JPH01286259A - Operation of fuel cell - Google Patents

Abstract

PURPOSE:To stop the flow of a load current and avoid the local abnormal temperature rise of a unit cell by providing multiple judging circuits and issuing a command signal when the fuel gas flow quantity or the oxidizer gas flow quantity is lower than the lower limit corresponding to the load current. CONSTITUTION:Lower limits of flow quantities of the fuel gas 9 and oxidizer gas 10 corresponding to a load current I are set in the % ratio. The flow quantities of the gases 9 and 10 are detected by flow quantity sensors 11 and 12, they are inputted to judging circuits 13 and 14 as actual values. On the other hand, the gases 9 and 10 are fed to a fuel cell 1, the cell 1 feeds the load current I to a load 7. The current I is detected by a current detector 5, its value 5A is inputted to the circuits 13 and 14. The circuits 13 and 14 compare the inputted actual values of the gases 9 and 10 with the lower limit values corresponding to the load current value 5A. When the actual values are lower than the lower limit values, the circuit 13 or 14 issues a command signal to a breaker 6 to open the breaker 6, the flow of the load current I is stopped.

Description

[Detailed description of the invention] [Industrial application field] This invention method is a method of operating a cynic acid fuel cell.

In particular, it relates to an operating method for preventing fuel cell performance from deteriorating due to insufficient reactant gas.

[Conventional technology]

In fuel cell power generation systems, the response speed of the fuel reforming system, which is a chemical plant, is generally slower than the response speed of the fuel cell to changes in electrical load. The supply of agent gas cannot keep up with the amount consumed by the fuel cell, and a so-called gas shortage may occur. Gas shortages also occur due to malfunctions in the reforming system. As an operating method to prevent the deterioration of fuel cell characteristics caused by such gas shortages, the drop in output voltage of the fuel cell that occurs due to gas shortage is detected and the value drops to, for example, about half of the steady flow rate. There is a known method for cutting off the load current of the fuel cell when this happens.

[Problem to be solved by the invention]

! Figure 2 is a characteristic diagram for explaining the conventional method. Curve IFM21 is the actual value curve of the fuel gas flow rate with the rated value of the fuel gas flow rate as 100%, and curve 22 shows the rated value of the output voltage as 100%. Curve 23 is the actual value curve of the fuel electrode temperature of the fuel cell at time 1. This figure shows the changes over time in terms of the amount of fuel gas when the fuel gas level decreases. In the figure, the supplied fuel gas flow rate of the fuel cell, which was outputting the rated current while maintaining the output voltage rated value Vf due to the supply of fuel gas and oxidizing gas at the rated value flow rate, decreased to 50% of the rated value from time 11 to +2. %, there is a distance between the flow thk meter placed on the inlet side of the fuel cell and the electrode section of the fuel cell, and the output voltage V will decrease until the fuel gas stored during this time is consumed. Time t1
As shown in curve 22, the rated value level v6 is maintained from 1 to +3, and the output voltage begins to decrease. In the conventional method, the load current is cut off and the output voltage becomes zero at time t4 when the output voltage drops to about half of the rated value level.
Simultaneously at time t3 when the output voltage begins to decrease, the cell temperature begins to rise, and at load cutoff time t4, an abnormal temperature rise exceeding the operating temperature of the fuel cell by several tens of degrees Celsius is exhibited.

Figures 6 and 4 are distribution charts of the hydrogen polar surface temperature of a single cell before and after a fuel gas shortage occurs, and Figure 6 is a diagram showing the distribution of the temperature at the light surface of the hydrogen pole at time t1.
As for the previous temperature distribution, FIG. 4 shows the m degree distribution with poor breakdown after time t4, and the arrow in the figure indicates the flow direction of the fuel gas 9.

In the figure, when the operating temperature of the fuel cell is 190°C, under the rated operating condition shown in Figure 6, the cell surface temperature is approximately equal to +1. However, when there is a fuel gas shortage, as shown in Figure 4, the fuel gas inlet side shows a high abnormal temperature rise, and other parts show an abnormally low temperature, and a drop in the output voltage is detected. The conventional method of load shedding after the temperature change cannot avoid the occurrence of temperature abnormalities.

The reason why the local abnormal temperature rise occurs as described above is thought to be that when a fuel gas shortage occurs, power generation is locally concentrated on the fuel gas inlet side. When such an abnormal temperature occurs, the water vapor pressure of the Q phosphoric acid liquid in the unit cell in the abnormally temperature raised part will be high, and the phosphoric acid liquid or water vapor will pass through the hydrogen electrode and the oxygen electrode and become a fuel gas or oxidizer. The so-called scattering phenomenon in which particles scatter into the gas becomes more intense. As a result, due to an increase in the concentration of the remaining phosphoric acid solution or a shortage of phosphoric acid solution, the internal resistance of the electrode becomes locally high, which not only hinders the subsequent power generation syndrome but also increases the internal resistance of the electrode. The gas sealing performance between the oxidizing gas system and the fuel gas system held by the cynic acid liquid decreases, and the risk of mixing oxygen and hydrogen increases. In addition, an increase in the concentration of phosphoric acid solution and an abnormal rise in temperature increase the corrosivity of the phosphoric acid solution, which in turn promotes sintering of the platinum catalyst in the electrode, accelerating the decline in the life characteristics of the fuel cell. This causes the inconvenience of

Note that although the above explanation has been made using the example of a shortage of fuel gas, similar phenomena and problems occur also due to a shortage of reaction air as an oxidant gas.

The purpose of the method of the present invention is to detect a shortage of fuel gas or reaction air at an early stage and cut off the load current, thereby avoiding a local abnormal temperature rise in the unit cell.

[Means to solve the problem]

Ninthly, according to the method of this invention to solve the above problems,
A power generation operation method for avoiding an abnormal temperature rise in a unit cell due to a shortage of reactant gas in a phosphoric acid fuel cell, the method includes measuring the load VT current of the fuel cell, maintaining the output voltage, and outputting the load current. Determine the required lower limit values for each of the fuel gas flow rate and oxidant gas flow rate, compare these lower limit values with the actual values of the fuel gas flow rate and oxidant gas flow rate, respectively, measured at the gas inlet side of the fuel cell, and calculate the actual values. When at least one of these is lower than the lower limit value, the flow of the load current is stopped.

[Effect]

In the above means, the fuel gas flow rate and the oxidant gas flow i
jk is measured with a flow meter placed on the fuel cell inlet side to obtain each actual value, the load current of the fuel cell is measured, and this output current is the fuel required to maintain and output a predetermined output voltage for a predetermined time. The gas flow rate and the oxidant gas flow rate are determined and set as their respective lower limit values, and the load current is cut off when either of the actual values falls below the lower limit value. Inner gas 9
It is possible to effectively utilize the predetermined time until the output voltage starts to drop after the fuel gas and oxidizer moving between the two are consumed by an electrochemical reaction to cut off the load current.
Therefore, it is possible to avoid the abnormal temperature rise of the single cell that occurs due to a decrease in the output voltage with plenty of time, and to prevent the characteristic deterioration of the fuel cell that occurs due to a local abnormal temperature rise. The risk of mixing oxidant gas and fuel gas is eliminated.

〔Example〕

The method of this invention will be explained below based on examples.

FIG. 1 is a schematic diagram of an apparatus for explaining an embodiment of the method of the present invention. In the figure, 1 is a fuel cell;
It consists of a laminate in which a plurality of unit cells 2 are laminated with a gas-impermeable separator interposed, in which an oxygen electrode 4A carrying an electrode catalyst and a hydrogen electrode 4F are closely arranged on both sides of a matrix 3 impregnated with a phosphoric acid solution. , supply passages for fuel gas 9 and reaction air 10 as oxidant gas are formed in directions orthogonal to each other between the unit cell 2 and a separator (not shown). Reference numeral 11 denotes a flow rate sensor of the fuel gas 9 provided in a supply pipe communicating with the supply passage of the fuel gas 9, and the detected fuel gas flow rate is determined as an actual value by the judgment circuit 1.
3 is input δ. Reference numeral 12 denotes a flow rate sensor provided in the supply pipe for the oxidizing gas 10, and the measured oxidizing gas flow rate is inputted to the judgment circuit 14 as an actual value of the oxidizing gas flow rate. Further, the fuel gas in which hydrogen has been consumed in the fuel cell 1 is sent as a return gas 9E to a reformer burner (not shown), and the combustible gas in the return gas 9E is used as a heat source for the endothermic reforming reaction, resulting in oxidation. The return gas 10E of the oxidant gas 10 is also used, for example, as a heat source for preheating the oxidant gas 10.

On the other hand, on the output side of the fuel cell 1, a current detector 5 and a circuit breaker 6 are provided in series with the load 7, and a detection signal of the load electric power detected by the current detector 5 is input to judgment circuits 13 and 14. Ru. Judgment circuits 13 and 14 each calculate the lower limit value of the gas flow rate, which calculates the flow rate of the fuel gas 9 and oxidizing gas 10 necessary to maintain the output voltage V for a predetermined time and supply the load electricity based on the detection signal. Compare the actual values of fuel gas 9 and oxidizing gas 10 with the lower limit value, and when the actual values are below the lower limit value, a negative
The comparison circuit is configured to include a comparison circuit that issues a signal instructing to shut off the lightning heavy. Note that the holding time of the output voltage ■ is the time t1 from when the actual value of the fuel gas (or oxidant gas) flow rate starts to decrease until the output voltage begins to decrease in Fig. 2.
It can be determined based on the time interval from t to t. Therefore, the lower limit values for each of the fuel gas flow rate and oxidant gas flow rate are as follows: You can choose from a range.

The method of operating the fuel cell constructed as described above is repeated in the second manner.
This will be explained using figures. While the fuel gas flow rate (and the oxidant gas flow is maintained at the rated value (100% level in curve 21), the rated load light weight and the rated output voltage V (curve 22
For example, due to a failure in the reforming system, the flow rate of the fuel gas 9 supplied to the fuel cell 1, which is in power generation operation while maintaining the 100% level of
%, the decrease in the fuel gas flow rate is detected moment by moment by the flow rate sensor +j11, and its actual output value No. 1g 11A is input to the judgment circuit 13. - The force rated current ■ is detected by the current detector 5, and its detection signal 5A is inputted to the lower limit calculation section of the fuel gas flow t of the judgment circuit 13, and for example, the rated value flow rate 25 is inputted as the lower limit value signal.
%, when the actual value signal 11A falls to the lower limit value (fi level), the judgment circuit 13 outputs the load turtle light weight cutoff command signal 13A, and when this signal is received, The circuit breaker 6 is opened.

At this time, the cause of the failure of the reforming system has not been eliminated, so
Although the fuel gas flow rate further decreases toward 50%, the fuel gas shortage is resolved by the load current becoming zero around time t2, and the decrease in output voltage V that conventionally starts at time t3 and the cause of this The abnormal rise in cell battery m degree at time t
This can be completely avoided by effectively utilizing the extra time from t2 to t3.

In addition, the cutoff of the load electric light weight is detected by the current detector 5, and the lower limit value signal level also decreases, so the actual value Ig goes above the lower PJi value signal level, and the cutoff command 1
Output of No. 6 stops. It goes without saying that the cutoff command signal can also be used as an emergency stop signal for the fuel cell power generator.

The above description of the operation is based on the case where the fuel gas flow rate decreases due to a failure of the reforming yarn, but the same applies to the case where the oxidant gas flow rate decreases. Gas shortage may also occur due to a sudden increase in load electric power due to a failure on the load Z side, but in this case as well, the load current is cut off in the same way as in the operation explained above.

〔Effect of the invention〕

As mentioned above, the method of this invention is based on the actual flow rate of fuel gas and oxidizing gas detected at the inlet side of the fuel tank,
The fuel gas flow cap and the lower limit values of the oxidizing gas flow rate determined in accordance with the negative current measurement value are compared, and when the actual value falls below the lower limit value, the flow of the load current is stopped. As a result, it becomes possible to eliminate the gas shortage as early as possible by making effective use of the extra time until the output voltage drops and the cell temperature begins to rise abnormally after a gas shortage occurs. This problem cannot be avoided using the conventional method of detecting the pressure drop and cutting off the load current.7? : The abnormal rise in cell temperature is almost completely eliminated, and the accompanying "a dissolution tI < dispersion, gas sealing performance decrease, 2 reaction gas mixing,"
It is possible to prevent deterioration in performance and life of the fuel cell, such as sintering of the electrode catalyst.

[Brief explanation of the drawing]

Figure WJ1 is a configuration diagram of an apparatus for explaining the embodiment method of the present invention, Figure 2 is a characteristic diagram showing an abnormal state of a fuel cell in a conventional method, and Figures @6 and 4 are a diagram of a single cell in a conventional method. It is a temperature distribution diagram. 1...Fuel'! Ic pond, 2... Cell, 5... Current detector, 6... Circuit breaker, 7... Load, 9... Fuel gas, 10... Oxidizing gas, 11.12. ...Flow rate sensor, 13.14... Judgment circuit, 11A... Actual value signal, 16A... Cutoff command signal. Figure 1: Bribe 2: Circulation Figure 3: Figure 4

Claims (1)

[Claims] 1) A power generation operation method that avoids an abnormal temperature rise in a single cell due to a shortage of reactive gas in a phosphoric acid fuel cell, which measures the load current of the fuel cell, maintains the output voltage, and outputs the load current. Find the lower limit values of the fuel gas flow rate and oxidant gas flow rate required for A method of operating a fuel cell, comprising: stopping the flow of the load current when at least one of the values is lower than the lower limit value.