JP2002021509A - Combined cycle power plant - Google Patents

Abstract

(57) [Summary] [PROBLEMS] When the exhaust gas temperature of a gas turbine is adjusted so as not to rise above a certain temperature in order to improve the durability and reliability of a superheater, the temperature set value is set low. If the temperature is too high, the gas turbine cannot be operated at a predetermined combustion temperature when the atmospheric temperature increases, and the thermal efficiency of the plant deteriorates. A method of controlling the flow rate of spray water of a desuperheater based on a predetermined function during operation at a peak value of a gas turbine exhaust gas temperature without lowering a combustion temperature of a gas turbine to reduce superheated steam flowing through a boiler superheater tube. Reduce the temperature so that the temperature of the boiler superheater tube itself does not exceed the design temperature.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a combined cycle power generation system comprising a gas turbine, a steam turbine and an exhaust heat recovery boiler, and more particularly to a combined cycle power generation plant for controlling the steam temperature generated by an exhaust heat recovery boiler. About.

[0002]

2. Description of the Related Art Conventionally, as a combined cycle power generation system of this type, cooling water is sprayed on superheated steam from a drum disposed between a first stage superheater and a second stage superheater of an exhaust heat recovery boiler. There is an exhaust heat recovery boiler steam temperature control device that controls the main steam temperature.

[0003] Due to the characteristics of gas turbines, the exhaust gas temperature of a gas turbine rises in the process of increasing the load, reaches a peak value at an intermediate load, then drops again, and when the rated operation is reached, the exhaust gas temperature becomes lower than the peak temperature. Even lower temperatures.

For this reason, an exhaust heat recovery boiler that recovers thermal energy of gas turbine exhaust gas to generate steam uses a design temperature of a superheater first exposed to the gas turbine exhaust gas based on a peak temperature value in the starting process. are doing. Since the superheater is operated in this manner, it is manufactured from a heat-resistant material. However, from the viewpoints of durability, reliability, and marketability, it has been conventionally desired to keep the design temperature low.

Conventionally, as a measure for reducing the design temperature in order to improve the durability and reliability of the superheater, the exhaust gas temperature of the gas turbine is controlled by a gas turbine compressor inlet guide vane (inlet guide vane: IGV). The temperature is adjusted so that it does not rise above the temperature.

[0006]

However, in this method,
If the temperature set value is set too low, it becomes impossible to operate the gas turbine at a predetermined combustion temperature when the atmospheric temperature becomes high, and the thermal efficiency of the plant deteriorates.

If the exhaust gas temperature is set low, the IGV
The value of the load at which the gas turbine begins to open becomes low, and accordingly, the rise in the combustion temperature of the gas turbine becomes slow. Then, it takes much time until the gas turbine reaches the combustion temperature at the time of switching from the diffusion combustion operation to the premix combustion operation, and as a result, the nitrogen oxide (NO _x ) emission during the load increase at the time of startup increases. There is a drawback to do.

The present invention has been made in view of the above-mentioned conventional disadvantages, and has as its object to provide a combined cycle power plant capable of lowering the main steam temperature of a superheater without lowering the combustion temperature of a gas turbine. It is.

[0009]

According to a first aspect of the present invention, there is provided a combined cycle power plant comprising: a gas turbine; and an exhaust heat recovery boiler for driving a steam turbine with steam generated by recovering exhaust heat of the gas turbine. In a combined cycle power plant having a superheater to convert the saturated steam from the drum of the exhaust heat recovery boiler into superheated steam and mixing the superheated steam with cooling water to control a main steam temperature, During the operation in which the gas turbine exhaust gas temperature reaches the peak value when the turbine load rises, the temperature of the superheated steam flowing through the boiler superheater tube is reduced by controlling the flow rate of the spray water of the desuperheater based on a predetermined function. In addition, the temperature of the boiler superheater tube itself is prevented from exceeding the design temperature.

According to a second aspect of the present invention, there is provided a combined cycle power plant according to the present invention, a gas turbine, an exhaust heat recovery boiler for driving a steam turbine with steam generated by recovering the exhaust heat of the gas turbine, and an exhaust heat recovery boiler. In a combined cycle power plant consisting of a superheater that converts saturated steam from the drum of the boiler into superheated steam and mixing the superheated steam with cooling water to control a main steam temperature, the combined cycle power plant has a gas turbine load, exhaust gas temperature, And a first function generator that outputs an exhaust gas temperature upper limit value corresponding to the gas turbine load as a set value,
A first control unit for controlling an air compressor inlet guide vane based on a difference between a set value output from the function generator and a measured exhaust gas temperature value;
A gas turbine inlet temperature control unit having an arithmetic unit, and a second function generator for setting a relationship between the exhaust gas temperature and the steam temperature set value in advance and outputting a steam temperature set value corresponding to the input exhaust gas temperature A combined cycle plant control comprising: a steam temperature control unit having a second calculator for controlling the opening of the steam temperature control valve based on a difference between the set value of the second function generator and the measured steam temperature. The apparatus is characterized in that the apparatus is configured.

In the combined cycle power plant according to the third aspect of the present invention, the first function generator provided in the gas turbine inlet temperature control section has a peak exhaust gas temperature during the gas turbine load increasing process. It is characterized by comprising a flat first function applied at the time of operation and a second function set in accordance with a period in which the exhaust gas temperature decreases as the load increases from a time point equal to or higher than a predetermined intermediate load.

[0014] In the combined cycle power plant according to the present invention, the second function generator provided in the steam temperature control section outputs the highest set value when the exhaust gas temperature is lower than the first predetermined value. A third function that outputs a set value that decreases in accordance with the rise of exhaust gas when the exhaust gas temperature is equal to or more than a first predetermined value and less than a second predetermined value; A fifth function that outputs the lowest set value when the value is equal to or greater than the second predetermined value. A combined cycle power plant according to the present invention according to claim 5 is characterized in that feed water is used as a deceleration medium for the desuperheater.

[0013]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A combined cycle power plant according to the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a system diagram showing an embodiment of a combined cycle power plant according to the present invention. Most of the recently constructed combined cycle power plants have a waste heat recovery boiler 4 of a three-pressure type consisting of a high pressure, a medium pressure, and a low pressure for high efficiency and large capacity. In order to make it easy to understand, a single pressure type drum will be described as an example.

This combined cycle power plant is an example of a single-shaft combined cycle power plant in which a gas turbine plant 1, a steam turbine 2, and a generator 3 are combined, and heat energy of gas turbine exhaust gas is recovered as exhaust heat. Boiler (Heat Recovery Steam Genera
(torr) 4.

The gas turbine plant 1 includes a gas turbine 5
And an air compressor 6 are provided coaxially, and air taken in from an intake filter 8 is introduced into the air compressor 6 by a gas turbine compressor inlet guide vane (inlet guide vane: abbreviated as IGV) 7 and compressed therein. To combustor 9
Mix with fuel and burn.

The high-temperature combustion gas burned in the combustor 9 is guided to the gas turbine 5 and performs expansion work to perform the expansion work.
Is driven to rotate. The exhaust gas EG of the gas turbine 5 passes through the exhaust duct 10 and is guided to the exhaust heat recovery boiler 4, where it exchanges heat with water supplied from the steam turbine 2 to be heated and turned into steam. It is discharged to the outside from the chimney 12 via.

A second superheater 14 and a first superheater are provided in the casing 13 of the single-pressure exhaust heat recovery boiler 4 from the upstream side to the downstream side of the exhaust gas EG (from right to left on the paper). The evaporator 17 and the economizer 18 are arranged in this order in order to communicate with the steam or the feed water. Water is supplied to the exhaust heat recovery boiler 4 configured as described above as follows.

After the steam of the steam turbine 2 is condensed by a condenser 19, the pressure of the steam is increased by a condensate pump 20 and sent to a water supply pump 22 through a pipe 21. The water supply pump 22 boosts the water supply,
Water is supplied to the economizer 18.

The feed water heat exchanged by the economizer 18 is supplied to the drum 16. The saturated steam generated in the drum 16 is guided to the first superheater 15 and is superheated. The superheated steam flowing out of the first superheater 15 is cooled by a desuperheater 23 by spray water whose flow rate is controlled by a steam temperature control valve 28 in feedwater branched from a pipe 21 on a downstream side of a feedwater pump 22. Thereafter, the process reaches the second superheater 14.

The superheated steam flowing out of the second superheater 14 is guided to the steam turbine 2 through the steam system 24, expands, and drives the steam turbine 2 and the generator 3 to generate electric power.

By the way, an exhaust gas temperature measuring device 25 is installed near the outlet of the gas turbine 5, and the measured temperature Tg is inputted to a combined cycle plant control device 26 described later. Further, a steam temperature measuring device 27 is installed at the outlet of the second superheater 14, and the outlet steam temperature Tr is measured, and is similarly input to the combined cycle plant control device 26. These temperature measuring devices 25 and 27 are composed of, for example, thermocouples or the like. Combined cycle plant controller
26 internally calculates using these process input values,
An opening command is output to the GV 7 and the steam temperature control valve 28.

Next, the details of the combined cycle plant control device 26 will be described with reference to the control logic circuit diagram of FIG. The functions of the combined cycle plant control device 26 include a gas turbine inlet temperature control unit 26A,
The steam temperature control unit 26B is roughly divided into two devices.

First, the gas turbine inlet temperature control unit 26A will be described. 26A1 is a function generator that determines in advance the relationship between the command value R of the gas turbine load (more precisely, the compressor suction air temperature and the compression ratio) and the corresponding exhaust gas temperature upper limit Teg.

The function of the function generator 26A1 is obtained by combining a flat function (a) having a high value applied in the process of increasing the load as shown in FIG. When the gas turbine load command value R is input, the exhaust gas temperature upper limit value T corresponding to the input at that time.
eg is output as a set value.

For convenience, (a) and (b) are called a first function and a second function, respectively. The output signal of the function generator 26A1 is input to the integration calculator 26A2 as the set value Teg, and is compared with the temperature Tg measured by the exhaust gas temperature measuring device 25.

The integration calculator 26A2 performs an integration operation on the difference between the set value and the measured value to generate an opening control command α for the entrance guide vane (IGV) 7, and based on the opening control command α, the entrance guide vane. (IGV) The opening degree of 7 is adjusted. In this way,
Control is performed so that the exhaust gas temperature, and thus the gas turbine combustion temperature, does not exceed a predetermined temperature.

Next, the steam temperature control section 26B will be described. 26B3 is a function generator in which the relationship between the exhaust gas temperature Tg and the corresponding steam temperature set value Ts is predetermined in consideration of the heat resistance of the superheater tube. That is, as shown in the figure, when the exhaust gas temperature is low, there is no problem with heat resistance even if the steam temperature flowing through the superheater tube is high. A function (d) of decreasing right which lowers the temperature of the steam flowing through the superheater tube, and a function (e) of a constant value (flat) which further lowers the temperature of the steam flowing through the superheater tube when the exhaust gas temperature further increases. Combined. In addition,
(C) to (e) are referred to as third to fifth functions for convenience.

26B4 is an integral operation unit, and a function generator 26
A difference is calculated using the set value Ts of B3 and the measured value Tr, and based on the difference, the opening degree command β to the steam temperature control valve 28 is controlled so that the amount of spray water sprayed on the superheated steam is controlled. Is output.

FIG. 3 is a characteristic diagram showing the state values of the combined cycle power plant according to the present invention when the plant is operated. The purging operation immediately after the start of the operation of the gas turbine 5 and the ignition of the combustor 9 are not directly related to the present invention, so that the description thereof will be omitted, and the process from the load increasing process to the rated load will be described. In the figure, the solid line (a) shows the temperature of the gas turbine exhaust gas EG, the broken line (b) shows the steam temperature generated from the exhaust heat recovery boiler 4, and the dashed line (c) shows the temperature of the superheater tube itself (metal temperature). ) Are shown. In describing the characteristic diagram of FIG. 3, a control logic diagram of FIG. 2 will be referred to.

First, the operation of the gas turbine inlet temperature control unit 26A will be described. As described above, the function generator 26A1
Since the exhaust gas temperature set value is composed of a flat first function (a) which is a peak value and a downwardly sloping second function (b) resulting from this, as shown in FIG. Until the exhaust gas temperature Tg reaches the set value, the exhaust gas temperature (a) increases with an increase in the gas turbine load, and accordingly, the superheater steam temperature (b) and the temperature of the superheater tube itself (c) also increase. I do.

Next, gas turbine exhaust gas temperature characteristics (a)
The explanation will be focused on. The gas turbine exhaust gas temperature Tg is
Until the peak value Tp is reached, the temperature rises as the gas turbine load increases. Then, the exhaust gas temperature Tg
Reaches the peak value Tp (the load at this time is the intermediate load L3), the integration calculator 26A2 sets the set value Teg
Thus, the opening degree control command α is output to the IGV 7 so that the exhaust gas temperature Tg maintains the peak value Tp. This control is performed while the flat first function is applied, that is,
The operation is continuously performed until the gas turbine load becomes L4.

When the gas turbine load reaches L4, the set value to be applied is set to the second function (b), which decreases to the right, until it reaches the rated load L6.
26A2 calculates the exhaust gas temperature to gradually decrease along the set value and controls the opening of the IGV7.

The following operation of the steam temperature control unit 26B is performed simultaneously with the operation of the steam gas turbine inlet temperature control unit 26A. Hereinafter, the response of the steam temperature control unit 26B will be described.

Since the function generator 26B3 sets the steam temperature set value as the third function (c) to the fifth function (e) as shown in FIG. 2, the steam temperature measurement is performed while the gas turbine load is increasing. When the value Tr is still low, a flat third function (c) is applied. For this reason, the superheater steam temperature follows the exhaust gas temperature (a) as the gas turbine load increases, as shown by the characteristic (b). When the measured steam temperature Tr reaches the steam turbine rated temperature Ti (the load at this time is L1) due to an increase in the load on the gas turbine 5, the integration calculator 26B4 calculates using the set value Ts and the measured value Tr. , An opening degree command β is output to the steam temperature control valve 28 so as to control the amount of spray water sprayed on the superheated steam. The temperature Tg of the exhaust gas subsequently rises as shown in the characteristic (a), but the superheated steam temperature is maintained at the steam turbine rated temperature Ti by controlling the amount of water sprayed.

Thereafter, when the exhaust gas temperature rises to Td (the load at this time is L2), the function generator 26B3 switches the applied set value from the third function (c) to the fourth function (d). Thereafter, the integration calculator 26B4 calculates so as to decrease the steam temperature according to the set value of the fourth function (d), and outputs an opening command to increase the amount of spray water of the steam temperature control valve 28. When the exhaust gas temperature Teg reaches the peak value Tp (at this time, the load L3), the function generator 26B3 switches the set value from the third function (d) falling to the right to a flat fourth function (e) this time. Is input as a set value to the integration calculator 26B4. As a result, the integral calculator 26B4 controls the opening of the steam temperature control valve 28 and controls the amount of spray water so that the superheater steam temperature is controlled to a constant value Tl according to the set value.

As the gas turbine load increases from L4 to L5 to L6, the gas turbine inlet temperature controller 26A
Since V7 is controlled so as to reduce the gas turbine exhaust gas temperature Tg as in the characteristic (a), the function applied by the function generator 26B3 is changed from the fifth function (e) to the fourth function (d). Then, the fourth function (d) is switched to the third function (c), and the characteristic shown in FIG.

Since the temperature characteristic of the superheater tube itself indicated by the one-dot chain line (c) corresponds to the difference between the exhaust gas temperature (a) and the superheated steam temperature (b), as shown in FIG. Become. The description of FIG. 3 has been completed, and FIG. 4 will be described next.

FIG. 4 is a diagram showing the metal and ambient temperature of the boiler tube of the combined cycle power plant according to the present invention, in which the superheater tube is cut away. T1 and T2 are the temperatures on the outer surface of the tube, respectively. T1 indicates the case where the exhaust gas temperature is low, and T2 indicates the case where the exhaust gas temperature is high. Further, t1 and t2 are the temperatures of the inner surface of the tube, respectively. T1 indicates a case where the superheater passing temperature is high, and t2 indicates a case where the superheater passing temperature is low.

As can be seen from this figure, in order to keep the center of the superheater tube itself at a constant temperature, as the temperature of the exhaust gas on the outer surface of the tube increases, the temperature of the superheater steam flowing in the tube may be lowered. You can see that.

During the operation of the gas turbine, the temperature of the superheater tube itself varies between the exhaust gas temperature and the outer surface of the tube due to surface convection on the outer surface of the tube itself. The temperature drop determined by the rate causes a temperature difference between the outer surface of the tube and the inner surface. Occurs. Thus, the combination of these three heat transfers determines the temperature of the tubes in the boiler superheater, and the metal temperature of the tubes is defined by the average of the outer and inner surfaces of the tubes.

When the gas turbine exhaust gas rises using this mechanism, the temperature of the steam flowing through the inner surface of the tube is determined by the average value of the inner surface temperature and the outer surface temperature of the tube with respect to the exhaust gas temperature. By defining the temperature by a function so that the temperature itself is kept constant, even if the exhaust gas temperature of the gas turbine rises, it is possible to perform an operation in which the temperature of the tube is not raised above the allowable temperature of the metal.

[0042]

As described above, according to the present invention, in addition to the exhaust gas temperature control using the compressor inlet guide valve of the gas turbine, the gas turbine exhaust gas temperature peak value operation when the gas turbine load rises is improved. Since the temperature of the superheated steam flowing through the superheater tube is controlled so as to keep the temperature of the superheater tube itself below a predetermined value, the metal temperature of the tube is raised above the allowable temperature even if the exhaust gas temperature of the gas turbine rises. It is possible to obtain a combined cycle power plant that can be operated without any problems.

[Brief description of the drawings]

FIG. 1 is a schematic system diagram showing an embodiment of a combined cycle power plant according to the present invention.

FIG. 2 is a control logic diagram of the combined cycle plant control device in the embodiment of FIG.

FIG. 3 is a characteristic diagram showing state values of the combined cycle power plant according to the present invention.

FIG. 4 is a diagram locally showing a tube itself and an ambient temperature state of the combined cycle power plant according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Gas turbine plant, 2 ... Steam turbine, 3 ... Generator, 4 ... Exhaust heat recovery boiler, 5 ... Gas turbine, 6 ... Air compressor, 7 ... Compressor inlet guide vane (IGV), 8 ... Suction filter, 9: combustor, 10: exhaust duct, 11 :, 12: chimney, 13: casing, 14: second superheater, 15: first superheater, 16: drum, 17: evaporator, 18: economizer, 19… Condenser, 20… Condenser pump, 21… Piping, 22… Feed pump, 23…
Temperature reducer, 24: Steam system, 25: Exhaust gas temperature measuring instrument, 26: Combined cycle controller, 26A: Gas turbine inlet temperature controller, 26B: Steam temperature controller, 26B1: First function generator, 26B2 ... 1 integration calculator, 26B3: second function generator, 26B4: second integration calculator, 27: steam temperature measuring instrument,
28: temperature control valve, b: first function, b: second function, c: third function, d: fourth function, e: fifth function.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F22G 5/12 F22G 5/12 B

Claims (5)

[Claims] 1. A gas turbine, an exhaust heat recovery boiler that drives a steam turbine with steam generated by recovering the exhaust heat of the gas turbine, and a superheater that superheats saturated steam from a drum of the exhaust heat recovery boiler. In a combined cycle power plant having a supercooler and a supercooler to control the main steam temperature by mixing cooling water with the superheated steam, when the gas turbine exhaust gas temperature at the time of increasing the gas turbine load reaches the peak value, By controlling the flow rate of the spray water of the desuperheater based on a predetermined function, the temperature of the superheated steam flowing in the boiler superheater tube was reduced so that the temperature of the boiler superheater tube itself did not exceed the design temperature. Combined cycle power plant. 2. A gas turbine, an exhaust heat recovery boiler that drives a steam turbine with steam generated by recovering exhaust heat of the gas turbine, and a superheater that superheats saturated steam from a drum of the exhaust heat recovery boiler. In a combined cycle power plant consisting of steam and a superheater that controls the main steam temperature by mixing cooling water with the superheated steam, the relationship between the gas turbine load and the exhaust gas temperature is determined in advance,
A first function generator that outputs an exhaust gas temperature upper limit corresponding to a gas turbine load as a set value, and an air compressor inlet based on a difference between the set value output from the first function generator and an exhaust gas temperature measurement value. A gas turbine inlet temperature control unit having a first computing unit for controlling the guide vanes, a relationship between the exhaust gas temperature and the steam temperature set value is determined in advance, and the steam temperature set value corresponding to the input exhaust gas temperature is determined. Steam temperature control comprising: a second function generator for outputting; and a second calculator for controlling an opening of the steam temperature control valve based on a difference between a set value of the second function generator and a measured steam temperature. A combined cycle power plant, comprising a combined cycle plant control device comprising: 3. A first function generator provided in the gas turbine inlet temperature control section includes a flat first function applied during an operation in which an exhaust gas temperature reaches a peak value in a gas turbine load increasing process; The combined cycle power plant according to claim 2, further comprising: a second function that is set in accordance with a period in which the exhaust gas temperature decreases as the load increases from a time point equal to or higher than a predetermined intermediate load. 4. A second function generator provided in the steam temperature control section, wherein a third function for outputting the highest set value when the exhaust gas temperature is less than a first predetermined value,
When the state is less than or equal to the second predetermined value and less than the second predetermined value, a fourth function that outputs a set value that decreases in reverse according to the rise of the exhaust gas, and when the exhaust gas temperature becomes equal to or more than the second predetermined value,
The combined cycle power plant according to claim 2, further comprising: a fifth function that outputs a lowest set value. 5. The combined cycle power plant according to claim 1, wherein feed water is used as a temperature reducing medium in the temperature reducing device.