High-pressure heater steam extraction throttling supercritical unit reheat steam temperature control method

Abstract

The invention discloses a supercritical unit reheat steam temperature control method for high-pressure heater steam extraction throttling, which comprises the following steps of: firstly, acquiring real-time data of thermal parameters of a boiler system and a steam turbine system of a supercritical unit, cleaning the data, and calculating to obtain insufficient feed water heating and each reheat steam flow variation corresponding to different high-pressure heater steam extraction throttling schemes; the method comprises the following steps of: calculating the change of the heat absorption capacity of a reheater arranged in front of a superheater, synthesizing the change of the flow of reheat steam and the change of the heat absorption capacity of the reheater to obtain reheat steam temperature change predicted values corresponding to different high-pressure heater steam extraction throttling schemes, and finally obtaining a specific high-pressure heater steam extraction throttling control scheme according to the real-time deviation of the temperature of the reheat steam. According to the method, the original supercritical unit reheat steam temperature control logic is supplemented and optimized, the control effect of the supercritical unit reheat steam temperature can be effectively improved, and the problem that in the rapid load rising process, the reheat steam is greatly overheated is solved; and the method is of great significance to improvement of the rapid load change capacity of the supercritical coal-fired power generation 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 reheat steam temperature of a supercritical unit with high-pressure steam extraction throttling. 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 thermal power systems and providing absorption services for renewable energy power generation are important technical directions. Taking coal-fired power generation as an example, 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 operating condition with frequent load changes for a long time.

[0003] The control quality of reheat steam temperature has become an important bottleneck restricting the further improvement of variable load capacity of coal-fired power generation thermal power system. When the load is increased rapidly, the reheat steam temperature is very likely to exceed the limit, which limits the improvement of unit flexibility. How to quickly and effectively suppress the soaring reheat steam temperature during the rapid load increase process is an important part of the optimization of the coordinated control system of coal-fired power generation units.

[0004] The reheated steam temperature is related to the heat absorption of the reheater in the boiler system and the reheated steam flow rate. Rapidly adjusting the above two parameters during rapid load changes can effectively control the reheated steam temperature. Therefore, the present invention proposes a reheated steam temperature control method for a supercritical coal-fired power generation unit with high-pressure steam extraction throttling. 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 reheat steam temperature control method for a supercritical unit with high-pressure steam extraction throttling. With the help of high-pressure steam extraction throttling, the reheat steam flow rate is increased and the flue gas temperature at the inlet of the boiler reheater is reduced, thereby achieving the purpose of quickly reducing the reheat steam temperature. The present invention can greatly improve the problem of reheat steam temperature overheating occurring in the process of rapid load change.

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

[0007] A method for controlling the reheat steam temperature of a supercritical unit with high-pressure steam extraction throttling comprises the following steps:

[0008] Step 1: Data Collection

[0009] Collect boiler system feed water flow m fw The feedwater flow measurement data of the steam turbine system flowing through each stage of high pressure heater mfwi , where i = 1 to k-1;

[0010] Collect the inlet and outlet thermal parameters of m working fluids between the boiler system and the steam turbine system, including the temperature and pressure T of m working fluids entering the boiler in,a 、p in,a , the temperature and pressure T of the working fluid leaving the boiler out,a 、p out,a , where a = 1 ~ m;

[0011] Collect the thermal parameters of the z-level regenerative heater, including the temperature T before and after each level of regenerative heater on the water supply side w,in,b , T w,out,b ; The temperature of each stage of extraction steam on the extraction side T s,b , pressure p s,b The temperature T of the water drain of each level of heat recovery heater d,b , where b = 1 ~ z;

[0012] Collect the water supply pressure p after the water supply pump fp and economizer inlet feed water pressure p eco,in , water wall inlet working medium temperature T ww,in and pressure p ww,in ;

[0013] Step 2: Data preprocessing

[0014] Clean the parameter data collected above;

[0015] Step 3: Calculate the enthalpy of the working fluid at each point

[0016] Using the temperature and pressure data, the enthalpy value of the working fluid at each point is calculated through thermophysical property calculation, including the enthalpy value h of the inlet and outlet of the m working fluids in the boiler. in,a and h out,a , where a = 1 ~ m; the enthalpy value of the inlet water of each level of the regenerative heater on the water supply side h w,in,b and the enthalpy of the outlet water h w,out,b ; Enthalpy value of each stage of extraction steam on the extraction side h s,b ; Enthalpy value of each level of hydrophobicity h d,b , where b = 1 ~ z; the enthalpy value of the working medium at the water wall inlet of the boiler system h ww,in ;

[0017] Step 4: Calculate the change in reheat steam flow rate caused by high-pressure steam extraction throttling

[0018] For the high pressure heater, all the extraction steam is returned to the turbine when the extraction steam is throttled, that is,

[0019]

[0020] Where: m seiis the steam flow rate returned to the steam turbine when the i-th stage high pressure heater is throttled, kg / s; m dw(i-1) is the drainage flow rate from the i-1th stage high pressure heater, kg / s; γ i is the heat released by the hydrophobicity from the previous stage in the i-th stage high pressure heater, kJ / kg; q i is the heat release of the i-th stage high pressure heater extraction steam, kJ / kg; τ i is the heat absorption of feed water of the i-th stage high pressure heater, kJ / kg;

[0021] The change in each reheat steam flow rate is the sum of the changes in all extraction steam flows whose extraction pressure is greater than or equal to the reheat steam pressure:

[0022]

[0023] Where: Δm rs,j is the change in the jth reheat steam flow rate, kg / s; Δm sei is the change in the extraction steam flow rate of the i-th stage high-pressure heater, which is equal to the total extraction steam flow rate of the throttled high-pressure heater of this stage, kg / s; p rs,j is the cold section pressure of the j-th reheat steam, MPa;

[0024] Step 5: Calculate the feedwater heating shortage corresponding to different high-pressure steam extraction throttling schemes

[0025] The throttling of the high-pressure heater extraction steam increases the insufficient heating of the feed water at this stage, resulting in a drop in the main steam temperature. In order to avoid the increase in the extraction of the heater with a higher extraction pressure affecting the throttling effect, each high-pressure heater extraction steam throttling scheme throttles all continuous high-pressure heaters including the highest-level high-pressure heater;

[0026] The insufficient feedwater heating due to full throttling of the corresponding HP heater extraction steam is equal to the enthalpy rise of the feedwater flowing through the heater of this stage, calculated as follows:

[0027] ΔQ fw,1 =m fw1 τ1 Option 1: Throttling No.1 High-Pressure Heater

[0028] ΔQ fw,2 =m fw1 τ1+m fw2 τ2 Option 2: Throttling No.1 and No.2 High-Pressure Heaters

[0029] Throttling No.1, No.2 and No.3 high pressure heaters

[0030] …

[0031] Throttling No.1, No.2, No.3, ..., No.h high pressure heater

[0032] …

[0033] Throttling No.1, No.2, No.3, ..., No.k-1 high pressure heater

[0034] Where: ΔQ fw,1 , ΔQ fw,2 , ΔQ fw,3 , ΔQ fw,h and ΔQ fw,k-1 The feedwater heating shortage caused by the extraction throttling of the high-pressure heater for Scheme 1, Scheme 2, Scheme 3, Scheme h and Scheme k-1, kJ / s; m fw1 、m fw2 and m fwi are the feed water flow rates flowing through the 1st, 2nd and i-th stage high pressure heaters, kg / s; τ1,

[0035] τ2 and τ i are the feed water enthalpy rise of the 1st, 2nd and i-th stage high pressure heaters, kJ / kg;

[0036] Step 6: Calculate the change in heat absorption of each reheater after the boiler superheater

[0037] The throttling of high-pressure steam extraction causes insufficient heating of feed water, and the temperature of feed water entering the boiler system drops significantly, which will lead to an increase in the heat absorption of the water-cooled wall and superheater heating surface before each reheater;

[0038] The increase in heat absorption of the water-cooled wall and superheater caused by insufficient heating of the feed water will cause a decrease in the heat absorption of each reheater after the above heating surface. The reduced heat absorption is distributed according to the original heat absorption ratio of each affected reheater;

[0039]

[0040] Where: ΔQ rh,j is the change in heat absorption of the jth reheated steam in the boiler system reheater, kJ / s; ΔQ sh,re Q is the increased heat absorption of the water-cooled wall and superheater caused by high-pressure steam extraction throttling, kJ / s; rh,j is the heat absorbed by the jth reheated steam in the boiler system reheater, kJ / s;

[0041] Step 7: Calculate the predicted value of reheat steam temperature change

[0042] Due to the throttling of the high-pressure steam extraction, the change in the reheat steam flow rate is Δm rs,j, and at the same time, the change in the amount of heat absorbed by each reheat steam caused by insufficient feed water heating is ΔQ rh,j ; Based on the above changes, the change in reheat steam enthalpy caused by high-pressure steam extraction throttling is obtained as follows:

[0043]

[0044] Where: Δh rs,j is the enthalpy change of the j-th reheated steam, kJ / kg; Q r ' h,j and Q rh,j are the jth reheater heat absorption after and before throttling of the high-pressure heater extraction steam, kJ / s; m r ' s,j and m rs,j are the jth reheat steam flow rates after and before throttling of the high-pressure heater extraction steam, kg / s;

[0045] The heat absorption of the jth reheater after throttling of the high-pressure steam extraction is:

[0046] Q r ' h,j =Q rh,j -ΔQ rh,j

[0047] Under the premise that the reheat steam temperature changes slightly, its specific heat capacity change can be ignored, so the predicted value of the reheat steam temperature change after high-pressure steam extraction throttling is:

[0048]

[0049] Where: ΔT rs,j is the predicted value of the jth reheat steam temperature change after high-pressure steam extraction throttling, ℃; c rs,j is the specific heat capacity of the j-th reheat steam, kJ / (kg·K);

[0050] Step 8: Calculate the real-time reheat steam temperature deviation and reasonably select the high-pressure steam extraction throttling scheme

[0051] Calculate different high-pressure steam extraction throttling schemes respectively, and obtain the predicted value of each reheat steam temperature change under various high-pressure steam extraction throttling schemes: ΔT rs,j,h , j = 1 ~ m-1, h = 1 ~ k-1; Since the actual load change process is very fast, different high-pressure steam extraction throttling schemes cannot achieve the maximum main steam temperature change, and the correction coefficient of the predicted value of the main steam temperature of the high-pressure steam extraction throttling is introduced, that is,

[0052] ΔT rs,j,exp,h =k rs,j,expchan,h ΔT rs,j,h ,j=1~m-1,h=1~k-1

[0053] Where: ΔT rs,j,exp,h is the predicted value of the jth reheat steam temperature change expected by the hth high-pressure steam extraction throttling scheme in the actual rapid load change process after correction, ℃; k rs,j,expchan,h k is the correction factor of the predicted value of reheat steam temperature change due to high pressure steam extraction throttling, 0<k rs,j,expchan,h <1;

[0054] At the same time, the deviation between the real-time temperature of each reheat steam and the set temperature is calculated.

[0055] ΔT rs,j,dev =T rs,j,set -T rs,j,rt

[0056] Where: ΔT rs,j,dev is the jth reheat steam temperature deviation, °C; T rs,j,set is the jth steam temperature setting value, kJ / s; T ls,rt is the real-time value of main steam temperature, ℃;

[0057] When the temperature deviation of each reheat steam is within a certain range, the method of controlling the reheat steam temperature by throttling the high-pressure steam extraction steam is not used. rs,j,dev ≤ΔT rs,j,bdy When the temperature of each reheat steam is controlled, only the flue gas damper or flue gas recirculation is used;

[0058] When the reheat steam temperature deviation is greater than the set value ΔT rs,j,bdy The method of high-pressure steam extraction throttling to control the reheat steam temperature is adopted only when the high-pressure steam extraction throttling is adopted, and the most appropriate high-pressure steam extraction throttling scheme is selected in sequence and in a timely manner according to the relative size of the reheat steam temperature deviation at each time and the predicted value of the reheat steam temperature change of each scheme.

[0059] In step 2, the parameter data collected above is cleaned. The specific process is as follows:

[0060] (1) First, the original measurement data collected in step 1 is subjected to noise reduction, and the original operation data is subjected to noise reduction filtering processing using the Kalman filtering method;

[0061] (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;

[0062] (3) Analyze the size and change trend of important basic parameters that are indispensable for supercritical units, mainly the unit load W p , main steam pressure p out,1 and water flow rate m fwAccording to the changing trend of basic parameters, combined with the physical mechanism and changing law of the supercritical unit in the actual operation process, determine whether the size and changing trend of the measured values ​​of other parameters except unit load, main steam pressure and feed water flow parameters collected in step 1 are inconsistent with the changes in the basic parameters of the supercritical unit, select more accurate measuring points for the data of multiple measuring points, correct or discard the data points that are inconsistent with the changes in the basic data of the supercritical unit, and finally complete the cleaning of the collected measurement data.

[0063] The calculation method for the various pressure parameters missing in the calculation of the enthalpy values ​​of each working fluid in step 3 is as follows: Calculate the hydrophobic enthalpy values ​​h of each heater through thermal properties d,i The required but unmeasured drain pressure P of each heater d,i According to the extraction steam pressure P s,i 95% is calculated, that is

[0064] P d,i =0.95P s,i , i=1~k-1

[0065] Calculate the enthalpy value h of the inlet water of each stage of the regenerative heater on the water supply side through the thermophysical properties w,in,i and the enthalpy of the outlet water h w,out,i The required but unmeasured water pressure P of each level of regenerative heater inlet w,in,i and outlet water pressure P w,out,i , where i = 1 ~ k-1, then the water supply pressure P after the water supply pump is used fp and economizer inlet feed water pressure P eco,in To calculate, that is

[0066]

[0067] The energy balance calculation method for the regenerative heater in steps 4 and 5 is as follows:

[0068] According to the calculation principle of energy balance, the feed water heat absorption τ of the high-pressure heater can be obtained: i , Extraction heat release q i and hydrophobic exothermicity γ i , the calculation method is as follows:

[0069] 1) For drain heater:

[0070] τ i =h w,out,i -h w,in,i

[0071] q i =h s,i -h d,i

[0072] γ i =h d,i-1 -h d,i

[0073] 2) For concentrating heaters:

[0074] τ i =h w,out,i -h w,in,i

[0075] q i =h s,i -h w,in,i

[0076] γ i =h d,i-1 -h w,in,i

[0077] Where: 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 enthalpy of the i-th stage regenerative heater, kJ / kg; h d,i is the enthalpy of hydrophobicity of the i-th stage regenerative heater, kJ / kg; h d,i-1 is the hydrophobic enthalpy of the i-1th stage regenerative heater, kJ / kg.

[0078] The calculation method for the change in heat absorption of the water-cooled wall and superheater after throttling of the high-pressure steam extraction in step 6 is as follows:

[0079] 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 change in heat absorption of the water-cooled wall and superheater;

[0080] The heat absorption changes of the water-cooled wall and superheater are calculated uniformly, and two limit boundaries are defined:

[0081] Boundary 1: The working medium temperature at the superheater outlet after throttling of the high-pressure steam extraction is the same as that before throttling. At this time, the increased heat absorption of the water-cooled wall and the superheater is the same as the insufficient heating of the feed water in the h-th high-pressure steam extraction throttling scheme. At this time, the maximum heat absorption change is:

[0082] ΔQ sh,max =ΔQ fw,h

[0083] Where: ΔQ sh,max is the maximum heat absorption change of water-cooled wall and superheater, kJ / s; h sh,out is the enthalpy of the working fluid at the superheater outlet, kJ / kg; h ww,in is the enthalpy of the working fluid at the water wall inlet, kJ / kg;

[0084] Boundary 2: The total heat absorption of the boiler system water-cooled wall and superheater remains unchanged, that is, ΔQ sh,min =0;

[0085] Where: ΔQ sh,min is the minimum heat absorption change of the water-cooled wall and superheater, kJ / s;

[0086] In the actual process, due to insufficient heating of feed water, the temperature of the working medium entering the water wall decreases, and the heat absorption of the water wall and superheater increases, but at the same time, the temperature of the working medium at the superheater outlet will also decrease to a certain extent; therefore, the actual increased heat absorption of the water wall and superheater caused by insufficient heating of feed water is between the above maximum and minimum values:

[0087] ΔQ sh,re =k sh,re ΔQ sh,max

[0088] Where: ΔQ sh,re is the actual amount of heat absorbed by the water-cooled wall and superheater, kJ / s; k sh,re is the equivalent coefficient of heat absorption change of water-cooled wall and superheater, 0<k sh,re <1.

[0089] The specific calculation method for each reheat steam flow rate before high-pressure heater extraction throttling in step 7 is as follows:

[0090] The Darcy-Weisbach formula is used to calculate the reheat steam flow rate at each time. The specific calculation formula is as follows:

[0091]

[0092] Where: m rs,j and m rs0,j are the real-time j-th reheat steam flow rate and the j-th reheat steam flow rate under design conditions, kg / s; Δp pipe,j and Δp pipe0,j are the real-time cold section pipe pressure drop of the j-th reheat steam and the cold section pipe pressure drop of the j-th reheat steam under design conditions, MPa; ρ pipe,j and ρ pipe0,j They are the real-time working fluid density of the cold section of the j-th reheat steam pipeline and the working fluid density of the cold section of the j-th reheat steam pipeline under the design condition, kg / m 3 .

[0093] The specific method for selecting the high-pressure steam extraction throttling scheme in step eight is as follows:

[0094] 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 each reheat steam temperature change of each scheme, and unified into the following form: ΔTrs,j,exp,h-1 <ΔT rs,j,dev ≤ΔT rs,j,exp,h , select the high-pressure heater extraction throttling scheme with the largest number of throttling high-pressure heaters;

[0095] And when the extraction throttling strategy of the high-pressure heater is used, when the temperature deviation of each reheat steam gradually decreases, the extraction throttling of each high-pressure heater is gradually and orderly exited in accordance with the above throttling scheme selection method, and when the temperature deviation of each reheat steam is less than or equal to the preset limit value ΔT rs,j,bdy When the steam is pumped out of the high-pressure heater, normal steam extraction of all high-pressure heaters is restored.

[0096] The beneficial effects of the present invention are as follows: the present invention adopts the method of high-pressure steam extraction throttling to control the reheat steam temperature of the supercritical coal-fired power generation unit, firstly collects the real-time data of the thermal parameters in the distributed control system of the supercritical coal-fired power generation unit, and uses data processing methods including data noise reduction, data filling, mechanism analysis, etc. to clean the collected operation data of the unit; then, by calculating the change of the reheat steam flow rate and the change of the heat absorption of the water-cooled wall and the superheater of different high-pressure steam extraction throttling schemes, the predicted value of the reheat steam temperature change corresponding to the different high-pressure steam extraction throttling schemes is calculated according to the energy balance equation, combined with the reheat steam temperature deviation collected and calculated in real time by the unit, by comparing the two, the most suitable high-pressure steam extraction throttling scheme corresponding to the current reheat steam temperature deviation is selected in order and in a timely manner. By supplementing and optimizing the automatic control logic of the reheat steam temperature by high-pressure steam extraction throttling, the problem of overheating of the reheat steam temperature can be effectively prevented when the supercritical coal-fired power generation unit is rapidly increased in load, and the bottleneck of the reheat steam temperature exceeding the limit, which limits the further increase of the unit load change rate, is eliminated, and the unit operation flexibility is improved.

[0097] Advantages of the present invention

[0098] 1) The present invention provides several high-pressure steam extraction throttling schemes. In order to maximize the throttling effect and prevent a substantial increase in the steam extraction of the heater with a higher steam extraction pressure when the high-pressure steam extraction throttling is performed, all high-pressure steam extraction throttling schemes provided by the present invention require throttling of continuous heaters including the highest-level high-pressure heater, which not only ensures the effect of high-pressure steam extraction throttling, but also facilitates the use and exit of specific implementation plans, simplifies the operational difficulty of high-pressure steam extraction throttling to control the reheat steam temperature, and makes it easier to achieve automatic control;

[0099] 2) The present invention uses the energy balance of the high-pressure regenerative heater to calculate the flow changes of reheated steam at each level and the insufficient heating of feed water corresponding to different high-pressure steam extraction throttling schemes, and then uses the energy balance of the boiler water-cooled wall, superheater and reheater to comprehensively consider all changes in the flow direction of energy, and finally calculates the predicted values ​​of the temperature changes of each reheated steam corresponding to different high-pressure steam extraction throttling schemes, which has important guiding significance for the selection of subsequent high-pressure steam extraction throttling schemes;

[0100] 3) The present invention discloses a method for selecting a throttling scheme based on the real-time collected and calculated reheat steam temperature deviation and the predicted value of reheat steam temperature change corresponding to each high-pressure steam extraction throttling scheme calculated through the above steps. By defining the high-pressure steam extraction throttling temperature deviation limit, when the reheat steam temperature deviation is greater than the set limit, different high-pressure steam extraction throttling schemes are selected in sequence, orderly and timely according to the size relationship between the temperature deviation and the temperature change predicted value; and when the reheat steam temperature deviation decreases, each heater throttling is exited in sequence and orderly according to the size relationship between the deviation and the predicted value, and when it is less than the set limit, the high-pressure steam extraction of the turbine system is fully restored; through the above high-pressure steam extraction throttling selection and scheduling scheme, throttling methods with different effects can be reasonably and timely selected to correspond to different reheat steam temperature deviations, so as to more scientifically schedule the reasonable flow of various energy flows inside the thermal power system, and ultimately improve the reheat steam temperature control effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0101] Figure 1 The present invention is a flow chart of a reheat steam temperature control method for a supercritical unit with high-pressure steam extraction throttling;

[0102] Figure 2 This is the thermal system diagram of a 1000MW ultra-supercritical single-reheat unit, where 1 is the No. 1 high-pressure heater, 2 is the No. 2 high-pressure heater, 3 is the No. 3 high-pressure heater, 4 is the reheater, 5 is the economizer, 6 is the superheater, 7 is the water-cooled wall, 8 is the boiler system, 9 is the turbine system, 10 is the turbine high-pressure cylinder, 11 is the turbine intermediate-pressure cylinder, and 12 is the turbine low-pressure cylinder;

[0103] Figure 3 The figure is a reheat steam temperature control logic diagram of a supercritical unit with high-pressure steam extraction throttling, wherein the bold part is the reheat steam temperature control logic of the supplementary and optimized high-pressure steam extraction throttling. DETAILED DESCRIPTION

[0104] 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.

[0105] A method for controlling the reheat steam temperature of a supercritical unit with high-pressure extraction throttling, such as Figure 2As shown, 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, wherein one working medium is converted into new steam by absorbing heat from feed water, the feed water flows out from the highest level heat recovery heater into the boiler 8, and the new steam flows out from the superheater 6 to the new steam inlet of the steam turbine; the remaining m-1 streams are reheated steam, which flows out from a certain level of steam extraction port of the steam turbine into the reheater 4 of the boiler system, and enters the reheat steam inlet of the steam turbine after reheating; the boiler system 8 includes heating surfaces such as economizer 5, water-cooled wall 7, superheater 6 and reheater 4, as well as important auxiliary equipment such as air preheater, coal mill and burner. The boiler feed water from the steam turbine feed water recovery system enters the economizer 5 for heating, and then absorbs heat in the water-cooled wall 7 of the boiler to become superheated steam, and then enters the superheater 6. Heating; the steam turbine system 9 includes a steam turbine, a z-stage regenerative heater, a feed water pump and a condenser. The z-stage regenerative heater is connected to the steam turbine extraction port through a pipeline and is arranged from high to low according to the extraction pressure; according to the water side pressure, the 1st to k-1th stage regenerative heaters are high-pressure heaters, the kth stage is a deaerator, and the k+1th to zth stages are low-pressure heaters, and finally the turbine exhaust enters the condenser; there are two ways to connect the water side and the steam side. For the partition-type regenerative heater, water flows in the tube and steam flows outside the tube. Heat is transferred from the steam side to the water side through the tube wall. The feed water or condensate is heated and heated, and the extraction steam releases heat and becomes hydrophobic, and flows step by step to the next stage regenerative heater; for the converging heater, water and steam are fully mixed and heat-exchanged in the heater, and combined into a working fluid to continue flowing along the water side; in this example, the thermal energy power system is as follows Figure 2 As shown, 8-stage heat recovery heaters are 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-cooled wall, 8 represents boiler system, 9 represents turbine system, 10 represents turbine high-pressure cylinder, 11 represents turbine intermediate-pressure cylinder, and 12 represents turbine low-pressure cylinder.

[0106] The thermal power system configuration characteristics used in the specific calculation case are:

[0107] 1) The ultra-supercritical unit is a 1000MW ultra-supercritical single-reheat condensing unit;

[0108] 2) Rated water supply temperature is 294.7℃;

[0109] 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;

[0110] 4) Reheat steam is taken from the exhaust steam of the high-pressure cylinder and enters the inlet of the medium-pressure cylinder after being heated by the boiler;

[0111] 5) The thermal system diagram of the ultra-supercritical unit is shown in the attached Figure 2 As shown;

[0112] like Figure 1 and Figure 3 As shown, the reheat steam temperature control method of a supercritical unit with high-pressure steam extraction throttling in this embodiment includes the following steps:

[0113] Step 1: Data Collection

[0114] Collect boiler system feed water flow m fw The feedwater flow measurement data of the steam turbine system flowing through each stage of high pressure heater m fwi , where i = 1 to k-1;

[0115] Collect the inlet and outlet thermal parameters of m working fluids between the boiler system and the steam turbine system, including the temperature and pressure T of m working fluids entering the boiler in,a 、p in,a , the temperature and pressure T of the working fluid leaving the boiler out,a 、p out,a , where a = 1 ~ m;

[0116] Collect the thermal parameters of the z-level regenerative heater, including the temperature T before and after each level of regenerative heater on the water supply side w,in,b , T w,out,b ; The temperature of each stage of extraction steam on the extraction side T s,b , pressure p s,b The temperature T of the water drain of each level of heat recovery heater d,b , where b = 1 ~ z;

[0117] Collect the water supply pressure p after the water supply pump fp and economizer inlet feed water pressure p eco,in , water wall inlet working medium temperature T ww,in and pressure p ww,in ;

[0118] Step 2: Data preprocessing

[0119] Clean the parameter data collected above;

[0120] Step 3: Calculate the enthalpy of the working fluid at each point

[0121] Using the temperature and pressure data, the enthalpy value of the working fluid at each point is calculated through thermophysical property calculation, including the enthalpy value h of the inlet and outlet of the m working fluids in the boiler. in,a and h out,a , where a = 1 ~ m; the enthalpy value of the inlet water of each level of the regenerative heater on the water supply side h w,in,b and the enthalpy of the outlet water h w,out,b ; Enthalpy value of each stage of extraction steam on the extraction side h s,b ; Enthalpy value of each level of hydrophobicity hd,b , where b = 1 ~ z; the enthalpy value of the working medium at the water wall inlet of the boiler system h ww,in ;

[0122] Step 4: Calculate the change in reheat steam flow rate caused by high-pressure steam extraction throttling

[0123] For the high pressure heater, all the extraction steam is returned to the turbine when the extraction steam is throttled, that is,

[0124]

[0125] Where: m sei is the steam flow rate returned to the steam turbine when the i-th stage high pressure heater is throttled, kg / s; m dw(i-1) is the drainage flow rate from the i-1th stage high pressure heater, kg / s; γ i is the heat released by the hydrophobicity from the previous stage in the i-th stage high pressure heater, kJ / kg; q i is the heat release of the i-th stage high pressure heater extraction steam, kJ / kg; τ i is the heat absorption of feed water of the i-th stage high pressure heater, kJ / kg;

[0126] The change in each reheat steam flow rate is the sum of the changes in all extraction steam flows whose extraction pressure is greater than or equal to the reheat steam pressure:

[0127]

[0128] Where: Δm rs,j is the change in the jth reheat steam flow rate, kg / s; Δm sei is the change in the extraction steam flow rate of the i-th stage high-pressure heater, which is equal to the total extraction steam flow rate of the throttled high-pressure heater of this stage, kg / s; p rs,j is the cold section pressure of the j-th reheat steam, MPa;

[0129] Step 5: Calculate the feedwater heating shortage corresponding to different high-pressure steam extraction throttling schemes

[0130] The throttling of the high-pressure steam extraction increases the insufficient heating of the feed water at this stage, resulting in a drop in the main steam temperature. In order to prevent the increase in steam extraction from the heater with higher extraction pressure from affecting the throttling effect, each high-pressure steam extraction throttling scheme throttles all continuous high-pressure heaters including the highest-level high-pressure heater.

[0131] The insufficient feedwater heating due to full throttling of the corresponding HP heater extraction steam is equal to the enthalpy rise of the feedwater flowing through the heater of this stage, calculated as follows:

[0132] ΔQ fw,1 =m fw1 τ1 Option 1: Throttling No.1 High-Pressure Heater

[0133] ΔQ fw,2 =m fw1 τ1+m fw2 τ2 Option 2: Throttling No.1 and No.2 High-Pressure Heaters

[0134] Throttling No.1, No.2 and No.3 high pressure heaters

[0135] …

[0136] Throttling No.1, No.2, No.3, ..., No.h high pressure heater

[0137] …

[0138] Throttling No.1, No.2, No.3, ..., No.k-1 High-pressure heater Where: ΔQ fw,1 , ΔQ fw,2 , ΔQ fw,3 , ΔQ fw,h and ΔQ fw,k-1 The feedwater heating shortage caused by the extraction throttling of the high-pressure heater for Scheme 1, Scheme 2, Scheme 3, Scheme h and Scheme k-1, kJ / s; m fw1 、m fw2 and m fwi are the feed water flow rates flowing through the 1st, 2nd and i-th stage high pressure heaters, kg / s; τ1,

[0139] τ2 and τ i are the feed water enthalpy rises of the 1st, 2nd and i-th stage high pressure heaters, kJ / kg respectively.

[0140] Step 6: Calculate the change in heat absorption of each reheater after the boiler superheater

[0141] The throttling of high-pressure steam extraction causes insufficient heating of the feed water, and the temperature of the feed water entering the boiler system drops significantly, which will lead to an increase in the heat absorption of the water-cooled walls and superheater heating surfaces before each reheater.

[0142] The increase in heat absorption of the water-cooled walls and superheaters caused by insufficient feed water heating will cause a decrease in the heat absorption of each reheater following the above heating surfaces. The reduced heat absorption is distributed according to the proportion of the original heat absorption of each affected reheater.

[0143]

[0144] Where: ΔQ rh,j is the change in heat absorption of the jth reheated steam in the boiler system reheater, kJ / s; ΔQ sh,reQ is the increased heat absorption of the water-cooled wall and superheater caused by high-pressure steam extraction throttling, kJ / s; rh,j is the heat absorbed by the jth reheated steam in the boiler system reheater, kJ / s;

[0145] Step 7: Calculate the predicted value of reheat steam temperature change

[0146] Due to the throttling of the high-pressure steam extraction, the change in the reheat steam flow rate is Δm rs,j , and at the same time, the change in the amount of heat absorbed by each reheat steam caused by insufficient feed water heating is ΔQ rh,j Based on the above changes, the change in reheat steam enthalpy caused by throttling of the high-pressure steam extraction steam can be obtained as follows:

[0147]

[0148] Where: Δh rs,j is the enthalpy change of the j-th reheated steam, kJ / kg; Q r ' h,j and Q rh,j are the jth reheater heat absorption after and before throttling of the high-pressure heater extraction steam, kJ / s; m r ' s,j and m rs,j are the jth reheat steam flow rates after and before throttling of the high-pressure heater extraction steam, kg / s;

[0149] The heat absorption of the jth reheater after throttling of the high-pressure steam extraction is:

[0150] Q r ' h,j =Q rh,j -ΔQ rh,j

[0151] Under the premise that the reheat steam temperature changes slightly, its specific heat capacity change can be ignored, so the predicted value of the reheat steam temperature change after high-pressure steam extraction throttling is:

[0152]

[0153] Where: ΔT rs,j is the predicted value of the jth reheat steam temperature change after high-pressure steam extraction throttling, ℃; c rs,j is the specific heat capacity of the j-th reheat steam, kJ / (kg·K);

[0154] Step 8: Calculate the real-time reheat steam temperature deviation and reasonably select the high-pressure steam extraction throttling scheme

[0155] Calculate different high-pressure steam extraction throttling schemes respectively, and obtain the predicted value of each reheat steam temperature change under various high-pressure steam extraction throttling schemes: ΔT rs,j,h, j = 1 ~ m-1, h = 1 ~ k-1; Since the actual load change process is very fast, different high-pressure steam extraction throttling schemes cannot achieve the maximum main steam temperature change, and the correction coefficient of the predicted value of the main steam temperature of the high-pressure steam extraction throttling is introduced, that is,

[0156] ΔT rs,j,exp,h =k rs,j,expchan,h ΔT rs,j,h ,j=1~m-1,h=1~k-1

[0157] Where: ΔT rs,j,exp,h is the predicted value of the jth reheat steam temperature change expected by the hth high-pressure steam extraction throttling scheme in the actual rapid load change process after correction, ℃; k rs,j,expchan,h k is the correction factor of the predicted value of reheat steam temperature change due to high pressure steam extraction throttling, 0<k rs,j,expchan,h <1;

[0158] At the same time, the deviation between the real-time temperature of each reheat steam and the set temperature is calculated.

[0159] ΔT rs,j,dev =T rs,j,set -T rs,j,rt

[0160] Where: ΔT rs,j,dev is the jth reheat steam temperature deviation, °C; T rs,j,set is the jth steam temperature setting value, kJ / s; T ls,rt is the real-time value of main steam temperature, ℃;

[0161] When the temperature deviation of each reheat steam is within a certain range, the method of controlling the reheat steam temperature by throttling the high-pressure steam extraction steam is not adopted, that is, ΔT rs,j,dev ≤ΔT rs,j,bdy When the temperature of each reheat steam is controlled, only the flue gas damper or flue gas recirculation is used;

[0162] When the reheat steam temperature deviation is greater than the set value ΔT rs,j,bdy The method of high-pressure steam extraction throttling to control the reheat steam temperature is adopted only when the high-pressure steam extraction throttling is adopted, and the most appropriate high-pressure steam extraction throttling scheme is selected in sequence and in a timely manner according to the relative size of the reheat steam temperature deviation at each time and the predicted value of the reheat steam temperature change of each scheme.

[0163] Preferably, in step 2, the parameter data collected above is cleaned, and the specific process is as follows:

[0164] (1) First, the original measurement data collected in step 1 is subjected to noise reduction, and the original operation data is subjected to noise reduction filtering processing using the Kalman filtering method;

[0165] (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;

[0166] (3) Analyze the size and change trend of important basic parameters that are indispensable for supercritical 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 supercritical unit in the actual operation process, determine whether the size and changing trend of the measured values ​​of other parameters except unit load, main steam pressure and feed water flow parameters collected in step 1 are inconsistent with the changes in the basic parameters of the supercritical unit, select more accurate measuring points for the data of multiple measuring points, correct or discard the data points that are inconsistent with the changes in the basic data of the supercritical unit, and finally complete the cleaning of the collected measurement data.

[0167] Before applying the measurement data of key thermal parameters collected from a supercritical unit to the calculation of control parameters, the present invention first cleans the data, reduces the noise of the data with the help of Kalman filtering, and then uses a simple data analysis method to supplement the missing values, correct the abnormal values, and eliminate the erroneous values. With the above means, most of the problems existing in the original measurement data are solved; at the same time, with the help of the internal mechanism and operation logic of the supercritical unit, with the help of the change law of a few core thermal parameters of the supercritical unit, it is determined whether the measurement points of other thermal parameters are accurate, and finally accurate and reliable measurement points are selected and the abnormal status data are repaired, so as to provide reliable data guarantee for the accurate calculation of subsequent control parameters.

[0168] Preferably, the calculation method for each pressure parameter missing in calculating the enthalpy value of each working fluid in step 3 is as follows:

[0169] Calculate the hydrophobic enthalpy h of each heater by thermophysical properties d,i The required but unmeasured drain pressure P of each heater d,i According to the extraction steam pressure P s,i 95% is calculated, that is

[0170] P d,i =0.95P s,i , i=1~k-1

[0171] Calculate the enthalpy value h of the inlet water of each stage of the regenerative heater on the water supply side through the thermophysical properties w,in,i and the enthalpy of the outlet water h w,out,i The required but unmeasured water pressure P of each level of regenerative heater inlet w,in,i and outlet water pressure P w,out,i, where i = 1 ~ k-1, then the water supply pressure P after the water supply pump is used fp and economizer inlet feed water pressure P eco,in To calculate, that is

[0172]

[0173] The present invention uses 95% of the extraction steam pressure to replace the unmeasurable heater drain pressure, and uses the pressure after the feedwater pump and the pressure before the economizer to estimate the pressure on the feedwater side of each high-pressure heater. With the above method, some thermodynamic parameters that were originally unmeasurable are simply obtained, laying a data foundation for the calculation of the feedwater heat absorption and extraction steam heat release of the high-pressure heater.

[0174] Preferably, the energy balance calculation method for the regenerative heater in step 4 and step 5 is as follows:

[0175] According to the calculation principle of energy balance, the feed water heat absorption τ of the high-pressure heater can be obtained: i , Extraction heat release q i and hydrophobic exothermicity γ i , the calculation method is as follows:

[0176] 1) For drain heater:

[0177] τ i =h w,out,i -h w,in,i

[0178] q i =h s,i -h d,i

[0179] γ i =h d,i-1 -h d,i

[0180] 2) For concentrating heaters:

[0181] τ i =h w,out,i -h w,in,i

[0182] q i =h s,i -h w,in,i

[0183] γ i =h d,i-1 -h w,in,i

[0184] Where: h w,out,i is the outlet feed water enthalpy of the i-th stage regenerative heater, kJ / kg; h w,in,iis the inlet feed water enthalpy of the i-th stage regenerative heater, kJ / kg; h s,i is the extraction enthalpy of the i-th stage regenerative heater, kJ / kg; h d,i is the enthalpy of hydrophobicity of the i-th stage regenerative heater, kJ / kg; h d,i-1 is the hydrophobic enthalpy of the i-1th stage regenerative heater, kJ / kg.

[0185] The present invention adopts the energy balance method to calculate the feed water heat absorption, steam extraction heat release and hydrophobic heat release of the high-pressure heater, which has the advantages of simplicity, rapidity and high accuracy. It ignores the heat storage changes of the high-pressure heater itself and can more simply obtain the key parameters of each stage of high-pressure heater, providing a data source for the calculation of parameters such as insufficient feed water heating during subsequent high-pressure heater extraction throttling.

[0186] Preferably, the calculation method for the change in the heat absorption of the water-cooled wall and the superheater after the high-pressure steam extraction throttling in step 6 is as follows:

[0187] Since the flue gas temperatures before and after each heating surface in the furnace cannot be measured, a simplified method is used to calculate the changes in the heat absorption of the water-cooled wall and superheater.

[0188] The heat absorption changes of the water-cooled wall and superheater are calculated uniformly, and two limit boundaries are defined:

[0189] Boundary 1: The working medium temperature at the superheater outlet after throttling of the high-pressure steam extraction is the same as that before throttling. At this time, the increased heat absorption of the water-cooled wall and the superheater is the same as the insufficient heating of the feed water in the h-th high-pressure steam extraction throttling scheme. At this time, the maximum heat absorption change is:

[0190] ΔQ sh,max =ΔQ fw,h

[0191] Where: ΔQ sh,max is the maximum heat absorption change of water-cooled wall and superheater, kJ / s; h sh,out is the enthalpy of the working fluid at the superheater outlet, kJ / kg; h ww,in is the enthalpy of the working fluid at the water wall inlet, kJ / kg;

[0192] Boundary 2: The total heat absorption of the boiler system water-cooled wall and superheater remains unchanged, that is, ΔQ sh,min =0.

[0193] Where: ΔQ sh,min is the minimum heat absorption change of the water-cooled wall and superheater, kJ / s;

[0194] In the actual process, due to insufficient heating of feed water, the temperature of the working medium entering the water wall decreases, and the heat absorption of the water wall and superheater increases, but at the same time, the temperature of the working medium at the superheater outlet will also decrease to a certain extent. Therefore, the actual increase in the heat absorption of the water wall and superheater caused by insufficient heating of feed water is between the maximum and minimum values ​​mentioned above:

[0195] ΔQ sh,re =k sh,re ΔQ sh,max

[0196] Where: ΔQ sh,re is the actual amount of heat absorbed by the water-cooled wall and superheater, kJ / s; k sh,re is the equivalent coefficient of heat absorption change of water-cooled wall and superheater, 0<k sh,re <1.

[0197] The present invention adopts two limit boundaries to represent the change in heat absorption of the water-cooled wall and the superheater after high-pressure steam extraction throttling, which greatly simplifies the nonlinear and large-inertia heat transfer calculation problems, and greatly reduces the calculation resources while ensuring acceptable accuracy of subsequent control parameter calculations.

[0198] Preferably, the specific calculation method for each reheat steam flow rate before high pressure heater extraction throttling in step seven is as follows:

[0199] The Darcy-Weisbach formula is used to calculate the reheat steam flow rate at each time. The specific calculation formula is as follows:

[0200]

[0201] Where: m rs,j and m rs0,j are the real-time j-th reheat steam flow rate and the j-th reheat steam flow rate under design conditions, kg / s; Δp pipe,j and Δp pipe0,j are the real-time cold section pipe pressure drop of the j-th reheat steam and the cold section pipe pressure drop of the j-th reheat steam under design conditions, MPa; ρ pipe,j and ρ pipe0,j They are the real-time working fluid density of the cold section of the j-th reheat steam pipeline and the working fluid density of the cold section of the j-th reheat steam pipeline under the design condition, kg / m 3 .

[0202] The present invention uses the Darcy-Weisbach formula to calculate the reheat steam flow rates before high-pressure steam extraction throttling, and directly calculates the real-time reheat steam flow rate of the unit with the help of supercritical unit design parameters and real-time operation data, thereby ensuring the calculation speed and feasibility of the method.

[0203] Preferably, the specific method for selecting the high-pressure steam extraction throttling scheme in step eight is as follows:

[0204] Specific control strategy optimization Figure 3 As shown in the figure, on the basis of the original reheat steam temperature control logic, different gradients of high-pressure steam extraction throttling are added to scientifically and reasonably control different reheat steam temperature deviations. The specific selection method of high-pressure steam extraction throttling scheme is introduced as follows:

[0205] 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 each reheat steam temperature change of each scheme, and is uniformly organized into the following form:

[0206] When ΔT rs,bdy <ΔT rs,j,dev ≤ΔT rs,j,exp,1 , select the first high-pressure steam extraction throttling scheme;

[0207] When ΔT rs,j,exp,1 <ΔT rs,j,dev ≤ΔT rs,j,exp,2 , select the second high-pressure steam extraction throttling scheme;

[0208] When ΔT rs,j,dev >ΔT rs,j,exp,2 , select the third high-pressure steam extraction throttling scheme;

[0209] For the final high-pressure steam extraction throttling scheme, the high-pressure steam extraction throttling scheme with the largest number of throttling high-pressure heaters corresponding to each reheat steam deviation should be selected.

[0210] And when the extraction throttling strategy of the high-pressure heater is used, when the temperature deviation of each reheat steam gradually decreases, the extraction throttling of each high-pressure heater is gradually and orderly exited in accordance with the above throttling scheme selection method, and when the temperature deviation of each reheat steam is less than or equal to the preset limit value ΔT rs,j,bdy When the steam is pumped out of the high-pressure heater, restore the normal steam extraction of all high-pressure heaters.

[0211] The present invention provides a detailed orderly entry and exit mechanism for high-pressure steam extraction throttling. By calculating the predicted value of the reheat steam temperature change of different high-pressure steam extraction throttling schemes and comparing them with the real-time reheat steam temperature deviation, the automatic selection and automatic recovery of the high-pressure steam extraction throttling scheme are completed.

[0212] The high-pressure steam extraction throttling control of the reheat steam temperature, combined with the original reheat steam temperature control logic of the supercritical unit automatic control system, can more effectively control the reheat steam temperature when the load is increased rapidly, thereby increasing the load change rate of the supercritical unit, which is of great significance to improving its operating flexibility.

[0213] The above description is only a preferred specific implementation example of the present invention and is not intended to limit the present invention. Any modifications, equivalent changes or improvements made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for controlling the reheat steam temperature of a supercritical unit with high-pressure steam extraction throttling, characterized in that: The steps include: Step 1: Data Collection Collect boiler system feed water flow m fw The feedwater flow measurement data of the steam turbine system flowing through each stage of high pressure heater m fwi , where i = 1 to k-1; Collect the inlet and outlet thermal parameters of m working fluids between the boiler system and the steam turbine system, including the temperature and pressure T of m working fluids entering the boiler in,a 、p in,a , the temperature and pressure T of the working fluid leaving the boiler out,a 、p out,a , where a = 1 ~ m; Collect the thermal parameters of the z-level regenerative heater, including the temperature T before and after each level of regenerative heater on the water supply side w,in,b , T w,out,b ; The temperature of each stage of extraction steam on the extraction side T s,b , pressure p s,b The temperature T of the water drain of each level of heat recovery heater d,b , where b = 1 ~ z; Collect the water supply pressure p after the water supply pump fp and economizer inlet feed water pressure p eco,in , water wall inlet working medium temperature T ww,in and pressure p ww,in ; Step 2: Data preprocessing Clean the parameter data collected above; Step 3: Calculate the enthalpy of the working fluid at each point Using the temperature and pressure data, the enthalpy value of the working fluid at each point is calculated through thermophysical properties, including the enthalpy value h of the inlet and outlet of the m working fluids in the boiler. in,a and h out,a , where a = 1 ~ m; the enthalpy value of the inlet water of each level of the regenerative heater on the water supply side h w,in,b and the enthalpy of the outlet water h w,out,b ; Enthalpy value of each stage of extraction steam on the extraction side h s,b ; Enthalpy value of each level of hydrophobicity h d,b , where b = 1 ~ z; the enthalpy value of the working medium at the water wall inlet of the boiler system h ww,in ; Step 4: Calculate the change in reheat steam flow rate caused by high-pressure steam extraction throttling For the high pressure heater, all the extraction steam is returned to the turbine when the extraction steam is throttled, that is, Where: m sei is the steam flow rate returned to the steam turbine when the i-th stage high pressure heater is throttled, kg / s; m dw(i-1) is the drainage flow rate from the i-1th stage high pressure heater, kg / s; γ i is the heat released by the hydrophobicity from the previous stage in the i-th stage high pressure heater, kJ / kg; q i is the heat release of the i-th stage high pressure heater extraction steam, kJ / kg; τ i is the heat absorption of feed water of the i-th stage high pressure heater, kJ / kg; The change in each reheat steam flow rate is the sum of the changes in all extraction steam flows whose extraction pressure is greater than or equal to the reheat steam pressure: Where: Δm rs,j is the change in the jth reheat steam flow rate, kg / s; Δm sei is the change in the extraction steam flow rate of the i-th stage high-pressure heater, which is equal to the total extraction steam flow rate of the throttled high-pressure heater of this stage, kg / s; p rs,j is the cold section pressure of the j-th reheat steam, MPa; Step 5: Calculate the feedwater heating shortage corresponding to different high-pressure steam extraction throttling schemes The throttling of the high-pressure heater extraction steam increases the insufficient heating of the feed water at this stage, resulting in a drop in the main steam temperature. In order to avoid the increase in the extraction of the heater with a higher extraction pressure affecting the throttling effect, each high-pressure heater extraction steam throttling scheme throttles all continuous high-pressure heaters including the highest-level high-pressure heater; The insufficient feedwater heating due to full throttling of the corresponding HP heater extraction steam is equal to the enthalpy rise of the feedwater flowing through the heater of this stage, calculated as follows: ΔQ fw,1 =m fw1 τ1 Option 1: Throttling No.1 High-Pressure Heater ΔQ fw,2 =m fw1 τ1+m fw2 τ2 Option 2: Throttling No.1 and No.2 High-Pressure Heaters Option 3: Throttling No.1, No.2 and No.3 high pressure heaters …… Scheme (h): Throttling No.1, No.2, No.3, ..., No.h high pressure heater …… Scheme (k-1): Throttling No.1, No.2, No.3, ..., No.k-1 High-pressure heater Where: ΔQ fw,1 , ΔQ fw,2 , ΔQ fw,3 , ΔQ fw,h and ΔQ fw,k-1 The feedwater heating shortage caused by the extraction throttling of the high-pressure heater for Scheme 1, Scheme 2, Scheme 3, Scheme h and Scheme k-1, kJ / s; m fw1 、m fw2 and m fwi are the feed water flow rates flowing through the 1st, 2nd and i-th stage high pressure heaters, kg / s; τ1, τ2 and τ i are the feed water enthalpy rise of the 1st, 2nd and i-th stage high pressure heaters, kJ / kg; Step 6: Calculate the change in heat absorption of each reheater after the boiler superheater The throttling of high-pressure steam extraction causes insufficient heating of feed water, and the temperature of feed water entering the boiler system drops significantly, which will lead to an increase in the heat absorption of the water-cooled wall and superheater heating surface before each reheater; The increase in heat absorption of the water-cooled wall and superheater caused by insufficient heating of the feed water will cause a decrease in the heat absorption of each reheater after the above heating surface. The reduced heat absorption is distributed according to the original heat absorption ratio of each affected reheater; Where: ΔQ rh,j is the change in heat absorption of the jth reheated steam in the boiler system reheater, kJ / s; ΔQ sh,re Q is the increased heat absorption of the water-cooled wall and superheater caused by high-pressure steam extraction throttling, kJ / s; rh,j is the heat absorbed by the jth reheated steam in the boiler system reheater, kJ / s; Step 7: Calculate the predicted value of reheat steam temperature change Due to the throttling of the high-pressure steam extraction, the change in the reheat steam flow rate is Δm rs,j , and at the same time, the change in the amount of heat absorbed by each reheat steam caused by insufficient feed water heating is ΔQ rh,j ; Based on the above changes, the change in reheat steam enthalpy caused by high-pressure steam extraction throttling is obtained as follows: Where: Δh rs,j is the enthalpy change of the j-th reheated steam, kJ / kg; Q r ' h,j and Q rh,j are the jth reheater heat absorption after and before throttling of the high-pressure heater extraction steam, kJ / s; m r ' s,j and m rs,j are the jth reheat steam flow rates after and before throttling of the high-pressure heater extraction steam, kg / s; The heat absorption of the jth reheater after throttling of the high-pressure steam extraction is: Q r ′ h,j =Q rh,j -ΔQ rh,j Under the premise that the reheat steam temperature changes slightly, its specific heat capacity change can be ignored, so the predicted value of the reheat steam temperature change after high-pressure steam extraction throttling is: Where: ΔT rs,j is the predicted value of the jth reheat steam temperature change after high-pressure steam extraction throttling, ℃; c rs,j is the specific heat capacity of the j-th reheat steam, kJ / (kg·K); Step 8: Calculate the real-time reheat steam temperature deviation and reasonably select the high-pressure steam extraction throttling scheme Calculate different high-pressure steam extraction throttling schemes respectively, and obtain the predicted value of each reheat steam temperature change under various high-pressure steam extraction throttling schemes: ΔT rs,j,h , j = 1 ~ m-1, h = 1 ~ k-1; Since the actual load change process is very fast, different high-pressure steam extraction throttling schemes cannot achieve the maximum main steam temperature change, and the correction coefficient of the predicted value of the main steam temperature of the high-pressure steam 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 jth reheat steam temperature change expected by the hth high-pressure steam extraction throttling scheme in the actual rapid load change process after correction, ℃; k rs,j,expchan,h k is the correction factor of the predicted value of reheat steam temperature change due to high pressure steam extraction throttling, 0<k rs,j,expchan,h <1; At the same time, the deviation between the real-time temperature of each reheat steam and 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 setting value, kJ / s; T ls,rt is the real-time value of main steam temperature, ℃; When the temperature deviation of each reheat steam is within a certain range, the method of controlling the reheat steam temperature by throttling the high-pressure steam extraction steam is not used. rs,j,dev ≤ΔT rs,j,bdy When the temperature of each reheat steam is controlled, only the flue gas damper or flue gas recirculation is used; When the reheat steam temperature deviation is greater than the set value ΔT rs,j,bdy The method of high-pressure steam extraction throttling to control the reheat steam temperature is adopted only when the high-pressure steam extraction throttling is adopted, and the most appropriate high-pressure steam extraction throttling scheme is selected in sequence and in a timely manner according to the relative size of the reheat steam temperature deviation at each time and the predicted value of the reheat steam temperature change of each scheme.

2. The reheat steam temperature control method for a supercritical unit with high-pressure steam extraction throttling according to claim 1 is characterized in that: In step 2, the parameter data collected above is cleaned. The specific process is as follows: (1) First, the original measurement data collected in step 1 is subjected to noise reduction, and the original operation data is subjected to noise reduction filtering processing using the Kalman filtering method; (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 supercritical 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 supercritical unit, determine 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 in step one are inconsistent with the changes in the basic parameters of the supercritical unit, select more accurate measuring points for the data of multiple measuring points, correct or discard the data points that are inconsistent with the changes in the basic data of the supercritical unit, and finally complete the cleaning of the collected measurement data.

3. The reheat steam temperature control method for a supercritical unit with high-pressure steam extraction throttling according to claim 1 is characterized in that: The calculation method for the various pressure parameters missing in the calculation of the enthalpy values ​​of each working fluid in step 3 is as follows: Calculate the hydrophobic enthalpy values ​​h of each heater through thermal properties d,i The required but unmeasured drain pressure P of each heater d,i According to the extraction steam pressure P s,i 95% is calculated, that is P d,i =0.95P s,i ,i=1~k-1 Calculate the enthalpy value h of the inlet water of each stage of the regenerative heater on the water supply side through the thermophysical properties w,in,i and the enthalpy of the outlet water h w,out,i The required but unmeasured water pressure P of each level of regenerative heater inlet w,in,i and outlet water pressure P w,out,i , where i = 1 ~ k-1, then the water supply pressure P after the water supply pump is used fp and economizer inlet feed water pressure P eco,in To calculate, that is 4. The reheat steam temperature control method for a supercritical unit with high-pressure steam extraction throttling according to claim 1 is characterized in that: The energy balance calculation method for the regenerative heater in steps 4 and 5 is as follows: According to the calculation principle of energy balance, the heat absorption of feed water of high pressure heater τ can be obtained: i , Extraction heat release q i and hydrophobic exothermicity γ i , the calculation method 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 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 enthalpy of the i-th stage regenerative heater, kJ / kg; h d,i is the enthalpy of hydrophobicity of the i-th stage regenerative heater, kJ / kg; h d,i-1 is the hydrophobic enthalpy of the i-1th stage regenerative heater, kJ / kg.

5. The reheat steam temperature control method for a supercritical unit with high-pressure steam extraction throttling according to claim 1 is characterized in that: The calculation method for the change in heat absorption of the water-cooled wall and superheater after throttling of the high-pressure steam extraction in step 6 is as follows: 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 change in heat absorption of the water-cooled wall and superheater; The heat absorption changes of the water-cooled wall and superheater are calculated uniformly, and two limit boundaries are defined: Boundary 1: The working medium temperature at the superheater outlet after throttling of the high-pressure steam extraction is the same as that before throttling. At this time, the increased heat absorption of the water-cooled wall and the superheater is the same as the insufficient heating of the feed water in the h-th high-pressure steam extraction throttling scheme. At this time, the maximum heat absorption change is: ΔQ sh,max =ΔQ fw,h Where: ΔQ sh,max is the maximum heat absorption change of water-cooled wall and superheater, kJ / s; h sh,out is the enthalpy of the working fluid at the superheater outlet, kJ / kg; h ww,in is the enthalpy of the working fluid at the water wall inlet, kJ / kg; Boundary 2: The total heat absorption of the boiler system water-cooled wall and superheater remains unchanged, that is, ΔQ sh,min =0; Where: ΔQ sh,min is the minimum heat absorption change of the water-cooled wall and superheater, kJ / s; In the actual process, due to insufficient heating of feed water, the temperature of the working medium entering the water wall decreases, and the heat absorption of the water wall and superheater increases, but at the same time, the temperature of the working medium at the superheater outlet will also decrease to a certain extent; therefore, the actual increased heat absorption of the water wall and superheater caused by insufficient heating of feed water is between the above maximum and minimum values: ΔQ sh,re =k sh,re ΔQ sh,max Where: ΔQ sh,re is the actual amount of heat absorbed by the water-cooled wall and superheater, kJ / s; k sh,re is the equivalent coefficient of heat absorption change of water-cooled wall and superheater, 0<k sh,re <1.

6. The main steam flow control method of a supercritical unit with high-pressure steam extraction throttling according to claim 1 is characterized in that: The specific calculation method for each reheat steam flow rate before high-pressure heater extraction throttling in step 7 is as follows: The Darcy-Weisbach formula is used to calculate the reheat steam flow rate at each time. The specific calculation formula is as follows: Where: m rs,j and m rs0,j are the real-time j-th reheat steam flow rate and the j-th reheat steam flow rate under design conditions, kg / s; Δp pipe,j and Δp pipe0,j are the real-time cold section pipe pressure drop of the j-th reheat steam and the cold section pipe pressure drop of the j-th reheat steam under design conditions, MPa; ρ pipe,j and ρ pipe0,j They are the real-time working fluid density of the cold section of the j-th reheat steam pipeline and the working fluid density of the cold section of the j-th reheat steam pipeline under the design condition, kg / m 3 .

7. The method for controlling reheat steam flow rate of a supercritical unit with extraction throttling of a high-pressure heater according to claim 1, characterized in that: The specific method for selecting the high-pressure steam extraction throttling scheme 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 predicted value of each reheat steam temperature change of each scheme, and unified into the following form: ΔT rs,j,exp,h-1 <ΔT rs,j,dev ≤ΔT rs,j,exp,h , select the high-pressure heater extraction throttling scheme with the largest number of throttling high-pressure heaters; And when the extraction throttling strategy of the high-pressure heater is used, when the temperature deviation of each reheat steam gradually decreases, the extraction throttling of each high-pressure heater is gradually and orderly exited in accordance with the above throttling scheme selection method, and when the temperature deviation of each reheat steam is less than or equal to the preset limit value ΔT rs,j,bdy When the steam is pumped out of the high-pressure heater, restore the normal steam extraction of all high-pressure heaters.

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