CN112228329A - System, device and method for automatically optimizing and adjusting running frequency of circulating water pump - Google Patents

System, device and method for automatically optimizing and adjusting running frequency of circulating water pump Download PDF

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Publication number
CN112228329A
CN112228329A CN202011140392.3A CN202011140392A CN112228329A CN 112228329 A CN112228329 A CN 112228329A CN 202011140392 A CN202011140392 A CN 202011140392A CN 112228329 A CN112228329 A CN 112228329A
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China
Prior art keywords
circulating water
water pump
condenser
unit
frequency
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韩立
荆涛
贾明晓
邹洋
王明勇
邓佳
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Xian Thermal Power Research Institute Co Ltd
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Xian Thermal Power Research Institute Co Ltd
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
    • F04B49/06—Control using electricity
    • F04B49/065—Control using electricity and making use of computers
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B23/00—Pumping installations or systems
    • F04B23/02—Pumping installations or systems having reservoirs
    • F04B23/025—Pumping installations or systems having reservoirs the pump being located directly adjacent the reservoir
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B23/00—Pumping installations or systems
    • F04B23/04—Combinations of two or more pumps
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04B—POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS
    • F04B49/00—Control, e.g. of pump delivery, or pump pressure of, or safety measures for, machines, pumps, or pumping installations, not otherwise provided for, or of interest apart from, groups F04B1/00 - F04B47/00
    • F04B49/007—Installations or systems with two or more pumps or pump cylinders, wherein the flow-path through the stages can be changed, e.g. from series to parallel
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28B—STEAM OR VAPOUR CONDENSERS
    • F28B9/00—Auxiliary systems, arrangements, or devices
    • F28B9/04—Auxiliary systems, arrangements, or devices for feeding, collecting, and storing cooling water or other cooling liquid

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Computer Hardware Design (AREA)
  • Control Of Positive-Displacement Pumps (AREA)

Abstract

The invention discloses a system, a device and a method for automatically optimizing and adjusting the running frequency of a circulating water pump, wherein the method comprises the steps of acquiring the load of a unit and the liquid level of a forebay, determining the micro-increase output of the unit by combining the parameters of the unit, determining the target output flow of the circulating water pump according to the micro-increase output of the unit, and determining the running frequency of the circulating water pump through the target output flow of the circulating water pump and the liquid level of the forebay; and the circulating water pump operates according to the operating frequency. During the shutdown period of the unit, related conclusions obtained by optimizing the operation of the cold end system of the steam turbine are used, an operation optimization algorithm is directly programmed and developed in the DCS of the unit, the operation optimization function of the variable-frequency circulating water pump is realized, the operation optimization result is directly fed back to the frequency setting system of the frequency converter of the circulating water pump, and the operation of the circulating water pump is intelligently controlled.

Description

System, device and method for automatically optimizing and adjusting running frequency of circulating water pump
[ technical field ] A method for producing a semiconductor device
The invention belongs to the field of energy conservation of coal-fired units, and relates to a system, a device and a method for automatically optimizing and adjusting the running frequency of a circulating water pump.
[ background of the invention ]
The circulating water pump is an important user of station power, generally occupies 0.8% of the station power, and the power consumption of the circulating water pump is directly related to the economy of a power plant. If the running frequency of a circulating water pump motor needs to be increased in order to maintain the low back pressure of the unit, so that the circulating water flow is increased, but the power consumption of the circulating water pump is increased in response; if the running frequency of the circulating water pump is reduced in order to reduce the power consumption of the circulating pump, the back pressure of the unit can be increased, and the economy of the unit is affected. It is necessary to find an optimum back pressure at which the power consumption of the circulating water pump is most economical. For cold end optimization of a circulating water pump in a seawater circulating water system with a frequency conversion function, an optimization curve is given in a traditional method, then the frequency is adjusted by operating personnel, and meanwhile, the influence of the change of the tide level on the flow is not considered during optimization. Because the condition of the pipeline has great influence on the measurement of the cooling water flow, if a plurality of units adopt an on-line flow measurement mode, the precision of the selected common flowmeter is low, the influence on the accuracy of an operation optimization result is great, and the investment cost is high by selecting an imported high-precision on-line flowmeter.
[ summary of the invention ]
The invention aims to overcome the defects of the prior art and provides a system, a device and a method for automatically optimizing and adjusting the running frequency of a circulating water pump; the problem that an existing circulating water pump frequency conversion system is difficult to accurately adjust the frequency of a circulating water pump is solved.
In order to achieve the purpose, the invention adopts the following technical scheme to realize the purpose:
a method for automatically optimizing and adjusting the running frequency of a circulating water pump collects the load of a unit and the liquid level of a forebay in real time, and determines the micro-increase output of the unit by combining the parameters of the unit; when the micro-increase output of the unit is the maximum value, obtaining the target output flow of the circulating water pump; determining the running frequency of the circulating water pump through the target output flow of the circulating water pump and the liquid level of the forebay; and the circulating water pump operates according to the operating frequency.
The invention is further improved in that:
preferably, the determining of the micro-incremental force of the unit comprises the following steps:
step 1, collecting unit load, cooling water flow of a condenser, power consumption of a circulating water pump and a forebay liquid level;
step 2, determining the heat load of the condenser corresponding to the unit load, and further determining the temperature rise values of the cooling water at two ends of the condenser;
step 3, determining the heat transfer end difference of the condenser according to the temperature rise value of the cooling water and the logarithmic mean difference of the condenser;
and 4, obtaining the saturation temperature of the condenser through the heat transfer end difference of the condenser, the temperature rise value of the cooling water at the two ends of the condenser and the inlet temperature of the cooling water, and further obtaining the pressure corresponding to the saturation temperature of the condenser.
And step 5, determining the micro-increase output according to the pressure corresponding to the saturation temperature of the condenser, the unit load and the power consumption of the circulating water pump.
Preferably, in step 2, the heat load Q of the condenserCONThe calculation formula is as follows:
QCON＝A×POWER-B (6)
wherein, POWERA and B are calculation coefficients;
cooling water temperature rise value Dt,CWThe calculation formula of (2) is as follows:
Dt，CW＝QCON÷GCW÷ρ÷C (7)
wherein G isCWIs the cooling water flow rate, m, of the condenser3H; rho is the density of cooling water, kg/m3(ii) a C is the specific heat capacity at constant pressure, kJ/(kg-DEG C).
Preferably, in step 3, the heat transfer end difference D of the condensert,TERThe calculation formula of (2) is as follows:
Dt,TER＝Dt,CW/[EXP(Dt,CW/LMTD)-1] (11)。
wherein D ist,CWThe temperature of cooling water is raised to the degree C, LMTDThe log mean difference of the condenser.
Preferably, the logarithmic mean difference L of the condenserMTDThe calculation formula of (2) is as follows:
LMTD＝QCON÷KTEST÷SC (10)
in the formula, SCTo cool the area, QCONFor the heat load of the condenser, KTESTThe heat transfer coefficient of the condenser.
Preferably, the heat transfer coefficient K of the condenserTESTThe calculation formula of (2) is as follows:
KTEST＝FD×vCW 1/2×FT,TEST×FM×CF,TEST (8)
wherein, FDIs the correction coefficient of the outer diameter of the cooling pipe of the condenser, vCWIs the flow velocity in the cooling tube in the condenser, FT,TESTIs the inlet water temperature correction coefficient of the condenser, FMFor the wall thickness correction factor of the cooling tube, CF,TESTIs the cleaning factor.
Preferably, in step 4, the calculation formula of the saturation temperature of the condenser is as follows:
tSAT＝tCWI+Dt,CW+Dt,TER， (12)
in the formula (12), tSATThe condenser saturation temperature, deg.C; t is tCWIIs the inlet water temperature of the cooling water at DEG C. Passing through tSATLooking up a table to obtain a pressure value P corresponding to the condenser at the saturation temperaturek。
Preferably, in step 5, Δ N is slightly increasedTThe calculation formula of (2) is as follows:
ΔNT＝-1×PP,TEST×POWER/1 000-Np (13)
in the formula, PP,TESTFor the back-pressure-to-load correction factor, PP,TESTCorresponding to the corresponding pressure of the saturation temperature of the condenser, NpFor circulating waterThe power consumption of the pump.
A system for automatically optimizing and adjusting the operating frequency of a circulating water pump, comprising:
the acquisition module is used for acquiring the unit load, the liquid level of the forebay and the parameters of the unit;
the calculation module is used for determining the operating frequency of the circulating water pump through the data acquired by the acquisition module;
and the output module outputs the operating frequency to the circulating water pump.
The device for automatically optimizing and adjusting the running frequency of the circulating water pumps for the system is characterized by comprising a forebay and a control cabinet, wherein the output end of the forebay is connected with two circulating water pumps;
two liquid level meters are arranged in the front pool, and a flow meter is arranged on a cooling water input pipe of the condenser;
the control cabinet acquires data of the liquid level meter and the flow meter, and controls the running frequency of the circulating water pump through the variable frequency motor; the control cabinet is connected with an upper computer.
Compared with the prior art, the invention has the following beneficial effects:
the invention discloses a method for automatically optimizing and adjusting the running frequency of a circulating water pump, which comprises the steps of acquiring the load of a unit and the liquid level of a forebay, determining the micro-increase output of the unit by combining the parameters of the unit, determining the target output flow of the circulating water pump according to the micro-increase output of the unit, and determining the running frequency of the circulating water pump through the target output flow of the circulating water pump and the liquid level of the forebay; and the circulating water pump operates according to the operating frequency. During the shutdown period of the unit, related conclusions obtained by optimizing the operation of the cold end system of the steam turbine are used, an operation optimization algorithm is directly programmed and developed in the DCS of the unit, the operation optimization function of the variable-frequency circulating water pump is realized, the operation optimization result is directly fed back to the frequency setting system of the frequency converter of the circulating water pump, and the operation of the circulating water pump is intelligently controlled. When the unit operates again, the purpose that the unit automatically optimizes and obtains the optimal frequency of the running of the pump according to the real-time cooling water inlet temperature and the load of the unit is achieved, and the purpose that the running of the pump is automatically performed according to the frequency is achieved. Therefore, the running of the circulating pump is finely adjusted, the power consumption of the circulating pump is effectively saved, and the unit is ensured to be at the optimal back pressure running point.
The invention also discloses a system for automatically optimizing and adjusting the running frequency of the circulating water pump, which is arranged in the upper computer, the running optimization algorithm is directly programmed and developed in the DCS of the unit, the running optimization function of the variable-frequency circulating water pump is realized, the running optimization result is directly fed back to the frequency setting system of the frequency converter of the circulating water pump, and the running of the circulating water pump is intelligently controlled.
The invention also discloses a device for automatically optimizing and adjusting the running frequency of the circulating water pump, which is used for the system, the device connects a variable frequency motor for controlling the frequency of the circulating water pump with an upper computer, a flowmeter and a thermometer at the outlet of the circulating water pump are both connected with a control cabinet, and the upper computer is connected with the control cabinet; the switch board can be in real time to host computer transmission relevant data, and the switch board can be according to the frequency real-time adjustment inverter motor's that passes back frequency, and then reaches the purpose that accurate control flows in to condenser cooling water flow, and this system realizes automatic control through optimizing, effectively promotes unit economy nature. The system also considers the influence of the sea water tide level change on the cooling water flow, and effectively avoids manual operation through automatic control.
[ description of the drawings ]
FIG. 1 is a connection diagram of the present invention;
wherein: 1. rotating the filter screen; 2. a liquid level meter; 3. a water circulating pump; 4. a variable frequency motor; 5. a pressure gauge; 6-platinum resistance thermometer; 7. a flow meter; 8. a condenser; 9. an open water pump; 10. a forebay; 11. a control cabinet; 12. an upper computer; 13. a user; 14. a manifold.
[ detailed description ] embodiments
The invention is described in further detail below with reference to the accompanying drawings:
in the description of the present invention, it should be noted that the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer", etc., indicate orientations or positional relationships based on the orientations or positional relationships shown in the drawings, and are only for convenience of description and simplicity of description, but do not indicate or imply that the device or element being referred to must have a particular orientation, be constructed and operated in a particular orientation, and thus, should not be construed as limiting the present invention; the terms "first," "second," and "third" are used for descriptive purposes only and are not to be construed as indicating or implying relative importance; furthermore, unless expressly stated or limited otherwise, the terms "mounted," "connected," and "connected" are to be construed broadly and encompass, for example, both fixed and removable connections; they may be connected directly or indirectly through intervening media, or they may be interconnected between two elements. The specific meanings of the above terms in the present invention can be understood in specific cases to those skilled in the art.
The invention aims to provide a circulating water system for automatically optimizing and adjusting the frequency of a circulating water pump, so that the frequency of the circulating water pump in a seawater circulating system is automatically controlled by optimizing a cold end in a DCS (distributed control system), and the economical efficiency of a unit is effectively improved. The system also considers the influence of tide level change on the cooling water flow, and avoids the improper and untimely manual regulation through automatic control.
Referring to fig. 1, the invention discloses a system, a device and a method for automatically optimizing and adjusting the running frequency of a circulating water pump, the system comprises a forebay 10, two rotary filter screens 1 are arranged at the front end of the forebay 10, two guided wave level meters 2 are arranged in the circulating water pump forebay 1, the two level meters 2 are guided wave radar level meters, two circulating water pumps 3 are connected in parallel at the rear end of the forebay 10, the water outlet end of each circulating water pump 3 is gathered to a main pipe 14, the main pipe 14 is divided, is connected to two water inlet ends of the condenser 8 through two branches, the water outlet end of the condenser 8 is connected with the cooling water outlet, condenser 8 between the outlet of circulating water pump 3 and the cooling water outlet is connected in parallel with user 13, the water inlet end of user 13 is connected with an open water pump 9, the water inlet end of open water pump 9 is connected with a branch of the outlet of header pipe 14, and the water outlet end of user 13 is connected to the cooling water outlet.
Each circulating water pump 3 is provided with a variable frequency motor 4 for driving the circulating water pump to operate, the water outlet end of each circulating water pump 3 is provided with a pressure gauge 5 for measuring the water outlet pressure of the circulating water pump, the water outlet end of one circulating water pump 3 is also connected with a platinum resistance thermometer 6, and the platinum resistance thermometer 6 and the pressure gauge 5 are both arranged in front of the header pipe 14. Two water inlet ends of the condenser 8 are respectively provided with a flowmeter 7.
The flowmeter 7 and the liquid level meter 2 are both connected to a control cabinet 11, and the control cabinet 13 is a control cabinet such as GE Xinhua, ABB or Hitachi, and has the functions of converting field process signals (temperature, pressure, flow, liquid level and the like) into digital signals, storing the digital signals in a main controller and displaying the digital signals to an operator through a human-computer interface (usually an industrial personal computer); the operator can also send commands to the field device via the human-machine interface, such as opening and closing valves, adjusting the rotational speed of the frequency converter, etc. The control 11 simultaneously controls the operating frequency of the circulating water pump 3.
The control cabinet 13 is connected with an upper computer 14, the upper computer 14 is a computer, and a DCS control system is stored in the upper computer (14).
The design and working principle of the invention are as follows:
under the condition that the temperature of circulating cooling water and the generating power of the unit are not changed, the back pressure of the unit is controlled by the change of the cooling water flow, and the operation mode of the circulating water pump 3 determines the cooling water flow entering the condenser 8. The cooling water flow is increased, the back pressure of the unit is reduced, the output of the unit is increased, but the power consumption of the circulating water pump is also increased at the same time. Under different running modes of the circulating water pump, the output increase value of the unit is beneficial to energy conservation, but the power consumption increase of the circulating water pump is unfavorable to energy conservation, so the output increase value of the unit is positive, and the power consumption increase value of the circulating water pump is negative. The sum of the two is the maximum, which is the optimized operation mode of the unit.
According to the backpressure and unit output correction curve provided by the relevant steam turbine manufacturer, the relation between the micro-output of the unit and the pressure of the circulating water pump 3 and the condenser 8 under different power generation powers of the unit is obtained as follows:
ΔNT＝f1(N,Pk) (1)
in the formula: delta NT-a micro-incremental force, kW;
n- -the power of the circulating water pump, kW;
Pk-condenser pressure, kPa;
f1-coefficient.
The relation between the pressure of the condenser 8 and the flow rate of the cooling water under the current cooling water inlet temperature condition can be obtained through experiments, and when the cooling water inlet temperature changes, the relation between the pressure of the condenser 8 and the power of the unit is determined through conversion of the variable working condition characteristics of the condenser 8.
Pk＝f2(N,t,W) (2)
In the formula: t- -cooling water inlet temperature, DEG C;
w- -cooling water flow, m3/s；
f2-coefficient.
When the circulating water pump 3 is in different operation modes, the relation between the cooling water flow of the condenser 8 and the power consumption of the circulating water pump is obtained:
Np＝f3(W) (3)
in the formula: n- -the power of the circulating water pump, kW;
f3-coefficient.
The optimal operation backpressure is an objective function taking the unit power, the cooling water inlet temperature and the cooling water flow as variables, and is the condenser pressure when the difference between the increment of the unit power and the power consumption increment of the circulating water pump is maximum in magnitude, namely:
F(N,t,W)＝ΔNT-ΔNp (4)
in the mathematical sense, when
Figure BDA0002738088820000081
When the pressure of the unit corresponding to the cooling water flow of the condenser 8 is an optimal value, namely
Figure BDA0002738088820000082
The cold end optimization test is conducted through the theoretical guidance, the frequency of the circulating water pump is changed in the process, the cooling water flow entering the condenser is measured under different tide levels, and then the cooling water flow can be fitted into a function with the frequency of the circulating water pump 3 and the liquid level of the forebay 10 as variables, so that the accuracy of the cooling water flow is guaranteed in the optimization process.
And combining the result of cold end optimization, and realizing the related optimization process in the DCS. According to the conditions of condenser performance, unit load, circulating water temperature and the like, calculating the micro-increase output corresponding to different circulating water pump operation modes (different frequency converter frequencies), and determining the optimal frequency of the circulating water pump frequency converter on line, wherein the optimal frequency corresponds to the optimal vacuum of the unit. The development is performed in the locomotive DCS system by the following algorithm description. The optimal frequency of the circulating pump motor is selected by the unit under different loads, and the automatic frequency conversion of the circulating pump of the seawater circulating water system is realized.
And combining the results of cold end optimization, and realizing the related optimization process in DCS (distributed control system). According to the performance of the condenser 8, the load of the unit, the temperature of circulating water and other conditions, the micro-increase output corresponding to different running modes (different frequency converter frequencies) of the circulating water pump 3 is calculated, and the optimal frequency of the frequency converter of the circulating water pump 3 is determined on line and corresponds to the optimal vacuum of the unit. The logic optimization is performed in the locomotive DCS by the following algorithmic description. The specific optimization measures and method steps are as follows:
and step 1, fitting through the heat loads of the condensers 8 corresponding to different unit loads to obtain a formula of the heat loads of the condensers 8.
QCON＝A×POWER-B (6)
In the formula (6), QCONIs the heat load of the condenser 8, MW; pOWERLoad on unit (known quantity), MW. A. B can be fitted according to the nearest performance test of the unit, and A and B are calculation coefficients
Step 2, by obtaining the heat load, the temperature rise value of the cooling water at the two ends of the condenser 8 can be calculated:
Dt，CW＝QCON÷GCW÷ρ÷C (7)
in the formula (7), Dt,CWThe temperature rise temperature of cooling water is DEG C; gCWFor cooling water flow (measured by ultrasonic flowmeter 7), m3H; rho is the density of cooling water, kg/m3(ii) a C is the specific heat capacity at constant pressure, kJ/(kg-DEG C).
Step 3, in order to calculate the logarithmic mean difference of the condenser 8, the heat transfer coefficient of the condenser 8 needs to be calculated,
KTEST＝FD×vCW 1/2×FT,TEST×FM×CF,TEST (8)
in the formula (8), KTESTThe heat transfer coefficient of the condenser 8; fDThe correction coefficient of the outer diameter of the cooling pipe of the condenser 8 can be set; v. ofCWFlow velocity in cooling tubes, m/s) (flow/area); fT,TESTThe inlet water temperature correction coefficient (fixed correction curve); fMThe correction coefficient (fixed correction curve) of the wall thickness of the pipe can be taken as a fixed value; cF,TESTThe cleaning coefficient is determined by the operation mode, the cleaning coefficient is obtained through the last condensation test, then a corresponding value is given according to each operation mode, meanwhile, the cleaning coefficient is considered to change along with the operation of the unit, and technicians in a power plant can calculate the cleaning coefficient and modify the value in logic.
vCW＝GCW÷STL (9)
In the formula (9), STLIs the flow area, m2(the unit parameters are known).
And 4, calculating the average logarithmic difference value to reflect the heat transfer of the condenser 8 in order to obtain the heat transfer end difference of the condenser 8.
LMTD＝QCON÷KTEST÷SC (10)
In the formula (10), LMTDLog mean difference, deg.C; sCThe cooling area (determined by the condenser 8).
Step 6, determining the heat transfer end difference of the condenser 8
Dt,TER＝Dt,CW/[EXP(Dt,CW/LMTD)-1] (11)
In formula (11), Dt,TERThe temperature is the heat transfer end difference of the condenser 8.
Step 7, determining the saturation temperature of the condenser 8 under pressure
tSAT＝tCWI+Dt,CW+Dt,TER， (12)
In the formula (12), tSATThe saturation temperature at 8 deg.C under the pressure of the condenser; t is tCWIIs the inlet water temperature of the cooling water at DEG C. Passing through tSATLooking up a table to obtain the pressure P of the condenser 8k。
And 8, determining the micro-increase force.
ΔNT＝-1×PP,TEST×POWER/1 000-Np (13)
In formula (13), Δ NTIn order to slightly increase the output, kW; pP,TESTFor the back pressure to load correction factor, the pressure P passing through the condenser 8 during usekObtaining the correction coefficient, wherein the correction coefficient is a known curve given by a steam turbine manufacturer aiming at different units, and the value can be obtained from a curve given by a host equipment manufacturer; pOWERThe load of the unit is taken as the load; n is a radical ofpThe power consumption of the circulating water pump 3 can be obtained directly from the control cabinet 11, and the control cabinet 11 is obtained from electric field data, kW.
The upper computer 14 stores the whole control system, the control system comprises an acquisition module, a calculation module and an output module, and the acquisition module is used for acquiring the unit load P from the control cabinet 13OWERObtaining the flow rate G of the cooling water through an ultrasonic flowmeterCWAnd the liquid level of the front pool of the circulating water pump is measured by the first liquid level meter 2 and the second liquid level meter 3;
and the calculation module obtains the frequencies of the first circulating water pump 4 and the second circulating water pump 8 according to the numerical values input by the acquisition module and the existing parameters.
Specifically, the calculation module compares micro-increase output forces calculated by different flow values under different circulating water pump operation modes through a computer, the flow of the circulating pump when the micro-increase output force is maximum is output flow, specifically, the micro-increase output force corresponding to each output flow is calculated through a formula (6) -a formula (13), the flow corresponding to the micro-increase output force which is maximum is selected as the output flow, as the frequency change of the circulating water pump can continuously adjust the circulating water flow, and meanwhile, the influence of the tide level on the flow is considered, the tide level value is combined with the output flow, a fixed relation is fitted through tests on the tide level value and the change value of the flow, the formula is placed in an upper computer 12, and the frequency of the frequency converter can be directly determined according to the tide level corresponding to the liquid level meter 2. On the basis of the online operation optimization of the circulating water pump, the optimal frequency value is directly fed back to a circulating water pump frequency converter setting system according to the obtained optimal frequency of the frequency converter, and the intelligent frequency control of the circulating water pump frequency converter is realized.
The output module inputs the obtained frequency of the circulating water pumps into the control cabinet 11, and the control cabinet 11 controls the corresponding variable frequency motors 4 of the two circulating water pumps 3 so as to control the operating frequency of the circulating water pumps 3.
During the shutdown period of the unit, related conclusions obtained by optimizing the operation of the cold end system of the steam turbine are used, an operation optimization algorithm is directly programmed and developed in the DCS of the unit, the operation optimization function of the variable-frequency circulating water pump is realized, the operation optimization result is directly fed back to the frequency setting system of the frequency converter of the circulating water pump, and the operation of the circulating water pump is intelligently controlled. When the unit operates again, the purpose that the unit automatically optimizes and obtains the optimal frequency of the running of the pump according to the real-time cooling water inlet temperature and the load of the unit is achieved, and the purpose that the running of the pump is automatically performed according to the frequency is achieved. Therefore, the running of the circulating pump is finely adjusted, the power consumption of the circulating pump is effectively saved, and the unit is ensured to be at the optimal back pressure running point.
The working principle of the invention is as follows:
circulating cooling water is filtered by a rotary filter screen 1 and then enters a front pool 10 in front of a circulating water pump, the liquid level of the circulating water in the front pool 10 is measured by a liquid level meter 2, the circulating water is pressurized by the circulating water pump 3 in the front pool 10 and then enters a main pipeline 14 of the circulating water, the outlet pressure of the circulating water pump is measured by respective pressure gauge 5 on the pipeline of the circulating water pump 3, and the water temperature of the outlet of the circulating water pump is measured by a platinum resistance thermometer 6 at the outlet of the circulating water pump; circulating water in the header pipe 14 is divided into two branches, the two branches enter the condenser 8 from two water inlet ends of the condenser 8, meanwhile, one branch of the header pipe 14 is used for pumping out a part of circulating water before entering the condenser 8, the part of circulating water is pressurized by the open water pump 9 and enters the corresponding user 13, and the circulating water returns to the outlet side of the condenser 8 after the open water cools the user 13.
In the process, the control cabinet 11 collects the numerical values of the liquid level meter 2 and the flowmeter 7, the numerical values are fed back to the upper computer 12, the corresponding calculation module in the upper computer 12 performs calculation, and the calculation result is used for controlling the circulating water pump 3 through the control cabinet 11.
Under the condition that the temperature of circulating cooling water and the generating power of the unit are not changed, the back pressure of the unit is controlled by the change of the cooling water flow, and the running mode of the circulating water pump determines the cooling water flow entering the condenser. The cooling water flow is increased, the back pressure of the unit is reduced, the output of the unit is increased, but the power consumption of the circulating water pump is also increased at the same time. Under different circulating water pump operation modes, the output increase value of the unit is different from the power consumption increase value of the circulating water pump, and the power consumption increase of the circulating water pump can offset the output increase value of the unit. Therefore, the condenser operating backpressure should be maintained at the most economical operating conditions.
And combining the result of cold end optimization, and realizing the related optimization process in the DCS. According to the conditions of condenser performance, unit load, circulating water temperature and the like, calculating the micro-increase output corresponding to different circulating water pump operation modes (different frequency converter frequencies), and determining the optimal frequency of the circulating water pump frequency converter on line, wherein the optimal frequency corresponds to the optimal vacuum of the unit. The development is performed in the locomotive DCS system by the following algorithm description. The optimal frequency of the circulating pump motor is selected by the unit under different loads, and the automatic frequency conversion of the circulating pump of the seawater circulating water system is realized.
Effect of putting into operation
The frequency of a circulating water pump in the seawater circulating system is optimized at the cold end in the DCS system to realize automatic control, and the economical efficiency of the unit is effectively improved. The system also considers the influence of tide level change on the cooling water flow, and effectively avoids the situation that manual adjustment is not in place and is not timely enough through automatic control.
The invention discloses a circulating water system for automatically optimizing and adjusting the frequency of a circulating water pump, which comprises a condenser cooling water inlet and outlet pipeline, a high-voltage frequency converter, a guided wave radar liquid level meter, a pump outlet pressure gauge, a pump outlet platinum resistance thermometer, a control system and the like. For cold end optimization of a circulating water pump in a seawater circulating water system with a frequency conversion function, an optimization curve is given in a traditional method, then the frequency is adjusted by operating personnel, and meanwhile, the influence of the change of the tide level on the flow is not considered during optimization. Because the condition of the pipeline has great influence on the measurement of the cooling water flow, if a plurality of units adopt an on-line flow measurement mode, the precision of the selected common flowmeter is low, the influence on the accuracy of an operation optimization result is great, and the investment cost is high by selecting an imported high-precision on-line flowmeter. The system monitors the change of the tide level through a guided wave radar liquid level meter installed in a front pool of the circulating water pump. The flow rate of the circulating pump when the micro-output force is maximum is the output flow rate, the frequency change of the circulating pump can continuously adjust the circulating water flow rate, and meanwhile, the influence of the tide level on the flow rate is considered, so the frequency of the frequency converter can be determined through the output flow rate and the tide level value in combination according to the corresponding relation. By compiling the programs into the unit DCS system, the unit can select the optimal circulating pump motor frequency under different loads, and the circulating water pump in the seawater circulating water system can be automatically switched in a variable frequency mode.

Claims (10)

1. A method for automatically optimizing and adjusting the running frequency of a circulating water pump is characterized in that the load of a unit and the liquid level of a forebay (10) are collected in real time, and the micro-increase output of the unit is determined by combining the parameters of the unit; when the micro-increase output of the unit is the maximum value, the target output flow of the circulating water pump (3) is obtained; determining the running frequency of the circulating water pump (3) through the target output flow of the circulating water pump (3) and the liquid level of the forebay (10); the circulating water pump (3) operates according to the operating frequency.
2. The method for automatically optimizing and adjusting the operating frequency of a circulating water pump according to claim 1, wherein the determination of the micro-boost power of the unit comprises the following steps:
step 1, collecting unit load, cooling water flow of a condenser (8), power consumption of a circulating water pump (3) and liquid level of a forebay (10);
step 2, determining the heat load of the condenser (8) corresponding to the unit load, and further determining the temperature rise value of the cooling water at the two ends of the condenser (8);
step 3, determining the heat transfer end difference of the condenser (8) according to the temperature rise value of the cooling water and the logarithmic mean difference of the condenser (8);
step 4, obtaining the saturation temperature of the condenser (8) through the heat transfer end difference of the condenser (8), the temperature rising value of the cooling water at the two ends of the condenser (8) and the inlet temperature of the cooling water, and further obtaining the pressure corresponding to the saturation temperature of the condenser (8);
and step 5, determining the micro-increase output through the pressure corresponding to the saturation temperature of the condenser (8), the unit load and the power consumption of the circulating water pump (3).
3. Method for automatically optimizing and adjusting the operating frequency of a circulating water pump according to claim 2, characterized in that in step 2, the heat load Q of the condenser (8)CONThe calculation formula is as follows:
QCON＝A×POWER-B (6)
wherein, POWERA and B are calculation coefficients;
cooling water temperature rise value Dt,CWThe calculation formula of (2) is as follows:
Dt，CW＝QCON÷GCW÷ρ÷C (7)
wherein G isCWIs the cooling water flow rate, m, of the condenser (8)3H; rho is the density of cooling water, kg/m3(ii) a C is the specific heat capacity at constant pressure, kJ/(kg-DEG C).
4. The method for automatically optimizing and adjusting the running frequency of the circulating water pump according to claim 2, wherein in the step 3, the heat transfer end difference D of the condenser (8)t,TERThe calculation formula of (2) is as follows:
Dt,TER＝Dt,CW/[EXP(Dt,CW/LMTD)-1] (11)
wherein D ist,CWThe temperature of cooling water is raised to the degree C, LMTDThe mean logarithmic difference of the condenser (8) is shown.
5. Method for automatically optimizing and adjusting the operating frequency of a circulating water pump according to claim 4, characterized in that the logarithmic mean difference L of the condenser (8)MTDThe calculation formula of (2) is as follows:
LMTD＝QCON÷KTEST÷SC (10)
in the formula, SCTo cool the area, QCONIs the heat load of a condenser (8), KTESTThe heat transfer coefficient of the condenser (8).
6. Method for automatically optimizing and adjusting the operating frequency of a circulating water pump according to claim 5, characterized in that the heat transfer coefficient K of the condenser (8)TESTThe calculation formula of (2) is as follows:
KTEST＝FD×vCW 1/2×FT,TEST×FM×CF,TEST (8)
wherein, FDIs the outside diameter correction coefficient v of the cooling pipe of the condenser (8)CWIs the flow velocity in a cooling pipe in a condenser (8), FT,TESTIs the inlet water temperature correction coefficient of the condenser (8), FMFor the wall thickness correction factor of the cooling tube, CF,TESTIs the cleaning factor.
7. The method for automatically optimizing and adjusting the running frequency of the circulating water pump according to claim 2, wherein in the step 4, the saturation temperature of the condenser (8) is calculated by the formula:
tSAT＝tCWI+Dt,CW+Dt,TER， (12)
in the formula (12), tSATThe saturation temperature of the condenser (8) is DEG C; t is tCWIIs the cooling water inlet water temperature, DEG C;
passing through tSATLooking up a table to obtain a pressure value P corresponding to the condenser (8) at the saturation temperaturek。
8. The method for automatically optimizing and adjusting the operating frequency of the circulating water pump according to claim 2, wherein in the step 5, the operation Δ N is slightly increasedTThe calculation formula of (2) is as follows:
ΔNT＝-1×PP,TEST×POWER/1 000-Np (13)
in the formula, PP,TESTFor the back-pressure-to-load correction factor, PP,TESTCorresponding to the corresponding pressure of the saturation temperature of the condenser (8), NpIs the power consumption of the circulating water pump (3).
9. A system for automatically optimizing and adjusting the operating frequency of a circulating water pump, comprising:
the acquisition module is used for acquiring the load of the unit, the liquid level of the forebay (10) and the parameters of the unit;
the calculation module is used for determining the operating frequency of the circulating water pump (3) through the data acquired by the acquisition module;
and the output module outputs the operating frequency to the circulating water pump (3).
10. The device for automatically optimizing and adjusting the running frequency of the circulating water pump for the system according to claim 9 is characterized by comprising a forebay (10) and a control cabinet (11), wherein two circulating water pumps (3) are connected to the output end of the forebay (10), the output ends of the circulating water pumps (3) are connected to a condenser (8), the output end of the condenser (8) is connected to a cooling water outlet, and the circulating water pumps (3) are connected with a variable frequency motor (4);
two liquid level meters (2) are arranged in the front pool (10), and a flow meter (7) is arranged on a cooling water input pipe of the condenser (8);
the control cabinet (11) collects data of the liquid level meter (2) and the flow meter (7), and the control cabinet (11) controls the running frequency of the circulating water pump (3) through the variable frequency motor (4); the control cabinet (11) is connected with an upper computer (12).
CN202011140392.3A 2020-10-22 2020-10-22 System, device and method for automatically optimizing and adjusting running frequency of circulating water pump Pending CN112228329A (en)

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Application publication date: 20210115