EP1746864B1

EP1746864B1 - System with high energy efficiency for indirectly heating a target medium using electromagnetic radiation

Info

Publication number: EP1746864B1
Application number: EP04077354A
Authority: EP
Inventors: Adrianus Gerardus De Ruiter
Original assignee: Individual
Current assignee: Individual
Priority date: 2004-08-18
Filing date: 2004-08-18
Publication date: 2010-01-20
Anticipated expiration: 2024-08-18
Also published as: DK1746864T3; DE602004025296D1; ATE456283T1; EP1746864A1

Abstract

The present invention generally relates to a system for indirectly heating a target medium, characterised by the fact that said system comprises an energy converter to convert electrical energy into electromagnetic radiation which is then absorbed by a suitable medium wherein said electromagnetic radiation is converted into heat, whereby the overall energy efficiency of the system is higher than 80 percent.

Description

The present invention generally relates to a system for indirectly heating a target medium, whereby said system comprises an energy converter to convert electrical energy into electromagnetic radiation which has a wavelength that is within the infra red wavelength range of 400 nm to 10000 nm, said energy converter producing said electromagnetic radiation being located within a housing, the inside of the housing being covered with a coating that is reflective to the electromagnetic radiation produced, characterised by the fact that the electromagnetic radiation is first absorbed by an accumulation medium wherein it is converted into heat, which heat is then transferred by thermal conduction to a transport medium that flows through the accumulation medium and then said transport medium transports the heat to the location of a target medium where the heat is transferred to said target medium by means of thermal conduction.
Most of the direct heating processes used in domestic and industrial applications are either based on the direct burning of fossil fuels like coal, natural gas or oil to convert de caloric contents of such fuels directly into thermal energy ('heat'), or use electrically resistive elements to convert electrical energy directly into heat. This heat is then directly transferred to the matter to be heated or to a transport medium for thermal energy. These methods of direct heating have, although very widely used, a very low energy efficiency since, in general, no more than 35 percent of the energy input is converted into useful output energy. Despite their low energy efficiency and the fact that the use of fossil fuels presents obvious dangers to the environment, for instance by the 'greenhouse effect', direct heating processes can be found everywhere in our daily lives: to generate electricity, to power our cars, to cook our food, to heat our house and our water. As an alternative to direct heating processes, indirect heating processes have been presented. In many indirect heating processes electrical energy is converted into some form of electromagnetic radiation or a nuclear reaction generates electromagnetic radiation that is absorbed by the matter that is to be heated, where it makes the matter's molecules vibrate faster causing the temperature of the matter to rise. Forms of such indirect heating processes are used in for instance nuclear power plants, the common microwave oven for domestic use or the infrared lamps used by physiotherapists. Most of these indirect heating processes are only efficient for very specific applications and kinds of matter, are hazardous to the human health or have other specific disadvantages. The energy efficiency of the indirect heating processes in nuclear power plants, for instance, is not much higher than the abovementioned energy efficiency of direct heating processes using fossil fuels, and the disposal of the resulting nuclear waste products presents serious dangers to the human health and the environment. The indirect heating process used in kitchen microwave ovens has an energy efficiency of about 60 percent, but this process only works with matters containing water, sugar or fat molecules. A serious drawback of many indirect heating processes is the fact that the energy efficiency of the processes increases when radiation with a higher intensity is used, which in turn presents more dangers to the human health and the environment, thus requires more expensive safety precautions.
Systems and methods for indirect heating that are presently known from prior art generally do not provide adequate solutions to the abovementioned drawbacks causing such indirect heating processes to be unsuitable for widespread use in common industrial and domestic heating applications. For instance the prior art documents US 6 268 596 B1 (Lauf, Robert J., et al. ), WO 03/039194 A (Micro Heat Ltd.) and US 4 114 011 A (Stubbs, Elmer L.) propose systems for indirectly heating a fluid medium by letting it flow through tubular conduits which pass through a space where the fluid medium is subjected to microwave radiation. As mentioned earlier, microwave heating is limited to matters containing water, sugar or fat molecules. Furthermore, the use of microwave heating on a larger (industrial) scale is seriously limited by the fact that this would require large amounts of energy and heavy shielding precautions because high-energy microwaves have a high risk of interfering with radio and data communications and radar, and are hazardous to human health. Furthermore the prior art documents US 4 420 677 A (Partington, Everett J. ) and US 2 607 877 A (Fenton Stevens, Edwin ) describe systems using, respectively, resistance heating of a fluid medium and heating of water by using infra red lamps. Both with the obvious drawbacks of very poor energy efficiency and non-conformance with today's energy conservation standards and regulations.
The present invention aims to remedy the aforementioned disadvantages associated with the prior art. To achieve this a system for indirectly heating a target medium is proposed, whereby said system comprises an energy converter to convert electrical energy into electromagnetic radiation which has a wavelength that is within the infra red wavelength range of 400 nm to 10000 nm, said energy converter producing said electromagnetic radiation being located within a housing, the inside of the housing being covered with a coating that is reflective to the electromagnetic radiation produced, characterised by the fact that the electromagnetic radiation is first absorbed by an accumulation medium wherein it is converted into heat, which heat is then transferred by thermal conduction to a transport medium that flows through the accumulation medium and then said transport medium transports the heat to the location of a target medium where the heat is transferred to said target medium by means of thermal conduction.
Indirect heating processes can achieve an energy efficiency higher than 80 percent when the energy conversion characteristics of the source of the electromagnetic radiation approximate the characteristics of a so-called 'black body'. A black body converts all of it's input energy into electromagnetic radiation and constitutes in this respect a perfect radiator. Presently there are energy converters readily available on the market that convert electrical energy into electromagnetic radiation and have energy conversion characteristics that approximate those of a black body. For instance the energy converters produced by the LEXIN^® Group in The Netherlands reach a very high energy efficiency in the far infrared wavelength range (3,000 nm. - 10,000 nm.). An important advantage of the use of this wavelength range is that in the electromagnetic spectrum infra red radiation, especially in the far infra red wavelength range (3,000 nm. - 10,000 nm.), is easily absorbed by most matter and presents the least risks for the human health, even at higher radiation intensities. For the sake of clarity of the remainder of this description it is assumed that said energy converter in the system for indirectly heating a target medium according to the present invention, has conversion characteristics that approximate those of a black body.
In an optimal situation all the electromagnetic radiation that is produced by said energy converter is absorbed by the accumulation medium. The walls of the housing of the energy converter should therefore be constructed from such material and in such a way that radiation photons that are not immediately absorbed by said medium, are reflected by said walls to increase the probability that they are finally absorbed by the accumulation medium or by the energy converter itself where these reflected photons stimulate emission of new radiation photons.
When water would be the transport medium and air would be the target medium, this embodiment of the system for indirectly heating a target medium according to the present invention could constitute a central heating system using indirect heating.
In a further advantageous embodiment of the system for indirectly heating a target medium according to the present invention, the system is characterised by the fact that said transport medium which flows through said accumulation medium is also the target medium that is to be heated. The said accumulation medium could for instance be soapstone (steatite), a material with very good heat retaining characteristics. When air would be the target medium, for instance to heat a room, the heat accumulated in the soapstone could be transferred to the air by blowing it over or through said soapstone thus in effect constituting a soapstone ventilator heater using indirect heating.
When water would be the transport medium and air would be the target medium, this embodiment of the system for indirectly heating a target medium according to the present invention could constitute a central heating system using indirect heating.
Another embodiment of the system for indirectly heating a target medium according to the present invention is advantageously characterised by the fact that, in case a transport medium is used, this consists of a thermal oil or a mixture of thermal oils. Thermal oils have better heat retaining characteristics than water.
In case thermal oil or a mixture of thermal oils is/are used as transport medium in the system for indirectly heating a target medium according to the present invention, said system may be advantageously characterised by the fact that graphite is added to said thermal oil or said mixture of thermal oils to increase the heat retaining characteristics of the oil or mixture of oils even further.
In case an accumulation medium is present in the system for indirectly heating a target medium according to the present invention, said system may be advantageously characterised by the fact that said accumulation medium consists of soapstone (steatite). This material is a magnesium silicate and is known for its excellent heat retaining properties. Soapstone furthermore is a very good absorber and radiator for infra red radiation.
In yet another advantageous embodiment of the system for indirectly heating a target medium according to the present invention, the system is characterised by the fact that said energy converter producing electromagnetic radiation is located in a pressurised housing and the medium which flows through said accumulation medium is water that is converted into superheated steam of approximately 250°C during its passage through said accumulation medium. This superheated steam could then for instance be used to drive a turbine, after which the condensed steam is reinjected in the pressurised housing of the energy converter to be re-heated.
Although the abovementioned energy converters produced by the LEXIN^® Group that were used in tests with this preferred embodiment of the system according to the present invention have a very high energy efficiency, the use of partial reflection of emitted radiation photons and the resulting stimulated emission of more photons, enables energy conversion characteristics that approximate those of a so called 'black body', which is a perfect radiator. From Stefan's Law applied to a black body $E_{total} = σ T^{4} with σ = 5.67 * 10^{- 8} {Wm}^{- 2} K^{- 4}$

we can see that the total energy that is radiated by a black body increases with the radiating surface temperature to the fourth power. Tests have shown that with this preferred embodiment of the system for indirectly heating a target medium according to the present invention, energy efficiencies higher than 80% can be attained and water flowing through said accumulation medium is almost instantly converted to superheated steam.
In the following a number of preferred embodiments of the system for indirectly heating a target medium according to the present invention will be described. The following description and the attached drawings will show to the reader in more detail how the invention remedies the aforementioned disadvantages associated with the prior art. However, the reader should observe that description and drawings are merely meant to illustrate application of the invention and should in no way be regarded as limiting the scope of the present invention.
Figures 1 and 3 show partly cross-sectional schematic views of two prior art systems for indirectly heating a target medium. These figures and the accompanying descriptions are merely meant to illustrate the technological field of the invention.
Figures 2 and 4 show partly cross-sectional schematic views of two preferred embodiments of the system for indirectly heating a target medium according to the present invention.
Figure 1 shows a prior art system for indirectly heating a target medium, constituting a highly energy-efficient water heater, for instance to heat tap water in a domestic environment. In figure 1 an energy converter (1) is located in a housing (2). The energy converter (1), which is in this case screen-shaped (in the figures the plane of the screen is oriented perpendicular to the drawing plane), converts electrical energy into electromagnetic radiation that is emitted into the inner part of the housing (2). The housing (2) is equipped with a layer (3) of thermally insulating material to keep as much of the thermal energy as possible inside. A spiral-shaped tube (5) of a suitable plastic material penetrates the walls of the housing (2) on the left and right side. When water flows through the tube (5) and enters the housing (2) it is subjected to the electromagnetic radiation produced by energy converter (1). The water absorbs part of the electromagnetic radiation and is heated up when it flows through the spiral inside the housing (2). The final temperature of the water when it leaves the housing depends on several parameters, like for instance the kind of radiation used, the radiation intensity, the original temperature of the water, the velocity of flow of the water, the length of the part of the tube (5) that is inside the housing (2), the material of the tube etc. To increase the chance that radiation photons are absorbed by the water, the inside of the housing (2) is covered with a coating (4) that is reflective for the radiation used. Tests have shown that with the use of screen-shaped energy converters produced by the LEXIN^® Group situated in The Netherlands, it is possible to continuously produce 10 litres of water per minute with a temperature of 60 °C. and thereby reach an energy efficiency of over 80 percent with the system for indirectly heating a target medium according to the present invention. The measures of the housing for the tested system were 40 cm. x 40 cm. x 10 cm. The LEXIN^® energy converter that was used in the tests, produces radiation in the far infra red wavelength range (3,000 nm. - 10,000 nm.). Due to the radiation characteristics of the LEXIN^® energy converter, which approximate those of a black body, in combination with the thermal insulation (3) and the reflective coating (4), an energy efficiency of over 80 percent was achieved. Comparable tap water heaters for domestic use have energy efficiencies that are generally below 35 percent.
Figure 3 shows another prior art system for indirectly heating a target medium, constituting a central heating system, for instance to be used in conventional domestic heating. The construction and functioning of the system is very similar to that of the system shown in figure 1 and described above. In this case however, the fluid that flows through the spiral (9) which is inside the housing (2), is not the target medium that is to be heated, as was the case for the tap water heater. In this embodiment such fluid constitutes a transport medium for transporting the heat that was generated by the electromagnetic radiation produced by energy converter (1), to one or more radiators (10), that transfer the transported heat to the ambient air by way of thermal conduction. Although with the use of water as transport medium high energy efficiencies can be achieved, the system performance can be increased by using a thermal oil or a mixture of thermal oils as transport medium instead. Adding graphite to the thermal oil or mixture of thermal oils increases the radiation absorption and heat retaining properties of the transport medium even further. Also in this case tests have shown that with the use of LEXIN^® energy converters producing radiation in the far infra red wavelength range, in combination with thermal insulation (3) and a reflective coating (4), energy efficiencies of over 80 percent can be achieved.
Figure 2 shows a preferred embodiment of the system for indirectly heating a target medium according to the present invention, whereby this embodiment constitutes an accumulation ventilator heater, for instance to be used for heating a room in a house. In figure 2 an energy converter (1) is located in a housing (2). The energy converter (1), which is in this case screen-shaped, converts electrical energy into electromagnetic radiation that is emitted into the inner part of the housing (2). The housing (2) is equipped with a layer (3) of thermally insulating material to keep as much of the thermal energy as possible inside. Located in the inner part of the housing (2) is an accumulation medium (6) that is continuously subjected to the electromagnetic radiation produced by energy converter (1). Within the accumulation medium (6) the absorbed radiation is converted into heat. For reaching an energy efficiency of over 80 percent with this embodiment of the system for indirectly heating a target medium according to the present invention, the accumulation medium must have good absorption and heat accumulation properties for the kind of radiation used. In this case soapstone (steatite) was used, which has excellent absorption and accumulation properties for radiation in the far infra red wavelength range that is produced by the screen-shaped energy converters produced by the LEXIN^® Group situated in The Netherlands that were used for testing. Within the soapstone accumulation medium (6) there is a network (7) of air channels between an inlet at the left side of the housing (2) and an outlet at the right side of the housing (2). A ventilator (8) situated at the outlet side of the network of air channels draws a flow of air through the channels in the soapstone. This air is heated by the heat accumulated in the soapstone through thermal conduction and the heated air is then dispersed into the environment. Accumulation ventilator heaters known from prior art are generally heated by resistive electrical heating elements and have a very low energy efficiency. With this embodiment of the system for indirectly heating a target medium according to the present invention however, an energy efficiency of over 80 percent can be achieved.
Figure 4 shows another preferred embodiment of the system for indirectly heating a target medium according to the present invention, similar to the prior art system shown in figure 3 and described above, also constituting a central heating system, suitable for use in for instance conventional domestic heating. In this embodiment however, the spiral (9) is embedded in an accumulation medium (6) to achieve even better radiation absorption and heat accumulation. As mentioned earlier, soapstone is the preferred material for such an accumulation medium in combination with the use of LEXIN^® energy converters producing radiation in the far infra red wavelength range, thermal insulation (3) and a reflective coating (4). Also in this embodiment the use of thermal oil or a mixture of thermal oils with added graphite can increase the energy efficiency of the system even further.
The system for indirectly heating a target medium according to the present invention enables the economically feasible, safe and highly energy-efficient use of indirect heating using electromagnetic radiation in a wide range of industrial and domestic heating processes. As such it overcomes numerous drawbacks of systems and methods known from prior art.
All parts of the described embodiments of the system for indirectly heating a target medium according to the present invention are commonly available and can be manufactured by using commonly available materials and commonly known production methods.

Claims

System for indirectly heating a target medium, whereby said system comprises an energy converter (1) to convert electrical energy into electromagnetic radiation which has a wavelength that is within the infra red wavelength range of 400 nm to 10,000 nm, said energy converter (1) producing said electromagnetic radiation being located within a housing (2), the inside of the housing (2) being covered with a coating (4) that is reflective to the electromagnetic radiation produced, characterised by the fact that the electromagnetic radiation is first absorbed by an accumulation medium (6) wherein it is converted into heat, which heat is then transferred by thermal conduction to a transport medium that flows through the accumulation medium (6) and then said transport medium transports the heat to the location of a target medium where the heat is transferred to said target medium by means of thermal conduction.
System according to claim 1 for indirectly heating a target medium, characterised by the fact that said transport medium which flows through said accumulation medium, is also the target medium that is to be heated.
System for indirectly heating a target medium according to claim 1, characterised by the fact that said transport medium consists of a thermal oil or a mixture of thermal oils.
System for indirectly heating a target medium according to claim 3, characterised by the fact that graphite is added to said thermal oil or said mixture of thermal oils to increase the heat retaining characteristics of the oil or mixture of oils.
System for indirectly heating a target medium according to one of the claims 1 - 4, characterised by the fact that said accumulation medium consists of steatite, which is more commonly known as soapstone.
System according to claim 1 or 2, characterised by the fact that said medium which flows through said accumulation medium, is water that is heated to superheated steam during its passage through said accumulation medium, whereby said energy converter is located in a pressurised housing.