JP2774665B2 - Combined cycle power plant and its overspeed prevention method and apparatus - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a combined cycle power plant combining a gas turbine and a steam turbine, and more particularly to a combined cycle power plant including an overspeed prevention device suitable for preventing overspeed. About.

[Prior Art] FIG. 3 is a system diagram of a combined cycle power plant. In this combined cycle power plant, the gas turbine 1, the air compressor 2, the steam turbine 3, and the generator 4 are connected in a single shaft, and the fuel burned in the combustor 5 becomes high-temperature gas, and the gas turbine 1, that is, the entire shaft is used. Drive rotationally. Air required for combustion is supplied from an air compressor, and the amount of fuel is controlled by a fuel flow control valve 6 according to a required output or the like. The exhaust gas after the thermal energy has been converted into rotational energy is sent to the exhaust heat recovery boiler 7, where it exchanges heat with feed water to generate steam. This steam is supplied to the steam turbine 3 and drives the steam turbine 3 to rotate. The water supply is sent from a condenser 8 to a waste heat recovery boiler 7 by a condensate pump 9, and steam generated by the low pressure drum 10 is supplied to a low pressure steam control valve 11.
The steam generated by the high-pressure drum 12 is supplied to the low-pressure stage of the steam turbine 3 through the high-pressure steam control valve 13 and supplied to the high-pressure stage of the steam turbine 4 as driving steam. The rotational energy of the gas turbine 1 and the steam turbine 3 obtained in this manner is converted into electric energy by the generator 4, and desired electric power is obtained. In addition, 14 and 15 are a high pressure turbine bypass valve and a low pressure turbine bypass valve.

In this combined power plant, output control or frequency (speed) control of the generator 4 is performed by opening control of the fuel control valve 6 and the steam control valves 11 and 13. On the other hand, the turbine bypass valves 14 and 15 are used to form a bypass path at the start of the plant, or to protect the plant when the steam pressure becomes abnormally high (usually about 10% of the specified pressure). Opened for.

When considering the protection of rotating bodies such as the gas turbine 1 and the steam turbine 3, the most important point to consider is prevention of overspeed. For this reason, the security device shown in FIG. 4 has been conventionally installed in the combined cycle power plant. This security device,
It is required to be installed by law, and it functions to shut off gas turbine fuel and steam supplied to the steam turbine as a driving power source when the speed (rotation speed) of the rotating body becomes a predetermined value or more. In the example of FIG. 4, when the rotation speed of the steam turbine becomes 110% or more of the rated rotation speed or when the rotation speed of the gas turbine becomes 111% or more of the rated rotation speed, the steam shutoff valves 16 and 16 of FIG. 17, steam control valve 11,13, fuel cutoff valve
18 and the fuel control valve 6 are fully closed.

Incidentally, as related to the prior art, for example,
There is -83821.

[Problems to be Solved by the Invention] The combined cycle power plant described with reference to FIG. 3 is of a type in which one generator 4 is driven by the gas turbine 1 and the steam turbine 3, and is generally called a single-shaft type. On the other hand, a type in which one turbine generator is driven by a plurality of gas turbine exhaust gases is called a multi-shaft type. In any of these types of combined cycle power plants, the contribution ratio of the gas turbine output and the steam turbine output to the total power generation output is usually about 3: 7 or 4: 6. For this reason,
When only the fuel control valve 6 is controlled for the purpose of stabilizing the frequency of the power system or for controlling the generator output, only 30% or 40% of the total power output can contribute to emergency output / frequency control. become. If the amount of fuel is controlled, the amount of exhaust gas from the gas turbine changes, and the amount of steam generated by the exhaust heat recovery boiler 7 changes. As a result, the output of the steam turbine also changes. -There is a delay time of several minutes or more in response to the frequency, and a sufficient effect cannot be obtained when the output / frequency control is performed urgently. In order to contribute 100% to emergency output / frequency control, the steam control valves 11, 13 also need to be operated by output / frequency control signals. For this reason, in the above-mentioned known example, the steam control valve 13 as well as the fuel control valve 6 is operated by the output / frequency control signal.

However, according to the study of the present inventors, in a power plant such as steam having no steam pressure control function, even if the steam control valve is operated by the output / frequency control signal, the steam turbine controls the output / frequency of the power system. Turned out to be unable to contribute enough.

The steam amount F flowing into the steam turbine is determined by the product of the difference between the pressures P ₁ and P ₂ before and after the steam control valve and the valve opening A, and it is generally understood that the power generation output is proportional to the steam amount. are, but steam control valve for most of the power plant, because it is used in a critical state, the steam control valve before pressure P ₁ and the valve opening degree a
And the product determines the amount of steam. This relationship is given by the following equation (1),
It is represented by (2).

F = A · (P ₁ −P ₂ ) (1) F = A · P ₁ (2) The steam flow rate F in the combined cycle power plant shown in FIG. since previous pressure P ₁ of the control valve is not controlled to be constant, responds as follows with respect to the application of the output-frequency control signal. For example, if the frequency is increased by the power supply excessive power system, even targeted steam control valve to decrease the frequency by reducing the power output, before pressure P ₁ ends up rising. As a result, as desired The flow rate F of steam cannot be reduced. Conversely, when opening the steam control valve in order to recover the frequency to increase the steam flow rate F of the previous would be reduced pressure P _1, it can not when the steam flow rate F is he wanted increased.

In contrast, pre-pressure P ₁ is only to be kept constant, proportionally increases or decreases the opening and the steam flow rate F of the steam control valve, thereby capable of performing good control. When the steam control valve is controlled by the output / frequency control signal, the fluctuation of the steam pressure when the steam control valve is opened and closed can be suppressed by opening and closing the turbine bypass valve in the reverse direction in conjunction with the signal. . Therefore, a sufficient output / frequency adjusting function can be exhibited by this, and it is possible to cope with a sudden output change particularly when a system alone occurs.

It is unavoidable that there is some delay in the operation of narrowing down the power generation output in response to a sudden decrease in system demand when the system alone occurs, and therefore, the overspeed when the system alone occurs Is somewhat useless. If the degree of the overspeed increases, the security device shown in FIG. 4 operates. In particular, when the system demand has dropped significantly and the gas turbine fuel has been reduced to the amount corresponding to the minimum load for stable combustion of the gas turbine, and the steam control valve is also fully closed, further suppression of the driving force will be possible. It becomes impossible (there is no speed regulation capability), and the supply / demand imbalance at this point increases the overspeed, and it is necessary to prevent the rotating body from overspeeding by the security device.

However, even though the safety device can prevent overspeeding, it is safe to keep an eye on the overspeed until the security device operates under the situation where it is clear that the vehicle will enter an overspeed condition. Not preferred. In other words, the fact that the governing ability is lost and the vehicle is still overspeed is almost the same as a failure of the governing device, and leaving it unattended is a safety problem.

It is an object of the present invention to provide a combined cycle power plant that enables safer operation than relying only on conventional security devices, and a method and apparatus for preventing overspeed of the combined power plant.

Means for Solving the Problems The object is to provide a gas turbine driven by combustion gas,
In a combined power plant including a steam turbine driven by steam generated by exhaust heat of the gas turbine, and a generator for converting mechanical energy of the gas turbine and the steam turbine into electric energy, This is achieved by shutting off the fuel supply to the gas turbine when the narrowing of the fuel supplied to the gas turbine becomes less than the stable combustion limit in a state where the supply steam is cut off.

Further, the above object is achieved when the supply of steam to the steam turbine is shut off and the narrowing down of the fuel supplied to the gas turbine falls below the stable combustion limit and an abnormality occurs on the power transmission system side. It is also achieved by shutting off the fuel supply to the system.

Further, the above object is to provide a gas turbine driven by combustion gas, a steam turbine driven by steam generated by exhaust heat of the gas turbine, and converting mechanical energy of the gas turbine and the steam turbine into electric energy. And a safety device that shuts off fuel supply to the gas turbine and steam supply to the steam turbine when the rotation speed of the gas turbine or the steam turbine becomes “rated speed + specified value”. In the method for preventing an overspeed of a power plant, when the supply of fuel to the gas turbine is reduced to a stable combustion limit or less in a state where steam supply to the steam turbine is shut off, the gas turbine is operated before the safety device operates. It is also achieved by shutting off the fuel supply to the system.

[Operation] In the present invention, when the steam supply to the steam turbine is cut off and the gas turbine has no speed regulation capability, that is, when the gas turbine obviously overspeeds and is left alone When the security device operates, the fuel supply to the gas turbine is shut off before the security device operates, so that safer plant operation is possible.

[Embodiment] Hereinafter, a preferred embodiment of the present invention will be described with reference to FIG. 1 and FIG.

FIG. 1 is a control configuration diagram of an overspeed prevention device provided in a combined cycle power plant according to one embodiment of the present invention. The conventional safety device installed in this combined cycle power plant is designed to operate when the rotation speed of the steam turbine is 110% or more of the rated rotation speed, or when the rotation speed of the gas turbine is 111% or more of the rated rotation speed. And shuts off the supply of steam to the steam turbine. This embodiment is characterized in that an overspeed prevention device surrounded by a dashed line is added to this security device. That is, when the condition of the steam control valve fully closed (the steam shutoff valve may be fully closed) is satisfied and the rotation speed of the gas turbine or the steam turbine becomes higher than the rated rotation speed by a specified value,
The fuel supply to the gas turbine is shut off.
Since the overspeed prevention device is operated before the operation of the security device, the specified value is 10% of the rated rotation speed of the gas turbine.
, For example, a value of 5% of the rated rotation speed. In order to shut off the fuel supply to the gas turbine, the fuel cutoff valve 18 may be fully closed and the fuel control valve 6 may be fully closed. In the overspeed prevention device according to the example, only the fuel preparation valve 6 is fully closed.

The speed control of the rotating body is performed by controlling the opening degree of the fuel control valve of the gas turbine and controlling the opening degree of the steam control valve of the steam turbine.
On the other hand, in the latter case, there is a heat recovery delay in the exhaust heat recovery boiler, and control is performed with this delay, so that the auxiliary colors are dark. Therefore, in order to prevent overspeed when a system alone occurs, control of the fuel supply to the gas turbine is mainly performed. However, when the fuel cannot be fully throttled (if the fuel is further narrowed down, the stable fuel of the gas turbine will be reduced). In the case where the minimum load is divided and the fuel amount is deviated from the adjustable region (the region where the valve opening of the fuel control valve is adjustable), the steam control valve is also controlled to be fully closed. In this case, it can be said that the speed control function has practically disappeared (of course, the adjustment control in the direction of increasing the speed is possible). In the present embodiment, it is determined that the speed adjustment is impossible when “the steam control valve is fully closed”, and when the vehicle is overspeeding at this time, that is, the rotation speed is, for example, 105% of the rated rotation speed. If so, shut off the fuel supply to the gas turbine. According to this embodiment, the drive source is cut off before the conventional security device operates, and overspeed is prevented.

FIG. 2 is a control configuration diagram of an overspeed prevention device according to another embodiment of the present invention. The present embodiment is an embodiment aiming to more reliably detect the condition of "overspeeding without speed regulation capability" of the embodiment of FIG. This is effective for preventing the shutoff of the gas turbine fuel supply due to a malfunction of the gas turbine overspeed detector or the like. In the embodiment of FIG. 2, the fuel supply to the gas turbine is shut off when all of the following conditions are satisfied in addition to the conditions in the embodiment of FIG. The configuration of the security device is the same as that of FIG.

Condition 1: The rate of increase in the speed of the gas turbine or the steam turbine is equal to or higher than a predetermined value (for example, 0.3% / sec of the rated rotation speed). Despite the overspeed, if the overspeed rise is small,
This is because it is considered that the security device is not operated.

Condition 2: The valve opening of the fuel control valve 6 is a predetermined valve opening γ% (for example,
40.0%) or less. This is to reliably detect that there is no adjustment capability of the fuel control valve, that is, that the throttle of the supplied fuel has fallen below the determination combustion limit and the throttle of the supplied fuel has deviated from the adjustable range.

Condition 3: An abnormality has occurred on the power transmission system side. If the "phenomena of overspeed without adjustment capability" is caused by the occurrence of a system alone or the like, adding this condition 3 can more reliably prevent overspeed.

In the present embodiment, by adding conditions 1 to 3 in addition to the two conditions in the embodiment of FIG. 1, it is possible to reliably detect that "the vehicle is overspeeding without any adjustment capability". However, it goes without saying that only one of these three conditions may be added to the embodiment of FIG.

The present invention is not limited to a single-shaft combined cycle power plant,
It goes without saying that the present invention can be similarly applied to a multi-shaft combined power plant.

[Effects of the Invention] According to the present invention, the gas turbine is not operated before the operation of the security device under the condition that the security device operates when the speed control capability is not provided, the speed is too high, and the safety device is left alone. Since the drive source can be shut off, the safety of plant operation can be improved.

[Brief description of the drawings]

FIG. 1 is a control configuration diagram of an overspeed prevention device according to one embodiment of the present invention, FIG. 2 is a control configuration diagram of an overspeed prevention device according to another embodiment of the present invention, and FIG. FIG. 4 is a configuration diagram of a power plant, and FIG. 4 is a control configuration diagram of a security device. DESCRIPTION OF SYMBOLS 1 ... Gas turbine, 3 ... Steam turbine, 4 ... Generator, 5 ... Combustor, 6 ... Fuel control valve, 7 ... Exhaust heat recovery boiler, 11 ... Low pressure steam control valve, 13 ... ... High pressure steam control valve, 16,17 ... Steam shutoff valve, 18 ... Fuel shutoff valve.

Continued on the front page. (72) Inventor Makoto Futagawahara 3-1-1 Sachimachi, Hitachi-shi, Ibaraki Pref. Hitachi, Ltd. Hitachi Plant (72) Inventor Masayuki Fukai 3-1-1 Sachimachi, Hitachi-shi, Ibaraki (56) References JP-A-1-219322 (JP, A) JP-A-56-98510 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F01K 23/10 F02C 9/28

Claims (4)

(57) [Claims] 1. A gas turbine driven by combustion gas, a steam turbine driven by steam generated by exhaust heat of the gas turbine, and converting mechanical energy of the gas turbine and the steam turbine into electric energy. In a combined cycle power plant comprising a power generator, when the supply of fuel to the gas turbine is reduced to a stable combustion limit or less in a state in which the supply of steam to the steam turbine is shut off, A combined cycle power plant comprising an overspeed prevention device for interrupting supply. 2. A gas turbine driven by combustion gas, a steam turbine driven by steam generated by exhaust heat of the gas turbine, and converting mechanical energy of the gas turbine and the steam turbine into electric energy. A generator,
A combined power plant comprising: a safety device that shuts off fuel supply to the gas turbine and steam supply to the steam turbine when the rotation speed of the gas turbine or the steam turbine becomes “rated speed + a”; An overspeed prevention device that shuts off the fuel supply to the gas turbine when the rotation speed of the gas turbine becomes “rated speed + b (here, 0 <b <a)” with the steam supply cut off. A combined cycle power plant characterized by the above. 3. A gas turbine driven by combustion gas, a steam turbine driven by steam generated by exhaust heat of the gas turbine, and converting mechanical energy of the gas turbine and the steam turbine into electric energy. An overspeed prevention apparatus for a combined cycle power plant including a generator, wherein when the supply of fuel to the gas turbine is reduced to a stable combustion limit or less in a state where the supply of steam to the steam turbine is shut off, An overspeed prevention device, comprising: means for interrupting fuel supply to a gas turbine. 4. A gas turbine driven by combustion gas, a steam turbine driven by steam generated by exhaust heat of the gas turbine, and converting mechanical energy of the gas turbine and the steam turbine into electric energy. In the method for preventing an overspeed of a combined cycle power plant including a power generator, at least the narrowing of fuel supplied to the gas turbine under a state in which steam supplied to the steam turbine is shut off is equal to or less than a stable combustion limit. An overspeed prevention method, wherein the fuel supply to the gas turbine is interrupted.