WO2003056266A1 - Apparatus for carrying out a physical and/or chemical process, such as a heat exchanger - Google Patents

Abstract

A heat exchanger in which a medium to be treated or to be heated can be kept in a quasi-stationary, fluidized condition by means of a fluidized bed consisting of granular material (73). In the upper space of the heat exchanger a screen (15) is incorporated for blocking, while passing the medium, the access of the granular material (73) to an outlet (19). Furthermore, along the screen surface flow guide means are arranged which together form a flow channel (74) for guiding a flow of medium with granular material (73) to another outlet (21).

Description

Title: Apparatus for carrying out a physical and/or chemical process, such as a heat exchanger.

The invention relates to an apparatus for carrying out a physical and/or chemical process, such as a heat exchanger, comprising a reservoir provided with upwardly directed pipes, which pipes are received at a top and bottom in pipe plates and are in open communication with a top box and a bottom box, in which bottom box at least one distribution plate is arranged to support a fluidized bed consisting of granular material, which can be kept in a quasi-stationary, fluidized condition by means of a medium to be treated or to be heated, supplied via the bottom box and flowing through the pipes, and which top box is provided with a first outlet for discharging with a partial flow of medium granular material separated from the medium in the top box to a downcomer placed outside the reservoir for returning to the bottom box granular material separated from the medium, and which top box is further provided with a second outlet for discharging a main flow of medium from which the granular material is separated. Such an apparatus is described in the later published international patent applications PCT/NL00/00677 and PCT/NLOO/00678. In these apparatuses a separation of fluidized bed particles and flowing medium is realized in the top box. All the fluidized bed particles and a partial flow of flowing medium are discharged by means of the first outlet from the lower part of the top box to the external downcomer. The remaining flow of flowing medium without fluidized bed particles is discharged to the top of the top box. In both cases a relatively dense and stable fluidized bed extending over a specific height in the outlet box is built up in the top box. The structure of such a relatively dense and stable fluidized bed ensures that, during use, no fluidized bed particles are discharged from the top box with the main flow of medium. In the apparatus described in PCT/NL00/00677 this stable and relatively dense fluidized bed is realized in the top box by discharging a part of the flowing medium via perforated pipe extensions so that a smaller volume flow of flowing medium flows into the top box from the pipes. In the apparatus described in PCT/NLOO/00678 the granular material is separated from the medium under the action of gravity, and it is described that in the top box flow velocity reducing means may be incorporated to support the formation of a stable and relatively dense fluidized bed in the top box. The flow velocity reducing means may be designed as an expansion space but also as a flow resistance, such as a fluidized bed or a distribution plate in the outlet box, provided with throughflow openings.

Depending on the viscosity of the flowing medium, the flow velocity of the medium and the sizes and type of granular material, a stable and relatively dense fluidized bed can be realized with one or more of the above- described measures.

A drawback of realizing a stable and relatively dense fluidized bed in the top box is that such a bed extends only over a specific height of the top box, and that superjacent parts of the top box do not come into contact with the particles of the granular material. As a result, in the part of the top box located above the bed the abrasive action of the particles lacks, and there is a risk that deposits may be formed in the upper part of the top box. Such deposits can grow to considerable sizes and additionally decompose during operation and fall back into the fluidized bed in the top box and therefore inhibit a proper fluidization of the fluidized bed in the top box. It is also possible that relatively large parts of decomposed material are discharged with the fluidized bed particles to the external downcomer and cause blockages there.

A further drawback of the above-described measures is that, for instance through a suddenly increasing volume flow of the medium or a suddenly decreasing viscosity of the medium, yet particles of granular material are carried along from the top box to the second outlet and may cause problems downstream in the process.

The invention has for its object to provide an apparatus of the type mentioned in the opening paragraph, in which the above drawbacks can be avoided while retaining the advantages. To this end, the apparatus according to the invention is characterized in that in the top box between the first outlet and the second outlet a screen is incorporated for blocking, while passing the medium, the access of the granular material to the second outlet and that, furthermore, in the top box along a screen surface of the screen directed to the first outlet flow guide means are arranged which form with the screen surface a flow channel for guiding, during use, a flow of medium with granular material along the screen surface.

This ensures that the fluidized bed in the top box can be adjusted so that deposits are removed from a larger part of the top box, including the screen, under the influence of the abrasive action of the particles. In particular, by using the screen it is ensured that the access of the granular material to the second outlet is blocked. Furthermore, to inhibit particles filtered by the screen from remaining stuck in the screen holes through the pressure difference over the screen and the screen from being clogged, flow guide means are arranged in the top box along the screen surface directed to the first outlet so that a flow channel is formed with which a flow of medium with granular material is guided along the screen surface as an abrasive flow to inhibit clogging of the screen surface. The flow guide means may be designed, for instance, as a guide plate or guide pipe which extends at least partly along the screen surface.

Preferably, the flow guide means and the screen surface are placed convergingly to each other, such that in the flow direction of the flow channel the passage of the flow of medium with granulate decreases. This ensures that despite the fact that a part of the medium, when flowing along the screen surface, flows through the screen, yet a relatively high flow velocity of the flow of medium with separated granular material along the screen surface can be maintained and the abrasive action of the granular material may be great. By adjusting the screen surface and flow guide means such that the flow channel extends at least partly downward, it can be ensured that the flow medium with granular material can be guided along the screen surface at least partly under the action of gravity. Preferably, the flow channel then extends substantially downward. Advantageously, the flow channel may further be provided with a reservoir for granular material, preferably at the end of the flow channel along the filter surface. Elegantly, the flow channel may be connected with the first outlet, so that after the flow of medium with granular material has been guided along the screen surface through the flow channel, a partial flow of medium having therein granular material separated from the medium can be discharged to the first outlet.

Preferably, driven conveying means are then provided for conveying granular material from the flow channel to the first outlet, such as a screw conveyor arranged in a connecting trough between the flow channel and the first outlet, which is driven by a motor placed outside the top box via a shaft extending through the top box.

In a very advantageous embodiment of the invention, the flow guide means are formed by walls of a pot incorporated in the top box, which extend along a screen incorporated in the pot while enclosing the flow channel. Such a pot may be of, for instance, prismatic design, such as a block or cylinder, and be arranged in the top box in upward direction, while at a bottom a reservoir for collecting granular material is arranged which connects to the flow channel and is connected with the first outlet. The screen may then be arranged, for instance, coaxially and be designed, for instance, as a truncated pyramid or cone with a downwardly increasing cross-section, so that between the walls of the pot and the filter a flow channel is formed with a passage decreasing in the flow direction of the flow channel. Preferably, the screen is then, seen in upward direction, arranged in the top box between the first and the second outlet and is supported by, for instance, a separation plate, while the pot is placed below the separation plate as a collecting vessel while enclosing an inflow opening for the flow channel. An advantage of such a pot is that it can later be built into the top box of an existing apparatus.

The screen may be elegantly formed by a plate provided with holes, the diameter of which holes is smaller than the diameter of the granular material of the fluidized bed. Of course, the screen may also be formed in other manners, for instance by braided wire.

To support the cleaning action of the granular material, a scraper placed for movement along the screen surface may further be provided for scraping deposits off the screen surface. Further advantageous embodiments of the invention are outlined in the claims.

The invention will be explained in more detail with reference to an exemplary embodiment shown in a drawing. In the drawing:

Fig. 1 shows a diagrammatic cross-section of a heat exchanger according to the invention, comprising a top box, a collecting vessel, a screen with a divided discharge of flowing medium for conveying the granular material to the external downcomer.

Figs. 2A-2C show a variant of the embodiment of Fig. 1 by using in the lower part of the collecting vessel a mechanically driven screw conveyor by which the separated and collected granular material is conveyed to the external downcomer.

Figs. 3A-3C show a variant of the embodiment of Fig. 2 using again a screw conveyor for conveying the separated and collected granular material to the external downcomer. The figures are only diagrammatic representations of preferred embodiments of the invention. In the figures, similar or corresponding parts are denoted by the same reference numerals.

The manner of supplying flowing medium to the bottom box of the apparatus and returning granular material via the downcomer is already known to those skilled in the art and can be carried out in various manners, for instance as described in the international patent applications PCT/NL00/00677 and PCT/NL00/00678.

Fig. 1 shows a heat exchanger 70 comprising a reservoir 1 in which a series of upwardly directed risers 2 are provided which are received at the top and bottom in a lower pipe plate 71 and an upper pipe plate 72. Situated below the lower pipe plate 71 is a bottom box 7 in which at least one distribution plate 8 is provided to support a fluidized bed consisting of granular material 73. The risers 2 are provided at the bottom with a inlet piece 9 in which openings 10 are provided. Arranged above or at a short distance from the upper pipe plate 72 is a throttling plate 11 provided with openings 12 which are in register with the openings of the risers 2 but have a smaller diameter than the inner diameter of the risers 2. Situated above the throttling plate 11 is the top box 3. The granular material 73, also referred to herein as fluidized bed particles, is brought by the flowing medium high into the top box 13 to subsequently collect, just below the top of the top box 13, in a pot 14, also referred to herein as collecting vessel, which is situated in the top box 13, and which is accessible at the top to the flowing medium and the granular material 73, while the bottom of this collecting vessel 14 communicates by means of a first outlet or conduit 21 with the top of the external downcomer 22. Situated in the collecting vessel is a filter element designed as screen 15, the wall of which, also referred to as screen surface 16, is permeable to the main flow of flowing medium, with the crystals possibly contained therein and scraped-off impurities, but cannot be passed by the granular material 73. On the other hand, the granular material 73 flowing down along the screen 15 exerts a cleaning action on the screen surface 16 so that clogging of the screen 15 is prevented. To achieve this, along the screen surface 16 directed to a second outlet or outlet conduit 19 flow guide means are arranged which form with the screen surface 16 a flow channel 74 for guiding, during use, a flow of medium with granular material 73 along the screen surface 16. In this embodiment, these flow guide means are designed as walls of the collecting vessel 14. Situated downstream of the screen 15 is the reservoir 17 with an opening 18 therein, to which is connected the outlet conduit 19 for discharging flowing medium. The granular material 73 that cannot pass the screen surface 16 of the screen 15 and a part of the flowing medium are discharged via an opening 20 in the collecting vessel 14 and via a first outlet or conduit 21 to the top of the external downcomer 22. In the upper part of the external downcomer 22 the flowing medium and the granular material 73 are separated from each other because as a result of a proper dimensioning of the upper part of the external downcomer 22 such a low upward velocity of the flowing medium is effected that the granular material 73 cannot be carried along upward but collects in the lower part of the external downcomer 34 and is passed from there to the bottom box 7 again. The division of the discharged flowing medium into a main flow passing the screen 15 and a partial flow flowing along the screen 15 and via the opening 20 and the conduit 21 into the upper part of the external downcomer 22 and into the conduit 23 is caused by a pressure difference over the screen 15. The amount of flowing medium separated from the main flow of flowing medium can be regulated with the valve 24 in the conduit

23. In the conduit 23 a settling vessel may further be placed which serves as separator for possibly entrained granular material 73. Eventually, the separated partial flow joins the main flow again which, in the present case, takes place in the reservoir 17. Clogging of the screen 15 is inhibited because particles that possibly remain "stuck" against the screen 15 are wiped off the screen 15 as a result of a pressure difference over the screen 15, through the abrasive effect of the continuous flow of successive particles, and carried along to the bottom of the collecting vessel 14. Optionally, the screen surface 16 may be extra cleaned by means of scrapers not shown, which are driven via a transmission, a shaft and a motor disposed outside the top box 13.

Deposits on the walls of the top box 13 can be avoided by the cleaning action of the granular material 73 on all the walls of the top box 13 so that problems resulting from the decomposition of such deposits and the clogging problems possibly arising therefrom at the top of the external downcomer 22 are prevented. At high velocities of the flowing medium in the risers 2, for instance lm/s to 3m/s, or at lower velocities of a viscous flowing medium, large sizes of the granular particles are recommended on the basis of economical considerations with respect to the diameter of the top of the external downcomer 22. Large granular particles may be combined with a self-cleaning screen 15 provided with relatively large openings which, as a result of the abrasive action of the granular material 73, does not clog and also effects a perfect separation of the flowing medium and the granular material 73. To effect this proper separation, no widened top box 13 needs to be used, nor is a cyclone necessary, which results in a much compacter, lighter and thus less expensive embodiment of the upper part of the heat exchanger 70.

The medium to be treated or to be heated may be supplied to the heat exchanger 70 in different manners, depending on the velocity of the flowing medium in the risers 2 and the viscosity of the flowing medium. The embodiment described below is intended for, but not limited to, a heat exchanger 70 with relatively high velocities in the risers 2 or a relatively high viscosity of the flowing medium. Relatively high velocities of the flowing medium in the risers 2 or a relatively high viscosity of the flowing medium often goes with relatively large granular particles, for instance with a diameter of 4.5 or 6 mm, which can be combined with openings in the screen surface 16 with a diameter of about 3, 4 or 5 mm. Considering the above, the flowing medium is supplied to the heat exchanger 70 via the conduit 30 which divides into a conduit 31 with inlets at the bottom box 7 and a conduit 32 to the collecting reservoir 33 situated at the bottom of the external downcomer 34. A part of the supply of flowing medium to the bottom box 7 below the distribution plates in this box takes place via conduit 35, another part is supplied to the bottom box 7 above the fluidized bed via a bypass conduit 36, optionally connected with a ring conduit 37 provided with several points of connection 38 to the bottom box 7, so as to realize a sufficiently heavy and filled fluidized bed above the distribution plates so that despite the high volume flow and associated relatively high velocities in the risers 2 yet a proper distribution of the granular material 73 and the flowing medium over all the risers 2 is realized. The collecting reservoir 33 is, by means of a distribution plate 39 for supporting the granular material 73 supplied through the bottom of the external downcomer 34, divided into a top section 41 and a bottom section 40. The top section 41 is connected via at least one conduit 42 to the bottom box 7 of the reservoir 1 for returning the granular material 73 thereto from the collecting reservoir 33. If desirable, the conduits 30, 32, 36 and 42 are provided with regulating valves.

Fig. 2 shows the embodiment of the top box 13 in which, by means of a mechanically driven screw conveyor 50 situated in a semi-cylindrical trough 51 permeable to the flowing medium, the separated and collected granular material 73 is conveyed from the lower part of the collecting vessel 14 via the pipe 52 to the top of the external downcomer 22. Here, the trough 51 functions as screen 15. The flowing medium passes the permeable trough 51 and then comes into a space which is shut off from the top box 13 but is connected with an opening through which the flowing medium can be discharged from the installation. The screw 50 is connected by means of the driving shaft 53 with the driving motor 54. To keep the trough 51 sufficiently filled with collected granular material 73 so that with a smallest possible screw diameter as much granular material 73 as possible can be moved, a reducing piece 55 between collecting vessel 14 and trough 51 is sometimes desirable. If a screw conveyor 50 is used, it is not always necessary to convey with the granular material 73 also a partial flow of flowing medium to the top of the external downcomer 22 so that the conduit 23, the regulating valve 24 and the vessel 25 can be omitted. Especially in the case of a very viscous flowing medium it may be desirable to omit the partial flow of flowing medium because this excludes the loss of granular material 73 via conduit 23, with the additional advantage of a smaller cross- section of the upper part of the external downcomer 22. Sometimes a partial flow is recommendable yet because in the lower part of the collecting vessel 14 and trough 51 both granular material 73 and solid particles from the process, impurities and/or crystals may collect. In the upper part of the external downcomer 22, on the basis of density difference and size a separation is then made between the granular material 73 and the above- mentioned solid particles, which granular material 73 is then eventually recycled via the bottom of the downcomer 34 and the bottom box 7, and which above-mentioned solid particles, coming from the process, are discharged with the upwardly directed partial flow at the top of the downcomer 22 via the conduit 23.

Fig. 3 shows an embodiment of the use of a screw conveyor 50 corresponding the embodiment of Fig. 2 in which the main flow of flowing medium is not discharged at the top of the top box 13 in the vertical direction but transverse to the top box 13 in a lateral direction. This embodiment generally requires less overall height. The invention is not limited to the exemplary embodiments described herein. Many variants are possible within the scope of the invention as outlined in the following claims.

Claims

1. An apparatus for carrying out a physical and/or chemical process, such as a heat exchanger, comprising a reservoir provided with upwardly directed pipes, which pipes are received at a top and bottom in pipe plates and are in open communication with a top box and a bottom box, in which bottom box at least one distribution plate is arranged to support a fluidized bed consisting of granular material, which can be kept in a quasi- stationary, fluidized condition by means of a medium to be treated or to be heated, supplied via the bottom box and flowing through the pipes, and which top box is provided with a first outlet for discharging with a partial flow of medium granular material separated from the medium in the top box to a downcomer placed outside the reservoir for returning to the bottom box granular material separated from the medium, and which top box is further provided with a second outlet for discharging a main flow of medium from which the granular material is separated, characterized in that in the top box between the first outlet and the second outlet a screen is incorporated for blocking, while passing the medium, the access of the granular material to the second outlet and that, furthermore, in the top box along a screen surface of the screen directed to the first outlet flow guide means are arranged which form with the screen surface a flow channel for guiding, during use, a flow of medium with granular material along the screen surface.

2. An apparatus according to claim 1, wherein the flow guide means and the screen surface are placed convergingly to each other, such that in the flow direction of the flow channel the passage of the flow of medium with granulate decreases.

3. An apparatus according to claim 1 or 2, wherein the flow channel extends at least partly in downward direction.

4. An apparatus according to any one of the preceding claims, wherein the flow channel is provided with a reservoir for granular material.

5. An apparatus according to any one of the preceding claims, wherein the flow channel is connected with the first outlet.

6. An apparatus according to claim 5, wherein driven conveying means are provided for conveying granular material from the flow channel to the first outlet.

7. An apparatus according to any one of the preceding claims, wherein the flow guide means are formed by walls of a pot placed in the top box, which extend along a screen incorporated in the pot while enclosing the flow channel.

8. An apparatus according to any one of the preceding claims, wherein the screen comprises a plate provided with holes, the diameter of which holes is smaller than the diameter of the granular material for the fluidized bed.

9. An apparatus according to any one of the preceding claims, wherein a scraper further provided for movement along the screen surface.