JP2000312035A - Thermoelectric generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress performance degradation due to overheating of a thermoelectric element related to a system wherein an exhaust pipe in which an exhaust gas having large temperature fluctuation flows is utilized as a heat source, and a BiTe thermoelectric module is provided at the heat source for heat exchange. SOLUTION: Between a thermoelectric module 10 and an exhaust pipe 30 which is a heat source, a heat bank 20 for reducing the effect of fluctuation in the heat amount supplied from the exhaust pipe 30 is provided. The heat bank 20 comprises a metal of large specific heat and heat medium oil. The exhaust pipe 30 is provided with a by-pass pipe 24 which communicates between the upper stream side and lower stream side of the heat bank 20, while the by-pass pipe 24 is provided with a valve device 26 which opens/closes according to the temperature of exhaust gas.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermoelectric power generation system utilizing heat of exhaust gas or the like having a large temperature fluctuation.

[0002]

2. Description of the Related Art A thermoelectric module generally comprises a p-type thermoelectric element and an n-type thermoelectric element which are electrically connected in series via an electrode plate. Etc. are provided. The thermoelectric module is provided so as to be capable of exchanging heat with the heat source and the cooling means, respectively, and a potential difference is generated by a temperature difference generated in the thermoelectric element. This phenomenon is known as the Seebeck effect,
BACKGROUND ART Thermoelectric modules are used in thermoelectric power generation systems that use combustion exhaust gas from industrial furnaces, incinerators, household stoves and the like, exhaust gas from automobile engines, and the like as heat sources.

[0003] This thermoelectric module has different thermoelectromotive characteristics depending on the material of the thermoelectric element to be used, and is a BiTe type which is effective in a low temperature range from room temperature to about 300 ° C.
PbTe system effective in middle temperature range of about 600 ° C, about 600 ° C
There is a SiGe system effective in a high temperature range of about 900 ° C. When the above-mentioned exhaust gas is used as a heat source, the temperature of the exhaust gas is in a temperature range of about 200 to 700 ° C., and therefore, a PbTe-based or BiTe-based thermoelectric module is generally used. However, since the use of Pb has been strictly regulated in recent years, the use of BiTe-based thermoelectric modules has been expanding.

[0004]

However, this BiTe
Generally, when the temperature of the thermoelectric module exceeds about 350 ° C., the performance of the thermoelectric element tends to deteriorate, and when the module is exposed to a temperature of about 400 ° C. or more, the life of the element is significantly reduced.
By the way, the temperature of the exhaust gas fluctuates depending on the amount of heat generated during combustion in an industrial furnace or the like, and every moment depending on the output of an engine in an automobile. In particular, in the case of automobile exhaust gas, the temperature fluctuates every second and the fluctuation range is large. Therefore, when a BiTe-based thermoelectric module is used in a thermoelectric power generation system using an exhaust pipe through which exhaust gas flows as a heat source,
There has been a problem that the element is overheated and performance is deteriorated, thereby shortening the life of the element.

An object of the present invention is to provide a thermoelectric module,
In a system in which an iTe-based thermoelectric module is arranged so as to be capable of exchanging heat with a heat source having a large temperature fluctuation to perform thermoelectric generation, performance degradation due to overheating of a thermoelectric element is suppressed as much as possible.

[0006]

The thermoelectric power generation system according to the present invention comprises a thermoelectric module, in which a p-type thermoelectric element and an n-type thermoelectric element are electrically connected in series, is connected to a high-temperature thermoelectric module having a large temperature fluctuation. A heat exchanger is provided so as to be able to exchange heat with an exhaust pipe through which exhaust gas flows, and the other side of the thermoelectric module is arranged so that heat can be exchanged with respect to a cooling means, and power is generated by a temperature difference generated in a thermoelectric element. In addition, a heat sink is provided between the exhaust pipe and the thermoelectric module to reduce the influence of fluctuations in the amount of heat supplied from the exhaust pipe. For the heat reservoir, a metal having a large heat capacity, a heat medium oil, or the like is used. The form of the heat reservoir is not particularly limited as long as it can be disposed in the exhaust pipe serving as a heat source so that heat can be exchanged. When using a heat transfer medium oil, it is used in a metal jacket having a large heat capacity in a liquid-tight manner.

[0007] In the thermoelectric power generation system of the present invention, the exhaust pipe is provided with a bypass pipe communicating with the upstream side and the downstream side of the heat reservoir, and the bypass pipe has a valve device that can be opened and closed according to the temperature of the exhaust gas. It is desirable to deploy.

[0008]

[Function] The thermal energy supplied from the exhaust pipe serving as a heat source is temporarily stored in a heat reservoir, and then transmitted to the thermoelectric element of the thermoelectric module. The temperature fluctuation range on the side becomes smaller. Therefore, by appropriately setting the heat capacity of the heat pool, it is possible to control the temperature of the thermoelectric element so as not to exceed 350 ° C., for example. Further, the power generation amount of the thermoelectric module is proportional to the square of the temperature difference. For this reason, by performing thermoelectric power generation at a temperature as short as possible without causing overheat deterioration of the thermoelectric element, a large temperature difference can be obtained, and maximum power generation efficiency can be achieved.

[0009] In the configuration in which the bypass pipe is provided, when a predetermined amount or more of heat energy is supplied from the heat source to the heat reservoir, the valve device of the bypass pipe is opened, so that excessive heat energy is supplied to the high temperature side of the thermoelectric module. Will not be supplied,
Overheating of the thermoelectric element is reliably prevented.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIG. 1, a thermoelectric module (10) is composed of a predetermined number of p-type thermoelectric elements (12) and n-type thermoelectric elements (13) arranged in rows and columns. 12) and (13) are used in which first and second electrode plates (14) and (15) are electrically connected in series. Electrode plate (1
4) On the (15), insulating plates (16) and (17) made of ceramics such as alumina and aluminum nitride are provided. The number of thermoelectric elements to be used is appropriately determined according to the required power generation capacity.

Although the material of the thermoelectric element is not particularly limited, the present invention is effective for improving the life of the BiTe-based thermoelectric material.
_{(Bi 2 Te 3) 1-} X (Sb 2 Te 3) a _X, x is from about 0.7
~ 0.85, as an n-type thermoelectric element, (Bi ₂ Te ₃ )
_{1-X (Bi 2 Se 3} ) a _X, it can x is mentioned as 0.05-0.15.

On the hot side of the thermoelectric module (30),
A heat sink (20) is provided so as to make contact over substantially the entire surface. Heat pool (20) consists of heat source and thermoelectric module
The form is not particularly limited as long as it can be disposed so as to be capable of exchanging heat with the high-temperature side of (10). Generally, it is made in a plate or block as shown in FIG. The heat pool (20) is made of a metal having a large heat capacity, preferably a metal having a specific heat of about 0.2 cal / K · g or more. As examples of the metal, for example, aluminum and magnesium are used. As the heat reservoir (20), a heat medium oil can be used. In this case, the heating medium oil (22) (see FIG. 2)
Is liquid-tightly housed inside a jacket, preferably made of a metal with a high specific heat. Since the oil expands due to heating, an expansion tank function is separately provided so that the oil may expand in advance.

A cooling means is provided on the side of the thermoelectric module (10) where the temperature is low so that heat can be exchanged. In the case of the air-cooling type, as shown in FIG. 1, a heat dissipating member (40) having a large number of fins (42) projecting from the surface thereof for increasing the amount of heat transfer is used as cooling means. In the case of the water cooling type, as shown in FIG. 2, a heat absorbing member (45) through which cooling water flows inside the block body having a hollow structure is used as cooling means.

A lead wire (not shown) is attached to a thermoelectric element serving as a base end and an end of the electric series circuit, and the generated power is directly converted into DC power supply equipment or converted into AC power. To the inverter.

[0015]

First Embodiment FIG. 3 shows an embodiment of a thermoelectric power generation system in which a thermoelectric module having the structure shown in FIG. 1 (a thermoelectric element uses a BiTe system) is installed in an exhaust pipe through which exhaust gas of an automobile engine flows. Is shown. Exhaust pipe (30) through which exhaust gas flows into the engine (32)
Is provided, and a thermoelectric module is provided in the middle of the exhaust pipe.
(10) is provided, and the base end and the end of the electric series circuit of the thermoelectric elements (12) and (13) are electrically connected to the battery (52) and the load (54). The exhaust pipe (30) is provided with a bypass pipe (24) communicating with the upstream side and the downstream side of the heat reservoir (20), and the bypass pipe (24) has a valve device (26) such as a solenoid valve. Be deployed.

The heat reservoir (20) is disposed between the hot side of the thermoelectric module (10) and the exhaust pipe (30) so as to be able to exchange heat. A thermocouple as a temperature sensor is embedded in the heat reservoir (20), and the thermocouple passes through a control unit (28), and is connected to a valve device (26).
A command is issued from the control unit to the valve device (26) in accordance with the temperature detected by the thermocouple, and the valve device is
(26) is opened and closed. When the temperature detected by the thermocouple is lower than the set temperature, the control unit (28) transmits a signal of `` closed '' to the valve device (26). An "open" signal is transmitted to the device (26). If more precise temperature control is desired, a valve device (26) whose opening can be adjusted can be used. Also,
More simply, a system that can be directly opened and closed by using a shape memory alloy or the like without using an electric control device can be used.

Next, the operation of the thermoelectric power generation system having the above configuration will be described. When the engine (32) starts, the exhaust pipe
High-temperature exhaust gas flows through (30). The thermal energy of the exhaust gas is supplied to the thermoelectric module (10) via the heat reservoir (20). The other side of the thermoelectric elements (12) and (13) is
In response to the cooling action from (0), the thermoelectric element is in a low temperature state, so that a temperature difference occurs between the thermoelectric elements and an electromotive force is generated. The power generated by the thermoelectric element is supplied to the battery (52) for charging, and is also directly supplied to the load (54) as required power of the load (54).

The temperature of the exhaust gas fluctuates every time within the range of about 200 to 700 ° C. depending on the rotational state of the engine and the like. In the above configuration of the present invention, the thermal energy of the exhaust gas is
Once stored in the heat reservoir (20), the temperature fluctuation of the exhaust gas is absorbed in the heat reservoir (20). That is, the exhaust gas is supplied to the thermoelectric module as thermal energy having small temperature fluctuation. As a result, by properly designing the heat capacity of the heat pool (20), the temperature rise to a temperature that causes deterioration of the performance of the BiTe-based thermoelectric element is substantially avoided. In addition,
In the configuration in which the bypass pipe (24) is provided in the exhaust pipe (30), when the temperature of the heat reservoir (20) exceeds the set value, the valve device (26) of the bypass pipe (24) opens, so that the exhaust pipe (30) is opened. ), The amount of heat energy supplied to the heat pool (20) is reduced, and the thermoelectric module
Unnecessary thermal energy is not supplied to (10), and overheating of the thermoelectric element is reliably prevented.

The weight of the heat pool can be designed in the following manner. For example, if the power generation output is 500 watts (1
In the case of a thermoelectric power generation system of 20 cal / sec), assuming that the conversion efficiency of the thermoelectric module is 10%, the amount of heat supplied per minute is 72 kcal. Double the amount of heat (144 kcal /
(144-72) in order to keep the temperature rise for 10 minutes within 50 ° C.
From kcal / min × 10 minutes１０50 ° C., 14.4 kcal with a heat capacity per unit temperature may be used as a heat reservoir.

Therefore, when aluminum is used as the material of the heat sink, the specific heat of aluminum is 0.25 cal /
Since it is K · g, the weight is 57.6 kg in order to satisfy the above set conditions. Note that aluminum has a high thermal conductivity of 230 W / m · K, and thus is suitable as a material for the heat reservoir. When using a heat transfer oil as a heat reservoir, if a commercially available heat transfer oil having a specific heat of 0.53 cal / K · g is used, to satisfy the above-mentioned set conditions, 27 kg is required inside the jacket.
May be used. Since the heat medium oil thermally expands by heating, it is necessary to provide a space capable of absorbing the expansion amount.

Under the above-mentioned design conditions, even if the heat quantity of 144 kcal / min is continuously supplied for 10 minutes, the temperature rise of the heat pool can be suppressed within 50 ° C. Further, in the configuration in which the bypass circuit is provided, the supply of the high-temperature exhaust gas can be controlled during the ten minutes.

Second Embodiment FIG. 4 shows a thermoelectric module (using a BiTe type thermoelectric element) having the structure shown in FIG.
1 shows an embodiment of a thermoelectric power generation system installed in an exhaust pipe through which a combustion exhaust gas of coal, gas, or the like flows. Stove
An exhaust pipe (30) through which the combustion exhaust gas flows is disposed in (33), and a thermoelectric module (10) is provided in the middle of the exhaust pipe, and the thermoelectric elements (12) and (13) are electrically connected in series. The base and end of the circuit are connected to an inverter (48).

The heat reservoir (20) is provided such that a jacket containing a heat transfer medium oil covers the outer periphery of the exhaust pipe. As the heat carrier oil, for example, silicone oil can be used. The specific heat of this heat transfer oil is about 0.53 cal / Kg.

As the cooling means, a heat absorbing member (45) through which cooling water flows inside the block having a hollow structure is used. The water in the tank (62) is supplied to the heat absorbing member (45) by the pump (58), and the temperature is increased by heat exchange with the thermoelectric elements (12) and (13) to become hot water. Application
After being used as the heat source of (60), it is returned to the tank (62). As another example of the application, warm water can be temporarily stored and used for cooking, washing, bathing, and the like.

The power generated by the thermoelectric module (10) is converted from DC power to AC power by an inverter (48), and a pump (58) for supplying cooling water, and a pump (58) for improving indoor heating efficiency. It is used as a power source for the fan (56) provided. Also in this embodiment, as in the first embodiment, the exhaust pipe is provided with a bypass pipe communicating with the upstream side and the downstream side of the heat reservoir, and the bypass pipe can be opened and closed according to the temperature of the exhaust gas. By disposing a suitable valve device, overheating of the thermoelectric element can be reliably prevented.

[0026]

As described above, according to the present invention, the thermoelectric element is always operated at the maximum power generation efficiency even under the condition where the temperature of the heat source fluctuates greatly, and deterioration due to overheating of the thermoelectric element is prevented. Can be prevented. INDUSTRIAL APPLICABILITY The present invention can be applied to a thermoelectric power generation system using combustion exhaust gas from an industrial furnace, an incinerator, a household stove, or the like, or exhaust gas from an automobile engine as a heat source. For example,
When the exhaust gas from a stove in a cold region is used as a heat source, the generated power is converted into AC power by an inverter, and water for cooling a thermoelectric module and for rotating a fan installed in a room to improve heating efficiency is improved. It can be used for driving a pump for feeding. The cooling water heated by the heat exchange with the thermoelectric module can be used as a heat source for underfloor heating, wall heating, and the like, and as water for cooking, washing, and bathing. When exhaust gas from an automobile engine is used as a heat source, the consumption of the battery can be prevented by using the generated power for charging the battery. Also, it can be directly supplied as necessary power to the load.

[Brief description of the drawings]

FIG. 1 is a partially exploded perspective view showing a configuration example in which a heat reservoir and a cooling means are provided in a thermoelectric module.

FIG. 2 is a partially exploded perspective view showing another configuration example in which a heat reservoir and a cooling means are provided in a thermoelectric module.

FIG. 3 is a schematic diagram illustrating one embodiment of the thermoelectric power generation system of the present invention.

FIG. 4 is a schematic diagram illustrating another embodiment of the thermoelectric power generation system of the present invention.

[Explanation of symbols]

 (10) Thermoelectric power generation system (20) Heat reservoir (22) Heat medium oil (24) Bypass pipe (30) Exhaust pipe (40) Heat radiating member (45) Heat absorbing member

Claims (6)

[Claims] 1. A high temperature exhaust gas having a large temperature fluctuation flows through one side of a thermoelectric module (10) in which a p-type thermoelectric element (12) and an n-type thermoelectric element (13) are electrically connected in series. Exhaust pipe
(30) and heat-exchangeable, and the other side of the thermoelectric module (10) is heat-exchangeable with respect to the cooling means, and the temperature generated in the thermoelectric elements (12) and (13) In a thermoelectric power generation system that generates power by the difference, a heat reservoir (20) between the exhaust pipe (30) and the thermoelectric module (10) to reduce the effect of fluctuations in the amount of heat supplied from the exhaust pipe (30) The thermoelectric power generation system characterized by having deployed. 2. The heat pool (20) has a specific heat of 0.2 cal / K · g.
The thermoelectric power generation system according to claim 1, wherein the thermoelectric power generation system is made of the above metal. 3. The thermoelectric power generation system according to claim 1, wherein the heat reservoir (20) contains a heat medium oil therein. 4. An exhaust pipe (30) is provided with a bypass pipe (24) communicating with an upstream side and a downstream side of the heat reservoir (20), and the bypass pipe can be opened and closed according to the temperature of exhaust gas. Valve device (2
The thermoelectric power generation system according to any one of claims 1 to 3, wherein (6) is provided. 5. The exhaust pipe (30) is an exhaust pipe through which exhaust gas from an automobile engine (32) flows, and the cooling means is a heat radiating member (40) having fins (42). The thermoelectric power generation system according to any one of the above. 6. The exhaust pipe (30) is an exhaust pipe through which combustion exhaust gas from the stove (33) flows, and the cooling means is a heat absorbing member (45) through which water flows, and passes through the heat absorbing member (45). The heated water is used for applications such as underfloor heating and wall heating (6
The thermoelectric power generation system according to any one of claims 1 to 4, wherein the thermoelectric power generation system is used in (0).