JPS6177273A - Control system for fuel cell power generation plant - Google Patents

Abstract

PURPOSE:To assure given amounts of steam so as to achieve improved control of a cell cooling water system by making control of the temperature of water for cooling a fuel cell and control of the temperature of a steam generator independent and temporarily reducing the internal pressure of the steam generator during a rapid increase of the load. CONSTITUTION:On the basis of an actual current signal from a current detector 29, a function generator 30 delivers a signal indicating the temperature of cooling water for maintaining the temperature of a fuel cell by taking the heat generated by the reaction of the fuel cell 5 into account. The above temperature-indicating signal and an actual temperature signal generated by a temperature detector 21 are subjected to deviation operation in a comparator 31 and the result of the operation is transferred to a valved 17 for controlling the temperature of water for cooling the fuel cell through an output control computing element 32. As the result, part of the steam from a steam generator 15 is cooled by a heat exchanger 20 to produce water. The temperature of water for cooling the fuel cell is controlled by varying the amount of thus produced water n the steam. By thus independently controlling the temperature of water for cooling the fuel cell 5 and that of the steam generator 15, it is possible to stably supply steam to a mixer 14. Furthermore, it is also possible to prevent any decrease in the pressure and the temperature of the steam generator 15 during application of a high load.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a fuel cell power generation plant control system, and particularly to a fuel cell power generation plant control system that can stably supply necessary steam during a sudden load increase.

[Problems with back technology] In general, mino-j is generated by rotating a generator using a prime mover such as a steam turbine, converting this given drive energy into AC power in the generator, and then using the AC power as it is on the demand side. This method has been adopted as the most convenient method from generation to consumption of electric power, and therefore most current electric power systems are AC systems.

On the other hand, the steam that drives steam turbines, etc. is generated from the thermal energy of burning fuel such as oil and gas in boilers, etc., but this fuel energy is extracted as thermal energy and converted into steam energy. Furthermore, since extracting electrical energy as electrical energy is disadvantageous in terms of efficiency, in recent years fuel cells have been developed that attempt to produce electrical energy directly by causing a chemical change in the fuel and using the flow of electrons generated during this chemical change. This power generation method has come to be adopted as an energy-saving power generation method.

This combustion cell chemically changes the supplied fuel □
In particular, it generates electricity, but its output is DC output, so if it is consumed in a specific area, it will be consumed as DC, and as part of energy saving measures, it will be used to cover large amounts of electricity. In some cases, the DC-AC converter converts the AC into AC and connects it to the power system.

FIG. 4 is a block diagram of a typical fuel cell power generation plant. In the figure, a portion 1 indicated by a dashed line is a fuel cell power generation plant. First, the fuel enters the mixer 14 with its flow rate controlled by the raw fuel control valve 10. On the other hand, steam whose flow rate is controlled enters the mixer 14 from the steam generator 15 via the steam control valve 16 . The fuel r1 mixed in the mixer 14 enters the reformer 4, where it is heated and reformed. The reformed fuel then passes through a high temperature shift converter 8 and a low temperature shift converter 9 to become reformed fuel with a high hydrogen content. The flow rate of this reformed fuel is controlled by the reformed fuel control valve 11, and it flows into the hydrogen electrode 5A of the fuel cell 5, where part of it is used as electrical energy, and the rest is used in the reformer 4 described above. It is combusted in the main burner 12, becomes high-temperature gas for heating the reformer 4, merges with gas 11 from the oxygen electrode 5B of the fuel cell 5, and further flows into the turbine 2 of the turbo combiner 1 through the combustor 7. , drives the compressor 3 connected thereto. The flow rate of the discharged air from the baffle sensor 3 is controlled by the air control valve 13, and the flow rate is controlled by the -C fuel r1 oxygen electrode 5B of the lightning pond 5.
to go into. A part of the oxygen that entered the oxygen electrode 5B becomes hydrogen ll5A
The remaining gas is exhausted from the oxygen electrode 5B, joins the exhaust gas from the main barbs 2 of the reformer 4, and passes through the combustor 7 to the turbine of the turbo compressor. It is used to drive 2. The fuel cell 5 is cooled by circulating the water from the steam generator 15 to the cooling plate 5C and the steam generator 15 by one cell cooling IJ1 water circulation pump. Further, temperature control of the battery cooling water is performed by cooling a part of the steam generated from the steam generator 15 with a heat exchanger 20 and using a battery cooling water temperature control valve 17.

Here, the fuel r3+ battery 5 is the hydrogen of the hydrogen electrode 5A and the oxygen electrode 5B.
By catalytic reaction with oxygen, oxygen i! i! J: where iB is the positive electrode and the hydrogen electrode 5A is the negative electrode, generates electrical energy and supplies the electrical energy to an electrical load connected between the two electrodes. At this time, the hydrogen and oxygen supplied to the inlets of both electrodes react in approximately proportion to the electrical energy absorbed by the electrical load to become water, and the unreacted portion is discharged from the outlet of each electrode. The DC output of the fuel cell 5 is supplied to a converter 6, where it is converted into AC power, and sent to the power system as AC power.

[Problems with backlash technology] In the case of a fuel cell power generation plant with the above configuration, in order to start up from a no-load state to 100% load in a short time,
A large amount of reformed fuel is required instantaneously. Therefore, the raw fuel that is the source of the reformed fuel is also suddenly introduced via the raw fuel control valve 10 and enters the mixer 14.

On the other hand, in the reformer 4, in order to reform the fuel to increase the hydrogen content, steam is required as shown in the following chemical reaction formula.

CH4→-H20→Co+3H2 G O+H20→CO2+ H2 Therefore, this required steam also rapidly enters the mixer 14 via the steam control valve 16. The raw fuel mixed with steam in the mixer 14 then enters the reformer 4 and is reformed to become reformed fuel.

Further, the amount of steam entering the mixer 14 usually needs to be theoretically determined by the formula shown below.

However, in an actual plant, the value should be approximately twice the initial value to allow for some margin. Hereinafter, this value will be referred to as S/C.

The molar flow rate of the main combustion I31 (usually S/C = 4) Therefore, conventionally, the pressure of the steam generator 15 is controlled by a pressure control valve 18, and the battery cooling water temperature control valve 17 is further controlled by a temperature detector. The measurement temperature of No. 21, that is, the humidity of the battery cooling water was controlled.The above control had the following drawbacks.

■When the load suddenly increases, a large amount of steam is required according to the S/C ratio, and if this exceeds the capacity limit of the steam generator 15, the S
/C ratio will decrease. Here, the S/C ratio decreases,
When the value is lower than a certain value (for example, 3.5), carbon adheres to the catalyst inside the reformer 4, resulting in a reduction in the reaction area of the catalyst and deterioration of the reforming reaction.

■If five batches of steam are taken out at once from the steam generator 15, the temperature and pressure inside the steam generator 15 will drop, and the bubbles will be sucked in, damaging the battery cooling water circulation pump 19, making it impossible to introduce steam to the mixer 14. There is a risk that it will disappear.

■If the above-mentioned drawbacks of ■ and ■ are to be solved, it is necessary to install a steam generator 15 with a human capacity in order to deal with the transient situation of a sudden increase in load.

■In order to suppress the heat generation of the battery during high loads, the temperature of the battery cooling water, skin temperature, and temperature measured by the temperature detector 21 are controlled to be lowered, so in this method, the temperature will drop to the temperature of the steam generator 15. , Therefore, the pressure also decreases, and the same phenomenon as in case ① above occurs.

[Object of the Invention] The present invention has been made to solve the above-mentioned problems, and provides a fuel cell power generation plant control system that can stably supply the steam necessary for fuel reforming during sudden load changes and during high loads. is intended to provide.

[Summary of the Invention] The present invention separates battery cooling water temperature control and steam generator temperature control as independent controls, and temporarily reduces the pressure inside the steam generator during a transient state such as a sudden increase in load. J: The objective is to lower the amount of steam and secure the amount of steam.

[Embodiments of the Invention] Examples will be described below with reference to the drawings. Figures 1 and 2
The figure is a configuration diagram of one embodiment of the fuel cell power generation plant control system according to the present invention, in which Figure 1 mainly shows the steam flow rate control system and the battery cooling water temperature control system, and Figure 2 shows the pressure of the steam generator. Mainly shows the control system. Note that in FIGS. 1 and 2, the same parts as those in FIG. 4 are designated by the same reference numerals, and the description thereof will be omitted.

In FIG. 1, U indicates a steam flow rate control system and Qin indicates a battery cooling water temperature control system. Although the control of the steam flow rate control system itself is the same as the conventional one, it will be briefly explained for the sake of overall explanation.

That is, this part includes the raw fuel flow rate detector 24 and the function generator 2.
5. It is composed of a comparison section 26, an output control calculation section 28, and a steam flow rate detector 27. First, based on the actual flow rate signal from the raw fuel flow rate detector 24, the function generation section 25
A steam flow rate command commensurate with the S/C ratio is determined. Then, the steam flow rate command signal and the actual flow rate signal from the steam flow rate detector 27 are inputted to the comparison section 26, where a deviation calculation is performed, and the deviation is outputted to the steam control valve 16 through the output control cylinder section 28. and controls the steam flow rate to the mixer 14.

Next, the battery cooling water temperature control valve will be explained.

The only difference between this control system and the conventional one is that the only object to be controlled is temperature control of the cell cooling water to the fuel cell 5. That is, conventionally, two temperatures, the temperature of the cooling water to the fuel R1 battery 5 and the temperature of the steam generator 15, were controlled by the battery cooling water temperature control valve 17, but in the embodiment of the present invention, the former Only the temperature of the cooling water to the fuel cell 5 is controlled, and the temperature control of the latter steam generator 15 is shifted to the control described later.

The battery cooling water temperature control system consists of a current detector 29, a function generating section 30, a comparing section 31, and an output control calculation section 32, and the other configurations are the same as in FIG.

In the above configuration, first, the function generating section 30 is capable of keeping the temperature of the fuel cell constant based on the actual current signal from the current detector 29 and taking into account the heat generated by the reaction of the fuel cell 5. Outputs the Z cooling water warm stone command signal. The temperature command signal and the actual temperature signal from the temperature detector 21 are manually input to a comparator 31 to perform a deviation calculation, and the result is transmitted to the battery cooling water temperature control valve 17 through the output control calculation unit 32. As a result, a portion of the steam from the steam generator 15 is cooled in the heat exchanger 20 and becomes water. The temperature of the battery cooling water is controlled by changing the amount of water mixed in. By dividing the objects to be controlled in this way, it is possible to stably supply steam to the mixer 14 and prevent pressure and temperature drops in the steam generator 15 during high loads. Note that 33 is a heat source of the steam generator 15.

In FIG. 3, temperature control and pressure control of the steam generator 15 will be explained. In FIG. 3, U indicates a temperature control system, and length indicates a pressure horn control system.

The temperature control system M is composed of a temperature detector 36, a comparison section 37, and an output control section 3B, and the temperature detector 36 inputs the actual temperature signal of the steam generator 15 to the comparison section 37, where it is compared with the temperature set value Tset. will be carried out. At this time, if the actual temperature of the steam generator 15 is higher than the temperature setting value T(8),
The heat source 33 in the steam generator 15 is turned off via the output control section 38. If the temperature is lower than the temperature set value Tseg, the heat source 33 is turned on via the output control section 38.

Note that the heat source 33 includes various types such as a heater and a combustor. The temperature setting value Tsez described above is set to a value higher than the setting temperature of the battery cooling water temperature control described above. This is because if the temperature setting value is low, the temperature of the battery cooling water will become lower than the temperature setting of the battery cooling water temperature control.

Next, the pressure control system sub-section includes a change rate calculation section 40, a comparison section 41,
Ramp signal generation section 42, lower limiter section 43, ratio branch section 4
4. Consists of an output control calculating section 45 and a setting section 46, which adjusts the pressure control valve 18 based on the actual current from the fuel cell 5 and the pressure from the steam generator 15.

Next, the operation will be explained. First, the actual current signal from the fuel cell 5 is detected by the current detector 39 and the change rate calculation unit 4
Enter 0. Then, this calculation result signal is sent to the comparison section 41.
and compare it with the rate of change set value Cm. As a result, if the rate of change of the actual current is greater than the rate of change set value C5ea, the ramp signal generator 42 sequentially lowers the pressure set value. The ramp signal generation section 42 is set for a time such that bumping does not occur due to pressure drop in the steam generator 15. Next, the signal from the ramp signal generation section 42 is set to to suppress the pressure to the lower limit pressure set value PLSI!t.

Note that the value of the lower limit pressure set value PLset needs to be set higher than the pressure of the line that performs combustion 1 reforming such as the mixer 14 and the reformer 4, and also higher than the pressure J that corresponds to the battery cooling water temperature. be. That is, if the pressure is low or close to it, the fuel reforming steam will flow to mixer 1.
This is because it will be difficult to introduce into 4. Next, the pressure setting signal from the lower limiter section 43 enters the comparison section 44,
Here, the actual pressure signal of the steam generator 15 by the pressure detector 47 and a deviation calculation are performed. The deviation signal is then transmitted to the pressure control valve 18 via the output control calculation section 45.

On the other hand, if the comparison result by the comparing section 41 is smaller than the change rate set value Cm, the setting section 46 sets the normal pressure set value Pg!
t is set, and this signal is input to the comparison section 44. As described above, the rate of change in the actual current from the fuel cell 5 is calculated, and when this rate of change becomes large, in other words, when the load suddenly increases, the internal pressure saw of the steam generator 15 is lowered, and a large amount of current is reduced. It becomes possible to supply steam to the mixer 14.

FIG. 3 is a diagram showing only the main parts of another embodiment according to the present invention.

In this embodiment, an attempt is made to suppress rapid changes in the rate of change and to continuously change the pressure setting value in accordance with changes in battery current.

That is, the configuration shown in FIG. 3 is installed in the pressure control system length section, the signal via the rate of change calculating section 40 is input to the rate of change limiting section 48 to suppress sudden changes, and the function generating section 49 controls the pressure. The set values are made continuous and input to the comparator 44. The other configurations are the same as in FIG. 2.

[Effect of the invention 1 As explained above, according to the present invention, battery cooling water temperature control and steam generator temperature control are separated as independent controls, and the pressure inside the steam generator is temporarily lowered when the load suddenly increases. With this structure, not only does a large-capacity steam generator not be required, but it can even be made more compact, eliminating insufficient steam volume and temperature and pressure drops within the steam generator when the load suddenly increases.
A fuel cell power generation plant control system that can improve control performance of a battery cooling water system can be provided.

[Brief explanation of drawings]

Figures 1 and 2 are fuel cell power generation plans according to the present invention]
・This is a configuration diagram of one embodiment of the control system; FIG. 1 is a diagram mainly showing a steam flow rate control system and a battery cooling water temperature control system, and FIG. 2 is a diagram mainly showing a steam generator pressure control system. FIG. 3 is a diagram showing only the essential parts of Haku's embodiment, and FIG. 4 is a diagram of a conventional example. 1...Fuel cell plant 2...Tardon 3...
Compressor 4...Reformer 5...Fuel cell
58... Hydrogen electrode 5B... Oxygen electrode
5C...Cooling plate 6...Converter 7...
- Combustor 8... High temperature transformer 9... Low temperature shift converter 10... Nuclear submarine O1 control valve 11... Reformed fuel control valve 12... Main burner 13... Air control valve 14. ...Mixer 15...Steam generator 16...Steam control valve 17...Battery cooling water humidity control valve 18...Pressure control valve 19...Battery cooling water circulation pump 20...Heat exchanger 21 .36...Temperature detector 22...Steam flow rate control system 23-=Battery cooling water temperature control system 24.27...Flow rate detector

Claims (1)

[Claims] a fuel supply means for mixing raw fuel and steam and supplying the mixture to the fuel cell via a reformer; an air supply means for supplying air to the fuel cell using a turbine and a compressor; and supplying steam to the raw fuel. In a fuel cell power generation plant, which is equipped with a steam generator and a battery cooling water supply means consisting of a pump, etc., and generates the required electric power according to the fuel supplied from the reformer, temperature control of the steam generator and battery cooling are performed. The fuel is characterized in that the temperature control of water is separated from each other as independent controls, and the pressure inside the steam generator is controlled to be temporarily lowered during transient conditions such as when the load suddenly increases, thereby securing the required amount of steam. Battery power plant control system.