ITMI20111746A1 - CONCENTRATION OPTICAL GROUP FOR A THERMAL ENERGY ACCUMULATION SYSTEM - Google Patents

Description

DESCRIPTION

of the patent for industrial invention entitled:

â € œ CONCENTRATION OPTICAL UNIT FOR A THERMAL ENERGY STORAGE SYSTEMâ €

The present invention relates to a concentrating optical unit for a thermal energy storage system.

Generally, point concentration solar plants include a solar receiver, placed on top of a tower, a cold tank, in which the cold molten salts are stored (at a temperature of about 290 ° C), a hot tank, in which they are stored the hot molten salts (at a temperature of about 550 ° C), a conduction line of the cold molten salts from the tank to the solar receiver and a conduction line of the hot molten salts from the solar receiver to the respective tank.

The conduction lines usually consist of insulated pipes that necessarily require a heating system (at about 290 ° C) to be activated before circulating the molten salts, in order to avoid their solidification and the consequent obstructions that could occur. The heating system is usually made by electric resistances.

Such heating is also necessary during a period of prolonged absence of the sun. Also in this case the pipes must be kept at a temperature of about 290 ° C with consequent thermal losses and electricity consumption. Alternatively, the pipes could be emptied by letting the molten salts flow into the tanks, with the drawback, however, of having to repeat the preheating of the pipes before reintroducing the salts themselves.

Furthermore, it should be considered that the above type of plant requires the use of special pumping systems capable of handling the molten salts efficiently and safely and with sufficient head to reach the receiver at the top of the tower whose height can exceed the 100 m.

As can be immediate from the above, the system solution described above involves the presence of numerous and even sophisticated components, which necessarily translates into high construction and management costs.

Furthermore, this type of solar system involves a considerable encumbrance of spaces, which can sometimes make their realization difficult, if not compromise.

The need was therefore felt to have a concentrating solar plant whose characteristics allowed to avoid the problems of the known art described above.

The object of the present invention is a concentration optical unit comprising at least one heliostat suitable for directly receiving solar radiation, a secondary mirror suitable for receiving solar radiation reflected by said heliostat and a concentrator suitable for receiving radiation solar reflection from said secondary mirror and concentrating it in a receiver; the said optical group being characterized by the fact that said at least one heliostat is able to move on a circular track around an axis of symmetry of the said concentrator following the azimuth movement of the sun, and by the fact that the said secondary mirror is a hyperbolic mirror rotating around said axis of symmetry of said concentrator so as to maintain unchanged the position relative to said at least one heliostat; said secondary mirror maintaining a curved and off-axis position with respect to the concentrator itself in order to maximize the radiation collection efficiency.

For a better understanding of the invention, an embodiment is given below for illustrative and non-limiting purposes with the aid of the figures in the attached drawing, in which:

Figure 1 illustrates as a whole a concentrating solar plant according to the present invention;

Figure 2 illustrates a detail of a concentrating optical unit of the system of Figure 1;

figure 3 is a longitudinal section of a tank of the plant of figure 1; And

figure 4 is a top view of a detail of the tank in figure 3.

In Figure 1, 1 indicates as a whole a concentrating solar plant according to the present invention.

The concentrating solar plant 1 comprises an accumulation tank 2 suitable for housing a heat transfer fluid and a concentration optical unit 3 suitable for concentrating the solar radiation in said accumulation tank. In this case, the heat transfer fluid is made up of a mixture of molten salts composed of 60% of Sodium Nitrate and 40% of Potassium Nitrate, but it can also be made up of another type of mixture of salts or fluid. high thermal capacity.

As illustrated in figure 3, the storage tank 2 comprises a containment structure 4 and a cavity receiver 5 housed inside the containment structure 4 and arranged to receive concentrated solar radiation from the optical concentration unit 3.

The containment structure 4 has a cylindrical conformation and is defined by a side wall 6 by a bottom wall 7 and by an upper wall 8. Inside the containment structure 4 the molten salts are housed in a stratified manner with the “cold melted salts” arranged in the bottom and “hot melted salts” arranged on the surface.

In the following, with the words `` cold melted salts '' we mean the mixture defined above at a temperature of about 290 ° C, while with the words `` hot melted salts '' we mean the mixture defined above at a temperature of about 550 ° C.

Generally speaking, the receiver 5 of the present invention is housed inside the containment structure 4 to take the cold molten salts from the bottom, heat them using concentrated solar radiation and deposit the hot molten salts obtained on the surface.

In this way it is possible to always guarantee the availability of hot molten salts to a user device, such as a steam generator, which will be able to take the hot molten salts from the liquid surface inside the containment structure 4 , use them by exploiting the accumulated thermal energy and redeposit them as cold molten salts on the bottom of the containment structure 4 itself.

In other words, while the user takes the hot molten salts from the containment structure 4 and returns them to it as cold molten salts, at the same time the receiver, inside the same containment structure 4, ensures a continuous transformation of the salts cold melts into hot melt salts.

The receiver 5 has a cylindrical shaped receiving cavity 9 with axis of symmetry X and suitable for directly receiving concentrated solar radiation. The reception cavity 9 is defined by a side wall 10, by a bottom wall 11 and by an upper wall 12, in which an opening 13 is coaxial to the X axis, which faces into a CPC concentrator (Compound Parabolic Concentrator) 14 also has an X axis of symmetry as will be shown below. In particular, the upper wall 12 is arranged externally to the containment structure 4 since a portion of the side wall 10 passes through an opening 15 made in the upper wall 8 of the containment structure 4 itself. As may seem obvious to a person skilled in the art, the upper wall 12 can also be arranged inside the containment structure 4 without this affecting the invention as a whole in the least.

The receiver 5 also comprises a cylindrical jacket 16 arranged around and coaxial to the receiving cavity 9 and comprising a side wall 17 and a bottom wall 18 while it is open at the top. The cylindrical jacket 16 forms with the receiving cavity 9 an interspace 19 for the passage of the molten salts as will be described below. In particular, the interspace 19 is defined between the side walls 10 and 17 and the bottom walls 11 and 18.

As illustrated in Figures 3 and 4, the bottom wall 18 has a central opening 20 to allow the entry of the molten salts into the cavity 19.

As shown in Figure 3, the receiver 5 comprises a sampling duct 21 having a lower end 22 arranged in proximity to the bottom wall 7 of the containment structure 4 and an upper end 23 facing into the opening 20. In the sampling duct 21 there is an impeller (known and not illustrated for simplicity) able to regulate the flow rate of the molten salts.

The molten salts, therefore, are collected `` cold '' at the bottom of the containment structure 4 from the duct 21, pass through the opening 20 and go up the interspace 19 and then come out of it `` hot '' overflowing from the upper end of the side wall 17. The presence of the impeller is important for regulating the flow rate of the molten salts and keeping the outlet temperature constant at around 550-600 ° C.

In the cavity 19 the heating of the molten salts occurs by thermal convection with the side walls 10 and bottom 11 of the receiving cavity 9. In order to increase the efficiency of the convective heat exchange and, therefore, the contact surface of the salts fused with the aforesaid walls, in the interspace 19 obligatory paths are obtained for the molten salts themselves.

In particular, an oblique wall 24 extends between the side walls 10 and 17, which defines a helical path of the molten salts around the receiving cavity 9, while (Figure 4) a plurality of vertical walls extend from the bottom wall 18 25 which impose on the molten salts, once they have entered through the opening 20, a prolonged stay between the bottom walls 11 and 18 before rising between the side walls 10 and 17 along the oblique wall 24.

Finally, the storage tank 2 (not shown for simplicity) externally includes an insulation jacket designed to ensure that there is no heat exchange between the molten salts flowing inside the receiver 5 and the molten salts stratified in the containment structure. 4. The mantle is made up of 5 mm diameter spheres of alumina immersed in still molten salts.

As can be immediate from the above, the integration between the thermal accumulation with fluid stratified by temperature and the receiver allows to eliminate all the connection pipes, including the components for their heating, as well as the need for pumping. for the circulation of molten salts in the pipes extended to the receiver usually at the top of the tower.

As illustrated in Figure 1, the concentrating optical unit 3 comprises, in sequence of irradiation, a plurality of primary mirrors 26, a secondary mirror 27 and the aforementioned concentrator CPC 14.

In this case, the primary mirrors 26 are heliostats, while the secondary mirror 27 is a hyperbolic mirror made from the combination of a plurality of flat mirrors and which, as illustrated in figure 2, is curved and out of axis with respect to the CPC concentrator 14. Such a conformation allows to obtain high concentration factors of solar radiation with a consequent reduction of radiative losses and the possibility of an efficient use of solar thermal energy even at temperatures close to 1000 ° C.

The secondary mirror 27 is subjected to rotation around the X axis of the CPC concentrator 14 and of the receiver 5 and operates with a rotating field of heliostats 26 which follow the azimuth movement of the sun. In particular, the heliostats 26, following the azimuth movement of the sun, move on one or more circular tracks (not shown for simplicity) around the X axis of the CPC 14 concentrator and of the receiver 5.

This avoids having to use a rotating receiver or one with a rotating aperture as it will be sufficient to rotate the secondary mirror 27 or its useful part around the common axis of the CPC 14 concentrator and the receiver 5.

In fact, the rotating heliostats are always in the most favorable position with respect to the sun and operate with a useful area very close to the physical one, thus reaching a high solar radiation collection efficiency even with a low elevation of the sun. on the horizon.

Finally, it should be emphasized that the solution of rotating heliostats described above allows both to have a station for cleaning the heliostats themselves, with the obvious advantages of structural simplification and costs, and to allow the ground inside the circular tracks to continue to be destined for another use, such as for agricultural use.

Claims (5)

CLAIMS 1. Concentration optical unit (3) comprising at least one heliostat (26) suitable for directly receiving solar radiation, a secondary mirror (27) suitable for receiving solar radiation reflected by said heliostat (26) and a concentrator (14) adapted to receive solar radiation reflected by said secondary mirror (27) and to concentrate it in a receiver (5); said optical group being characterized by the fact that said at least one heliostat (26) is able to move on a circular track around an axis of symmetry (X) of said concentrator (14) following the azimuth movement of the sun, and by the fact that said secondary mirror (27) is a hyperbolic mirror rotating around said axis of symmetry (X) of said concentrator (14) so as to maintain unchanged the position relative to said at least one heliostat (26); said secondary mirror (27) maintaining a curved and off-axis position with respect to the concentrator (14) itself in order to maximize the radiation collection efficiency. 2. Concentrating optical group (3) according to claim 1, characterized in that said concentrator (14) is of the CPC type (Compound Parabolic Concentrator). Concentrating optical group (3) according to claim 1 or 2, characterized in that it comprises a plurality of heliostats (26) as primary mirrors. 4. Concentrating optical unit (3) according to one of the preceding claims characterized in that the said secondary mirror (27) and the said concentrator (14) are made from a combination of flat mirrors. 5. Concentrating solar plant (1) characterized in that it comprises a concentrating optical unit (3) as claimed in any one of the preceding claims.