EP1724544A1 - Method of heat exchanging and heat exchanger - Google Patents

Abstract

The method involves exchanging heat between a primary fluid (P) and a secondary fluid(s). The primary fluid is provided by a heat exchanger pipe which partly flows around by the secondary fluid(s) (9, 10, 11). The primary fluid is provided in a first direction of flow (100) and after a flow reversal, in an opposite second direction of flow (200) by the heat exchange pipe. The flow reversal is accomplished at expiration of a time interval which is somewhat shorter than the life span of the heat exchanger pipe. The direction of flow of the primary fluid is turned around and repeated. An independent claim is included for a heat exchanger.

Description

The invention relates to a heat exchange method in which heat is exchanged between a primary fluid and a secondary fluid, wherein the primary fluid is passed through at least one of the secondary fluid at least partially flow around the heat exchanger tube and a heat exchanger with at least one heat exchanger tube.

Such basically known heat exchange methods and the heat exchangers suitable for carrying them out are used in many areas, for example in the chemical industry, in order to transfer heat from one fluid to another fluid. The commonly used fluids, also referred to as media, are generally liquids, gases or mixtures thereof. Here, the two fluids for better distinctness referred to as the primary fluid and secondary fluid, wherein the primary fluid in the heat exchanger tube and the secondary fluid is guided outside the heat exchanger tube along.

In general, especially the very demanding operating conditions in the primary fluid in the known heat exchangers lead to wear and corrosion phenomena on the heat exchanger tubes, which limit their life. For example, reactions such as carburization, decarburization and / or nitration on the heat exchanger tubes are observed in tube bundle heat exchangers in the industry. If these processes are well advanced, either the entire heat exchanger or at least its heat exchanger tubes must be replaced. This is very expensive and expensive.

In order to extend the life of a heat exchanger, various protective measures have already been developed in the past, in particular for the heat exchanger tubes. Among other things, protective coatings or protective tubes have been provided in the heat exchanger tubes, but have the disadvantage of reducing the heat exchange capability of the heat exchanger tube.

Upon closer examination of the damage processes, it has been found that these are mainly temperature-dependent. Thus, the damage extends primarily to the hotter area of a heat exchanger tube. In a heat exchanger that cools the primary fluid, this is the area in which the then hot primary fluid flows into the heat exchanger tube.

In order to lower the thermal load on the tubes, the tubes held at their hot inlet region in a tube disc have been guided in known tube bundle heat exchangers such that a hot tube inlet is alternately arranged next to a colder tube outlet in the tube plate. As a result, the tube temperature is reduced overall and at least slows down the respective damage processes. This has already very successfully led to extended lifetimes of the heat exchangers.

In order to reduce the operating costs of heat exchangers still further, there is a need to significantly increase the life of the known heat exchanger again and at the same time reduce the maintenance.

The invention is therefore based on the object to significantly extend the life of a heat exchanger.

The solution of this object is achieved according to the invention with a heat exchange method in which heat is exchanged between a primary fluid and a secondary fluid, wherein the primary fluid is passed through at least one of the secondary fluid at least partially flow around the heat exchanger tube. According to the invention, the primary fluid is first passed through the heat exchanger tube in a first flow direction and after a flow reversal in an opposite second flow direction. This three-stage process makes each pipe end hot at least once and the cold pipe side at least once. The heat exchanger tube is thus now similarly loaded at both pipe ends by damage processes and not as before one-sided only on one side of the pipe. This almost doubles the time in which the affected heat exchanger tube can be used to carry out the process.

In principle, it makes sense to perform the flow reversal after an operating time that corresponds approximately to the conventional life of a heat exchanger ear. This is the case when the heat exchanger tube already has significant damage at one point. Advantageously, however, the implementation of the method is carried out so that the flow reversal is carried out after a period of time which is slightly shorter than the life of the heat exchanger tubes or the. In other words, the flow is reversed when the damage processes just have not yet limited the heat exchanger tube in its serviceability so that repair measures are necessary. The flow reversal thus takes place after a predicted lifetime. This predicted lifetime of the heat exchanger tube can be based on empirical values or predicted by means of suitable theoretical material models.

Further, the flow direction of the primary fluid can be reversed several times.
This can lead to a further homogenization of the wear of the heat exchanger tubes. Conveniently, the flow direction of the primary fluid is automatically reversed. This has the advantage that no intervention on the part of the operating personnel are necessary.

The flow direction of the primary fluid is preferably reversed until the maximum sum of the flow times in the same flow direction is only slightly shorter than the service life of the heat exchanger tube. This means that the number of flow reversals or the duration of a single flow period of the same flow direction are determined so that the theoretical life of the heat exchanger tube is just not exceeded.

Preferably, the position of at least one flow guiding means is changed to reverse the flow. These may be suitable pipes, duct sections, duct components, baffles, flaps, manifolds, branches, pumps, valves or the like, for example in the supply of the primary fluid to the heat exchanger tube. The flow guiding means can be swiveled or displaced by hand or by machine or remounted or be changed in position with the aid of suitable drives.

In a particularly preferred embodiment of the method, an inlet guide means instead of an outlet guide means and / or an outlet guide means are arranged instead of an inlet guide means for the flow reversal. Both the inlet guide means and the outlet guide means may also be flow guide means, wherein the inlet guide means may be exchanged with the outlet guide means. Alternatively, both can also be replaced by new inlet guide means or outlet guide means. In any case, the original tube inlet of the heat exchanger tube is replaced by the tube outlet and the original tube outlet to the tube inlet. The replacement of the inlet guide means or outlet guide means is advantageously carried out manually or automatically, for example by means of a device suitable for this purpose, such as a hydraulic drive.

Alternatively, the direction of flow of a primary fluid pump is reversed to reverse the flow. In other words, the flow through the cooling or heating circuit of the primary fluid of the entire system in which the heat exchange method is used is reversed.

According to the device, the object is achieved with a heat exchanger having at least one heat exchanger tube which has at least one switching means for reversing the direction of flow through the at least one heat exchanger tube. This switching means is generally a means that reverses the flow direction of the primary fluid. This can be, for example, a swiveling or displaceable flow guiding means or else an electrical or hydraulic circuit, for example a delivery pump for the primary fluid.

Preferably, the switching means is disposed within a housing of the heat exchanger. This has the advantage that, for example, in the case of switchovers in which the position of the switchover means changes, for example, the flow reversal does not lead to a changed connection situation of the heat exchanger. The heat exchanger can thus be maintained or connected in its outer shape even after the flow reversal. Then, the entire system in which the heat exchanger is used to be operated in the same manner even after the flow reversal. Expediently, the switching means itself has at least one flow-guiding means that is variable in its position. Such a flow guiding means may be, for example, a baffle which is changed in position in the switching means.

Preferably, the switching means reverses the conveying direction of a pump. This can be done for example by a suitable hydraulic or electrical circuit.

Conveniently, the switching means itself is electrically and / or mechanically actuated, so that the operator can operate the switching means as needed for flow reversal.

Fig. 1

einen Schnitt durch einen ersten Rohrbündelwärmetauscher bei Durchführung eines ersten Ausführungsbeispiels des erfindungsgemäßen Wärmeaustauschverfahrens;

Fig. 2

einen Schnitt durch den in Fig. 1 gezeigten Wärmetauscher nach der Strömungsumkehr;

Fig. 3

einen Schnitt B-B durch einen Rohrbündelwärmetauschers mit wechselnd warmer und kalter Berohrung bei Durchführführung eines zweiten Ausführungsbeispiels des erfindungsgemäßen Wärmeaustauschverfahrens;

Fig. 4

die Draufsicht auf den in Fig. 3 eingezeichneten Schnitt A-A;

Fig. 5

den vergrößerten Ausschnitt D der in Fig. 3 dargestellten Rohrplatte vor einer Strömungsumkehr;

Fig. 6

den in Fig. 5 dargestellten Ausschnitt D nach einer Strömungsumkehr.

The invention will be explained below with reference to two embodiments of the method shown in the drawing. In it show schematically:

Fig. 1

a section through a first shell and tube heat exchanger when carrying out a first embodiment of the heat exchange method according to the invention;

Fig. 2

a section through the heat exchanger shown in Figure 1 after the flow reversal.

Fig. 3

a section BB through a shell-and-tube heat exchanger with alternating warm and cold pipe at feed-through of a second embodiment of the heat exchange method according to the invention;

Fig. 4

the top view of the drawn in Figure 3 section AA.

Fig. 5

the enlarged section D of the tube plate shown in Figure 3 before a flow reversal.

Fig. 6

the section D shown in Fig. 5 after a flow reversal.

Fig. 1 and Fig. 2 show a tube bundle heat exchanger 1 when carrying out a first embodiment of the heat exchange method according to the invention. For reasons of better representability, the middle part of the very long heat exchanger 1 and the walls of the three U-shaped heat exchanger tubes 9, 10, 11 are not shown in the upper area.

The heat exchanger 1 has a heat exchanger housing 2 with an inlet 3 and an outlet 4 for the primary fluid P, which in this embodiment is hot steam. This primary fluid P is cooled by means of a secondary fluid S. Here, the secondary fluid S is cold water, which is guided into the heat exchanger housing 2 through two secondary fluid inlets 5 and 6 mounted laterally on the heat exchanger 1 and out of the heat exchanger housing 2 through a secondary fluid outlet 7. In the heat exchanger housing 2 is a tube plate 8, in which the three U-shaped bent heat exchanger tubes 9, 10 and 11 are fixed so that they are washed above the tube plate 8 from the cool secondary fluid S. The cooled with a cooling system 25 tube plate 8 therefore also serves to seal the located below the pipe pane areas of the heat exchanger 1 relative to the secondary fluid S.

In the first method step shown in FIG. 1, the heat exchanger tubes 9, 10, 11 flow through in a first flow direction 100 from the primary fluid P, namely from right to left. In a second process step, the flow reversal takes place. Thereafter, the heat exchanger tubes 9, 10, 11 are flowed through in a second flow direction 200 from left to right. This third process step is shown in FIG. 2.

The initially hot primary fluid P is here designated P _h and is conveyed by a pump 26 into the heat exchanger 1 and passed as a cold primary fluid P _k from the heat exchanger 1. So that the hot and the cold primary fluid do not mix, an intermediate tube 13 is arranged below the tube plate 8 as an outlet guide means, which separates the two differently tempered primary fluid streams from each other. For this purpose, the heat exchanger tubes 9, 10, 11 are guided with their in Fig. 1 right tube inlet ends through the intermediate tube 13 down, while their left in Fig. 1 left tube outlet ends flush with the underside of the tube plate 8.

In the first method step shown in FIG. 1, the still-hot primary fluid P _{h is} guided from the primary fluid inlet 3 by means of an inlet guide means to the right-hand side of the intermediate tube 13. In this case, the hot primary fluid P _{h flows} in the first process step into the right-hand tube ends of the heat exchanger tubes 9, 10, 11, flows through them from right to left and leaves them via their left tube ends as now cooled primary fluid P _k . There, the cooled primary fluid P _{k is} guided along the upper side of the intermediate tube 13 from left to right in the direction of the primary fluid outlet 4, via which it leaves the heat exchanger 1.

The first method step shown in FIG. 1 is carried out until approximately the service life of the heat exchanger tubes 9, 10, 11 has been reached. Then, the flow reversal takes place, in which the flow guiding means of the primary fluid P is converted into the shape shown in FIG. For this purpose, the first inlet hood 12 is exchanged for a second inlet hood 20, which is more curved than the first inlet hood 12. As a result, the hot primary fluid P _{h is} now guided to the left side of the intermediate tube 13, the right half has been cut off and removed. Likewise, the right-hand tube ends of the three heat exchanger tubes 9, 10, 11 are separated flush with the tube plate 8 and set three pipe sockets on the original left tube ends of the heat exchanger tubes 9, 10, 11 and passed through the intermediate tube 13. The fixing of the pipe socket to the intermediate pipe 13 takes place here by welding but can also be done for example by hydraulic expansion or the like. After this manually made flow reversal, the heat exchanger 1 can be operated again for a time corresponding to almost the life of a conventional heat exchanger tube. Thus, the life of the heat exchanger 1 has almost doubled compared to the known conventional heat exchange method due to the heat exchange method according to the invention.

In Fig. 3, 4, 5 and 6, a heat exchanger with Wechselberohrung in carrying out a second embodiment of the heat exchange method according to the invention is shown. Under Wechselberohrung is as mentioned above, the alternate arrangement of hot and cold pipe ends next to each other in the tube plate 8 to understand the heat exchanger 1. The adjacent heat exchanger tubes 9, 10, 11 are thus flowed through alternately in different steps in each process step. In the first method step shown in FIG. 3 and FIG. 5, the primary fluid P flows in the first flow direction in the heat exchanger tubes 9 and 11 from left to right and in the heat exchanger tube 10 from right to left. This is also apparent from the plan view shown in FIG. 4 on the section AA shown in FIG. 3, in which the primary fluid flows flowing out of the plane of the drawing are symbolized by crosses.

Also in this heat exchanger 1, the separation of the hot primary fluid flow P _h from the already cooled primary fluid flow P _k by means of an intermediate tube 13 and beyond the tube plate 8 protruding tube ends of the heat exchanger tubes 9,10, 11. As can be seen from the enlarged view of the tube plate 8 and the 5, the tubes 9 and 11 in the first method step with their left tube ends 15 and 16 extend beyond the tube plate 8 into the intermediate tube 13, while the tube 10 with its left tube end 17 is flush with the tube plate 8 concludes. Conversely, close the right pipe ends 14, 18 of the tubes 9 and 11 flush with the tube plate 8 and the pipe end 19 of the heat exchanger tube 11 projects into the intermediate tube 13 into it.

FIG. 5 shows the detail D of the heat exchanger 1 shown in FIG. 3 in the first method step, while FIG. 6 shows the detail D after a flow reversal as a second method step, ie in the third method step. As can be seen from the comparison of FIG. 5 and FIG. 6, in this embodiment of the heat exchange method according to the invention, the flow reversal is such that first the tube ends 14, 18, 17 protruding beyond the underside of the tube plate 8 are cut flush with the tube plate 8 become. Then the original Zwischenrohrschreibe 13 is exchanged for a new reversed perforated Zwischenrohrschreibe 24. Finally, the pipe ends 16, 19, 15 are extended by means of welded-on pipe sockets 21, 22, 23 and welded to the new intermediate pipe disk 24. Thus, the original inlet ends 14, 18, 17 of the heat exchanger tubes 9, 10, 11 have become the outlet openings of the primary fluid P and the tube ends 16, 19, 15 to the inlet ends of the heat exchanger tubes 9, 10, 11. By the flow reversal has in other words changed the hot side of the heat exchanger tubes, so that the much greater wear underlying hot region of the heat exchanger tubes 9, 10, 11 have been moved from the pipe ends 14, 18, 17 towards the pipe ends 16, 19, 15.

Claims (13)

Heat exchange method in which heat is exchanged between a primary fluid (P) and a secondary fluid (S), the primary fluid (P) being passed through at least one heat exchanger tube (9, 10, 11) at least partially surrounded by the secondary fluid (S),
characterized,
that the primary fluid (P) is guided firstly in a first flow direction (100) and after a flow reversal in an opposite second direction of flow (200) through the heat exchange tube (9, 10, 11). Method according to claim 1,
characterized,
that the flow reversal is carried out after a period of time which is slightly shorter than the life of the heat exchanger tube (9, 10, 11). Method according to one of claims 1 or 2,
characterized,
is that the flow direction of the primary fluid (P) repeatedly reversed. Method according to one of the preceding claims,
characterized,
is that the flow direction of the primary fluid (P) is automatically reversed. Method according to one of claims 3 to 4,
characterized,
that the flow direction of the primary fluid (P) is reversed until the maximum sum of the flow times in the same flow direction is only slightly shorter than the lifetime of the heat exchanger tube (9, 10, 11). Method according to one of the preceding claims,
characterized,
that the position of at least one flow-guiding means is changed to reverse the flow. Method according to claim 6,
characterized,
in that, instead of an outlet guide means (13) and / or an outlet guide means (13), instead of an inlet guide means (12), an inlet guide means (12) is arranged for the flow reversal. Method according to one of claims 1 to 5,
characterized,
in that the direction of flow of a primary fluid (P) pump (26) is reversed to reverse the flow. Heat exchanger with at least one heat exchanger tube,
characterized,
in that it has at least one switching means for reversing the direction of flow through the at least one heat exchanger tube (9, 10, 11). Heat exchanger according to one of the preceding claims,
characterized,
in that the switching means is arranged within a housing (2) of the heat exchanger (1). Heat exchanger according to one of the preceding claims,
characterized,
in that the switching means has at least one flow guide means that is variable in its position. Heat exchanger according to claim 9 or 10,
characterized,
that the switching means reverses the conveying direction of a pump (26). Heat exchanger according to one of the preceding claims,
characterized,
that the switching means is electrically and / or mechanically actuated.

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