A reheating steam temperature control method for a high-pressure extraction throttling supercritical unit

Abstract

The application discloses a high-pressure heater extraction throttling supercritical unit reheat steam temperature control method, first, collecting the real-time data of the thermal parameters of the supercritical unit boiler system and the steam turbine system, performing data cleaning, calculating the water heating deficiency and the reheat steam flow variation of different high-pressure heater extraction throttling schemes, and then calculating the reheat absorber heat variation arranged before the superheater, comprehensively considering the reheat steam flow variation and the reheat absorber heat variation, obtaining the reheat steam temperature variation prediction value corresponding to different high-pressure heater extraction throttling schemes, and finally obtaining the specific high-pressure heater extraction throttling control scheme according to the real-time deviation of the reheat steam temperature. The method optimizes the original supercritical unit reheat steam temperature control logic, can effectively improve the control effect of the supercritical unit reheat steam temperature, prevents the problem of large reheat steam over-temperature easily occurring in the rapid load increasing process, and has important significance for improving the rapid load varying capacity of the supercritical coal-fired power generating unit.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of control optimization of thermal power systems, and particularly relates to a reheating steam temperature control method for a supercritical unit with high-pressure heater extraction throttling. BACKGROUND

[0002] The control quality of reheating steam temperature becomes an important bottleneck restricting the further improvement of variable load capacity of coal-fired power thermal power systems. In the process of rapid load increase, the reheating steam temperature is prone to over-limit, which limits the improvement of unit flexibility. How to quickly and effectively suppress the rapid rise of reheating steam temperature in the process of rapid load increase is an important content of the optimization of boiler-turbine coordinated control system of coal-fired power units.

[0003] The reheating steam temperature is related to the heat absorption of the reheater in the boiler system and the reheating steam flow. In the process of rapid load change, rapid adjustment of the above two parameters can achieve the purpose of effectively controlling the reheating steam temperature. Therefore, the application provides a reheating steam temperature control method for a supercritical coal-fired power unit with high-pressure heater extraction throttling. SUMMARY

[0004] In order to overcome the problems existing in the prior art, the purpose of the application is to provide a reheating steam temperature control method for a supercritical unit with high-pressure heater extraction throttling. With the help of high-pressure heater extraction throttling, the reheating steam flow is increased, and the flue gas temperature at the inlet of the boiler reheater is reduced, so that the purpose of rapidly reducing the reheating steam temperature is achieved. The application can greatly improve the reheating steam temperature over-temperature problem in the process of rapid load change.

[0005] In order to achieve the above purpose, the application adopts the following technical scheme:

[0006] A reheating steam temperature control method for a supercritical unit with high-pressure heater extraction throttling, comprising the following steps:

[0007] Step 1: data acquisition

[0008] Acquire the boiler system feed water flow m fw and the feed water flow measurement data m fwi of the steam turbine system flowing through each high-pressure heater, wherein i=1~k-1;

[0009] Acquire m working fluid inlet and outlet thermodynamic parameters between the boiler system and the steam turbine system, including the temperature and pressure T in,a , p in,a of the working fluid flow entering the boiler, and the temperature and pressure T out,a , p out,a of the working fluid flow leaving the boiler, wherein a=1~m;

[0010] Collect the thermodynamic parameters of the Z-stage regenerative heater, including the temperature T before and after each stage of the regenerative heater on the feedwater side. w,in,b T w,out,b Temperature T of each stage of extraction steam on the extraction side s,b Pressure p s,b Temperature T of the condensate drain of each stage of the regenerator d,b Where b = 1 to z;

[0011] Collect the water supply pressure p after the water pump fp and economizer inlet feedwater pressure p eco,in Water-cooled wall inlet working fluid temperature T ww,in and pressure p ww,in ;

[0012] Step 2: Data Preprocessing

[0013] The collected parameter data will be cleaned.

[0014] Step 3: Calculate the enthalpy of the working fluid at each point.

[0015] Using temperature and pressure data, the enthalpy of the working fluid at each point is calculated through thermophysical property analysis, including the enthalpy h of the working fluid flowing into and out of the boiler at m points. in,a and h out,a Where a = 1 to m; the enthalpy h of the inlet water of each stage of the regenerator on the feedwater side. w,in,b and the enthalpy h of the outlet water w,out,b ; enthalpy h of each stage of extraction steam on the extraction side s,b ; enthalpy h of each level of hydrophobicity d,b Where b = 1 to z; the enthalpy h of the working fluid at the inlet of the water-cooled wall of the boiler system. ww,in ;

[0016] Step 4: Calculate the changes in reheat steam flow rate caused by throttling of the high-pressure heater extraction steam.

[0017] For high-pressure heaters, during extraction steam throttling, all extracted steam returns to the turbine, i.e.

[0018]

[0019] Where: m sei The steam flow rate returning to the turbine during the extraction and throttling of the i-th stage high-pressure heater is expressed in kg / s and m³. dw(i-1) γ represents the condensate flow rate from the (i-1)th stage high-pressure heater, in kg / s; i The heat released by the hydrophobic material from the previous stage in the i-th stage high-pressure heater is expressed in kJ / kg; q i The heat release from the steam extracted by the i-th stage high-pressure heater is expressed in kJ / kg; τ i The heat absorbed by the feedwater in the i-th stage high-pressure heater is kJ / kg;

[0020] The change amount of the reheat steam flow rate is the sum of the change amounts of all the extraction steam flow rates whose extraction pressures are greater than or equal to the reheat steam pressure of the reheat steam:

[0021]

[0022] In the formula, Δm rs,j is the change amount of the jth reheat steam flow rate, kg / s; Δm sei is the change amount of the ith high-pressure heater extraction steam flow rate, which is equal in quantity to all the extraction steam flow rates of the high-pressure heater being throttled, kg / s; p rs,j is the jth reheat steam cold section pressure, MPa;

[0023] Step five: Calculate the water heating deficiency corresponding to different high-pressure heater extraction throttling schemes

[0024] The high-pressure heater extraction throttling increases the water heating deficiency of the stage, resulting in a decrease in the main steam temperature. In order to avoid the influence of the heater extraction at a higher extraction pressure on the throttling effect, all the continuous high-pressure heaters including the highest high-pressure heater are throttled in each high-pressure heater extraction throttling scheme;

[0025] The water heating deficiency caused by the throttling of the corresponding high-pressure heater extraction is equal to the enthalpy rise of the water flowing through the stage, which is calculated as follows:

[0026]

[0027] In the formula, ΔQ fw,1 , ΔQ fw,2 , ΔQ fw,3 , ΔQ fw,h , and ΔQ fw,k-1 are the water heating deficiencies caused by the high-pressure heater extraction throttling of the scheme 1, the scheme 2, the scheme 3, the scheme h, and the scheme k-1, respectively, kJ / s; m fw1 , m fw2 , and m fwi are the water flow rates flowing through the 1st high-pressure heater, the 2nd high-pressure heater, and the ith high-pressure heater, respectively, kg / s; τ1、

[0028] τ2, and τ i are the water enthalpy rises of the 1st high-pressure heater, the 2nd high-pressure heater, and the ith high-pressure heater, respectively, kJ / kg;

[0029] Step six: Calculate the heat absorption amount changes of the reheaters after the boiler superheater

[0030] The high-pressure heater extraction throttling causes the water heating deficiency, and the temperature of the water entering the boiler system decreases significantly, thus causing an increase in the heat absorption amount of the water wall and the superheater before the reheaters;

[0031] The increased heat absorption of the water wall and superheater caused by insufficient heating of the feed water will cause the decreased heat absorption of the reheater after the above heating surface, and the decreased heat absorption is distributed according to the proportion of the original heat absorption of each reheater affected;

[0032]

[0033] ΔQ rh,j is the change of the heat absorption of the jth reheated steam in the reheater of the boiler system, kJ / s; sh,re is the increased heat absorption of the water wall and superheater caused by throttling of the high-pressure heater extraction steam, kJ / s; rh,j is the heat absorption of the jth reheated steam in the reheater of the boiler system, kJ / s;

[0034] Step seven: calculate the predicted value of the temperature change of the reheated steam

[0035] Due to the throttling of the high-pressure heater extraction steam, the change of the flow rate of the reheated steam is Δm rs,j , and at the same time, the change of the heat absorption of the reheated steam caused by insufficient heating of the feed water is ΔQ rh,j ; by comprehensively considering the above changes, the change of the enthalpy of the reheated steam caused by the throttling of the high-pressure heater extraction steam is:

[0036]

[0037] Δh rs,j is the change of the enthalpy of the jth reheated steam, kJ / kg; rh,j and Q rh,j are the heat absorption of the jth reheater after and before the throttling of the high-pressure heater extraction steam, kJ / s; rs,j and m rs,j are the flow rate of the jth reheated steam after and before the throttling of the high-pressure heater extraction steam, kg / s;

[0038] The heat absorption of the jth reheater after the throttling of the high-pressure heater extraction steam is:

[0039] Q′ rh,j = Q rh,j - ΔQ rh,j

[0040] Under the premise that the temperature change of the reheated steam is small, the change of the specific heat capacity can be ignored, and the predicted value of the temperature change of the reheated steam after the throttling of the high-pressure heater extraction steam is:

[0041]

[0042] ΔT rs,j is the predicted value of the temperature change of the jth reheated steam after the throttling of the high-pressure heater extraction steam, ℃; rs,jCp,j is the specific heat capacity of the jth reheat steam, kJ / (kg·K);

[0043] Step eight: calculate the real-time reheat steam temperature deviation, and reasonably select the high-pressure heater extraction throttling scheme

[0044] Calculate the reheat steam temperature change prediction value under each high-pressure heater extraction throttling scheme, respectively, and obtain the reheat steam temperature change prediction value under each high-pressure heater extraction throttling scheme: ΔT rs,j,h j = 1 ~ m-1, h = 1 ~ k-1; Since the actual variable load process is very fast, different high-pressure heater extraction throttling schemes cannot achieve the maximum main steam temperature change, so a high-pressure heater extraction throttling main steam temperature prediction value correction coefficient is introduced, that is, k

[0045] ΔT rs,j,exp,h = k rs,j,expchan,h ΔT rs,j,h j = 1 ~ m-1, h = 1 ~ k-1

[0046] In the formula: ΔT rs,j,exp,h is the prediction value of the jth reheat steam temperature change expected by the hth high-pressure heater extraction throttling scheme in the actual fast variable load process, ℃; k rs,j,expchan,h is the high-pressure heater extraction throttling reheat steam temperature change prediction value correction coefficient, 0 < k rs,j,expchan,h < 1;

[0047] At the same time, calculate the deviation of each reheat steam real-time temperature and the set temperature,

[0048] ΔT rs,j,dev = T rs,j,set - T rs,j,rt

[0049] In the formula: ΔT rs,j,dev is the jth reheat steam temperature deviation, ℃; T rs,j,set is the jth steam temperature set value, kJ / s; T ls,rt is the real-time value of the main steam temperature, ℃;

[0050] When the reheat steam temperature deviation is within a certain range, the high-pressure heater extraction throttling method for controlling the reheat steam temperature is not used. That is, ΔT rs,j,dev ≤ ΔT rs,j,bdy , only use the flue gas damper or flue gas recirculation to control the reheat steam temperature;

[0051] When the reheat steam temperature deviation is greater than the set value ΔT rs,j,bdy , the high-pressure heater extraction throttling method for controlling the reheat steam temperature is used, and according to the relative size of the reheat steam temperature deviation and the reheat steam temperature change prediction value of each scheme, the most suitable high-pressure heater extraction throttling scheme is selected in order and in time.

[0052] The parameter data collected above is cleaned in step two, and the specific process is as follows:

[0053] (1) First, the original measurement data collected in step one is denoised, and Kalman filtering method is adopted to perform denoising filtering processing on the original operation data;

[0054] (2) Then, the measurement data set after denoising is analyzed, and the missing values, abnormal values and error values in the measurement data are screened, the data missing values are filled, the data abnormal values are corrected, and the data error values are removed;

[0055] (3) The size and change trend of the important basic parameters indispensable in the supercritical unit are analyzed, mainly the change trend of the unit load W p , the main steam pressure p out,1 and the feedwater flow m fw ; according to the change trend of the basic parameters, combined with the physical mechanism and change law in the actual operation process of the supercritical unit, whether the size and change trend of the measurement values of other parameters except the unit load, main steam pressure and feedwater flow parameters collected in step one are contrary to the change of the basic parameters of the supercritical unit is judged, more accurate measurement points are selected for the data of multiple measurement points, and the data points contrary to the change of the basic data of the supercritical unit are corrected or removed, and finally the cleaning work of the collected measurement data is completed.

[0056] The calculation method of the pressure parameters lacking in the calculation of the enthalpy values of each working medium in step three is as follows: the enthalpy values h d,i of the drainages of each heater necessary for the calculation but without measurement points are calculated through thermophysical properties, the drainages pressures P d,i of each heater are calculated according to 95% of the extraction pressures P s,i of each level, that is,

[0057] P d,i = 0.95P s,i , i = 1 ~ k-1

[0058] The enthalpy values h w,in,i of the inlet water and the enthalpy values h w,out,i of the outlet water of each regenerative heater on the feedwater side necessary for the calculation but without measurement points are calculated through thermophysical properties, the pressures P w,in,i of the inlet water and the pressures P w,out,i of the outlet water of each regenerative heater are calculated, wherein i = 1 ~ k-1, and the feedwater pressure P fp after the feedwater pump and the feedwater pressure P eco,in at the inlet of the coal economizer are adopted to calculate and obtain, that is,

[0059]

[0060] The heat recovery heater energy balance calculation method in step four and step five is as follows:

[0061] According to the energy balance calculation principle, the high-pressure heater feedwater heat absorption τ i , extraction heat release q i and drain heat release γ i can be obtained, and the calculation method is as follows:

[0062] 1) For the drain flow type heater:

[0063] τ i = h w,out,i - h w,in,i

[0064] q i = h s,i - h d,i

[0065] γ i = h d,i-1 - h d,i

[0066] 2) For the collection type heater:

[0067] τ i = h w,out,i - h w,in,i

[0068] q i = h s,i - h w,in,i

[0069] γ i = h d,i-1 - h w,in,i

[0070] In the formula, h w,out,i is the enthalpy value of the i-th stage of the heat recovery heater outlet feedwater, kJ / kg; h w,in,i is the enthalpy value of the i-th stage of the heat recovery heater inlet feedwater, kJ / kg; h s,i is the enthalpy value of the i-th stage of the heat recovery heater extraction steam, kJ / kg; h d,i is the enthalpy value of the i-th stage of the heat recovery heater drain, kJ / kg; h d,i-1 is the enthalpy value of the i-1-th stage of the heat recovery heater drain, kJ / kg.

[0071] The calculation method of the heat absorption change of the high-pressure heater extraction throttling water wall and superheater in step six is as follows:

[0072] Since the flue gas temperature before and after each heating surface in the furnace cannot be measured, a simplified method is used to calculate the heat absorption change of the water wall and the superheater;

[0073] The heat absorption changes of the water wall and the superheater are calculated together, and two limit boundaries are defined:

[0074] Boundary 1: the working medium temperature at the superheater outlet after throttling of the high-pressure heater extraction is the same as that before throttling, at this time, the increased heat absorption of the water wall and the superheater is the same as the water heating deficiency of the hth high-pressure heater extraction throttling scheme, at this time, it is the maximum heat absorption change:

[0075] ΔQ sh,max = ΔQ fw,h

[0076] In the formula, ΔQ sh,max is the maximum heat absorption change of the water wall and the superheater, kJ / s; h sh,out is the enthalpy value of the working medium at the superheater outlet, kJ / kg; h ww,in is the enthalpy value of the working medium at the water wall inlet, kJ / kg;

[0077] Boundary 2: the total heat absorption of the water wall and the superheater of the boiler system is unchanged, i.e. ΔQ sh,min = 0;

[0078] In the formula, ΔQ sh,min is the minimum heat absorption change of the water wall and the superheater, kJ / s;

[0079] In the actual process, due to the water heating deficiency, the working medium temperature entering the water wall decreases, the heat absorption of the water wall and the superheater increases, but at the same time, the working medium temperature at the superheater outlet also decreases to a certain extent; therefore, the increased heat absorption of the water wall and the superheater caused by the actual water heating deficiency is between the maximum and minimum values:

[0080] ΔQ sh,re = k sh,re ΔQ sh,max

[0081] In the formula, ΔQ sh,re is the actual increased heat absorption of the water wall and the superheater, kJ / s; k sh,re is the equivalent coefficient of the heat absorption change of the water wall and the superheater, 0 < k sh,re < 1.

[0082] The specific calculation method of the reheat steam flow before throttling of the high-pressure heater extraction in step seven is as follows:

[0083] The Darcy-Weisbach formula is used to calculate the reheat steam flow, and the specific calculation formula is as follows:

[0084]

[0085] In the formula, m rs,j and m rs0,jrespectively, the jth reheat steam flow rate in real time and the jth reheat steam flow rate under the design condition, kg / s; Δp pipe,j and Δp pipe0,j respectively, the jth reheat steam cold section pipe pressure drop in real time and the jth reheat steam cold section pipe pressure drop under the design condition, MPa; ρ pipe,j and ρ pipe0,j respectively, the jth reheat steam cold section pipe working medium density in real time and the jth reheat steam cold section pipe working medium density under the design condition, kg / m 3 .

[0086] The specific selection method of the high-pressure heater steam extraction throttling scheme in step eight is as follows:

[0087] When the temperature deviation of each reheat steam exceeds the set value, the temperature deviation of each reheat steam exceeding the set value is compared with the predicted value of the temperature change of each reheat steam of each scheme, and is uniformly arranged in the following form: ΔT rs,j,exp,h-1 <ΔT rs,j,dev ≤ΔT rs,j,exp,h , and the high-pressure heater steam extraction throttling scheme with the largest number of throttled high-pressure heaters is selected;

[0088] And when the high-pressure heater steam extraction throttling strategy is used, the temperature deviation of each reheat steam gradually decreases, and the above-mentioned throttling scheme selection method is still used to sequentially and orderly exit the steam extraction throttling of each high-pressure heater, and when the temperature deviation of each reheat steam is less than or equal to the preset limit ΔT rs,j,bdy , the normal steam extraction of all high-pressure heaters is restored.

[0089] The beneficial effects of the present application are that the present application adopts the method of high-pressure heater steam extraction throttling to regulate the reheat steam temperature of the supercritical coal-fired generating unit, first collects the thermal parameter real-time data in the distributed control system of the supercritical coal-fired generating unit, uses the data processing method including data noise reduction, data filling, mechanism analysis and the like to clean the collected operation data of the unit; then calculates the change amount of the reheat steam flow rate and the change amount of the heat absorption of the water wall and the superheater of different high-pressure heater steam extraction throttling schemes, and then calculates the predicted value of the reheat steam temperature change corresponding to different high-pressure heater steam extraction throttling schemes according to the energy balance equation, combines the reheat steam temperature deviation collected and calculated by the unit in real time, compares the two values, and sequentially and orderly selects the most suitable high-pressure heater steam extraction throttling scheme corresponding to the current reheat steam temperature deviation. By supplementing and optimizing the reheat steam temperature automatic control logic through high-pressure heater steam extraction throttling, the problem of reheat steam temperature overtemperature can be effectively prevented when the supercritical coal-fired generating unit rapidly increases the load, the bottleneck of eliminating the reheat steam temperature overlimit which limits the further improvement of the variable load rate of the unit is eliminated, and the operation flexibility of the unit is improved.

[0090] Advantages of the present application

[0091] 1) The present application provides several high-pressure heater extraction throttling schemes, in order to maximize the use of throttling effect and prevent the heater extraction from increasing significantly when throttling the high-pressure heater extraction, all high-pressure heater extraction throttling schemes provided by the present application throttle the continuous heaters including the highest level high-pressure heater, which not only ensures the throttling effect of the high-pressure heater extraction, but also facilitates the use and exit of the specific implementation scheme, simplifies the operation difficulty of the high-pressure heater extraction throttling control of the reheated steam temperature, and is more easily realized in automatic control;

[0092] 2) The present application calculates the flow changes of each reheated steam and the insufficient heating of the feed water corresponding to different high-pressure heater extraction throttling schemes by means of the energy balance of the high-pressure regenerative heater, and finally calculates the predicted values of the reheated steam temperature changes corresponding to different high-pressure heater extraction throttling schemes by comprehensively considering all energy flow changes through the energy balance of the boiler water wall, the superheater and the reheater, which has important guiding significance for the selection of subsequent high-pressure heater extraction throttling schemes;

[0093] 3) The present application discloses a method for selecting a throttling scheme according to the real-time collected and calculated reheated steam temperature deviation and the predicted values of the reheated steam temperature changes corresponding to each high-pressure heater extraction throttling scheme calculated through the above steps, by defining the high-pressure heater extraction temperature deviation limit value, when the reheated steam temperature deviation is greater than the set limit value, different high-pressure heater extraction throttling schemes are selected in order and timely according to the size relationship between the temperature deviation and the predicted value of the temperature change; and when the reheated steam temperature deviation decreases, each heater throttling is sequentially and orderly exited according to the size relationship between the deviation and the predicted value, and when it is less than the set limit value, the high-pressure heater extraction of the steam turbine system is fully restored; through the above high-pressure heater extraction throttling selection and scheduling scheme, different throttling methods with different effects can be reasonably and timely selected to correspond to different reheated steam temperature deviations, so that each energy flow in the thermal energy power system flows reasonably, and the control effect of the reheated steam temperature is finally improved. BRIEF DESCRIPTION OF DRAWINGS

[0094] Figure 1 It is a flow chart of a high-pressure heater extraction throttling supercritical unit reheated steam temperature control method;

[0095] Figure 2 It is a thermal system diagram of a certain 1000MW ultra-supercritical once-reheated unit, wherein 1 is No.1 high-pressure heater, 2 is No.2 high-pressure heater, 3 is No.3 high-pressure heater, 4 is reheater, 5 is economizer, 6 is superheater, 7 is water wall, 8 is boiler system, 9 is steam turbine system, 10 is steam turbine high-pressure cylinder, 11 is steam turbine intermediate-pressure cylinder, and 12 is steam turbine low-pressure cylinder;

[0096] Figure 3A high-pressure heater extraction throttling supercritical unit reheated steam temperature control logic diagram, wherein the bold part is a high-pressure heater extraction throttling reheated steam temperature control logic supplemented and optimized. DETAILED DESCRIPTION

[0097] In order to make the purpose, technical scheme and advantages of the present application more clear, the method of the present application is further described in detail below in combination with specific implementation cases. It should be understood that the specific implementation cases described herein are only used to explain the present application and do not limit the present application.

[0098] A high-pressure heater extraction throttling supercritical unit reheated steam temperature control method, as shown in Figure 2 The supercritical unit is composed of a supercritical boiler system 8 and a steam turbine system 9. The boiler system 8 and the steam turbine system 9 are connected through m working medium inlets and outlets. One working medium is changed from feed water into new steam. The feed water flows out of the highest level regenerative heater and enters the boiler 8. The new steam flows out of the superheater 6 and reaches the steam turbine new steam inlet. The remaining m-1 working media are reheated steam. The reheated steam flows out of the steam turbine extraction port, enters the reheater 4 of the boiler system, and then enters the steam turbine reheated steam inlet after being reheated. The boiler system 8 includes the economizer 5, the water wall 7, the superheater 6, the reheater 4, and other heating surfaces, and also includes important auxiliary equipment such as the air preheater, the coal mill, and the combustor. The boiler feed water from the steam turbine feed water regenerative system enters the economizer 5 after being heated, and then absorbs heat in the water wall 7 of the boiler to become superheated steam, and then enters the superheater 6 for heating. The steam turbine system 9 includes the steam turbine, the z-level regenerative heater, the feed water pump, and the condenser. The z-level regenerative heater is connected to the steam turbine extraction port through a pipeline and is arranged in order of high to low according to the extraction pressure. According to the water side pressure, the first to the k-1 level regenerative heaters are high-pressure heaters, the k level is a deaerator, and the k+1 to the z level are low-pressure heaters. The final steam turbine exhaust enters the condenser. There are two kinds of water side and steam side connection modes. For the partition type regenerative heater, the water flows in the pipe, the steam flows outside the pipe, the heat is transferred from the steam side to the water side through the pipe wall, the feed water or condensate water is heated and warmed, and the extraction is cooled and becomes drain water, which flows to the next level regenerative heater. For the collection type heater, the water and the steam are fully mixed and heat exchanged in the heater, and then become one working medium and continue to flow along the water side. In this example, the thermal power system is shown in Figure 2 The 8-level regenerative heater is used, wherein 1 represents No. 1 high-pressure heater, 2 represents No. 2 high-pressure heater, 3 represents No. 3 high-pressure heater, 4 represents reheater, 5 represents economizer, 6 represents superheater, 7 represents water wall, 8 represents boiler system, 9 represents steam turbine system, 10 represents steam turbine high-pressure cylinder, 11 represents steam turbine medium-pressure cylinder, and 12 represents steam turbine low-pressure cylinder.

[0099] The thermal power system configuration characteristics used in the specific calculation case are as follows:

[0100] 1) The ultra-supercritical unit is a 1000MW ultra-supercritical once-through reheat condensing steam turbine unit;

[0101] 2) The rated feedwater temperature is 294.7℃;

[0102] 3) The rated main steam temperature is 600℃, the rated main steam pressure is 25MPa, the rated reheat steam temperature is 600℃, and the rated reheat steam pressure is 4.366MPa;

[0103] 4) The reheat steam is taken from the high-pressure cylinder exhaust steam, heated by the boiler, and then enters the inlet of the medium-pressure cylinder;

[0104] 5) The thermal system diagram of the ultra-supercritical unit is shown in the accompanying drawings; Figure 2

[0105] As shown in the accompanying drawings, the reheat steam temperature control method of the supercritical unit with high-pressure heater extraction throttling in the embodiment includes the following steps: Figure 1 Figure 3 Step one: data acquisition

[0106] Acquire the feedwater flow rate m fw of the boiler system and the feedwater flow rate measurement data m fwi of the steam turbine system flowing through each high-pressure heater, wherein i=1~k-1;

[0107] Acquire the m working fluid inlet and outlet thermodynamic parameters between the boiler system and the steam turbine system, including the temperature and pressure T in,a , p in,a of the working fluid flow entering the boiler, and the temperature and pressure T out,a , p out,a of the working fluid flow leaving the boiler, wherein a=1~m;

[0108] Acquire the thermodynamic parameters of the z-stage regenerative heater, including the temperatures T w,in,b , T w,out,b before and after each stage of the regenerative heater on the feedwater side, the temperatures T s,b , pressures p s,b of each stage of extraction, and the temperature T d,b of the drain of each stage of the regenerative heater, wherein b=1~z;

[0109] Acquire the feedwater pressure p fp after the feedwater pump and the feedwater pressure p eco,in at the inlet of the economizer, the working fluid temperature T ww,in at the inlet of the water wall, and the pressure p ww,in ;

[0110] Step two: data preprocessing

[0111]

[0112] ​​​The parameter data collected above is subjected to data cleaning;

[0113] Step three: calculate the enthalpy of each point of working medium

[0114] Using temperature and pressure data, the enthalpy of each point of working medium is obtained through thermophysical property calculation, including the enthalpy h of m working medium flow in and out of the boiler in,a and h out,a , wherein a = 1 ~ m; the enthalpy h of the inlet water of each stage of regenerative heater on the feedwater side w,in,b and the enthalpy h of the outlet water w,out,b ; the enthalpy h of each stage of extraction steam s,b ; the enthalpy h of each stage of drain d,b , wherein b = 1 ~ z; the enthalpy h of the working medium at the inlet of the water wall of the boiler system ww,in ;

[0115] Step four: calculate the change of the flow rate of each reheat steam caused by throttling of high-pressure heater extraction steam

[0116] For the high-pressure heater, when the extraction steam is throttled, all the extraction steam returns to the steam turbine, that is,

[0117]

[0118] In the formula: m sei is the steam flow rate returned to the steam turbine when the extraction steam of the i-th stage of high-pressure heater is throttled, kg / s; m dw(i-1) is the drain flow rate from the i-1-th stage of high-pressure heater, kg / s; γ i is the heat release of the drain from the upper stage in the i-th stage of high-pressure heater, kJ / kg; q i is the heat release of the extraction steam of the i-th stage of high-pressure heater, kJ / kg; τ i is the heat absorption of the feedwater of the i-th stage of high-pressure heater, kJ / kg;

[0119] The change of the flow rate of each reheat steam is the sum of the changes of the flow rates of all the extraction steam whose pressure is greater than or equal to the pressure of the reheat steam:

[0120]

[0121] In the formula: Δm rs,j is the change of the flow rate of the j-th reheat steam, kg / s; Δm sei is the change of the flow rate of the extraction steam of the i-th stage of high-pressure heater, which is equal to the flow rate of all the extraction steam of the throttled high-pressure heater in quantity, kg / s; p rs,j is the cold section pressure of the j-th reheat steam, MPa;

[0122] Step five: calculate the insufficient heating of feedwater corresponding to different throttling schemes of high-pressure heater extraction steam

[0123] The high-pressure heater extraction throttling increases the water heating deficiency of the stage, which leads to the decrease of the main steam temperature. In order to avoid the influence of the heater extraction increase on the throttling effect caused by the higher extraction pressure, each high-pressure heater extraction throttling scheme throttles all the continuous high-pressure heaters including the highest stage high-pressure heater.

[0124] The water heating deficiency caused by the throttling of the corresponding high-pressure heater extraction is equal to the enthalpy rise of the water flowing through the heater, which is calculated as follows:

[0125]

[0126] In the formula, ΔQ fw,1 , ΔQ fw,2 , ΔQ fw,3 , ΔQ fw,h and ΔQ fw,k-1 are the water heating deficiencies of the high-pressure heater extraction throttling of the scheme 1, the scheme 2, the scheme 3, the scheme h and the scheme k-1, respectively, kJ / s; m fw1 , m fw2 and m fwi are the water flow rates flowing through the first stage, the second stage and the i-th stage high-pressure heaters, respectively, kg / s; τ1、

[0127] τ2and τ i are the water enthalpy rises of the first stage, the second stage and the i-th stage high-pressure heaters, respectively, kJ / kg.

[0128] Step six: Calculate the heat absorption changes of each reheater after the boiler superheater

[0129] The high-pressure heater extraction throttling causes the water heating deficiency, and the temperature of the water entering the boiler system decreases significantly, thus causing the heat absorption of the water wall and the superheater before each reheater to increase.

[0130] The heat absorption increase of the water wall and the superheater caused by the water heating deficiency will cause the heat absorption of each reheater after the above heating surface to decrease, and the decreased heat absorption is distributed according to the proportion of the original heat absorption of each reheater affected.

[0131]

[0132] In the formula, ΔQ rh,j is the heat absorption change of the j-th reheated steam in the boiler system reheater, kJ / s; ΔQ sh,re is the increased heat absorption of the water wall and the superheater caused by the high-pressure heater extraction throttling, kJ / s; Q rh,j is the heat absorption of the j-th reheated steam in the boiler system reheater, kJ / s;

[0133] Step seven: Calculate the temperature change prediction value of the reheated steam

[0134] The change of the reheat steam flow rate is Δm rs,j And at the same time, the change of the reheat steam heat absorption caused by the insufficient feed water heating is ΔQ rh,j The change of the reheat steam enthalpy caused by the high-pressure turbine extraction throttling can be obtained by combining the above changes:

[0135]

[0136] In the formula: Δh rs,j is the change of the jth reheat steam enthalpy, kJ / kg; Q′ rh,j and Q rh,j are the jth reheater heat absorption after and before the high-pressure turbine extraction throttling, kJ / s; m′ rs,j and m rs,j are the jth reheat steam flow rate after and before the high-pressure turbine extraction throttling, kg / s;

[0137] The jth reheater heat absorption after the high-pressure turbine extraction throttling is:

[0138] Q′ rh,j = Q rh,j - ΔQ rh,j

[0139] Under the premise that the reheat steam temperature change is small, the change of the specific heat capacity can be ignored, and the predicted value of the reheat steam temperature change after the high-pressure turbine extraction throttling is:

[0140]

[0141] In the formula: ΔT rs,j is the predicted value of the jth reheat steam temperature change after the high-pressure turbine extraction throttling, ℃; c rs,j is the jth reheat steam specific heat capacity, kJ / (kg·K);

[0142] Step eight: Calculate the real-time reheat steam temperature deviation and reasonably select the high-pressure turbine extraction throttling scheme

[0143] The predicted values of the reheat steam temperature changes under various high-pressure turbine extraction throttling schemes are obtained by calculating the different high-pressure turbine extraction throttling schemes: ΔT rs,j,h , j = 1 ~ m-1, h = 1 ~ k-1; Since the actual variable load process is very fast, the maximum main steam temperature change cannot be achieved under different high-pressure turbine extraction throttling schemes, so the high-pressure turbine extraction throttling main steam temperature predicted value correction coefficient is introduced, that is,

[0144] ΔT rs,j,exp,h = k rs,j,expchan,h ΔT rs,j,hj = 1 to m-1, h = 1 to k-1

[0145] Where: ΔT rs,j,exp,h The predicted value of the j-th reheat steam temperature change under the h-th high-pressure heater extraction throttling scheme during the actual rapid load change process is given in °C; k rs,j,expchan,h The correction factor for the predicted reheat steam temperature change due to high-pressure steam extraction throttling is 0 < k. rs,j,expchan,h <1;

[0146] Simultaneously calculate the deviation between the real-time temperature of the reheat steam and the set temperature for each reheat cycle.

[0147] ΔT rs,j,dev =T rs,j,set -T rs,j,rt

[0148] Where: ΔT rs,j,dev The temperature deviation of the reheat steam for the j-th time is expressed in °C; T rs,j,set The setpoint for the j-th steam temperature is given in kJ / s; T ls,rt Main steam temperature real-time value, °C;

[0149] When the temperature deviation of the reheat steam in each cycle is within a certain range, the method of controlling the reheat steam temperature by throttling the high-pressure heater extraction steam is not used, i.e., ΔT rs,j,dev ≤ΔT rs,j,bdy At that time, only flue gas dampers or flue gas recirculation are used to control the temperature of each reheat steam cycle;

[0150] When the reheat steam temperature deviation is greater than the set value ΔT rs,j,bdy Only when the high-pressure heater extraction steam throttling method is used to control the reheat steam temperature, and the most suitable high-pressure heater extraction steam throttling scheme is selected in an orderly and timely manner according to the relative magnitude of the reheat steam temperature deviation of each reheat steam cycle and the predicted value of the reheat steam temperature change of each scheme.

[0151] Preferably, the specific process for cleaning the collected parameter data in step two is as follows:

[0152] (1) First, the original measurement data collected in step one is denoised. The Kalman filter method is used to denoise and filter the original running data.

[0153] (2) Then analyze the noise-reduced measurement dataset, filter out missing values, outliers and errors in the measurement data, fill in missing values, correct outliers and remove errors.

[0154] (3) Analyze the magnitude and variation trend of essential basic parameters indispensable in supercritical units, mainly the unit load W. p Main steam pressure p out,1 and water supply flow rate (m)fw The changing trend of the basic parameters; based on the changing trend of the basic parameters, combined with the physical mechanism and changing law in the actual operation of the supercritical unit, determine whether the magnitude and changing trend of the measured values ​​of other parameters collected in step one, except for the unit load, main steam pressure and feedwater flow parameters, are contrary to the changes of the basic parameters of the supercritical unit. For data from multiple measuring points, select more accurate measuring points. For data points that are contrary to the changes of the basic data of the supercritical unit, correct or discard the data, and finally complete the cleaning of the collected measurement data.

[0155] Before applying the measurement data of key thermodynamic parameters collected from supercritical units to the calculation of control parameters, this invention first cleans the data by using Kalman filtering to reduce noise, and then uses simple data analysis methods to fill in missing values, correct outliers, and eliminate erroneous values. These methods address most of the problems in the original measurement data. Simultaneously, by leveraging the internal mechanisms and operating logic of supercritical units and analyzing the variation patterns of a few core thermodynamic parameters, the accuracy of the measurement points for other thermodynamic parameters is determined. Finally, accurate and reliable measurement points are selected, and abnormal data is repaired, providing reliable data assurance for the accurate calculation of subsequent control parameters.

[0156] Preferably, the calculation method for the pressure parameters that are missing in the calculation of the enthalpy values ​​of each working fluid in step three is as follows:

[0157] The hydrophobic enthalpy h of each stage of the heater was calculated using thermophysical properties. d,i The necessary but unmeasurable condensate pressure P of each stage of the heater d,i According to the extraction steam pressure P at each level s,i Calculate using 95%, that is

[0158] P d,i =0.95P s,i i = 1 to k-1

[0159] The enthalpy h of the inlet water of each stage of the regenerator on the feedwater side was calculated using thermophysical properties. w,in,i and the enthalpy h of the outlet water w,out,i The necessary but unmeasurable pressure P of the inlet water of each stage of the regenerative heater w,in,i and the pressure P of the outlet water w,out,i Where i = 1 to k-1, then the water supply pressure P after the water pump is used. fp Economizer inlet feedwater pressure P eco,in To calculate and obtain, that is

[0160]

[0161] The present application uses 95% of the extraction steam pressure instead of the unmeasurable heater drain pressure, and uses the feed water pump post pressure and the pre-coal economizer pressure to estimate the pressure of each high pressure heater feed water side. With the above method, the originally unmeasurable part of the thermal parameters is simply obtained, which lays a data foundation for the calculation of the high pressure heater feed water heat absorption and extraction steam heat release.

[0162] Preferably, the regenerative heater energy balance calculation method in step four and step five is as follows:

[0163] According to the calculation principle of energy balance, the high pressure heater feed water heat absorption τ i , extraction steam heat release q i and drain heat release γ i can be obtained, and the calculation method is as follows:

[0164] 1) for drain flow type heater:

[0165] τ i = h w,out,i - h w,in,i

[0166] q i = h s,i - h d,i

[0167] γ i = h d,i-1 - h d,i

[0168] 2) for the collection type heater:

[0169] τ i = h w,out,i - h w,in,i

[0170] q i = h s,i - h w,in,i

[0171] γ i = h d,i-1 - h w,in,i

[0172] In the formula: h w,out,i is the outlet feed water enthalpy of the i-th stage regenerative heater, kJ / kg; h w,in,i is the inlet feed water enthalpy of the i-th stage regenerative heater, kJ / kg; h s,i is the extraction steam enthalpy of the i-th stage regenerative heater, kJ / kg; h d,i is the drain enthalpy of the i-th stage regenerative heater, kJ / kg; h d,i-1 is the drain enthalpy of the i-1-th stage regenerative heater, kJ / kg.

[0173] The application adopts the energy balance method to calculate the water feed heat absorption, extraction steam heat release and drain heat release of the high-pressure heater, has the advantages of simplicity, rapidness and higher accuracy, ignores the heat storage change of the high-pressure heater itself, can more simply obtain the key parameters of each stage of the high-pressure heater, and provides data source for the calculation of the water feed heating deficiency and other parameters of the high-pressure heater after extraction throttling.

[0174] Preferably, the calculation method of the heat absorption change of the water wall and the superheater after extraction throttling of the high-pressure heater in step six is as follows:

[0175] Since the flue gas temperatures before and after each heating surface in the furnace cannot be measured, the heat absorption change of the water wall and the superheater is calculated by using the simplified processing method.

[0176] The heat absorption changes of the water wall and the superheater are uniformly calculated, and two limit boundaries are defined.

[0177] Boundary 1: The working medium temperature at the outlet of the superheater after extraction throttling of the high-pressure heater is the same as before throttling, at this time, the increased heat absorption of the water wall and the superheater is the same as the water feed heating deficiency of the hth high-pressure heater extraction throttling scheme, at this time, it is the maximum heat absorption change:

[0178] ΔQ sh,max = ΔQ fw,h

[0179] In the formula, ΔQ sh,max is the maximum heat absorption change of the water wall and the superheater, kJ / s; h sh,out is the enthalpy value of the working medium at the outlet of the superheater, kJ / kg; h ww,in is the enthalpy value of the working medium at the inlet of the water wall, kJ / kg;

[0180] Boundary 2: The total heat absorption of the water wall and the superheater of the boiler system is unchanged, that is, ΔQ sh,min = 0.

[0181] In the formula, ΔQ sh,min is the minimum heat absorption change of the water wall and the superheater, kJ / s;

[0182] In the actual process, due to the water feed heating deficiency, the temperature of the working medium entering the water wall decreases, the heat absorption of the water wall and the superheater increases, but at the same time, the temperature of the working medium at the outlet of the superheater also decreases. Therefore, the increased heat absorption of the water wall and the superheater caused by the actual water feed heating deficiency is between the maximum and minimum values:

[0183] ΔQ sh,re = k sh,re ΔQ sh,max

[0184] In the formula, ΔQ sh,reThe added heat absorption of the actual water-cooled wall and superheater, kJ / s; k sh,re The equivalent coefficient of the heat absorption change of the water-cooled wall and superheater, 0 < k sh,re < 1.

[0185] The present application uses two limit boundaries to represent the heat absorption change of the water-cooled wall and superheater after the throttling of the high-pressure turbine extraction steam, greatly simplifies the non-linear and large-inertia heat transfer calculation problem, and greatly reduces the calculation resources while ensuring the acceptable accuracy of the subsequent control parameter calculation.

[0186] Preferably, the specific calculation method of the flow rate of each reheated steam before the throttling of the high-pressure turbine extraction steam in step seven is as follows:

[0187] The Darcy-Weisbach formula is used to calculate the flow rate of each reheated steam, and the specific calculation formula is as follows:

[0188]

[0189] In the formula, m rs,j and m rs0,j are the real-time flow rate of the jth reheated steam and the flow rate of the jth reheated steam under the design condition, kg / s; Δp pipe,j and Δp pipe0,j are the real-time cold section pipeline pressure drop of the jth reheated steam and the cold section pipeline pressure drop of the jth reheated steam under the design condition, MPa; ρ pipe,j and ρ pipe0,j are the real-time cold section pipeline working medium density of the jth reheated steam and the cold section pipeline working medium density of the jth reheated steam under the design condition, kg / m 3 .

[0190] The present application uses the Darcy-Weisbach formula to calculate the flow rate of each reheated steam before the throttling of the high-pressure turbine extraction steam, directly calculates the real-time reheated steam flow rate of the unit by means of the design parameters and real-time operation data of the supercritical unit, and ensures the operation speed and method feasibility.

[0191] Preferably, the specific selection method of the high-pressure turbine extraction throttling scheme in step eight is as follows:

[0192] The specific control strategy optimization is shown in Figure 3 On the basis of the original reheated steam temperature control logic, different gradient high-pressure turbine extraction throttling is added to scientifically and reasonably control different reheated steam temperature deviations, and the selection method of the specific high-pressure turbine extraction throttling scheme is introduced as follows:

[0193] When the temperature deviation of each reheated steam exceeds the set value, the temperature deviation of each reheated steam exceeding the set value is compared with the predicted value of the temperature change of each reheated steam of each scheme, and is uniformly arranged in the following form:

[0194] When ΔT rs,bdy <ΔT rs,j,dev ≤ΔT rs,j,exp,1 , the first high-pressure heater extraction throttling scheme is selected;

[0195] When ΔT rs,j,exp,1 <ΔT rs,j,dev ≤ΔT rs,j,exp,2 , the second high-pressure heater extraction throttling scheme is selected;

[0196] When ΔT rs,j,dev >ΔT rs,j,exp,2 , the third high-pressure heater extraction throttling scheme is selected;

[0197] For the final high-pressure heater extraction throttling scheme, the high-pressure heater extraction throttling scheme with the largest number of high-pressure heaters corresponding to the reheat steam deviation is selected.

[0198] When the high-pressure heater extraction throttling strategy is used and the reheat steam temperature deviation gradually decreases, the extraction throttling of each high-pressure heater is sequentially and orderly selected according to the above-mentioned throttling scheme selection method, and when the reheat steam temperature deviation is less than or equal to the preset limit ΔT rs,j,bdy , the normal extraction of all high-pressure heaters is restored.

[0199] The application provides a detailed high-pressure heater extraction throttling orderly input and orderly exit mechanism, and the automatic selection and automatic recovery of the high-pressure heater extraction throttling scheme are completed by comparing the reheat steam temperature change prediction value of different high-pressure heater extraction throttling schemes with the real-time reheat steam temperature deviation.

[0200] The high-pressure heater extraction throttling controls the reheat steam temperature, combines the original reheat steam temperature control logic of the supercritical unit automatic control system, can more effectively control the reheat steam temperature during the rapid load increase, improves the variable load rate of the supercritical unit, and has important significance for improving the operation flexibility.

[0201] The above-mentioned is only a better specific embodiment case of the application, and does not limit the application, and any modification, equivalent transformation or improvement within the spirit and principle of the application should be included in the protection scope of the application.

Claims

1. A high-pressure extraction throttling supercritical unit reheat steam temperature control method, characterized in that: Comprising the following steps: Step one: data acquisition Collecting the feed water flow rate m of the boiler system fw And the feed water flow rate measurement data m of the steam turbine system flowing through each stage of the high-pressure heater fwi Where i = 1 ~ k-1; Collecting m working medium inlet and outlet thermal parameters between the boiler system and the steam turbine system, including the temperature and pressure T in,a in,a of the working medium flow entering the boiler out,a out,a wherein a = 1 ~ m;​​ Collect the thermodynamic parameters of the Z-stage regenerative heater, including the temperature T before and after each stage of the regenerative heater on the feedwater side. w,in,b T w,out,b Temperature T of each stage of extraction steam on the extraction side s,b Pressure p s,b Temperature T of the condensate drain of each stage of the regenerator d,b Where b = 1 to z; collecting feedwater pump after feedwater pressure p fp and coal economizer inlet feedwater pressure p eco,in , water cooling wall inlet working medium temperature T ww,in and pressure p ww,in ; Step two: data preprocessing The above collected parameter data is cleaned up; Step three: calculate the enthalpy value of each point working medium Using temperature and pressure data, the enthalpy of each point of working medium is obtained by thermophysical calculation, including the enthalpy h of m working medium flow in and out of the boiler in,a and h out,a , wherein a=1~m; the enthalpy h of inlet water of each stage of regenerative heater on the feedwater side w,in,b and the enthalpy h of outlet water w,out,b ; the enthalpy h of each stage of extraction steam on the extraction steam side s,b ; the enthalpy h of each stage of drain d,b , wherein b=1~z; the enthalpy h of working medium at the inlet of water wall of the boiler system ww,in ; Step four: calculate the change of each reheat steam flow caused by high pressure heater extraction throttling For high pressure heater, when extraction throttling, all extraction returns to turbine, that is where: m sei is the steam flow rate returned to the steam turbine when the extraction steam of the ith high-pressure heater is throttled, kg / s; m dw(i-1) is the drain flow rate from the (i-1)th high-pressure heater, kg / s; γ i is the heat release of the drain from the previous stage in the ith high-pressure heater, kJ / kg; q i is the heat release of the extraction steam of the ith high-pressure heater, kJ / kg; τ i is the heat absorption of the feedwater of the ith high-pressure heater, kJ / kg; The change of each reheat steam flow is the sum of the change of all extraction flow whose extraction pressure is greater than or equal to the pressure of the reheat steam: wherein: Δm rs,j is the change of the jth reheat steam flow, kg / s; Δm sei is the change of the ith high-pressure heater extraction steam flow, which is equal in quantity to all the extraction steam flow of the throttled high-pressure heater, kg / s; p rs,j is the jth reheat steam cold section pressure, MPa; Step five: calculate the water heating deficiency corresponding to different high pressure heater extraction throttling schemes High pressure heater extraction throttling increases the water heating deficiency of this stage, which leads to the decrease of main steam temperature. In order to avoid the influence of the extraction of heater with higher extraction pressure on the throttling effect, all continuous high pressure heaters including the highest stage high pressure heater are throttled in each high pressure heater extraction throttling scheme. Since the corresponding high pressure heater extraction is all throttled, the water heating deficiency is equal to the enthalpy rise of the water flowing through the heater, which is calculated as follows: ΔQ fw,1 = m fw1 Scheme 1: Throttling No. 1 High Pressure Heater ΔQ fw,2 = m fw1 τ1+ m fw2 τ2Scheme 2: Throttling No. 1 and No. 2 High Pressure Heaters Throttling No.1, No.2 and No.3 high-pressure heaters … … throttling No. 1, No. 2, No. 3, b, No. h high-pressure heater … … Throttling No. 1, No. 2, No. 3, …, No. k-1 high-pressure heater type: AQ fw,1 , AQ fw,2 , AQ fw,3 , AQ fw,h , and AQ fw,k-1 respectively are the heating deficiency of feedwater caused by extraction throttling of scheme 1, scheme 2, scheme 3, scheme h, and scheme k-1 high-pressure heater, kJ / s; m fw1 , m fw2 , and m fwi respectively are the feedwater flow rate through the 1st stage, 2nd stage, and i-th stage high-pressure heater, kg / s; τ1, τ2 and τ i H2 and Hi are the enthalpy rises of feedwater for the first, second and i-th high-pressure heaters, respectively, kJ / kg; Step six: calculate the heat absorption change of each reheat heater after the boiler superheater High pressure heater extraction throttling causes water heating deficiency, and the temperature of the water entering the boiler system decreases significantly, which will lead to the increase of the heat absorption of the water wall and superheater before each reheat heater. The increase of the heat absorption of the water wall and superheater caused by water heating deficiency will lead to the decrease of the heat absorption of each reheat heater after the above heating surface. The decreased heat absorption is distributed according to the proportion of the original heat absorption of each reheat heater affected. wherein: AQ rh,j is the change in heat absorption of the jth reheat steam in the boiler system reheater, kJ / s; AQ sh,re is the increased heat absorption of the water wall and superheater caused by the high-pressure turbine extraction throttling, kJ / s; Q rh,j is the heat absorption of the jth reheat steam in the boiler system reheater, kJ / s; Step seven: calculate the predicted value of reheat steam temperature change Due to the throttling of high-pressure-steam extraction, the change of the flow rate of each reheat steam is Δm rs,j , and at the same time, the change of the heat absorption of each reheat steam caused by insufficient heating of feed water is ΔQ rh,j ; and in combination of the above changes, the change of the enthalpy of reheat steam caused by the throttling of high-pressure-steam extraction is: wherein: Δh rs,j is the enthalpy change of the jth reheat steam, kJ / kg; Q′ rh,j and Q rh,j are the heat absorption of the jth reheat steam after and before throttling of the high-pressure extraction steam, kJ / s; m′ rs,j and m rs,j are the flow rate of the jth reheat steam after and before throttling of the high-pressure extraction steam, kg / s; The heat absorption of the jth reheat heater after high pressure heater extraction throttling is: Q' rh,j = Q rh,j - ΔQ rh,j Under the premise that the reheat steam temperature change is small, the specific heat capacity change can be ignored, so the predicted value of the reheat steam temperature change after high pressure heater extraction throttling is: where ΔT rs,j is the predicted value of the temperature change of the jth reheat steam after throttling of the high-pressure extraction, °C; c rs,j is the specific heat capacity of the jth reheat steam, kJ / (kg·K); Step eight: calculate the real-time reheat steam temperature deviation and reasonably select the high pressure heater extraction throttling scheme The predicted values of the temperature changes of the reheated steam under different high-pressure turbine extraction throttling schemes are obtained, respectively: ΔT rs,j,h j = 1 ~ m-1, h = 1 ~ k-1; since the actual variable load process is very fast, different high-pressure turbine extraction throttling schemes cannot reach the maximum main steam temperature change, so the predicted value correction coefficient of the main steam temperature of high-pressure turbine extraction throttling is introduced, that is, ΔT rs,j,exp,h = k rs,j,expchan,h ΔT rs,j,h j = 1 ~ m - 1, h = 1 ~ k - 1 where ΔT rs,j,exp,h is the predicted value of the change in the jth reheat steam temperature expected for the hth high-pressure heater extraction throttling scheme during the actual rapid load change, °C; k rs,j,expchan,h is the correction factor for the predicted value of the change in the reheat steam temperature due to high-pressure heater extraction throttling, 0 < k rs,j,expchan,h < 1; At the same time, the deviation of each reheat steam real-time temperature from the set temperature is calculated, ΔT rs,j,dev = T rs,j,set - T rs,j,rt where: ΔT rs,j,dev is the jth reheat steam temperature deviation, °C; T rs,j,set is the jth steam temperature setpoint, kJ / s; T ls,rt is the main steam temperature real-time value, °C; When the temperature deviation of each reheating steam is within a certain range, the method of controlling the reheating steam temperature by throttling the extraction steam of the high pressure turbine is not used, i.e. ΔT rs,j,dev ≤ ΔT rs,j,bdy Only the flue gas damper or flue gas recirculation is used to control the temperature of each reheating steam. When the reheat steam temperature deviation is greater than the set value ΔT rs,j,bdy only then the method of high-pressure heater extraction throttling control of reheat steam temperature is adopted, and according to the relative size of the reheat steam temperature deviation of each time and the reheat steam temperature change prediction value of each scheme of each time, the most appropriate high-pressure heater extraction throttling scheme is selected in order and timely.

2. The high-pressure reheat supercritical unit with extraction throttling reheating steam temperature control method according to claim 1, characterized in that: In step two, the above collected parameter data is cleaned up, and the specific process is as follows: (1) First, the original measurement data collected in step one is denoised, and Kalman filtering method is used to denoise and filter the original operation data; (2) Then, the denoised measurement data set is analyzed, and the missing values, abnormal values and error values in the measurement data are selected. The data missing values are filled, the data abnormal values are corrected, and the data error values are removed; (3) Analyzing the size and variation trend of the important basic parameters indispensable in the supercritical unit, mainly the unit load W p , the main steam pressure p out,1 and the variation trend of the feed water flow m fw ; According to the change trend of the basic parameters, combined with the physical mechanism and change law in the actual operation process of the supercritical unit, whether the size and change trend of the measurement value of other parameters collected in step one except the unit load, main steam pressure and feedwater flow parameters are contrary to the change of the basic parameters of the supercritical unit is judged. The data of more measurement points are selected more accurately. The data points that are contrary to the change of the basic data of the supercritical unit are corrected or discarded, and finally the cleaning work of the collected measurement data is completed.

3. The high-pressure reheat supercritical unit with extraction throttling reheating steam temperature control method according to claim 1, characterized in that: The calculation method of the missing pressure parameters of each working medium enthalpy value in Step 3 is as follows: the enthalpy value h of the steam at each stage of the heater is calculated by thermophysical properties d,i The steam pressure P of each stage of the heater necessary but without measuring points d,i According to the 95% of the steam pressure P of each stage of extraction s,i , that is P d,i = 0.95P s,i , i = 1 ~ k - 1 The enthalpy h of the feedwater at the inlet of each stage of regenerative heater on the water side is calculated by thermophysical calculation w,in,i and the enthalpy h of the outlet water w,out,i The pressure P of the feedwater at the inlet of each stage of regenerative heater which is necessary but has no measuring point w,in,i and the pressure P of the outlet water w,out,i Where i = 1 ~ k-1, the feedwater pressure P after the feedwater pump is calculated to obtain, i.e. fp and the feedwater pressure P at the inlet of the coal economizer eco,in ​ 4. The high-pressure reheat supercritical unit with extraction throttling reheating steam temperature control method of claim 1, wherein: The energy balance calculation method of regenerative heater in step four and step five is as follows: According to the calculation principle of energy balance, the feedwater heat absorption quantity τ of the high-pressure heater can be obtained i , the extraction steam heat release quantity q i and the drain steam heat release quantity γ i , and the calculation method is as follows: 1) for the drain flow type heater: τ i = h w,out,i - h w,in,i q i = h s,i - h d,i gamma i = h d,i-1 - h d,i 2) for the collection type heater: τ i = h w,out,i - h w,in,i q i = h s,i - h w,in,i gamma i = h d,i-1 - h w,in,i wherein: h w,out,i hi is the enthalpy of the feedwater at the outlet of the i-th regenerative heater, kJ / kg; h w,in,i hi is the enthalpy of the feedwater at the inlet of the i-th regenerative heater, kJ / kg; h s,i hi is the enthalpy of the extraction steam at the i-th regenerative heater, kJ / kg; h d,i hi is the enthalpy of the drain at the i-th regenerative heater, kJ / kg; h d,i-1 hi is the enthalpy of the drain at the i-1-th regenerative heater, kJ / kg.

5. The high-pressure reheat supercritical steam turbine with extraction control method of claim 1, wherein: The calculation method of the heat absorption change of water wall and superheater after high pressure heater extraction throttling in step six is as follows: Because the flue gas temperature before and after each heating surface in the furnace can not be measured, the heat absorption of the water wall and the superheater is calculated by a simplified method; The heat absorption of the water wall and the superheater is calculated uniformly, and two limit boundaries are defined: Boundary 1: the working medium temperature at the outlet of the superheater after the extraction throttling of the high-pressure heater is the same as that before the extraction throttling, at this time, the increased heat absorption of the water wall and the superheater is the same as the water heating deficiency of the hth extraction throttling scheme of the high-pressure heater, at this time, it is the maximum heat absorption change: ΔQ sh,max = ΔQ fw,h where: AQ sh,max is the maximum heat absorption change of the water wall and superheater, kJ / s; h sh,out is the enthalpy of the working medium at the outlet of the superheater, kJ / kg; h ww,in is the enthalpy of the working medium at the inlet of the water wall, kJ / kg; Boundary 2: The total heat absorption of the boiler system water wall and superheater is unchanged, i.e., AQ sh,min = 0; where: AQ sh,min is the minimum heat absorption change for the water wall and superheater, kJ / s; In the actual process, due to the water heating deficiency, the working medium temperature entering the water wall decreases, the heat absorption of the water wall and the superheater increases, but at the same time, the working medium temperature at the outlet of the superheater also decreases to a certain extent; therefore, the increased heat absorption of the water wall and the superheater caused by the actual water heating deficiency is between the above maximum and minimum values: ΔQ sh,re = k sh,re ΔQ sh,max where: AQ sh,re Q is the actual water wall and superheater heat absorption, kJ / s; k sh,re k is the water wall and superheater heat absorption change equivalent coefficient, 0 < k sh,re < 1.

6. The high-pressure reheat supercritical steam turbine with extraction control method of claim 1, wherein: The specific calculation method of the flow rate of each reheated steam before the extraction throttling of the high-pressure heater in step seven is as follows: The Darcy-Weisbach formula is used to calculate the flow rate of each reheated steam, and the specific calculation formula is as follows: In the formula: m rs,j and m rs0,j are the jth reheat steam flow rate in real time and the jth reheat steam flow rate under the design condition, kg / s; Δp pipe,j and Δp pipe0,j are the jth reheat steam cold section pipe pressure drop in real time and the jth reheat steam cold section pipe pressure drop under the design condition, MPa; ρ pipe,j and ρ pipe0,j are the jth reheat steam cold section pipe working medium density in real time and the jth reheat steam cold section pipe working medium density under the design condition, kg / m 3 .

7. The high-pressure reheat supercritical steam turbine with extraction control method of claim 1, wherein: The specific selection method of the extraction throttling scheme of the high-pressure heater in step eight is as follows: When the temperature deviation of each reheat steam exceeds the set value, the temperature deviation of each reheat steam exceeding the set value is compared with the temperature change prediction value of each reheat steam of each scheme respectively, and is arranged in the following form: ΔT rs,j,exp,h-1 < ΔT rs,j,dev ≤ ΔT rs,j,exp,h The high-pressure heater extraction throttling scheme with the largest number of throttled high-pressure heaters is selected. And when the high-pressure heater throttling strategy is used, the temperature deviation of each reheated steam gradually decreases, and the throttling scheme selection method is still selected according to the above method, and the extraction throttling of each high-pressure heater is gradually and orderly withdrawn, and when the temperature deviation of each reheated steam is less than or equal to the preset limit value ΔT rs,j,bdy , the normal extraction of all high-pressure heaters is restored.

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