A Cold End Optimization Algorithm for Steam Turbines

Abstract

The present invention provides a cold end optimization algorithm for a steam turbine, and the method comprises the following steps: S1, determining a power ratio K1 value; S2, determining a functional relationship between a circulating water temperature rise and a to-be-fitted formula K2; S3, determining a steam turbine saturated back pressure Pa and / or determining a current exhaust temperature T1; S4, assuming that a circulating pump current slightly increases △A, determining a circulating water temperature rise variable △T or an exhaust temperature T3 after a slight increase in the circulating pump; S5, determining a steam turbine back pressure Pb after a slight increase in the circulating pump current; S6, obtaining empirical consumption difference analysis data K3, and calculating a coal saving amount M1 according to a reduction in the steam turbine back pressure; S7, judging whether to increase the output of the circulating pump according to an energy consumption dispatching mode or an economic dispatching mode, and making a circulating pump current matrix table to guide operation. The present invention only needs to collect the current exhaust temperature T1 and the current low-pressure cylinder inlet steam pressure P2 in real time, or replace the exhaust temperature calculation with the circulating water cooling water temperature and the condenser end difference, thereby avoiding complex thermal tests and thermal calculations, and the calculated data is true and reliable.

Description

Technical Field

[0001] The invention relates to the field of steam turbine generators, and in particular to a cold end optimization algorithm for a steam turbine. Background Art

[0002] The economic dispatch of circulating pumps is a conventional cold-end optimization performance test for steam turbine generator sets. Generally, the relationship between the increase in circulating pump power consumption and the increase in unit output is found through the slight increase in power method, and the circulating pump dispatch curve based on the changes in circulating water temperature and power generation load is summarized. The test process has many working conditions and variables, and needs to be completed by professional institutions.

[0003] The prior art with publication number CN113864013A discloses a cold end optimization method for a wet-cooled thermal power unit under all-operating conditions. When the unit electrical load P, heating amount x1, x2, ..., xn, and circulating cooling water inlet temperature tw1 are determined, the circulating water flow rate Dw is changed by the operating mode of the circulating water pump to obtain the maximum value of the objective function F(P, x1, x2, ..., xn, Dw, tw1)max. At this time, the corresponding condenser pressure Ps, that is, the condenser is at an optimal vacuum, and the corresponding circulating water pump operating mode is the optimal circulating water pump operating mode. However, there are many variables involved in determining the optimal operating mode of the circulating pump, and the thermal calculation process is complicated, requiring many experiments to fit mathematical relationships, resulting in reduced accuracy. Summary of the invention

[0004] In view of this, the present invention aims to propose a cold end optimization algorithm for a steam turbine to solve the problems in the prior art that the test process has many working conditions and variables, the thermal calculation process is complex and needs to be completed by professional institutions.

[0005] To achieve the above object, the technical solution of the present invention is achieved as follows:

[0006] A cold end optimization algorithm for a steam turbine comprises the following steps:

[0007] S1: Determine the power ratio K1 value;

[0008] S2: Determine the functional relationship between the circulating water temperature rise and the K2 equation to be fitted;

[0009] S3: Determine the turbine saturated back pressure Pa and / or determine the current exhaust steam temperature T1;

[0010] S4: Assuming that the current of the circulating pump increases slightly by △A, determine the circulating water temperature rise variable △T or the exhaust steam temperature T3 after the circulating pump increases slightly;

[0011] S5: Determine the turbine back pressure Pb after assuming a slight increase in the circulating pump current;

[0012] S6: Obtain the empirical consumption difference analysis data K3 and determine the coal saving amount M1;

[0013] S7: Determine whether to increase the output of the circulation pump according to the energy consumption scheduling mode or the economic scheduling mode.

[0014] Furthermore, the energy consumption scheduling mode includes the following steps:

[0015] S7a1: Obtain the actual average power generation coal consumption K4, and determine the coal consumption M2 corresponding to the excess power consumption of the circulating pump;

[0016] S7a2: Compare the sizes of M1 and M2 to decide whether to increase the output of the circulation pump.

[0017] Furthermore, the economic dispatch mode includes the following steps:

[0018] S7b1: Obtain economic dispatch conversion coefficient K5;

[0019] S7b2: Determine the converted coal consumption M3;

[0020] S7b3: Compare the sizes of M2 and M3 to decide whether to increase the output of the circulation pump.

[0021] Further, the method comprises the following steps: S3: determining the saturated back pressure Pa of the steam turbine; S4: assuming that the current of the circulating pump increases slightly by △A, determining the circulating water temperature rise variable △T.

[0022] Further, the method includes the following steps: S3: determining the current exhaust steam temperature T1 and the turbine saturated back pressure Pa; S4: assuming that the circulating pump current slightly increases △A, determining the exhaust steam temperature T3 after the circulating pump is slightly increased.

[0023] Furthermore, the functional relationship between the circulating water temperature rise and K2 in step S2 is calculated by the following formula:

[0024] T = (G / i) * K2;

[0025] In the formula, T is the circulating water temperature rise in °C, G is the electric power in MW, i is the circulating pump current in A, and K2 is the formula to be fitted.

[0026] Furthermore, the specific functional formula of K2 is K2=a+b*i 0.67 , where a, b are the coefficients to be fitted, and i is the circulating pump current A.

[0027] Furthermore, in step S3, the current exhaust steam temperature T1 and the turbine saturated back pressure Pb are calculated by the following formula:

[0028] T1=T0+K1*P1 / i1*K2+δ;

[0029] Among them: T1 is the current exhaust temperature, T0 is the circulating water cooling temperature ℃, K1 is the equation to be fitted, P1 is the low-pressure cylinder inlet steam pressure, i1 is the current circulating pump current A, and δ is the condenser end difference ℃.

[0030] Furthermore, the exhaust steam temperature T3 is calculated by the following formula:

[0031] T3=T0+K1*P1 / (i1+△A)*K2″+δ;

[0032] Where: T3 is the exhaust temperature of the circulating pump after a slight increase in °C, K is the power ratio, P1 is the low-pressure cylinder inlet steam pressure, i1 is the current circulating pump current A, △A is the slight increase in the circulating pump current A, K2” is the value of the circulating pump current after a slight increase in °C, δ is the condenser end difference in °C;

[0033] Furthermore, the energy consumption dispatch mode and the economic dispatch mode are calculated online in the DCS and SIS systems, or calculated offline according to different variables, to make an optimal circulating pump current matrix table to guide the operation.

[0034] Compared with the prior art, the cold end optimization algorithm of the steam turbine described in the present invention has the following advantages:

[0035] 1. The core of this method is to invent an algorithm for circulating water temperature rise. Through a simple black box test, the functional relationship between the electrical load, the circulating pump current and the circulating water temperature rise can be directly obtained, and the temperature rise coefficient K2=a+b*i can be summarized. 0.67 This characteristic function greatly simplifies the cold end optimization calculation.

[0036] 2. After consulting relevant literature, it is considered that the change in the condenser end difference can be ignored when calculating the slightly increased circulating pump output. When the method using the exhaust temperature as the boundary condition is used for calculation, factors affecting the end difference, such as changes in ambient temperature, changes in vacuum tightness, and changes in the condenser cleanliness coefficient, are reflected in the initial exhaust temperature. Therefore, it is only necessary to calculate the change in temperature rise to reflect the change in exhaust temperature. This method has only two variables, exhaust temperature and low-pressure cylinder inlet steam pressure, and is suitable for online automatic calculation. When using the circulating water cooling water temperature as the boundary condition for calculation, it is necessary to obtain the real-time value of the condenser end difference. This method is suitable for both online and offline calculations.

[0037] 3. This method uses the low-pressure cylinder inlet steam pressure to characterize the condenser heat load as the boundary condition, which can be applied to the high- and medium-pressure cylinder steam extraction heating conditions, and can adapt to the impact of changes in the unit cycle efficiency on the condenser heat load.

[0038] 4. This method uses the total current of the circulating pump to represent the circulating water flow rate as the regulating variable, which can be widely applied to complex combined operation modes such as industrial frequency pumps, variable frequency pumps, high and low speed pumps, etc.

[0039] 5. This method adds coal price, coal consumption for power generation and conversion coefficient of electricity price to realize two-way selection between energy consumption dispatch mode and economic dispatch mode. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Figure 1 A circulation pump matrix table in the energy consumption scheduling mode of Example 1 of the present invention;

[0041] Figure 2 This is a circulation pump matrix table under the economic dispatch mode of Example 2 of the present invention. DETAILED DESCRIPTION

[0042] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, specific embodiments of the present invention are described in detail below with reference to the accompanying drawings.

[0043] 1. The significance of economic dispatch of circulating pumps

[0044] The exhaust steam of the steam turbine generator set needs circulating water cooling and condensation. The back pressure of the steam turbine affects the heat consumption of the steam turbine and the coal consumption of the unit. Generally, the lower the back pressure, the lower the coal consumption of the unit. However, reducing the back pressure requires increasing the amount of circulating cooling water, and increasing the amount of cooling water requires increasing the power consumption of the circulating pump. The focus of the economic dispatch of the circulating pump is to compare the extra energy consumed by the circulating pump with the energy saved by the unit due to the reduction in back pressure. Dispatching by energy consumption is to minimize the coal consumption of the unit by reasonably adjusting the output of the circulating pump; dispatching by economy is to consider the price factors of coal and electricity, and reasonably adjust the output of the circulating pump to maximize the economic benefits of the unit after deducting the loss of electricity consumption of the circulating pump from the coal saving benefits.

[0045] 2. Relationship between cold end parameters of steam turbine

[0046] Circulating water inlet temperature + circulating water temperature rise = circulating water return temperature + condenser end difference = saturation temperature corresponding to back pressure = exhaust steam temperature

[0047] 2.1. Main factors affecting cold end parameters

[0048] The inlet temperature of circulating water is mainly affected by the ambient temperature and the performance of the water tower; the temperature rise of circulating water is mainly affected by the heat load of the condenser and the circulating water flow rate; the end difference of the condenser is mainly affected by the heat transfer coefficient of the condenser, and the heat transfer coefficient is affected by the dirt and scaling of the condenser heat exchange tube wall and the tightness of the vacuum system; the direct factor affecting the heat consumption of the turbine by the cold end parameters is the turbine back pressure, and other factors indirectly affect the heat consumption of the turbine by affecting the turbine back pressure.

[0049] The influence of turbine back pressure on heat consumption is approximately linear over a large range, and the data of the corresponding unit consumption difference analysis can be referred to. There is usually a saturated steam correspondence between turbine back pressure and turbine exhaust temperature. The higher the saturation temperature, the greater the increase in saturation pressure at the same temperature rise (see Table 1 below); secondly, there are many factors affecting the condenser end difference, and the uncertainty is large; the relationship between the circulating pump power and the circulating water flow rate requires experimental fitting of the quantitative relationship because the system resistance changes with the flow rate. The above three aspects lead to many cold end optimization variables, complex relationships, and few units are actually implemented.

[0050] Table 1: Correspondence between saturation temperature and saturation pressure

[0051] Saturation temperature / ℃ 20 25 30 35 40 45 50 Saturation pressure / Kpa 2.31 3.14 4.22 5.60 7.36 9.57 12.33

[0052] 3. Characteristics of black box

[0053] The traditional cold-end method uses the circulating water temperature and power generation load as the boundary, and finds the optimal working condition by assuming that the circulating pump output is changed. There are many variables involved, and the thermal calculation process is complicated. It requires a lot of experiments to fit the mathematical relationship, resulting in reduced accuracy. The black box method uses the exhaust temperature to replace the circulating water temperature, and the low-pressure cylinder inlet steam pressure to replace the generator load. Through the black box test, the quantitative relationship between the turbine power generation load, the circulating pump current and the circulating water temperature rise is found. The optimal working condition is found by assuming a slight increase in the circulating pump output, omitting the heat transfer calculation process, and directly obtaining the turbine exhaust temperature change through the circulating water temperature rise change. The detailed process is described in the embodiment.

[0054] The present invention provides a cold end optimization algorithm for a steam turbine, comprising the following steps:

[0055] S1: Determine the power ratio K1 value;

[0056] S2: Determine the functional relationship between the circulating water temperature rise and the K2 equation to be fitted;

[0057] S3: Determine the turbine saturated back pressure Pa and / or determine the current exhaust steam temperature T1;

[0058] S4: Assuming that the current of the circulating pump increases slightly by △A, determine the circulating water temperature rise variable △T or the exhaust steam temperature T3 after the circulating pump increases slightly;

[0059] S5: Determine the turbine back pressure Pb after assuming a slight increase in the circulating pump current;

[0060] S6: Obtain the empirical consumption difference analysis data K3 and determine the coal saving amount M1;

[0061] S7: Determine whether to increase the output of the circulation pump according to the energy consumption scheduling mode or the economic scheduling mode.

[0062] S7a1: Obtain the actual average power generation coal consumption K4, and determine the coal consumption M2 corresponding to the excess power consumption of the circulating pump:

[0063] S7a2: Compare the sizes of M1 and M2 to decide whether to increase the output of the circulation pump.

[0064] S7b1: Obtain economic dispatch conversion coefficient K5;

[0065] S7b2: Determine the converted coal consumption M3;

[0066] S7b3: Compare the sizes of M2 and M3 to decide whether to increase the output of the circulation pump.

[0067] Specifically, the cold end optimization algorithm with exhaust steam temperature and low pressure cylinder inlet steam pressure as the boundary includes the following steps:

[0068] S1: Obtain the relationship between the steam turbine low-pressure cylinder inlet pressure P1, electric power G and power ratio K1. The specific formula is: K1 = G / P1;

[0069] Where: G is the electrical power in MW; P1 is the low-pressure cylinder inlet steam pressure in MPa, and the data source is selected based on the pure condensing 75% load design condition. The low-pressure cylinder inlet steam pressure has a good linear relationship with the turbine electrical power. The low-pressure cylinder inlet steam pressure can more accurately represent the low-pressure cylinder exhaust heat load. Selecting the low-pressure cylinder inlet steam pressure to represent the electrical load can avoid the influence of the high- and medium-pressure cylinder steam extraction of the turbine on the condenser heat load and the unit back pressure consumption difference analysis. In actual application, attention should be paid to the deviation of the measuring point itself, and the pressure measuring point needs to be calibrated and corrected to absolute pressure.

[0070] S2: Obtain the relationship between the circulating water temperature rise T, the circulating pump current i, the electric power G, and the equation to be fitted K2, the specific formula of which is: T = (G / i) * K2;

[0071] Among them: T is the temperature rise of circulating water in °C, G is the electric power in MW, i is the circulating pump current in A, and K2 is the equation to be fitted, because the electric power represents the heat load of the condenser, the circulating pump current represents the circulating pump power, the circulating pump power is affected by the circulating water flow rate and the circulating pump head, and the system resistance increases with the increase of flow rate. Under stable working conditions, the function of K2 changing with the circulating pump current can be fitted according to the test.

[0072] Specifically, the circulating water temperature rise T∝(condenser heat load Q / circulating pump water flow W);

[0073] Because: condenser heat load Q∝electric power G; circulating water flow W=circulating pump power P / circulating pump head H,

[0074] Therefore: circulating water temperature rise T∝ electric power G / (circulating pump power P / circulating pump head H);

[0075] Because: circulating pump power P∝ circulating pump current i; circulating pump head H=circulating water level differential pressure+extended resistance+dynamic pressure head,

[0076] Therefore: circulating water temperature rise T∝ electric power G / circulating pump current I*(circulating water circulating water level high differential pressure + extended stroke resistance + dynamic pressure head);

[0077] Therefore, the relevant quantity that affects the K2 function is: (liquid level differential pressure + extended resistance + dynamic pressure head)

[0078] The liquid level difference is a constant determined by the system layout. The extended resistance and dynamic pressure head are proportional to the square of the flow rate, and the current is proportional to the cube of the flow rate. Therefore, the structure of the function can be formulated as: K2 = a + b*i 0.67 ;

[0079] In the formula, a and b are coefficients to be fitted, and 0.67 is a divisor of 2 / 3, which is the flow rate obtained by first cube the circulating pump current and then square it to get the extended resistance.

[0080] After the values ​​of a and b are determined through experiments, the circulating water temperature rise value can be calculated through circulating water temperature rise = (electric power / circulating pump current) * K2.

[0081] Preferably, the K2 function fitting is an approximate fitting assuming that the efficiency of the circulation pump remains unchanged.

[0082] The power factor of the variable frequency pump is 0.95, and the power factor of the industrial frequency pump is 0.75. The current on the power supply side of the inverter is multiplied by 1.27 to be equivalent to the current of the industrial frequency pump. The sum of the current values ​​of multiple pumps is used as the adjustment object of the circulating pump.

[0083] In addition, the fitting function relationship between the circulating pump current and the circulating water flow rate can also be tested and measured.

[0084] S3: Obtain the current exhaust temperature T1 of the steam turbine and calculate the saturated back pressure Pa of the steam turbine. The specific formula is: Pa=power(10,7.07406-1657.46 / (T1+227.02));

[0085] Where: T1 is the exhaust temperature °C, Pa is the turbine saturated back pressure KPa;

[0086] The exhaust steam of the low-pressure cylinder of the steam turbine generally operates in the wet steam area. (According to the Antony equation, lgP0 = 7.07406-(1657.46 / (T0+227.02)) (10℃ < T0 < 168℃)

[0087] Among them, P0 is the saturated vapor pressure of water at temperature T0 kPa; T0 is the temperature of water ℃.

[0088] The exhaust steam pressure is calculated using the exhaust steam temperature, and the exhaust steam temperature is used as a real-time variable, covering the influencing factors such as the circulating water inlet temperature, the condenser end difference, the low-pressure cylinder heat load, and the circulating water flow rate. Pa does not use real-time data because the temperature measurement point is more stable than the pressure measurement point, and it can also ensure that the comparison benchmark of the influence of the slight increase in current on the change in the exhaust steam temperature is consistent. Only when the low-pressure cylinder steam flow is extremely low under the winter heating steam extraction condition, will the exhaust steam be overheated. At this time, because the low-pressure cylinder steam inlet pressure is very low, calculations show that when the exhaust steam temperature is 40 degrees, the optimal current of the circulating pump is still at the lower limit of the allowable current.

[0089] S4: Obtain the current circulating pump current i1 and the current low-pressure cylinder steam inlet pressure P2. Assuming that the circulating pump current increases slightly by △A, substitute the following formula according to K1 in step S1 and K2 in step S2 to calculate the circulating water temperature rise variable △T. The specific formula is:

[0090] △T=K1*P2 / i1*K2-K1*P2 / (i1+△A))*K2”;

[0091] Among them: △T is the circulating water temperature rise variable ℃, K1 is the power ratio, P2 is the current low-pressure cylinder inlet steam pressure, i1 is the current circulating pump current A, △A is the circulating pump current slightly increased A, K2 is the equation to be fitted, K2" is the value after the circulating pump current slightly increased, that is, K2 = a + b * (i1 + △A) 0.67 ;

[0092] S5: According to T1 in step S3 and ΔT in step S4, the following formula is substituted to calculate the turbine back pressure Pb after assuming that the circulating pump current increases slightly. The specific formula is:

[0093] Pb=POWER(10,7.07406-1657.46 / (T1-△T+227.02));

[0094] Where Pb is the turbine back pressure KPa after assuming a slight increase in circulating pump current;

[0095] S6: According to K1 in step S1, Pa in S3, P2 in S4, and Pb in S5, substitute into the following formula, and calculate the coal saving amount M1 according to the reduction of the back pressure of the steam turbine. The specific formula is: M1 = (Pb-Pa)*K3*K1*P2;

[0096] Where: Pb is the turbine back pressure after a slight increase in the circulating pump current, Pa is the turbine saturated back pressure, K1 is the formula to be fitted, and K3 takes the consumption difference data g / kWh / kPa of the impact of the empirical back pressure on coal consumption of this type of unit. The consumption difference has good linear characteristics in a large range. The specific value is determined according to the commonly used values ​​of the corresponding unit type or the heat consumption correction manual of the steam turbine plant.

[0097] S7: Determine whether to increase the output of the circulation pump according to the energy consumption scheduling mode or the economic scheduling mode.

[0098] S7a: The energy consumption scheduling mode also includes the following steps:

[0099] S7a1: According to △A in step S4, calculate the coal consumption M2 corresponding to the excess power consumption of the circulation pump, the specific formula is: M2 = 1.732*U*△A*0.75*K4;

[0100] Among them: K4 is the actual average coal consumption of the unit in kg / kWh, U is 6KV voltage, and 0.75 is the power factor of the circulating pump;

[0101] S7a2: If M1>M2, the circulating pump output is increased; otherwise, the output is not increased.

[0102] S7b: The economic dispatch mode also includes the following steps:

[0103] S7b1: Economic scheduling is to compare the fuel cost: (coal price*M1) and the electricity cost: (circulating pump power consumption*electricity price).

[0104] After dividing both sides by the electricity price and multiplying the coal consumption for power generation K4, the electricity fee is the same as before M2 = 1.732*U*0.75*K4*△A;

[0105] The fuel cost is then converted into coal price*M1*coal consumption for power generation / electricity price=(coal price*coal consumption for power generation / electricity price)*M1

[0106] Preferably, coal price*power generation coal consumption / electricity price is defined as K5, and calculating and comparing the size of K5*M1 and M2 is economic dispatch;

[0107] That is: the specific formula is: K5 = c*d / e;

[0108] Among them: c is the coal price yuan / ton, d is the coal consumption for power generation kg / kWh, and e is the electricity price yuan / kWh;

[0109] S7b2: Obtain the converted coal consumption M3 according to K5 in step S91, the specific formula is: M3 = K5 * M1;

[0110] S7b3: Compare the sizes of M2 and M3 to decide whether to increase the output of the circulation pump. Specifically, if M2>M3, increase the output of the circulation pump; otherwise, do not increase the output.

[0111] Specifically, the cold end optimization algorithm with the circulating water cooling water temperature, the condenser end difference and the low pressure cylinder inlet steam pressure as the boundary includes the above steps S1-S2, S6-S9, and also includes the following steps:

[0112] S3: Determine the current exhaust steam temperature T1 and the turbine saturated back pressure Pa;

[0113] Specifically, the current values ​​of the circulating pump current i1, the circulating water cooling water temperature T0 and the condenser terminal difference δ are obtained, and the current exhaust temperature T1 of the current turbine and the saturated back pressure Pa of the turbine are calculated. The specific formula is:

[0114] T1=T0+K1*P1 / i1*K2+δ

[0115] Pa=power(10,7.07406-1657.46 / (T1+227.02))

[0116] Where: T1 is the current exhaust temperature of the current turbine, T0 is the circulating water cooling temperature °C, K1 is the equation to be fitted, P1 is the low-pressure cylinder inlet steam pressure, i1 is the current circulating pump current A, δ is the condenser end difference °C, Pa is the turbine saturated back pressure KPa;

[0117] The exhaust of the low-pressure cylinder of the steam turbine generally operates in the wet steam area, and Pa does not use real-time data, because the stability of the temperature measurement point is better than that of the pressure measurement point, and at the same time, it can ensure that the comparison benchmark of the influence of the slight increase in current on the change of the exhaust temperature is consistent. Only in the winter heating extraction condition, when the steam flow of the low-pressure cylinder is extremely low, will the exhaust steam be overheated. At this time, because the steam inlet pressure of the low-pressure cylinder is very low, calculations show that when the exhaust temperature is 40 degrees, the optimal current of the circulating pump is still at the lower limit of the allowable current.

[0118] S4: Assuming that the circulating pump current increases slightly by △A, determine the exhaust steam temperature T3 after the circulating pump current increases slightly;

[0119] T3=T0+K1*P1 / (i1+△A)*K2”+δ

[0120] Where: T3 is the exhaust temperature of the circulating pump after a slight increase in °C, K is the power ratio, P1 is the low-pressure cylinder inlet steam pressure, i1 is the current circulating pump current A, △A is the slight increase in the circulating pump current A, K2” is the value of the circulating pump current after a slight increase in °C, δ is the condenser end difference in °C;

[0121] S5: Determine the turbine back pressure Pb after the circulating pump current is slightly increased;

[0122] Specifically, according to T3 in step S4, the following formula is substituted to calculate the turbine back pressure Pb assuming that the circulating pump current is slightly increased. The specific formula is:

[0123] Pb=POWER(10,7.07406-1657.46 / (T3+227.02));

[0124] Where: Pb is the turbine back pressure KPa after the circulating pump current is slightly increased, T3 is the exhaust steam temperature ℃ after the circulating pump current is slightly increased;

[0125] The above process can establish a mathematical model. After determining the five data K1, K2, K3, K4, and K5, on the one hand, only two variables, the current exhaust temperature and the low-pressure cylinder steam inlet pressure, need to be collected in real time, and the optimal circulating pump current can be found through the circulating pump current slightly increased column matrix calculation. On the other hand, three variables, the circulating water cooling water temperature, the condenser terminal difference, and the low-pressure cylinder steam inlet pressure, are collected, and the optimal circulating pump current can be found through the circulating pump current slightly increased column matrix calculation.

[0126] Specifically, the cold end optimization algorithm, whether it is based on the exhaust temperature and the low-pressure cylinder steam inlet pressure or the circulating water cooling water temperature and the condenser end difference and the low-pressure cylinder steam inlet pressure, can be calculated online or offline in the DCS and SIS system to make the optimal circulating pump current matrix table to guide the operation. For the power frequency circulating pump with discontinuous current, it can be scheduled according to the current approximate value.

[0127] Example 1

[0128] 1. Obtain the relationship between the steam turbine low-pressure cylinder inlet pressure P1, electric power G and power ratio K1;

[0129] The steam inlet pressure of the low pressure cylinder of a 300MW subcritical unit at 230MW is designed to be 0.397MPa

[0130] K1=G / P1=230 / 0.397=579.34

[0131] 2. Obtain the relationship between the circulating water temperature rise T, electric power G and circulating pump current i to determine the equation to be fitted K2.

[0132] K2 = temperature rise × circulating pump current / electric power

[0133] According to the test data as shown in Table 2, the functional relationship is established as follows:

[0134] K2=a+b*i 0.67 , the function relationship after fitting calculation is: K2=5.5+0.12*i 0.67

[0135] Table 2, test data table

[0136]

[0137] Among them: A is a single circulation pump, A+B is two circulation pumps.

[0138] 3. Obtain the current exhaust temperature T1 of the steam turbine and calculate the back pressure Pa of the steam turbine based on T1

[0139] For example: The current exhaust steam temperature is 40℃

[0140] Pa=POWER(10,7.07406-1657.46 / (T1+227.02))

[0141] =POWER(10,7.07406-1657.46 / (40+227.02))

[0142] =7.36KPa

[0143] 4. Calculate the reduction in circulating water temperature rise △T.

[0144] For example: the current circulating pump current is 300A, and the current low-pressure cylinder steam inlet pressure is 0.25MPa. Assuming that the circulating pump current increases slightly by 20A, i1=300A, P2=0.25MPa, △A=20A

[0145] K2=5.5+0.12*POWER(300,0.67)=10.98

[0146] K2”=5.5+0.12*POWER(300+20,0.67)=11.22

[0147] △T=K1*P2 / i1*K2-K1*P2 / (i1+△A))*K2”

[0148] =579.34*0.25 / 300*10.98-579.34*0.25 / (300+20)*11.22

[0149] =0.223℃

[0150] 5. Based on T1 = 40°C, △T = 0.223°C, calculate the back pressure Pb after the circulating pump current increases slightly

[0151] Pb=POWER(10,7.07406-1657.46 / (T1-△T+227.02))

[0152] =POWER(10,7.07406-1657.46 / (40-0.223+227.02))

[0153] =7.27KPa

[0154] 6. Based on the above K1=579.34, Pa=7.36, P2=0.25, Pb=7.27, calculate the coal saving M1 according to the back pressure reduction, where the empirical consumption difference analysis data K3=2.5g / kWh / kPa of the back pressure of this type of unit affecting the coal consumption of power generation is taken

[0155] M1 = (Pa - Pb) * K3 * K1 * P2 = (7.36 - 7.27) * 2.5 * 579.34 * 0.25 = 32.59 Kg

[0156] 7. Calculate the coal consumption M2 corresponding to the increased power consumption of the circulating pump according to the energy consumption scheduling mode. Here, K4 takes the empirical average power generation coal consumption of this unit, which is 0.31 kg / kWh

[0157] M2 = 1.732 * U * △A * 0.75 * K4 = 1.732 * 6 * 20 * 0.75 * 0.31 = 48.32 Kg

[0158] Where: K4 takes the empirical actual average power generation coal consumption of this unit in kg / kWh, U is the 6KV voltage, △A is the incremental current in A, and 0.75 is the power factor of the circulating pump.

[0159] 7.1. Compare the magnitudes of M1 and M2 to determine whether to increase the output of the circulating pump.

[0160] From the calculation, M1 = 32.59; M2 = 48.32, M1 < M2, so it is not appropriate to increase the output of the circulating pump.

[0161] According to the above calculations, the changes in the circulating pump current under different low-pressure cylinder inlet steam pressures are as Figure 1 shown Figure 1 in the circulating pump matrix table under the energy consumption scheduling mode. Here, 1 represents M1 > M2, 0 represents M1 < M2, corresponding to the exhaust steam temperature of 40°C, K1 = 579, K3 = 2.5, K4 = 0.31. Specifically, the corresponding optimal circulating pump current obtained after changing the low-pressure cylinder inlet steam pressure is shown in Table 3. More specifically, under the boundary conditions of the current low-pressure cylinder exhaust steam temperature of 40°C and the low-pressure cylinder inlet steam pressure of 0.25 MPa, the optimal circulating pump current is 230A, and the obtained data is consistent with the actual working conditions. The above calculation method is accurate and reliable.

[0162] Table 3. Optimal circulating pump current under different low-pressure cylinder inlet steam pressures calculated according to the energy consumption scheduling mode

[0163] Low pressure cylinder steam inlet pressure / MPa 0.21 0.23 0.25 0.27 0.29 0.31 0.33 0.35 Optimum circulation pump current / A 190 210 230 250 270 290 310 330 Corresponding pure condensation load / MW 122 133 145 156 168 179 191 203

[0164] Example 2

[0165] The present invention relates to another cold-end optimization algorithm for steam turbines. Calculate the power consumption M3 according to the economic scheduling mode, including steps 1 to 6 of Example 1, and further include the following steps:

[0166] 8. For example: the unit price of standard coal is 1500 yuan / ton, the on-grid electricity price is 0.4 yuan / kWh, and the power generation coal consumption is 0.31 Kg / kWh

[0167] K5 = coal price * coal consumption for power generation / electricity price = 1.5 * 0.31 / 0.4 = 1.1625

[0168] M3=M1*K5=32.59*1.1625=37.88Kg;

[0169] 8.1. Compare the sizes of M3 and M2 to decide whether to increase the output of the circulation pump.

[0170] M2 is the same as above, 48.32Kg, 48.32>37.88, M2>M3, it is not advisable to increase the output of the circulation pump.

[0171] According to the above steps, the change of circulating pump current under different low-pressure cylinder steam inlet pressure is as follows: Figure 2 As shown, Figure 2 It is the circulating pump matrix table under the economic dispatch mode, where 1 represents M2<M3, and 0 represents M2>M3, corresponding to exhaust temperature 40℃, K1=579, K3=2.5, K4=0.31, standard coal price 1500 yuan / ton, and electricity price 0.4 yuan / kWh. Specifically, the corresponding optimal circulating pump current obtained after changing the low-pressure cylinder inlet steam pressure is shown in Table 4. More specifically, under the boundary conditions of the current low-pressure cylinder inlet steam pressure of 40℃ and the low-pressure cylinder inlet steam pressure of 0.25MPa, the optimal circulating pump current is 250A, and the obtained data is consistent with the actual working conditions. The above calculation method is accurate and reliable.

[0172] Table 4, Optimal circulating pump current for different low-pressure cylinder steam inlet pressures calculated according to economic dispatch mode

[0173] Low pressure cylinder steam inlet pressure / MPa 0.21 0.23 0.25 0.27 0.29 0.31 0.33 0.35 Optimum circulation pump current / A 190 230 250 270 290 310 330 370 Corresponding pure condensation load / MW 122 133 145 156 168 179 191 203

[0174] Although the present invention is disclosed as above, the present invention is not limited thereto. Any person skilled in the art can make various changes and modifications without departing from the spirit and scope of the present invention. Therefore, the protection scope of the present invention shall be subject to the scope defined by the claims.

Claims

1. A cold end optimization algorithm for a steam turbine, characterized in that: The steps include: S1: Determine the power ratio K1 value; S2: Determine the functional relationship between the circulating water temperature rise and the K2 equation to be fitted; S3: Determine the turbine saturated back pressure Pa and / or determine the current exhaust steam temperature T1; S4: Assuming that the current of the circulating pump increases slightly by △A, determine the circulating water temperature rise variable △T or the exhaust steam temperature T3 after the circulating pump increases slightly; S5: Determine the turbine back pressure Pb after assuming a slight increase in the circulating pump current; S6: Obtain the empirical consumption difference analysis data K3 and determine the coal saving amount M1; S7: Determine whether to increase the output of the circulation pump according to the energy consumption dispatch mode or the economic dispatch mode; The functional relationship between the circulating water temperature rise and the fitting formula K2 in step S2 is calculated by the following formula: T=(G / i)*K2; In the formula, T is the circulating water temperature rise in °C, G is the electric power in MW, i is the circulating pump current in A, and K2 is the equation to be fitted; The specific functional formula of K2 is K2=a+b*i 0.67 ; In the formula, a and b are the coefficients to be fitted, and i is the circulating pump current A.

2. The cold end optimization algorithm according to claim 1, characterized in that: The energy consumption scheduling mode includes the following steps: S7a1: Obtain the actual average power generation coal consumption K4, and determine the coal consumption M2 corresponding to the excess power consumption of the circulating pump: S7a2: Compare the sizes of M1 and M2 to decide whether to increase the output of the circulation pump.

3. The cold end optimization algorithm according to claim 1, characterized in that: The economic dispatch mode includes the following steps: S7b2: Obtain economic dispatch conversion coefficient K5; S7b2: Determine the converted coal consumption M3; S7b3: Compare the sizes of M2 and M3 to decide whether to increase the output of the circulation pump.

4. The cold end optimization algorithm according to claim 1, characterized in that: The steps include: S3: Determine the turbine saturated back pressure Pa; S4: Assuming that the circulating pump current increases slightly by △A, determine the circulating water temperature rise variable △T.

5. The cold end optimization algorithm according to claim 1, characterized in that: The steps include: S3: Determine the current exhaust steam temperature T1 and the turbine saturated back pressure Pa; S4: Assuming that the circulating pump current increases slightly by △A, determine the exhaust steam temperature T3 after the circulating pump current increases slightly.

6. The cold end optimization algorithm according to claim 5, characterized in that: The current exhaust steam temperature T1 in step S3 is calculated by the following formula: T1=T0+K1*P1 / i1*K2+δ; Among them: T1 is the current exhaust temperature, T0 is the circulating water cooling temperature ℃, K1 is the equation to be fitted, P1 is the low-pressure cylinder inlet steam pressure, i1 is the current circulating pump current A, and δ is the condenser end difference ℃.

7. The cold end optimization algorithm according to claim 5, characterized in that: The exhaust steam temperature T3 in step S4 is calculated by the following formula: T3=T0+K1*P1 / (i1+△A)*K2”+δ; Among them: T3 is the exhaust temperature of the circulating pump after a slight increase in °C, K1 is the power ratio, P1 is the low-pressure cylinder inlet steam pressure, i1 is the current circulating pump current A, △A is the circulating pump current slight increase in A, K2" is the value of the circulating pump current after a slight increase in °C, and δ is the condenser end difference in °C.

8. The cold end optimization algorithm according to claim 1, characterized in that: The energy consumption dispatching mode and the economic dispatching mode are calculated online in the DCS and SIS systems, or calculated offline according to different variables, and an optimal circulating pump current matrix table is made to guide the operation.

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