Device and method for electric power generation

The present invention relates to the field concerning the energy transformation and in particular it relates to a device for electric power generation suitable to exploit thermal jumps of reduced size, but not only, and that can also be used in different environments such as domestic, commercial, industrial and assigned for communities.

Said invention also relates to a method for electric power generation wherein the meaning of "electric power generation" is the transformation of thermal energy into mechanical energy suitable for operating an electric power generator, for example an alternator or similar or for operating other types of users.

Document EP1801364A1 discloses to a heat pump for feeding a refrigerant without using a mechanical pump, a heat pump system, and a transcritical Rankine cycle system, the heat pump having a function to feed a refrigerant by vaporizing a liquid refrigerant liquefied in a condenser by a heat source outside the system or by utilizing a part of heat used to operate the system and raising pressure of the vaporized refrigerant, the heat pump system comprising a plurality of the heat pumps, the transcritical Rankine cycle system comprising the heat pump or the heat pump system. The invention is suitably applied to a transcritical Rankine cycle, etc. without need for a mechanical pump which induces mechanical loss in feeding working refrigerant.

Document DE10126403A1 discloses a power station having carbon dioxide fluid as its working means, a forward line with at least one turbine or piston engine and a return line with at least one pressure build-up device. The forward line and the return line realize a closed liquid circuit. The station has a high pressure container and a low pressure container, each divided by an inner floating partition wall in a liquid carbon dioxide space and a nitrogen space. The liquid carbon dioxide space of the high and low pressure containers have respective constant temperature controller. The turbine in the forward line from the high to the low pressure container and the pressure build-up device in the low pressure line from the low to the high pressure container.

Document DE102009057179 discloses to an engine which consists of an evaporator vessel or working cylinder and a fluid turbine where additionally suitable control mechanisms are used by significantly increase efficiency. The vapor is used to pressurize the feeding turbine liquid.

Document DE3624357 discloses a method for obtaining energy from the ambient air where a liquid operated turbine is fed by pressurized liquid stored in a pressure vessel provided with a piston having a weight resting onto it to keep the liquid into the pressure vessel under pressure while said liquid is fed into the pressure vessel by a static pump operated by the environment temperature changes. Several liquids as water, glycol and alcohol are used.

Document DE102005049215 discloses a method and device for generating mechanical or electrical energy from heat where a refrigerant circuit provides heat from a geothermal probe to an operative circuit through a set of heat exchanger. The operative circuit includes a turbine operated by a fluid heated by the refrigerant circuit and by compression heat produced by compressors of the operative circuit the same. A turbine replaces a throttling valve o thermal expansion valve.

The above mentioned prior art presents the disadvantages consisting in their complexity and, sometimes, in their elevate costs and inadequate reliability.

Another disadvantage of certain known solutions consists in the requirements of fluids and operating conditions, in particular temperature, involving state changes, from gaseous to liquid and vice versa, of the fluid itself with consequent operating limitations.

An object of the present invention is to propose an electric or mechanical power generation device and to propose a method for electric power generation that are simple, cheap and reliable.

Another object is to propose a device of reduced size and modular used individually or in multiple copies interconnected to obtain a continuous supply of power.

Further object is to propose a device and a method feasible and operable with fluids of almost any nature, both in conditions of phase transition and without any transitions of phase.

Another object is to propose a device suitable to exploit thermal sources with relatively low temperatures also negative, for example at -10°C, and thermal sources having very small temperature differences, for example also of only 10°C.

Further object is to propose a device suitable for domestic use, for applications in environments such as industrial, livestock breeding, agriculture, renewable energy generation, and everywhere thermal sources are available even having low enthalpy.

The characteristics of the invention are highlighted in the following with particular reference to the accompanying drawings wherein:

• Figure 1 shows a schematic view of the electric power generation device of the present invention associated with a motor means connected to a generator means;
• Figures 2 to 5 show schematic views of respective variants of the device of Figure 1;
• Figure 6 shows an operating cycle diagram of the device according to the method of the invention wherein the abscissa axis refers to the enthalpy, the ordinate axis refers to the pressure and wherein the curves with arrows indicate the trend of the fluid state inside the tanks and lines, with respective directions and ways, indicate the cycle points of the system process fluid.

With reference to figure 1, numeral 1 indicates the electric power generation device, object of the present invention, comprising a first tank 2 and a second tank 3 for an operating fluid. These tanks can be made of steel, aluminum alloys, synthetic materials and composites, such as carbon, aramide, and/or glass or the like fibers, bonded in a resin matrix and are suitable to withstand the pressures and the provided pressure variation cycles, that can range from dozen of kg/cm² to hundreds of kg/cm². Said tanks can have any form, generally cylindrical and they are preferably stacked arranged, with the first tank 2 below the second tank 3. The device 1 comprises a first opening and closing means 4, for example of tubular type and equipped with a respective remotely operated opening and closing valve. The first opening and closing means 4 is connected to the upper portion of the first tank 2 and to the lower portion of the second tank 3 to connect or separate the inner volumes.

The first tank 2 is provided with a first connecting means 7 having a respective remote controlled opening and closing valve connecting or separating the inner volume of said first tank 2 with the input of a motor means 5, for example consisting of a turbine or a micro-turbine of gas expansion or steam or biphasic mixture in another apparatus converting pressure energy in mechanical energy or for the direct exploitation of the pressure energy. The second tank 3 is provided with a second tubular connecting means 17 which puts said second tank 3 in flow communication with the expanded fluid outlet of the motor means 5.

The first tank 2 contains a first heat exchanger means 8, for example tubular kind exchanger, fed by a respective circuit 8a, 8b wherein a first thermal fluid circulates, thanks to a pump, of remotely controlled blower or compressor or similar type, the fluid is heated by a first thermal source and it is assigned to heat, by means of the first heat exchanger 8, the operating fluid contained in the first tank 2 yielding to it the heat taken from said first source. This first source may consist, for example, in a solar collector, in a condenser of a refrigeration system or an air conditioner, or in a duct for hot water exhausted and derived from an industrial process or from households, or from any other source also marginal or wasted.

The second tanks 3 contains a second heat exchanger means 9 tubular fed by a respective circuit 9a, 9b wherein a second thermal fluid circulates, thanks to a respective pump, of remotely controlled blower or compressor or similar respective type, the second thermal fluid is cooled by a second heat source having a lower temperature in respect to the first heat source and/or to the environment temperature. This second thermal fluid is assigned to cool by means of the second heat exchanger means 9 the operating fluid contained in the second tank 3 by withdrawing from it the heat that is transferred to said second source consisting of, for example, the evaporator of a refrigeration circuit, the external environment, the marine water below the thermocline, or any other source also marginal or wasted having temperature below the ambient temperature one or to a predetermined value.

Alternatively the device can be equipped with a single heat exchanger means of one tank while the other tank can be exposed directly to air and to ambient conditions. Preferably the device comprises both the above mentioned heat exchangers and the tanks are insulated for increase the heat insulation.

The invention provides that the embodiment of Figure 1 exploits first and second thermal fluids equal and consisting in a liquid, preferably water, but also it provides alternatives, described in the variants, and consisting for example of a phase transition fluid such as a refrigerating fluid or a gas such as air.

Optionally, to speed up a rebalancing phase of the device described in the following, the first tank may contain a third heat exchanger means SCa inside the first tank 2 and connected in shunt to the circuit 9a, 9b feeding the second heat exchanger means 9 where such a circuit is provided of valves S2, S1 for the selective exclusion of the second 9 and the third SCa heat exchanger means.

The device also comprises temperature and/or pressure sensors associated, for example, to tanks, to circuits 8a, 8b, 9a, 9b of the thermal fluid and/or to the first 7 and second 17 connecting means. These sensors are connected, for instance in electrical manner, to respective ports for the signals of control and management means of the device, for example of the microprocessor type, with memories, A/D and/or D/A interfaces , which remotely control and command valves, diverters, pumps and other active elements of the device based on a control and management program.

The invention provides that the operating fluid is of a type which in the operating conditions may undergo phase transitions or of a type which under such conditions remains at the gaseous phase. In particular, the invention provides that the operating fluid of the embodiment of Figure 1 consists of carbon dioxide.

Optionally the device may comprise first countercurrent or parallel heat exchanger means SCb having two distinct ducts and in mutual connection of the thermal flow. A first duct of the first countercurrent or parallel heat exchanger means SCb is inserted in series in the feeding circuit 8a, 8b of the heated first thermal fluid in the first heat exchanger means 8, downstream of the latter first exchanger means 8 with respect to the flow direction in said circuit 8a, 8b, and in this first duct.

The second duct is inserted in series in the second connecting means 17 downstream of the motor means 5.

Optionally the device may further comprise second countercurrent or parallel heat exchanger means SCc having two distinct ducts and in connection to the thermal flow. The first duct is inserted in series in the circuit 9a, 9b feeding the cooled second fluid to the second heat exchanger means 9 downstream of the latter second heat exchanger means 9 and the second duct is inserted in series in the second connecting means 17 downstream motor means 5.

The second countercurrent or parallel heat exchanger means SCc is placed downstream the first countercurrent or parallel heat exchanger means SCb.

These heat countercurrent or parallel heat exchanger means SCb, SCc don't directly improve the efficiency because they are used mainly to keep stable the system.

The operation of the device 1 provides, starting from an initial condition of thermal and pressure equilibrium of the operating fluid of the two tanks 2, 3, that the control means operates the closing of the valves of the first opening and closing means 4 and of the first connecting means 7 thereby separating the portions of the operating fluid in the two tanks.

Immediately after the valves closing, the control means operates the flows of hot and cold thermal fluid, heated and cooled to temperatures respectively higher and lower than the balance temperature of the operating fluid, in the first 8 and second 9 heat exchanger means through the actuation of respective circulation pumps.

Consequently the temperature and the pressure of the operating fluid in the first tank increase and the temperature and the pressure of the operating fluid in the second tank decrease with respect to temperature and pressure of equilibrium up to reaching a predetermined temperature or pressure difference between the two tanks.

Upon reaching the predetermined difference the control means operate the opening of the valve of the first connecting means 7 allowing the operating fluid of the first tank 2 to flow in the second tank 3 through the first 7 and second 17 connecting means and through the motor means 5 operating the latter.

The motor means 5 can rotate the electric power generator 6 connected to it, or another user, until the pressure difference between the two tanks reaches or falls below a predetermined value at which the control means operate the stop of the flows of hot and cold fluid in the first 8 and second 9 heat exchanger means, the control means operate also the opening of the first opening and closing means 4 until reaching the equilibrium condition of the operating fluid of the two tanks 2, 3 possibly speeding up by means of the third heat exchanger means SCa.

As an example of operation, considering the embodiment of the device of Figure 1 without the two optional countercurrent or parallel heat exchanger means and having two tanks of 30 liters each, filled with 22kg of total CO₂ where the upper tank is maintained at constant temperature of 31°C using, for example, ambient temperature at maximum of 26°C and the lower tank at a temperature of 55°C by means of, for example, water at 60°C coming from a solar collector, it is achieved a maximum difference in pressure of 32bar, a maximum power of 940W, an average power of 670W and an efficiency of 8% considering as efficiency the electrical or mechanical energy obtained divided by the energy used to keep hot the lower tank.

One of the possible operations of the device above mentioned is diagrammatically shown in Figure 6 where:

• the point A represents the heating end point of the first tank 2 hot lower wherein the fluid contained in it reaches maximum pressure;
• the point B represents the point of thermal and pressure equilibrium of the fluid contained in the two tanks 2, 3;
• the curve C represents the evolution of the state of the fluid of the first tank 2 lower hot during the motor means operation;
• the curve D represents the evolution of the state of the fluid of the second tank 3 upper cold during the motor means operation;
• the points CE and DE represent the expansion end points of the fluid in which the pressure of the first 2 and second 3 tanks is equal;
• the line E represents the heating isochoric transformation of the first tank 2 lower;
• line F represents the curve of the first expansion of the fluid in the motor means 5, for example in a turbine or similar;
• line G represents the i-th curve of the i-th expansion in the motor means 5.

The variant of Figure 2 differs from the embodiment of Figure 1 in that the first heat exchanger means 8 and the respective circuit 8a, 8b and the second heat exchanger means 9 and the respective circuit 9a, 9b use as thermal fluids gas type fluids, for example two identical thermal fluids consisting of air.

The hot and cold air flows of respectively the first 8 and second 9 exchanger means are operated by respective blowers of the two circuits 8a, 8b, 9a, 9b controlled by the control means.

The variant of figure 3 differs from the embodiment of Figure 1 in that the first heat exchanger means 8 and the respective circuit 8a, 8b are of hot air type while the second heat exchanger means 9, the third heat exchanger means SCa and their circuit 9a, 9b use water or other liquid.

The variant of figure 4 differs from the embodiment of Figure 1 in that it comprises a second opening and closing means 14, parallel to the first 4, equipped with a respective opening and closing valve and connected to the first 2 and second 3 tanks to connect and separate their inner volume.

This second opening and closing means 14 is assigned, in cooperation with the first opening and closing means 4, to achieve a movement, for example of natural type, of the operating fluid for speeding up the reaching of the equilibrium condition of the operating fluid.

Furthermore, the first 4 and/or second 14 opening and closing means can be equipped with a fan or pump means, applied in series to the respective valves. Such pump means establish a forced circulation of the operating fluid to further speed up the achievement of the equilibrium condition of the operating fluid.

The variant of Figure 5 refers to a coupled system and with appropriate recoveries.

In particular, this variant provides two copies of the device 1 connected together in parallel and to the same motor means 5. The control means operate and command the two copies or, in other word, two reproductions 1 with temporally offset phases for extended or continuous operation of the common motor means 5.

Each first tank 2 is internally provided with a respective fourth recovery exchanger means 19 whose input is connected via a diverter valve 20 to the output of the common motor means 5 and whose output is connected to a first tank 3 and to the other adjacent copy of the device 1. The invention provides that the number of specimens connected in parallel can be greater than two.

At the same above conditions for the device of Figure 1, the variant of Figure 5 reaches maximum power of 805W, average power of 450W and efficiency of 25% considering as efficiency the electrical or mechanical energy obtained divided by the energy used to keep hot the coupled system only during the electric power or mechanical energy generation.

The electric power generation method object of the present invention comprises the following steps:

• containing a predetermined amount of an operating fluid in two tanks first 2 and second 3 mutually separable and connectable via a first closing and opening means 4 provided with a respective opening and closing valve, and by a motor means 5 whose input and output are connected to said tanks by means of connecting means 7, 17 provided with at least a respective opening and closing valve;
• starting from a thermal and pressure equilibrium condition of the operating fluid in the two tanks, separate the latter 2, 3 by means of the first opening and closing means 4;
• heating the operating fluid contained in the first tank 2 through a first heat exchanger 8 controlled supplied with a first thermal fluid heated by a first heat source;
• optionally cooling the operating fluid contained in the second tank 3 via a second heat exchanger means 9 controlled supplied with a second thermal fluid cooled by a second heat source;
• the achievement of a predetermined temperature or pressure difference between the contents of the first 2 and second 3 tanks, putting in flow communication said tanks respectively with the input and the output of the motor means 5, actuating it, via the opening of the at least one valve of the first 7 and 17 seconds connecting means.

An advantage of the present invention is to provide an electric power or mechanical energy generation device and to propose a method for electric power generation that are simple, cheap and reliable.

Another advantage is to provide a device of reduced size and modular used individually or in multiple copies interconnected to obtain a continuous supply of power.

Further advantage is to provide a device and a method feasible and practicable with fluids of almost any nature, both in phase transition conditions both without any transitions.

Another advantage is to provide a device suitable to exploit thermal sources with relatively low temperatures and very small temperature differences, for example also of only 10°C.

Further advantage is to provide a device suitable for domestic use, for applications in environments such as industrial, livestock, agriculture, renewable energy generation, and everywhere sources are available even having low enthalpy.