JPH0325860A - Reaction gas supply flow rate controller of fuel cell - Google Patents

Abstract

PURPOSE:To suitably control of a reaction gas by detecting the measuring error of gas supply amount, time dependent deterioration of a fuel cell, and quality variation of reaction gas, and by correcting them. CONSTITUTION:If increase in reaction gas is smaller compared with increase in output current l, a fuel cell 1 is short in the gas. This concentration drop is detected at times t2, t3 with an analyzer 29, and supply amount correction circuit 21 outputs a correction signal 215 which requests additional gas supply to a flow rate control circuit 28. The flow rate control circuit 28 outputs a corrected flow rate control signal 28S which requests additional gas supply with the correction signal 21 to an electropneumatic positioner 4A to increase the opening of a supply control valve 4. The supply amount of reaction air is increased from the time t2 and that of fuel gas from the time t3 over the reference increase line. As a result, the concentration of oxygen in offgas and that of hydrogen are repeatedly controlled toward the reference concentration.

Description

[Detailed Description of the Invention] [Field of Application of Santojo] This invention provides a reaction system that controls the supply amount of fuel gas and reaction air as a reaction gas to be supplied to a fuel cell without excess or deficiency in response to an increase or decrease in load power. Regarding gas supply flow rate control device. [Prior Art] Fig. 3 is a configuration diagram showing a conventional reaction gas supply flow rate control device together with a schematic cross-sectional view of the fuel gas supply/discharge system of a fuel cell, and the b1 reaction air supply/discharge system side is also shown in Fig. 1. It is omitted from the drawing because it has the same structure as . In the figure, 1 is a fuel cell (cell stack) consisting of a stack of single cells;
Each unit cell has a pair of electrodes sandwiching a matrix, a fuel gas passage supplying fuel gas to one electrode, and an oxidizer passage supplying reaction air as an oxidizer to the other electrode, which are orthogonal to each other. 2A and 2B are a pair of fuel gas manifolds, an inlet and an outlet, which are attached to the side wall surface of the am tank 1 so as to communicate with the fuel gas passage. Fuel gas 19, which is mainly used as hydrogen fuel, is inlet q19A, population side manifold 2A
The off-gas 9 whose hydrogen concentration has been reduced by direct reaction with reaction air supplied through an oxidizer manifold (not shown) and which is supplied to the fuel gas passage through the
The residual hydrogen is sent to, for example, a PANA of a fuel reformer via the outlet side manifold 2B> and the outlet pipe 19B, and the residual hydrogen is combusted, and the generated heat is used as a heat source for the reforming reaction.

The inlet piping 19A is provided with a fuel gas flow control valve 4 driven by dry air by an electro-pneumatic system 4A, an orifice type flow rate detector 5, and a gas assembly analyzer 9 for the fuel gas 19. The hydrogen performance is displayed on the display 9A. 7 is a detector for the output current of the fuel cell 1, 6 is a power converter such as a step-down chipper or an imperter, 6A
is the control section of the power converter 6, and the power generated by the fuel cell 1 is supplied to the load circuit via the power converter 6. The control circuit 8 for the supply flow rate of the fuel gas 19 is operated by a startup button? When the operation mode signal 118 that commands the output in the range of 25': The supply control valve is outputted toward the positioner 5A, and the opening of the supply control valve is controlled by air pressure. Whether or not the standard amount of fuel gas is supplied is detected by the flow rate detector 5, and the output signal 5S of the flow rate oscillator 5A is compared with the command value in the flow rate control circuit 8, so that control is performed to approach the commanded supply amount. will be carried out. On the other hand, the immediate output current of the fuel cell 1 is detected by the current detector 7, and the output signal 7S is compared with the operation mode signal 118 in the flow rate control circuit 8, whereby a command control signal 8S is generated. is corrected, and fuel gas commensurate with the output IE flow is supplied.

Nauta, the power generation reaction of a fuel cell is the reaction between 1/2 mole of oxygen (0■) and 1 mole of hydrogen (Hz) (2 x 96500)
The total amount of coulomb charge and 1 mole of water is generated, and when converted to the amount of hydrogen and oxygen at normal pressure required to output a DC current of klA for 1 minute, the amount of hydrogen is 6. 9 6
41Lt/-, reaction air amount 3. 4 8yd/M
It becomes iR. Therefore, by determining in advance the standard supply gas amount commensurate with the operation mode signal 118 based on the above relationship and storing this value in the arithmetic unit of the flow rate control circuit 8, it is possible to can supply fuel gas. The same applies to the reaction air supply system.

[Problem to be solved by the invention]

FIG. 4 is an enlarged view of the inlet piping section shown in FIG. 3.

As shown in the figure, fuel gas 19 (or reaction air) generally contains moisture and is cooled in a long pipe 19A of a plant or the like, producing condensed water and causing rust etc. in the pipe. This moisture and foreign matter inside the pipe together with the reaction gas
Foreign matter 5F't or 5G gradually adheres or accumulates inside the chair 5B and the transmitter differential pressure pipe 5C. When the reaction gas passes through the fixed hole of the orifice 7 seat 5B, a slight pressure (from 0 to
In a flow rate detector that measures flow rate by detecting 10001WIA (1 level), foreign objects 5F' and 5G cause erroneous measurements. This also applies to various types of flow meter detection.

Further, the following problems occur in the nozzle 4B that determines the control of the supply control valve 4 when the frequency of use thereof increases.

In other words, the tightening part that tightens and adjusts the flow becomes deformed, and the control valve gland 4C becomes stiff, making the movement of the nozzle worse. In the supply control valve 4, which receives the control signal 8S of the flow rate control circuit 8 and uses the air pressure generated in the electropneumatic gas cylinder 4A as the driving operation force of the control valve, the stroke, that is, the opening degree is determined, the air pressure and the opening degree of the valve are changed. Since these are determined to have a certain relationship, the opening degree of the valve will change by the amount that the valve operation becomes heavier.

Therefore, malfunctions in the valves and flow rate detectors cause measurement errors of about 5% to 10% in the amount of supplied gas, which frequently causes gas shortages and gas surpluses. In particular, if the fuel cell runs out of gas due to these measurement errors, the fuel! A problem arises in that the lifetime of the pond is shortened, but conventional devices that do not have means for detecting gas shortage have the disadvantage of not being able to prevent the shortening of the lifetime.

Furthermore, the voltage generated by the fuel cell gradually decreases as power generation continues, and it is necessary to gradually increase the amount of reactant gas supplied to prevent the voltage from decreasing due to aging. However, in conventional devices, the standard supply gas amount is fixed for the operation mode in the range of 25% to 100% of the rated output, so there is a problem that it is impossible to prevent the output voltage from decreasing. There is a problem in that it cannot respond to qualitative changes such as changes in air pressure or changes in hydrogen concentration of fuel gas.

The purpose of this invention is to detect and correct errors in measurement of gas supply amount, deterioration of the fuel cell over time, or qualitative changes in the reactant gas, thereby realizing control to ensure that there is no excess or deficiency of the reactant gas. It's about doing.

[Means to solve the problem]

In order to solve the above problems, according to the present invention, power is generated by supplying fuel gas and reaction air as a reaction gas to the fuel gas passage and the oxidizer passage of each cell, which is composed of a stack of cells. The fuel cell has a pair of flow control valves provided in the inlet piping for the reaction gas, and a control signal for supplying flow rates of predetermined amounts of fuel gas and reaction air determined by the power demand of the load to the flow control valves, respectively. a pair of analyzers installed in the outlet piping of each of the fuel gas and reaction air to continuously analyze the hydrogen concentration and oxygen concentration in the off-gas; a supply amount correction circuit that compares the analysis result of the meter with a predetermined reference concentration and outputs a signal to the flow rate control circuit to correct the supply amount of the fuel gas and reaction air so that the analysis result approaches the reference concentration. shall be prepared.

[Effect]

By using the above means, the hydrogen concentration and oxygen concentration in the off-gas are each continuously analyzed at the exit side of the reactant gas passage of the fuel cell, and the off-gas concentration is determined in advance based on the hydrogen consumption rate and oxygen consumption rate of the fuel cell. The structure is configured to correct the supply of fuel gas and reaction air as reaction gases so as to keep the reference concentration level and reference oxygen concentration constant respectively. Whether it is due to aging of the battery or a qualitative change in the reactant gas, it is possible to detect this and correct the reactant gas supply amount to an appropriate value. [Example] This invention will be explained below based on an example. FIG. 1 is a configuration diagram showing only the fuel gas system of the fuel cell of a reactant gas supply flow rate control device for a fuel cell according to an embodiment of the present invention;
FIG. 2 is a time chart showing the control state applied to the apparatus shown in FIG. 1. The same reference numerals are used for the same parts as in the conventional apparatus, and detailed explanation thereof will be omitted. In the figure, the off gas 9 is connected to the outlet pipe 19B side which communicates with the outlet side manifold 2B of the fuel gas passage.
It is equipped with an analyzer 29 that continuously analyzes B to determine the hydrogen concentration. In addition, the flow rate control circuit 28 includes an operation mode signal 11s that specifies at what percentage of the rated output the power generation operation should be performed, and an output increase/decrease command signal 12 from the control unit 6A of the power converter 6.
8 is input.

Furthermore, the two signals 11s> and 123 are applied as gate signals to the AND gate 26 via the OR gate 22,
The concentration signal 29St is outputted to the supply amount correction circuit 21 according to the AND condition with the output concentration signal 298 of the analyzer 29. A reference hydrogen concentration in the off-gas 9B is stored in the supply amount correction circuit 21 in advance, and when the concentration signal 298 falls below the reference hydrogen concentration, the supply of the fuel gas 19 is increased, and when it exceeds the reference hydrogen concentration, the supply is stopped. A correction signal "f" to be reduced is outputted to the flow rate control circuit 28.A reaction air supply flow rate control device having a structure similar to that shown in FIG. 1 is also provided in the reaction air system of the fuel cell 1.

The reference hydrogen concentration to be set in the supply amount correction circuit 21 is as follows:
Hydrogen concentration t-77 in fuel gas 19 on the fuel cell inlet side
%, assuming that the oxygen concentration of the reaction air is 21%, and the hydrogen utilization rate of the fuel cell 1 is 75%. Oxygen utilization rate 50%
In the case of concentration and reference oxygen concentration.

In the device configured as described above, the operating mode signal 118 is used to set the rated current to 50, for example, as shown in FIG.
Output current equivalent to %. . Assume that an increase/decrease command signal 128 requesting an increase in the output current is input to the fuel cell flow fffflJ control circuit 28 at time tx while the output current is being output. The flow rate control circuit 28 sends a flow rate control signal 28St that commands an increase in the supply of reactant gas to meet this increase request.
- Output towards the electropneumatic body cylinder 4A, supply control valve 4
As the opening degree increases, the supply amount of b1 reaction air and fuel gas gradually increases along the reference increase line shown in Fig. 4. However, when the amount of increase in the reactant gas is smaller than the increase in the output current I, the fuel cell 1 tends to run out of gas, and the oxygen and hydrogen concentrations in the off-gas are 11.7% and 45%, respectively. 5% less. This decrease in concentration is detected by the analyzer 29 at times 1, > and 1, respectively, and the supply amount correction circuit 21 outputs a correction signal 21Se to the flow rate control circuit 28, which urges addition of the supply amount. The flow rate control circuit 28 receives the correction signal 213 and generates a corrected flow rate control signal 28St- for prompting the additional supply of the reaction gas.
The reaction air moves towards the electro-pneumatic positioner 4A, which increases the opening degree of the supply control valve 4.
From that point on. The supply amount of the fuel gas increases beyond the reference increase line from time point t, and as a result, control is repeatedly performed to stabilize the concentrations of oxygen and hydrogen in the off-gas toward the reference concentration. Among these, an increase in the supply amount is detected by the flow rate detector 5, and the output signal 5S of the flow rate oscillator is compared with a command value in the flow rate control circuit 28, and control is performed to stabilize the supply amount toward the commanded supply amount. Since the time required for analysis by the analyzer 29 can be known in advance, by setting the calculation conditions in advance to output a larger correction signal 213k in conjunction with the manifold volume, correction including the effect of time delay can be made. can do. Keita, AN
The D gate 23 was provided to prevent the supply amount correction circuit from operating unless the concentration signal 293, operation mode signal 11S, or increase/decrease command signal 12S were input. 298, the supply amount correction circuit 21 detects an excessive correction signal 2.
By outputting 1S, it is possible to prevent a gas surplus phenomenon caused by supplying an excessive amount of reaction gas.

〔Effect of the invention〕

As mentioned above, this invention adds the hydrogen concentration button and oxygen concentration in the off-gas to the control requirements for reaction gas supply flow rate control.
The reactant gas supply amount is corrected according to the deviation from the predetermined standard concentration, and as a result, there are no direct effects on the hydrogen or oxygen concentration in the off-gas, such as measurement errors in the supply flow rate or qualitative changes in the reactant gas. By detecting the off-gas concentration and correcting the supply amount, it is possible to suppress gas shortages and gas surpluses and perform efficient power generation operations. On the other hand, a decrease in output voltage due to age-related deterioration of the fuel cell leads to a decrease in output power, so by increasing the command power, extra reaction gas is supplied, and even then, the output power is insufficient. By detecting a gas shortage using the off-gas concentration and correcting the reaction gas supply f't, it is possible to continue the power generation operation without causing a drop in the output voltage.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram showing a control device for reactant gas supply flow of a fuel tank according to an embodiment of the present invention, FIG. 2 is a time chart showing the control status applied to the device shown in FIG. 1, and FIG. 4 is a block diagram showing the configuration of a conventional device, and FIG. 4 is an enlarged cross-sectional view showing an inlet piping section connected to a button of the conventional device. 1... Fuel electric M, 2A, 2B... Manifold, 4
...Supply control valve, 4A...Electric body positioner, 5.
...Flow rate detector, 6...Power converter, 7...Current detector, 8, 28...Flow rate control circuit, 9...Analyzer (
Inlet side), 9B...off gas, 19...fuel gas,
19A...Inlet piping, 19B...Outlet piping, 21.
・・Supply amount correction circuit 29 ・・Analyzer (outlet @), 11
S... Operation mode signal, 128... Increased IA command signal (power signal), 8'8 2B 4th

Claims (1)

[Claims] 1) A fuel cell, which is composed of a stack of unit cells and generates electricity by supplying fuel gas and reaction air as a reaction gas to the fuel gas passage and oxidizer passage of each unit cell, respectively, is installed in the inlet piping for the reaction gas. a pair of flow rate control valves, and a flow rate control circuit that outputs control signals for supply flow rates of predetermined amounts of fuel gas and reaction air determined by the power demand of the load to the flow rate control valves, A pair of analyzers are installed in the outlet pipes of the fuel gas and reaction air to continuously analyze the hydrogen concentration and oxygen concentration in the off-gas, and the analysis results of the pair of analyzers are compared with a predetermined reference concentration. and a supply amount correction circuit that outputs a signal to the flow rate control circuit to correct the supply amount of fuel gas and reaction air so that the analysis result approaches the reference concentration. Supply flow control device.