EP2322854B1 - Heat exchanger for creating steam for solar power plants - Google Patents

Description

The invention relates to a heat exchanger for generating steam for solar power plants according to the preamble of claim 1.

Modular heat exchangers are known from the prior art, which operate according to the so-called circulation principle, natural or forced circulation. In this case, the heat exchanger comprises a number of heat exchanger modules, for example a preheater module, one or more evaporator modules and a superheater module, which are interconnected by means of respective inlet and outlet headers, circulation pipes and an external steam drum to form a functional unit. A generic heat exchanger with running parallel to the longitudinal axis of the outer shell circulation pipe layers is eg in FR 1,359,081 A disclosed.

In solar power plants occur, inter alia, depending on the season, time of day and the weather often large load and temperature changes, so that the design of the steam generator for solar thermal power plants proves difficult. Fast approach speeds with high temperature gradients, small footprint and low manufacturing and operating costs are just some of the important requirements for a heat exchanger for steam generation for a solar power plant.

There is therefore a need for even more compact and even more efficient heat exchangers for solar power plants, which can also be manufactured inexpensively and safely operated.

Therefore, the invention has for its object to provide a heat exchanger, which allows a compact design, cost-effective production and safe operation.

The object is achieved with a heat exchanger according to the independent claim. Preferred developments are given in the dependent claims.

The heat exchanger according to the invention for generating steam for solar power plants comprises an outer jacket with an inlet and an outlet for a heat-emitting medium. Furthermore, the heat exchanger comprises an inlet and an outlet header for a heat-absorbing medium, preferably water, wherein the inlet and the outlet header are arranged substantially inside the outer shell. In addition, located within the outer shell, a tube bundle with a number of tube layers with continuous tubes, which are formed by the heat-emitting medium completely flow around and which are formed as flow paths for the heat-absorbing medium from the inlet collector to the outlet collector. In this case, the tube bundle is formed meandering. The heat exchanger according to the invention is designed for steam generation according to the forced-circulation principle, so that the heat-absorbing medium fed into the inlet collector successively undergoes preheating, evaporation and superheating in the course of the flow paths, so that a superheated steam exits from the outlet collector. In this case, the energy required for the preheating, evaporation and overheating is provided essentially only by the heat transfer from the heat-emitting medium to the heat-absorbing medium within the outer shell.

The heat exchanger thus combines at least three different apparatus, namely preheater, evaporator and superheater, in one. Due to the meandering arrangement of the tubes, the heat exchange takes place according to the counter or cross flow principle. The meandering tubes are flowed through by a heat-absorbing medium, preferably water. Due to the meandering arrangement of the tube bundles, the size of the heat exchanger is reduced overall, improves the heat transfer from the heat-emitting to the heat-absorbing medium and also increases the thermal resilience of the structure.

Due to the design of the heat exchanger for steam generation for solar power plants according to the forced flow principle, ie the heat-absorbing medium, preferably water, "preheated in one pass" from the inlet header to the outlet header, then evaporated and then superheated, becomes an extremely compact and efficient steam generator realized. Instead of using a plurality of separate heat exchanger modules, which require a costly and complicated interconnection, the water entering the heat exchanger via the inlet header in the liquid state is preheated, evaporated and superheated in the course of its flow within the heat exchanger tubes in the direction of the outlet header that via the outlet collector, a superheated steam leaves the heat exchanger, which can be supplied to the steam turbine for power generation.

By saving additional steam drums, circulation lines and connections between the individual modules not only material costs are significantly reduced, but also the manufacturing and operating costs, since a large part of elaborate welding and the subsequent examination account for the same. By eliminating the located outside the outer shell components, such as steam drum and various pipelines, a compact design is achieved and at the same time achieves a higher efficiency of the heat exchanger, since the heat transfer takes place to generate steam substantially only within the outer jacket of the heat exchanger and thus no additional heat losses due to located outside the heat exchanger outer shell components occur.

"Continuous tubes" in this context means that each tube, which defines a respective flow path for the heat-absorbing medium, has no branching or mixing points between the inlet header and the outlet header. In addition, the tubes run completely "inside the outer jacket", which means that no parts of the tube bundle are outside the outer jacket and that the pipes are completely surrounded by the heat-emitting medium. So no external energy sources are needed to promote preheating, evaporation or overheating. The heating surfaces of the continuous tubes themselves thus form successively the preheater, evaporator and superheater zones viewed in the direction of flow. Externally, these individual "zones" are not recognizable, since only one tube bundle is arranged between the inlet header and the outlet header and the tube bundle has a constant course with a repetitive meandering pattern.

According to the invention, the heat exchanger is set up vertically. Vertical placement is preferred because it allows even better land use. In this case, several of the heat exchangers according to the invention can be operated side by side in parallel on a relatively small area. In thermal solar power plants, the space conditions are unfavorable because the parabolic trough collectors take up a lot of space. The space-saving design of the heat exchanger according to the invention allows an almost location-independent installation, so that the flow paths of the heated media can be shortened to the heat exchanger expedient manner. The temperatures of the heat-emitting medium when entering the heat exchanger are higher, so that the heat yield is better.

A further preferred embodiment of the invention provides that the tube bundle has a number of vertical pipe layers when mounted vertically, each pipe layer an equal number of tubes is formed, and that the tube layers are arranged so that the tubes of the individual tube layers in the horizontal direction are aligned exactly juxtaposed, the flow directions of the heat-absorbing medium in the horizontally adjacent, arranged transversely to the central axis of the outer shell pipe sections opposite are. The design of the tube bundles in individual tube layers allows an extremely compact design. The fact that the tubes lie horizontally exactly next to each other, conventional spacers between the tubes can be used. The opposite flow in the horizontally adjacent pipe sections, which are arranged transversely to the central axis of the outer shell, favors the symmetrical temperature distribution in the heat exchanger with respect to the central axis.

Preferably, the inlet and the outlet header have a circular cross-section. The tubes of a pipe layer on a circumferential line of the inlet or outlet collector are offset from each other by an equal angle with the inlet and outlet collector. In this way, the manufacturing process is facilitated because there is enough space for welding, machining or other work on the collectors.

Further preferably, the tubes of the adjacent tube layers are connected to the inlet and outlet header such that the tubes of one tube layer are offset relative to the tubes of the adjacent tube layer by an angle on an adjacent circumferential line of the respective inlet and outlet header. As a result, the peripheral surfaces of the inlet and outlet collector can be optimally utilized, so that the arrangement of the pipe layers can be made compact. There is still enough space for welding, machining or other work on the collectors.

According to a further embodiment of the invention, the tube bundle has a separate section, in which predominantly the preheating of the heat-absorbing medium takes place. The separate preheater section can be realized for example by a local separation within the outer shell. It is also possible to control the flow of the heat-emitting medium and thus the temperature distribution in the heat exchanger so that in this preheater section takes place mainly the preheating of the heat-absorbing medium. Alternatively, the preheating could be done completely outside the outer shell, ie in a separate preheater. In this case, the heat exchanger according to the invention would be designed primarily for the evaporation and overheating of the heat-absorbing medium.

According to a further embodiment of the invention, the tube bundle has a separate section in which predominantly the evaporation of the heat-absorbing medium takes place. The separate evaporator section can be realized for example by a local separation within the outer shell. It is also possible to control the flow of the heat-emitting medium and thus the temperature distribution in the heat exchanger so that in this evaporator section mainly the evaporation of the heat-absorbing medium takes place. Alternatively, the evaporation could completely outside the outer shell, d. H. in a separate evaporator. In this case, the heat exchanger according to the invention would be designed primarily for preheating and overheating of the heat-absorbing medium.

According to a further embodiment of the invention, the tube bundle has a separate section in which predominantly the overheating of the heat-absorbing medium takes place. The separate superheater section can be realized for example by a local separation within the outer jacket. It is also possible to control the flow of the heat-emitting medium and thus the temperature distribution in the heat exchanger so that in this superheater section takes place mainly the overheating of the heat-absorbing medium. Alternatively, the overheating could be completely outside the outer shell, d. H. in a separate superheater, done. In this case, the heat exchanger according to the invention would be designed primarily for the preheating and the evaporation of the heat-absorbing medium.

Preferably, the tubes are connected via nipples to the inlet and outlet header. As a result, the connection of the compact tube bundle at the inlet and outlet collector is simplified. The connection between the nipples and the individual tubes is preferably cohesively, for example by welding. The welding process can be automated. Subsequently, the welds are checked individually, for example with the help of X-rays.

In a preferred embodiment of the invention, the tubes are connected without nipple directly to the inlet and outlet header. Also in this case, the connection between the collectors and the individual tubes is preferably cohesively, for example by welding. The welding process can also be automated here. Subsequently, the welds are checked individually, for example with the help of X-rays.

Preferably, the nipples are in turn cohesively, for example by welding, connected to the inlet and outlet collector. Again, the welding process can take place automatically.

According to a further embodiment of the invention, the nipples are machined directly from the material of the inlet or outlet collector. For example, the nipples can be milled out of the initially tubular material of the inlet or outlet collector. This will reduce any damage due to welding. In addition, this eliminates the examination of the individual welds between the nipples and the respective collector.

According to a preferred embodiment of the invention, the tubes of the tube bundle are arranged in an inner housing, which is arranged concentrically within the outer jacket and has an inlet and an outlet opening for the heat-emitting medium. The cross-sectional profile of the inner housing is preferably rectangular, so that the Rohbündel is as closely as possible enclosed by this inner housing. The additional enclosure of the heat exchanging components provides further insulation between the heat exchanger modules and the environment. In this case, the inlet and the outlet opening of the inner housing may be connected to the corresponding inlet or outlet nozzle in such a way that a separate space between the outer shell and the inner housing is provided. Alternatively, a flow of the heat-emitting medium along the inner wall of the outer shell can be allowed.

In an advantageous embodiment of the invention, the inlet and the outlet of the heat-emitting medium in the vertical installation of the heat exchanger in the lower part of the outer shell are arranged. As a result, the compactness of the heat exchanger is further increased. Furthermore, the maintenance is facilitated because the shell-side connections are located within reach of the ground. The space between the outer shell and the inner housing is used as a flow channel for the heat-emitting medium. The hot heat-emitting medium passes through the inlet port of the outer shell and the inlet opening of the inner housing in the interior of the inner housing and flows upward. Subsequently, the heat-emitting medium flows through the annular flow channel, which results from the concentric arrangement of the outer shell and the inner housing, back down, where it then leaves the outer jacket via the outlet port. In this way, the residence time of the heat-emitting medium is prolonged in the heat exchanger, so that the heat transfer to the heat-absorbing medium is improved overall.

• Fig. 1 eine Seitenansicht einer Ausführungsform des erfindungsgemäßen Wärmetauschers;
• Fig. 2 eine Schnittansicht entlang der Linie A-A aus Fig. 1;
• Fig. 3 eine Detailansicht "X" aus Fig. 2;
• Fig. 4 eine Schnittansicht entlang der Linie B-B aus Fig. 3;
• Fig. 5 eine Detailansicht des Eintrittssammlers aus Fig. 1 und 2;
• Fig. 6 eine Draufsicht des Eintrittssammlers aus Fig. 5;

The invention will be described in more detail with reference to figures. They show schematically:

• Fig. 1 a side view of an embodiment of the heat exchanger according to the invention;
• Fig. 2 a sectional view taken along the line AA Fig. 1 ;
• Fig. 3 a detail view "X" off Fig. 2 ;
• Fig. 4 a sectional view taken along the line BB Fig. 3 ;
• Fig. 5 a detailed view of the entrance collector from Fig. 1 and 2 ;
• Fig. 6 a plan view of the inlet collector Fig. 5 ;

Figures 1 and 2 show an embodiment of the heat exchanger according to the invention 1. The heat exchanger 1 is placed vertically in a space-saving manner. In the outer casing 2 is an inner housing 3, which has a rectangular cross-sectional profile. In the inner housing 3, the meandering tubes of the tube bundle 11 are arranged. The heat-absorbing medium, for example water, enters the heat exchanger 1 via the inlet header 6. After flowing through the tubes of the tube bundle 11, it passes out of the heat exchanger 1 via the outlet collector 7. On the way from the inlet collector 6 to the outlet collector 7, the water is preheated, then evaporated and then superheated. The exiting from the heat exchanger 1 superheated steam is passed to generate electricity in the downstream steam turbine (not shown). Externally, the individual "zones", namely preheater, evaporator and superheater, are not recognizable. The forced-circulation principle, for example Benson principle, working heat exchanger 1 for steam generation generated from the feed water, which enters the inlet collector in liquid form, in the course of the flow within the heat exchanger 1, a superheated steam, which can be removed from the outlet collector 7 , This eliminates the commonly used steam drums, circulation pipes, inlet and outlet collectors and countless welds, so that the compactness is increased and the production costs are saved. The claws 8 are used to mount the heat exchanger 1. About the manholes 9, which have transparent glass windows and / or closure means, maintenance work can be performed in a simple manner.

The heat-emitting medium is preferably thermal oil, which is heated in the absorber tubes of the parabolic troughs to about 400 ° C. Alternatively, liquid salts or other suitable heat transfer media may be used. The thermal oil enters via the inlet port 4 of the outer shell 2 in the heat exchanger 1. From there it flows in the direction of the outlet nozzle 5 and flows around the meandering shaped tube bundle 11. After the thermal oil has released a portion of its heat energy to the water, it passes through the outlet nozzle 5 from the heat exchanger 1 out.

According to an embodiment, not shown, the shell-side flow of the thermal oil can be directed so that the thermal oil in the lower part of the heat exchanger 1 and exits. The space between the inner housing 3 and the outer shell 2 serves as a flow path for the downwardly flowing thermal oil. In this case, both the inlet and the outlet are arranged in the lower region of the vertically mounted heat exchanger 1.

In FIG. 2 two pipes of a pipe layer are indicated. Of course, the number of tubes and the tube layers of a tube bundle 11 can be adapted to the different conditions. For example, in FIG. 3 a pipe layer 20 with four tubes 21, 22, 23, 24 shown. This clearly shows the meandering pattern of the tube bundle 11.

FIG. 4 the arrangement of the individual pipe layers 20, 30 relative to one another is illustrated. In the pipe sections 15 ( Fig. 3 ), which are arranged transversely to the central axis 10 of the outer shell 1, each tube with respect to its horizontally adjacent tube when mounted vertically an opposite direction of the pipe flow. This means, for example, that the flow in the tube 21 is opposite to the flow in the horizontally adjacent tube 34. This opposite flow in the respectively adjacent pipe layers 20, 30 additionally ensures a uniform temperature distribution within the heat exchanger 1. Due to the uniform and compact arrangement of pipes and pipe layers to each other simple spacers 12 can be used.

In FIG. 5 an inventive collector is shown enlarged. These are the inlet header 6. Inlet and outlet header 6, 7 differ only slightly from each other. Well recognizable are the nipples 22a, 33a, which serve to secure the tubes 22, 33 to the inlet header 6. The nipples 21a, 22a, 23a, 24a and thus also the tubes 21, 22, 23, 24 of the first tube layer 20 lie on a first circumferential line 13 and each open at an equal angle α offset in the collector 6. Likewise, the tubes open 31st , 32, 33, 34 with the respective nipples 31 a, 32 a, 33 a, 34 a on an adjacent circumferential line 14 offset by the same angle α in the collector. 6

FIG. 6 shows a plan view of the collector 6. The angle α, by which a tube of a layer is offset from the next tube of the same position, in this case is in each case 45 °. The second layer 30, which is adjacent to the first layer 20, is arranged offset on the collector 6 with respect to the first layer 20 by exactly β = 22.5 °, so that the tubes 31, 32, 33, 34 of the second layer 30 in FIG. 6 each centrally between the tubes 21, 22, 23, 24 of the first layer 20 are visible. Through this Regularly horizontally and vertically staggered arrangement of nipples on the collector 6 remains despite the high compactness always a sufficient distance for welding or other manufacturing steps.

Claims (12)

1. A heat exchanger (1) for generating steam for solar power plants, with the heat exchanger being erected vertically, comprising:

   - an outer casing (2) with an inlet nozzle (4) and an outlet nozzle (5) for a heat-emitting medium;

   - an inlet header (6) and an outlet header (7) for a heat-absorbing medium, preferably water, with the inlet header (6) and the outlet header (7) being arranged substantially within the outer casing (2);

   - a tube bundle (11) within the outer casing (2) with a number of tube layers (20, 30) with continuous tubes (21, 22, 23, 24, 33, 34) which are arranged so that the heat-emitting medium can flow around said tubes completely and which are arranged as flow paths for the heat-absorbing medium from the inlet header (6) to the outlet header (7);

   with the tube bundle (11) being arranged in a meandering manner, with the heat exchanger (1) for generating steam being arranged according to the forced-flow principle, so that the heat-absorbing medium supplied to the inlet header (6) is successively subjected in the course of the flow paths to a preheating, an evaporation and a superheating, so that superheated steam exits from the outlet header (7), and with the energy required for the preheating, evaporation and superheating being made available substantially solely by heat transfer from the heat-emitting medium to the heat-absorbing medium within the heat exchanger (1),
   characterized in that
   the tube layers (20, 30) are arranged in such a way that the tubes (21, 22, 23, 24, 33, 34) of the individual tube layers (20, 30) are aligned to lie precisely next to one another in the horizontal direction, with the directions of flow of the heat-absorbing medium being opposite in the horizontally adjacent tube sections (15) which are arranged transversely to the central axis (10) of the outer casing (2), and that the tube layers (20, 30) are vertically adjacent, wherein each tube layer (20, 30) is formed from an equal number of tubes (21, 22, 23, 24, 33, 34).
2. The heat exchanger (1) according to claim 1,
   characterized in that
   the inlet header (6) and the outlet header (7) have a circular cross section, and the tubes (21, 22, 23, 24) of a tube layer (20) are connected with the inlet header (6) and outlet header (7) on a circumferential line (13) of the inlet header (6) and outlet header (7) offset from one another by the same angle (α).
3. The heat exchanger (1) according to any one of the preceding claims,
   characterized in that
   the tubes (21, 22, 23, 24, 33, 34) of the adjacent tube layers (20, 30) are connected with the inlet header (6) and outlet header (7) in such a way that the tubes (33, 34) of the one tube layer (30) are arranged with respect to the tubes (21, 22, 23, 24) of the adjacent tube layer (20) offset by an angle (ß) on an adjacent circumferential line (14) of the inlet header (6) and outlet header (7).
4. The heat exchanger (1) according to any one of the preceding claims,
   characterized in that
   the tube bundle (11) comprises a separate section in which mainly the preheating of the heat-absorbing medium occurs.
5. The heat exchanger (1) according to any one of the preceding claims,
   characterized in that
   the tube bundle (11) has a separate section in which mainly the evaporation of the heat-absorbing medium occurs.
6. The heat exchanger (1) according to any one of the preceding claims,
   characterized in that
   the tube bundle (11) has a separate section in which mainly the superheating of the heat-absorbing medium occurs.
7. The heat exchanger (1) according to any one of the preceding claims,
   characterized in that
   the tubes (21, 22, 23, 24, 33, 34) are connected with the inlet header (6) and outlet header (7) via nipples (21 a, 22a, 23a, 24a, 31 a, 32a, 33a, 34a).
8. The heat exchanger (1) according to any one of the preceding claims,
   characterized in that
   the tubes (21, 22, 23, 24, 33, 34) are directly connected without nipples with the inlet header (6) and outlet header (7).
9. The heat exchanger (1) according to claim 7,
   characterized in that
   the nipples (21 a, 22a, 23a, 24a, 31 a, 32a, 33a, 34a) are materially connected with the inlet header (6) and outlet header (7).
10. The heat exchanger (1) according to claim 7,
    characterized in that
    the nipples (21 a, 22a, 23a, 24a, 31 a, 32a, 33a, 34a) are made by metal cutting from the material of the inlet header (6) and outlet header (7).
11. The heat exchanger (1) according to any one of the preceding claims,
    characterized in that
    the tube bundle (11) is arranged in an inner housing (3) which is arranged concentrically within the outer casing (2) and comprises an inlet and an outlet opening for the heat-emitting medium.
12. The heat exchanger (1) according to any one of the preceding claims,
    characterized in that
    the inlet (4) and the outlet nozzle (5) for the heat-emitting medium are arranged in the bottom part of the outer casing (2) of the vertically erected heat exchanger (1).

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