JP2005190802A - Operation control method of fuel cell generator - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a control method in which an optimum operation is performed under given conditions without stopping the fuel cell generator, even if the variation of the composition of the raw fuel exceeds the upper limit of the raw fuel supply system. <P>SOLUTION: Utilizing the fact that the instruction values of a thermoregulator of a reformer change correspondingly when the methane richness of the raw fuel decreases, the electric output of a fuel cell is controlled according to these instruction values. As a control method, in order to demonstrate the original temperature regulating function based on the variations of the external temperatures, the electric output of the fuel cell is changed for the first time, or changed gradually step by step, when the instruction values deviate from the upper limit or the lower limit for a prescribed time or more. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is a fuel cell power generation of a type in which a raw fuel having a fuel composition that may fluctuate significantly, such as biogas, is reformed into a hydrogen-rich reformed gas, and this reformed gas is used as a fuel to generate power. The present invention relates to an operation control method in an apparatus.

  City gas, biogas, etc. are used as the fuel gas used in the fuel cell power generation system. Usually, city gas is dry and its composition is basically stable. The conventional fuel cell power generator can calculate the amount of heat generation, that is, the fuel flow rate required for power generation, only by performing correction in the standard state (0 ° C., 1 atm state) at the fuel inlet.

  On the other hand, when biogas is used as the raw fuel, the methane concentration in the generated biogas changes depending on the day and night and the season. Therefore, it is necessary to perform control corresponding to this change.

  For example, in Patent Document 1, a fuel cell plant that generates electricity using biogas obtained by methane fermentation treatment of wastewater from a beer factory as a fuel, the amount of biogas is measured using a biogas concentration sensor or a biogas flow sensor. A method is disclosed in which a power generation load is controlled based on a calculation value obtained by calculation. However, in this prior art, the use of a reformer that uses the exhaust gas (off-gas) of a fuel cell as a heat source as a biogas treatment device, and the effect of biogas fluctuations in that case are not considered or studied. .

  Further, in Patent Document 2, the component concentration of the exhaust reformed gas changes depending on the operating state of the fuel cell system. As a result, the amount of heat generated in the combustor of the reformer changes. Recognizing that the reactor outlet temperature is disturbed and the balance of the entire system is lost, the exhaust reforming gas component concentration in the fuel cell main body is estimated by calculation using predetermined parameters, and the exhaust gas is discharged based on this estimated value. Control is performed to suppress the influence of disturbance caused by changes in the component concentration of the reformed gas. However, since this control method is based on the premise that a raw material having a somewhat stable concentration such as methanol is reformed, the control method is applied to a system that uses a gas having extremely large component concentration fluctuations such as biogas. I can't.

  Therefore, in general, in a fuel cell power generation facility using biogas as fuel, attention is paid to a command value of a temperature controller of a reformer that uses off-gas of the fuel cell as fuel, and based on this command value. The fuel flow is adjusted.

  When the methane concentration of the methane fermentation gas decreases and the calorific value of the raw fuel decreases, the raw fuel is increased by feeding back this composition variation to the command value of the temperature controller of the reformer. The amount of hydrogen supplied to the fuel cell is increased to prevent hydrogen shortage, so-called gas shortage, in the fuel cell. When this gas shortage occurs, hydrogen for the electrochemical reaction is not supplied to the fuel cell, and the cell is damaged.

  However, this method of adjusting the raw fuel flow has drawbacks. This is because the upper limit of the flow rate of the raw fuel is mechanically determined in the flow meter, raw fuel valve, raw fuel system piping, and desulfurization device. The amount of hydrogen supplied from the mass device to the fuel cell is reduced, and there is a risk that the fuel cell will run out of gas.

  In addition, the off-gas that has consumed hydrogen in the fuel cell is returned to the reformer and burned to become the heat required for reforming. However, if this amount of heat decreases due to insufficient hydrogen, the reformer temperature decreases and the reforming reaction occurs. Cannot be maintained.

In order to solve this, it is necessary to increase the capacity of the raw fuel equipment and increase the raw fuel supplied to the reformer. However, there is a risk of increasing the equipment cost and the size of the apparatus. There are many problems.
JP 2000-90953 A (page 5, column 7, line 28 and below) Japanese Patent Laid-Open No. 2001-229941 (page 3, column 3, line 20 and below)

  The present invention provides a control method capable of optimal operation under given conditions without stopping the fuel cell power generation device even if the fluctuation of the raw fuel composition exceeds the upper limit of the raw fuel supply system. .

  In order to solve the above problems, the present invention provides a reformer that reforms a raw fuel to generate a hydrogen-rich reformed gas, and an electrochemical reaction between the reformed gas and an oxidant to generate power. In the operation control method of the fuel cell power generation apparatus including the fuel cell, the raw fuel flow rate is controlled by changing the fuel cell output power according to the command value of the temperature regulator of the reformer. .

  According to this operation method, when the raw fuel concentration is lowered, the reformed gas hydrogen concentration in the reformer is lowered and the hydrogen in the battery off-gas returning to the reformer is reduced, so that the temperature of the reformer is lowered. The command value moves in the direction of increasing the temperature of the reformer temperature controller, and the raw fuel flow rate is increased.

  The power generation load is reduced before the supply amount of raw fuel reaches the upper limit. Thus, it is possible to provide a control system in which the fuel composition variation is fed back to the fuel cell electrical output according to the command value of the temperature controller of the reformer.

  At steady times when the load of the fuel cell power generator does not fluctuate, the temperature of the combustion air and the amount of heat dissipated by the reformer change due to fluctuations in the outside air temperature, resulting in temperature fluctuations of the reformer. The temperature controller of the quality device must work.

  Therefore, in order to compensate for the effects of fluctuations in the composition of the raw fuel without being affected by these temperature fluctuation factors in the steady state, the command value of the reformer temperature controller is set to the upper limit value or the lower limit value for a predetermined time. When the operation is continued, the fuel cell electrical output is preferably changed (the invention of claim 2).

  Specifically, it is desirable to change and control the raw fuel concentration constant when the command value of the temperature controller of the reformer continues the upper limit and lower limit values for 1 to 10 minutes or longer (invention of claim 3). .

  In addition, by continuously changing the step width of the raw fuel concentration constant, the fluctuation range of the raw fuel flow rate can be reduced and stable control can be achieved (invention of claim 4).

  The purpose of the fluctuation range is, for example, in increments of 1 to 5% (the invention of claim 5).

  It is also possible to change the control constant (PID constant) of the temperature regulator of the reformer so that the command value directly affects the increase / decrease of the fuel cell output, and to perform control linked to the temperature of the reformer. (Invention of Claim 6).

  According to the present invention, the fuel cell electrical output is controlled from the command value of the temperature controller of the reformer. Therefore, even if the raw fuel composition during operation exceeds the raw fuel supply limit, the fuel cell including the raw fuel flow rate is included. A fuel cell power generator that can properly control the control system (steam, air, water), prevent cell damage due to hydrogen shortage in the fuel cell, and enable stable operation of the equipment accompanying proper temperature control of the reformer Can be provided.

  Before explaining an embodiment of the present invention, an example of the overall configuration of a fuel cell power generation system that reforms biogas and uses it as fuel for a fuel cell will be described with reference to FIG.

  Since FIG. 3 is drawn with attention paid only to the oxidant (air) and fuel flow of the fuel cell power generation system, for example, the electrolyte matrix necessary for causing the power generation reaction from the fuel cell 30 is omitted. is there. Air 31 as an oxidant is supplied to the air electrode of the fuel cell 30 through a blower, and raw fuel 32 is supplied to the fuel electrode after performing necessary processing. That is, the raw fuel 32 is sent to the desulfurizer 34 through the flow control valve 33, where the sulfur content is removed and reaches the suction port of the ejector 35. As the driving steam of the ejector 35, for example, steam obtained by steam separation of the cooling water heated by flowing through the cooling plate of the fuel cell 30 by the steam separator 36 is supplied via the flow control valve 37. The desulfurized raw fuel and water vapor are sent to the reformer 38 in a state where they are mixed in the ejector 35. The reformer 38 is attached with a furnace 39 for combusting exhaust gas (off gas) discharged from the fuel electrode of the fuel cell, for example, and the combustion heat in the furnace absorbs heat of methane components and water vapor contained in the raw fuel. The reaction is promoted to reform the raw fuel into a fuel gas rich in hydrogen components (so-called hydrogen-rich). Since this fuel gas contains carbon monoxide that poisons the catalyst of the fuel cell, it is converted into harmless carbon dioxide by the CO converter 40 and then supplied to the fuel cell 30. The DC generated power of the fuel cell can be used after being converted into AC power via an inverter or the like, for example.

  The fuel cell system shown in FIG. 3 is known per se, and equipment that is not directly related to the present invention, such as an ejector, can be replaced by another equivalent equipment.

  Now, two embodiments for applying the present invention in a fuel cell system as shown in FIG. 3 will be described below.

  FIG. 1 is a control block diagram of an embodiment of the present invention in a case where the output of a fuel cell is increased or decreased stepwise, and a reformer temperature controller 1 which can be a PID controller is connected to a reformer temperature. By inputting 2 and the reformer temperature set value 3, the reformer temperature command value 4 is output. From this reformer temperature command value 4, for example, the function generator 5 derives a fuel cell electrical output increase / decrease value (vertical axis) with respect to the reformer temperature command value (horizontal axis). For example, when the reformer temperature command value 4 continues below 10% for a certain period of time, the fuel cell electrical output is decreased by 5 KW, and after this operation, if 10% or less continues for a certain period of time, it is decreased again by 5 KW. This operation is performed up to the lower limit of 40 KW. Similarly, when the reformer temperature command value 4 continues 90% or more for a certain period of time, the fuel cell electrical output is increased by 5 kW. If 90% or more continues for a certain period after this operation, the reformer temperature command value 4 is increased again by 5 kW. This operation is performed until the fuel cell output reaches the upper limit value. That is, the fuel cell other output increase / decrease value 6 obtained by the function generator 5 is added to the fuel cell output set value 7 as a correction value to obtain the fuel cell output command value 8. The fuel cell load is increased or decreased by the fuel cell power command value 8, and as a result, the raw fuel flow rate 9 is controlled and fed back to the reformer temperature. This fuel cell output increase / decrease process changes the composition of the actual raw fuel that is supplied, so even if the hydrogen in the cell off-gas decreases and the reformer temperature decreases, the load is reduced and reforming is performed. The temperature of the vessel can be controlled.

    FIG. 2 is a control block diagram of an embodiment of the present invention in the case where the output of the fuel cell is continuously increased or decreased. The reformer temperature controller 11 which can be a PID controller is connected to the reformer temperature. 12 and the reformer temperature set value 13 are input, the reformer temperature command value 14 is output. A fuel cell electrical output increase / decrease value 16 is derived by the function generator 15 from the reformer temperature command value 14. In the following, as in the embodiment of FIG. 1, the fuel cell other output increase / decrease value 16 is added to the fuel cell output set value 17 as a correction value to obtain the fuel cell output command value 18. The fuel cell load is increased / decreased by the fuel cell power command value 18, and as a result, the raw fuel flow rate 19 is controlled and fed back to the reformer temperature. This fuel cell output increase / decrease process changes the composition of the actual raw fuel that is supplied, so even if the hydrogen in the cell off-gas decreases and the reformer temperature decreases, the load is reduced and reforming is performed. The temperature of the vessel can be controlled.

  Thus, according to the present invention, focusing on the temperature command value that is the output of the temperature regulator of the reformer, the electric output of the fuel cell is controlled rather than the flow rate of the raw fuel. It is possible to perform control in consideration of changes and other disturbances to the reformer.

Control block diagram of an embodiment of the present invention Control block diagram of another embodiment of the present invention Configuration diagram of a fuel cell power generation system as an example of implementation of the present invention

Explanation of symbols

DESCRIPTION OF SYMBOLS 1,11 Reformer temperature controller 2,12 Reformer temperature 3,13 Reformer temperature set value 4,14 Reformer temperature command value 5,15 Function generator 6,16 Fuel cell output increase / decrease value 7, 17 Fuel cell output set value 8, 18 Fuel cell output command value 9, 19 Raw fuel flow rate

Claims (6)

  A reformer that reforms a raw fuel mainly composed of biogas to produce a reformed gas rich in hydrogen components, and a fuel cell that generates electricity by electrochemically reacting the reformed gas and an oxidant. In the fuel cell power generator equipped with the fuel cell power generator, the electric output of the fuel cell is controlled by the command value of the temperature controller of the reformer that varies according to the change in the biogas concentration. .   2. The operation control of a fuel cell power generator according to claim 1, wherein when the command value of the temperature controller of the reformer continues the upper limit value or the lower limit value for a predetermined time or longer, the fuel cell electrical output is changed. Method.   3. The fuel cell power generator according to claim 2, wherein when the command value of the temperature controller of the reformer continues the upper limit value or the lower limit value for 1 to 10 minutes or longer, the fuel cell electrical output is changed. Operation control method.   2. The operation control method for a fuel cell power generator according to claim 1, wherein the fluctuation range of the fuel cell electric output is continuously changed.   5. The operation control method for a fuel cell power generator according to claim 4, wherein the fluctuation range of the fuel cell electric output is continuously changed in increments of 1 to 5%. 2. The operation control of the fuel cell power generator according to claim 1, wherein the control value (PID constant) of the temperature regulator of the reformer is changed, and the command value directly affects the increase or decrease of the fuel cell output. Method.

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