JPH045404A - Compound electric power generating plant and method and device for preventing overspeed thereof - Google Patents

Abstract

PURPOSE:To increase safety for plant operation by arranging an overspeed- preventive device to cut off fuel supply to a gas turbine at a specific time under a condition that steam supply to a steam turbine is cut off. CONSTITUTION:A compound electric power generating plant is constituted by connecting a gas turbine 1, an air compressor 2, a steam turbine 3 and an electric power generator 4 to one shaft. An overspeed-preventive device cuts off gas turbine fuel and steam turbine supply steam by shutting completely steam-cutoff valves 16 and 17, steam-regulation valves 11 and 13, a fuel-cutoff valve 18 and a fuel-adjusting valve 6. The fuel supply to said gas turbine 1 is cut off when the volume reduction of fuel supply to the gas turbine 1 reaches below a stable combustion limit under a condition that steam supply to the steam turbine 3 is cut off. In this way, safety for a plant operation can be increased.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a combined power generation plant that combines a gas turbine and a steam turbine, and particularly to a combined power generation plant that is equipped with an overspeed prevention device suitable for preventing overspeed. Regarding.

[Conventional technology] FIG. 3 is a system diagram of a combined power generation plant.

In this combined power generation plant, a gas turbine 1, an air compressor 2, a steam turbine 3, and a generator 4 are connected to one shaft, and the fuel combusted in the combustor 5 turns into high-temperature gas and consumes the entire gas turbine 1, that is, the shaft. Drive rotation. Air necessary for combustion is supplied by an air compressor, and the amount of fuel is controlled by a fuel flow control valve 6 according to the required output and the like.

After the thermal energy has been converted into rotational energy, the exhaust gas is sent to the exhaust heat recovery boiler 7, where it exchanges heat with the 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
Water is sent from the condenser 8 to the exhaust heat recovery boiler 7 by the condensate pump 9, and the steam generated in the low pressure drum 10 is sent to the low pressure stage of the steam turbine 3 via the low pressure steam control valve 11, and then to the high pressure drum 12. The generated steam is supplied to the high pressure stages of the steam turbine 4 as driving steam via the high pressure steam control valve 13, respectively.

The rotational energy of the gas turbine 1 and the steam turbine 3 thus obtained is converted into electrical energy by the first generator 4, and desired electric power is obtained.

In addition, 14.15 is a high pressure turbine bypass valve and a low pressure turbine bypass valve.

In this combined power generation plant, the output control or frequency (speed) control of the generator 4 is performed by controlling the opening degree of the fuel control valve 6 and the steam control valves 11 and 13. On the other hand,
Turbine bypass valves 14 and 15 are used to form a bypass path when starting up the plant, or are opened to protect the plant when steam pressure becomes abnormally high (usually about 10% higher than the rated pressure). Ru.

When considering the protection of rotating bodies such as the gas turbine 1 and the steam turbine 3, the most important consideration is overspeed prevention. For this reason, a safety device shown in FIG. 4 has conventionally been installed in combined power generation plants. This safety device is required to be installed by law, and the speed of the rotating body (
It functions to cut off the gas turbine fuel and the steam turbine supply steam, which are the driving power sources, when the rotational speed (rotation speed) reaches a predetermined value or more. In the example shown in FIG. 4, when the rotation speed of the steam turbine becomes 110% or more of the rated rotation speed or the rotation speed of the gas turbine becomes 111% or more of the rated rotation speed,
Steam cutoff valve 16.17 and steam control valve 11.13 in Figure 3
, fully open the fuel cutoff valve 18 and fuel control valve 6.

Incidentally, as related to the prior art, for example, Japanese Patent Application Laid-open No. 57
There is No.-83821.

[Problem to be solved by the invention] The combined power generation plant illustrated in FIG.
This is a type in which one generator 4 is driven by a steam turbine 3, and is generally called a single-shaft type. On the other hand,
A type in which a single turbine generator is driven by multiple gas turbine exhaust gases is called a multi-shaft type. In any type of combined power generation plant, 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. Therefore, when only the fuel control valve 6 is controlled for the purpose of stabilizing the frequency of the power system or controlling the generator output, only 30 to 40% of the total power generation output is required for emergency output/frequency control. You will not be able to contribute. If the amount of fuel is controlled, the amount of gas turbine exhaust gas will change, the amount of steam generated by the exhaust heat recovery boiler 7 will change, and as a result, the steam turbine output will also change, but the generator output in this process will change.・There is a delay time of several minutes or more in frequency response, and sufficient effects cannot be obtained when output/frequency control is performed urgently. In order to contribute 100% to the emergency output/frequency control, the steam control valves 11 and 13 must also be operated by the output/frequency control signals. Therefore, in the above-mentioned known example, in addition to the fuel control valve 6, the steam control valve 13 is also operated by the output/frequency control signal.

However, according to the study conducted by the present inventors, in the above-mentioned power plants that do not have a steam pressure control function, even if the steam control valve is operated by the output/frequency control signal, the steam turbine does not control the output/frequency control of the power system. It turned out that it was not possible to make a sufficient contribution to the

The amount of steam F flowing into the steam turbine is determined by the pressure P1 before and after the steam control valve. It is determined by the product of the difference in P2 and the valve opening A, and it is generally understood that the power generation output is proportional to the amount of steam, but the steam control valve in most power plants is used in a critical state. The amount of steam is determined by the product of the front pressure P1 of the steam control valve and the valve opening A. This relationship is expressed by the following formula (L
It is expressed as L (2).

F=A・(P□−p'−)...
(1) F=A-Pl...(2
) The steam flow rate F in the combined cycle power plant shown in Figure 3 is (
2) Since the front pressure P of the steam control valve is not controlled to be constant, it responds to the application of the output/frequency control signal as follows.

For example, if the frequency increases due to an oversupply of power in the power system, even if the steam control valve is throttled to reduce the power generation output and lower the frequency, the front pressure P will rise.
As a result, the steam flow rate F cannot be reduced as desired. Conversely, when the steam control valve is opened to increase the steam flow rate F and restore the frequency, the prepressure P decreases, making it impossible to increase the steam flow rate F as desired.

On the other hand, if the prepressure P is kept constant, the opening degree of the steam control valve and the steam flow rate F will increase or decrease proportionally, and good control can be performed. When the steam control valve is controlled by the output/frequency control signal, by opening and closing the turbine bypass valve in the opposite direction in conjunction with the signal, it is possible to suppress fluctuations in steam pressure when the steam control valve is opened and closed. . Therefore, this makes it possible to exhibit a sufficient output/frequency adjustment function, and in particular, it becomes possible to cope with sudden changes in output such as when a single system occurs.

It is unavoidable to some extent that there will be some delay in the operation to reduce power generation output in response to a sudden drop in grid demand when grid isolation occurs. It can be said that overspeeding is unavoidable to some extent. If the degree of overspeed becomes large, the safety device shown in FIG. 4 will be activated. In particular, when the system demand has significantly decreased, the gas turbine fuel has been reduced to the amount equivalent to the minimum load for stable combustion of the gas turbine, and the steam control valve is fully closed, further reduction of driving force is required. is disabled (no speed regulating ability), and the supply-demand imbalance at this point increases overspeeding, making it necessary to prevent overspeeding of the rotating body using a safety device.

However, although safety devices are used to prevent overspeeding,
In a situation where it is clearly known that the vehicle will enter an overspeeding state, it is not desirable from a safety standpoint to wait until the safety device is activated. In other words, if the speed regulating ability is lost and the vehicle is still overspeeding, this is likely due to a failure of the speed regulating device and a road failure, and leaving this as it is is a safety problem.

An object of the present invention is to provide a combined power generation plant and an overspeed prevention method and device thereof that enable safer operation than relying only on conventional safety devices.

[Means for Solving the Problem] 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 a gas turbine and a steam turbine driven by the gas turbine and the steam turbine. In a combined power generation plant comprising a generator that converts mechanical energy into electrical energy, the fuel supply to the gas turbine is reduced to below a stable combustion limit while the steam supply to the steam turbine is cut off. This is accomplished by cutting off the fuel supply to the gas turbine when this happens.

In addition, the above purpose is to prevent the gas turbine from turning off when the throttle of the fuel supplied to the gas turbine becomes below the stable combustion limit and an abnormality occurs on the power transmission system side in a state where the steam supplied to the steam turbine is cut off. This can also be achieved by cutting off the fuel supply to the

The above object also includes a gas turbine driven by combustion gas, a steam turbine driven by steam generated by exhaust heat of the gas turbine, and converting the mechanical energy of the gas turbine and the steam turbine into electrical energy. and a safety device that shuts off the fuel supply to the gas turbine and the steam supply to the steam turbine when the rotational speed of the gas turbine or the steam turbine reaches the "rated speed 10 specified value" In an overspeed prevention device for a power generation plant, when the restriction of fuel supplied to the gas turbine becomes below a stable combustion limit while the steam supply to the steam turbine is cut off, the overspeed prevention device prevents the gas turbine from operating before the safety device operates. This can also be achieved by cutting off the fuel supply to the

[Operation] In the present invention, when the steam supply to the steam turbine is cut off and the gas turbine has no speed regulating ability,
In other words, if the gas turbine clearly overspeeds and if left unchecked, the safety device will activate, the fuel supply to the gas turbine will be cut off before the safety device activates, making the plant safer. Driving becomes possible.

Preferred embodiments of the present invention will now be described with reference to FIGS. 1 and 2.

FIG. 1 is a control configuration diagram of an overspeed prevention device provided in a combined power generation plant according to an embodiment of the present invention. Conventional safety devices installed in this combined power generation plant are designed to prevent the gas turbine from shutting down when the speed of the steam turbine reaches 110% or more of the rated speed, or when the speed of the gas turbine reaches 111% or more of the rated speed. In addition to cutting off the fuel supply to the steam turbine, it also cuts off the steam supply to the steam turbine.

In addition to this safety device, this embodiment is characterized by the addition of an overspeed prevention device surrounded by a dashed line. In other words,
When the conditions for the steam control valve to be fully open (the steam cutoff valve may be fully closed) are met, and the rotational speed of the gas turbine or steam turbine is higher than the rated rotational speed by a specified value, the fuel supply to the gas turbine is stopped. I'm trying to block it. This overspeed prevention device is activated before the safety device operates, so
The specified value is a value smaller than 10% of the rated rotational speed of the gas turbine, for example, a value of 5% of the rated rotational speed.

In order to cut off the fuel supply to the gas turbine, the fuel cutoff valve 18 may be fully opened and the fuel control valve 6 may also be fully opened, but since a conventional safety device is also installed separately, this embodiment In the overspeed prevention device, only the fuel control valve 6 is fully opened.

The speed of the rotating body is controlled by controlling the opening of the gas turbine's fuel control valve and the opening of the steam regulating valve of the steam turbine, but the former is directly controlled (as soon as the fuel is throttled, the output and On the other hand, in the latter case, there is a delay in heat recovery in the waste heat recovery boiler, and control is performed using this delay, so the auxiliary effect is strong. Therefore, in order to prevent overspeed when an isolated system occurs, etc., the main focus is to control the amount of fuel supplied to the gas turbine. (e.g., when the minimum load of the steam control valve falls below the minimum load and the fuel amount falls outside the adjustable range of the fuel amount (the range where the valve opening of the fuel control valve can be adjusted)), there is a high probability that the steam control valve will also be controlled to be fully open. In this case, it can be said that the speed regulating function has virtually disappeared (of course, speed regulating control in the direction of increasing the speed is possible). In this embodiment, it is determined that speed regulation is not possible when "the steam control valve is fully opened", and if the speed is overspeeding at this point, for example,
When the rotation speed is 0.5%, the fuel supply to the gas turbine is cut off. According to this embodiment, the drive source is cut off before the conventional safety device operates, thereby preventing overspeeding.

FIG. 2 is a control configuration diagram of an overspeed prevention device according to another embodiment of the present invention. This embodiment is an embodiment aimed at more reliably detecting the condition of "overspeeding without speed regulating capability" in the embodiment shown in FIG. This is effective in preventing erroneous cutoff of gas turbine fuel supply due to malfunction of a turbine overspeed detector or the like. In the embodiment shown in FIG. 2, fuel supply to the gas turbine is cut off when all of the following conditions are met in addition to the conditions in the embodiment shown in FIG. Note that the configuration of the security device is the same as the first @.

Condition 1: The speed increase rate of the gas turbine or steam turbine is a predetermined value (for example, the rated rotation speed).

3%/5ee) or more. This is because even if the vehicle is overspeeding, if the increase in overspeed is small, it is unlikely that the safety device will be activated.

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

Condition 3: An abnormality has occurred on the power transmission system side.

``If the phenomenon of overspeeding without adjustment capability is caused by an isolated system, etc., adding this condition 3 will more reliably prevent overspeeding.

In this 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 "overspeeding without adjustment ability". but,
It goes without saying that it is sufficient to add only one of these three conditions to the embodiment shown in FIG.

It goes without saying that the present invention is applicable not only to a -shaft type combined power generation plant but also to a multishaft type combined power generation plant.

[Effects of the Invention] According to the present invention, in a situation where the gas turbine does not have speed regulating ability and is overspeeding, and if left unchecked, the safety device will operate, the gas turbine is activated before the safety device operates. Since the drive source can be shut off, it is possible to improve the safety of plant operation.

[Brief explanation of the drawing]

FIG. 1 is a control configuration diagram of an overspeed prevention device according to an 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. 3 is a uniaxial type composite FIG. 4 is a block diagram of the power generation plant, and FIG. 4 is a control block diagram of the safety device. 1... Gas turbine, 3... Steam turbine, 4... Generator, S... 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 cutoff valve, 1
8. Fuel cutoff valve. Agent Patent Attorney Tadashi Akimoto Actual Diagram Diagram

Claims (1)

[Scope of Claims] 1. A gas turbine driven by combustion gas, a steam turbine driven by steam generated from exhaust heat of the gas turbine, and a system that converts the mechanical energy of the gas turbine and the steam turbine into electrical energy. In a combined cycle power generation plant comprising a generator that converts the gas turbine into A combined power generation plant characterized by being equipped with an overspeed prevention device that cuts off fuel supply to. 2. A gas turbine driven by combustion gas, a steam turbine driven by steam generated from exhaust heat of the gas turbine, and a generator that converts the mechanical energy of the gas turbine and the steam turbine into electrical energy. In a combined power generation plant equipped with, when the restriction of the fuel supplied to the gas turbine becomes below the stable combustion limit while the steam supply to the steam turbine is cut off, and an abnormality occurs on the power transmission system side. A combined power generation plant characterized by being equipped with an overspeed prevention device that cuts off fuel supply to a gas turbine. 3. A gas turbine driven by combustion gas, a steam turbine driven by steam generated by exhaust heat of the gas turbine, and a generator that converts the mechanical energy of the gas turbine and the steam turbine into electrical energy. In a combined power generation plant, the fuel supply to the gas turbine is cut off when the narrowing of the fuel supplied to the gas turbine deviates from an adjustable range while the steam supply to the steam turbine is cut off. A combined power generation plant characterized by being equipped with an overspeed prevention device. 4. A gas turbine driven by combustion gas, a steam turbine driven by steam generated by exhaust heat of the gas turbine, and a generator that converts the mechanical energy of the gas turbine and the steam turbine into electrical energy. In a combined power generation plant equipped with the following, when the throttle of fuel to the gas turbine deviates from an adjustable range under a state in which the supply of steam to the steam turbine is cut off and an abnormality occurs on the power transmission system side, the gas A combined power generation plant characterized by being equipped with an overspeed prevention device that cuts off fuel supply to a turbine. 5. A gas turbine driven by combustion gas, a steam turbine driven by steam generated by exhaust heat of the gas turbine, and a generator that converts the mechanical energy of the gas turbine and the steam turbine into electrical energy. , 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 rotational speed of the gas turbine or the steam turbine reaches "rated speed + a"; An overspeed prevention device that cuts off the fuel supply to the gas turbine when the rotational speed of the gas turbine reaches "rated speed + b (here, 0<b<a)" while the steam supply to the gas turbine is cut off. A combined power generation plant characterized by: 6. A gas turbine driven by combustion gas, a steam turbine driven by steam generated by the exhaust heat of the gas turbine, and a generator that converts the mechanical energy of the gas turbine and the steam turbine into electrical energy. , 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 rotational speed of the gas turbine or the steam turbine reaches "rated speed + a"; An abnormality occurs on the power transmission system side while the steam supply to the
A combined power generation plant characterized by comprising an overspeed prevention device that cuts off fuel supply to the gas turbine when the condition becomes <a). 7. A gas turbine driven by combustion gas, a steam turbine driven by steam generated from exhaust heat of the gas turbine, and a generator that converts the mechanical energy of the gas turbine and the steam turbine into electrical energy. , a combined power generation plant comprising a safety device that shuts off fuel supply to the gas turbine and steam supply to the steam turbine when the rotational speed of the gas turbine or the steam turbine reaches "rated speed + specified value", overspeeding to cut off the fuel supply to the gas turbine before the safety device operates when the restriction of the fuel supplied to the gas turbine becomes below the stable combustion limit while the steam supply to the steam turbine is cut off; A combined power generation plant characterized by being equipped with a prevention device. 8. A gas turbine driven by combustion gas, a steam turbine driven by steam generated from exhaust heat of the gas turbine, and a generator that converts the mechanical energy of the gas turbine and the steam turbine into electrical energy. In an overspeed prevention device for a combined cycle power generation plant, when the restriction of the fuel supplied to the gas turbine becomes below a stable combustion limit in a state where the supply of steam to the steam turbine is cut off, the gas turbine is supplied to the gas turbine. An overspeed prevention device characterized by comprising means for cutting off fuel supply. 9. A gas turbine driven by combustion gas, a steam turbine driven by steam generated from exhaust heat of the gas turbine, and a generator that converts the mechanical energy of the gas turbine and the steam turbine into electrical energy. , a safety device for cutting off fuel supply to the gas turbine and steam supply to the steam turbine when the rotational speed of the gas turbine or the steam turbine reaches "rated speed + specified value". In the speed prevention device, when the restriction of the fuel supplied to the gas turbine becomes below the stable combustion limit while the steam supply to the steam turbine is cut off, the fuel supply to the gas turbine is stopped before the safety device operates. An overspeed prevention device characterized by comprising means for interrupting. 10. A gas turbine driven by combustion gas, a steam turbine driven by steam generated by exhaust heat of the gas turbine, and a generator that converts the mechanical energy of the gas turbine and the steam turbine into electrical energy. In the overspeed prevention method for a combined cycle power plant comprising: at least when the restriction of the fuel supplied to the gas turbine becomes below the stable combustion limit under a state in which the steam supplied to the steam turbine is cut off, the gas An overspeed prevention method characterized by cutting off fuel supply to a turbine. 11. A gas turbine driven by combustion gas, a steam turbine driven by steam generated from exhaust heat of the gas turbine, and a generator that converts the mechanical energy of the gas turbine and the steam turbine into electrical energy. , a safety device for cutting off fuel supply to the gas turbine and steam supply to the steam turbine when the rotational speed of the gas turbine or the steam turbine reaches "rated speed + specified value". In the speed prevention device, when the restriction of the fuel supplied to the gas turbine becomes below the stable combustion limit while the steam supply to the steam turbine is cut off, the fuel supply to the gas turbine is stopped before the safety device operates. An overspeed prevention method characterized by cutting off.