WO1998035151A2

WO1998035151A2 - Device for generating electrical energy from low-temperature heat

Info

Publication number: WO1998035151A2
Application number: PCT/AT1998/000026
Authority: WO
Inventors: Herbert Bachler
Original assignee: Herbert Bachler
Priority date: 1997-02-10
Filing date: 1998-02-10
Publication date: 1998-08-13
Also published as: WO1998035151A3; AU5846898A; ATA19897A; AT404626B

Abstract

The invention concerns a device for generating electrical energy from low-temperature heat, the device comprising: two substantially vertical working cylinders (Z1, Z2) partially filled with a working fluid; a gas container (WT1) intended to be maintained at a higher temperature; a gas container (WT2) intended to be maintained at a lower temperature; a connection line between the working cylinders (Z1, Z2) for the overflow of working fluid between the working cylinders (Z1, Z2); and a piston (K1) which is disposed in the connection line in order to obtain mechanical work from the movement of the working fluid, the piston (K1) preferably co-operating with a linear generator (L1) in order to generate electrical energy from the movement. A particularly advantageous degree of efficiency is attained owing to the provision of control valves for selectively connecting the gas containers (WT1, WT2) to the working cylinders (Z1, Z2) and of a pump arrangement for varying the amount of working fluid in the working cylinders (Z1, Z2).

Description

DEVICE FOR GENERATING ELECTRICAL ENERGY FROM LOW TEMPERATURE HEAT

The present invention relates to a device for generating electrical energy from low-temperature heat, comprising: two essentially vertically arranged working cylinders which are partially filled with a working fluid; a connecting line between the working cylinders for overflowing the working fluid between the working cylinders; a piston which is arranged in the connecting line. to obtain mechanical work from the movement of the working fluid, the piston preferably cooperating with a linear generator in order to generate electrical energy from the movement.

Low temperature heat comes from solar panels, for example. Biomass stoves. Solid fuel boilers and other heat sources are available. This thermal energy has so far been insufficiently converted into mechanical work.

An electrical generator is known from WO 88/05223, which is able to generate electrical current due to the temperature difference between two heat stores. An electrically conductive liquid serves as a hydraulic piston and at the same time as part of a power generator.

Although such a device is functional in itself, the efficiency, in particular the electrical implementation, is modest. Furthermore, the electrically conductive liquid as a sodium and potassium compound is critical to handle and difficult to dispose of.

From DE 38 15 606 A a gas-liquid heat engine is also known which essentially works according to the Stirling process. Each of the gas work rooms is alternately heated or cooled using a heat exchanger liquid. Such a device is not only complex, but its efficiency is limited, since a heat transfer between the heat exchanger liquid and the working gas must take place in each working cycle.

The object of the present invention is to avoid these disadvantages and to further develop the above device in such a way that higher efficiencies are achieved with a simpler construction.

According to the invention, this is achieved by a gas container which is intended for this purpose. to be kept at a higher temperature, a gas container designed to do so. to be kept at a lower temperature, which gas containers are filled with a working gas are, and at least one control valve for the optional connection of the gas container with the working cylinders.

Is essential to the present invention. that the working gas itself, which causes the piston to move in the working cylinders, is permanently heated or cooled in corresponding gas containers. These gas containers can in principle be of any size, so that the heating or cooling of the working gas can be carried out continuously and with an optimal efficiency. A particular advantage of the present invention is that no heat transfer takes place between different working media in the area of the working cylinder.

With the help of this device, electrical energy can be obtained from the temperature difference between the hot end of the heating medium or the store and the cold part of the heating medium or the store or the ambient temperature. Only the energy that is needed for the heat engine is extracted from the available medium. The residual heat of the hot container and the residual heat of the cold container can be reused for further heating purposes or as a preheated heating medium for processing. In the heat engine, a working gas is compressed as a result of isothermal changes in state and expanded in a second container. The best efficiency is achieved according to the invention in such a process when the cyclic process isochoric changes in state, i. H. without any work, is closed. The thermal engine according to the invention tries to approximate such an ideal thermal power process.

The working process running in the device according to the invention essentially corresponds to a Stirling process. Thermal energy is applied to the working gas via a heating medium in the expansion phase.

The working gas is cooled in counter-expansion to expansion via a cooling medium in the second gas container. Both gas containers are alternately connected to a working cylinder. The volume ratio of the two working cylinders is in a predetermined ratio to the displacement of the piston. The gas pressure in the cold gas container increases in this ratio. It is essential that there is no mass shift from the warm to the cold gas container.

The two working cylinders are connected to one another by one or more pistons made of high-performance magnets in a working fluid. Switching the valves causes the pistons to move back and forth, which is converted into electrical energy via the inductance. The voltage is stabilized with known electronic controllers, and the frequency can be adapted to the respective consumers by means of suitable frequency converters.

The resting pressure in the gas containers can be varied within wide limits. Sealing the gas is easy. The device according to the invention is particularly suitable for low-temperature heat. With a temperature difference of 35 ° and using helium as the working gas, up to 5% efficiency can be achieved. This efficiency can be increased even further by using a regenerator described below.

The control is simplified if the control valves are coupled to one another in order to connect the other gas container to the other working cylinder when a gas container is connected to one working cylinder. In this way, only a single control pulse is required for switching the two valves, which reduces the corresponding control effort.

A further simplification of the control is preferably possible in that the control valve is designed as a four-way valve, which connects a gas container with a working cylinder and the other gas container with the other working cylinder.

It is particularly expedient if the pump device consists of a pump that pumps the working fluid from an intermediate store into the working cylinder or pumps it out of the working cylinder into the intermediate store. Since in this way the sufficiency can be found with a single pump, the apparatus structure of the device becomes particularly simple. This enables cost-effective production.

The overall efficiency of the device according to the invention can be improved in a particularly advantageous embodiment of the invention in that one gas container is connected to a heating circuit, and in that the other gas container is connected to a cooling circuit and that the heating circuit and the cooling circuit are connected via a regenerator for heat exchange stand.

Furthermore, the present invention relates to a method in which the pump device is controlled by a control device which receives signals about the pressure and / or the temperature in the gas containers via sensors. The method according to the invention is characterized in that working fluid is withdrawn from the working cylinders via a pump device, or is fed to the working cylinders, in order to keep the amount of gas in the two gas containers constant. This type of control ensures the optimal efficiency of the process.

It has been found that over a wide range of working conditions, the stroke ratio, i. i. the ratio between the volume of the working gas at the top dead center of the piston in relation to the volume of the working gas at the bottom dead center of the piston is optimal at about 1: 1.08. This means that with a cubic capacity of 1 1, the gas volume is 12.5 1 or 13.5 1 at the respective dead centers.

The working gas is heated using the pump on the heat exchanger in the hot gas container. Since the volume remains constant at the beginning, the pressure in the hot gas container increases according to the formula P _w = P _N. T _w / 293 (1)

in which

P _w pressure of the hot gas container

P _N gas pressure at 20 ° C in bar,

T _w Temperature of the hot gas container in Kelvin.

At a hot gas temperature of 90 ° C and P _N of 30 bar, this results in a gas pressure of 37.167 bar.

In the cold gas container, which is kept at the cooling temperature by the heat exchanger, there is a pressure according to the following formula.

P _K = P _N. T _K. V / 293 (2) with

P _κ pressure of the cold gas container P _N gas pressure at 20 ° C in bar. T _k cold temperature in Kelvin

V Volume ratio of the gas at the top and bottom dead center.

At a cold gas temperature of 20 ° C, P _N of 30 bar and a volume ratio of 1.08, this results in a gas pressure of 32.4 bar. After opening the valve, the pressure difference P _w - P _κ moves the piston with a power according to the following formula.

PD = (P _w - P _κ ). f. V (3)

PD printing performance

P _w , P in Pascal f valve frequency in Hertz

V displacement in m ³

The valve switches to the next setting after the piston has reached the maximum displacement. Since there are the same number of gas molecules in both working cylinders, there is no mass shift.

According to the general gas equation, the cold working cylinder is located

Pκ * V = N _κ . T _κ (4)

P _κ pressure in bar of the cold gas container

T _k temperature of cold working gas in Kelvin

V Volume of the working cylinder in liters N Number of particles In the example above, this gives for

N _κ = 32.4. 12.5 / 293 (5)

In the hot working cylinder are according to the gas equation

P _W. V = N _K. T _W (6)

P _w pressure in bar of the hot gas container

T _w temperature of hot working gas in Kelvin

V Volume of the working cylinder and the displacement in liters

N particle number

In the example above, this gives for

N _κ = 37,167. 13.5 / 363 (7)

Since both working cylinders must have the same number of molecules, the following applies:

32.4. 12.5 / 293 = 37.16723549488. 13.5 / 363 (8)

The amount of cold working gas that was in the working cylinder must be in the gas container. heated to the warm temperature in order to keep the gas pressure in the hot gas container constant.

In the cold gas container, the warm working gas is cooled to the cold temperature by the working cylinder and displacement.

For the heating output there is the energy which is necessary to heat the gas quantity in the working cylinder from the cold temperature to the warm temperature, in addition to the expansion work from the piston, i.e. the pressure output. It depends on the specific heat of the gas.

For the cooling capacity, it can be calculated what energy is required to cool the hot working gas from the working cylinder and piston displacement to the cold temperature, since the gas masses are the same in both working cylinders, the heating capacity is without expansion work - pressure capacity.

The following assumption applies to the heating output plus the pressure output or cooling output without regenerator, depending on the working gas:

P. V = N _K T (9)

P pressure in Pascal V in m ^* '

K 1.38. 10 ^"23

6. 10 ²⁶ gives 1 kMol

1 kMol of air is about 30 kg of air

1 kMol of helium is 4 kg of helium for 1 kg of air, about 1 kW of power is required per degree and second

Part of the cooling capacity can be returned to the heating medium via a plate heat exchanger via a regenerator.

The pressure output / heating output thus results in the efficiency: η = PD / PH (10)

with η efficiency

PD printing performance

PH heating power

The highest efficiency can be achieved with hydrogen as the working gas. However, hydrogen is problematic in practice as a flammable and explosive gas. By using helium, safe operation with good efficiency can be achieved.

The invention is explained in more detail below on the basis of the exemplary embodiment shown schematically in the figures.

1 shows a first embodiment of the present invention and FIG. 2 shows a further embodiment of the invention in the form of schematic circuit diagrams.

1, a working gas under high pressure is heated in a hermetically sealed gas container WT1 by a large-area heat exchanger with the hot temperature of a heating medium. According to the general gas equation p x V = nRT, the gas would expand isothermally. However, since the volume remains the same, the pressure of the working gas in the container WTl increases.

In the second hermetically sealed gas container WT2, with the same amount of gas as WTl, the working gas is brought to ambient temperature once by the energy loss given by the gas equation when the working gas expands and, in addition, the residual heat of the working gas can be supplied to the cold part of the heating medium or heat accumulator by means of a heat exchanger become.

According to the gas equation, there is a greater or lesser pressure difference between the tanks WT1 and WT2, depending on the temperature difference. With the help of valves VI and V2, the containers WT1 and WT2 are connected synchronously to one end of the U-shaped working cylinder. The gas pressure from WTl causes the working fluid FI and thus the magnetic piston fitted in the lower part of the working cylinder to move linearly. According to the gas equation, the cavities between the working liquid on both sides and the valves VI and V2 must be in the same ratio as the pressure differences between the two tanks WT1 and WT2.

After the linear movement of the piston Kl has taken place, the control electronics El switch the valves VI and V2 and the pressure equalization takes place in the opposite direction.

The ratio for the gas free space is set by the working liquid so that this is equal to the pressure ratios of the working gas of the two containers. This ensures that there is approximately the same number of gas molecules in each of the two gas containers. The control electronics with sensors S l and S4 permanently calculate the TARGET value of the two containers and compare them with the ACTUAL values. If there is a deviation, the space ratio is determined using the working fluid FI and the working fluid pump Pl on both sides of the working cylinder set in a continuous control loop.

With the help of the magnetic piston Kl and the coil Ll, a voltage is generated as in a linear synchronous generator. This voltage is brought to a constant voltage by means of the electronics E2 as in a switching power supply. Depending on the intended use, this voltage can be processed further and thus be available as a 230 V 50 Hz mains-synchronous voltage.

The embodiment variant of FIG. 2 represents a modification of the embodiment variant of FIG. 1. The essential differences are explained below.

In this embodiment variant, the working cylinders ZI and Z2 are connected to the gas containers WT1 and WT2 via purge lines 17a, 17n, 17c and 17d, which are coupled by two four-way valves 10, 11. In this way, after switching the valves 10, 1 1, the thermal equilibrium between the gas containers WT1 or WT2 and ZI or 22 can be established more quickly. The gas container ^* WTl is heated via a heating circuit 12, which is circulated by a pump 13. Analogously, the gas container WT2 is cooled via a cooling circuit 14, which is circulated via a pump 15. The heating circuit 12 is guided downstream of the gas container WT1 through a regenerator 16, which is likewise flowed through by the cooling circuit 14 downstream of the gas container WT2.

The present invention enables a thermal power process to be performed with high efficiency.

Claims

PATENT CLAIMS

1. Device for generating electrical energy from low temperature heat, consisting of: two substantially vertically arranged working cylinders (ZI, Z2), which are partially filled with a working fluid; a connecting line between the working cylinders (ZI, Z2) for overflowing the working fluid between the working cylinders (ZI, Z2); a piston (Kl) which is arranged in the connecting line in order to obtain mechanical work from the movement of the working fluid, the piston (Kl) preferably cooperating with a linear generator (L1) to generate electrical energy from the movement, characterized by a gas container (WTl), which is intended for this. to be kept at a higher temperature, a gas container (WT2), which is designed to do so. to be kept at a lower temperature, which gas containers (WTl, WT2) are filled with a working gas, and at least one control valve (VI, V2) for the optional connection of the gas containers (WTl, WT2) with the working cylinders (ZI, Z2).

2. Device according to claim 1, characterized in that two control valves (VI, V2) are coupled to one another in order to connect the other gas container (WT2) with the other working cylinder (Z2 , ZI).

3. Device according to one of claims 1 or 2, characterized in that the control valve is designed as a four-way valve. that connects a gas container (WTl) with a working cylinder (ZI, Z2) and the other gas container (WT2) with the other working cylinder (Z2, ZI).

4. Device according to one of claims 1 to 3, characterized in that a pump device for changing the amount of working fluid in the working cylinders (ZI, Z2) is provided, which consists of a pump, the working fluid from an intermediate store (Bl) in pumps the working cylinders (ZI, Z2) or pumps them out of the working cylinders (ZI, Z2) into the intermediate store (B1).

5. Device according to one of claims 1 to 4, characterized in that a gas container (WTl) is connected to a heating circuit (12), and that the other gas container (WT2) is connected to a cooling circuit (14) and that the heating circuit and the cooling circuit is connected via a regenerator (16) for heat exchange.

6. Device according to one of claims 1 to 5, characterized in that two purge lines (17a, 17b, 17c, 17d) are provided for connecting the gas containers (WTl, WT2) with the working cylinders (ZI, Z2).

7. A process for producing electrical energy from low temperature heat, in which the following steps are carried out repeatedly:

- connecting a first gas container (WT1) containing a high temperature gas to a first working cylinder (21) and simultaneously connecting a second gas container (WT2) containing a cold gas to a second working cylinder (22);

- Overflow of a working fluid from the first working cylinder (21) into the second working cylinder (22), whereby a piston is moved to generate electrical energy;

- Connecting the first gas container (WT1) to the second working cylinder (22) and simultaneously connecting the second gas container (WT2) to the first working cylinder (21);

- Overflow of the working fluid from the second working cylinder (22) into the first working cylinder (21), whereby a piston is moved to generate electrical energy.

8. The method according to claim 7, characterized in that at the beginning of each step a predetermined amount of gas is allowed to flow back into the hot gas container (WTl) and that the same amount of gas flows again in the further course of the step.

9. The method according to any one of claims 7 or 8, characterized in that working fluid is removed from the working cylinders (ZI, Z2) via a pump device, or the working cylinders (ZI, Z2) is supplied in order to change the stroke ratio in the working cylinders .

10. The method according to any one of claims 7 to 9, characterized in that a gas container (WTl) is heated by a heating medium, and that the gas container (WT2) is cooled by a cooling medium and that the heating medium after flowing through the gas container (WTl) by a regenerator (16) is guided, which is simultaneously flowed through by the cooling medium that emerges from the gas container (WT2).