Fuel cell system

Abstract

To provide a fuel cell system capable of raising a temperature of a fuel cell gently for a long time as much as possible at an actuation step.SOLUTION: A fuel cell system comprises: a fuel cell 1 that is installed at a facility and is capable of outputting power; and an operation control section C for controlling an amount of fuel gas, an amount of air, and an amount of water to be supplied to the fuel cell 1. The operation control section C is configured to be capable of outputting power after executing long time temperature raising processing of making a temperature of the fuel cell 1 gently rise while taking a time longer than a time required for normal temperature raising processing, when receiving at least one of an output decreasing requirement and system abnormality information before starting an actuation step for the fuel cell 1 or during the actuation step.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a fuel cell system connected to an electric power grid. [Background technology]

[0002] BACKGROUND ART Conventionally, a fuel cell system including a fuel cell connected to a commercial grid (electric power grid) is known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses a fuel cell system including a fuel cell arranged in a facility, an operation control unit, and a management device. The fuel cell of the fuel cell system is capable of converting DC power generated during operation into AC power using a power conversion unit and supplying it to power loads within the facility. The fuel cell is also connected to the power grid so that the DC power generated during operation can be converted into AC power using the power conversion unit and supplied to the power grid, and so that power can be supplied from the power grid to the power loads. The operation control unit performs preliminary operation to increase or decrease at least one of the fuel gas amount, air amount, and water amount while maintaining the power receiving point, before the date and time when an output control command is expected from the management device to increase or decrease the power receiving point power of the facility. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2022-155268 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, virtual power plants (VPPs) that aggregate demand-side resources such as fuel cells installed in various facilities to increase or decrease demand and provide supply capacity have become increasingly common. In VPPs, for example, a resource aggregator that controls resources such as fuel cells increases or decreases the power receiving point of each facility based on a supply command from an aggregation coordinator to provide adjustment capacity. For example, the resource aggregator can supply power to the power grid by issuing a command to each facility to decrease the power receiving point.

[0006] In the fuel cell system described in Patent Document 1, for example, the date and time when an output increase request (a command to reduce power at the power receiving point) is expected is known in advance, and if the amount of fuel gas is a predetermined amount according to load-following operation and excess air or water is being supplied, the amount of fuel gas is increased before the output increase request date and time, thereby virtually securing the required amount of power to be supplied to the power grid. As a result, the output increase request can be responded to quickly and reliably.

[0007] However, in a fuel cell system, the system is periodically started and stopped under gas meter control, and then restarted through a startup process. The startup process generally takes several hours, but if, for example, a request for output reduction (a command to increase the power at the power receiving point) is expected after the startup process is complete, the system may operate for a long time in an idling state (a state in which preparations for power generation are complete but no power is being generated, or a state in which power is being generated at a low output) after the startup process is complete. Operating in an idling state for a long time reduces the power generation efficiency of the fuel cell and also reduces the durability of the fuel cell cells that make up the fuel cell, which leaves room for improvement.

[0008] Therefore, there is a demand for a fuel cell system that can gradually increase the temperature of the fuel cell over as long a period as possible during the startup process. [Means for solving the problem]

[0009] The characteristic configuration of the fuel cell system of the present invention is a fuel cell system comprising a fuel cell installed in a facility and capable of outputting electric power, and an operation control unit that controls the amount of fuel gas, air, and water supplied to the fuel cell, wherein the fuel cell is capable of converting DC power generated by operation into AC power by a power conversion unit and supplying it to a power load unit, and is connected to the power system in a state in which the DC power generated by operation can be converted into AC power by the power conversion unit and supplied to the power system, and in a state in which power can be supplied from the power system to the power load unit, and the operation control unit is configured to, when it receives at least one of an output reduction request and system abnormality information before the start of the startup process of the fuel cell or during the startup process, perform a long-term heating process in which the temperature of the fuel cell is gradually raised over a longer period of time than is required for a normal heating process, so that the power can be output.

[0010] When the operation control unit receives at least one of an output reduction request and grid abnormality information during the fuel cell startup process, it is unable to generate power immediately after the startup process is completed, even if it performs a normal fuel cell temperature rise process. In this configuration, when at least one of an output reduction request and grid abnormality information is received during the fuel cell startup process, it is configured to perform a long-term temperature rise process, which gradually raises the fuel cell temperature over a longer period of time than the normal temperature rise process, before it can output power. This makes the startup process take longer than usual, and as a result, the time spent idling after the startup process is completed is reduced. This makes it possible to suppress the decline in the fuel cell's power generation efficiency and durability that would occur if the fuel cell were to operate in an idling state for a long period of time.

[0011] Another characteristic feature is that during the long-term heating process, the operation control unit reduces the amount of fuel gas and increases the amount of air supplied to the fuel cell compared to the amount of fuel gas and the amount of air supplied during the normal heating process.

[0012] In this configuration, when performing the long-term heating process, the operation control unit controls the amount of fuel gas to be reduced and the amount of air to be increased, compared to the amounts of fuel gas and air supplied to the fuel cell during the normal heating process, thereby gradually increasing the temperature of the fuel cell over a longer period than is required for the normal heating process, thereby preventing a decrease in the power generation efficiency and durability of the fuel cell.

[0013] Another characteristic feature of the fuel cell is that when the power output decreases, the power generation efficiency and durability of the fuel cell decrease.

[0014] When the output power of a fuel cell decreases, the power generation efficiency and durability decrease. Therefore, as in the present configuration, by controlling the supply amount of at least one of the fuel gas, air, and water to decrease during the startup process, the temperature of the fuel cell is gradually increased over a period of time longer than that required for a normal temperature increase process, thereby suppressing the decrease in the power generation efficiency and durability of the fuel cell. [Brief explanation of the drawings]

[0015] [Figure 1] FIG. 2 is a diagram showing the relationship between facilities, management devices, and an aggregation coordinator. [Figure 2] FIG. 1 is a diagram illustrating an example of the configuration of a fuel cell system. [Figure 3] 1 is a diagram illustrating the overall configuration of a fuel cell device. [Figure 4] 10 is a flowchart illustrating a long-term temperature rise process in the start-up process of the fuel cell device. DETAILED DESCRIPTION OF THE INVENTION

[0016] An embodiment of a fuel cell system according to the present invention will be described below with reference to the drawings. In this embodiment, a fuel cell system used in a supply and demand balancing market, a wholesale electricity market, a capacity market, etc. will be described as an example of a fuel cell system. However, the present invention is not limited to the following embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0017] [Overview] FIG. 1 is a diagram showing the relationship between a facility 100 in which a fuel cell device X and a power load unit 3 are installed, a management device G, and an aggregation coordinator Z. FIG. 2 is a diagram showing an example configuration of the facility 100. A fuel cell system A includes a fuel cell device X that is installed in each of a plurality of facilities 100 and is capable of outputting power, and a management device G that is capable of communicating with the plurality of fuel cell devices X from a remote location outside the facility 100. Note that the number of management devices G and the number of facilities 100 shown in FIG. 1 can be changed as appropriate.

[0018] The management device G is also called a resource aggregator, and is an operator that controls the consumer-side energy resources of the facility 100 that has concluded a virtual power plant (VPP) service contract by transmitting control information to the fuel cell device X and the power load unit 3 as consumer-side energy resources. The aggregation coordinator Z is an operator that aggregates the amount of power controlled by each management device G and trades power with general power transmission and distribution companies and retail power companies in the electricity trading market (supply and demand adjustment market, wholesale power market, capacity market, etc.).

[0019] As shown in FIGS. 1 and 2, the management device G sequentially collects and stores power information from multiple facilities 100, such as the output power of the fuel cell device X, the load power of the power load unit 3, and the power receiving point power of the power meter M at the facility 100. In this embodiment, the term "load power of the power load unit 3" refers to the total load power of all the power load units 3 installed in the facility 100. The management device G then predicts the power that can be supplied from each facility 100 during a predetermined time period in the future, and transmits this to the aggregation coordinator Z. This supplyable power is the adjustment margin, such as the facility 100's ability to increase or decrease the power receiving point power. In this embodiment, "increasing the power receiving point" means increasing the power received from the power system 15 to the power line PL (forward flow power) or decreasing the reverse flow power from the power line PL to the power system 15, and "decreasing the power receiving point" means decreasing the power received from the power system 15 to the power line PL (forward flow power) or increasing the reverse flow power from the power line PL to the power system 15.

[0020] For example, in order to increase the power receiving point power of the facility 100, it is sufficient to at least either reduce the output power of the fuel cell device X or increase the load power of the power load unit 3, so the upward adjustment margin when increasing the power receiving point power of the facility 100 indicates how much margin there is for reducing the output power of the fuel cell device X, and how much margin there is for increasing the load power of the power load unit 3. Also, in order to decrease the power receiving point power of the facility 100, it is sufficient to at least either increase the output power of the fuel cell device X or decrease the load power of the power load unit 3, so the downward adjustment margin when decreasing the power receiving point power of the facility 100 indicates how much margin there is for increasing the output power of the fuel cell device X, and how much margin there is for decreasing the load power of the power load unit 3.

[0021] The management device G also determines baseline power receiving point power for the facilities 100 it manages. This baseline power receiving point power corresponds to the total power receiving point power of each facility 100 predicted when each facility 100 is not allowed to provide adjustment capacity, etc. (i.e., including adjustment capacity provided to the electricity transmission and distribution company and supply capacity provided to the retailer, etc.).

[0022] The aggregation coordinator Z aggregates the available power received from each management device G and trades with general electricity transmission and distribution companies and retail electricity companies by bidding on trading markets such as the supply and demand adjustment market, the wholesale electricity market, and the capacity market. When the aggregation coordinator Z receives a supply command for adjustment capacity, etc. for a specified future control period from the general electricity transmission and distribution company or retail electricity company with which it has traded, it distributes and transmits the adjustment capacity, etc. specified in the supply command to each management device G.

[0023] When the management device G receives a supply command from the aggregation coordinator Z, it distributes and transmits the adjustment capacity and the like specified in the supply command to each facility 100. As a result, in each facility 100, the fuel cell device X and the power load unit 3 as consumer-side energy resources are controlled during a predetermined future control period, and thereby adjustment capacity and the like are supplied, so that the power at the receiving point of the facility 100 increases or decreases compared to when the control is not performed.

[0024] The facility 100 is provided with a fuel cell device X and a power load unit 3. The fuel cell device X and the power load unit 3 are connected to a power line PL that is linked to the power grid 15. A power meter M that measures the power received by the facility 100 is installed on the power line PL. Although FIGS. 1 and 2 show an example in which one fuel cell device X is installed in each facility 100, the number of installed fuel cell devices X can be changed as appropriate.

[0025] Information about the power receiving point power measured by the power meter M is transmitted to the management device G via the gateway GW and the router RT. For example, the information about the power receiving point power is transmitted to the management device G at a predetermined timing, such as every 10 seconds.

[0026] The power load unit 3 is various devices such as a lighting device, an air conditioner, etc., and can receive power supply from at least one of the fuel cell device X installed in the facility 100 and the power system 15.

[0027] The fuel cell device X includes a solid oxide fuel cell 1 (an example of a fuel cell) connected to an electric power grid 15. The power generated by the solid oxide fuel cell 1 is converted into a predetermined voltage, frequency, and phase by a power conversion unit 13 and supplied to a power line PL. The operation of the fuel cell device X and the power conversion unit 13 is controlled by an operation control unit C.

[0028] The operation control unit C can adjust the output power from the fuel cell apparatus X to the power line PL between a predetermined upper limit output power and a predetermined lower limit output power. For example, the operation control unit C can maintain the output power of the fuel cell apparatus X at the upper limit output power to perform continuous operation (rated output operation). The operation control unit C can also perform operation (load following operation) in which the output power of the fuel cell apparatus X follows the load power of the power load unit 3. For example, the operation control unit C can perform operation in which the output power of the fuel cell apparatus X follows the load power of the power load unit 3 by adjusting the output power of the fuel cell apparatus X so that the power supplied from the power grid 15 becomes zero or close to zero.

[0029] The operation control unit C has information about the output power supplied from the power conversion unit 13 to the power line PL and information about the power measured by the power meter M, and is therefore able to derive the load power (= output power + measured power) of the power load unit 3. When the sign of the power measured by the power meter M is positive (forward flow), this means that the load power is greater than the output power of the fuel cell device X, and when the sign of the power measured by the power meter M is negative (reverse flow), this means that the output power of the fuel cell device X is greater than the load power.

[0030] The fuel cell apparatus X is connected to a remote control RM that is operated by a user of the facility 100 when issuing commands to the fuel cell apparatus X. Information about the output power and load power of the fuel cell apparatus X is transmitted to the management device G via the remote control RM and the router RT. For example, the information about the output power and load power of the fuel cell apparatus X is transmitted to the management device G at a predetermined timing, such as every minute.

[0031] As described above, the management device G can transmit an output control command that determines the output power of the fuel cell device X to each of the operation control units C of the multiple facilities 100 that it manages. Then, when the operation control unit C receives an output control command from the management device G, it controls the operation of the fuel cell device X based on the command. The fuel cell device X that has received the command from the operation control unit C operates in a first operation mode that aims to supply output power determined based on the output control command during a control period that is the target of the output control command, and operates in a second operation mode that is different from the first operation mode during a non-control period that is outside the control period.

[0032] The first operating mode is an operating mode that adjusts the output power of the multiple fuel cell devices X on days (days when a power receiving point power decrease command is issued or a power receiving point power increase command is issued) when an output control command (such as a request to increase or decrease output in the power receiving market or a command to activate the capacity market) is expected in the supply and demand balancing market, wholesale electricity market, or capacity market. In this first operating mode, the date and time when a request to decrease the power receiving point power of the facility 100 is made is referred to as the "output increase request date and time," and the date and time when a request to increase the power receiving point power of the facility 100 is made is referred to as the "output decrease request date and time."

[0033] The second operation mode is an operation mode that is preset in the plurality of fuel cell devices X. Furthermore, the management device G can transmit an operation mode control command that determines the second operation mode to the plurality of fuel cell devices X, and the fuel cell devices X determine the second operation mode in accordance with the operation mode control command received from the management device G. For example, the second operation mode is an operation that maintains the output power of the fuel cell device X at an upper limit output power (rated output operation), an operation that makes the output power of the fuel cell device X follow the load power of the power load unit 3 (load following operation), etc.

[0034] The operation control unit C can also acquire information about the power grid 15 from a distribution board (not shown). The information about the power grid 15 is, for example, information about the grid voltage and the grid frequency. This allows the operation control unit C to acquire grid abnormality information, which is information about minor abnormalities (hereinafter also referred to as grid abnormalities) that have occurred in the power grid 15. A grid abnormality is, for example, an increase in the grid voltage or the grid frequency, and the grid abnormality information is the value of the increased grid voltage or the increased grid frequency. When the operation control unit C acquires the grid abnormality information, it controls the operation of the multiple fuel cell devices X in accordance with the grid abnormality information. Specifically, when the grid voltage increases, the fuel cell devices X reduce their generated power or stop generating power. When the grid frequency increases, the fuel cell devices X stop generating power and enter a state of waiting for grid connection. Hereinafter, a state in which the fuel cell devices X are capable of generating power but have stopped generating power, and a state in which their generated power is reduced, are referred to as an idling state. In the idling state, the reduced generated power is consumed by the power load unit 3.

[0035] [Configuration of fuel cell system] The fuel cell system A includes the above-mentioned management device G, the fuel cell device X, the power conversion unit 13, and an operation control unit C that controls the operation of the fuel cell device X and the power conversion unit 13. The operation control unit C is composed of hardware and software having information processing functions, information storage functions, information communication functions, etc., and is provided in each facility 100, but part or all of it may be provided in the management device G.

[0036] The fuel cell device X includes a solid oxide fuel cell 1 that converts DC power generated during operation into AC power using a power conversion unit 13 and supplies the AC power to a power load unit 3. The power load unit 3 is capable of consuming power supplied from a power grid 15 in addition to power supplied from the solid oxide fuel cell 1. In other words, the solid oxide fuel cell 1 is connected to the power grid 15 in a state in which the DC power generated during operation can be converted into AC power by the power conversion unit 13 and supplied to the power load unit 3, and in which the power grid 15 can supply power to the power load unit 3, and in which the DC power generated during operation can be converted into AC power by the power conversion unit 13 and supplied to the power grid 15.

[0037] The fuel cell device X has a solid oxide fuel cell 1, and inside the solid oxide fuel cell 1, there are a cell stack 7 having a plurality of fuel cell cells 4, a reforming section 8 that steam reforms raw fuel to generate fuel gas, a fuel gas supply path 16 that supplies fuel gas from the reforming section 8 to the fuel cell cells 4, and a combustion section 9 that combusts off-gas discharged from the cell stack 7.

[0038] The fuel cell device X also includes a raw fuel supply unit 10 that supplies raw fuel to the reforming unit 8 from the outside, an air supply unit 11 that supplies air to the cell stack 7 from the outside, and a reforming water supply unit 12 that supplies reforming water to the reforming unit 8 from the outside.

[0039] Next, the operation of the startup process of the fuel cell device X will be described. As shown in FIG. 3, in the startup process for starting the operation of the solid oxide fuel cell 1, the operation control unit C supplies raw fuel and reforming water (an example of water) to the reforming unit 8 and supplies air to the cell stack 7 of the solid oxide fuel cell 1. The raw fuel is supplied from a raw fuel supply unit 10. The reforming water is supplied from a reforming water supply unit 12. The air is supplied from an air supply unit 11. Then, during startup of the cell stack 7, the operation control unit C performs an ignition process to activate the igniter 20 while supplying raw fuel to the reforming unit 8 and air to the cathode (not shown) of the cell stack 7, and combusts the off-gas discharged from the cell stack 7 in the combustion unit 9. By burning the off-gas in this way in the combustion unit 9, combustion heat is transferred to the interior of the fuel cell device X, and the temperature inside the fuel cell device X increases. Then, when the temperature of a predetermined part inside the fuel cell device X (for example, the temperature of the reforming section 8, the temperature of the cell stack 7, etc.) rises, the operation control section C can determine that the startup process of the fuel cell system A has ended. Incidentally, the combustion exhaust gas is discharged from the combustion section 9 to the outside.

[0040] The fuel cell system A may be periodically restarted after being started and stopped due to gas meter control, such as by a start-up process. The start-up process requires a heating process to raise the temperature of the fuel cell device X to a predetermined temperature, which takes several hours. Therefore, the heating process takes up most of the time during the start-up process. Hereinafter, the heating process performed during a normal start-up process will also be referred to as a normal heating process. During the start-up process, the fuel cell device X cannot generate power and cannot respond to output requests from the management device G. Therefore, it is preferable to shorten the time required for the heating process. However, rather than generating power immediately after the start-up process is completed, it is not preferable to operate the fuel cell device X in an idling state for a long time until the date and time of the output reduction request. This is because operating the fuel cell device in an idling state for a long time reduces the power generation efficiency of the solid oxide fuel cell 1 and the durability of the cell stack 7. Furthermore, the above-mentioned increases in the grid voltage and grid frequency also result in operation in an idling state, which is undesirable. In the normal temperature-raising process executed in the normal start-up step, the solid oxide fuel cell 1 is supplied with a normal amount of fuel gas, a normal amount of reforming water, and a normal amount of air.

[0041] Therefore, the fuel cell system A of this embodiment is configured to perform a long-term heating process in which the temperature of the fuel cell device X (solid oxide fuel cell 1) is gradually increased over a longer period of time than the normal heating process if (1) the operation control unit C acquires system abnormality information before the start of the startup process or during the startup process, and (2) the operation control unit C receives an output reduction request from the management device G to set the output to 0 W.

[0042] Specifically, in the above cases (1) and (2), the operation control unit C performs a long-term temperature rise process to gradually raise the temperature of the fuel cell device X over as long a period as possible. The long-term temperature rise process is specifically a process in which the operation control unit C reduces the amount of fuel gas and increases the amount of air compared to the amounts of fuel gas and air supplied to the solid oxide fuel cell 1 during normal temperature rise process. If the amount of fuel gas supplied to the fuel cell device X decreases, the combustion rate in the combustion unit 9 decreases, and therefore the temperature rise process takes time. Note that the time periods for the long-term temperature rise processes in the above cases (1) and (2) may be different. Furthermore, in the above cases (1) and (2), there is a possibility that the fuel cell system A will operate in an idling state after the start-up process using the long-term temperature rise process is completed.

[0043] The long-term heating process will be described with reference to Figure 4. After the fuel cell system A is shut down, it is restarted and the startup process begins (step S1). Next, the operation control unit C of the fuel cell system A determines whether or not it has acquired system abnormality information before the start of the startup process or during the startup process (step S2). If the operation control unit C has acquired system abnormality information (Yes in step S2, (1) above), the operation control unit C performs a long-term heating process in which the amount of fuel gas supplied to the cell stack 7 is increased and the amount of air is decreased compared to the normal heating process, thereby gradually increasing the temperature of the fuel cell device X over as long a period as possible (step S4).

[0044] If the operation control unit C has not acquired system abnormality information (No in step S2), the operation control unit C determines whether or not it has received a 0 W output reduction request from the management device G (step S3). If the operation control unit C has received a 0 W output reduction request (Yes in step S3, (2) above), the operation control unit C performs a long-term heating process in which the amount of fuel gas supplied to the cell stack 7 is increased and the amount of air is reduced compared to the normal heating process, and the temperature of the fuel cell device X is gradually increased over as long a period as possible (step S4).

[0045] If the operation control unit C has not received a 0 W output reduction request (No in step S3), the operation control unit C controls the fuel cell device X to perform a normal start-up process (step S5). If the output reduction request is other than 0 W (for example, 200 W), the fuel cell device X starts power generation after completing the normal start-up process. The generated power is supplied to the power load unit 3.

[0046] In this way, by performing the temperature rise process for a long time, it is possible to reduce the time that the fuel cell system A operates in an idling state after the start-up process is completed, thereby suppressing a decrease in the power generation efficiency of the fuel cell device X and a decrease in the durability of the fuel cell cells 4 that constitute the fuel cell device X.

[0047] Other Embodiments In the above-described embodiment, the fuel cell device X includes a solid oxide fuel cell 1, but the fuel cell device X may also include a polymer electrolyte fuel cell (PEFC), a phosphoric acid fuel cell (PAFC), or a molten carbonate fuel cell (MCFC).

[0048] The configurations disclosed in the above-described embodiments (including other embodiments, the same applies hereinafter) can be applied in combination with configurations disclosed in other embodiments, unless a contradiction arises. Furthermore, the embodiments disclosed in this specification are merely examples, and the present invention is not limited to these, and can be modified as appropriate within the scope of the purpose of the present invention. [Industrial Applicability]

[0049] The present invention can be used in a fuel cell system connected to an electric power grid. [Explanation of symbols]

[0050] 1:Solid oxide fuel cell (fuel cell) 3: Power load section 15: Power system 100: Facilities A: Fuel cell system C: Operation control unit G: Management device

Claims

1. A fuel cell system including a fuel cell installed in a facility and capable of outputting electric power, and an operation control unit that controls an amount of fuel gas, an amount of air, and an amount of water supplied to the fuel cell, the fuel cell is connected to the power grid in a state in which direct current power generated by operation can be converted into alternating current power by a power conversion unit and supplied to a power load unit, the direct current power generated by operation can be converted into alternating current power by the power conversion unit and supplied to the power grid, and power can be supplied from the power grid to the power load unit, The fuel cell system is configured such that when the operation control unit receives at least one of an output reduction request and system abnormality information before the start of the fuel cell startup process or during the startup process, the operation control unit performs a long-term heating process to gradually raise the temperature of the fuel cell over a longer period of time than is normally required for a heating process, before the power can be output.

2. The fuel cell system of claim 1, wherein the operation control unit reduces the amount of fuel gas and increases the amount of air supplied to the fuel cell during the long-term heating process, compared to the amount of fuel gas and the amount of air supplied during the normal heating process.

3. 3. The fuel cell system according to claim 1, wherein the fuel cell has a reduced power generation efficiency and a reduced durability when the power output from the fuel cell decreases.

Images