Control system and method for medium-pressure steam admission in a gas-steam combined cycle unit

Abstract

The application provides a control system and method for medium-pressure steam admission in a gas-steam combined cycle unit, comprising a medium-pressure water extraction pump, a superheater, a medium-pressure bypass regulating valve, a condenser, a medium-pressure steam regulating valve, a reheater and a steam turbine, the medium-pressure water extraction pump is connected with the superheater through a pipeline, the water outlet of the superheater is connected with the condenser and the medium-pressure cylinder of the steam turbine through pipelines, the medium-pressure bypass regulating valve is arranged on the pipeline corresponding to the condenser, the medium-pressure steam regulating valve is arranged on the pipeline corresponding to the steam turbine, and the reheater is arranged between the medium-pressure steam regulating valve and the steam turbine. The control system and method for medium-pressure steam admission in the gas-steam combined cycle unit can maintain the medium-pressure drum liquid level in a safe liquid level range through the medium-pressure feedwater regulating valve, realize automatic control during medium-pressure steam admission through the opening and closing of the medium-pressure steam regulating valve and the medium-pressure bypass regulating valve, and reduce misoperation.

Description

Technical Field

[0001] This invention relates to the field of gas-fired steam combined cycle units, and in particular to a control system and method for medium-pressure steam inlet in a gas-fired steam combined cycle unit. Background Technology

[0002] In recent years, with the adjustment of the national energy structure and the increasing environmental emission requirements, gas turbines and their combined cycle units have developed rapidly due to their advantages such as high efficiency, low emissions, flexible start-up and shutdown, and good peak-shaving performance. Waste heat boilers recover waste heat from gas turbines, heat feedwater, and generate high-temperature, high-pressure steam, which then enters the turbine to drive the generator. During the intake of medium-pressure steam, the medium-pressure bypass regulating valve and the medium-pressure steam regulating valve need to be switched. The medium-pressure bypass regulating valve is closed while the medium-pressure steam regulating valve is opened. The exhaust from the high-pressure cylinder mixes with the medium-pressure steam after passing through the reheater, ensuring that all the medium-pressure steam that was originally intended for the condenser enters the turbine's medium-pressure cylinder. During the steam intake period, the pressure in the medium-pressure steam drum changes significantly. Since the steam drum of the waste heat boiler is usually relatively small, large pressure fluctuations can cause severe false water level readings in the medium-pressure steam drum, leading to rapid rises or falls in the water level. Existing control strategies are insufficient to achieve fully automatic water level monitoring in the waste heat boiler steam drum.

[0003] Currently, most power plants still rely primarily on manual operation for medium-pressure steam inlet. During the manual opening of the medium-pressure steam regulating valve, the medium-pressure bypass regulating valve is slowly closed. Simultaneously, the medium-pressure feedwater regulating valve is continuously adjusted based on the medium-pressure steam drum liquid level to maintain the medium-pressure steam drum liquid level at the normal level. This continues until the medium-pressure bypass is fully closed, the medium-pressure steam regulating valve is fully open, and the medium-pressure steam inlet is complete. Once the medium-pressure steam inlet is finished and the medium-pressure steam drum pressure and liquid level have stabilized, the automatic operation of the medium-pressure feedwater regulating valve and the medium-pressure bypass regulating valve is activated. The medium-pressure steam inlet process requires significant human judgment and operation, increasing the workload of operators and increasing the likelihood of operator errors or improper operation, which can adversely affect the safety and stability of the unit. Summary of the Invention

[0004] This invention provides a control system and method for medium-pressure steam inlet in a gas-fired steam combined cycle unit, which solves the technical problem in the prior art that requires a large amount of subjective judgment and operation by operators during medium-pressure steam inlet, which is prone to misoperation.

[0005] This invention provides a control system and method for medium-pressure steam inlet in a gas-fired combined cycle unit, comprising: a medium-pressure water pump, a superheater, a medium-pressure bypass regulating valve, a condenser, a medium-pressure steam regulating valve, a reheater, and a steam turbine. The medium-pressure water pump is connected to the superheater via pipelines. The outlet of the superheater is connected to the condenser and the medium-pressure cylinder of the steam turbine via pipelines. The medium-pressure bypass regulating valve is installed on the pipeline corresponding to the condenser. The medium-pressure steam regulating valve is installed on the pipeline corresponding to the steam turbine. The reheater is installed between the medium-pressure steam regulating valve and the steam turbine.

[0006] In some embodiments, a medium-pressure water supply regulating valve and a medium-pressure boiler drum are sequentially arranged between the medium-pressure water pump and the superheater.

[0007] In some embodiments, the heat source for the superheater is a gas turbine.

[0008] In some embodiments, the high-pressure cylinder exhaust port of the steam turbine is connected to the inlet of the reheater.

[0009] In some embodiments, pressure gauges are provided on both the medium-pressure boiler drum and the steam inlet pipe of the reheater.

[0010] A method for controlling the intermediate-pressure steam inlet of a gas-fired steam combined cycle unit includes setting target setpoints for the intermediate-pressure bypass regulating valve and the intermediate-pressure steam regulating valve, setting the reheater inlet steam pressure as the target setpoints, setting an offset function for the target setpoints, and setting a rate limiting function for the opening commands of the intermediate-pressure bypass regulating valve and the intermediate-pressure steam regulating valve.

[0011] In some embodiments, when the actual value of the intermediate pressure steam regulating valve is the reheater inlet steam pressure and the target setting value is the reheater inlet steam pressure minus the pressure offset value, the target setting value is always lower than the actual value of the intermediate pressure steam regulating valve, and the intermediate pressure steam regulating valve is gradually opened.

[0012] When the actual value of the medium-pressure bypass regulating valve is the reheater inlet steam pressure, and the target setting value is the reheater inlet steam pressure plus the pressure offset value, the target setting value is always higher than the actual value of the medium-pressure steam regulating valve, and the medium-pressure bypass regulating valve is gradually closed.

[0013] Right now,

[0014] PV1 = Steam_IP

[0015] SP1 = Max[Steam_IP - △P1, L]

[0016] PV2 = Steam_IP

[0017] SP2 = Steam_IP + △P2

[0018] In the formula:

[0019] PV1: Actual pressure control value of the medium-pressure steam regulating valve;

[0020] Steam_IP: Reheater inlet steam pressure;

[0021] SP1: Target setpoint for pressure control of medium-pressure steam regulating valve;

[0022] Max[]: Max value function;

[0023] △P1: Offset of the target setpoint for pressure control of the medium-pressure steam regulating valve;

[0024] L: Lower limit of the target setpoint for pressure control of the medium-pressure steam regulating valve;

[0025] PV1: Actual pressure control value of the medium-pressure bypass regulating valve;

[0026] SP1: Target setpoint for pressure control of medium-pressure bypass regulating valve;

[0027] △P1: Target setpoint offset for pressure control of medium-pressure bypass regulating valve.

[0028] In some embodiments, during the automatic steam inlet process of medium-pressure steam, when the pressure of the medium-pressure boiler drum changes, the rate limiting function is triggered to slow down the steam inlet. When the rate of change of the pressure of the medium-pressure boiler drum exceeds a certain range, the valve opening command rate limit is set to 0% / s, maintaining the medium-pressure steam regulating valve and the medium-pressure bypass regulating valve at a fixed opening until the steam drum pressure tends to stabilize. Then, the medium-pressure steam regulating valve continues to open slowly, the medium-pressure bypass regulating valve closes slowly, and the medium-pressure steam inlet begins.

[0029] During the initial steam inlet stage, when the medium-pressure steam inlet regulating valve is in the small opening range, the opening command rate limiting function is applied. The smaller the opening of the medium-pressure steam regulating valve, the stronger the rate limiting function is. The valve opening command rate limiting function is slowed down or released after the medium-pressure steam inlet stabilizes.

[0030] In some embodiments, when medium-pressure steam is introduced, the pressure of the medium-pressure boiler drum decreases, the saturation temperature of the feedwater in the medium-pressure boiler drum decreases, and the opening of the medium-pressure feedwater regulating valve is increased; conversely, the opening of the medium-pressure feedwater regulating valve is decreased.

[0031] In some embodiments, after the high-pressure steam intake is completed and the medium-pressure steam regulating valve is fully opened, medium-pressure steam intake is permitted only after the medium-pressure steam quality is deemed acceptable. The permitted conditions for medium-pressure steam intake are as follows:

[0032] (1) Main steam pressure > K1;

[0033] (2) The high-pressure main steam inlet is completed and the main steam regulating valve is fully open;

[0034] (3) High lateral opening < K2;

[0035] (4) Medium-pressure steam superheat > K3;

[0036] (5) No tripping condition triggered by the steam turbine;

[0037] (6) Liquid level in medium-pressure boiler drum < K4;

[0038] (7) The steam pressure at the outlet of the medium-pressure superheater is <K5;

[0039] Where K1 = HP + ΔHP, K4 = IPL + ΔIPL

[0040] HP: Minimum main steam pressure when medium-pressure steam is introduced;

[0041] △HP: Main steam pressure margin;

[0042] IPL: Target liquid level setpoint for the pressure vessel drum during unit operation;

[0043] △IPL: Liquid level margin in medium-pressure boiler drum;

[0044] K3: High lateral opening limit;

[0045] K4: Minimum superheat value for medium-pressure steam;

[0046] K5: Upper limit of steam pressure at the outlet of the medium-pressure superheater.

[0047] The control system and method for medium-pressure steam intake in a gas-fired steam combined cycle unit provided by the present invention maintains the liquid level of the medium-pressure boiler drum within a safe range by controlling the medium-pressure feedwater regulating valve, and achieves automatic control during medium-pressure steam intake by controlling the opening and closing of the medium-pressure steam regulating valve and the medium-pressure bypass regulating valve, thereby reducing misoperation. Attached Figure Description

[0048] To more clearly illustrate the technical solutions in this invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0049] Figure 1 This is a flowchart illustrating the control system provided by the present invention;

[0050] Figure 2 This is a schematic diagram of the fully automatic control process for medium-pressure steam inlet provided by the control method of the present invention;

[0051] Figure 3This is a schematic diagram of the adaptive control process of the feedforward loop of the medium-pressure water supply regulating valve in the control method provided by the present invention.

[0052] Figure 4 This is a schematic diagram of the control logic flow for determining the medium-pressure steam inlet conditions in the control method provided by the present invention.

[0053] Figure label:

[0054] 1-Medium-pressure water pump; 2-Superheater; 3-Medium-pressure bypass regulating valve; 4-Condenser; 5-Medium-pressure steam regulating valve; 6-Reheater; 7-Steam turbine; 8-Medium-pressure feedwater regulating valve; 9-Medium-pressure boiler drum. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0056] The following is combined Figures 1-4 This invention describes a control system and method for medium-pressure steam intake in a gas-fired combined cycle unit, comprising: a medium-pressure pump 1, a superheater 2, a medium-pressure bypass regulating valve 3, a condenser 4, a medium-pressure steam regulating valve 5, a reheater 6, and a steam turbine 7. The medium-pressure pump 1 is connected to the superheater 2 via pipelines. The outlet of the superheater 2 is connected to the condenser 4 and the medium-pressure cylinder of the steam turbine 7 via pipelines. The medium-pressure bypass regulating valve 3 is installed on the pipeline corresponding to the condenser 4. The medium-pressure steam regulating valve 5 is installed on the pipeline corresponding to the steam turbine 7. The reheater 6 is installed between the medium-pressure steam regulating valve 5 and the steam turbine 7.

[0057] The control system and method for medium-pressure steam intake in a gas-fired steam combined cycle unit provided by the present invention maintains the liquid level of the medium-pressure boiler drum 9 within a safe range by controlling the medium-pressure feedwater regulating valve 8, and achieves automatic control during medium-pressure steam intake by controlling the opening and closing of the medium-pressure steam regulating valve 5 and the medium-pressure bypass regulating valve 3, thereby reducing misoperation.

[0058] Preferably, a medium-pressure feedwater regulating valve 8 and a medium-pressure boiler drum 9 are sequentially arranged between the medium-pressure water pump 1 and the superheater 2, the exhaust port of the high-pressure cylinder of the steam turbine 7 is connected to the inlet of the reheater 6, and pressure gauges are installed on the steam inlet pipes of both the medium-pressure boiler drum 9 and the reheater 6.

[0059] Specifically, the heat source for the superheater 2 comes from the gas turbine.

[0060] The unit uses a medium-pressure feedwater pump to replenish water to the medium-pressure boiler drum 9, while simultaneously controlling the liquid level in the medium-pressure boiler drum 9 within a safe range via the medium-pressure feedwater regulating valve 8. The boiler feedwater, after being heated by waste heat from the gas turbine, undergoes steam-water separation to generate steam. This steam is then heated by the superheater 2 to form medium-pressure steam. Before the medium-pressure steam meets the inlet steam conditions, it is desuperheated and discharged to the condenser 4 via a medium-pressure bypass for recovery. Once the medium-pressure steam meets the inlet steam conditions, the medium-pressure bypass is closed while the medium-pressure steam regulating valve 5 is opened. The medium-pressure steam mixes with the exhaust gas from the high-pressure cylinder via the medium-pressure steam inlet valve, is heated by the reheater 6, and then enters the medium-pressure cylinder of the turbine 7, activating the turbine 7 to drive the generator and generate electricity.

[0061] The control method provided by the present invention is described below. The control method described below can be referred to in correspondence with the control system described above.

[0062] like Figure 2 As shown, a control method for medium-pressure steam inlet of a gas-fired steam combined cycle unit includes setting target setpoints for the medium-pressure bypass regulating valve and the medium-pressure steam regulating valve, setting the reheater inlet steam pressure as the target setpoint, setting an offset function for the target setpoint, and setting a rate limiting function for the opening commands of the medium-pressure bypass regulating valve and the medium-pressure steam regulating valve.

[0063] Specifically, once the medium-pressure steam inlet conditions are met, the medium-pressure bypass regulating valve and the medium-pressure steam regulating valve automatically activate their automatic functions. The reheater inlet steam pressure is set to the target setpoint for the medium-pressure bypass regulating valve and the medium-pressure steam regulating valve, and a bias function for the target setpoint is set. At the same time, a rate limit function is set for the opening command of the medium-pressure bypass regulating valve and the medium-pressure steam regulating valve, so as to achieve automatic and slow opening of the medium-pressure steam regulating valve and automatic and slow closing of the medium-pressure bypass regulating valve, realizing the automatic switching of the medium-pressure bypass regulating valve and the medium-pressure steam regulating valve, and the automatic inlet of medium-pressure steam.

[0064] in,

[0065] The actual value of the medium-pressure steam regulating valve is the reheater inlet steam pressure; the target setting value is the reheater inlet steam pressure minus the pressure offset value. That is, the target setting value is always lower than the actual value, and the medium-pressure steam regulating valve is gradually opened.

[0066] The actual value of the medium-pressure bypass regulating valve is the reheater inlet steam pressure; the target setpoint is the reheater inlet steam pressure plus the pressure offset value. That is, the target setpoint is always higher than the actual value, and the medium-pressure bypass regulating valve is gradually closed.

[0067] Right now,

[0068] PV1 = Steam_IP

[0069] SP1 = Max[Steam_IP - △P1, L]

[0070] PV2 = Steam_IP

[0071] SP2 = Steam_IP + △P2

[0072] In the formula:

[0073] PV1: Actual pressure control value of the medium-pressure steam regulating valve;

[0074] Steam_IP: Reheater inlet steam pressure;

[0075] SP1: Target setpoint for pressure control of medium-pressure steam regulating valve;

[0076] Max[]: Max value function;

[0077] △P1: Offset of the target setpoint for pressure control of the medium-pressure steam regulating valve;

[0078] L: Lower limit of the target setpoint for pressure control of the medium-pressure steam regulating valve;

[0079] PV1: Actual pressure control value of the medium-pressure bypass regulating valve;

[0080] SP1: Target setpoint for pressure control of medium-pressure bypass regulating valve;

[0081] △P1: Offset of the target setpoint for pressure control of the medium-pressure bypass regulating valve;

[0082] Preferably, in some exemplary embodiments, ΔP1 is 0.1MPa to 0.15MPa, L is 1.4MPa to 1.45MPa, and ΔP2 is 0.2MPa to 0.25MPa.

[0083] Meanwhile, during the automatic steam inlet process at medium pressure, the rate of the opening command output for the medium-pressure bypass regulating valve and the medium-pressure steam regulating valve is limited, causing the regulating valves to close or open slowly in the initial stage of medium-pressure steam inlet. This avoids imbalance in the pressure control regulation of the medium-pressure bypass regulating valve and the medium-pressure steam regulating valve, which could lead to sudden pressure changes in the medium-pressure boiler drum and consequently, untimely control of the medium-pressure boiler drum liquid level, affecting the safe and stable operation of the unit.

[0084] The output rate limit function for the valve opening command can be set from two aspects: the rate of change of medium-pressure boiler drum pressure and the opening degree of medium-pressure steam regulating valve.

[0085] (1) Rate limiting based on the rate of change of medium-pressure boiler drum pressure: During the process of medium-pressure steam intake, if the pressure of the medium-pressure boiler drum changes, the rate limiting function is triggered to slow down the steam intake. When the rate of change of medium-pressure boiler drum pressure exceeds a certain range, the valve opening command rate limit is set to 0% / s, that is, the medium-pressure steam regulating valve and the medium-pressure bypass regulating valve are kept at a fixed opening until the medium-pressure boiler drum pressure tends to stabilize. Then, the medium-pressure steam regulating valve continues to open slowly, the medium-pressure bypass regulating valve closes slowly, and medium-pressure steam intake begins.

[0086] (2) Rate restriction based on the opening of the medium-pressure steam regulating valve: At the beginning of the steam inlet stage, that is, when the medium-pressure steam inlet regulating valve is in the small opening range, the opening command rate restriction function is implemented. The smaller the opening of the medium-pressure steam regulating valve, the stronger the rate restriction; until the medium-pressure steam inlet is stable, the valve opening command rate restriction function is slowed down or released.

[0087] The pressure change rate of the medium-pressure boiler drum is:

[0088] △Boiler_P=Boiler_P-Boiler_PZ

[0089] Boiler_PRate=|△Boiler_P / Boiler_PZ|*100%

[0090] T = N * △t

[0091] In the formula,

[0092] Boiler_P: Optimized medium-pressure boiler drum pressure;

[0093] Boiler_PZ: Medium-pressure boiler drum pressure after a certain time delay T;

[0094] △Boiler_P: Pressure change in the medium-pressure boiler drum;

[0095] Boiler_PRate: Pressure change rate of the medium-pressure boiler drum;

[0096] △t: Controller scan cycle;

[0097] Preferably, in some exemplary embodiments, N is 25, and the gas turbine controller scanning period Δt is 40 milliseconds, i.e., T = N * Δt = 1 second.

[0098] The function of limiting the rate of the opening command output of the medium-pressure steam regulating valve is as follows:

[0099] F1(x) = Min[F11(x), F12(x)]

[0100] F11(x)=Max[0.25-Boiler_PRate*Boiler_PRat, 0]

[0101]

[0102] In the formula,

[0103] F1(x): Rate limiting function for the opening command output of the medium-pressure steam regulating valve;

[0104] OUT1: Output value of the opening command for the medium-pressure steam regulating valve;

[0105] Min[]: Minimum value function;

[0106] K1, T1: coefficients of the inertia function;

[0107] The function of limiting the rate of the opening command output of the medium-pressure bypass regulating valve is as follows:

[0108] F2(x) = MIN[F21(x), F22(x)]

[0109] F21(x) = △K1*F11(x)

[0110] F22(x)=△K2*F12(x)

[0111] In the formula,

[0112] F2(x): Rate limiting function for the opening command output of the medium-pressure bypass regulating valve;

[0113] △K1, △K2: Correction coefficients for the rate limiting function;

[0114] Preferably, in some exemplary embodiments, the coefficients of the inertia function K1 are 0.1 to 0.15, T1 is 5 to 10, ΔK1 is 0.5 to 0.8, and ΔK2 is 0.5 to 0.8.

[0115] Medium-pressure steam inlet automation: During the medium-pressure steam preparation process, the medium-pressure steam regulating valve and the medium-pressure bypass regulating valve are automatically controlled. The medium-pressure reheat inlet steam pressure is set as the target set value, and a pressure bias function is set. At the same time, the regulating valve opening command is set with a rate limit, so that the medium-pressure steam regulating valve automatically and slowly opens, and the medium-pressure bypass regulating valve automatically and slowly closes, thereby realizing automatic medium-pressure steam inlet.

[0116] like Figure 3 As shown, preferably, when medium-pressure steam is introduced, the pressure of the medium-pressure boiler drum decreases, the saturation temperature of the feedwater in the medium-pressure boiler drum decreases, and the opening of the medium-pressure feedwater regulating valve is increased; conversely, the opening of the medium-pressure feedwater regulating valve is decreased.

[0117] Specifically, when medium-pressure steam is introduced, the pressure in the medium-pressure boiler drum drops rapidly for a short period when the medium-pressure feedwater regulating valve opens. This reduces the saturation temperature of the feedwater in the boiler drum, generating more saturated steam. Consequently, the volume of steam bubbles below the water surface increases, causing the water level to rise rapidly and creating a false high water level. In this case, the feedwater flow should be increased to lower the water temperature in the boiler drum, reducing the volume of steam bubbles below the water surface and lowering the water level to eliminate the false high water level. Conversely, the feedwater flow should be reduced to eliminate the false low water level. Based on the pressure change in the boiler drum, a feedforward loop correction is applied to the medium-pressure boiler drum feedwater regulating valve to improve its regulation rate under special operating conditions such as medium-pressure steam introduction. This allows for rapid response in opening or closing the regulating valve to maintain a stable water level in the boiler drum. Simultaneously, during medium-pressure steam introduction, a target water level setpoint offset function is set for the medium-pressure feedwater regulating valve to increase the safety margin for boiler drum water level control.

[0118] During the automatic steam inlet of medium-pressure steam, the target liquid level offset of the medium-pressure feedwater regulating valve is F3(x) = ΔL. Once the steam inlet of medium-pressure steam is stable or completed, the target liquid level offset function of the medium-pressure feedwater regulating valve is canceled, that is, F3(x) = 0 at this time.

[0119] SP3 = SP - F3(x)

[0120] In the formula,

[0121] SP3: Target liquid level setting value for medium-pressure water supply regulating valve;

[0122] SP: Target liquid level setting value of the medium-pressure feedwater regulating valve during normal unit operation;

[0123] F3(x): Target liquid level offset of the medium-pressure water supply regulating valve;

[0124] Preferably, in some exemplary embodiments, △L is 10mm to 20mm.

[0125] Feedforward control of medium-pressure water supply regulating valve:

[0126] FF3 = F4(x)

[0127]

[0128] In the formula,

[0129] FF3: Feedforward amount of medium-pressure water supply regulating valve;

[0130] △Boiler_P: Pressure change in the medium-pressure boiler drum;

[0131] K2, T2: coefficients of the inertia function;

[0132] Preferably, in some exemplary embodiments, the coefficients K2 of the inertial function are 15 to 20, and T2 is 5 to 10.

[0133] Adaptive control of feedforward loop for medium-pressure feedwater regulating valve: The feedforward loop function of medium-pressure feedwater regulating valve is set according to the rate of change of medium-pressure boiler drum pressure. When the medium-pressure boiler drum pressure changes, the medium-pressure feedwater regulating valve is quickly adjusted, which improves the unit's regulation capability under special operating conditions such as medium-pressure steam inlet and rapid load disturbance, and ensures that the water level parameter of medium-pressure boiler drum is controlled within a safe range throughout the process.

[0134] like Figure 4 As shown, preferably, after the high-pressure steam is introduced and the medium-pressure steam regulating valve is fully opened, the medium-pressure steam is allowed to be introduced only after the medium-pressure steam quality is qualified.

[0135] Specifically, based on the actual operating conditions of the unit and the steam intake requirements, complete conditions for allowing medium-pressure steam intake are set, which serve as the basis for enabling automatic medium-pressure steam intake.

[0136] After high-pressure steam is introduced and the intermediate-pressure steam regulating valve is fully open, intermediate-pressure steam can be introduced once the quality of the intermediate-pressure steam is deemed acceptable. To ensure the safe and stable operation of the unit during the steam introduction process, certain limits are set for the unit's main steam pressure, intermediate-pressure superheater outlet steam pressure, and intermediate-pressure boiler drum liquid level. The permissible conditions for intermediate-pressure steam introduction include, but are not limited to, the following:

[0137] Permissible conditions for medium-pressure steam inlet (all of the following conditions must be met):

[0138] (1) Main steam pressure > K1;

[0139] (2) The high-pressure main steam inlet is completed, and the medium-pressure steam regulating valve is fully open;

[0140] (3) High lateral opening < K2;

[0141] (4) Medium-pressure steam superheat > K3;

[0142] (5) No tripping condition triggered by the steam turbine;

[0143] (6) Liquid level in medium-pressure boiler drum < K4;

[0144] (7) The steam pressure at the outlet of the medium-pressure superheater is <K5;

[0145] Where K1 = HP + ΔHP, K4 = IPL + ΔIPL

[0146] HP: Minimum main steam pressure when medium-pressure steam is introduced;

[0147] △HP: Main steam pressure margin;

[0148] IPL: Target liquid level setpoint for the pressure vessel drum during unit operation;

[0149] △IPL: Liquid level margin in medium-pressure boiler drum;

[0150] K3: High lateral opening limit;

[0151] K4: Minimum superheat value for medium-pressure steam;

[0152] K5: Maximum steam pressure limit at the outlet of the intermediate-pressure superheater;

[0153] Preferably, in some exemplary embodiments, ΔHP is 0.05MPa to 0.1MPa, ΔIPL is 50mm to 100mm, K2 is 15% to 20%, K3 is 40℃ to 45℃, and K5 is 1.4MPa to 1.5MPa.

[0154] Automatic judgment of medium-pressure steam inlet conditions: Based on the actual operating conditions of the unit and the steam inlet requirements, complete allowable conditions for medium-pressure steam inlet are set, which serve as the basis for the automatic inlet of medium-pressure steam.

[0155] Meanwhile, to improve the flexibility of judging the allowable conditions for medium-pressure steam inlet, a manual judgment function for medium-pressure steam inlet conditions has been added to the existing automatic judgment function.

[0156] Medium-pressure steam can be introduced once the conditions for medium-pressure steam inlet are met, or after manual confirmation.

[0157] The device embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Those skilled in the art can understand and implement this without any creative effort.

[0158] Through the above description of the embodiments, those skilled in the art can clearly understand that each embodiment can be implemented by means of software plus necessary general-purpose hardware platforms, and of course, it can also be implemented by hardware. Based on this understanding, the above technical solutions, in essence or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product can be stored in a computer-readable storage medium, such as ROM / RAM, magnetic disk, optical disk, etc., and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute the methods described in the various embodiments or some parts of the embodiments.

[0159] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for controlling the intake of medium-pressure steam in a gas-fired combined cycle unit, characterized in that, The method is applied to the control system of medium-pressure steam inlet in a gas-fired combined cycle unit. The control system includes: a medium-pressure water pump, a superheater, a medium-pressure bypass regulating valve, a condenser, a medium-pressure steam regulating valve, a reheater, and a steam turbine. The medium-pressure water pump is connected to the superheater via pipelines. The outlet of the superheater is connected to the condenser and the medium-pressure cylinder of the steam turbine via pipelines. The medium-pressure bypass regulating valve is located on the pipeline corresponding to the condenser. The medium-pressure steam regulating valve is located on the pipeline corresponding to the steam turbine. The reheater is located between the medium-pressure steam regulating valve and the steam turbine. A medium-pressure feedwater regulating valve and a medium-pressure boiler drum are sequentially arranged between the medium-pressure water pump and the superheater. The heat source for the superheater is the gas turbine. The exhaust port of the high-pressure cylinder of the steam turbine is connected to the inlet of the reheater. Pressure gauges are installed on the steam inlet pipes of both the medium-pressure boiler drum and the reheater. The method includes: setting target setpoints for the medium-pressure bypass regulating valve and the medium-pressure steam regulating valve, setting the reheater inlet steam pressure to the target setpoint, setting a bias function for the target setpoint, and setting a rate limiting function for the opening command of the medium-pressure bypass regulating valve and the medium-pressure steam regulating valve. When the actual value of the intermediate pressure steam regulating valve is the reheater inlet steam pressure, and the target setting value is the reheater inlet steam pressure minus the pressure offset value, the target setting value is always lower than the actual value of the intermediate pressure steam regulating valve, and the intermediate pressure steam regulating valve is gradually opened. When the actual value of the medium-pressure bypass regulating valve is the reheater inlet steam pressure, and the target setting value is the reheater inlet steam pressure plus the pressure offset value, the target setting value is always higher than the actual value of the medium-pressure steam regulating valve, and the medium-pressure bypass regulating valve is gradually closed. Right now, PV1=Steam_IP SP1 = Max[Steam_IP - △P1, L] PV2=Steam_IP SP2 = Steam IP + △P2 In the formula: PV1: Actual pressure control value of the medium-pressure steam regulating valve; Steam_IP: Reheater inlet steam pressure; SP1: Target setpoint for pressure control of medium-pressure steam regulating valve; Max[]: Max value function; △P1: Offset of the target setpoint for pressure control of the medium-pressure steam regulating valve; L: Lower limit of the target setpoint for pressure control of the medium-pressure steam regulating valve; PV2: Actual pressure control value of the medium-pressure bypass regulating valve; SP2: Target setpoint for pressure control of medium-pressure bypass regulating valve; △P2: Target setpoint offset for pressure control of the medium-pressure bypass regulating valve.

2. The method for controlling the intake of medium-pressure steam in a gas-fired combined cycle unit according to claim 1, characterized in that, During the automatic steam intake process of medium-pressure steam, when the pressure of the medium-pressure boiler drum changes, the rate limiting function is triggered to slow down the steam intake. When the rate of change of the medium-pressure boiler drum pressure exceeds a certain range, the valve opening command rate limit is set to 0% / s, maintaining the medium-pressure steam regulating valve and the medium-pressure bypass regulating valve at a fixed opening until the steam drum pressure tends to stabilize. Then, the medium-pressure steam regulating valve continues to open slowly, and the medium-pressure bypass regulating valve slowly closes, starting the medium-pressure steam intake. During the initial steam inlet stage, when the medium-pressure steam inlet regulating valve is in the small opening range, the opening command rate limiting function is applied. The smaller the opening of the medium-pressure steam regulating valve, the stronger the rate limiting function is. The valve opening command rate limiting function is slowed down or released after the medium-pressure steam inlet stabilizes.

3. The method for controlling the intake of medium-pressure steam in a gas-fired combined cycle unit according to claim 1, characterized in that, When medium-pressure steam is introduced, the pressure in the medium-pressure boiler drum decreases, the saturation temperature of the feedwater in the medium-pressure boiler drum decreases, and the opening of the medium-pressure feedwater regulating valve is increased; conversely, the opening of the medium-pressure feedwater regulating valve is decreased.

4. The method for controlling the intake of medium-pressure steam in a gas-fired combined cycle unit according to claim 1, characterized in that, After the high-pressure steam is introduced and the medium-pressure steam regulating valve is fully opened, and the medium-pressure steam quality is qualified, medium-pressure steam is allowed to be introduced. The conditions for allowing medium-pressure steam to be introduced are as follows: (1) Main steam pressure > K1; (2) The high-pressure main steam inlet is completed and the main steam regulating valve is fully open; (3) High lateral opening < K2; (4) Medium-pressure steam superheat > K3; (5) No tripping condition triggered by the steam turbine; (6) Liquid level in medium-pressure boiler drum < K4; (7) The steam pressure at the outlet of the medium-pressure superheater is <K5; Where K1 = HP + ΔHP, K4 = IPL + ΔIPL HP: Minimum main steam pressure when medium-pressure steam is introduced; △HP: Main steam pressure margin; IPL: Target liquid level setpoint for the pressure vessel drum during unit operation; △IPL: Liquid level margin in medium-pressure boiler drum; K3: High lateral opening limit; K4: Minimum superheat value for medium-pressure steam; K5: Upper limit of steam pressure at the outlet of the medium-pressure superheater.

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