Supercritical unit reheat steam temperature control method

Abstract

The invention discloses a supercritical unit reheat steam temperature control method, which comprises the following steps of: 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 the unit steam extraction throttling flow of different high-pressure heater steam extraction throttling schemes; and then heat absorption capacity change of a reheater arranged behind the superheater is calculated, reheat steam flow change and heat absorption variable quantity of the reheater are synthesized, reheat steam temperature change predicted values corresponding to unit steam extraction throttling flows of different high-pressure heater steam extraction throttling schemes are obtained, and finally, according to the real-time deviation of the reheat steam temperature, the real-time deviation of the reheat steam temperature is calculated. And a specific high-pressure heater steam extraction throttling scheme and steam extraction throttling flow are obtained. According to the method, the control effect of the temperature of the reheat steam in the transient process of the supercritical unit is effectively improved, the problem that the temperature of the reheat steam is extremely prone to being greatly overheated in the rapid load rising process is solved, and the method is of great significance to improvement of the rapid load changing and flexible operation capacity of the supercritical coal-fired power generation unit.

Description

Technical Field

[0001] The present 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. Background Art

[0002] Since the beginning of the 21st century, the global energy mix has been continuously transforming toward clean, low-carbon, efficient, and diversified energy. However, the highly time-varying nature of renewable energy sources such as wind and solar power has made it difficult to absorb and consume renewable energy generation in my country, leading to serious problems with wind and solar power curtailment. Improving the operational flexibility of conventional thermal power systems to accommodate renewable energy generation is a key technological direction. For example, coal-fired power generation will shift from a primary energy source to a foundational energy source, and the magnitude and frequency of load fluctuations in coal-fired generating units will gradually increase. Consequently, coal-fired units will be subject to frequent transient load fluctuations for extended periods of time.

[0003] The quality of reheat steam temperature control has become a significant bottleneck hindering the further improvement of the variable load capability of coal-fired power generation thermal power systems. During rapid load increases, due to inadequate steam temperature control, reheat steam is prone to overheating, limiting further improvements in unit flexibility. Preventing or effectively suppressing reheat steam temperature surges during rapid load increases is a key component of optimizing the coordinated boiler control system for coal-fired power generation units. Summary of the Invention

[0004] In order to overcome the problems existing in the above-mentioned prior art, the purpose of the present invention is to provide a method for controlling the reheat steam temperature of a supercritical unit. By adding extraction throttle valves to the extraction pipes of high-pressure heaters at each stage, with the help of precise high-pressure extraction throttling, the reheat steam flow rate is increased and the flue gas temperature at the boiler reheater inlet 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 during rapid load increase.

[0005] In order to achieve the above object, the present invention adopts the following technical solutions:

[0006] A method for controlling the temperature of reheat steam in a supercritical unit comprises the following steps:

[0007] Step 1: Data Collection

[0008] Collect boiler system feed water flow m fw And the feed water flow measurement data of the steam turbine system flowing through each stage of high pressure heater m fwi , where i = 1 to k-1, k-1 is the number of high-pressure heaters;

[0009] 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 boilerin,a 、p in,a , the temperature and pressure T of the working fluid leaving the boiler out,a 、p out,a , where a = 1 to m;

[0010] 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 to z, z is the number of regenerative heaters;

[0011] Collect the water supply pressure p after the water supply pump fp and economizer inlet feed water pressure p eco,in , working medium temperature at water wall inlet T ww,in and pressure p ww,in ;

[0012] Step 2: Data preprocessing

[0013] Clean the parameter data collected in step 1;

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

[0015] Using 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 at the inlet and outlet of the m working fluid flows of the boiler. in,a and h out,a , where a = 1 ~ m; the enthalpy value of the inlet water of each level of heat recovery heater on the water supply side h w,in,b and the outlet water enthalpy 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 ;

[0016] Step 4: Calculate the maximum change in reheat steam flow rate caused by different high-pressure steam extraction throttling schemes

[0017] For the high pressure heater, since the extraction throttle valve is installed on the extraction pipe, the steam flow rate of the extraction throttle is in the range of 0~m sei,max , that is, at most all the extraction steam of this stage is returned to the turbine, the maximum is:

[0018]

[0019] Where: m sei,maxThe maximum 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 drain flow rate from the i-1th stage high pressure heater, kg / s; γ i is the heat released by unit mass of hydrophobic water from the previous stage in the i-stage high-pressure heater, kJ / kg; q i is the heat release per unit mass of extraction steam in the i-th stage high-pressure heater, kJ / kg; τ i is the heat absorption per unit mass of feed water in the i-th stage high-pressure heater, kJ / kg; γ i ,q i and τ i It needs to be obtained by using the energy balance calculation method of the regenerative heater;

[0020] 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. The maximum change in each reheat steam flow rate is the sum of the maximum changes in all extraction steam flows whose extraction pressure is greater than or equal to the reheat steam pressure:

[0021]

[0022] Where: Δm rs,j,max is the maximum change in the jth reheat steam flow rate, kg / s; Δm sei,max is the maximum change in the extraction steam flow of the i-th stage high-pressure heater, which is equal to the extraction steam flow of the stage, kg / s; p s,i is the extraction steam pressure of the i-th stage regenerative heater, MPa; p rs,j is the cold section pressure of the j-th reheat steam, MPa;

[0023] Step 5: Calculate the feedwater heating shortfall corresponding to unit extraction throttling for different HPH extraction throttling schemes. HPH extraction throttling increases the feedwater heating shortfall for the corresponding stage, resulting in increased superheater heat absorption and increased reheat steam flow. However, increased HPH extraction throttling will also increase the extraction flow of higher-pressure HPH heaters. To prevent the increased extraction of higher-extraction-pressure heaters from affecting the throttling effect, all HPH extraction throttling schemes throttle all consecutive HPH heaters, including the highest-stage HPH heater.

[0024] The insufficient feedwater heating caused by the unit extraction throttling amount of different high-pressure heater extraction throttling schemes is the heat released per unit mass of the high-pressure heater extraction steam in the high-pressure heater of that stage. The specific calculation is as follows:

[0025] ΔQ fw,1 =Δm se1 q1 Option 1: Throttling No.1 High-Pressure Heater

[0026] ΔQ fw,2 =Δmse1 q1+Δm se2 q2 Option 2: Throttling No.1 and No.2 high-pressure heaters

[0027] Option 3: Throttling No. 1, No. 2 and No. 3 high-pressure heaters

[0028] … …

[0029] Solution (h): Throttling No.1, No.2, No.3, ..., No.h high-pressure heater

[0030] … …

[0031] Solution (k-1): Throttling No.1, No.2, No.3, ..., No.k-1 high-pressure heater Where: ΔQ fw is the insufficient heating of feedwater caused by the unit extraction throttling rate of the high-pressure heater, kJ / s; Δm sei is the unit throttling rate of the high-pressure heater extraction steam flow, which is 1kg / s;

[0032] Step 6: Calculate the heat absorption change of each reheater after the boiler superheater corresponding to the unit extraction throttling amount for different high-pressure steam extraction throttling schemes

[0033] Throttling of high-pressure steam extraction causes insufficient feed water heating, and the feed water temperature entering the boiler system drops significantly, which leads to an increase in the heat absorption of the water-cooled walls and superheater heating surfaces before each reheater.

[0034] The increase in heat absorption of the water-cooled wall and superheater caused by insufficient feedwater heating will cause a decrease in the heat absorption of each reheater after the water-cooled wall and superheater. The reduced heat absorption is distributed according to the proportion of the original heat absorption of each affected reheater.

[0035]

[0036] Where: ΔQ rh,j is the reduction in heat absorption of the jth reheated steam in the boiler system reheater due to unit extraction throttling amount under different high-pressure heater extraction throttling schemes, kJ / s; ΔQ sh,re Q is the additional heat absorption of the water-cooled wall and superheater caused by the unit extraction throttling rate of different high-pressure steam extraction throttling schemes, kJ / s; rh,j is the heat absorption of the jth reheated steam in the boiler system reheater before throttling of the high-pressure heater extraction steam, kJ / s;

[0037] Step 7: Calculate the predicted reheat steam temperature change corresponding to the unit extraction throttling amount for different high-pressure steam extraction throttling schemes

[0038] Due to the high-pressure steam extraction throttling, the change in the reheat steam flow rate caused by the unit extraction throttling amount of different high-pressure steam extraction throttling schemes is Δm rs,j At the same time, the change in the amount of heat absorbed by the reheated steam caused by insufficient feedwater heating corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes is ΔQ rh,j Based on the above changes, the change in the outlet enthalpy of the reheated steam corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes is obtained as follows:

[0039]

[0040] Where: Δh rs,j is the change in enthalpy of the jth reheat steam outlet corresponding to the unit extraction throttling amount for different high-pressure heater extraction throttling schemes, kJ / kg; Q′ rh,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′ rs,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;

[0041] The heat absorption of the jth reheater after unit extraction steam throttling of different high-pressure steam extraction throttling schemes is:

[0042] Q′ rh,j =Q rh,j -ΔQ rh,j

[0043] Assuming that the reheat steam temperature changes little and its specific heat capacity change is negligible, the predicted value of the reheat steam temperature change after unit extraction steam throttling for different high-pressure heater extraction steam throttling schemes is:

[0044]

[0045] Where: ΔT rs,j is the predicted value of the jth reheat steam temperature change after unit extraction throttling for different high-pressure heater extraction throttling schemes, ℃; c rs,j is the specific heat capacity of the j-th reheat steam, kJ / (kg·K);

[0046] Step 8: Calculate the real-time reheat steam temperature deviation, select the appropriate HVHP extraction throttling scheme, and calculate the extraction throttling amount required for each regenerative heater under different HVHP extraction throttling schemes.

[0047] Calculate different HPH extraction throttling schemes respectively. The maximum extraction throttling amount of different HPH extraction throttling schemes is the minimum extraction amount of all HPHs with extraction throttling. According to steps 1 to 7, the predicted value of each reheat steam temperature change ΔT corresponding to the maximum extraction throttling amount under various HPH extraction throttling schemes is obtained. rs,j,h,max ,j=1~m-1,h=1~k-1;

[0048] Since the actual load change process is fast, different high-pressure steam extraction throttling schemes cannot achieve the maximum reheat steam temperature change at each time. Therefore, the correction coefficient of the predicted value of the reheat steam temperature of the high-pressure steam extraction throttling is introduced, that is,

[0049] ΔT rs,j,exp,h,max =k rs,j,expchan,h ΔT rs,j,h,max ,j=1~m-1,h=1~k-1

[0050] Where: ΔT rs,j,exp,h,max is the predicted value of the jth reheat steam temperature change corresponding to the maximum extraction throttling amount of the hth high-pressure heater extraction throttling scheme during the corrected actual rapid load change process, °C; k rs,j,expchan,h k is the correction coefficient of the predicted value of reheat steam temperature change due to high pressure steam extraction throttling, 0<k rs,j,expchan,h <1;

[0051] At the same time, calculate the real-time deviation between the real-time temperature of each reheat steam and the set temperature.

[0052] ΔT rs,j,dev =T rs,j,set -T rs,j,rt

[0053] Where: ΔT rs,j,dev is the real-time deviation of the j-th reheat steam temperature, °C; T rs,j,set is the set value of the jth reheat steam temperature, ℃; T rs,j,rt is the real-time value of the j-th reheat steam temperature, °C;

[0054] When the real-time deviation of each reheat steam temperature is within the preset range, the method of controlling the reheat steam temperature by adjustable high-pressure steam extraction throttling is not used; that is, ΔT rs,j,dev ≤ΔT rs,j,bdy When using, only flue gas dampers or flue gas recirculation are used to control the reheat steam temperature at each time;

[0055] When the real-time deviation of the reheat steam temperature is greater than the set value ΔT rs,j,bdy When the reheat steam temperature is controlled by the adjustable high-pressure steam extraction throttling method, 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 real-time deviation of each reheat steam temperature and the predicted value of the maximum reheat steam temperature change caused by each scheme.

[0056] The beneficial effects of the present invention are as follows: the present invention adopts an adjustable high-pressure steam extraction throttling method to regulate the reheat steam temperature of a supercritical coal-fired power generation unit, firstly collects real-time data of thermal parameters in a 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 changes in the reheat steam flow rate of each reheat steam and the changes in the heat absorption of the water-cooled wall and the superheater corresponding to the unit mass extraction throttling amount of different high-pressure steam extraction throttling schemes, the predicted values ​​of the changes in the reheat steam temperature of each reheat steam corresponding to the unit mass extraction throttling amount of different high-pressure steam extraction throttling schemes are obtained according to the energy balance equation, combined with the reheat steam temperature deviations of each reheat steam collected and calculated in real time by the unit, by comparing the sizes of the two, the most suitable high-pressure steam extraction throttling scheme and the precise high-pressure steam extraction throttling amount corresponding to the current reheat steam temperature deviations are selected in order and in a timely manner. By supplementing and optimizing the original automatic control logic of the reheat steam temperature through adjustable high-pressure steam extraction throttling, the problem of overheating of the reheat steam temperature at each time can be effectively prevented or suppressed when the supercritical coal-fired power generation unit rapidly increases its load, thereby improving the bottleneck of reheat steam temperature exceeding the limit, which restricts the further increase of the unit's load change rate, and further improving the unit's operating flexibility.

[0057] Advantages of the present invention

[0058] 1) The present invention provides several HPP extraction throttling schemes. To maximize the HPP extraction throttling effect and prevent a significant increase in extraction from heaters with higher extraction pressures during HPP extraction throttling, which would weaken the steam temperature control effect of extraction throttling, all HPP extraction throttling schemes provided by the present invention require throttling of consecutive high-pressure heaters, including the highest-level high-pressure heater. This not only ensures the HPP extraction throttling effect, but also facilitates the use and exit of specific implementation schemes, simplifies the operational difficulty of HPP extraction throttling to control the reheat steam temperature at each stage, and makes automated control easier to achieve.

[0059] 2) The present invention proposes to install extraction throttle valves on the extraction pipes of the high-pressure heaters at each stage of the steam turbine system of a supercritical unit. In addition to providing multiple high-pressure heater extraction throttling schemes, the specific throttling amount of each high-pressure heater extraction can be precisely adjusted. Compared with the high-pressure heater extraction throttling scheme that can only be opened or closed, it can achieve more precise adjustment of the reheat steam temperature at each stage.

[0060] 3) The present invention uses the energy balance of the high-pressure reheat heater to calculate the flow rate change of each reheat steam and the feedwater heating shortage corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes. Through the energy balance of the boiler water-cooled wall, superheater and each reheater, all energy flow direction changes of the coal-fired unit are comprehensively considered. Finally, the predicted value of the temperature change of each reheat steam corresponding to the unit mass extraction throttling amount of different high-pressure steam extraction throttling schemes and the maximum change of each reheat steam temperature caused by different high-pressure steam extraction throttling schemes are calculated. This has important guiding significance for the subsequent selection of high-pressure steam extraction throttling schemes and the calculation of high-pressure steam extraction throttling amount.

[0061] 4) The present invention selects a throttling scheme based on the real-time collected and calculated deviations of each reheat steam temperature and the calculated predicted maximum change in each reheat steam temperature caused by each high-pressure steam extraction throttling scheme. By defining a limit for each reheat steam temperature deviation, when each reheat steam temperature deviation is greater than the set limit, different high-pressure steam extraction throttling schemes are selected in sequence and in a timely manner based on the relationship between the temperature deviation and the predicted value of the temperature change, and the high-pressure steam extraction throttling amount of each stage is determined. When each reheat steam temperature deviation decreases, the throttling of each heater is sequentially and orderly exited based on the relationship between the deviation and the predicted value. When the deviation 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 and extraction throttling amount calculation method, different high-pressure steam extraction throttling schemes can be reasonably and timely selected and the extraction throttling amount of each stage can be calculated to correspond to different reheat steam temperature deviations, thereby more scientifically scheduling the rational flow of various energy flows within the thermal system of the coal-fired unit, and ultimately improving the reheat steam temperature control effect of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0062] Figure 1 This is a flow chart of the supercritical unit reheat steam temperature control method of the present invention;

[0063] 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.

[0064] Figure 3 This is the reheat steam temperature control logic diagram of the supercritical unit of the present invention, wherein the bold part is the supplementary optimized reheat steam temperature control logic. DETAILED DESCRIPTION

[0065] In order to make the purpose, technical solutions and advantages of the present invention more clearly understood, 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 intended to limit the present invention.

[0066] A method for controlling the reheat steam temperature of a supercritical unit, such as Figure 2 As shown, the supercritical unit consists of a boiler system 8 and a steam turbine system 9, which are connected by m working medium inlets and outlets. One working medium is converted from feed water into new steam by absorbing heat, and 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; 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, pulverizer and burner. The boiler system feed water from the steam turbine feed water regenerative system 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 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 are combined into a working medium and continue to flow along the water side; in this example, the thermal energy power system is as follows Figure 2 As shown, 8-stage regenerative 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, 9 represents turbine system, 10 represents turbine high-pressure cylinder, 11 represents turbine intermediate-pressure cylinder, and 12 represents turbine low-pressure cylinder.

[0067] Thermal system configuration characteristics used in specific calculation cases:

[0068] 1) The ultra-supercritical unit is a 1000MW ultra-supercritical single-reheat condensing unit;

[0069] 2) Rated water supply temperature is 294.7℃;

[0070] 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;

[0071] 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;

[0072] 5) The thermal system diagram of the ultra-supercritical unit is shown in the attached Figure 2 As shown;

[0073] like Figure 1 and Figure 3 As shown, the supercritical unit reheat steam temperature control method of this embodiment includes the following steps:

[0074] Step 1: Data Collection

[0075] Collect boiler system feed water flow m fw And the feed water flow measurement data of the steam turbine system flowing through each stage of high pressure heater m fwi , where i = 1 to k-1, k-1 is the number of high-pressure heaters;

[0076] 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 to m;

[0077] 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 to z, z is the number of regenerative heaters;

[0078] Collect the water supply pressure p after the water supply pump fp and economizer inlet feed water pressure p eco,in , working medium temperature at water wall inlet T ww,in and pressure p ww,in ;

[0079] Step 2: Data preprocessing

[0080] Clean the parameter data collected in step 1;

[0081] Step 3: Calculate the enthalpy of the working fluid at each point

[0082] Using 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 at the inlet and outlet of the m working fluid flows of the boiler. in,a and h out,a , where a = 1 ~ m; the enthalpy value of the inlet water of each level of heat recovery heater on the water supply side h w,in,b and the outlet water enthalpy 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 ;

[0083] Step 4: Calculate the maximum change in reheat steam flow rate caused by different high-pressure steam extraction throttling schemes

[0084] For the high pressure heater, since the extraction throttle valve is installed on the extraction pipe, the steam flow rate of the extraction throttle is in the range of 0~m sei,max , that is, at most all the extraction steam of this stage is returned to the turbine, the maximum is:

[0085]

[0086] Where: m sei,max The maximum 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 drain flow rate from the i-1th stage high pressure heater, kg / s; γ i is the heat released by unit mass of hydrophobic water from the previous stage in the i-stage high-pressure heater, kJ / kg; q i is the heat release per unit mass of extraction steam in the i-th stage high-pressure heater, kJ / kg; τ i is the heat absorption per unit mass of feed water in the i-th stage high-pressure heater, kJ / kg; γ i ,q i and τ i It needs to be obtained by using the energy balance calculation method of the regenerative heater;

[0087] 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. The maximum change in each reheat steam flow rate is the sum of the maximum changes in all extraction steam flows whose extraction pressure is greater than or equal to the reheat steam pressure:

[0088]

[0089] Where: Δm rs,j,max is the maximum change in the jth reheat steam flow rate, kg / s; Δm sei,maxis the maximum change in the extraction steam flow of the i-th stage high-pressure heater, which is equal to the extraction steam flow of the stage, kg / s; p s,i is the extraction steam pressure of the i-th stage regenerative heater, MPa; p rs,j is the cold section pressure of the j-th reheat steam, MPa;

[0090] Step 5: Calculate the feedwater heating shortage corresponding to the unit extraction throttling amount for different HPH extraction throttling schemes. The HPH extraction throttling increases the feedwater heating shortage of the corresponding stage, resulting in an increase in superheater heat absorption and an increase in reheat steam flow. However, the increase in HPH extraction throttling will cause an increase in the extraction flow of the higher pressure HPH. In order to avoid the increase in extraction of the higher extraction pressure heater affecting the throttling effect, all HPH extraction throttling schemes throttle all consecutive HPH heaters, including the highest stage HPH heater.

[0091] The insufficient feedwater heating caused by the unit extraction throttling amount of different high-pressure heater extraction throttling schemes is the heat released per unit mass of the high-pressure heater extraction steam in the high-pressure heater of that stage. The specific calculation is as follows:

[0092] ΔQ fw,1 =Δm se1 q1 Option 1: Throttling No.1 High-Pressure Heater

[0093] ΔQ fw,2 =Δm se1 q1+Δm se2 q2 Option 2: Throttling No.1 and No.2 high-pressure heaters

[0094] Option 3: Throttling No. 1, No. 2 and No. 3 high-pressure heaters

[0095] … …

[0096] Solution (h): Throttling No.1, No.2, No.3, ..., No.h high-pressure heater

[0097] … …

[0098] Solution (k-1): Throttling No.1, No.2, No.3, ..., No.k-1 high-pressure heater Where: ΔQ fw is the insufficient heating of feedwater caused by the unit extraction throttling rate of the high-pressure heater, kJ / s; Δm sei is the unit throttling rate of the high-pressure heater extraction steam flow, which is 1kg / s;

[0099] Step 6: Calculate the heat absorption change of each reheater after the boiler superheater corresponding to the unit extraction throttling amount for different high-pressure steam extraction throttling schemes

[0100] Throttling of high-pressure steam extraction causes insufficient feed water heating, and the feed water temperature entering the boiler system drops significantly, which leads to an increase in the heat absorption of the water-cooled walls and superheater heating surfaces before each reheater.

[0101] The increase in heat absorption of the water-cooled wall and superheater caused by insufficient feedwater heating will cause a decrease in the heat absorption of each reheater after the water-cooled wall and superheater. The reduced heat absorption is distributed according to the proportion of the original heat absorption of each affected reheater.

[0102]

[0103] Where: ΔQ rh,j is the reduction in heat absorption of the jth reheated steam in the boiler system reheater due to unit extraction throttling amount under different high-pressure heater extraction throttling schemes, kJ / s; ΔQ sh,re Q is the additional heat absorption of the water-cooled wall and superheater caused by the unit extraction throttling rate of different high-pressure steam extraction throttling schemes, kJ / s; rh,j is the heat absorption of the jth reheated steam in the boiler system reheater before throttling of the high-pressure heater extraction steam, kJ / s;

[0104] Step 7: Calculate the predicted reheat steam temperature change corresponding to the unit extraction throttling amount for different high-pressure steam extraction throttling schemes

[0105] Due to the high-pressure steam extraction throttling, the change in the reheat steam flow rate caused by the unit extraction throttling amount of different high-pressure steam extraction throttling schemes is Δm rs,j At the same time, the change in the amount of heat absorbed by the reheated steam caused by insufficient feedwater heating corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes is ΔQ rh,j Based on the above changes, the change in the outlet enthalpy of the reheated steam corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes is obtained as follows:

[0106]

[0107] Where: Δh rs,j is the change in enthalpy of the jth reheat steam outlet corresponding to the unit extraction throttling amount for different high-pressure heater extraction throttling schemes, kJ / kg; Q′ rh,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′ rs,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;

[0108] The heat absorption of the jth reheater after unit extraction steam throttling of different high-pressure steam extraction throttling schemes is:

[0109] Q′ rh,j =Q rh,j -ΔQ rh,j

[0110] Assuming that the reheat steam temperature changes little and its specific heat capacity change is negligible, the predicted value of the reheat steam temperature change after unit extraction steam throttling for different high-pressure heater extraction steam throttling schemes is:

[0111]

[0112] Where: ΔT rs,j is the predicted value of the jth reheat steam temperature change after unit extraction throttling for different high-pressure heater extraction throttling schemes, ℃; c rs,j is the specific heat capacity of the j-th reheat steam, kJ / (kg·K);

[0113] Step 8: Calculate the real-time reheat steam temperature deviation, select the appropriate HVHP extraction throttling scheme, and calculate the extraction throttling amount required for each regenerative heater under different HVHP extraction throttling schemes.

[0114] Calculate different HPH extraction throttling schemes respectively. The maximum extraction throttling amount of different HPH extraction throttling schemes is the minimum extraction amount of all HPHs with extraction throttling. According to steps 1 to 7, the predicted value of each reheat steam temperature change corresponding to the maximum extraction throttling amount under various HPH extraction throttling schemes is obtained: ΔT rs,j,h,max ,j=1~m-1,h=1~k-1;

[0115] Since the actual load change process is fast, different high-pressure steam extraction throttling schemes cannot achieve the maximum reheat steam temperature change at each time. Therefore, the correction coefficient of the predicted value of the reheat steam temperature of the high-pressure steam extraction throttling is introduced, that is,

[0116] ΔT rs,j,exp,h,max =k rs,j,expchan,h ΔT rs,j,h,max ,j=1~m-1,h=1~k-1

[0117] Where: ΔT rs,j,exp,h,max is the predicted value of the jth reheat steam temperature change corresponding to the maximum extraction throttling amount of the hth high-pressure heater extraction throttling scheme during the corrected actual rapid load change process, °C; k rs,j,expchan,h k is the correction coefficient of the predicted value of reheat steam temperature change due to high pressure steam extraction throttling, 0<k rs,j,expchan,h <1;

[0118] At the same time, calculate the real-time deviation between the real-time temperature of each reheat steam and the set temperature.

[0119] ΔT rs,j,dev =T rs,j,set -T rs,j,rt

[0120] Where: ΔT rs,j,dev is the real-time deviation of the j-th reheat steam temperature, °C; T rs,j,set is the set value of the jth reheat steam temperature, ℃; T rs,j,rt is the real-time value of the j-th reheat steam temperature, °C;

[0121] When the real-time deviation of each reheat steam temperature is within the preset range, the method of controlling the reheat steam temperature by adjustable high-pressure steam extraction throttling is not used; that is, ΔT rs,j,dev ≤ΔT rs,j,bdy When using, only flue gas dampers or flue gas recirculation are used to control the reheat steam temperature at each time;

[0122] When the real-time deviation of the reheat steam temperature is greater than the set value ΔT rs,j,bdy When the reheat steam temperature is controlled by the adjustable high-pressure steam extraction throttling method, 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 real-time deviation of each reheat steam temperature and the predicted value of the maximum reheat steam temperature change caused by each scheme.

[0123] Preferably, in step 2, the parameter data collected in step 1 is cleaned, and the specific process is as follows:

[0124] (1) First, the original measurement data collected in step 1 is subjected to noise reduction and filtering by using the Kalman filter method;

[0125] (2) Then, the noise-reduced measurement data set is analyzed to screen out 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;

[0126] (3) Analyze the size and changing 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, it is judged 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, and more accurate measuring points are selected for the data of multiple measuring points. The data points that are inconsistent with the changes in the basic data of the supercritical unit are corrected or discarded, and finally the cleaning of the collected measurement data is completed.

[0127] Before applying the measurement data of key thermal parameters collected from the supercritical unit to the calculation of control parameters, the present invention first cleans the data, reduces noise with the help of Kalman filtering, and then uses a simple data analysis method to supplement vacant values, correct abnormal values, and eliminate erroneous values. With the help of 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, and the change rules of a few core thermal parameters of the supercritical unit, it is determined whether the measurement points of other thermal parameters are accurate. Finally, accurate and reliable measurement points are selected and abnormal status data are repaired, providing reliable data guarantee for the accurate calculation of subsequent control parameters.

[0128] Preferably, the calculation method for each pressure parameter missing in calculating the working fluid enthalpy value at each point in step 3 is as follows:

[0129] Calculate the hydrophobic enthalpy h of each heater by thermophysical properties d,i The required but unmeasured hydrophobic pressure P of each heater stage d,i According to the extraction steam pressure P s,i 95% is calculated, that is

[0130] P d,i =0.95P s,i , i=1~k-1

[0131] Calculate the enthalpy value h of the inlet water of each stage of the regenerative heater on the feed water side through thermophysical properties w,in,i and the outlet water enthalpy h w,out,i The required but unmeasured water pressure P at the inlet of each regenerative heater 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

[0132]

[0133] This method uses 95% of the extraction steam pressure to replace the unmeasured heater drain pressure. It also uses the pressure after the feedwater pump and the pressure before the economizer to estimate the feedwater pressure of each high-pressure heater. This method easily obtains some previously unmeasured thermodynamic parameters, laying the foundation for calculating the feedwater heat absorption and extraction steam heat release of the high-pressure heaters.

[0134] Preferably, the energy balance calculation method for the regenerative heater in step 4 is as follows:

[0135] According to the calculation principle of energy balance, the feed water heat absorption τ of the high-pressure heater is obtained i , extraction steam heat release q iand the hydrophobic heat release amount γ i The calculation method is as follows:

[0136] 1) for the hydrophobic flow heater:

[0137] τ i = h w,out,i -h w,in,i

[0138] q i = h s,i -h d,i

[0139] γ i = h d,i-1 -h d,i

[0140] 2) for the collection type heater:

[0141] τ i = h w,out,i -h w,in,i

[0142] q i = h s,i -h w,in,i

[0143] γ i = h d,i-1 -h w,in,i

[0144] In the formula: h w,out,i is the enthalpy value of the i-th stage regenerative heater outlet feed water, kJ / kg; h w,in,i is the enthalpy value of the i-th stage regenerative heater inlet feed water, kJ / kg; h s,i is the enthalpy value of the i-th stage regenerative heater extraction steam, kJ / kg; h d,i is the enthalpy value of the i-th stage regenerative heater drain, kJ / kg; h d,i-1 is the enthalpy value of the i-1-th stage regenerative heater drain, kJ / kg.

[0145] The present application adopts the energy balance method to calculate the feed water heat absorption amount, extraction steam heat release amount and hydrophobic heat release amount of the high-pressure heater, has the advantages of simplicity, rapidness and higher accuracy, ignores the heat storage change of the high-pressure heater itself, can more simply obtain the key parameters of each stage high-pressure heater, and provides data source for the calculation of subsequent high-pressure heater extraction throttling and feed water heating deficiency parameters.

[0146] Preferably, the calculation method of the water wall and superheater heat absorption amount change caused by the unit mass extraction throttling amount of different high-pressure heater extraction throttling schemes in step six is as follows:

[0147] Because the flue gas temperature before and after each heating surface in the furnace cannot be measured, the heat absorption variation of the water wall and the superheater is calculated by using a simplified method;

[0148] The heat absorption variation of the water wall and the superheater is calculated uniformly, and two limit boundaries are defined:

[0149] Boundary 1: the working medium temperature at the outlet of the superheater after the high-pressure heater steam throttling is the same as that before the throttling, at this time, the increased heat absorption of the water wall and the superheater is the same as the insufficient heating of the feed water caused by the unit mass steam flow of different high-pressure heater steam throttling schemes, at this time, it is the maximum heat absorption variation that can be caused:

[0150] ΔQ sh,max = ΔQ fw,h

[0151] In the formula, ΔQ sh,max is the maximum heat absorption variation of the water wall and the superheater, kJ / s;

[0152] Boundary 2: the total heat absorption of the water wall and the superheater of the boiler system is unchanged, that is, ΔQ sh,min = 0;

[0153] In the formula, ΔQ sh,min is the minimum heat absorption variation of the water wall and the superheater, kJ / s;

[0154] In the actual process, due to the insufficient heating of the feed water, the working medium temperature entering the water wall is reduced, the heat absorption of the water wall and the superheater is increased, but at the same time, the working medium temperature at the outlet of the superheater also decreases; therefore, the increased heat absorption of the water wall and the superheater caused by the actual insufficient heating of the feed water is between the maximum and minimum values:

[0155] ΔQ sh,re = k sh,re ΔQ sh,max

[0156] In the formula, ΔQ sh,re is the actual increased heat absorption of the water wall and the superheater, kJ / s; k sh,re is the equivalent coefficient of the heat absorption variation of the water wall and the superheater, 0 < k sh,re < 1.

[0157] The present application adopts two limit boundaries to represent the heat absorption variation of the water wall and the superheater after the high-pressure heater steam throttling, greatly simplifies the heat transfer calculation problem of nonlinearity and large inertia, and greatly reduces the calculation resources while ensuring the acceptable accuracy of the subsequent control parameter calculation.

[0158] Preferably, the specific calculation method of the reheated steam flow before the high-pressure heater steam throttling in step seven is as follows:

[0159] The Darcy-Weisbach formula is used to calculate the reheat steam flow rate at each stage. The specific calculation formula is as follows:

[0160]

[0161] Where: m rs,j and m rs0,j are the jth reheat steam flow rate before the real-time high-pressure heater extraction throttling and the jth reheat steam flow rate under the design condition, kg / s; Δp pipe,j and Δp pipe0,j are the real-time pressure drop of the cold section of the j-th reheat steam pipeline and the pressure drop of the cold section of the j-th reheat steam pipeline under the 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 working condition, kg / m 3 .

[0162] The present invention uses the Darcy-Weisbach formula to calculate the reheat steam flow rates before high-pressure steam extraction throttling. With the help of supercritical unit design parameters and real-time operating data, the real-time reheat steam flow rate of the unit is directly calculated, ensuring the calculation speed and feasibility of the method.

[0163] Preferably, the specific method for selecting the high-pressure heater extraction steam throttling scheme and the specific method for calculating the high-pressure heater extraction steam throttling amount in step eight are as follows:

[0164] Specific control strategy optimization Figure 3 As shown in the figure, based on 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 method for selecting the high-pressure steam extraction throttling scheme is introduced as follows:

[0165] First, select the HPHJ extraction throttling scheme. The selection principle is to throttle as few HPHJs as possible while meeting the temperature control requirements of each reheat steam. Therefore, it is necessary to compare the relationship between the predicted values ​​of each reheat steam change corresponding to the maximum extraction throttling amount of different HPHJ extraction throttling schemes and the real-time values ​​of each reheat steam temperature deviation. Based on this, the most suitable HPHJ extraction throttling scheme can be selected in an orderly and timely manner.

[0166] When the temperature deviation of each reheat steam exceeds the set value ΔT rs,j,bdy When the reheat steam temperature deviations exceeding the set value are compared with the maximum predicted values ​​of the reheat steam temperature changes caused by each extraction throttling scheme, and the results are summarized in the following form: ΔT rs,j,exp,h-1,max <ΔT rs,j,dev ≤ΔT rs,j,exp,h,max , select the high-pressure heater extraction steam throttling scheme with the largest number of throttling high-pressure heaters;

[0167] After selecting the HV HE extraction throttling scheme, it is necessary to calculate the specific extraction throttling amount required under this HV HE extraction throttling scheme:

[0168]

[0169] Where: Δm rs,j,sei is the extraction throttling flow required for the jth reheat steam temperature deviation control, kg / s; k rs,sei is the extraction throttle flow rate adjustment coefficient; ΔT ls,j,dev is the real-time value of the j-th reheat steam temperature deviation, ℃; ΔT ls,j is the j-th reheat steam temperature change corresponding to unit extraction throttling flow, °C;

[0170] Finally, the maximum value of the extraction throttling amount required for each reheat steam temperature deviation control is selected as the final extraction throttling amount corresponding to the high-pressure heater extraction throttling scheme;

[0171] And when the high-pressure heater extraction throttling scheme is used and 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 ΔT rs,j,bdy When the normal steam extraction of all high-pressure heaters is restored.

[0172] 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 during rapid load increase, thereby increasing the load change rate of the supercritical unit, which is of great significance to improving its operational flexibility.

[0173] The above description is merely 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 principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for controlling the reheat steam temperature of a supercritical unit, characterized by: The steps include: Step 1: Data Collection Collect boiler system feed water flow m fw And the feed water flow measurement data of the steam turbine system flowing through each stage of high pressure heater m fwi , where i = 1 to k-1, k-1 is the number of high-pressure heaters; 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 to 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 to z, z is the number of regenerative heaters; Collect the water supply pressure p after the water supply pump fp and economizer inlet feed water pressure p eco,in , working medium temperature at water wall inlet T ww,in and pressure p ww,in ; Step 2: Data preprocessing Clean the parameter data collected in step 1; Step 3: Calculate the enthalpy of the working fluid at each point Using 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 at the inlet and outlet of the m working fluid flows of the boiler. in,a and h out,a , where a = 1 ~ m; the enthalpy value of the inlet water of each level of heat recovery heater on the water supply side h w,in,b and the outlet water enthalpy h w,out,b ; Enthalpy value of extraction steam at each stage 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 maximum change in reheat steam flow rate caused by different high-pressure steam extraction throttling schemes For the high pressure heater, since the extraction throttle valve is installed on the extraction pipe, the steam flow rate of the extraction throttle is in the range of 0~m sei,max , that is, at most all the extraction steam of this stage is returned to the turbine, the maximum is: Where: m sei,max The maximum 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 drain flow rate from the i-1th stage high pressure heater, kg / s; γ i is the heat released by unit mass of hydrophobic water from the previous stage in the i-stage high-pressure heater, kJ / kg; q i is the heat release per unit mass of extraction steam in the i-th stage high-pressure heater, kJ / kg; τ i is the heat absorption per unit mass of feed water in the i-th stage high-pressure heater, kJ / kg; γ i ,q i and τ i It needs to be obtained by using the energy balance calculation method of the regenerative heater; 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. The maximum change in each reheat steam flow rate is the sum of the maximum changes in all extraction steam flows whose extraction pressure is greater than or equal to the reheat steam pressure: Where: Δm rs,j,max is the maximum change in the jth reheat steam flow rate, kg / s; Δm sei,max is the maximum change in the extraction steam flow of the i-th stage high-pressure heater, which is equal to the extraction steam flow of the stage, kg / s; p s,i is the extraction steam pressure of the i-th stage regenerative heater, MPa; p rs,j is the cold section pressure of the j-th reheat steam, MPa; Step 5: Calculate the feedwater heating shortfall corresponding to unit extraction throttling for different HPH extraction throttling schemes. HPH extraction throttling increases the feedwater heating shortfall for the corresponding stage, resulting in increased superheater heat absorption and increased reheat steam flow. However, increased HPH extraction throttling will also increase the extraction flow of higher-pressure HPH heaters. To prevent the increased extraction of higher-extraction-pressure heaters from affecting the throttling effect, all HPH extraction throttling schemes throttle all consecutive HPH heaters, including the highest-stage HPH heater. The insufficient feedwater heating caused by the unit extraction throttling amount of different high-pressure heater extraction throttling schemes is the heat released per unit mass of the high-pressure heater extraction steam in the high-pressure heater of that stage. The specific calculation is as follows: Where: ΔQ fw is the insufficient heating of feedwater caused by the unit extraction throttling rate of the high-pressure heater, kJ / s; Δm sei is the unit throttling rate of the high-pressure heater extraction steam flow, kg / s; Step 6: Calculate the heat absorption change of each reheater after the boiler superheater corresponding to the unit extraction throttling amount for different high-pressure steam extraction throttling schemes Throttling of high-pressure steam extraction causes insufficient feed water heating, and the feed water temperature entering the boiler system drops significantly, which leads to an increase in the heat absorption of the water-cooled walls and superheater heating surfaces before each reheater. The increase in heat absorption of the water-cooled wall and superheater caused by insufficient feedwater heating will cause a decrease in the heat absorption of each reheater after the water-cooled wall and superheater. The reduced heat absorption is distributed according to the proportion of the original heat absorption of each affected reheater. Where: ΔQ rh,j is the reduction in heat absorption of the jth reheated steam in the boiler system reheater due to unit extraction throttling amount under different high-pressure heater extraction throttling schemes, kJ / s; ΔQ sh,re Q is the additional heat absorption of the water-cooled wall and superheater caused by the unit extraction throttling rate of different high-pressure steam extraction throttling schemes, kJ / s; rh,j is the heat absorbed by the jth reheated steam in the boiler system reheater before throttling of the high-pressure heater extraction steam, kJ / s; Step 7: Calculate the predicted reheat steam temperature change corresponding to the unit extraction throttling amount for different high-pressure steam extraction throttling schemes Due to the high-pressure steam extraction throttling, the change in the reheat steam flow rate caused by the unit extraction throttling amount of different high-pressure steam extraction throttling schemes is Δm rs,j At the same time, the change in the amount of heat absorbed by the reheated steam caused by insufficient feedwater heating corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes is ΔQ rh,j Based on the above changes, the change in the outlet enthalpy of the reheated steam corresponding to the unit extraction throttling amount of different high-pressure steam extraction throttling schemes is obtained as follows: Where: Δh rs,j is the change in enthalpy of the jth reheat steam outlet corresponding to the unit extraction throttling amount for different high-pressure heater extraction throttling schemes, kJ / kg; Q′ rh,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′ rs,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 unit extraction steam throttling of different high-pressure steam extraction throttling schemes is: Q′ rh,j =Q rh,j -ΔQ rh,j Assuming that the reheat steam temperature changes little and its specific heat capacity change is negligible, the predicted value of the reheat steam temperature change after unit extraction steam throttling for different high-pressure heater extraction steam throttling schemes is: Where: ΔT rs,j is the predicted value of the jth reheat steam temperature change after unit extraction throttling for different high-pressure heater extraction throttling schemes, ℃; 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, select the appropriate HVHP extraction throttling scheme, and calculate the extraction throttling amount required for each regenerative heater under different HVHP extraction throttling schemes. Calculate different HPH extraction throttling schemes respectively. The maximum extraction throttling amount of different HPH extraction throttling schemes is the minimum extraction amount of all HPHs with extraction throttling. According to steps 1 to 7, the predicted value of each reheat steam temperature change ΔT corresponding to the maximum extraction throttling amount under various HPH extraction throttling schemes is obtained. rs,j,h,max ,j=1~m-1,h=1~k-1; Since the actual load change process is fast, different high-pressure steam extraction throttling schemes cannot achieve the maximum reheat steam temperature change at each time. Therefore, the correction coefficient of the predicted value of the reheat steam temperature of the high-pressure steam extraction throttling is introduced, that is, ΔT rs,j,exp,h,max =k rs,j,expchan,h ΔT rs,j,h,max ,j=1~m-1,h=1~k-1 Where: ΔT rs,j,exp,h,max is the predicted value of the jth reheat steam temperature change corresponding to the maximum extraction throttling amount of the hth high-pressure heater extraction throttling scheme during the corrected actual rapid load change process, °C; k rs,j,expchan,h k is the correction coefficient 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, calculate the real-time deviation between the real-time temperature of each reheat steam and the set temperature. ΔT rs,j,dev =T rs,j,set -T rs,j,rt Where: ΔT rs,j,dev is the real-time deviation of the j-th reheat steam temperature, °C; T rs,j,set is the set value of the jth reheat steam temperature, ℃; T rs,j,rt is the real-time value of the j-th reheat steam temperature, °C; When the real-time deviation of each reheat steam temperature is within the preset range, the method of controlling the reheat steam temperature by adjustable high-pressure steam extraction throttling is not used; that is, ΔT rs,j,dev ≤ΔT rs,j,bdy When using, only flue gas dampers or flue gas recirculation are used to control the reheat steam temperature at each time; When the real-time deviation of the reheat steam temperature is greater than the set value ΔT rs,j,bdy When the reheat steam temperature is controlled by the adjustable high-pressure steam extraction throttling method, 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 real-time deviation of each reheat steam temperature and the predicted value of the maximum reheat steam temperature change caused by each scheme.

2. The method for controlling the reheat steam temperature of a supercritical unit according to claim 1, wherein: In step 2, the parameter data collected in step 1 is cleaned. The specific process is as follows: (1) First, the original measurement data collected in step 1 is subjected to noise reduction and filtering by using the Kalman filter method; (2) Then, the noise-reduced measurement data set is analyzed to screen out 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 changing 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 the changing trend of According to the changing trend of basic parameters and combined with the physical mechanism and changing law during the actual operation of the supercritical unit, it is judged whether the size and changing trend of the measured values ​​of other parameters except the unit load, main steam pressure and feed water flow parameters collected in step 1 are inconsistent with the changes in the basic parameters of the supercritical unit. For the data of multiple measuring points, more accurate measuring points are selected, and the data points that are inconsistent with the changes in the basic data of the supercritical unit are corrected or discarded, and finally the cleaning of the collected measurement data is completed.

3. The method for controlling the reheat steam temperature of a supercritical unit according to claim 1, wherein: The calculation method for each pressure parameter missing in the calculation of the working fluid enthalpy at each point in step 3 is: Calculate the hydrophobic enthalpy h of each heater by thermophysical properties d,i The required but unmeasured hydrophobic pressure P of each heater stage 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 feed water side through thermophysical properties w,in,i and the outlet water enthalpy h w,out,i The required but unmeasured water pressure P at the inlet of each regenerative heater 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 reheat steam temperature of a supercritical unit according to claim 1, wherein: The energy balance calculation method for the regenerative heater in step 4 is as follows: According to the calculation principle of energy balance, the feed water heat absorption τ of the high-pressure heater is obtained i , extraction steam heat release q i and hydrophobic exothermicity γ i , the calculation method is as follows: 1) For drain heaters: 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 converging 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 hydrophobic enthalpy 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 method for controlling reheat steam temperature of a supercritical unit according to claim 1, wherein: The calculation method for the change in heat absorption of the water wall and superheater caused by the unit mass extraction throttling amount for different high-pressure heater extraction throttling schemes 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 HPHE extraction steam is the same as that before throttling. At this point, the increased heat absorption by the water-cooled wall and superheater is the same as the insufficient feedwater heating caused by the unit mass extraction steam throttling amount of different HPHE extraction steam throttling schemes. This is the maximum heat absorption change that may be caused: ΔQ sh,max =ΔQ fw,h Where: ΔQ sh,max is the maximum heat absorption change of the water wall and superheater, kJ / s; 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 wall and superheater, kJ / s; In practice, due to insufficient feedwater heating, the temperature of the fluid entering the water wall decreases, and the heat absorption of the water wall and superheater increases. However, at the same time, the temperature of the fluid at the superheater outlet also decreases. Therefore, the actual increased heat absorption of the water wall and superheater caused by insufficient feedwater heating is between the maximum and minimum values ​​mentioned above: ΔQ sh,re =k sh,re ΔQ sh,max Where: ΔQ sh,re is the actual heat absorption of 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 method for controlling reheat steam temperature of a supercritical unit according to claim 1, wherein: The specific calculation method for each reheat steam flow rate before throttling of the high-pressure heater extraction steam in step 7 is as follows: The Darcy-Weisbach formula is used to calculate the reheat steam flow rate at each stage. The specific calculation formula is as follows: Where: m rs,j and m rs0,j are the jth reheat steam flow rate before the real-time high-pressure heater extraction throttling and the jth reheat steam flow rate under the design condition, kg / s; Δp pipe,j and Δp pipe0,j are the real-time pressure drop of the cold section of the j-th reheat steam pipeline and the pressure drop of the cold section of the j-th reheat steam pipeline under the 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 working condition, kg / m 3 .

7. The method for controlling reheat steam flow of a supercritical unit according to claim 1, wherein: The specific method for selecting the HVHP extraction throttling scheme and the specific method for calculating the HVHP extraction throttling amount in step 8 are as follows: First, select the HPHJ extraction throttling scheme. The selection principle is to throttle as few HPHJs as possible while meeting the temperature control requirements of each reheat steam. Therefore, it is necessary to compare the relationship between the predicted values ​​of each reheat steam change corresponding to the maximum extraction throttling amount of different HPHJ extraction throttling schemes and the real-time values ​​of each reheat steam temperature deviation. Based on this, the most suitable HPHJ extraction throttling scheme can be selected in an orderly and timely manner. When the temperature deviation of each reheat steam exceeds the set value ΔT rs,j,bdy When the reheat steam temperature deviations exceeding the set value are compared with the maximum predicted values ​​of the reheat steam temperature changes caused by each extraction throttling scheme, and the results are summarized in the following form: ΔT rs,j,exp,h-1,max <ΔT rs,j,dev ≤ΔT rs,j,exp,h,max , select the high-pressure heater extraction steam throttling scheme with the largest number of throttling high-pressure heaters; After selecting the HV HE extraction throttling scheme, it is necessary to calculate the specific extraction throttling amount required under this HV HE extraction throttling scheme: Where: Δm rs,j,sei is the extraction throttling flow required for the jth reheat steam temperature deviation control, kg / s; k rs,sei is the extraction throttle flow rate adjustment coefficient; ΔT ls,j,dev is the real-time value of the j-th reheat steam temperature deviation, ℃; ΔT ls,j is the j-th reheat steam temperature change corresponding to unit extraction throttling flow, °C; Finally, the maximum value of the extraction throttling amount required for each reheat steam temperature deviation control is selected as the final extraction throttling amount corresponding to the high-pressure heater extraction throttling scheme; And when the high-pressure heater extraction throttling scheme is used and 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 ΔT rs,j,bdy When the normal steam extraction of all high-pressure heaters is restored.

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