IT201700010774A1 - HIGH ENERGY EFFICIENCY DEVICE AND PLANT FOR THE USE OF THERMAL SOLAR ENERGY - Google Patents

Description

HIGH ENERGY EFFICIENCY DEVICE AND SYSTEM FOR

THE USE OF THERMAL ENERGY OF SOLAR ORIGIN

DESCRIPTION

Technical field of the invention

The present invention refers to a device for accumulating and transferring thermal energy of solar origin and to an energy production plant which includes said device.

Background

The use of concentrated solar energy by means of heliostats is known. It is also known the possibility of accumulating the heat not immediately used by means of devices based on fluidized particle beds, or other thermal vectors, exposed to the solar radiation concentrated by the heliostats.

In general, the aforesaid accumulation devices are equipped with means for receiving concentrated solar radiation, in particular a transparent window, typically made of quartz, or a metal wall which defines a receiving cavity immersed in the fluidized particle bed. In the latter case, the particle bed removes the heat deriving from concentrated solar radiation from the cavity wall.

In the presence of high incident radiative fluxes, the aforementioned receiving means are exposed to high temperatures and high thermal gradients which can negatively affect their thermo-mechanical resistance and durability. In order to attenuate and control these gradients, in the case of a cavity receiver the aforementioned heliostat field can be organized into four sub-fields, for example arranged according to the cardinal points, so as to distribute the thermal flows over the maximum possible extension of the cavity surface. However, this configuration of the heliostat field provides a considerable occupation of the land associated with each solar generation unit.

Another limit associated with the use of these receiving means is related to the maximum operating temperature of the energy storage device, which is determined by the maximum sustainable temperature of the material constituting the receiving means themselves. The operating temperature of the storage device is then further penalized by the method of transferring thermal energy from the receiving means to the bed of particles, depending on the conductivity / transmissibility characteristic of the material constituting the receiving means themselves.

Furthermore, the devices that receive concentrated solar radiation in correspondence with a window of transparent material cannot provide for the direct contact of this window with the fluidized solid, and this to avoid the occurrence, over time, of surface opacification phenomena that they would reduce its reception efficiency and cause it to overheat. However, even in the configurations in which the transparent window is not placed in direct contact with the fluidized bed, phenomena of deposition of fine elutriated particulate are determined which cause the aforementioned drawbacks. The technical expedients put in place to avoid said deposition of particulates on the windows result in greater system complexity and parasitic energy losses.

A further disadvantage associated with the use of transparent window-type receiving means is related to the difficulty of producing self-supporting quartz windows larger than those used for laboratory or prototype-type systems. In particular, as the transversal dimensions of the window increase, the thickness must increase to the detriment of the percentage of solar radiation actually transmitted through the window itself.

Another disadvantage deriving from both types of receiver means considered above is related to the thermal losses due to re-emission to the external environment of an incident solar energy rate.

The two types of solar thermal energy storage devices just mentioned can be based on systems for the production of thermal / electrical energy, which by providing one or more storage and / or exchange units depending on the thermal power to be obtained. . As a result of what has just been noted, the aforementioned prior art storage devices may have high electricity production costs and in any case far from the so-called "parity grid".

Summary of the invention

The technical problem posed and solved by the present invention is therefore that of providing a device for the accumulation and / or exchange of thermal energy of solar origin which allows to overcome the drawbacks mentioned above with reference to the known art.

This problem is solved by a device according to claim 1.

Preferred features of the present invention are the subject of the dependent claims.

The present invention relates to a device for the accumulation and / or exchange of thermal energy of solar origin based on a bed of fluidized solid particles, preferably in a boiling regime, with direct irradiation of the same bed without the interposition of means for receiving concentrated solar radiation. .

The device is configured in such a way that the fluidized solid includes a portion of accumulation and / or exchange and a portion of irradiation continuously mixed with each other. The portion of irradiation is directly exposed to concentrated solar radiation and is fluidized through an ascension duct, or “riser”. The latter is made in the form of a tubular structure inside the bed of particles, through which a part of the same particles goes up to the free surface of the bed and here is made to bubble above the free surface itself. This bubbling regime, which we can also say "spouted" or erupting, is preferably obtained inside a "solar collector". The latter can be achieved by means of a tapered or funnel-shaped structure, circumscribed to the "riser" and associated at the top with a direct irradiation opening. Therefore, as mentioned above, the solid bed, fluidized in the bubbling regime, is directly exposed to the solar radiation incident in the “solar collector”.

The accumulation / exchange portion of the bed of particles can be fluidized by means of dedicated means, for example a distribution plate for a fluidization gas and an air chamber arranged at a base of the device or the bed of particles.

Preferably, the fluidization conditions that are established in the "solar collector" are such as to ensure high degrees of vacuum and therefore behavior as a "volumetric" receiver of the fluidized suspension struck by the incident radiation. In fact, in this configuration, the particles in the “spouted” regime expose the maximum surface to concentrated solar radiation, thus maximizing the amount of thermal energy they accumulate.

In particular, the tapered structure continues inside the bed of particles in the form of a descending duct, or "standpipe", immersed in the bed itself and circumscribed to the "riser", so that a re-entry path remains defined between the two of the bed particles falling back after irradiation into the remaining accumulation / exchange portion.

Preferably, the operation of the "solar collector" and the characteristics of the "standpipe" are such as to ensure a hydraulic seal ("seal") which avoids a dispersion in the atmosphere of the fluidization gas necessary for the operation of the exchange / accumulation bed . Furthermore, this fluidization gas can be intercepted at the exit of the free pile and sent to energy recovery operations by means of dedicated suction elements. Therefore, only the gas necessary to ensure the fluidization of the irradiation portion is dispersed in the atmosphere. It also represents a largely minority share of the fluidization gas flow rate required to exercise the exchange / accumulation portion.

As highlighted above - and unlike what happens for prior art devices equipped with wall or window receiving means - in the device of the invention there is no interposition of a material medium between the incident solar radiation and the bed of particles which acts as a vector thermal.

In a preferred configuration, the solar radiation is concentrated in correspondence with a central part of the device, where the aforementioned irradiation aperture is arranged. The optical system used to concentrate the solar radiation can be favorably of the "beam down" type, in particular consisting of a heliostat field on the ground associated with a secondary reflector at high altitude.

As mentioned above, the concentrated solar radiation directly affects the granular material constituting the bed, which is made to bubble at the irradiation opening, preferably located at the top of the device. Again as already mentioned, this hydrodynamic arrangement of the irradiation portion of the bed of particles is obtained by means of a physical partition of the bed itself determined by the aforementioned "riser", within which a stream of air or other fluidization gas is made to flow. The fluidization speed of this irradiation portion of the bed of particles can be suitably modulated to have a fluid-dynamic regime of the bed such as to allow a transport (in dense phase or in dilute phase) of granular material from the bottom of the bed to its free surface where, in fact, the eruption of granular material meets the radiative beam concentrated there, allowing the heat exchange.

The irradiated particles, once at the top of the free surface, fall laterally to the jet, reentering, through the aforementioned "standpipe", to form part of the remaining portion of the fluidized granular bed and allowing, thanks to the high thermal diffusivity of a granular material in steady state of fluidized bed, the transport of energy within the bed itself.

In this way, the transport of energy from the concentrated radiative beam to the fluidized bed is entrusted to the granular material which becomes the primary vector of thermal energy, unlike traditional wall or window reception means which, interposing between the concentrated energy and the correlated thermal vector, determine a physical separation.

The opening at the top of the inventive device that allows you to directly receive the concentrated radiation has a geometric arrangement that facilitates the gravity fall of the vector particles into the fluidized bed. This geometric structure is such as to present an enlargement of the section towards the external environment which slows down the speed of the air flow and of the particles dragged by it.

As an expedient that allows the control of the losses of fine granular material towards the external environment, a diverging conical opening is preferably provided at the entrance to the opening of the device, i.e. the aforementioned tapered structure, which (also) performs the function of a calm to drastically reduce the surface velocity of the gases and the ejected solid.

Furthermore, the control of the fine particulate ejection can also be obtained by means of a system of nozzles or nozzles, arranged for example orthogonally to the aforementioned tapered structure, which suck in the suspension of gas and fine conveying it inside the free surface and generating a field of motion that opposes the upward flow of the solid suspension.

An alternative to the previous expedient to stop the travel of the vector particles allowing a relative loss of momentum can consist of the same series of outlets or nozzles mentioned above, through which air is flowed rather than sucked in, in order to create a blade. of gas on the top of the opening of the device suitable to counteract any leaks of particulate material towards the external environment. The number of nozzles and the specific air flow can be calibrated according to the size of the irradiation opening of the device.

As an alternative to a configuration with a single irradiation opening, a plurality of such openings can be provided, each preferably with a configuration similar to the one described above for the case of single opening.

It will be appreciated that the device of the invention has some significant advantages, as indicated below.

The device allows a direct transfer of the incident radiative power to the fluidized solid without the interposition of walls or windows. It follows that the maximum achievable temperature is limited exclusively by the properties of the fluidized solid, and is therefore intrinsically higher than that tolerable in indirect irradiation systems.

The device allows to increase the concentration factor of the incident solar radiation. In fact, the upper limit of this concentration factor must be connected to the thermal efficiency of the receiver and the characteristics of the optical system rather than, as in the known art, to the thermal and mechanical resistance of the materials.

� The internal components and containment surfaces that make up the aforementioned "solar collector" and the "riser" are not the seat of heat exchange, but serve exclusively for the purpose of ensuring the correct fluidization and circulation of the bed of particles. Therefore, these components and containment surfaces must not possess the high thermal conductivities typical of known systems with indirect radiation. These internal components and containment surfaces can therefore also be made using non-metallic material (for example refractory), with economic benefits, thermomechanical resistance and durability.

Compared to known systems of the transparent window type, the device of the invention avoids the aforementioned drawbacks relating to opacification and thermal limits. The absence of a window therefore contributes to giving the system superior strength and durability.

The advantages of applying the device of the invention to an industrial plant for the production of electrical and / or thermal energy are also numerous, as indicated below.

� First of all, the absence of a means of receiving concentrated solar radiation allows to increase the working temperature of the fluidized bed, with a consequent significant increase in thermal efficiency. The possibility of increasing the operating temperature of the particle bed also leads to a decrease in the particle load for the same solar multiple.

Furthermore, since there is no physical resistance, it will be possible to have a less constrained concentrated radiative beam configuration, for example a beam not necessarily uniformly distributed on a circular ring.

� Even in the case of a "beam down" type optical system, the secondary reflector and the mirror field can be repositioned in such a way as to obtain a higher efficiency of the field compared to the case of arrangement of sub-fields according to the four cardinal points . It is therefore possible to have a configuration of the heliostats field that exploits a positioning dedicated to maximizing the optical efficiency to minimize the so-called "cosine effect" which, as known, represents the difference between the amount of energy coming from the sun collected on a surface orthogonal to the rays solar energy and that collected on an inclined surface with respect to the sun's rays.

Other advantages, characteristics and methods of use of the present invention will become evident from the following detailed description of some embodiments, presented by way of non-limiting example.

Brief description of the figures

Reference will be made to the figures of the attached drawings, in which:

Figure 1 shows a schematic longitudinal section of a preferred embodiment of a fluidized bed and direct irradiation device according to the present invention;

Figure 2 shows a schematic longitudinal section of a variant embodiment of the device according to the present invention, relating to an alternative mode of distribution of a fluidization gas; Figure 3 shows a schematic longitudinal section of another embodiment variant of the device according to the present invention, which highlights a way of blocking the escape of particles from the free surface of the fluidized bed; And

Figure 4 shows a schematic top view of the device of Figure 3.

Detailed description of preferred embodiments

Various embodiments and variants of the invention will be described below, and this with reference to the figures introduced above.

Similar components are denoted in the various figures and in the relative description with the same numerical reference.

In the following detailed description, further embodiments and variants with respect to embodiments and variants already dealt with in the same description will be illustrated limitedly to the differences with what has already been disclosed.

Furthermore, the different embodiments and variants described below are capable of being used in combination, where compatible.

With reference initially to Figure 1, a device for the accumulation and / or exchange of thermal energy of solar origin according to a preferred embodiment of the invention is generally denoted with 1.

The device 1 is suitable for use in an energy production plant, in particular electricity, and is configured to receive concentrated solar radiation by means of an optical system.

The device 1 comprises an external casing 2 having a lower base 21, an upper wall 22 and a lateral casing 23. The casing has an internal compartment 20, in direct communication with the outside at an irradiation opening 200. The latter is practiced, in the present example, centrally on the upper wall 22.

The opening 200 is configured to allow the entry of concentrated solar radiation and, as mentioned, places the internal compartment 20 in direct communication with the external environment as it lacks, in use, closing means or screens.

Inside the compartment 20 a bed of fluidizable solid particles is received, generally denoted by 3.

With reference to the operating modes of the device 1, in the bed of particles 3 there can be identified, in use, a portion of irradiation 30, directly exposed to the concentrated solar radiation which enters through the opening 200, and a portion of accumulation and / or heat exchange 31, arranged circumscribed to the irradiation portion 30. In the present embodiment, the irradiation portion 30 is arranged centrally with respect to the accumulation and / or exchange portion 31. The two portions 30 and 31 each extend in the longitudinal direction L within the bed of particles, ie between the base 21 and the upper wall 22 thereof. The free surface ("freeboard") of bed 3, denoted by 35, is, in general, arranged below the upper wall 22 of the envelope 2, being separated from the latter by a leaf 36.

The two bed portions 30 and 31 are in dynamic particle communication, in the sense that, in use, the particles of the two portions exchange, undergoing continuous mixing. The extension of the leaf 36 can also be variable depending on the specific application.

At the base of the bed of particles 3, or of the envelope 2, first and second fluidization means are provided, denoted as a whole with 4 and 400 and configured precisely to determine a fluidization of the bed 3, and in particular of its portions 30 and 31 respectively. .

Going into greater detail, the first fluidization means 4 comprise an element 41 for supplying air or other fluidization gas, centrally arranged so as to be in correspondence with a base of the irradiation portion 30.

The first fluidization means 4 then comprise an ascension duct ("riser") 40, which extends longitudinally within the bed 3, in particular having a first end 42 near the base of the bed and a second end 43 arranged above the free surface 35. The ascending duct 40 is precisely configured to receive the particles of the irradiation portion 30 inside and guide them up to a bubbling or eruption motion above the free surface 35 and in correspondence with the irradiation opening 200.

The second fluidization means 400 also comprise an element 401 for supplying air or other fluidization gas, arranged laterally at the base of the casing 2. This element 401 conveys the gas into an air box ("windbox") 402 , which distributes it at the base of the accumulation and / or exchange portion 31.

Preferably, the fluidization means 4 and / or 400 are configured to determine, in use, a boiling bed rate throughout the particle bed 3 or in portions or sub-portions thereof.

In a variant embodiment shown in Figure 2, the second fluidization means comprise a plurality of distributing elements ("spargers"), one of which denoted by way of example with 403.

With reference again to Figure 1, the device 1 then comprises a confinement structure 5, integral with the envelope 2 and positioned in correspondence with the irradiation opening 200 so as to completely circumscribe it.

The confinement structure 5 cooperates with the first fluidization means 4 to determine a dynamic exchange of particles between the two bed portions 30 and 31. To this end, the structure 5 is arranged circumscribed to the ascension duct 40.

In the present embodiment, the confinement structure 5 has a diverging geometry from the bottom up, or tapered, with a decreasing section towards the inside of the envelope 2, in particular an inverted truncated cone shape. The lower base of this truncated cone continues with a descending duct 50 arranged circumscribed to the ascending duct 40 and extending into the bed of particles. Preferably, the confinement structure 5 is arranged at least partially protruding towards the outside with respect to the irradiation opening 20.

The overall configuration is such that the particles of the irradiation portion 30, downstream of said bubbling or eruption, fall between the ascending duct 40 and the confinement structure 5 and are guided by the descending duct 50 in a motion of re-entry into the portion accumulation and / or exchange 31.

The longitudinal compartment defined within the bed 3 between the two ducts 40 and 50 creates a hydraulic guard with respect to the escape of the particles and the fluidization gas brought by the second means 400 towards the outside of the device 1 through the opening 200.

Therefore, in use, the particles of the irradiation portion 30 absorb thermal energy from the solar radiation in their bubbling or eruption motion and release it to the particles of said accumulation and / or exchange portion 31 once guided through the descending duct 50.

Preferably, the confinement structure 5 defines, above the free surface 35 of the bed 3, a calm chamber 24 for the fluidization motion of the particles of the irradiation portion 30.

Advantageously, therefore, the first and second fluidization means 4 and 400 are configured to determine different fluid dynamic regimes in the irradiation portion 30 with respect to the portion 31, preferably based on different fluidization rates of the particles.

The device shown in Figure 2 is entirely similar to that of Figure 1, apart from the variant in the second fluidization means already mentioned above.

With regard to Figures 3 and 4, these refer to a further embodiment which provides suction means 6 for the fluidization gas, arranged inside the casing 2 above the free surface 35 of the bed of particles 3, and in particular associated to the confinement facility, denoted here by 500.

Said means 6 comprise, in the present example, one or more suction nozzles or nozzles arranged in correspondence with a lateral skirt of the structure 500. In the configuration shown, the latter does not provide the aforementioned descending duct and ends above the free surface 35 of the bed. 3. The presence of the outlets prevents the fluidization gas fed through the second fluidization means 400 from escaping through the opening 200.

Figure 3 also shows heat exchange elements 10, in particular tube bundles, crossed, in use, by an operating fluid and arranged in correspondence with said accumulation and / or exchange portion 31 of the bed of fluidizable particles. Naturally, these elements 10 are also provided in the other embodiments and variants described above.

The device 1 described in relation to all the figures considered above can also comprise means for introducing a confinement gas, preferably air, above the free surface 35, configured to emit a laminar flow of gas suitable for producing a barrier against the escape of particles. outwards. These means can also be implemented by means of the same openings or nozzles considered in Figure 3.

As mentioned above, the device of the invention is suitable for working in conjunction with an optical system, the latter preferably having a "beam down" configuration which provides one or more primary optical elements arranged on the ground and one or more secondary reflective optical elements arranged at high altitude. The optical system employed is configured to concentrate the incident solar radiation in correspondence with the aforementioned irradiation aperture.

The present invention has been described up to now with reference to preferred embodiments. It is to be understood that there may be other embodiments that pertain to the same inventive core, as defined by the scope of the claims set out below.

Claims (14)

CLAIMS 1. Device (1) for the accumulation and / or exchange of thermal energy of solar origin, suitable for use in an energy production plant and configured to receive concentrated solar radiation through an optical system, which device (1) includes: - a casing (2), which defines an internal compartment (20) and has an irradiation opening (200) arranged in correspondence with its own upper part (22), which opening (200) is configured to allow the entry of the concentrated solar radiation and places said internal compartment (20) in direct communication with the external environment, being without, in use, closing means or screen; - a bed (3) of fluidizable solid particles, received within said internal compartment (20) of said envelope (2), which bed (3) has an irradiation portion (30) directly exposed, in use, to concentrated solar radiation which enters through said opening (200) and a heat accumulation and / or exchange portion (31) in dynamic communication of particles with said irradiation portion (30); - fluidization means (4) of said irradiation portion (30), comprising an ascending duct (40) disposed longitudinally within said bed of particles (3) and extending at least up to the free surface (35) of the latter, which ascending duct (40) is configured to guide the particles of said irradiation portion (30) up to a bubbling or eruption above said free surface (35) and in correspondence with said irradiation opening (200); - a confinement structure (5), integral with said casing (2) and positioned in correspondence with said irradiation opening (200), which confinement structure (5) is arranged circumscribed to said ascension duct (40) and has a descending duct (50) extending within said bed of particles (3) to guide the particles of the irradiation portion (30), downstream of said bubbling or eruption, in a re-entry motion into the accumulation and / or exchange portion ( 31), in which the overall configuration is such that, in use, the particles of said irradiation portion (30) absorb thermal energy from the solar radiation and transfer it to the particles of said accumulation and / or exchange portion (31). Device (1) according to claim 1, wherein said ascension duct (40) has a portion (43) extending above the free surface (35) of said bed of particles (3). Device (1) according to claim 1 or 2, wherein said irradiation aperture (200) is arranged in correspondence with an upper wall (22) of said enclosure (2). Device (1) according to any one of the preceding claims, in which said confinement structure (5) has a part with a tapered geometry, with a section decreasing towards the inside of said casing (2), in particular with a truncated shape of inverted cone. 5. Device (1) according to any one of the preceding claims, wherein said confinement structure (5) defines, above the free surface (35) of said bed of particles (3), a stilling chamber (24) for the motion of fluidization of the particles of said irradiation portion (30). 6. Device (1) according to any one of the preceding claims, in which said confinement structure (5) is arranged at least partially protruding towards the outside with respect to said irradiation opening (200). Device (1) according to any one of the preceding claims, comprising further fluidization means (400) configured to feed a fluidization gas into said compartment (20) in correspondence with said accumulation and / or exchange portion (31) of said bed of particles (3), which fluidization means (4) and further fluidization means (400) are configured to determine a first fluid dynamic regime in said irradiation portion (30) different from a second fluid dynamic regime in said accumulation portion and / or exchange (31), said first and second fluid dynamic regimes being in particular based on different fluidization rates. Device (1) according to the preceding claim, wherein said further fluidization means (400) are arranged at or near a lower base (21) of said casing (2). 9. Device (1) according to claim 7 or 8, wherein said further fluidization means (400) comprise an air chamber (402) or a plurality of distribution elements (403) of the fluidization gas. Device (1) according to any one of the preceding claims, wherein said fluidization means (4, 400) are configured to determine, in use, a boiling bed rate in said particle bed (3) or in portions (30 , 31) of it. Device (1) according to any one of the preceding claims, comprising means (6) for aspirating fluidization gas, arranged inside said casing (2) above the free surface (35) of said bed of particles (3), preferably in correspondence of said confinement structure (5). Device (1) according to any one of the preceding claims, comprising means (7) for introducing confinement gas, arranged inside said casing (2) above the free surface (35) of said bed of particles (3), preferably in correspondence with said confinement structure (5), which inlet means (7) are configured to deliver a laminar flow of gas suitable for producing a barrier against the escape of particles towards the outside. Device (1) according to any one of the preceding claims, comprising heat exchange elements (10) crossed, in use, by an operating fluid and preferably arranged in correspondence with said bed accumulation and / or exchange portion (31) of fluidizable particles (3). 14. Thermal energy production plant, comprising: At least one device (1) according to any one of the preceding claims; and An optical system configured to concentrate an incident solar radiation at said irradiation aperture (200) of said at least one device (1), in which said optical system preferably has a "beam down" configuration comprising one or more primary optical elements arranged on the ground and one or more secondary reflective optical elements arranged at height.