Patent Description:
A combined power plant includes a gas turbine that generates power by burning fuel, a heat recovery steam generator that produces steam by recovering exhaust heat from the gas turbine, and a steam turbine that uses the steam supplied from the heat recovery steam generator to generate power.

A conventional combined power generation system includes a high-pressure steam line for supplying a high-pressure turbine with steam produced by a high-pressure superheater, a medium-pressure steam line for supplying a medium-pressure turbine with the steam that has passed through the high-pressure turbine, a high-pressure bypass line connected from the high-pressure steam line to the medium-pressure steam line, and a reheat steam bypass line connected from downstream of the medium-pressure steam line to a condenser.

When rapidly starting the combined power generation system, there is a significant increase in the amount of steam produced by the heat recovery steam generator.

Hence, the excessive steam production can lead to the reheat steam pressure becoming uncontrollable, which may impede the rapid startup of the system itself.

In addition, if the reheat steam bypass capacity is increased to manage overproduced steam, it can result in a decrease in steam density and subsequently reduce the efficiency of steam discharge. This, in turn, leads to high treatment costs.

<CIT> presents a first steam turbine and a second steam turbine of a combined cycle plant are connected by a reheat steam line via a reheat section of an exhaust heat recovery boiler. The reheat steam line and a condenser are connected by a second bypass line. A control device includes: a determination unit that determines whether or not the flow rate of first steam flowing into the first steam turbine has reached a stipulated flow rate; a command output unit that, upon determining that the flow rate of the first steam flowing into the first steam turbine has reached the stipulated flow rate, outputs a close command to close a ventilator valve that is provided in the second bypass line and is open; and a threshold alteration unit that alters the threshold with which the determination unit determines whether or not the stipulated flow rate has been reached, the threshold being positively correlated with a temperature of the first steam.

<CIT> presents a start-up method of a steam turbine plant includes a first step and a second step. The first step is performed at an aeration start time. In the first step, a reheat steam pressure of an aeration boiler is set to be a reheat steam pressure required by a steam turbine or less. Besides, a reheat steam pressure of a standby boiler is set to be a reheat steam pressure required for the standby boiler or more. The second step is performed when a load of the steam turbine becomes a predetermined value. In the second step, the reheat steam pressure of the aeration boiler is increased to the same degree as the reheat steam pressure of the standby boiler. After that, steam from the aeration boiler and steam from the standby boiler are merged to be supplied to the steam turbine.

<CIT> provides a steam power plant for generating electrical energy. The steam power plant comprises a steam turbine having a plurality of turbine sections, a steam generator, and a reheating unit. Also, the steam power plant comprises a main steam pipeline which fluidically interconnects a steam inlet of the first turbine section with the steam generator, and a hot reheat pipeline which fluidically interconnects the reheating unit with the a steam inlet of a second turbine section. Moreover, the steam power plant comprises a first bypass station which fluidically interconnects the main steam pipeline with the hot reheat pipeline. Additionally, the steam power plant comprises a second bypass station which fluidically interconnects the hot reheat pipeline with a condenser.

Aspects of one or more exemplary embodiments provide a combined power generation system and a control method thereof, which are capable of reducing a startup time of a combined power plant by including an additional high-pressure bypass line and valve provided between a high-pressure steam line and a condenser of a steam turbine to increase an effect of steam discharge, facilitate pressure control, and ensure system stability.

Additional aspects will be set forth in part in the description which follows and, in part, will become apparent from the description, or may be learned by practice of the exemplary embodiments.

According to an aspect of an exemplary embodiment, there is provided a combined power generation system that includes a heat recovery steam generator configured to recover exhaust heat from a gas turbine to produce steam, the heat recovery steam generator including a high-pressure superheater and a reheater, a steam turbine operated by receiving the produced steam, the steam turbine including a high-pressure turbine, a medium-pressure turbine, and a low-pressure turbine, a condenser installed under the low-pressure turbine to condense steam, a high-pressure steam line for supplying the high-pressure turbine with the steam produced by the high-pressure superheater, a medium-pressure steam line for supplying the medium-pressure turbine with the steam that has passed through the high-pressure turbine, a high-pressure bypass line connected from the high-pressure steam line to the medium-pressure steam line, and an additional high-pressure bypass line connected from the high-pressure steam line to the condenser.

The combined power generation system may further include a reheat steam bypass line connected from downstream of the medium pressure steam line to the condenser. The combined power generation system may further include a high-pressure bypass valve provided in the high-pressure bypass line, a reheat steam bypass valve provided in the reheat steam bypass line, and an additional high-pressure bypass valve provided in the additional high-pressure bypass line.

A capacity of the additional high-pressure bypass line may be determined by obtaining a product of density and sound speed under design pressure and temperature conditions and then multiplying a reciprocal of the product by a design flux to derive a reference cross-sectional area, by obtaining a product of density and sound speed under steam turbine pressure and temperature conditions required at startup and then multiplying this product by the reference cross-sectional area to derive an amount of steam that is able to be discharged at startup, and by obtaining a difference in the amount of steam that is able to be discharged from the high-pressure bypass line and from the reheat steam bypass line and then multiplying the difference by a ratio of a design condition flux of the high-pressure bypass line and a discharge flux at startup.

When the reference cross-sectional area is derived, in the high-pressure bypass line, a maximum cross-sectional area may be obtained by dividing a design flux by a maximum steam flux per unit area and dividing the same by a valve position at the time of design, and in the reheat steam bypass line, a maximum cross-sectional area may be obtained by dividing a design flux by a maximum steam flux per unit area and dividing the same by a valve position at the time of design.

When the amount of steam that is able to be discharged at startup is derived, in the high-pressure bypass line, under conditions at startup, a steam flux may be calculated by multiplying a maximum steam flux per unit area by the reference cross-sectional area, and in the reheat steam bypass line, under conditions at startup, a steam flux may be calculated by multiplying a maximum steam flux per unit area by the reference cross-sectional area.

When the capacity of the additional high-pressure bypass line is determined, for conversion into design conditions, the difference in the amount of steam that is able to be discharged from the high-pressure bypass line and from the reheat steam bypass line may be multiplied by the ratio of the design condition flux and the discharge flux at startup, and the capacity of the additional high-pressure bypass line may be designed to be a maximum valve position by dividing the design condition flux by a valve position at the time of design.

According to an aspect of another exemplary embodiment, there is provided a method for controlling a combined power generation system that includes a heat recovery steam generator including a high-pressure superheater and a reheater, a steam turbine including a high-pressure turbine, a medium-pressure turbine, and a low-pressure turbine, a condenser, a high-pressure steam line, a medium-pressure steam line, a high-pressure bypass line, a high-pressure bypass valve, a reheat steam bypass line, a reheat steam bypass valve, an additional high-pressure bypass line connected from the high-pressure steam line to the condenser, and an additional high-pressure bypass valve installed in the additional high-pressure bypass line, the method including controlling the additional high-pressure bypass valve to operate when a valve position of the reheat steam bypass valve is equal to or greater than a predetermined value.

A reheat steam pressure in the medium-pressure steam line may be a process variable for system control, a steam pressure required for the medium-pressure turbine may be a target set point for system control, and a valve position of the additional high-pressure bypass valve may be a manipulated variable.

A control signal of the reheat steam bypass valve may be set as an enable trigger signal of the additional high-pressure bypass valve, and the enable trigger may be set when the valve position of the reheat steam bypass valve is between <NUM>% and <NUM>%.

A disable trigger signal of the additional high-pressure bypass valve may be set to be <NUM> to <NUM>% less than the valve position at the enable trigger signal.

It is to be understood that both the foregoing general description and the following detailed description of exemplary embodiments are exemplary and explanatory and are intended to provide further explanation of the disclosure as claimed.

The above and other aspects will become more apparent from the following description of the exemplary embodiments with reference to the accompanying drawings, in which:.

Various modifications and different embodiments will be described below in detail with reference to the accompanying drawings so that those skilled in the art can easily carry out the invention. The scope of the invention is defined in the following claims.

The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the scope of the disclosure. In the disclosure, terms such as "comprises", "includes", or "have/has" should be construed as designating that there are such features, integers, steps, operations, components, parts, and/or combinations thereof, not to exclude the presence or possibility of adding of one or more of other features, integers, steps, operations, components, parts, and/or combinations thereof.

Exemplary embodiments will be described below in detail with reference to the accompanying drawings. It should be noted that like reference numerals refer to like parts throughout various drawings and exemplary embodiments. In certain embodiments, a detailed description of functions and configurations well known in the art may be omitted to avoid obscuring appreciation of the disclosure by those skilled in the art. For the same reason, some components may be exaggerated, omitted, or schematically illustrated in the accompanying drawings.

<FIG> is a configuration diagram illustrating a combined power generation system according to an exemplary embodiment.

The combined power generation system, which is designated by reference numeral <NUM>, according to an embodiment of the present invention, includes a heat recovery steam generator <NUM>, a steam turbine <NUM>, a condenser <NUM>, a high-pressure steam line <NUM>, a medium-pressure steam line <NUM>, a high-pressure bypass line <NUM>, a reheat steam bypass line <NUM>, and an additional high-pressure bypass line <NUM>. The heat recovery steam generator <NUM> recovers exhaust heat from a gas turbine to produce steam and includes a high-pressure superheater <NUM> and a reheater <NUM>. The steam turbine <NUM> is operated by receiving the produced steam and includes a high-pressure turbine <NUM>, a medium-pressure turbine <NUM>, and a low-pressure turbine <NUM>. The condenser <NUM> is installed under the low-pressure turbine <NUM> to condense steam. The high-pressure steam line <NUM> supplies the high-pressure turbine <NUM> with the steam produced by the high-pressure superheater <NUM>. The medium-pressure steam line <NUM> supplies the medium-pressure turbine <NUM> with the steam that has passed through the high-pressure turbine <NUM>. The high-pressure bypass line <NUM> is connected from the high-pressure steam line <NUM> to the medium-pressure steam line <NUM>. The reheat steam bypass line <NUM> is connected from downstream of the medium-pressure steam line <NUM> to the condenser <NUM>. The additional high-pressure bypass line <NUM> is connected from the high-pressure steam line <NUM> to the condenser <NUM>.

A combined power plant includes a gas turbine (not shown) that generates power by burning fuel, a heat recovery steam generator <NUM> that produces steam by recovering exhaust heat from the gas turbine, and a steam turbine <NUM> that uses the steam supplied from the heat recovery steam generator to generate power.

The heat recovery steam generator (HRSG) <NUM> includes the high-pressure superheater <NUM> and the reheater <NUM> as illustrated in <FIG>. The high-pressure superheater <NUM> may produce superheated steam by exchanging heat with the exhaust gas of the gas turbine and supply the superheated steam to the high-pressure turbine <NUM>. The reheater <NUM> may reheat the steam that has passed through the high-pressure turbine <NUM> by exchanging heat with the exhaust gas of the gas turbine and supply the steam to the medium-pressure turbine <NUM>.

The steam turbine <NUM> may include the high-pressure turbine <NUM>, the medium-pressure turbine <NUM>, and the low-pressure turbine <NUM>, which are connected by a rotary shaft. The rotary shaft of the steam turbine <NUM> may be connected to a generator <NUM> to generate electric power by rotating the generator <NUM>. The high-pressure turbine <NUM> may be operated by receiving the steam produced by the high-pressure superheater <NUM> through the high-pressure steam line <NUM>. The medium-pressure turbine <NUM> may be operated by receiving, through the medium-pressure steam line <NUM>, the steam reheated by the reheater <NUM> connected to the medium-pressure steam line <NUM>. The low-pressure turbine <NUM> may be operated by receiving the steam that has passed through the medium-pressure turbine <NUM>. The condenser <NUM> may be installed under the low-pressure turbine <NUM> to condense steam that has passed through or bypassed the steam turbine <NUM>.

The high-pressure steam line <NUM> is a main pipe used to supply steam produced by the high-pressure superheater <NUM> to the steam turbine <NUM>. The high-pressure bypass line <NUM> and the additional high-pressure bypass line <NUM> may be connected to the middle of the high-pressure steam line <NUM>.

The medium-pressure steam line <NUM> is connected from the high-pressure turbine <NUM> to the medium-pressure turbine <NUM> via the reheater <NUM> of the heat recovery steam generator <NUM>. This connection facilitates the supply of reheated steam to the medium-pressure turbine <NUM>. The high-pressure bypass line <NUM> may be connected to upstream of the medium-pressure steam line <NUM>, and the reheat steam bypass line <NUM> may be connected downstream of the medium-pressure steam line <NUM>. The reheater <NUM> may be disposed between the upstream of the medium-pressure steam line <NUM> where the high-pressure bypass line <NUM> is connected to and the downstream of the medium-pressure steam line <NUM> where the reheat steam bypass line <NUM> is connected to.

When a large amount of steam is produced by the high-pressure superheater <NUM>, such as during startup of the gas turbine, the high-pressure bypass line <NUM> may allow some of the steam to bypass to the medium-pressure steam line <NUM>. The steam that have bypassed may be combined with steam that has passed through the high-pressure turbine <NUM> in the medium-pressure steam line <NUM>, and may be reheated by the reheater <NUM> to be supplied to the medium-pressure turbine <NUM>.

When a large amount of steam is reheated by the reheater <NUM>, the reheat steam bypass line <NUM> may allow some of the steam to be directly sent to the condenser <NUM>.

When an excessive amount of steam is produced during rapid startup of the gas turbine that surpasses the capacity of the high-pressure bypass line <NUM>, the additional high-pressure bypass line <NUM> can be utilized. The additional high-pressure bypass line <NUM> enables a portion of the steam produced by the high-pressure superheater <NUM> to be directly directed to the condenser <NUM>. The additional high-pressure bypass line <NUM> may be connected to the high-pressure steam line <NUM> at a location downstream from the point where the high-pressure bypass line <NUM> is connected to the high-pressure steam line <NUM>.

The combined power generation system <NUM> according to the present embodiment may further include a high-pressure bypass valve <NUM> provided in the high-pressure bypass line <NUM>, a reheat steam bypass valve <NUM> provided in the reheat steam bypass line <NUM>, and an additional high-pressure bypass valve <NUM> provided in the additional high-pressure bypass line <NUM>.

The high-pressure bypass valve <NUM> may adjust a valve position thereof or its opening degree to regulate or adjust the amount of steam that bypasses through the high-pressure bypass line <NUM>.

The reheat steam bypass valve <NUM> may adjust a valve position thereof or its opening degree to regulate or adjust the amount of steam that bypasses through the reheat steam bypass line <NUM>.

The additional high-pressure bypass valve <NUM> may adjust a valve position thereof or its opening degree to regulate or adjust the amount of steam that bypasses through the additional high-pressure bypass line <NUM>. The valve position or the opening of the additional high-pressure bypass valve <NUM> may be adjusted depending on the valve position or the opening of the high-pressure bypass valve <NUM> and the valve position or the opening of the reheat steam bypass valve <NUM>.

<FIG> is a graph illustrating a change in density with pressure for each temperature of steam. <FIG> is a graph illustrating a change in sound speed with pressure for each temperature of steam. <FIG> is a graph illustrating a change in maximum mass flux per unit area with pressure for each temperature of steam.

The purpose and configuration of the additional high-pressure bypass line <NUM>, as well as how to determine the steam treatment capacity thereof, will be described with reference to <FIG>.

The capacity of the additional high-pressure bypass line <NUM> may be determined by obtaining a product of density and sound speed under design pressure and temperature conditions and then multiplying a reciprocal of the product by a design flux to derive a reference cross-sectional area, by obtaining a product of density and sound speed under steam turbine pressure and temperature conditions required at startup and then multiplying this product by the reference cross-sectional area to derive an amount of steam that is able to be discharged at startup, and by obtaining a difference in the amount of steam that is able to be discharged from the high-pressure bypass line <NUM> and from the reheat steam bypass line <NUM> and then multiplying the difference by a ratio of a design condition flux of the high-pressure bypass line <NUM> and a discharge flux at startup.

As illustrated in <FIG>, steam increases in density as the pressure thereof increases at a certain temperature. That is, the density and pressure of steam are statically correlated. Also, steam decreases in density as the temperature thereof increases at a certain pressure. Furthermore, it has been observed that the higher the temperature of steam is, the greater the linearity of the static correlation between the density and pressure of steam becomes. In other words, it can be seen that the curve in the graph of <FIG> becomes closer to a straight line as the temperature of the steam becomes closer toward <NUM>, compared to <NUM>.

As illustrated in <FIG>, steam decreases in sound speed when the pressure thereof increases at a certain temperature. That is, the pressure and sound speed of steam are negatively correlated. Also, steam increases in sound speed as the temperature thereof increases at a certain pressure. Furthermore, it is found that the higher the temperature of steam is, the greater the linearity of the negative correlation between the sound speed and pressure of steam becomes. In other words, it can be seen that the curve in the graph of <FIG> becomes closer to a straight line as the temperature of the steam becomes closer toward <NUM> compared to <NUM>.

Since the steam turbine generally requires a temperature of <NUM> or higher during rapid startup, the correlation between the density and pressure of the steam and the correlation between the sound speed and the temperature of the steam can be considered approximately linear as seen in the graphs of <FIG> and <FIG>. It can be seen that the range of change in steam density with the change in steam pressure is relatively larger than the range of change in steam sound speed with the change in steam pressure.

As illustrated in <FIG>, the maximum mass flux of steam that is able to pass per unit area increases as the pressure of steam increases at a certain temperature. Also, steam decreases in maximum mass flux as the temperature thereof increases at a certain pressure. Furthermore, the higher the temperature of steam is, the greater the linearity of the static correlation between the maximum mass flux and pressure of steam becomes. In other words, it can be seen that the curve in the pressure-maximum mass flux graph of <FIG> becomes closer to a straight line as the temperature of the steam becomes closer toward <NUM> compared to <NUM>.

The flow velocity of steam is equal to the sound speed of steam during choking flow (when choking occurs). Therefore, the maximum mass flux of steam that is able to pass per unit area may be expressed as a product of density and sound speed, as shown in Equation <NUM> below.

That is, since the mass flux (G) is a product of density (ρ) and flow velocity (V), the maximum steam flux (Gmax) per unit area may be calculated from the product of density (ρ) and sound speed (C). As the pressure of steam increases, the discharge effect of steam increases.

Considering these physical characteristics, in treating overproduced steam, it is more effective to connect a bypass line capable of diverting steam from the high-pressure steam line <NUM> with high steam pressure directly to the condenser, rather than routing the steam from the medium-pressure steam line <NUM> to the condenser. Hence, in the present embodiment, the additional high-pressure bypass line <NUM> is directly connected from the high-pressure steam line <NUM> to the condenser <NUM>.

Based on these physical behavior characteristics, the capacities of the additional high-pressure bypass line <NUM> and the additional high-pressure bypass valve <NUM> are selected as follows. <MAT> <MAT>.

As described in Equation <NUM>, the maximum steam flux (Gmax. HP) of the high-pressure bypass line <NUM> is a product of density (ρ) and sound speed (C) under design pressure and temperature conditions. Thus, the reference cross-sectional area (A) may be obtained by dividing a design flux (ṁ) by the maximum steam flux (Gmax. HP) per unit area. In this case, the maximum cross-sectional area may be obtained by dividing the above value by a valve position (VPOS) at the time of design.

As described in Equation <NUM>, the maximum steam flux (Gmax. IP) of the reheat steam bypass line <NUM> is a product of density (ρ) and sound speed (C) under design pressure and temperature conditions. Thus, the reference cross-sectional area (A) may be obtained by dividing a design flux (ṁ) by the maximum steam flux (Gmax. IP) per unit area. In this case, the maximum cross-sectional area may be obtained by dividing the above value by a valve position (VPOS) at the time of design.

Next, how to calculate the amount of steam that is able to be discharged at startup will be described. <MAT> <MAT>.

As described in Equation <NUM>, the steam flux at startup () in the high-pressure bypass line <NUM> may be calculated by multiplying a maximum steam flux (ρ×C) per unit area by a reference cross-sectional area (A).

As described in Equation <NUM>, the steam flux at startup () in the reheat steam bypass line <NUM> may be calculated by multiplying a maximum steam flux (ρ×C) per unit area by a reference cross-sectional area (A).

Next, how to determine the capacity of the additional high-pressure bypass line <NUM> will be described.

As described in Equation <NUM>, the capacity additionally required for the additional high-pressure bypass line <NUM> is determined by obtaining a difference between a steam flux at startup (ṁ) in the high-pressure bypass line and a steam flux at startup (ṁ) in the reheat steam bypass line.

For conversion into design conditions, the difference may be multiplied by a design condition flux (ṁ) and a discharge flux at startup (ṁ). In addition, the capacity of the additional high-pressure bypass line <NUM> may be designed to be a maximum valve position by dividing the design condition flux (ṁ) by a valve position (VPOS) at the time of design. Thus, the additional high-pressure bypass valve <NUM> may be designed to be fully (<NUM>%) open.

As such, the combined cycle system of the present embodiment can be efficiently configured by accurately calculating and designing the steam treatment capacity of the additional high-pressure bypass line.

<FIG> is a configuration diagram illustrating a method for controlling a combined power generation system according to another exemplary embodiment of the present invention.

The method for controlling a combined power generation system according to another exemplary embodiment of the present invention will be described with reference to <FIG>.

As described above, the combined power generation system <NUM> according the exemplary embodiment includes the heat recovery steam generator <NUM>, the steam turbine <NUM>, the condenser <NUM>, the high-pressure steam line <NUM>, the medium-pressure steam line <NUM>, the high-pressure bypass line <NUM>, the high-pressure bypass valve <NUM>, the reheat steam bypass line <NUM>, the reheat steam bypass valve <NUM>, the additional high-pressure bypass line <NUM>. The heat recovery steam generator <NUM> includes the high-pressure superheater <NUM> and the reheater <NUM>. The steam turbine <NUM> includes the high-pressure turbine <NUM>, the medium-pressure turbine <NUM>, and the low-pressure turbine <NUM>. The additional high-pressure bypass line <NUM> is connected from the high-pressure steam line to the condenser. The additional high-pressure bypass valve <NUM> is installed in the additional high-pressure bypass line <NUM>.

The method for controlling a combined power generation system may control the additional high-pressure bypass valve <NUM> to operate when the valve position of the reheat steam bypass valve <NUM> is equal to or greater than a predetermined value.

The reheat steam pressure in the medium-pressure steam line <NUM> may be a process variable for system control, the steam pressure required for the medium-pressure turbine <NUM> may be a target set point for system control, and the valve position of the additional high-pressure bypass valve <NUM> may be a manipulated variable.

That is, when the reheat steam pressure in the medium-pressure steam line <NUM> is set as a process variable, the steam pressure required for the medium-pressure turbine <NUM>, which is a target set point, may be within a predetermined value range and the valve position of the additional high-pressure bypass valve <NUM> may be manipulated and adjusted. When the valve position of the reheat steam bypass valve <NUM> reaches or exceeds than a predetermined value, the additional high-pressure bypass valve <NUM> may be activated to increase its valve position.

According to an embodiment, the control signal of the reheat steam bypass valve <NUM> can be used as the enable trigger signal for the additional high-pressure bypass valve <NUM>. For example, the enable trigger signal may be set when the valve position of the reheat steam bypass valve <NUM> falls within the range of <NUM>% and <NUM>%. This allows the activation of the additional high-pressure bypass valve <NUM> when the valve position of the reheat steam bypass valve <NUM> meets this specific condition.

In addition, the control signal of the reheat steam bypass valve <NUM> can be used as the disable trigger signal for the additional high-pressure bypass valve <NUM>. For example, the disable trigger signal may be set when the valve position of the reheat steam bypass valve <NUM> falls within the range of <NUM>% to <NUM>%, less than the valve position at the enable trigger signal. This allows the deactivation of the additional high-pressure bypass valve <NUM> when the valve position of the reheat steam bypass valve <NUM> meets this specific condition.

As illustrated in <FIG>, in order to minimize the capacity of the additional high-pressure bypass valve <NUM> in terms of cost reduction, according to an embodiment, the additional high-pressure bypass valve <NUM> is preferably operated when the valve position of the reheat steam bypass valve <NUM> is equal to or greater than a predetermined value. Accordingly, the operation of the additional high-pressure bypass valve <NUM> may be controlled by setting the control signal of the reheat steam bypass valve <NUM> as a trigger signal.

In <FIG>, PID control may be performed by setting the reheat steam pressure (IP Pressure) in the medium-pressure steam line <NUM> as a process variable and setting the steam pressure (IP Pressure) required for the medium-pressure turbine <NUM> as a target set point for system control.

In addition, the PID control may be performed by setting the steam pressure (IP BP Demand) required for the reheat steam bypass line <NUM> and the target set point (SP) for the valve position of the reheat steam bypass valve <NUM> to be <NUM>%.

The enable trigger signal of the additional high-pressure bypass valve <NUM> may be set when the control signal of the reheat steam bypass valve <NUM> is about <NUM>% open.

In order to stably operate the additional high-pressure bypass valve <NUM>, the disable trigger signal of the additional high-pressure bypass valve <NUM> may be set when the control signal of the reheat steam bypass valve <NUM> is about <NUM>% open, which is less by about <NUM>%.

The PID control value using the valve position of the reheat steam bypass valve as a trigger signal and the PID control value using the reheat steam pressure as a process variable may be combined with different weights (for example, at a weight of <NUM> :<NUM>).

Finally, it is possible to accurately control the valve position (Add BP Demand) of the additional high-pressure bypass valve <NUM>, which is a manipulated variable.

As is apparent from the above description, it is evident that the combined power generation system and its control method according to the present invention offer several advantages. According to the combined power generation system and the control method, by incorporating the additional high-pressure bypass line and valve provided between the high-pressure steam line and the condenser of the steam turbine, it is possible to reduce the startup time of the combined power plant. This addition also enhances the effectiveness of steam discharge, facilitate pressure control, and ensure system overall system stability.

Claim 1:
A combined power generation system (<NUM>) comprising:
a heat recovery steam generator configured to recover exhaust heat from a gas turbine to produce steam, the heat recovery steam generator comprising a high-pressure superheater (<NUM>) and a reheater (<NUM>);
a steam turbine (<NUM>) operated by receiving the produced steam, the steam turbine (<NUM>) comprising a high-pressure turbine (<NUM>), a medium-pressure turbine (<NUM>), and a low-pressure turbine (<NUM>);
a condenser (<NUM>) installed under the low-pressure turbine (<NUM>) to condense the steam;
a high-pressure steam line (<NUM>) for supplying the high-pressure turbine (<NUM>) with the steam produced by the high-pressure superheater (<NUM>);
a medium-pressure steam line (<NUM>) for supplying the medium-pressure turbine (<NUM>) with the steam that has passed through the high-pressure turbine (<NUM>); and
a high-pressure bypass line (<NUM>) connected from the high-pressure steam line (<NUM>) to the medium-pressure steam line (<NUM>);
characterized in that: the combined power generation system (<NUM>) further comprising:
an additional high-pressure bypass line (<NUM>) connected from the high-pressure steam line (<NUM>) to the condenser (<NUM>).