Main steam temperature control method for ultra-supercritical unit

Abstract

The invention discloses a main steam temperature control method for an ultra-supercritical unit. A steam extraction valve is additionally arranged on a steam extraction pipeline of the high-pressure heater, and accurate steam extraction throttling adjustment is carried out. Thermal parameters of a boiler system and a steam turbine system are collected, data cleaning is carried out, feed water heating insufficiency corresponding to unit steam extraction throttling rates of different high-pressure heater steam extraction throttling schemes and reheat steam flow variable quantities of all times are obtained through calculation, and then heat absorption variable quantities of heating surfaces of an economizer arranged behind a reheater and part of a superheater are calculated; and finally, main steam temperature change predicted values corresponding to the unit steam extraction section flow of different high-pressure heater steam extraction throttling schemes are obtained, and the high-pressure heater steam extraction throttling scheme and the required steam extraction section flow are selected according to the main steam temperature real-time deviation. And finer control over the main steam temperature is achieved by adjusting the steam extraction section flow of each high-pressure heater, the problem of main steam overtemperature easily occurring in the rapid load rising process is solved, and the method has important significance on improvement of the operation flexibility of an ultra-supercritical unit.

Description

Technical Field

[0001] The invention belongs to the technical field of coal-fired unit control optimization, and in particular relates to a main steam temperature control method for an ultra-supercritical unit. Background Art

[0002] Since the beginning of the 21st century, the world's energy structure has continued to develop and transform in the direction of clean, low-carbon, high-efficiency and diversified. However, due to the strong time-varying characteristics of renewable energy such as wind energy and solar energy, it is difficult to absorb renewable energy power generation in my country, and the problems of wind and solar power abandonment are serious. Improving the operating flexibility of conventional coal-fired units 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 units will gradually increase. Therefore, coal-fired units will be in a transient operating condition with frequent load changes for a long time.

[0003] The control quality of the main steam temperature has become an important bottleneck that restricts the ultra-supercritical unit from further improving its variable load capacity. When the load is increased rapidly, the main steam temperature is very likely to exceed the limit, which limits the improvement of the unit's flexibility. How to quickly and effectively suppress the surge in the main steam temperature during the rapid load increase process is an important part of the optimization of the ultra-supercritical unit boiler coordinated control system.

[0004] The change of main steam temperature is related to the change of feed water heat absorption, the heat absorption in the boiler economizer and water wall, and the heat absorption in the superheater. The purpose of effectively controlling the main steam temperature can be achieved by quickly adjusting the size of these three heat absorptions during the rapid load change process. Therefore, the present invention proposes a main steam temperature control method for an ultra-supercritical unit. 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 main steam temperature control method for an ultra-supercritical unit. First, extraction throttle valves are added to the extraction pipes of each stage of the ultra-supercritical unit. The throttle valves are used to accurately control the throttling amount of the high-pressure steam extraction. This not only increases the insufficient heating of feed water, but also reduces the heat absorption of the economizer and the superheater, thereby achieving the purpose of quickly and accurately lowering the main steam temperature. The present invention can greatly improve the main steam temperature overtemperature problem occurring during rapid load changes.

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

[0007] A method for controlling the main steam temperature of an ultra-supercritical unit comprises the following steps:

[0008] Step 1: Data Collection

[0009] Collect boiler system feed water flow m fwThe 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;

[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 ; Temperature and pressure of each stage of extraction steam on the extraction side T s,b , 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 ;

[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 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;

[0017] Step 4: Calculate the feedwater heating shortage corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes. The high-pressure steam extraction throttling increases the feedwater heating shortage of this stage, resulting in a decrease in the main steam temperature. In order to avoid the increase in steam extraction of the heater with higher extraction pressure affecting the throttling effect, each high-pressure steam extraction throttling scheme throttles all continuous high-pressure heaters including the highest-level high-pressure heater;

[0018] The insufficient heating of feedwater caused by unit extraction throttling amount of different high-pressure heater extraction throttling schemes is the heat release of this part of extraction steam in the high-pressure heater of this stage. The specific calculation is as follows:

[0019] ΔQ fw,1 =Δm se1 q1 Option 1: Throttling No.1 High-pressure Heater

[0020] ΔQ fw,2 =Δm se1 q1+Δm se2 q2 Option 2: Throttling No.1 and No.2 high pressure heaters Throttling No.1, No.2 and No.3 high pressure heaters

[0021] …

[0022] Throttling No.1, No.2, No.3, ..., No.h high pressure heater

[0023] …

[0024] Throttling No.1, No.2, No.3, ..., No.k-1 High-pressure heater Where: ΔQ fw is the heat release due to insufficient heating of feed water caused by unit extraction throttling of high-pressure heater, kJ / s; Δm sei is the change in the extraction flow rate of the high-pressure heater, which is 1kg / s; q i is the extraction of the i-th stage high pressure heater

[0025] Steam enthalpy drop, kJ / kg;

[0026] Step 5: Calculate the change in reheat steam flow rate caused by unit extraction throttling amount for different high-pressure steam extraction throttling schemes

[0027] For the high-pressure heater, when the unit flow rate of extraction steam is throttled, the throttled extraction steam returns to the turbine, that is, Δm sei Return to the turbine;

[0028] The change in the reheat steam flow rate at each time is the sum of the changes in the flow rates of all extraction steams whose extraction pressure is greater than or equal to the reheat steam pressure at that time:

[0029]

[0030] Where: Δm rs,j is the change in the jth reheat steam flow rate, kg / s; Δm sei is the change in the steam extraction flow rate of the i-th stage high-pressure heater, kg / s; p rs,j is the cold section pressure of the j-th reheat steam, MPa;

[0031] Step 6: Calculate the heat absorption changes of the economizer and part of the superheater after the boiler reheater corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes

[0032] As the reheat steam flow rate increases, the overall heat absorption of the heating surface of each reheater increases. At the same time, the heat absorption of the working medium in the economizer and some superheaters after the reheater heating surface will decrease accordingly. The reduced heat absorption is distributed according to the original heat absorption ratio of the affected superheater and economizer:

[0033]

[0034] Where: ΔQ eco is the change in heat absorption of the working fluid in the economizer, kJ / s; Q eco is the original heat absorption of the working fluid in the economizer, kJ / s; Q sh,part is the original heat absorption of the working fluid in the affected superheater, kJ / s; ΔQ sh,part is the change in heat absorption of the working fluid in the affected superheater, kJ / s; ΔQ rh,tot is the total heat absorption change of the reheater, kJ / s;

[0035] Step 7: Calculate the predicted value of main steam temperature change corresponding to unit extraction throttling amount for different high-pressure steam extraction throttling schemes

[0036] Due to the throttling of the HP heater extraction steam, the total heating deficiency of the feed water in the HP heater is ΔQ fw , the total heat at the boiler feed water inlet after high-pressure steam extraction throttling can be calculated as:

[0037] Q e ' co,in =Q eco,in -ΔQ fw

[0038] Where: Q e ' co,in is the total heat at the economizer inlet after high-pressure steam extraction throttling, kJ / s; Q eco,in is the total heat at the economizer inlet before throttling of the high-pressure steam extraction, kJ / s;

[0039] Step 6 calculates the change in heat absorption of the working fluid in the economizer after the high-pressure steam extraction throttling, and then the total heat of the working fluid at the economizer outlet after the high-pressure steam extraction throttling can be calculated as:

[0040] Q e ' co,out =Q eco,out -ΔQ fw -ΔQ eco

[0041] Where: Q e ' co,outQ is the total heat at the economizer outlet after high-pressure steam extraction throttling, kJ / s; eco,out is the total heat at the economizer outlet before throttling of the high-pressure steam extraction, kJ / s;

[0042] The amount of heat absorbed by the working fluid in the water-cooled wall does not change, so there is no need to calculate the energy balance of the water-cooled wall;

[0043] Step 6 Calculate the heat absorption change of the superheated steam generated by the water-cooled wall in the superheater as ΔQ sh,part Therefore, the total heat of the boiler main steam after high-pressure steam extraction throttling can be calculated as:

[0044] Q s ' h,ls =Q sh,ls -ΔQ fw -ΔQ eco -ΔQ sh,part

[0045] Where: Q s ' h,ls Q is the total heat at the high temperature superheater outlet after high pressure steam extraction throttling, kJ / s; sh,ls is the total heat at the high-temperature superheater outlet before throttling of the high-pressure steam extraction, kJ / s;

[0046] Because Q sh,ls =m fw h ls , the change in main steam enthalpy is:

[0047]

[0048] Where: m fw is the boiler feed water flow rate, kg / s; Δh ls Main steam enthalpy change, kJ / kg; h l ' s is the total heat at the high temperature superheater outlet after high pressure extraction steam throttling, kJ / s; h ls is the total heat at the high-temperature superheater outlet before throttling of the high-pressure steam extraction, kJ / s;

[0049] Under the premise that the main steam temperature changes little and its specific heat capacity change is ignored, the predicted value of the main steam temperature change after high-pressure steam extraction throttling is:

[0050]

[0051] Where: ΔT ls is the predicted value of main steam temperature change corresponding to unit extraction throttling amount for different high-pressure steam extraction throttling schemes, ℃; c sh,ls is the specific heat capacity of main steam, kJ / (kg·K);

[0052] Step 8: Calculate the required extraction throttling amount for each regenerative heater for different high-pressure steam extraction throttling schemes based on the real-time main steam temperature deviation

[0053] Calculate different high-pressure steam extraction throttling schemes respectively. The maximum extraction throttling amount of different high-pressure steam extraction throttling schemes is the minimum extraction amount of all high-pressure heaters with extraction throttling. According to the above calculation steps, the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount under various high-pressure steam extraction throttling schemes is obtained: ΔT ls,h,max ,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. The correction coefficient of the predicted value of the main steam temperature change of the high-pressure steam extraction throttling is introduced, that is,

[0054] ΔT ls,exp,h,max =k ls,expchan,h ΔT ls,h,max ,h=1~k-1

[0055] Where: ΔT ls,exp,h,max is the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount of the hth high-pressure steam heater extraction throttling scheme during the corrected actual rapid load change process, ℃; k ls,expchan,h is the correction coefficient of the predicted value of the main steam temperature of the high-pressure heater extraction throttling, 0<k ls,expchan,h <1;

[0056] As the number of high-pressure heaters with extraction throttling increases, the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount also gradually increases, as shown in the following:

[0057] ΔT ls,exp,k-1,max <ΔT ls,exp,k,max

[0058] At the same time, calculate the deviation between the real-time temperature of the main steam and the set temperature:

[0059] ΔT ls,dev =T ls,set -T ls,rt

[0060] Where: ΔT ls,dev is the main steam temperature deviation, °C; T ls,set is the main steam temperature setting value, kJ / s; T ls,rt is the real-time value of main steam temperature, ℃;

[0061] When the main steam temperature deviation is within a certain range, the method of controlling the main steam temperature by throttling the high-pressure steam extraction steam is not adopted, that is, ΔT ls,dev ≤ΔT ls,bdy When the main steam temperature is controlled, only water spraying is used for cooling;

[0062] When the main steam temperature deviation is greater than the set value ΔT ls,bdyOnly when the high-pressure steam extraction throttling method is used to control the main steam temperature.

[0063] In step 2, the parameter data collected above is cleaned. The specific process is as follows:

[0064] (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;

[0065] (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;

[0066] (3) Analyze the size and change trend of important basic parameters that are indispensable for ultra-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 ultra-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 1 are inconsistent with the changes in the basic parameters of the ultra-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 ultra-supercritical unit, and finally complete the cleaning of the collected measurement data.

[0067] The calculation method for each pressure parameter missing in the calculation of the enthalpy value of each parameter in step 3 is as follows:

[0068] 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

[0069] P d,i =0.95P s,i , i=1~k-1

[0070] 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

[0071]

[0072] The calculation method for the change in the overall heat absorption of the reheater heating surface after throttling of the high-pressure steam extraction in step 6 is:

[0073] 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 reheater heating surface;

[0074] There are two limit boundaries for the change of heat absorption of the reheater heating surface: Boundary 1: The steam temperature at the reheater outlet remains unchanged. At this time, the increase in heat absorption of the reheater heating surface caused by the increase in the reheat steam flow rate is:

[0075] ΔQ rh,j,max =Δm rs,j (h rh,out,j -h rh,in,j )

[0076] Where: ΔQ rh,j,max is the maximum heat absorption change of the jth reheat steam, kJ / s; h rh,out,j is the outlet enthalpy of the reheater of the jth reheat steam boiler, kJ / kg; h rh,in,j is the inlet enthalpy of the reheater of the j-th reheat steam boiler, kJ / kg;

[0077] Boundary 2: The total heat absorption of the boiler reheater remains unchanged, that is, ΔQ rh,j,min =0

[0078] Where: ΔQ rh,j,min is the minimum heat absorption change of the jth reheat steam, kJ / s;

[0079] In the actual process, due to the increase in reheat steam flow, the reheater heat absorption will increase, but at the same time, the reheat steam outlet temperature will also decrease to a certain extent, so the actual reheater heat absorption changes as follows:

[0080] ΔQ rh,j =k qrh,j ΔQ rh,j,max

[0081] Where: ΔQ rh,j is the change in heat absorption of the jth reheated steam, kJ / s; k qrh,j is the equivalent coefficient of the jth reheat steam heat absorption change, 0<k qrh,j <1.

[0082] Then the total heat absorption change of all reheat steam flows is:

[0083]

[0084] Where: ΔQrh,tot is the total heat absorption change of all reheat steam, kJ / s.

[0085] The specific method for calculating the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount under different high-pressure steam extraction throttling schemes in step 8 is as follows:

[0086] First, calculate the steam extraction capacity of each stage of high-pressure heater with the help of the energy balance of the regenerative heater:

[0087]

[0088] Where: m sei,tot is the steam flow rate returned to the steam turbine when the extraction steam of the i-th stage high pressure heater is fully throttled, kg / s; m dw(i-1) is the drainage flow rate from the i-1th stage high pressure regenerative heater, kg / s; γ i is the heat released by the drain from the previous stage in the i-th stage high-pressure regenerative heater, kJ / kg; q i is the heat release of the extraction steam of the i-th stage high-pressure regenerative heater, kJ / kg;

[0089] The maximum extraction steam throttling amount of different high-pressure steam extraction throttling schemes is the minimum extraction steam flow rate Δm before the high-pressure steam extraction throttling se,max,h , the insufficient feedwater heating caused by extraction steam throttling is calculated using step 4;

[0090] Then, according to the calculation steps of step 5, step 6 and step 7, the changes in the reheat steam flow corresponding to the maximum extraction throttling amount of the high-pressure heater extraction throttling, the changes in the heat absorption of the economizer and part of the superheater after the boiler reheater, and the predicted value of the main steam temperature change are calculated in turn, and finally the predicted value of the main steam temperature change ΔT corresponding to the maximum extraction throttling amount under the h-th high-pressure heater extraction throttling scheme is calculated. ls,h,max ,h=1~k-1.

[0091] The energy balance calculation method for the regenerative heater is as follows:

[0092] According to the calculation principle of energy balance, the feed water heat absorption τ of the high-pressure regenerative heater is obtained r , Extraction heat release q r and hydrophobic exothermicity γ r , the calculation method is as follows:

[0093] 1) For drain heater:

[0094] τ r =h w,out,r -h w,in,r

[0095] q r =h s,r -h d,r

[0096] γ r =h d,r-1 -h d,r

[0097] 2) For concentrating heaters:

[0098] τ r =h w,out,r -h w,in,r

[0099] q r =h s,r -h w,in,r

[0100] γ r =h d,r-1 -h w,in,i

[0101] Where: h w,out,r is the outlet feed water enthalpy of the rth stage regenerative heater, kJ / kg; h w,in,r is the inlet feed water enthalpy of the rth stage regenerative heater, kJ / kg; h s,r is the extraction enthalpy of the rth stage regenerative heater, kJ / kg; h d,r is the enthalpy of water drainage of the rth stage regenerative heater, kJ / kg; h d,r-1 is the hydrophobic enthalpy of the r-1 stage regenerative heater, kJ / kg.

[0102] The specific selection method of the high-pressure steam extraction throttling scheme and the specific calculation method of the high-pressure steam extraction throttling amount in step 8 are as follows:

[0103] First, select the high-pressure heater extraction throttling scheme. The selection principle is to throttle as few high-pressure heaters as possible under the premise of meeting the main steam temperature control requirements. Therefore, it is necessary to first compare the main steam change prediction value corresponding to the maximum extraction throttling amount of different high-pressure heater extraction throttling schemes and the real-time main steam temperature deviation, and then select the most appropriate high-pressure heater extraction throttling scheme in order and in a timely manner;

[0104] When ΔT ls,exp,h-1,max <ΔT ls,dev ≤ΔT ls,exp,h,max , select the hth high pressure steam extraction throttling scheme;

[0105] After selecting the high-pressure steam extraction throttling scheme, it is necessary to calculate the specific extraction throttling amount required under the high-pressure steam extraction throttling scheme:

[0106]

[0107] Where: Δm ls,sei The extraction throttling volume used to control the main steam temperature, kg / s; kls,sei is the steam extraction throttling rate adjustment coefficient, kg / s; ΔT ls,dev Main steam temperature deviation, °C; ΔT ls is the main steam temperature change corresponding to unit extraction throttling amount, °C;

[0108] And when the main steam temperature deviation gradually decreases after the high-pressure heater extraction throttling scheme is used, the extraction throttling of each high-pressure heater is gradually and orderly exited in accordance with the throttling scheme selection method, and when the main steam temperature deviation is less than or equal to the preset limit ΔT ls,bdy When the steam is pumped out of the high-pressure heater, normal steam extraction of all high-pressure heaters is restored.

[0109] The beneficial effects of the present invention are as follows: the present invention adopts an adjustable high-pressure steam extraction throttling method to control the main steam temperature of an ultra-supercritical unit, firstly collects real-time data of thermal parameters in a distributed control system of the ultra-supercritical 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 different changes of unit steam extraction throttling amounts of different high-pressure steam extraction throttling schemes for the feed water heat absorption of the feed water heat recovery system, the reheat steam heat absorption, the working medium heat absorption in the economizer, and the superheated steam heat absorption, the predicted value of the main steam temperature change corresponding to the unit steam extraction throttling amounts of different high-pressure steam extraction throttling schemes is calculated according to the energy balance equation, combined with the main steam temperature deviation collected and calculated in real time by the unit, by comparing the two, the most appropriate high-pressure steam extraction throttling scheme corresponding to the current main steam temperature deviation is selected in order and in a timely manner, and then the steam extraction throttling amount required under the high-pressure steam extraction throttling scheme is calculated. By accurately adjusting the high-pressure extraction steam throttling to supplement and optimize the main steam temperature automatic control logic, the main steam temperature overheating problem can be effectively prevented when the ultra-supercritical unit is rapidly increased in load, eliminating the main steam temperature over-limit, which is the bottleneck that restricts the further increase of the unit's load change rate, and improving the unit's operating flexibility.

[0110] Advantages of the present invention

[0111] 1) The present invention provides several high-pressure steam extraction throttling schemes. In order to maximize the throttling effect and prevent the high-pressure steam extraction of the heater with higher extraction pressure from significantly increasing when the high-pressure steam extraction throttling is performed, which weakens the control effect of the high-pressure steam extraction throttling on the main steam temperature, all the high-pressure steam extraction throttling schemes provided by the present invention need to throttle the continuous high-pressure heaters including the highest-level high-pressure heater, which can not only ensure the effect of the high-pressure steam extraction throttling, but also facilitate the orderly use and exit of the specific implementation scheme, simplify the actual operation difficulty of the high-pressure steam extraction throttling to control the main steam temperature, and make it easier to realize automatic control;

[0112] 2) The present invention installs extraction throttle valves on the extraction pipes of high-pressure heaters at various stages of the steam turbine system, which can not only provide a variety of high-pressure heater extraction throttling schemes, but also accurately adjust the specific throttling amount of each stage of extraction. Compared with the high-pressure heater extraction throttling scheme that can only be opened or closed, it can achieve a more precise adjustment of the main steam temperature;

[0113] 3) The present invention calculates the insufficient heating of feed water and the flow change of reheated steam at each level corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes by means of the energy balance of the high-pressure heater, and calculates the change in the heat absorption of reheated steam at each level and the influence on the heat absorption of the working medium in the subsequent boiler economizer and superheater through the energy balance of the boiler reheater, economizer and superheater. By comprehensively considering all changes in the direction of energy flow, the present invention finally calculates the predicted value of the main steam temperature change corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes, which has important guiding significance for the subsequent selection of extraction throttling amount for different high-pressure steam extraction throttling schemes;

[0114] 4) The present invention discloses a method for selecting a throttling scheme based on the main steam temperature deviation collected and calculated in real time and the main steam temperature change predicted value 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 main steam temperature deviation is greater than the set limit, according to the size relationship between the temperature deviation and the temperature change predicted value, different high-pressure steam extraction throttling schemes are selected in sequence, orderly and timely to determine the extraction throttling amount of each level; and when the main steam temperature deviation decreases, according to the size relationship between the deviation and the predicted value, each heater throttling is exited in sequence and orderly, 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 scheme selection scheduling scheme and the extraction throttling amount calculation process of each level, throttling methods with different effects can be reasonably and timely selected to correspond to different main steam temperature deviations, and the extraction throttling amount of each level can be reasonably selected, so as to more scientifically schedule the reasonable flow of each energy flow inside the thermal power system, and ultimately improve the main steam temperature control effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0115] Figure 1 The present invention is a flow chart of a method for controlling the main steam temperature of an ultra-supercritical unit;

[0116] Figure 2 This is a 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 steam turbine system, 10 is the No. 1 high-pressure heater extraction throttle valve, 11 is the No. 2 high-pressure heater extraction throttle valve, and 12 is the No. 3 high-pressure heater extraction throttle valve;

[0117] Figure 3 The figure is a main steam temperature control logic diagram of an ultra-supercritical unit, wherein the bold part is the main steam temperature control logic of the supplementary optimized adjustable high-pressure steam extraction throttling. DETAILED DESCRIPTION

[0118] 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.

[0119] The present invention discloses a method for controlling the main steam temperature of an ultra-supercritical unit. Figure 2 As shown, the ultra-supercritical unit is composed of an ultra-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 system 8, and the new steam flows out from the superheater 6 to the new steam inlet of the steam turbine system; the remaining m-1 streams are reheated steam, which flows out from a certain level of steam extraction port of the steam turbine system 9 into the reheater 4 of the boiler system, and enters the reheat steam inlet of the steam turbine system 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 system feed water from the feed water heat recovery system of the steam turbine system 9 enters the economizer 5 for heating, and then absorbs heat in the water-cooled wall 7 of the boiler system to become superheated steam, and then enters the superheater 6 for 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 of the 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 to flow along the water side; Extraction throttling valves are installed on the extraction pipes of each stage of the steam turbine system 9; In this example, the ultra-supercritical unit is as follows Figure 2 As shown, 8-stage heat recovery heaters are used, where 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, and 9 represents turbine system; 10, 11 and 12 represent extraction throttle valves of No. 1, No. 2 and No. 3 high-pressure heaters respectively.

[0120] The thermal power system configuration characteristics used in the specific calculation case are:

[0121] 1) The ultra-supercritical unit is a 1000MW ultra-supercritical single-reheat condensing unit;

[0122] 2) Rated water supply temperature is 294.7℃;

[0123] 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;

[0124] 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;

[0125] 5) The thermal system diagram of the ultra-supercritical unit is shown in the attached Figure 2 shown.

[0126] like Figure 1 and Figure 3 As shown, the main steam temperature control method of the ultra-supercritical unit in this embodiment includes the following steps:

[0127] Step 1: Data Collection

[0128] 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;

[0129] 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;

[0130] 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 ; Temperature and pressure of each stage of extraction steam on the extraction side T s,b , P s,b The temperature T of the water drain of each level of heat recovery heater d,b , where b = 1 ~ z;

[0131] Collect the water supply pressure P after the water supply pump fp and economizer inlet feed water pressure P eco,in ;

[0132] Step 2: Data preprocessing

[0133] Clean the parameter data collected above;

[0134] Step 3: Calculate the enthalpy of the working fluid at each point

[0135] 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;

[0136] Step 4: Calculate the feedwater heating shortage corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes. The high-pressure steam extraction throttling increases the feedwater heating shortage of this stage, resulting in a decrease in the main steam temperature. In order to avoid the increase in steam extraction of the heater with higher extraction pressure affecting the throttling effect, each high-pressure steam extraction throttling scheme throttles all continuous high-pressure heaters including the highest-level high-pressure heater;

[0137] The insufficient heating of feedwater caused by unit extraction throttling amount of different high-pressure heater extraction throttling schemes is the heat release of this part of extraction steam in the high-pressure heater of this stage. The specific calculation is as follows:

[0138] ΔQ fw,1 =Δm se1 q1 Option 1: Throttling No.1 High-pressure Heater

[0139] ΔQ fw,2 =Δm se1 q1+Δm se2 q2 Option 2: Throttling No.1 and No.2 high pressure heaters Throttling No.1, No.2 and No.3 high pressure heaters

[0140] …

[0141] Throttling No.1, No.2, No.3, ..., No.h high pressure heater

[0142] …

[0143] Throttling No.1, No.2, No.3, ..., No.k-1 High-pressure heater Where: ΔQ fw is the heat release due to insufficient heating of feed water caused by unit extraction throttling of high-pressure heater, kJ / s; Δm seiis the change in the extraction flow rate of the high-pressure heater, which is 1kg / s; q i is the extraction of the i-th stage high pressure heater

[0144] Steam enthalpy drop, kJ / kg;

[0145] Step 5: Calculate the change in reheat steam flow rate caused by unit extraction throttling amount for different high-pressure steam extraction throttling schemes

[0146] For the high-pressure heater, when the unit flow rate of extraction steam is throttled, the throttled extraction steam returns to the turbine, that is, Δm sei Return to the turbine;

[0147] The change in the reheat steam flow rate at each time is the sum of the changes in the flow rates of all extraction steams whose extraction pressure is greater than or equal to the reheat steam pressure at that time:

[0148]

[0149] Where: Δm rs,j is the change in the jth reheat steam flow rate, kg / s; Δm sei is the change in the steam extraction flow rate of the i-th stage high-pressure heater, kg / s; p rs,j is the cold section pressure of the j-th reheat steam, MPa;

[0150] Step 6: Calculate the heat absorption changes of the economizer and part of the superheater after the boiler reheater corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes

[0151] As the reheat steam flow rate increases, the overall heat absorption of the heating surface of each reheater increases. At the same time, the heat absorption of the working medium in the economizer and some superheaters after the reheater heating surface will decrease accordingly. The reduced heat absorption is distributed according to the original heat absorption ratio of the affected superheater and economizer:

[0152]

[0153] Where: ΔQ eco is the change in heat absorption of the working fluid in the economizer, kJ / s; Q eco is the original heat absorption of the working fluid in the economizer, kJ / s; Q sh,part is the original heat absorption of the working fluid in the affected superheater, kJ / s; ΔQ sh,part is the change in heat absorption of the working fluid in the affected superheater, kJ / s; ΔQ rh,tot is the total heat absorption change of the reheater, kJ / s;

[0154] Step 7: Calculate the predicted value of main steam temperature change corresponding to unit extraction throttling amount for different high-pressure steam extraction throttling schemes

[0155] Due to the throttling of the HPH extraction steam, the total heating deficiency of the feed water in the HPH is ΔQ fw , the total heat at the boiler feed water inlet after high-pressure steam extraction throttling can be calculated as:

[0156] Q e ' co,in =Q eco,in -ΔQ fw

[0157] Where: Q e ' co,in is the total heat at the economizer inlet after high-pressure steam extraction throttling, kJ / s; Q eco,in is the total heat at the economizer inlet before throttling of the high-pressure steam extraction, kJ / s;

[0158] Step 6 calculates the change in heat absorption of the working fluid in the economizer after the high-pressure steam extraction throttling, and then the total heat of the working fluid at the economizer outlet after the high-pressure steam extraction throttling can be calculated as:

[0159] Q e ' co,out =Q eco,out -ΔQ fw -ΔQ eco

[0160] Where: Q e ' co,out Q is the total heat at the economizer outlet after high-pressure steam extraction throttling, kJ / s; eco,out is the total heat at the economizer outlet before throttling of the high-pressure steam extraction, kJ / s;

[0161] The amount of heat absorbed by the working fluid in the water-cooled wall does not change, so there is no need to calculate the energy balance of the water-cooled wall;

[0162] Step 6 Calculate the heat absorption change of the superheated steam generated by the water-cooled wall in the superheater as ΔQ sh,part Therefore, the total heat of the boiler main steam after high-pressure steam extraction throttling can be calculated as:

[0163] Q s ' h,ls =Q sh,ls -ΔQ fw -ΔQ eco -ΔQ sh,part

[0164] Where: Q s ' h,ls Q is the total heat at the high temperature superheater outlet after high pressure steam extraction throttling, kJ / s; sh,ls is the total heat at the high-temperature superheater outlet before throttling of the high-pressure steam extraction, kJ / s;

[0165] Because Q sh,ls =mfw h ls , the change in main steam enthalpy is:

[0166]

[0167] Where: m fw is the boiler feed water flow rate, kg / s; Δh ls Main steam enthalpy change, kJ / kg; h l ' s is the total heat at the high temperature superheater outlet after high pressure extraction steam throttling, kJ / s; h ls is the total heat at the high-temperature superheater outlet before throttling of the high-pressure steam extraction, kJ / s;

[0168] Under the premise that the main steam temperature changes slightly, its specific heat capacity change can be ignored, so the predicted value of the main steam temperature change after high-pressure steam extraction throttling is:

[0169]

[0170] Where: ΔT ls is the predicted value of main steam temperature change corresponding to unit extraction throttling amount for different high-pressure steam extraction throttling schemes, ℃; c sh,ls is the specific heat capacity of main steam, kJ / (kg·K);

[0171] Step 8: Calculate the required extraction throttling amount for each regenerative heater for different high-pressure steam extraction throttling schemes based on the real-time main steam temperature deviation

[0172] Calculate different high-pressure steam extraction throttling schemes respectively. The maximum extraction throttling amount of different high-pressure steam extraction throttling schemes is the minimum extraction amount of all high-pressure heaters with extraction throttling. According to step 7, the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount of various high-pressure steam extraction throttling schemes is obtained: ΔT ls,h,max ,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. The correction coefficient of the predicted value of the main steam temperature change of the high-pressure steam extraction throttling is introduced, that is,

[0173] ΔT ls,exp,h,max =k ls,expchan,h ΔT ls,h,max ,h=1~k-1

[0174] Where: ΔT ls,exp,h,max is the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount of the hth high-pressure steam heater extraction throttling scheme during the corrected actual rapid load change process, ℃; k ls,expchan,h is the correction coefficient of the predicted value of the main steam temperature of the high-pressure heater extraction throttling, 0<k ls,expchan,h <1;

[0175] As the number of high-pressure heaters with extraction throttling increases, the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount also gradually increases, as shown in the following:

[0176] ΔT ls,exp,k-1,max <ΔT ls,exp,k,max

[0177] At the same time, calculate the deviation between the real-time temperature of the main steam and the set temperature:

[0178] ΔT ls,dev =T ls,set -T ls,rt

[0179] Where: ΔT ls,dev is the main steam temperature deviation, °C; T ls,set is the main steam temperature setting value, kJ / s; T ls,rt is the real-time value of main steam temperature, ℃;

[0180] When the main steam temperature deviation is within a certain range, the method of controlling the main steam temperature by throttling the high-pressure steam extraction steam is not adopted, that is, ΔT ls,dev ≤ΔT ls,bdy When the main steam temperature is controlled, only water spraying is used for cooling;

[0181] When the main steam temperature deviation is greater than the set value ΔT ls,bdy The method of controlling the main steam temperature by throttling the high-pressure steam extraction steam is adopted. Preferably, in the step 2, the parameter data collected above are cleaned, and the specific process is as follows:

[0182] (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;

[0183] (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;

[0184] (3) Analyze the size and change trend of important basic parameters that are indispensable for ultra-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 during the actual operation of the ultra-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 1 are inconsistent with the changes in the basic parameters of the ultra-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 ultra-supercritical unit, and finally complete the cleaning of the collected measurement data.

[0185] The present invention cleans the measurement data collected in the ultra-supercritical unit, firstly adopts Kalman filtering to reduce noise, then fills in vacant values, corrects abnormal values, removes erroneous values, and adopts mechanism analysis method to further clean the original data, thus completing the deep preprocessing of the original measurement data, which is of great significance for the accurate calculation of the specific extraction throttling amount of different high-pressure steam extraction throttling schemes obtained according to the measurement data.

[0186] Preferably, the calculation method of each pressure parameter missing in calculating the enthalpy value of each parameter in step 3 is as follows:

[0187] 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

[0188] P d,i =0.95P s,i , i=1~k-1

[0189] 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

[0190]

[0191] 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.

[0192] Preferably, the calculation method for the change in the overall heat absorption amount of the heating surface of the reheater after the high-pressure steam extraction throttling in step 6 is:

[0193] 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 reheater heating surface.

[0194] There are two limit boundaries for the change of heat absorption of the reheater heating surface: Boundary 1: The steam temperature at the reheater outlet remains unchanged. At this time, the increase in heat absorption of the reheater heating surface caused by the increase in the reheat steam flow rate is:

[0195] ΔQ rh,j,max =Δm rs,j (h rh,out,j -h rh,in,j )

[0196] Where: ΔQ rh,j,max is the maximum heat absorption change of the jth reheat steam, kJ / s; h rh,out,j is the outlet enthalpy of the reheater of the jth reheat steam boiler, kJ / kg; h rh,in,j is the inlet enthalpy of the reheater of the j-th reheat steam boiler, kJ / kg;

[0197] Boundary 2: The total heat absorption of the boiler reheater remains unchanged, that is, ΔQ rh,j,min =0.

[0198] Where: ΔQ rh,j,min is the minimum heat absorption change of the jth reheat steam, kJ / s;

[0199] In the actual process, due to the increase in reheat steam flow, the reheater heat absorption will increase, but at the same time, the reheat steam outlet temperature will also decrease to a certain extent. Therefore, the actual reheater heat absorption changes as follows:

[0200] ΔQ rh,j =k qrh,j ΔQ rh,j,max

[0201] Where: ΔQ rh,j is the change in heat absorption of the jth reheated steam, kJ / s; k qrh,j is the equivalent coefficient of the jth reheat steam heat absorption change, 0<k qrh,j <1.

[0202] Then the total heat absorption change of all reheat steam flows is:

[0203]

[0204] Where: ΔQ rh,tot is the total heat absorption change of all reheat steam, kJ / s.

[0205] The present invention uses two limit boundaries to represent the change in heat absorption of the reheater heating surface after high-pressure steam extraction throttling, simplifies the complex flow heat exchange problem, and greatly speeds up the overall calculation speed under limited measurement data.

[0206] Preferably, the specific method for calculating the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount under the high-pressure steam extraction throttling scheme in step eight is:

[0207] First, calculate the steam extraction capacity of each stage of high-pressure heater with the help of the energy balance of the regenerative heater:

[0208]

[0209] Where: m sei,tot is the steam flow rate returned to the steam turbine when the extraction steam of the i-th stage high-pressure heater is fully throttled, kg / s; m dw(i-1) is the drainage flow rate from the i-1th stage high pressure regenerative heater, kg / s; γ i is the heat released by the drain from the previous stage in the high-pressure regenerative heater of stage i, kJ / kg; q i is the heat release of the extraction steam of the i-th stage high-pressure regenerative heater, kJ / kg;

[0210] The maximum extraction throttling amount of different high-pressure heater extraction throttling schemes is the minimum extraction flow rate of the throttled high-pressure heater Δm se,max,h , the insufficient feedwater heating caused by extraction steam throttling is calculated using step 4;

[0211] Then, according to the calculation steps of step 5, step 6 and step 7, the changes in the reheat steam flow corresponding to the maximum extraction throttling amount of the high-pressure heater extraction throttling, the changes in the heat absorption of the economizer and part of the superheater after the boiler reheater, and the predicted value of the main steam temperature change are calculated in turn, and finally the predicted value of the main steam temperature change ΔT corresponding to the maximum extraction throttling amount under the h-th high-pressure heater extraction throttling scheme is calculated. ls,h,max ,h=1~k-1.

[0212] The present invention regards the minimum steam extraction flow of the heater in each high-pressure steam extraction throttling scheme as the maximum steam extraction throttling amount of the entire scheme, simplifies the specific algorithm design of each high-pressure steam extraction throttling scheme, and makes it easier to automatically select the high-pressure steam extraction throttling scheme and automatically calculate the steam extraction throttling amount while ensuring the high-pressure steam extraction throttling accuracy;

[0213] Preferably, the energy balance calculation method of the regenerative heater is as follows:

[0214] According to the calculation principle of energy balance, the feed water heat absorption τ of the high-pressure regenerative heater can be obtained: r , Extraction heat release q r and hydrophobic exothermicity γr , the calculation method is as follows:

[0215] 1) For drain heater:

[0216] τ r =h w,out,r -h w,in,r

[0217] q r =h s,r -h d,r

[0218] γ r =h d,r-1 -h d,r

[0219] 2) For concentrating heaters:

[0220] τ r =h w,out,r -h w,in,r

[0221] q r =h s,r -h w,in,r

[0222] γ r =h d,r-1 -h w,in,i

[0223] Where: h w,out,r is the outlet feed water enthalpy of the rth stage regenerative heater, kJ / kg; h w,in,r is the inlet feed water enthalpy of the rth stage regenerative heater, kJ / kg; h s,r is the extraction enthalpy of the rth stage regenerative heater, kJ / kg; h d,r is the enthalpy of water drainage of the rth stage regenerative heater, kJ / kg; h d,r-1 is the hydrophobic enthalpy of the r-1 stage regenerative heater, kJ / kg.

[0224] 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.

[0225] Preferably, the specific method for selecting the high-pressure steam extraction throttling scheme and the specific method for calculating the high-pressure steam extraction throttling amount in step eight are:

[0226] First, select the high-pressure heater extraction throttling scheme. The selection principle is to throttle as few high-pressure heaters as possible under the premise of meeting the main steam temperature control requirements. Therefore, it is necessary to first compare the main steam change prediction value corresponding to the maximum extraction throttling amount of different high-pressure heater extraction throttling schemes and the real-time main steam temperature deviation, and then select the most appropriate high-pressure heater extraction throttling scheme in order and in a timely manner;

[0227] When ΔT ls,exp,h-1,max <ΔT ls,dev ≤ΔT ls,exp,h,max , select the hth high pressure steam extraction throttling scheme;

[0228] After selecting the high-pressure steam extraction throttling scheme, it is necessary to calculate the specific extraction throttling amount required under the high-pressure steam extraction throttling scheme:

[0229]

[0230] Where: Δm ls,sei The extraction throttling volume used to control the main steam temperature, kg / s; k ls,sei is the steam extraction throttling rate adjustment coefficient, kg / s; ΔT ls,dev Main steam temperature deviation, °C; ΔT ls is the main steam temperature change corresponding to unit extraction throttling amount, °C;

[0231] And when the main steam temperature deviation gradually decreases after the high-pressure heater extraction throttling scheme is used, 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 main steam temperature deviation is less than or equal to the preset limit value ΔT ls,bdy When the steam is pumped out of the high-pressure heater, normal steam extraction of all high-pressure heaters is restored.

[0232] The present invention provides a detailed orderly input and exit mechanism for high-pressure steam extraction throttling. By calculating the predicted value of the main steam temperature change of the maximum extraction throttling amount of different high-pressure steam extraction throttling schemes and comparing it with the real-time main steam temperature deviation, the automatic selection and automatic recovery of the high-pressure steam extraction throttling scheme are completed.

[0233] The adjustable high-pressure steam extraction throttling controls the main steam temperature. Combined with the original main steam temperature control logic of the ultra-supercritical unit automatic control system, it can more effectively control the main steam temperature when the load is increased rapidly, thereby increasing the load change rate of the ultra-supercritical unit, which is of great significance to improving its operating flexibility.

[0234] 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 main steam temperature of an ultra-supercritical unit, 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 ; Temperature and pressure of each stage of extraction steam on the extraction side T s,b , 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 ; 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; Step 4: Calculate the feedwater heating shortage corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes. The high-pressure steam extraction throttling increases the feedwater heating shortage of this stage, resulting in a decrease in the main steam temperature. In order to avoid the increase in steam extraction of the heater with higher extraction pressure affecting the throttling effect, each high-pressure steam extraction throttling scheme throttles all continuous high-pressure heaters including the highest-level high-pressure heater; The insufficient heating of feedwater caused by unit extraction throttling amount of different high-pressure heater extraction throttling schemes is the heat release of this part of extraction steam in the high-pressure heater of this stage. The specific calculation is as follows: ΔQ fw,1 =Δm se1 q1 Option 1: Throttling No.1 High-pressure Heater ΔQ fw,2 =Δm se1 q1+Δm se2 q2 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 The heat released by insufficient feedwater heating caused by unit extraction throttling of the high-pressure heater, kJ / s; Δm sei is the change in the extraction flow rate of the high-pressure heater, which is 1kg / s; q i is the extraction of the i-th stage high pressure heater Steam enthalpy drop, kJ / kg; Step 5: Calculate the change in reheat steam flow rate caused by unit extraction throttling amount for different high-pressure steam extraction throttling schemes For the high-pressure heater, when the unit flow rate of extraction steam is throttled, the throttled extraction steam returns to the turbine, that is, Δm sei Return to the turbine; The change in the reheat steam flow rate at each time is the value of the extraction pressure being greater than or equal to the reheat steam flow rate at that time. The sum of the flow changes of all extraction 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 steam extraction flow rate of the i-th stage high-pressure heater, kg / s; p rs,j is the cold section pressure of the j-th reheat steam, MPa; Step 6: Calculate the heat absorption changes of the economizer and part of the superheater after the boiler reheater corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes As the reheat steam flow rate increases, the overall heat absorption of the heating surface of each reheater increases. At the same time, the heat absorption of the working medium in the economizer and some superheaters after the reheater heating surface will decrease accordingly. The reduced heat absorption is distributed according to the original heat absorption ratio of the affected superheater and economizer: Where: ΔQ eco is the change in heat absorption of the working fluid in the economizer, kJ / s; Q eco is the original heat absorption of the working fluid in the economizer, kJ / s; Q sh,part is the original heat absorption of the working fluid in the affected superheater, kJ / s; ΔQ sh,part is the change in heat absorption of the working fluid in the affected superheater, kJ / s; ΔQ rh,tot is the total heat absorption change of the reheater, kJ / s; Step 7: Calculate the predicted value of main steam temperature change corresponding to unit extraction throttling amount for different high-pressure steam extraction throttling schemes Due to the throttling of the HP heater extraction steam, the total heating deficiency of the feed water in the HP heater is ΔQ fw , the total heat at the boiler feed water inlet after high-pressure steam extraction throttling can be calculated as: Q e ′ co,in =Q eco,in -ΔQ fw Where: Q e ' co,in is the total heat at the economizer inlet after high-pressure steam extraction throttling, kJ / s; Q eco,in is the total heat at the economizer inlet before throttling of the high-pressure steam extraction, kJ / s; Step 6 calculates the change in heat absorption of the working fluid in the economizer after the high-pressure steam extraction throttling, and then the total heat of the working fluid at the economizer outlet after the high-pressure steam extraction throttling can be calculated as: Q e ′ co,out =Q eco,out -ΔQ fw -ΔQ eco Where: Q e ' co,out Q is the total heat at the economizer outlet after high-pressure steam extraction throttling, kJ / s; eco,out is the total heat at the economizer outlet before throttling of the high-pressure steam extraction, kJ / s; The amount of heat absorbed by the working fluid in the water-cooled wall does not change, so there is no need to calculate the energy balance of the water-cooled wall; Step 6 Calculate the heat absorption change of the superheated steam generated by the water-cooled wall in the superheater as ΔQ sh,part Therefore, the total heat of the boiler main steam after high-pressure steam extraction throttling can be calculated as: Q s ′ h,ls =Q sh,ls -ΔQ fw -ΔQ eco -ΔQ sh,part Where: Q s ' h,ls Q is the total heat at the high temperature superheater outlet after high pressure steam extraction throttling, kJ / s; sh,ls is the total heat at the high-temperature superheater outlet before throttling of the high-pressure steam extraction, kJ / s; Because Q sh,ls =m fw h ls , the change in main steam enthalpy is: Where: m fw is the boiler feed water flow rate, kg / s; Δh ls Main steam enthalpy change, kJ / kg; h l ' s is the total heat at the high temperature superheater outlet after high pressure extraction steam throttling, kJ / s; h ls is the total heat at the high-temperature superheater outlet before throttling of the high-pressure steam extraction, kJ / s; Under the premise that the main steam temperature changes little and its specific heat capacity change is ignored, the predicted value of the main steam temperature change after high-pressure steam extraction throttling is: Where: ΔT ls is the predicted value of main steam temperature change corresponding to unit extraction throttling amount for different high-pressure steam extraction throttling schemes, ℃; c sh,ls is the specific heat capacity of main steam, kJ / (kg·K); Step 8: Calculate the required extraction throttling amount for each regenerative heater for different high-pressure steam extraction throttling schemes based on the real-time main steam temperature deviation Calculate different high-pressure steam extraction throttling schemes respectively. The maximum extraction throttling amount of different high-pressure steam extraction throttling schemes is the minimum extraction amount of all high-pressure heaters with extraction throttling. According to the above calculation steps, the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount under various high-pressure steam extraction throttling schemes is obtained: ΔT ls,h,max ,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. The correction coefficient of the predicted value of the main steam temperature change of the high-pressure steam extraction throttling is introduced, that is, ΔT ls,exp,h,max =k ls,expchan,h ΔT ls,h,max ,h=1~k-1 Where: ΔT ls,exp,h,max is the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount of the hth high-pressure steam heater extraction throttling scheme during the corrected actual rapid load change process, ℃; k ls,expchan,h is the correction coefficient of the predicted value of the main steam temperature of the high-pressure heater extraction throttling, 0<k ls,expchan,h <1; As the number of high-pressure heaters with extraction throttling increases, the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount also gradually increases, as shown in the following: ΔT ls,exp,k-1,max <ΔT ls,exp,k,max At the same time, calculate the deviation between the real-time temperature of the main steam and the set temperature: ΔT ls,dev =T ls,set -T ls,rt Where: ΔT ls,dev is the main steam temperature deviation, °C; T ls,set is the main steam temperature setting value, kJ / s; T ls,rt is the real-time value of main steam temperature, ℃; When the main steam temperature deviation is within a certain range, the method of controlling the main steam temperature by throttling the high-pressure steam extraction steam is not adopted, that is, ΔT ls,dev ≤ΔT ls,bdy When the main steam temperature is controlled, only water spraying is used for cooling; When the main steam temperature deviation is greater than the set value ΔT ls,bdy Only when the high-pressure steam extraction throttling method is used to control the main steam temperature.

2. The method for controlling the main steam temperature of an ultra-supercritical unit according to claim 1, 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 ultra-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 ultra-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 1 are inconsistent with the changes in the basic parameters of the ultra-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 ultra-supercritical unit, and finally complete the cleaning of the collected measurement data.

3. The method for controlling the main steam temperature of an ultra-supercritical unit according to claim 1, characterized in that: The calculation method for each pressure parameter missing in the calculation of the enthalpy value of each parameter in step 3 is as follows: 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 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 method for controlling the main steam temperature of an ultra-supercritical unit according to claim 1, characterized in that: The calculation method for the change in the overall heat absorption of the reheater heating surface after throttling of the high-pressure steam extraction in step 6 is: 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 reheater heating surface; There are two limit boundaries for the change of heat absorption of the reheater heating surface: Boundary 1: The steam temperature at the reheater outlet remains unchanged. At this time, the increase in heat absorption of the reheater heating surface caused by the increase in the reheat steam flow rate is: ΔQ rh,j,max =Δm rs,j (h rh,out,j -h rh,in,j ) Where: ΔQ rh,j,max is the maximum heat absorption change of the jth reheat steam, kJ / s; h rh,out,j is the outlet enthalpy of the reheater of the jth reheat steam boiler, kJ / kg; h rh,in,j is the inlet enthalpy of the reheater of the j-th reheat steam boiler, kJ / kg; Boundary 2: The total heat absorption of the boiler reheater remains unchanged, that is, ΔQ rh,j,min =0 Where: ΔQ rh,j,min is the minimum heat absorption change of the jth reheat steam, kJ / s; In the actual process, due to the increase in reheat steam flow, the reheater heat absorption will increase, but at the same time, the reheat steam outlet temperature will also decrease to a certain extent, so the actual reheater heat absorption changes as follows: ΔQ rh,j =k qrh,j ΔQ rh,j,max Where: ΔQ rh,j is the change in heat absorption of the jth reheated steam, kJ / s; k qrh,j is the equivalent coefficient of the jth reheat steam heat absorption change, 0<k qrh,j <1. Then the total heat absorption change of all reheat steam flows is: Where: ΔQ rh,tot is the total heat absorption change of all reheat steam, kJ / s.

5. The method for controlling the main steam temperature of an ultra-supercritical unit according to claim 1, characterized in that: The specific method for calculating the predicted value of the main steam temperature change corresponding to the maximum extraction throttling amount under different high-pressure steam extraction throttling schemes in step 8 is as follows: First, calculate the steam extraction capacity of each stage of high-pressure heater with the help of the energy balance of the regenerative heater: Where: m sei,tot is the steam flow rate returned to the steam turbine when the extraction steam of the i-th stage high pressure heater is fully throttled, kg / s; m dw(i-1) is the drainage flow rate from the i-1th stage high pressure regenerative heater, kg / s; γ i is the heat released by the drain from the previous stage in the i-th stage high-pressure regenerative heater, kJ / kg; q i is the heat release of the extraction steam of the i-th stage high-pressure regenerative heater, kJ / kg; The maximum extraction steam throttling amount of different high-pressure steam extraction throttling schemes is the minimum extraction steam flow rate Δm before the high-pressure steam extraction throttling se,max,h , the insufficient feedwater heating caused by extraction steam throttling is calculated using step 4; Then, according to the calculation steps of step 5, step 6 and step 7, the changes in the reheat steam flow corresponding to the maximum extraction throttling amount of the high-pressure heater extraction throttling, the changes in the heat absorption of the economizer and part of the superheater after the boiler reheater, and the predicted value of the main steam temperature change are calculated in turn, and finally the predicted value of the main steam temperature change ΔT corresponding to the maximum extraction throttling amount under the h-th high-pressure heater extraction throttling scheme is calculated. ls,h,max ,h=1~k-1.

6. The method for controlling the main steam temperature of an ultra-supercritical unit according to claim 5, characterized in that: The energy balance calculation method for the regenerative heater is as follows: According to the calculation principle of energy balance, the feed water heat absorption τ of the high-pressure regenerative heater is obtained r , Extraction heat release q r and hydrophobic exothermicity γ r , the calculation method is as follows: 1) For drain heater: t r =h w,out,r -h w,in,r q r =h s,r -h d,r γ r =h d,r-1 -h d,r 2) For concentrating heaters: t r =h w,out,r -h w,in,r q r =h s,r -h w,in,r γ r =h d,r-1 -h w,in,i Where: h w,out,r is the outlet feed water enthalpy of the rth stage regenerative heater, kJ / kg; h w,in,r is the inlet feed water enthalpy of the rth stage regenerative heater, kJ / kg; h s,r is the extraction enthalpy of the rth stage regenerative heater, kJ / kg; h d,r is the enthalpy of water drainage of the rth stage regenerative heater, kJ / kg; h d,r-1 is the hydrophobic enthalpy of the r-1 stage regenerative heater, kJ / kg.

7. The method for controlling the main steam temperature of an ultra-supercritical unit according to claim 1, characterized in that: The specific selection method of the high-pressure heater extraction throttling scheme and the specific calculation method of the high-pressure heater extraction throttling amount in step eight are as follows: firstly, the high-pressure heater extraction throttling scheme is selected. The selection principle is to throttle as few high-pressure heaters as possible under the premise of meeting the main steam temperature control requirements. Therefore, it is necessary to first compare the main steam change prediction value corresponding to the maximum extraction throttling amount of different high-pressure heater extraction throttling schemes and the real-time main steam temperature deviation. The most appropriate high-pressure heater extraction throttling scheme is selected in order and in a timely manner. When ΔT ls,exp,h-1,max <ΔT ls,dev ≤ΔT ls,exp,h,max , select the hth high-pressure steam extraction throttling scheme; After selecting the high-pressure steam extraction throttling scheme, it is necessary to calculate the specific extraction throttling amount required under the high-pressure steam extraction throttling scheme: Where: Δm ls,sei The extraction throttling volume used to control the main steam temperature, kg / s; k ls,sei is the steam extraction throttling rate adjustment coefficient, kg / s; ΔT ls,dev Main steam temperature deviation, °C; ΔT ls is the main steam temperature change corresponding to unit extraction throttling amount, °C; And when the main steam temperature deviation gradually decreases after the high-pressure heater extraction throttling scheme is used, the extraction throttling of each high-pressure heater is gradually and orderly exited in accordance with the throttling scheme selection method, and when the main steam temperature deviation is less than or equal to the preset limit ΔT ls,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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