ITLE20090011A1 - ACCUMULATION SYSTEM OF THERMAL ENERGY FROM SOLAR RADIATION. - Google Patents

Description

DESCRIPTION

accompanying an application for an Invention Patent entitled;

"System for the accumulation of thermal energy from solar radiation",

The present invention relates to a system for the accumulation of thermal energy from solar radiation, suitable for transferring heat in a simple and effective manner, even in delayed times, to a fluid which operates a thermodynamic cycle for the generation of electrical energy,

In recent years, due to the progressive increase in the cost of fossil fuels, their inevitable depletion and the environmental damage linked to their consumption, much attention has been paid to research aimed at exploiting solar energy, in the various and various forms of use. , as a valid alternative energy source. Solar energy, in fact, represents the cleanest and most available form of energy as well as being potentially unlimited.

The exploitation of only the direct component of solar radiation for the production of electricity is now preferably carried out in the so-called "high temperature concentration" or "solar thermodynamic" plants, with applications that often see them as integrative of conventional fossil fuel ones. With this technological solution, in which only part of the heat necessary for the entire power cycle is supplied through the thermo-vector fluid used, it is possible to reduce the costs of the electricity produced and eliminate the inevitable production discontinuities related to the variability of the solar source. By entrusting the continuity of the service only to the solar system, it is absolutely necessary to adopt a thermal energy storage system to limit as much as possible the short-term transients linked to irregularities in solar radiation and, more generally, to separate the moment of harvesting from that of the use carried out, respectively, by the concentration system through the heat carrier fluid and by an exchanger with the process fluid.

If no other system intervenes, the maximum temperature that can be reached by the process fluid is very close to that of the storage system (differing from the latter only for the inevitable losses) and conditions, the efficiency that can be reached from the entire power cycle as established in Carnet's ideal heating machine.

Better thermodynamic solar systems with thermal storage it is therefore generally possible to distinguish two operating fluids; the Lermovector fluid which collects the heat from the concentration system and defines, with its chemical-physical characteristics, the peculiarities of the storage; the process fluid which receives the heat from the heat transfer fluid in an exchanger and operates the thermodynamic or power cycle. Leaving aside the purely experimental or demonstrative applications, there are two heat transfer fluids used in plants that have exceeded a considerable number of operating hours: synthetic / mineral oils and mixtures of molten sodium and potassium salts - Kramer Junction plants, Harper Lake, and of Barstow named Solar Two in California -. Both fluids, which operate at the operating temperature in the liquid state, have highlighted a series of problems and limits of use: oils, for example, can be used up to a temperature of about 400 T; they have a high cost and, in case of leaks, they are easily flammable and dangerous for the environment; the molten salts of sodium and potassium, compared to oìi, allow to operate at higher temperatures (550 "C but not beyond dissociation) but the mixtures cannot be carefully cooled below 29D" C since they crystallize at 238T and solidify at 221 " C. Furthermore, in the latter case, beyond the problems relating to temperatures, rather particular technological solutions and operating methods are also required for the management of these mixtures: it is in fact necessary to arrange a continuous circulation of the same (even at night) to prevent any solidifications; the pipes must be heated during the start-up or shutdown phases to prevent the fluid from cooling; there is always the danger of blocking the circulation in the cold areas of the circuit; pumps, valves and gaskets must be studied ad hoc as well as the materials, with which the salts come into contact, to limit corrosion phenomena.

The main purpose of the following invention is to overcome the problems and disadvantages of the systems indicated above and to provide a new system for the accumulation of thermal energy from solar radiation, simple, efficient and which uses only materials and fluids that are totally compatible with the 'environment,

The specific object of the present invention therefore forms a different storage system for the thermal energy from solar radiation, comprising

a) a bed of perfectly mixed solid particles,

b) a device for the exchange of heat between said solid particles and a fluid which operates a thermodynamic cycle,

c) a concentrator of solar rays,

characterized by the fact that, in defense of direct solar radiation, said concentrator of solar rays c) raises the temperature of the single perfectly mixed solid particles constituting said bed 3) and allows the system, even in deferred times, through said device to heat exchange b}, the transfer of the thermal energy, accumulated in the perfectly mixed solid particles, to the fluid that operates the thermodynamic cycle - Preferably according to the invention Sa perfect mixing of the solid particles is obtained by fluidizing them with a gas 0 a steam.

Preferably, according to the invention, the fluid which operates the thermodynamic cycle coincides with the fluid which fluidizes the solid particles constituting the (hecto,

Preferably according to the invention, the solar radiation concentrator c) consists of a FresneJ lens.

Preferably, according to Finvenzone, the heating of the perfectly mixed solid particles can take place by the direct action of the solar radiation concentrator c) on the same and / or by the indirect action of a material or device, interposed between the bed of solid particles a) and the concentrator of the solar rays cj in contact with the solid particles perfectly mixed and on which the concentrator of the solar rays cj acts,

The present invention will now be described by way of illustration, but not of limitation, according to its preferred embodiments, with particular reference to the figures of the attached drawings, in which the

Figure 1 of Table 1 shows a general schematic comprising the elements of the storage system according to the invention;

Figure 2 of Table 1 shows a schematic of the accumulation system in which the concentrator acts indirectly on the solid particles of the fluidized bed;

Figure 3 of Table 1 shows a schematic of the storage system in which a Fresnel lens acts directly on the solid particles of the fluidized bed; Figure 4 of Table 2 shows a schematic diagram of the storage system that can be used for the production of electricity;

Figure 5 of Table 3 shows a schematic of the solar system consisting of a series of storage systems according to the invention, integrated with other devices that use different forms of energy that supplement or replace the solar one.

With reference to Figure 1 of Table 1, a schematic embodiment of the storage system according to the invention can be observed, comprising the perfectly mixed bed of particles 3 inside a generic containment structure 6; the system of concentration 2 of the solar rays 1; a generic heat exchange device 4, inside which the fluid 5 which operates the thermodynamic cycle flows, The thermal energy coming from solar radiation is accumulated in the particles that make up the bed 3 and not in a liquid substance such as a melted salt or oil. The nature of the particles determines the maximum operating temperature of the system.The advantages of this storage system appear evident since, using a very common material such as quartz, temperatures even higher than 1000 ° C can be reached without compromising its state and characteristics in the time.

There are, of course, no problems of agglomeration of particles with high and low operating temperatures: the particles are not flammable and dangerous for the environment as happens for molten salts and olfs.

To ensure uniform temperature conditions for the entire mass involved in thermal accumulation, the bed of particles must be continuously mixed, especially in the concentration zone, where very high temperatures are reached and dependent on the concentration system used, * the term used to ensure this condition is that of a perfectly mixed bed.

In Figure 2 of Table 1, it is possible to observe an embodiment of the accumulation system according to the invention in which the conditions of perfect mixing can be considered reached when the solid particles 3 are fluidized with a gas or steam as for bed systems. cut fluid, in the various industrial embodiments, the characteristics and performances are well known. A fluid bed of solid particles is characterized by a very high thermal inertia, by a constant temperature throughout the mass and by very high exchange coefficients with the surfaces immersed in the dense phase. the fluid 9 passes through the duct 12 in the distribution area 10. bounded by the bottom of the container 6 and by a perforated plate 11: the fluid 9, after having passed through the bed of particles with adequate speed, having reached the freeboard 13, leaves the system , isolated from the outside by means of cover 8, through 3⁄4 duct 14. The thermal energy accumulated by the fluidized particles 3, is transferred to the fluid 5 through the exchanger 4. The scheme adopted to represent the fluidization of the system of solid particles must be understood as an example but not limiting of the application: so even if the distribution of the fluid is depicted a By providing a perforated distributor 11, many other types of distributors can be used for this function, such as, for example, sintered or ceramic plates and / or distributor nozzles in the most diverse configurations. However, all types have the sole purpose of distributing the flow of the fluid used in the best and simplest possible form. The same considerations can be adopted for the container 6, preferably made of steel resistant to high temperatures insulated to limit its dispersions and cylindrical in shape but different materials and sections can be used without however departing from the scope of the following invention.

According to what is reported in the diagram of Figure 2, the solar rays 1, concentrated through the device 2, do not directly strike the particles causing the progressive heating of the whole mass, but a device 7 which, by heating up, in turn transmits the heat to the mass of the perfectly mixed bed 3 through direct contact with its constituent particles. This heating is of the indirect type and the device 7 that can be adopted can be, by way of example but not limiting, a simple material with good thermal conductivity characteristics or a more complex system such as, for example, a heat pipe.

In Figure 2 the fluid 5 that operates the thermodynamic cycle and the fluid 9, which operates the fluidization, are of a different nature and naturally separate. It is known that in fluid bed systems the temperature of the fluid leaving E in the dense phase is practically identical to that of the bed and therefore, the fluid 9 leaving the duct 14 is at the same temperature as the bed 3: since, at least in theory, it is an energy that would be lost, it is desirable to recover it with exchange devices, not shown in Figure 2, inserted between the fluid 9 exiting the duct 14 and the same fluid entering the duct 12.

In general, and only by way of example, the temperature level that can be reached with a system thus represented in Figure 2 could allow the carrying out of an Stretching cycle where the gases of the thermodynamic cycle 5, usually hydrogen or helium at high pressure, are heated through the exchange surfaces 4 immersed in the dense phase of the perfectly mixed bed 3,

In Figure 3 of Table 1, the storage system object of the invention is characterized by the adoption of a Fresnel lens 19, which acts directly on the particles of the fluidized bed through a window of material transparent to solar radiation 18, replacing the system generic of concentration; the perfect mixing of the solid particles 3, as shown in the diagram shown, is entrusted to! fluid 9 introduced through the duct 12, or to the fluid 5 through the duct 15: in the latter case a part of the fluid 5, normally used for carrying out the thermodynamic cycle, is tapped out of the exchanger 4 and used for fluidization. Depending on the operating conditions used, either the fluid 9 or the fluid 5 may be at the outlet from the duct 14: although the opening of the valve 17 usually provides for the closure of the valve 16, the possibilities of mixing of the two fluids. It appears extremely evident that, by adopting a fluidization regime with a fluid that coincides with the one that operates the thermodynamic cycle, significant energy recoveries are possible.

Only and exclusively by way of example, the adoption of a FresneJ lens, made of a plastic material such as polymethylmethacrylate (PMMA), has considerable advantages: among these, excellent optical properties, low cost and considerable dimensions. In Figures 2 and 3 of Table 1, a further advantage of the invention is also evident: since the storage system raises the temperature of the particles only during the hours of insolation, it is possible, in the absence of the latter, completely block the fluidization and avoid the losses connected to it. This advantage can be exploited only during the phase of reaching the temperature set for storage and unwinding from the thermodynamic cycle, in the cut phase the heat exchanger 4 is not operational; the system accumulates energy during insolation by fluidizing the particles and maintains the temperature level reached, without fluidization, during t periods in oils there is no thermal load. Obviously, the blocking of the fluidization, or in any case delta mixing, can be implemented not only at night but also during the interruptions of the insolation due to the momentary passage of clouds and variable weather *, consequently, all possible cases of thermal shocks are avoided. in other storage systems,

In Figure 4 of Table 2, by way of example but not of limitation *, a different embodiment according to the invention is represented: the fluid which carries out the working acid is water, in the form of superheated steam, which expands in the turbine 21 for power generation, the superheated steam was generated inside the exchange surface 4, immersed in the dense phase of the bed of perfectly mixed solid particles, contained inside a fluidization column 24. A condenser 22 a pump for the water 23 completes the classic scheme of a Rankine odo.In the scheme, part of the superheated steam S Leaving the exchanger 4, is taken and used through the opening of the valve 26, for the fluidization of the column: the steam leaving the freeboard, it re-enters the circuit between the condenser 22 and the turbine 21.

In the initial phases when the system 8 has not reached a sufficient temperature and the heat exchanges are reduced, the opening of the valve 27 allows the introduction of the fluid 5 from another system or application,

It appears evident from Figure 4 of Table 2 a further advantage according to the invention deriving from the use of steam as a process fluid and fluidization: the thermal accumulation, carried out through the melt of the solid particles fiuidized, physically resides in the same concentration zone. and it is the steam that, even at a considerable distance, reaches the place of use. The reduced environmental impact of an accumulation system created in this way is also evident, where the fluidization column 24 and all the steam and water lines that reach high can be placed under the ground, therefore not visible.

Figure S of Table 3 shows, for demonstration and non-limiting purposes only, a diagram in which many storage systems as in Figure 4, numbered from 28 to 37, are part of a single energy production plant together with the generators of steam 38 and 39 connected to processes that use a form of energy that replaces solar energy such as, for example, that contained in biomass or fossil fuels. The fluid 5 circulated by the pump 23 runs through all the accumulation systems, some placed in series, others in parallel in an absolutely generic manner.

generating steam that can be used in the turbine 21. In the diagram, the plants have generally different powers and dimensions and can work with their own internal exchanger with water or steam depending on their arrangement.

The one shown is of course a so-called hybrid system in which, in operation, part of the overall power is generated by traditional systems, part of the solar radiation storage systems: in limited cases they would work exclusively or systems 38 and 39 for total lack of solar radiation or storage systems from 28 to 37 in particular situations of insolation. Furthermore, even if not shown in the diagrams, many accumulation systems could be excluded with suitable by-passes of the steam line 5, creating flexibility in operation and maintenance.

An obvious advantage in the application of Figure 5 is that the efficiency of the entire system must be evaluated between the condensation temperature and the storage temperature: both temperatures are not affected by the upper (550 ° C) and lower (290 ° C) limits, such as for example for molten salts: the result is a significant increase in the overall performance under the same conditions and with respect to the state of the art.

According to one of the purposes of the invention, an accumulation plant composed in this way works with totally compatible materials (solid particles and water) and uses widely known and tested technologies.

The present invention has been described for illustrative, but not limitative purposes, according to its preferred embodiments, but it is understood that variations and / or modifications may be made by those skilled in the art without thereby departing from the relative scope of protection as defined. from the attached claims,

Claims (1)

CLAIMS 1) System for the accumulation of thermal energy from solar radiation comprising: a) a roof of perfectly mixed solid particles, bf a device for the exchange of heat between said solid particles and a fiuid which operates a thermodynamic cycle. c) a concentrator of solar rays, characterized by the fact that, in the presence of direct solar radiation, said concentrator of solar rays c) raises the temperature of the single perfectly mixed solid particles constituting said bed a} and allows, even in deferred times, for the passage of said exchange device heat b), the transfer of the thermal energy, accumulated in the perfectly mixed solid particles, to the fluid that operates the thermodynamic cycle. 2} System according to claim 1) characterized in that the perfect mixing of the solid particles is obtained by fluidizing them with a gas or a vapor. 3) System according to claim 2, characterized by the fact that the fluid which operates the thermodynamic coincides with that which fluidizes the solid particles constituting the object. 4) System according to claim 3) characterized in that the fluid is water vapor. S) System according to claim II, characterized in that perfect mixing is obtained through the use of mechanical or electromechanical or acoustic devices. 6) System according to each of the preceding claims characterized by the fact that the solar radiation concentrator c) consists of a Fresnel temperature 7) System according to each of the preceding claims, characterized by the fact that the heating of the perfectly mixed solid particles can take place by the direct action of the solar radiation concentrator c) on the same and / α by the indirect ration of a material or device, interposed between the iect of solid particles a) and I concentrator of the solar rays t), in contact with the solid particles perfectly mixed and on which the concentrator of the solar rays acts c), S) System according to each of the preceding claims made using solid particles of any shape, nature and size and fluids of different nature and characteristics referable both to the thermodynamic cycle and to the fluidization process. 9J Solar system for the production of electricity from solar radiation characterized by the fact of providing for the use of one or more solar energy storage systems according to the preceding claims, possibly integrated with other systems generating energy from different sources, between them connected through the common use of the fluid that operates the thermodynamic reduction.