JPH11317234A - Fuel cell power generation system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a fuel cell power generation system capable of stably supplying air to a fuel cell and a reformer for a wide range of the flow rate. SOLUTION: This fuel cell power generation system is provided with an air blower 10 for supplying air to a fuel cell 1 and a reformer 2; control valves 6 and 7 provided on an air supplying piping 4 of the fuel cell 1 and an air supplying piping 5 of the reformer 2, respectively, for controlling the flow rate according to a battery load; and an inverter 11 for controlling the rotation frequency of the air blower 10 according to the battery load so as to avoid surging. When the battery load is in a range between a rating load and a partial load, control of air supply to the fuel cell 1 and the reformer 2 is performed by controlling the rotation frequency of the air blower 10 with specified opening of the control valves 6 and 7, and when the battery load is in a range between the partial load and a minimum load, the control of air supply to the fuel cell 1 and the reformer 2 is performed by controlling the opening of the control valves 6 and 7 with the specified rotation frequency of the air blower 10.

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 generation system, and more particularly to control of an air flow rate according to a load of a fuel cell.

[0002]

2. Description of the Related Art Fuel cell power generation systems have advantages such as higher efficiency than conventional steam power generation and good environmental preservation, and have been actively developed in recent years for practical use. The fuel cell power generation system includes a fuel cell including an air electrode, a fuel electrode, and an electrolyte layer, and a reformer that reforms a hydrocarbon-based fuel such as natural gas and supplies a hydrogen-rich gas to the fuel electrode of the fuel cell. ing. Further, an air supply source is provided for supplying air as an oxidant to the air electrode of the fuel cell and for combustion for the reformer. In the case of a so-called on-site system having a relatively small capacity of about several hundreds of kW, the fuel cell has a capacity of several hundred mmA.
A normal pressure type operating at a pressure of about q is generally adopted, and in this case, an air blower is applied to an air supply source.

In such a fuel cell power generation system, the amount of fuel or air is generally changed in accordance with the load of the fuel cell for the purpose of improving the efficiency of the partial load. As a specific conventional method, for example, there is a method shown in the fuel cell system diagram on pages 53 to 54 of "Technical Investigation Report of On-Site Type Fuel Cell" published by Japan Industrial Machinery Manufacturers Association in May 1984. The outline is shown in FIG. 3, reference numeral 1 denotes a fuel cell having a fuel electrode 1a and an air electrode 1b, and reference numeral 2 denotes a fuel electrode 1a of a fuel cell 1 which reforms a hydrocarbon fuel (natural gas in this example).
The reformer supplies a reformed gas containing a large amount of hydrogen to the fuel cell, and includes a reforming reaction section 2a and a burner section 2b. Reference numeral 3 denotes an air blower for supplying air to the air electrode 1b of the fuel cell 1 and the burner 2b of the reformer 2, and 4 denotes a fuel cell air supply for supplying air from the air blower 3 to the air electrode 1b of the fuel cell 1. A pipe 5 is a reformer air supply pipe for supplying air from the air blower 3 to the burner section 2b of the reformer 2, and 8 is a supply air to the air electrode 1b of the fuel cell 1 and a flow from the air electrode 1b. This is a heat exchanger that exchanges heat with the exhaust air. 6 is a fuel cell air control valve provided in the middle of the fuel cell air supply pipe 4, 7 is a reformer air control valve provided in the middle of the reformer air supply pipe 5, and 9 is a control valve of these control valves 6 and 7. It is a controller that adjusts the opening degree.

Next, the operation of the conventional system configured as described above will be described. A hydrocarbon-based fuel such as natural gas is charged into the reaction section 2a of the reformer 2, in which a reforming reaction is performed, and is converted into a reformed gas containing hydrogen as a main component. The reformed gas is supplied to the fuel electrode 1a of the fuel cell 1, where it is consumed for the reaction. The remaining surplus fuel after consumption is sent to the burner section 2b of the reformer 2. Burner part 2b
Then, excess fuel is burned, and heat necessary for the reforming reaction is given to the reaction section 2a. Part of the air from the air blower 3 is
After passing through the fuel cell air supply pipe 4, it is further preheated by the heat exchanger 8 and supplied to the air electrode 1 b of the fuel cell 1. The remaining air from the air blower 3 is supplied to the burner section 2b of the reformer 2 via the reformer air supply pipe 5, where it is consumed as combustion air. The remaining exhaust air used for the reaction at the air electrode 1b passes through the heat exchanger 8 and is released to the atmosphere together with the combustion exhaust gas from the burner 2b. Fuel cell air control valve 6 provided on fuel cell air supply pipe 4, reformer air control valve 7 provided on reformer air supply pipe 5
Is for appropriately adjusting the air flow rate according to the load of the fuel cell 1, and a valve opening command corresponding to the load is given from the controller 9 to each control valve. Under partial load conditions, it is necessary to reduce the amount of fuel and air from those under rated conditions from the viewpoints of efficiency improvement, heat balance in the system, and the like. , An opening command corresponding to the load is given.

[0005]

As described above, the conventional system attempts to control the air flow rate only with the control valve, but in such a method, due to the characteristics of the air blower, There is a problem that it is difficult to stably control the air flow rate in a wide range. That is, since a general air blower causes an unstable phenomenon called surging in a low flow rate range, there is a problem that the flow rate control range is limited to a certain value or more. In addition, the method of controlling the air flow rate by restricting the discharge side control valve of the air blower does not significantly reduce the power of the air blower, and reducing the air flow rate hardly improves the partial load efficiency. There was also.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and the flow rate of air supplied from an air blower to a fuel cell and a reformer can be varied over a wide range according to the load of the fuel cell. It is an object of the present invention to provide a fuel cell power generation system capable of performing stable control.

[0007]

A fuel cell power generation system according to the present invention comprises: a fuel cell; a reformer for reforming a hydrocarbon-based fuel to supply hydrogen gas to the fuel cell; One air blower for supplying air to the reformer, and on a fuel cell air supply pipe from the air blower to the fuel cell, or on a reformer air supply pipe from the air blower to the reformer Installed on at least one side,
A control valve for adjusting a flow rate according to a battery load, and control means for controlling a rotation speed of the air blower according to a battery load so as to avoid surging, wherein the fuel between a rated load and a partial load is provided. Adjustment of the amount of air supplied to the battery and the reformer is performed by controlling the number of rotations of the air blower while keeping the opening of the control valve constant, and the fuel cell and the fuel cell between a partial load and a minimum load are controlled. Adjustment of the air supply amount of the reformer, the rotation speed of the air blower is constant,
The control is performed by controlling the opening degree of the control valve.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be described below with reference to the drawings. Embodiment 1 FIG. FIG. 1 is a system diagram showing a fuel cell power generation system according to Embodiment 1 of the present invention. In the figure, the same or corresponding parts as those of the conventional fuel cell power generation system shown in FIG. Description is omitted. FIG.
, 10 is an air blower whose rotation speed can be controlled, 11
Is a control means (hereinafter referred to as an inverter) for controlling the number of revolutions of the air blower 10, for example, comprising an inverter.

Next, the operation of the fuel cell power generation system according to Embodiment 1 will be described. A hydrocarbon-based fuel such as natural gas is converted into a reformed gas in a reforming reaction section 2a of the reformer 2, and the reformed gas is led to a fuel electrode 1a of the fuel cell 1, where the remaining fuel consumed in the reaction is used. Excess fuel is sent to the burner section 2b of the reformer 2 and consumed for combustion. After a part of the air supplied from the air blower 10 is preheated by the heat exchanger 8 through the fuel cell air supply pipe 4, the air electrode 1 of the fuel cell 1 is
b, and the remaining air from the air blower 10 is sent through the reformer air supply pipe 5 to the burner 2b of the reformer 2 for combustion. The remaining exhaust air used for the reaction at the air electrode 1b passes through the heat exchanger 8 and is discharged to the atmosphere together with the combustion exhaust gas from the burner 2b. The above operation is the same as the above-described operation of the related art. In the first embodiment, the control of the flow rate of the supply air to the fuel cell 1 and the reformer 2 is performed by controlling the control valves 6 and 7 provided in the fuel cell air supply pipe 4 and the reformer air supply pipe 5, respectively. Control and air blower 1
This is performed in combination with the rotation speed control of 0.

An example of this control method will be described with reference to FIG. In FIG. 2, reference numeral 12 denotes a characteristic curve of the air blower, and reference numerals 13 and 14 denote a wind pressure (P)-of the air blower 10.
It is a plot of the operating point of the system on the airflow (Q) characteristic curve.

[0011] First, in the rated load condition of the system, the air blower 10 is operated at a rotational speed N ₁ of only maintains required air flow at rated conditions, the wind pressure. Air blower 10
The controller 9 gives a command value to the inverter 11 from the controller 9, whereby the frequency of the electric motor of the air blower 10 connected to the inverter 11 is controlled and maintained at a required value. In this state, the air pressure-air volume characteristic curve of the air blower 10 and the pressure loss curve of the air system of the system are 13 and 16 in FIG.
The point at which 6 crosses (point A in FIG. 2) is the air blower 10
Rated operating point. A curve 15 indicated by a broken line is a surging limit line of the air blower 10. Since a surging may occur in a zone on the left side (low air volume side) of the curve 15, a zone on a right side of the curve 15 (high air volume side). Operating point. The rated operating point (A)
There is sufficient margin for this surging limit line 15 and there is no problem.

Next, when the partial load operation is performed, the operating point of the air blower 10 is changed to the rotation speed N ₁ when the air flow is controlled only by narrowing the control valves 6 and 7 as in the prior art.
In order to move on the characteristic curve 13 at the low air volume side, there is a possibility of entering or approaching a surging area. Shows an example of a conventional part load operating point B _1. In the method according to the present invention, first, the rotational speed of the air blower 10 is reduced while the opening of the control valves 6 and 7 is kept constant while the load is reduced. The fuel cell 1 and the range of the necessary air to the reformer 2 to the rotational speed N ₂ lowest can supply (range A~X the figure), corresponding with the rotational speed control of the air blower 10. To further reduce the load, the rotation speed of the air blower 10 is fixed, and the control valve 6,
The opening of 7 is throttled to reduce the air flow rate. By throttling the control valve 6, the pressure loss of the air system of the system is increased, the operating point, the upper rotational speed N ₂ constant characteristic curve 14 moved to the low air volume side, for example, reaches the point B. Air blower 1
In the case of 0, the surging limit changes as shown in the figure depending on the number of revolutions. The lower the number of revolutions, the narrower the surging limit, and conversely, the stable region tends to be widened. For this reason, at the same partial load air flow rate (Q ₂ ), in the related art, the surging limit is 1
Those 5 had the inside _(point B) is able to stably operate outside (B point) of the surging limit 15 in the process of this invention.

According to the present invention, for example, when the point B in the figure corresponds to the minimum load condition of the system, the operating point of the air blower 10 moves stably between the points A ← → X ← → B. 18 and 19 are characteristic curves of the power (L) -air flow (Q) of the air blower 10 corresponding to the above-mentioned rotation speeds N ₁ and N ₂ , respectively. A, which is plotted on the air pressure (P) -air volume (Q) characteristic curve of the air blower 10 described above,
X, B, and B ₁ points correspond to a, a on curves 18 and 19, respectively.
x, b, corresponding to _{b 1.} As shown, in the prior art, the air blower power under the partial load condition does not decrease much as compared with the rated load, whereas the method according to the present invention significantly reduces the air blower power under the partial load condition. It is possible to improve the partial load efficiency of the system accordingly. Although a method in which the partial load operation is performed only by controlling the rotation speed of the air blower 10 and the control valve is not used is conceivable, the discharge pressure of the air blower 10 decreases in a low load region. It is difficult to supply air in a well-balanced manner, and practical use is difficult.

In the first embodiment, an example is shown in which the air flow rate control at the partial load is divided into a load area by controlling the rotation speed of the air blower 10 and a load area by controlling the control valves 6 and 7. It is not always necessary to divide in this way, and the control of the rotation speed of the air blower 10 and the control of the control valves 6 and 7 may be used together with the reduction of the load.
Has the same effect as. An example of the operation point movement by this method is shown in FIG. In short, it is important to combine the control of the rotation speed of the air blower 10 and the control of the control valves 6 and 7.
Thereby, the object of the present invention is achieved.

In the first embodiment, the control valves 6 and 7 are provided on both the fuel cell air supply pipe 4 and the reformer air supply pipe 5, but the control valves are not necessarily provided on both. It is not necessary, and a control valve may be provided in only one of them. For example, when the air supply pressure required for the reformer 2 is higher than the air supply pressure required for the fuel cell 1, the control valve 7 on the reformer air supply pipe 5 is not always necessary and can be omitted. In this case, when the load changes, the air flow to the reformer 2 is basically controlled by controlling the rotation speed of the air blower 10, and the air flow to the fuel cell 1 is controlled by controlling the control valve 6. The same applies to the opposite case.

[0016]

As described above, according to the present invention, a fuel cell, a reformer for reforming a hydrocarbon-based fuel and supplying hydrogen gas to the fuel cell, the fuel cell and the reformer One air blower for supplying air to the fuel cell, and at least one on a fuel cell air supply pipe from the air blower to the fuel cell or on a reformer air supply pipe from the air blower to the reformer. A control valve installed to control the flow rate according to the battery load, and control means for controlling the rotation speed of the air blower according to the battery load so as to avoid surging. The adjustment of the amount of air supplied to the fuel cell and the reformer in the above is performed by controlling the number of rotations of the air blower while keeping the opening of the control valve constant, and adjusting the fuel supply between a partial load and a minimum load. Battery and above The air supply amount of the reformer is adjusted by controlling the opening of the control valve while keeping the rotation speed of the air blower constant. Is provided.

[Brief description of the drawings]

FIG. 1 is a system diagram showing a fuel cell power generation system according to Embodiment 1 of the present invention.

FIG. 2 is a characteristic diagram showing an example of a characteristic curve of an air blower in the fuel cell power generation system according to Embodiment 1 of the present invention.

FIG. 3 is a system diagram showing a conventional fuel cell power generation system. 1 fuel cell body, 1a fuel electrode, 1b air electrode, 2
Reformer, 4 fuel cell air supply pipe, 5 reformer air supply pipe, 6 fuel cell air control valve, 7 reformer air control valve, 10 air blower, 11 inverter.

Claims (1)

[Claims] 1. A fuel cell, a reformer for reforming a hydrocarbon-based fuel and supplying hydrogen gas to the fuel cell, and one air blower for supplying air to the fuel cell and the reformer. Installed on at least one of a fuel cell air supply pipe from the air blower to the fuel cell or a reformer air supply pipe from the air blower to the reformer,
A control valve for adjusting a flow rate according to a battery load, and control means for controlling a rotation speed of the air blower according to a battery load so as to avoid surging, wherein the fuel between a rated load and a partial load is provided. Adjustment of the amount of air supplied to the battery and the reformer is performed by controlling the number of rotations of the air blower while keeping the opening of the control valve constant, and the fuel cell and the fuel cell between a partial load and a minimum load are controlled. Adjustment of the air supply amount of the reformer, the rotation speed of the air blower is constant,
A fuel cell power generation system, wherein the control is performed by controlling the opening of the control valve.