WO2012153264A2

WO2012153264A2 - Exchanger/collector and connection method with a high level of energy efficiency

Info

Publication number: WO2012153264A2
Application number: PCT/IB2012/052275
Authority: WO
Inventors: Mario Magaldi
Original assignee: Magaldi Industrie S.R.L.
Priority date: 2011-05-10
Filing date: 2012-05-08
Publication date: 2012-11-15
Also published as: ITRM20110234A1; TW201319488A; WO2012153264A3; AR086311A1

Abstract

Device (1 ) for storage and transfer of heat energy for an energy production plant, which device (1 ) is apt to receive the concentrated solar radiation and is based on the use of a modular fluidizable granular bed, a recirculation, outside the bed, of the particles inside tubular collectors, a heat exchanger associated with the particle bed and the activation of the storage step and the production step independently of each other. The external recirculation of the particles, the thermal separation of the fluidization gas from the operating fluid, the selective fluidization of bed zones, the variation of the heat exchange speed and the additional thermal input of combustible gas result in a device which is efficient and reliable as a whole and extremely versatile adjustment of the thermal power generated. Said device comprises principally: - at least one bed of particles (3, 30) suitable for storing and exchange of heat energy, contained in said containment casing (2); - at least one inlet (21 ) for feeding a fluidization gas through said particle bed (3, 30), the overall arrangement being such that, in use, such fluidization gas moves the particles of said bed (3, 30) causing or fostering heat exchange between the particles themselves and/or between these and further members; and - means (400) for receiving solar radiation, contained in said casing (2) and comprising means (40, 41, 44) for circulating particles coming from said bed (30), which circulating means are apt to cause a dedicated flow of said particles in an irradiation region (200) of the device (1 ) concerned by the solar radiation; wherein also the overall arrangement is such that, in use, portions of said particle bed (3, 30) are apt to be selectively moved by the fluidization gas so as to store heat energy received from the concentrated solar radiation in a storage step and to release the stored heat energy to said heat exchange members (4) in a release step, and wherein moreover the overall arrangement is such as to allow an activation of the storage step independent of the heat release step (Fig. 1 A).

Description

EXCHANGER/COLLECTOR AND CONNECTION METHOD

WITH A HIGH LEVEL OF ENERGY EFFICIENCY

DESCRIPTION

Field of the invention

The present invention relates to an industrial generation plant based on the use and storage of solar energy, to a device for storing heat energy of solar origin suitable for use in said plant and to an associated method.

Background of the invention

Devices for storing and releasing heat obtained from solar radiation concentrated by means of heliostats, suitable for allowing simultaneous or subsequent use of the stored heat energy, are known. The possibility of storing the unused heat in solid materials with a high thermal conductivity (typically graphite) for subsequent use, is therefore known. In order to make u se of the stored heat, normally a heat exchanger is employed, where said exchanger may also be embedded in the storage material and is passed through by an operating fluid - typically water, steam or other carriers - which are able to absorb and transport the heat energy. Commonly solar collectors which are able to capture the solar radiation are associated with said storage and release devices and for this pu rpose are designed in the form of a "trough", namely they have a generally concave profile so that the incoming solar radiation may be fully absorbed by the walls of the collector itself.

Generally, the actual storage device comprises a sealed and thermally insulated metallic containment casing which is fitted with or incorporates one or more solar radiation collectors which are usually also made of metal.

The arrangement described has a number of drawbacks.

Firstly, the connection between the internal surfaces of the collecting trough(s) and those of the storage device are affected by the different temperature range of the walls of the trough, which is directly acted on by the concentrated solar radiation, and the inside of the device. In addition, the nominal temperature ranges subject the solar collector to major thermal stresses in the zones between the irradiated and non-irradiated walls. Furthermore, during the working life of the device, there will be innumerable temperature fluctuations due to the change in seasons, day/night cycle and weather conditions, such as to cause heat fatigue and creep due to the high-temperature stresses.

On account of all the above factors, the collector may be subject to permanent deformations which, even in the presence of materials which are resistant to high temperatures, may give rise to breakages and/or fissuring and/or in any case may affect the reliability of the device.

Moreover, depending on the absorption of solar energy by the collector and the efficiency of the mechanism for transferring the heat to the operating fluid, the surface of the collector itself may reach temperatures such that irradiation back in to the environment becomes a critical factor which has a negative impact on the efficiency of the device as a whole and of the plant with which it is associated.

Summary of the invention

The technical problem posed and solved by the present invention is therefore that of overcoming the drawbacks mentioned above with reference to the prior art.

The abovementioned problem is solved by a heat energy storage device according to claim 1 and by a method according to Claim 22.

Preferred features of the invention are defined in the dependent claims.

An important advantage of the invention consists in the fact that it allows storage of heat energy of solar origin to be performed in a reliable and efficient manner, eliminating the need for a sheet-metal solar collector which is subject to thermal stress and major mechanical stresses.

The novel device is characterized by special solar radiation receiving means which are based on the circulation of fluidizable particles suitable for storing the heat energy and exchanging it with other particles or with further components of the device. Moreover, according to a preferred characteristic feature of the invention, the replacement of a flat, circular or elliptical surface with structural elements which have a tubular shape results in an increase in the receiving surface area and reduction of the heat flow for the same incident power.

The proposed device provides for a fluidizable granular bed from which the aforementioned dedicated flow of particles is taken. Preferably, this particle bed is fluidizable selectively so as to perform the dual function of a storage system for the captured heat and exchange system, whereby the storage step is independent from the step of heat exchange with the operating fluid.

In a preferred embodiment, the device consists of two beds (or zones) of fluidizable granular material, i.e. a first bed, essentially intended for storage and associated with the solar radiation inlets, and a second bed, for receiving the heat from the first bed, essentially intended for exchange with the operating fluid.

Again in a preferred embodiment, fluidization of the bed(s) and recirculation outside of the bed of the particles which receive heat from the solar radiation is performed by using air taken from the environment as the fluidization gas. In order to achieve maximum recovery of the energy, the hot air output from the fluidized bed(s) is conveyed to an air/air exchanger where it releases its heat to the cold fluidization air taken from the environment.

In the embodiment comprising two beds (or in any case two fluidization zones), during the storage step the first aforementioned bed receives heat from a heliostat field via means for receiving the solar radiation which generate the aforementioned dedicated recirculation of particles. This first bed is kept in the fluidization state by air which is preferably preheated inside the air/air exchanger mentioned above and this first bed supplies the particles which are recirculated outside said bed and receive the solar radiation.

If it is required to keep the stored heat in a state where it does not release heat to the operating fluid , the first bed, which performs storage, is kept in the rest condition.

During an energy production step, the storage bed, which this time is fluidized, will exchange heat with the second fluid bed adjacent to it. A tube bundle passed through by an operating fluid is preferably immersed inside the second bed. In this case also, preferably the fluidization air is preheated using the air/air exchanger. In a preferred configuration, the receiving means are based on a tubular solar collector, the ducts of which are made of material which is resistant to h igh temperatures, preferably silicon carbide. The latter, owing to its high conductivity and optimum resistance to high temperatures, is able to absorb high flows of solar energy.

In a further configuration, the receiving means are based on a solar collector with tubes made of quartz. This material, because of its transparency to solar radiation and its considerable heat resistance, is able to contain the bed particles without hindering absorption of the heat energy by those particles which are directly exposed to the concentrated solar radiation.

An alternative configuration provides that the ducts of the solar collector have a main body which is made of silicon carbide and inside which the particles flow and which in turn is contained inside quartz pipes. A suitable optical filter for increasing the absorption of the solar radiation may be provided on the external quartz tube or on the surface of the internal body.

Brief description of the figures

Reference shall be made to the figures of the accompanying drawings in which: - Fig.1 shows a d iagram of a storage device according to a first preferred embodiment of the invention, which device is shown inserted in a plant for the production of electric energy;

- Fig. 1A shows solely the storage device according to Fig. 1 , again in schematic form;

- Figure 1 B shows a cross-sectional view of the device according to Fig. 1 A, along the line B-B of this latter figure;

- Fig. 1 C shows solely the storage device according to Fig. 1 , with a variation relating to the type of connection for the ducts of the collector;

- Fig. 2 shows a schematic front view of a part of the plant according to Fig. 1 which incorporates a tower structure with air/air heat exchanger and illustrates a circuit for introducing fluidization gas and the path of the latter; - Figs. 3 and 3A relate to a second preferred embodiment of the device according to the invention, which may in any case be used in a plant similar to that of Fig. 1 , which device provides the use of combustible gas as auxiliary energy source and is shown in a cross-sectional and plan view, respectively; and

- Fig. 4 shows a layout of the plant according to Fig . 1 where four storage devices, each similar to that shown in Fig. 1 , can be seen.

Detailed description of preferred embodiments

With reference to Figure 1 , a plant for the production of electric energy from concentrated solar radiation according to a preferred embodiment of the invention is denoted overall by 100.

The plant 100 in turn incorporates one or more devices for storing heat energy received from the concentrated solar radiation , each according to a preferred embodiment of the invention. The illustrations considered here show a single device denoted overall by 1 .

As mentioned, the device 1 is suitable for storing the heat energy which originates from solar radiation which is conveyed/concentrated onto it, for example by means of heliostats and, as shown further below, in the present example it is also suitable for releasing the heat energy stored to an operating fluid, typically water or steam.

With reference also to Figures 1A, 1 B and 2, the device 1 comprises a containment casing 2, preferably made of metallic material, which is thermally insulated so as to reduce to a minimum the dispersion of heat into the external environment. The casing 2 may have one or more openings 20 towards which the concentrated solar radiation is conveyed. Opposite this opening or these openings 20 the casing 2 defines corresponding irradiation chambers 200 wh ich are open towards the outside precisely by means of the respective openings 20 and inside which means 400 for receiving the solar radiation (described further below) are arranged.

In addition to the open irradiation chambers 200, the casing 2 also defines a main fluidization chamber 250 inside which two beds of fluidizable particles 3 and 30 described further below are housed.

In the present example, the overall arrangement is such that the irradiation chambers 200 are arranged surrounding the main fluidization chamber 250. At a base of the fluidization chamber 250 one or more feed inlets 21 are provided for a fluidization gas, the role of which will be clarified shortly. At the inlets 21 a distribution baffle or distributor (for the sake of simplicity is also identified by 21 ) is provided for this fluidization gas, said distributor being suitable for allowing uniform introduction of said gas into the device 1 opposite the two fluidizable-particle beds 3, 30. An air supply header 14 is provided underneath the distributor 21 and also helps ensure a uniform flow of air into the distributor 21 .

The fluidization chamber 250 is provided internally with a storage zone which contains the first bed of fluidizable particles 30 which is suitable precisely for heat storage according to preferred characteristics which are described further below.

The fluidization chamber 250 is also provided internally with a heat exchange zone which contains the second bed of fluidizable particles 3. The latter is apt to flow over heat exchange elements - and in particu lar tu be bu nd les 4 of a heat exchanger - passed through, in use, by the operating fluid, in this case also during energy release modes described further below.

In the present embodiment, the zone of the storage bed 30 is arranged next to the peripheral walls of the fluidization chamber 250 and therefore adjacent to the irradiation chamber 200 , wh ile the zone of the exchange bed 3 is arranged centrally with respect to the storage bed 30 and may be separated from the former by means of baffles 141 , which are preferably metallic.

In a variation of embodiment, the two beds of particles 3, 30 may form adjacent portions of a same bed which can be selectively fluidized by means of throttling of the air header 14 using the baffles 143.

The choice of the particle material of the storage and exchange beds 3 and 30 is based in particular on the limited propensity for abrasion and fragmentation, so as to meet the need to minimize the phenomenon of elutriation of the particles of the bed itself, thus limiting the production and transportation of fine particles in the fluidization air. On the basis of these considerations, a preferred configuration provides the preferred use, as bed particles, of oxidation-inert granular material having a regular - for example spheroid - shape and/or preferably with dimensions of the order of 50-500 microns.

In the region of each irradiation chamber 200, the walls of the fluidization chamber 250 - and therefore of the storage zone which receives the first bed 30 - have one or more outlet openings 201 and one or more corresponding openings 202 for reintroduction of the particles of the storage bed 30. Each outlet opening 201 is in fluid communication with a corresponding reintroduction opening 202 via a first connection 41 and a circulation (or irradiation) duct 44 or an equivalent means arranged in sequence.

The circulation duct 44 extends inside the corresponding irradiation chamber 22, opposite the opening 20, acting as a collector of the solar radiation, and leads into an expansion chamber 251 which is in communication with the opening 202 for reintroducing the particles into the bed 30.

The overall arrangement is such that the openings 202 are preferably immersed in the particle bed when it is fluidized . It will therefore be u nderstood that the described arrangement of openings 201 , 202, ducts 44 and connections 41 inside irradiation chambers 200 forms means for receiving the solar radiation, in particular a collector which may be referred to as being of the tubular type and which replaces the trough-type collectors known in the art, said collector being denoted overall by 400.

Preferably, the connections 41 are made of ceramic materials and the ducts 44 of silicon carbide, but it is possible to use also other materials which are suitable because of their high thermal conductivity properties and resistance to high temperatures and abrasion; alternatively it is possible to use conveniently a metal alloy which is resistant to high temperatures or a composite material consisting of said metal alloy lined with ceramic material which is resistant to high temperatures.

In an alternative embodiment shown in Figure 1 C, the circulation duct 44 may be connected to the fluidization chamber 250 by means of a connection 42 which is also preferably made of ceramic materials and silicon carbide.

In another alternative configuration, the ducts 44 of the tubular collector 400 are made of quartz, with the advantage that, since quartz is transparent to solar radiation and resistant to the high temperatures, it allows direct exposure of the passing particles to the concentrated solar radiation. I n this configuration, the particles of the fluidized bed, in addition to the properties already mentioned, will be chosen so as to have a high emissivity.

Yet another variant of embodiment provides that the ducts 44 comprise a main body which is made of silicon carbide and inside which the particles flow and which is in turn contained inside quartz liners or pipes. In this case, an optical filter applied on the external surface of the main body made of silicon carbide allows an increase in the absorption of the concentrated radiation, this filter being permeable to the solar radiation and impermeable to the re-irradiation of the tu bes 44. Alternatively the optical filter may be applied on the internal surfaces of the quartz tube.

The inlet openings 20 for the solar radiation may be provided with one or more synthetic q uartz windows, with the advantage of red ucing the losses due to convection, said quartz being preferably lined with optical filters which are transparent to the solar radiation and are able to reflect the infrared radiation emitted by the collector 400, so as to increase the absorption of the solar radiation and the overall efficiency of the device.

In a variant embodiment (not shown) it is provided a system for closing the inlets 20 by means of shutters made of insulating material. Said shutters, operation of which is preferably automated, allow the device to be shut off during the night-time hours or because of the prolonged absence of solar radiation , with the dual aim of preventing dispersion of heat into the environment and reducing the temperature fluctuations of the collectors 400 as well as protecting from adverse weather conditions the inlets 20, the drainage systems 50 described below, the collectors 400 and the irradiation chambers 200 as a whole.

Each connection 41 associated with an outlet opening 210 is of the three-way type, being in communication, not only with the opening 201 itself and the corresponding circulation duct 44, but also with a means for feeding fluidization gas apt to generate a dedicated flow of particles through the outlet opening 201 , the duct 44 and the reintrod uction open ing 202, which flow may be defined as being a recirculation flow.

Typically, this feed means comprises a dedicated air header 15. Distribution baffles 18 are arranged between said air header and each connection 41 in order to ensure a uniform fluidization flow inside each duct 44 and prevent particle matter from accidentally falling into the air header.

As can be seen more clearly in Figure 1 B, one or more of the aforementioned pairs of openings 201 , 202 and corresponding connections and duct 41 and 44 may be provided for each irradiation chamber 200. In the case of maintenance or replacement of one of the ducts 44 or in any case a component of the tubular collector 400, it is preferable for safety reasons to shut off the particle bed. For this purpose closing or interruption means 203, preferably of the mechanical type, are provided , said means having one or more closing members 205 arranged inside the storage bed 30 and opposite the outlet openings 201 . Preferably, it is provided a single closing member 205 consisting of a continuous plate of ceramic material which is associated with the openings and which , once moved downwards, covers simultaneously all the openings 201 , preventing the particles from passing back up through the ducts 44. These closing means 203 also comprise an actuating system 204, preferably position at the base of the particle bed 30, outside of the fluidization chamber 250.

Moreover, still based on a preferred embodiment, it is provided a drainage system 50 which is positioned between the openings 20 and the tubular collector 400 and wh ich may convey any particles expelled by means of gravity to a duct 72 connected to a collection tank 73. From this tank the particles may be conveyed back, for example pneumatically, into the fluidization chamber 250.

Obviously, it is also provided a system for introducing the particles into the beds 3 and 30, which is not shown in the figures since it may be easily deduced from concepts already known to the person skilled in the art.

The operating modes of the device 1 will now be explained , together with a description of the plant 100 in which the device is incorporated.

As mentioned above, the inlets 21 of the device 1 are suitable for allowing feeding inside the casing 2 - and specifically through the base of the particle beds 3, 30 - of the fluidization gas which in the present preferred configuration is air. In particular, the overall arrangement is such that the gas, propelled through the distribution baffle 21 , moves the particles of the bed 30, generating a flow of particles which passes through the outlet openings 201 and flows inside the connections 41 and the circulation ducts 44 which are directly exposed to the solar radiation concentrated through the openings 20. The particles of the recirculating flow then return into the fluidization chamber 250, and in particular into the storage zone thereof, through the reintroduction opening 202, being propelled by the ventilation flow from the air header 15, thereby conveying the heat extracted along the path from the walls of the ducts 44. During energy storage, therefore, the solar energy is concentrated, through the openings 20, onto the collector ducts 44 inside which the fluidized particles flow, said particles storing heat energy extracted from the walls of the tubes 44 or instead capturing the direct radiation in the case of quartz tubes. The particles propelled by a ventilation flow produced by the fluidization gas entering the connection 44 travel along the ducts 44 and return into the bed with the heat extracted from the said ducts 44.

In particular, the fluidization condition of the particles inside the d ucts 44 is preferably turbulent and ensures a high coefficient of heat exchange between the inner surfaces of the said ducts 44 which are exposed to the concentrated solar radiation and the particles themselves. The fluidization gas which is also heated when it passes through the ducts 44 emerges inside the expansion chamber 251 together with the conveyed particles [and] passes through the fluidized bed 30, releasing heat to the latter before returning into a pipe or duct 71 , the function of which will be explained more fully further below.

The expansion chamber 251 therefore has the function of promoting separation of the solid particles from the fluidization gas, improving the heat exchange and reducing the quantity of particles which fall back into the duct 44.

The coefficient of heat exchange inside the duct 44 may be modulated by varying the ventilation flow from the air header 1 5 by means of adjustment means 144 arranged upstream thereof.

The quantity of particles recirculated through the ducts 44 is determined so as to establish a heat balance in respect of the minimum temperature reached by the ducts 44 , th is being equivalent to reducing to a minimum the losses due to irradiation of the collector 400.

The fluidization condition of the storage bed 30 is preferably boiling, i.e. such as to ensure a homogeneous temperature, distributing the heat content supplied by the particles coming from the tubular collector 400 and generating a corresponding exchange of heat between the particles of the said bed 30 and in particular between the particles of bed portions adjacent to each other.

As mentioned, this step is independent of the production step. During storage alone, only the first bed 30 is fluidized.

During production , the second exchange bed 3 is also activated - namely is fluidized - so that the passage of heat occurs from the storage bed 30, which is also fluidized, to the particles of the exchange bed 3, and from these to the tube bundles 4 and then to the operating fluid which flows inside the latter.

Therefore, the operating fluid which passes through the tube bundles 4 receives from the second bed 3 the heat energy stored by the first bed 30, transfer of heat occurring by activating the beds 3, 30 namely by fluidizing the particles of the bed zones 30 and 3.

In addition to the diffusive heat-exchange mechanism, which is typical of a boiling fluid bed, it is possible to promote the heat exchange inside the bed by varying the fluidization speed between the storage bed 30 and the exchange bed 3 or between portions of the latter via adjustment means 145, 146.

As already mentioned, the particle bed for releasing heat 3 may be physically separate from the particle bed 30, while having on the whole a modular structure which allows a selective fluidization of the bed zones. I n general, the device 1 allows selective and/or differentiated fluidization of one or more portions of the particle beds 3 and 30 and/or selective and/or differentiated fluidization of beds themselves or portions thereof.

It is thus possible to operate portions of the bed as thermal switches which close off the heat exchange circuit only if fluidized . Said controlled and selective fluidization of zones of the granular means of the bed ensures continuous extraction of the heat and flexibility of the plant i n relation to the en ergy requirements downstream.

The fluidization condition of the particles of the beds 3 and/or 30 is preferably boiling or in any case such as to maximize the heat exchange coefficient.

The position of the tube bundles 4 with respect to the particle bed 3, or rather the exposure of the surface of the tubes with respect to the particle bed, is such as to maximize the quantity of heat exchanged , the latter being proportional to the product of the heat exchange coefficient and the surface area affected by the heat exchange itself.

As mentioned, for improved versatility of the plant, preferably means are provided for varying the speed of the fluidization air and therefore also its flowrate.

Therefore, by varying the through-flow speed of the fluidization gas, it is possible to control and modify the overall coefficient of heat exchange between the fluidized bed and the collecting tubes, with consequent flexible adjustment of the quantity of thermal power transferred. It is thus possible to obtain a substantial reduction in the heat transfer when there is no fluidization.

As shown more clearly in Fig. 2 in the present example the device 1 has or is associated with a raised tower structure 70. A gas/gas exchanger 7, in the present example an air/air exchanger, is located in the central zone of said tower structure and extends vertically inside the structure supporting the device itself.

The environment inside the device 1 , and in particular the fluidization chamber 250 thereof, communicates with the air/air exchanger 7. In particular, a section of the air/air exchanger 7 from which preheated ambient air emerges is connected to the distribution baffle 21 at the base of the fluidization chamber 250 which contains the particle beds 3 and 30, and to the connections 41 by means of the air header 14 and the air header 15 associated with the ducts 44 of the tubular collector 400. The other section of the exchanger 7 receives instead an incoming flow of hot fluidization air from the beds 3 and/or 30 and/or from the tubular collector 400, which is conveyed through the already mentioned pipe 71 which passes centrally through the fluidization chamber 250.

In this way the exchanger 7 allows backflow preheating of ambient air entering the distributor 21 and the connections 41 at the expense of the hot fluidization air output from the particle bed 3 and/or 30, and therefore recovery of the heat content of the outgoing fluidization air.

The fluidization air circuit provides that the cold ambient air is propelled by a forced-circulation means, in particular one or more blowers/compressors 8, inside the air/air exchanger 7, and preheating is performed along the path at the expense of the hot fluidization air which, being output from the particle bed 3 and/or 30, is propelled as a backflow inside said exchanger 7. The preheated ambient air reaches the air headers 14, 15, the distribution baffle 21 and the connections 41 via a respective dedicated feed circuits 140 (for the exchange bed 3 and the associated air header part 14), 142 (for the storage bed 30 and associated air chamber part 14) and 150 (for the air header 15 and the tubular collector 400). Preferably, these feed circuits 140, 142 and 150 provide, also independently from the exchanger 7 described above, the respective dedicated adjustment means already presented and denoted by 146, 145 and 144, respectively.

Still on the basis of a preferred configuration, it is possible to have independent adjustment of the two flows which concern the fluidization chamber 250 and the tubular collector 400, in particular with regard to speed. The air output from the particle bed 3, 30, which is cooled after passing through the air/air exchanger 7, is fed, by means of a discharge duct 5, to a dust separator 6, or deduster, and is then expelled into the external environment.

Preferably, the dust separator 6 - typically of the type comprising inertial impactors or equivalent devices with low head losses and cyclonic operation - is situated at the base of the structure of the device 1 in line with the discharge duct 5 and therefore performs dedusting of the fluidization air from any elutriated particles of the beds 3, 30.

With reference to Figure 1 and considering now the general configuration of the plant 100, in the example considered here, the operating fluid is water in the liquid state which, when it passes through the exchanger 4, receives the heat energy transferred from the particles of the bed 3 until it becomes superheated steam. Said steam in predetermined temperature and pressure conditions is then used to produce electric energy by means of expansion i nside a steam tu rbi ne 1 0 associated with a generator.

The operating fluid circuit provides ducts 90 which define tube bundles 4 inside the device 1 and, in the example considered, the already mentioned steam turbine 10 is provided as being connected to an electric power generator, a condenser 1 1 , a gas stripper 40 with bleed-off to the turbine 10, a supply pump 12, an extraction pump 120 or means equivalent to those mentioned above.

With reference to Figure 4, this shows the layout of the plant 100 which, by way of example, is composed of four devices 1 with a tower structure 70, each of the devices 1 being provided with four collectors 400, each of which with its own mirror field 60. Figure 4 shows a station 61 which incorporates the turbine 10 associated with the current generator, the pumps 12 and 120 as well as the gas stripper 40, all mentioned above. The figure also shows the operating fluid circuit 90 which has, along the same line, the ducts for delivery of the operating fluid to the turbine 10 and return to the device 1 from the gas stripper 40.

I n the description above, reference has been made by way of example to the application of the storage device according to the invention to a stand-alone plant for the production of electric energy. It will be understood, however, that the possible applications of the device are broad and relate to the production of steam or heat for industrial plants such as thermoelectric power stations, desalinators, remote heating systems, and so on.

On the basis of the configuration described hitherto, even when there is no solar energy - as during night-time hours - continuity of operation and delivery of steam and therefore of thermal power by the storage device is ensured.

In particular, the dimensional design of the device 1 , the collector ducts 44, the particle beds 3 and 30, the surfaces of the tube bundles 4 and the speed range of the fluidization gas both inside the fluidization chamber 250 and inside the tubular collector 400 may be such as to ensure storage of heat energy during the hours of sunshine by fluidizing only the bed 30 and the ducts 44 and ensuring release of said heat energy during the night-time hours to the heat exchanger by means of fluidization of the particles of the beds 3 and 30.

Moreover, as already mentioned, by using a modular structure of the fluidizable beds and modulating for each section the speed of fluidization of the particles themselves, it is possible to adjust the quantity of heat energy transferred to the tube bundles 4, by choosing to assign one or more sections to heat transfer or storage by means of selective and/or differentiated fluidization of said sections, thereby ensuring continuous operation of the plant.

Furthermore, in the case of plants which have a plu rality of devices 1 , the possibility of adjusting for each device the quantity of heat transferred to the operating fluid and required to keep the temperature and the pressure of the steam produced constant results in the advantage of being able to keep constant, reduce or increase the temperature of the operating fluid or, for the same temperature, increase the flowrate of the operating fluid.

The dimensional design of the storage devices according to the invention and the operating logic may be coordinated so as to obtain a given production of energy even when there is no solar radiation.

On the basis of another preferred variation of embodiment of the invention which can be used in association with all the other configurations described hitherto, it is provided using gaseous fuel inside the fluidized bed, in order to make up for the prolonged absence of sunshine and/or ensure that a given power level is reached depending on the downstream requirements of the production plant.

Another important advantage arises from the possibility of performing combustion of said gaseous fuel directly inside the fluidizable bed. Usually, in fact, in the case of devices of the prior art, this operation is performed in production units separate from the main production plant.

This latter configuration is schematically shown in Figs. 3 and 3A which show a possible circuit for the combustible gas, which circuit comprises feed means 16 and associated adjustment means 161 . Moreover, the circuit provides a dedicated distributor 162 or sparger provided at the distributor 21 .

Where combustible gas is present, the device 1 is provided with one or more burners 22, which are arranged inside the device 1 for triggering combustion and for protecting the system from any dangerous accumulation of gas inside the device, and one or more rupture discs 22 on the casing 2. These features - along with others which may be applicable - are intended to prevent the risk of explosion.

As regards the combustion of gas per se, this is a known technique so that no further detailed description will be provided.

The use of this additional configuration is rendered even more convenient by the fact that the regulations governing the production of energy from renewable sources allow for the production of a minimum quota, generally less than or equal to 15% of the nominal power of the plant, via the combustion of fossil fuels.

A simplified variant embodiment of the device according to the invention may provide, as already mentioned, a single fluidized bed with the function of storage and if necessary also exchange of heat energy.

Moreover, in further variants, the heat energy transferred to the operating fluid may be used for industrial purposes which are also different from the example considered here.

It will be understood at this point how the invention achieves significant advantages in terms of:

dimensional design of the plant, and in particular the storage and exchange devices and the associated structure which are particularly compact - this arising substantially from the preferred configuration in wh ich the air/air exchanger extends heightwise inside the support structure of the device itself; elimination of thermal stresses and consequent deformation of the receiving surfaces by using particles of the bed as direct and/or indirect collectors of the concentrated solar radiation; dimensional design and operation of the plant blowers/separators which process a cold fluid, namely ambient air;

dimensional design and operation of the deduster which, in a manner similar to the blowers/compressors 8, operates with low temperature (e.g. 100°C) exhaust fluidification air;

dimensional design of the tube bundles which pass through the storage device and the dimensions of which may be drastically reduced since evaporation preheating and superheating of the operating fluid are performed by the heat exchange inside the bed with typical coefficients of 300 - 500 W/m²K.

Finally, it will be understood how the invention also provides a heat storage and exchange method as defined in the claims which fol low and with the same preferred characteristic features described above in relation to the various embodiments and variations of embodiment of the device and the plant according to the invention.

The present invention has been described hitherto with reference to preferred embodiments thereof. It is understood that other embodiments relating to the same inventive idea may exist, as defined by the scope of protection of the claims which are provided hereinbelow.

Claims

1. A device (1 ) for storing heat energy received from solar radiation, which device (1 ) comprises:

- a containment casing (2);

- at least one bed (3, 30) of particles suitable for storage and exchange of heat energy, contained in said containment casing (2);

- at least one inlet (21 ) for feeding a fluidization gas through said particle bed (3, 30), the overall arrangement being such that, i n u se, such fluidization gas moves the particles of said bed (3, 30) causing or fostering heat exchange between the particles themselves and/or between these and further members; and

- means (400) for receiving the solar radiation, arranged at said casing (2) and comprising means (40, 41 , 44) for circulating particles coming from said bed (30), which circulating means is apt to cause a dedicated flow of said particles at an irradiation region (200) of the device (1 ) concerned by the solar radiation.

2. The device (1 ) according to claim 1 , wherein said irradiation region comprises one or more chambers (200) defined by said casing (2) and associated to one or more irradiation openings (20) obtained in the latter.

3. The device (1 ) according to the preceding claim, wherein said casing (2) defines a fluidization chamber (250) containing said particle bed (3, 30) and wherein said one or more irradiation chambers (200) are arranged surrounding said fluidization chamber (250).

4. The device (1 ) according to any one of the preceding claims, wherein said circulating means comprises one or more irradiation ducts (44) apt to receive said dedicated flow of particles and extending in said irradiation region (200).

5. The device (1 ) according to the preceding claim, comprising a fluidization chamber (250) containing said particle bed (3, 30) and wherein said circulating means comprises, for said or each irradiation duct (44), an outlet (201 ) for particles from said fluidization chamber (250) to said duct (44), preferably arranged at a base of said fluidization chamber (250), and an inlet (202) for reintroducing the particles into said fluidization chamber (250), preferably obtained at a portion of said chamber placed below the free surface of said bed of particles (30) in a fluidized condition.

6. The device (1 ) according to claim 4 or 5, comprising a three-way connection (41 ) for said or each irradiation duct (44), setting the latter in fluid connection with said particle bed (30) and with a feed line (15) for fluidization gas.

7. The device (1 ) according to any one of the claims 4 to 6, wherein said irradiation duct(s) (44) is/are made of a refractory material, preferably a high-temperature resistant metal alloy, silicon carbide and/or a ceramics material.

8. The device (1 ) according to any one of claims 4 to 7, wherein said or each irradiation duct (44) has a main body made of silicon carbide and in turn contained in a quartz liner and preferably an optical filter applied on the external surface of said main body.

9. The device (1 ) according to any one of the preceding claims, comprising feed means (140, 142, 150) and preferably independent flow adjustment means (146, 145, 144) respectively for the fluidization of said bed of particles (3, 30) and for the generation of said dedicated flow in said means (400) for receiving the solar radiation.

10. The device (1 ) according to any one of the preceding claims, comprising means (203) for interdicting said dedicated flow of particles.

11. The device (1 ) according to any one of the preceding claims, comprising one or more irradiation openings (20) obtained in said casing (2) and one or more quartz windows arranged at said one or more openings (20).

12. The device (1 ) according to the preceding claim, comprising one or more optical filters which are transparent to solar radiation and capable of reflecting infrared radiation and which line said quartz windows.

13. The device (1 ) according to any one of the preceding claims, comprising one or more irradiation openings (20) obtained in said casing (2) and a system for closing said irradiation openings (20), the operation of wh ich is preferably automated.

14. The device (1 ) accord ing to any one of the preced ing claims, further comprising

- heat exchange members (4) crossed, in use, by an operating fluid and arranged at or near said bed (3, 30) of fluidizable particles,

wherein the overall arrangement is such that, in use, portions of said particle bed (3, 30) are apt to be selectively moved by the fluidization gas to store heat energy received from the solar radiation in a storage step and to release the stored heat energy to said heat exchange members (4) in an exchange step, and wherein the overall arrangement is moreover such as to allow an activation of the storage step independent of the heat exchange step.

15. The device (1 ) according to the preceding claim, wherein said particle bed in turn is comprised of:

- a first storage portion (30), apt to store heat energy received from the solar radiation and in fluid communication with said means (40, 41 , 44) for circulating particles; and

- a second exchange portion (3), arranged adjacent to said first portion (30) and apt to release heat energy stored by the latter to said heat exchange members (4),

wherein said first storage portion (30) and said second exchange portion (3) are apt to carry out respectively said storage step and said exchange step by a respective fluidization.

16. The device (1 ) according to claim 1 1 or 12, wherein said heat exchange members (4) are arranged so as to be in contact with at least part (3) of said particle bed (3, 30) and/or so as to be passed over, in use, by at least part (3) of said bed (3, 30) when fluidized by said fluidization gas.

17. The device (1 ) according to any one of the preceding claims, comprising means (1 6, 1 61 , 1 62) for feeding and means (22, 222) for safely burning a combustible gas inside said particle bed (3, 30) or part thereof.

18. The device (1 ) according to any one of the preceding claims, comprising, at said fluidization gas feeding inlet (21 ), a partition (141 ) apt to allow a selective and/or differentiated fluidization of one or more parts of said particle bed (3, 30) by the fluidization gas and/or a selective and/or differentiated fluidization of said first portion (30) and second portion (3) of said particle bed or of parts of said portions.

19. The device (1 ) according to any one of the preceding claims, comprising a gas/gas, preferably air/air heat exchanger (7), wherein the overall arrangement is such that, in use, the following are fed into said exchanger (7):

- a first cold gas, which is the fluidization gas to be used for the fluidization of said particle bed (3, 30) or of said first portion (30) and/or second portion (3) thereof and/or the gas for the generation of said dedicated flow of particles into said receiving means (400), and

- a second hot gas, which is the fluidization gas output from said particle bed (3, 30) or from said first portion (30) and/or second portion (3) thereof.

20. The device (1 ) according to the preceding claim, which is arranged on a tower structure (70) housing said gas/gas exchanger (7) therein.

21. A plant (100) for producing steam or heat for industrial uses, comprising one or more devices (1 ) according to any one of the preceding claims, which plant is preferably an electric power plant or a desalination plant.

22. A method for storage and subsequent exchange of heat energy of solar origin, providing for the use of a bed (3, 30) of particles apt to receive and store heat energy of solar origin and a fluidization of said particle bed (3, 30) such as to cause or foster a heat exchange between the latter and the tube bundles (4) of a heat exchanger, wherein there is produced a dedicated flow of particles collected from said bed (30) at an irradiation region (200) concerned by the solar radiation.

23. The method according to the preceding claim, wherein said fluidization is performed by controlled feeding of a fluidization gas, preferably air.

24. The method according to claim 22 or 23, providing a differentiated fluidization of selected portions of said particle bed (3, 30).

25. The method according to any one of claims 22 to 24, wherein an operating fluid which is water and/or steam flows inside said tube bundles (4).

26. The method according to any one of claims 22 to 25, providing the use of one or more devices (1 ) or of a plant (100) according to any one of claims 1 to 19.

27. The method according to any one of claims 22 to 26, providing combustion of gaseous fossil fuel inside said particle bed (3, 30).

28. The method according to any one of claims 22 to 27, comprising:

- a first step of storage of heat energy received from the concentrated solar radiation by moving a first portion (30) of said particle bed; and

- a second step of exchange of said heat energy stored in said first step with a second portion (3) of said particle bed, and exchange between the latter and said tube bundles (4),

wherein said storage and heat exchange steps can be activated independently of each other.

29. The method according to any one of the claims 22 to 28, providing a step of gas/gas, preferably air/air heat exchange, between a first cold gas which is the fluidization gas to be used for the fluidization of said particle bed (3, 30) and for the generation of said flow dedicated to receive the solar radiation and a second hot gas which is the fluidization gas output from said particle bed (3, 30).

30. The method according to any one of the claims 22 to 29, wherein said fluidization gas is air.

31. The method according to any one of the claims 22 to 30, which is a method for the production of electric energy.