Method for automatically controlling load of gas turbine in starting stage of gas-steam combined cycle unit

Abstract

The invention relates to the technical field of gas-steam combined cycle units, and discloses a gas turbine load automatic control method in the starting stage of a gas-steam combined cycle unit, and automatic adjustment of the gas turbine load is achieved through a DCS logic module. After the gas turbine is connected to the grid, the control mode is switched from TCS to DCS, and the initial load is automatically set to be 40MW. The DCS judges whether the load of the gas turbine is increased or not according to the high-pressure steam drum wall temperature of the waste heat boiler so as to prevent overlarge thermal stress of the steam drum The required gas turbine exhaust temperature is calculated by determining the starting state of the steam turbine and the impulse steam temperature, and the load of the gas turbine is reversely deduced by using a historical data fitting curve. According to the method, the starting safety of the unit is effectively guaranteed, the operation amount of operators is reduced, and hysteresis and uncertainty caused by manual operation are avoided. Under the condition that the thermal expansion mean values of the steam turbine high-pressure cylinder are different, the DCS automatically adjusts the load lifting rate of the gas turbine, it is ensured that the steam turbine expansion difference does not exceed the limit, the starting efficiency and economic benefits are improved, and good popularization performance is achieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of gas-steam combined cycle units, and particularly relates to a method for automatically controlling the load of a gas turbine during the start-up stage of a gas-steam combined cycle unit. Background Art

[0002] In current gas-steam combined cycle units, during normal start-up, the gas turbine starts first and takes the initial load. The exhaust gas of the gas turbine all enters the waste heat boiler to exchange heat with the boiler water and generate steam simultaneously. After the steam parameters meet the conditions, it enters the steam turbine for impulse starting. Subsequently, the steam turbine is synchronized to the grid and the main steam control valve is gradually opened to full open. After the overall start-up is completed, the unit load is mainly controlled by the gas turbine, and the steam turbine load changes with the change of the gas turbine load. The metal temperature of the steam turbine varies due to different shutdown times, and different start-up states of the steam turbine are specified according to the metal temperature at the high-pressure steam inlet of the steam turbine, thereby determining the main steam parameters for impulse starting and obtaining the required initial load of the gas turbine.

[0003] Long-term practical experience shows that since the boiler cools faster than the steam turbine after shutdown, there is a situation where the main steam temperature required for the steam turbine impulse starting is relatively high while the wall temperature of the boiler steam drum is relatively low. At this time, if the initial load after starting the gas turbine is set too high in order to meet the impulse steam temperature, the excessive exhaust gas temperature may cause the temperature difference between the upper and lower walls of the steam drum to widen due to insufficient heat exchange in the initial stage of the boiler, and this phenomenon is particularly obvious in the high-pressure steam drum. Therefore, before the wall temperature of the steam drum rises to a relatively high value, it is necessary to limit the load of the gas turbine to ensure that the temperature difference between the upper and lower walls of the steam drum is within the specified range.

[0004] Long-term practical experience shows that the exhaust gas temperature of the gas turbine is mainly affected by the gas turbine load and the air temperature at the inlet of the gas turbine compressor. Therefore, after determining the required impulse steam parameters, on the premise of meeting a certain hot end temperature difference, the required exhaust gas temperature of the gas turbine can be obtained, and then through correction of the air temperature at the inlet of the gas turbine compressor, the required gas turbine load can be inversely deduced. Accurately obtaining the gas turbine load required to meet the steam turbine impulse starting conditions can not only avoid the situation where the impulse starting conditions cannot be met due to too low load, but also avoid the situation where a large amount of energy of the gas turbine is wasted due to too high load, ensuring the high-efficiency start-up of the unit and reducing the inevitable errors brought by the load value calculated by the operating personnel based on experience.

[0005] Long-term practical experience shows that when the shutdown time of the steam turbine is relatively long, the metal temperature of the steam turbine will drop to a relatively low value. During the startup process, especially after the steam turbine is synchronized to the grid, as the main steam temperature increases, the differential expansion between the stationary and rotating parts of the cylinder will also increase due to different heating and expansion rates. If the heating rate is slowed down and sufficient time is given for the cylinder to expand thermally, the differential expansion can be controlled and will not exceed the limit, thus ensuring the safe startup of the unit. In the past, the method of controlling the heating rate mainly relied on operators to make judgments manually based on conditions such as the differential expansion of the steam turbine and the metal temperature difference between the inner and outer cylinders of the steam turbine, and manually adjust the load of the gas turbine. This manual control method has significant drawbacks. First, operators need to continuously judge the changes in conditions such as the differential expansion of the steam turbine in real time and then manually increase the load. This not only increases the operation volume but also makes it difficult to avoid the situation where the differential expansion rises too quickly due to too rapid an increase in load, increasing the operation risk of the unit. Second, if the load is increased too slowly to avoid exceeding the differential expansion limit, the time point for the unit to enter the AGC (Automatic Generation Control mode, that is, the unit load is controlled by the dispatching center) and carry high load will be postponed, which is not conducive to the operation efficiency of the unit.

[0006] In view of this, a method for automatically controlling the load of a gas turbine during the startup stage of a gas-steam combined cycle unit is proposed. Through this method for automatically increasing the load of the gas turbine, under the premise of ensuring the safe startup of the unit, the unit load can be quickly increased to a load that meets the AGC input conditions, greatly reducing the operation of the operators and improving the operation efficiency of the unit. Summary of the Invention

[0007] The present invention aims to solve the technical problems in the above-mentioned prior art, such as the difficulty in precisely controlling the load of the gas turbine to ensure that the temperature difference between the walls of the steam drum is within a safe range, the error is easily caused by relying on operators to manually adjust the load, affecting the startup efficiency and energy utilization, the exhaust gas temperature of the gas turbine is affected by various factors, it is difficult and inefficient to manually correct the load, the difficulty in controlling the differential expansion during the startup process of the steam turbine, there are safety hazards in manual adjustment, the operation volume of the manual control method is large, the response is slow, and it is not conducive to the unit quickly entering the AGC control.

[0008] The purpose of the present invention is to utilize the existing DCS logic to provide a method for automatically increasing the load of a gas turbine during the startup stage of a gas-steam combined cycle unit, improving the automatic control level of the unit and reducing the gas consumption during the unit startup.

[0009] To achieve the above object, the present invention provides the following technical solutions: A method for automatically controlling the load of a gas turbine during the startup stage of a gas-steam combined cycle unit, comprising the following steps: Step 1: After the gas turbine of the gas-steam combined cycle unit is synchronized to the grid, switch the gas turbine control mode from "TCS control" to "DCS control", and automatically set the initial load to 40 MW; Step 2: The DCS control logic determines whether the average temperature of the lower outer wall of the high-pressure steam drum of the waste heat boiler is greater than 135°C - 150°C; Step 3: The DCS processes separately according to the judgment result of Step 2 to determine whether to increase the load of the gas turbine; Step 4: After the DCS determines that the condition for increasing the load of the gas turbine in Step 3 is met, it automatically increases the load of the gas turbine to the load required to meet the steam turbine turning-gear engagement condition; Step 5: Maintain the load described in Step 4 until the "pressure control request" condition is triggered when the steam turbine is connected to the grid and the load is increased. The DCS logic determines whether the average thermal expansion of the high-pressure cylinder of the steam turbine is greater than 18 mm; Step 6: Based on the judgment result of Step 5, the DCS automatically increases the load of the gas turbine at different rates to the load required to meet the AGC input condition.

[0010] Preferably, in Step 1, the gas-steam combined cycle unit selects the Mitsubishi M701F4 gas-steam combined cycle unit.

[0011] Preferably, in Step 4, the specific calculation method for the load required to meet the steam turbine turning-gear engagement condition is as follows: Based on the metal temperature at the high-pressure steam inlet of the steam turbine, determine whether the steam turbine is in a cold, warm, or hot start state; Based on the turning-gear engagement steam temperature required in the start state of the steam turbine, obtain the required gas turbine exhaust temperature; Control the hot end temperature difference of the boiler within 10 - 25°C. The hot end temperature difference of the boiler is the value by which the gas turbine exhaust temperature is higher than the required turning-gear engagement steam temperature; Regard the gas turbine inlet temperature and the gas turbine load as the main influencing factors of the gas turbine exhaust temperature. By collecting the historical values of the gas turbine exhaust temperature corresponding to each load at different inlet temperatures in the past, form a database, and fit the curve of the gas turbine load corresponding to the exhaust temperature at different inlet temperatures; On the premise of knowing the current gas turbine inlet temperature and the required exhaust temperature, use the above-fitted curve to inversely calculate the corresponding gas turbine load.

[0012] Preferably, when the metal temperature at the high-pressure steam inlet of the steam turbine is less than 150°C, it is in a cold state, and the corresponding required turning-gear engagement steam temperature is 370 ± 10°C; When the metal temperature at the high-pressure steam inlet of the steam turbine is 150°C - 300°C, it is in a warm state, and the corresponding required turning-gear engagement steam temperature is 420 ± 10°C; When the metal temperature at the high-pressure steam inlet of the steam turbine is greater than 300°C, it is in a hot state, and the corresponding required turning-gear engagement steam temperature is 470 ± 10°C or the metal temperature at the high-pressure steam inlet plus 50°C, and the larger value of the two is taken.

[0013] Preferably, in step five, the triggering condition of the "pressure control request" is specifically as follows: the main steam inlet control valve of the steam turbine operating at sliding pressure is fully open. At this time, the load regulation of the steam turbine mainly relies on the change of the gas turbine load rather than throttling regulation through the main steam inlet control valve, specifically referring to the steam turbine load > 35 MW and the opening degrees of the high and medium pressure main steam inlet control valves are both > 98%. Preferably, in step six, the average thermal expansion of the high-pressure cylinder of the steam turbine being 18 mm is 65% of the rated value of the thermal expansion of the high-pressure cylinder of the steam turbine.

[0014] Preferably, in step six, the different rates of increasing the gas turbine load are specifically as follows: When the average thermal expansion of the high-pressure cylinder of the steam turbine is less than 18 mm, the rate of increasing the gas turbine load is 0.02 MW / s; 0.02 MW / s is an empirical value. Increasing the gas turbine load at this rate can ensure that the differential expansion of the high-pressure cylinder does not exceed the limit; When the average thermal expansion of the high-pressure cylinder of the steam turbine is greater than 18 mm, the rate of increasing the gas turbine load is 0.34 MW / s. Here, 0.34 MW / s is the maximum limit of the load increase rate of the Mitsubishi M701F4 gas-steam combined cycle unit.

[0015] Compared with the prior art, the technical effects and advantages of the present invention are as follows: The automatic control method for the gas turbine load during the start-up stage of the gas-steam combined cycle unit uses the distributed control system (DCS) of the gas-steam combined cycle unit to automatically control the load of the gas turbine. After the gas turbine is connected to the grid, the control system first switches the control mode of the gas turbine from the operating system of the Mitsubishi gas turbine (TCS control) to DCS control and sets the initial load. Subsequently, DCS determines whether the gas turbine load can be increased by monitoring the average temperature of the outer wall of the high-pressure steam drum of the heat recovery steam generator. After meeting the conditions, DCS automatically calculates and increases the gas turbine load to the load required to meet the steam turbine turning. During this process, DCS comprehensively considers the start-up state of the steam turbine, the turning steam temperature, the exhaust gas temperature of the gas turbine, and the relationship curve between the load and the exhaust gas temperature fitted from historical data to ensure the precise control of the gas turbine load.

[0016] The automatic control method for the gas turbine load during the start-up stage of the gas-steam combined cycle unit significantly improves the start-up safety of the unit. Through real-time monitoring and automatic adjustment, it effectively avoids the risk of thermal stress damage to the steam drum due to excessive temperature difference and the differential expansion of the steam turbine exceeding the limit. Secondly, it reduces the operation amount of the operating personnel, reduces the errors and risks caused by improper manual operation, and the operating personnel can release more energy to monitor the overall operation of the unit. In addition, the automatic control method can increase the unit load to meet the AGC input conditions faster, thereby improving the operation efficiency and economic benefits of the unit.

[0017] The automatic control method for the gas turbine load during the startup stage of the gas-steam combined cycle unit controls the gas turbine load automatically through the DCS. The present invention realizes the unity of safety and efficiency during the unit startup process. On the basis of ensuring the safety of the unit, the application of the automatic control logic reduces the startup time, optimizes the energy utilization, and at the same time reduces the operating cost. This innovative method is easy to integrate into the existing system and can be upgraded and optimized according to the actual operating conditions, having good popularization value and application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a flow block diagram of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0020] The following is combined with Figure 1 to further elaborate on the present application. The embodiment of the present application discloses an automatic control method for the gas turbine load during the startup stage of a gas-steam combined cycle unit, including the following steps: Step 1: After the gas turbine of the gas-steam combined cycle unit is connected to the grid, switch the gas turbine control mode from "TCS control" to "DCS control", and automatically set the initial load to 40 MW; The Mitsubishi M701F4 gas-steam combined cycle unit is selected for the gas-steam combined cycle unit. TCS control is the operating system of the Mitsubishi gas turbine, and DCS control is the distributed control system. Switching to DCS control can also achieve the control of the gas turbine load, and it is more convenient to write logic in DCS than in TCS to implement the following control logic; Step 2: The DCS control logic judges whether the average temperature of the lower outer wall of the high-pressure steam drum of the heat recovery steam generator is greater than 135°C - 150°C; Step 3: The DCS processes separately according to the judgment result of Step 2 to judge whether to increase the gas turbine load; When the average temperature of the lower outer wall of the high-pressure steam drum of the heat recovery steam generator does not exceed 135°C - 150°C, if the gas turbine load is directly increased to the high value, due to the rapid increase in the exhaust gas temperature, the temperature difference between the upper and lower walls of the high-pressure steam drum may be enlarged to an unacceptable value, and then the thermal stress of the steam drum is too large, resulting in damage; Step 4: After the DCS judges that the condition for increasing the gas turbine load in Step 3 is satisfied, automatically increase the gas turbine load to the load required to meet the steam turbine turning condition; Among them, the specific calculation method for the load required to meet the turbine turning - on conditions is as follows: Determine the starting state and turning - on steam temperature: First, based on the metal temperature at the high - pressure steam inlet of the turbine, determine whether the turbine is in a cold, warm, or hot start. According to different starting states, determine the corresponding turning - on steam temperature. For example, when the metal temperature at the high - pressure steam inlet of the turbine is less than 150°C, it is a cold start, and the required turning - on steam temperature is 370 ± 10°C; when the metal temperature at the high - pressure steam inlet of the turbine is 150°C - 300°C, it is a warm start, and the required turning - on steam temperature is 420 ± 10°C; when the metal temperature at the high - pressure steam inlet of the turbine is greater than 300°C, it is a hot start, and the required turning - on steam temperature is 470 ± 10°C or the metal temperature at the high - pressure steam inlet plus 50°C, taking the larger value.

[0021] Calculate the required gas turbine exhaust temperature: The gas turbine exhaust temperature needs to be higher than the turning - on steam temperature by a hot - end temperature difference, usually between 10°C and 25°C. This temperature difference ensures sufficient heat transfer efficiency and avoids energy loss caused by too long heat - exchange time.

[0022] For example, if the turning - on steam temperature is 470°C and the hot - end temperature difference is taken as 25°C, then the required gas turbine exhaust temperature is 495°C.

[0023] Utilize historical data and curve fitting: Collect historical data on the exhaust temperatures of the gas turbine at different intake temperatures and loads in the past to form a database. Analyze these data and fit the relationship curve between the gas turbine load and the exhaust temperature at different intake temperatures.

[0024] Back - calculate the required gas turbine load: On the premise of knowing the current gas turbine intake temperature and the required exhaust temperature, use the above - fitted curve to back - calculate the corresponding gas turbine load.

[0025] For example, if the current gas turbine intake temperature is 25°C and the required exhaust temperature is 495°C, by querying or calculating the fitted curve, the required gas turbine load can be obtained as 94 MW.

[0026] Step Five: Maintain the load described in Step Four until the "pressure control request" condition is triggered when the turbine is synchronized and the load increases. The DCS logic judges whether the average thermal expansion of the turbine's high - pressure cylinder is greater than 18 mm (65% of the rated thermal expansion of the turbine's high - pressure cylinder); The triggering conditions for the "pressure control request" are specifically as follows: The main steam inlet regulating valve of the turbine operating under sliding pressure has been fully opened. At this time, the turbine load regulation mainly relies on the change of the gas turbine load rather than throttling regulation through the main steam inlet regulating valve, specifically referring to the turbine load > 35 MW and the opening degrees of both the high - and medium - pressure main steam inlet regulating valves > 98%.

[0027] Step 6: Based on the judgment result in Step 5, the DCS automatically increases the gas turbine load to the load required to meet the AGC input conditions at different rates.

[0028] When the average thermal expansion of the high-pressure cylinder of the steam turbine is less than 18 mm, if the gas turbine load is increased too fast, it may cause the main steam temperature to rise too fast, and then cause the differential expansion of the high-pressure cylinder of the steam turbine to increase to an unacceptable value, resulting in rubbing between the moving and static parts of the steam turbine and causing damage.

[0029] When the average thermal expansion of the high-pressure cylinder of the steam turbine is less than 18 mm, the rate of increasing the gas turbine load is 0.02 MW / s; 0.02 MW / s is an empirical value, and increasing the gas turbine load at this rate can ensure that the differential expansion of the high-pressure cylinder does not exceed the limit; When the average thermal expansion of the high-pressure cylinder of the steam turbine is greater than 18 mm, the rate of increasing the gas turbine load is 0.34 MW / s. Here, 0.34 MW / s is the maximum limit of the gas turbine load increase rate of the Mitsubishi M701F4 gas-steam combined cycle unit.

[0030] In order to further improve the automation level of the 9F gas-steam combined cycle unit, the present invention integrates it into the APS automatic start-stop program of the unit, so that the load control from after the gas turbine is connected to the grid to before the unit inputs AGC can be automatically controlled in the non-startable state.

[0031] On the premise of considering the unit startup status and ensuring safety in many aspects, this method can achieve full-process automation, greatly reducing the operation volume of operating personnel.

[0032] The automatic control method for the gas turbine load in the startup stage of the gas-steam combined cycle unit is integrated into the DCS logic, forming a built-in DCS logic module of the unit. The built-in DCS logic module of the unit can reasonably adjust the gas turbine load according to the steam drum wall temperature and the thermal expansion of the high-pressure cylinder of the steam turbine, effectively preventing thermal stress damage caused by excessive temperature difference of the steam drum and the differential expansion of the steam turbine from exceeding the limit, and improving the safety in the startup stage.

[0033] By automatically controlling the gas turbine load through the DCS, the load and steam parameters required for the steam turbine to rotate can be quickly and accurately reached, shortening the startup time and improving the startup efficiency of the unit. Automatic control reduces the need for operating personnel to manually adjust the load, reducing errors and risks caused by improper human operation.

[0034] The automatic control method of the gas turbine load during the startup phase of the gas-steam combined cycle unit ensures that the temperature difference at the hot end is within a reasonable range by accurately controlling the gas turbine load, avoiding energy loss caused by insufficient or excessive heat exchange, and optimizing energy utilization. The automatic control logic takes into account different startup states and operating conditions, and can adjust the load according to parameters such as the metal temperature of the steam turbine and the intake temperature, with good adaptability and flexibility. Through the automatic control method, the unit can reach the AGC input conditions more quickly, improve the economy of the unit operation, and reduce operating costs. The integration capability and logic programming flexibility of the DCS control system enable the new control method to be easily embedded in the existing system, and can be upgraded and optimized according to actual operating conditions.

[0035] The present invention uses the DCS logic module that comes with the unit. Without the need to connect new load control contacts or other modifications, the unit can automatically increase the load of the gas turbine to the load required for AGC under different startup conditions. The present invention improves the previous operating method that relies on operators to judge load requirements through experience and manually input load values, avoiding the lag and uncertainty caused by manual operation. At the same time, as an important part of the fully automatic startup process of the unit, the present invention has the advantages of both safety and efficiency and has good promotion. The operation flow of the present invention summarizes a large number of previous unit startup process data samples, and increases the unit load to meet the AGC input conditions as soon as possible under the premise of ensuring the safety of the unit. Since the new control method is DCS automatic control of the gas turbine load increase, the operation workload of the operator is greatly reduced, ensuring that the operator can devote more time and energy to checking the operation of the newly started unit. Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, it is still possible for those skilled in the art to modify the technical solutions described in the aforementioned embodiments or to make equivalent substitutions for some of the technical features therein. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for automatically controlling the load of a gas turbine during the startup phase of a gas-steam combined cycle unit, characterized in that: The following steps are involved: Step 1: After the gas turbine of the gas-steam combined cycle unit is connected to the grid, the control mode of the gas turbine is switched from "TCS control" to "DCS control", and the initial load is automatically set to 40MW; Step 2: The DCS control logic determines whether the average temperature of the lower outer wall of the high-pressure drum of the waste heat boiler is greater than 135°C-150°C; Step 3: DCS processes the results of step 2 to determine whether to increase the load of the gas turbine; Step 4: After the DCS determines that the conditions for increasing the gas turbine load in step 3 are met, it automatically increases the gas turbine load to the load required to meet the turbine start-up conditions; Step 5: Maintain the load described in step 4 until the turbine is connected to the grid and the load is increased to the point where the "pressure control request" condition is triggered. The DCS logic determines whether the average thermal expansion value of the turbine high-pressure cylinder is greater than 18 mm. Step 6: Based on the judgment result of step 5, DCS automatically increases the load of the gas turbine from different rates to the load required to meet the conditions for AGC input.

2. The method for automatic control of engine load during the startup phase of a gas-steam combined cycle unit according to claim 1, characterized in that: In step 1, the gas-steam combined cycle unit uses the Mitsubishi M701F4 gas-steam combined cycle unit.

3. The method for automatic control of engine load during the startup phase of a gas-steam combined cycle unit according to claim 1, characterized in that: In step 4, the specific calculation method for the load required to meet the turbine start-up conditions is: According to the metal temperature at the high-pressure steam inlet of the steam turbine, it is judged whether the steam turbine is in cold, warm or hot start state; The required turbine exhaust temperature is obtained based on the required start-up steam temperature when the turbine is in the startup state; The hot end temperature difference of the boiler is controlled at 10-25℃. The hot end temperature difference of the boiler is the value at which the exhaust temperature of the gas turbine is higher than the required steam temperature. The gas turbine intake temperature and gas turbine load are taken as the main influencing factors of the gas turbine exhaust temperature. By collecting the historical values ​​of the gas turbine exhaust temperature corresponding to each load at different gas turbine intake temperatures, a database is formed, and the curve of the gas turbine load corresponding to the exhaust temperature at different intake temperatures is fitted; Under the premise that the current engine intake temperature and the required exhaust temperature are known, the above fitted curve is used to infer the corresponding engine load.

4. The method for automatic control of engine load during the startup phase of a gas-steam combined cycle unit according to claim 3, characterized in that: The metal temperature at the high-pressure steam inlet of the steam turbine is less than 150℃, which is considered cold. The corresponding steam temperature required for the start-up is 370±10℃. The metal temperature at the high-pressure steam inlet of the steam turbine is 150℃-300℃, which is the warm state. The corresponding steam temperature required for the start-up is 420±10℃. The metal temperature at the high-pressure steam inlet of the steam turbine is greater than 300℃ and is considered hot. The corresponding required steam temperature is 470±10℃ or the metal temperature at the high-pressure steam inlet plus 50℃, whichever is greater.

5. The method for automatic control of engine load during the startup phase of a gas-steam combined cycle unit according to claim 1, characterized in that: In step 5, the triggering condition of "pressure control request" is specifically: the main steam inlet regulating valve of the steam turbine in sliding pressure operation is fully opened. At this time, the steam turbine load regulation mainly relies on the change of the gas turbine load rather than the throttling regulation of the main steam inlet regulating valve. Specifically, the steam turbine load is greater than 35MW and the opening of the high and medium pressure main steam inlet regulating valves are both greater than 98%.

6. The method for automatic control of engine load during the startup phase of a gas-steam combined cycle unit according to claim 1, characterized in that: In step six, the average thermal expansion value of the steam turbine high-pressure cylinder is 18mm, which is 65% of the rated thermal expansion value of the steam turbine high-pressure cylinder.

7. The method for automatic control of engine load during the startup phase of a gas-steam combined cycle unit according to claim 1, characterized in that: In step 6, the different rates of increasing the engine load are as follows: When the average thermal expansion value of the high-pressure cylinder of the steam turbine is less than 18mm, the load rate of the gas turbine is increased to 0.02MW / s; When the average thermal expansion value of the turbine high-pressure cylinder is greater than 18mm, the turbine load rate is increased to 0.34MW / s.

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