JPH0146682B2 - - Google Patents

Description

Detailed Description of the Invention [Technical Field of the Invention] The present invention relates to load control of a combined cycle power plant system in which a plurality of uniaxial combined cycle plants in which a gas turbine, a generator, and a steam turbine are arranged on one axis are installed. Regarding equipment.

[Technical background of the invention and its problems] Liquefied natural gas (hereinafter abbreviated as LNG) is often used as fuel for combined cycle power plants.
The system of the LNG terminal is explained in Figure 1. LNG transported by ship or the like is stored in an LNG tank 1, and pumps 2, 3a, 3b pull out the LNG and put it into vaporizers 4, 5. On the other hand, by pouring the seawater 7 pumped up by the seawater pump 6 into the vaporizers 4 and 5, the liquefied gas at -162℃ is heated to 20℃.
It is regasified by heating it with seawater before and after it. This gas is sent to the power plant through the fuel pipe 9 and used as fuel for a boiler, gas turbine, or the like.

In addition, the LNG stored in LNG tank 1 is
Although it is liquefied at a low temperature (-162°C), the temperature outside the tank is around 0°C to 35°C, so if there is a large temperature difference between the two, a portion of it will always gasify. This gas is called boil-off gas (hereinafter abbreviated as BOG).
Since this BOG fills the tank 1, it is extracted by the compressor 10, regasified, and supplied to the fuel pipe 9. And this fuel pipe 9
The fuel pressure 14 is controlled by regulating valves 12 and 13 to maintain a constant pressure.

In a single-shaft combined cycle power plant, gas from the fuel line 9 of FIG. 1 is controlled by a fuel control valve and supplied to the combustor of the gas turbine. The control method calculates and processes the speed setting signal and the detection signal of the rotational speed of the interconnected gas turbine, steam turbine, and generator, and uses the result to control the fuel flow rate entering the combustor of the gas turbine. control to control the output of the gas turbine. In addition, in a single-shaft combined cycle power plant,
Since the generator is directly connected to the gas turbine and the steam turbine, the output of the generator is the sum of the outputs of the gas turbine and the steam turbine. Then, the actual load detected by the load detector and the load setting value outputted from the load target value are calculated, and the load, that is, the generator output, is controlled to be equal to the load setting.

As mentioned above, in combined cycle power plants, load control is always performed, but
If vaporizers 4, 5, etc. at the LNG terminal shown in Figure 1 stop due to malfunction, the power plant will be forced to shut down due to an accident at the LNG terminal shown in Figure 1 because not enough gas will be sent to the power plant. I had no choice but to stop. In this case, the boil-off gas from the tank 1 was constantly generated and had to be released into the air.

[Objective of the Invention] The object of the present invention is to use boil-off gas from the fuel tank in a power plant for stable load control without releasing the boil-off gas from the fuel tank into the air in the event of a failure of a vaporizer at an LNG terminal. The object of the present invention is to provide a load control device for a combined cycle power plant system capable of performing the following steps.

[Summary of the Invention] A load control device for a combined cycle power plant system according to the present invention supplies fuel to a gas turbine in a single-shaft combined cycle power plant.
The present invention is characterized in that when the vaporizer at the LNG terminal is stopped, the load within the power plant is controlled to a constant level by controlling the fuel pressure caused by the boil-off gas to a constant level.

[Embodiments of the Invention] The present invention will be described below with reference to embodiments shown in FIGS. 2 and 3. First, in FIG. 1 showing a single-shaft combined cycle power plant to which the present invention is applied, a gas turbine 21 configuring the power plant,
The steam turbine 25 and the generator 26 are directly connected together with the air compressor 23 by the same shaft. The gas from the fuel pipe 9 of the LNG terminal in Figure 1 is
It is controlled by a fuel control valve 20 and supplied to a combustor 22 of a gas turbine 21 . gas turbine 2
The exhaust gas of No. 1 passes through the exhaust heat recovery boiler 24 to generate steam. This steam is supplied to a steam turbine 25 via a steam control valve 28, and the enthalpy of the steam rotates the turbine 25, driving a generator 26 directly connected to the same shaft to generate electric power. The steam that has finished its work becomes condensed water in the condenser 27.

The control of the combined cycle power plant shown in Figure 2 is as follows:
Speed setting signal 31a output from speed setting 31
and the rotational speed 29a of the gas turbine 21, steam turbine 25, and generator 26 from the rotational speed detector 29.
is input to the subtracter 32, and the deviation signal obtained from the subtraction result is subjected to proportional calculation using an arithmetic amplifier and adjustment rate gain 33, and the opening degree of the fuel control valve 20 is adjusted or decreased through the servo amplifier 34. It is done by twisting. As a result, the fuel flow rate entering the combustor 22 of the gas turbine 21 is controlled, and the output of the gas turbine 21 is controlled. On the other hand, in the steam turbine 25, the steam enthalpy from the exhaust heat recovery boiler 24 is determined by the enthalpy of the exhaust gas from the gas turbine 21, so if the steam control valve 28 is kept at a constant opening, the condenser 27 The output is uniquely determined by the degree of vacuum.

As a result, since the generator 26 is connected to the gas turbine 21 and the steam turbine 25, the sum of the outputs of the gas turbine 21 and the steam turbine 25 becomes the output of the generator 26. A subtracter 37 calculates the deviation between the actual load detected by the generator load detector 35 and the load setter signal output from the load target value 36.
According to the output, the speed setting device 31
By changing , the deviation is finally controlled to be zero, that is, the generator load output 35 which is the load becomes equal to the load setting 36 .

Next, Fig. 3 shows a single-shaft combined cycle power plant system in which multiple shafts from the first shaft to the nth shaft are installed in parallel to form a combined cycle power plant system, and this power plant system is seen as one unit from the power system. Figure 3 shows a central load controller as planned for operation. In FIG. 3, each axis is indicated by the subtractor 3 in FIG.
7. Generator load detector 35 and speed setting device 31
and each subtractor 3 of each axis.
A rate of change setting device 50 is provided on the input side of 7.

The load target value i commanded to the rate of change setter 50 for each of these axes is created by the illustrated load control system 67. That is, either the load target value 41 of the combined cycle power generation plant system given by the central dispatch center or the local mode load target value 42 given by the load setter in the power plant is selected by the switch 43.
is selected and becomes the load target value signal 43a. This signal 43a passes through the load change rate setting device 44 and becomes a load signal 44a, which is a signal Ta of the fuel pressure control system 66 that controls the fuel pressure detected from the fuel pipe 9 of FIG. 1 provided according to the present invention. and in Figure 1
It is added by the adder 65 when the vaporizers 4, 5, etc. at the LNS base are out of order. Therefore, the signal Ta from the fuel pressure system 66 is not input to the adder 65 during normal operation.

The signal 65a of the adder 65 is the load lower limit limiter 45.
Then, it passes through a load upper limit limiter 46 and becomes a load command value 46a for the power plant. Also, from the first axis
The subtracter 4 calculates the deviation h between the actual output g of the combined cycle plant system, which is obtained by adding the load up to the shaft in the adder 47, and the load command value 46a.
The load target value i for each axis is obtained by the proportional-integral calculator 49 which is calculated by 8 and inputs the deviation. Target load value i for each axis given to each axis
is the load command value 36 for each axis, which is limited so that the rate of change is within the rate of change limit value set by the rate of change setter 50 for each axis. Load command value for each axis 36
and the deviation l of the generator output 35 of each axis is calculated by the calculator 37, and the speed setting device 31 is calculated according to the deviation l.
The set value of is increased or decreased. From this point on, the output control of the combined cycle plant is performed by the control circuit shown in FIG.

Now, the fuel pressure system 66 provided in the present invention is
The pressure detector 14 detects the fuel pressure 14a in the fuel pipe 9 of the LNG terminal shown in FIG.
a and the fuel pressure setting value 61a of the fuel pressure setting device 61
A subtracter 62 calculates the deviation from
The signal is configured to be sent to the adder 65 as Ta. The switch 64 is configured to select the no signal Tb and be grounded when the LNG terminal in FIG. 1 is normal, and to select the signal Ta when the LNG terminal is abnormal.

Next, the operation of the load control device for a combined cycle power plant according to the present invention will be explained based on FIG. During normal operation of the plant, the fuel pressure control system 6
6 is switched to the no-signal Tb side by the switch 64. Then, in the load control system 67, the switch 43 selects either the load target value 41 or the power plant mode load target value 42, and control calculations are performed each time it passes through each circuit to set the load target value i to each axis. obtain.
This load target value i becomes the load command value 36 of each axis by the change rate setting device 50 of each axis, and the set value of the speed setting device 31 is changed according to the deviation l from the generator output 35 of each axis. Increased or decreased. From this point on, the output control of the combined cycle plant is performed by the control circuit shown in FIG.

Next, if the vaporizers 4, 5, etc. fail at the LNG terminal shown in Figure 1 during normal operation of the plant and the fuel cannot be sent normally to the power plant, the fuel pressure control system 66 The switch 64 is switched to the signal Ta side. At that time, if the load setter 41 from the central power dispatch center is selected by the switch 43, the switch is switched to the load setter 42 within the power plant. In this case, the load setting value is set to a low value in response to an accident at the LNG terminal.

In addition, in the case of an LNG terminal accident, the signal 61a from the fuel pressure setting device 61 that has been previously set in accordance with the newly set low load setting value and the actual fuel pressure 14a (this fuel 14a is boil-off gas The deviation 62 from the actual fuel pressure is taken, and the fuel pressure is applied to the load 44a set in the power plant as a load command while maintaining the set fuel pressure. The load target value 65a as a series determined in this way passes through the load upper limit value 45 and the load lower limit value 46 as described above, and becomes the load target value 46a as a series. The following controls are the same as those described above, and will therefore be omitted.
In this way, even if an accident occurs at an LNG terminal and the vaporizer stops, only the boil-off gas can maintain a constant pressure, so load control can be carried out to effectively utilize the boil-off gas to operate the power plant. Continued.

[Effects of the Invention] As described above, in the present invention, in a combined cycle plant system in which a plurality of single-shaft combined cycle power plants combining gas turbines, generators, and steam turbines are installed, The load control system that receives the load set value from within the power plant and makes the load within the power plant follow the load set value is controlled by the fuel pressure caused by boil-off gas when the vaporizer at the LNG terminal that supplies fuel to the gas turbine is stopped. By adding a fuel pressure control system that controls the pressure to a constant level, even if the LNG terminal's vaporizer malfunctions, the boil-off gas from the LNG tank will not be released into the air.
In turn, this gas can be used in power plants to continue operation under constant control.

[Brief explanation of drawings]

Fig. 1 is a system diagram showing gas piping relationships at an LNG terminal, Fig. 2 is a schematic configuration diagram showing a single-shaft combined cycle power plant, and Fig. 3 is an implementation of the load control device of the combined cycle power plant system according to the present invention. It is a system diagram showing an example. 1...LNG tank, 4, 5...vaporizer, 9...
...Fuel piping, 21...Gas turbine, 22...Combustor, 23...Air compressor, 24...Exhaust heat recovery boiler, 25...Steam turbine, 31...Speed setter, 33...Adjustment rate gain , 34... Servo amplifier, 35... Generator load detector, 36... Load target value, 41, 42... Load target value, 43... Switcher, 44... Load change rate setting device, 45 ... Load lower limit limiter, 46 ... Load upper limit limiter, 49 ... Proportional and integral calculator, 50 ... Rate of change setter, 61 ...
...Fuel pressure setter, 63...Arithmetic unit, 64...Switcher, 65...Adder, 66...Fuel pressure control system, 67...Load control system.

Claims (1)

[Scope of Claims] 1. In a combined cycle plant system in which a single shaft or multiple shafts of a single-shaft combined cycle power plant combining a gas turbine, a generator, and a steam turbine are installed, a load setting value from a central power dispatch center or from within the power plant and a load control system that follows the load in the power plant to the load setting value based on the load, and a fuel pressure control system that controls the fuel pressure by boil-off gas to a constant pressure when the vaporizer at the LNG terminal that supplies fuel to the gas turbine is stopped. and the above-mentioned system.
When the LNG terminal's vaporizer is stopped, the difference between the preset fuel pressure signal of the fuel pressure control system and the actual fuel pressure is calculated, and this is used as the load command for the load control system so that the preset fuel pressure is reached. A load control device for a combined cycle power generation plant system, characterized in that it is configured to be added to. 2. The fuel pressure control system includes a subtractor that calculates the deviation between a preset fuel pressure setting value and the fuel pressure detected from the fuel piping at the LNG terminal, and a calculator that calculates proportionality and integral values for this deviation. 2. A load control device for a combined cycle power generation plant system according to claim 1, comprising: a switch that applies the calculation result to a load control system only when a vaporizer at an LNG terminal is stopped.