EP0171558A2 - Heat-exchange apparatus - Google Patents

Abstract

The heat exchanger is constructed in various embodiments such that the crevice duct between the outermost coil of tubes and the jacket defining the crevice duct is maintained at a constant width during operation. In some embodiments, the outermost coil tubes is carried on the jacket to maintain a constant width of the crevice duct. In other embodiments, a separate set of cooling tubes in provided to maintain the jacket cool. In other embodiments, the amount of heat drawn off through the outermost coil of tubes is increased.

Description

The invention relates to a heat exchanger with a pressure vessel, in particular for the cooling of gas from a high-temperature reactor, wherein there is a cylindrical gas duct containing a bundle of cooling tubes in the pressure vessel, which leads a gas to be cooled from an inlet area to an outlet area and which is between itself and leaves the adjacent, outer tubes of the tube bundle an annular gap channel which is dimensioned such that at operating temperature the average temperature of the gas emerging from the gap channel is substantially equal to the average temperature of the gas emerging from the other tube bundle.

Such a heat exchanger is known in which a hot gas - for example helium - is cooled by water circulating in the cooling tubes, which evaporates in the process. This heat exchanger has no particular problems at relatively low gas temperatures. At higher gas temperatures, however, for example 900 ⁰ C, and before Especially when the gas flue has a large diameter, for example more than 3.5 m, as occurs, for example, in heat exchangers for cooling helium from a high-temperature reactor, considerable so-called gap losses occur when flowing through the gap channel. The reason for this is the greater radial thermal expansion of the cylindrical gas flue at the transition to the operating temperature compared to the radial thermal expansion of the cooling tube bundle, as a result of which the gap duct has a disproportionately large increase in cross section, so that a considerable, insufficiently cooled gas flow then flows through the gap duct. In addition, as seen over the circumference of the gap channel, poor gas distribution in the gap channel arises as a result of inevitable manufacturing inaccuracies of the heat exchanger, as a result of which hot gas streaks are formed in the outlet area of the heat exchanger. Because of the high temperatures, heat transfer processes take place so intensely that significant excess temperatures and associated reductions in strength as well as thermal stresses or deformations can occur in the shortest possible time. Under certain circumstances, the gap losses can question the applicability of the known heat exchanger for high temperatures.

The previous attempts to solve the problem of gap losses have assumed that the gas flow in the gap channel is contained, for example by means of packing elements, ribs placed transversely to the gas flow and protruding into the tube bundle, and the like.However, such measures cannot be used at high temperatures because they lead to excess temperatures in the area of the gap channel due to the material accumulation. In addition, there is a thermodynamically very complex behavior that is difficult to ascertain both mathematically and experimentally. It is an object of the invention to largely eliminate the gap losses increasing at the transition to the operating temperature in the heat exchanger of the above type in a safe, simple and inexpensive manner while avoiding excess temperatures, so that the heat exchanger can be used in particular for high gas temperatures and large diameters.

This object is achieved according to the invention in that means are provided by which the average heat flow density through the wall of the outer cooling tubes is kept substantially equal to the average heat flow density through the wall of the other tubes of the cooling tube bundle. Because the average heat flow density through the wall of the cooling tubes is kept the same in the entire cooling tube bundle with the means according to the invention, the gap losses can be avoided in a simple and reliable manner. This means that excess temperatures can no longer occur. Due to the omission of means that contain the gas flow through the gap channel, the behavior of the heat exchanger according to the invention can be determined particularly well by calculation.

The formation of the means according to claim 2 acts directly on the cause of the gap losses in order to prevent their occurrence. Claims 3, 4 and 6 characterize three different embodiments, the effectiveness of the embodiment according to claim 4 being substantially increased by the further development according to claim 5.

The cooling of the inside of the throttle cable according to claim 7 represents a further advantageous embodiment of the invention, wherein in the case of further development according to Claim 14 an almost complete alignment of the fluidic and thermodynamic conditions in the gap channel to those in the cooling tube bundle is achieved.

The developments according to claims 8 and 9 bring about a reduction in the flow rate through the gap channel by increasing the pressure losses of the gas, and the turbulence arising in this channel improves both the heat transfer and the temperature distribution in the area of the gap channel. With a narrow gap, the variant according to claim 8 is preferred, with a larger gap that according to claim 9 is preferred. The latter variant can be designed so that currents also arise in the gap channel transverse to the longitudinal axis of the throttle cable.

The design of the inside of the throttle cable according to claim 10 has similar effects as those according to claims 8 and 9, but has - in some applications - advantages in terms of manufacture.

The measure according to claim 11 enables the removal of additional heat from the gap channel without increasing the heat flow density through the tube walls of the outer cooling tubes.

The arrangement of deflecting means according to claim 12 causes cooling of the gap channel, the heat from this area being distributed to at least part of the cooling tube bundle, so that the heat flow density in the bundle is evened out and excess temperatures are prevented.

• Fig. 1 einen schematischen Längsschnitt durch einen bekannten, vertikal angeordneten Wärmeübertrager zur Kühlung von Helium aus einem Hochtemperaturreaktor,
• Fig. 2 eine Draufsicht auf das Detail A der Fig. 1 bei einem nach der Erfindung ausgebildeten Wärmeübertrager, in grösserem Massstab als Fig. l,
• Fig. 3 einen Schnitt nach der Ebene III - III in Fig. 2, jedoch in kleinerem Massstab als Fig. 2,
• Fig. 4 eine Draufsicht des Details A der Fig. 1 bei einer anderen Ausführungsform der Erfindung, in vergrössertem Massstab,
• Fig. 5 einen Schnitt nach der Ebene IV - IV in Fig. 5,
• Fig. 6 einen vertikalen Schnitt des Details A in Fig. 1 bei einer weiteren Ausführungsform der Erfindung, in vergrössertem Massstab,
• Fig. 7 bis 12 je ein weiteres Ausführungsbeispiel in kleinerem Massstab als Fig. 6 und
• Fig. 13 bis 16 je einen vertikalen Schnitt des Details A in Fig. 1 bei weiteren Ausführungsformen der Erfindung.

Some embodiments of the invention are in the following description explained in more detail with reference to the drawing and their advantages highlighted more clearly. Show it:

• 1 shows a schematic longitudinal section through a known, vertically arranged heat exchanger for cooling helium from a high-temperature reactor,
• 2 is a plan view of detail A of FIG. 1 in a heat exchanger designed according to the invention, on a larger scale than FIG. 1,
• 3 shows a section along the plane III-III in FIG. 2, but on a smaller scale than FIG. 2,
• 4 is a plan view of detail A of FIG. 1 in another embodiment of the invention, on an enlarged scale,
• 5 shows a section along the plane IV-IV in FIG. 5,
• 6 shows a vertical section of detail A in FIG. 1 in a further embodiment of the invention, on an enlarged scale,
• 7 to 12 each another embodiment on a smaller scale than Fig. 6 and
• 13 to 16 each a vertical section of the detail A in Fig. 1 in further embodiments of the invention.

The known heat exchanger according to Fig. 1 has a cylindrical pressure vessel 2, which is closed by a lower, outwardly curved bottom. A gas inlet connection 3 is provided near the lower end of the pressure vessel 2, via which hot helium gas is supplied from a high-temperature reactor, not shown. In its upper region, the container 2 is provided with a gas outlet cover 4 which is curved downwards and has a central opening, which is supported on an edge 15 which projects into the interior of the pressure container 2 and is fastened to the latter by means of screws, not shown. In the lower part of the pressure vessel 2, a tube bundle 5 is arranged, which consists of approximately 500 water or steam-carrying cooling tubes. The cooling tubes are bent over most of their length along helical lines, the tubes of the outermost tube cylinder of the tube bundle 5 being designated 7 and the remaining tubes of the tube bundle being designated 6.

Close below the gas outlet cover 4, the pressure vessel 2 has a steam outlet connector 10 and below this a water inlet connector 9. Both nozzles expand within the pressure vessel 2 and each end in a vertical tube plate 10 'or 9' with horizontal bores. In the interior of the pressure vessel 2, an essentially C-shaped tube box 11 is attached to the steam outlet nozzle 10, to which a central tube 12 connects coaxially to the pressure vessel 2, which extends to below the gas inlet nozzle 3.

The cooling pipes 6 and 7 are connected at their one ends to the pipe plate 9 'of the water inlet connector 9 and at their other ends to the pipe plate 10' of _D ampfaustrittsstutzens 10. 3ie spread, from the tube plate 9 'starting initially uniformly around the central tube 12 and then go around concentrically to the central pipe 12 in the helical shape about. Below the gas inlet connection 3, they are bent toward the central tube 12 and penetrate a horizontal end plate 12 'which is tightly inserted into the central tube at the bottom. The cooling tubes 6, 7, which are welded in tightly at the piercing point, then extend vertically upward within the central tube 12, run inside the tube box 11 in an approximately C-shaped manner up to the tube plate 10 '. In the area of their helical course, the cooling tubes 6, 7 are screwed into eight support plates 13, which are evenly distributed over the circumference of the tube bundle 5 and are fastened to the central tube 12.

A cylindrical jacket 14, which is coaxial with the tank 2 and surrounds the tube bundle 5 and rests on an inner, horizontal flange 2 'of the pressure vessel 2 arranged below the water inlet connector 9, which forms the accelerator cable and extends to below the cooling tubes 6, 7. The inside of the jacket 14 and a theoretical vertical cylinder on which the axes of the helically curved outer cooling tubes 7 lie define an annular gap channel 8 with a gap width d. An inner flange 14 'near the lower end of the jacket 14 guides the cooling pipes 6, 7 in their course between the support plates 13 and the end plate 12'. A plurality of perforated plates, not shown, are arranged within the central tube 12 and the tube box 11 and serve to support the cooling tubes laterally.

• Durch den Gaseintrittsstutzen 3 fliesst heisses Helium mit ca. 700⁰C und einem Druck von etwa 65 bar in den Druckbehälter 2, wo es sich in dem Ringraum zwischen dem Druckbehälter und dem Mantel 14 verteilt. Es strömt in dem Zwischenraum abwärts und fliesst dann innerhalb des Mantels 14 durch das Rohrbündel 5 nach oben und verlässt den Wärmeübertrager - immer noch einen Druck von ca. 65 bar, aber eine Temperatur von nur noch 280°C aufweisend - über die zentrale Oeffnung des Gasaustrittsdeckels 4. Das zur Kühlung des Heliumgases dienende Wasser tritt über den Wassereintrittsstutzen 9 mit ca. 200°C in die Kühlrohre 6, 7 ein, durchströmt deren schraubenlinienförmig gewickelten Abschnitte, wobei es verdampft und verlässt als Dampf mit etwa 530°C und 185 bar den Dampfaustrittsstutzen 10.

The heat exchanger according to Fig. 1 works as follows:

• Hot helium flows at approximately 700 ^° C. and a pressure of approximately 65 bar through the gas inlet nozzle 3 into the pressure vessel 2, where it is distributed in the annular space between the pressure vessel and the jacket 14. It flows downwards in the intermediate space and then flows upwards within the jacket 14 through the tube bundle 5 and leaves the heat exchanger - still at a pressure of approx. 65 bar, but at a temperature of only 280 ° C - via the central opening of the Gas outlet cover 4. The water used to cool the helium gas enters the cooling pipes 6, 7 via the water inlet connection 9 at approximately 200 ° C., flows through the helically wound sections thereof, evaporating and leaving as steam at approximately 530 ° C. and 185 bar the steam outlet connection 10.

When the temperature of the helium rises to the operating temperature, the width d of the gap channel 8 increases by a certain amount due to thermal expansion of the jacket 14 and the tube bundle 5, whereby - as already described above - the amount of helium gas flowing through the gap channel 8 increases disproportionately more than the gap width . Thus, an increase in the gap width of 5 mm can increase the effective gas flow rate through the gap channel 8 by approximately 30%. The temperature of the helium gas in the gap channel 8 also rises correspondingly strongly, since the amount of heat additionally entrained by the increased gas flow rate cannot easily be removed from the outer cooling tubes 7. With the assumed increase of 5 mm, the temperature increase is already more than 20 ° C.

As a result of inevitable manufacturing inaccuracies with regard to the shape and dimension of the throttle cable, an additional one can also occur within the gap channel 8 uneven mass flow and temperature distribution occur, which then leads to the hot gas streams already mentioned.

With the embodiments of the invention shown in FIGS. 2 to 16, the gap losses can be counteracted. 2 and 3, the jacket 14 has eight vertical slots distributed over its circumference, of which FIG. 2 shows two. In the area of each slot, the jacket is cranked outwards - parallel to the slot. In each case the two end faces 24 '' of the cranks 24 'thus formed delimit a slot. Two adjacent cranks 24' are slidably guided between two metal strips 20 'which are held together by pins 21 which penetrate radially through the slot. Each pin 21 is by a spacer sleeve 22 surround, which determines the mutual distance between two sheet metal strips 20. The surfaces of the cranks 24 'sliding on the sheet metal strips 20 are coated with a material which has good sliding properties, and the pins 21 are connected to the sheet metal strips 20 by welding the vertical length of the slots uniformly distributed tensioning cables 25, which are supported on the jacket 14 by cubes 27 and whose ends are connected to one another by means of tensioning sleeves 26. The tensioning cables 25 are made of a material which has a smaller tangential thermal expansion than that of the jacket 14; they thus cause that with increasing temperature of the helium gas, the cranks 24 'between the sheet metal strips 20 slide tangentially against one another in pairs, the diameter of the jacket 14 remaining essentially the same and the gap width d decreasing as a result of the radial thermal expansion of the cooling tube bundle 5. As a result, the gas flow rate in the gap channel 8 kept small enough and an inadmissible increase in the temperature in the gap channel 8 prevented. In principle, this variant also works without tension cable 25; However, these offer additional security against possible jamming of the crankings 24 ′ between the metal strips 20, for example as a result of contamination.

In the exemplary embodiment according to FIGS. 4 and 5, the support plates 13 have a smaller radial dimension than in FIG. 1, so that they only accommodate the cooling tubes 6 of the tube bundle 5. The outer cooling tubes 7 of the tube bundle 5 are screwed into eight radial webs 140, each aligned with a support plate 13, which are made in one piece with the jacket 14 or are welded to the jacket in the form of strips. Thus, as the temperature rises, the outer cooling tubes 7 are carried along by the jacket 14 when the diameter is increased, so that the gap width d - apart from a small radial thermal expansion of the cooling tubes 7 themselves and the linear thermal expansion of the webs 140 - remains practically constant at all temperatures.

6, the jacket 14 is cooled on the inside by means of additional helical cooling tubes 30. The jacket cooling tubes 30 have the same diameter as the cooling tubes 6, 7 and also have the same pitch as this. The horizontal distance between the jacket cooling tubes 30 and the outer cooling tubes 7 is approximately equal to the horizontal distance between the adjacent cooling tubes 6 and 7 in the cooling tube bundle 5. Between the jacket cooling tubes 30, helical sheet-metal strips 31 are provided, which have a plurality of pins welded to the jacket 14 32 are attached. The strips 31 and the Pins 32 are connected to one another via welding bores 31 'which are provided in the strips. Some strips 31 are welded in pairs of sheet-steel brackets 33, which are bent into a quarter-circle shape and which each abut a jacket cooling tube 30 and serve as tube holders. Each pair of brackets 33 is fixed in position by a reinforcing plate 34 connecting them. The sheet metal strips 31 delimit a cylindrical surface on which the helically bent tube axis of the jacket cooling tubes 30 lies and which is used to measure the width d of the gap channel 8, which in this case is equal to the horizontal distance between the cooling tubes 5 and 7. This embodiment is particularly advantageous at very high operating temperatures because the jacket cooling tubes 30 are attached to the jacket 14 in a simple and inexpensive manner without weld seams. The amount of cooling water flowing through the jacket cooling tubes 30 is adjusted by means of throttling elements, not shown, such that the cooling of the helium gas in the gap channel 8 is equal to the cooling in the tube bundle 5. Another advantage of this embodiment is that the gas-side flow conditions in the gap channel 8 can be substantially matched to the gas-side flow conditions in the tube bundle 8.

The cooling of the jacket 14 can also be achieved with the embodiments according to FIGS. 7 to 12 while maintaining the adjusted flow conditions. 7, the jacket 14 is designed as a so-called membrane wall, in that the jacket cooling tubes 30 are welded to one another in a gas-tight manner by means of webs 141. 8, the jacket cooling tubes 30 are embedded in a groove which is worked into the jacket 14 according to a helical line. According to FIG. 9, the jacket cooling water circulates in a helical one Channel which is formed by half pipes 35 welded tightly to the smooth cylindrical inside of the jacket 14. 10 and 11, a corrugated sheet 36 or 36 'is provided instead of the half-tubes 35. 10, the corrugated sheet 36 is in turn welded to the smooth, cylindrical inside of the casing 14, whereas in FIG. 11 the corrugated sheet 36 'is welded together with webs 141' which together form the wall of the casing 14. According to FIG. 12, the jacket 14 is formed by tubes 37 which are welded to one another and are helically wound and which are produced in one piece with fins which are located on one side outside the tube axis.

In the embodiment according to FIG. 13, horizontal, piston ring-like, flat steel rings 40 are clamped in suitable grooves on the inside of the jacket 14. The steel rings 40 form a kind of labyrinth seal along the inside, which throttles the helium gas flow in the gap channel 8 and at the same time swirls it strongly. This reduces the flow rate and improves cooling in the gap channel 8.

In the exemplary embodiment according to FIG. 14, the jacket 14 is designed such that the gap channel 8 has a variable gap width in the vertical direction, in that narrower gap cross sections alternate with further gap cross sections. This produces a similar effect to that of the steel rings 40 in FIG. 13. This embodiment is largely insensitive to manufacturing-related deviations in the gap width.

The outer cooling tubes 7 according to FIG. 15 have a larger diameter than the cooling tubes 6 of the tube bundle 5 and have the same wall thickness as these. There through, the outer cooling tubes 7, when the gap width is larger at operating temperature, can dissipate more heat from the correspondingly larger amount of gas flowing through the gap channel 8 without the heat flow density through their walls exceeding the heat flow density through the walls of the other cooling tubes 6. A temperature sensor 60 monitors the temperature of the helium gas in the gap channel 8 and controls a control valve 62, which is provided for each outer cooling tube 7, via a signal line 61 in a manner known per se. The amount of cooling water through the outer cooling tubes 7 is regulated so that the average temperature of the helium gas in the gap channel 8 remains the same as the average temperature of the helium gas in the area of the cooling tubes 6 of the tube bundle 5 and that the average heat flow density through the wall of the cooling tubes 6, on the one hand, and the outside Cooling tubes 7, on the other hand, is also kept the same.

In the exemplary embodiment according to FIG. 16, a plurality of ring-shaped baffle plates 50 of different diameters are staggered in the tube bundle 5 in such a way that they conduct helium gas from the interior of the tube bundle in the direction of the gap channel 8 and also enable helium gas from the gap channel 8 back into the interior of the tube bundle 5 is pushed. This results in a uniformization of the temperatures of the gas in the gap channel 8 and in the remaining area of the cooling tube bundle 5. The baffle plates 50 are connected to the support plates 13, so that the heat absorbed by the baffle plates flows through the support plates to the cooling tubes 6, 7, whereby the Cooling of the baffles is guaranteed.

Deviating from the previously described execution shapes, the outer cooling tubes 7 can be provided with a larger slope than the other cooling tubes 6, so that cooler cooling water is available in the area of the gap channel 8 for each height level than in the other areas of the tube bundle 5. Combine this embodiment, for example, with that according to FIG 15 or 16, the greater slope of the outer cooling tubes 7 allows relatively large amounts of heat to be removed from the gap duct 8 without excessive temperatures occurring in the gas flue.

The invention can e.g. also apply to heat exchangers with straight or meandering cooling tubes. It is also possible to arrange the cylindrical throttle cable horizontally or otherwise inclined.

The control of the temperature in the gap channel 8 according to FIG. 15 can be used in all embodiments of the invention.

Claims (14)

1-. Heat exchanger with a pressure vessel, in particular for the cooling of gas from a high-temperature reactor, wherein there is a cylindrical gas duct containing a bundle of cooling tubes in the pressure vessel, which leads a gas to be cooled from an inlet area to an outlet area and which is between itself and the neighboring ones _. outer tubes of the tube bundle leaves an annular gap channel, which is dimensioned such that at operating temperature the average temperature of the gas emerging from the gap channel is substantially equal to the average temperature of the gas emerging from the remaining tube bundle, characterized in that means are provided by which the average heat flow density through the wall of the outer cooling tubes is kept substantially equal to the average heat flow density through the wall of the other tubes of the cooling tube bundle. 2. Heat exchanger according to claim 1, characterized in that the means prevent an increase in the width of the gap channel with increasing temperature of the gas. 3. Heat exchanger according to claim 2, characterized in that the material of the gas flue has a smaller coefficient of thermal expansion than the material of the cooling tube bundle. 4. Heat exchanger according to claim 2, characterized in that the gas flue has at least one slot extending approximately on a surface line at least in the region of the gas inlet side of the cooling tube bundle. 5. Heat exchanger according to claim 4, characterized in that clamping elements are present which act in the direction of a reduction in the diameter of the throttle cable. 6. Heat exchanger according to claim 2, characterized in that the outer cooling tubes are attached to the inner wall of the throttle cable. 7. Heat exchanger according to claim 1, characterized in that for cooling the gas flue pipes are arranged on the inside, which are charged with coolant independently of the cooling tubes of the tube bundle. 8. Heat exchanger according to claim 1, characterized in that in the area of the gap channel, the inside of the throttle cable and / or the outer surface of the outer cooling tubes are or are heavily roughened. 9. Heat exchanger according to claim 1, characterized in that the inside of the throttle cable is designed in the manner of a labyrinth seal. 10. Heat exchanger according to claim 1, characterized in that the width of the gap channel is alternately smaller and larger by appropriate shaping of the inside of the throttle cable - seen in the longitudinal direction of the gas cable. 11. Heat exchanger according to claim 1, characterized in that the surface of the outer cooling tubes is larger than that of the other cooling tubes of the cooling tube bundle. 12. Heat exchanger according to claim l, characterized in that baffles are arranged distributed in the cooling tube bundle, which lead gas from the cooling tube bundle to the gap channel. 13. Heat exchanger according to one of claims 1 to 12, characterized in that the tube bundle consists of helically bent tubes. 14. Heat exchanger according to claim 13, characterized in that for cooling the throttle cable at least one helically guided along the inside of the throttle cable, through which a coolant flows and which is firmly connected to it, is provided.

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