JPH07101613B2 - Fuel cell power generation system - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an inter-electrode differential pressure control means for controlling the inter-electrode differential pressure between a fuel electrode and an oxidizer electrode (hereinafter, referred to as an air electrode) of a fuel cell to a constant value. The present invention relates to an improvement of a fuel cell power generation system including the.

[Technical background of the invention]

BACKGROUND ART Conventionally, a fuel cell is known as a device that directly converts the chemical energy of fuel into electrical energy. In this fuel cell, usually, a pair of porous electrodes are arranged with an electrolyte sandwiched between them, fuel such as hydrogen is brought into contact with the back surface of the fuel electrode that is one electrode, and oxygen is used on the back surface of the air electrode that is the other electrode. It is designed to bring electrical energy out between the electrodes by using an electrochemical reaction that occurs at the time of contact with an oxidizing agent such as It can extract energy.

Further, in this type of fuel cell, a fuel cell power generation system is often configured with a fuel reformer for producing hydrogen gas as a fuel by steam reforming a raw material gas. In this fuel reformer, a mixed gas of a raw material gas and steam is introduced inside a reforming pipe having a reforming reaction catalyst layer provided inside, and combustion fuel and combustion air are introduced outside the reforming pipe. By passing a high-temperature heating gas obtained by combusting the above with a combustor, the mixed gas is reformed into a reformed gas and supplied to a fuel cell as a load.

By the way, in a fuel cell power generation system including a fuel reformer of this type, the reformed gas containing hydrogen obtained by steam reforming in the fuel reformer is used as the heat source of the steam reforming reaction, From the viewpoint of the thermal efficiency of the fuel cell power generation system, it is preferable to use the exhaust fuel containing hydrogen, which has been used for power generation in the battery, as the combustion fuel.

FIG. 2 shows a configuration example of a fuel cell power generation system equipped with this type of fuel reformer. In the figure, reference numeral 1 is an air treatment apparatus for compressing air to obtain compressed air, which is composed of, for example, a turbo compressor, and 2 is a raw fuel supply apparatus for supplying a mixed gas of a raw material gas and steam. Also, 3
Introduces the mixed gas of the raw material gas and the steam from the raw fuel supply device 2 into the reforming pipe 31 in which the reforming reaction catalyst layer is provided, and the combustion fuel to the outside of the reforming pipe 31. And a fuel reformer for reforming the mixed gas into a reformed gas by passing a high-temperature heating gas obtained by burning the combustion air in the combustor 32. Further, 4 introduces the reformed gas from the fuel reformer 3 as a fuel into the fuel electrode 41 through the fuel supply line 5 and the fuel flow rate control valve 6, and at the same time, the compressed air obtained by the air treatment device 1 is introduced. Is introduced into the air electrode 42 as an oxidant through the air supply line 7 and the air flow rate control valve 8, and these are electrochemically reacted to generate electric power. The fuel reformer 3 through the differential pressure control valve 9 and the exhaust fuel line 10
In addition to being discharged as combustion fuel to the fuel reformer 3, the air that has been used for power generation is also discharged to the fuel reformer 3 through the exhaust air line 11. Furthermore, 12 is based on the detection output from the differential pressure detector 13 which detects the differential pressure between the fuel electrode 41 and the air electrode 42 of the fuel cell 4, so as to maintain the differential pressure at a constant value. A valve controller that controls the opening degree of the differential pressure adjusting valve 9, and the inter-electrode differential pressure controlling means comprises the inter-electrode differential pressure adjusting valve 9, the valve controller 12 and the differential pressure detector 13.

[Problems of Background Art] However, in the fuel cell power generation system including the fuel reformer as described above, the following problems occur when the load is rapidly increased from the continuous minimum load of the system to the target load. That is, for example, from the continuous minimum load (for example, 25%) of the fuel cell power generation system to the target load (for example, 10%).
When the load is rapidly increased to 0%), the flow rates of the compressed air and the reformed gas introduced into the fuel cell 4 are rapidly increased by controlling the opening of the fuel flow rate control valve 6 and the air flow rate control valve 8. Thus, if the inter-electrode differential pressure on the air electrode 42 side becomes excessive, the valve controller 12 keeps the differential pressure at a constant value based on the detection output from the differential pressure detector 13. Thus, the opening degree of the inter-electrode differential pressure control valve 9 is controlled in the closing direction. However, in such a fuel cell power generation system,
As described above, the fuel after being used for power generation in the fuel cell 4 is introduced into the fuel reformer 3 as its combustion fuel through the inter-electrode differential pressure control valve 9 and the exhaust fuel line 10. Therefore, when the load of the system is suddenly increased (transient fluctuation) as described above, the opening degree of the inter-electrode differential pressure control valve 9 is narrowed in the closing direction, so that the combustor 32 of the fuel reformer 3 becomes stable. It becomes impossible to secure the minimum required fuel flow rate for combustion to continue combustion. As a result, the combustion of the combustor 32 of the fuel reformer 3 becomes extremely unstable, and in some cases, there is a problem that the combustor 32 misfires (fire disappears).

[Object of the Invention] The present invention has been made to solve the above problems, and its purpose is to rapidly increase the load of the system (during transient fluctuation).
It is possible to avoid insufficiency of fuel supply to the combustor due to throttling of the inter-electrode differential pressure control valve, to always ensure the minimum combustion fuel flow rate, and to reliably prevent combustion instability and misfire in the combustor. To provide a highly reliable fuel cell power generation system.

[Summary of the Invention] In order to achieve the above object, in the present invention, an air treatment device for compressing air to obtain compressed air and a reforming reaction catalyst layer are provided inside, and a mixed gas of a raw material gas and steam is provided. A fuel reformer for introducing and burning the combustion fuel and the combustion air by the internal combustor to transfer the heat obtained to the mixed gas to reform the mixed gas into a reformed gas;
The reformed gas from the fuel reformer is introduced into the fuel electrode as fuel, and the compressed air obtained in the air treatment device is introduced into the oxidant electrode as an oxidant, and these are reacted electrochemically to generate electricity. And a fuel cell that discharges the fuel after being used for power generation as a fuel for combustion to the fuel reformer through the exhaust fuel line, and misfire prevention in the combustor of the fuel reformer provided on the exhaust fuel line. Fuel flow rate control mechanism that always secures the minimum fuel flow rate passage for fuel control, and controls the fuel flow rate in the fuel flow rate control mechanism so that the differential pressure between the fuel electrode and the oxidizer electrode of the fuel cell is maintained at a constant value. And a flow rate controller.

Further, the fuel flow rate adjusting mechanism is provided on the exhaust fuel line, and the opening degree is controlled by the flow rate controller so that the differential pressure between the fuel electrode and the oxidant electrode of the fuel cell is maintained at a constant value. A valve, a bypass line provided to bypass the first valve, and a second valve provided on the bypass line and having a valve opening set to obtain a minimum fuel flow rate. ing.

Further, the fuel flow rate adjusting mechanism is provided with a passage for a minimum fuel flow rate at all times, and a flow rate controller adjusts the opening so as to keep the differential pressure between the fuel electrode and the oxidant electrode of the fuel cell at a constant value. It consists of a controlled orifice valve.

With this configuration, even if the flow rate controller drastically reduces the fuel flow rate in the fuel flow rate adjusting mechanism in order to keep the differential pressure between the fuel electrode and the oxidizer electrode of the fuel cell at a constant value, Since the control mechanism is provided with a passage for the minimum fuel flow rate for preventing misfire, the minimum required fuel is supplied to the combustor, and combustion in the combustor is performed stably.

The minimum fuel flow rate ensured by the opening degree of the second valve or the minimum opening degree of the orifice valve that constitutes the fuel flow rate adjusting mechanism is the minimum fuel quantity for preventing misfire in the combustor of the fuel reformer. The flow rate. The minimum fuel flow rate for preventing misfire is, for example, 1/10 of the opening of the first valve or the opening of the orifice valve when the differential pressure is maintained at a constant value in a normal state. The following is a very small flow rate. Therefore, even if a small amount of fuel equal to or less than 1/10 is constantly flowing, the valve controller adjusts the opening of the first valve or the orifice valve to set the differential pressure to a constant value. It can be controlled sufficiently.

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment of the present invention shown in the drawings will be described below.
FIG. 1 shows a configuration example of a fuel cell power generation system according to the present invention. The same parts as those in FIG. 2 are designated by the same reference numerals and the description thereof will be omitted. Only different parts will be described here. That is, FIG. 1 is provided with a bypass line 14 for bypassing the inter-electrode differential pressure adjusting valve 9 as the first valve in FIG.
A bypass valve 15 as a second valve having a valve opening fixedly set so as to obtain a minimum required fuel flow rate for combustion in the combustor 32 of the fuel reformer 3 is provided on the valve 14. It is something that is done. Here, the inter-electrode differential pressure control valve 9, the bypass run 14, and the bypass valve 15 constitute a fuel flow rate control mechanism.

In the fuel cell power generation system having such a configuration, the mixed gas of the raw material gas and the steam supplied from the raw fuel supply device 2 is introduced into the reforming pipe 31 of the fuel reformer 3 and burned by the combustor 32. The reformed gas is reformed by the high-temperature heating gas, and the flow rate according to the load command value is adjusted by the fuel flow rate control valve 6 on the fuel supply line 5 and supplied to the fuel electrode 41 of the fuel cell 4. On the other hand, the compressed air supplied from the air treatment device 6 is supplied to the air electrode 42 of the fuel cell 4 after the flow rate according to the load command value is adjusted by the air flow rate adjusting valve 8 on the air supply line 7. . Then, in the fuel cell 4, these are electrochemically reacted to generate power, and the exhaust fuel used for this power generation is burned to the combustor 32 of the fuel reformer 3 through the exhaust fuel line 10 as combustion fuel. Similarly, the exhaust air used for power generation is supplied to the combustor 32 of the fuel reformer 3 as combustion air through the exhaust air line 11. On the other hand, the inter-electrode differential pressure control valve 9 provided on the exhaust fuel line 10 is provided with the combustion electrode 41 and the air electrode in the combustion cell 4.
The degree of opening is controlled by the valve controller 12 as a flow rate controller so that the inter-electrode differential pressure with 42 becomes a constant value. In addition, the bypass valve 15 provided on the bypass line 14 that bypasses the inter-electrode differential pressure control valve 9 has the bypass valve 15
The valve opening is constantly fixed so as to obtain the minimum required fuel flow rate for the combustor 32 of FIG.

Next, if, for example, the load command value is increased from this state and the load of the fuel cell power generation system is rapidly increased from the continuous minimum load (for example, 25%) to the target load (for example, 100%), By controlling the opening of the fuel flow rate control valve 6 and the air flow rate control valve 8, the flow rates of the compressed air and the reformed gas introduced into the fuel cell 4 increase rapidly. Thus, if the inter-electrode differential pressure on the air electrode 42 side becomes excessive, the valve controller 12 keeps the differential pressure at a constant value based on the detection output from the differential pressure detector 13. As a result, the opening degree of the inter-electrode differential pressure control valve 9 is throttle-controlled in the closing direction. In this case, in the fuel cell power generation system of the present embodiment, the inter-electrode differential pressure control valve on the exhaust fuel line 10 that supplies the fuel after being used for power generation in the fuel cell 4 to the combustor 32 of the fuel reformer 3 9 is configured to have a bypass line 14 having a bypass valve 15 whose valve opening is always fixed so as to bypass it, so that the gap between poles is increased when the load suddenly increases (transient fluctuation). Even if the opening degree of the pressure control valve 9 is narrowed in the closing direction, the combustor 32 of the fuel reformer 3 is provided with the minimum required flow rate of fuel regardless of the valve opening degree of the inter-electrode differential pressure control valve 9. It will always be secured. As a result, the combustion of the combustor 32 of the fuel reformer 3 becomes extremely stable, and it is possible to reliably prevent the misfire of the combustor 32 as in the conventional case.

From the above, the fuel cell power generation system of the present embodiment can obtain the following effects.

(A) Insufficient supply of combustion fuel to the combustor 32 of the fuel reformer 3 due to narrowing of the opening of the inter-electrode differential pressure control valve 9 during a rapid load increase (transient change) of the system, which has been a problem in the past. It is possible to solve the problem, and it is possible to reliably prevent unstable combustion and misfire of the combustor 32.

(B) Even if the inter-electrode differential pressure control valve 9 malfunctions and the valve is fully closed, the fuel flow rate bypassing the inter-electrode differential pressure control valve 9 is constantly flowing, so the inter-electrode differential pressure exceeds the limit. It can be prevented from becoming large and is extremely effective in protecting the fuel cell 4.

In the above embodiment, the inter-electrode differential pressure control valve 9 is bypassed as a means for ensuring the minimum required fuel flow rate to be supplied to the combustor 32 of the fuel reformer 3 when the system load increases suddenly (transient change). The case where the bypass line 14 and the bypass valve 15 are provided has been described, but the same effect can be obtained even if the following means are taken.

(A) Bypass line that bypasses the inter-electrode differential pressure control valve 9
The bypass valve 15 above 14 may be replaced with a control valve.

(B) Bypass line that bypasses the inter-electrode differential pressure control valve 9
The bypass valve 15 located above 14 may be replaced with an element having a flow rate adjusting function, such as an orifice in which a minimum fuel flow rate for preventing misfire is secured in the combustor 32 of the fuel reformer 3.

(C) Bypass line that bypasses the inter-electrode differential pressure control valve 9
The inter-electrode differential pressure adjusting valve 9 may be an orifice valve without providing 14. In this case, the opening degree of the orifice valve as the fuel flow rate adjusting mechanism that secures the minimum fuel flow rate for preventing misfire is the same as in the case of the inter-electrode differential pressure adjusting valve 9.
The opening degree is controlled so that the differential pressure between the fuel electrode and the oxidizing electrode of the fuel cell is maintained at a constant value based on the opening control command from the. With this configuration, the system configuration can be simplified.

(D) A mechanical interlock may be applied to the inter-electrode differential pressure control valve 9 so that the valve cannot be throttled beyond a certain opening.

In addition, the present invention can be variously modified and implemented within the scope of the invention.

[Effects of the Invention] As described above, according to the present invention, the minimum fuel flow rate for preventing misfire in the combustor of the fuel reformer is provided on the exhaust fuel line connecting the fuel cell and the fuel reformer. Is provided with a fuel flow rate adjusting mechanism in which the passage is always secured. Therefore, avoid a shortage of fuel supply to the combustor due to throttling of the inter-pole differential pressure control valve during a sudden increase in system load (transient fluctuation), and always ensure a minimum combustion fuel flow rate to ensure combustion instability of the combustor. It is possible to provide a highly reliable fuel cell power generation system capable of reliably preventing fire and misfire.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention, and FIG. 2 is a block diagram showing a conventional fuel cell power generation system. 1 ... Air treatment device, 2 ... Raw fuel supply device, 3 ... Fuel reformer, 31 ... Reforming reaction tube, 32 ... Combustor,
4 ... Fuel cell, 41 ... Fuel electrode, 42 ... Air electrode, 5 ... Fuel supply line, 6 ... Fuel flow rate control valve, 7 ... Air supply line, 8 ... Air flow rate control valve, 9 ... … Differential pressure control valve between poles, 10 …… Exhaust fuel line, 11 …… Exhaust air line, 12 …… Valve controller, 13 …… Differential pressure detector, 14 …… Bypass line, 15 …… Bypass valve.

Claims (3)

[Claims] 1. An air treatment device for compressing air to obtain compressed air, and a reforming reaction catalyst layer provided therein, for introducing a mixed gas of a raw material gas and steam, and for producing a combustion fuel and a combustion air. A fuel reformer for reforming the mixed gas into a reformed gas by transmitting the heat obtained by combustion by an internal combustor to the mixed gas; and the reformed gas from the fuel reformer as a fuel. The compressed air obtained by the air treatment device is introduced into the oxidant electrode as an oxidant and introduced into the fuel electrode, and these are electrochemically reacted to generate power, and the fuel after being used for this power generation is A fuel cell for discharging as combustion fuel to the fuel reformer through an exhaust fuel line, and a minimum fuel flow rate for preventing misfire in the combustor of the fuel reformer, which is provided on the exhaust fuel line. The passage is always secured A fuel flow rate adjusting mechanism, and a flow rate controller for controlling the fuel flow rate in the fuel flow rate adjusting mechanism so as to maintain the pressure difference between the fuel electrode and the oxidizer electrode of the fuel cell at a constant value. Fuel cell power generation system. 2. The fuel flow rate adjusting mechanism is provided on the exhaust fuel line, and the opening degree is controlled by the flow rate controller so as to maintain the differential pressure between the fuel electrode and the oxidant electrode of the fuel cell at a constant value. A first valve, a bypass line provided to bypass the first valve, and a valve opening provided on the bypass line to obtain the minimum fuel flow rate. A second valve and a second valve.
The fuel cell power generation system according to the item. 3. The fuel flow rate adjusting mechanism always secures a passage for the minimum fuel flow rate, and keeps a differential pressure between a fuel electrode and an oxidizer electrode of the fuel cell at a constant value by the flow rate controller. The fuel cell power generation system according to claim 1, wherein the fuel cell power generation system is an orifice valve whose opening is controlled as described above.