WO2015118255A1

WO2015118255A1 - Absorbing pipe mounting for a linear-concentration solar power plant

Info

Publication number: WO2015118255A1
Application number: PCT/FR2015/050247
Authority: WO
Inventors: Quentin RABUT; David ITSKHOKINE; 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: FR3017198A1; FR3017198B1

Abstract

The present invention relates to a linear-concentration solar power plant comprising a set of reflectors, referred to as primary reflectors, such as Fresnel reflectors, which are rigidly connected to a supporting structure and are oriented to reflect and concentrate the solar radiation toward a receiver extending longitudinally at the top of vertical masts which are rigidly connected to said supporting frame, said receiver comprising at least one absorbing pipe in which a heat-transfer fluid flows, a secondary reflector extending above and parallel to the absorbing pipe, such as to concentrate the solar radiation from the set of primary reflectors toward the absorbing pipe, and said absorbing pipe being supported on a mounting which is rigidly connected to the upper end of the vertical masts; said plant being characterized in that said mounting consists of a roller having a central cylindrical body that is provided with an annular groove such that the contact surface of the absorbing pipe on the annular groove of the roller is reduced at two points, and is provided with shafts which are freely rotatably mounted in openings provided in the arms of a generally U-shaped yoke, said yoke being rigidly connected to the upper end of the vertical masts.

Description

ABSORBER TUBE SUPPORT FOR SOLAR POWER PLANT WITH LINEAR CONCENTRATION TECHNICAL FIELD

The present invention relates to a linear concentration solar power plant and more particularly to an absorber tube support in which circulates a heat transfer fluid allowing longitudinal expansion of the tube while limiting the wear of the thin selective layer of the tube during its expansion.

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 in the direction of catcher 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. The 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 fixed frame of the ground so that said mirrors extend 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. In this document, the linear receiver comprises a plurality of receiver tubes mounted in parallel and supported on a roller mounted free to rotate, said roller having a plurality of substantially square section grooves. The international patent application WO 2012/156624 describes a solar installation with linear concentration and a secondary reflector that can be used in such an installation. At least one absorber tube is supported on each of the masts, independently of the secondary receiver, through an anti-friction plate secured to the mast transversely to the absorber tube which is bilaterally held on the antifriction plate resting in a notch of this plate.

Thus, in these linear concentration solar power plants, the length of the absorber tube can reach 800 meters. The entire absorber tube is composed of several tubes, whose length is between two and twelve meters, assembled together end to end. Because of its function, the tube is strongly irradiated and absorbs a very large part of this energy in the form of heat, and under the effect of the temperature rise the tube expands. This expansion is usually greater than two meters and can cause damage to the system if it is not controlled. The phenomenon of transverse expansion is also present, however the variations of dimensions are not significant and do not risk damaging the surrounding elements.

Moreover, the positioning of the absorber tube relative to the primary reflectors is very important in Fresnel technology. Its axis of revolution must be confused with the focal line of the primary reflectors so that the concentration on the collector is maximum. It is then necessary to use a piece to accurately position the tube height but also in the transverse plane. Finally, this positioning element must allow the longitudinal expansion of the absorber tube.

Usually, there are several ways of fixing the tube:

i) from above: a collar is used to support the tube. This collar is connected to a carriage equipped with a wheel allowing it to move linearly along a rail in the same axis of the tube.

ii) it is also possible to separately support each component component of the tube without allowing displacement relative to the support. A flexible is then placed between each element to resolve the expansion of the components locally.

iii) By a set consisting of two metal rollers mounted in "V" supporting the tube. These rollers are mounted on axes thus allowing their rotation. This degree of freedom allows the tube to expand longitudinally.

All these solutions nevertheless have many disadvantages. The use of a hose clamp on the tube reduces its surface exposed to radiation, thereby decreasing the optical performance of the system. The presence of rail above the assembly increases the shadow on the solar field having the same effect on the efficiency of the installation. In addition, the resistance to displacement due to expansion is all the more important with the increasing number of wheels. The rails guiding in translation can expand under the effect of the temperature. The use of flexible joints between each section of the absorber tube also reduces the area exposed to radiation. In addition, this solution does not support the tube and does not allow its expansion in one point. The use of metal rollers causes abrasion damage to the selective layer which coats the outer surface of the absorber tube. Indeed the tube undergoes a surface treatment allowing it to increase its thermal properties. This thin selective layer is very fragile. It is then imperative to reduce the contact between the absorber tube and its support. The change of a defective roller is not possible, it is imperative to change the roller assembly and support. In addition, the axis allowing the rotation of the rollers can deform thus blocking its rotation.

SUMMARY OF THE INVENTION

One of the aims of the invention is therefore to overcome these drawbacks by proposing an absorber tube support of simple and inexpensive design, limiting the wear of the absorber tube and allowing a quick and easy maintenance 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 mats vertical members integral with said frame, said receiver comprising at least one absorber tube in which a heat transfer fluid circulates, a secondary reflector extending above the absorber tube parallel to the latter so as to concentrate the solar radiation coming from the absorber tube towards the absorber tube; set of primary reflectors, and said absorber tube bearing on a support integral with the upper end of the vertical mats; said central unit is characterized in that said support consists of a roll having a cylindrical central body provided with an annular groove such that the contact surface of the absorber tube on the annular groove of the roll is reduced to two points and the axes mounted free rotation in the slots in the branches of a stirrup generally U-shaped, said stirrup being secured to the upper end of the vertical mats.

The coefficient of friction between the axes of the roller and the yoke is less than or equal to the coefficient of friction between the roller and the absorber tube.

Furthermore, the annular groove has a substantially semicircular section whose concavity has a radius of curvature less than the radius of curvature of the absorber tube. Alternatively, the annular groove has a substantially trapezoidal section having a flat bottom and two inclined walls on either side of said bottom.

In addition, the stirrup consists of a generally U-shaped piece having a horizontal base and two vertical wings extending on either side of the base, the lights receiving the axes of the roll opening at the free ends of said branches.

Said yoke is secured to a base adapted to fit on the upper end of the vertical mats.

Said base consists of a substantially trapezoidal piece whose large base is provided with lugs adapted to fit into corresponding holes formed at the upper end of the vertical mats and secondly of a triangle-shaped piece. right whose right sides are respectively provided with a lug adapted to fit one hand in a corresponding hole made at the upper end of the vertical mats and secondly in a hole in the central part of the room trapezoidal. SUMMARY DESCRIPTION OF THE FIGURES

Other advantages and features will become more apparent from the following description of several alternative embodiments, given by way of non-limiting examples, of the absorber tube support according to the invention, with reference to the appended drawings 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 secondary reflector and the absorber tube support of the linear concentration solar power plant according to the invention,

FIG. 4 is a perspective view of the upper end of a mat bearing the support of the absorber tube of the linear concentration solar power plant according to the invention,

FIG. 5 is a perspective view of the support of the absorber tube of the linear concentration solar power plant according to the invention,

FIG. 6 is a front view of the support of the absorber tube of the linear concentration solar power plant according to the invention,

FIG. 7 is a side view of the support of the absorber tube of the linear concentration solar power plant according to the invention,

FIG. 8 is a perspective view of a leg of the support base of the absorber tube of the linear concentration plant according to the invention,

Figure 9 is a perspective view of a second leg of the support base of the absorber tube of the linear concentration plant according to the invention.

DETAILED DESCRIPTION OF THE INVENTION For the sake of clarity, in the remainder of the description, the same elements have been designated by the same references in the various figures. 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 in a secondary reflector (6) integral with 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 path of the Sun to direct the sun all 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).

Referring to Figures 3 to 6, the absorber tube (5) extends into the secondary reflector (6) bearing on a support (8) integral with the upper end of the vertical mats (7). In this particular embodiment, said vertical mats (7) have an inverted V shape whose apex comprises a plate (9) on which is secured the support (8) of the absorber tube (5) and the secondary reflector (6). .

It is obvious that the mats (7) may have any shape, such as a vertical column form for example, without departing from the scope of the invention.

Said support (8) consists of a roll (10) having a cylindrical central body (11) provided with an annular groove (12) so that the surface of the contact of the absorber tube (5) on the annular groove (12) of the roll (10) is reduced at two points and axes (13) mounted free to rotate in the slots (14) formed in the branches (15) of a yoke (16) generally U-shaped, said yoke (16) being integral with the upper end of the vertical mats (7). Particularly advantageously, the coefficient of friction between the axes (13) of the roller (10) and the stirrup (16) is less than or equal to the coefficient of friction between the roller (10) and the absorber tube (5). For example, the roller (10) and its axes (13) and the stirrup (16) are made of stainless steel and / or alumina silicate. In this particular embodiment, the annular groove (12) has a substantially trapezoidal shaped section comprising a flat bottom (17) and two inclined walls (18) on either side of said bottom (17); However, it is obvious that the annular groove (12) may have a substantially semicircular 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 .

Furthermore, the stirrup (16) consists of a U-shaped piece having a horizontal base (19) and two vertical wings forming the branches (15) and extending on either side of the base (19). ), the slots (14) receiving the axes (13) of the roller (10) opening at the free ends of said legs (15). The bottom of the lights (14) is rounded such that the radius of curvature of said bottom of the lights is slightly greater than the radius of the axes (13) of the roller (10). Said stirrup (16) is integral with a base (20) adapted to fit on the upper end of the vertical mats (7). This base (20) consists of a first substantially trapezoidal part (21) whose large base is provided with lugs (22) adapted to fit into corresponding holes (23) formed at the upper end of the vertical mats (7) and secondly a second piece in the form of a right triangle (24) whose right sides are respectively provided with a lug (25) adapted to fit on the one hand into a hole (26) corresponding at the upper end of the vertical mats (7) and secondly in a hole (27) formed in the central portion of the trapezoidal piece (21).

It will be noted that the invention thus has many advantages. Firstly, the small contact area between the roll (10) and the absorber tube (5) limits the efforts of friction between said tube (5) and the roll (10). 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

Furthermore, the support according to the invention also makes it possible not to use lubricant, the bearing being produced by dry friction. Maintenance of such an assembly is simplified, as is assembly. Indeed, the two parts constituting the invention are simply placed one on the other.

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 - 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 a coolant circulates, a secondary reflector extending above the absorber tube parallel to the latter so as to concentrate the solar radiation from the set of primary reflectors, and said absorber tube bearing on a support secured to the upper end of the vertical mats, characterized in that said support consists of a roller having a cylindrical central body provided with an annular groove so that the surface of the contact of the absorber tube on the annular groove of the roller is reduced to two points and axes mounted free to rotate in the slots in the branches of a U-shaped stirrup, said stirrup being secured to the upper end of the vertical mats.

2 - Plant according to the preceding claim characterized in that the coefficient of friction between the axes of the roller and Γ caliper is less than or equal to the coefficient of friction between the roller and the absorber tube.

3 - plant according to any one of claims 1 or 2 characterized in that the annular groove has a substantially semi-circular section whose concavity has a radius of curvature less than the radius of curvature of the absorber tube.

4 - Plant according to any one of claims 1 or 2 characterized in that the annular groove has a substantially trapezoidal section having a flat bottom and two inclined walls on either side of said bottom.

5 - Central according to any one of claims 1 to 4 characterized in that Γ caliper consists of a generally U-shaped part comprising a base horizontal and two vertical wings extending on either side of the base, the lights receiving the axes of the roller opening at the free ends of said branches.

6 - Central according to any one of claims 1 to 5 characterized in that the stirrup is secured to a base adapted to fit on the upper end of the vertical mats.

7 - Central according to claim 6 characterized in that the base consists of a substantially trapezoidal piece whose large base is provided with lugs adapted to fit into corresponding holes formed at the upper end of the vertical mats and d on the other hand a piece in the form of a right triangle whose right sides are respectively provided with a lug adapted to fit on the one hand into a corresponding hole made at the upper end of the vertical mats and secondly in a hole made in the central part of the trapezoidal part.