HEAT EXCHANGER WITH TUBES SUSPENDED INTO A LOWER END PLATE ALLOWING THERMAL MOVEMENT; AND END PLATE THEREFOR

Abstract: A tube heat exchanger intended to be used for the production of carbon black, comprising a cylindrical closed chamber which includes a plurality of tubes (13) which extend through the entire, essentially cylindrically shaped, chamber from an upper end wall to a lower tube or tube plate (18). The tubes are attached to the upper end wall, preferably by welding and hang down to the tube plate, said tube plate being equipped with compensating devices to enable thermally induced expansions and contractions of the tubes (13) to occur. By arranging said tubes (13) so that they hang rather than stand, as is the case with prior art techniques, damage due to the tubes becoming overheated and consequently being unable to support their own weight is avoided.

Description: HEAT EXCHANGER WITH TUBES SUSPENDED INTO A LOWER END PLATE ALLOWING THERMAL MOVEMENT; AND END PLATE THEREFOR The present invention relates to a tube heat exchanger and a tube plate for 5 a tube heat exchanger, specifically a heat exchanger with vertical tubes of considerable lengths having weights which in combination with high temperature expose the tubes themselves and the tube plate to considerable stresses. This tube plate is particularly suitable for use in tube heat exchangers for the production of carbon black. Carbon black is the term used for the finely divided powder forms of 10 carbon which are produced by incomplete combustion or thermic degradation of natural gas or mineral oil. Depending on the method of production, different types of carbon black arise, namely so called channel black, furnace black and pyrolysis black (also called thermal black). Furnace black is by far the most important form of carbon black and is used to a considerably larger extent than the other two. The present invention 15 relates specifically to this type of carbon black, which in the present application is referred to simply as just " carbon black". Fig. 1 A illustrates a conventional plant for the production of carbon black (i.e. of the furnace black type). Incoming combustion air flows through a tube conduit 1 into the upper part of a tube heat exchanger 2, in which it is preheated before the 20 subsequent combustion of oil in the burner 9 and the combustion reactor 3. The thus preheated air is passed into the combustion chamber 10 via a conduit 5. Oil is added to said reactor via a tube conduit 4. The amount of air corresponding to about 50% of the stoichiometric amount of oxygen gas required for a complete combustion of the oil, whereby carbon black is formed. It is also possible to add water into the reactor 3, which 25 has an impact on the quality of the final product. The mixture of the suspended carbon black in the consumed combustion air is led away from the top of the heat exchanger via a conduit 6, through a cooler 7 which is normally water cooled to a filter arrangement 8, conventionally equipped with textile bag filters. In this filter arrangement the carbon black is filtered off from the gas flow, which is then passed out through a non-return 30 valve 16 for further purification in a plant 11 , before it is exhausted into the ambient air via a chimney 12. The construction of the conventional heat exchanger 2 may be more clearly seen in fig. IB. The heat exchanger is of the tube type, with a plurality of through, substantially vertical, tubes 13. The gases from the combustion process rise up the insides of these tubes, whereby they are cooled by the air that enters via the inlet 1 and passes outside the tubes 13 downwards towards the outlet 5, enclosed by the outer jacket wall 14. In order to increase heat transfer the air coming through the inlet 1 is subjected to a reciprocal movement by arranging a plurality of mainly horizontal baffles 15. These are made of plates which extend across about % of the diameter of the heat exchanger whereby each plate is provided with a plurality of holes for the receipt of the tubes 13. The temperature at the inlet 1 of the heat exchanger tubes 13 may be about 1000° and the air coming through conduit 1 may be heated to about 800°. These conditions result in utmost severe stresses for the materials in the heat exchanger. The part of the heat exchanger that is submitted to the highest mechanical stress is the lower part of the jacket and the tube plate where the temperature may amount to 900°. Thus, with an internal pressure of approximately 1 bar at the said temperature, a jacket wall diameter of about 2000 mm, tubes numbering between 50 and 150, plus a height of the tower of approximately 13m, it can be easily understood that the tube plate must be able to withstand exceptionally large stresses, particularly since the tubes 13 rest with their entire weight on the tube plate. Furthermore even the lower portions of the actual tubes 13 are exposed to heavy loads via their own weight in combination with the high temperatures. The tubes 13 have individual compensator devices placed at the top of each tube the function of which is to off load the thermally induced stresses in the tubes, as a result, for example of clogging. The equivalent problem for the actual outer jacket wall 14 has been solved via our earlier Swedish patent application 9504344-4, the contents of which are hereby incoφorated via this reference. According to the said patent application the heat exchanger includes a further jacket wall, which is substantially cylindrical and is placed inwards and mainly concentrically to the outer jacket wall so that at both ends open, mainly cylinder formed spaces are formed in the gap between the two jacket walls, whereby the gas which flows in through the inlet passes through this space before coming into contact with the tubes of the heat exchanger. Occasionally the tube plate has failed to stand up to the heavy loads to which it has been exposed leading to very high repair costs. Attempts have been made to cool the lower tube plate through a double bottom construction as shown in fig. 2. In this design a portion of the incoming air which enters through the inlet 1 is lead away in a vertical pipe 17 and down into the double tube plate 18, which includes an upper thermally insulated wall 19 and a lower thermally insulated wall 20, so that a space (manifold) 21 is formed between the two. Air from the vertical pipe 17 flows into the manifold 21 and hence cools the tube plate, after which the air flows out through the exhaust pipe 22 and is returned to the heat exchanger. However this design has not proved to be sufficiently effective since it does not cool the tube plate sufficiently. Therefore it has been proposed that, in accordance with Swedish patent application 9603739-5, the manifold 21 be split up into a number of channels through the use of dividing walls, whereby each channel is provided with an inlet and an exhaust and a number of heat exchange tubes pass through each channel. This has solved the problem with excessive temperatures in the base plate in a satisfactory manner, but the lower portions of the heat exchanger tubes are still very hot and can, for example, bend or buckle. It should be borne in mind that a 13m long heat exchanger tube can weigh approximately 100 kg. Since the tube stands with its entire weight on the tube plate, the tube plate and the lower, very hot parts of the tubes are particularly heavily loaded. When a buckle is induced, stress on the tubes increases and the deformation process can accelerate. A prime objective with the actual invention is thus to produce a heat exchanger in which the lower parts of the tubes are protected from large loads. A second objective of the invention in question is even to protect the lower tube plate from large loads. These and other objectives have been successfully achieved in a surprisingly simple manner by designing the heat exchanger in accordance with the "characterized in" part of patent claim 1. For illustrative but non-limiting purposes, the invention will now be further described with reference to the appended drawings. These are herewith presented in brief: Figure 1 A shows a schematic view of a conventional plant for the manufacture of carbon black, such has already been described above. Figure IB shows a heat exchanger according to the state of the art, such has already been described above. Figure 2 shows a heat exchanger according to the state of the art, such has already been described above. Figure 3 shows a heat exchanger tube passing through a tube plate according to this invention, in a first embodiment. Figure 4 shows the same section as in figure 3 but in an another embodiment. Figure 3 shows how the lower parts of the heat exchanger tubes 13 pass through a double walled tube or support plate in the lower region of the heat exchanger. In accordance with the Swedish patent applications 9504344-4 and 9603739-5 which were submitted earlier, the heat exchanger tubes 13 are securely welded at the foot to the tube plate, whereby the upper part of the tubes run in collars or compensators at the upper end of the heat exchanger, in order to permit thermal expansions or contractions. This known design has been changed in accordance with the present invention in such a way that the tubes 13 now hang from their upper parts instead of standing on the lower parts. In order to hang the tubes from their upper portion they are simply welded at the point where they pass through a hole in a horizontal plate which is placed at the upper end of the heat exchanger (not shown), for example at the step 23 in fig. IB and/or fig. 2. The compensators 24 in said figures are replaced by simple welded joints, whereby the tubes 13 hang down from tube plate 18, whereby the bond between each tube 13 and the tube plate is so formed so that it permits thermal movement in the tube. In figure 3 the upper wall 19 and the lower wall 20 of the tube plate are to be found. The upper wall 19 consists of a ceramic insulation 25 and a wall of iron or steel plate. The lower wall can consist of a refractory ceramic compound 27, an insulating ceramic compound 28 and a steel wall 29. The refractory ceramic material 27 can be required in order to insulate the tube plate from heat radiation from the combustion chamber 10 which is positioned under it. The space 21 in the tube plate can be sub-divided into a number of channels by ribs 30 in accordance with the Swedish patent application 9603739-5. This is however not an important characteristic of the present invention, since this invention off-loads the tube plate. A protective tube or a so called ferrule 30 is provided at the lower part of the tube 13 for the inflow of very hot gases. The ferrules function is to impede the aggressive gases from coming in contact with tube 13 plus, via insulation, to limit the absorption of heat by the tube plate. An intermediate insulation 31, made for example from ceramic blanketing, is provided between this ferrule 30 and tube 13. In order to create space for this insulation 31 , the ferrule 31 has enlarged inlets at both ends. A fitting ring 42 can be welded in place along the upper edge of the ferrule partly for press fitting of the ferrule in the tube, partly in order to secure the insulation 31 in place. In order to facilitate welding of ferrule 30 in tube 13, a welding ring 43 can be provided right next to the end surface of the tube. Furthermore a protecting sleeve 32 is provided outside tube 13, whereby a further insulation 33, preferably a ceramic blanket, is provided between the said protective sleeve 32 and tube 13. The protecting sleeve 32 is welded at the foot to the tube 13, whilst at the top it quite simply rests against the tube 13, the insulation is thereby enclosed. At the top, a conical part 34 is welded to the outside of the protective sleeve 32, the said part 34 is then terminated in a cylindrical part 35 which has a larger diameter than that of the protective sleeve 32. Radially outside the protective sleeve 32 and substantially concentric to it an outer sleeve 37 is to be found. This outer sleeve is fixed at the top in the wall of the upper support 26 and is welded to the lower tube plate 29 at a distance above its bottom edge. An end cap 38 is fastened against the lower edge of the outer sleeve. This end cap can have a number of outwardly projecting flaps, for example three in total, which are bent up and over the lower edge of the outer sleeve and are then welded to the outside of the outer sleeve, whilst the end cap 38 otherwise only lies in abutment against the lower edge of the outer sleeve. A ring fastener with a mainly L-shaped cross section is welded in proximity to the lower part of the outer sleeves and to its inside. The ring shaped space which is limited by the locking ring 36, protective sleeve 32, the outer sleeve 37 and the end cap 38 is filled by one or two sealing rings 39a, 39b. These sealing rings can be made of ceramic blanketing, ceramic rope or such like. A compensating bellows 40 is provided in the cylindrical space between the protective sleeve 32 and the outer sleeve 37, which is welded gas-tight at the top in the transition area between the conical 34 and the upper cylindrical end part 35 of the protective sleeve. At the foot the bellows is gas tight welded to the holding ring 36. Because the bellows can be pressed together or pulled apart, the tube 13 is allowed to expand and contract because of variations in the temperature. In the situation illustrated in figure 3 when the protective sleeve 32 with its cylindrical end part abutting against the upper tube plate wall 26, the tube 13 will exhibit a relatively lower temperature. In the situation illustrated in figure 4 when the protective sleeve 32 with its cylindrical end part distanced from the upper tube plate wall 26, the tube 13 will exhibit a relatively higher temperature compared with the situation in figure 3. By hanging the heat exchanger tubes downwards from the tube plate the risk that the tubes will bend or deform because of the load from the weight of the tubes themselves is eliminated. As a result of the design of the bellows described in figures 3 and 4 the pipes can, whatsmore, expand and contract freely at different temperatures. Bearing in mind that the tubes are often 13 - 15 m long it can be easily understood that these expansions and contractions can be very significant and of the order of anything up to 5 cm. An additional advantage has also been achieved as a result of this invention. In heat exchangers known to the present with tubes standing on the tube plate, it has been necessary to produce tubes which have had greater wall thicknesses at the lower region, in order to give improved resistance to bending and buckling. Thus for example a 13 m long tube has been manufactured with 3mm wall thickness in the upper 9 m and 5mm thick walls in the lower 4 m. Through the invention described here it is possible to dispense with the lower, thicker wall thickness and hence the tube can be manufactured with for example 3 mm wall thickness along its entire length. Even the attached abstract forms a part of the total description.

Claims: CLAIMS 1. A tube heat exchanger, particularly to be used for the production of carbon black, comprising a substantially cylindrical closed vessel, which encloses a plurality of heat exchanger tubes (13), which extend over the whole of the substantially cylinder formed space, between the upper end or support wall and a lower tube plate (18), characterized in that the tubes are secured in the upper end wall, preferably by welding, and hang down from the tube plate, whereby the tube plate is equipped with compensators in order to permit thermal expansion and contraction of the tubes (13). 2. A tube heat exchanger according to claim 1 , wherein each compensator includes a bellows (40). 3. A tube heat exchanger according to claims 1 and 2, wherein the tube plate is double walled and encloses a space (21) for the through flow of a cooling medium. 4. A tube heat exchanger according to any of claims 1 - 3, wherein a protective sleeve (32) surrounds the lower part of each tube (13), that an outer sleeve (37) is to be found outside said protective sleeve (32), whereby the bellows (40) are to be found in the space between said sleeves (32, 37). 5. A tube heat exchanger according to any of the previous claims, wherein the said bellows (40) prevent the flow of gas through the space between said sleeves (32, 37). 6. Tube plate (18) for a tube heat exchanger, in particular one to be used for the production of carbon black, comprising an upper tube plate wall (26), a lower tube plate wall (29) plus a space formed between these walls (21), through which tube plate heat exchanger tubes (13) run, characterized in that a compensator is provided around each tube in order to permit thermally induced expansions and contractions of the tubes (13). 7. A tube plate according to claim 6, wherein each compensator includes a metallic bellows (40). 8. A tube plate according to claims 6 or 7, wherein a protective sleeve (32) surrounds the lower part of every tube (13), that an outer sleeve (37) is to be found outside said protective sleeve (32), whereby the bellows (40) are to be found between said sleeves (32, 37). AMENDED CLAIMS [received by the International Bureau on 12 October 1998 (12.10.98); original claims 1-8 replaced by amended claims 1-5 (1 page)] 1. A tube heat exchanger, to be used for the production of carbon black, comprising a substantially cylindrical closed vessel, which encloses a plurality of heat exchanger tubes (13), which extend over the whole of the substantially cylinder formed space, between the upper end or support wall and a lower tube plate (18), whereby the tubes are secured in the upper end wall preferably by welding, characterized in thai, the tubes are so arranged that they hang down from the tube plate which is double walled and encloses a space (21) through which a cooling medium can flow, in addition to which the tube plate is equipped with a compensator in the form of a metallic bellows (40) in order to permit thermally induced expansion and contraction of the tubes (13). 2. A tube heat exchanger according to claim 1, characterized in that a protective sleeve (32) surrounds the lower part of each tube (13), that an outer sleeve (37) is to be found outside said protective sleeve (32), whereby the bellows (40) are to be found in the space between said sleeves (32, 37). 3. A tube heat exchanger according to any of the previous claims, wherein the said bellows (40) prevent the flow of gas through the space between said sleeves (32, 37). 4. Tube plate (18) for a tube heat exchanger, to be used for the production of carbon black, comprising an upper tube plate wall (26), a lower tube plate wall (29) plus a space formed between these walls (21), through which tube plate heat exchanger tubes (13) run, characterized in that a compensator in the form of a metallic bellows (40) is provided around each tube in order to permit thermally induced expansions and contractions of the tubes (13). 5. A tube plate according to claim 4. wherein a protective sleeve (32) surrounds the lower part of every tube (13), that an outer sleeve (37) is to be found outside said protective sleeve (32), whereby the bellows (40) are to be found in the space between said sleeves (32, 37).

Inventors: BERGLUND GOERAN, ERIKSSON ULF, BERGLUND, GOERAN, ERIKSSON, ULF
Applicants: BERGLUND GOERAN, ERIKSSON ULF, SANDVIK AB, BERGLUND, GOERAN, ERIKSSON, ULF, SANDVIK AKTIEBOLAG
Application year: 1998
Main classification: F28F9
IPC codes: F28D7, F28F9