JP3080757B2 - Alkali metal thermoelectric combined cycle power generator - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combined alkali metal thermoelectric power generator constructed by combining an alkali metal thermoelectric power generator and a solid oxide fuel cell.

[0002]

2. Description of the Related Art As is well known, in order to construct a high-efficiency combined power generation system, a topping cycle using a high-temperature side heat source and a bottoming cycle using a temperature difference between the exhaust gas and a normal temperature level are generally used. A combination is performed. Also in the alkali metal power generation, since the power generation efficiency of this cycle alone is only about 30 to 40%, it is necessary to effectively use heat by combining with another cycle. FIG. 2 shows an example of a conventional combined alkali metal thermoelectric generator having a configuration in which the alkali metal thermoelectric generator is installed on the topping side and steam turbon is installed on the bottoming side.

[0003] Reference numeral 1 in the figure denotes an alkali metal thermoelectric generator. A sodium vapor condenser 2, an electromagnetic pump 3, and a sodium boiler 4 are sequentially connected to the power generator 1 in a loop. At the sodium boiler 4
The sodium 5 heated to about 1000 ° C. is guided to the power generator 1 to generate power. The sodium vapor after power generation is condensed and stored in the sodium vapor condenser 2.
After being liquefied and pressurized by the electromagnetic pump 3, it is again guided to the sodium boiler 4 and heated.

[0004] The sodium vapor condenser 2 includes:
An exhaust heat recovery boiler 6, a steam turbine 7, and a condenser 8 are sequentially connected in a loop. That is, for example, even if the alkali metal thermoelectric generator alone supplies sodium at 1000 ° C. to the high temperature side, only power generation efficiency of 30 to 40% can be obtained. Perform compounding. As an example, the steam supplied to the steam turbine 7 undergoes heat exchange in the sodium steam condenser 2, and is evaporated and preheated to, for example, 300 ° C., and then discharged from the sodium boiler 4 in the exhaust heat recovery boiler 6 (about 1%).
000 ° C.) and supplies the steam turbine 7. In addition, 9 in a figure shows a chimney.

[0005] Depending on the capacity of the whole system, when the steam turbine is used as a single-stage heat regeneration cycle in a medium- to large-capacity system, power generation efficiency of about 50% can be obtained by the combined power generation system. At this time, in order to supply steam having a certain amount of energy to the steam turbine 7 , the low-temperature side of the alkali metal thermoelectric generator 1 is raised from an ideal 200 ° C. level to a 300 ° C. level, and the output of the alkali metal thermoelectric generator 1 is increased. The power of the steam turbine 7 is increased at the expense of a small amount, so that the optimum power generation efficiency as the whole combined power generation device can be achieved.

[0006]

However, according to the conventional combined alkali metal thermoelectric generator, the power generation efficiency is at most about 50%. This is a steam turbine
7 , because the heat loss from the condenser 8 and the low-temperature side of the alkali metal thermoelectric generator cannot be sufficiently cooled, and there is a limit to further significant improvement in efficiency. Therefore, it can be said that it is ideal that combined power generation can be performed under the conditions where the performance of each of the topping and bombing cycles can be exhibited as much as possible.

The present invention has been made in view of the above circumstances, and it is possible to supply high-temperature sodium suitable for a high-temperature side temperature level of an alkali metal thermoelectric generator by using excess thermal energy of fuel cell exhaust gas. It is an object of the present invention to provide an alkali metal thermoelectric hybrid power generation device capable of high-efficiency power generation by cooling to a low-temperature side temperature level.

[0008]

According to the present invention, there is provided an alkali metal thermoelectric converter to which exhaust gas from a solid electrolyte fuel cell is supplied, and a method for generating steam generated by exhaust heat from the low temperature side of the alkali metal thermoelectric converter. And a supply means for supplying fuel to the battery for fuel reforming.

The present inventors have studied a combination with a solid electrolyte fuel cell which operates at a temperature of 1000 ° C. and has a high-temperature exhaust gas in order to constitute a high-efficiency power generation system. By burning the unreacted fuel component on the anode side from the solid oxide fuel cell, a fuel cell exhaust gas at 1000 ° C. to 1400 ° C. is obtained. On the other hand, the gas component containing the fuel supplied to the fuel cell is 700 ° C. to 800 ° C. It is necessary to raise the temperature to about ° C. Therefore, the thermal energy at the temperature level of the exhaust gas of the fuel cell and the temperature of the inlet gas becomes excessive, but this can be used at a temperature level (800 ° C. to 1200 ° C.) suitable for use as a high-temperature side heat source of the alkali metal thermoelectric generator. . The low temperature side of the alkali metal thermoelectric generator is 200
C. is desirable, but it is suitable for cooling by producing steam necessary for internal reforming of the solid oxide fuel cell. In this way, the thermal energy in the system can be effectively utilized at a level close to the ideal, and a high-efficiency power generation system is configured.

Further, since both the alkali metal thermoelectric generator and the solid electrolyte fuel cell are essentially direct power generation systems having no mechanical working parts, high efficiency light emission is basically obtained without being affected by the system capacity. It is possible. For this reason, medium and small capacities are particularly advantageous as compared with other power generation systems.

[0011]

The operation of the combined alkali metal thermoelectric conversion power generator according to the present invention is as follows.

Exhaust gas after combustion of an unreacted gas in a solid oxide fuel cell (SOFC) has a surplus of thermal energy corresponding to a temperature difference up to the gas temperature at the inlet of the fuel cell. This temperature level is an appropriate level for the high-temperature side of the alkali metal thermoelectric generator (800 ° C. to 1000 ° C.).

In order to keep the low-temperature side of the alkali metal thermoelectric generator at an appropriate temperature level of about 200 ° C., it is appropriate to supply water to produce steam, and this steam is generated inside the solid oxide fuel cell. Effectively used for reforming. The reaction at this time is as shown in the following formula. CH ₄ + nH ₂ O → 3H ₂ + CO + (n−1) H ₂ O

The combined alkali metal thermoelectric conversion power generation device according to the present invention is a combination of an alkali metal thermoelectric power generation device and a solid oxide fuel cell, and the thermal energy in the system is controlled at a temperature level suitable for the performance of each. Since it can be used effectively, a high efficiency power generation efficiency of 60% or more can be obtained. Further, since the alkali metal thermoelectric generator and the solid oxide fuel cell are separated via the heat exchanger, there is no need to consider the matching of the respective system pressures, and the combination is easy. Furthermore, all of the power generation devices are 10 kg / cm ² Since it is configured at a low pressure level less than the above, it is not subject to the high pressure gas regulation of each device, and the structure can be simplified. Furthermore, since both topping and bottoming generate power directly, high-efficiency power generation can be performed basically irrespective of system capacity.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, a combined alkali metal thermoelectric conversion power generation device according to an embodiment of the present invention will be described with reference to FIG.

Reference numeral 21 in the figure denotes an alkali metal thermoelectric generator. Here, the thermoelectric conversion efficiency of the power generation device 21 is:
As shown in FIG. 1, it largely depends on operating conditions represented by the high temperature side and the low temperature side. However, for example, when sodium is used as the working medium, the conversion efficiency does not change significantly at a low temperature side of 200 ° C. or less due to its characteristics. About 200 ° C. is appropriate. A sodium vapor condenser 22, an electromagnetic pump 23, a heat converter 24, and a sodium boiler 25 are sequentially connected to the power generator 21 in a loop.

A solid electrolyte fuel cell (hereinafter referred to as SOFC) 26 is connected to the sodium boiler 25. Here, this SOFC 26 operates at about 1000 ° C.
For example, a fuel at 700 ° C. to 800 ° C. (internally reformed with CH ₄ + nH ₂ O) is supplied to the anode side, and air is supplied to the cathode side. Since the SOFC 26 operates at a fuel utilization of, for example, 80%, a high-temperature gas of 1100 ° C. to 1200 ° C. is obtained by supplying and burning the battery exhaust gas including the unreacted portion of 20% to the sodium boiler 25. , Heat exchange with this, high temperature sodium of 1000 ℃ class
27 is supplied to the high temperature side of the alkali metal thermoelectric generator 21 at a suitable temperature level.

The sodium vapor that has contributed to the power generation by the alkali metal thermoelectric generator 21 is converted to a sodium vapor condenser.
The liquid is liquefied by heat exchange at 22, but is cooled with ice so that the low-temperature side has an appropriate level of about 200 ° C. so as to increase the output of the power generation device 21. As a result, the water supplied to the sodium vapor condenser 22 becomes, for example, water vapor of about 180 ° C., and most of the water can be supplied for the internal reforming of the SOFC 26, and the remainder can be supplied as heat output by the vapor. For example, assuming that the fuel of the SOFC 26 is the main component of CH ₄ and the steam / carbon ratio for steam internal reforming is 1.5, the ratio of the heat output obtained as surplus steam to the total power generation of the combined power generation system is about 1: It is about 9. In addition, sodium boiler 25
The exhaust gas cooled to 850 ° C. to 900 ° C. by heat exchange with sodium 27 at the above is subjected to heat exchange with the SOFC supply gas and sodium 27 supplied from the sodium boiler 25 to be effectively heat recovered and cooled to about 100 ° C. Discharged from chimney 28. As described above, according to the present combined alkali metal thermoelectric conversion power generation apparatus, the following effects can be obtained.

(1) High-efficiency power generation becomes possible by effectively using thermal energy at a level matching each device. Also, as shown in FIG. 4, by changing the fuel utilization rate of the SOFC 26, the ratio of the topping output / bottoming output, which is the heat energy ratio in the power generation device, can be changed to optimize and increase the efficiency of the power generation device. . For example, in this estimation, a fuel utilization rate of 80% is optimal, a power generation efficiency of about 48% for SOFC, a power generation efficiency of about 15% for alkali metal thermoelectric generator 21, and a total of about 63% for combined power generation ( High power generation efficiency).

(2) Further, in the combined power generation device, the respective cycles are mainly combined by performing heat conversion in the sodium boiler 25 and the sodium vapor condenser 22, and each cycle can be separated into an independent system. Therefore, being able to operate under appropriate conditions in each cycle is useful for configuring an optimum combined power generation device with high efficiency.

(3) Further, the alkali metal thermoelectric generator 21,
Since the SOFC26 also generates power directly, its capacity basically does not affect its performance. Therefore, each of these cycles is generally configured as a module, and the capacity is dealt with by increasing or decreasing the number of modules. The module performance is expected to be slightly lower than that of large-capacity ones due to the performance of auxiliary equipment that requires some power and the amount of heat dissipated. However, since there is almost no mechanical drive like a conventional steam turbine, it is small and medium. It is possible to exhibit high power generation efficiency even with capacity.

(4) The present combined alkali metal thermoelectric conversion power generation device of the present invention has a water vapor system having the highest level of 8 kg.
/ Cm ² abs, SOFC 26 at normal pressure, alkali metal thermoelectric generator 21 at 3.3 kg / cm ² abs and low pressure level operation, high pressure gas regulation (10Kg / cm ² Above), the structure can be simplified.

[0023]

As described above in detail, according to the present invention, the excess heat energy level of the exhaust gas of the fuel cell is 900 ° C.
800 ° C. to 110 suitable for the high-temperature side temperature level of the alkali metal thermoelectric generator by the heat energy of about 1200 ° C.
The steam of about 180 ° C. obtained by supplying high-temperature sodium at 0 ° C. and cooling to about 200 ° C. suitable for the low-temperature side of the alkali metal thermoelectric generator is mainly used for internal reforming of solid electrolyte fuel cells. When used effectively, it is possible to provide an alkali metal thermoelectric combined cycle device capable of high-efficiency power generation.

[Brief description of the drawings]

FIG. 1 1 A / cm ² FIG. 6 is a characteristic diagram showing a relationship between conversion efficiency and low-temperature side temperature at the time.

FIG. 2 is an explanatory view of a conventional combined alkali metal thermoelectric generator.

FIG. 3 is an explanatory view of the combined alkali metal thermoelectric generator according to one embodiment of the present invention.

FIG. 4 is a characteristic diagram showing a relationship between combined power generation system efficiency and a solid oxide fuel utilization unit.

[Explanation of symbols]

21 ... alkali metal thermoelectric generator, 22 ... sodium vapor condenser, 23 ... electromagnetic pump, 24 ... heat exchanger, 25 ... sodium boiler, 26 ... solid oxide fuel cell (SOFC),
27… sodium, 28… chimney.

Continued on the front page (72) Inventor Mitsuo Kansaka 5-717-1 Fukahori-cho, Nagasaki-shi, Nagasaki Mitsubishi Heavy Industries, Ltd. Nagasaki Research Laboratory (72) Inventor Hiroshi Tsukuda 5-717-1 Fukahori-cho, Nagasaki-shi, Nagasaki Mitsubishi (56) References JP-A-63-166158 (JP, A) JP-A-2-197274 (JP, A) JP-A-60-119305 (JP, A) JP-A-3-39386 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H02N 3/00

Claims (1)

(57) [Claims] 1. An alkali metal thermoelectric converter to which exhaust gas of a solid electrolyte fuel cell is supplied, and steam generated by exhaust heat from the low temperature side of the alkali metal thermoelectric converter is supplied to the solid electrolyte fuel cell for fuel reforming. And a supply unit that performs the operation.