JPH0993968A - Thermoelectric generator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermoelectric generator which can take out power with high fuel consumption efficiency by reducing uncombusted gas discharged to the outside. SOLUTION: Porous bodies 11 and 12 consisting of two pieces of thermoelectric heating media are arranged in the flow direction of combustion assisting gas, and space 13 for fuel feed is provided between the porous bodies 11 and 12. For the combustion assisting gas, the direction of flow is switched alternately between (1) and (2). A difference in temperature occurs inside the porous bodies 11 and 12 by the combustion of the fuel fed in the space 13, and the electromotive force caused by this temperature difference is taken out as power.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gas combustion type thermoelectric power generator using a porous body made of a thermoelectric power generation medium.

[0002]

2. Description of the Related Art When a temperature difference is applied to two contact points of different metals or semiconductors, an electromotive force is generated by the Seebeck effect. The direct conversion power generation device that uses this electromotive force to convert heat into electric energy has the advantages of a simple device structure, low noise, and small size. Is being actively conducted. But,
At present, sufficient materials including cost are not yet developed, and thermoelectric power generation has various advantages, but is only put to practical use in a special field. Under such circumstances, in Japanese Patent Laid-Open No. 6-302867,
A thermoelectric generator that burns a premixed fuel inside a porous body of a thermoelectric generator has been introduced. The amount of heat generated by the fuel inside the porous body is confined in a narrow region by the superadiabatic effect of the porous body, and is taken out as electric energy by the electrodes arranged on both end surfaces of the porous body.
In addition, K. NAKAMURA, R.M. ECHIGO "I
nst. J. Mass. Transfer "vol.3
6 no. 13 (1993), p3201, it is also reported that a temperature difference is efficiently created when the gas flow direction is switched at regular intervals.

[0003]

However, a combustion reaction in which a combustible gas is introduced from one end surface of the porous body toward the other end surface to burn inside the porous body and a combustion reaction in the opposite direction are alternately performed. In the method of repeating, in principle, it is inevitable to discharge a certain amount of unburned gas from the exhaust gas outlet when switching the gas flow direction. Emission of unburned gas becomes an obstacle to improve energy conversion efficiency in the process of developing and developing a thermoelectric generator as an effective power generation method in the future. In order to suppress the discharge of unburned gas, Japanese Patent Laid-Open No. 6-302867 introduces a method of supplying only fuel gas in the middle of the porous body. However, it is difficult to select the structural design, manufacture, supply position, etc. for that purpose, and the gas supply system also requires additional piping including a switching valve, which inevitably complicates the system.

In addition, the supply of the fuel gas is interrupted in the combustion zone at the center of the porous body until the fuel gas sent from the opposite direction reaches when the gas flow direction is switched. Since this state transitions to the combustion state again,
The combustion state in the combustion zone becomes unstable, depending on conditions such as the gas flow velocity. This tendency becomes more significant as the gas flow direction is switched more frequently and the volume between the valve controlling the flow and the gas combustion region in the porous body is larger. Therefore, it is not possible to freely set the time interval that places importance on efficiency, and the switching frequency is restricted. In addition, as the combustion state becomes unstable, it becomes difficult to control the temperature gradient in order to stabilize it. The present invention has been devised to solve such a problem, and by separately supplying the fuel to the central portion of the divided porous body, the fuel utilization efficiency is high and the electric power can be efficiently extracted. An object is to provide a thermoelectric generator.

[0005]

In order to achieve the object, the thermoelectric power generator of the present invention has two thermoelectric power generation media arranged in series along the flow direction of the auxiliary gas, and sandwiched between these thermoelectric power generation media. And a means for alternately switching the flow direction of the auxiliary combustion gas at regular intervals, in the flow direction of the gas inside the porous body generated by the combustion of the fuel fed into the space part. It is characterized in that electric power is taken out from the temperature difference along the line. As the thermoelectric power generation medium, the thermoelectric power generation medium proposed by the present inventors in Japanese Patent Application No. 7-78262 can be used. This thermoelectric power generation medium has a structure in which a plurality of two types of metal plates or metal foils having a thermocouple relationship are alternately connected to each other so that a large number of thermocouples connected in series are formed and stacked in a zigzag shape. Hold. Air, oxygen, oxygen-enriched air, or the like is used as the supporting gas. As the fuel, various gaseous fuels and vaporized or atomized liquid fuels are used, including hydrocarbon-based gas fuels.

[0006]

The present inventors have investigated and studied from various viewpoints a thermoelectric power generator that burns fuel inside the porous body to extract electric power. As a result, the cause of the required steep temperature gradient is It is not that the combustible gas burns, but that a large amount of gas passes while transferring heat from the low temperature side to the high temperature side inside the porous body, and the fuel burned inside the porous body It was found that gas is a very small amount of about 1% with respect to air. Therefore, the porous body made of a thermoelectric power generation medium is divided into two and arranged in series along the gas flow, and a space for introducing the fuel is provided in the middle part of the porous body, and only the auxiliary combustion gas such as air is provided. The method of alternately flowing from both sides of the porous body was adopted. That is, as shown in FIG.
A pair of porous bodies 11 and 12 are housed inside
A space 13 is provided between 1 and 12. The auxiliary combustion gas is supplied from the supply / discharge pipe 21 to the inside of the porous body 11 or the other supply / discharge pipe 2
It is sent into the inside of the porous body 12 from 2. The fuel is supplied from the fuel introduction pipe 23 opened in the space 13 to the porous bodies 11 and 12
Sent into the space 13 between the porous body 11 and 12
It is burned by the supporting gas from. The combustion exhaust gas passes through the inside of the other porous body 12 or 11 and is discharged from the supply / discharge pipe 22 or 21.

By separating the fuel and auxiliary gas supply paths in this manner, the combustion zone is limited to a narrow area inside the space 13 and the porous bodies 11 and 12 near the space 13. That is, when the auxiliary combustion gas is in the flow direction, the auxiliary combustion gas that has become hot due to passing through the inside of the porous body 11 comes into contact with the fuel in the space portion 13, so that the fuel has a sufficiently high temperature and a sufficient amount. Combustion reaction occurs instantly with the supporting gas. As a result, a temperature distribution having a steep gradient is formed inside the porous bodies 11 and 12 as shown in FIG. Further, the oxygen concentration distribution along the flow direction sharply decreases with the space 13 as a boundary, as shown in FIG. On the other hand, combustion waste gas such as CO, CO ₂ and H ₂ O rapidly increases at the space 13. That is,
Almost all the fuel sent in is burned in the space 13,
The remaining unburned portion burns inside the porous body 12 adjacent to the space portion 13. Therefore, the fed fuel is not discharged without being burnt.

When the flow direction of the auxiliary combustion gas is switched from to, the auxiliary combustion gas used for combustion returns from the porous body 12 to the porous body 11. However, in the stable state, since the auxiliary combustion gas is in excess, the amount of oxygen necessary and sufficient for combustion is secured, and the combustion is not interrupted by switching the flow direction. In this respect, in the conventional method, as shown in FIG. 1D, the combustion waste gas is discarded from the other porous body 12, and the fuel is supplied until the combustion gas newly supplied from the supply / discharge pipe 22 reaches. There is a period when it is not supplied. On the other hand, in the present invention, even the combustion-assisting gas returned from the porous body 12 to the porous body 11 has a sufficient oxygen concentration, so that the fuel fed into the space 13 can be continuously burned. Moreover, since the fuel concentration is lean and small, even if the fuel is supplied to the space portion 13 without preheating, the temperature does not decrease and the stable combustion zone is maintained.

As described above, the thermoelectric generator according to the present invention does not discharge the unburned exhaust gas to the outside of the system at the time of switching the flow direction unlike the conventional method, and efficiently burns the fuel. Further, since the stable combustion state is maintained without interruption of fuel supply, electric energy can be extracted with high efficiency. Further, when a metal mesh, an assembly of metal wires, or the like is arranged in the space 13, the combustion efficiency is further improved. The metal mesh or the aggregate of metal wires used at this time may be arranged as a single body in the space 13, but it is preferably arranged opposite to the porous body 11 or 12 facing the space 13. As a result, the fuel sent out from the fuel introduction pipe 23 comes into contact with the metal mesh or the metal wire before entering the hole of the porous body 11 or 12, and the combustion efficiency is improved. In the thermoelectric power generator of the present invention, the time interval of flow direction switching can be shortened to the time t when all the oxygen-depleted air is discharged. This time t is
When the volume of the combustor 10 is V and the gas flow rate is F, t
= V / F Therefore, the optimum time can be set with a high degree of freedom. In this respect, in the conventional power generation system, time t
If the time interval of flow direction switching is shortened to (= V / F), the fuel gas utilization efficiency drops to about 50%.

[0010]

EXAMPLE As the thermoelectric power generation medium, the one proposed by the present inventors in Japanese Patent Application No. 7-78262 was used. That is, 35 mm × alumel and chromel with a plate thickness of 50 μm
Cut into 40 mm strips, 31 strips of alumel and chromel are alternately stacked, and both ends are spot-welded alternately. Two blocks having a width of 40 mm, a thickness of 40 mm, and a length of 35 mm in which pairs were connected in series were prepared. This block was heat-oxidized for 45 minutes in the atmosphere of 1000 ° C.
An insulating film of chromium oxide was formed on the chromel surface. Two
As shown in FIG. 2, one thermoelectric power generation medium is used as the porous body 11,1.
No. 2 was housed in the combustor casing 10, and a space 13 having a space of 0.5 cm was provided between the porous bodies 11 and 12. And
In the combustor casing 10, the extraction electrodes 31, 31, ... Are set so as to be on the low temperature side.

Air was supplied from one of the supply / discharge pipes 21 at a flow rate of 10 liters / minute, and fuel gas was sent from the fuel introduction pipe 23 to the space 13 at a flow rate of about 3% of the air supply amount to ignite. Due to combustion, the porous bodies 11 and 12 near the space portion 13
Became red and the temperatures of the porous bodies 11 and 12 became sufficiently high, the flow rate of the fuel gas was reduced to about 1% of the air feed amount, and the air feed direction was switched. Then 5
Stable combustion was achieved by alternately switching the feeding directions at intervals of about 10 seconds. In the stable combustion state, a temperature difference of about 900 K could be obtained as shown in FIG. 3 showing the temperature distribution. As a result, the terminal open circuit voltage E is obtained when the extraction electrodes 31, 31 of both porous bodies 11, 12 are connected in series.
= 2V, internal resistance during operation R = 1.6Ω, and the output power P at this time was 625 mW from P = E ² / 4R.

In this embodiment, the porous bodies 11, 1 having a cross section of 4 cm × 4 cm and a length of 3.5 cm in the gas flow direction.
2 is used. A porous body 1 with a small cross-sectional area like this
Since the fuel cells 1 and 12 are used, the fuel introduction pipe 23 may be simply exposed to the space 13. However, when the power generation capacity is improved by using a porous body having a large cross section, the fuel is fed into the space with a uniform concentration distribution, and therefore a metal tube having a large number of nozzle holes is arranged in the space 13. It is preferable. In addition, when arranging the air-permeable porous body in which the metal mesh and the metal thin wires are collected in a block shape in the space 13,
The combustion reaction is made uniform, and a more stable combustion state is obtained. Some metal meshes and metal wires have a catalytic action depending on the type, and the entire region of the space 13 and the entire cross section of the porous bodies 11 and 12 are efficiently used for combustion, and the temperature distribution is made uniform.

[0013]

As described above, in the thermoelectric power generator of the present invention, two porous bodies made of a thermoelectric power generation medium are arranged in series along the flow direction of combustion gas, and the fuel is placed between the porous bodies. It forms a space for supply. Then, the supply systems of the auxiliary combustion gas and the fuel are separated, the auxiliary combustion gas is caused to flow from the one end surface of the porous body to the other end surface or in the opposite direction, and the fuel fed into the space between the porous bodies is burned. When the fuel thus fed is burned, the fuel utilization efficiency is higher than in the conventional method, a stable combustion zone is formed, and electric energy can be extracted with high efficiency. Moreover, since the fuel gas supply system has a simple structure, maintenance and inspection is easy.

[Brief description of drawings]

FIG. 1 schematically shows a thermoelectric generator according to the present invention and its performance, showing the structure of the thermoelectric generator (a), the temperature distribution inside the porous body during fuel combustion (b), the flow direction of the combustion gas Concentration distribution of oxygen and combustion waste gas (c) and fuel gas distribution along the graph comparing with the conventional method (d)

FIG. 2 is a thermoelectric generator used in Examples of the present invention.

FIG. 3 Temperature distribution obtained using the same device

[Explanation of symbols]

10: Combustor housing 11, 12: Porous body (thermoelectric power generation medium) 13: Space portion 21, 22: Supply / discharge pipe 23: Fuel introduction pipe 31: Extraction electrode

Claims (3)

[Claims] 1. A thermoelectric power generation medium arranged in series along the flow direction of the auxiliary combustion gas, a space for fuel feeding sandwiched between these thermoelectric power generation media, and a flow direction of the auxiliary combustion gas for a predetermined time. A thermoelectric power generation device that includes means for switching each of them alternately, and extracts electric power from the temperature difference along the flow direction of the gas inside the porous body generated by the combustion of the fuel fed into the space. 2. A thermoelectric power generation medium in which a plurality of two kinds of metal plates or metal foils having a thermocouple relationship are alternately connected to each other so as to form a large number of thermocouples connected in series and stacked in a zigzag shape. The thermoelectric generator according to claim 1, wherein the thermoelectric generator is used. 3. The thermoelectric generator according to claim 1, wherein a single or a plurality of air-permeable porous bodies made of a metal mesh, an assembly of metal wires or the like are provided in the space.