Arrangement for obtaining electrical energy from low temperature heat or waste heat

Abstract

The invention relates to an arrangement for obtaining electrical energy from low temperature or waste heat. The heat energy is then converted into electrical energy. Two heat exchangers (1, 2) are configured as two pressure vessels and are connected to a gas-pressure machine (4) built into a pressure vessel (3). Process gas is introduced into the heat exchangers (1, 2) at a pressure of 20 to 200 MPa and thereafter, simultaneously, heat is introduced via a flow channel (7) into the heat exchanger (1) and the cold is introduced into the heat exchanger (2) via a flow channel (8).

Description

FIELD OF THE INVENTION

The invention relates to an arrangement for obtaining electrical energy from low temperature heat or waste heat. Thereafter, the thermal energy is converted into electrical energy.

BACKGROUND OF THE INVENTION

According to a market study of the Fraunhofer Institut für Umwelt-, Sicherheits- und Energietechnik (UMSICHT) of December 2005, one can assume for Germany alone, a technically realizable waste heat potential of 85 GWth which is broken down as follows:

6.7 GWth as industrial waste heat;

approximately 1 GWth from power plant facilities;

63 GWth in the context of hydrothermal geothermics (depths of 1500 to 3000 m); and,

14 GWth in the context of further expansion of solar thermal facilities.

Assuming a real electrical degree of efficiency in the range of 6% to 10%, electrical power in the range of 5 to 8.5 GWel could be obtained from waste heat sources with a use of suitable thermal power processes. In this connection, reference can be made to the internet address:

www.presseportal.de/story_rss.htx?nr=763828.

An enormous potential of low temperature heat remains unused at the present time because of a lack of suitable energy converters.

European patent publication 0,943,789 discloses an arrangement for converting low temperature heat into electrical energy. This arrangement includes at least two hermetically sealable pressure vessels which are connected via a line. Means for supplying heat to one vessel and cooling to another vessel are provided which are in the form of heat exchangers arranged within the interior spaces of respective vessels. The heat exchangers have feed and outlet lines configured to be pressure tight toward the outside.

The disadvantage of this arrangement is that the technical realization is unfavorable and substantially disadvantageous for an economic use because the possible power of such an arrangement is greatly limited because of the arrangement of the heat exchangers in the pressure vessels. In addition, work volume is lost to the process because of the introduction of the heat exchangers in the pressure vessels.

Gas-pressure machines available conventionally in the marketplace require a very high volume flow. For this reason, the above arrangements lead to component sizes which are not economical.

SUMMARY OF THE INVENTION

It is an object of the invention to provide an arrangement wherein the available heat energy is converted into electrical energy at a relatively low temperature level at an economically high degree of effectiveness.

According to a feature of the invention, process gas is compressed at an absolute high pressure in two heat exchangers configured as respective pressure vessels and the heat exchangers are connected via lines to a gas-pressure machine which, in turn, is built into a pressure vessel. The process gas can be, for example, carbon dioxide, air, helium and/or other inert gases.

Thereafter, heat is supplied to the first heat exchanger via a liquid or gaseous medium and, simultaneously, cold is supplied to the second heat exchanger via respective flow channels. Because of the occurring pressure difference, the medium flows from the first heat exchanger via the gas-pressure machine into the second heat exchanger thereby causing the gas-pressure machine to be driven.

According to a feature of the invention, the pressure is adjusted within the range of 20 to 200 MPa. An advantage of the solution of the invention is that the heat exchangers can simultaneously be used as pressure vessels. In this way, the arrangement of the invention can be configured to be compact and is also suitable for small applications.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described with reference to the drawings wherein:

FIG. 1 is a schematic showing the arrangement of the invention for obtaining electric energy from low temperature heat or waste heat; and,

FIG. 2 is a schematic showing the process gas flow circuit and the flows of the first and second mediums through the first and second heat exchangers.

DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

In FIG. 1, heat exchangers 1 and 2 are connected to each other on the one hand and to a pressure vessel 3 on the other hand.

A gas-pressure machine 4 is arranged in the pressure vessel 3 in such a manner that this gas-pressure machine 4 is connected via the pressure vessel 3, on the one hand, to heat exchanger 1 and, on the other hand, to heat exchanger 2. In this way, heat exchangers (1, 2) and the gas-pressure machine 4, which is arranged in the pressure vessel 3, define a process-gas loop filled with a process gas such as carbon dioxide, air, helium and/or other inert gases. Reference numeral 10 identifies an opening for pressure equalization between pressure vessel 3 and gas-pressure machine 4.

The gas-pressure machine drives a generator 12 for generating electric power.

Furthermore, the heat exchanger 1 is surrounded by a medium 5 and the heat exchanger 2 by a medium 6. The medium 5 is conducted in a flow channel 7 and the medium 6 in a flow channel 8 and the heat exchanger 1 is arranged in the flow channel 7 and the heat exchanger 2 in the flow channel 8. The medium 5 is warm and lies, for example, in a temperature range of +20° C. to +400° C. and the medium 6 is cold and lies, for example, in a temperature range of −50° C. to +50° C. The process gas in the gas-pressure machine 4 is at a pressure lying in the range between 20 and 200 MPa, preferably in a range lying between 20 to 50 MPa.

A warm medium 5 is disposed in the flow channel 7 and a cold medium 6 is disposed in the flow channel 8. The process gas disposed in the heat exchanger 1 is heated by the heat exchanger 1 and the process gas has a pressure of 50 MPa.

As a consequence of the temperature difference of the process gas in the heat exchanger 1 and heat exchanger 2, the heated process gas flows through the gas-pressure machine 4 into the heat exchanger 2 because of a pressure difference which results from the temperature difference. In the process, the process gas performs work in the gas-pressure machine 4. The process gas is cooled down in the heat exchanger 2 by the cold medium 6 and flows as a cold process gas out of heat exchanger 2 directly into heat exchanger 1. In the heat exchanger 1, the process gas is again heated by the warm medium 5 and the cycle begins anew.

The warm medium 5 as well as the cold medium 6 can be at rest or can be flowing mediums. An at-rest medium can, for example, be a lake and a flowing medium can, for example, be a river or a ground water flow. It is, however, also conceivable that any other suitable medium can be used as the warm medium 5 and/or cold medium 6.

It is understood that the foregoing description is that of the preferred embodiments of the invention and that various changes and modifications may be made thereto without departing from the spirit and scope of the invention as defined in the appended claims.

Claims

1. An arrangement for obtaining electrical energy from low temperature heat or exhaust heat, the arrangement comprising: first and second flow channels;first and second heat exchangers disposed in corresponding ones of said first and second channels;a pressure vessel; and,a gas-pressure machine built into said pressure vessel and being connected to said first and second heat exchangers.

2. The arrangement of claim 1, further comprising first and second mediums disposed in corresponding ones of said first and second flow channels so as to cause said first and second heat exchangers to be externally surrounded by said first and second mediums, respectively.

3. The arrangement of claim 2, wherein said first medium is warm and said second medium is cold.

4. The arrangement of claim 2, wherein a process gas is disposed in said first and second heat exchangers and in said gas-pressure machine with said process gas being at a pressure lying in the range of 20 MPa to 200 MPa.

5. The arrangement of claim 4, wherein said first medium is a warm medium for imparting heat to said first heat exchanger and said second medium is a cold medium for imparting cold to said second heat exchanger and said second medium is colder than said first medium; and, said pressure vessel is adapted to introduce said process gas into said gas-pressure machine and into said first and second heat exchangers at a pressure lying in the range of 20 to 200 MPa.

6. The arrangement of claim 5, wherein said pressure lies in the range of 20 to 50 MPa.

7. The arrangement of claim 1, further comprising an electric generator driven by said gas-pressure machine.

8. A method for operating an arrangement for obtaining electrical energy from low temperature heat or exhaust heat, the arrangement including: first and second flow channels; first and second heat exchangers disposed in corresponding ones of said first and second channels; a pressure vessel; a gas-pressure machine built into said pressure vessel and being connected to said first and second heat exchangers; first and second mediums disposed in corresponding ones of said first and second flow channels so as to cause said first and second heat exchangers to be externally surrounded by said first and second mediums, respectively; and, said first medium being a warm medium and said second medium being a cold medium; the method comprising the steps of: introducing a process gas into said first and second heat exchangers and into said gas-pressure machine at a pressure in the range of 20 to 200 MPa; and,then introducing heat from said first medium into said first heat exchanger via said first channel and introducing cold from said second medium into said second heat exchanger via said second channel.

9. The method of claim 8, wherein said pressure lies in a range of 20 to 50 MPa.