JP3930426B2 - Fuel cell combined power generation system - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a fuel cell combined power generation system, and more particularly, to a fuel cell combined power generation system that allows the operation of a fuel cell to respond to fluctuations in actual power demand.
[0002]
[Prior art]
A combined power generation system in which a gas turbine and a solid oxide fuel cell (hereinafter also referred to as “SOFC”) are combined is known. In this combined power generation system, first, fuel gas and air gas are supplied to the preceding SOFC to generate power. Next, the outlet fuel gas (exhaust fuel gas) discharged from the SOFC and the outlet air gas are mixed, burned in the combustor, and charged into the subsequent gas turbine. Then, power is generated by a generator coupled to the gas turbine. Thereafter, the exhaust gas energy discharged from the gas turbine is recovered by an exhaust heat recovery system.
[0003]
Next, the relationship between power demand and power generation will be described. FIG. 3 is a graph showing the relationship between power demand and power generation. The vertical axis is power demand, and the horizontal axis is time.
Electricity demand fluctuates according to the season and time. These vary depending on the temperature and social situation, but can be predicted to some extent (curve Q in FIG. 3). However, the actual power demand varies finely depending on on / off of individual devices in the consumer (curve D in FIG. 3). It is difficult to predict the frequency and extent of this change. At the power plant, the power generation equipment is operated in accordance with the demand forecast, but it cannot cope with sudden load fluctuations. Therefore, in order to stabilize the system power, the power generator is operated with a margin with respect to the load so as not to be short of supply (curve M in FIG. 3). As a result, excess fuel is consumed, leading to power transmission loss in the grid and reduced efficiency in the power plant.
[0004]
There is a demand for a technology that can quickly respond to the power demands of finely varying consumers. There is a need for a technology that can cope with sudden load fluctuations without impairing the stability of the system power. A technique capable of improving the efficiency of the power generation system is desired.
[0005]
As a related technique, Japanese Patent Laid-Open No. 8-287958 discloses a technique of an operation method for a secondary battery power storage system. The operation method of the secondary battery power storage system of this technology is an operation method of the secondary battery power storage system in which the power charged at night is discharged and used in a predetermined time zone in the daytime. The operation method first detects the outside air temperature, the load power, and the load power increase rate. Next, a power demand prediction value is calculated based on those detected values. Then, when the predicted value of power demand is compared with the set value, when the predicted value is smaller than the set value, an operation is performed to discharge the constant power on an average over the time period, and when the predicted value is larger than the set value. The operation is performed to intensively discharge high power at a specific time within the time zone. When calculating the power demand prediction value, the air conditioning load on the corresponding day on the calendar is taken into account.
The purpose of this technology is to provide an operation method and apparatus for a secondary battery power storage system that can appropriately perform operation mode selection based on autonomous determination without relying on artificial determination. There is to do.
[0006]
[Patent Document] Japanese Patent Application Laid-Open No. 8-287958
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a combined fuel cell power generation system capable of quickly responding to the power demands of consumers that vary finely.
[0008]
Another object of the present invention is to provide a combined fuel cell power generation system that can cope with a sudden load fluctuation without impairing the stability of the system power.
[0009]
Still another object of the present invention is to provide a combined fuel cell power generation system capable of improving the efficiency of the power generation system.
[0010]
Another object of the present invention is to provide a combined fuel cell power generation system capable of reducing an environmental load.
[0011]
[Means for Solving the Problems]
Hereinafter, means for solving the problem will be described using the numbers and symbols used in the embodiments of the present invention. These numbers and symbols are added in parentheses in order to clarify the correspondence between the description of [Claims] and [Embodiments of the Invention]. However, these numbers and symbols should not be used for the interpretation of the technical scope of the invention described in [Claims].
[0012]
Therefore, in order to solve the above problem, the combined fuel cell power generation system of the present invention includes a fuel cell system (7), a bottoming cycle system (8), and a control unit (10).
The fuel cell system (7) includes a fuel cell (1) that is supplied with a fuel gas and an oxidant gas and generates a first electric power (B). The bottoming cycle system (8) is supplied with the exhaust fuel gas discharged from the fuel cell (1) and the exhaust oxidant gas discharged from the fuel cell (1), and the predicted power demand as the predicted power demand. The second power (A) based on (Q) is generated. The control unit (10) controls the fuel cell system (7) so that the first power (B) is a difference between the actual power demand (D) and the second power (A) as actual power demand. To do.
[0013]
In the above fuel cell combined power generation system, the control unit (10) controls the supply of the fuel gas based on the predicted power demand (Q).
[0014]
In the above combined fuel cell power generation system, the fuel gas supply amount is such that the bottoming cycle system (8) generates the second output (A), and the fuel cell system (7) generates the second output from the predicted power demand (Q). Control is performed so that the predicted first power obtained by subtracting the power (A) can be generated at a predetermined fuel utilization rate.
However, the predetermined fuel usage rate is determined by the difference between the power generated at the highest fuel usage rate of the fuel cell system (7) and the power generated at the predetermined fuel usage rate as the actual power demand (D ) And the predicted power demand (Q).
[0015]
In the above fuel cell combined power generation system, the fuel cell (1) is a solid oxide fuel cell.
[0016]
In the fuel cell combined power generation system, the bottoming cycle system (8) includes a gas turbine (2) and a first generator (4). The gas turbine (2) is operated using the exhaust fuel gas and the exhaust oxidant gas. The first generator (4) generates power using the rotational force of the gas turbine (2).
[0017]
The fuel cell combined power generation system further includes an exhaust heat recovery boiler (not shown), a steam turbine (not shown), and a second generator (not shown).
An exhaust heat recovery boiler (not shown) is operated using exhaust gas discharged from the gas turbine (2). A steam turbine (not shown) is operated using steam generated in an exhaust heat recovery boiler (not shown). The second generator (not shown) is connected to a steam turbine (not shown) and generates power based on the rotation of the steam turbine (not shown).
[0018]
In the above fuel cell combined power generation system, the fuel gas is at least one of hydrogen, methane, natural gas, and coal gasification gas.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of a combined fuel cell power generation system according to the present invention will be described with reference to the accompanying drawings.
In the present embodiment, a solid oxide fuel cell (hereinafter also referred to as “SOFC”) will be described as an example, but the present invention can also be applied to other types of fuel cells.
[0020]
First, the configuration of the fuel cell combined power generation system according to the embodiment of the present invention will be described.
FIG. 1 is a diagram showing a configuration in an embodiment of a fuel cell combined power generation system according to the present invention. The combined fuel cell power generation system includes a fuel cell system 7, a bottoming cycle system 8, and a control device 10.
In this figure, piping relating to the oxidant gas is omitted.
[0021]
The fuel cell system 7 is supplied with a fuel gas and an oxidant gas, and generates a first power as a power by a reaction between them. A solid oxide fuel cell (SOFC) 1, an inverter 3, and a fuel gas flow rate control unit 5 are provided.
[0022]
The fuel gas flow rate control unit 5 is provided in the middle of a pipe for supplying fuel gas to the solid oxide fuel cell (SOFC) 1. And based on the control signal from the control apparatus 10, the flow volume of the fuel gas supplied to SOFC1 is adjusted. The fuel gas flow rate control unit 5 is exemplified by a flow rate control valve.
[0023]
The solid oxide fuel cell (SOFC) 1 is a solid oxide fuel cell that is supplied with a fuel gas and an oxidant gas and generates a first power. The first power is controlled by the inverter 3. The SOFC 1 uses methane gas (natural gas), propane gas, hydrogen gas, or the like as the fuel gas, and a gas containing oxygen such as air as the oxidant gas. The SOFC 1 is exemplified as an internal reforming type cylindrical fuel cell using stabilized zirconia as an electrolyte.
[0024]
The inverter 3 controls the operation of the SOFC 1 based on the control signal of the control device 10. And the 1st electric power (output B in Drawing 1) generated with SOFC1 is outputted to the exterior (system).
[0025]
The bottoming cycle system 8 includes exhaust fuel gas discharged from the SOFC 1 (including unused fuel gas and produced water), exhaust oxidant gas discharged from the SOFC 1 (supplemented with oxidant gas as required), To generate second power as power. The second power is determined based on the predicted power demand as the predicted power demand. The second power is calculated by, for example, a predetermined function set in advance. However, the present invention is not limited to this example.
The bottoming cycle system 8 includes a gas turbine system 2 and a generator 4.
[0026]
The gas turbine system 2 burns exhaust fuel gas and exhaust oxidant gas discharged from the SOFC 1 in the combustor, and converts the energy of the combustion gas into rotational energy. It is connected to the generator 4.
[0027]
The generator 4 generates the second electric power using the rotational energy generated by the gas turbine system 2. Then, the second power (output A in FIG. 1) is output to the outside (system). The measured value of the second power is output to the control device 10.
[0028]
The control device 10 controls the fuel cell system based on the actual power demand as the actual power demand and the second power so that the first power is the difference between the actual power demand and the second power. The control device 10 includes a fuel cell system control unit 11, a bottoming control unit 12, a power demand prediction unit 13, and a power demand database 14.
[0029]
The power demand database 14 stores information related to time (example: year, month, day, time), actual power demand, and predicted power demand in association with each other.
[0030]
The power demand prediction unit 13 determines the power based on the information affecting the power demand exemplified in the past power demand (example: power demand in the same period in the past several years and its average), temperature, and trends from the past. Predict demand. The predicted data is stored in the power demand database 14. The prediction of power demand may be performed all the time including the correction, or may be performed every predetermined period. A conventionally known method can be used for prediction of power demand.
The past power demand is stored in the power demand database 14.
[0031]
The bottoming control unit 12 reads the predicted power demand at each time from the power demand database 14, and determines the second power based on the predicted power demand. The second power is, for example, a predetermined ratio of the predicted power demand. In this case, the predetermined ratio is set in advance according to the magnitude of the predicted power demand. For example, 60% when the predicted power demand is large, 20% when the predicted power demand is small. However, the present invention is not limited to this example. Then, the bottoming cycle system 8 is controlled so as to generate the second electric power.
[0032]
The fuel cell system control unit 11 acquires actual power demand by a measuring device (not shown). Moreover, the measured value of the 2nd electric power output from the generator 4 is acquired. Then, based on the actual power demand and the second power, the fuel cell system 7 so that the first power becomes a difference between the actual power demand and the second power (or a difference added to the difference). The inverter 3 is controlled. At that time, the fuel gas flow rate control unit 5 is controlled as necessary.
The actual power demand is stored in the power demand database 14.
[0033]
In FIG. 1, only the gas turbine system 2 is shown as the bottoming cycle system 8, but a system applicable to another conventionally known bottoming cycle system 8 can also be used. Such a system is exemplified by a conventionally known exhaust heat recovery system including an exhaust heat recovery boiler, a steam turbine, and a generator. In that case, the electric power generated by this generator is also included in the second electric power.
[0034]
Next, the operation in the embodiment of the fuel cell combined power generation system according to the present invention will be described.
FIG. 2 is a graph showing a relationship between power generation and power demand in the operation of the embodiment of the fuel cell combined power generation system according to the present invention. The vertical axis is power demand, and the horizontal axis is time. However, curve P represents the second power. Area A is covered by the second power. Curve Q shows the predicted power demand. Curve D shows the actual power demand. Area B (= actual power demand−second power) is covered by the first power. Curve M shows the maximum power that the system can supply.
[0035]
Next, the operation will be described with reference to FIG. 1 and FIG.
In FIG. 1, the fuel cell system control unit 11 reads the predicted power demand at a corresponding time t (a point on the curve Q at time t in FIG. 2) from the power demand database 14. Further, the second power (a point on the curve P at time t in FIG. 2) by the generator 4 is acquired by a measuring device (not shown). Then, the flow rate control unit 5 is controlled to supply the fuel gas having a flow rate determined by the following two conditions to the SOFC 1. Condition (1) The SOFC 1 can generate the predicted first power at a predetermined fuel utilization rate (example: 60%). However, predicted first power = predicted power demand−second power. Condition (2) The bottoming cycle system 8 can generate the measured second electric power by using the exhaust fuel gas of the SOFC 1 and the exhaust oxidant gas (which can be supplemented with the oxidant gas if necessary).
[0036]
The fuel cell system control unit 11 acquires actual power demand (a point on the curve D at time t in FIG. 2) by a measuring device (not shown). Then, based on the actual power demand and the second power, the inverter 3 of the fuel cell system 7 is controlled so that the first power = the actual power demand−the second power (or + α).
The SOFC 1 is supplied with the fuel at the above flow rate, is controlled by the inverter 3, generates the first electric power, and outputs it as an output B to the system. Then, the exhaust fuel gas and the exhaust oxidant gas are output to the gas turbine system 2.
[0037]
The bottoming control unit 12 reads the predicted power demand at each time (a point on the curve Q at time t in FIG. 2) from the power demand database 14, and determines the second power based on the predicted power demand. For example, predicted power demand × predetermined ratio. In this case, the predetermined ratio is set in advance for each category of the predicted power demand. For example, it is 60% when the predicted power demand is large, 40% when it is medium, and 20% when it is small. Then, the bottoming control unit 12 controls the bottoming cycle system 8 so as to generate the determined second power.
The bottoming cycle system 8 is supplied with the exhaust fuel gas and the exhaust oxidant gas, generates the second electric power, and outputs it as an output A to the system.
[0038]
As shown in the above process, the SOFC 1 is basically controlled so that it can be operated at a predetermined fuel utilization rate (for example, 60%) with respect to the predicted power demand. When the fuel cell system 7 (the SOFC 1) instead of the bottoming cycle system 8 has a difference between the actual power demand and the predicted power demand that change from moment to moment, the operating conditions are changed to satisfy the difference. Correspond. This is possible because the load followability of the SOFC 1 is high.
That is, the power generation part of the SOFC 1 does not have a rotating machine, so that no time delay due to inertia occurs. Further, since the fuel gas is supplied with a slightly excessive supply amount (operable up to a fuel utilization rate of 80%), it is not necessary to follow the flow rate of the fuel gas or the like for non-variable fluctuations of a certain size. Therefore, when the load fluctuates, it is possible to quickly change the power generation amount (first power) by the command of the inverter 3.
[0039]
Further, the supply amount of exhaust fuel gas to the bottoming cycle system 8 changes with load following. At this time, if the supply amount of the exhaust fuel gas to the SOFC 1 is constant, the SOFC 1 tends to decrease in efficiency as the load increases. (1) When the SOFC 1 load increases, the supply amount of the exhaust fuel gas decreases. However, the amount of sensible heat supplied to the bottoming cycle system 8 increases. Conversely, (2) when the SOFC1 load is reduced, the exhaust fuel gas increases, but the sensible heat exhaust heat decreases. As a result, the bottoming cycle system 8 can maintain a stable operation state regardless of the load factor of the SOFC 1.
[0040]
According to the present invention, since a sudden load change is absorbed by the fuel cell, it becomes possible for the plant to perform an operation plan according to the true predicted power demand. As a result, it is possible to reduce power transmission loss and improve the energy efficiency of the plant.
[0041]
【The invention's effect】
According to the present invention, it is possible to respond quickly to the power demands of finely varying consumers and improve the efficiency of the power generation system.
[Brief description of the drawings]
FIG. 1 is a diagram showing a configuration in an embodiment of a combined fuel cell power generation system according to the present invention.
FIG. 2 is a graph showing a relationship between power generation and power demand in the operation of the embodiment of the combined fuel cell power generation system of the present invention.
FIG. 3 is a graph showing the relationship between power demand and power generation.
[Explanation of symbols]
1 Solid oxide fuel cell (SOFC)
2 Gas Turbine System 3 Inverter 4 Generator 5 Flow Rate Control Unit 7 Fuel Cell System 8 Bottoming Cycle System 10 Controller 11 Fuel Cell System Control Unit 12 Bottoming Control Unit 13 Power Demand Prediction Unit 14 Power Demand Database

Claims (6)

A fuel cell system including a fuel cell that is supplied with a fuel gas and an oxidant gas and generates a first electric power;
A bottoming cycle system that is supplied with exhaust fuel gas discharged from the fuel cell and exhaust oxidant gas discharged from the fuel cell and generates second power based on the predicted power demand as the predicted power demand When,
Wherein the first power, so that the difference between the actual second power and the actual power demand as a power demand, and ingredients Bei and a control unit for controlling the fuel cell system,
The control unit generates the second output from the bottoming cycle system based on the predicted power demand based on the supply amount of the fuel gas, and the fuel cell system subtracts the second power from the predicted power demand. Control so that the predicted first electric power can be generated at a predetermined fuel utilization rate,
The predetermined fuel utilization rate is the difference between the electric power generated at the highest fuel utilization rate of the fuel cell system and the electric power generated at the predetermined fuel utilization rate. Fuel cell combined power generation system set to absorb the difference between the two . The combined fuel cell power generation system according to claim 1,
The bottoming cycle system generates the second electric power without compensating for fluctuations in the supply amount of the exhaust fuel gas accompanying fluctuations in the actual power demand.
Fuel cell combined power generation system. The fuel cell combined power generation system according to claim 1 or 2 ,
The fuel cell is a solid oxide fuel cell. In the fuel cell combined power generation system according to any one of claims 1 to 3 ,
The bottoming cycle system includes:
A gas turbine operated using the exhaust fuel gas and the exhaust oxidant gas;
A fuel cell combined power generation system comprising: a first generator that generates electric power using the rotational force of the gas turbine. The fuel cell combined power generation system according to any one of claims 1 to 4 ,
An exhaust heat recovery boiler operated using the exhaust gas discharged from the gas turbine;
A steam turbine operated using steam generated in the exhaust heat recovery boiler;
A fuel cell combined power generation system, further comprising: a second generator connected to the steam turbine and generating power based on rotation of the steam turbine. The combined fuel cell power generation system according to any one of claims 1 to 5 ,
The fuel gas is at least one of hydrogen, methane, natural gas, and coal gasification gas.

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