Quantitative calculation and analysis method for influence of steam turbine exhaust steam pressure on exhaust steam volume flow

Abstract

The invention relates to a method for quantitatively calculating and analyzing the influence of the exhaust steam pressure of a steam turbine on the exhaust steam volume flow, which comprises the following steps of: establishing a quantitative control model of the exhaust steam pressure and the volume flow through three core links of variable back pressure test, mathematical model construction and dynamic limit value back calculation to break through the traditional experience control; a discrete data set is constructed through a stepped variable back pressure test, a partial load polynomial function is established, and the quantization problem of the nonlinear relation between exhaust steam pressure and volume flow is solved; a per-unit value-back pressure inversion algorithm is provided, a real-time volume flow per-unit value is calculated based on THA reference flow, exhaust steam pressure corresponding to a 30% safety threshold value is inversely solved through a fitting polynomial, and dynamic adjustment of a limit value along with loads is achieved. Compared with the prior art, the risk of breakage of a tail blade is greatly reduced, the tail blade is prevented from entering a dynamic stress hump area, the dynamic stress peak value threat is eliminated, and the service life of the tail blade is prolonged. Overtemperature caused by the blast effect is prevented, and the regulation and control efficiency is remarkably improved; the service life of equipment is prolonged.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of operation control of thermal power generating units, in particular to a calculation and analysis method for calculating the influence characteristics of the exhaust steam pressure of a low-pressure cylinder of a steam turbine on the exhaust steam volume flow, which is used to guide the operation control of the unit. BACKGROUND

[0002] With large-scale grid connection of new energy, coal-fired units gradually change from basic power supply to regulating power supply, and deep peak shaving and frequent start-stop become the norm. In order to improve the flexibility of heat supply, the "low-pressure cylinder zero (micro) output" modification is widely implemented for heat supply units. Under this background, the low-pressure cylinder is often in a small volume flow operating condition, which raises the following core problems:

[0003] (1) Safety hazard of last-stage blades: when the exhaust steam volume flow is reduced to below 30% of the rated value (THA), the steam flow field is seriously uneven, which leads to: wind effect: large-scale backflow of steam at the blade root, which presses towards the blade tip, causing over-temperature of the last stage; vortex excitation effect: vortex is formed at the root of the last-stage static blade and the top of the moving blade, which greatly increases the dynamic stress. The exhaust steam volume flow of the low-pressure cylinder has a "hump curve" relationship with the dynamic stress of the last-stage blade: the dynamic stress reaches the peak value in the range of 15%-20% THA, and the safety margin decreases sharply below 30% THA, and the risk of fracture increases significantly.

[0004] (2) Blind area of operation control: the exhaust steam volume flow of the low-pressure cylinder cannot be monitored in real time and is difficult to be directly controlled. Although it is affected by the power of the generator (positively correlated), the heat extraction flow (negatively correlated), and the exhaust steam pressure (negatively correlated), the first two are constrained by power grid dispatching and heat users, and only the exhaust steam pressure can be controlled by the circulating water pump. The existing technology lacks a quantitative mapping model of the exhaust steam pressure and the volume flow, and cannot accurately set the safety operating threshold.

[0005] Traditional operation control relies on empirical operation and cannot quantify the safety limit of the exhaust steam pressure under different loads, which leads to the fact that the last-stage blades are in the hump area or wind area (volume flow < 30% THA) for a long time under small volume flow conditions; and lacks a warning mechanism, and blade damage cases occur frequently (such as wind over-temperature, crack propagation, etc.). Therefore, improvement and innovation are imperative. SUMMARY

[0006] In view of the above situation, in order to overcome the defects of the prior art, the purpose of the present application is to provide a quantitative calculation and analysis method for the influence of the exhaust steam pressure of a steam turbine on the exhaust steam volume flow, which establishes a mathematical model of load-pressure-volume flow, accurately calculates the limit value of the exhaust steam pressure when the volume flow is greater than or equal to 30% THA, provides a scientific basis for the control of the circulating water pump, and avoids the low-pressure last-stage blades from entering a high-risk operating condition.

[0007] The technical solution solved by the present application is:

[0008] A quantitative calculation and analysis method of influence of steam turbine exhaust pressure on exhaust volume flow, comprising the following steps:

[0009] Step 1: on-site development of steam turbine variable back pressure characteristic test, collection of operation data after completion of the test;

[0010] Step 2: obtaining of average value of each operation data under each test working condition in step 1, calculation of steam turbine low pressure cylinder exhaust mass flow and low pressure cylinder efficiency under each working condition;

[0011] Step 3: calculation of low pressure cylinder inlet steam enthalpy and low pressure cylinder inlet steam entropy according to water vapor characteristics by using low pressure cylinder inlet steam pressure and low pressure cylinder inlet steam temperature under each working condition, then calculation of low pressure cylinder exhaust ideal enthalpy according to water vapor characteristics by using low pressure cylinder exhaust pressure and low pressure cylinder inlet steam entropy, and calculation of low pressure cylinder exhaust actual enthalpy by using low pressure cylinder efficiency;

[0012] Step 4: calculation of low pressure cylinder exhaust specific volume according to water vapor characteristics by using low pressure cylinder exhaust pressure and low pressure cylinder exhaust enthalpy;

[0013] Step 5: calculation of low pressure cylinder exhaust volume flow by using low pressure cylinder exhaust mass flow and low pressure cylinder exhaust specific volume;

[0014] Step 6: fitting of multiple expression of exhaust pressure influence characteristic on exhaust volume flow under each load by taking different exhaust pressure under each load as independent variable and exhaust volume flow as dependent variable;

[0015] Step 7: calculation of exhaust volume flow under THA working condition and design back pressure by using above steps according to operation data under THA working condition and design back pressure, taking exhaust volume flow under THA working condition and design back pressure as rated value, then calculation of low pressure cylinder exhaust volume flow unit value under the rest working conditions, unit value calculation formula as follows:

[0016]

[0017] In the formula: Gv lpco-s is low pressure cylinder exhaust volume flow unit value under current working condition, %; Gv lpco-1 is actual value of low pressure cylinder exhaust volume flow under current working condition, m 3 / s; Gv lpco-0 is actual value of low pressure cylinder exhaust volume flow under THA working condition and design back pressure, m 3 / s;

[0018] Step 8: When the volume flow rate standard value is greater than 30%, it represents that the last blade can be safely operated for a long time; when the volume flow rate standard value is in the interval of 10%-30%, the last blade is in the dynamic stress hump interval, the stress is large, the blade operation safety margin decreases, and the risk of fracture damage is easy to occur, this interval cannot be operated for a long time, the continuous operation time cannot exceed 120 min, the cumulative operation time cannot exceed 800 min, and an alarm prompt is given to the operator; when the volume flow rate is less than 10%, the last blade will appear blast over-temperature, and cannot be operated for a long time, the continuous operation time cannot exceed 60 min, the cumulative operation time cannot exceed 800 min, and an alarm prompt is given to the operator.

[0019] Step 9: According to the multiple expressions of the influence characteristics of the exhaust pressure of the low-pressure cylinder on the exhaust volume flow rate of the low-pressure cylinder under various loads, the linear interpolation algorithm is used to inversely calculate the low-pressure cylinder exhaust pressure value corresponding to the volume flow rate standard value of 30% under the current actual load, and the low-pressure cylinder exhaust pressure is taken as the operation limit value.

[0020] In the deep peak shaving working condition and the large flow heating, low-pressure cylinder cut-off heating and other working conditions, the low-pressure cylinder is in small volume flow operation, and the steam flow field characteristics of the through-flow stage group, especially the last stage, are extremely uneven. The exhaust steam of the last blade appears large-scale backflow from the blade root along the blade height, and the steam is squeezed to the blade top to produce a "blast" effect. At the same time, vortexes appear at the root of the last stage stator blade and the top of the last stage rotor blade to produce a "vortex excitation" effect, which will cause the dynamic stress of the blade to increase significantly. The safety of the last blade of the low-pressure cylinder of the steam turbine is directly related to the dynamic stress it bears. The greater the dynamic stress, the lower the safety margin of the blade, and the greater the risk of fracture damage. Research shows that when the exhaust volume flow rate of the low-pressure cylinder decreases to 30% THA, the dynamic stress of the last blade of the low-pressure cylinder begins to increase significantly, and reaches a peak value in the interval of 15% THA-20% THA. When the volume flow rate is further reduced to less than 10% THA, the dynamic stress will decrease significantly due to the small steam density. The exhaust volume flow rate of the low-pressure cylinder and the dynamic stress of the last blade of the low-pressure cylinder show a "hump curve" relationship.

[0021] From the perspective of operation control, the low-pressure cylinder end blade should be avoided to be in the dynamic stress "hump area" and "blowing area" operation, that is, the low-pressure cylinder exhaust volume flow should be controlled not less than 30% THA. However, since the low-pressure cylinder exhaust volume flow is difficult to monitor in real time and cannot be directly controlled, it is necessary to study the factors affecting the low-pressure cylinder exhaust volume flow. After analysis, the main operating parameters affecting the low-pressure cylinder exhaust volume flow include generator power, heating extraction flow, turbine low-pressure cylinder exhaust pressure, etc. Among them, the greater the generator power, the greater the low-pressure cylinder exhaust volume flow, the greater the heating extraction flow, the smaller the low-pressure cylinder exhaust volume flow, and the higher the turbine low-pressure cylinder exhaust pressure, the smaller the low-pressure cylinder exhaust volume flow. Among them, the generator power is directly controlled by the power grid scheduling, and the heating extraction flow is determined by the heating user demand, so it is difficult for the power generation enterprise to adjust independently. Therefore, only by adjusting the turbine low-pressure cylinder exhaust pressure can the volume flow be changed. The main means to adjust the turbine low-pressure cylinder exhaust pressure is to control the speed of the circulating water pump or start or stop one circulating water pump, so as to increase or decrease the circulating water pump outlet flow and change the turbine exhaust pressure.

[0022] Since the low-pressure cylinder exhaust pressure and the exhaust volume flow are inversely related, in order to control the low-pressure cylinder exhaust volume flow not less than 30%, it is necessary to reduce the cylinder exhaust pressure, and the key to reducing the turbine low-pressure cylinder exhaust pressure is to obtain the target value of the turbine low-pressure cylinder exhaust pressure. This target value should correspond to 30% volume flow, and in operation, the low-pressure cylinder exhaust pressure should be lower than this target value. This target value can be used as a limit value for operation, so as to avoid the low-pressure cylinder exhaust volume flow being less than 30%.

[0023] The present application establishes a quantitative control model of exhaust pressure and volume flow through three core links of variable back pressure test, mathematical model construction and dynamic limit value back calculation, breaks through the traditional experience control, constructs a discrete data set through a ladder variable back pressure test, establishes a polynomial function under different loads, solves the quantization problem of the nonlinear relationship between exhaust pressure and volume flow, proposes a unit value-back pressure inversion algorithm, calculates the real-time volume flow unit value based on the THA reference flow, and inversely solves the exhaust pressure corresponding to the 30% safety threshold by using the fitting polynomial, so as to realize the dynamic adjustment of the limit value with the load. Compared with the prior art, the method of the present application greatly reduces the risk of end blade fracture, avoids entering the dynamic stress hump area, eliminates the threat of dynamic stress peak value, prevents over-temperature caused by blowing effect, and significantly improves the regulation efficiency; avoids the frequent over-hump area problem of the cut cylinder modified unit, and prolongs the service life of the equipment through the time-limited operation strategy, taking into account the flexibility of the unit and the reliability of the components. BRIEF DESCRIPTION OF DRAWINGS

[0024] Figure 1 The figure is a typical low-pressure end blade dynamic stress and volume flow relationship curve.

[0025] Figure 2The application example of the application is a relationship curve of exhaust pressure and exhaust volume flow under each load.

[0026] Figure 3 The DCS historical curve chart of the low-pressure last blade over-temperature of the typical fault case of the application.

[0027] Figure 4 The physical diagram of the crack of the low-pressure last blade phenomenon of the typical fault case of the application. DETAILED DESCRIPTION

[0028] The specific embodiments of the application are further described in detail below in combination with the drawings and application examples.

[0029] The application is a quantitative calculation and analysis method of the influence of the exhaust pressure of a steam turbine on the exhaust volume flow, comprising the following steps:

[0030] Step 1: On-site development of steam turbine variable back pressure characteristic test, the steam turbine exhaust pressure is less than 4kPa before the test (the test time is generally selected in winter, and the ambient temperature is less than 5℃), and the steam turbine thermal system is isolated according to the following system isolation list before the test; the test method is as follows: the unit load is 30%THA, 40%THA, 50%THA, 75%THA and THA, respectively, firstly, stable operation for 30min under the current back pressure, then gradually open the vacuum breaking valve under each load, so that the steam turbine exhaust pressure is respectively 5kPa, 7kPa, 9kPa and 11kPa, and stable operation for 30min, the working condition is shown in Table 1; during the test, the unit operation parameters should meet the requirements in Table 2; after the test is completed, the operation data is collected, and the parameter list is shown in Annex 2;

[0031] System isolation list

[0032] The following systems and valves should be strictly isolated, for example, if there is leakage in the valve, the manual door should be closed.

[0033] 1 Main steam, reheat steam and extraction system

[0034] 1.1 First and second stage bypass valves

[0035] 1.2 First and second stage bypass temperature and pressure reducing valve front and rear stop valves and each drain valve in the pipe section

[0036] 1.3 First and second stage bypass temperature reducing water pipeline valves

[0037] 1.4 Main steam pipeline drain valves

[0038] 1.5 Reheat steam pipeline drain valves

[0039] 1.6 Each stage extraction pipeline drain valves and extraction check valve drain valves

[0040] 1.7 Steam turbine main drain valves

[0041] 1.8 Other piping connected to adjacent units

[0042] 2 Condensate, auxiliary steam, deaerating system

[0043] 2.1 Condenser outlet header drain valve, condensate recirculation valve, cold water tank, expansion tank

[0044] 2.2 Condensate piping and each heater water, steam measuring each vent air, maintenance drain valve

[0045] 2.3 Low pressure heater condensate bypass valve

[0046] 2.4 Condensate drain to sewer valve

[0047] 2.5 Condenser make-up water regulating valve, manual valve

[0048] 2.6 Deaerator water tank drain valve

[0049] 2.7 Deaerator oxygen vent valve

[0050] 3 Auxiliary steam system

[0051] 3.1 Unit to auxiliary steam valve and connection valve to adjacent units

[0052] 3.2 Auxiliary steam to small units, deaerator regulating valve

[0053] 3.3 Auxiliary steam to boiler steam valve

[0054] 4 Feed water system

[0055] 4.1 Feed water pump recirculation valve

[0056] 4.2 High pressure heater bypass valve

[0057] 4.3 Feed water piping and each high pressure heater water, steam measuring each vent air, drain valve

[0058] 5 Steam seal, steam leakage system

[0059] 5.1 Auxiliary steam, high cylinder exhaust steam to steam seal steam supply valve

[0060] 5.2 Steam seal steam supply piping and drain valve of door rod steam leakage piping

[0061] 5.3 Connection valve to adjacent units

[0062] 6 Heater drain system

[0063] 6.1 Low pressure heater emergency drain to condenser each valve

[0064] 6.2 Each high pressure heater emergency drain (fixed drain or condenser, etc.) each valve

[0065] 6.3 Each heater drain to drain pit each valve

[0066] 7 Demineralized water system

[0067] 7.1 Demineralized water to condenser and deaerator feed and bypass valves

[0068] 8 Boiler section

[0069] 8.1 Each backwash valve, each drain valve of boiler

[0070] 8.2 Each air vent valve of boiler side surface heating surface

[0071] 8.3 Each valve of soot blowing system

[0072] 8.4 Boiler air heater

[0073] 8.5 Boiler fixed and continuous blowdown

[0074] 9 Chemical water section

[0075] 9.1 Each sampling point sampling valve

[0076] 9.2 Chemical dosing valve

[0077] The above valves are general cases, if inconsistent with the site, the site valve is used as the reference.

[0078] Table 1 Variable back pressure characteristic test working condition table

[0079]

[0080]

[0081] Table 2 Maximum deviation and fluctuation of operating condition 1)

[0082] Parameters Maximum permissible deviation of test average from specified value Main steam pressure ±5% 2) ]] Main steam temperature ±15°C 2) ]]> Dryness ±0.005 Bleed steam pressure (regulated) ±5% 2) <!-- 5 --> Bleed steam pressure (feedwater heating) See 3) ]]> Exhaust steam pressure ± 2.5% if condenser is not guaranteed Bleed steam flow ±10％ Reheated steam temperature ±15℃ Isentropic enthalpy drop ±7％ Output power or flow of live steam ± 5% after correction for specified conditions Cooling water flow ± 15% if condenser is guaranteed Cooling water inlet temperature ± 5°C if condenser is guaranteed Final feedwater temperature ±10℃ Speed ± 2% 4 )

[0083] Table 2 Example of original parameter list calculated from historical data

[0084]

[0085]

[0086]

[0087]

[0088]

[0089] Step 2: Calculate the average value of each operating data obtained in Step 1 under each test condition, and calculate the low-pressure cylinder exhaust mass flow rate and low-pressure cylinder efficiency under each operating condition according to the turbine thermal performance calculation method provided in GB / T8117.1-2008 Steam Turbine Thermal Performance Acceptance Test Procedure Part 1: Method A High Accuracy Test of Large Condensing Steam Turbines.

[0090] Step 3: Using the low-pressure cylinder inlet steam pressure and temperature under various operating conditions, calculate the low-pressure cylinder inlet steam enthalpy and entropy based on the characteristics of water vapor; then, using the low-pressure cylinder exhaust steam pressure and inlet steam entropy, calculate the ideal exhaust steam enthalpy based on the characteristics of water vapor; finally, calculate the actual exhaust steam enthalpy using the low-pressure cylinder efficiency; the calculation formulas are as follows:

[0091] h lpci =f(p lpci ,T lpci )

[0092] s lpci =f(p lpci ,T lpci )

[0093] h lpcos =f(p lpco ,s lpci )

[0094] h lpco =h lpci -(h lpci -h lpcos )×η lpco

[0095] In the formula: p lpci The low-pressure cylinder inlet steam pressure is measured in MPa; T lcpi The low-pressure cylinder inlet steam temperature is ℃; p lpco The exhaust pressure of the low-pressure cylinder is expressed in MPa; s lpci The low-pressure cylinder inlet steam entropy is expressed in kJ / kg·K; h lpcos The ideal enthalpy of exhaust steam from the low-pressure cylinder is given in kJ / kg; h. lpco The low-pressure cylinder exhaust enthalpy is 1 kJ / kg; η lpco For low-pressure cylinder efficiency, %.

[0096] Step 4: Using the low-pressure cylinder exhaust pressure and enthalpy, and based on the characteristics of water vapor, calculate the specific volume of the low-pressure cylinder exhaust. The calculation formula is as follows:

[0097] v lpco =f(p lpco ,h lpco )

[0098] In the formula: vlpco m is the low-pressure cylinder exhaust specific volume, m / kg 3 p is the low-pressure cylinder exhaust pressure, MPa lpco h is the low-pressure cylinder exhaust enthalpy, kJ / kg lpco m is the low-pressure cylinder exhaust specific volume, m / kg

[0099] Step 5: The low-pressure cylinder exhaust volume flow rate is calculated using the low-pressure cylinder exhaust mass flow rate and the low-pressure cylinder exhaust specific volume, and the calculation formula is as follows:

[0100]

[0101] In the formula, Gv is the low-pressure cylinder exhaust volume flow rate, m lcpo / s; m is the low-pressure cylinder exhaust specific volume, m / kg 3 / s;

[0102] Step 6: The multinomial expression of the influence characteristics of the exhaust pressure on the exhaust volume flow rate under each load is fitted by taking different exhaust pressures under each load as the independent variable and taking the exhaust volume flow rate as the dependent variable;

[0103]

[0104] The expression is expressed in the following matrix form:

[0105]

[0106] Step 7: The exhaust volume flow rate under the THA condition and the design back pressure is calculated using the above steps according to the operating data under the THA condition and the design back pressure, and the exhaust volume flow rate under the THA condition and the design back pressure is taken as the rated value (the design back pressure of the steam turbine is generally about 5 kPa, if it is not 5 kPa, then the volume flow rate under the THA condition and the design back pressure should be calculated by linear interpolation), and then the low-pressure cylinder exhaust volume flow rate unit value under the remaining conditions is calculated, and the unit value calculation formula is as follows:

[0107]

[0108] In the formula, Gv is the low-pressure cylinder exhaust volume flow rate, m lpco-s / s; m is the low-pressure cylinder exhaust specific volume, m / kg lpco-1 Gv is the actual value of the low-pressure cylinder exhaust volume flow rate under the current condition, m 3 / s; m is the low-pressure cylinder exhaust specific volume, m / kg lpco-0 Gv is the actual value of the low-pressure cylinder exhaust volume flow rate under the THA condition and the design back pressure, m 3 / s;

[0109] Step 8: When the volume flow rate unit value is greater than 30%, it represents that the last blade can be safely operated for a long time; when the volume flow rate unit value is in the interval of 10%-30%, the last blade is in the dynamic stress hump interval (such as Figure 1When the volume flow rate is lower than 10%, the last blade will appear blast over-temperature, and cannot be operated for a long time, the continuous operation time should not be more than 60 min, the cumulative operation time should not be more than 800 min, and an alarm should be given to the operator.

[0110] Step 9: According to the multiple expression of the influence characteristics of the exhaust pressure of the low-pressure cylinder on the exhaust volume flow rate under each load, the linear interpolation algorithm is used to inversely calculate the low-pressure cylinder exhaust pressure value corresponding to the volume flow rate standard value of 30% under the current actual load, and the low-pressure cylinder exhaust pressure is used as the operation limit value, and the low-pressure cylinder exhaust pressure of the unit during operation should not exceed the limit value, otherwise the load should be increased, the circulating water pump should be started, and the like, and the specific algorithm of the limit value is as follows:

[0111] ①According to the current actual load, the last load point and the next load point are found among THA, 75%THA, 50%THA, 40%THA and 30%THA, and then the low-pressure cylinder exhaust pressure corresponding to the volume flow rate standard value of 30% is inversely calculated according to the polynomial of step 6.

[0112] ②The linear interpolation algorithm is used to calculate the low-pressure cylinder exhaust pressure corresponding to 30% volume flow rate under the current actual load.

[0113] If the current actual load is greater than THA load or less than 30%THA, the extrapolation interpolation algorithm is used to calculate the low-pressure cylinder exhaust pressure corresponding to 30% volume flow rate under the current actual load.

[0114] The application has achieved good technical effects through actual application, and the application is as follows:

[0115] (1)Taking a supercritical 600MW unit as an example (the design back pressure is 5kPa), the variable back pressure characteristics test of the steam turbine is carried out on site, the unit load is 30%THA, 40%THA, 50%THA, 75%THA and THA respectively, firstly, the unit is stably operated for 30min under the current back pressure, then the vacuum breaker valve is gradually opened under each load, so that the steam turbine exhaust pressure is stably operated for 30min at 5kPa, 7kPa, 9kPa and 11kPa respectively. After the test, the test data is collected.

[0116] (2) Calculate the average value of each operating parameter obtained in step 1 under each test condition, and calculate the turbine thermal performance according to the turbine thermal performance calculation method provided in GB / T8117.1-2008 "Test Procedure for Acceptance of Steam Turbine Thermal Performance Part 1: Method A High Accuracy Test of Large Condensing Steam Turbines". Then, according to steps 2 to 5, calculate the per-unit values ​​of the turbine low-pressure cylinder exhaust mass flow rate, low-pressure cylinder efficiency, and low-pressure cylinder exhaust volumetric flow rate under each operating condition, as shown in Table 3; the curves showing the relationship between exhaust pressure and exhaust volumetric flow rate under each load are shown in Table 3. Figure 2 As shown.

[0117] Table 3 Calculation results under various working conditions

[0118]

[0119]

[0120] (3) According to Table 3, the volumetric flow rate under THA condition and design back pressure is 1043.11 m3 / s, and the corresponding 30% volumetric flow rate is 312.933 m3 / s. This volumetric flow rate will be used as the limiting volumetric flow rate during unit operation.

[0121] (4) Using the exhaust pressure under each load as the independent variable and the exhaust volume flow rate as the dependent variable, the coefficient matrix of the influence of exhaust pressure on exhaust volume flow rate under each load is shown below. From top to bottom, they are the polynomial coefficients of THA, 75% THA, 50% THA, 40% THA and 30% THA.

[0122]

[0123] (5) According to step 9, taking a 600MW capacity unit as an example, the current load of the unit is 210MW, so its load rate is 35%THA; the following calculates the exhaust pressure corresponding to 30% volumetric flow per unit value: First, find the previous load point and the next load point of 35%THA, that is, 40%THA and 30%THA load; then use the polynomial coefficients of the 40%THA and 30%THA conditions in (9) to calculate the turbine exhaust pressure corresponding to 30% volumetric flow per unit value; then calculate the difference to obtain the turbine exhaust pressure corresponding to 30% volumetric flow per unit value under the 35%THA condition. The calculation is as follows:

[0124] ① Calculation of exhaust pressure for 40% THA condition with 30% volumetric flow rate

[0125]

[0126] Based on the above formula, the turbine exhaust pressure corresponding to 30% volumetric flow rate under 40% THA conditions is calculated to be 8.15 kPa.

[0127] ② 30% THA condition corresponding to 30% volumetric flow of exhaust pressure calculation

[0128]

[0129] According to the above formula, the inverse calculation of 30% THA condition corresponding to 30% volumetric flow of steam turbine exhaust pressure is 6.07kPa.

[0130] ③ 21 0MW (35% THA) condition corresponding to 30% volumetric flow of exhaust pressure calculation

[0131]

[0132] According to the above formula, the calculation of 35% THA condition corresponding to 30% volumetric flow of steam turbine exhaust pressure is 7.11kPa. This value can be used as the limit of back pressure under 35% THA condition, and the back pressure should be strictly controlled not to exceed 7.11kPa during the operation of the unit.

[0133] (6) Similarly, the turbine exhaust pressure limit value corresponding to 30% volumetric flow under each load of the unit can be obtained respectively, as shown in the following table. This table can be used as the basis for operation control guidance.

[0134] Table 4 Turbine exhaust pressure limit value under each load

[0135]

[0136] Other typical fault cases are shown in the following table:

[0137]

[0138]

Claims

1. A method for quantitative calculation and analysis of the influence of the exhaust pressure of a steam turbine on the exhaust volume flow, characterized in that Comprising the following steps: Step 1: on-site steam turbine variable back pressure characteristic test is carried out, and operation data are collected after the test is completed; Step 2: average values of each operation data obtained in step 1 under each test working condition are obtained, and the steam turbine low-pressure cylinder exhaust mass flow and the low-pressure cylinder efficiency under each working condition are calculated; Step 3: the low-pressure cylinder inlet steam pressure and the low-pressure cylinder inlet steam temperature under each working condition are utilized, and the low-pressure cylinder inlet steam enthalpy and the low-pressure cylinder inlet steam entropy are calculated according to the water vapor characteristics; then, the low-pressure cylinder exhaust pressure and the low-pressure cylinder inlet steam entropy are utilized, and the low-pressure cylinder exhaust ideal enthalpy is calculated according to the water vapor characteristics; and the low-pressure cylinder exhaust actual enthalpy is calculated by utilizing the low-pressure cylinder efficiency; The calculation formula is as follows: h lpci = f(p lpci ,T lpci ) s lpci = f(p lpci , T lpci ) h lpcos = f(p lpco ,s lpci ) h lpco = h lpci - (h lpci - h lpcos ) x η lpco wherein: p lpci P is the low-pressure cylinder inlet pressure, MPa; T lcpi is the low-pressure cylinder inlet steam temperature, °C; p lpco is the low-pressure cylinder exhaust pressure, MPa; s lpci is the low-pressure cylinder inlet steam entropy, kJ / kg·K; h lpcos is the low-pressure cylinder exhaust ideal enthalpy, kJ / kg; h lpco is the low-pressure cylinder exhaust enthalpy, kJ / kg; η lpco is the low-pressure cylinder efficiency, %; Step 4: the low-pressure cylinder exhaust pressure and the low-pressure cylinder exhaust enthalpy are utilized, and the low-pressure cylinder exhaust specific volume is calculated according to the water vapor characteristics; the calculation formula is as follows: v lpco = f(p lpco , h lpco ) In the formula: v lpco For the exhaust volume of the low-pressure cylinder, m 3 / kg; p lpco The exhaust pressure of the low-pressure cylinder is MPa; h lpco The enthalpy of low-pressure cylinder exhaust steam is kJ / kg; Step 5: the low-pressure cylinder exhaust mass flow and the low-pressure cylinder exhaust specific volume are utilized, and the low-pressure cylinder exhaust volume flow is calculated; the calculation formula is as follows: where: Gv lcpo is the low-pressure cylinder exhaust volume flow, m3 / s 3 / s; Step 6: different exhaust pressures under each load are taken as independent variables, and the exhaust volume flow is taken as dependent variable, and a polynomial expression of the influence characteristic of the exhaust pressure on the exhaust volume flow under each load is fitted; The expression is expressed in the following matrix form: Step 7: according to the THA working condition and the design back pressure operation data, the above steps are utilized to calculate the exhaust volume flow under the THA working condition and the design back pressure, and the exhaust volume flow under the THA working condition and the design back pressure is taken as a rated value, and then the low-pressure cylinder exhaust volume flow unit value under the remaining working conditions is calculated; the unit value calculation formula is as follows: where: Gv lpco-s is the low-pressure cylinder exhaust volume flow rate standard value, %; Gv lpco-1 is the low-pressure cylinder exhaust volume flow rate actual value, m 3 / s; Gv lpco-0 is the low-pressure cylinder exhaust volume flow rate actual value under THA conditions and design back pressure, m 3 / s; Step 8: when the volume flow unit value is greater than 30%, the last blade can be safely operated for a long time; when the volume flow unit value is in the interval of 10%-30%, the last blade is in a dynamic stress hump interval, the stress is large, the blade operation safety margin is reduced, and the risk of fracture damage is easy to appear, the interval cannot be operated for a long time, the continuous operation time cannot exceed 120 min, the cumulative operation time cannot exceed 800 min, and an alarm prompt is given to the operator; when the volume flow is less than 10%, the last blade will appear blast over-temperature, and cannot be operated for a long time, the continuous operation time cannot exceed 60 min, the cumulative operation time cannot exceed 800 min, and an alarm prompt is given to the operator.

2. The method of quantitative calculation analysis of the influence of the steam turbine exhaust pressure on the exhaust steam volume flow according to claim 1, characterized in that The application also comprises step 9: according to the polynomial expression of the influence characteristic of the exhaust pressure on the low-pressure cylinder exhaust volume flow under each load, a linear interpolation algorithm is utilized to inversely calculate the low-pressure cylinder exhaust pressure value corresponding to the volume flow unit value of 30% under the current actual load, and the low-pressure cylinder exhaust pressure is taken as an operation limiting value; the specific algorithm of the limiting value is as follows: ① according to the current actual load, an upper load point and a lower load point are found in THA, 75%THA, 50%THA, 40%THA and 30%THA, and then the low-pressure cylinder exhaust pressure corresponding to the volume flow unit value of 30% is inversely calculated according to the polynomial of step 6. ②Using linear interpolation algorithm, the low-pressure cylinder exhaust pressure corresponding to 30% volume flow under the current actual load is calculated.

Images