Coal-fired unit main steam pressure control method with feed water flow asynchronously adjusted

Abstract

The invention discloses a control method for main steam pressure of a coal-fired unit with feed water flow asynchronously adjusted. The method comprises the following steps: firstly, calculating to obtain the steam extraction flow variation of a high-pressure heater, a deaerator and a low-pressure heater with unit feed water flow variation, so as to obtain the flow variation of each stage group in a steam turbine and the flow variation in each connecting pipeline, and combining the calculated main steam flow variation when the feed water flow is changed; deducing to obtain a pressure change predicted value of each stage of extraction steam in the steam turbine, and finally obtaining a change predicted value of the main steam pressure when the unit feed water flow changes. The main steam pressure is controlled through asynchronous adjustment of the feed water flow, the control effect of the main steam pressure can be obviously improved, and the method has important significance on improvement of the rapid load changing capacity of a coal-fired unit.

Description

Technical Field

[0001] The invention belongs to the technical field of thermal power system control optimization, and in particular relates to a method for controlling the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation. Background Art

[0002] Since the beginning of the 21st century, the world's energy structure has continued to develop and transform in the direction of clean, low-carbon, high-efficiency and diversified. However, due to the strong time-varying characteristics of renewable energy such as wind energy and solar energy, it is difficult to absorb renewable energy power generation in my country, and the problems of wind and solar power abandonment are serious. Improving the operating flexibility of conventional coal-fired power generation units and providing absorption services for renewable energy power generation are important technical directions. Coal-fired power generation will shift from the main energy source to the basic energy source, and the load variation amplitude and load variation frequency of coal-fired power generation units will gradually increase. Therefore, the thermal power system will be in a transient condition with frequent load changes for a long time, and the requirements for its rapid load change capability are getting higher and higher.

[0003] As an important part of the power system, coal-fired units will take on more and more important peak-shaving tasks, and the requirements for their rapid load-changing capabilities are getting higher and higher. In model simulation and actual power plant operation, it is found that the control quality of the main steam pressure has become a key factor restricting the coal-fired units from further improving their load-changing capabilities. When the unit changes load rapidly, the main steam pressure is prone to excessive deviations, which limits the improvement of the unit's flexibility. How to quickly and effectively control the main steam pressure in a reasonable range during the load change process is an important part of the optimization of the coal-fired unit boiler coordinated control system.

[0004] One of the biggest features of subcritical units is that they have an important working fluid and energy storage device, the steam drum, which enables partial decoupling of feedwater flow and saturated steam flow, and also reflects the characteristics different from supercritical direct current units, which means that the regulation of feedwater flow is no longer strongly dependent on load fluctuations and coal feeding, but can be adjusted asynchronously in a certain range. The regulation of the main steam pressure inside the coal-fired generator set mainly relies on methods such as adjusting the coal feeding amount and adjusting the opening of the high-pressure regulating valve. The control of the coal feeding amount is mainly related to the boiler main control signal, and the adjustment of the opening of the high-pressure regulating valve is synchronized with the main control signal of the steam turbine. In the process of rapid load increase and decrease, the machine-boiler coordinated control system needs to adjust the unit power, main steam pressure and main reheat steam temperature at the same time. It is difficult to ensure the control quality of the main steam pressure by relying solely on the above-mentioned adjustment methods. Therefore, how to quickly and effectively adjust the main steam flow and the flow rate of each group in the steam turbine system during rapid load changes becomes the key to effectively control the main steam pressure. Summary of the invention

[0005] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a control method for the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation. By means of asynchronous feedwater flow regulation, the total heat entering the boiler evaporation system is changed, thereby affecting the saturated steam flow and the main steam flow; by changing the steam extraction flow of the regenerative heater, the flow rate of each group inside the steam turbine is changed. The above two work together to assist in controlling the main steam pressure of the coal-fired unit. The present invention can greatly improve the problem of poor main steam pressure control quality in the rapid load change process of the coal-fired unit.

[0006] In order to achieve the above object, the present invention adopts the following technical solution:

[0007] A method for controlling the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation is provided. The feedwater flow asynchronous regulation is used to assist in controlling the main steam pressure. The feedforward value of the feedwater flow regulation is calculated based on the real-time deviation of the main steam pressure calculated from the collected and processed coal-fired unit operation measurement data and the predicted value of the main steam pressure change corresponding to the unit feedwater flow change to obtain:

[0008] The calculation formula for the feedforward value of water flow regulation is:

[0009]

[0010] Where: Δm fwr Main steam pressure deviation feedforward value for boiler system feed water flow regulation, kg / s; k fwr The feedforward adjustment coefficient of the main steam pressure deviation on the feedwater flow rate; Δp ls,dev The real-time deviation between the main steam pressure of the coal-fired unit collected and calculated in real time and the set value, MPa; Δp ls is the predicted value of the main steam pressure change corresponding to the unit feed water flow rate change, MPa;

[0011] Among them, the real-time deviation of the main steam pressure of the coal-fired unit is calculated using the real-time value of the main steam pressure of the coal-fired unit and the set value of the main steam pressure:

[0012] Δp ls,dev =p ls,set -p ls,rt

[0013] Where: p ls,set is the main steam pressure setting value of the coal-fired unit, MPa; p ls,rt Real-time value of main steam pressure of coal-fired unit, MPa;

[0014] The predicted value of the change in main steam pressure caused by a unit feedwater flow rate change is calculated using the main steam pressure before and after the unit feedwater flow rate change:

[0015] Δp ls =pl ' s -p ls

[0016] Where: p ls and p l ' s are the main steam pressure before and after the unit feedwater flow rate changes, MPa;

[0017] The feedwater flow rate is asynchronously regulated to assist in controlling the feedwater flow rate of the main steam pressure, and the feedwater control logic of the coal-fired unit cooperates with the original feedwater control logic of the coal-fired unit to control the feedwater flow rate of the coal-fired unit;

[0018] The auxiliary control of the main steam pressure by asynchronous regulation of the feed water flow and the original main steam pressure control of the coal-fired unit coordinately regulate the main steam pressure of the coal-fired unit.

[0019] The specific processing process of the collected coal-fired unit operation measurement data is as follows:

[0020] Since the measurement data collected from coal-fired units are accompanied by some data noise, data missing and data errors, it is necessary to clean the collected data;

[0021] (1) First, the collected raw measurement data is subjected to noise reduction, and the Kalman filter method is used to perform noise reduction and filtering on the raw measurement data;

[0022] (2) Then, the noise-reduced measurement data set is analyzed to screen missing values, abnormal values, and erroneous values ​​in the measurement data, fill in the missing values, correct the abnormal values, and remove the erroneous values;

[0023] (3) Analyze the size and change trend of important basic parameters that are indispensable for coal-fired units, mainly the unit load W p , main steam pressure p out,1 and water flow rate m fw According to the changing trend of basic parameters, combined with the physical mechanism and changing law of the actual operation of the coal-fired unit, it is judged whether the size and changing trend of the measured values ​​of other parameters except the unit load, main steam pressure and feed water flow parameters collected are inconsistent with the changes in the basic parameters of the coal-fired unit, and more accurate measuring points are selected for the data of multiple measuring points. For the data points that are inconsistent with the changes in the basic data of the coal-fired unit, the data are corrected or discarded, and finally the cleaning of the collected measurement data is completed.

[0024] The main steam pressure p after unit feed water flow changes l ' s Calculation method:

[0025] The main steam pressure after the unit feed water flow rate changes is related to the main steam flow rate and the pressure after the first stage of the steam turbine system. The calculation formula of the main steam pressure after the unit feed water flow rate changes is derived from the Flugel formula:

[0026] p l ' s =p ls +p t ' j -p tj

[0027]

[0028] Where: m ls It is the main steam flow rate before the feed water flow rate changes. The main steam flow rate collected and calculated by the unit itself is used first. If the data is inaccurate, it is calculated. kg / s; Δm ls is the change in main steam flow caused by a unit change in feed water flow, kg / s; p tj and p t ' j are the regulating stage pressure before and after the change of feed water flow, MPa; p s,1 and p s ' ,1 They are the pressure after the first stage of the steam turbine before and after the change of feed water flow, MPa.

[0029] Regarding the pressure p after the first stage of the steam turbine after the feed water flow rate changes s ' ,1 Calculation method:

[0030] The pressure p after the first stage of the steam turbine after the feedwater flow rate changes s ' ,1 It is also the pressure before the second level group;

[0031] The pressure after the last stage of the low-pressure cylinder of the steam turbine is taken as the starting point for calculation. The pressure before different stages of the steam turbine system is calculated from low pressure to high pressure using the Flugel formula. The pressure before the pipes connecting different cylinders of the steam turbine is calculated using the Darcy-Weisbach formula.

[0032] Among them, the pressure after the i-th stage group of the steam turbine, that is, the pressure before the i+1-th stage group is:

[0033]

[0034] Pressure before connecting pipe:

[0035]

[0036] Where: p s,i and ps ' ,i are the pressure before the i+1th stage of the steam turbine before and after the change of feedwater flow, MPa; p s,i+1 and p s ' ,i+1 are respectively the pressure after the i+1th stage of the steam turbine before and after the change of feedwater flow, MPa; m smf,i+1 is the flow rate of the i+1th stage of the steam turbine before the feedwater flow rate changes, kg / s; Δm smf,i+1 is the change in flow rate of the i+1th stage of the steam turbine caused by the change in feedwater flow rate, kg / s; p s,pin and p s ' ,pin are the pressure before and after the change of water flow rate, MPa; p s,pout and p s ' ,pout They are the pressure after the connecting pipe before and after the water flow rate changes, MPa; m smf,pi is the flow rate of the connecting pipe before the water supply flow changes, kg / s; Δm smf,pi It is the change in flow rate of the connecting pipe caused by the change in water flow rate, kg / s;

[0037] Then the pressure after the first stage of the steam turbine after the feedwater flow changes is s ' ,1 for:

[0038]

[0039] Change Δm of the flow rate of the i-th stage of the steam turbine caused by the change of feedwater flow rate smf,i The change in the flow rate of the connecting pipe caused by the change in the water supply flow rate Δm smf,pi The specific calculation method is:

[0040]

[0041] Where: Δm se,r is the change of steam extraction flow rate of the rth stage of the steam turbine, kg / s;

[0042] Changes in flow rate in connecting pipes due to changes in water supply flow rate Δm smf,pi Calculation method:

[0043]

[0044] Where: nst is the nearest extraction stage that is higher than the inlet pressure of the connecting pipeline;

[0045] Among them, the change of steam extraction flow rate of each stage of the steam turbine is Δm se,rMainly includes: Change of extraction steam flow rate of high pressure regenerative heater Δm se,i , i = 1 ~ k-1; the change of the extraction steam flow rate of the deaerator is Δm se,k , k is the number of deaerator extraction steam stages; the change in the extraction steam flow rate of the low-pressure regenerative heater Δm se,j , j = k + 1 ~ Z; Z is the total steam extraction stage number of the coal-fired generator set;

[0046] The extraction steam flow rate of the high-pressure regenerative heater changes as follows:

[0047]

[0048] Where: Δm se,i is the change in extraction steam flow rate of No.i high-pressure regenerative heater before and after the unit feedwater flow rate changes, kg / s; τ i is the feed water enthalpy rise of No.i high pressure regenerative heater, kJ / kg; q i is the extraction enthalpy drop of No.i high pressure regenerative heater, kJ / kg; γ i is the enthalpy drop of the No.i high pressure regenerative heater, kJ / kg; where i = 1 to k-1; Δm fw is the change in water flow rate, kg / s;

[0049] The extraction steam flow rate of the deaerator changes as follows:

[0050]

[0051] Where: Δm se,k is the change in the extraction steam flow rate of the deaerator before and after the unit feed water flow rate changes, kg / s; τ k is the feed water enthalpy rise of the deaerator, kJ / kg; q k is the extraction enthalpy drop of the deaerator, kJ / kg; γ k is the enthalpy drop of the deaerator, kJ / kg;

[0052] After the feed water flow changes, in order to maintain the water level balance of the deaerator, the condensate flow will also change accordingly, causing the extraction steam flow of the low-pressure regenerative heater to change to:

[0053]

[0054] Where: Δm se,j is the change in extraction steam flow rate of No.j low-pressure regenerative heater before and after the unit feedwater flow rate changes, kg / s; τ j is the feed water enthalpy rise of No.j low-pressure regenerative heater, kJ / kg; q j is the extraction enthalpy drop of No.j low-pressure regenerative heater, kJ / kg; γ jis the enthalpy drop of the No. j low-pressure regenerative heater, kJ / kg; where j = k+1~Z; Δm cw is the change in condensate flow rate, kg / s;

[0055] Among them, the change of condensate flow is:

[0056]

[0057] About the enthalpy drop of extraction steam in high pressure regenerative heater of steam turbine system i , hydrophobic enthalpy drop γ i and feed water enthalpy rise τ i The specific calculation method is:

[0058] According to the principle of energy balance, the extraction enthalpy drop q of the high-pressure regenerative heater is obtained i , hydrophobic enthalpy drop γ i and feed water enthalpy rise τ i The calculation formula is as follows:

[0059] 1) For drain heater:

[0060] τ i =h w,out,i -h w,in,i

[0061] q i =h s,i -h d,i

[0062] γ i =h d,i-1 -h d,i

[0063] 2) For concentrating heaters:

[0064] τ i =h w,out,i -h w,in,i

[0065] q i =h s,i -h w,in,i

[0066] γ i =h d,i-1 -h w,in,i

[0067] Where: h w,out,i and h w,in,i are the outlet and inlet feed water enthalpies of No.i high pressure regenerative heater, kJ / kg; h s,i is the extraction enthalpy of No.i high pressure regenerative heater, kJ / kg; h d,i and hd,i-1 are the hydrophobic enthalpy values ​​of No.i and No.i-1 regenerative heaters, kJ / kg;

[0068] Extraction enthalpy drop of low pressure regenerative heater q j , hydrophobic enthalpy drop γ j and feed water enthalpy rise τ j The calculation formula is the same as that of the high pressure regenerative heater.

[0069] The change in main steam flow rate Δm caused by the change in unit feed water flow rate ls Calculation method:

[0070] When the feed water flow rate changes, the change in the main steam flow rate is equal to the change in the saturated steam flow rate generated by the drum of the boiler system. According to the mass balance and energy balance of the drum, the calculation formula is:

[0071]

[0072] Where: Δm ssmf is the change in saturated steam flow rate generated by the drum of the boiler system, kg / s; ΔQ eco is the total heat absorption change of the working fluid in the economizer of the boiler system, kJ / s; Δm fw is the change in water flow rate, kg / s; h sw is the enthalpy of saturated water in the drum of the boiler system, kJ / kg; h ssmf is the enthalpy of saturated steam generated by the boiler system drum, kJ / kg; h eco,in It is the enthalpy of the working fluid at the economizer inlet of the boiler system, kJ / kg.

[0073] The main steam flow rate m before the feed water flow rate changes ls The specific calculation method of the flow rate of each stage group in the steam turbine and the flow rate in each connecting pipeline is:

[0074] First, the relationship between the flow rate of each stage of the steam turbine and the inlet flow rate of each cylinder of the steam turbine and the steam extraction flow rate of each stage is clarified:

[0075]

[0076] Where: m smf,i is the flow rate of the i-th stage of the steam turbine, kg / s; m tut,in is the inlet flow rate of the steam turbine cylinder of the i-th stage group, kg / s; m ser is the steam extraction flow rate of each stage before the i-th stage group, kg / s; j is the number of the first stage steam extraction of the steam turbine cylinder where the i-th stage group is located;

[0077] The extraction steam flow rate at each stage is calculated using the energy balance of the regenerative heater:

[0078]

[0079] Where: m sei is the steam extraction flow rate of No.i regenerative heater, kg / s; m wi is the feed water flow rate flowing through No.i regenerative heater before the feed water flow rate changes, kg / s; m dw(i-1) is the drain flow rate of No.i-1 regenerative heater, kg / s;

[0080] The main steam flow rate before the feedwater flow rate change is calculated using the Flugel formula:

[0081]

[0082] Where: m ls0 is the main steam flow rate under design conditions, kg / s; p tj0 is the design operating condition regulating stage pressure, MPa; p ehp and p ehp0 are the real-time high-pressure cylinder exhaust pressure and the design high-pressure cylinder exhaust pressure, MPa; T tj and T tj0 They are the real-time regulating stage temperature and the design condition regulating stage temperature, ℃;

[0083] The inlet flow of the medium-pressure cylinder and the low-pressure cylinder is the flow of the connecting pipes connecting the high-pressure cylinder and the medium-pressure cylinder and the medium-pressure cylinder and the low-pressure cylinder, and is calculated using the Darcy-Weisbach formula:

[0084]

[0085] Where: m tut,in and m tut,in0 are the cylinder real-time inlet flow rate and the cylinder inlet flow rate under design conditions, kg / s; Δp pipe and Δp pipe0 They are the real-time pressure drop of the cylinder connecting pipe and the pressure drop of the cylinder connecting pipe under the design condition, MPa; ρ pipe,s and ρ pipe0,s They are the real-time density of the cylinder connection pipe working fluid and the density of the cylinder connection pipe working fluid under the design working condition, kg / m 3 .

[0086] The specific coordinated control method of the feedwater control logic of the feedwater flow asynchronous regulation auxiliary control of the main steam pressure and the original feedwater control logic of the coal-fired unit is as follows:

[0087] The original control method for feedwater flow in the coordinated control system of coal-fired units is mainly achieved by relying on the deviation between the real-time water level of the drum and the set water level, and superimposing the feedforward control of the main steam flow. When the unit increases or decreases the load, the feedwater flow will show the characteristics of synchronous regulation with the coal supply; the feedforward regulation of the main steam pressure deviation is introduced into the feedwater flow control logic. With the help of the real-time deviation of the main steam pressure of the coal-fired unit, the predicted value of the main steam pressure change when the unit feedwater flow changes is calculated, combined with the feedforward regulation coefficient of the main steam pressure deviation on the feedwater flow, the feedforward value of the main steam pressure deviation of the coal-fired unit on the feedwater flow regulation is finally obtained, thereby forming an optimized control logic that assists in controlling the main steam pressure through the feedforward regulation of the feedwater flow; the final feedwater flow command calculation formula is:

[0088] m fwc =f PID (ΔH drum )+k ls m ls +Δm fwr

[0089] Where: m fwc is the final water supply flow instruction, kg / s; ΔH drum is the drum water level deviation, mm; k ls is the main steam flow feedforward coefficient; the PID algorithm is an incremental PID algorithm;

[0090] The main purpose of the original feed water flow control method of coal-fired units is to maintain the stability of the drum water level and ensure the reliability of steam-water separation; after adding the main steam pressure deviation to the feed water feedforward, it can be used to assist in controlling the main steam pressure.

[0091] The specific coordinated control method of the main steam pressure of the coal-fired unit by the auxiliary control of the main steam pressure by asynchronous regulation of the feed water flow and the original main steam pressure control of the coal-fired unit is as follows:

[0092] The original main steam pressure control loop of the coal-fired unit relies on the coordinated control of the boiler main control signal and the turbine main control signal, and is controlled by the coal feed rate, water feed rate and main steam valve opening respectively. The original control loop plays a major control role; the main steam pressure control method of the coal-fired unit with asynchronous feed water regulation calculates the feedforward value of the feed water flow rate by the real-time deviation of the main steam pressure, which plays an auxiliary role in regulating the main steam pressure.

[0093] The beneficial effect of the present invention is that: by using the important working fluid and energy storage equipment of the subcritical coal-fired unit drum, the adjustment range of the feed water flow is liberated, and the asynchronous adjustment of the feed water flow when the load is raised or lowered can be realized. By supplementing and optimizing the automatic control logic of the main steam pressure of the coal-fired unit through asynchronous adjustment of the feed water flow, the main steam pressure deviation can be effectively prevented from exceeding the limit when the coal-fired unit changes load rapidly, and the main steam pressure exceeding the limit, which is the bottleneck that limits the further increase of the unit's load change rate, can be suppressed, thereby improving the unit's operating flexibility.

[0094] Advantages of the present invention

[0095] 1) The present invention provides a method for controlling the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation, and its advantages are embodied in the specific auxiliary control method of the main steam pressure of the coal-fired unit by asynchronous feedwater flow regulation: the present invention uses the calculated main steam pressure deviation and the predicted value of the main steam pressure change corresponding to the unit feedwater flow change to calculate the feedforward value of the feedwater flow regulation required to eliminate the deviation when the main steam pressure deviation increases, and organically combines the feedwater control logic of the auxiliary control of the main steam pressure by asynchronous feedwater flow regulation with the original feedwater control logic of the coal-fired unit, and organically combines the auxiliary control of the main steam pressure by asynchronous feedwater flow regulation with the original main steam pressure control loop of the coal-fired unit, and finally realizes the auxiliary control of the main steam pressure by asynchronous feedwater flow regulation;

[0096] 2) The present invention provides a main steam pressure control method for a coal-fired unit with asynchronous feedwater flow regulation, and its advantages are specifically reflected in the method for calculating the predicted value of the main steam pressure change corresponding to a unit feedwater flow change: the present invention calculates the change in the main steam flow when the unit feedwater flow changes through the mass balance and energy balance of the boiler evaporation system, and uses the energy balance of the heat recovery heater to calculate the change in the flow rate of each stage in the turbine system when the unit feedwater flow changes, comprehensively considering the effects of the change in the main steam flow and the change in the flow rate of each stage on the main steam pressure of the coal-fired unit, and finally calculates the predicted value of the main steam pressure change corresponding to the unit feedwater flow regulation.

[0097] 3) The present invention provides a main steam pressure control method for a coal-fired unit with asynchronous regulation of feedwater flow, and its advantages are specifically embodied in the data processing method for the measurement data collected from the coal-fired unit: the present invention performs data cleaning on the collected measurement data of the coal-fired unit, adopts Kalman filtering to reduce data noise, and fills in vacant values, corrects abnormal values, and proposes error values. For more hidden data anomalies, a mechanism analysis method is used to perform data cleaning according to the overall operating status and operating trend of the unit. Through data cleaning, data noise, data missing and data errors in the original measurement data can be avoided as much as possible, and the errors of the data itself can be minimized before subsequent calculations, which not only retains the characteristics of the measurement data, but also eliminates the interference of the data, thereby enhancing the accuracy of subsequent calculations of feedwater regulation.

[0098] 4) The present invention provides a main steam pressure control method for a coal-fired unit with asynchronous regulation of feedwater flow, the advantages of which are specifically reflected in the method for calculating the predicted value of the pressure change before each stage of the steam turbine corresponding to the unit feedwater flow change: when calculating the change in the pressure before each stage of the steam turbine, the present invention takes into account the change in the pressure before the stage caused by the change in the flow rate of each stage of the high, medium and low pressure cylinders of the steam turbine, and also takes into account the change in the pressure before the connecting pipe caused by the change in the flow rate inside the connecting pipe between the cylinders, thereby making the calculation result of the pressure change before each stage of the steam turbine system after the unit feedwater flow changes more accurate.

[0099] 5) The present invention provides a main steam pressure control method for a coal-fired unit with asynchronous feedwater flow regulation, and its advantages are specifically reflected in the method for calculating the flow rates of each group inside the steam turbine corresponding to the unit feedwater flow change: when calculating the change in the flow rates of each group inside the steam turbine caused by the unit feedwater flow change, the present invention takes into account both the change in the extraction flow rate of the high-pressure heat recovery heater directly caused by the change in feedwater flow, and the change in the extraction flow rate of the low-pressure heat recovery heater caused by the change in condensate flow caused by the deaerator water level control, thereby increasing the accuracy of the calculation of the flow rates of each group inside the steam turbine. BRIEF DESCRIPTION OF THE DRAWINGS

[0100] Figure 1 The control effect diagram of the main steam pressure of a 330MW subcritical coal-fired power generation unit using a main steam pressure control method for a coal-fired power generation unit with asynchronous feedwater flow regulation when the load is rapidly reduced from 75% to 50%. DETAILED DESCRIPTION

[0101] In order to make the purpose, technical solution and advantages of the present invention more clear, the method of the present invention is further described in detail below in conjunction with specific implementation cases. It should be understood that the specific implementation cases described herein are only used to explain the present invention and are not used to limit the present invention.

[0102] The present invention discloses a main steam pressure control method for a coal-fired unit with asynchronous feedwater flow regulation, wherein asynchronous feedwater flow regulation is used to assist in controlling the main steam pressure, and a feedforward value of the feedwater flow regulation is calculated based on the real-time deviation of the main steam pressure calculated from the collected and processed coal-fired unit operation measurement data and the predicted value of the main steam pressure change corresponding to the unit feedwater flow change to obtain:

[0103] The calculation formula for the feedforward value of water flow regulation is:

[0104]

[0105] Where: Δm fwr Main steam pressure deviation feedforward value for boiler system feed water flow regulation, kg / s; k fwr The feedforward adjustment coefficient of the main steam pressure deviation on the feedwater flow rate; Δp ls,dev The real-time deviation between the main steam pressure of the coal-fired unit collected and calculated in real time and the set value, MPa; Δp ls is the predicted value of the main steam pressure change corresponding to the unit feed water flow rate change, MPa;

[0106] Among them, the real-time deviation of the main steam pressure of the coal-fired unit is calculated using the real-time value of the main steam pressure of the coal-fired unit and the set value of the main steam pressure:

[0107] Δp ls,dev =p ls,set -p ls,rt

[0108] Where: p ls,set is the main steam pressure setting value of the coal-fired unit, MPa; p ls,rt Real-time value of main steam pressure of coal-fired unit, MPa;

[0109] The predicted value of the change in main steam pressure caused by a unit feedwater flow rate change is calculated using the main steam pressure before and after the unit feedwater flow rate change:

[0110] Δp ls =p l ' s -p ls

[0111] Where: p ls and p l ' s are the main steam pressure before and after the unit feedwater flow rate changes, MPa;

[0112] The feedwater flow rate is asynchronously regulated to assist in controlling the feedwater flow rate of the main steam pressure, and the feedwater control logic of the coal-fired unit cooperates with the original feedwater control logic of the coal-fired unit to control the feedwater flow rate of the coal-fired unit;

[0113] The auxiliary control of the main steam pressure by asynchronous regulation of the feed water flow and the original main steam pressure control of the coal-fired unit coordinately regulate the main steam pressure of the coal-fired unit.

[0114] Preferably, the specific processing process of the collected coal-fired unit operation measurement data is as follows:

[0115] Since the measurement data collected from coal-fired units are accompanied by some data noise, data missing and data errors, it is necessary to clean the collected data;

[0116] (1) First, the collected raw measurement data is subjected to noise reduction, and the Kalman filter method is used to perform noise reduction and filtering on the raw measurement data;

[0117] (2) Then, the noise-reduced measurement data set is analyzed to screen missing values, abnormal values, and erroneous values ​​in the measurement data, fill in the missing values, correct the abnormal values, and remove the erroneous values;

[0118] (3) Analyze the size and change trend of important basic parameters that are indispensable for coal-fired units, mainly the unit load W p , main steam pressure p out,1 and water flow rate m fw According to the changing trend of basic parameters, combined with the physical mechanism and changing law of the actual operation of the coal-fired unit, it is judged whether the size and changing trend of the measured values ​​of other parameters except the unit load, main steam pressure and feed water flow parameters collected are inconsistent with the changes in the basic parameters of the coal-fired unit, and more accurate measuring points are selected for the data of multiple measuring points. For the data points that are inconsistent with the changes in the basic data of the coal-fired unit, the data are corrected or discarded, and finally the cleaning of the collected measurement data is completed.

[0119] Preferably, the main steam pressure p after the unit feedwater flow rate changes l ' s Calculation method:

[0120] The main steam pressure after the unit feed water flow rate changes is related to the main steam flow rate and the pressure after the first stage of the steam turbine system. The calculation formula of the main steam pressure after the unit feed water flow rate changes is derived from the Flugel formula:

[0121] p l ' s =p ls +p t ' j -p tj

[0122]

[0123] Where: m lsIt is the main steam flow rate before the feed water flow rate changes. The main steam flow rate collected and calculated by the unit itself is used first. If the data is inaccurate, it is calculated. kg / s; Δm ls is the change in main steam flow caused by a unit change in feed water flow, kg / s; p tj and p t ' j are the regulating stage pressure before and after the change of feed water flow, MPa; p s,1 and p s ' ,1 They are the pressure after the first stage of the steam turbine before and after the change of feed water flow, MPa.

[0124] Preferably, the pressure p after the first stage of the steam turbine after the feed water flow rate changes s ' ,1 Calculation method:

[0125] The pressure p after the first stage of the steam turbine after the feedwater flow rate changes s ' ,1 It is also the pressure before the second level group;

[0126] The pressure after the last stage of the low-pressure cylinder of the steam turbine is taken as the starting point for calculation. The pressure before different stages of the steam turbine system is calculated from low pressure to high pressure using the Flugel formula. The pressure before the pipes connecting different cylinders of the steam turbine is calculated using the Darcy-Weisbach formula.

[0127] Among them, the pressure after the i-th stage group of the steam turbine, that is, the pressure before the i+1-th stage group is:

[0128]

[0129] Pressure before connecting pipe:

[0130]

[0131] Where: p s,i and p s ' ,i are the pressure before the i+1th stage of the steam turbine before and after the change of feedwater flow, MPa; p s,i+1 and p s ' ,i+1 are respectively the pressure after the i+1th stage of the steam turbine before and after the change of feedwater flow, MPa; m smf,i+1 is the flow rate of the i+1th stage of the steam turbine before the feedwater flow rate changes, kg / s; Δm smf,i+1 is the change in flow rate of the i+1th stage of the steam turbine caused by the change in feedwater flow rate, kg / s; p s,pin and p s ' ,pinare the pressure before and after the change of water flow rate, MPa; p s,pout and p s ' ,pout They are the pressure after the connecting pipe before and after the water flow rate changes, MPa; m smf,pi is the flow rate of the connecting pipe before the water supply flow changes, kg / s; Δm smf,pi It is the change in flow rate of the connecting pipe caused by the change in water flow rate, kg / s;

[0132] Then the pressure after the first stage of the steam turbine after the feedwater flow changes is s ' ,1 for:

[0133]

[0134] Preferably, the change in the flow rate of the i-th stage group of the steam turbine caused by the change in the feedwater flow rate is Δm smf,i The change in the flow rate of the connecting pipe caused by the change in the water supply flow rate Δm smf,pi The specific calculation method is:

[0135]

[0136] Where: Δm se,r is the change of steam extraction flow rate of the rth stage of the steam turbine, kg / s;

[0137] Changes in flow rate in connecting pipes due to changes in water supply flow rate Δm smf,pi Calculation method:

[0138]

[0139] Where: nst is the nearest extraction stage that is higher than the inlet pressure of the connecting pipeline;

[0140] Among them, the change of steam extraction flow rate of each stage of the steam turbine is Δm se,r Mainly includes: Change of extraction steam flow rate of high pressure regenerative heater Δm se,i , i = 1 ~ k-1; the change of the extraction steam flow rate of the deaerator is Δm se,k , k is the number of deaerator extraction steam stages; the change in the extraction steam flow rate of the low-pressure regenerative heater Δm se,j , j = k + 1 ~ Z; Z is the total steam extraction stage number of the coal-fired generator set;

[0141] The extraction steam flow rate of the high-pressure regenerative heater changes as follows:

[0142]

[0143] Where: Δm se,iis the change in extraction steam flow rate of No.i high-pressure regenerative heater before and after the unit feedwater flow rate changes, kg / s; τ i is the feed water enthalpy rise of No.i high pressure regenerative heater, kJ / kg; q i is the extraction enthalpy drop of No.i high pressure regenerative heater, kJ / kg; γ i is the enthalpy drop of the No.i high pressure regenerative heater, kJ / kg; where i = 1 to k-1; Δm fw is the change in water flow rate, kg / s;

[0144] The extraction steam flow rate of the deaerator changes as follows:

[0145]

[0146] Where: Δm se,k is the change in the extraction steam flow rate of the deaerator before and after the unit feed water flow rate changes, kg / s; τ k is the feed water enthalpy rise of the deaerator, kJ / kg; q k is the extraction enthalpy drop of the deaerator, kJ / kg; γ k is the enthalpy drop of the deaerator, kJ / kg;

[0147] After the feed water flow changes, in order to maintain the water level balance of the deaerator, the condensate flow will also change accordingly, causing the extraction steam flow of the low-pressure regenerative heater to change to:

[0148]

[0149] Where: Δm se,j is the change in extraction steam flow rate of No.j low-pressure regenerative heater before and after the unit feedwater flow rate changes, kg / s; τ j is the feed water enthalpy rise of No.j low-pressure regenerative heater, kJ / kg; q j is the extraction enthalpy drop of No.j low-pressure regenerative heater, kJ / kg; γ j is the enthalpy drop of the No. j low-pressure regenerative heater, kJ / kg; where j = k+1~Z; Δm cw is the change in condensate flow rate, kg / s;

[0150] Among them, the change of condensate flow is:

[0151]

[0152] Preferably, regarding the steam extraction enthalpy drop q in the high-pressure regenerative heater of the steam turbine system i , hydrophobic enthalpy drop γ i and feed water enthalpy rise τ i The specific calculation method is:

[0153] According to the principle of energy balance, the extraction enthalpy drop q of the high-pressure regenerative heater is obtained i , hydrophobic enthalpy drop γ i and feed water enthalpy rise τ i The calculation formula is as follows:

[0154] 1) For drain heater:

[0155] τ i =h w,out,i -h w,in,i

[0156] q i =h s,i -h d,i

[0157] γ i =h d,i-1 -h d,i

[0158] 2) For concentrating heaters:

[0159] τ i =h w,out,i -h w,in,i

[0160] q i =h s,i -h w,in,i

[0161] γ i =h d,i-1 -h w,in,i

[0162] Where: h w,out,i and h w,in,i are the outlet and inlet feed water enthalpies of No.i high pressure regenerative heater, kJ / kg; h s,i is the extraction enthalpy of No.i high pressure regenerative heater, kJ / kg; h d,i and h d,i-1 are the hydrophobic enthalpy values ​​of No.i and No.i-1 regenerative heaters, kJ / kg;

[0163] Extraction enthalpy drop of low pressure regenerative heater q j , hydrophobic enthalpy drop γ j and feed water enthalpy rise τ j The calculation formula is the same as that of the high pressure regenerative heater.

[0164] Preferably, the change in main steam flow rate Δm caused by the change in unit feed water flow rate is ls Calculation method:

[0165] When the feed water flow rate changes, the change in the main steam flow rate is equal to the change in the saturated steam flow rate generated by the drum of the boiler system. According to the mass balance and energy balance of the drum, the calculation formula is:

[0166]

[0167] Where: Δm ssmf is the change in saturated steam flow rate generated by the drum of the boiler system, kg / s; ΔQ eco is the total heat absorption change of the working fluid in the economizer of the boiler system, kJ / s; Δm fw is the change in water flow rate, kg / s; h sw is the enthalpy of saturated water in the drum of the boiler system, kJ / kg; h ssmf is the enthalpy of saturated steam generated by the boiler system drum, kJ / kg; h eco,in It is the enthalpy of the working fluid at the economizer inlet of the boiler system, kJ / kg.

[0168] Preferably, the main steam flow rate m before the feed water flow rate changes ls The specific calculation method of the flow rate of each stage group in the steam turbine and the flow rate in each connecting pipeline is:

[0169] First, the relationship between the flow rate of each stage of the steam turbine and the inlet flow rate of each cylinder of the steam turbine and the steam extraction flow rate of each stage is clarified:

[0170]

[0171] Where: m smf,i is the flow rate of the i-th stage of the steam turbine, kg / s; m tut,in is the inlet flow rate of the steam turbine cylinder of the i-th stage group, kg / s; m ser is the steam extraction flow rate of each stage before the i-th stage group, kg / s; j is the number of the first stage steam extraction of the steam turbine cylinder where the i-th stage group is located;

[0172] The extraction steam flow rate at each stage is calculated using the energy balance of the regenerative heater:

[0173]

[0174] Where: m sei is the steam extraction flow rate of No.i regenerative heater, kg / s; m wi is the feed water flow rate flowing through No.i regenerative heater before the feed water flow rate changes, kg / s; m dw(i-1) is the drain flow rate of No.i-1 regenerative heater, kg / s;

[0175] The main steam flow rate before the feedwater flow rate change is calculated using the Flugel formula:

[0176]

[0177] Where: m ls0 is the main steam flow rate under design conditions, kg / s; p tj0 is the design operating condition regulating stage pressure, MPa; p ehp and p ehp0 are the real-time high-pressure cylinder exhaust pressure and the design high-pressure cylinder exhaust pressure, MPa; T tj and T tj0 They are the real-time regulating stage temperature and the design condition regulating stage temperature, ℃;

[0178] The inlet flow of the medium-pressure cylinder and the low-pressure cylinder is the flow of the connecting pipes connecting the high-pressure cylinder and the medium-pressure cylinder and the medium-pressure cylinder and the low-pressure cylinder, and is calculated using the Darcy-Weisbach formula:

[0179]

[0180] Where: m tut,in and m tut,in0 are the cylinder real-time inlet flow rate and the cylinder inlet flow rate under design conditions, kg / s; Δp pipe and Δp pipe0 They are the real-time pressure drop of the cylinder connecting pipe and the pressure drop of the cylinder connecting pipe under the design condition, MPa; ρ pipe,s and ρ pipe0,s They are the real-time density of the cylinder connection pipe working fluid and the density of the cylinder connection pipe working fluid under the design working condition, kg / m 3 .

[0181] Preferably, the specific coordinated control method of the feedwater control logic for auxiliary control of the main steam pressure by asynchronous regulation of the feedwater flow and the original feedwater control logic of the coal-fired unit is as follows:

[0182] The original control method for feedwater flow in the coordinated control system of coal-fired units is mainly achieved by relying on the deviation between the real-time water level of the drum and the set water level, and superimposing the feedforward control of the main steam flow. When the unit increases or decreases the load, the feedwater flow will show the characteristics of synchronous regulation with the coal supply; the feedforward regulation of the main steam pressure deviation is introduced into the feedwater flow control logic. With the help of the real-time deviation of the main steam pressure of the coal-fired unit, the predicted value of the main steam pressure change when the unit feedwater flow changes is calculated, combined with the feedforward regulation coefficient of the main steam pressure deviation on the feedwater flow, the feedforward value of the main steam pressure deviation of the coal-fired unit on the feedwater flow regulation is finally obtained, thereby forming an optimized control logic that assists in controlling the main steam pressure through the feedforward regulation of the feedwater flow; the final feedwater flow command calculation formula is:

[0183] m fwc =f PID (ΔH drum )+kls m ls +Δm fwr

[0184] Where: m fwc is the final water supply flow instruction, kg / s; ΔH drum is the drum water level deviation, mm; k ls is the main steam flow feedforward coefficient; the PID algorithm is an incremental PID algorithm;

[0185] The main purpose of the original feed water flow control method of coal-fired units is to maintain the stability of the drum water level and ensure the reliability of steam-water separation; after adding the main steam pressure deviation to the feed water feedforward, it can be used to assist in controlling the main steam pressure.

[0186] Preferably, the specific coordinated control method of the auxiliary control of the main steam pressure by asynchronous regulation of the feed water flow and the original main steam pressure control of the coal-fired unit for coordinated control of the main steam pressure of the coal-fired unit is as follows:

[0187] The original main steam pressure control loop of the coal-fired unit relies on the coordinated control of the boiler main control signal and the turbine main control signal, and is controlled by the coal feed rate, water feed rate and main steam valve opening respectively. The original control loop plays a major control role; the main steam pressure control method of the coal-fired unit with asynchronous feed water regulation plays an auxiliary role in regulating the main steam pressure by calculating the feedforward value of the feed water flow rate for the real-time deviation of the main steam pressure;

[0188] p ls =f1(BHCC)+f2(THCC)+f3(Δm fwr )

[0189] Where: BHCC and THCC are the boiler main control signal and the turbine main control signal respectively.

[0190] Figure 1 The relative deviation of the main steam pressure of a 330MW subcritical coal-fired power generation unit during a 75%-50% rapid load reduction process is shown. The control effects of the original control method and the control method of the present invention are compared in the figure. The maximum allowable value of the main steam pressure deviation during the load change process is 3.0%.

[0191] The maximum load reduction rate using the original control method is 2.0%Pe / min. When the load reduction rate is 2.5%Pe / min, the maximum deviation of the main steam pressure reaches 3.1%, exceeding the maximum limit of 3.0%; using the control method of the present invention, when the load reduction rate is also 2.5%Pe / min, the maximum deviation of the main steam pressure is reduced to 2.88%, meeting the limit requirement. After using the control method of the present invention, the maximum load reduction rate of the coal-fired power generation unit in the 75%-50% load reduction process is increased from 2.0%Pe / min to 2.5%Pe / min.

[0192] When the load reduction rate is 2.5%Pe / min, the control method of the present invention reduces the maximum relative deviation of the main steam pressure by 7.10% and reduces the cumulative deviation of the main steam pressure by 22.97%.

[0193] In summary, after using the control method of the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation of the present invention, the control effect of the main steam pressure is significantly enhanced, and the load change rate of the unit is significantly improved. Therefore, the control method of the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation of the present invention significantly improves the operating flexibility of the coal-fired power generation unit.

Claims

1. A method for controlling the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation, characterized in that: The feedwater flow asynchronous regulation is used to assist in controlling the main steam pressure. The feedforward value of the feedwater flow regulation is calculated based on the real-time deviation of the main steam pressure calculated from the collected and processed coal-fired unit operation measurement data and the predicted value of the main steam pressure change corresponding to the unit feedwater flow change: The calculation formula for the feedforward value of water flow regulation is: Where: Δm fwr Main steam pressure deviation feedforward value for boiler system feed water flow regulation, kg / s; k fwr The feedforward adjustment coefficient of the main steam pressure deviation on the feedwater flow rate; Δp ls,dev The real-time deviation between the main steam pressure of the coal-fired unit collected and calculated in real time and the set value, MPa; Δp ls is the predicted value of the main steam pressure change corresponding to the unit feed water flow rate change, MPa; Among them, the real-time deviation of the main steam pressure of the coal-fired unit is calculated using the real-time value of the main steam pressure of the coal-fired unit and the set value of the main steam pressure: Δp ls,dev =p ls,set -p ls,rt Where: p ls,set is the main steam pressure setting value of the coal-fired unit, MPa; p ls,rt Real-time value of main steam pressure of coal-fired unit, MPa; The predicted value of the change in main steam pressure caused by a unit feedwater flow rate change is calculated using the main steam pressure before and after the unit feedwater flow rate change: Δp ls =p l ′ s -p ls Where: p ls and p l ' s are the main steam pressure before and after the unit feedwater flow rate changes, MPa; The feedwater flow rate is asynchronously regulated to assist in controlling the feedwater flow rate of the main steam pressure, and the feedwater control logic of the coal-fired unit cooperates with the original feedwater control logic of the coal-fired unit to control the feedwater flow rate of the coal-fired unit; The auxiliary control of the main steam pressure by asynchronous regulation of the feed water flow and the original main steam pressure control of the coal-fired unit coordinately regulate the main steam pressure of the coal-fired unit.

2. The main steam pressure control method of a coal-fired unit based on asynchronous regulation of feedwater flow according to claim 1, characterized in that: The specific processing process of the collected coal-fired unit operation measurement data is as follows: Since the measurement data collected from coal-fired units are accompanied by some data noise, data missing and data errors, it is necessary to clean the collected data; (1) First, the collected raw measurement data is subjected to noise reduction, and the Kalman filter method is used to perform noise reduction and filtering on the raw measurement data; (2) Then, the noise-reduced measurement data set is analyzed to screen missing values, abnormal values, and erroneous values ​​in the measurement data, fill in the missing values, correct the abnormal values, and remove the erroneous values; (3) Analyze the size and change trend of important basic parameters that are indispensable for coal-fired units, mainly the unit load W p , main steam pressure p out,1 and water flow rate m fw ; According to the changing trend of basic parameters, combined with the physical mechanism and changing law during the actual operation of the coal-fired unit, it is judged whether the size and changing trend of the measured values ​​of other parameters except the unit load, main steam pressure and feed water flow parameters are inconsistent with the changes in the basic parameters of the coal-fired unit, and more accurate measuring points are selected for the data of multiple measuring points. For the data points that are inconsistent with the changes in the basic data of the coal-fired unit, the data are corrected or discarded, and finally the cleaning of the collected measurement data is completed.

3. The method for controlling the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation according to claim 1, characterized in that: The main steam pressure p after unit feed water flow changes l ' s Calculation method: The main steam pressure after the unit feed water flow rate changes is related to the main steam flow rate and the pressure after the first stage of the steam turbine system. The calculation formula of the main steam pressure after the unit feed water flow rate changes is derived from the Flugel formula: p l ′ s =p ls +p t ′ j -p tj Where: m ls It is the main steam flow rate before the feed water flow rate changes. The main steam flow rate collected and calculated by the unit itself is used first. If the data is inaccurate, it is calculated. kg / s; Δm ls is the change in main steam flow caused by a unit change in feed water flow, kg / s; p tj and p t ' j are the regulating stage pressure before and after the change of feed water flow, MPa; p s,1 and p s ' ,1 They are the pressure after the first stage of the steam turbine before and after the change of feed water flow, MPa.

4. The method for controlling the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation according to claim 3, characterized in that: Regarding the pressure p after the first stage of the steam turbine after the feed water flow rate changes s ' ,1 Calculation method: The pressure p after the first stage of the steam turbine after the feedwater flow rate changes s ' ,1 It is also the pressure before the second level group; The pressure after the last stage of the low-pressure cylinder of the steam turbine is taken as the starting point for calculation. The pressure before different stages of the steam turbine system is calculated from low pressure to high pressure using the Flugel formula. The pressure before the pipes connecting different cylinders of the steam turbine is calculated using the Darcy-Weisbach formula. Among them, the pressure after the i-th stage group of the steam turbine, that is, the pressure before the i+1-th stage group is: Pressure before connecting pipe: Where: p s,i and p s ' ,i are the pressure before the i+1th stage of the steam turbine before and after the change of feedwater flow, MPa; p s,i+1 and p s ' ,i+1 are respectively the pressure after the i+1th stage of the steam turbine before and after the change of feedwater flow, MPa; m smf,i+1 is the flow rate of the i+1th stage of the steam turbine before the feedwater flow rate changes, kg / s; Δm smf,i+1 is the change in flow rate of the i+1th stage of the steam turbine caused by the change in feedwater flow rate, kg / s; p s,pin and p s ' ,pin are the pressure before and after the change of water flow rate, MPa; p s,pout and p s ' ,pout They are the pressure after the connecting pipe before and after the water flow rate changes, MPa; m smf,pi is the flow rate of the connecting pipe before the water supply flow changes, kg / s; Δm smf,pi It is the change in flow rate of the connecting pipe caused by the change in water flow rate, kg / s; Then the pressure after the first stage of the steam turbine after the feedwater flow changes is s ' ,1 for:

5. The method for controlling the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation according to claim 4, characterized in that: Change Δm of the flow rate of the i-th stage of the steam turbine caused by the change of feedwater flow rate smf,i The change in the flow rate of the connecting pipe caused by the change in the water supply flow rate Δm smf,pi The specific calculation method is: Where: Δm se,r is the change of steam extraction flow rate of the rth stage of the steam turbine, kg / s; Changes in flow rate in connecting pipes due to changes in water supply flow rate Δm smf,pi Calculation method: Where: nst is the nearest extraction stage that is higher than the inlet pressure of the connecting pipeline; Among them, the change of steam extraction flow rate of each stage of steam turbine is Δm se,r Mainly includes: Change of extraction steam flow rate of high pressure regenerative heater Δm se,i , i = 1 ~ k-1; the change of the extraction steam flow rate of the deaerator is Δm se,k , k is the number of deaerator extraction steam stages; the change in the extraction steam flow rate of the low-pressure regenerative heater Δm se,j , j = k + 1 ~ Z; Z is the total steam extraction stage number of the coal-fired generator set; The extraction steam flow rate of the high-pressure regenerative heater changes as follows: Where: Δm se,i is the change in extraction steam flow rate of No.i high-pressure regenerative heater before and after the unit feedwater flow rate changes, kg / s; τ i is the feed water enthalpy rise of No.i high pressure regenerative heater, kJ / kg; q i is the extraction enthalpy drop of No.i high pressure regenerative heater, kJ / kg; γ i is the enthalpy drop of the No.i high pressure regenerative heater, kJ / kg; where i = 1 to k-1; Δm fw is the change in water flow rate, kg / s; The extraction steam flow rate of the deaerator changes as follows: Where: Δm se,k is the change in the extraction steam flow rate of the deaerator before and after the unit feed water flow rate changes, kg / s; τ k is the feed water enthalpy rise of the deaerator, kJ / kg; q k is the extraction enthalpy drop of the deaerator, kJ / kg; γ k is the enthalpy drop of the deaerator, kJ / kg; After the feed water flow changes, in order to maintain the water level balance of the deaerator, the condensate flow will also change accordingly, causing the extraction steam flow of the low-pressure regenerative heater to change to: Where: Δm se,j is the change in extraction steam flow rate of No.j low-pressure regenerative heater before and after the unit feedwater flow rate changes, kg / s; τ j is the feed water enthalpy rise of No.j low-pressure regenerative heater, kJ / kg; q j is the extraction enthalpy drop of No.j low-pressure regenerative heater, kJ / kg; γ j is the enthalpy drop of the No. j low-pressure regenerative heater, kJ / kg; where j = k+1~Z; Δm cw is the change in condensate flow rate, kg / s; Among them, the change of condensate flow is:

6. A method for controlling main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation according to claim 5, characterized in that: About the enthalpy drop of extraction steam in high pressure regenerative heater of steam turbine system i , hydrophobic enthalpy drop γ i and feed water enthalpy rise τ i The specific calculation method is: According to the principle of energy balance, the extraction enthalpy drop q of the high-pressure regenerative heater is obtained i , hydrophobic enthalpy drop γ i and feed water enthalpy rise τ i The calculation formula is as follows: 1) For drain heater: t i =h w,out,i -h w,in,i q i =h s,i -h d,i γ i =h d,i-1 -h d,i 2) For concentrating heaters: t i =h w,out,i -h w,in,i q i =h s,i -h w,in,i γ i =h d,i-1 -h w,in,i Where: h w,out,i and h w,in,i are the outlet and inlet feed water enthalpies of No.i high pressure regenerative heater, kJ / kg; h s,i is the extraction enthalpy of No.i high pressure regenerative heater, kJ / kg; h d,i and h d,i-1 are the hydrophobic enthalpy values ​​of No.i and No.i-1 regenerative heaters, kJ / kg; Extraction enthalpy drop of low pressure regenerative heater q j , hydrophobic enthalpy drop γ j and feed water enthalpy rise τ j The calculation formula is the same as that of the high pressure regenerative heater.

7. The method for controlling the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation according to claim 3, characterized in that: The change in main steam flow rate Δm caused by the change in unit feed water flow rate ls Calculation method: When the feed water flow rate changes, the change in the main steam flow rate is equal to the change in the saturated steam flow rate generated by the drum of the boiler system. According to the mass balance and energy balance of the drum, the calculation formula is: Where: Δm ssmf is the change in saturated steam flow rate generated by the drum of the boiler system, kg / s; ΔQ eco is the total heat absorption change of the working fluid in the economizer of the boiler system, kJ / s; Δm fw is the change in water flow rate, kg / s; h sw is the enthalpy of saturated water in the drum of the boiler system, kJ / kg; h ssmf is the enthalpy of saturated steam generated by the boiler system drum, kJ / kg; h eco,in It is the enthalpy of the working fluid at the economizer inlet of the boiler system, kJ / kg.

8. The method for controlling the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation according to claim 4, characterized in that: The main steam flow rate m before the feed water flow rate changes ls The specific calculation method of the flow rate of each stage group in the steam turbine and the flow rate in each connecting pipeline is: First, the relationship between the flow rate of each stage of the steam turbine and the inlet flow rate of each cylinder of the steam turbine and the steam extraction flow rate of each stage is clarified: Where: m smf,i is the flow rate of the i-th stage of the steam turbine, kg / s; m tut,in is the inlet flow rate of the steam turbine cylinder of the i-th stage group, kg / s; m ser is the steam extraction flow rate of each stage before the i-th stage group, kg / s; j is the number of the first stage steam extraction of the steam turbine cylinder where the i-th stage group is located; The extraction steam flow rate at each stage is calculated using the energy balance of the regenerative heater: Where: m sei is the steam extraction flow rate of No.i regenerative heater, kg / s; m wi is the feed water flow rate flowing through No.i regenerative heater before the feed water flow rate changes, kg / s; m dw(i-1) is the drain flow rate of No.i-1 regenerative heater, kg / s; The main steam flow rate before the feedwater flow rate change is calculated using the Flugel formula: Where: m ls0 is the main steam flow rate under design conditions, kg / s; p tj0 is the design operating condition regulating stage pressure, MPa; p ehp and p ehp0 They are the real-time high-pressure cylinder exhaust steam pressure and the design working condition high-pressure cylinder exhaust steam pressure, MPa; T tj and T tj0 They are the real-time regulating stage temperature and the design condition regulating stage temperature, ℃; The inlet flow of the medium-pressure cylinder and the low-pressure cylinder is the flow of the connecting pipes connecting the high-pressure cylinder and the medium-pressure cylinder and the medium-pressure cylinder and the low-pressure cylinder, and is calculated using the Darcy-Weisbach formula: Where: m tut,in and m tut,in0 are the cylinder real-time inlet flow rate and the cylinder inlet flow rate under design conditions, kg / s; Δp pipe and Δp pipe0 They are the real-time pressure drop of the cylinder connecting pipe and the pressure drop of the cylinder connecting pipe under the design working condition, MPa; ρ pipe,s and ρ pipe0,s They are the real-time density of the cylinder connection pipe working fluid and the density of the cylinder connection pipe working fluid under the design working condition, kg / m 3 .

9. The method for controlling the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation according to claim 1, characterized in that: The specific coordinated control method of the feedwater control logic of the feedwater flow asynchronous regulation auxiliary control of the main steam pressure and the original feedwater control logic of the coal-fired unit is as follows: The original control method for feedwater flow in the coordinated control system of coal-fired units is mainly achieved by relying on the deviation between the real-time water level of the drum and the set water level, and superimposing the feedforward control of the main steam flow. When the unit increases or decreases the load, the feedwater flow will show the characteristics of synchronous regulation with the coal supply; the feedforward regulation of the main steam pressure deviation is introduced into the feedwater flow control logic. With the help of the real-time deviation of the main steam pressure of the coal-fired unit, the predicted value of the main steam pressure change when the unit feedwater flow changes is calculated, combined with the feedforward regulation coefficient of the main steam pressure deviation on the feedwater flow, the feedforward value of the main steam pressure deviation of the coal-fired unit on the feedwater flow regulation is finally obtained, thereby forming an optimized control logic that assists in controlling the main steam pressure through the feedforward regulation of the feedwater flow; the final feedwater flow command calculation formula is: m fwc =f PID (ΔH drum )+k ls m ls +Δm fwr Where: m fwc is the final water supply flow instruction, kg / s; ΔH drum is the drum water level deviation, mm; k ls is the main steam flow feedforward coefficient; the PID algorithm is an incremental PID algorithm; The main purpose of the original feed water flow control method of coal-fired units is to maintain the stability of the drum water level and ensure the reliability of steam-water separation; after adding the main steam pressure deviation to the feed water feedforward, it can be used to assist in controlling the main steam pressure.

10. The method for controlling the main steam pressure of a coal-fired unit with asynchronous feedwater flow regulation according to claim 1, characterized in that: The specific coordinated control method of the main steam pressure of the coal-fired unit by the auxiliary control of the main steam pressure by asynchronous regulation of the feed water flow and the original main steam pressure control of the coal-fired unit is as follows: The original main steam pressure control loop of the coal-fired unit relies on the coordinated control of the boiler main control signal and the turbine main control signal, and is controlled by the coal feed rate, water feed rate and main steam valve opening respectively. The original control loop plays a major control role; the main steam pressure control method of the coal-fired unit with asynchronous feed water regulation calculates the feedforward value of the feed water flow rate by the real-time deviation of the main steam pressure, which plays an auxiliary role in regulating the main steam pressure.

Images