WO2008004861A1

WO2008004861A1 - System for generating mechanical energy based on thermal energy

Info

Publication number: WO2008004861A1
Application number: PCT/NL2007/000168
Authority: WO
Inventors: Pieter Van Ittersum
Original assignee: Pieter Van Ittersum
Priority date: 2006-07-04
Filing date: 2007-07-04
Publication date: 2008-01-10

Abstract

A system for generating mechanical energy on the basis of thermal energy is presented. This system comprises two circuits in mutual heat-exchanging contact, each of which is filled with a heat-transfer medium. The circuits are both provided with means for causing circulation of the medium therethrough, for instance in the form of pumps. Both circuits are further adapted to subject the medium circulating therein to an expansion/compression cycle. Means powered by an external energy source are incorporated in a first of the two circuits for the purpose of heating the medium circulating therein, for instance in the form of a magnetron. External means are incorporated in the second circuit for extracting mechanical energy therefrom, for instance in the form of a turbine.

Description

SYSTEM FOR GENERATING MECHANICAL ENERGY BASED ON THERMAL ENERGY

The invention relates to a system for generating mechanical energy on the basis of thermal energy.

As is known, the stocks of fossil fuels are being consumed at a rapid rate due to the increasing demand for energy in all parts of the world, and this high energy consumption is moreover causing increasing environmental problems. It is therefore of great importance that more efficient use be made of energy in the future in order to use remaining stocks effectively and to spare the environment as much as possible.

In addition to heating and lighting, energy is usually used to generate movement, for instance to drive machines or transport means. There is therefore a need for efficient systems with which such mechanical kinetic energy can be generated.

The invention therefore has for its object to provide a system for generating mechanical energy on the basis of thermal energy which has a greatly improved efficiency compared to known systems. According to the invention this is achieved by a generating system provided with two circuits in mutual heat-exchanging contact, each of which is filled with a heat-transfer medium, these circuits both being provided with means for causing circulation of the medium therethrough and both being adapted to subject the medium circulating therein to an expansion/compression cycle, wherein means powered by an external energy source are incorporated in a first of the two circuits for the purpose of heating the medium circulating therein, while external means are incorporated in the second circuit for extracting mechanical energy therefrom. Preferred embodiments of the energy-generating system according to the invention are described in the sub-claims .

The invention is now elucidated on the basis of two non-limitative embodiments, wherein reference is made to the accompanying drawing, in which:

Figure 1 is a schematic representation of a first embodiment of the generating system according to the invention, wherein the mechanical energy is produced by a turbine incorporated in the second circuit,

Figure 2 shows a detail view on enlarged scale according to arrow 1 in figure 1,

Figure 3 shows a detail view on enlarged scale according to arrow 2 in figure 1, and Figure 4 is a diagram corresponding to figure 1 of a second embodiment of the generating system according to the invention, wherein the mechanical energy is produced not only by a turbine incorporated in the second circuit but also by a piston engine incorporated in this circuit.

A system 1 for generating mechanical energy on the basis of thermal energy comprises a first circuit 2 comprising two conduits 21, 22 and a second circuit 3 comprising two conduits 23, 24 (figure 1) . These circuits 2, 3, which are in mutual heat-exchanging contact, are each filled with a heat-transfer medium 4, 5. In the shown example the medium 4 in first circuit 2 is a hydrocarbon, while medium 5 in second circuit 3 is water. Isobutane can advantageously be used for medium 4, although other hydrocarbons or media of other composition can also be envisaged.

Circuits 2, 3 are both provided with means 6, 7 for causing circulation therethrough of the relevant medium 4, 5. In the shown example the circulation means 6, 7 in the first and second circuit 2, 3 comprise in each case a hydraulically driven pump.

Circuits 2, 3 are both adapted to subject the medium 4, 5 circulating therein to an expansion/compression cycle. Means 8 are here incorporated in first circuit 2 for heating the medium 4 circulating therein. These heating means 8, which in the shown embodiment comprise a magnetron, are powered by an external energy source. The magnetron used here requires for start-up a power of 3 x 20 kW, which falls to about 20 kW during continuous operation.

Conversely, external means 9 are incorporated in second circuit 3 for extracting mechanical energy therefrom. These external energy-extracting means 9 here comprise a turbine 25, in the shown example with a power of about 500 kW. Turbine 25 drives a generator 29 which in the shown example produces a maximum power of about 60 kW. This generator 29 produces the electric current which powers magnetron 8. In addition, generator 25 drives a hydraulic pump 30 which here has a power of about 80 kW. This pump 30 in turn drives hydraulic pumps 6, 7 in first and second circuit 2, 3. In order to start up the system said power must be provided by an external energy source, although as soon as the system is in operation the power required is provided by turbine 25. Finally, turbine 25 has an output shaft 31 from which the excess power can be taken off.

First circuit 2 and second circuit 3 further comprise two shared heat exchangers 10, 11. The first heat exchanger 10 hereof functions as condenser in first circuit 2 and as evaporator in second circuit 3. Conversely, second heat exchanger 11 functions as evaporator in first circuit 2 and as condenser in second circuit 3. Both heat exchangers 10, 11 are here of the counterflow type. First heat exchanger 10 is formed by a substantially cylindrical housing 12 having an end panel 13 on both sides. Debouching into these end panels 13 are inner exchanger tubes 14 which form part of first circuit 2 and through which flows medium 4. Placed some distance from end panels 13 are secondary panels 15 into which debouch outer exchanger tubes 16. These outer exchanger tubes 16 have a larger section than inner exchanger tubes 14 and are placed concentrically therearound. The annular spaces 26 between the inner and outer tubes 14, 16 form part of second circuit 3 and medium 5 flows therethrough.

A pressure-relief valves 27, 28 is placed in both circuits 2, 3 downstream of first heat exchanger 10.

Second heat exchanger 11 is larger (for instance 120 cm high with a diameter of 80 to 90 cm) but of simpler construction than first heat exchanger 10. Second heat exchanger 11 is likewise formed by a substantially cylindrical housing 17 with an end panel 18 on either side. Debouching once again into these end panels 18 are exchanger tubes 19, which in this case however form part of second circuit 3 and through which flows medium 5. Space 20 between the end panels 18 and exchanger tubes 19 here forms part of first circuit 2 and medium 4 flows therethrough.

The cycle which medium 4 runs through in first circuit 2 is now as follows. Medium 4 flows as gas from conduit 22 into space 20 of second heat exchanger 11. It then has a temperature of about -20° C. In second heat exchanger 11 the gaseous medium 4 is heated to a temperature of about 130 'C. The heat absorption is here about 75 kcal per litre. Gaseous medium 4 is further heated in magnetron 8, whereafter the pressure of medium 4 is increased by hydraulic pump 6 from about 4 bar to about 180 bar. When leaving pump 6 the gaseous medium 4 has a temperature of about 450° C. At this pressure and temperature medium 4 flows via conduit 21 to first heat exchanger 10. As it runs through this first heat exchanger 10, gaseous medium 4 is cooled to a temperature of about 250° C. The pressure of medium 4 is then reduced by valve 27 from 180 to 30, or even to 4 bar. Medium 4 herein becomes liquid. In this state it flows again through conduit 22 to second heat exchanger 11.

Medium 5 runs through a similar cycle in second circuit 3. It flows from conduit 24 as steam at a pressure of 0 bar into second heat exchanger 11 and is there cooled and condensed in exchanger tubes 19. Medium 5 leaves second heat exchanger 11 as water with a temperature of about 95° C. When entering the heat exchanger the medium 5 has an energy content of about 640 kcal per kg, while when leaving this has decreased to about 95 kcal per kg. 545 kcal per kg is thus transferred from medium 5 to medium 4. It then flows through conduit 23 to pump 7 where the pressure thereof is increased to about 225 bar. Medium 5 then flows at this high pressure from the underside into first heat exchanger 10 where it is heated to a temperature of about 360^° C. After leaving this heat exchanger 10 the pressure of medium 5, which has obtained an energy content of about 640 kcal per kg in heat exchanger 10, is reduced in valve 28 from 225 bar to 200 bar. The water herein transposes into steam, which involves an expansion of about 4000 times the original volume. This steam with a temperature of 360° C subsequently flows via conduit 24 into turbine 25, where it expands further until the pressure has dropped to 0 bar. Turbine 25 is herein driven rotatingly, wherein power is generated which is used to drive generator 29, pump 30 and power take-off 31. The steam flows from turbine 25 back again to second heat exchanger 11.

In order to generate said power of 500 kW in turbine 25 a mass flow is necessary of about 3.5 to 4 kg of steam per minute. With this quantity of steam about 545/75 * 4 = 30 litres per minute of medium 4 can be heated from -20° C to 130° C in second heat exchanger 11. In order to bring 30 1/min of medium 4 and 4 1/min of medium 5 to a pressure of respectively 180 and 225 bar, the pumps 6, 7 require about 80 kW, this power being delivered by pump 29 which is connected to turbine 25.

In an alternative embodiment of device 1 the external energy-extracting means 9 in second circuit 3 comprise a piston engine 32 (figure 4) in addition to turbine 25. In the shown example use is made for this purpose of half a conventional combustion engine, for instance a six-cylinder truck engine with a cylinder capacity of 12 litres. An engine block is thus created with three cylinders 33, each having piston displacement of 2 litres. Engine 32 is provided with electrically operated exhaust valves and with built-in injectors for water which is drained at a pressure of 225 bar and a temperature of 360° C from conduit 24 before reaching pressure-relief valve 28 and carried via a conduit 34 to engine 32. Per injection about 0.5 - 0.6 cm³ of water is injected into cylinders 33, where it is once again expanded about 4000 times to steam. This steam is discharged via a conduit 35 to conduit 24. When 3 kg or litres of water are guided to motor 32 per minute, this produces a power of about 400 kW at a rotation speed of about 1500 rpm. If motor 32 is not in use, medium 5 flows from conduit 34 to a pressure-relief valve 36 and from here returns as steam to second heat exchanger 11, so that the heat circulates. Because in this embodiment a part of the water is diverted round turbine 25, a smaller turbine can be used with a power of for instance 120 kW at a mass flow of about 1 kg/min. Engine 32 can otherwise be considerably simplified structurally relative to a conventional combustion engine, since an air inlet and an exhaust system are not necessary, while components such as camshaft, cooling system, fuel pump, fuel tank, batteries, starter motor and turbo with intercooler can also be omitted.

Device 1 is intended for fully continuous operation and, as soon as engine 32 has to be used, this is also possible.

The scope of the invention is not limited to the examples given above, but is defined solely by the now following claims.

Claims

1. System for generating mechanical energy on the basis of thermal energy, characterized by two circuits in mutual heat-exchanging contact, each of which is filled with a heat-transfer medium, these circuits both being provided with means for causing circulation of the medium therethrough and both being adapted to subject the medium circulating therein to an expansion/compression cycle, wherein means powered by an external energy source are incorporated in a first of the two circuits for the purpose of heating the medium circulating therein, while external means are incorporated in the second circuit for extracting mechanical energy therefrom.

2. Energy-generating system as claimed in claim 1, characterized in that the medium in the first circuit is a hydrocarbon and the medium in the second circuit is water.

3. Energy-generating system as claimed in claim 1 or 2, characterized in that the externally powered heating means in the first circuit comprise a magnetron.

4. Energy-generating system as claimed in any of the foregoing claims, characterized in that the external energy-extracting means in the second circuit comprise a turbine .

5. Energy-generating system as claimed in any of the foregoing claims, characterized in that the external energy-extracting means in the second circuit comprise a piston engine.

6. Energy-generating system as claimed in any of the foregoing claims, characterized in that the first and second circuit comprise two shared heat exchangers, a first of which functions as condenser in the first circuit and evaporator in the second circuit, while the second heat exchanger functions as evaporator in the first circuit and condenser in the second circuit.

7. Energy-generating system as claimed in claim 6, characterized in that the heat exchangers are of the counterflow type, and at least the first heat exchanger has concentric tubes for the first and second medium.

8. Energy-generating system as claimed in any of the foregoing claims, characterized in that the circulation means in the first and second circuit comprise in each case a hydraulically driven pump.