WO2015118256A1

WO2015118256A1 - Linear-concentration solar power plant having a secondary reflector

Info

Publication number: WO2015118256A1
Application number: PCT/FR2015/050248
Authority: WO
Inventors: David ITSKHOKINE; Quentin RABUT; Amine KHAROUB; Simon BENMARRAZE; Marc BENMARRAZE
Original assignee: Ssl Investissements
Priority date: 2014-02-04
Filing date: 2015-02-03
Publication date: 2015-08-13
Also published as: FR3017195B1; FR3017195A1

Abstract

The present invention relates to a linear-concentration solar power plant including a set of reflectors, referred to as primary reflectors, such as Fresnel mirrors, which are rigidly connected to a frame and oriented such as to reflect and concentrate the solar radiation toward a receiver which extends longitudinally at the top of vertical masts which are rigidly connected to said frame, said receiver comprising at least one absorbing pipe in which a heat-transfer fluid flows, a secondary reflector extending above the absorbing pipe and parallel therewith, such as to concentrate the solar radiation from the set of primary reflectors toward the absorbing pipe; said power plant is characterised in that the secondary reflector consists of a plurality of substantially semi-cylindrical shells which are made of cellular glass, the concave wall of each cellular glass shell receiving a mirror.

Description

CENTRALE SOLAI RE HAS CONCENTRATI ON LI N EAR WITH

REFLECTIVE R SECON DAI RE

TECHNICAL AREA

The present invention relates to a linear concentration solar power plant and more particularly to a receiver for such a linear concentration solar power station. PRIOR ART

In the field of energy production, it is well known thermal solar power plants that are an alternative to power plants operating from fossil fuels such as oil or coal for example.

There are several types of solar thermal power plant. The four main types of plants are parabolic trough plants, tower plants, parabolic trough plants and Fresnel solar mirrors.

The cylindro-parabolic collector plants consist of parallel rows of long cylindro-parabolic mirrors that rotate around a horizontal axis to follow the course of the sun. The sun's rays are concentrated on a horizontal absorber tube, in which circulates a coolant whose temperature generally reaches 400 ° C. This fluid is then pumped through exchangers to produce superheated steam that drives a turbine or electric generator.

Tower solar power plants consist of numerous mirrors concentrating the sun's rays towards a boiler located at the top of a tower. The uniformly distributed mirrors are called primary reflectors. Each primary reflector is orientable, and follows the sun individually and reflects it precisely towards the receiver at the top of the solar tower. The concentration factor can exceed 1000, which makes it possible to reach high temperatures, from 600 ° C to 1000 ° C. energy concentrated on the receiver is then either directly transferred to a thermodynamic fluid to generate steam driving a turbine or to heat air supplying a gas turbine, or used to heat an intermediate heat transfer fluid. This heat transfer fluid is then sent to a boiler and the steam generated drives turbines. In all cases, the turbines drive alternators producing electricity.

In parabolic power plants, the latter operate autonomously. They automatically orient themselves and follow the sun on two axes in order to reflect and concentrate the sun's rays towards a point of convergence called focus usually consisting in a closed chamber containing gas which is raised in temperature under the effect of the concentration. . This drives a Stirling engine that converts solar thermal energy into mechanical energy and then electricity. The concentration ratio of this system is often greater than 2000 and the receiver can reach a temperature of 1000 ° C.

All these types of plant have the disadvantage of being particularly expensive. The least expensive solar power plants consist of solar power plants called Fresnel mirrors. Indeed, the latter are similar to cylindro-parabolic collector plants with the exception that the cylindro-parabolic collectors, which are expensive to manufacture, are replaced by a succession of flat mirrors which approximates the parabolic form of the collector. Each of the mirrors can be rotated by tracking the sun's course to continuously redirect and focus the sun's rays to a tube or set of fixed linear receiver tubes. While circulating in this horizontal receiver, the thermodynamic fluid can be vaporized and then superheated up to 500 ° C. The steam then produced drives a turbine that produces electricity. The thermodynamic cycle is usually direct, which avoids heat exchangers.

Usually, a linear concentration solar power plant comprises a set of mirror modules constituting so-called primary reflectors, in this case Fresnel mirrors, mounted on a frame integral with the ground so that said mirrors extend in parallel, each line of mirrors comprising a series of several mirrors. This plant also comprises a linear receiver supported by a series of poles extending vertically from the central part of the frame so that the linear receiver extends longitudinally above the mirrors which are oriented to reflect and focus solar radiation. to the linear receiver.

Said linear receiver generally consists of one or more parallel longiline tubes in each of which circulates a coolant, such as for example water, brought to the vapor state by the focusing of the solar radiation on each tube by the mirrors . It will be noted that the number as well as the size of each of the receiver tubes are determined on the one hand as a function of the characteristics of the coolant and on the other hand as a function of the geometry of the mirrors.

The linear receiver receives solar radiation energy in radiative form and converts it into heat energy, which may be used as heat or to generate electricity from a turbo-alternator assembly.

Such solar concentrating solar power plants are described in particular in international patent applications WO 2009/029277 and WO 2012/156624.

International patent application WO 2009/029277 discloses examples and variants of solar collector systems comprising a raised linear receiver and first and second reflector fields located on opposite sides of the receiver. These reflector fields are designed and controlled to reflect solar radiation on the receiver. This document also describes examples and variants of receivers and reflectors which may, in certain variants, be used in said solar collector systems.

The international patent application WO 2012/156624 describes a solar installation with linear concentration and a receiver that can be used in such an installation. According to the invention, the installation is characterized in that at least one absorber tube is supported on each of the masts, independently of the secondary receiver, by means of an anti-friction plate secured to the mast transversely to the tube. absorber which is bilaterally held on the antifriction plate while resting in a notch of this plate.

In all these linear concentration solar power plants, the linear receiver is carried by the metal frame and comprises a so-called secondary reflector consisting of folded metal elements, polished and coated to ensure good reflectivity. This secondary reflector, extending above the tube in which the coolant circulates, allows overconcentration of a portion of the radiation from the primary concentration system. The receiver also has thermal insulation that limits heat loss from the system. Usually, the thermal insulation consists of rock wool or glass wool which is inserted into a metal box also ensuring the rigidity and tightness of the system.

Thus, all existing solutions require the inclusion of the receiver in a metal box providing a greater weight of the receiver assembly and, therefore, a metal frame dimensioned accordingly. This sizing involves a significant cost in the receiver assembly and causes a drop shadow on the primary focusing system, reducing the optical performance of the latter. In addition, the presence of a metal box causes large expansions that must be compensated at the end of the line. In addition, the relative expansions between the various elements can cause the breakage of the equipment and therefore maintenance costs. Indeed, the metal used for the box expands a lot, the glass quite little and the thermal insulation almost not. It should be noted that the ductility of the high temperature sheet can also cause deformation of the secondary reflector which reduces its optical performance by modifying its profile.

In addition, high temperatures combined with the presence of air can cause oxidation of the metal on the surface of the secondary reflector thereby reducing its reflective properties and decreasing the optical efficiency of the system.

SUMMARY OF THE INVENTION One of the aims of the invention is therefore to overcome these disadvantages by providing a receiver of simple and inexpensive design, having constant reflective properties by greatly limiting the expansion of said reflector in particular.

For this purpose and in accordance with the invention, it is proposed a linear concentration solar power plant comprising a set of so-called primary reflectors, such as Fresnel mirrors, integral with a frame and oriented to reflect and focus the solar radiation to a receiver extending longitudinally at the top of vertical mats integral with said frame, said receiver comprising at least one absorber tube in which circulates a coolant, a secondary reflector extending above the absorber tube parallel to the latter so as to concentrate towards the solar radiation absorber tube from the set of primary reflectors; said central unit is remarkable in that the secondary reflector consists of a plurality of substantially semicylindrical shells obtained in cellular glass, the concave wall of each cellular glass shell receiving a mirror.

Said mirror consists of a glass mirror whose rear face consists of a reflective silver layer.

In addition, the receiver has anti-reflective windows closing the hemi-cylindrical hulls.

Each hemi-cylindrical shell has on the concave wall a longitudinal groove near the free end of each branch of the hull, said grooves receiving the anti-reflective panes.

Preferably, the convex wall of the hemi-cylindrical shells is coated with a protective layer.

In addition, the hemi-cylindrical shells are obtained in cellular glass having a density of between 110 and 165 kg / m 3. Said semicylindrical shells are obtained in cellular glass having a thermal conductivity of between 0.040 and 0.055 W / mK.

Another object of the invention relates to a method of manufacturing a receiver of a linear concentration solar power plant according to the invention which is remarkable in that it comprises at least the following steps of:

forming at least one substantially semicylindrical shell in a cellular glass matrix,

- Assembling a mirror on the concave wall of the hemi-cylindrical shell.

Preferably, the formation of the cellular glass shell is obtained by molding.

Alternatively, the formation of the cellular glass shell is obtained by cutting into a cell glass matrix.

Furthermore, the method comprises a gravitational hot bending step of a glass mirror whose rear face consists of a reflective silver layer protected by sintered glass. Incidentally, the method comprises a step of forming longitudinal grooves on the concave wall of each shell, near the free end of each branch of the shell, said grooves receiving anti-reflective glass.

Said cell glass has a density of between 110 and 165 kg / m3 and / or a thermal conductivity of between 0.040 and 0.055 W / mK.

SUMMARY DESCRIPTION OF THE FIGURES

Other advantages and features will emerge more clearly from the following description of several variant embodiments, given by way of non-limiting examples, of the receiver of a linear concentration solar power plant according to the invention, with reference to the drawings. annexed in which: FIG. 1 is a perspective view of a linear concentration solar power plant according to the invention,

FIG. 2 is a perspective view of a collection field of the linear concentration solar power plant according to the invention,

FIG. 3 is a cross-sectional view of the receiver of the linear concentration solar power plant according to the invention,

FIG. 4 is a cross-sectional view of an alternative embodiment of the receiver of the linear concentration solar power plant according to the invention,

FIG. 5 is a cross-sectional view of a detail of the alternative embodiment of the receiver of the linear concentration solar power plant according to the invention,

FIG. 6 is a perspective view of the anti-reflective canopy of the alternative embodiment of the receiver of the linear concentration solar power plant according to the invention,

FIG. 7 is a view from above of the anti-reflective canopy of the variant embodiment of the receiver of the linear concentration solar power plant according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

In the following description of the receiver according to the invention, the same reference numerals designate the same elements. In addition, the different views are not necessarily drawn to scale.

With reference to FIGS. 1 and 2, the solar thermal power station with linear concentration is of the Fresnel mirror type and comprises several solar concentration collection fields (1), a so-called production unit (2) comprising means for transforming the thermal energy in electricity for example. Each solar concentrating collection field (1) comprises a plurality of primary reflectors (3) integral with a metal frame (4) which concentrate the solar rays on an absorber tube (5) in which a coolant circulates, said coolant consisting of a fluid such as water or a gas such as air for example. Said absorber tube (5) extends into a receiver (6) secured to the upper ends of vertical mats (7) carried by the frame (4) as will be detailed a little further. The term "primary reflector" means a device for tracking the course of the sun for direct sunlight all the day to the absorber tube (5) using mirrors. The plane mirrors (3) are articulated to the frame (4) so as to approximate a parabolic shape. Thus, each of the mirrors can rotate following the path of the sun to redirect and constantly focus the sunlight to the tube (5).

With reference to FIG. 3, the receiver (6) consists of a plurality of substantially semicylindrical shells (8) obtained in cellular glass, the concave wall of each cellular glass shell (8) receiving a mirror (9). ). Said mirror (9) consists of a glass mirror whose rear face consists of a reflective silver layer. Said semi-cylindrical shells (8) are obtained in cellular glass preferably having a density of between 10 and 165 kg / m3 and a thermal conductivity of between 0.040 and 0.055 W / mK. The formation of each cellular glass shell (8) is obtained by molding or by cutting in a cellular glass matrix. Said mirror (9) is preferably obtained by gravitational hot bending of a glass mirror whose rear face consists of a reflective silver layer protected by sintered glass. Said mirror (9) may, for example, consist of a mirror as described in US Pat. No. 8,585,225 filed by Guardian Industries or in any equivalent mirror. In addition, the receiver (6) has anti-reflective panes (10) closing the hemi-cylindrical shells (8). To this end, each hemi-cylindrical shell (8) comprises on the concave wall a longitudinal groove (11) near the free end of each branch of the shell (8), said grooves (11) receiving the longitudinal edges of the anti-reflective glass (10).

Incidentally, the convex wall of the hemi-cylindrical shells (8) is coated with a protective layer. This protective layer may consist, for example, in an aluminum foil, similar to the aluminum foils used for the heat insulation of tubes, bonded to the convex wall of said semi-cylindrical shells (8) or in a layer of a self-adhesive sealing material called Terostat® and marketed by Foamglas. It will be observed that the use of insulating shells made of cellular glass (8) makes it possible to dispense with the metal casing allowing the mechanical strength of the receiver. Indeed, the cellular glass is very rigid, in comparison with other insulating materials generally used. This makes it possible to limit the weight of the assembly, its cost, as well as the shadow carried by the receiver on the primary reflectors located below. Unlike mineral wool, cellular glass also has a high water and water vapor tightness, which can form when the air temperature rises in the event of high humidity. The choice of secondary glass reflectors makes it possible to reach higher temperatures without any adverse effect associated with the corrosion of the front face, or the deformation of the mirrors, unlike the secondary reflectors of the prior art. Moreover, the coefficient of expansion being almost identical between the glass and the cellular glass, the effects of the relative dilation are very strongly limited. Finally, glass mirrors have optical characteristics (reflectivity and specularity) much higher than those of polished aluminum sheets.

Mounting and maintenance on the receiving system are greatly facilitated. Indeed, the insulating shells, including secondary reflectors and windows, are simply placed on brackets (12) which are secured to the upper end of the mats (7), which facilitates their initial placement and their possible replacement .

According to an alternative embodiment of the receiver according to the invention, with reference to FIGS. 4 to 7, the receiver (6) consists of a plurality of substantially semicylindrical shells (8) obtained in cellular glass, the concave wall each cellular glass shell (8) receiving a mirror (9). Said mirror (9) consists of a glass mirror whose rear face consists of a reflective silver layer. Said hemi-cylindrical hulls (8) are obtained in cellular glass preferably having a density of between 110 and 165 kg / m 3 and a thermal conductivity of between 0.040 and 0.055 W / m 2. The formation of each cellular glass shell (8) is obtained by molding or by cutting in a cellular glass matrix. Said mirror (9) is preferably obtained by gravitational hot bending of a glass mirror whose rear face consists of a reflective silver layer protected by glass obtained by sintering. Said mirror (9) may, for example, consist of a mirror as described in US Pat. No. 8,585,225 filed by Guardian Industries or in any equivalent mirror. Said receiver (6) comprises stiffeners (13) extending on either side of the semi-cylindrical shells (8), said stiffeners (13) consisting of L-shaped parts whose branches are respectively integral with the outer wall semi-cylindrical shells (8) and the free edge of said shells (8). It also comprises second U-shaped stiffeners (14) whose branches are folded inwards and are integral with the first stiffener (13), said second stiffeners (14) being secured to the upper end of the mats (7). ) by means of bolts (15).

Furthermore, with reference to FIG. 4, the absorber tube (5) extends into the receiver (6) while resting on a support (16) integral with the upper end of the mat (7). Said support (16) consists of a roller (17) having a cylindrical central body (18) provided with an annular groove (19) so that the contact surface of the absorber tube (5) on the annular groove (19) the roller (17) is reduced to two points and the shafts (20) mounted free to rotate in slots in the legs (21) of a stirrup (22) generally U-shaped. Particularly advantageously, the coefficient friction between the axes (20) of the roller (17) and the stirrup (22) is less than or equal to the coefficient of friction between the roller (17) and the absorber tube (5). For example, the roller (17) and its axes (20) and the stirrup (22) are made of stainless steel and / or alumina silicate.

In this particular embodiment, the annular groove (19) has a section of substantially trapezoidal shape comprising a flat bottom (23) and two inclined walls (24) on either side of said bottom (23); However, it is obvious that the annular groove (19) may have a substantially semi-circular section whose concavity has a radius of curvature less than the radius of curvature of the absorber tube (5) without departing from the scope of the invention .

It will be noted that the invention thus has many advantages. First, the small contact area between the roller (17) and the absorber tube (5) limits the frictional forces between said tube (5) and the roller (17). This low friction reduces the wear of the thin selective layer of the tube (5) during its expansion. In addition, the rotation of the roller allows the free longitudinal expansion of the tube (5). Indeed, the absorber tube (5) is irradiated by the concentrated radiation of the sun; the more the temperature of its selective layer is hot, the more it is sensitive to abrasion. A coolant circulates inside the tube (5), which generates a temperature gradient along its longitudinal axis. By fixing the hot end of the absorber tube (5), the expansion is forced to proceed towards the cold end. The relative movement of the hot part relative to its support will then be lower, the selective layer on the outer surface of the tube will thus be preserved.

In addition, with reference to FIGS. 4 to 7, the receiver (6) also comprises anti-reflective glasses (10) extending between two mats (7) under the absorber tube (5). Said anti-reflective glasses (10) are carried by a metal frame (25) substantially rectangular and whose ends are provided with a shoulder (26) adapted to be secured to the upper end of the mats (7). The metal frame (25) is obtained from generally L-shaped metal profile, the base of the L forming a shoulder on which the anti-reflective panes (10) resting, whose edges are provided with an expansion joint and sealing (27). The same metal frame (25) supports a plurality of anti-reflective panes (10) joined in pairs by an expansion and sealing joint (27).

Finally, it is obvious that the examples which have just been given are only particular illustrations and in no way limiting as to the field of application of the invention.

Claims

1 - Solar power station with linear concentration comprising a set of so-called primary reflectors (3), such as Fresnel mirrors, integral with a frame (4) and oriented to reflect and focus the solar radiation to a receiver extending longitudinally to vertex of vertical mats (7) integral with the chassis (4), said receiver comprising at least one absorber tube (5) in which circulates a heat transfer fluid, a secondary reflector (6) extending above the absorber tube (5) in parallel to the latter so as to concentrate towards the absorber tube (5) the solar radiation from the set of primary reflectors, characterized in that the secondary reflector (6) consists of a plurality of substantially semicylindrical shells (8) obtained in cellular glass, the concave wall of each cellular glass shell (8) receiving a mirror (9).

2 - Plant according to the preceding claim characterized in that said mirror (9) consists of a glass mirror whose rear face is made of a reflective silver layer. 3 - Central according to any one of claims 1 or 2 characterized in that the receiver comprises anti-reflective panes (10) closing the hemicellular hulls (8).

4 - Plant according to any one of claims 1 to 3 characterized in that each hemi-cylindrical shell (8) has on the concave wall a longitudinal groove (11) near the free end of each branch of the hull ( 8), said grooves (11) receiving the anti-reflective panes (10).

5 - Plant according to any one of claims 1 to 4 characterized in that the convex wall of the semi-cylindrical shells (8) is coated with a protective layer. 6 - Plant according to any one of claims 1 to 5 characterized in that the hemi-cylindrical shells (8) are obtained in cellular glass having a density of between 110 and 165 kg / m3. 7 - Plant according to any one of claims 1 to 6 characterized in that the hemi-cylindrical shells (8) are obtained in cellular glass having a thermal conductivity of between 0.040 and 0.055 W / mK.

8 - Process for manufacturing a receiver of a linear concentration solar power plant according to any one of claims 1 to 7 characterized in that it comprises at least the following steps of:

forming at least one substantially semi-cylindrical shell (8) in a cellular glass matrix,

- Assembling a mirror (9) on the concave wall of the hemi-cylindrical shell (8).

9 - Process according to claim 8 characterized in that the formation of the shell (8) of cellular glass is obtained by molding. 10 - Process according to claim 8 characterized in that the formation of the shell (8) of cellular glass is obtained by cutting in a cell glass matrix.

11 - Process according to any one of claims 8 to 10 characterized in that it comprises a heat gravity bending step of a glass mirror whose rear face consists of a reflective silver layer protected by glass obtained by sintering.

12 - Process according to any one of claims 8 to 11 characterized in that it comprises a step of forming longitudinal grooves (11) on the concave wall of each shell (8), near the free end of each branch of the shell (8), said grooves (11) receiving anti-reflective glass.

13 - Process according to any one of claims 8 to 12 characterized in that the cellular glass has a density of between 110 and 165 kg / m3. 14 - Process according to any one of claims 8 to 13 characterized in that the cell glass has a thermal conductivity of between 0.040 and 0.055 W / mK.