TECHNICAL FIELD

The present invention relates to an electric energy generation system to be supplied by a low-enthalpy heat source. By low-enthalpy heat source it is meant a primary energy source at low temperature and/or pressure, for example solar energy or geothermal energy, or the so-called "thermal waste" of an industrial plant that works with large amounts of thermal energy and which generates heat to be released to the environment (e.g., furnaces or chemical reactors) .

BACKGROUND ART

The currently known electric energy generation systems supplied directly by heat sources comprise an electric generator, for example an alternator, coupled to a turbine driven by a jet of a fluid in gaseous phase (steam or gas in general) with a high kinetic energy that is produced by a heat generator, for example a boiler, supplied with methane, coal or nuclear energy. Moreover, there are cogeneration systems for the generation of electric and thermal energy that comprise an electric generator coupled to an endothermic motor that is supplied with a liquid or gaseous fuel, for example methane, LPG, gasoline or diesel fuel .

All of the systems described above are supplied by high-enthalpy heat sources, wherein heat is produced in large amounts by the combustion of a natural or fossil fuel or by the nuclear fission of fissile material. However, such systems would be highly inefficient if supplied by low-enthalpy heat sources, that is, if the heat generator was adapted to be supplied by solar energy or geothermal energy .

DISCLOSURE OF INVENTION

The object of the present invention is to provide an electric energy generation system to be supplied by a low- enthalpy heat source for a vehicle which is free from the above drawbacks while being easy and cost-effective to be implemented .

According to the present invention, an electric energy generation system to be supplied by a low-enthalpy heat source is provided as defined in the accompanying claims. BRIEF DESCRIPTION OF THE DRAWINGS

A preferred embodiment will now be described for a better understanding of the present invention by way of a non-limiting example only, with reference to the accompanying drawings, in which:

- figure 1 shows, according to a schematic and partly sectional view, the electric energy generation system implemented according to the teachings of the present invention;

- figure 2 shows, according to a perspective view, the impeller of a turbine of the system in figure 1;

- figure 3 shows, according to a front view, only a part of the impeller in figure 2;

- figure 4 shows, according to a front view, the outer body of the turbine;

- figure 5 shows, again according to a schematic and partly sectional view, a further embodiment of the system of figure 1; and

- figure 6 shows a variant of the outer body of the turbine of figure 4.

BEST MODE FOR CARRYING OUT THE INVENTION

In figure 1, reference numeral 1 generally indicates, as a whole, the electric energy generation system of the present invention. System 1 comprises a closed hydraulic circuit 2 wherein a heat transfer fluid (not shown) flows, which fluid consists of a liquid component and a gaseous component which is insoluble in the liquid component, and on which an innovative thermodynamic cycle, which will be described hereinafter in this document, is carried out. The liquid component, which for brevity will be hereinafter called liquid, essentially consists of water and additives whose purpose is to prevent oxidation and decay of the various parts of circuit 2. The gaseous component, which for brevity will be hereinafter called gas, consists of a low density and low condensation point and preferably inert gas, for example argon or nitrogen.

Circuit 2 comprises: a heat exchanger 3 flown through by the fluid and thermally coupled with a low-enthalpy heat source, not shown, and consisting, for example, of one or more solar panels, a geothermal system, or thermal waste, for transferring heat to the fluid so as to increase the gas pressure; a turbine 4 having an impeller 5 integral with a rotation shaft 6 rotating about a horizontal axis 6a, a fluid-tight chamber 7 for impeller 5, filled with the fluid in such a way that impeller 5 is completely immersed in the fluid, a radial inlet 8 for the entry of the fluid and an axial outlet or drain 9 for the discharge of the fluid, connected via a conduit 10 to inlet 3a of the heat exchanger 3; and a compressor 11 arranged between an outlet 3b of the heat exchanger 3 and the radial inlet 8 of turbine 4 for circulating the fluid in circuit 2 in a direction of circulation D that enters in the radial inlet 8.

System 1 also comprises an electric generator 12 whose rotation shaft 13 is rigidly coupled with the rotation shaft 6 of turbine 4 for converting the kinetic rotation energy of impeller 5 into electric energy. Circuit 2 and the heat exchanger 3 are sized to bring the gas into the fluid to a pressure of about 150000 Pa. Moreover, circuit 2, the heat exchanger 3 and compressor 11 are sized to keep the fluid at a relatively low temperature, i.e. a temperature ranging from about 30 °C at inlet 3a of the heat exchanger 3 to about 100 °C at outlet 3b of the heat exchanger 3. In such conditions, the fluid is also to be considered with low-enthalpy, i.e. at low temperature and/or pressure.

Compressor 11 is a hybrid compressor, i.e. able to work both with liquids and with gases. Compressor 11 creates a low pressure difference between two points of circuit 2, having a value of approximately between 25000 and 35000 Pa to circulate the fluid in the direction of circulation D. The electric generator 12 consists, for example, of an alternator for producing electric energy in alternating current.

Circuit 2 further comprises two Venturi nozzles, indicated with reference numerals 30 and 31, connected to an inlet 15 and to an outlet 16, respectively, of compressor 11. The Venturi nozzle 30 has an inlet section 30a connected, through a conduit 17, to outlet 3b of the heat exchanger 3 and an outlet section 30b which is directly connected to inlet 15 of compressor 11 and which is narrower than the inlet section 30a for producing, in the flow of fluid which enters into compressor 11, a sudden drop of pressure of the gas (the liquid is incompressible) and a consequent increase in the speed of the fluid with a stronger acceleration of the gas with respect to the liquid, because of the higher density of the liquid with respect to the gas, thus favouring the separation between the gas and the liquid and thus the formation of bubbles of gas in the fluid within compressor 11. The Venturi nozzle 31 has an inlet section 31a connected to outlet 16 of compressor 11 and an outlet section 31b which is connected to the radial inlet 8 of turbine 4 and which is larger than the inlet section 31a for producing, in the flow of fluid which enters into turbine 4, a sudden increase of pressure of the gas and a consequent decrease in the speed of the fluid with a stronger deceleration of the liquid with respect to the bubbles of gas, because of the higher density of the liquid with respect to the gas, thus strengthening the separation process between the gas and the liquid and thus favouring the injection of bubbles of gas in turbine 4.

The bubbles of gas injected into turbine 4 flow through chamber 7 hitting against blades 14 of impeller 5. Impeller 5 rotates due to the thrust of the bubbles of gas on blades 14 and, to a much lesser extent, due to the thrust, on blades 14, of the liquid that is circulated by compressor 11.

Turbine 4 is arranged with the radial inlet 8 facing downwards. This way, the bubbles of gas in the flow of fluid which, in use, enters into turbine 4 through the radial inlet 8 and flows through chamber 7, are subjected to the hydrostatic thrust (Archimedes' principle) for at least a stretch of chamber 7. The hydrostatic pressure, by pushing the bubbles of gas upwards, helps pushing the bubbles of gas against blades 14 of impeller 5.

Compressor 11 is arranged with outlet 16 facing upwards and underneath turbine 4, in a position substantially vertically aligned with the radial inlet 8 of turbine 4 in such a way that the Venturi nozzle 31 is in a substantially vertical position. In this way, the Venturi nozzle 31 does not obstruct, but rather favours, the upward movement of bubbles of gas due to the hydrostatic thrust. Therefore, the vertical position of the Venturi nozzle 31 favours the injection of bubbles of gas into turbine 4.

With reference to figure 2, which shows the impeller according to a perspective view, and to figure 3, which shows the inside of impeller 5 according to a front view, impeller 5 is a closed impeller, which has a plurality of centripetal helical blades 14, a respective plurality of peripheral openings 18 for the fluid inlet and an axial opening 19, coaxial with axis 6a, for the axial discharge of the fluid.

Blades 14 are evenly distributed about a through hole 20 coaxial with axis 6a in which the rotation shaft 6, not shown in figures 2 and 3, is fitted. The peripheral openings 18 have the same size and are evenly distributed along the outer circumference of impeller 5. Each radial opening 18 is delimited, parallel to axis 6a, by the outer ends 21 of two adjacent blades 14 and, perpendicular to axis 6a, by a rear wall 22 and a front wall 23 of impeller 5. The axial opening 19 is formed in the front wall 23 and communicates with all the peripheral openings 18 through respective channels 24 (figure 3), each of which is defined between the walls of two adjacent blades 14 and therefore has a centripetal curved shape. Each blade 14 extends from a respective outer end 21 parallel to axis 6a to a respective inner end 25, which is transverse to axis 6a, and which does not protrude outside of the central opening 19. In the example shown in figures 2 and 3, blades 14, as well as the peripheral openings 18, are six in number.

With reference to figure 3 and figure 4, the latter showing the outside of the body of turbine 4 according to a front view, the body of turbine 4 comprises a curved injection conduit 27, which puts the radial inlet 8 in communication with chamber 7 and is shaped so as to convey the fluid entering from the radial inlet 8 towards the peripheral openings 18 of impeller 5 according to flow lines F (figure 3) substantially tangential to impeller 5. The curved injection conduit 27 is also visible in figure 1.

With reference again to figure 1, system 1 comprises a cooling chamber 26, wherein chamber 7 of turbine 4 is arranged and which is flooded with a cooling liquid (not shown) which completely submerges chamber 7 on the outside to absorb heat from the fluid as it flows through chamber 7. The cooling chamber 26 is coupled with a heat accumulator, not shown, for producing thermal energy, for example, for producing hot water for domestic or industrial use or for air conditioning of rooms. The cooling chamber 26 is sized to prevent the liquid of the fluid in circuit 2 from warming up to vaporizing. Therefore, the cooling chamber 26 is actually a heat exchanger that transfers heat from the fluid flowing in circuit 2 of the heat accumulator, thus making system 1, when provided with the heat accumulator, a cogeneration system for the production of electric and thermal energy.

In use, the heat exchanger 3, as previously mentioned, transfers heat to the fluid. The gas of the fluid that flows through the heat exchanger 3 is mixed with the liquid of the fluid itself, i.e. it is not aggregated in bubbles. Consequently, the heat transferred to the fluid causes a heating of the gas in the fluid and as a result, the pressure of the gas in the fluid increases. Since the gas is a poor heat conductor, if the gas of the fluid in the heat exchanger 3 was aggregated in bubbles it would not get warmed up adequately. The weak depression generated by compressor 11 extracts the hot fluid from the heat exchanger 3 and injects it in the radial inlet 8 of turbine 4 through the Venturi nozzles 30 and 31.

The Venturi nozzle 30 connected to inlet 15 of compressor 11 favours the separation between the gas and the liquid and thus the formation of bubbles of gas. The Venturi nozzle 31 connected to outlet 16 of compressor 11 increases the separation between the gas and the liquid and thus it favours the injection of bubbles of gas into turbine 4. The overall effect of the two Venturi nozzles 30 and 31 therefore is to produce bubbles of gas and increase the kinetic energy of the gas, precisely in the form of bubbles, with respect to the liquid. The bubbles of gas enter into turbine 4 through the radial inlet 8 and the injection conduit 27 and, flowing through a part of chamber 7, push blades 14 of impeller 5, which rotates due to the combined effect of the thrust of the liquid, due to the action of compressor 11 and to the convective motion, and especially due to the thrust of the bubbles of gas.

The radial inlet 8 of turbine 4 facing downwards and outlet 16 of compressor 11 facing upwards and connected to the radial inlet 8 through the Venturi nozzle 31 in a vertical position favour the upward movement of the bubbles of gas due to the hydrostatic thrust and thus maximize the kinetic energy of the bubbles of gas upon their impact with blades 14 of impeller 5. The impact of bubbles of gas on blades 14 transforms the kinetic energy of the bubbles of gas into kinetic rotation energy of impeller 5. The bubbles of gas disintegrate progressively flowing through channels 24 of impeller 5 in rotation and then in the fluid discharged from turbine 4 through the axial outlet 9, the gas is again substantially mixed with the liquid.

Therefore, a thermodynamic cycle is carried out on the fluid flowing through circuit 2 which transforms part of the heat acquired from the low-enthalpy heat source in an increase of pressure of the gas in the fluid, transforms the gas pressure into kinetic energy of the bubbles of gas and converts the kinetic energy of the bubbles of gas into mechanical rotation energy, i.e. into kinetic rotation energy of impeller 5. Of course, impeller 5 also moves due to the thrust of the liquid produced by compressor 11 and by the convective motion of the liquid, but the contribution to the thrust that comes from the bubbles of gas is predominant and is essentially due to the energy transformation of the heat acquired by the fluid through the heat exchanger 3 and to the hydrostatic thrust acting on the bubbles.

However, a part of the heat transferred to the fluid in the heat exchanger 3 is not converted into mechanical energy, due to the inherent inefficiency of the conversion process. This residual part of the heat could progressively increase the temperature of the fluid in circuit 2 and thus increase the risk of vaporization of the liquid of the fluid. The residual part of the heat is transferred to the outside through the cooling chamber 26 flooded with the cooling fluid in which turbine 4 is immersed.

The fluid exits from the axial outlet 9 of turbine 4 energetically exhausted, i.e. at a lower speed than that it has at the radial inlet 8 of turbine 4, due to the impact of the bubbles of gas on blades 14 of the impeller, and with a lower temperature than that it has at inlet 15 of compressor 11, due to the transformation of a part of the heat of the fluid into kinetic energy of the gas and of the transfer to the outside of the residual part of the heat of the fluid through the cooling chamber 26. The fluid exiting from turbine 4 is conveyed to inlet 3a of the heat exchanger 3 to restart the thermodynamic cycle, again absorbing heat.

According to a further embodiment of the present invention shown in figure 5, in which the corresponding elements are indicated with the same reference numerals and abbreviations as in figure 1, circuit 2 is a mixed hydraulic-pneumatic circuit that has the following differences compared to circuit 2 in figure 1.

Circuit 2 comprises a gravity separating device 32 for separating the gas from the liquid of the fluid exiting from the axial outlet 9, a pneumatic branch 33, which is flown through only by the gas supplied by the separating device 32 and comprises a heat exchanger 34 especially designed to overheat the gas through the heat absorbed from the low-enthalpy heat source, and a mixing device 35, which is adapted to mix the gas exiting from branch 33 with the liquid supplied by the separating device 32 and is connected with the inlet section 30a of the Venturi nozzle 30 to introduce the fluid thus obtained into the Venturi nozzle 30 itself.

In particular, the separating device 32 essentially consists of a vertical cylindrical container, which comprises a ceiling 36 having an outlet 37 for the gas, an inlet 38 connected to the axial outlet 9 and positioned at a lower height of ceiling 36, and a bottom region 39 communicating with the inlet section 30a.

Branch 33 comprises a conduit 40 for connecting outlet 37 with inlet 34a of the heat exchanger 34 and a conduit 41 for connecting outlet 34b of the heat exchanger 3 with the mixing device 35.

The mixing device 35 comprises a mixing chamber 42, which connects the bottom region 39 of the separating device 32 with the inlet section 30a to be flown through by the liquid in the direction of circulation D, and an injection conduit 43, which is connected to the outlet of branch 33 for receiving the gas coming from the heat exchanger 34 and is arranged in the mixing chamber 42 so as to inject the gaseous component in direction D.

In the example in figure 5, the mixing chamber 42 consists of a curved duct which is made in one piece with the cylindrical container which defines the separating device 32 and the injection conduit 43 essentially consists of an extension portion of conduit 40, which extends inside the curved conduit that defines the mixing chamber 42 parallel to an outlet branch 44 of such a curved conduit so as to inject the gas parallel to the liquid flow in the outlet branch 44.

With reference again to figure 5, turbine 4 comprises a radial outlet 45 for the discharge of the gas, arranged on top of chamber 7, and circuit 2 comprises a pneumatic gas recovery branch 46 which connects the radial outlet 45 to branch 33 at a point upstream of the heat exchanger 34, and in particular at the inlet of conduit 40 through a T- joint 47 which also connects outlet 37 of the separating device 32, for collecting that part of the gas accumulating into chamber 7.

Therefore, turbine 4, the separating device 32, the mixing chamber 42, and the Venturi nozzles 30 and 31 define the hydraulic part of circuit 2, while branch 33 and branch 46 define the pneumatic part of circuit 2.

The heat exchanger 34 and compressor 11 are sized to keep the gas at a temperature ranging from about 30 °C at inlet 34a to about 100 °C at outlet 34b and the cooling chamber 26 is sized to keep the liquid at a temperature of about 30 °C.

In use, as for the system in figure 1, the fluid that exits from the axial outlet 9 comprises the gas practically mixed in the liquid. However, in system 1 in figure 5 the liquid falls towards the bottom region 39 of the separating device 32 while the gas tends to rise up to reach ceiling 36 of the separating device 32 to then exit from outlet 37 and flow in branch 33 in a direction of circulation G that goes from inlet 34a to outlet 34b of the heat exchanger 34, i.e. a direction concordant with the direction of circulation D of the liquid in the separating device 32. The circulation of the gas in branch 33 according to direction G is ensured by the suction effect produced in the injection pipe 43 by the circulation of the liquid in the mixing chamber 42. The heat exchanger 34 is flown through only by the gas and therefore only the latter is heated by the heat source, undergoing the subsequent increase in pressure. The liquid, on the other hand, goes through the separating device 32 to directly flow into the mixing device 35, where it is mixed with the overheated gas before being introduced into the Venturi nozzle 30. In this way, the time of contact between the overheated gas and the liquid is reduced, thereby reducing the heat transfer from the gas to the liquid, with the result of increasing the efficiency of system 1. From this point of view, also the Venturi nozzles 30 and 31 have a beneficial effect since they increase the relative speed of the gas with respect to the liquid in the fluid that enters into turbine 4 and thus contribute to the reduction of the time of contact between the gas and the liquid.

A part of the heat transferred to the gas in the heat exchanger 34 is, however, transferred to the liquid in the mixing chamber 42 and while flowing through the Venturi nozzles 30 and 31 and turbine 4. This residual part of the heat is transferred to the outside through the cooling chamber 26.

Advantageously, circuit 2 comprises a fan device 48 consisting, for example, of a turbo blower of known type arranged in conduit 40 for favouring the circulation of the gas in branch 33 according to direction G. Advantageously, circuit 2 comprises a check valve 49 arranged in conduit 41 to prevent the liquid in the separating device 32 from rising up in branch 33 when system 1 is stopped.

Figure 6 shows a variant of the shape of the body of turbine 4 which comprises, in place of the curved injection duct 27 in figure 4, a straight injection conduit 50 which is arranged vertically for facilitating the ascent of the bubbles of gas from the radial inlet 8 towards chamber 7 of turbine 4. Turbine 4 in figure 6 can be used in both embodiments of system 1 shown in figures 1 and 5.

While the invention described above makes particular reference to a very specific embodiment example, it is not to be considered limited to this example embodiment, all those variants, modifications or simplifications that would be evident to the man skilled in the art falling within its scope, such as for example:

- a fluid consisting of a liquid component other than water and a gaseous component other than argon and nitrogen, provided that the gaseous component is insoluble in the liquid component and is with low density and low condensation point;

- a turbine 4 with a different number of blades 14 and/or with blades 14 having a different shape.

It is worth also noting that system 1 described above is easily adaptable to operate efficiently even when supplied by a high-enthalpy heat source. In fact, it is sufficient to adopt simple changes that allow the fluid to be kept at low enthalpy, such as for example adjusting compressor 11 to increase the flowing speed of the fluid in the heat exchanger 3 and oversizing chamber 26.