ES2648737B1 - Receiver for solar power tower - Google Patents

Abstract

Solar tower receiver that has at least one tubular assembly (1) comprising an inner tube (2) and an outer tube (3) external and eccentric to the inner tube (2). A first end of the inner tube (6) is connected to a first manifold (4) and a first end of the outer tube (7) is connected to a second manifold (5), the first manifold (4) and the second manifold (5 ) arranged one above the other and both on the same side of the tubular assembly (1). A second end of the inner tube (8) is connected to a second end of the outer tube (9) by means of a bayonet assembly (10) that allows the flow of heat transfer fluid between both tubes (8, 9) of so that the heat transfer fluid is heated along the tubular assembly (1).

Description

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DESCRIPTION

Receiver for solar power tower Technical field

The present invention encompasses the field of solar energy, specifically high concentration thermal solar systems, and more specifically solar power tower technologies.

This invention relates, in particular, to a solar power tower receiver with at least one tubular assembly having an inner tube and an outer outer tube and eccentric to the inner tube, both connected to manifolds and configured for fluid flow. Heat transfer (HTF).

The inner tube and the outer tube are connected by means of a bayonet joint that allows the flow of heat transfer fluid, heated the HTF along the tubular assembly.

Prior art

The use of solar energy as a renewable source to produce electricity in thermal power plants has increased in recent years, thanks to innovations and design improvements. One of the most promising technologies in terms of power and efficiency is the Solar Energy Tower (SPT).

In SPT technology, direct solar radiation is reflected by a plurality of solar tracking mirrors that concentrate solar radiation on a receiver, located at the top of a tower. In this way, the direct radiation is concentrated in the effective area of the receiver allowing to reach the maximum radiation peak. Solar energy is collected at the receiver using an HTF which is then used to transfer the energy to a thermodynamic power cycle, or for a different use.

The central receiver is one of the most important subsystems of SPT systems. In general, 80-90% of the reflected energy is absorbed and transferred to the working fluid, which is HTF. The HTF can be any fluid with a high capacity of absorption and transfer of thermal energy. Some examples are water, air, molten salts or synthetic oils that withstand high temperatures. Today, there are different configurations of the receiver, such as cylindrical, cavity, or fluidized or volumetric bed. The main differences between the receivers refer to the working fluid used, how solar radiation is absorbed and transferred to the working fluid and, finally, how the receiver is protected against heat losses.

While the cavity and volumetric receptors are receiving a lot of attention from the academic community, external solar receivers are the most commercially used. In cylindrical receptors, solar radiation is absorbed by several tubes located in the external environment; the tubes are cooled in their internal part by the HTF flow. In the absence of highly selective coatings on the surface of the tube, the

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Direct exposure to the environment implies high thermal losses, so it is not possible to work at very high temperatures. On the other hand, the fact that the outer surface of the tubes directly intercepts the solar radiation, while the cooling fluid flows into the inner part of the wall, causes the solar concentration rate is not high enough to avoid Overheating in the tubes or burning. This leads to reduced interception of reflected solar radiation (reduction of the optical efficiency of the solar plant).

Improved efficiency and durability of the receiver have an important effect on the available power and maintenance cost of SPT systems. The search for optimal receiver designs is, today, one of the main priorities in the development of solar thermal power plants. There are numerous documents that develop different receivers or other aspects. Some examples are the following:

Document US3924604 discloses an exterior type receiver with tubes arranged around the central axis of the tower. This receiver is located at the top of the tower and is also in the middle of a field of circularly arranged heliostats.

Document US4400946 proposes a new configuration for a solar tower concentration plant, where steam generation is defined in a receiver arranged in a ring of a circular sector of the circle described by the tower.

The documents US6911110 and WO2008118980 have been published with respect to the previous technology, trying to optimize the various elements and processes of the system.

Document ES2363288 discloses a tubular molten salt receiver with a new operative method to reduce thermal gradients in the tubes. In this document, a new receiver design is proposed that solves the problem of the resistance of the material so that it is able to homogenize the temperature of the receiver and reduce the temperature of the wall.

In order for SPT technology to be competitive, it is essential to increase the overall efficiency and reduce the damage of the different elements in real working conditions, especially in the receiver due to the high density of energy exchanged and the hard working conditions.

The current SPT technology has presented technical and economic difficulties. These have resulted in short operating periods, the commercial implementation of tower plants being difficult, which require a long service life (between 20 and 25 years).

The technical inconveniences during the operation of these plants are mainly related to the resistance of the material and the control of the transient states (passing clouds). Some of the technical difficulties encountered were the appearance of cracks in critical regions such as in the pipes and weld joints of the heads due to high thermal gradients, stresses and corrosion.

At present, solar radiation reflected to a receiver by a field of heliostats produces a working state with high temperatures and therefore high losses of

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thermal energy in the environment and damage to the structure due to high working temperatures, uneven distribution of solar radiation, thermal stresses and corrosive effects on the material.

All these facts give rise to certain problems, which are mainly:

• The need for special materials that withstand high temperatures, but are expensive.

• Decrease in the proportion of concentrate, with the following decrease in energy efficiency.

• Blur of heliostats so that there are some points of the objective that reach a decrease in the optical efficiency of the solar plant.

Therefore, an efficient receiver for the solar power tower that overcomes the disadvantages of prior art solar power tower technologies is necessary, being able to withstand high temperatures, reduce losses and increase life expectancy, reduce maintenance costs and increasing the overall efficiency of the plant.

Summary of the Invention

The present invention provides an advantage over current SPT technologies by means of a solar power tower receiver as set forth in claim 1 of the present application.

The present invention relates to a receiver for SPT having tubular assemblies which in turn comprise an inner tube and an outer outer tube and eccentric to the inner tube, which provides an annular space between the inner tube and the outer tube. The inner tube and the annular space are configured for the flow of an HTF.

According to the invention, a first end of the inner tube is connected to a first manifold, and a first end of the outer tube is connected to a second manifold, such that the first manifold and the second manifold are arranged one above the other and both on the same side of the tubular assembly. In addition, a second end of the inner tube is connected to a second end of the outer tube by means of a bayonet assembly, which allows the flow of the HTF between both tubes, and the HTF is heated along the tubular assembly by solar radiation.

With respect to a preferred embodiment of the invention, the receiver has a plurality of tubular assemblies connected to the first and second collectors as described above, the HTF in each tubular assembly being heated by solar radiation. Thus, the receiver is formed by a variable number of tubular assemblies connected in series and / or in parallel that intercept the solar radiation reflected by the heliostats. A plurality of tubular assemblies forms a set, also called a panel. Thus, when the HTF flows in parallel through the tubular assemblies they all form part of the same assembly or panel, however when the HTF flows in series through different assemblies they are arranged in different panels. Each panel has its own first and second collector.

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Through this configuration, the HTF enters the receiver through one of the collectors, flows in parallel through all the tubular assemblies that form the first panel and exits through the other collector to pass through the next panel, in which it is repeated the process. The HTF flows in series through the different panels to the end of the receiver.

The main feature of this receiver is that both collectors are on the same side of the tubular assemblies. The number of tubular assemblies in the receiver and the eccentricity of the tubes vary depending on the diameter of the receiver, the incident solar radiation and the characteristics of the power cycle.

Therefore, the present invention uses tubular assemblies with an eccentric inner tube and an outer tube of different diameters connected through a bayonet joint, or, in other words, also called "eccentric bayonet" tubes. The bayonet joint can have different shapes and dimensions to minimize the pressure drop.

These tubular assemblies can be placed vertically or horizontally in the receiver located in the solar power towers.

The use of these "eccentric bayonet" tubes homogenizes the temperatures and reduces the temperatures along the walls of the receiver, reducing the risk of thermal corrosion and improving the behavior of the receiver before transient states. On the other hand, the "eccentric bayonet" tubes would lead to an increase in the convection coefficient in selected areas of the inner part of the tubes while maintaining the pressure drop or even reducing it.

This "eccentric bayonet" receiver configuration provides the most efficient and safe operation and also has an extra degree of freedom (eccentricity) in its configuration. This is an improvement compared to the performance of flat tubes or standard bayonet tubes (ie, not eccentric).

Additional advantages of the present invention are the following:

- Increase in the global heat transfer coefficient and, more importantly, the increase in the local heat transfer coefficient in areas where the separation between pipes is maximum.

-The area with the highest heat transfer coefficient should coincide with the frontal region, more irradiated by heliostats, reducing the frontal temperature of the tube wall.

-Increase the homogeneity of the temperature in the receiver, without reducing the incident solar radiation.

- Reducing the temperature of the outer wall also reduces thermal losses without reducing the overall temperature of the heat transfer fluid.

-Increase in efficiency, which allows reducing the number of tubes in the receiver or the number of heliostats in the field.

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-Reduction of temperatures and mechanical stresses which makes it possible to use cheaper materials in the construction of the receiver.

Therefore, the present receiver overcomes the problem of the conventional receiver of low heat transfer coefficients. This receiver, object of the present invention, increases the overall heat transfer coefficient and additionally the eccentricity allows to increase the local heat transfer coefficient in the front zone of the tubes where the solar radiation is highest.

The present receiver solves many problems presented in conventional receivers. The design of the "eccentric bayonet" tubes in the receiver can homogenize the temperature of the receiver, reducing thermal stress and wall temperature and increasing thermal efficiency. This creates the possibility of using suitable materials for lower temperatures and At the same time, reduce your construction and maintenance costs.

With respect to a particular embodiment of the receiver, each tubular assembly has a liner that covers the outer tube, which is made of a stable selective material in the temperature range of 300-800 ° C. In the absence of selective materials, this coating should have as much absorption as possible, with Black Pyromark® being one of the preferable materials.

With reference to a particular embodiment of the invention, the first collector provides the flow of HTF to the tubular assemblies and the second collector collects the flow of HTF from the tubular assemblies, such that the temperature of the HTF in the second collector is higher than in the first collector.

According to an alternative embodiment of the invention, it is the second collector that provides the flow of HTF to the tubular assemblies while the first collector collects the flow of HTF from the tubular assemblies, such that the temperature of the HTF in the The first collector set is higher than in the second collector.

Therefore, in operation, the flow direction of the inlet and outlet fluid may vary. The cold fluid can be pumped to the inner tube that enters through the first manifold or to the annular space that first flows through the second manifold and the hot fluid flows through the annular space that exits through the second manifold or through the inner tube that leaves by the first collector, respectively. In addition, it should be taken into account that the front part of the tubular assembly is the part that is exposed to solar radiation, and it is this front part that has the greatest separation between the inner tube and the outer tube.

The features, functions and advantages that have been discussed can be achieved independently in various embodiments or can be combined in other embodiments, the details of which can be seen with reference to the following description and drawings.

Brief description of the drawings

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Next, in order to facilitate the understanding of this description, in an illustrative rather than limiting manner, a series of embodiments will be made with reference to a series of figures.

Figure 1 shows a plan view of an embodiment of the receiver of the present invention, in which the inner tube is the hot HTF outlet and the outer tube is the cold HTF inlet.

Figure 2 shows a front sectional view of the receiver of Figure 1 in which the inner tube is the hot HTF outlet and the outer tube is the cold HTF inlet.

Figure 3 shows a side sectional view of the receiver of Figures 1-2 in which the inner tube is the hot HTF outlet and the outer tube is the cold HTF inlet.

Figure 4 shows a plan view of an alternative embodiment of the receiver of the present invention, in which the inner tube is the cold HTF inlet and the outer tube is the hot HTF outlet.

Figure 5 shows a front sectional view of the receiver of Figure 4 in which the inner tube is the cold HTF inlet and the outer tube is the hot HTF outlet.

Figure 6 shows a side sectional view of the receiver of Figures 4-5 in which the inner tube is the cold HTF inlet and the outer tube is the hot HTF outlet.

Figure 7 shows a front view of an embodiment of a receiver of the present invention that includes four tubular assemblies and two manifolds located at the bottom of the receiver, in which the inner tube is the outlet of the HTF fluid and the outer tube is the entrance of the cold HTF.

Figure 8 shows a front view of an embodiment of a receiver of the present invention that includes four tubular assemblies and two collectors located at the bottom of the receiver, in which the inner tube is the cold HTF inlet and the outer tube is the Hot HTF output.

Figure 9 shows a front view of an embodiment of a receiver of the present invention that includes four tubular assemblies and two collectors located at the top of the receiver, in which the inner tube is the hot HTF outlet and the outer tube is the entrance of the cold HTF.

Figure 10 shows a front view of an embodiment of a receiver of the present invention that includes four tubular assemblies and two manifolds located at the top of the receiver, in which the inner tube is the cold HTF inlet and the outer tube is Hot HTF output.

Figure 11 shows a perspective view of an embodiment of a receiver of the present invention that includes three tubular assemblies and two manifolds located at the bottom of the receiver.

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Figure 12 shows a perspective view of an embodiment of a receiver of the present invention that includes three tubular assemblies and two manifolds located at the top of the receiver.

Figure 13 shows a perspective view of an embodiment of a receiver of the present invention that includes two groups of four tubular assemblies and two groups of two collectors, these assemblies called panels located at the top of the receiver connected in series.

Figure 14 shows a perspective view of a cylindrical embodiment of a receiver of the present invention that includes a number of panels whose collectors are located at the top of the receiver.

These figures refer to the following set of elements:

1. tubular receiver sets

2. inner tube of the tubular assembly

3. outer tube of the tubular assembly

4. first collector

5. second collector

6. first end of inner tube

7. first end of outer tube

8. second end of the inner tube

9. second end of the outer tube

10. bayonet assembly

11. solar radiation.

12. hot heat transfer fluid

13. cold heat transfer fluid

14. outer tube lining

15. panel

Description of realizations

The present disclosure refers to a receiver for Solar Energy Tower (SPT).

As can be seen in the figures, the receiver has at least one tubular assembly 1 which in turn comprises an inner tube 2 and an outer outer tube 3 and eccentric to the inner tube 2, providing an annular space between the inner tube 2 and the tube 3 outside.

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The inner tube 2 and the annular space are configured for the flow of a Heat Transfer Fluid (HTF).

A first end of the inner tube 6 is connected to a first manifold 4 and a first end of the outer tube 7 is connected to a second manifold 5. The first manifold 4 and the second manifold 5 are arranged one above the other and both are arranged in the same side of the tubular assembly 1.

Additionally, a second end of the inner tube 8 is connected to a second end of the outer tube 9 by means of a bayonet assembly 10 that allows the flow of the HTF between both tubes 2, 3, just as the HTF is heated along the 1 tubular set by solar radiation.

Figures 2-3 and 5-6 schematically represent the sectional view of the tubular assembly 1 that ends on one of its sides with a bayonet assembly 10 that connects the inner tube 8 and the outer tube 9. This bayonet assembly 10 is schematically represented since there are different configurations that minimize the pressure losses of the tubular assembly 1.

Figures 1-6 show the front part of the tubular assembly, which is the part where it is exposed to solar radiation 11, and this front part is the one with the greatest separation between the inner tube 2 and the outer tube 3.

With respect to preferred embodiments of the invention, the receiver has a plurality of tubular assemblies 1 connected to the first and second manifolds 4 and 5 as described above. In each tubular set 1 the HTF is heated by solar radiation. Figures 7-14 show various embodiments of the receiver, called panels 15 that include a plurality of tubular assemblies 1.

With respect to a particular embodiment of the invention, each tubular assembly 1 comprises a coating 14 covering the outer tube 2, made this coating 14 of a selective material having a high solar absorption capacity and a low solar emissivity. Preferably, the material will have a solar absorptivity of 80% and will be stable in the temperature range of 300-800 ° C. In the absence of selective materials, this coating must have a high absorption capacity, one of the preferable materials may be Black Pyromark.

Depending on the direction of circulation of the heat transfer fluid along the inner tube 2 and the outer tube 3 of the tubular assemblies 1, there will be different work configurations and different embodiments.

With reference to a particular embodiment of the invention, the first manifold 4 provides the flow of HTF to the tubular assemblies 1 and the second manifold 5 collects the HTF flow of the tubular assemblies 1, such that the temperature of the HTF assembly in the second manifold 5 is larger than in the first manifold 4. In this embodiment, the inner tube 2 is the inlet 13 of the cold HTF and the outer tube 3 is the outlet 12 of the hot HTF.

Figures 1-3, 7, 9 show different views of an embodiment of the receiver of the present invention in which the inner tube 2 is the outlet 12 of the hot HTF and the outer tube 3 is the inlet 13 of the cold HTF.

According to an alternative embodiment of the invention, the second manifold 5 which 5 provides the flow of HTF to the tubular assemblies 1 while the first manifold 4 collects the HTF flow of the tubular assemblies 1, such that the temperature of the HTF in the first collector 4 is higher than in the second collector 5. In this embodiment the inner tube 2 is the outlet 12 of the hot HTF and the outer tube is the inlet 13 of the cold HTF.

10 Figures 4-6, 8, 10 show different views of an embodiment of the receiver of the present invention in which the inner tube 2 is the inlet 13 of the cold HTF and the outer tube 3 is the outlet 12 of the hot HTF.

Figure 13 shows a perspective view of an embodiment of a receiver of the present invention that includes two panels 15, consisting of four sets 1

15 tubular and two manifolds 4, 5 located at the top of the receiver, connected in series.

Figure 14 shows a perspective view of a cylindrical embodiment of a receiver of the present invention that includes several numbers of panels 15, each of two manifolds 4 and 5 and a determined number of tube assembly 1.

However, a preferred embodiment of the invention is a cylindrical tubular receiver comprising a plurality of panels 15 formed by tubular assemblies 1 with "eccentric bayonet" tubes positioned vertically and a first manifold 4 and a second manifold 5 arranged in the bottom of the receiver to allow the receiver to drain by gravity.

Once the invention has been clearly described, it is noted that the particular embodiments described above may be subject to detailed modifications as long as they do not alter the fundamental principle and essence of the invention.

Claims (4)

5 10 fifteen twenty 25 30 ES 2 648 737 A1 1. - Receiver for solar power tower characterized in that it comprises at least one tubular assembly (1) which in turn comprises -a tube (2) inside - and an outer outer tube (3) and eccentric to the inner tube (2) that provides an annular space between said inner tube (2) and the outer tube (3), - the inner tube (2) and the annular space configured for the flow of a heat transfer fluid, - a first end of the inner tube (6) connected to a first manifold (4) and a first end of the outer tube (7) connected to a second manifold (5), the first manifold (4) and the second manifold (5) arranged one above the other and both on the same side of the tubular assembly (1), - and a second end of the inner tube (8) connected to a second end of the outer tube (9) by means of a bayonet assembly (10) allowing the flow of heat transfer fluid between both tubes (8, 9) , the heat transfer fluid being heated along the tubular assembly (1) by solar radiation. 2. - Receiver for solar energy tower according to claim 1, characterized in that each tubular assembly (1) comprises a coating (14) covering the outer tube (2), the coating having a solar absorptivity of 80% and being stable in the temperature range of 300-800 ° C. 3. - Receiver for solar power tower, according to any of the preceding claims, characterized in that the first manifold (4) provides the flow of heat transfer fluid to the tubular assemblies (1) and the second manifold (5) collects the heat transfer fluid flow of the tubular assemblies (1), the temperature of the heat transfer fluid in the second manifold (5) being higher than in the first manifold (4). 4. - Receiver for solar energy tower, according to any of claims 1-2, characterized in that the second manifold (5) provides the flow of heat transfer fluid to the tubular assemblies (1) and the first manifold (4) collects the heat transfer fluid flow of the tubular assemblies (1), the temperature of the heat transfer fluid in the first manifold (4) being higher than in the second manifold (5).