JP4934950B2 - Fuel cell power generator and operation control method - Google Patents

Description

  The present invention relates to a fuel cell power generator that controls the flow rates of fuel gas and air based on the output power of a fuel cell, and in particular, stable operation control is possible not only during rated operation but also during startup and shutdown. The present invention relates to operation control of a fuel cell power generator.

A fuel cell having a laminated structure in which a solid electrolyte layer made of an oxide ion conductor is sandwiched between an air electrode layer (cathode) and a fuel electrode layer (anode) from both sides is a high-performance fuel cell that directly converts chemical energy of fuel into electrical energy. It is attracting attention as an efficient and clean power generator. In the solid oxide fuel cell, an oxidant gas (oxygen) is supplied to the air electrode layer side, and a fuel gas (H ₂ , CO, CH _4, etc.) is supplied to the fuel electrode layer side.

Oxygen supplied to the air electrode layer passes through the pores in the air electrode layer and reaches the vicinity of the interface with the solid electrolyte layer, and receives electrons from the air electrode layer at this portion to receive oxide ions (O ²⁻ ). Is ionized. The oxide ions diffuse and move in the solid electrolyte layer toward the fuel electrode layer. Oxide ions that have reached the vicinity of the interface with the fuel electrode layer react with the fuel gas at this portion to generate reaction products (H ₂ O, CO _2, etc.), and discharge electrons to the fuel electrode layer.
Electrons generated by such an electrode reaction can be taken out as an electromotive force at an external load of another route.

The electrode reaction when hydrogen is used as the fuel is as follows.
Air electrode: 1/2 O ₂ + 2e ⁻ → O ²⁻
Fuel electrode: H ₂ + O ²⁻ → H ₂ O + 2e ⁻
Overall: H ₂ +1/2 O ₂ → H ₂ O

  By the way, the maximum output of the fuel cell is determined by the amount of supplied fuel gas and the amount of oxidant gas (air), and the gas flow rate for stably operating the fuel cell supplies a somewhat excessive flow rate. It is common. This excess rate is called the utilization rate, and is defined as the ratio of the gas flow rate used for the power generation reaction to the supplied gas flow rate.

In general, the usage rate is set to a preferable standard value for operation according to the structure and performance of the fuel cell, and the load (output current amount) is set so that the fuel cell does not operate beyond a certain usage rate. Control is performed so as to stably maintain the output voltage by controlling the flow rate of fuel gas and the flow rate of air supplied to the fuel cell in response to the change. When the utilization rate exceeds a certain level, a decrease in battery voltage due to an increase in current occurs.
For example, Patent Literature 1, Patent Literature 2, and the like are disclosed as prior arts related to fuel cell operation control with such a gas flow rate.
Japanese Patent Laid-Open No. 3-122971 JP-A-9-147893

  By the way, normally, in a fuel cell, the temperature inside the battery module is gradually raised to a predetermined operating temperature (that is, a rated output temperature) at the time of start-up (when power generation is started), and the temperature is kept constant at a predetermined output. When the operation is stopped, it is necessary to decrease the output while gradually lowering the temperature. This is because if the temperature is not raised or lowered while keeping the temperature of the entire fuel cell module constant, temperature distribution occurs in the power generation cell, and the power generation cell may be damaged by the thermal stress at that time.

  However, in the conventional operation control, the gas flow rate based on the preferable fuel utilization rate is not strictly controlled especially in the temperature rising period and the temperature falling period, and thus the fuel utilization rate is deviated from the reference value. The rapid change in temperature of the power generation cell and the significant increase / decrease in the output power are repeated, and the problem is that damage (characteristic deterioration and breakage) of the power generation cell due to the fuel cell being exposed to an overload state is promoted. there were.

  The present invention was made in view of such problems, and not only in the rated output period, but also in less than rated operation in the start / stop period, while obtaining stable output power by smooth temperature rise / fall, It is an object of the present invention to provide a fuel cell power generation apparatus and an operation control method thereof that prevent the deterioration and breakage of the characteristics of the power generation cell due to the thermal cycle and extend the life.

That is, the invention described in claim 1 is a method for controlling the operation of a fuel cell that generates output power in accordance with the fuel gas supply amount and the air supply amount. Data, and control the fuel gas supply amount so that the fuel utilization rate is less than or equal to the fuel utilization rate data when the temperature rises and the fuel utilization rate is equal to or greater than the fuel utilization rate data when the temperature falls Thus, the output power is controlled.

Further, the invention according to claim 2 is the operation control method according to claim 1, wherein each output current versus fuel in the temperature rising period from the output power of 0 to the rated output and the temperature falling period from the rated output to 0 in the operation control method of the first aspect. It has utilization rate data, and controls output power by controlling the fuel gas supply amount based on the output current versus fuel utilization rate data in each operation period.

The invention described in claim 3 is characterized in that, in the operation control method described in claim 1 , further, the air supply amount is controlled within the rated output period to maintain the heat self-sustaining state.

According to a fourth aspect of the present invention, there is provided a fuel cell power generator that generates output power in accordance with a fuel gas supply amount and an air supply amount, a fuel supply system that supplies fuel gas to the fuel cell, and a fuel cell. An air supply system that supplies air and a control unit that controls each of these systems to perform operation control according to any one of claims 1 to 3 are provided.

Further, the invention according to claim 5 is the fuel cell power generator according to claim 4 , wherein the fuel cell discharges the remaining gas that has not been used in the power generation reaction from the outer periphery of the power generation cell. This is a solid oxide fuel cell.

Here, according to the operation control method according to any one of claims 1 to 3 , the operation temperature of the fuel cell can be maintained efficiently only with heat generated by itself without applying heat from the outside during the rated output period. In addition to being able to perform a self-sustained operation, smooth operation control can be performed and stable output power can be obtained even during a temperature rising period at the start of operation and a temperature decreasing period at the time of operation stop.
Further, in the fuel cell power generation device according to claim 4 , smooth temperature increase / decrease control prevents the thermal distortion of the fuel cell stack and other high-temperature parts due to the thermal cycle, and the deterioration or damage of the power generation cell characteristics. Thus, the life of the fuel cell power generator can be extended.
Further, since the output current vs. fuel utilization rate data corresponding to each operation period is held and the control is simply made by referring to the data, the amount of data held in the control unit is small, and the microcomputer control is facilitated.

  As described above, according to the present invention, in the rated output period, an efficient thermal self-sustained operation can be performed, and not only the rated output period can be controlled by smooth temperature increase / decrease control during start / stop. Stable output power can be obtained even during operation below the rated value during the temperature rising or cooling period, and the occurrence of thermal distortion of the fuel cell stack 1 and other high-temperature parts in the heat cycle is prevented, and the characteristics of the power generation cell are deteriorated. The life of the fuel cell power generator can be extended by avoiding damages.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
Here, FIG. 1 shows a schematic configuration of a fuel cell power generator to which the present invention is applied, FIG. 2 shows an operation control flow of the fuel cell power generator of the present invention, and FIG. 3 shows an output current pair used for the operation control. FIG. 4 shows the internal structure of the fuel cell stack.

  As shown in FIG. 1, the fuel cell power generator according to this embodiment includes a solid oxide fuel cell 1 (P = IV) that generates DC output power P (P = IV) according to the fuel gas supply amount and the air supply amount. The fuel cell stack 1), the air blower 22 and each air supply pipe are configured to introduce an oxidant gas (air) into the fuel cell stack 1, the fuel gas blower 21, the desulfurizer 23, and each fuel gas supply. A fuel supply system 40 configured by piping or the like to introduce fuel gas (city gas) into the fuel cell stack 1 and disposed in the fuel cell module to convert the hydrocarbon gas from the desulfurizer 23 into a hydrogen-rich fuel gas. A reformer 19 for reforming, an inverter 24 for converting a DC output from the fuel cell stack 1 into an AC output and supplying AC power Pa to an external load (not shown), the above-described fuel supply system 40 and air supply system And a control unit 20 for controlling the 0.

  In addition, the control unit 20 outputs output current detection information I and output voltage detection information V of the fuel cell stack 1 sent from detectors (not shown) arranged at appropriate positions in the fuel cell power generator. Each detection information such as temperature detection information T of the fuel cell stack 1 and output power detection information Pa of the inverter 24 is input.

  As shown in FIG. 4, the fuel cell stack 1 includes a power generation cell 5 in which a fuel electrode layer 3 and an air electrode layer 4 are disposed on both sides of a solid electrolyte layer 2, and a fuel electrode current collector disposed outside the fuel electrode layer 3. The body 6, the air electrode current collector 7 disposed outside the air electrode layer 4, and the separator 8 disposed outside each current collector 6, 7 constitute a single cell, and the single cell is arranged in the vertical direction. Many are stacked.

Here, the solid electrolyte layer 2 is composed of stabilized zirconia (YSZ) or the like to which yttria is added, and the fuel electrode layer 3 is composed of a metal such as Ni or Co or a cermet such as Ni—YSZ or Co—YSZ, and air. The electrode layer 4 is made of LaMnO ₃ , LaCoO ₃ or the like, the fuel electrode current collector 6 is made of a sponge-like porous sintered metal plate such as a Ni-based alloy, and the air electrode current collector 7 is made of an Ag-based alloy or the like. The separator 8 is made of stainless steel or the like.

The separator 8 has a function of electrically connecting the power generation cells 5 and supplying a reaction gas to the power generation cells 5. The fuel of the separator 8 is introduced by introducing fuel gas from the outer peripheral surface of the separator 8. A fuel gas passage that discharges from substantially the center of the surface facing the electrode current collector 6, and an approximately center of the surface of the separator 8 that faces the air electrode current collector 7 by introducing oxidant gas from the outer peripheral surface of the separator 8. An oxidant gas passage 12 is provided for discharge from the exhaust gas.
Note that the temperature T of the fuel cell stack 1 (stack temperature T) detects the temperature of the separator.

  Further, a pair of end plates 8A and 8B made of stainless steel or the like are disposed at both ends of the fuel cell stack 1, and the electric power of the fuel cell stack 1 is passed through the pair of upper and lower end plates 8A and 8B. It can be taken out.

Further, on the side of the fuel cell stack 1, a fuel gas manifold 15 that distributes and supplies external fuel gas to each separator 8, and an oxidant gas (air) from the outside is distributed and supplied to each separator 8. An oxidant gas manifold 16 is erected in the stacking direction. The fuel gas manifold 15 is connected to the fuel gas passage 11 of each separator 8 via a number of connection pipes 13, and the oxidant gas manifold 16 is connected to the oxidant of each separator 8 via a number of connection pipes 14. The gas passage 12 is connected.
The fuel cell module 100 is configured by housing the fuel cell stack 1 and the manifolds 15 and 16 in a cylindrical heat insulating housing.

  The fuel cell stack 1 has a sealless structure in which a gas leakage prevention seal is not provided on the outer peripheral portion of the power generation cell 5. During operation, the fuel cell stack 1 passes through the fuel gas passage 11 and the oxidant gas passage 12 to substantially the center of the separator 8. The fuel gas and the oxidant gas (air) supplied from the unit toward the power generation cell 5 are spread with good distribution over the entire surface of the fuel electrode layer 3 and the air electrode layer 4 while diffusing in the outer peripheral direction of the power generation cell 5. As a result, a power generation reaction is caused, and surplus gas (high-temperature exhaust gas) that has not been consumed in the power generation reaction is freely discharged from the outer periphery of the power generation cell 5 into the housing. The exhaust gas discharged into the internal space of the housing is discharged out of the module through the exhaust hole.

Next, the operation control of the fuel cell power generation device having the above configuration will be described with reference to FIGS.
The operation control is performed by the control unit 20. The control unit 20 is appropriately input with detection information (I, V, Pa, T, etc.) from the various detectors described above, and the control unit 20. In a storage device (not shown), a preferable correlation between the output current used for operation control and the fuel utilization rate is stored in advance in the form of, for example, a function formula or conversion table data (see FIG. 3). .

  In FIG. 3, data (2) indicates a thermal self-sustainability limit curve showing the relationship between the fuel utilization rate and the output current that can enable the fuel cell stack 1 to perform the heat self-sustaining operation, and is determined by the structure and performance of the fuel cell module 10. ing. Data (1) shows a temperature rise curve indicating the relationship between the fuel utilization rate that can raise the stack temperature and the output current, and data (3) shows the relationship between the fuel utilization rate that can lower the stack temperature and the output current. The temperature decrease curve is shown, and the temperature increase curve data and the temperature decrease curve data are set based on the thermal self-supporting limit curve data.

  In addition, heat self-sustainment means the state which can maintain the operating temperature of a fuel cell only with the heat | fever which generate | occur | produces itself, without adding heat from the outside. A constant stack temperature is maintained at the thermal self-supporting limit, and the stack temperature rises within the thermal self-supporting range. On the other hand, outside the heat self-supporting range, the ratio of heat loss to the heat generation amount of the fuel cell stack increases, the stack temperature decreases, and the power generation efficiency decreases.

In the flowchart of FIG. 2, when the fuel cell module 10 in the cold standby state (normal temperature state) is started by a button operation of the apparatus or the like, first, in step 101, the fuel cell module 10 is heated by heating means such as a heater (not shown). The temperature is raised and the start-up process for shifting the fuel cell stack 1 from the cold standby state to the hot standby state is executed.
For example, in the case of a solid oxide fuel cell, the stack temperature in the hot standby state is set to around 650 ° C., which is the operable lower limit temperature. Power acquisition) is possible.

The operation in the power generation process described above is controlled by three operation patterns according to the output state (stack temperature) of the fuel cell.
The first operation pattern is an operation in a temperature rising period in which the acquired current is gradually increased from the hot standby state (output 0 W) to a rating (for example, output 300 W) while raising the stack temperature, and the output is acquired to the rating. The second operation pattern is an operation control in a rated output period in which the stack temperature and the output are kept constant within the rated output range (for example, output 300 W to 1 kW) after reaching the rated output. The operation pattern is operation control during a temperature lowering period in which the acquired current is gradually decreased while lowering the stack temperature at the rated output, and the state shifts to the hot standby state (output 0 W).

  Note that the switching determination of each operation pattern in step 103 can be performed based on output power detection information Pa, temperature detection information T, and the like input to the control unit 20.

First, in the operation control during the temperature rising period in step 104, the data (1) in the characteristic diagram shown in FIG. 3 is referred to.
Here, the fuel utilization rate is a ratio of “the flow rate of the fuel gas used for the power generation reaction” to “the flow rate of the fuel gas supplied to the power generation cell 5”, and the fuel utilization rate is the power generation cell 5. Can be derived from the current value (output current) flowing through the fuel gas and the flow rate of the fuel gas used for the power generation reaction by the following calculation.
Fuel utilization rate = output current / fuel gas flow rate x constant

Accordingly, the control unit 20 sequentially derives a preferable fuel utilization rate based on the data (1) from the output current detection information I sequentially input during the temperature rise process, and also requires the fuel utilization rate and the detected current value at that time. A fuel gas flow rate is calculated. Then, the fuel gas flow rate is controlled to this calculated value (that is, during the temperature rise period, the fuel gas supply amount is controlled so that the fuel utilization rate becomes equal to or less than the fuel utilization rate data), so that the temperature rises. Stable output power can be obtained. When the output approaches the desired rated output, the fuel utilization rate is controlled from the operation control based on the data (1) so as to gradually approach the data (2) so that the desired rated output can be smoothly shifted to the heat self-sustaining state. I have to.
The fuel gas flow rate can be controlled by controlling the air flow rate of the fuel gas blower 21 (or a control valve (not shown)) using a feedback loop.

  The operation control during the cooling period in step 106 is the same as the operation control in step 104 described above except that the data (3) in the characteristic diagram shown in FIG. However, during this temperature decrease period, the fuel gas supply amount is controlled by the fuel utilization rate and the detected current value based on the data (3) so that the fuel utilization rate becomes equal to or higher than the fuel utilization rate data. Stable output power can be obtained as in the rising period.

In this way, by setting the fuel utilization rate sequentially in accordance with the change in the acquired current I during the temperature increase / decrease process of the fuel cell, stable output power can be obtained even in operation below the rating.
Incidentally, in the control based on the data (1), by setting the fuel utilization rate in the low current region low and supplying a large amount of fuel gas, a rapid temperature rise is achieved and the fuel utilization rate near the rated output range is achieved. Is set high to slow the temperature rise.
Further, in the control based on the data (3), at the start of temperature decrease, the fuel utilization rate is set high so that the amount of fuel gas is reduced and the temperature decrease is slowed down. As a result, smooth temperature increase / decrease operation can be realized, and characteristic deterioration and breakage of the power generation cell 5 due to a severe heat cycle can be prevented, thereby extending the life of the fuel cell power generation device.

  In the operation control in the rated output period in step 105, the data (2) in the characteristic diagram shown in FIG. 3 is referred to. In this rated output period, the fuel gas flow rate is controlled along the thermal self-supporting limit while referring to the data (2), and a stable output is obtained. This control is the same as in step 104.

  However, if the fuel utilization rate deviates from the thermal independence limit due to the control during this rated output period, the air flow rate of the air blower 22 is controlled together with the above-described flow control of the fuel gas, and the fuel is supplementarily supplied. The amount of air supplied to the battery stack 1 is increased or decreased to keep the stack temperature at the thermal self-supporting limit. Thereby, in the rated output period, high-efficiency power generation by thermal self-sustained operation becomes possible.

  As described above, according to the present embodiment, not only the rated output period but also the temperature increase period and temperature decrease are achieved by the efficient thermal self-sustaining operation control during the rated output period and the smooth temperature increase / decrease control during start / stop. Stable output power can be obtained even during operation below the rated value in the period, and the generation of thermal distortion of the fuel cell stack 1 and other high-temperature parts in the thermal cycle can be prevented, and the deterioration and breakage of the power generation cell characteristics can be avoided. The life of the fuel cell power generator can be extended.

  In addition, since the operation control of the present embodiment is simple control that simply refers to each data of output current versus fuel utilization rate that is set in advance according to each operation period, the amount of data retained compared to conventional operation control This is a preferable control method that requires less and can easily perform microcomputer control.

1 is a schematic configuration diagram of a fuel cell power generator to which the present invention is applied. The operation control flowchart of a fuel cell power generator. The fuel cell output current vs. fuel utilization characteristic diagram. The disassembled cross section which shows the internal structure of a fuel cell stack.

Explanation of symbols

1 Fuel cell (fuel cell stack)
20 control unit 30 air supply system 40 fuel supply system

Claims (5)

A fuel cell operation control method for generating output power according to a fuel gas supply amount and an air supply amount,
It has output current vs. fuel usage rate data that enables thermal self-sustained operation, and when the temperature rises, the fuel usage rate becomes equal to or less than the fuel usage rate data. As described above, an operation control method for controlling output power by controlling a fuel gas supply amount. Each output current has fuel usage rate data in the temperature rising period from 0 to the rated output and the temperature falling period from the rated output to 0. Based on the output current vs. fuel usage rate data in each operation period The operation control method according to claim 1, wherein the output power is controlled by controlling a fuel gas supply amount. The operation control method according to claim 1 , further comprising controlling the air supply amount within a rated output period to maintain a heat self-sustaining state . A fuel cell that generates output power according to a fuel gas supply amount and an air supply amount, a fuel supply system that supplies fuel gas to the fuel cell, an air supply system that supplies air to the fuel cell, and controls each of these systems A fuel cell power generator comprising a control unit that performs operation control according to any one of claims 1 to 4 . 5. The fuel cell power generation according to claim 4, wherein the fuel cell is a solid oxide fuel cell having a sealless structure that discharges residual gas that has not been used in a power generation reaction from an outer peripheral portion of the power generation cell. apparatus.

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