used in this application, the method is applicable to both. Significant variations in reacting fluid mass flow rates in the tubes of the tube-bundle can cause sub-optimal performance of the process. By placement of precise partial obstruction to flow of the reacting fluids at the tube exits to an outlet plenum chamber, these flow variations can be controlled. By adding remotely readable temperature measurement, and making the obstructions adjustable, the operator of the production facility can minimize production losses due to the variations in flow between tubes in the tube-bundle.

Claims

1) A method to reduce variation in mass flow between individual tubes in a plurality of fluid tubes in a tube-bundle of a heat exchanger used to quench chemical reactions in the fluid, said heat exchanger comprising; a) an inlet plenum chamber from which the hot fluid flows into the tubes of the tube-bundle through an inlet tube-sheet, b) a plurality of fluid tubes in a tube-bundle used to cool the fluid with some form of pressure containing shell to contain a different cooling fluid, including either a shell and inlet and outlet tube-sheets, or a plurality of outer tubes with the fluid tubes forming a bundle of tube in tube heat exchangers surrounding each fluid tube, and joined at inlet and outlet tube sheets, c) an outlet plenum chamber where flow from each of the tubes in the tube-bundle merge, d) the imposition of some precision designed and positioned object or set of objects in the outflow of at least some portion of the individual tubes such that the fluid mass flow from those tubes is reduced by predictable amounts, the effect of which is to make individual tube flows predictable and allow them to be controlled.

2) Claim 1 where the object(s) inserted into the outflow of individual tubes are movable during operation of the heat exchanger such that the obstruction to fluid flow out of individual tubes in the tube-bundle is adjustable during operation.

3) Claim 1 where a remotely readable temperature indicating device is built into at least one of the objects used to reduce the mass flow in a given tube to allow measurement of the quenched fluid temperature.

4) Claim 1 where a remotely readable temperature indicating device is built into at least one of the objects used to reduce the mass flow in a given tube to allow measurement of the quenched fluid temperature, and where the object(s) inserted into the outflow of individual tubes are movable during operation of the heat exchanger such that the obstruction to fluid flow out of individual tubes in the tube-bundle is adjustable during operation.

5) A device to control variation in mass flow between individual tubes in a plurality of fluid tubes in the tube-bundle of a heat exchanger used to quench chemical reactions in the fluid where: a) the quenched fluid flows from an inlet plenum chamber, through an inlet tube-sheet manifold where the flow is distributed to individual tubes in the tube-bundle, b) a cooling fluid to which heat in transferred is contained by the tubes, inlet and outlet tube-sheets, and some form of shell either around all the tubes in the tube-bundle, or individual shells around individual tubes, c) an outlet plenum chamber where flow of the quenched fluid merges on leaving the tubes of the tube-bundle, d) a plurality of obstructing objects are placed on or near at least some of the tube exits to the exit plenum chamber, that can be arranged to partially obstruct the flow of the reacting gas from the tube into the outlet plenum chamber.

6) Claim 5 where the object(s) inserted into the outflow of individual tubes are movable during operation of the heat exchanger such that the obstruction to fluid flow out of individual tubes in the tube-bundle is adjustable during operation.

7) Claim 5 where a remotely readable temperature indicating device is built into at least one of the objects used to reduce the mass flow in a given tube to allow measurement of the quenched fluid temperature.

8) Claim 5 where a remotely readable temperature indicating device is built into at least one of the objects used to reduce the mass flow in a given tube to allow measurement of the quenched fluid temperature, and where the object(s) inserted into the outflow of individual tubes are movable during operation of the heat exchanger such that the obstruction to fluid flow out of individual tubes in the tube-bundle is adjustable during operation.

Description

BRIEF DESCRIPOTION OF THE DRAWINGS

[0013] For a proper understanding of the current invention, reference should be made to following detailed description taken in conjunction with the accompanying drawings, in which like parts are given like reference numerals, and wherein:

[0014] FIG. 1A is a horizontal center-line section view of a typical transfer line exchanger in the area of the inlet tube-sheet, and section view of the cone. The design shown is that of the inventor which follows the inventor's U.S. Pat. No. 8,672,021. The general arrangement of inlet cone and tube sheet with respect to gas side flow only is also similar in this design to those of Vollhard, and Albano et. al, or of Koontz. Arrows inside the cone indicate the general pattern of gas flow toward the inlet exchanger inlet tube-sheet. A number of tubes are in this design but only three are shown in this figure for clarity. The section in this figure becomes FIG. 1B.

[0015] FIG. 1B is a vertical section view of the transfer line exchanger inlet tube-sheet, this figure indicates where the FIG. 1A section slice is taken.

[0016] FIG. 2 is a horizontal section view of the exit tube-sheet and exit plenum chamber in the same plane as FIG. 1A showing the preferred embodiment of the present invention.

[0017] FIG. 3 is a horizontal section view of the exit tube-sheet and plenum chamber in the same plane as FIG. 1A showing an alternative embodiment of the present invention.

[0018] FIG. 4 is a detail view of a small part used in the alternative embodiment of the present invention.

DETAILED DISCRIPTION OF THE INVENTION

[0019] The current invention is a technique and device applied to a shell and tube, or tube in tube bundle type heat exchanger intended primarily for use to rapidly cool or quench thermally cracked hydrocarbon gasses to allow the production of olefins, it may however be used for other purposes. The invention in the preferred embodiment is shown in detail in FIGS. 1A, 1B and 2, a variation showing an alternative embodiment that also references figures is shown in FIGS. 3 and 4. In the primary application the intent is that the cracked gasses will flow up through the inlet cone (item 1). The transfer line exchanger in this application (item 5) will will be oriented such that the cracked gas inlet is on the bottom of the exchanger, through a tube-sheet (item 3). The general direction of gas flow inside the inlet cone is indicated by arrows (item 2). The gas flow proceeds into the transfer line exchanger through holes in the tube-sheet (item 3), into the gas tubes in the transfer line exchanger (item 4). Due to the nature of the geometry of flow in the inlet cone, and the high inertia of the crack-gas coming into the inlet cone, and as has been noted by others as discussed above, generalized zones of higher or lower crack gas pressure are formed across the tube-sheet. On examination of FIG. 1B,we note the pattern of inlet tubes (item 4), and note from experience a lower pressure zone, and middle pressure zone, the boundary between them roughly denoted by the phantom line labeled (item 6) in FIG. 1B. A high pressure zone would tend to form in the middle the boundary between the high pressure zone and the intermediate pressure zone would be denoted by a phantom line labeled (item 7) in FIG. 1B.

[0020] As previously mentioned, without use of the present invention, higher pressure in front of a tube inlet means higher mass flow rate in that tube, and necessarily lower flow rates in other tubes, this leads to sub-optimal quenching of the product, and lower product production rates for a given input stream. The present invention addresses this in FIGS. 2, 3, and 4. In FIG. 2 the outlet side of the transfer line exchanger is shown (item 5) with the outlet tube-sheet (item 8). The quenched crack-gas proceeds from the transfer line exchanger tubes (item 4) into the exhaust side cracked gas plenum chamber (item 9), then out an exit (item 18) to further processing. The general gas flow pattern within this plenum chamber is indicated with arrows (item 2). To facilitate control and adjustment of gas flow a rod (item 12) is placed in line with either all or some significant fraction of the gas tubes (item 4) in the tube-bundle. The position of each rod is separately adjustable along the axis of the gas tube. A small downward pointing rod cone cap or roughly conical cap (item 13) with at least one thermocouple at it's tip (item 16) is mounted on the tip of each rod. This conical shape when moved along the axis of the gas tube it is aligned with will alter the exhaust area of the tube and so the mass flow rate. Several means of forcing linear motion on the rod are possible. The means shown is to have screw threads on the rod contained in the screw thread chamber (item 10), along with a nut (item 15). That nut is supported on both sides with frames (item 14) affixed to the screw thread chamber such that turning the nut forces the rod to move linearly. The nut can be turned by any of several obvious means. Above the screw thread chamber is a rod end chamber (item 11) allowing for motion of the rods, and connection of the thermocouples, wires to which are strung in the hollow shaft of the rods. The screw thread chamber and rod end chamber can be filled with an inert gas of some type at a pressure slightly higher than that of the produced crack gas in the cracked gas plenum chamber (item 9) such that any leaking around the rod seals will be inert gas into the product stream, rather than the dangerously flammable cracked gas back into the screw thread chamber. The great advantage of this above embodiment over the other herein discussed is that it allows for adjustment of flow during operations, which can be based on information gained from the thermocouple(s) at each tube exit.

[0021] An alternative embodiment is shown in FIG. 3. In that figure the rod is replaced by a simple disk with a hole in it acting as an orifice (item 17). At least a large fraction of the transfer line exchanger gas tubes in this embodiment will have such disks affixed to them to increase the frictional pressure loss of the gas flow in that tube to balance the mass flow with other tubes in the tube-bundle.

TABLE-US-00001 PARTS LIST Part Number Description 1 inlet cone 2 arrow showing flow direction 3 inlet tube-sheet 4 gas tube 5 transfer line exchanger 6 boundary line between intermediate & low pressure zones on tube-sheet 7 boundary line between high & intermediate pressure zones on tube-sheet 8 outlet tube-sheet 9 cracked gas plenum chamber 10 screw thread chamber 11 rod end chamber 12 rod 13 rod tip cone cap 14 frame to support rod nut 15 rod nut 16 rod tip thermocouple 17 orifice disk 18 cracked gas plenum chamber outlet

[0022] Because many varying and different embodiments may be made within the scope of the inventive concept herein taught, and because many modifications may be made in the embodiments herein detailed in accordance with the descriptive requirements of the law, it is to be understood that the details herein are to be interpreted as illustrative and in a limiting sense.