No.0 high-pressure heater dynamic modeling and depth flexible peak shaving performance evaluation method based on Modelica

Abstract

The invention discloses a No.0 high-pressure heater dynamic modeling and depth flexible peak regulation performance evaluation method based on Modelica. The method comprises the following steps: establishing a dynamic coupling model of a subcritical coal-fired unit; parameters of the model are set, different load working conditions are simulated, and key operation data are obtained; real-time dynamic simulation is carried out, and the influence of commissioning and removal of the No.0 high-pressure heater under different load working conditions on unit performance is evaluated; and the response performance of the No.0 high-pressure heater in the frequency modulation process is deeply analyzed, simulation results are integrated, the operation effect is evaluated, and an optimized control strategy is provided. According to the method, through dynamic simulation analysis, the frequency modulation capability and the heat economy of the unit are optimized, and the flexibility of the unit under the deep peak regulation working condition is improved. Performance evaluation indexes provide scientific optimization basis and control strategy suggestions for deep peak regulation of the coal-fired unit. The dynamic modeling and evaluation method can comprehensively analyze various performance numbers of the unit in the flexible peak regulation process, and has good theoretical value and practical application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of power system and power engineering, and in particular relates to a Modelica-based No. 0 high-voltage power converter dynamic modeling and deep flexible peak-shaving performance evaluation method. Background Art

[0002] With the expansion of renewable energy access, coal-fired units are facing the need for deep peak regulation. Under deep peak regulation conditions, the low-load operation of coal-fired units usually causes the boiler feed water temperature to drop, affecting the boiler thermal efficiency and adversely affecting the operation of the SCR denitrification system. To address this problem, some power plants have added No. 0 high-pressure heaters to increase the boiler feed water temperature and optimize the unit's operating performance during deep peak regulation.

[0003] However, existing research focuses on performance analysis under steady-state conditions, lacking modeling and performance evaluation of No. 0 high-pressure booster under dynamic conditions. In particular, there are still deficiencies in the quantitative analysis of the No. 0 high-pressure booster's deep peak-shaving capability. Therefore, there is an urgent need for a modeling method based on dynamic simulation that can deeply analyze the operating characteristics of No. 0 high-pressure booster and evaluate its performance under deep flexible peak-shaving conditions. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a method for dynamic modeling of No. 0 high-pressure heater and deep flexible peak-shaving performance evaluation based on Modelica. The purpose is to optimize the frequency regulation capability and thermal economy of the unit through dynamic simulation analysis, and improve its flexibility under deep peak-shaving conditions.

[0005] Technical solution: A Modelica-based method for dynamic modeling and deep flexible peak-shaving performance evaluation of No. 0 high-pressure heating comprises the following steps:

[0006] Step 1: Based on Modelica language, a dynamic coupling model of a 300MW subcritical coal-fired unit is established;

[0007] Step 2: Set the model parameters and simulate different load conditions to obtain key operating data;

[0008] Step 3: Real-time dynamic simulation to evaluate the impact of the commissioning and removal of the No. 0 high-pressure heater on the unit performance under different load conditions;

[0009] Step 4: In-depth analysis of the response performance of the No. 0 high-voltage heater during frequency modulation, especially the response speed and power regulation capability when the load changes;

[0010] Step 5: Integrate the simulation results, evaluate the operating performance of the No. 0 high-pressure heater, and propose an optimized control strategy.

[0011] Furthermore, in step one, the 300MW subcritical coal-fired unit includes a steam turbine, a boiler heating surface and a steam turbine heat recovery system; the steam turbine includes a high-pressure cylinder, a medium-pressure cylinder and a low-pressure cylinder; the boiler heating surface includes a water-cooled wall, a superheater, a reheater and an economizer; the steam turbine heat recovery system includes three high-pressure heaters, four low-pressure heaters, a deaerator and a No. 0 high-pressure heater.

[0012] Furthermore, step one is specifically as follows: modeling each component of the above-mentioned unit based on the Modelica language, focusing on describing the dynamic interaction process between the high, medium and low pressure cylinders of the steam turbine and the heating surface of the boiler;

[0013] Based on the steam turbine part, the dynamic simulation of the high-pressure cylinder, intermediate-pressure cylinder and low-pressure cylinder is described by the following physical equations:

[0014]

[0015] Where λ is a dimensionless constant; k is the adiabatic index; ε n is the pressure ratio of the nozzle inlet and outlet; ε c is the critical pressure ratio; A is the area of ​​the nozzle interface; ρ 0 is the steam density at the nozzle outlet; G, G 1 are the steam flow through the stage under design conditions and variable conditions respectively; p o 、p o1 p is the pressure before and after the stage group under variable working conditions; z 、p z1 T is the pressure after the stage group under variable working conditions; 0 , T 01 It is the temperature before and after the stage group under variable working conditions.

[0016] In the regenerative system, the dynamic performance of each regenerative heater is described by the following physical equations:

[0017]

[0018] Q h =βA h (T h -T p )

[0019] Q s =α s A s (T s -T p )

[0020] Where, T m is the temperature of the fluid in the tube; T w1 , T w2 are the inlet and outlet water temperatures of the heater respectively; Q wConvective heat transfer in the tube; α w is the heat transfer coefficient; A w is the heat transfer area in the tube; C m is the specific heat capacity of the metal tube; Q h is the heat brought by the previous level of hydrophobicity; β is the heat transfer coefficient on the hydrophobic side; A h is the heat exchange area on the drain side; T h is the hydrophobic temperature; Q s Extraction steam condensation heat exchange; α s is the heat transfer coefficient; A s is the heat exchange area of ​​the tube in the condensation zone; T s is the saturation temperature corresponding to the steam side pressure of the heater; T P is the pipe wall temperature.

[0021] For the main heating surface of the boiler, the heat exchange between the high-temperature flue gas and the working fluid can be described by the following physical equation:

[0022]

[0023] In the formula, are the flue gas mass flow rates flowing into and out of the i-th section of the shell, respectively; m g,i is the mass of the flue gas in section i on the shell side; h g,i is the specific enthalpy of the flue gas in section i on the shell side; h gin,i 、h gout,i are the specific enthalpy of the flue gas flowing into and out of the i-th section of the shell, respectively; Q g,i The heat released by the flue gas to the metal pipe sideways; are the water vapor mass flow rates flowing into and out of section i on the tube side, respectively; m s,i is the mass of water vapor in section i on the shell side; h s,i is the specific enthalpy of water vapor in section i on the shell side; Q s,i h is the heat released from the metal pipe wall to the working fluid; sin,i 、h sout,i are the specific enthalpies of water vapor flowing into and out of section i on the tube side, respectively.

[0024] The key component to achieve variable load response is the steam extraction valve, which is used to adjust the steam extraction amount of the No. 0 high-pressure heater by adjusting the valve opening of the No. 0 high-pressure heater steam extraction pipeline and adjust the process flow;

[0025] After constructing the physical equations of each component, the Modelica language is used to modularize the components. In the Dymola simulation platform, the high-pressure cylinder, medium-pressure cylinder, low-pressure cylinder of the steam turbine, each level of regenerative heaters and the heating surfaces of the boiler are connected in sequence to form a complete dynamic coupling simulation model of the subcritical coal-fired unit.

[0026] Furthermore, the flow calculation formula of the regulation process is:

[0027]

[0028] Where FlowChar(θ) is the flow characteristic function of the valve, which depends on the valve opening θ; ρ is the fluid density; p f is the fluid inlet pressure; is the pressure drop ratio; x s is the saturation pressure drop ratio; dp is the pressure difference; A v,internal is the effective flow area of ​​the valve; is the compression factor.

[0029] Furthermore, in step 2, the load conditions include typical loads of 75% THA and 50% THA; key parameters of the unit's flue gas flow, flue gas temperature and steam flow are set; and the inlet and outlet rated pressures of each cylinder of the turbine are optimized and adjusted.

[0030] Furthermore, the optimization adjustment of the inlet and outlet rated pressures of each cylinder of the steam turbine is specifically as follows: by adjusting the intake pressure of the high-pressure cylinder, the effective expansion of the steam in the high-pressure cylinder is ensured, thereby maximizing its power output; by gradually adjusting the intake pressure and outlet pressure of the intermediate-pressure cylinder and the low-pressure cylinder, the flow of steam in each stage is ensured to reach the optimal state, thereby enhancing the overall performance of the unit; the inlet and outlet pressures of the regenerative heater are adjusted to ensure that the reheating effect of the steam is optimized.

[0031] Furthermore, step three is specifically as follows: according to the dynamic coupling model, the operation and removal process of the No. 0 high-pressure heater is simulated through the Dymola dynamic simulation platform, and the opening of the regulating valve is controlled to achieve a smooth change in the steam flow rate; the regulating valve is connected to the controller, and the opening of the regulating valve is gradually adjusted according to the control input signal to control the change in the steam flow rate;

[0032] To evaluate the thermal economy of the unit, taking the heat rate of the steam turbine as an example, the calculation formula is as follows:

[0033]

[0034] Q in =D 0 (H 0 -H main )+D zr (H zr -H zl )

[0035] Where, q is the heat rate of the steam turbine; Q in The heat input to the steam turbine system; P e is the generator output power; D 0 is the main steam flow rate; H 0is the main steam enthalpy; H main is the enthalpy of the boiler main feed water; D zr H is the hot end flow rate of the reheat steam pipeline; zr is the hot end enthalpy of reheat steam; H zl is the cold end enthalpy of reheat steam;

[0036] At the same time, the flue gas temperature at the SCR inlet is monitored in real time to evaluate the regulating effect of the No. 0 high-pressure heater on the flue gas temperature; the changes in the flue gas temperature are recorded by gradually adjusting the steam extraction valve of the No. 0 high-pressure heater.

[0037] Furthermore, step four is specifically as follows: using dynamic simulation technology to quickly close the operation of the No. 0 high-pressure heater steam extraction valve to observe and record the dynamic response of the unit under sudden load changes; setting the regulating valve to be connected to the step signal controller so that the valve gradually changes from a fully open state to a fully closed state within 5-10s. During the adjustment process, the changes in the parameters of the boiler feed water temperature and the unit load are monitored in real time. During load fluctuations, the power regulation capability of the unit is a key indicator for evaluating its performance. By quantitatively analyzing the power variation amplitude, the flexibility and stability of the No. 0 high-pressure heater in responding to sudden load changes are determined.

[0038] Furthermore, step five is as follows: based on the simulation data, comprehensively evaluate the overall operating effect of the No. 0 high-pressure heater, and draw different deep peak-shaving performance evaluation diagrams according to different analysis needs, that is, under different unit load conditions, display different performance indicators on the vertical axis, including frequency regulation capability, thermal economy and flue gas temperature.

[0039] Beneficial effects: Compared with the prior art, the present invention has the following significant advantages:

[0040] The present invention constructs a dynamic coupling model of a subcritical coal-fired unit covering boilers, steam turbines and steam turbine reheat systems through a dynamic modeling method based on Modelica. Compared with traditional problem analysis, the present invention can more accurately reflect the dynamic behavior of the unit under deep peak load regulation conditions, and can capture the impact of the commissioning and removal of the No. 0 high-pressure heater on various performance indicators of the unit (such as boiler feed water temperature and turbine heat rate) in real time.

[0041] In addition, the present invention proposes a series of performance evaluation indicators, including frequency regulation capability, thermal economy and SCR denitrification performance, which provide scientific optimization basis and control strategy suggestions for deep peak regulation of coal-fired units. The dynamic modeling and evaluation method of the system can comprehensively analyze the various performance numbers of the unit during the flexible peak regulation process, and has good theoretical value and practical application prospects. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] Figure 1A schematic diagram of a typical coal-fired unit and control variables provided by the present invention;

[0043] Figure 2 A schematic diagram of load regulation by adjusting flue gas flow and temperature provided by the present invention;

[0044] Figure 3 A schematic diagram of the control of the No. 0 high pressure steam extraction valve provided by the present invention;

[0045] Figure 4 A curve diagram showing the effect of the No. 0 high pressure heater provided by the present invention on the SCR inlet flue gas temperature when put into operation and removed at different loads;

[0046] Figure 5 It is a schematic diagram of the effect of cutting off No. 0 high pressure heater on the unit under the 75% THA condition provided by the present invention. DETAILED DESCRIPTION

[0047] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0048] The present invention discloses a Modelica-based No. 0 high-pressure heating dynamic modeling and a method for evaluating its deep flexible peak-shaving performance, comprising the following steps:

[0049] Step 1: Based on Modelica language, a dynamic coupling model of a 300MW subcritical coal-fired unit is established;

[0050] The structure of a typical 300MW subcritical coal-fired unit used in the present invention is as follows: Figure 1 As shown, the unit includes a steam turbine (high-pressure cylinder, medium-pressure cylinder, low-pressure cylinder), boiler heating surface (water-cooled wall, superheater, reheater and economizer) and a steam turbine heat recovery system. The heat recovery system is based on the conventional three highs (high-pressure heater), four lows (low-pressure heater) and deaerator, and an additional No. 0 high-pressure heater is added.

[0051] In this step, the components of the above-mentioned unit are modeled based on the Modelica language, focusing on describing the dynamic interaction process between the high, medium and low pressure cylinders of the turbine and the heating surface of the boiler.

[0052] Based on the steam turbine part, the dynamic simulation of the high-pressure cylinder, intermediate-pressure cylinder and low-pressure cylinder is described by the following physical equations:

[0053]

[0054] Where λ is a dimensionless constant; k is the adiabatic index; ε n is the pressure ratio of the nozzle inlet and outlet; ε c is the critical pressure ratio; A is the area of ​​the nozzle interface; ρ 0 is the steam density at the nozzle outlet; G, G1 are the steam flow through the stage under design conditions and variable conditions respectively; p 0 、p 01 p is the pressure before and after the stage group under variable working conditions; z 、p z1 It is the pressure after the front and rear stages under variable working conditions.

[0055] In the regenerative system, the dynamic performance of each regenerative heater is described by the following physical equations:

[0056]

[0057] Q h =βA h (T h -T p )

[0058] Q s =α s A s (T s -T p )

[0059] Where, T m is the temperature of the fluid in the tube; T w1 , T w2 are the inlet and outlet water temperatures of the heater respectively; Q w Convective heat transfer in the tube; α w is the heat transfer coefficient; A w is the heat exchange area in the tube; C m is the specific heat capacity of the metal tube; Q h is the heat brought by the previous level of hydrophobicity; β is the heat transfer coefficient on the hydrophobic side; A h is the heat exchange area on the drain side; T h is the hydrophobic temperature; Q s Extraction steam condensation heat exchange; α s is the heat transfer coefficient; A s is the heat exchange area of ​​the tube in the condensation zone; T s is the saturation temperature corresponding to the steam side pressure of the heater; T P is the pipe wall temperature.

[0060] For the main heating surface of the boiler, the heat exchange between the high-temperature flue gas and the working fluid can be described by the following physical equation:

[0061]

[0062] In the formula, are the flue gas mass flow rates flowing into and out of the i-th section of the shell, respectively; m g,i is the mass of the flue gas in section i on the shell side; h g,i is the specific enthalpy of the flue gas in section i on the shell side; h gin,i、h gout,i are the specific enthalpy of the flue gas flowing into and out of the i-th section of the shell, respectively; Q g,i The heat released by the flue gas to the metal pipe sideways; are the water vapor mass flow rates flowing into and out of section i on the tube side, respectively; m s,i is the mass of water vapor in section i on the shell side; h s,i is the specific enthalpy of water vapor in section i on the shell side; Q s,i h is the heat released from the metal pipe wall to the working fluid; sin,i 、h sout,i are the specific enthalpies of water vapor flowing into and out of section i on the tube side, respectively.

[0063] After constructing the physical equations of each component, the Modelica language is used to modularize each component. Figure 1 The model shown connects the high-pressure cylinder, medium-pressure cylinder, low-pressure cylinder of the steam turbine, each stage of regenerative heaters and each heating surface of the boiler in sequence to form a complete dynamic coupling simulation model of a subcritical coal-fired unit.

[0064] Step 2: Set parameters for the model and obtain operating data under different load conditions;

[0065] According to the actual situation of the 300MW unit, the typical loads of 75% THA and 50% THA are selected, and the key parameters of the unit such as flue gas flow, flue gas temperature and steam flow are set to accurately simulate the performance of the unit under different loads. Usually, in actual operation, the load regulation of the unit is mainly achieved by adjusting the coal supply and water supply. However, in this model, since the coal supply cannot be directly adjusted, the steps adopt the method of adjusting the flue gas flow and flue gas temperature to indirectly reflect the load changes. For details, please see the attached Figure 2 shown.

[0066] Furthermore, in addition to the flue gas flow and temperature, the rated inlet and outlet pressures of each cylinder of the steam turbine need to be optimized and adjusted. When setting the load, the inlet and outlet pressures of the high-pressure cylinder are one of the key parameters. By adjusting the intake pressure of the high-pressure cylinder, the effective expansion of steam in the high-pressure cylinder can be ensured, thereby maximizing its power output. According to different load conditions, the inlet and outlet pressures are optimized to match the actual operating data to achieve ideal thermal performance.

[0067] Furthermore, the inlet and outlet pressures of the intermediate pressure cylinder and the low pressure cylinder directly affect the flow characteristics of the steam and the overall efficiency of the system. Under the load conditions of 75%THA and 50%THA, the inlet and outlet pressures of the two cylinders were adjusted accordingly to optimize the steam flow and improve its thermal efficiency. Specifically, by gradually adjusting the inlet and outlet pressures, the steam flow at each stage can be ensured to reach the optimal state, thereby enhancing the overall performance of the unit.

[0068] The regenerative heater plays a vital role in the entire thermal cycle. To this end, the inlet and outlet pressures of the regenerative heater are appropriately adjusted under different load conditions to ensure that the steam reheating effect is optimized. This not only helps to improve the thermal economy of the unit, but also reduces the fuel consumption of the unit to a certain extent and achieves higher operating efficiency.

[0069] Through the above adjustment steps, the operating status of the unit under different load conditions can be more comprehensively simulated. On the Dymola simulation platform, these adjustments make it possible to obtain real-time operating data such as flue gas temperature, pressure and feed water flow at the boiler inlet and outlet. These data are the basis for subsequent simulation analysis, ensuring that the operating characteristics of the No. 0 high-pressure heater under different operating conditions can be accurately simulated.

[0070] This step involves the precise setting of the model input parameters, and the acquisition of real-time operating data through sensors and data acquisition systems, including but not limited to flue gas temperature, pressure, mass flow, feed water temperature, etc. Since traditional load regulation methods (such as adjusting the coal supply) cannot be directly implemented in this simulation, the flue gas volume and temperature are adjusted to indirectly reflect the load changes. This method can accurately capture the dynamic response of the system under different loads and obtain key working fluid parameters such as flue gas temperature and steam flow.

[0071] Step 3: Real-time dynamic simulation to evaluate the impact of the commissioning and removal of No. 0 high-pressure booster on the unit performance under different load conditions;

[0072] Using the model set in step 2, the commissioning and removal process of No. 0 high pressure heater is simulated through the dynamic simulation platform. The implementation of dynamic simulation is to control the opening of the regulating valve through the Dymola dynamic simulation platform to achieve smooth changes in steam flow. The regulating valve is connected to the controller, and the opening of the regulating valve is gradually adjusted according to the control input signal to control the change of steam flow. This control strategy can avoid system instability caused by sudden changes in regulation and ensure the smooth commissioning and removal process of No. 0 high pressure heater. Figure 3 The connection between the controller and the regulating valve is demonstrated, explaining how the regulating valve gradually adjusts the valve opening according to the control input signal, thereby achieving smooth control of the steam flow.

[0073] Furthermore, in order to evaluate the improvement of the overall performance of the unit by the No. 0 high pressure heater, simulation analysis under different working conditions was carried out. The impact of the removal of the No. 0 high pressure heater on the boiler feed water temperature, turbine heat rate and SCR inlet flue gas temperature was studied, and the improvement of the overall performance of the unit by the No. 0 high pressure heater was comprehensively evaluated.

[0074] In order to further evaluate the thermal economy of the unit, taking the heat rate of the steam turbine as an example, the calculation formula is as follows:

[0075]

[0076] Q in =D 0 (H 0 -H main )+D zr (H zr -H zl )

[0077] Where, q is the heat rate of the steam turbine; Q in The heat input to the steam turbine system; P e is the generator output power; D 0 is the main steam flow rate; H 0 is the main steam enthalpy; H main is the enthalpy of the boiler main feed water; D zr H is the hot end flow rate of the reheat steam pipeline; zr is the hot end enthalpy of reheat steam; H zl is the cold end enthalpy of reheat steam.

[0078] The dynamic simulation also involves real-time monitoring of the flue gas temperature at the SCR inlet to evaluate the regulating effect of the No. 0 high-pressure heater on the flue gas temperature. Under different load conditions (such as 75% THA and 50% THA), the steam extraction valve of the No. 0 high-pressure heater is gradually adjusted to record the changes in the flue gas temperature. The simulation results show that the commissioning of the No. 0 high-pressure heater significantly increases the flue gas temperature at the SCR inlet, ensuring that the SCR system can still maintain efficient denitrification performance when operating at low load.

[0079] This simulation analysis provides basic data for the performance optimization of the SCR denitrification system and verifies the positive impact of the No. 0 high pressure heater on environmental performance under deep peak load conditions. By increasing the flue gas temperature, the generation of emissions is effectively reduced, allowing the unit to meet environmental emission standards. Figure 4 The influence curve of the commissioning and removal of No. 0 high pressure heater under different loads on the flue gas temperature at the SCR inlet is shown, providing an important technical basis for further optimizing system operation.

[0080] After the load regulation simulation is completed, the dynamic simulation analysis of the commissioning and removal of No. 0 high-pressure booster is started. Furthermore, by analyzing the impact of No. 0 high-pressure booster on boiler feed water temperature, turbine heat rate and SCR inlet flue gas temperature under different operating conditions (such as 75% THA and 50% THA), the improvement of No. 0 high-pressure booster on the overall performance of the unit can be fully evaluated. Through this stage of simulation, the specific contribution of No. 0 high-pressure booster under different loads will be gradually revealed, and its operating advantages under deep peak-shaving conditions will be analyzed.

[0081] Step 4: In-depth analysis of the response performance of No. 0 high-voltage booster during frequency modulation, especially the response speed and power regulation capability when the load changes;

[0082] In order to deeply analyze the response performance of No. 0 high-pressure booster during frequency modulation, especially the response speed and power regulation capability when the load changes, dynamic simulation technology is used for research. In the research experiment, the operation of quickly closing the No. 0 high-pressure booster steam extraction valve is implemented to observe and record the dynamic response of the unit under load mutation.

[0083] Taking the 75% THA load condition set in step 2 as an example, the control strategy for adjusting the No. 0 high-pressure steam extraction valve is as follows: set the regulating valve to be connected to the step signal controller so that the valve gradually changes from a fully open state to a fully closed state within 5 seconds. During the adjustment process, the changes in parameters such as the boiler feed water temperature and the unit load are monitored in real time. By quickly closing the steam extraction valve, it was found that under a load of 75% THA, after quickly cutting off the No. 0 high-pressure heater, the unit power increased from 235.6MW to 245.4MW, an increase of 9.8MW. According to the simulation results, it can be similar to the attached Figure 5 The power and feed water temperature change curves of the unit are plotted in the format of . This can intuitively show the amplitude of power change and its response speed. The analysis of the power curve not only provides the dynamic characteristics of the unit under load changes, but also reveals the ability of the No. 0 high-pressure booster in the frequency modulation process.

[0084] During load fluctuations, the power regulation capability of the unit is a key indicator for evaluating its performance. By quantitatively analyzing the power variation amplitude, the flexibility and stability of the No. 0 high-pressure booster in dealing with sudden load changes can be determined. This analysis helps to identify the strengths and weaknesses of the unit in the frequency regulation process and provide a basis for subsequent optimization solutions.

[0085] After reaching a preliminary conclusion, the corresponding performance of No. 0 high-pressure booster during the frequency modulation process is analyzed in depth, especially the power regulation capability when the load changes. The corresponding performance of No. 0 high-pressure booster during the load change is further evaluated through dynamic simulation during the frequency modulation process. This process quantitatively evaluates the contribution of No. 0 high-pressure booster to power regulation by quickly adjusting the steam extraction valve of No. 0 high-pressure booster and observing the power change of the unit. Under different load conditions, the impact on power stability and rapid response capability is evaluated to ensure that No. 0 high-pressure booster can provide sufficient flexibility and stability during the frequency modulation process.

[0086] Step 5: Comprehensively evaluate the operating effect of No. 0 high pressure heater and propose an optimized control strategy;

[0087] Based on the above simulation data, the overall operation effect of No. 0 high pressure heater is comprehensively evaluated. According to different analysis requirements, different deep peak load performance evaluation diagrams are drawn, that is, different performance indicators (such as frequency regulation capability, thermal economy, flue gas temperature, etc.) are displayed on the vertical axis under different unit load conditions.

[0088] Through these performance evaluation diagrams, we can intuitively observe the impact of the No. 0 high-pressure booster on the overall performance of the unit under different load conditions. For example, changes in frequency regulation capability will reveal the unit's flexible response capabilities when facing load fluctuations, while thermal economy shows the energy efficiency of the unit under different conditions. Changes in flue gas temperature can help determine the adaptability and optimization space of the denitrification system. This visualization method can provide strong support for subsequent optimization control strategies, helping decision makers to better adjust unit parameters in actual operation and achieve efficient and flexible operation.

Claims

1. A method for dynamic modeling and deep flexible peak load performance evaluation of No. 0 high-voltage heating based on Modelica, characterized in that: The steps include: Step 1: Based on Modelica language, a dynamic coupling model of a 300MW subcritical coal-fired unit is established; Step 2: Set the model parameters and simulate different load conditions to obtain key operating data; Step 3: Real-time dynamic simulation to evaluate the impact of the commissioning and removal of the No. 0 high-pressure heater on the unit performance under different load conditions; Step 4: In-depth analysis of the response performance of the No. 0 high-voltage heater during frequency modulation, especially the response speed and power regulation capability when the load changes; Step 5: Integrate the simulation results, evaluate the operating performance of the No. 0 high-pressure heater, and propose an optimized control strategy.

2. According to the Modelica-based method for dynamic modeling and deep flexible peak-shaving performance evaluation of No. 0 high-pressure heating unit according to claim 1, it is characterized in that: In step one, the 300MW subcritical coal-fired unit includes a steam turbine, a boiler heating surface and a steam turbine heat recovery system; the steam turbine includes a high-pressure cylinder, a medium-pressure cylinder and a low-pressure cylinder; the boiler heating surface includes a water-cooled wall, a superheater, a reheater and an economizer; the steam turbine heat recovery system includes three high-pressure heaters, four low-pressure heaters, a deaerator and a No. 0 high-pressure heater.

3. The method for dynamic modeling and deep flexible peak-shaving performance evaluation of No. 0 high-pressure heating unit based on Modelica according to claim 1, characterized in that: Step 1 is as follows: Model the components of the above-mentioned unit based on the Modelica language, focusing on describing the dynamic interaction process between the high, medium and low pressure cylinders of the steam turbine and the heating surface of the boiler; Based on the steam turbine part, the dynamic simulation of the high-pressure cylinder, intermediate-pressure cylinder and low-pressure cylinder is described by the following physical equations: Where λ is a dimensionless constant; k is the adiabatic index; ε n is the pressure ratio of the nozzle inlet and outlet; ε c is the critical pressure ratio; A is the area of ​​the nozzle interface; ρ0 is the steam density at the nozzle outlet; G and G1 are the steam flow rates through the stage under design conditions and variable conditions respectively; p o 、p o1 p is the pressure before and after the stage group under variable working conditions; z 、p z1 is the pressure after the stage group before and after the variable working condition; T0, T 01 The temperature before and after the stage group under variable working conditions; In the regenerative system, the dynamic performance of each regenerative heater is described by the following physical equations: Q h =βA h (T h -T p ) Q s =α s A s (T s -T p ) Where, T m is the temperature of the fluid in the tube; T w1 、T w2 are the inlet and outlet water temperatures of the heater respectively; Q w Convective heat transfer in the tube; α w is the heat transfer coefficient; A w is the heat transfer area in the tube; C m is the specific heat capacity of the metal tube; Q h is the heat brought by the previous level of hydrophobicity; β is the heat transfer coefficient on the hydrophobic side; A h is the heat exchange area on the drain side; T h is the hydrophobic temperature; Q s Extraction steam condensation heat exchange; α s is the heat transfer coefficient; A s is the heat exchange area of ​​the tube in the condensation zone; T s is the saturation temperature corresponding to the steam side pressure of the heater, T P is the tube wall temperature; For the main heating surface of the boiler, the heat exchange between the high-temperature flue gas and the working fluid can be described by the following physical equation: In the formula, are the flue gas mass flow rates flowing into and out of the i-th section of the shell, respectively; m g,i is the mass of the flue gas in section i on the shell side; h g,i is the specific enthalpy of the flue gas in section i on the shell side; h gin,i 、h gout,i are the specific enthalpy of the flue gas flowing into and out of the i-th section of the shell, respectively; Q g,i The heat released by the flue gas to the metal pipe sideways; are the water vapor mass flow rates flowing into and out of the i-th section of the tube side, respectively; m s,i is the mass of water vapor in section i on the shell side; h s,i is the specific enthalpy of water vapor in section i on the shell side; Q s,i h is the heat released from the metal pipe wall to the working fluid; sin,i 、h sout,i are the specific enthalpies of water vapor flowing into and out of section i on the tube side, respectively; The key component to achieve variable load response is the steam extraction valve, which is used to adjust the steam extraction amount of the No. 0 high-pressure heater by adjusting the valve opening of the No. 0 high-pressure heater steam extraction pipeline and adjust the process flow; After constructing the physical equations of each component, the Modelica language is used to modularize the components. In the Dymola simulation platform, the high-pressure cylinder, medium-pressure cylinder, low-pressure cylinder of the steam turbine, each level of regenerative heaters and the heating surfaces of the boiler are connected in sequence to form a complete dynamic coupling simulation model of the subcritical coal-fired unit.

4. The method for dynamic modeling and deep flexible peak load regulation performance evaluation of No. 0 high voltage heating unit based on Modelica according to claim 3 is characterized in that: The flow calculation formula of the regulation process is: Where FlowChar(θ) is the flow characteristic function of the valve, which depends on the valve opening θ; ρ is the fluid density; p f is the fluid inlet pressure; is the pressure drop ratio; x s is the saturation pressure drop ratio; dp is the pressure difference; A v,internal is the effective flow area of ​​the valve; is the compression factor.

5. The method for dynamic modeling and deep flexible peak load regulation performance evaluation of No. 0 high-voltage heating unit based on Modelica according to claim 1, characterized in that: In step 2, the load conditions include typical loads of 75% THA and 50% THA; key parameters of the unit's flue gas flow, flue gas temperature and steam flow are set; and the inlet and outlet rated pressures of each cylinder of the steam turbine are optimized and adjusted.

6. The method for dynamic modeling and deep flexible peak load regulation performance evaluation of No. 0 high voltage heating unit based on Modelica according to claim 5, characterized in that: The optimization and adjustment of the rated inlet and outlet pressures of each cylinder of the steam turbine is specifically as follows: by adjusting the intake pressure of the high-pressure cylinder, the effective expansion of the steam in the high-pressure cylinder is ensured, thereby maximizing its power output; by gradually adjusting the intake pressure and outlet pressure of the medium-pressure cylinder and the low-pressure cylinder, the flow of steam in each stage is ensured to reach the optimal state, thereby enhancing the overall performance of the unit; the inlet and outlet pressures of the regenerative heater are adjusted to ensure that the reheating effect of the steam is optimized.

7. The method for dynamic modeling and deep flexible peak-shaving performance evaluation of No. 0 high-pressure heating unit based on Modelica according to claim 1, characterized in that: Step three is as follows: according to the dynamic coupling model, the operation and removal process of the No. 0 high-pressure heater is simulated through the Dymola dynamic simulation platform, and the opening of the regulating valve is controlled to achieve a smooth change in the steam flow rate; the regulating valve is connected to the controller, and the opening of the regulating valve is gradually adjusted according to the control input signal to control the change in the steam flow rate; To evaluate the thermal economy of the unit, taking the heat rate of the steam turbine as an example, the calculation formula is as follows: Q in =D0(H0-H main )+D zr (H zr -H zl ) Where, q is the heat rate of the steam turbine; Q in The heat input to the steam turbine system; P e is the generator output power; D0 is the main steam flow rate; H0 is the main steam enthalpy; H main is the enthalpy of the boiler main feed water; D zr H is the hot end flow rate of the reheat steam pipeline; zr is the hot end enthalpy of reheat steam; H zl is the cold end enthalpy of reheat steam; At the same time, the flue gas temperature at the SCR inlet is monitored in real time to evaluate the regulating effect of the No. 0 high-pressure heater on the flue gas temperature; the changes in the flue gas temperature are recorded by gradually adjusting the steam extraction valve of the No. 0 high-pressure heater.

8. The method for dynamic modeling and deep flexible peak-shaving performance evaluation of No. 0 high-pressure heating unit based on Modelica according to claim 1, characterized in that: Step four is as follows: using dynamic simulation technology to quickly close the operation of the No. 0 high-pressure heater extraction valve to observe and record the dynamic response of the unit under sudden load changes; setting the regulating valve to be connected to the step signal controller so that the valve gradually changes from a fully open state to a fully closed state within 5-10s. During the adjustment process, real-time monitoring of changes in the parameters of the boiler feed water temperature and the unit load is performed. During load fluctuations, the power regulation capability of the unit is a key indicator for evaluating its performance. Through quantitative analysis of the power variation amplitude, the flexibility and stability of the No. 0 high-pressure heater in responding to sudden load changes are determined.

9. The method for dynamic modeling and deep flexible peak-shaving performance evaluation of No. 0 high-pressure heating unit based on Modelica according to claim 1, characterized in that: Step five is as follows: Based on the simulation data, comprehensively evaluate the overall operating effect of the No. 0 high-pressure heater, and draw different deep peak-shaving performance evaluation diagrams according to different analysis needs, that is, under different unit load conditions, display different performance indicators on the vertical axis, including frequency regulation capability, thermal economy and flue gas temperature.

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