JP2008066016A - Operation method of fuel cell system and fuel cell system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide the operation method of a fuel cell system capable of efficiently operating the fuel cell system in consideration of the quantity of heat capable of storing the quantity of heat in a heat storage chamber; and to provide the fuel cell system. <P>SOLUTION: The operation method of the fuel cell system is equipped with a process forecasting power demand and heat demand until the prescribed time based on the past actual operation results; a process preparing an operation plan based on the demand forecast; and a process operating a fuel cell 15 based on the operation plan, and the process preparing the operation plan uses a heat suppressing operation plan as an operation plan of the base of the operation of the fuel cell 15 when a value being calculated in accordance with a prescribed reference by the heat suppressing operation plan for operating the fuel cell 15 within the range of the quantity of heat of the fuel cell 15 capable of storing in the heat storage chamber 31 becomes higher. The fuel cell system is equipped with a controlling device 50 controlling the fuel cell system 100 according to the operation method. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a fuel cell system operation method and a fuel cell system, and more particularly to a fuel cell system operation method and a fuel cell system for efficiently operating a fuel cell system in consideration of the amount of heat that can be stored in a heat storage tank. is there.

  With the recent increase in awareness of global environmental conservation, the spread of fuel cells that contribute to the prevention of global warming is expected. A fuel cell is a device that extracts electric power generated by an electrochemical reaction between hydrogen and oxygen, and generates heat when the electrochemical reaction is performed. In order to continue the power generation of the fuel cell, it is necessary to maintain the fuel cell at a predetermined temperature, so that the generated heat is taken away by supplying cooling water. And in order to effectively use the heat generated in the fuel cell, it is common to build a cogeneration system that supplies the cooling water and stores the heat taken away in the heat storage tank and supplies it to the heat demand as needed. . Generally, there is an upper limit to the amount of heat stored in the heat storage tank, and when the amount of heat generated in the fuel cell is greater than the heat demand, and the amount of stored heat reaches the upper limit (this state is generally referred to as “full storage”). Therefore, when the operation of the fuel cell is stopped, or when the operation of the fuel cell is continued, it is necessary to maintain a state in which the fuel cell can be cooled by radiating heat by using a radiator or the like. Alternatively, in order to avoid full storage, it is necessary to perform an operation (generally referred to as “thermal suppression”) that limits the power generation output of the fuel cell and reduces the amount of heat recovered from the fuel cell. .

Conventionally, whether or not the heat storage tank is fully charged is determined by detecting the temperature of the fluid (heat storage medium) entering and exiting the heat storage tank with a temperature sensor or the like to obtain the average temperature of the heat storage medium in the heat storage tank. It was detected by comparing with the temperature of the heat storage medium during storage. The amount of heat that can be stored in the heat storage tank has been calculated by the difference between the heat storage tank's full heat storage amount and the current heat storage amount. In addition, the heat amount at the time of full storage and the current heat storage amount of the heat storage tank are calculated by the following formula. However, Tf is the temperature of the heat storage medium at the time of full storage in the heat storage tank, Ta is the average temperature of the heat storage medium, Tb is the reference temperature of the heat storage medium, Ve is the heat storage tank capacity (effective capacity), and Cw is the specific heat of the heat storage medium. To express. The heat storage medium is typically tap water, and the reference temperature Tb at this time is the temperature of tap water when being supplied from outside the system to the cogeneration system.
(Amount of heat at full storage) = (Tf−Tb) × Ve × Cw
(Current heat amount) = (Ta−Tb) × Ve × Cw

  However, in the past, as a simple method of suppressing heat, the power generation output of the fuel cell was sometimes suppressed when the average temperature of the heat storage medium in the heat storage tank exceeded a threshold value. In some cases, both the power generation efficiency and heat recovery efficiency of the system will be higher (and therefore energy savings will be higher) if the power generation output of the system is not suppressed rather than extending the operating time, and simple thermal suppression is not necessarily effective. I couldn't say that.

  An object of the present invention is to provide a fuel cell system operation method and a fuel cell system capable of efficiently operating a fuel cell system in consideration of the amount of heat that can be stored in a heat storage tank. To do.

  In order to achieve the above object, the fuel cell system operating method according to the first aspect of the present invention generates electricity by generating an electric power by an electrochemical reaction between hydrogen and oxygen, as shown in FIGS. 1 and 2, for example. An operation method of a fuel cell system 100 having a fuel cell 15 and a heat storage tank 31 for storing heat generated in the fuel cell 15; based on past operation results, electric power demand and heat up to a predetermined time ahead A step of predicting demand (S10); a step of creating an operation plan for the fuel cell 15 based on the result obtained in the step of predicting the demand (S20); and an operation of the fuel cell 15 based on the operation plan. The step of creating the operation plan is a thermal suppression operation plan for operating the fuel cell 15 within the range of the calorific value of the fuel cell 15 capable of storing heat in the heat storage tank 31, and the heat storage tank 31. Heat storage A steady operation plan that does not take into account the calorific value of the active fuel cell 15, and the fuel cell 15 was operated according to the thermal suppression operation plan rather than assuming that the fuel cell 15 was operated according to the steady operation plan. When the value calculated according to a predetermined standard is improved, the thermal suppression operation plan is configured as an operation plan that is the basis of the operation of the fuel cell 15.

  With this configuration, the value calculated according to the predetermined standard is improved when it is assumed that the fuel cell is operated according to the thermal suppression operation plan rather than when the fuel cell is assumed to be operated according to the steady operation plan. In this case, since the thermal heat suppression operation plan is an operation plan that is the basis of the operation of the fuel cell, the fuel cell system can be operated efficiently.

  The fuel cell system operating method according to claim 2 is the fuel cell system operating method according to claim 1, wherein the predetermined standard is a standard for energy consumption reduction, a standard for cost reduction, One of the standards for reducing carbon dioxide emissions.

  If comprised in this way, it will become a driving | running method of the fuel cell system which implements an effective driving | operation with respect to the element selected from the standard regarding energy consumption reduction, the standard regarding cost reduction, and the standard regarding emission carbon dioxide reduction.

  Moreover, the operation method of the fuel cell system according to the invention described in claim 3 is the operation method of the fuel cell system according to claim 1 or claim 2, for example, as shown in FIG. The amount of heat that can be stored is represented by the sum of the amount of heat that can be stored for each of the divisions obtained by dividing the heat storage tank 31 into a predetermined number.

  When configured in this way, the amount of heat that can be stored in the heat storage tank is represented by the sum of the amount of heat that can be stored for each division of the heat storage tank divided into a predetermined number, so the temperature distribution in the heat storage tank collapses. Even in the case that the amount of heat that can be stored is appropriate.

  When the heat storage tank is divided, the heat storage tank may be divided on a line connecting the inlet and the outlet of the heat storage medium.

  If comprised in this way, the suitable amount of heat which can be stored heat along the temperature stratification formed in the thermal storage tank is computable.

  In order to achieve the above object, a fuel cell system according to a fourth aspect of the present invention includes a fuel cell 15 that generates electricity and generates heat by an electrochemical reaction between hydrogen and oxygen, as shown in FIG. The heat storage tank 31 which stores the heat which generate | occur | produced in the battery 15; The control apparatus 50 which controls the fuel cell system 100 according to the operating method of the fuel cell system of any one of Claim 1 thru | or 3 is provided.

  If comprised in this way, it will become a fuel cell system in which a highly efficient driving | operation is possible.

  In order to achieve the above object, a fuel cell system according to a fifth aspect of the present invention includes a fuel cell 15 that generates electricity and generates heat by an electrochemical reaction between hydrogen and oxygen, as shown in FIG. A heat storage tank 31 for storing heat generated in the battery 15; a temperature detector 38 for detecting the temperature at each end of the section obtained by dividing the heat storage medium w in the heat storage tank 31 into a predetermined number of 2 or more; and temperature detection The amount of heat that can be stored for each section is calculated from the temperature of the heat storage medium w detected by the vessel 38, the amount of heat that can be stored for each section is summed, and the amount of heat that can be stored in the entire heat storage tank 13 is calculated and calculated. And a control device 50 that limits the output of the fuel cell 15 based on the amount of heat that can be stored in the entire heat storage tank 13.

  If comprised in this way, even if the temperature distribution in a thermal storage tank collapses, it will become a fuel cell system which can be calculated and calculated and can operate | move appropriately.

  According to the present invention, the value calculated according to the predetermined standard is improved when it is assumed that the fuel cell is operated according to the thermal suppression operation plan rather than when the fuel cell is operated as per the steady operation plan. In this case, since the thermal heat suppression operation plan is an operation plan that is the basis of the operation of the fuel cell, the fuel cell system can be operated efficiently. In addition, when the amount of heat that can be stored in the heat storage tank is represented by the sum of heat amounts that can be stored for each of the divisions of the heat storage tank divided into a predetermined number, even if the temperature distribution in the heat storage tank collapses Appropriate amount of heat that can be stored can be calculated.

  Embodiments of the present invention will be described below with reference to the drawings. In each drawing, the same or corresponding members are denoted by the same or similar reference numerals, and redundant description is omitted.

  First, the configuration of a fuel cell system 100 according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a system diagram illustrating a fuel cell system 100 according to an embodiment of the present invention. In FIG. 1, a solid line connecting the devices represents piping, a one-dot chain line represents an electric cable, and a broken line represents a control signal. The fuel cell system 100 includes a reformer 11 that generates a reformed gas g rich in hydrogen, a fuel cell 15 that generates electricity and generates heat by an electrochemical reaction between hydrogen and oxygen, a cooling water c, and a heat storage medium w. A heat exchanger 21 that exchanges heat between them, a hot water storage tank 31 as a heat storage tank, and a control device 50 that controls the fuel cell system 100 are provided.

  The reformer 11 is a device that generates a reformed gas g rich in hydrogen by introducing a raw material fuel m and water vapor (not shown), heating and reforming. The reformed gas g rich in hydrogen is a gas supplied to the fuel cell 15 containing hydrogen in an amount of 40% by volume or more, typically about 70 to 80% by volume. The hydrogen concentration in the reformed gas g may be 80% by volume or more, that is, it may be a concentration that allows power generation by an electrochemical reaction with oxygen in the oxidant gas t when supplied to the fuel cell 15. A raw material fuel pipe 12 for introducing the raw material fuel m and a reformed gas pipe 13 for leading the reformed gas g toward the fuel cell 15 are connected to the reformer 11. The reformer 11 has a heating unit (not shown) for generating reforming heat necessary for reforming.

  The fuel cell 15 is typically a polymer electrolyte fuel cell. Although the fuel cell 15 is simply shown in FIG. 1, actually, the solid polymer membrane is sandwiched between the fuel electrode for introducing the reformed gas g and the air electrode for introducing the oxidant gas t. A single cell is formed, and a plurality of such cells are stacked through a cooling unit. In the fuel cell 15, hydrogen in the reformed gas g supplied to the fuel electrode is decomposed into hydrogen ions and electrons, and the hydrogen ions pass through the solid polymer film and move to the air electrode. It moves to the air electrode through the external electric wire 41 connecting to the air electrode, reacts with oxygen in the oxidant gas t supplied to the air electrode to generate water, and generates heat during this reaction. In this reaction, when the electrons pass through the external electric wire 41, DC power can be taken out. A power conditioner 42 that converts DC power to AC power is connected to the fuel cell 15. Further, the fuel cell 15 has a reformed gas pipe 13 for introducing the reformed gas g and an oxidant gas pipe 14 for introducing an oxidant gas t (typically air is used). It is connected. The fuel cell 15 is connected to a cooling water pipe 16 that circulates the cooling water c that takes away heat generated by an electrochemical reaction. The cooling water pipe 16 is provided with a cooling water pump 18 for circulating the cooling water c. The fuel cell 15 is connected to a signal cable for transferring a control signal to and from the control device 50.

  The heat exchanger 21 is a device that causes heat exchange between the cooling water c and the heat storage medium w (typically liquid water), lowers the temperature of the cooling water c, and increases the temperature of the heat storage medium w. It is. As the heat exchanger 21, a plate heat exchanger is typically used, but a shell and tube type or other heat exchanger may be used. The heat exchanger 21 is connected to a cooling water pipe 16 that introduces and leads out the cooling water c, and a heat storage medium pipe 22 that introduces and leads out the heat storage medium w. By using the heat exchanger 21, the cooling water pipe 16 can be used as a closed flow path, thereby preventing the entry of oxygen, impurities, etc., and protecting the fuel cell 15 from corrosion. Moreover, the edge of the heat storage medium w used as the warm water h and water supplied to a heat demand, and the cooling water c can be cut by using the heat exchanger 21.

  The hot water storage tank 31 is a tank that stores heat generated by an electrochemical reaction in the fuel cell 15. The heat generated in the fuel cell 15 is transmitted to the heat storage medium w through the cooling water c and the heat exchanger 21 and stored in the hot water storage tank 31 in a form held in the heat storage medium w. The hot water storage tank 31 is connected to a heat storage medium pipe 22 that introduces and leads out the heat storage medium w. The heat storage medium pipe 22 is connected on the introduction side of the heat storage medium w to the upper part of the hot water storage tank 31, preferably directly below the liquid level in the hot water storage tank 31, and on the outlet side to the lower part of the hot water storage tank 31, preferably Connected to the bottom. By being connected in this way, temperature stratification is formed in the heat storage medium w in the hot water storage tank 31. Further, since the heat storage medium w is led out from only a part of the hot water storage tank 31 by the dynamic pressure when the heat storage medium w is introduced into the hot water storage tank 31, the temperature stratification is not destroyed. It is preferable to provide a plurality of connection ports of the medium pipe 22 and / or to provide a weir so as to surround the connection port of the heat storage medium pipe 22 above and below the hot water storage tank 31. The hot water storage tank 31 is also supplied with a hot water supply pipe 32 for supplying the heat storage medium w stored therein as hot water h toward the heat demand (not shown), and for supplementing the reduced water supplied to the heat demand. A makeup water pipe 33 for introducing water is connected. The hot water supply pipe 32 is provided with a hot water pump 34 that pumps hot water h toward heat demand (not shown) and a flow meter 35 that detects the flow rate of the hot water h sent to the heat demand. A signal cable for transmitting a flow signal to the control device 50 is connected to the flow meter 35. Further, the hot water supply pipe 32 is provided with a backup boiler 36 that heats the hot water h that is supplied to a heat demand (not shown). A signal cable for receiving a control signal from the control device 50 is connected to the backup boiler 36.

  The hot water storage tank 31 is provided with a temperature detector 38 for detecting the temperature of the heat medium in the hot water storage tank 31 in order to detect the heat storage capacity. The temperature detector 38 includes a plurality of sensors 38a to 38f for virtually dividing the hot water storage tank 31 in the direction in which temperature stratification is formed and calculating the heat storage capacity. In the present embodiment, the hot water storage tank 31 is virtually divided into five parts, and the sensors are arranged at the boundaries of the virtually divided areas, and thus there are six sensors. An appropriate number of sensors may be provided according to the virtual division number in the hot water storage tank 31.

  A heat storage medium pump 23 that circulates the heat storage medium w between the heat exchanger 21 and the hot water storage tank 31 is disposed in the heat storage medium pipe 22 upstream of the heat exchanger 21. A reverse tide heater 24 is disposed in the heat storage medium pipe 22 on the downstream side of the heat exchanger 21. The reverse power heater 24 converts the surplus power into heat in order to prevent the surplus power that exceeds the power from flowing back to the commercial power supply 45 when the power generated by the fuel cell 15 exceeds the power demand. Is provided.

  A three-way valve 26 is disposed in the heat storage medium pipe 22 on the downstream side of the reverse tide heater 24. A bypass pipe 25 is connected to a connection port of the three-way valve 26 that is not connected to the heat storage medium pipe 22. The other end of the bypass pipe 25 is connected to the heat storage medium pipe 22 on the suction side of the heat storage medium pump 23. A radiator 28 as a radiator is disposed in the bypass pipe 25. The radiator 28 is stored so that the hot water storage tank 31 can no longer store heat (fully stored), but when the operation of the fuel cell 15 needs to be continued, the cooling water c is brought to a temperature necessary for cooling the fuel cell 15. This is a device that forcibly cools the heat storage medium w so as to supply the heat storage medium w that holds the cold energy to the heat exchanger 21. A signal cable for receiving a control signal from the control device 50 is connected to the radiator 28. The radiator 28 has a fan that is interlocked with a flow switch (not shown) disposed in the bypass pipe 25. Whether the heat storage medium w is guided to the hot water storage tank 31 or the bypass pipe 25 is determined by switching the three-way valve 26. A signal cable for receiving a control signal from the control device 50 is connected to the three-way valve 26.

  In addition to the external electric wire 41 connected to the fuel cell 15, a cable 43 and a cable 49 that transmit AC power are connected to the power conditioner 42. The cable 43 is connected to a cable 44 that connects the commercial power supply 45 and the power load. That is, the power generated by the fuel cell is linked to the grid power. A wattmeter 48 for detecting electric power is disposed on the cable 44 upstream of the interconnection point. The wattmeter 48 is configured to be able to detect both forward and reverse power. A signal cable for transmitting a power signal to the control device 50 is connected to the wattmeter 48. The cable 49 is connected to the reverse power heater 24 and is configured to transmit surplus power generated in the fuel cell 15 to the reverse power heater 24 when the reverse power flow to the system power is not allowed.

  The control device 50 includes a time measuring unit, a calculating unit, and a data holding unit for controlling the operation of the fuel cell system 100. Typically, the time measuring means is constituted by a timer, the computing means is constituted by a CPU and a memory, and the data storage means is constituted by a memory. The control device 50 is connected to the fuel cell 15, the three-way valve 26, the radiator 28, the flow meter 35, the backup boiler 36, the temperature detector 38, and the wattmeter 48 through signal cables.

  With continued reference to FIG. 1, the operation of the fuel cell system 100 will be described. When the fuel cell system 100 is activated, the raw material fuel m and water vapor (not shown) are introduced into the reformer 11 and heated to generate the reformed gas g. Immediately after the reformer 11 is started, the composition of the reformed gas g is not stable, so that it is not sent to the fuel cell 15 but sent to the heating section (not shown) of the reformer 11 for combustion to generate reformed heat. It is preferable. When the composition of the reformed gas g generated in the reformer 11 becomes stable, the reformed gas g is introduced into the fuel cell 15 and the oxidant gas t is introduced into the fuel cell 15. Then, in the fuel cell 15, power is generated by an electrochemical reaction between hydrogen in the reformed gas g and oxygen in the oxidant gas t to generate heat. The generated DC power is converted into AC power by the power conditioner 42 and transmitted to power demand outside the system, or a blower (not shown) for sending the oxidant gas t to the fuel cell 15 and cooling of the fuel cell system 100. Used as power for the water pump 18.

  On the other hand, the cooling water c pumped by the cooling water pump 18 is introduced into the fuel cell 15, takes heat generated by the electrochemical reaction, rises in temperature, and is led out from the fuel cell 15. The cooling water c whose temperature has risen is introduced into the heat exchanger 21, where it exchanges heat with the heat storage medium w to drop the temperature and is led out from the heat exchanger 21, and is introduced into the fuel cell 15 again. The heat storage medium w whose temperature has increased by exchanging heat with the cooling water c in the heat exchanger 21 flows through the heat storage medium pipe 22 and is introduced into the hot water storage tank 31 from above. The heat storage medium w having a low temperature for exchanging heat with the cooling water c and the heat exchanger 21 is led out from the lower part of the hot water storage tank 31.

  The heat storage medium w having an increased temperature introduced into the hot water storage tank 31 is pumped as hot water h to the heat demand outside the system by the hot water pump 34. At this time, when the temperature of the hot water h does not reach the temperature required by the heat demand outside the system, it is heated by the backup boiler 36. In the hot water storage tank 31, a heat storage medium w (typically makeup water) corresponding to the amount of water reduced by being sent to heat demand outside the system is replenished from the makeup water pipe 33.

  When the heat storage medium w having a high temperature is stored in the hot water storage tank 31 and there is no heat storage medium w having a temperature low enough to cool the cooling water c, but the operation of the fuel cell 15 is to be continued, the control device 50 switches the three-way valve 26. Then, the heat storage medium w bypasses the hot water storage tank 31 and flows to the radiator 28, dissipates heat, drops it to a predetermined temperature, and then guides it to the heat exchanger 21. The temperature detector 38 detects whether or not the heat storage medium w having a temperature capable of cooling the cooling water c remains in the hot water storage tank 31.

  Next, a method for operating the fuel cell system will be described with reference to FIG. In the following description, FIG. 1 will be referred to as appropriate. FIG. 2 is a flowchart illustrating a method for operating the fuel cell system according to the embodiment of the present invention. In the present invention, in order to prevent a loss due to operation stop of the fuel cell 15 due to full storage and operation of the radiator 28, thermal suppression control described below is performed.

  First, the control device 50 predicts power demand and heat demand based on past operation results (S10). The power demand and the heat demand are predicted because the fuel cell system has the following characteristics. The fuel cell system 100 cannot start the power generation of the fuel cell 15 immediately after being started, and generates the reformed gas g, and the fuel cell 15, the reformed gas g, and the oxidant gas t to a predetermined temperature. In order to do so, a lead time of about 1 hour is required. While the fuel is consumed during the lead time, there is no power generation or heat generation, resulting in fuel loss. When the hot water storage tank 31 is full, the operation of the fuel cell 15 cannot be continued unless the heat is discarded outside the system by using the radiator 28 or the like. When the fuel cell 15 is temporarily stopped, a loss of power and fuel of ancillary equipment such as a pump, which is consumed in the lead time at the time of activation, occurs.

  If the hot water storage tank 31 is fully stored during a period of high power demand, it is necessary to stop the fuel cell 15 and receive power supply from the commercial power supply 45 or to operate the fuel cell 15 while radiating heat from the radiator 28 There is. Therefore, in the present invention, in principle, the fuel cell 15 is prevented from being stopped or the radiator 28 is activated due to the hot water storage tank 31 being fully stored in a time zone when the power demand is high. Demand and heat demand are to be predicted. In addition, for example, the time until the power demand increases is relatively long, and the low output operation of the fuel cell 15 is maintained in the time period until the fuel cell 15 is operated in order to operate the fuel cell 15 during the time period when the power demand increases. If, on the other hand, energy loss occurs on the whole (generally, the power generation efficiency of the fuel cell is low in low-power operation), it is better to stop the fuel cell 15 when the hot water storage tank 31 is fully stored. In order to make such a determination, it is meaningful to predict power demand and heat demand.

  In the step of predicting power demand and heat demand based on past operation results (S10), prediction is performed up to a predetermined time ahead, and this predetermined time is typically 24 hours (one day). The reason why the predetermined time is set to 24 hours is that, for example, at home, demand for electric power and heat are often repeated in a cycle of one day. Even in the case of apartment houses, offices, factories, etc., power demand and heat demand are generally repeated on a daily basis. However, when power demand and heat demand are not repeated on a daily basis, for example, when repeated for a week as a minimum unit, it may be performed in a weekly unit, or 48 hours, 72 hours, 96 hours, 2 weeks, a month, etc. It may be performed in other time units. In addition, the past results are the average values within the range of conditions that are considered to be equivalent, considering various factors such as season, day of the week, temperature, weather, etc. It is good to decide by. At this time, the accuracy of the prediction can be improved by excluding the case where the actually measured value is significantly different from the predicted value even under the same conditions due to the absence of the user, etc. and determining the past results. .

  If the electric power demand and the heat demand are predicted based on the past operation results, the control device 50 next creates an operation plan (S20). The operation plan predicts a time zone in which electric power demand and heat demand are generated from past operation results, the time in which electric power and / or heat demand occurs, the current state of the fuel cell 15 and the heat storage in the hot water storage tank 31. The scheduled time for operating the fuel cell 15, the planned power generation amount, and the upper limit power generation amount (the output limit of the fuel cell 15) are determined in consideration of the quantity state and the lead time.

  The scheduled power generation amount is typically set to a value that is lower than the predicted value of power demand by a predetermined amount. The value to be set is, for example, a value of 90% of the predicted value of power demand or a value obtained by subtracting 100 W from the predicted value of power demand. The reason why the value is lower than the predetermined amount is because it is assumed that the generated power of the fuel cell 15 does not flow backward to the commercial power supply 45. That is, in general, since fuel cells cannot generate electricity following the power demand completely, if reverse power flow to the grid power is not allowed, In many cases, the power output is a value that is lower than the demand by a predetermined amount. Further, the upper limit of the planned power generation amount is the rated output of the fuel cell 15 unless the upper limit power generation amount is set. Even if the value that is lower than the predicted value of power demand by a predetermined amount is equal to or greater than the rated output of the fuel cell 15, the value of the rated output is set as the upper limit. This is because the fuel cell 15 is damaged if it is operated beyond the rated output. When the upper limit power generation amount is set, this is set as the upper limit. However, since the upper limit power generation amount is normally equal to or lower than the rated output for that purpose, damage to the fuel cell 15 can be prevented. In addition, when it is better to set a lower limit of the planned power generation amount in view of characteristics of the fuel cell to be used, a lower limit is appropriately set. For example, in a fuel cell with a rated output of 1 kW, operation at an output of 300 W or less is not suitable for operation at an output of 300 W or less because the power generation efficiency is drastically reduced and the heat balance is lost. In such a case, the lower limit of the planned power generation amount may be set to 300W.

  Here, with reference to FIG. 3, a procedure for creating an operation plan will be described. FIG. 3 is a flowchart illustrating a procedure for creating an operation plan. The control device 50 first calculates the coolable amount of the fuel cell 15 (S21). In other words, the coolable amount is the amount of heat generated by the fuel cell 15 that can store heat in the hot water storage tank 31. The temperature that can be used as the cooling water c to cool the fuel cell 15 has an upper limit, and is generally about 50 to 70 ° C. at the inlet of the fuel cell 15. If the temperature of the cooling water c is lower than this temperature, the fuel cell 15 can be cooled and maintained at a predetermined temperature. The cooling water c deprived of heat from the fuel cell 15 rises to about 60 to 80 ° C. It is difficult to simply calculate the coolable amount based on the amount of heat retained by the heat storage medium w in the hot water storage tank 31. Considering the heat exchange efficiency of the heat exchanger 21, the amount of the heat storage medium w of 40 to 50 ° C. or less stored in the hot water storage tank 31 has a correlation with the coolable amount (hereinafter, coolable). The temperature in consideration of the heat exchange efficiency with the cooling water temperature is referred to as “derived heat medium upper limit temperature Tc”). The temperature of the heat storage medium w introduced into the hot water storage tank 31 from the upper part (hereinafter referred to as “introduction heat medium temperature Tr”) is higher than the temperature of the heat storage medium w derived from the lower part, and the hot water storage tank 31 has temperature stratification. Since it is formed, the heat storage medium w having a low temperature is stored in the lower part of the hot water storage tank 31. However, the temperature stratification in the hot water storage tank 31 may collapse due to the dynamic pressure of the heat storage medium w entering and exiting the hot water storage tank 31 and other causes. The conventional method of obtaining the amount of heat that can be stored from the average temperature of the heat storage medium in the heat storage tank is to determine the amount of heat that can be stored relatively correctly when temperature stratification is formed and maintained in the heat storage tank. However, when the temperature stratification collapses, in many cases it is actually full before it becomes full in calculation, and it is often impossible to correctly determine the amount of heat that can be stored. Therefore, as will be described below, the hot water storage tank 31 may be divided into five and the cooling possible amount may be calculated for each section. In addition, the number which divides the inside of a hot water storage tank is not restricted to five, You may divide into 2 or more other numbers.

  When dividing, it is preferable to carry out on the line which connects the inlet and outlet of the heat storage medium w of the hot water storage tank 31. For example, in the case where the hot water storage tank 31 is vertically long and the temperature stratification is formed in the vertical direction so that the heat storage medium w flows in from the upper part and flows out from the lower part, it is divided in the vertical direction. When the hot water storage tank 31 is horizontally long, the inlet and outlet of the heat storage medium w are formed so that the flow of the heat storage medium w in the hot water storage tank 31 is in the horizontal direction, and the temperature stratification is formed in the horizontal direction, Divide horizontally. In this embodiment, the sensor is divided into five regions in the vertical direction by the sensors 38a to 38f of the temperature detector 38 disposed in the hot water storage tank 31 shown in FIG.

  Here, the calculation of the coolable amount will be described with reference to FIG. First, it is detected which of the regions divided into five corresponds to one of FIGS. In the numerical formula shown in the description of FIG. 4 below, the amount of heat that can be cooled is Qj (Wh), the temperatures at both ends are T1, T2 (° C.), the amount of heat storage medium is V (L), and the specific heat is C ( J / g · ° C.) Note that T1 <T2 and j is a variable represented by an integer according to the number of divided areas. Also, the division by 3.6 is for unit conversion.

FIG. 4A shows a case where both the temperatures at both ends of the divided area are equal to or lower than the derived heat medium upper limit temperature Tc. In this case, it is possible to use all of the heat storage medium amount in the region for cooling the fuel cell 15, and the amount of heat that can be cooled in the region is expressed by the following equation (1).
Qj = {Tr− (T1−T2) / 2} × V × C × (1 / 3.6) (1)
FIG. 4B shows a case where both the temperatures at both ends of the divided area exceed the derived heat medium upper limit temperature Tc. In this case, the fuel cell 15 cannot be cooled, and the amount of heat that can be cooled in this region is 0 as expressed by the equation (2).
Qj = 0 (2)
FIG. 4C shows a case where the temperature T1 is equal to or lower than the derived heat medium upper limit temperature Tc and the temperature T2 exceeds the derived heat medium upper limit temperature Tc among the temperatures at both ends of the divided area. In this case, a part of the heat storage medium amount in the region can be used for cooling the fuel cell 15, and the amount of heat that can be cooled in the region is expressed by the following equation (3).
Qj = {Tr− (Tc + T1) / 2} × V × {(Tc−T1) / (T2−T1)} × C × (1 / 3.6) (3)

図４（ｄ）に、貯湯タンク３１の冷却可能量の例を示す。図４（ｄ）中、Ｔ３８ａ〜Ｔ３８ｆが、それぞれ温度検出手段３８のセンサー３８ａ〜３８ｆが検出した温度である。図中の斜線で囲んだ部分が冷却可能熱量に該当する。 When the coolable heat quantity Qj is calculated by the above formulas (1) to (3) for each of the divided areas, the sum of these is the coolable quantity of the hot water storage tank 31. That is, the coolable amount Qt of the hot water storage tank 31 is expressed by the following equation (4).

FIG. 4 (d) shows an example of the coolable amount of the hot water storage tank 31. In FIG. 4D, T38a to T38f are temperatures detected by the sensors 38a to 38f of the temperature detecting means 38, respectively. The portion surrounded by the diagonal line in the figure corresponds to the heat quantity that can be cooled.

  Returning to FIG. 3 again, the description of the procedure for creating the operation plan will be continued. When the coolable amount is calculated as described above, the required operation time (h) of the fuel cell 15 is calculated from the predicted value of heat demand (S22). The “required operation time” is the time from the start of the thermal suppression control to the time when the fuel cell 15 is operated (when the fuel cell 15 is operating at the start of the thermal suppression control, at the start of the thermal suppression control). This is the time until the heat demand exceeding the threshold is generated, and includes the time to which extra time is added. When there is no heat demand equal to or greater than the threshold, the time required until the maximum heat demand occurs up to a predetermined time (24 hours) ahead is set as the required operation time.

After calculating the required operation time, the upper limit power generation amount (W) of the fuel cell 15 is calculated (S23). The upper limit power generation amount is as follows based on the coolable amount and the required operation time calculated in the previous two steps (S21, S22), the power generation efficiency specific to the fuel cell 15, and the heat recovery efficiency of the fuel cell system 100 as follows: calculate.
“Maximum power generation amount” = “Coolable amount” × “Power generation efficiency” / (“Heat recovery efficiency” × “Necessary operation time”)

  Next, a thermal control operation plan that is an operation plan created by setting the planned power generation amount within the range of the upper power generation amount calculated as described above, and a steady operation plan that is created without considering the upper limit power generation amount An operation plan is created (S24). Whether or not the value calculated according to the predetermined standard is improved when it is assumed that the fuel cell 15 is operated according to the thermal suppression operation plan than when the fuel cell 15 is operated according to the steady operation plan. Is determined (S25). Here, it is assumed that the fuel cell 15 is operated according to each operation plan. As will be described later, the operation plan is only one guideline, and when the fuel cell 15 is actually operated, it is not always according to the operation plan. It is because it does not necessarily drive. The predetermined standard is a standard from the viewpoint of energy saving, economic efficiency, environmental conservation, etc. In the following description, a standard regarding energy consumption reduction will be described as an example. A value calculated according to a predetermined standard (hereinafter referred to as “operation plan selection reference value”) is a value for determining whether or not to adopt a thermal suppression operation plan, and is obtained by a simulation described below. Here, it is assumed that the higher the operation plan selection reference value, the more the energy consumption can be reduced.

  The operation plan selection reference value is actually a value converted into one reference for energy consumed in various forms. Typically, a value obtained by converting the raw material fuel m input to the fuel cell system 100, energy used for power generation at the power plant, and the like into the same dimension is used. Formulas used to calculate the operation plan selection reference value are stored in advance in the calculation means of the control device 50. The control device 50 calculates the operation plan selection reference value based on the current operation state of the fuel cell 15, the state of the heat storage amount of the hot water storage tank 31, and information on the generated operation plan.

  FIG. 5 is a flowchart for explaining a calculation procedure for calculating the operation plan selection reference value. In the present embodiment, the range to be subjected to the following simulation is within the required operation time. First, the power purchase amount is obtained from the prediction of power demand in the operation plan and the planned power generation amount (S301). Usually, since the operation plan is prepared so that the predicted value of power demand exceeds the planned power generation amount (see paragraph 0039), the power purchase amount is a positive value, but the planned power generation amount exceeds the predicted power demand value. In this case, the power purchase amount is set to zero. In this way, when the planned power generation amount exceeds the predicted value of power demand, the power purchase amount is set to 0, but when a reverse power flow is recognized, it may be expressed as a negative value. Next, the heating amount of the reverse tide heater 24 is calculated (S302). The amount of heating of the reverse tide heater 24 is a power value obtained by subtracting a predicted value of power demand from the planned power generation amount, the efficiency of the reverse tide heater 24, and a predetermined calculation time interval (a unit for performing simulation, for example, 1 hour). It is calculated by the product of The power value obtained by subtracting the predicted value of power demand from the planned power generation amount is the reverse power amount.

  Next, the power generation efficiency and heat recovery efficiency of the fuel cell 15 are obtained (S303). The power generation efficiency and the heat recovery efficiency are values inherent to the fuel cell 15, but are generally not constant values, but are turndown ratios ρ (ρ = “planned”, which is a value obtained by dividing the planned power generation amount by the rated output value. In many cases, it varies with the amount of power generation / rated output value). Therefore, the values of the power generation efficiency and the heat recovery efficiency are stored in the data holding means of the control device 50 as a database corresponding to each turndown ratio ρ, and correspond to the turndown ratio ρ at that time from the database. Calculate power generation efficiency and heat recovery efficiency. Next, a heat recovery amount is obtained (S304). The heat recovery amount is obtained by “heat recovery amount” = “planned power generation amount” × “power generation efficiency” × “predetermined calculation time interval (for example, 1 hour)” / “heat recovery efficiency”. Next, a piping system heat loss amount is obtained (S305). The piping system heat loss is heat radiation from the cooling water pipe 16 that connects the fuel cell 15 and the heat exchanger 21 and heat radiation from the heat storage medium pipe 22 that connects the heat exchanger 21 and the hot water storage tank 31. The amount of heat loss in the piping system is determined by the product of the heat loss rate at the time of exhaust heat recovery determined by the heat insulation state of the cooling water pipe 16 and the heat storage medium pipe 22 and the amount of heat recovery determined in the previous process.

  Next, the amount of heat loss in the hot water storage tank 31 is obtained (S306). The amount of heat loss in the hot water storage tank 31 is determined by the product of the amount of heat stored in the hot water storage tank 31, the hot water storage tank heat loss rate determined by the heat insulation state of the hot water storage tank 31, and a predetermined calculation time interval (for example, 1 hour). . Next, the amount of stored hot water before use is obtained (S307). The hot water storage amount before use of hot water supply is obtained as the sum of a value obtained by subtracting the hot water tank heat loss rate from the heat storage amount in the hot water storage tank 31 and a value obtained by subtracting the piping system heat loss amount from the heat recovery amount. Next, the hot water supply heat amount from the hot water storage tank 31 and the heating amount of the backup boiler are obtained (S308). When the amount of stored hot water before use of hot water is equal to or greater than the predicted value of heat demand, the amount of hot water supplied from the hot water storage tank 31 is equal to the value of heat demand, and the heating amount of the backup boiler is zero. On the other hand, when the amount of hot water stored before using hot water is below the predicted value of heat demand, the amount of hot water supplied from hot water storage tank 31 is equal to the amount of stored hot water before using hot water, and the predicted value of heat demand and the amount of hot water supplied from hot water tank 31 are The difference is the heating amount of the backup boiler.

  Next, the amount of stored hot water after use of hot water and the amount of heat released from the radiator 28 are obtained (S309). When the difference between the amount of hot water stored before using hot water and the amount of hot water supplied from the hot water storage tank 31 is equal to or less than the maximum value of the amount of stored heat in the hot water storage tank 31, the amount of stored hot water after using hot water is the amount of stored hot water before using hot water and the amount of hot water supplied from the hot water tank 31. The amount of heat released from the radiator 28 is zero. On the other hand, when the difference between the hot water storage amount before use of hot water supply and the hot water supply amount from the hot water storage tank 31 is larger than the maximum value of the heat storage amount of the hot water storage tank 31, the hot water storage amount after use of hot water supply becomes the maximum value of the heat storage amount of the hot water storage tank 31, The heat release amount of the radiator 28 is obtained by “radiation amount of the radiator” = (“hot water storage amount before hot water supply” − “heat supply heat amount from the hot water storage tank 31”) − “maximum value of heat storage amount of the hot water storage tank 31”. The maximum value of the heat storage amount of the hot water storage tank 31 is obtained by (“hot water storage tank temperature at full storage” − “makeup water temperature”) × “hot water storage tank capacity” × “specific heat”.

  Next, the power consumption of the radiator 28 is obtained (S310). The power consumption amount of the radiator 28 is obtained by “radiator power consumption amount” = “radiator heat radiation amount” / “radiator efficiency”. Here, “radiator efficiency” is a value of the amount of electric power used per unit of heat radiation, and is a value unique to the radiator. Next, the amount of fuel consumed by the fuel cell system 100 is obtained (S311). This is calculated by “fuel consumption of fuel cell system” = (“power generation amount” / “power generation efficiency”) × “predetermined calculation time interval (for example, 1 hour)” / “heat generation amount of raw material fuel”. Next, the amount of fuel consumed by the backup boiler is obtained (S312). This is obtained by “backup boiler consumption fuel amount” = (“backup boiler heating amount” / “backup boiler efficiency”) / “fuel heat generation amount”.

  Next, when there is no planned power generation amount within the required operation time (there is a possibility in the steady operation plan), the power consumption at startup and the fuel consumption at startup are obtained (S313). When there is a planned power generation amount within the required operation time, the values of power consumption at startup and fuel consumption at startup are zero. Here, the power consumption at start-up and the fuel consumption at start-up are values specific to the fuel cell system 100. In general, the temperature of the reformer 11 needs to be raised to a predetermined temperature when the fuel cell 15 is started, but the reformer is shorter when the fuel cell 15 is stopped for a shorter time than when the fuel cell 15 is stopped. Therefore, the power consumption at startup and the fuel consumption at startup are reduced. Conversely, if the time during which the fuel cell 15 is stopped is long, the temperature drop of the reformer 11 increases, and the power consumption during startup and the amount of fuel consumed during startup increase. Therefore, the power consumption at start-up and the fuel consumption at start-up are made into a database as values corresponding to the stop time of the fuel cell 15 and stored in the data holding means of the control device 50, and the power consumption at start-up at that time is stored from the database. Calculate power and fuel consumption at startup. Next, stop power consumption and stop fuel consumption are determined (S314). The stop power consumption and the stop fuel consumption are added when the fuel cell 15 stops (there is a possibility in the steady operation plan). The power consumption during stoppage and the fuel consumption during stoppage are calculated by referring to the database from the time when the fuel cell 15 is stopped, respectively, similarly to the calculation of the power consumption during start-up and the fuel consumption during start-up (S313). The Next, standby power consumption is calculated (S315). The standby power consumption (possibly in the steady operation plan) is a constant value unique to the fuel cell system 100.

The operations in the above-described steps (S301) to (S315) are performed at predetermined calculation time intervals until the required operating time. For example, in this embodiment, it is performed at an interval of 1 hour until the required operating time. For this reason, after calculating the standby power consumption (S315), it is determined whether or not the calculation has been performed up to the required operating time (S316). If the calculation up to the required operating time has not been completed, the process returns to the step (S301) for determining the amount of power purchase, and the above-described series of calculations is performed. When the calculation up to the required operating time is completed, the total primary energy consumption is obtained (S317). The total primary energy consumption Pfc is expressed as follows using the total power consumption Efc, the total fuel consumption Gfc, the primary energy conversion factor Ke of power, and the fuel heat generation amount Hf.
Pfc = Ke × Efc + Hf × Gfc
Of the above formulas, using the values obtained in the steps (S301) to (S315), the total power consumption Efc is Efc = “power purchase amount” + “radiator power consumption” + “power consumption at startup” "+" Power consumption during stop "+" power consumption during standby ". The total fuel consumption Gfc is expressed by Gfc = “fuel consumption amount of fuel cell” + “backup boiler fuel consumption amount” + “consumption fuel amount at startup” + “consumption fuel amount at stop”. As the primary energy conversion factor Ke for power, for example, a value of 9.84 kJ / Wh can be used, but since a plurality of conversion factors have been proposed, an appropriate value may be used.

Evaluation of the operation plan of the fuel cell system is often performed by comparison with a conventional system in which power demand is supplied from grid power and heat demand is supplied from a boiler. The primary energy use amount Pp of the conventional system is expressed as follows using the predicted value EL of power demand, the fuel consumption amount GL, the primary energy conversion coefficient Ke of the power and the fuel heat generation amount Hf described above. .
Pp = Ke × EL + Hf × GL
In the above formula, the predicted value EL of the power demand is based on the premise that all power to the power demand is supplied from the grid power. The fuel consumption GL is calculated by “heat demand” ÷ “boiler efficiency” ÷ “fuel heat generation amount”, and it is assumed that all heat to the heat demand is supplied from the boiler. The primary energy reduction rate ηe is obtained by the following equation based on the total primary energy use amount Pfc obtained as described above and the primary energy use amount Pp of the conventional system.
ηe = (Pp−Pfc) / Pp
The primary energy reduction rate ηe calculated in this way becomes the operation plan selection reference value. There are various concepts in the concept of the primary energy reduction rate ηe, and a plurality of methods have been proposed for the calculation. Any one of them may be used, and the above-described calculation method is an example. The operation plan selection reference value is calculated for each of the thermal suppression operation plan and the steady operation plan by the simulation described so far.

  Returning to FIG. 3 again, the description of the procedure for creating the operation plan will be continued. When the operation plan selection reference value is calculated for each of the thermal suppression operation plan and the steady operation plan, when it is assumed that the fuel cell 15 is operated according to the thermal suppression operation plan, it is assumed that the fuel cell 15 is operated according to the steady operation plan. Since it can be determined whether or not the operation plan selection reference value has been improved compared to when the operation plan has been improved (S25), if it has been improved, the thermal suppression operation plan is adopted as the operation plan that is the basis of the operation of the fuel cell 15 (S26). . If the operation plan selection reference value has not improved, the steady operation plan is adopted as the operation plan that is the basis of the operation of the fuel cell 15 (S27). When the heat suppression operation plan is adopted, the stop of the fuel cell 15 and the operation of the radiator 28 due to the hot water storage tank 31 becoming full can be prevented. When the steady operation plan is adopted, it is possible to prevent a decrease in power generation efficiency and heat recovery efficiency due to limiting the power generation amount.

  Next, returning to FIG. 2, the description of the operation method of the fuel cell system will be continued. After the operation plan is created, the fuel cell 15 is operated based on the created operation plan (S30). The operation of the fuel cell 15 is not necessarily performed according to the prepared operation plan. When the thermal control is not required, the fuel according to the actual power demand and heat demand is referred to while referring to the prepared operation plan. Operation is performed with the output of the battery 15. On the other hand, when the upper limit power generation amount is set during the operation plan created in the previous step (S20) (when thermal suppression is required), it follows the actual power demand and heat demand within a range not exceeding the upper limit power generation amount. The operation is performed with the output of the fuel cell 15. Note that the “operation” in the step (S30) of operating the fuel cell 15 includes the case where the fuel cell 15 is stopped due to the lack of demand for electric power and / or heat.

  The thermal suppression control described above is preferably executed at an appropriate interval. The prediction of power demand and heat demand and the actual power consumption and heat consumption do not always coincide, and the heat storage amount of the hot water storage tank 31 often deviates from the predicted value. Accordingly, it is preferable to appropriately review the prediction of power demand and heat demand (S10) and the creation of an operation plan (S20) and operate the fuel cell 15 according to the current heat storage amount of the hot water storage tank 31 (S30).

  In the above description, the fuel cell 15 has been described as a solid polymer fuel cell. However, other types of fuel cells such as a phosphoric acid fuel cell and a solid oxide fuel cell can be used in addition to the solid polymer fuel cell. Can be used. However, the polymer electrolyte fuel cell can be operated at a relatively low temperature and can be downsized, so that it is suitable for use in homes, small apartment houses, or small offices.

1 is a system diagram illustrating a fuel cell system according to an embodiment of the present invention. It is a flowchart explaining the operating method of the fuel cell system which concerns on embodiment of this invention. It is a flowchart explaining the procedure which produces an operation plan. It is a figure explaining calculation of the amount of cooling possible. (A) When all the amount of heat storage medium can be used for cooling the fuel cell, (b) When all the heat storage medium amount cannot be used for cooling the fuel cell, (c) (D) is a figure which shows the example of the coolable amount of a hot water storage tank, when a medium amount can be utilized for cooling of a fuel cell. It is a flowchart explaining the calculation procedure which calculates an operation plan selection reference value.

Explanation of symbols

15 Fuel Cell 21 Heat Exchanger 24 Reverse Tide Heater 28 Radiator 31 Hot Water Storage Tank (Heat Storage Tank)
38 Temperature Detector 50 Control Device 100 Fuel Cell System

Claims (5)

A method for operating a fuel cell system, comprising: a fuel cell that generates electricity by an electrochemical reaction between hydrogen and oxygen and generates heat; and a heat storage tank that stores heat generated in the fuel cell;
Predicting power demand and heat demand up to a predetermined time ahead based on past operating results;
Creating an operation plan for the fuel cell based on the result obtained in the step of predicting the demand;
Operating the fuel cell based on the operation plan;
The step of creating the operation plan includes: a heat suppression operation plan for operating the fuel cell within a range of heat generation amount of the fuel cell capable of storing heat in the heat storage tank; and a heat generation of the fuel cell capable of storing heat in the heat storage tank. A steady operation plan that does not consider the amount, and when it is assumed that the fuel cell is operated according to the thermal suppression operation plan rather than when the fuel cell is operated according to the steady operation plan. The thermal suppression operation plan is configured to be an operation plan that is a basis for the operation of the fuel cell when a value calculated according to a predetermined standard is improved;
Operation method of fuel cell system. The predetermined standard is any one of a standard for energy consumption reduction, a standard for cost reduction, and a standard for emission carbon dioxide reduction;
The operation method of the fuel cell system according to claim 1. The amount of heat that can be stored in the heat storage tank is represented by the sum of the amount of heat that can be stored for each section obtained by dividing the heat storage tank into a predetermined number;
The operation method of the fuel cell system according to claim 1 or 2. A fuel cell that generates electricity and generates heat by an electrochemical reaction between hydrogen and oxygen;
A heat storage tank for storing heat generated in the fuel cell;
A control device for controlling the fuel cell system according to the method for operating the fuel cell system according to any one of claims 1 to 3;
Fuel cell system. A fuel cell that generates electricity and generates heat by an electrochemical reaction between hydrogen and oxygen;
A heat storage tank for storing heat generated in the fuel cell;
A temperature detector for detecting the temperature at both ends of each of the divided heat storage media in the heat storage tank into two or more predetermined numbers;
Calculate the amount of heat that can be stored for each section from the temperature of the heat storage medium detected by the temperature detector, calculate the amount of heat that can be stored in the entire heat storage tank by summing the amount of heat that can be stored for each section, A control device that limits the output of the fuel cell based on the calculated amount of heat that can be stored in the entire heat storage tank;
Fuel cell system.

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