WO2018162779A1 - Solar linear beam-down optical system - Google Patents

Abstract

Solar linear beam-down optical system comprising a field of heliostats (1) for concentrating solar radiation in a tower reflector (2) that is configured to redirect the solar radiation towards a ground gas-particle receiver (3) positioned below the tower reflector (2), said receiver being configured for the horizontal flow of a mixture of gas and particles received by the solar radiation. The tower reflector (2) and the gas-particle receiver (3) are linear, the heliostats (1 ) being arranged in a plurality of rows (4) disposed linearly on the two longitudinal sides of the tower reflector (2) and the gas-particle receiver (3).

Description

 SOLAR LINEAR DESCENDING OPTICAL SYSTEM

Field of the Invention

 The present invention is comprised within the field of solar energy, specifically refers to the solar linear down-beam optical systems, and more specifically to the particle energy collection means of these systems.

 State of the art

 Solar energy as a renewable source has gained the attention of the industry in recent years and has experienced a high degree of development due to innovations and improvements in this field. Especially, the generation of solar energy by concentration (CSP) using alternative heat transfer fluids, such as dense gas-particle suspensions (DPS), is one of the most prominent and innovative technologies in relation to transfer and storage of energy

 On the one hand, in CSP technologies, direct solar radiation is usually reflected by a field of heliostats to an upper receiver, which is placed on top of a tower. This upper receiver transfers the solar radiation to a working fluid, which is pumped from the bottom to the top of the tower and then returned to a tank placed at the bottom. This so-called up beam technology has several drawbacks. In addition to the high costs due to the continuous pumping of the working fluid to the top of the tower, the high thermal stresses produced in the receiver due to non-uniform solar energy radiation make its optimal operation difficult and can cause damage to the receiver .

Some of these inconveniences can be solved by means of the so-called down beam optical towers, which are designed following a quadratic curve and can redirect solar radiation to a ground receiver, so that there will be no need to pump the working fluid to the upper part of the tower, and more uniform solar energy radiation on the receiver will avoid high thermal stresses, since placing the receiver at ground level provides a homogeneous distribution of energy. Optical down-beam towers concentrate the energy reflected by hundreds of heliostats at one point, the lower focus point, where the ground receiver is placed. A power of up to 3000 kW / m ² can be concentrated at the top of the ground receiver, which has led to design of combustion chambers, gasifiers and solar-powered units for thermal storage.

 On the other hand, the potential of the DPS that acts as an energy recipient has been widely recognized among the academic community. In these systems, a suitable mixture between the particle phase and the gas phase produces a dense phase, with high heat and mass transfer coefficients. These properties can be used to absorb and / or store solar radiation both in the dense phase and in the gas phase. As a consequence, high temperatures can be obtained, improving the overall efficiency of the system. Usually, the transfer of solar energy to the DPS has been done by intercepting solar radiation by an outer wall and, therefore, the energy transferred to the particles is limited by the low heat transfer coefficient between the wall and the suspension .

 Some systems have been proposed that combine a down beam tower reflector with a ground receiver to process solar energy. The applications range from gasification of carbonaceous materials to energy storage in molten salt receivers. See, for example, documents US4038557, US4455153, US2012 / 0186251 A1 or GB2073869A. However, these strategies focus the reflected solar flow at a single point below the descending beam system, in which the ground receiver is placed. Therefore, these approaches are limited to a single point concentration and none of these inventions considers the use of linear reflectors to distribute the solar flux reflected on a linear absorber.

Description of the invention

 Briefly, the invention relates to a down-beam optical system comprising a linear particle receiver for storing the energy received from the sun. In preferred embodiments, the linear heliostats reflect the solar flux radiation to the down-beam optical system. In addition, the receiver configuration helps increase the transfer of energy to both the particles and the upward flow of the gas.

The present invention relates to a down-beam optical system that has a heliostat field, which concentrates solar radiation in a tower reflector configured to redirect solar radiation to a ground-gas receiver placed under the tower reflector. . This gas-particle soil receiver is configured for the horizontal flow of a mixture of gas and particles, or a dense gas-particle suspension (DPS), which receives solar radiation from of the down beam optics.

 The invention provides a gas-particle receiver in which the falling beam tower reflector and the receiver are linear and parallel. Several lines of linear heliostats can be assembled to concentrate solar radiation on a down beam reflector tower. Preferably, the heliostat lines will be of the Fresnel type, although other types of reflectors may be used. In addition, said heliostats are arranged in a plurality of parallel rows with respect to the tower reflector and the gas-particle receiver.

 In systems known from the prior art, heliostats are arranged in concentric circles around the tower reflector, since in such systems the receiver is a focus point below the tower reflector. On the contrary, in the system of the present invention, the heliostats are arranged in parallel rows with respect to the tower reflector and the receiver, placed on both sides thereof, thereby achieving the most efficient reflection of solar radiation at along the entire length of the linear tower reflector.

 Therefore, several rows of heliostats can be assembled to concentrate solar radiation on a down beam tower reflector. This tower reflector is the first concentrator, it can be designed according to a quadratic curve, specifically hyperbolic or elliptic curves, although current technical knowledge prefers hyperbolic design, and intercepts solar radiation reflected by heliostats. The soil gas-particle receiver intercepts concentrated solar radiation from the top of it.

 The ground-particle gas receiver of the down-beam optical system absorbs concentrated solar flux radiation from the top of the enclosure through a window transparent to solar radiation. Another embodiment shows an external enclosure with a plurality of windows that act as an isolation barrier. Said enclosure may be in low pressure conditions. Below the outer enclosure, the gas-particle soil receiver has a plurality of compartments connected in series, through which the mixture of gas and particles flows absorbing solar radiation.

Each compartment of the floor gas-particle receiver comprises two containers, which are an outer container and an inner container, which provide the outer walls and the inner walls. These interior walls form an interior enclosure. The outer container allows the exit and entry of granular material and the proper orientation of the flowing gas. The outer container also contains the upper opening to radiation, the windows mentioned above, and the inner vessel is the section in which the mixture of gas and granular material can behave as a fluidized or fixed bed depending on the speed of the gas and the properties of the particles. The inner container comprises a gas distributor, which is a distributor plate configured to support the deposited particles, allowing the flow of gas through them.

 In this way, the plurality of compartments connected in series acts as an integrated cavity that encloses the absorption of radiation from the upper part, providing the horizontal transport of the particles and the upward flow of the gas. The interior walls divide the compartments into several adjacent compartments, each of which supports a bed of particles. In this way, the consecutive stages of the passage of gas through the beds increase the solar energy absorbed by both the gas and the particles.

 According to a preferred embodiment of the invention, the floor particle gas receiver has a double outer wall. This double wall may comprise an insulating barrier inside, which will preferably be a vacuum barrier. By means of this double wall, the gas-soil particles receiver reduces heat losses to the environment and optimizes the energy transferred by the radiation.

 During operation, the flow of gas pumped in the dense phase may vary. Depending on this mass flow, you can change the dynamic behavior of the dense suspension, improving the absorption of energy in the gas flow or in the particles. In addition, the mass flow of the particles, the transverse dimensions of the compartments, the type of particles, the type of distribution, and the geometric shape of the compartment can affect the solar energy absorbed by the dense gas-particle suspension.

 The system of the present invention comprising a ground-level gas-particle receiver overcomes several problems of prior art systems, such as the distribution of non-homogeneous energy in CSP towers and the low heat transfer coefficients shown. by conventional dense gas particle suspensions. The arrangement of consecutive compartments can homogenize the temperature of the receiver, making the flexible operation of the absorption system feasible and increasing the thermal efficiency.

Therefore, the present invention is an alternative system for absorbing solar energy by means of the combination of a linear descending beam tower coupled with a linear field of heliostats to homogeneously redirect the power to a DPS receiver.

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

Brief description of the figures

 Next, in order to facilitate the understanding of the present description, in a more illustrative than limiting way, a series of embodiments will be developed with reference to a series of figures.

 Figure 1 is a schematic perspective view of a system object of the present invention showing the main features, with linear Fresnel heliostats, a solar tower and a gas-particle soil receiver.

 Figure 2 is an illustrative schematic view of the system of Figure 1 showing solar radiation and the relationship between the main elements of the system.

 Figure 3 shows a specific embodiment of the soil gas-particle receiver of a system object of the invention.

 Figure 4 shows a specific embodiment of the soil gas-particle receiver of a system object of the invention with an isolation barrier in the upper part of the enclosure.

 Figure 5 is a cross-sectional view of A-A shown in Figure 4.

Figure 6 is a cross-sectional view of B-B shown in Figure 4.

Figure 7 is a cross-sectional view of C-C shown in Figure 4.

These figures refer to the following set of elements:

 one . heliostats

 2. tower reflector

 3. gas receiver-soil particles

 4. rows of heliostats

 5. gas receiver compartments-soil particles

 6. exterior walls

 7. particles

 8. interior walls of the compartments

 9. transparent window to solar radiation

 10. upper enclosure

 eleven . distributor plate

Description of the realizations The present description refers to a down-beam optical system, which comprises a field of heliostats 1 to concentrate solar radiation on a tower reflector 2, which is configured to redirect solar radiation to a gas receiver-soil particles 3 placed under the tower reflector 2. The ground gas-particle receiver 3 is configured for the horizontal flow of a mixture of gas and particles, or a dense gas-particle suspension (DPS), which receives solar radiation.

 As can be seen in Figures 1-2, the tower reflector 2 and the gas-particle receiver 3 are linear and parallel, and the heliostats 1 are linearly positioned on both longitudinal sides of the tower reflector 2 and the gas receiver. particles 3. Heliostats 1 are arranged in a plurality of parallel rows 4 with respect to the tower reflector 2 and the gas-particle receiver 3.

 As Figure 3 shows, the floor-gas receiver 3 comprises two containers, which are an outer container and an inner container, which provide the outer and inner walls, through which the gas and particles circulate. The outer container of the gas-particle receiver 3 is formed by a window 9 to allow direct radiation of the absorption means, and a plurality of outer walls 6 arranged in such a way that they allow the particles to enter 7. The window 9 and the wall of the upper enclosure 10 of the outer container is configured in such a way that they allow radiation to enter, reducing heat losses. The particles are made of a material chosen in such a way that it has high radiant and thermal energy properties, which preferably show high absorption capacity and low emissivity. The particles 7 enter through an opening of the outer walls 6 and exit through the opposite side. The inner container comprises a plurality of compartments 5 connected in series, through which the mixture of gas and particles absorbing solar radiation flows.

 Each compartment 5 comprises a gas distributor 1 1 that supports the deposited particles 7 allowing the gas flow through them. Each compartment 5 comprises a plurality of interior walls 8 that form an enclosure therein. The upper part of the inner container coincides with the upper part of the outer container which is the window 9 and the upper enclosure 10.

The design and height of the inner side walls 8 can be modified to modify the gas flow between each compartment 5. In the front and bottom inner walls 8 there are openings for the mass flow of particles, and they can be modified to regulate the horizontal mass flow of solids between each compartment 5. The openings in the inner side walls 8 allow the flow of gas through the different compartments 5, which show a vertical upward flow through the bed of particles 7. A vertical interior wall 8 divides both compartments 5 while allowing horizontal movement of solids through an opening.

 According to a specific embodiment of the invention, the floor gas-particle receiver 3 can have a double outer window 9 as shown in the figure. 4. This double window 9 can comprise an insulating barrier inside. Low pressure conditions or a cooling system between the two windows 9 may be preferable to reduce heat losses to the environment. Figures 5-7 clearly show the isolation barrier of the double window 9 of the soil particle receiver 3. The configuration of the outer walls 6 and the inner walls 8, the gas distributor 1 1 and the windows 9 pursues them objectives than the embodiment shown in Figure 3, which is the control of gas and particle flows in order to improve the capture of solar radiation. Therefore, the previous description of Figure 3 is incorporated herein for Figure 4. Figure 4 incorporates some marks indicating the cross-sectional views depicted in Figure 5, Figure 6 and Figure 7, which they are included for a better understanding of the ground receiver 3.

 The embodiments of Figure 3 and Figure 4 can be configured by placing a plurality of floor receivers 3 in series, that is, placed continuously following the horizontal movement of the solids, so that the exit of particles 7 from a receiver of floor enters through the opening of the outer wall 6 of the next floor receiver. Said configuration is schematically illustrated in Figure 1 as a linear solar particle receiver.

Figure 5 shows the cross-sectional view AA of the embodiment depicted in Figure 4. In this specific view, the configuration of the outer walls 6 and the inner walls 8 is described for the first compartment 5 of the floor receiver 3. The Figure 5 shows the outer walls 6 and the inner walls 8 that form the outer container and the inner container, respectively. Solar radiation comes from the upper part of the outer container through the double windows 9, which is represented by continuous arrows, and hits the bed of the particles 7. The configuration of the walls 6, 8 and the gas distributor allows the upward flow of gas through the bed of particles 7. After passing through the gas distributor 1 1 and the bed of the particles 7 the upward flow of gas is directed through an opening of the inner side walls 8 leaving the first compartment 5 of the inner container and is redirected to the next compartment 5 and the gas distributor 1 1 through the outer container.

 Figure 6 shows the cross-sectional view of BB of the embodiment depicted in Figure 4. This specific view shows a cross-sectional view of the second compartment 5 of the receiver 3. In Figure 6, the gas stream that is contained within the outer and inner containers between the right side inner wall 8 and the right side outer wall 6 comes from the front compartment 5 after passing through the gas distributor 1 1 and the bed of particles 7 shown in Figure 5 After redirecting this gas to the gas distributor 1 1, the gas flows up through the bed of the particles 7 and leaves the inner container through an opening in the inner side wall 8, which is contained between the containers exterior and interior

 Figure 7 shows the cross-sectional view of CC of the embodiment shown in Figure 4. In this specific view, the longitudinal cross-section of the floor receiver 3 shows the two compartments 5 containing the bed of the particles 7 in which their horizontal movement is outlined by horizontal continuous arrows that indicate its entrance through the outer wall 6, its entrance from the first compartment 5 to the second through a vertical inner wall 8, and its exit through the outer wall 6; while the movement of the gas is described by dotted line arrows through the gas distributor 1 1 and the inner vessel; and the incoming solar radiation is signaled vertically by continuous arrows through the windows 9. Obviously, the size of the openings, or on the outer wall 6 for the entry and exit of solids, or on the inner wall 8 for the Control of the horizontal movement of particles and gas can change the thermal behavior of the soil receiver.

 Once the invention has been clearly described, it is noted that the specific embodiments described above may be subject to detailed modifications provided that the fundamental principle and essence of the invention are not altered.

Claims

1 .- Solar linear descending beam optical system comprising  a field of heliostats (1) configured to concentrate solar radiation on  a tower reflector (2) configured to redirect solar radiation to a gas-ground particles receiver (3) placed under the tower reflector (2), configured for the horizontal flow of a mixture of gas and particles received by the solar radiation,  where  - the tower reflector (2) and the gas-particle receiver (3) are linear, - and because the heliostats (1) are arranged in a plurality of rows (4) placed linearly on both longitudinal sides of the tower reflector (2) and the gas-particle receiver (3),  the down-beam optical system being characterized in that the gas-soil particles receiver (3) comprises an inner container comprising a plurality of compartments (5) connected in series, each compartment (5) comprising a plurality of interior walls ( 8) comprising openings for the mass flow of particles (7), said inner walls (8) forming an inner enclosure configured to direct the flow of gas and particles (7), said inner container being placed inside an outer container through which the mixture of gas and particle flow (7) absorbs solar radiation, said outer container comprising an outer wall (6) with openings for the entry and exit of particles (7), each compartment (5) comprising a distributor plate (1 1) that allows the flow of gas and configured to support the particles (7) deposited through which the gas flows, and comprising the container exterior an upper enclosure (10) which, in turn, comprises a plurality of windows (9) that allow solar radiation to enter. 2. Optical solar linear beam system, according to claim 1, characterized in that the tower reflector (2) and the gas-particle receiver (3) are parallel. 3.- Solar linear downward beam optical system, according to any of the preceding claims, characterized in that the gas-particle receiver of Soil (3) comprises a plurality of receivers connected in series configured to linearly absorb solar radiation. 4. - Solar linear descending beam optical system according to claim 1, characterized in that the distributor plate (1 1) is made of a porous material. 5. - Solar linear down beam optical system according to claim 1, characterized in that the distributor plate (1 1) comprises a plurality of holes. 6. Optical system of linear solar descending beam, according to the preceding claim, characterized in that the upper enclosure (10) of the outer container comprises an insulating barrier inside. 7. - Solar linear descending beam optical system according to the preceding claim, characterized in that the isolation barrier of the upper enclosure (10) of the outer container comprises a vacuum barrier. 8. - Solar linear descending beam optical system, according to any of the preceding claims, characterized in that the heliostats (1) are Fresnel type reflectors.