WO2019238999A1 - Outdoor solar tower receiver - Google Patents

Abstract

The invention relates to an outdoor solar receiver (10) for solar tower plants, which comprises at least one panel (1) such that each panel (1) comprises an input collector (2), an output collector (3) and a plurality of tubes (4) that join the input collector (2) to the output collector (3), wherein the tubes (4) have an oval or elliptical cross-section in at least one central area between the input collector (2) and the output collector (3), and wherein the input collector (2), the at least one tube (4) and the output collector (3) form at least one circuit (11) for a heat-carrying fluid, the oval/elliptical shape of the tubes allowing the solar radiation reflected along the perimeter of the tubes to be redistributed, thereby reducing heat losses to the environment and increasing the efficiency of the receiver.

Description

 OUTDOOR TOWER SOLAR RECEIVER

DESCRIPTION

Field of the Invention

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

Background

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

Within the solar energy systems, it is worth highlighting the great development experienced by the technologies of electrical production through solar concentration. Among them, the central or tower receiver systems appear to be the technology with the greatest future projection 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, in the form of thermal energy. This thermal energy can be stored or sent to a steam generator, where it will be converted by a traditional cycle of power into electrical energy.

Although there are numerous configurations of central receivers, the most commercially extended are the tubular outer receivers. These receivers consist of a series of panels, formed by inlet and outlet manifolds and vertical tubes, arranged in a polyhedral shape, approaching a cylinder. The collectors located at the top of the tower are embedded with restriction of movement, while the tubes are guided periodically, allowing displacements in the vertical direction. The solar radiation is captured by the tubes that are subject to extreme working conditions since on the outside they intercept a high non-homogeneous and cyclic solar radiation, which causes large gradients of temperatures, tensions and fatigue, and on the other hand the tubes are subjected to a corrosive environment due to the working fluid.

Tower-type solar plants with an external receiver known in the state of the art present technical difficulties, mainly related to the strength of the materials. Among the most common technical difficulties of these plants is the early appearance of fissures in the tubes due mainly to the joint action of tensions 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 the solar receptors, we have acted trying to homogenize the incident solar radiation, breaking up heliostats or using multi-pointing strategies, but this solution significantly reduces the optical efficiency of the heliostat field, and therefore the overall efficiency of the solar plant.

It has also been acted upon making design modifications 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 can be highlighted: US6668555, US2013 / 0319501,

US2010 / 0018522, and the Spanish patent application P201730456. However, none of these documents focuses on reducing the stresses generated in the receiver, which is the main culprit for the early failure of the tubes.

It is important to keep in mind that the tensions in the receiver tubes are not only due to 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 produce tube bending and therefore only generate stresses due to temperature gradients. However, 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 constraints. Therefore, to reduce the technical difficulties of the solar receivers it is essential to reduce the thermal gradients in the circumferential direction, thus restricting the displacements and therefore the tensions produced by the thermal gradients and the movement restrictions.

Description of the invention

The invention relates to a new receiver for tower-type solar plants, comprising at least one panel, such that each panel comprises an input manifold, an output manifold and at least one tube joining the input manifold and the output manifold. , where the at least one 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 at least one tube and The outlet manifold configures at least one circuit for a heat transfer fluid.

The 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 solar receiver object of the invention comprises welding between the guides and the tubes.

In the 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 by means of at least one connector, such that the panels connected to each other configure a circuit for a heat transfer fluid, with an input of heat transfer fluid to the circuit through the input manifold of the first circuit panel and an output of heat transfer fluid from the circuit through the output manifold of the last circuit panel. There may be more than one circuit of heat transfer fluid in the same receiver.

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

The tubes of the solar receiver object of the invention comprise an end zone with a curvature to favor assembly with the input and output manifolds. In the solar receiver object of the invention the tubes are covered with a material of 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 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 is described very briefly.

Figure 1 shows a schematic perspective view of a receiver formed by a single panel with a detail of the collector located at the top 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 encounter with the collector.

Figure 2 shows a schematic perspective view of a panel showing the inlet and outlet pipes for connecting 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 receiver of Figure 3.

1. panel

 2. input collector,

 3. outlet manifold,

 4. tube,

 5. connectors between collectors,

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

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

 7. guide

 8. welding

 9th circuit entrance,

 9.b circuit output,

10. receiver 1 1. heat transfer fluid circuit

 1 1.1 first circuit;

 1 1.2 second circuit.

Detailed description of one embodiment

 As can be seen in the figures, the object of the invention is a 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; Y

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

The junction of the inlet manifold (2), the plurality of tubes (4) and the outlet manifold (3) shapes a circuit (11) where the cold heat transfer fluid is accessed by the inlet (6a) of the inlet manifold ( 2) it is heated in transit by the plurality of tubes (4) that receive solar radiation, and leaves the circuit (1 1) through the outlet (6b) of the output manifold (3).

Thus, inside each of the tubes (4) is where the absorption of solar radiation by the heat transfer fluid circulating through the tubes (4) occurs, solar radiation that is transformed into thermal energy, so that the inlet manifold (2) is responsible for distributing the fluid through the different tubes (4) of the panel (1) and the outlet manifold (3) is responsible for receiving the already hot fluid from the different tubes (4) of the 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 manifolds (2, 3), progressively passing from an oval or elliptical section in the central area 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 thereby increasing efficiency of the receiver (10). In addition, the oval or elliptical cross section results in a greater 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 that the tubes support, with respect 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 an axial direction movement. The guides (7) prevent bending and torsional stresses on the tubes (4).

With the idea of maximizing the number of tubes (4) of each panel (1), in the preferred embodiment of the invention, the tubes (4) do not leave the collectors (2,3) vertically, but have a area near the ends with some curvature. That is to say, the tubes have a central area that is straight, of variable length, with a view to maximizing the number of tubes (4) that each panel (1) houses 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 output manifold (3) of a panel (1) with the input manifold (2) of the following 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 panel (1) immediately afterwards, to rise again in the next panel (1), so that the relative position of the input and output manifolds ( 2 and 3) is modified between a panel (1) and the immediate previous / subsequent one.

In accordance with the above, there are many possibilities for a receiver (10), since it can contain a number of independent circuits (11) for the heat transfer fluid, depending on whether or not the output manifolds (3) and collectors of entry (2). Thus, the number of circuits (1 1) that can be configured with the same receiver (10) is comprised between one and the number of panels (1) that form the receiver (10), which would be that embodiment in which each panel (1) forms a single circuit (1 1). As an exemplary embodiment, Figure 3 shows a receiver (10) containing a first circuit (11.1) and a second circuit (11.2), where each circuit (1 1) has its own input to the heat transfer fluid circuit (9a) in cold state through the inlet (6a) of an input manifold (2), and its own circuit output (9b) of the heat transfer fluid in a hot state through the outlet (6b) of an output manifold (3).

In this case the cold fluid enters the receiver (10) at one end, and runs two symmetrical circuits (1 1) to the exit, once hot, from the opposite end. In this embodiment the fluid rises through a panel (1) and down 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 input manifold (2) is located at the top.

The receiver object of the invention solves the problem related to the resistance of materials, and reduces the risk of failure of solar receivers without penalizing their thermal performance. This improves the competitiveness of solar tower technology with respect to traditional forms of electricity production.

The manifold (2, 3) located at the top of the panel (1) has restricted movement while the tubes (4) and the manifold (2, 3) located at the bottom 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 formed by different materials, with the condition that the materials withstand the temperatures to be generated in the panel (1). As an example of the materials, mention may be made of stainless steels and ceramic materials.

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

Claims

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