LU500844B1

LU500844B1 - A multi-dimensional online optimization control method of optimal vacuum for a condenser

Info

Publication number: LU500844B1
Application number: LU500844A
Authority: LU
Inventors: Xiaolin Li
Original assignee: Huaneng Weihai Power Generation Co Ltd
Priority date: 2021-11-10
Filing date: 2021-11-10
Publication date: 2022-05-10

Abstract

The invention relates to the technical field, in particular to a multi-dimensional online optimization control method of optimal vacuum for a condenser. The system comprises controller, frequency converter, circulating water pump and condenser, the condenser is connected with the circulating water pump, the circulating water pump is connected with the controller through frequency converter, and the inlet of the circulating water pump is provided with an inlet temperature detector,an atmospheric pressure detector is installed on the chassis of the condenser, the outlet of the circulating water pump is provided with an outlet temperature detector, and the pipeline connecting the circulating water pump and the condenser is provided with an ultrasonic flowmeter, through (I) determining the optimal vacuum target value, (II) determining the variable working condition characteristics of the condenser, and (III) by using the calculation method of the power consumption of the circulating water pump to determine the optimal vacuum value, which has the advantages of simple structure, strong reliability, flexible adjustment, energy saving and so on.

Description

A MULTI-DIMENSIONAL ONLINE OPTIMIZATION CONTROL METHOD OF OPTIMAL VACUUM FOR A CONDENSER FIELD OF THE INVENTION

[0001] The invention relates to the technical field of condenser vacuum optimization, in particular to a multi-dimensional online optimization control method of optimal vacuum for a condenser with simple structure, strong reliability, flexible adjustment and energy saving.

BACKGROUND OF THE RELATED ART

[0002] As we all know, condenser vacuum is the most important index affecting the economy of steam turbine generator unit, every 1kPa change in vacuum affects the power supply coal consumption rate of 300 ~ 600MW units by about 2.5g/kWh. Reducing the cooling circulating water volume can reduce the power consumption, but it will worsen the vacuum of the steam turbine and increase the heat loss. When the steam parameters and flow remain unchanged, increasing the vacuum will increase the available enthalpy drop of steam in the steam turbine and increase the output power of the generator accordingly. However, while increasing the vacuum value, it is necessary to supply more cooling circulating water to the condenser, so as to increase the power consumption of the circulating water pump. If the cooling circulating water is excessively increased, it is easy to make the vacuum degree too high, resulting in the energy consumed by increasing the cooling circulating water is higher than that generated by the unit, so as to obtain the opposite effect. Therefore, the most favorable cooling circulating water volume and the best vacuum should be determined. The optimum vacuum refers to the vacuum when the difference between the increase of steam turbine power and the excessive power consumption of circulating water pump is the maximum due to the improvement of condenser vacuum. The optimum vacuum is traditionally determined by test.

[0003] Determine the optimum vacuum value under the design load and design ambient temperature. No matter what load and environmental conditions, the condenser vacuum will 1 remain unchanged. If the unit always operates according to this optimal vacuum value, the 0500844 unit economy will deteriorate when the unit load changes or when the ambient temperature (or atmospheric pressure) changes. In fact, the unit load of the thermal power plant is adjusted in real time according to the power dispatching curve issued by the provincial dispatching, and the ambient temperature will change with the seasons. Especially for the coastal power plant, if the seawater cooling mode is adopted, the cooling circulating water volume of the condenser is also affected by the rising and falling tide of the seawater. Therefore, the optimal vacuum value of condenser should also change in real time.

[0004] At present, for the optimal vacuum value of condenser, only the optimal vacuum value of condenser under rated load is adopted, regardless of unit load change and environmental change. For the flow of cooling circulating water pump, two constant speed pumps are generally used. Two constant speed cooling circulating water pumps are opened in summer and one constant speed cooling circulating water pump is opened in winter. There are few ways to adjust the cooling circulating water volume. The cooling circulating water volume is controlled by shutting down and starting one constant speed cooling circulating water pump. Since the water volume increases or decreases in multiple, it is impossible to keep the condenser running under the optimal vacuum value. For example, the ideal flow of cooling circulating water of a 300MW unit in summer under full load is 27000t / h. If a circulating water pump is opened in summer, the cooling circulating water is insufficient (the rated flow of cooling circulating water is 22000 t / h, which is about 5000 t / h different from the actual water demand), resulting in the increase of exhaust steam temperature and the decrease of vacuum. At this time, the vacuum value of the unit under full load is lower than 93 kPa; If two cooling circulating water pumps are opened, it will cause other problems, such as too much cooling circulating water and too much power consumption of circulating water pumps. The ideal cooling circulating water flow under full load in winter should be 13000 t / h. in particular, the unit usually operates under 70% load. Even if a circulating water pump is opened, the circulating water volume is too large, which not only causes the vacuum to be too high (the unit vacuum is close to 98kPa), but also causes the condensate temperature to be much lower than its saturation temperature, resulting in difficult precipitation of oxygen in the condensate and high dissolved oxygen in the condensate.

2

[0005] With the development of energy-saving technology, many power plants now transform 0500844 the constant speed cooling circulating water pump into a two speed circulating water pump. Although the cooling circulating water volume regulation mode is added, it is still unable to realize the accurate control and real-time on-line control of the optimal vacuum value of the condenser.

SUMMARY OF THE INVENTION

[0006] The purpose of the invention is to solve the shortcomings of the existing technology, and to provide a multi-dimensional online optimization control method of optimal vacuum for a condenser with simple structure, strong reliability, flexible adjustment and energy saving.

[0007] The technical scheme adopted by the invention to solve the technical problem is:

[0008] The multi-dimensional online optimization control system of optimal vacuum for a condenser, which comprises a controller, a frequency converter, a circulating water pump and a condenser, the condenser is connected with the circulating water pump, and the circulating water pump is connected with the controller through the frequency converter, an inlet temperature detector is arranged at the inlet of the circulating water pump, the chassis of the condenser is provided with an atmospheric pressure detector, the outlet of the circulating water pump is provided with an outlet temperature detector, and the pipeline connected between the circulating water pump and the condenser is provided with an ultrasonic flowmeter. After the data are detected by the inlet temperature detector, the outlet temperature detector, the ultrasonic flow meter and the atmospheric pressure detector, the frequency converter is controlled after being calculated by the controller, Finally, the circulating water pump is controlled to realize the optimal vacuum value control of the condenser.

[0009] The multi-dimensional online optimization control method of optimal vacuum for a condenser, which is characterized in that the steps of the control method are as follows:

[0010] ( I ) Determination of the optimal vacuum target value:

[0011] Under the four seasons of spring, summer, autumn and winter, under loads of 100%, 90%, 80%, 70% and 60% respectively, according to the test, the best vacuum values of the condenser in different seasons and different loads is determined through the test method, and then the curve is made in the Excel scatter diagram, and the polynomial formula of the best 3

Lo. . . . LU500844 vacuum value 1s simulated through the curve (1), The relationship between unit load x and the optimal vacuum target value Pr of condenser is obtained:

[0012] (II) Determination of the characteristics of the condenser under different working conditions:

[0013] During normal operation of steam extraction equipment of steam turbine, there is the following relationship between condenser vacuum and initial temperature of cooling circulating water, circulating water flow and unit load, namely: 7,46 100+#, | p, = f (A4 1,5 Dos D,)=0.0098065x | — 7 | Po (2)

57.66 A t= fw2- tyr Where ?——Vacuum value of the condenser, kPa; Po ——Atmospheric pressure, kPa; ts— Exhaust saturation temperature, C ; twi— Inlet temperature of cooling circulating water, °C; Dy—— Cooling circulating water flow, t/h; t,2——Outlet temperature of cooling circulating water, C ; A t——Temperature rise of cooling circulating water, C »

[0014] Therefore, the exhaust steam saturation temperature ts is related to the inlet temperature 7,7, the flow Dy, and the temperature rise At of the cooling circulating water.

[0015] Due to the end difference © t of the condenser has the following relationship with exhaust steam saturation temperature ts: t=ts- fy1- At At Ste e 4.187D, 1 At Therefore ts =————+ tut At (3) e+187P, _ 1 Where A——Cooling area of the condenser, m° 4

. LU500844 K-—— Total heat transfer coefficient of the condenser.

[0016] Once the unit is designed and installed, the total heat transfer coefficient K and cooling area À of the condenser are basically unchanged, and the atmospheric pressure Po is also determined,

[0017] Obtained according to formulas (2) and (3) 7,46 P:-0.0098065 x [12215 | _P0

57.66

7.46 At 100 + —5— + 4, + At

4. 187D, =0.0098065x| —— 2 | -Po (4)

57. 66

[0018] Formula (4) shows that: The vacuum value of condenser 1s only related to the cooling circulating water inlet temperature #,;, cooling circulating water flow D, and cooling circulating water temperature rise À t, the total heat transfer coefficient K, cooling area À and atmospheric pressure Po of the condenser are constants for the determined unit, which are at the inlet temperature #,; of the cooling circulating water and the temperature rise of the cooling circulating water At is the real-time monitoring quantity, so the cooling circulating water flow Dy of the circulating pump can be adjusted through the frequency converter, and the optimal vacuum value of the condenser in step (I) can be obtained by controlling the cooling circulating water flow Dy;

[0019] (I) Calculation method of power consumption of circulating water pump

[0020] The mechanical energy obtained from the pump in unit time through the liquid of the pump is called the effective power of the pump, and the calculation formula is pgD,H Np= 1000 (5) Where Np—— Power consumption of cooling circulating water pump (effective power), kW; Dy—— Cooling circulating water flow, t/h; g—— Gravitational acceleration, g=9.81m/s*;

p —— Liquid density of circulating water pump, P =1000kg/m°; 0500844 H——Head of circulating water pump, m.

[0021] Once the circulating water pump is installed and operated, the head and liquid density of the circulating water pump are determined values, so the power consumption of the circulating water pump is a linear function of the cooling circulating water flow of the condenser. In Step (II), the cooling circulating water flow Dy and the power consumption of the circulating water pump are obtained.

[0022] Due to the adoption of the above structure, the invention has the advantages of simple structure, strong reliability, flexible adjustment, energy saving, etc.

BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Fig. 1 1s a control flow chart of the invention.

[0024] Fig. 2 is the test curve of the best vacuum value of the condenser of 125MW unit in autumn.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] As shown in the attached figure, a multi-dimensional online optimization control system of optimal vacuum for a condenser includes controller, frequency converter, circulating water pump and condenser, the condenser is connected with the circulating water pump, the circulating water pump is connected with the controller through the frequency converter, and the inlet of the circulating water pump is provided with an inlet temperature detector, the chassis of the condenser is provided with an atmospheric pressure detector, the outlet of the circulating water pump is provided with an outlet temperature detector, and the pipeline connected between the circulating water pump and the condenser is provided with an ultrasonic flowmeter. After the data are detected by the inlet temperature detector, the outlet temperature detector, the ultrasonic flow meter and the atmospheric pressure detector, the frequency converter is controlled after being calculated by the controller, Finally, the circulating water pump is controlled to realize the optimal vacuum value control of the condenser.

[0027] The multi-dimensional online optimization control method of optimal vacuum for a 6

Le . . LU500844 condenser, which 1s characterized in that the steps of the control method are as follows:

[0028] ( I ) Determination of the optimal vacuum target value:

[0029] Under the four seasons of spring, summer, autumn and winter, under the loads of 100%, 90%, 80%, 70% and 60% respectively, according to the test, the best vacuum values of condenser in different seasons and different loads are determined through the test method, and then the curve is made in the Excel scatter diagram, and the polynomial formula of the best vacuum value is simulated through the curve (1). The relationship between unit load x and the optimal vacuum target value Pk of condenser is obtained;

[0030] For example, according to the test of a 125MW unit under 100%, 90%, 80%, 70% and 60% load in autumn (when the seawater cooling water temperature is 4.1 °C), and then make the curve as shown in Figure 2 in the Excel scatter diagram. Through the curve simulation, the polynomial formula of the optimal vacuum value is obtained. When the seawater cooling water temperature is 4.1 °C, the calculation formula of the optimal vacuum value is p, = 0.0000311x* — 0.021255x° + 1.5623x + 33.12 CD Where x is the unit load, MW.

This formula is the optimal vacuum value of the condenser, that is, the optimal vacuum target value of the condenser.

(I) Determination of the characteristics of the condenser under different working conditions:

[0031] During normal operation of steam extraction equipment of steam turbine, there is the following relationship between condenser vacuum and initial temperature of cooling circulating water, circulating water flow and unit load, namely:

7.46 py = HALL 00D) 0098065 x | 100+*% | M 0)

57.66 A t= fw2- tyr Where ?+——Condenser vacuum value, kPa; Po ——Atmospheric pressure, kPa; ts——Exhaust saturation temperature, C ; 7

. . . ° LU500844 twi—Inlet temperature of cooling circulating water, C; Dy—— Cooling circulating water flow, t/h; t,2——Outlet temperature of cooling circulating water, C ; A t——Temperature rise of cooling circulating water, C .

[0032] Therefore, the exhaust steam saturation temperature ts is related to the inlet temperature 7,7, the flow Dy, and the temperature rise At of the cooling circulating water.

[0033] Due to the end difference © t of the condenser has the following relationship with exhaust steam saturation temperature ts: t=ts- fy1- At At Ste e 4.187D, 1 At Therefore ts =————+ tut At (3) e+187P, _ 1 Where A——Cooling area of the condenser, m° K——Total heat transfer coefficient of condenser.

[0034] Once the unit is designed and installed, the total heat transfer coefficient K and cooling area A of the condenser are basically unchanged, and the atmospheric pressure Po is also determined, Obtained according to formulas (2) and (3) 7,46 P:-0.0098065 x [12215 | _P0

57.66 7,46 At 100+ — Th + At 4187D, =0.0098065X | —¢—"—— | -Po (4)

57.66

[0035] Formula (4) shows that: The vacuum value of condenser 1s only related to the cooling circulating water inlet temperature #,;, cooling circulating water flow D, and cooling circulating water temperature rise À t, the total heat transfer coefficient K, cooling area À and 8 atmospheric pressure Po of the condenser are constants for the determined unit, which are at the inlet temperature #,; of the cooling circulating water and the temperature rise of the cooling circulating water At is the real-time monitoring quantity, so the cooling circulating water flow Dy of the circulating pump can be adjusted through the frequency converter, and the optimal vacuum value of the condenser in step (I) can be obtained by controlling the cooling circulating water flow Dy; (IT) Calculation method of power consumption of circulating water pump

[0036] The mechanical energy obtained from the pump in unit time through the liquid of the pump is called the effective power of the pump, and the calculation formula is Np= pb Ho (5) 1000 Where Np——Power consumption of cooling circulating water pump (effective power), kW; Dy—— Cooling circulating water flow, t/h; g—— Gravitational acceleration, g=9.81m/s*; p —— Liquid density of circulating water pump, P =1000kg/m°; H——Circulating water pump head, m.

[0037] Once the circulating water pump is installed and operated, the head and liquid density of the circulating water pump are determined values, so the power consumption of the circulating water pump is a linear function of the cooling circulating water flow of the condenser. In Step (II), the cooling circulating water flow Dy and the power consumption of the circulating water pump are obtained.

[0038] Embodiment

[0039] Before the transformation of the control system of 125MW Unit, only the No. 2 circulating water pump is opened in winter and when the tide level 1s high. See Table 1 for the operation data. After the transformation, No. 2 circulating water pump is controlled by the optimal vacuum multi-dimensional online optimization control system. See Table 2 for the operation data.

[0040] Table 1 Operation Data of No. 2 Circulating Water Pump of Unit 1 Before Transformation of Multi-dimensional Control System (in winter and with high tide level) 9

Before the circulating water pump is controlled by optimal vacuum multi-dimensional online optimization Cooling Outlet Circula Atmosph Condenser Motor Motor d . . spee ; Unit load circulating pressure of ting etic vacuum voltag current ¢ x Fe circulating Sm ressure ë NV X water pump water 4 P (KP) Fada BY $ Su eh y su water pump pump (kPa) £301 ES EN LR Ww] LAE a A (mPa) De PRE xx Erg) Er yom go Am am nm. a. un WE = 2, + 35 MEN 2 RS WIT OX Lis © xs fe sit oe oR wi Au do = EW le = mn — = 7m — = 2 u. mar ni = nm us Pa IEE IR = Yee SSI Mas "x AZ OW WEY à MEN Ka ES AS Hé 2 Mae wD SS DEN mw. m mue x wm à max ni = mm : mn ERE SA 5 RR: fi ik aod om Hil ox ne À ges À at à dd ab GE Fa = A dr a + = x ae _ = a = m. u mx 5 mw. m mn REF Ra TY REE fs ie mens em WAT A Ne S Es B00 Fda SEE LE SE = Sud, w aad SC SA =» = ome = = vie £ “eu ne x zm ce = WE SEY m le IF Ig wm OÙ Sm, hi x WE wm vs

[0041] Table 2 Operation Data of Multi-dimensional Online Optimization Control of No. 2 Circulating Water Pump After Transformation (in winter and with high tide level)

After intelligent control of circulating water pump Inlet / oo Condenser Cooling outlet Current meute Outlet ; Motor seawater vacuum Speed Unit load Voltage cireulatin a ; € aus pressure power | (KP) {prep | a ; ES Ia (mP.) a i Gd pump LE IER % i Has Asa) ma #4 Lis Ta à fie Ÿ + WS BR ce = se sas LE seu x | RGAE 0.4 aa Se i Le au à 5 di pie E 0a a & aa | Eee | wae wee | marshy | NE X N ve + Sets Le 2. + di pick si a &

[0042]Before the transformation of the multi-dimensional online optimization control system of optimal vacuum, unit 1 operates at about 90MW load for a long time, and the average electric power of circulating water pump is 571kW; after control, the average electric power of circulating water pump is 323.3kW, and the power saving rate = (558-323.3) / 558 = 42.1%. The vacuum is increased from 96.4kPa to 98.3kPa, and the generating capacity of the unit is increased by 2064 kW. 11

Claims

Claims

1. The multi-dimensional online optimization control method of optimal vacuum for a condenser, which 1s characterized in that the system comprises controller, frequency converter, circulating water pump and condenser. The condenser 1s connected with the circulating water pump, the circulating water pump is connected with the controller through the frequency converter, and the inlet of the circulating water pump is provided with an inlet temperature detector, the condenser is connected with the circulating water pump, the circulating water pump is connected with the controller through the frequency converter, and the inlet of the circulating water pump is provided with an inlet temperature detector, the pipeline connecting the circulating water pump and the condenser is equipped with ultrasonic flowmeter. After the data are detected by the inlet temperature detector, outlet temperature detector, ultrasonic flowmeter and atmospheric pressure detector respectively, the frequency converter is controlled after calculation by the controller, and finally the circulating water pump is controlled to realize the optimal vacuum value control of the condenser.

2. The multi-dimensional online optimization control method of optimal vacuum for a condenser, which is characterized in that the steps of the control method are as follows: (I) Determination of the optimal vacuum target value: Under the four seasons of spring, summer, autumn and winter, under the loads of 100%, 90%, 80%, 70% and 60% respectively, according to the test, the best vacuum values of condenser in different seasons and different loads are determined through the test method, and then the curve is made in the Excel scatter diagram, and the polynomial formula (1) of the best vacuum value is simulated through the curve, the relationship between unit load x and the optimal vacuum target value Pk of condenser is obtained; (II) Determination of the characteristics of the condenser under different working conditions: During normal operation of steam extraction equipment for the steam turbine, there is the following relationship among the vacuum value of the condenser and the initial temperature, flow of the cooling circulating water, and unit load, namely: 12

100+ 1 7.46 LU500844 p, = f(At,t,,, py, D,)=0.0098065x| — | -Po (2) k 1 wl 0 57 66 A t= fw2- tyr Where ?——Vacuum value of the condenser, kPa; Po ——Atmospheric pressure, kPa; ts— Exhaust saturation temperature, °C; twi— Inlet temperature of the cooling circulating water, °C; Dy——Flow of the cooling circulating water, t/h; t,2——Outlet temperature of the cooling circulating water, C; A t——Temperature rise of the cooling circulating water, °C.

Therefore, the exhaust steam saturation temperature ts is related to the inlet temperature tw, the flow Dy, and the temperature rise At of the cooling circulating water.

Due to the end difference &t of the v has the following relationship with the saturation temperature ts of exhaust steam: t=ts- fy1- At At Ste e 4.187D, 1 At Therefore ts =————+ tut At (3) e+187P, _ 1 Where A—— Cooling area of the condenser, m°; K-—— Total heat transfer coefficient of the condenser.

Once the unit is designed and installed, the total heat transfer coefficient K and cooling area À of the condenser are basically unchanged, and the atmospheric pressure Po is also determined, The following is obtained according to the formulas (2) and (3) 7,46 100+#, | Pi =0.0098065 x | — + | -Po

57.66 13

A 746 LU500844 100+ — Th + At =0.0098065 X me -Po (4)

57.66 Formula (4) shows that: The vacuum value of the condenser is only related to the inlet temperature #,;, flow Dy and temperature rise At of the cooling circulating water. The total heat transfer coefficient K, cooling area À and atmospheric pressure Po of the condenser are constants for the determined unit. When the inlet temperature #,; and the temperature rise At of the cooling circulating water are the values of real-time monitoring, therefore, the cooling circulating water flow D of the circulating pump can be adjusted by the frequency converter, and the optimal vacuum value of the condenser in step (I) can be obtained by controlling the cooling circulating water flow Dy; (IT) Calculation method of power consumption of circulating water pump The mechanical energy obtained from the pump in unit time through the liquid of the pump is called the effective power of the pump, and the calculation formula is Np= PEDAL (5) 1000 Where Np—— Power consumption of cooling circulating water pump (effective power) , kW; Dy—— Cooling circulating water flow, t/h; g——Gravitational acceleration, g=9.81m/s’; p —— Liquid density of circulating water pump, © =1000kg/m°; H—— Head of circulating water pump, mo Once the circulating water pump is installed and operated, the head and liquid density of the circulating water pump are determined values, so the power consumption of the circulating water pump is a linear function of the cooling circulating water flow of the condenser; In Step (IT), the cooling circulating water flow D, and the power consumption of the circulating water pump are obtained. 14