TITLE COGENERATION PLANT

DESCRIPTION

Field of the invention The present invention relates to the field of energetics and more precisely it relates to a cogeneration plant that uses a gas turbine.

In particular, the invention relates to a gas cogeneration plant that can be assisted by solar energy. Background of the invention

As well known, solar power plants exist for making thermal and electrical energy. However, such plants cannot normally be the only energy source and they must be associated to other cogenerating sources. This is due to the discontinuity of solar irradiation owing to the day/night cycle, to cloudy sky, to the rising-decreasing daily irradiation parabola and to the different levels of solar irradiation due to the seasons.

Another limit of solar power plants is high cost as well as additional costs for the cogeneration plant that has to be necessarily provided for integrating the solar plant to assure flexibility of the power supply to the users. An actual advantage of exploiting solar energy is the possibility to install small plants that have also a limited cost, and that would be associated to small cogeneration plants.

Many types of cogeneration plants exist that are widely used, among which there are gas turbine plants. They are very reliable and efficient and, furthermore, they are very flexibly responsive to the demand of a user. However, they require a conspicuous investment especially concerning the turbine, which normally has a compressor

and a combustion chamber incorporated tpgether in a single apparatus, and where the compressor and the turbine are mounted on the same shaft that produces the mechanical energy that feeds the electric generator. Summary of the invention

It is therefore a feature of the present invention to provide a cogeneration plant that uses a gas turbine and that has reasonably limited production costs.

It is another feature of the invention to provide a cogeneration plant that uses a gas turbine and that is suitable for an application assisted by solar power production.

These and other features are accomplished with one exemplary cogeneration plant according to the present invention, comprising a power gas turbine associated to an electricity generator that exploits its mechanical energy, whose characteristic is that said power turbine is fed by gas produced by a turbo-compressor unit associated to a combustion chamber, said turbo-compressor unit being separated mechanically from said power turbine.

In particular, the turbo-compressor unit provides a centrifugal compressor and a centripetal turbine mounted close to each other on a single rotatable shaft arranged in a compact support body. Preferably, the turbo-compressor unit is a turbocharger for internal combustion engines. This is allowed by the particular configuration of the plant according to the invention that provides separating the power turbine from the turbo-compressor unit that supplies the gas necessary for powering it. The use of a component widely available on the market like a turbocharger, very

common in the automotive field, determines a high reliability and duration at a relatively low cost.

For starting up the cogeneration plant and raising the rpm as necessary for activating the power turbine an aerodynamic starter is provided that directs towards said compressor an air jet with high content of kinetic energy.

In particular, said aerodynamic starter comprises a supercharger associated to a duct having an outlet mouth in the suction duct of said compressor and oriented towards said compressor. Preferably, said outlet mouth is preceded by a converging portion of said duct.

The cogeneration plant preferably provides a pre- heater of the compressed air exiting from said compressor directed towards said combustion chamber. In particular," the pre-heater is an exchanger crossed by the exhaust hot gas exiting from said power turbine. Alternatively, or in addition, the pre-heater is an exchanger crossed by a fluid coming from a concentrator of solar radiation.

Advantageously, the exhaust. gas at the outlet of the power turbine crosses an exchanger that transmits heat to a closed fluid circuit that crosses an absorption chiller, capable of providing warm air and cold air.

Preferably, the closed circuit, which crosses said absorption chiller and said exchanger, provides a further exchanger that supplies heat coming from a concentrator of solar radiation.

Always advantageously, the exhaust gas at the outlet of the power turbine crosses an exchanger that transmits heat to a circuit of sanitary water. Brief description of the drawings

Further characteristics and the advantages of the cogeneration plant, according to the present invention, will be made clearer with the following description of an

exemplary embodiment thereof, exemplifying but not limitative, with reference to the attached drawings wherein:

- figure 1 shows a block diagram of a cogeneration plant according to the invention; - figure 2 shows the block diagram of figure 1 where a solar energy air pre-heater is provided;

- figure 3 shows diagrammatically a compact turbo- compressor unit associated to a combustion chamber;

- figure 4 shows diagrammatically the turbo- compressor unit of figure 2 in combination with an aerodynamic starter;

- figure 5 shows an exemplary embodiment of the cogeneration plant of figure 1 with a heat recovering system assisted by solar power production. Description of a preferred exemplary embodiment

With reference to figure 1, a cogeneration plant according to the invention has an electric generator 1

\ that receives, by a shaft 2 of a reduction gear 3, mechanical energy transmitted by a power turbine 5 to a shaft 4 through reduction gear 3. Power turbine 5 is supplied by a superheated and pressurized gas 6 coming from a turbo-compressor unit 10. The exhaust gas 7 at the outlet of turbine 5 can be used for preheating, by an exchanger 8, the air 9 that was previously compressed at 14 by turbo-compressor unit 10. Alternatively, as shown in figure 2, a fluid 37, superheated in a not shown solar concentrator, pre-heats compressed air 14 in an exchanger 38.

According to the invention, unit 10 is mechanically separated from shaft 4 of power turbine 5. More precisely, unit 10 provides a further turbine 11 that receives the superheated and pressurized gas 6 exiting from a

combustion chamber 12 where a fuel 13 is fed, for example methane. The combustion process C is carried out in chamber 12 with pressurized air 14 delivered by a compressor 15, wheeled by shaft 17 of turbine 11. As above said, the compressed air 14 can be preheated by exchangers 8 or 38 of figures 1 or 2.

In particular, turbo-compressor unit 10 can provide a centrifugal compressor 15 and a centripetal turbine 11 mounted close to each other on a single shaft 17 rotatable in a same compact support body 30. In particular, the support 30 and the rotors 11 and 15 form together a turbocharger for internal combustion engines. This way, the use of a component widely available on the market as a turbocharger is cheap with high reliability and duration. As known, turbochargers are supercharging units for internal combustion engines and use the exhaust gas from the turbine side for compressing the comburent air. They do not have a starting system, since they are activated by the increasing motive-power obtained pushing further the accelerator of an already started up internal combustion engine. Furthermore, they are not combined to any combustion chamber, since the compressed air is conveyed a car engine block and the exhaust gas comes from the engine block. For starting up the cogeneration plant of figure 1 and raising the rpm necessary for activating power turbine 5, according to a preferred exemplary embodiment of the invention, an aerodynamic starter is provided that directs towards compressor 15 an air jet 16 with high content of kinetic energy. The aerodynamic starter provides a compressor 19 fed by air 18 and wheeled by the shaft 23 of a engine 22 through a reduction gear 21 and a transmission shaft 20.

With reference to figure 4, the aerodynamic starter 50 is a supercharger 51 available on the market associated to a duct 52 having an outlet mouth 53 that flows in the air 9 suction duct of compressor 15 and directs an air jet 16 towards compressor 15 same. In particular, the outlet mouth 53 comprises a converging tube portion connected to duct 52 exiting from supercharger 51.

This way, the start-up of the cogeneration plant is carried out turning on aerodynamic starter 50, which provides an air jet 16 that produces an air flow with high content of kinetic energy and in the right direction for causing impeller 15 of the compressor to rotate, at enough rpm to cause the suction of further air 9 that feeds the combustion chamber 12. Once triggered the combustion at a predetermined power, the supercharger 51 can be turned off. The mouth 53 is of minimum encumbrance and obstructs the flow of air 9 much less than an extension of shaft 17 that could be used to start mechanically the rotation of compressor 15 through a suitable transmission. The turbocharger 30 can be mounted then without mechanical modifications, which would cause additional costs and would require inertial balancing. The mouth 53 can also be withdrawn to a position that does not obstruct the suction air flow 9 by a mechanical system not shown. With reference to figure 5, the cogeneration plant shown in figures 1 and 2 can provide in addition a heat recovering system of the exhaust gas 7 at the outlet of power turbine 5. The recovering system comprises an exchanger 24 that transmits part of the heat of the exhaust gas 7 to a closed fluid circuit 26 that crosses an absorption chiller 27, capable of providing warm air 28 and cold air 29. In particular, the closed fluid circuit 26 that crosses the absorption chiller 27 and the

exchanger 24 can provide a further exchanger 39 that provides to fluid 26 an additional heat that is transmitted to a fluid 37 by a concentrator of solar radiation not shown. Furthermore, the exhaust gas 7 at the outlet of power turbine 5 can cross an exchanger 25 that transmits heat to a circuit of sanitary water 31.

The exchangers 8 and 38 of figures 1 and 2 can be put in the cogeneration plant with the exchangers 24, 25 and 39 of figure 5. In this case, according to the conditions of solar irradiation and of the application of warm air or cold and hot water, it is possible to direct the heat of the exhaust gas 7 selectively for increasing efficiency of combustion in exchanger 8, decreasing thus the request of gas methane 13, or to direct it towards exchangers 24 and 25.

The foregoing description of a specific embodiment will so fully reveal the invention according to the conceptual point of view, so that others, by applying current knowledge, will be able to modify and/or adapt for various applications such an embodiment without further research and without parting from the invention, and it is therefore to be understood that such adaptations and modifications will have to be considered as equivalent to the specific embodiment. The means and the materials to realise the different functions described herein could have a different nature without, for this reason, departing from the field of the invention. It is to be understood that the phraseology or terminology employed herein is for the purpose of description and not of limitation.