JPH08167419A - Fuel cell power plant and its exhaust device - Google Patents

Abstract

PURPOSE: To reduce the number of delivery ports from a power plant by exhausting air by mixing exhaust gas proper to a system and discharge air from ventilating air of respective cells. CONSTITUTION: A change in generating full pressure of an exhaust fan 4 is detected by a micropressure sensor 6 installed at a control point, and this detecting pressure is converted into a control signal corresponding to a difference between pressure preset by being inputted to a controller 7 and detecting pressure. This control signal is impressed on an inverter 8, and supply electric power to an exhaust fan driving motor 9 is changed in a frequency of AC output corresponding to the control signal. As a result, the number of generating times of surplus wind pressure Hs 2 is avoided, and performance of the exhaust fan 4 can be reduced to a performance level corresponding to a loss in weight of mixed gas C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fuel cell power plant, in which a combustible gas reactor and energizing devices such as a pump driving motor are arranged in two or more compartments provided in an enclosure, and a combustible gas and an energizing member are energized. In order to avoid contact with equipment, each compartment is equipped with an independent ventilation system to take in clean outside air into the enclosure to ventilate the compartment, while at the same time stimulating air and fuel cell-specific exhaust gas. The present invention relates to a fuel cell power plant that discharges to the outside as a mixed gas with.

[0002]

2. Description of the Related Art Exhaust gas from a fuel cell power plant is divided into several compartments that are specific to power generation and the fuel cell power plant, and are ventilated by independent ventilation systems. In this case, it is configured to avoid contact between combustible gas and energized equipment.

In an outdoor plant, it is desirable that each exhaust gas is discharged from an appropriate discharge point,
For this reason, many discharge ports were provided. When the fuel cell power plant is installed indoors, the exhaust duct of the power plant is installed over a long distance in the indoor space for the purpose of exhausting ventilation air inside the power plant inner wall room and exhaust gas specific to the fuel cell to the outside. To be done.

In this case, the pressure loss in the exhaust duct varies depending on the equipment conditions such as the length of the exhaust duct, the cross-sectional size, etc., and the exhaust gas amount. It is necessary to install a ventilation fan in the middle of the exhaust duct in order to apply a pressure commensurate with this pressure loss.

[0005]

However, it is desirable to combine a large number of outlets into a small number of outlets.
In particular, in a plant installed indoors, there has been a demand to reduce the number of exhaust ducts for various exhaust gases collectively in order to exhaust the plant exhaust gas to the outside.

Further, the exhaust gas peculiar to power generation contains water, and while moving the exhaust duct, it may be condensed as water droplets on the wall surface of the duct, which may corrode the duct, thus preventing or reducing the generation of water droplets. There was a request to do so.

In the case of outdoor installation, condensed water droplets become white smoke in the air, which catches the eye, and there has been a demand for reducing the white smoke. The present invention has been made to meet the above demands, and it is possible to reduce the number of outlets from the power plant, and the vapor partial pressure in the exhaust gas peculiar to the power plant decreases due to mixing, and in the case of indoor installation Reduces the condensation of moisture in the exhaust duct, prevents the exhaust duct from corroding, and when installed outdoors, reduces the vapor partial pressure in the exhaust gas peculiar to the fuel cell due to mixing, reducing moisture condensation and reducing whiteness. An object of the present invention is to provide a fuel cell power plant capable of reducing the amount of smoke generation and an exhaust system thereof.

[0008]

In order to achieve the above object, the present invention comprises a fuel cell power plant and its exhaust system by the following means. (1) It is configured as a power generation system using a fuel cell main body, a combustible gas reaction device, a heat exchanger, a pump, a proofer, etc.,
In addition, the energizing device driven by the electric motor such as the pump and the blower and the device that handles the combustible gas such as the battery body and the reactor are separated by a partition wall to form two or more compartments. In the fuel cell power plant in which each compartment is equipped with an independent ventilation system to supply external clean air to independently ventilate each compartment, Exhaust means for mixing and exhausting the exhaust gas specific to the fuel cell power generation system discharged from the reactor and at least one of the exhaust air from the ventilation air in each compartment is provided. (2) In the fuel cell power plant according to the above (1), an exhaust duct of the power plant for exhausting a mixed gas of air for ventilation of the power plant inner wall chamber and exhaust gas specific to the fuel cell to the outside is attached, and this exhaust duct Configure an exhaust device with an exhaust fan installed midway. (3) In the exhaust device for a fuel cell power plant described in (2) above, a pressure sensor for detecting the exhaust fan suction pressure and a detection signal corresponding to the suction pressure detected by this pressure sensor are input, and this detection is performed. A controller that outputs a control signal obtained based on the signal, and an inverter that controls the rotation speed of the exhaust fan drive motor by changing the AC output frequency based on the control signal input from the controller. And a control function for controlling the exhaust fan so that the suction side pressure is substantially constant. (4) In the exhaust system for a fuel cell power plant described in (2) above, pressure sensors are attached to the discharge side and the suction side of the exhaust fan, and the detection values of both pressure sensors are used to determine the exhaust fan's differential pressure from the pressure difference between the two. Calculate the total generated pressure and compare it with the upper and lower limits of the specified range of the exhaust fan generated total pressure for the mixed gas flow rate during rated operation of the target fuel cell power plant and the mixed gas flow rate for the mixed gas flow rate during power plant partial load operation. Limiter is installed to provide a control function to control the exhaust fan drive motor speed so that the exhaust fan speed is minimized at the lower limit of the total generated pressure, and to control the exhaust fan suction side pressure at a constant level. . (5) In the exhaust device for a fuel cell power plant described in (2) above, focusing on the fact that the wind pressure generated by the exhaust fan is proportional to the square of the fan drive motor speed, the pressure detected by the micro pressure sensor. The signal is converted into a signal converted into the number of revolutions and inputted to the inverter, and the control function of controlling the exhaust fan by securing the number of revolutions of the drive motor corresponding to the AC output frequency from the inverter is provided. (6) In the exhaust device for a fuel cell power plant described in (2) above, focusing on the fact that the flow rate of the exhaust gas mixture from the fuel cell power plant changes corresponding to the operating load of the fuel cell power plant, the operating load The relationship between the conditions and the total pressure generated by the exhaust fan is confirmed and stored in advance by simulation, and the load signal of the fuel cell power plant is input to the inverter, and the drive motor speed corresponds to the AC output frequency from this inverter. It has a control function to control the exhaust fan.

[0009]

In the fuel cell power plant configured as described above in (1), the exhaust gas specific to the fuel cell power generation system and at least one of the exhaust air from the ventilation air in each compartment are mixed and exhausted. As a result, the number of discharge ports from the power plant can be reduced.

Further, in the exhaust device of the fuel cell power plant having the above-mentioned configuration (2), the vapor partial pressure in the exhaust gas inherently decreases due to the mixing, and in the case of indoor installation, the vapor partial pressure in the exhaust duct is reduced. Water condensation can be reduced and exhaust duct corrosion can be prevented. Further, in the case of outdoor installation, the vapor partial pressure in the exhaust gas peculiar to the fuel cell is lowered by mixing, water condensation can be reduced, and it is effective in reducing white smoke.

In the exhaust system of the fuel cell power plant having the above-mentioned structure (3), the occurrence of an unstable phenomenon of the exhaust system such as an increase in the negative pressure and an expansion of the negative pressure region due to the generation of excess wind pressure of the exhaust fan is prevented. For this purpose, by providing a control point at one point of the exhaust fan suction side flow path and controlling the exhaust fan performance level so as to maintain the pressure at this control point constant, the negative pressure upstream from this control point is controlled. It is possible to prevent the increase and the negative pressure region from spreading.

In the exhaust system for a fuel cell power plant having the above-mentioned configurations (4) and (5), it is noted that the exhaust gas flow rate peculiar to the fuel cell changes depending on the load operating conditions of the fuel cell power plant. Then, the exhaust gas pressure at the position upstream of the mixing point of the exhaust gas peculiar to the fuel cell with the ventilation air in the compartment is taken out as a detection signal, and the exhaust fan performance level is controlled through the rotation speed control to control the exhaust gas pressure. It becomes possible to maintain it at a substantially constant level.

In the exhaust system of the fuel cell power plant having the above-mentioned configuration (6), the operating load signal of the fuel cell power plant is used as the control signal of the power plant exhaust system as in the case of the above (3). As a result, the control speed can be made faster than the control operation that follows changes in the flow rate of the exhaust gas mixture.

[0014]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 conceptually shows a case where the fuel cell power plant according to the first embodiment of the present invention is installed especially indoors.

In FIG. 1, a combustible gas reactor storage compartment, an energization equipment storage compartment and the like are formed inside the power plant enclosure 1. In addition, power plant
An independent duct provided on the ceiling or outside of the enclosure 1 is connected to the exhaust duct 2 for the purpose of discharging a mixed gas of ventilation air in the compartment and exhaust gas specific to the fuel cell.

The exhaust duct 2 is attached to the indoor space over a long distance and is guided to the exhaust port 3. Furthermore, FIG.
In the above, the flow of the ventilation air for the compartment and the exhaust gas specific to the fuel cell, which are partitioned by the partition wall 30, are schematically represented by A and B, respectively. The ventilation air A for the compartment and the exhaust gas B peculiar to the fuel cell become a mixed gas C at the ceiling of the power plant enclosure 1 and are discharged to the outside from the exhaust port 3 via the inside of the exhaust duct 2. ing.

An exhaust fan 4 is installed in the upstream portion of the exhaust duct 2 for the purpose of applying a pressure corresponding to the pressure loss of the mixed gas C inside the duct. This exhaust fan 4
The performance of is designed so as to give an air volume corresponding to the maximum flow rate of the mixed gas C and a wind pressure higher than the pressure loss inside the exhaust duct 2 when exhausting this air volume.

On the other hand, the flow rate of the ventilation air A in the compartment is considered to be almost constant, but the flow rate of the exhaust gas B peculiar to the fuel cell increases or decreases in accordance with the fluctuation of the load increase or decrease of the fuel cell power plant. The flow rate also changes according to the operating load of the fuel cell. Therefore, the operating point of the exhaust fan 4 also changes, and the surplus energy of the exhaust fan 4 is consumed on the suction side of the exhaust fan 4 with respect to the decrease in pressure loss due to the decrease in the mixed gas flow rate. This causes problems such as increase in negative pressure on the suction side and expansion of negative pressure area.

FIG. 2 schematically shows the performance curve of the exhaust fan 4 and changes in operating points. That is, in the coordinates where the horizontal axis is the air volume Q and the vertical axis is the wind pressure H,
When the performance curve of the exhaust fan 4 is represented by X and the resistance curve of the internal flow path of the exhaust duct 2 is represented by Y, the intersection O1 of the two curves X and Y is the operating point of the exhaust fan 4.

Operating point O1 of the exhaust fan 4 in FIG.
Indicates a case where the flow rate of the mixed gas C during the maximum load operation of the fuel cell power plant is maximum. Further, as the load of the fuel cell power plant decreases, the flow rate of the mixed gas C also decreases from Q1 to Q2, and the operating point of the exhaust fan 4 moves from O1 to O2.

In this case, as the flow rate of the mixed gas C decreases, the predetermined total pressure loss inside the exhaust duct 2 changes from HT1 to HT2, but the total pressure generated by the exhaust fan 4 HT2.
Of these, HS2 becomes an excess and is consumed on the suction side of the exhaust fan 4, increasing the negative pressure of the suction side pressure of the exhaust fan 4 and causing a problem of expanding the negative pressure region. .

Therefore, for the purpose of avoiding the negative pressure increase and the negative pressure region expansion phenomenon on the suction side of the exhaust fan 4 due to the surplus performance of the exhaust fan 4 due to the fluctuation (reduction) of the flow rate of the mixed gas C, FIG. An exhaust device 5 having the exhaust fan performance and control function as shown is installed.

Here, the system configuration of the fuel cell power plant exhaust system 5 is shown in FIG. That is, in FIG. 3, the low pressure sensor 6 attached to the suction side of the exhaust fan 4,
A controller 7 that outputs a control signal based on the pressure detection signal detected by the slight pressure sensor 6, an inverter 8 controlled by the control signal output by the controller 7, and an exhaust fan drive operated by the inverter 7. The motor 9 constitutes the main equipment.

Next, the operation of the fuel cell power plant configured as described above will be described. As shown in FIGS. 1 and 2, when the flow rate of the mixed gas C in the exhaust duct 2 changes (decreases) from Q1 to Q2 due to load fluctuations of the fuel cell power plant, etc., the operating point of the exhaust fan 4 Moves from O1 to O2.

In this case, the total pressure generated by the exhaust fan 4 is H
Although it changes from T1 to HT2, the change situation of the generated total pressure is schematically shown in FIG. In FIG.
The horizontal axis shows the flow path of the mixed gas before and after the exhaust fan 4, and the vertical axis shows the wind pressure generated by the exhaust fan 4.

In FIG. 4, the discharge pressure and the suction pressure with respect to the total generated pressure HT1 are shown by Hd1 and Hs1, respectively, and the pressure at the control point X on the suction side of the exhaust fan 4 is shown by Hc1.

The control point X on the suction side of the exhaust fan 4
The pressure Hc1 at is detected by the slight pressure sensor 6, and the performance level of the exhaust fan 4 is tried to be tracked according to the situation change in order to keep the pressure Hc1 constant.
That is, the flow rate of the exhaust gas mixture in the exhaust duct 2 is Q rather than Q1.
The total pressure generated by the exhaust fan 4 also changes to H
Although it changes from T1 to HT2, this change in generated total pressure is detected by the slight pressure sensor 6 attached to the control point X.

As the total pressure generated by the exhaust fan 4 changes to HT2, the pressure at the control point X changes from Hc1 to Hc.
Although it changes to 2, the detection signal Hc2 detected by the slight pressure sensor 6 is input to the controller 7.

The controller 7 converts the control signal into a control signal corresponding to the difference (Hc1-Hc2) between the preset pressure and the detected pressure input from the slight pressure sensor 6, and supplies the control signal to the inverter 8.

In the inverter 8, the frequency of the AC output corresponding to the input control signal is converted to change the power supply to the exhaust fan drive motor 9. Since the exhaust fan drive motor 9 is AC rated, it changes from the initial rotation speed N1 to a rotation speed N2 matching the power supply frequency supplied from the inverter 8.

As the number of revolutions of the exhaust fan drive motor 9 changes (N1 → N2), the operating point of the exhaust fan 4 shifts from O2 to O22, and the performance of the exhaust fan 4 becomes excessive. The performance will be reduced by Hs2.

That is, the flow rate of the exhaust gas mixture C changes from Q1 to Q2 in accordance with the fluctuation of the operating load of the fuel cell power plant.
Despite the fact that the operating point of the exhaust fan 4 changes from O1 to O2 by changing (decreasing) to 1, the rotation speed of the exhaust fan 4 is controlled through the above-described control operation of the exhaust device. By changing from N1 to N2, it becomes possible to shift the operating point of the exhaust fan 4 from O1 to O2.

As a result, the pressure Hc1 at the control point X on the suction side of the exhaust fan 4 can be controlled to be substantially constant, and the negative pressure increase on the suction side and the negative pressure region expansion phenomenon can be avoided.

As described above, in this embodiment, the change in the total pressure generated by the exhaust fan 4 is detected by the slight pressure sensor 6 attached to the control point X, and this detected pressure is input to the controller 7 to set a preset pressure. To a control signal corresponding to the difference (Hc1−Hc2) between the detected pressure and the detected pressure, and apply this to the inverter 8 to change the power supply to the exhaust fan drive motor 9 at the frequency of the AC output corresponding to the control signal. Therefore, the following effects can be obtained. (1) Although the operating point of the exhaust fan 4 should originally shift from O1 to O2 on the performance curve due to the decrease in the flow rate of the exhaust gas mixture C, the actual operating point is It becomes O22. This makes it possible to avoid the number of times of generation of the excess wind pressure Hs2 and reduce the performance of the exhaust fan 4 to a performance level commensurate with the reduction of the mixed gas C. (2) In the pressure distribution with respect to the operating point on the performance curve of the exhaust fan 4 schematically shown in FIG. 4, the operating point is 0.
When the flow rate is 1, the flow rate Q1 of the mixed gas C is the maximum, and the fan characteristic with respect to the rotation speed N1 of the exhaust fan 4 is shown by the curve U. Therefore, no excess wind pressure is generated with respect to the total generated pressure HT1 of the exhaust fan 4.

When exhaust control is not performed, the operating operating point O2, the mixed gas flow rate Q2, the exhaust fan rotation speed N1.
It is assumed that the excessive wind pressure Hs2 is generated under the operating condition of the curve V as shown by the curve V, and as a result, the negative pressure increase and the negative pressure region expansion phenomenon on the suction side of the exhaust fan 4 are caused.

Further, as a result of adding the above-mentioned exhaust fan performance control function under the operating conditions of the operation operating point 022, the mixed gas flow rate Q2, and the exhaust fan rotation speed N2, the rotation speed is N.
By decreasing as 1 → N2, the performance of the exhaust fan 4 decreases to a level commensurate with the reduction of the mixed gas as shown by the curve W, so that the excess wind pressure Hs2 disappears and the negative pressure on the suction side of the exhaust fan 4 is reduced. It is possible to prevent the increase and the negative pressure region expansion phenomenon from occurring.

FIG. 5 schematically shows a situation in which a limiter is installed on the performance curve of the exhaust fan 4 for explaining the second embodiment of the present invention. In the second embodiment, paying attention to the fact that the mixed gas flow rate at the time of rated load operation of the fuel cell power plant is maximum and that the mixed gas flow rate is minimum when only ventilation air flows, the maximum and minimum flow rates are set. A limiter is installed for the discharge pressure of the exhaust fan at this time, and the exhaust fan rotation speed is maximized at the upper limit of the discharge pressure, and the exhaust fan rotation speed is controlled at the lower limit of the discharge pressure. In this case, it can be realized by providing a limiter circuit in the controller 7 shown in FIG. 3 and inputting the detected pressure detected by the slight pressure sensor to this limiter circuit to obtain the same control signal as described above.

FIG. 6 conceptually shows a case where the fuel cell power plant according to the third embodiment of the present invention is installed indoors in particular. The same parts as those in FIG. The description is omitted.

In the third embodiment, paying attention to the fact that the flow rate of exhaust gas peculiar to the fuel cell changes depending on the operating load condition of the fuel cell power plant, a slight increase in the position upstream of the mixing point with the ventilation air in the compartment is performed. A pressure sensor 6 is attached to detect the exhaust gas pressure peculiar to the fuel cell and to maintain the exhaust gas pressure peculiar to the fuel cell constant through the control function of the exhaust device.

That is, as shown in FIG. 6, the exhaust gas pressure peculiar to the fuel cell in the power plant enclosure 1 is detected as a pressure (HB) control point by a micro pressure sensor 6 not shown, and the detection signal is input to the controller. The number of revolutions of the exhaust fan 4 is controlled.

FIG. 7 is a diagram for explaining the control of the fuel cell power plant according to the fourth embodiment of the present invention.
In the fourth embodiment, the relationship between the operating load of the fuel cell power plant and the mixed gas flow rate is confirmed in advance by simulation, and the operating load signal of the power plant is directly input to the inverter to determine the AC output frequency of the inverter. The number of rotations of the exhaust fan motor is changed to control it.

That is, the power plant loads P1, P2, ...
... The relationship between Pi and the flow rate of the mixed gas is previously obtained by simulation, and the exhaust fan motor drive rotation speed N1,
N2 ... Controls Ni.

[0043]

According to the exhaust system for a fuel cell power plant according to the present invention described above, the following effects can be obtained. (1) The number of discharge ports from the power plant can be reduced. Further, the vapor partial pressure in the exhaust gas inherently decreases due to mixing, and in the case of indoor installation, water condensation in the exhaust duct can be reduced and corrosion of the exhaust duct can be prevented. Also,
In the case of outdoor installation, the partial pressure of vapor in the exhaust gas peculiar to the fuel cell is reduced by mixing, water condensation can be reduced, and it is effective in reducing white smoke. (2) When the flow rate of the exhaust gas mixture changes (decreases) due to changes in the operating load of the fuel cell power plant,
Originally, the operating point of the exhaust fan should change to the position of the specified flow rate on the performance curve, but the actual operation is performed by the exhaust fan rotation speed control function configured by combining the low pressure sensor, the inverter and the exhaust fan drive motor. It becomes possible to shift the operating point to the point (022) at which the generation of excess wind pressure (Hs2) is avoided. That is, by reducing the performance of the exhaust fan to a performance level commensurate with the reduction of the mixed gas, it becomes possible to avoid the generation of excess wind pressure of the exhaust fan. (3) A control point is provided at one point of the exhaust fan suction side flow path for the purpose of preventing the occurrence of an instability phenomenon of the exhaust system such as an increase in the negative pressure and an expansion of the negative pressure area due to the generation of excess wind pressure of the exhaust fan. By controlling the exhaust fan performance level so as to maintain the pressure at constant, it is possible to prevent the negative pressure increase upstream of the control point and the negative pressure region from spreading. (4) Exhaust gas pressure at a position upstream of the mixing point of the exhaust gas specific to the fuel cell with the ventilation air in the compartment, paying attention to the fact that the flow rate of the exhaust gas specific to the fuel cell changes depending on the load operating conditions of the fuel cell power plant. It is possible to maintain the exhaust gas pressure at a substantially constant level by taking out as a detection signal and controlling the exhaust fan performance level through rotation speed control. (5) As in the case of (3) above, by using the operation load signal of the fuel cell power plant as the control signal of the power plant exhaust device, the control speed is made faster than the control operation that follows the change in the flow rate of the exhaust gas mixture. Will also be possible.

[Brief description of drawings]

FIG. 1 is a configuration diagram schematically showing a first embodiment of an exhaust device for a fuel cell power plant according to the present invention.

FIG. 2 is a curve diagram schematically showing a performance curve of an exhaust fan and a change situation of a driving operation point in the embodiment.

FIG. 3 is a configuration diagram showing an exhaust fan control system in the embodiment.

FIG. 4 is a curve diagram schematically showing how the total pressure generated by the exhaust fan changes in the embodiment.

FIG. 5 is a curve diagram schematically showing a situation in which a limiter is installed on a performance curve of an exhaust fan for explaining a second embodiment of the present invention.

FIG. 6 is a curve diagram of an exhaust gas flow rate by an exhaust fan and a configuration for explaining a third embodiment of the present invention.

FIG. 7 is a curve diagram of an exhaust gas flow rate by an exhaust fan and a configuration for explaining a fourth embodiment of the present invention.

[Explanation of symbols]

1 ... Power plant enclosure, 2 ... Exhaust duct, 3 ... Exhaust port, 4 ... Exhaust fan, 30 ... Partition wall, 5 ... Exhaust device, 6 ... Micro pressure sensor, 7 ... Controller, 8 …… Inverter, 9 …… Drive motor.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Mitsuo Sato 1-1-1, Shibaura, Minato-ku, Tokyo Inside Toshiba Headquarters office (72) Inventor Kiyoshi Hoshino 3-7-1 Nishishinbashi, Minato-ku, Tokyo Inside Toshiba Plant Construction Co., Ltd. (72) Inventor Naoki Shiobara 3-7-1, Nishishimbashi, Minato-ku, Tokyo Inside Toshiba Plant Construction Co., Ltd.

Claims (6)

[Claims] 1. A current-carrying device configured as a power generation system using a fuel cell main body, a combustible gas reaction device, a heat exchanger, a pump, a proofer, etc., and driven by an electric motor such as the pump, a blower, etc., a battery main body, and a reaction. Separate the equipment that handles combustible gas such as a container with a partition wall to form two or more compartments, avoid contact between combustible gas and energized equipment, and equip each compartment with an independent ventilation system. In a fuel cell power plant in which each compartment is independently ventilated by supplying external clean air, the exhaust gas peculiar to the fuel cell power generation system discharged from the cell body and the reactor and each compartment A fuel cell power plant, characterized by comprising exhaust means for mixing and exhausting at least one of exhaust air from ventilation air. 2. The fuel cell power plant according to claim 1, further comprising an exhaust duct of the power plant for exhausting a mixed gas of air for ventilating the power plant inner wall chamber and exhaust gas peculiar to the fuel cell to the outside. An exhaust device for a fuel cell power plant, which is characterized by installing an exhaust fan in the middle of. 3. The exhaust system for a fuel cell power plant according to claim 2, wherein a pressure sensor for detecting an exhaust fan suction pressure and a detection signal corresponding to the suction pressure detected by the pressure sensor are input, and the detection is performed. A controller that outputs a control signal obtained based on the signal, and an inverter that controls the rotation speed of the exhaust fan drive motor by changing the AC output frequency based on the control signal input from the controller. And a control function for controlling the exhaust fan so that the suction side pressure is substantially constant. 4. The exhaust system for a fuel cell power plant according to claim 2, wherein pressure sensors are attached to an exhaust fan discharge side and an exhaust fan side, and the detected values of these pressure sensors are used to detect the exhaust fan from the differential pressure between them. Calculate the total generated pressure, and compare the generated total pressure of the exhaust fan with the mixed gas flow rate during rated operation of the target fuel cell power plant and the upper and lower limits of the specified range of the total generated pressure with respect to the mixed gas flow rate during partial load operation of the power plant. A limiter is installed to control the rotation speed of the exhaust fan drive motor so that the exhaust fan rotation speed is minimized at the lower limit of the total generated pressure, and a control function to control the exhaust fan suction side pressure to a constant value is provided. An exhaust device for a fuel cell power plant, which is characterized in that 5. The exhaust device according to claim 2, wherein the pressure signal detected by the slight pressure sensor is used as the rotation speed, paying attention to the fact that the wind pressure generated by the exhaust fan is proportional to the square of the fan drive motor rotation speed. A fuel cell power plant characterized by having a control function of converting the converted signal and inputting it to an inverter, securing a drive motor speed corresponding to the AC output frequency from this inverter, and controlling an exhaust fan Exhaust system. 6. The operating load of the exhaust system for a fuel cell power plant according to claim 2, wherein the flow rate of the exhaust gas mixture from the fuel cell power plant changes in accordance with the operating load of the fuel cell power plant. The relationship between the conditions and the exhaust fan generated total pressure is confirmed and stored in advance by simulation, and the load signal of the fuel cell power plant is input to the inverter, and the drive motor speed corresponding to the AC output frequency from this inverter is obtained. An exhaust device for a fuel cell power plant, which has a control function for controlling an exhaust fan as described above.