JPH0834104B2 - Control method for fuel reformer of fuel cell system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a method for controlling a fuel reformer, which is incorporated in a fuel cell system to reform a liquid fuel such as alcohol into hydrogen-rich gas and supply it to a fuel cell. In particular, it relates to a method for controlling the combustion air amount.

[Conventional technology]

In order to use a liquid fuel such as alcohol as a fuel for a fuel cell, it is necessary to gasify the liquid fuel, reform it into a hydrogen-rich fuel gas, and send it to the fuel cell.
For this reason, a fuel reformer is incorporated in the fuel cell system. A conventional fuel cell system of this type will be described with reference to FIG. In the figure, reference numeral 1 is a fuel cell, 2 is a fuel tank containing a liquid fuel such as alcohol, and a fuel supply system passage between the fuel tank 2 and the fuel cell 1 is provided with a fuel tank which is the object of the present invention. The quality device 3 is installed. The fuel reformer 3 includes a vaporizer 6 for gasifying liquid fuel in a combustion chamber of a furnace vessel 3A equipped with a burner 4, and a reformer for reforming fuel gas into hydrogen-rich fuel gas by catalytic reaction with a catalyst. The off-gas discharged from the fuel cell 1 is supplied to the burner 4 via the pipe 4A and burned in the furnace, and the heat vaporizes the liquid fuel and reforms the gas. In addition, 8 is a liquid fuel supply pump, 9 is a blower for supplying air as an oxidant reaction gas to the fuel cell 1, 10 is a blower for supplying air for cooling the fuel cell, and 5 is for supplying combustion air to the burner. Blower,
Reference numeral 14 is a pump for feeding methanol to be burned as auxiliary fuel at the time of start-up or load fluctuation, and 15 is a tank for the methanol.

By the way, when the fuel cell 1 is operated, it is important to keep the pressure difference between the air pressure as the reaction gas supplied to the fuel cell main body and the supply pressure of the fuel gas to be equal to or less than a certain level to prevent the life of the cell main body from being shortened. It is also extremely important. For this purpose, it is necessary to maintain the supply pressure of the fuel gas supplied to the fuel cell main body 1 through the fuel reformer 3 of the fuel gas supply system in correspondence with the supply amount.

By the way, generally, when gasifying a liquid fuel, a large latent heat of vaporization is required, and the fuel undergoes a large volume change with the gasification. On the other hand, the heat capacity of the carburetor part is compared with the conventional reformer configuration in which the carburetor 6 is simply installed in the combustion chamber of the furnace vessel 5 to heat the carburetor 6 with the heat of the combustion gas. Small For this reason, it is difficult to constantly and stably supply the large latent heat of vaporization required for gasification of liquid fuel from the furnace side to the entire area of the vaporizer, and especially the load of the fuel cell fluctuates rapidly, and the vaporizer of liquid fuel vaporizes. If the supply amount to the fuel increases sharply, the temperature of the liquid fuel vaporizes in the vaporizer where the latent heat of vaporization is lost in the portion where the liquid fuel vaporizes. It constantly fluctuates in the vaporizer, which causes pressure fluctuations in the fuel gas delivered from the outlet of the vaporizer.

FIG. 5 is a pressure fluctuation curve of the fuel gas in the conventional apparatus. In the process of shifting from the pressure level 101 before the sudden load increase of the fuel cell to the pressure level 102 after the rapid increase, a large pressure oscillation 103 having an amplitude P is generated.

For this reason, in the conventional fuel cell system, as shown in FIG.
11 is installed to reduce the pressure fluctuation of the fuel gas supplied to the fuel cell 1.

Further, as shown in FIG. 6, a method of installing a buffer tank 12 dedicated to reforming fuel gas between the reforming device 3 and the fuel cell 1 so as to suppress the fluctuation of the supply gas pressure to the fuel cell 1. Has also been tried.

[Problems to be solved by the invention]

In the conventional device in which the throttle 11 is provided on the outlet side of the reformer 3 in order to suppress the transient pressure fluctuation of the fuel gas in the fuel cell 1, the internal pressures of the reformer 7 and the carburetor 6 rise and It becomes necessary to improve the pressure resistance of the
There is a problem that vaporization performance is reduced. Further, in the conventional device provided with the buffer tank 12, there is a problem that the entire system becomes large. Further, in these conventional devices, only the countermeasures for suppressing the influence of the transient pressure oscillation generated in the reforming system of the fuel gas due to the sudden change of the electric load of the fuel cell are taken without sufficiently pursuing the cause. There is a problem that is.

An object of the present invention is to obtain a control method of a fuel reformer of a fuel cell system having a small transient pressure fluctuation by eliminating a transient temperature drop of a carburetor which is a cause of transient pressure oscillation. Especially.

[Means for solving problems]

To solve the above problems, according to the present invention, there is provided a fuel reformer having a liquid fuel vaporizer and a reformer, and supplying hydrogen-rich fuel gas to a fuel cell, and the fuel reformer. A burner for burning off-gas from the fuel cell to heat the fuel reformer, an air supply means for supplying combustion air to the burner by a combustion air blower, and a liquid for the carburetor. Liquid fuel supply means for supplying liquid fuel by a fuel supply pump, auxiliary fuel supply means for supplying auxiliary fuel for start-up and load fluctuation to the burner, and a carburetor outlet side of the fuel reformer Temperature detector, a current detector provided on the circuit side of the load of the fuel cell, an air amount calculation unit, an air amount control unit having a function of correcting the supply amount of air for combustion, a liquid fuel calculation unit, and Liquid fuel system A method of controlling a fuel reformer of a fuel cell system including a fuel cell system, the air amount calculation for reducing a combustion air supply amount when a temperature detected by the temperature detector falls below a threshold value. Based on a command signal calculated and output from the liquid fuel calculation unit, the air amount control unit drives the combustion air blower, and based on a command signal calculated and output from the liquid fuel calculation unit by the current signal of the current detector, the liquid fuel A control unit drives the liquid fuel supply pump,
For the decrease in the temperature detected by the temperature detector due to the sudden increase in the liquid fuel supply amount due to the load change,
The air amount control unit, according to the correction signal by the current signal of the liquid fuel operation unit and the command signal from the air amount operation unit,
The supply amount of combustion air is calculated, and the supply amount of combustion air is corrected so that the temperature detected by the temperature detector does not significantly deviate from the threshold value, and the combustion air blower is controlled and driven.

[Work]

By arranging a temperature detector on the carburetor outlet side of the fuel reformer and comparing its output level with a threshold value determined by the set temperature, a decrease in the amount of off gas supplied from the fuel cell to the burner is detected, The air amount calculation unit calculates the amount of air required to burn the hydrogen in the reduced off gas, and the air amount control unit reduces the amount of combustion air supplied to the burner to optimize the off gas combustion. The calorific value of the burner increases, and the temperature of the vaporizer recovers. On the other hand, based on the command signal of the liquid fuel calculation unit that detects a sudden increase in load by the output current detector, the amount of liquid fuel sent to the vaporizer increases and the amount of reformed gas also increases. The temperature decrease of the above can be recovered rapidly, and the transient pressure oscillation generated with the temperature decrease can be prevented. Further, by controlling the air amount control unit by the command signal of the liquid fuel calculation unit to correct the heat generation amount in the transient state to a higher level, it is possible to prevent the temperature drop due to the rapid increase of the liquid fuel, and therefore the transient state. The pressure fluctuation can be suppressed more effectively.

〔Example〕

 The present invention will be described below based on examples.

FIG. 1 is a block diagram showing the apparatus of the embodiment, and the same parts as those of the prior art are designated by the same reference numerals and detailed description thereof will be omitted. In the figure, 21 is a current detector provided on the circuit side of the load 40 of the fuel cell 1, and 22 is a liquid fuel calculation unit that calculates the liquid fuel supply amount based on the output signal of the current detector 21 and issues a command signal. Yes, the difference between the output signal and the output signal of the flow rate detector 23 is obtained by the comparator 24. Based on this difference, the control unit 25 causes the pump 8
Is driven, the flow rate of the liquid fuel such as alcohol sent to the vaporizer 6 is controlled in accordance with the output current of the fuel cell 1.

On the other hand, 31 is a temperature detector on the outlet side of the carburetor 6 of the fuel reformer 3, the output of which is input to the comparator 32 and compared with the optimum operating temperature Ts of the carburetor 6. Reference numeral 33 is an air amount calculation unit, and when the temperature detected by the temperature detector 31 falls below a threshold value Ts, it is determined that the amount of hydrogen in the off gas supplied to the burner 4 has decreased and the combustion air blower. A command signal is issued to reduce the amount of air sent to the burner 4 via 5 to obtain an amount of air suitable for completely burning the hydrogen in the offgas,
When the detected temperature exceeds the threshold value Ts, on the contrary, a command signal for increasing the air amount is issued. The output signal of the air amount calculation unit 33 is compared with the output signal of the air amount detector 35 in the comparator 34, and the combustion air blower 5 is driven by the air amount control unit 36 based on the difference between the two, whereby the burner is burned. The calorific value of No. 4 can be controlled so as to maintain the optimum temperature Ts based on the temperature on the outlet side of the reformer 7. Further, the output signal of the liquid fuel calculation unit 22 is given to the air amount control unit 36, and when the liquid fuel supply amount and the air supply amount have a large difference, the air supply amount is gently corrected.

FIG. 2 is a characteristic diagram of the heat transfer amount Q of the carburetor versus the combustion air amount V for explaining the operation of the air amount control device 30 for the combustion air configured as described above, and the curve 110 is the burner 4
Curve 109 shows the characteristics when the amount of off gas containing unused hydrogen in the fuel cell 1 supplied to the fuel cell 1 is constant, curve 109 shows the characteristics when the amount of off gas decreases, and curve 111 shows the characteristics when the amount of off gas increases. Shows. In the figure, it is assumed that the load sharply increases in the stable operation state indicated by the point A on the curve 110 corresponding to the output current of the fuel cell 1. At this time, the hydrogen consumption in the fuel cell 1 increases and the amount of off-gas supplied to the burner 4 decreases, so that the operating state is B on the curve 109.
Moving to the point, the heat transfer amount Q to the carburetor 6 decreases from Q ₁ to Q ₂ , and based on this, the temperature of the carburetor 6 lowers and the risk of pressure fluctuation occurrence increases. This temperature decrease is detected by the outlet side temperature detector 31, and when the output thereof falls below the threshold value Ts, a command signal for reducing the combustion air amount is issued from the air amount calculation unit 33, and the combustion air As the amount decreases from V ₁ to V ₂ , the amount of heat transfer increases from Q ₂ to Q ₃ and the operating state C
Along with this, the temperature of the carburetor is recovered, and the unequalization of the carburetor temperature is eliminated, so that the occurrence of pressure oscillation can be prevented. On the other hand, the amount of reformed fuel gas generated increases with the recovery of the carburetor temperature, and the amount of off-gas supplied to the burner 4 also increases, so the operating conditions are point D on curve 110 and point E on 111. Try to move to. This state is detected when the output signal of the temperature detector 31 raises a threshold value, and the air amount calculation unit 33 outputs a command signal to increase the combustion air amount. It will shift to the operating state. For example, the operating state at point F is based on the output signal of the current detector 21 and is based on the output signal of the liquid fuel computing unit.
When the air amount control unit 36 receives a signal output from the fuel cell 22 and corrects the output of the air amount control unit 36 toward the air amount commensurate with the liquid fuel supply amount, the fuel corresponding to the output current of the fuel cell 1 is fueled. It shows a reformed state.For example, if the output of the air amount control unit 36 is function-controlled by the output signal of the liquid fuel calculation unit 22 so that a higher heat transfer amount can be obtained in the transient state, the load current It is possible to prevent the temperature of the carburetor 6 from lowering again due to the liquid fuel that increases in response to the sudden increase, and thus it is possible to more effectively suppress the pressure oscillation.

FIG. 3 is a characteristic diagram of the change over time of the reformer outlet pressure in the embodiment apparatus. As a result of eliminating the cause of the pressure fluctuation, the pressure changes from the pressure level 101 before the sudden increase in the load current to the pressure level 102 after the rapid increase. It is possible to quickly shift without vibration.

〔The invention's effect〕

As described above, the present invention detects the temperature on the outlet side of the carburetor of the fuel reformer and compares it with a threshold value, detects a sudden change in the load of the fuel cell as a temperature change, and supplies the combustion air to the burner. The amount is controlled by the air amount calculation unit and the air amount control unit so that the recovery of the temperature change is accelerated. As a result, the amount of off-gas supplied to the burner decreases due to a rapid increase in load, and the transient oscillation of the reformed fuel gas pressure caused by the decrease in carburetor temperature can be eliminated from the cause of its occurrence. It is possible to provide a fuel cell system including a fuel reformer that does not require a throttle, a buffer tank, and the like in the conventional device, and therefore has a simple structure and has no pressure vibration that hinders long-term reliability of the fuel cell. Further, since the output of the air amount control unit is corrected by the output signal of the liquid fuel calculation unit, it is possible to prevent the carburetor temperature from changing again due to a sudden change in the liquid fuel supply amount due to a sudden change in load. This has the advantage that less transient pressure oscillations occur.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing an embodiment apparatus, FIG. 2 is a heat transfer amount-air amount characteristic diagram of a reformer in the embodiment apparatus, and FIG. 3 is a reforming fuel gas pressure characteristic diagram in the embodiment apparatus. , 4th
FIG. 5 is a configuration diagram showing a conventional device, FIG. 5 is a pressure characteristic diagram in the conventional device, and FIG. 6 is a configuration diagram showing a different conventional device. 1 ... Fuel cell main body, 2 ... Liquid fuel tank, 3 ... Fuel reformer, 4 ... Burner, 5 ... Combustion air blower, 6 ... Vaporizer, 7 ... Reformer, 8, 14 …… Pump, 11
…… Aperture, 12 …… Buffer tank, 21 …… Current detector,
22 …… Liquid fuel computing unit, 23 …… Flow rate detector, 24,32,34…
Comparator, 25 ... Liquid fuel control unit, 30 ... Air amount control device, 31 ... Temperature detector, 33 ... Air amount calculation unit, 35 ... Air amount detector, 36 ... Air amount control unit .

Claims (1)

[Claims] 1. A fuel reformer having a liquid fuel vaporizer and a reformer for supplying hydrogen-rich fuel gas to a fuel cell, and an off-gas from the fuel cell, which is installed in the fuel reformer. A burner that heats the fuel reformer by burning the fuel, an air supply unit that supplies combustion air to the burner by a combustion air blower, and a liquid that supplies liquid fuel to the carburetor by a liquid fuel supply pump. Fuel supply means, auxiliary fuel supply means for supplying auxiliary fuel to the burner at the time of start-up and load fluctuation, a temperature detector provided on the carburetor outlet side of the fuel reformer, and the fuel cell A fuel cell including a current detector provided on the circuit side of the load, an air amount calculation unit, an air amount control unit having a function of correcting an air supply amount for combustion, a liquid fuel calculation unit, and a liquid fuel control unit system A method for controlling a fuel reformer, comprising: an air amount calculation unit for reducing a combustion air supply amount when a temperature detected by the temperature detector falls below an optimum operating temperature (hereinafter referred to as a threshold value). Based on the command signal calculated and output from the liquid fuel control unit, the air amount control unit drives the combustion air blower, and based on the command signal calculated and output from the liquid fuel calculation unit by the current signal of the current detector, the liquid fuel control is performed. The drive unit drives the liquid fuel supply pump, and suddenly increases the liquid fuel supply amount in order to cope with a sudden increase in load, the temperature detected by the temperature detector is lowered. The unit calculates the air supply amount for combustion according to the correction signal by the current signal of the liquid fuel calculation unit and the command signal from the air amount calculation unit, and the temperature detected by the temperature detector is detected from the threshold value. Control method of the fuel reformer of a fuel cell system which comprises bringing Ku the combustion air blower to correct the amount of air supplied for combustion so as not to deviate controlled driven.