JP2013076388A - Uniaxial combined cycle power generation plant and method for operating the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a uniaxial combined cycle power generation plant capable of securing a required flow volume of cooling steam for a low-pressure steam turbine during a non-load rated speed operation without installing a separated steam source generator.SOLUTION: A gas turbine 1, a high-pressure steam turbine 3a, a low-pressure steam turbine 3c and a generator 4 are coaxially coupled. Exhaust gas of the combustion gas of the gas turbine 1 is used as a heat source to generate high-pressure steam and low-pressure steam in a waste heat recovery boiler 7, the high-pressure steam is supplied through a high-pressure regulator valve 17 to work in the high-pressure steam turbine 3a, and the low-pressure steam is supplied through a low-pressure regulator valve 22 to work in the low-pressure steam turbine 3c. During the non-load rated speed operation, the high-pressure regulation valve 17 is controlled to completely close while an opening degree of a variable guide blade 6 is controlled to increase a generation flow volume of the low-pressure steam.

Description

  Embodiments of the present invention relate to a single-shaft combined cycle power plant in which a gas turbine, a steam turbine, and a generator are connected to a single shaft, and an operation method thereof.

  Generally, in a gas turbine, a steam turbine driven by steam generated in an exhaust heat recovery boiler by exhaust gas of the gas turbine, and a single shaft combined cycle power plant in which a generator is connected to a single shaft, two-pressure exhaust heat recovery is performed. The steam generated from the boiler is composed of two pressures, high pressure steam and low pressure steam.

  Of these, low-pressure steam generated from the low-pressure drum is supplied to the low-pressure steam turbine via a low-pressure control valve. On the other hand, the high-pressure steam generated in the high-pressure drum performs work in the high-pressure steam turbine through the high-pressure control valve, and then merges with the low-pressure steam from the low-pressure control valve and is supplied to the low-pressure steam turbine.

  These high-pressure steam and low-pressure steam are for driving the steam turbine to generate power. At the same time, these high-pressure steam and low-pressure steam are vented into the low-pressure steam turbine to prevent overheating due to windage of the low-pressure steam turbine (power loss due to air agitation in the steam turbine casing). It also plays a role as cooling steam for cooling the turbine.

  On the other hand, in the initial startup of the single shaft combined cycle power plant, the amount of high-pressure steam and low-pressure steam generated is not sufficient. Therefore, before starting the plant startup, the auxiliary boiler is started in advance to generate auxiliary steam. Is used as cooling steam for the low-pressure steam turbine.

  That is, auxiliary steam is supplied to the low-pressure steam turbine at the initial startup of the power plant. Furthermore, as the starting process proceeds, the amount of high-pressure steam and low-pressure steam generated increases, and these steams are sufficient as cooling steam for the low-pressure steam turbine. Is stopped, the supply of auxiliary steam is cut off, and only high-pressure steam and low-pressure steam are supplied to the low-pressure steam turbine. In this way, the cooling steam is supplied to the low-pressure steam turbine of the single-shaft combined cycle power plant at the time of startup, and normal operation is performed.

  By the way, in general, urgently opening the breaker of the generator due to an electrical accident or the like is called load breaking. After such a generator load cut-off occurs, the gas turbine is set to FSNL (Full Speed No Load) operation, and after an electrical accident is restored, an operation is quickly prepared for an increase in reload. . In the process of shifting from normal operation to no-load rated speed operation, the amount of fuel supplied to the gas turbine decreases rapidly because of no-load operation. In a high-pressure steam turbine, the high-pressure regulator is fully closed and the low-pressure regulator is In order to prevent overspeed, the valve is closed once and then opened to secure the cooling steam of the low-pressure steam turbine.

  By the way, the reason for closing the high pressure regulator in no-load rated speed operation is that the torque generated by the gas turbine is relatively increased by reducing the torque generated by the high pressure steam turbine by closing the high pressure regulator. This is because it is possible to further stabilize the combustion state by increasing the fuel flow rate of the gas turbine.

However, in the no-load rated speed operation, however, the low-pressure steam turbine has insufficient cooling steam for the following reasons. That is,
i) Since the high-pressure control valve is closed, there is no supply of high-pressure steam to the high-pressure steam turbine, and only low-pressure steam is supplied to the low-pressure steam turbine. In this case, the high-pressure steam generated from the high-pressure drum is sent to the condenser via the bypass valve.

  ii) Since the gas turbine has a small amount of fuel, the amount of heat of the exhaust gas from the gas turbine is low, and therefore the amount of low-pressure steam generated from the exhaust heat recovery boiler is also small.

  iii) Since the load interruption occurs due to a sudden accident, it is impossible to start up the operation of the auxiliary boiler in advance and secure auxiliary steam, unlike at the time of startup.

  Therefore, if the cooling steam of the low-pressure steam turbine is insufficient during the no-load rated speed operation as described above, the exhaust temperature of the low-pressure steam turbine rises due to the windage loss of the low-pressure steam turbine, and the no-load rated speed operation can be continued. As a result, the single-shaft combined cycle power plant must be stopped.

  As described above, as an operation method for securing cooling steam of a low-pressure steam turbine at the time of no-load rated speed operation of the gas turbine after the load interruption of the generator as described above, for example, there is a technique described in Patent Document 1. The operation method described in this Patent Document 1 is based on the fact that a separate steam source generator in an existing combined cycle power plant and a single shaft combined cycle power plant are connected in advance by piping. In this method, generated steam is used as cooling steam for a low-pressure steam turbine.

Japanese Patent Laid-Open No. 11-117715

  However, the technique described in Patent Document 1 described above is installed separately in an existing combined cycle power plant in order to secure the cooling steam of the low-pressure steam turbine during the no-load rated speed operation of the gas turbine after the load interruption of the generator. It is necessary to install the separate steam source generator and connect the separately installed steam source generator and the single-shaft combined cycle power plant by piping. Therefore, there is a problem that the single-shaft combined cycle power plant becomes large and complicated.

  The embodiment of the present invention ensures the necessary cooling steam flow rate of the low-pressure steam turbine during no-load rated speed operation without installing a separate steam source generator, and prevents overheating due to windage loss of the low-pressure steam turbine. It is an object of the present invention to provide a single-shaft combined cycle power plant that can be prevented and an operation method thereof.

  In order to achieve the above object, the single-shaft combined cycle power plant of the present embodiment is coaxially arranged and coupled to supply high-pressure steam from a high-pressure drum of an exhaust heat recovery boiler via a high-pressure control valve. The high-pressure steam turbine driven and the low-pressure steam from the low-pressure drum that generates low-pressure steam having a pressure lower than that of the high-pressure drum is supplied via a low-pressure control valve. And a low-pressure turbine steam supply system for supplying steam combined with the high-pressure steam, which is combined with the gas turbine and the high-pressure steam turbine, and connected to the low-pressure turbine steam and driven by the low-pressure turbine steam A low-pressure steam turbine, a variable guide vane for adjusting the intake air flow rate of the gas turbine, and a coaxial arrangement with the gas turbine. In the no-load rated speed operation after the load interruption of the generated generator, the high pressure control valve is controlled to be fully closed, and the opening of the variable guide blade is controlled so that the flow rate of the low pressure steam is increased. And a control means.

  In addition, the single-shaft combined cycle power plant of the present embodiment is arranged to be coaxially connected to the gas turbine, and is driven by being supplied with high-pressure steam from a high-pressure drum of an exhaust heat recovery boiler via a high-pressure control valve. A steam turbine, a low-pressure steam turbine that is coaxially disposed and coupled to the gas turbine and the high-pressure steam turbine and driven by low-pressure steam; and medium-pressure steam that is lower in pressure than the high-pressure steam and higher in pressure than the low-pressure steam. A low-temperature reheat system that combines medium-pressure steam from the generated intermediate-pressure drum with exhaust steam from the high-pressure steam turbine to supply a reheater that generates high-temperature reheat steam, the high-pressure steam turbine, and the low-pressure steam An intermediate pressure steam turbine disposed coaxially with the turbine and driven by high temperature reheat steam from the reheater supplied via a reheat control valve; and the intermediate pressure steam turbine A low-pressure turbine steam supply system for driving the low-pressure steam turbine by combining the high-temperature reheated steam and the low-pressure steam that have been decompressed by work, and a variable guide vane that adjusts the intake air flow rate of the gas turbine And at the time of no-load rated speed operation after the load interruption of the generator arranged coaxially with the gas turbine, the high pressure control valve and the reheat control valve are controlled to be fully closed, and the variable guide Control means for controlling the opening of the blade so that the flow rate of the low-pressure steam is increased.

  The operation method of the single-shaft combined cycle power plant according to the present embodiment includes a gas turbine, a high-pressure steam turbine, a low-pressure steam turbine, and a generator that are coaxially arranged and coupled, and a combustion gas is sent to the gas turbine to drive it. The exhaust gas of the combustion gas is used as a heat source to generate high-pressure steam in the exhaust heat recovery boiler, and low-pressure steam having a pressure lower than that of the high-pressure steam is generated, and the high-pressure steam is supplied via a high-pressure control valve. In a method for operating a single-shaft combined cycle power plant that performs work in a turbine and supplies the low-pressure steam through a low-pressure control valve to perform work in the low-pressure steam turbine, the no-load rated speed after the load of the generator is interrupted A fully-closed control step for performing control to fully close the high-pressure control valve during operation, and an opening degree of the variable guide blade for adjusting the intake air flow rate of the gas turbine It characterized by having a a opening control step of generating a flow rate of the low pressure steam is controlled so as to increase.

  Further, the operation method of the single-shaft combined cycle power plant according to the present embodiment is such that a gas turbine, a high-pressure steam turbine, an intermediate-pressure steam turbine, a low-pressure steam turbine, and a generator are coaxially arranged and connected, and the combustion gas is connected to the gas turbine. The high-pressure steam is generated in the exhaust heat recovery boiler using the exhaust gas of the combustion gas as a heat source, and the medium-pressure steam having a pressure lower than the high-pressure steam and the low-pressure steam having a pressure lower than the medium-pressure steam are generated. The intermediate pressure steam is combined with the exhaust steam from the high pressure steam turbine, supplied to a reheater that generates high-temperature reheat steam, and passes through a reheat control valve in the intermediate pressure steam turbine. In a method for operating a single-shaft combined cycle power plant in which the high-temperature reheat steam that has been decompressed by work and the low-pressure steam are combined to perform work in the low-pressure steam turbine A fully-closed control step for performing control to fully close the high-pressure control valve and the reheat control valve during no-load rated speed operation after the generator load is interrupted, and a variable for adjusting the intake air flow rate of the gas turbine And an opening degree control step for controlling the opening degree of the guide blades so that the flow rate of the low-pressure steam is increased.

  According to the embodiment of the present invention, it is not necessary to install a separate steam source generator, and it is not necessary to connect to this steam source generator by piping, and the required low pressure steam turbine is required during no-load rated speed operation. Therefore, it is possible to prevent overheating due to windage loss of the low-pressure steam turbine.

1 is a system diagram showing a first embodiment of a single-shaft combined cycle power plant according to the present invention. It is a block diagram which shows the control apparatus of the variable guide vane of FIG. It is a figure which shows an example of the function set to the function generator of FIG. It is a distribution diagram showing a 2nd embodiment of a single axis combined cycle power plant concerning the present invention. It is a block diagram which shows the control apparatus of the variable guide vane of FIG. It is a distribution diagram showing a 3rd embodiment of the single axis type combined cycle power plant concerning the present invention.

  Below, each embodiment of the uniaxial combined cycle power plant concerning the present invention is described with reference to drawings.

(First embodiment)
(Power plant configuration)
FIG. 1 is a system diagram showing a first embodiment of a single-shaft combined cycle power plant according to the present invention.

  As shown in FIG. 1, in the single-shaft combined cycle plant of the present embodiment, the gas turbine 1, the compressor 2, the high-pressure steam turbine 3a, the low-pressure steam turbine 3c, and the generator 4 constitute a prime mover unit 100, and The rotating shafts are arranged coaxially and coupled. The gas turbine 1 is supplied with the combustion gas burned in the combustor 5 and is driven by the combustion gas to discharge the exhaust gas. The compressor 2 sucks the atmosphere through variable guide vanes (hereinafter also referred to as VGV) 6 to increase the pressure, and supplies the high-pressure air to the combustor 5 for generating combustion gas. The high-pressure steam turbine 3a is supplied with high-pressure steam from a high-pressure main steam pipe 16, while the low-pressure steam turbine 3c is supplied with low-pressure steam from a low-pressure main steam pipe 21 serving as a low-pressure turbine steam supply system. The low-pressure steam turbine 3c drives the generator 4 together with the gas turbine 1 and the high-pressure steam turbine 3a to generate electric power. The rotational speed of the output shaft of the generator 4 is detected by a rotational speed detector 38.

  An exhaust gas side inlet end of the exhaust heat recovery boiler 7 is connected to an outlet end of the gas turbine 1, and the exhaust heat recovery boiler 7 is supplied with exhaust gas from the gas turbine 1 to generate steam. Specifically, the exhaust heat recovery boiler 7 includes a high-pressure superheater 10 connected to a high-pressure drum 13 that generates high-pressure steam, and a low-pressure superheater 12 connected to a low-pressure drum 15 that generates low-pressure steam. . The steam generated from the high-pressure drum 13 and the low-pressure drum 15 is supplied to the high-pressure steam turbine 3a and the low-pressure steam turbine 3c, respectively. In the following description, the high pressure steam turbine 3a and the low pressure steam turbine 3c are collectively referred to as the steam turbine 3. The low pressure steam pressure generated in the low pressure drum 15 is detected by the detector 39.

  The high-pressure main steam pipe 16 has a pipe configuration including a detector 57 for detecting a high-pressure steam pressure and a high-pressure control valve 17. The low-pressure main steam pipe 21 has a pipeline configuration including a low-pressure steam isolation valve 35, a detector 56 that detects a low-pressure steam pressure, a detector 40 that detects a low-pressure steam flow rate, and a low-pressure control valve 22.

  In the high-pressure main steam pipe 16, a high-pressure turbine bypass system 81 is branched upstream of the detector 57, and the high-pressure turbine bypass valve 50 is interposed in the high-pressure turbine bypass system 81. Similarly, in the low-pressure main steam pipe 21, a low-pressure turbine bypass system 83 is branched on the upstream side of the detector 56, and a low-pressure turbine bypass valve 52 is interposed in the low-pressure turbine bypass system 83. These high-pressure turbine bypass system 81 and low-pressure turbine bypass system 83 are each connected to the condenser 30.

  The outlet end of the low-pressure steam turbine 3 c is connected to the low-pressure drum 15 of the exhaust heat recovery boiler 7 via the condenser 30 and the feed water pump 28. The low pressure turbine exhaust pressure of the low pressure steam turbine 3 c is detected by the detector 55. Circulating water is supplied to the condenser 30 by driving the circulating water pump 29. The circulating water uses high-pressure steam and low-pressure steam supplied from the high-pressure turbine bypass system 81 and the low-pressure turbine bypass system 83 as condensate, respectively.

  The startup boiler 27 is connected to the auxiliary steam supply pipe 24, one end of the auxiliary steam system 60 is connected to the auxiliary steam supply pipe 24, and the other end is connected to the low-pressure main steam pipe 21. The auxiliary steam system 60 is provided with a control valve 34 and a detector 41 for detecting the auxiliary steam flow rate.

  The control device 70 receives detection signals of the detector 40 for detecting the low-pressure steam flow rate and the detector 55 for detecting the low-pressure turbine exhaust pressure, while the control device 70 opens the opening of the variable guide vane 6. A control signal is output.

(Operation of power plant)
Next, the operation of the uniaxial combined cycle power plant of this embodiment will be described.

  Before startup, the condenser 30 is evacuated by a vacuum pump (not shown), and when the specified vacuum degree is reached, the motor unit 100 is rotationally driven by a starting motor (not shown) and the combustor 5 is ignited to ignite the gas turbine 1. And the compressor 2 enters the combined operation.

  Further, at the time of starting the plant, the start-up boiler 27 is started to generate auxiliary steam. The auxiliary steam is supplied to the auxiliary steam system 60 through the auxiliary steam supply pipe 24, and the flow rate is adjusted by the control valve 34 and supplied to the low-pressure main steam pipe 21.

  That is, the startup boiler 27 is installed separately from the exhaust heat frequency boiler 7 for the purpose of supplying auxiliary steam at the time of startup when no steam is generated in the exhaust heat recovery boiler 7. The auxiliary steam generated in the start-up boiler 27 is supplied to the low-pressure main steam pipe 21 via the auxiliary steam supply pipe 24 and the control valve 34 interposed in the auxiliary steam system 60 as described above. To be supplied to the steam turbine 3. Thus, at the initial stage of plant start-up, since the amount of high-pressure steam and low-pressure steam generated from the exhaust heat recovery boiler 7 is not sufficient, auxiliary steam from the start-up boiler 27 is used in combination as low-pressure turbine cooling steam.

  Furthermore, as the starting process proceeds, the amount of high-pressure steam and low-pressure steam generated by the exhaust heat recovery boiler 7 increases, so that these are sufficient as cooling steam for the low-pressure steam turbine 3c. As a result, the driving of the startup boiler 27 is stopped for economic operation, the supply of auxiliary steam is stopped, and only high-pressure steam and low-pressure steam are supplied to the low-pressure steam turbine 3c.

  The compressor 2 sucks the atmosphere through the variable guide vanes 6 to increase the pressure, and supplies the high-pressure air to the combustor 5 for generating combustion gas. Fuel is added to the combustor 5 together with high-pressure air, and high-temperature combustion gas is generated. This high-temperature combustion gas is supplied to the gas turbine 1 and performs expansion work in the gas turbine 1.

  Exhaust gas discharged from the gas turbine 1 is introduced into the exhaust heat recovery boiler 7 as a heat source for generating steam, and feed water or steam that circulates through the high pressure superheater 10, the low pressure superheater 12, an evaporator of each pressure not shown, and the like. After exchanging heat with it, it is dissipated into the atmosphere through a chimney.

  The high-pressure steam generated in the high-pressure drum 13 is superheated by the high-pressure superheater 10, and after working in the high-pressure steam turbine 3 a from the high-pressure main steam pipe 16 through the high-pressure control valve 17, It merges with the low pressure steam and is introduced into the low pressure steam turbine 3c. In the present embodiment, the low pressure steam merges in the middle stage of the high pressure steam turbine 3a (in the vicinity of the exhaust part).

  On the other hand, the low-pressure steam generated in the low-pressure drum 15 is superheated by the low-pressure superheater 12, and the low-pressure steam isolation valve 35 is opened when the temperature condition and pressure condition become appropriate. It is guided to the control valve 22. The low-pressure steam guided to the low-pressure adjusting valve 22 is supplied to the low-pressure steam turbine 3c together with the high-pressure steam that has worked as described above, thereby driving the generator 4 together with the gas turbine 1 and the high-pressure steam turbine 3a. Generate power.

  By the way, after the occurrence of a load break that urgently opens the circuit breaker of the generator 4 due to an electrical accident or the like, the gas turbine 1 is set to a no-load rated speed operation, and the load is quickly increased after the electrical accident is restored. Operation to prepare for is performed. In the process of shifting from normal operation to no-load rated speed operation, the amount of fuel supplied to the gas turbine 1 rapidly decreases because of no-load operation. As the fuel flow rate decreases, the opening of the variable guide vane 6 operates in the closing direction to reduce the intake air flow rate into the gas turbine 1.

  In the steam turbine 3, the high pressure adjusting valve 17 is fully closed, and the low pressure adjusting valve 22 is once fully closed to prevent overspeed, and then opened to secure the cooling steam of the low pressure steam turbine 3c. Incidentally, the reason why the high pressure regulating valve 17 is closed in the no-load rated speed operation is that the torque generated by the gas turbine 1 is relatively reduced by reducing the generated torque of the steam turbine 3 by closing the high pressure regulating valve 17. This is because it is possible to increase the fuel flow rate of the gas turbine 1 and to stabilize the combustion.

  Therefore, when the load is interrupted, the high pressure control valve 17 is closed. Therefore, the high pressure steam generated in the high pressure drum 13 is released to the condenser 30 by opening the high pressure turbine bypass valve 50, thereby increasing the pressure. Prevents increase in steam pressure. Similarly, since the low pressure control valve 22 is closed, the low pressure steam generated in the low pressure drum 15 is released to the condenser 30 by opening the low pressure turbine bypass valve 52, thereby increasing the low pressure steam pressure. Is preventing.

  In this way, the condenser 30 is supplied with high-pressure steam and low-pressure steam, and this steam is condensed by the circulating water supplied from the circulating water pump 29, and this condensed water is discharged from the heat recovery boiler by the feed water pump 28. 7 is supplied.

(Configuration of control device)
Next, control of the variable guide vane 6 in this embodiment will be described with reference to FIGS. 2 and 3. FIG. 2 is a block diagram showing the control device 70 of the variable guide vane 6 of FIG. FIG. 3 is a diagram showing an example of a function set in the function generator of FIG.

  In FIG. 2, a steam enthalpy necessary for cooling the low-pressure steam turbine 3c is set in the setting device 101. The function generator 102 uses the steam enthalpy signal necessary for cooling the low-pressure steam turbine 3c from the setting device 101 and the low-pressure turbine exhaust pressure signal a detected by the detector 55 to reduce the low pressure required during the current operation. A turbine cooling steam flow rate signal b is obtained.

  An example of a function set in the function generator 102 is shown in FIG. The horizontal axis of FIG. 3 shows the steam enthalpy required for cooling the low-pressure turbine, and the vertical axis shows the required low-pressure turbine cooling steam flow. The required low pressure turbine cooling steam flow curve varies with the low pressure turbine exhaust pressure conditions. The function generator 102 generates a low-pressure turbine cooling steam flow signal b required by linear interpolation or the like based on the steam enthalpy signal necessary for cooling the low-pressure steam turbine 3c from the setting device 101 and the low-pressure turbine exhaust pressure signal a. It is what you want.

  The low-pressure steam flow rate passing through the low-pressure control valve 22 is detected by the detector 40 and input to the comparator 103 as the low-pressure control valve passing steam flow signal c. The comparator 103 compares the low-pressure turbine cooling steam flow signal b with the low-pressure adjusting valve passing steam flow signal c detected by the detector 40, and the low-pressure adjusting valve passing steam flow signal c is the low-pressure turbine cooling steam flow signal. When it is smaller than b, the output signal is turned on and output to the AND circuit 104.

  In addition to the output signal of the comparator 103, the AND circuit 104 includes a low pressure regulating valve loading permission command signal d (valid opening permission command for the low pressure regulating valve 22) generally calculated by other logic, and a NOT circuit 105. And a high-pressure adjusting valve loading signal e (an index indicating that the high-pressure adjusting valve 17 is opened) is input.

  The AND circuit 104 performs an AND process on the output signal of the comparator 103, the low pressure regulating valve loading permission command signal d, and the output signal of the NOT circuit 105, and the output is output to the switch 106.

  In the setting device 107, a rate of change (positive value) when increasing the opening of the variable guide vane 6 is set in advance. The output of the setting device 107 is output to the switching device 106 as a positive change rate signal f.

  On the other hand, a zero value (current value) is set in advance in the setting device 108, and this zero value is output to the switching device 106. In the switch 106, when the output of the AND circuit 104 is on, the positive change rate signal f from the setter 107 is output as the signal g, and when the output is off, a zero value is output from the setter 108. g is output to the adder 109.

  The adder 109 adds the signal g from the switch 106 to the opening command value signal m that is an output signal of the low value selector 114, and outputs the result to the upper limiter 110. The upper limiter 110 is preset with an upper limit value for the opening setting value of the variable guide vane 6 determined by the system or operation. Specifically, the upper limit value for the opening setting value of the variable guide vane 6 is a value at which the air flow rate into the gas turbine 1 increases and the air flow rate does not stop combustion. The upper limiter 110 compares this set value signal with the signal from the adder 109, and the smaller one is output to the lower limiter 111.

  The lower limit limiter 111 is preset with a lower limit limit value for the opening set value of the variable guide vane 6 determined by the system or operation. Specifically, the lower limit limit value for the opening setting value of the variable guide vane 6 is a value that provides an air flow rate that allows heat exchange with the exhaust gas of the gas turbine 1 in a low-pressure steam system that generates low-pressure steam.

  The lower limit limiter 111 compares the set value signal with the signal from the upper limit limiter 110, and the larger one is output to the change rate limiter 112. In the change rate limiter 112, mechanical restrictions (change rate) of the gas turbine 1 and the like on the change rate of the opening setting value of the variable guide vane 6 are set in advance. The rate-of-change limiter 112 limits the rate of change with respect to the signal from the lower limit limiter 111 to obtain a set value signal h of the opening for the variable guide vane 6, and this set value signal h is the high value selector 113. Is output.

  The high value selector 113 receives a VGV temperature control opening signal i and a VGV surge protection lower limit opening signal j, which are generally calculated by other logic, in addition to the opening set value signal h. ing. Specifically, the VGV temperature control opening signal i is an opening signal for controlling the temperature of the intake air to the gas turbine 1. Further, the VGV surge protection lower limit opening degree signal j is an opening degree signal for preventing abnormal vibration of the compressor 2 at an air flow rate that does not cause surging in the compressor 2.

  The high value selector 113 compares the set value signal h from the change rate limiter 112 and outputs the largest value to the low value selector 114 as the output signal k. The low value selector 114 is inputted with a VGV corrected speed schedule opening signal l which is generally calculated by other logic. The low value selector 114 compares with the set value signal k from the high value selector 113, and a small value is output to the variable guide vane 6 as the opening command value signal m.

(Operation of control device)
The control device 70 of the present embodiment is a condition that the low pressure regulating valve 22 after the occurrence of load interruption may be opened, and sufficient cooling steam is supplied to the low pressure steam turbine 3c via the high pressure regulating valve 17 and the high pressure steam turbine 3a. If the flow rate of low-pressure steam passing through the low-pressure control valve 22 is less than the required low-pressure turbine cooling steam flow rate under the condition that is not supplied, the opening setting value of the variable guide vane 6 is increased and variable guidance is performed. The opening degree of the blade 6 is controlled.

  That is, in the present embodiment, when the low-pressure turbine cooling steam flow rate is insufficient when the low-pressure adjusting valve 22 is opened after the load is cut off, the opening setting value of the variable guide blade 6 is increased. As a result, the intake air flow rate of the gas turbine 1 increases, the exhaust gas temperature of the gas turbine 1 decreases due to the relationship between the fuel and air ratio, and the exhaust gas flow rate increases.

  The gas turbine in the exhaust heat recovery boiler 7 in the high-pressure steam system that generates high-pressure steam by reducing the temperature difference between the saturated steam temperature and the exhaust gas temperature in the high-pressure drum 13 as the exhaust gas temperature decreases. The amount of heat exchange with the exhaust gas of 1 is reduced, and the amount of steam generated from the high-pressure drum 13 is reduced.

  Further, as the exhaust gas flow rate increases, for the high-pressure steam system, the temperature difference between the saturated steam temperature and the exhaust gas temperature in the high-pressure drum 13 is reduced due to the decrease in the exhaust gas temperature. Although not increasing, the flow rate of the exhaust gas sent to the low-pressure steam system that generates low-pressure steam increases by increasing the opening setting value of the variable guide vane 6.

  As a result, the amount of heat exchange in the low-pressure steam system increases, so the amount of low-pressure steam generated from the low-pressure drum 15 can be increased, and the amount of cooling steam supplied to the low-pressure steam turbine 3c can be secured. It is possible to prevent overheating due to windage of the low-pressure steam turbine 3c.

(Effect of 1st Embodiment)
As described above, according to the present embodiment, by changing the opening degree of the variable guide vane 6 that adjusts the intake air flow rate of the gas turbine 1, the high-pressure steam that is not used is reduced in the case of the two-pressure exhaust heat recovery boiler 7. Then, control is performed to adjust the thermal balance so that the low-pressure steam of the low-pressure steam turbine 3c is increased. Therefore, it is not necessary to install a separate steam source generator, and it is not necessary to connect to this steam source generator with piping, to secure a low-pressure turbine cooling steam flow rate, and to prevent overheating due to windage of the low-pressure steam turbine 3c. It can be prevented in advance.

(Second Embodiment)
(Power plant configuration)
FIG. 4 is a system diagram showing a second embodiment of the single-shaft combined cycle power plant according to the present invention. FIG. 5 is a block diagram showing a control device for the variable guide vanes of FIG. In FIGS. 4 and 5, the same components as those in the first embodiment shown in FIGS. 1 and 2 are denoted by the same reference numerals, description thereof is omitted, and only different configurations and operations are described.

  While the first embodiment is a single-shaft combined cycle power plant configured with a high-pressure and low-pressure two-pressure steam system, this embodiment shown in FIG. 4 is a high-pressure, medium-pressure, and low-pressure three-pressure steam. This is a single-shaft combined cycle power plant configured by the system.

  As shown in FIG. 4, in the uniaxial combined cycle power plant of the present embodiment, the exhaust heat recovery boiler 7 includes an intermediate pressure drum 14 that generates intermediate pressure steam that is lower in pressure than high pressure steam and higher in pressure than low pressure steam. The intermediate pressure superheater 11 connected to the intermediate pressure drum 14 and the reheater 9 for generating high-temperature reheat steam are further provided.

  Moreover, this embodiment arrange | positions coaxially with the low temperature reheat system 18 which combines the exhaust steam from the high pressure steam turbine 3a with medium pressure steam, and supplies it to the reheater 9, and the high pressure steam turbine 3a and the low pressure steam turbine 3c. And an intermediate pressure steam turbine 3b driven by the high-temperature reheat steam supplied from the reheater 9 via the high-temperature reheat steam pipe 61. The high-temperature reheat steam pipe 61 is provided with a reheat control valve 20 and a detector 58 that detects a low-pressure steam pressure on the inlet side of the reheat control valve 20.

  In the high temperature reheat steam pipe 61, an intermediate pressure turbine bypass system 82 is branched upstream of the detector 58, and the intermediate pressure turbine bypass valve 51 is interposed in the intermediate pressure turbine bypass system 82. The intermediate pressure turbine bypass system 82 is connected to the condenser 30 in the same manner as the high pressure turbine bypass system 81 and the low pressure turbine bypass system 83 described above.

  Further, the low-pressure turbine steam supply system 62 is configured to join the high-pressure reheat steam and the low-pressure steam, which are decompressed by work in the intermediate-pressure steam turbine 3b, to form the low-pressure turbine steam of the low-pressure steam turbine 3c. Yes.

  The control device 71 receives detection signals of the detector 40 that detects the low-pressure steam flow rate and the detector 55 that detects the low-pressure turbine exhaust pressure, while the control device 71 opens the variable guide blade 6. Degree control signal is output.

(Configuration of control device)
As shown in FIG. 5, in the control device 71 of the present embodiment, a high-pressure adjusting valve loading signal e (an index indicating that the high-pressure adjusting valve 17 is open) is input to the AND circuit 104 via the NOT circuit 105. In addition, a reheat control valve loading signal n (an index indicating that the reheat control valve 20 is open) is input to the AND circuit 104 via the NOT circuit 205.

(Operation of control device)
The control device 71 of the present embodiment is a condition that the low-pressure control valve 22 after the occurrence of load interruption may open, and is sufficient for the low-pressure steam turbine 3c via the reheat control valve 20 and the intermediate-pressure steam turbine 3b. When the flow rate of low-pressure steam passing through the low-pressure control valve 22 is less than the required low-pressure turbine cooling steam flow rate under the condition that the cooling steam is not supplied, the opening setting value of the variable guide blade 6 is increased, The opening degree of the variable guide vane 6 is controlled.

  That is, in the present embodiment, when the low-pressure turbine cooling steam flow rate is insufficient when the low-pressure adjusting valve 22 is opened after the load is cut off, the opening setting value of the variable guide blade 6 is increased. As a result, the intake air flow rate of the gas turbine 1 increases, the exhaust gas temperature of the gas turbine 1 decreases, and the exhaust gas flow rate increases.

  By reducing the exhaust gas temperature, the temperature difference between the saturated steam temperature and the exhaust gas temperature in the high-pressure drum 13 and the intermediate-pressure drum 14 is reduced, thereby reducing the exhaust heat recovery boiler 7 in the high-pressure steam system and the intermediate-pressure steam system. The amount of heat exchange with the exhaust gas of the gas turbine 1 is reduced, and the amount of steam generated from the high-pressure drum 13 and the intermediate-pressure drum 14 is reduced.

  Further, as the exhaust gas flow rate increases, the difference in temperature between the saturation temperature and the exhaust gas temperature in the high-pressure drum 13 and the intermediate-pressure drum 14 is reduced due to the decrease in the exhaust gas temperature in the high-pressure steam system and the intermediate-pressure steam system. Therefore, although the amount of heat exchange does not increase, the flow rate of the exhaust gas sent to the low pressure steam system increases by increasing the opening setting value of the variable guide vane 6.

  As a result, since the amount of heat exchange in the low-pressure steam system is increased, the amount of steam generated from the low-pressure drum 15 can be increased, and the amount of cooling steam supplied to the low-pressure steam turbine 3c can be secured. It becomes possible to prevent overheating due to windage loss of the low-pressure steam turbine 3c.

(Effect of 2nd Embodiment)
As described above, according to the present embodiment, by changing the opening degree of the variable guide vane 6 that adjusts the intake air flow rate of the gas turbine 1, in the case of the three-pressure exhaust heat recovery boiler 7, Control is performed to reduce the pressure steam and adjust the thermal balance so that the low pressure steam important as the steam of the low pressure steam turbine 3c is increased. Therefore, as in the first embodiment, it is not necessary to install a separate steam source generator, and it is not necessary to connect to this steam source generator by piping, ensuring a low-pressure turbine cooling steam flow rate, Overheating due to windage loss of the steam turbine 3c can be prevented in advance.

(Third embodiment)
FIG. 6 is a system diagram showing a third embodiment of the single-shaft combined cycle power plant according to the present invention. The third embodiment is a modification of the second embodiment shown in FIGS. 4 and 5, and in FIG. 6, the same components as those in FIG. Only different configurations and operations will be described.

  In the single-shaft combined cycle power plant shown in FIG. 4, the gas turbine 1 is an air cooling system that uses air as a cooling medium in the high-temperature portion, whereas the gas turbine 1 of the single-shaft combined cycle power plant according to the present embodiment. Adopts a steam cooling method using steam as a cooling medium in the high temperature part.

  As shown in FIG. 6, in the single-shaft combined cycle power plant of the present embodiment, a cooling steam system 45 for cooling a high temperature part of the gas turbine 1 is interposed between the low temperature reheat system 18 and the reheater 9. Is provided. The steam of the cooling steam system 45 is guided to the gas turbine 1 by a steam forward pipe (not shown), and after cooling the high temperature portion, the steam is led to a steam return pipe (not shown) and returned to the cooling steam system 45. Yes.

  The discharge air pressure of the compressor 2 is connected to the low-temperature reheat system 18 via a pipe 46 and a check valve 47.

  As described above, according to the present embodiment, the cooling steam system 45 for cooling the high temperature portion of the gas turbine 1 is provided between the low temperature reheating system 18 and the reheater 9, thereby cooling the high temperature portion. Despite the use of steam as the medium, the same effect as in the second embodiment can be obtained.

  Although several embodiments of the present invention have been described, these embodiments are presented by way of example and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, replacements, and changes can be made without departing from the scope of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are included in the invention described in the claims and the equivalents thereof.

  For example, in the third embodiment, the example in which the cooling steam system 45 is provided in the second embodiment has been described. However, the present invention is not limited thereto, and the cooling steam system 45 may be provided in the first embodiment.

DESCRIPTION OF SYMBOLS 1 ... Gas turbine, 2 ... Compressor, 3 ... Steam turbine, 4 ... Generator, 5 ... Combustor, 6 ... Variable guide blade, 7 ... Exhaust heat recovery boiler, 9 ... Reheater, 10 ... High pressure superheater, DESCRIPTION OF SYMBOLS 11 ... Medium pressure superheater, 12 ... Low pressure superheater, 13 ... High pressure drum, 14 ... Medium pressure drum, 15 ... Low pressure drum, 16 ... High pressure main steam pipe, 17 ... High pressure control valve, 18 ... Low temperature reheat system, 20 Reheating control valve, 21 Low pressure main steam pipe, 22 Low pressure control valve, 24 Auxiliary steam supply pipe, 27 Startup boiler, 28 Water pump, 29 Circulating water pump, 30 Condenser, 34 Control valve, 35 ... Low pressure steam isolation valve, 38 ... Revolution detector, 39 ... Detector, 40 ... Detector, 41 ... Detector, 45 ... Cooling steam system, 46 ... Piping, 47 ... Check valve, 50 ... High pressure turbine bypass valve, 51 ... Medium pressure turbine bypass valve, 52 ... Low pressure turbine Bypass valve, 55 ... detector, 56 ... detector, 57 ... detector, 58 ... detector, 61 ... high temperature reheat steam pipe, 70 ... control device, 71 ... control device, 81 ... high pressure turbine bypass system, 82 ... Intermediate pressure turbine bypass system, 83 ... Low pressure turbine bypass, 100 ... Primary motor unit, 101 ... Setting device, 102 ... Function generator, 103 ... Comparator, 104 ... AND circuit, 105 ... NOT circuit, 106 ... Switch, 107 ... Setter, 108 ... Setter, 109 ... Adder, 110 ... Upper limit limiter, 111 ... Lower limit limiter, 112 ... Change rate limiter, 113 ... High value selector, 114 ... Low value selector, 205 ... NOT circuit

Claims (6)

A high-pressure steam turbine that is arranged coaxially with the gas turbine and is driven by being supplied with high-pressure steam from a high-pressure drum of an exhaust heat recovery boiler via a high-pressure control valve;
The low-pressure steam from the low-pressure drum that generates low-pressure steam having a pressure lower than that of the high-pressure drum is supplied via a low-pressure control valve, and the low-pressure steam and the high-pressure steam that has worked in the high-pressure steam turbine are merged. A low pressure turbine steam supply system for supplying steam as low pressure turbine steam;
A low-pressure steam turbine disposed coaxially and coupled to the gas turbine and the high-pressure steam turbine and driven by the low-pressure turbine steam;
A variable guide vane for adjusting the suction air flow rate of the gas turbine;
During the no-load rated speed operation after the load interruption of the generator connected coaxially with the gas turbine, the high pressure control valve is controlled to be fully closed, and the opening of the variable guide vane is controlled to the low pressure steam. Control means for controlling the generated flow rate to increase,
A single-shaft combined cycle power plant comprising: A high-pressure steam turbine that is arranged coaxially with the gas turbine and is driven by being supplied with high-pressure steam from a high-pressure drum of an exhaust heat recovery boiler via a high-pressure control valve;
A low-pressure steam turbine that is coaxially disposed and coupled to the gas turbine and the high-pressure steam turbine and is driven by low-pressure steam;
Reheating to generate high-temperature reheat steam by combining medium-pressure steam from an intermediate-pressure drum that generates intermediate-pressure steam at a pressure lower than that of the high-pressure steam and higher than that of low-pressure steam with exhaust steam from the high-pressure steam turbine. A low-temperature reheat system to supply
An intermediate pressure steam turbine that is arranged coaxially with the high pressure steam turbine and the low pressure steam turbine and is driven by being supplied with high temperature reheat steam from the reheater via a reheat control valve;
A low-pressure turbine steam supply system for driving the low-pressure steam turbine by joining the high-temperature reheat steam and the low-pressure steam, which are decompressed by working in the intermediate-pressure steam turbine;
A variable guide vane for adjusting the suction air flow rate of the gas turbine;
At the time of no-load rated speed operation after load interruption of a generator arranged coaxially with the gas turbine, the high pressure control valve and the reheat control valve are controlled to be fully closed, and the variable guide blade Control means for controlling the opening so that the flow rate of the low-pressure steam increases;
A single-shaft combined cycle power plant comprising:   The upper limit value of the opening degree of the variable guide vane is a value that results in an air flow rate at which the intake air flow rate into the gas turbine increases and combustion of the gas turbine does not stop. 3. The single-shaft combined cycle power generation according to claim 1 or 2, wherein the value is a value that provides an air flow rate that allows heat exchange with the exhaust gas of a gas turbine in the low-pressure steam system that generates the low-pressure steam. plant.   The single-shaft combined cycle power plant according to claim 2, wherein the low-temperature reheat system is provided with a cooling steam system for cooling a high-temperature part of the gas turbine. A gas turbine, a high-pressure steam turbine, a low-pressure steam turbine, and a generator are coaxially arranged and connected, and a combustion gas is sent to the gas turbine to drive it, and the exhaust gas of the combustion gas is used as a heat source to generate high pressure Generating low-pressure steam having a pressure lower than that of the high-pressure steam, supplying the high-pressure steam via a high-pressure control valve to work on the high-pressure steam turbine, and generating the low-pressure steam via the low-pressure control valve. In the operation method of the single-shaft combined cycle power plant in which the low-pressure steam turbine supplies the work and supplies the work,
A fully-closed control step for performing control to fully close the high-pressure adjusting valve during no-load rated speed operation after load interruption of the generator;
An opening degree control step for controlling the opening degree of the variable guide vane for adjusting the suction air flow rate of the gas turbine so that the flow rate of the low-pressure steam is increased;
A method for operating a single-shaft combined cycle power plant, comprising: A gas turbine, a high-pressure steam turbine, an intermediate-pressure steam turbine, a low-pressure steam turbine, and a generator are arranged coaxially and connected, and a combustion gas is sent to the gas turbine to drive it. The recovery boiler generates high-pressure steam, and generates low-pressure steam having a pressure lower than that of the high-pressure steam and low-pressure steam having a pressure lower than that of the high-pressure steam, and the intermediate-pressure steam is discharged from the high-pressure steam turbine. The high-temperature reheat steam and the low-pressure steam, which are supplied to a reheater that generates high-temperature reheat steam and is reduced in pressure by working in the intermediate-pressure steam turbine via a reheat control valve. In a method for operating a single-shaft combined cycle power plant in which the low-pressure steam turbines are combined to perform work,
A fully-closed control step for performing control to fully close the high-pressure control valve and the reheat control valve at the time of no-load rated speed operation after the load interruption of the generator;
An opening degree control step for controlling the opening degree of the variable guide vane for adjusting the suction air flow rate of the gas turbine so that the flow rate of the low-pressure steam is increased;
A method for operating a single-shaft combined cycle power plant, comprising:

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