ES2735303B2 - OUTDOOR TOWER SOLAR RECEIVER - Google Patents

Description

DESCRIPTION

OUTDOOR TOWER SOLAR RECEIVER

Field of the invention

The present invention is encompassed within the field of high temperature concentration solar energy, and more specifically in tower-type thermosolar generation plants and in the conversion of solar radiation into thermal energy.

Background

The sun is a renewable energy source that has captured the industry's attention in recent decades due to the growing interest in renewable energy and the increasing demand for electricity.

Within solar energy systems, it is worth highlighting the great development experienced by electricity production technologies through solar concentration. Among them, central receiver or tower systems seem to be the technology with the greatest future prospects due to their large storage capacity and their adaptability to produce according to the demand of the energy market.

In tower-type solar plants, direct solar radiation is concentrated and reflected by a set of mirrors, called heliostats, on the surface of a solar receiver located at the top of a tower. In the receiver typically 80% -90% of the reflected energy is absorbed and transferred to a working fluid, which circulates inside it, in the form of thermal energy. This thermal energy can be stored or sent to a steam generator, where it will be converted into electrical energy through a traditional power cycle.

Although there are numerous central receiver configurations, the most common commercially are tubular outer receivers. These receivers consist of a series of panels, made up of inlet and outlet collectors and vertical tubes, arranged in a polyhedral shape, approaching a cylinder. The collectors located in the upper part of the tower are embedded with movement restriction, while the tubes are periodically guided, allowing displacements in a vertical direction. Solar radiation is captured by the tubes that are subjected to extreme working conditions since, on the outside, they intercept high inhomogeneous solar radiation of a cyclical nature, which causes large gradients of temperatures, stresses and fatigue, and internally the tubes are subjected to a corrosive environment due to the working fluid.

The tower-type solar power plants with an external receiver known in the state of the art present technical difficulties, mainly related to the resistance of the materials. Among the most common technical difficulties of these plants is the early appearance of cracks in the tubes, mainly due to the joint action of stresses and thermochemical corrosion. Thus, it is desirable to achieve a receiver design that makes it possible to work at high temperatures, minimize losses and increase the life time, so that maintenance costs are reduced and the overall performance of the plant is increased.

Until now, to extend the life of solar receivers, efforts have been made to homogenize the incident solar radiation, de-pointing heliostats or using multi-pointing strategies, but this solution notably reduces the optical efficiency of the heliostat field, and therefore the overall efficiency. of the solar plant.

Design modifications have also been carried out with a view to reducing thermal gradients, mainly in the axial direction. Numerous proposals are known that modify the design of the receiver trying to increase its efficiency, among them the documents: US6668555, US2013 / 0319501, US2010 / 0018522, and the Spanish patent application P201730456 can be highlighted. However, none of these documents focuses on reducing the stresses generated in the receiver, the main culprit for the early failure of the tubes.

It is important to bear in mind that the stresses in the receiver tubes are not only due to the thermal gradients, but are increased by the mechanical movement restrictions produced by their fasteners. Likewise, the direction in which the thermal gradients appear in the receiver tubes has different effects on the displacements of the tubes and the stresses generated. For example, thermal gradients in the radial direction do not cause tube bending and therefore only generate stresses due to temperature gradients. However, the thermal gradients in the circumferential direction generate bending of the tubes, increasing the total stresses, which in this case are produced by thermal gradients and mechanical restrictions.

Therefore, in order to reduce the technical difficulties of solar receivers, it is essential to reduce the thermal gradients in the circumferential direction, thus restricting the displacements and therefore the stresses produced by the thermal gradients and movement restrictions.

Description of the invention

The invention refers to a new receiver for tower-type solar plants, comprising at least one panel arranged vertically, such that each panel comprises an inlet collector, an outlet collector and a plurality of tubes joining the inlet collector and the collector outlet, where each tube comprises a cross section with a shape to choose between oval and elliptical in at least one central area between the inlet manifold and the outlet manifold, and where the inlet manifold, the plurality of pipes and the manifold Outlets configure at least one circuit for a heat transfer fluid.

The outdoor solar receiver object of the invention comprises a plurality of guides attached to the tubes configured to allow only the movement of the tubes in the axial direction. The outdoor solar receiver object of the invention comprises a weld between the guides and the tubes.

In the outdoor solar receiver object of the invention, in the embodiment with more than one panel, at least one output collector of one panel is connected to an input collector of another panel through at least one connector, such that the panels connected to each other configure a circuit for a heat transfer fluid, with an inlet of heat transfer fluid to the circuit through the inlet manifold of the first panel of the circuit and an outlet of heat transfer fluid from the circuit through the outlet manifold of the last panel of the circuit. There may be more than one heat transfer fluid circuit in the same receiver.

In the outdoor solar receiver object of the invention, the tubes can be oval or elliptical in their entire length or comprise a section with a circular shape at the junction with the collectors, with a progressive transition between the shape to choose between oval and elliptical and the circular shape. .

The tubes of the outdoor solar receiver object of the invention comprise an end zone with a curvature to favor assembly with the inlet and outlet collectors.

In the outdoor solar receiver object of the invention, the tubes are covered with a material with high absorption in the spectrum of solar radiation and low emission in the infrared spectrum.

Brief description of the drawings

Next, a series of drawings will be described very briefly that help to better understand the invention and that expressly relate to an embodiment of said invention that is presented as a non-limiting example thereof.

Figure 1 shows a schematic perspective view of a receiver formed by a single panel with a detail of the collector located in the upper part of the panel (inlet) in the embodiment of the panel in which the section of the tubes changes from oval or elliptical until circulating in the meeting with the collector.

Figure 2 shows a schematic perspective view of a panel showing the inlet and outlet pipes to connect the working fluid with another panel, a detail of a guide welded to a tube appears.

Figure 3 shows a perspective view of a receiver formed by eighteen panels arranged in a cylindrical shape, formed by two independent heat transfer fluid circuits.

Figure 4 shows a plan view of the outdoor solar receiver of Figure 3.

1. panel,

2. inlet manifold,

3. outlet manifold,

4. tube,

5. connectors between collectors,

6th. inlet for cold heat transfer fluid from the inlet manifold,

6b. outlet for the cold heat transfer fluid from the outlet manifold,

7. guide,

8. welding,

9. at entrance to the circuit,

9. b circuit output,

10. outdoor solar receiver,

11. heat transfer fluid circuit,

11.1 first circuit, and

11.2 second circuit.

Detailed description of an embodiment

As can be seen in the figures, the object of the invention is an outdoor solar receiver (10) comprising at least one panel (1) arranged vertically, so that it forms at least one circuit (11) for circulating a heat transfer fluid.

Each panel (1) comprises:

- an inlet manifold (2) with an inlet (6a) for the cold heat transfer fluid; - an outlet manifold (3) with an outlet (6b) for the hot heat transfer fluid;

and

- a plurality of tubes (4), of oval or elliptical section, which join the inlet manifold (2) to the outlet manifold (3).

The union of the inlet manifold (2), the plurality of tubes (4) and the outlet manifold (3) forms a circuit (11) where the cold heat transfer fluid enters through the inlet (6a) of the inlet manifold ( 2) is heated in transit through the plurality of tubes (4) that receive solar radiation, and leaves the circuit (11) through the outlet (6b) of the outlet collector (3).

Thus, inside each of the tubes (4) is where solar radiation is absorbed by the heat transfer fluid circulating through the tubes (4), solar radiation that is transformed into thermal energy, so that the inlet manifold (2) is in charge of distributing the fluid through the different tubes (4) of the panel (1) and the outlet manifold (3) is in charge of receiving the already hot fluid from the different tubes (4) panel (1).

There is an alternative embodiment of the tubes (4), in which the section is modified near the ends where the tubes (4) join the collectors (2, 3), progressively passing from an oval or elliptical section in the central zone to a circular section in contact with the collectors (2, 3) (see figure 1).

The oval or elliptical cross section of the tubes (4) allows a redistribution of the solar radiation reflected by the heliostats along the perimeter of the tubes (4), reducing heat losses with the environment and therefore increasing efficiency of the outdoor solar receiver (10). Furthermore, the oval or elliptical cross section results in a higher moment of inertia with respect to tubes (4) of circular section, which reduces the deformation of the tubes (4).

This embodiment of the tubes (4) reduces the stresses supported by the tubes (4), compared to the embodiment in which the tubes (4) have a constant circular section.

Each panel (1) comprises a plurality of guides (7) joined by welding (8) to the tubes (4), such that said guides (7) restrict the movement of the tubes (4) to a movement in the axial direction. The guides (7) prevent bending and torsion stresses on the tubes (4).

With the idea of maximizing the number of tubes (4) in each panel (1), in the preferred embodiment of the invention, the tubes (4) do not exit vertically from the collectors (2,3), but rather have a area near the ends with some curvature. That is, the tubes have a central area that is straight, of variable length, with a view to maximizing the number of tubes (4) that houses each panel (1), as already mentioned (see figure 2).

In an embodiment formed by a plurality of panels (1), the different panels (1) are connected to each other in series, joining the outlet manifold (3) of one panel (1) with the inlet manifold (2) of the next panel (1) through connectors (5) and so on, so that said circuit (11) for the heat transfer fluid is formed by more than one panel (1). In this way the heat transfer fluid rises in a panel (1) and descends in the immediately subsequent panel (1), to rise again in the next panel (1), so that the relative position of the inlet and outlet collectors ( 2 and 3) is modified between a panel (1) and the one immediately before / after.

Considering the above, there are many possibilities for an outdoor solar receiver (10), since it can contain a different number of independent circuits (11) for the heat transfer fluid, depending on whether or not the outlet collectors (3) and inlet manifolds (2). Thus, the number of circuits (11) that can be configured with the same outdoor solar receiver (10) is between one and the number of panels (1) that make up the outdoor solar receiver (10), which would be that embodiment in the that each panel (1) forms a single circuit (11). As an example of embodiment, figure 3 shows an external solar receiver (10) that contains a first circuit (11.1) and a second circuit (11.2), where each circuit (11) has its own input to the circuit (9a) of heat transfer fluid in the cold state through the inlet (6a) of an inlet manifold (2), and its own outlet from the circuit (9b) of the heat transfer fluid in the hot state through the outlet (6b) of an outlet manifold (3).

In this case, the cold fluid enters the outdoor solar receiver (10) at one end, and travels through two symmetrical circuits (11) until the outlet, once hot, at the opposite end. In this embodiment, the fluid rises through a panel (1) and descends through the panel (1) located immediately below, so that in some panels (1) the inlet manifold (2) is at the bottom and in other panels (1) the inlet manifold (2) is at the top.

The outdoor solar receiver (10) object of the invention, solves the problem related to the resistance of materials, and reduces the risk of failure of the solar receivers without penalizing their thermal performance. In this way, the competitiveness of solar tower technology is improved compared to traditional forms of electricity production.

The collector (2, 3) located in the upper part of the panel (1) has restricted movement while the tubes (4) and the collector (2, 3) located in the lower part of the panel (1) have free movement in axial direction, the rest of the movements being restricted by the guides (7) fixed to the tubes (4).

The tubes (4) of each panel (1) can be made of different materials, provided that the materials withstand the temperatures that will be generated in the panel (1). Examples of the materials include stainless steels and ceramic materials.

Furthermore, with a view to increasing the thermal efficiency of the outdoor solar receiver (10), the tubes (4) can be coated with selective paints, which have high absorption in the spectrum of solar radiation and low emission in the infrared spectrum.

Claims (7)

1. Outdoor solar receiver (10) for tower-type solar plants, comprising at least one panel (1) arranged vertically, characterized in that each panel (1) comprises: - an inlet manifold (2) - an outlet manifold (3) - a plurality of independent tubes (4) joining the inlet collector (2) and the outlet collector (3) that receive solar radiation reflected by heliostats, where each tube (4) comprises a section with a shape to choose between oval and elliptical in at least one central area between the inlet manifold (2) and the outlet manifold (3), and where the inlet manifold (2) , the plurality of tubes (4) and the outlet manifold (3) configure at least one circuit (11) for a heat transfer fluid. 2. Outdoor solar receiver (10) according to claim 1, characterized in that it comprises a plurality of guides (7) attached to the tubes (4), such that each tube is attached to at least one guide (7), and where the guides (7) are configured to only allow movement in the axial direction of the tubes (4). 3. Outdoor solar receiver (10) according to claims 1 and 2 characterized in that it comprises a weld (8) between the guides (7) and the tubes (4). 4. Outdoor solar receiver (10) according to any of claims 1 to 3 characterized in that at least one output collector (3) of a panel (1) is connected to an input collector (2) of another panel (1) by means of at least one connector (5), such that two panels (1) configure a circuit (11) for a heat transfer fluid, with an inlet (9a) of heat transfer fluid to the circuit (11) through an inlet manifold (2) of a panel (1) and an outlet (9b) of heat transfer fluid from the circuit (11) through the outlet manifold (3) of another panel (1). 5. Outdoor solar receiver (10) according to any of claims 1 to 4 characterized in that each tube (4) comprises a section with a circular shape at the junction with the collectors (2, 3), there being a progressive transition between the shape to choose between oval and elliptical and the circular shape. 6. Outdoor solar receiver (10) according to any of claims 1 to 5, characterized in that the tubes (4) comprise an end zone with a curvature. 7. Outdoor solar receiver (10) according to any of claims 1 to 6, characterized in that each tube (4) is covered with a material of high absorptivity in the spectrum of solar radiation and low emissivity in the infrared spectrum.