JPS61126310A - Run back control device in compound cycle power plant - Google Patents

Abstract

PURPOSE:To enable a stable and reliable run back operation, by providing a parallel-off run back circuit which operates upon failures in an electrical system and a stop run back circuit which operates upon failures in a fuel supply installation. CONSTITUTION:A parallel run back circuit is composed of discriminating circuits 14, 22, 23 for detecting the output conditions of power units, a selecting circuit 20 for selecting some units to be continuously operated, and a trip circuit 21 for a generator breaker. Further, the units are subjected to parallel-off upon failures in an electrical system to rapidly restrain the output of the power plant. Meanwhile a stop run back successively stops the power units upon failures in a fuel supply installation to aim at restraining the output power of the power plant. With this arrangement it is possible to carry out a stable and reliable run back operation.

Description

Detailed Description of the Invention [Technical Field of the Invention 1] The present invention relates to a fuel equipment base that supplies fuel gas such as LNG to a gas turbine, and a gas turbine that is driven by steam generated by recovering exhaust heat from the gas turbine. The present invention relates to a runback control device for controlling a combined cycle power plant configured with a plurality of combined cycle power generation units that generate power by driving a generator using a steam turbine.

[Technical background of the invention and its problems] In a conventional steam power plant consisting of a steam turbine, a generator, and a boiler, runback of the turbine load (
Load runback) was performed by rapidly reducing the load input to the boiler. That is, when the turbine of a power plant is normally in a rated output operating state, a runback operation is performed based on a system fault or the like inside or outside the power plant. For example, if an accident occurs in the system around a power plant,
The generator is used to protect system equipment such as transformers and insulation equipment.
A runback request is generated for control purposes to suppress the power to a fraction of the rated value. In addition, if an accident occurs in a transformer, etc. within a power plant, the power plant may be disconnected from the grid and the turbine load may be suddenly reduced until independent operation within the plant is possible, or the electrical system as described above may be In addition to an accident, in the case of an accident involving large auxiliary equipment such as a BFP or fuel equipment, a runback request is generated to suppress the turbine load to the fuel supply length that is possible with the equipment after the accident. Such runbacks are necessary to protect equipment, but if a power plant were to completely shut down due to an accident, not only would it be impossible to secure the workforce at the power plant, but the power supply to the grid would be delayed after the accident is restored. Therefore, it is essential to prevent these situations.

Such load landback is performed by rapidly reducing the flow rate of fuel supplied to the boiler, the amount of water supplied, the flow rate of air, etc. However, due to the equipment configuration of the power plant, it is not possible to set the rate of change in the output of the turbine to be unnecessarily large, and if the output is suddenly reduced beyond this limit, it may cause combustion instability in the boiler and cause the turbine to trip. There is a risk of this happening. Further, during runback operation, the water supply and fuel supply become transiently unbalanced, and even after the runback ends, temperature changes continue, resulting in inconvenience that stable operation cannot be achieved.

Next, an outline of a conventional combined cycle power generation plant will be explained using FIG.

Combined cycle power generation plants using the so-called exhaust heat recovery method can be roughly divided into single-shaft types and multi-shaft types. -A shaft type is a system in which the gas turbine, steam turbine, and generator are connected by a common shaft, and a multishaft type is a system in which the gas turbine and steam turbine are separated into separate shafts, This is a system in which a generator is connected to each shaft. Here, in accordance with this classification, we will discuss two types: those with a configuration in which multiple series of -shaft types are installed, and multi-shaft configurations with multiple series of gas turbines installed for a single or multiple steam turbine loads. In either case, the target is a plant with multiple gas turbines.

A combined cycle power plant is constructed as shown in FIG. 3, illustrating a negative axis type case. In FIG. 3, a compressor (CP) 1, a gas turbine (GT) 2, a generator 3, and a steam turbine 4 are connected to each other via a common shaft 5.

The fuel whose flow rate is controlled by adjusting the opening degree of the fuel regulating valve 6 is supplied to the combustor 7 together with compressed air from the compressor 1, where the fuel is mixed and combusted under equal pressure to generate high-temperature and high-pressure combustion gas. The gas turbine 2 is driven by this combustion gas. Exhaust gas from the gas turbine 2 is guided to an exhaust heat recovery boiler 8 to generate steam. Heat is recovered by the exhaust heat recovery boiler 8, and the low-temperature gas is discharged into the atmosphere as exhaust gas. The steam generated by the exhaust heat recovery boiler 87 is guided to the steam turbine 4 via the steam control valve 9 to drive it. The steam that has passed through the steam turbine 4 is passed through the condenser iot:
The water is then condensed here. This combined cycle power plant supplies fuel to the combustor 7 as an input, and obtains electrical output from the generator 3 through the generator breaker 11 as the final output.

The following points can be cited as characteristics of such a combined cycle power plant.

-The unit capacity of each unit is small, and - series power plants are composed of multiple units, and the output of the power plant is the sum of the outputs of each unit.

・Due to the characteristics of gas turbines, it takes a short time after stopping and restarting to obtain rated output.

・Uses gas fuel as fuel and has fuel supply equipment for that purpose. For example, it is equipment that vaporizes liquid fuel and supplies it to a plant. One of these is installed per power plant, but to improve reliability, the carburetor is multi-staged.
This prevents the entire power plant from shutting down in the event of equipment failure.

Even in the above combined cycle power generation plant, it is possible to employ the runback method used in the steam power generation plant described above. That is, runback is achieved by equally suppressing the output of each unit in operation at this time.

However, in a combined cycle power plant having the above-mentioned characteristics, it is desired to employ a runback system that enables more flexible plant operation. This is one of the operating units of a combined cycle power plant.
Disconnect or trip the units one after another or all at once, such as by continuing to operate only one unit and disassembling or tripping all remaining units, or by continuing to operate multiple units and tripping the remaining units depending on the accident condition. This is a runback method that also suppresses plant output.

[Object of the Invention] The present invention was made in view of the above points, and an object of the present invention is to provide a runback control device that implements runback suitable for a combined cycle power plant.

[Summary of the Invention] The present invention is a runback control device that includes a decoupling runback circuit that operates in response to an electrical system failure and a stop runback circuit that operates in response to a fuel supply facility failure.

The decoupling runback circuit uses an output detector and an output comparator provided in each unit, and based on their signals, selects one of the units that is operated at the most advantageous output in the plant, in other words, the rated output. It consists of an operation continuation selection circuit that selects a unit as a continued operation unit and all remaining units as disconnected units, and a generator breaker trip circuit.When an accident in the electrical system is detected, units other than the operation continued unit This causes the generator breaker to trip, that is, to disconnect the generator, rapidly reducing the output of the plant.

On the other hand, the stop runback circuit sets the fuel flow rate that can be supplied to the plant based on the damage state if an accident occurs in the fuel supply equipment! l setting device; a detector for detecting the fuel flow rate supplied to each unit; an adder for adding up the fuel flow rate detected by the detector; and a sum of the setting value of the fuel flow rate setting device and the adder. The gas turbine fuel trip circuit is equipped with a comparator that compares the power consumption, a fuel trip selection circuit that selects to stop the unit based on the signal from the comparator, and a gas turbine fuel trip circuit. This aims to suppress plant output.

[Embodiments of the Invention] Examples of the present invention will be described below with reference to the accompanying drawings. In addition, in this example, for convenience of explanation, a combined cycle power generation plant consisting of three units #1 to #3 is targeted.

FIG. 1 shows an embodiment of a unit disassembly runback circuit, and this unit disassembly runback circuit is composed of three circuits as a whole.

That is, unit output state determination circuits 14, 22, and 23 detect the output state of each unit, and an operation continuation unit selection circuit 20 that selects a unit to continue operation. and a generator breaker trip circuit 21 that trips the generator breaker of each unit.

In the unit output state determination circuit 14, the output signal a detected by the output detector 15 of the #1 unit is branched and input to the comparators 17 and 18, of which the comparator 17 sets the output signal to the rated output setter 16. If a>b, the #1 unit is defined as operating at the rated output.

On the other hand, in the comparator 18, the output signal a is compared with the minimum load value C set in the minimum load setting device 19, and when a>C and the #1 unit is not operating at the rated output, the #1 unit is defined as operating at low output. be done. Similarly #2. #3. The units are also defined by the respective unit output state determination circuits 22 and 23 as operating at rated output (■■) or operating at low output (■■). Based on the operation status of each unit defined above, the operation continuation selection circuit 20 selects the unit with the lowest unit number that is in rated operation as the unit to continue operation, and if any of the three units is in rated operation. If not, select the unit with the lowest number as the unit to continue operation. However, N11
The IL and disconnection trip circuit 21 receive an electrical accident occurrence signal 24
and the unit operation normal signal O indicating that one of the units #1 to #3 is selected to continue operation, and as a result, the generator breaker of the unit that does not correspond is tripped and disconnected. do.

FIG. 2 shows an embodiment of the unit stop runback circuit, and the unit stop runback circuit is composed of three circuits as a whole.

That is, a fuel supply status determination circuit 40 detects fuel supply and waste conditions, and a fuel trip selection circuit 30 determines which gas turbine to trip when fuel supply is low. and a gas turbine trip circuit 31 that trips the selected gas turbine.

In the fuel supply state determination circuit 40, the flow of fuel supplied to each unit is detected by fuel flow rate detectors 41, 42, and 43, and each detected value p is detected.

q and r are added by an adder 44, and the sum S is compared by a comparator 45 with the supplyable fuel flow at set in the setting device 46, and when the comparison result is t<s, a unit stop request signal is generated. O is output. When the unit stop request signal 0 is output and at least one of the units is in operation, the fuel trip selection circuit 3
o is activated. The fuel trip selection circuit 30 includes a timer 3
2゜33.34, 35.36, and this timer selects the units to be tripped in sequence from among the operating units that have the largest unit number and are operated at low output. It looks like this. This selection is continued until the unit stop request signal O disappears. Therefore, the unit selected by the fuel trip selection circuit 30 is selected from the gas turbine trip circuit 31.
This causes the fuel to be cut off, causing the affected gas turbine to trip.

In the unit disconnection runback circuit shown in FIG. 1, the unit output state determination circuit 14 determines whether each ! The units are classified as operating at rated output or at low output in order to selectively continue operating the units operating at rated output, which is most advantageous for the power plant, after runback. In addition, the operation continuation selection circuit 20 always selects only one unit operating at rated output with a small unit number to continue operating preferentially, or if there is no unit operating at rated output, the unit is operated at low output. The unit with the smallest unit number is selected. Such selection is always performed even when no runback cause occurs, and the generator breaker trip circuit 21 disconnects the generator breaker of the unit that has not been selected to continue operation as soon as an electrical accident occurs. In this manner, in the event of an electrical accident, all but one unit are operated with their generator circuit breakers disconnected, and a runback of the power plant is realized.

Additionally, if an accident occurs with fuel supply equipment such as a fuel carburetor,
The unit stop runback circuit shown in FIG. 2 is activated. In other words, if a malfunction occurs in the fuel supply equipment, the setting device 4
The supplyable fuel flow ffi[ of 6 decreases to t times S with respect to the total fuel flow ff1s required for the system, and a unit stop request signal 0 is output. The fuel trip selection circuit 30 and the gas turbine trip circuit 31 sequentially stop the units, and compare the system fuel flow rate S, which changes accordingly, with the above t, and determine the optimal number of units commensurate with the fuel supply capacity after the accident. The unit will be stopped until the Furthermore, by prioritizing the units to be stopped in the order of those operating at low output, the units operating at rated output remain after the runback, thereby increasing operational efficiency. Furthermore, by inserting a condition for unit operation normal O before reaching the fuel trip selection circuit 30, and by inserting a negative condition for #3 unit operation continuing ■O in the gas turbine trip circuit 31, it is possible to ensure that one or more units are in operation. is set to continue.

Use of the runback control device according to the present embodiment described above has the following advantages over conventional runback control.

(1) In conventional control, the rate of change in output could not be increased unnecessarily, but in this embodiment, it is possible to run back the power plant in an extremely short time.

■There will be no temporary negative effects caused by sudden suppression of introversion.

(3) The load can be suppressed to the minimum stable output of one unit.

4) Since the control reduces the number of operating units, the operating efficiency is excellent even during runback.

[Effects of the Invention] Since the present invention sequentially disconnects or stops the units in a combined cycle power plant consisting of a plurality of units, the present invention enables stable and highly reliable load runback. It has the following effects.

[Brief explanation of drawings]

Fig. 1 is a system diagram of a unit disassembly runback circuit according to an embodiment of the present invention, Fig. 2 is a system diagram of a unit stop runback circuit, and Fig. 3 is an explanatory diagram showing the system of a combined cycle power generation plant. It is. 14.22.23... Output state determination circuit 20... Operation continuation selection circuit 21... Engine breaker trip circuit 30... Fuel trip selection circuit 31... Gas turbine trip circuit 40... Fuel supply status determination circuit agent Patent attorney Kensuke Norichika (and 1 other person) 1st figure 3rd cause procedural amendment (voluntary) 1939 4/94 Town

Claims (1)

[Claims] In a runback control device for a combined cycle power generation plant consisting of multiple units, there is an output state discrimination circuit that detects the operating state of each unit, and an operation continuation selection that selects the unit to continue operating according to the operating state. and a generator breaker trip circuit that disconnects the generators of the units not selected in the operation continuation selection circuit in the event of an accident in the electrical system, and the fuel for each unit. A fuel supply status determination circuit compares the demand for fuel with the amount of fuel that can actually be supplied and outputs a unit stop request when the demand is greater than the supplyable amount; Combined cycle power generation comprising a runback stop circuit consisting of a fuel trip selection circuit that selects units one by one, and a gas turbine trip circuit that stops the gas turbine by stopping the fuel supply to the selected units. Plant runback control device.