JP2009087955A - Waste heat recovery system having thermoelectric conversion system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To consume energy efficiently as much as possible by converting waste heat directly into electricity using a thermoelectric conversion system. <P>SOLUTION: A waste heat recovery system having the thermoelectric conversion system comprises a means for supplying power by the thermoelectric conversion system, and a means for utilizing heat released from the thermoelectric conversion system. The heat released from the thermoelectric conversion system is utilized for heating, defrosting, defogging, heat insulation of fuel heat insulation of an internal combustion engine, heat insulation of a fuel cell, and the like. The waste heat recovery system is mounted on a vehicle, an incinerator, a fuel cell, an industrial machine, and the like. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a waste heat recovery system that converts waste heat into electricity by a thermoelectric conversion system, and obtains hot water for use in heating, defrosting, and the like.

  In recent years, as an effective means for increasing environmental awareness and fossil fuel depletion, it has been demanded to efficiently consume energy as much as possible by directly converting waste heat into electricity using a thermoelectric conversion system.

  For example, in the case of automobiles, only 15% of the fuel energy is used for driving, 10% is used as electricity, and the other is released into the atmosphere as heat from radiators, exhaust gas, and engine casings. .

  Hybrid vehicles have begun to spread in order to use fuel energy effectively to reduce fuel consumption. However, because there are many equipments and special vehicles, the spread is likely to be limited. The contribution of is also limited.

  The most effective measure for energy saving is to effectively use the fuel of gasoline cars or diesel cars that are currently widely used. For this purpose, waste heat is recovered and converted into electricity, Therefore, it is effective to reduce the fuel consumed.

  Several methods have been devised for recovering waste heat. Among them, it is known that a Stirling engine that recovers energy by driving a piston using waste gas can recover energy with high efficiency. Yes.

  The thermoelectric conversion system has advantages such as having no drive part, being able to generate electricity immediately if a temperature difference occurs, and having a simple structure, so that it can be used in automobiles. Research and development is underway.

JP 2004-36499 A JP 2004-76046 A Edited by Takenobu Kajikawa et al., Realize, Thermoelectric conversion system technology overview (2004)

In a conventional thermoelectric conversion system, a heat exchanger for heat radiation is employed to prevent overheating of the entire thermoelectric module. However, such heat is not used but is released into the atmosphere as waste heat.
Conventional thermoelectric materials have the drawback of not being able to obtain sufficient effects due to their low performance for effectively converting the heat of exhaust gas, so new materials need to be developed to achieve high-efficiency thermoelectric conversion. Furthermore, development of mass production technology for high-performance devices was required for practical use.

  In addition, since the thermoelectric element peels off from the electrode due to thermal stress and poor conduction occurs, it is necessary to improve reliability.

The present invention has been made based on the above findings and includes the following inventions.
(1) A waste heat recovery system having a thermoelectric conversion system, comprising: means for supplying electric power by the thermoelectric conversion system; and means for using heat released from the thermoelectric conversion system.
(2) The heat released from the thermoelectric conversion system is used for (1) one or more selected from the group consisting of heating, defrosting, anti-fogging, fuel insulation, internal combustion engine insulation, and fuel cell insulation. The waste heat recovery system described.
(3) The waste heat recovery system according to (1) or (2), wherein the thermoelectric conversion system uses a sintered body composed of crystals having a particle size of 200 μm or less as a thermoelectric power generation element.
(4) The waste heat recovery system according to (3), wherein the thermoelectric power generation element is obtained by pulverizing and sintering an alloy produced by a rapid solidification method.
(5) The thermoelectric power generation element includes one or more kinds of crystals selected from the group consisting of a half-Heusler structure, a Heusler structure, a filled skutterudite structure, and a skutterudite structure, and any one of (3) to (5) The waste heat recovery system according to one.
(6) The waste heat recovery system according to any one of (1) to (5), wherein the waste heat recovery system is for vehicle use.
(7) A vehicle equipped with the waste heat recovery system according to any one of (1) to (5).
(8) A fuel cell system equipped with the waste heat recovery system according to any one of (1) to (5).
(9) An incinerator equipped with the waste heat recovery system according to any one of (1) to (5).
(10) An industrial machine equipped with the waste heat recovery system according to any one of (1) to (5).

According to a preferred embodiment of the present invention, heat is recovered from a high-temperature exhaust gas of up to 950 ° C. by a ceramic heat exchanger and supplied to the thermoelectric conversion module, while cooling water is supplied to the low temperature side. Since the heat released from the thermoelectric conversion module can be recovered and given a large thermal gradient, a large electric power can be obtained.

  Since the heat recovered in the cooling water can be used as a heat source for heating or as a heat source for defrosting and defrosting in winter, further energy saving effect can be expected.

The hot water collected by the present system is not limited to heating, defrosting, anti-fogging, etc., and can be used for engine and fuel temperature control, so that further low fuel consumption can be expected.
By applying this system, a system that can efficiently use various types of energy can be established.

In a preferred embodiment of the present invention, the thermoelectric conversion unit is connected to the battery via the battery charge wiring, and the electric power obtained by the power generation is charged in the battery.

For example, in the case of a vehicle-mounted thermoelectric conversion unit, the low temperature side is connected to a radiator, an air conditioning unit, and an engine via a cooling system pipe, and the temperature difference from the high temperature part of the thermoelectric power generation unit that becomes high temperature due to exhaust gas discharged from the engine It can be forced to occur. For example, exhaust gas at about 600 ° C. after passing through the catalyzer can be used as exhaust gas. It is preferable to make the dimension in the exhaust gas flow direction as small as possible to avoid generation of a large temperature gradient in the thermoelectric module.
As a cooling method, either air cooling or water cooling can be adopted, but air cooling is preferable when avoiding hot water treatment in summer.

In the air conditioning unit connected to the cooling system pipe, heating, defrosting and anti-fogging can be performed using waste heat recovered from the thermoelectric conversion unit as a heat source. Further, the temperature of the fuel and the engine casing can be controlled by connecting a part of the piping to the engine.

  The thermoelectric conversion basic unit consists of high-temperature heat exchangers, electrical insulators, electrodes, thermoelectric elements, low-temperature heat exchangers, etc., and multiple units can be installed, and the number is adjusted according to the amount of exhaust gas heat and heat exchanger capacity be able to.

  There are two types of thermoelectric elements, p-type elements and n-type elements. A high voltage can be obtained by connecting a plurality of thermoelectric elements in series via electrodes.

The heat of the high temperature exhaust gas recovered by the high temperature heat exchanger is given to the p-type element and the n-type element. On the other hand, a low-temperature heat exchanger is connected to a water cooling system.
Known ceramics can be used as the high temperature side heat exchanger, but silicon carbide, silicon nitride, sialon, aluminum nitride, titanium nitride, titanium boride, etc. are used from the viewpoint of heat resistance, thermal shock resistance and thermal conductivity. Silicon carbide is particularly preferable. A known metal material can be used for the low temperature side heat exchanger, but it is preferable to use aluminum or stainless steel from the viewpoint of workability and cost.

  For joining the thermoelectric conversion module and the high-temperature side heat exchanger, chemical joining using Ni or Ti or mechanical joining of screws or springs can be used, and buffering is used to relieve stress as necessary. A layer can be provided.

  Silver solder or solder can be used for joining the thermoelectric conversion module and the low temperature side heat exchanger, and a buffer layer can be provided to relieve stress as necessary.

  In order to relieve thermal stress, the thermoelectric conversion module can use a so-called skeleton structure that does not use a fixing ceramic substrate. In this case, an insulating layer is provided between the electrode and the heat exchanger. it can.

  The shape of the heat exchanger is not particularly limited, but a fin-type heat exchanger can be employed in order to efficiently recover heat, particularly in the high temperature side heat exchanger.

The thermoelectric element used in the thermoelectric conversion module is not particularly limited, and any known thermoelectric element can be used. For example, both p-type and n-type elements are filled skutterudite sintered bodies, p-type or n-type. At least one of which is a Zn ₃ Sb ₄ element, cobalt oxide element, Mn—Si element, Mg—Si element, Bi—Te element, Pb—Te element, Heusler and half-Heusler element, Si—Ge It is also possible to employ a system material or the like. These thermoelectric elements can also be protected by applying plating or vapor deposition films to the elements in order to prevent oxidation.
For example, as a thermoelectric element, RE _x (Fe _1-y My) ₄ Sb ₁₂ (RE is at least one of La and Ce, M is at least one selected from the group consisting of Ti, Zr, Sn, and Pb. 0 < A filled skutterudite type rare earth alloy represented by x ≦ 1, 0 <y <1) can be used. This alloy is suitably used as a p-type thermoelectric conversion material. This alloy may contain inevitable impurities such as Pb, As, Si, Al, Fe, Mo, W, C, O, and N, and may be in the form of a thin film, alloy, or sintered body. The crystal structure is more preferably a skutterudite type crystal structure. In the rare earth alloy, if x is less than 0.01, the thermal conductivity is deteriorated and the characteristics are deteriorated. If y exceeds 0.15, both the Seebeck coefficient and the electric conductivity are remarkably lowered. Is preferred. If y is less than 0.01, the performance improvement by addition is insufficient, so 0.01 or more is preferable. When M is added within the above range, both the Seebeck coefficient and the electrical conductivity can be improved.

Further, as the rare earth alloy, RE _x (Co _1-y My) ₄ Sb ₁₂ (RE is at least one of La and Ce, M is at least one selected from the group consisting of Ti, Zr, Sn, and Pb. 0 < x ≦ 1, 0 <y <1) can also be adopted. This alloy is suitably used as an n-type thermoelectric conversion material. The rare earth alloy may contain inevitable impurities such as Pb, As, Si, Al, Fe, Mo, W, C, O, and N, and may be in any form of a thin film, an alloy, and a sintered body. The crystal structure is more preferably a skutterudite type crystal structure. In this rare earth alloy, if x is less than 0.01, the thermal conductivity is deteriorated and the characteristics are deteriorated. If y exceeds 0.15, both the Seebeck coefficient and the electric conductivity are remarkably lowered. Is preferred. If y is less than 0.01, the performance improvement by addition is insufficient, so 0.01 or more is preferable. When M is added within the above range, the Seebeck coefficient can be mainly improved, so that the performance can be improved.

These rare earth alloys are RE _x (Fe _1-y M _y ) ₄ Sb ₁₂ (RE is at least one of La and Ce, and M is at least one selected from the group consisting of Ti, Zr, Sn, and Pb. 0 <X ≦ 1, 0 <y <1) The raw materials are weighed so as to have a composition, dissolved in an inert gas atmosphere, and then rapidly solidified.
Also, RE _x (Co _1-y My) ₄ Sb ₁₂ (RE is at least one of La and Ce, M is at least one selected from the group consisting of Ti, Zr, Sn, and Pb. 0 <x ≦ 1, The raw materials can be weighed so as to have a composition represented by 0 <y <1), and the raw materials can be dissolved in an inert gas atmosphere and then rapidly solidified.
A strip casting method can be used as a method for quenching the above two alloys, and a known method can be used as another method for quenching a molten metal. These cooling rates are preferably 1 × 10 ² ° C./second or more, more preferably 1 × 10 ² ° C./second or more and 1 × 10 ⁴ ° C./second or less, more preferably 1400 ° C. to 800 ° C. It is 2 × 10 ² ° C./second or more and 1 × 10 ³ ° C./second or less. 1 × 10 ² ℃ / fluctuation components due to slower and phase pulverized separated seconds increases, undesirably 1 × 10 ⁴ ℃ / sec faster amorphous and become for pulverization efficiency becomes worse than.
If such a quenching method is employed, the average thickness of the alloy flakes is about 0.1 to 2 mm, preferably about 0.2 to 0.4 mm, and the most preferred quenching rate is adopted. The average thickness is about 0.25 to 0.35 mm.

The Heusler alloy is represented by the general formula A _3-x B _x C, A and B are composed of transition metals, C is composed of Group III and Group IV metals, and the space group is Fm3m. The half-Heusler alloy is represented by the general formula ABC. Similarly, A and B are transition metals, C is a group III or group IV metal, and the space group is F43m.

B, C, Mg, Cu, Zn, or rare earth metals Y, La, Ce, Nd, Pr, Dy, Tb, Ga, Yb, etc. are added to the Heusler alloy and half-Heusler alloy as additives. Thermal properties can be adjusted. In a preferred embodiment of the present invention, the strongest peak ratio of the Heusler phase or the half-Heusler phase is preferably 85% or more, and more preferably 90% or more. In addition, the peak ratio is the strongest peak (IHS) of the Heusler phase or the half-Heusler phase, the strongest peak intensity (IA) of the impurity phase A, and the strongest peak intensity (IB) of the impurity phase B measured in the powder X-ray diffraction measurement. Than,
It is defined as IHS / (IHS + IA + IB) × 100 (%).
These Heusler alloys are, for example, sponge Ti (purity 99% or more) and sponge Zr (purity 99%) so that the composition after casting is half-Heusler (Ti _x Zr _1-x ) NiSn (0 ≦ x ≦ 1). Above), electrolytic Ni (purity 99% or more), Sn metal (purity 99.9% or more) are weighed and melted by high frequency in an Ar atmosphere of 0.1 MPa up to 1700 ° C. and rapidly solidified. it can.

  The pulverizing method for pulverizing the alloy is not limited, and any known method can be adopted. For example, a ball mill, pot mill, attritor, pin mill, and jet mill can be used. For example, although the jet mill has a relatively high pulverization cost, it can be continuously operated and can easily cope with oxidation prevention and dust explosion prevention, and even a fine powder of about 20 μm can be processed in a relatively short time. This is preferable because it is possible. Since the rapidly solidified alloy has good pulverizability, fine powders of 20 μm or less can be obtained in a short time and in a high yield.

The method of molding the alloy is not particularly limited.
. 5t ^/ cm 2 ~5.0t ^/ cm ² of molding pressure and compact inert atmosphere, when the normally liquid phase sintering at the melting point just below the respective alloy, the crystal grain diameter 100μm or less fine crystals A thermoelectric element composed of grains can be produced. The crystal grain size of the thermoelectric element is preferably as small as possible considering the decrease in thermal conductivity due to lattice scattering, and is preferably 100 μm or less, and more preferably 10 to 15 μm, and high performance can be achieved by heat scattering at grain boundaries.

  It is preferable that the thermoelectric elements of the p-type semiconductor and the n-type semiconductor are electrically connected in series to form a thermoelectric conversion module. As a method of electrical connection, a metal cap is attached to the semiconductor via an electrode. A method of connection is preferred.

The material of the cap made of metal is not particularly limited, but a cap having a material having the same or small thermal expansion coefficient as the material constituting the thermoelectric element is preferable. For example, stainless steel is used for a thermoelectric element having a large linear thermal expansion coefficient. Molybdenum, zirconium, titanium, tungsten, or the like can be used for thermoelectric elements having a small linear expansion coefficient, such as copper, iron, silver, and gold. It is also effective to load alloy or metal particles that become liquid at a high temperature between the cap and the thermoelectric element in order to prevent generation of a gap due to temperature rise.
The shape of the metal cap is not particularly limited, but is preferably cylindrical, and the bottom surface may have a flat plate or a curvature. However, the height of the cap is preferably less than half the height of the thermoelectric element. It is also possible to form a fine hole in the bottom surface or form a groove in a part of the side surface to release air remaining in the gap between the thermoelectric element expanded by the temperature rise and the cap.
For example, the cap and the electrode can be bonded by heating to 700 ° C. using silver solder or the like. However, the cap can be bonded to the electrode in advance, thereby further improving productivity. be able to. Also, a structure in which the electrode and the cap are integrated is possible. If necessary, the cap is covered with a metal or conductive ceramics that functions as a diffusion prevention layer, or this material is used as the cap. Since the step of coating the elements on these elements can be omitted, productivity can be further improved.

In addition, when the back surface of the electrode is covered with an insulating film such as ceramics, a conventional insulating plate is not required, so that the production cost can be reduced. The material of the insulator film is not particularly limited, but oxide ceramics can be employed in addition to aluminum nitride, silicon nitride, sialon, and preferably alumina which is generally available and inexpensive.
The thickness of the insulator film may be selected according to the module shape to be applied, but is preferably about 100 nm.

  In the thermoelectric conversion system configured as described above, a temperature difference is generated in each of the p-type semiconductor and the n-type semiconductor connected to the high temperature contact portion side and the low temperature contact portion side, and the temperature difference based on the Seebeck effect is applied. Electricity is generated by thermoelectric conversion.

  The shape of the module can be made according to the heat source, such as a cylindrical shape, in addition to the flat plate shape. The thermoelectric conversion module can have a sealed structure in order to prevent oxidation of the element.

  An air-cooled heat exchanger can be used in the cooling water system in order to release the excessively recovered heat.

  The power collected by this system may be supplied to the battery and reused indirectly, or a hydraulic pump or the like may be driven directly, or used as an electrical source for electrochemical reactions for exhaust gas purification. May be.

EXAMPLES Hereinafter, although an Example demonstrates this invention further in detail, this invention is not limited to these Examples at all.
(Example)

  The case where this invention is attached to a motor vehicle is demonstrated. FIG. 1 illustrates a case where the waste heat recovery system of the present invention is installed taking a moving body heat source such as an automobile as an example. The thermoelectric conversion unit 4 is installed between the engine 3 and the exhaust pipe 5.

The thermoelectric conversion unit 4 is connected to the battery 6 through the battery charge wiring 8, and the battery 6 is charged with the electric power obtained by the power generation.

The low temperature side of the thermoelectric conversion unit 4 is connected to the radiator 2, the air conditioning unit 7, and the engine 3 via the cooling system pipe 1, and the high temperature portion of the thermoelectric power generation unit 4 that has become high temperature due to the exhaust gas discharged from the engine 3 A temperature difference can be forcibly generated.

In the air conditioning unit 7 connected to the cooling system pipe 1, heating, defrosting and anti-fogging can be performed using waste heat recovered from the thermoelectric conversion unit 4 as a heat source. Further, by connecting a part of the piping to the engine 3, the temperature of the fuel and the engine casing can be controlled.

  FIG. 2 shows an enlarged view of the thermoelectric conversion unit 4. The gas discharged from the engine 3 flows from the exhaust duct inlet 9 to the exhaust duct outlet 11, and the high-temperature exhaust gas at the exhaust duct inlet 9 gives heat to the thermoelectric elements in the thermoelectric conversion unit 12 by the thermoelectric conversion basic unit 12. It is discharged from the exhaust duct 11.

  The thermoelectric conversion basic unit 12 is cooled to a constant temperature by flowing cooling water from the cooling water inlet 13 to the cooling water outlet 14 via the cooling system pipe 1.

  A plurality of thermoelectric conversion basic units 12 can be installed, and the number thereof can be adjusted by the amount of exhaust gas heat and the heat exchanger capacity.

  FIG. 3 shows a detailed view of the thermoelectric conversion basic unit 12. The thermoelectric conversion basic unit 12 includes a high temperature heat exchanger 15, electrical insulators 16 and 20, an electrode 17, thermoelectric elements 18 and 19, and a low temperature heat exchanger 21.

  There are two types of thermoelectric elements, p-type element 18 and n-type element 19, and a high voltage can be obtained by connecting a plurality of 18 and 19 in series via electrode 17.

  Electrical insulators 16 and 20 are inserted in the p-type element 18 and the n-type element 19 electrically connected by the electrode 17 in order to be electrically insulated from the high-temperature heat exchanger 15 and the low-temperature heat exchanger 19.

The heat of the high-temperature exhaust gas recovered by the high-temperature heat exchanger 15 is given to the p-type element 18 and the n-type element 19 through the electrical insulators 16 and 17. On the other hand, the low-temperature heat exchanger 21 is connected to the water cooling system via the cooling system pipe 1 and is kept at a constant temperature. For this reason, since a temperature difference can be forcedly generated, a large temperature difference can be obtained, and the power generation capacity can be improved.

The waste heat recovery system of the present invention can contribute to high-efficiency energy conversion from not only a mobile heat source such as an automobile but also a stationary heat source such as a fuel cell and an incinerator.

It is an example showing an example of adaptation to automobiles. It is a schematic diagram of a thermoelectric unit. It is an example of the enlarged view of a thermoelectric conversion unit.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Cooling system piping 2 Radiator 3 Engine 4 Thermoelectric conversion unit 5 Exhaust pipe 6 Battery 7 Air conditioning unit 8 Battery charge wiring 9 Exhaust duct inlet 10 Water-cooled heat exchanger 11 Exhaust duct outlet 12 Thermoelectric conversion basic unit 13 Cooling water inlet 14 Cooling water outlet 15 High-temperature heat exchanger 16 Electrical insulator 17 Electrode 18 P-type thermoelectric element 19 n-type thermoelectric element 20 Electrical insulator 21 Low-temperature heat exchanger

Claims (10)

  A waste heat recovery system having a thermoelectric conversion system, comprising: means for supplying electric power by the thermoelectric conversion system; and means for using heat released from the thermoelectric conversion system.   The waste according to claim 1, wherein the heat released from the thermoelectric conversion system is used for at least one selected from the group consisting of heating, defrosting, anti-fogging, fuel insulation, internal combustion engine insulation, and fuel cell insulation. Heat recovery system.   The waste heat recovery system according to claim 1 or 2, wherein the thermoelectric conversion system uses a sintered body composed of crystals having a particle diameter of 200 µm or less as a thermoelectric power generation element.   The waste heat recovery system according to claim 3, wherein the thermoelectric generator is obtained by pulverizing and sintering an alloy produced by a rapid solidification method.   6. The thermoelectric power generation element according to claim 3, comprising at least one crystal selected from the group consisting of a half-Heusler structure, a Heusler structure, a filled skutterudite structure, and a skutterudite structure. Waste heat recovery system.   The waste heat recovery system according to any one of claims 1 to 5, wherein the waste heat recovery system is for vehicle use.   A vehicle equipped with the waste heat recovery system according to any one of claims 1 to 5.   A fuel cell system equipped with the waste heat recovery system according to any one of claims 1 to 5.   An incinerator equipped with the waste heat recovery system according to any one of claims 1 to 5. An industrial machine equipped with the waste heat recovery system according to any one of claims 1 to 5.

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