CN114111369A - Method for determining optimal operation mode of natural ventilation cooling tower wet cooling unit circulating water pump in frequency conversion mode - Google Patents

Method for determining optimal operation mode of natural ventilation cooling tower wet cooling unit circulating water pump in frequency conversion mode Download PDF

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CN114111369A
CN114111369A CN202111395252.5A CN202111395252A CN114111369A CN 114111369 A CN114111369 A CN 114111369A CN 202111395252 A CN202111395252 A CN 202111395252A CN 114111369 A CN114111369 A CN 114111369A
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circulating water
water pump
frequency
unit
tower
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CN114111369B (en
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杨海生
李路江
闫晓沛
李宁
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State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Hebei Electric Power Co Ltd
State Grid Hebei Energy Technology Service Co Ltd
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State Grid Corp of China SGCC
Electric Power Research Institute of State Grid Hebei Electric Power Co Ltd
State Grid Hebei Energy Technology Service Co Ltd
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    • 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
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F28—HEAT EXCHANGE IN GENERAL
    • F28B—STEAM OR VAPOUR CONDENSERS
    • F28B11/00—Controlling arrangements with features specially adapted for condensers
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02B—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO BUILDINGS, e.g. HOUSING, HOUSE APPLIANCES OR RELATED END-USER APPLICATIONS
    • Y02B30/00—Energy efficient heating, ventilation or air conditioning [HVAC]
    • Y02B30/70—Efficient control or regulation technologies, e.g. for control of refrigerant flow, motor or heating

Abstract

The invention relates to a method for determining an optimal operation mode under a frequency conversion mode of a circulating water pump of a wet cooling unit matched with a natural ventilation cooling tower, which comprises the following steps: (1) determining the configuration and the operation mode of a unit circulating water pump; (2) collecting performance curve or parameter data; (3) determining actual cooling characteristics of the natural draft cooling tower; (4) determining the resistance characteristic of a circulating water pipeline system; (5) and determining the optimal frequency conversion operation mode of the circulating water pump under a certain load state and a certain environment wet bulb temperature of the unit. The invention solves the problem that the frequency conversion optimal operation mode of the circulating water pump of the wet cooling unit with the natural ventilation cooling tower is difficult to select in the prior art, and has small experimental workload and reliable result.

Description

Method for determining optimal operation mode of natural ventilation cooling tower wet cooling unit circulating water pump in frequency conversion mode
Technical Field
The invention relates to a method for determining an optimal operation mode under a frequency conversion mode of a circulating water pump of a wet cooling unit matched with a natural ventilation cooling tower.
Background
In an open circulating water system of a generator set, a circulating water pump is used as the most important cooling medium conveying equipment of the power plant unit and has the important function of conveying circulating cooling water of the unit to a condenser for heat exchange.
With the development of power units to high capacity and high parameter, the working performance of circulating water pumps in power plants has more and more influence on the economy of the power plants. Taking a steam turbine of a 600MW wet cooling unit as an example, two circulating water pumps are usually operated in a working part in summer under a full load state, the consumed power is about 4000kW, the consumed power accounts for about 0.7% of the plant power rate of the power plant unit, and the power supply coal consumption of the power plant unit is almost affected by about 2 g/kW.h. Therefore, the circulating water pump adopts frequency conversion adjustment as an important technical means for saving energy of a power plant and is increasingly applied.
At present, in a closed circulating water system matched with a natural ventilation cooling tower, although the variable frequency regulation of a circulating water pump has the regulation flexibility, the selection of the optimal running mode of the circulating water pump is difficult for field operators and technical managers because of multiple optional running schemes and the performance change of the cooling tower in the middle. Meanwhile, the optimal frequency conversion adjustment mode of the circulating water pump is determined by completely adopting the technical means of field test, although the method is feasible theoretically, the workload of the field test is large, the influence factors are many, and how to determine the optimal operation mode under the frequency conversion mode of the circulating water pump of the wet cooling unit of the natural ventilation cooling tower is a technical problem to be solved urgently on site.
Therefore, a method for determining an optimal operation mode under a frequency conversion mode of a circulating water pump of a wet cooling unit matched with a natural ventilation cooling tower is urgently needed to solve the problems in the field at present.
Disclosure of Invention
The invention aims to provide a method for determining an optimal operation mode under a variable frequency mode of a circulating water pump of a wet cooling unit of a natural ventilation cooling tower, which has small experimental workload and reliable result.
The invention adopts the following technical scheme:
a method for determining an optimal operation mode under a frequency conversion mode of a circulating water pump of a wet cooling unit matched with a natural ventilation cooling tower is characterized by comprising the following steps: (1) the method comprises the following steps that a configuration mode of two circulating water pumps of one unit is adopted, and the two circulating water pumps adopt a frequency conversion regulation mode; the two water pumps adopt a single operation mode or two parallel operation modes; (2) collecting a performance curve of a water pump and parameter data of cold end system equipment; (3) determining actual cooling characteristics of the natural draft cooling tower; (4) determining the resistance characteristic of a circulating water pipeline system; (5) determining an optimal operation mode: collecting various operating parameters of the unit under the current operating load and the environmental wet bulb temperature; determining the current running frequency f of the circulating water pump of the unitbpThe lower circulating water flow and the consumed power; determining the increase delta f of the running frequency of the circulating water pump under the conditions of the current running load of the unit and the environmental wet bulb temperaturebpIn time, the corresponding circulating water flow, the consumed power of a circulating water pump, the change of the outlet water temperature of a cooling tower, the change of the pressure of a condenser and the increment of the coal consumption rate of the power supply of the unit; increasing Δ f according to circulating water pump frequencybpAnd determining an optimized operation mode according to the increment of the coal consumption rate of the power supply of the unit.
Further, the performance curves in the step (2) comprise a flow-lift performance curve and a flow-shaft power performance curve under the power frequency of the water pump;
the parameter data comprises: the minimum pressure difference of an inlet and an outlet of the condenser and the corresponding minimum circulating water flow when the unit condenser rubber ball cleaning system is put into operation; the lowest frequency operation limit value when the unit circulating water pump operates in a frequency conversion mode;
design parameters of the condenser: designing the number of the flow, the design area of the condenser, the type of the condenser pipe, the outer diameter of the condenser pipe, the wall thickness of the condenser pipe, the inner diameter of the condenser pipe, the length of the condenser pipe and the number of the condenser pipes;
design parameters of the natural draft cooling tower: designing the flow rate of circulating cooling water, designing the temperature of a wet bulb in the environment, designing the water inlet temperature of a water tower, designing the water outlet temperature of the water tower, designing the flow rate ratio of water to the designed water of the water tower and the number of heat exchange units of the water tower.
Further, the step (3) specifically comprises the following steps:
(a) carrying out two cooling tower tests;
test conditions 1: controlling the load of the unit to be 100%, wherein the circulating water amount is close to the rated water amount, and the wet bulb temperature is close to the designed wet bulb temperature and deviates to less than 6 ℃;
test condition 2: the load of the unit is controlled to be 100%, the control of the circulating water amount is reduced by about 10% compared with the working condition 1, the wet bulb temperature is close to the designed wet bulb temperature, and the deviation is less than 6 ℃;
recording the flow G of circulating water entering the cooling tower under two test conditionswAnd the temperature t of the circulating water entering the towerw1And the temperature t of the circulating water out of the towerw2Ambient wet bulb temperature ta1Temperature t of air at outlet of water towera2；
(b) Calculating water-air ratio Rwa under two test working conditions;
Figure BDA0003370096450000021
in the formula, hta1、hta2Respectively corresponding to the ambient wet bulb temperature ta1And the temperature t of the air at the outlet of the water towera2The enthalpy value of the saturated humid air is kJ/kg; cwTaking 4.182kJ/(kg. DEG C) as the specific heat capacity of circulating water; rwa is the water-gas ratio;
(c) calculating the cooling numbers of the cooling towers under two test working conditions;
Figure BDA0003370096450000031
in the formula, omegadIs the cooling number of the cooling tower; h iswIs saturated air enthalpy corresponding to water temperature, and the unit is kJ/kg; h isaThe enthalpy value of the wet air corresponding to the water temperature can be expressed in kJ/kg according to the temperature t of the environment wet bulba1Corresponding saturated humid air enthalpy value hta1Water-gas ratio and circulating water inlet tower water temperature tw1And the temperature t of the circulating water out of the towerw2' calculate, formula: h isa＝hta1+Rwa×Cw×(tw2′-tw1)
(d) According to the water-gas ratio and cooling number data of the cooling tower obtained by calculating the two test working conditions, the characteristics of the cooling tower are calculated as follows:
Ωp＝C×(Rwa)-m
wherein C, m is a characteristic coefficient, and is obtained from the water-gas ratio and cooling number data of the cooling tower obtained from two test working conditions, and the formula is as follows:
Figure BDA0003370096450000032
Figure BDA0003370096450000033
in the formula, the lower corner marks "1" and "2" respectively represent data of the test condition 1 and the test condition 2.
Further, the step (4) specifically comprises the following steps:
(A) collecting operation data of two circulating water pump mode operation conditions of one unit; the operation data comprises unit load, condenser inlet circulating water flow, circulating water pump suction forebay water level, cooling tower water distribution well water feeding level, relative elevation of a circulating water pump outlet pipeline relative to a suction forebay, and circulating water pump outlet main pipe pressure; the water level and the liquid level are relative values relative to a certain plane;
(B) the lift of the circulating water pump is as follows:
Figure BDA0003370096450000034
in the formula, H is the lift of a circulating water pump, and the unit is m; p is a radical ofpoutThe pressure of a main pipe of an outlet of the circulating water pump is unit MPa; Δ HpioThe relative elevation of the outlet pipeline of the circulating water pump relative to the suction forebay is m; rho is the density of the circulating water, and can be directly taken as 1000kg/m in the calculation3(ii) a g is gravity acceleration in the unit of N/kg;
(C) the system resistance under the test conditions is as follows:
Δpst＝H-(H2-H1)
in the formula,. DELTA.pstIs the system resistance value, in m; h1、H2Respectively sucking a front pool water level and a cooling tower water distribution well water feeding level for a circulating water pump, wherein the water level and the liquid level are relative values relative to a certain plane and are in a unit of m;
(D) the system resistance characteristic may be expressed as:
Figure BDA0003370096450000041
in the formula, G, GptThe unit m is the circulating water flow of the condenser inlet under any working condition and test working condition respectively3/h；ΔpsThe unit is the system resistance under any working condition and the unit is m; condenser inlet circulating water flow F under test working conditionptAnd carrying out field measurement by adopting a testing instrument.
Further, the current operation load of the unit and the operation parameters of the unit at the ambient wet bulb temperature include: circulating water pump suction forebay water level H1tWater level H of water well of cooling tower2tNumber of circulating water pumps operating and circulating water pump operating frequency fbpRunning load of the unit PGAmbient dry bulb temperature and wet bulb temperature, condenser circulating water inlet temperature t1TAnd the temperature t of the circulating water of the condenser2TCurrent pressure p of condenserct(ii) a Recording the temperature t of circulating water entering the tower under the current operating conditionw1And the temperature t of the circulating water out of the towerw2Ambient dry bulb temperature ta0And wet bulb temperature ta1Temperature t of air at outlet of water towera2。
Furthermore, the current running frequency f of the circulating water pump of the unitbpThe following circulating water flow and consumed power are determined by the following method:
(i) assuming that the circulating water flow under the current running frequency of the circulating water pump is GwT；
(ii) The lift of the current circulating water pump under the operation frequency is as follows:
Figure BDA0003370096450000042
in the formula, HbptThe unit is the lift of the circulating water pump under the current working condition; h1t、H2tRespectively sucking a front pool water level and a cooling tower water distribution well water feeding level by a circulating water pump under the current working condition;
(iii) the lift of the circulating water pump under the power frequency is as follows:
Figure BDA0003370096450000051
in the formula (f)gpThe power frequency is 50 Hz;
(iv) determining the corresponding circulating water pump flow G according to a circulating water pump flow-lift performance curve H-Q under the power frequency of the circulating water pumpwgp；
(v) Determining the frequency conversion frequency lower flow G corresponding to the circulating water pump power frequency lower flowwbp；
Figure BDA0003370096450000052
(vi) Judgment of abs (G)wT-Gwbp) Whether the water flow rate is less than 0.01, if so, the circulating water flow rate of the circulating water pump under the current operating frequency is GwTThe lift is HbptEntering step (vii); if not, set GwT＝Gwbp(iii) returning to step (ii) for recalculation;
(vii) determining the flow G of the circulating water pump under the frequency conversion frequencywTCorresponding shaft power Pwbp(ii) a Firstly, determining the flow G of the circulating water pump according to a circulating water pump flow-shaft power curve P-Q under the power frequency of the circulating water pumpwgpLower corresponding shaft power Pwgp(ii) a Shaft power P at variable frequencywbpComprises the following steps:
Figure BDA0003370096450000053
the power consumed by the circulating water pump at this time is as follows:
Figure BDA0003370096450000054
in the formula, Ppbp、PwbpRespectively the consumed electric power and the shaft power under the variable frequency of the circulating water pump, and the unit kW is; etaM、ηfcAnd respectively taking corresponding design values of the motor efficiency and the frequency converter efficiency of the circulating water pump in unit percent.
Further, the change of the outlet water temperature of the cooling tower is determined by the following method:
i) when the circulating water pump keeps the original frequency, the temperature t of the dry bulb is determined according to the environmenta0And wet bulb temperature ta1Temperature t of air at outlet of water towera2Condition, calculating the air density rho entering the towert1Air density rho out of the towert2Average density of air entering and leaving tower rhotmAnd difference in tower entry and exit air density Δ ρt；
ii) when the circulating water pump keeps the original frequency, determining the current operation load and the water-air ratio under the dry environment wet bulb temperature condition, and solving the tower inlet air flow Ga(ii) a Calculated using the formula:
Figure BDA0003370096450000061
Figure BDA0003370096450000062
in the formula, hta1、hta2Respectively corresponding to the ambient wet bulb temperature ta1And the temperature t of the air at the outlet of the water towera2The enthalpy value of the saturated humid air is kJ/kg; cwTaking 4.182kJ/(kg. ℃) as the specific heat capacity of circulating water; rwabThe water-gas ratio is obtained; gwbpFor maintaining the original frequency of the circulating water pumpThe fixed circulating water flow rate is unit kg/s;
iii) assuming an increase of Δ f in the operating frequency of the circulating water pumpbpAir flow of the rear inlet tower is Ga', calculating the air enthalpy value h of the tower by adopting the following formulata2′；
Figure BDA0003370096450000063
According to the calculated enthalpy value h of the air out of the towerta2', determining the temperature t of the air at the outlet of the water towera2'; the density of air entering the tower is still rhot1Value, calculating the tower air density rhot2', average density of air entering and leaving tower rhotm', and difference in tower entry and tower exit air density Δ ρt′；
Calculating the density difference delta rho of the water tower with equal air resistance and suction forcec', calculated as:
Figure BDA0003370096450000064
in the formula, Gwbp' increase the running frequency of the circulating water pump by delta fbpThe corresponding circulating water flow rate in unit kg/s is calculated according to the new frequency conversion frequency fb′pSolving, taking fb′p＝fbp+Δfbp；
iv) repeating the presumption of four-intake tower air flow Ga', four sets of corresponding density differences Δ ρ are obtainedt' difference in value and density Deltarhoc' numerical value; delta ρ 'is plotted on the abscissa of the air flow rate and on the ordinate of the density difference't-Ga'Curve and Δ ρ'c-Ga' Curve, intersection abscissa G of two curvesa0' i.e. increasing the required circulating water pump operation frequency by delta fbpThe corresponding air flow value entering the tower;
v) calculating the increase delta f of the running frequency of the circulating water pumpbpThe latter new water-gas ratio value;
Figure BDA0003370096450000065
vi) Cooling Tower characteristic Ω obtained in Water Tower testp＝C×(Rwa)-mCalculating the increase delta f of the running frequency of the circulating water pumpbpLate new water-to-air ratio value Rwab' time corresponding to new cooling tower cooling number omegap′；
vii) calculating the increase of the running frequency of the circulating water pumpbpThe temperature rise value of the new cooling tower; according to the following formula:
Figure BDA0003370096450000071
viii) ambient wet bulb temperature ta1New water-to-air ratio Rwab', New Cooling Tower temperature rise Δ tw', calculate Cooling amplitude height value Δ t 'satisfying New Cooling Tower Cooling number'fg(ii) a Amplitude by delta t'fg＝t′w1-ta1Calculating; the specific method comprises the following steps:
suppose a certain high value Δ t'fgThen the water tower outlet water temperature t 'can be solved'w1＝Δt′fg+ta1Water inlet temperature t 'of water tower'w2＝Δtw′+t′w1Combined ambient wet bulb temperature ta1New water-to-air ratio Rwab', the cooling number omega of the cooling tower can be solvedpg' (the specific method can be calculated by referring to the formula in the substep (c) of the step (III));
if ABS (omega)p′-Ωpg') is less than or equal to 0.001, then the amplitude value delta t ' is assumed 'fgThe final water tower outlet water temperature is t 'according to the required amplitude'w1＝Δt′fg+ta1；
If ABS (omega)p′-Ωpg′)>0.001, then assume again amplitude height value Δ t'fgThe foregoing calculation is repeated.
Further, the change in condenser pressure is determined by:
1) determining the heat exchange coefficient of a condenser when the circulating water pump operates at the original frequency under the conditions of the current operation load of the unit and the environmental wet bulb temperature;
calculating the heat load of the condenser under the current operation condition:
QT＝Gwbp·Cw·(t2T-t1T)
calculating the heat exchange coefficient of the condenser under the current operating condition:
Figure BDA0003370096450000072
in the formula: qTkW for the condenser running heat load; kTFor circulating water pump operating frequency fbpTotal heat transfer coefficient of condenser, W/(m)2Deg.c); a is condenser area, m2；tsTFor condenser pressure pctThe corresponding saturation temperature in units; t is t2TThe outlet temperature of the circulating water of the condenser is unit ℃; t is t1TThe inlet temperature of the circulating water of the condenser is unit ℃; gwbpFor circulating water pump operating frequency fbpThe flow rate of circulating water is t/h; cwTaking 4.182kJ/(kg. ℃) as the specific heat capacity of circulating water;
2) determining the circulating water flow of the condenser as Gwbp', the inlet water temperature of the circulating water of the condenser is t1T′(t′1T＝t′w1) Condenser pressure; the method comprises the following steps:
total heat transfer coefficient K after flow change of condensert' is:
Figure BDA0003370096450000081
in the formula, betatIs a performance correction coefficient beta of the circulating water inlet temperature of the condenser when the primary variable frequency of the circulating water pump is operated'tThe performance correction coefficient of the inlet water temperature of the circulating water of the condenser when the circulating water pump changes the frequency and operates; calculating the performance correction coefficient according to the actual circulating water inlet temperature and a method specified by an HEI standard;
the new condenser pressure value is calculated according to the following formula:
Figure BDA0003370096450000082
Figure BDA0003370096450000083
pct′＝f(tct′)
in the formula: p is a radical ofct' increase the running frequency of the circulating water pump by delta fbpThe corresponding new condenser pressure, kPa; t is tct' increase the running frequency of the circulating water pump by delta fbpThe corresponding new condenser saturation temperature value is DEG C; x is the logarithmic mean temperature difference coefficient after the overall heat transfer coefficient is corrected; kt' is the overall heat transfer coefficient after the flow of the condenser is changed; formula pct′＝f(tct') obtaining the corresponding saturation pressure according to the saturation temperature of the steam; the parameter with the prime sign in the formula is increased by delta f corresponding to the running frequency of the circulating water pumpbpThe latter variation parameter.
Further, the unit power supply coal consumption rate increase value is determined by the following method:
1) determining the influence of the pressure change of the condenser on the change of the coal consumption of the unit for power generation; the method comprises the following steps:
circulating water pump frequency increase Δ fbpThe pressure increment of the condenser is as follows:
Δpct＝p′ct-pct
when the generating power of the unit is not changed, the increasing amount of the coal consumption caused by the increase of the pressure of the condenser is as follows:
Figure BDA0003370096450000084
in the formula, K is a correction coefficient of the change of the backpressure of the unit to the change of the heat rate of the unit, the unit is%/kPa, and K is a positive value according to the heat rate provided by a steam turbine manufacturerObtaining a unit correction curve; pGThe unit is the power of the unit under the current working condition, namely kW; Δ pctIncreasing the frequency of the circulating water pump by delta fbpIncreasing the pressure of the condenser in unit of kPa; delta BGThe unit t/h is the increase of the coal consumption for power generation caused by the increase of the pressure of the condenser; bfAccording to the power generation coal consumption and load function b provided by the power plant for the power generation coal consumption rate under the current working condition of the unitf＝f(PG) Obtaining a unit g/kWh;
2) the net power supply coal consumption rate increase value of the computer set is as follows:
the unit power supply coal consumption rate under the original operation condition is as follows:
Figure BDA0003370096450000091
circulating water pump frequency increase Δ fbpThe unit power supply coal consumption rate is changed into:
Figure BDA0003370096450000092
in the formula, bgAnd bg' increase of delta f for original operation condition of unit and frequency of circulating water pump respectivelybpThe later unit supplies power to coal consumption rate, unit g/kWh;
3) calculating the frequency increase deltaf of the circulating water pumpbpTime-dependent unit power supply coal consumption rate increase value delta bg：
Δbg＝bg′-bg。
Further, the frequency of the circulating water pump is increased by delta fbpThe method for determining the optimized operation mode of the increment value of the coal consumption rate of the power supply of the unit specifically comprises the following steps:
in the direction of increasing the frequency of the circulating water pump, if the frequency of the circulating water pump increases for the first time by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgIf the value is negative, the frequency of the circulating water pump is increased by delta fbpIn order to optimize the operation mode, the optimization is continuously carried out towards the direction of increasing the frequency of the circulating water pump; increasing the frequency of the circulating water pump by delta fbpThe parameters obtained later comprise newly obtained running frequency of the circulating water pump, unit power, condenser pressure, circulating water flow and circulating water pump consumed power which are used as initial parameters, and the initial parameters are recalculated; when the frequency of the nth circulating water pump is increased by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgWhen the frequency is positive, the frequency of the (n-1) th circulating water pump is increased by delta fbpThe rear state is an optimized operation mode;
in the direction of increasing the frequency of the circulating water pump, if the frequency of the circulating water pump increases for the first time by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgIf the frequency is positive, the original running frequency of the circulating water pump is in an optimized running mode, and optimization is carried out in the direction of reducing the frequency of the circulating water pump;
in the direction of reducing the frequency of the circulating water pump, if the frequency of the circulating water pump is reduced for the first time by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgIf the value is negative, the frequency of the circulating water pump is reduced by delta fbpIn order to optimize the operation mode, the optimization is continuously carried out in the direction of reducing the frequency of the circulating water pump; reducing the frequency of the circulating water pump by delta fbpThe parameters obtained later comprise newly obtained running frequency of the circulating water pump, unit power, condenser pressure, circulating water flow and circulating water pump consumed power which are used as initial parameters, and the initial parameters are recalculated; when the frequency of the m-th circulating water pump is reduced by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgWhen the frequency is positive, the frequency of the m-1 th circulating water pump is reduced by delta fbpThe rear state is an optimized operation mode; if the frequency of the j (j is less than or equal to m) th circulating water pump is reduced by delta fbpThe circulating water flow in the obtained parameters is lower than the minimum circulating water flow corresponding to the minimum pressure difference of the inlet and the outlet of the condenser when the condenser rubber ball cleaning system is put into operation or the frequency of the circulating water pump is lower than the minimum frequency operation limit value when the circulating water pump is in variable frequency operation, and the frequency of the circulating water pump is reduced by delta f for the (j-1) th timebpThe rear state is an optimized operation mode.
The invention has the beneficial effects that: according to the invention, the actual cooling characteristic of the natural ventilation cooling tower and the resistance characteristic of the circulating water pipeline system are determined through field tests by collecting the performance parameters of the cold end system of the wet cooling unit, the net increase value of the coal consumption rate of the unit power supply after the operation frequency of the circulating water pump changes can be obtained through specific calculation steps, and the net increase value of the coal consumption rate of the unit power supply after the operation frequency of the circulating water pump changes is used as an evaluation index of the optimal operation mode of the circulating water pump to quickly determine the optimal operation mode of the circulating water pump, so that the problem that the frequency conversion optimal operation mode of the circulating water pump of the wet cooling unit of the natural ventilation cooling tower is difficult to select in the prior art is solved.
Detailed Description
The technical solutions in the embodiments of the present invention will be clearly and completely described below, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
A method for determining an optimal operation mode under a frequency conversion mode of a circulating water pump of a wet cooling unit matched with a natural ventilation cooling tower comprises the following steps:
determining the configuration and the operation mode of a unit circulating water pump.
The configuration mode of two circulating water pumps of one unit is adopted, and the two circulating water pumps run in a frequency conversion regulation mode. The two water pumps can be operated singly or in parallel.
And (II) collecting a water pump performance curve and parameter data of cold end system equipment.
And collecting a flow-lift performance curve and a flow-shaft power performance curve under the power frequency provided by a circulating water pump manufacturer. When the test conditions are met on site, the flow-lift performance curve and the flow-shaft power performance curve of the circulating water pump under the power frequency can be actually measured.
The parameter data comprises: the minimum pressure difference of an inlet and an outlet of the condenser and the corresponding minimum circulating water flow when the unit condenser rubber ball cleaning system is put into operation; and (4) the lowest frequency operation limit value when the unit circulating water pump operates in a frequency conversion mode.
Design parameters of the condenser: the design flow number, the design area of the condenser, the type of condenser pipes, the outer diameter of the condenser pipes, the wall thickness of the condenser pipes, the inner diameter of the condenser pipes, the length of the condenser pipes and the number of the condenser pipes.
Design parameters of the natural draft cooling tower: designing the flow rate of circulating cooling water, designing the temperature of a wet bulb in the environment, designing the water inlet temperature of a water tower, designing the water outlet temperature of the water tower, designing the flow rate ratio of water to the designed water of the water tower and the number of heat exchange units of the water tower.
(III) determining actual cooling characteristics of a natural draft cooling tower
(a) Two cooling tower tests were performed.
Test conditions 1: the load of the unit is controlled to be 100%, the circulating water quantity is close to the rated water quantity, and the wet bulb temperature is close to the designed wet bulb temperature and deviates to less than 6 ℃.
Test condition 2: the load of the unit is controlled to be 100 percent, the control of the circulating water amount is reduced by about 10 percent compared with the working condition 1, and the wet bulb temperature is close to the designed wet bulb temperature and deviates to less than 6 ℃.
Recording the flow G of circulating water entering the cooling tower under two test conditionswAnd the temperature t of the circulating water entering the towerw1And the temperature t of the circulating water out of the towerw2Ambient wet bulb temperature ta1Temperature t of air at outlet of water towera2。
(b) The water-to-air ratio for the two test conditions was calculated Rwa.
Figure BDA0003370096450000111
In the formula, hta1、hta2Respectively corresponding to the ambient wet bulb temperature ta1And the temperature t of the air at the outlet of the water towera2The enthalpy value of the saturated humid air is kJ/kg; cwTaking 4.182kJ/(kg. DEG C) as the specific heat capacity of circulating water; rwa is the water to gas ratio required.
(c) The cooling tower cooling numbers for the two test conditions were calculated.
Figure BDA0003370096450000112
In the formula, omegadIs the cooling number of the cooling tower; h iswIs saturated air enthalpy corresponding to water temperature, and the unit is kJ/kg; h isaThe enthalpy value of the wet air corresponding to the water temperature can be expressed in kJ/kg according to the temperature t of the environment wet bulba1Corresponding saturated humid air enthalpy value hta1Water-gas ratio and circulating water inlet tower water temperature tw1And the temperature t of the circulating water out of the towerw2' calculate, formula: h isa＝hta1+Rwa×Cw×(tw2′-tw1)。
(d) According to the water-gas ratio and cooling number data of the cooling tower obtained by calculating the two test working conditions, the characteristics of the cooling tower are calculated as follows:
Ωp＝C×(Rwa)-m
wherein C, m is a characteristic coefficient, and is obtained from the water-gas ratio and cooling number data of the cooling tower obtained from two test working conditions, and the formula is as follows:
Figure BDA0003370096450000121
Figure BDA0003370096450000122
in the formula, the lower corner marks "1" and "2" respectively represent data of the test condition 1 and the test condition 2.
And (IV) testing the resistance characteristic of the closed circulating water pipeline system.
The resistance characteristic of a circulating water pipeline system is determined through the power frequency operation of two circulating water pumps of one unit.
(A) Collecting operation data of two circulating water pump mode operation conditions of one unit; the operation data comprises unit load, condenser inlet circulating water flow, circulating water pump suction forebay water level, cooling tower water distribution well water feeding level, relative elevation of a circulating water pump outlet pipeline relative to a suction forebay, and circulating water pump outlet main pipe pressure; the water level and the liquid level are relative values relative to a certain plane.
(B) The lift of the circulating water pump is as follows:
Figure BDA0003370096450000123
in the formula, H is the lift of a circulating water pump, and the unit is m; p is a radical ofpoutThe pressure of a main pipe of an outlet of the circulating water pump is unit MPa; Δ HpioThe relative elevation of the outlet pipeline of the circulating water pump relative to the suction forebay is m; rho is the density of the circulating water, and can be directly taken as 1000kg/m in the calculation3(ii) a g is the acceleration of gravity in N/kg.
(C) The system resistance under the test conditions is as follows:
Δpst＝H-(H2-H1)
in the formula,. DELTA.pstIs the system resistance value, in m; h1、H2The water level of a front pool sucked by a circulating water pump and the water level of the water on a water distribution well of the cooling tower are respectively, and the water level and the liquid level are relative values in unit of m relative to a certain plane.
(D) The system resistance characteristic may be expressed as:
Figure BDA0003370096450000131
in the formula, G, GptThe unit m is the circulating water flow of the condenser inlet under any working condition and test working condition respectively3/h；ΔpsThe unit is the system resistance under any working condition and the unit is m; condenser inlet circulating water flow F under test working conditionptAnd carrying out field measurement by adopting a testing instrument.
And (V) determining the optimal frequency conversion operation mode of the circulating water pump under a certain load state and a certain environment wet bulb temperature.
(I) And collecting various operating parameters of the unit under the current operating load and the environmental wet bulb temperature.
The current operation load of the unit and the operation parameters of the unit at the environment wet bulb temperature comprise: circulating water pump suction forebay water level H1tWater level H of water well of cooling tower2tNumber of circulating water pumps operating and circulating water pump operating frequency fbpRunning load of the unit PGAmbient dry bulb temperature and wet bulb temperature, condenser circulating water inlet temperature t1TAnd the temperature t of the circulating water of the condenser2TCurrent pressure p of condenserct. Recording the temperature t of circulating water entering the tower under the current operating conditionw1And the temperature t of the circulating water out of the towerw2Ambient dry bulb temperature ta0And wet bulb temperature ta1Temperature t of air at outlet of water towera2。
(II) determining the current running frequency f of the circulating water pump of the unitbpThe lower circulating water flow and the consumed power.
(i) Assuming that the circulating water flow under the current running frequency of the circulating water pump is GwT。
(ii) The lift of the current circulating water pump under the operation frequency is as follows:
Figure BDA0003370096450000132
in the formula, HbptThe unit is the lift of the circulating water pump under the current working condition; h1t、H2tRespectively the water level of the circulating water pump sucking forebay and the water level of the cooling tower water distribution well under the current working condition.
(iii) The lift of the circulating water pump under the power frequency is as follows:
Figure BDA0003370096450000133
in the formula (f)gpThe power frequency is 50 Hz.
(iv) Determining the corresponding circulating water pump flow G according to a circulating water pump flow-lift performance curve H-Q under the power frequency of the circulating water pumpwgp。
(v) Determining the frequency conversion frequency lower flow G corresponding to the circulating water pump power frequency lower flowwbp。
Figure BDA0003370096450000141
(vi) Judgment of abs (G)wT-Gwbp) Whether the water flow rate is less than 0.01, if so, the circulating water flow rate of the circulating water pump under the current operating frequency is GwTThe lift is HbptEntering step (vii); if not, set GwT＝GwbpAnd (5) returning to the step (ii) for recalculation.
(vii) Determining the flow G of the circulating water pump under the frequency conversion frequencywTCorresponding shaft power Pwbp(ii) a Firstly, determining the flow G of the circulating water pump according to a circulating water pump flow-shaft power curve P-Q under the power frequency of the circulating water pumpwgpLower corresponding shaft power Pwgp(ii) a Shaft power P at variable frequencywbpComprises the following steps:
Figure BDA0003370096450000142
the power consumed by the circulating water pump at this time is as follows:
Figure BDA0003370096450000143
in the formula, Ppbp、PwbpRespectively the consumed electric power and the shaft power under the variable frequency of the circulating water pump, and the unit kW is; etaM、ηfcAnd respectively taking corresponding design values of the motor efficiency and the frequency converter efficiency of the circulating water pump in unit percent.
(III) determining the increase delta f of the running frequency of the circulating water pump under the conditions of the current running load of the unit and the environmental wet bulb temperaturebpAnd the corresponding circulating water flow and the circulating water pump consume power.
The determination step is shown as the step (II). The determined circulating water flow is Gwbp', the circulating water pump consumes power Ppbp′。
(IV) determining the increase delta f of the running frequency of the circulating water pump under the conditions of the current running load of the unit and the environmental wet bulb temperaturebpAnd the corresponding outlet water temperature of the cooling tower changes.
i) When the circulating water pump keeps the original frequency, the temperature t of the dry bulb is determined according to the environmenta0And wet bulb temperature ta1Temperature t of air at outlet of water towera2Condition, calculating the air density rho entering the towert1Air density rho out of the towert2Average density of air entering and leaving tower rhotmAnd difference in tower entry and exit air density Δ ρt。
ii) when the circulating water pump keeps the original frequency, determining the current operation load and the water-air ratio under the dry environment wet bulb temperature condition, and solving the tower inlet air flow Ga(ii) a Calculated using the formula:
Figure BDA0003370096450000151
Figure BDA0003370096450000152
in the formula, hta1、hta2Respectively corresponding to the ambient wet bulb temperature ta1And the temperature t of the air at the outlet of the water towera2The enthalpy value of the saturated humid air is kJ/kg; cwTaking 4.182kJ/(kg. ℃) as the specific heat capacity of circulating water; rwabThe water-gas ratio is obtained; gwbpThe unit kg/s is the circulating water flow determined when the original frequency of the circulating water pump is kept.
iii) assuming an increase of Δ f in the operating frequency of the circulating water pumpbpAir flow of the rear inlet tower is Ga', calculating the air enthalpy value h of the tower by adopting the following formulata2′；
Figure BDA0003370096450000153
According to the calculated enthalpy value h of the air out of the towerta2', determining the temperature t of the air at the outlet of the water towera2'; the density of air entering the tower is still rhot1Value, calculating the tower air density rhot2', average density of air entering and leaving tower rhotm', and difference in tower entry and tower exit air density Δ ρt′。
Calculating the density difference delta rho of the water tower with equal air resistance and suction forcec', calculated as:
Figure BDA0003370096450000154
in the formula, Gwbp' increase the running frequency of the circulating water pump by delta fbpThe corresponding circulating water flow rate is in unit kg/s, and the new frequency conversion frequency f 'is adopted according to the step (III)'bpSolving is carried out, f 'is taken'bp＝fbp+Δfbp。
iv) repeating the presumption of four-intake tower air flow Ga', four sets of corresponding density differences Δ ρ are obtainedt' difference in value and density Deltarhoc' numerical value; delta ρ 'is plotted on the abscissa of the air flow rate and on the ordinate of the density difference't-Ga'Curve and Δ ρ'c-Ga' Curve, intersection abscissa G of two curvesa0' i.e. increasing the required circulating water pump operation frequency by delta fbpAnd the corresponding air flow value entering the tower.
v) calculating the increase delta f of the running frequency of the circulating water pumpbpThe latter new water-gas ratio value;
Figure BDA0003370096450000155
vi) Cooling Tower characteristic Ω obtained in Water Tower testp＝C×(Rwa)-mCalculating the increase delta f of the running frequency of the circulating water pumpbpLate new water-to-air ratio value Rwab' time corresponding to new cooling tower cooling number omegap′。
vii) calculating the increase of the running frequency of the circulating water pumpbpThe temperature rise value of the new cooling tower; according to the following formula:
Figure BDA0003370096450000161
viii) ambient wet bulb temperature ta1New water-to-air ratio Rwab', new cooling tower temperature rise Deltatw', calculated to satisfyCooling amplitude height value delta t 'of new cooling tower cooling number'fg(ii) a Amplitude by delta t'fg＝t′w1-ta1Calculating; the specific method comprises the following steps:
suppose a certain high value Δ t'fgThen the water tower outlet water temperature t 'can be solved'w1＝Δt′fg+ta1Water inlet temperature t 'of water tower'w2＝Δtw′+t′w1Combined ambient wet bulb temperature ta1New water-to-air ratio Rwab', the cooling number omega of the cooling tower can be solvedpg' (the specific method can be calculated by referring to the formula in the substep (c) of the step (III)).
If ABS (omega)p′-Ωpg') is less than or equal to 0.001, then the amplitude value delta t ' is assumed 'fgThe final water tower outlet water temperature is t 'according to the required amplitude'w1＝Δt′fg+ta1。
If ABS (omega)p′-Ωpg′)>0.001, then assume again amplitude height value Δ t'fgThe foregoing calculation is repeated.
(VI) determining the increase delta f of the running frequency of the circulating water pump under the conditions of the current running load of the unit and the environmental wet bulb temperaturebpAnd the corresponding change of the condenser pressure and the increased value of the coal consumption rate of the power supply of the unit.
(1) And determining the heat exchange coefficient of the condenser under the current operation load of the unit and the original operation frequency of the circulating water pump under the condition of the environmental wet bulb temperature.
Calculating the heat load of the condenser under the current operation condition:
QT＝Gwbp·Cw·(t2T-t1T)
calculating the heat exchange coefficient of the condenser under the current operating condition:
Figure BDA0003370096450000162
in the formula: qTkW for the condenser running heat load; kTFor circulating water pump operating frequency fbpTotal heat transfer coefficient of condenser, W/(m)2.℃)；A is condenser area, m2；tsTFor condenser pressure pctThe corresponding saturation temperature in units; t is t2TThe outlet temperature of the circulating water of the condenser is unit ℃; t is t1TThe inlet temperature of the circulating water of the condenser is unit ℃; gwbpFor circulating water pump operating frequency fbpThe flow rate of circulating water is t/h; cwThe specific heat capacity of the circulating water is 4.182kJ/(kg. ℃).
(2) Determining the circulating water flow of the condenser as Gwbp', the inlet water temperature of the circulating water of the condenser is t1T′(t′1T＝t′w1) Condenser pressure; the method comprises the following steps:
total heat transfer coefficient K after flow change of condensert' is:
Figure BDA0003370096450000171
in the formula, betatIs a performance correction coefficient beta of the circulating water inlet temperature of the condenser when the primary variable frequency of the circulating water pump is operated'tThe performance correction coefficient of the inlet water temperature of the circulating water of the condenser when the circulating water pump changes the frequency and operates; and calculating the performance correction coefficient according to the actual circulating water inlet temperature and a method specified by an HEI standard.
The new condenser pressure value is calculated according to the following formula:
Figure BDA0003370096450000172
Figure BDA0003370096450000173
pct′＝f(tct′)
in the formula: p is a radical ofct' increase the running frequency of the circulating water pump by delta fbpThe corresponding new condenser pressure, kPa; t is tct' increase the running frequency of the circulating water pump by delta fbpPost-corresponding new coagulationThe steam generator saturation temperature value, DEG C; x is the logarithmic mean temperature difference coefficient after the overall heat transfer coefficient is corrected; kt' is the overall heat transfer coefficient after the flow of the condenser is changed; formula pct′＝f(tct') obtaining the corresponding saturation pressure according to the saturation temperature of the steam; the parameter with the prime sign in the formula is increased by delta f corresponding to the running frequency of the circulating water pumpbpThe latter variation parameter.
(3) And determining the influence of the pressure change of the condenser on the change of the coal consumption of the unit for power generation.
Circulating water pump frequency increase Δ fbpThe pressure increment of the condenser is as follows:
Δpct＝p′ct-pct
when the generating power of the unit is not changed, the increasing amount of the coal consumption caused by the increase of the pressure of the condenser is as follows:
Figure BDA0003370096450000174
in the formula, K is a correction coefficient of the change of the backpressure of the unit on the change of the heat rate of the unit, and is obtained according to a unit correction curve provided by a steam turbine manufacturer, wherein the unit%/kPa and K are positive values; pGThe unit is the power of the unit under the current working condition, namely kW; Δ pctIncreasing the frequency of the circulating water pump by delta fbpIncreasing the pressure of the condenser in unit of kPa; delta BGThe unit t/h is the increase of the coal consumption for power generation caused by the increase of the pressure of the condenser; bfAccording to the power generation coal consumption and load function b provided by the power plant for the power generation coal consumption rate under the current working condition of the unitf＝f(PG) The unit g/kWh was obtained.
(4) And the net power supply coal consumption rate of the computer group is increased.
The unit power supply coal consumption rate under the original operation condition is as follows:
Figure BDA0003370096450000181
circulating water pump frequency increase Δ fbpTime group power supply coalThe rate of consumption was changed to:
Figure BDA0003370096450000182
in the formula, bgAnd bg' increase of delta f for original operation condition of unit and frequency of circulating water pump respectivelybpThe later unit supplies power to coal consumption rate, unit g/kWh;
3) calculating the frequency increase deltaf of the circulating water pumpbpTime-dependent unit power supply coal consumption rate increase value delta bg：
Δbg＝bg′-bg。
(V) increasing delta f according to the frequency of the circulating water pumpbpAnd determining an optimized operation mode according to the increment of the coal consumption rate of the power supply of the unit.
In the direction of increasing the frequency of the circulating water pump, if the frequency of the circulating water pump increases for the first time by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgIf the value is negative, the frequency of the circulating water pump is increased by delta fbpIn order to optimize the operation mode, the optimization is continuously carried out towards the direction of increasing the frequency of the circulating water pump; increasing the frequency of the circulating water pump by delta fbpThe parameters obtained later comprise newly obtained running frequency of the circulating water pump, unit power, condenser pressure, circulating water flow and circulating water pump consumed power which are used as initial parameters, and the initial parameters are recalculated; when the frequency of the nth circulating water pump is increased by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgWhen the frequency is positive, the frequency of the (n-1) th circulating water pump is increased by delta fbpThe rear state is an optimized operation mode;
in the direction of increasing the frequency of the circulating water pump, if the frequency of the circulating water pump increases for the first time by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgIf the frequency is positive, the original running frequency of the circulating water pump is in an optimized running mode, and optimization is carried out in the direction of reducing the frequency of the circulating water pump;
in the direction of reducing the frequency of the circulating water pump, if the frequency of the circulating water pump is reduced for the first time by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgIf the value is negative, the frequency of the circulating water pump is reduced by delta fbpTo optimize the mode of operation, the cycle continuesOptimizing the direction of the reduction of the frequency of the water pump; reducing the frequency of the circulating water pump by delta fbpThe parameters obtained later comprise newly obtained running frequency of the circulating water pump, unit power, condenser pressure, circulating water flow and circulating water pump consumed power which are used as initial parameters, and the initial parameters are recalculated; when the frequency of the m-th circulating water pump is reduced by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgWhen the frequency is positive, the frequency of the m-1 th circulating water pump is reduced by delta fbpThe rear state is an optimized operation mode. If the frequency of the j (j is less than or equal to m) th circulating water pump is reduced by delta fbpThe circulating water flow in the obtained parameters is lower than the minimum circulating water flow corresponding to the minimum pressure difference of the inlet and the outlet of the condenser when the condenser rubber ball cleaning system is put into operation or the frequency of the circulating water pump is lower than the minimum frequency operation limit value when the circulating water pump is in variable frequency operation, and the frequency of the circulating water pump is reduced by delta f for the (j-1) th timebpThe rear state is an optimized operation mode.

Claims (10)

1. A method for determining an optimal operation mode under a frequency conversion mode of a circulating water pump of a wet cooling unit matched with a natural ventilation cooling tower is characterized by comprising the following steps: (1) the method comprises the following steps that a configuration mode of two circulating water pumps of one unit is adopted, and the two circulating water pumps adopt a frequency conversion regulation mode; the two water pumps adopt a single operation mode or two parallel operation modes; (2) collecting a performance curve of a water pump and parameter data of cold end system equipment; (3) determining actual cooling characteristics of the natural draft cooling tower; (4) determining the resistance characteristic of a circulating water pipeline system; (5) determining an optimal operation mode: collecting various operating parameters of the unit under the current operating load and the environmental wet bulb temperature; determining the current running frequency f of the circulating water pump of the unitbpThe lower circulating water flow and the consumed power; determining the increase delta f of the running frequency of the circulating water pump under the conditions of the current running load of the unit and the environmental wet bulb temperaturebpIn time, the corresponding circulating water flow, the consumed power of a circulating water pump, the change of the outlet water temperature of a cooling tower, the change of the pressure of a condenser and the increment of the coal consumption rate of the power supply of the unit; increasing Δ f according to circulating water pump frequencybpAnd determining an optimized operation mode according to the increment of the coal consumption rate of the power supply of the unit.
2. The method according to claim 1, wherein the performance curves in step (2) include a flow-head performance curve and a flow-shaft power performance curve at the power frequency of the water pump;
the parameter data comprises: the minimum pressure difference of an inlet and an outlet of the condenser and the corresponding minimum circulating water flow when the unit condenser rubber ball cleaning system is put into operation; the lowest frequency operation limit value when the unit circulating water pump operates in a frequency conversion mode;
design parameters of the condenser: designing the number of the flow, the design area of the condenser, the type of the condenser pipe, the outer diameter of the condenser pipe, the wall thickness of the condenser pipe, the inner diameter of the condenser pipe, the length of the condenser pipe and the number of the condenser pipes;
design parameters of the natural draft cooling tower: designing the flow rate of circulating cooling water, designing the temperature of a wet bulb in the environment, designing the water inlet temperature of a water tower, designing the water outlet temperature of the water tower, designing the flow rate ratio of water to the designed water of the water tower and the number of heat exchange units of the water tower.
3. The determination method according to claim 1, wherein the step (3) specifically comprises the steps of:
(a) carrying out two cooling tower tests;
test conditions 1: controlling the load of the unit to be 100%, wherein the circulating water amount is close to the rated water amount, and the wet bulb temperature is close to the designed wet bulb temperature and deviates to less than 6 ℃;
test condition 2: the load of the unit is controlled to be 100%, the control of the circulating water amount is reduced by about 10% compared with the working condition 1, the wet bulb temperature is close to the designed wet bulb temperature, and the deviation is less than 6 ℃;
recording the flow G of circulating water entering the cooling tower under two test conditionswAnd the temperature t of the circulating water entering the towerw1And the temperature t of the circulating water out of the towerw2Ambient wet bulb temperature ta1Temperature t of air at outlet of water towera2；
(b) Calculating water-air ratio Rwa under two test working conditions;
Figure FDA0003370096440000021
in the formula, hta1、hta2Respectively corresponding to the ambient wet bulb temperature ta1And the temperature t of the air at the outlet of the water towera2The enthalpy value of the saturated humid air is kJ/kg; cwTaking 4.182kJ/(kg. DEG C) as the specific heat capacity of circulating water; rwa is the water-gas ratio;
(c) calculating the cooling numbers of the cooling towers under two test working conditions;
Figure FDA0003370096440000022
in the formula, omegadIs the cooling number of the cooling tower; h iswIs saturated air enthalpy corresponding to water temperature, and the unit is kJ/kg; h isaThe enthalpy value of the wet air corresponding to the water temperature can be expressed in kJ/kg according to the temperature t of the environment wet bulba1Corresponding saturated humid air enthalpy value hta1Water-gas ratio and circulating water inlet tower water temperature tw1And the temperature t of the circulating water out of the towerw2' calculate, formula: h isa＝hta1+Rwa×Cw×(tw2′-tw1)
(d) According to the water-gas ratio and cooling number data of the cooling tower obtained by calculating the two test working conditions, the characteristics of the cooling tower are calculated as follows:
Ωp＝C×(Rwa)-m
wherein C, m is a characteristic coefficient, and is obtained from the water-gas ratio and cooling number data of the cooling tower obtained from two test working conditions, and the formula is as follows:
Figure FDA0003370096440000023
Figure FDA0003370096440000024
in the formula, the lower corner marks "1" and "2" respectively represent data of the test condition 1 and the test condition 2.
4. The determination method according to claim 1, wherein the step (4) specifically comprises the steps of:
(A) collecting operation data of two circulating water pump mode operation conditions of one unit; the operation data comprises unit load, condenser inlet circulating water flow, circulating water pump suction forebay water level, cooling tower water distribution well water feeding level, relative elevation of a circulating water pump outlet pipeline relative to a suction forebay, and circulating water pump outlet main pipe pressure; the water level and the liquid level are relative values relative to a certain plane;
(B) the lift of the circulating water pump is as follows:
Figure FDA0003370096440000031
in the formula, H is the lift of a circulating water pump, and the unit is m; p is a radical ofpoutThe pressure of a main pipe of an outlet of the circulating water pump is unit MPa; Δ HpioThe relative elevation of the outlet pipeline of the circulating water pump relative to the suction forebay is m; rho is the density of the circulating water, and can be directly taken as 1000kg/m in the calculation3(ii) a g is gravity acceleration in the unit of N/kg;
(C) the system resistance under the test conditions is as follows:
Δpst＝H-(H2-H1)
in the formula,. DELTA.pstIs the system resistance value, in m; h1、H2Respectively sucking a front pool water level and a cooling tower water distribution well water feeding level for a circulating water pump, wherein the water level and the liquid level are relative values relative to a certain plane and are in a unit of m;
(D) the system resistance characteristic may be expressed as:
Figure FDA0003370096440000032
in the formula, G, GptThe unit m is the circulating water flow of the condenser inlet under any working condition and test working condition respectively3/h；ΔpsThe unit is the system resistance under any working condition and the unit is m; condenser inlet circulating water flow F under test working conditionptAnd carrying out field measurement by adopting a testing instrument.
5. The method of claim 1, wherein the operating parameters of the unit at the current operating load and the ambient wet bulb temperature comprise: circulating water pump suction forebay water level H1tWater level H of water well of cooling tower2tNumber of circulating water pumps operating and circulating water pump operating frequency fbpRunning load of the unit PGAmbient dry bulb temperature and wet bulb temperature, condenser circulating water inlet temperature t1TAnd the temperature t of the circulating water of the condenser2TCurrent pressure p of condenserct(ii) a Recording the temperature t of circulating water entering the tower under the current operating conditionw1And the temperature t of the circulating water out of the towerw2Ambient dry bulb temperature ta0And wet bulb temperature ta1Temperature t of air at outlet of water towera2。
6. Method for determining according to claim 1, characterised in that said current frequency f of operation of the unit of circulating water pumpsbpThe following circulating water flow and consumed power are determined by the following method:
(i) assuming that the circulating water flow under the current running frequency of the circulating water pump is GwT；
(ii) The lift of the current circulating water pump under the operation frequency is as follows:
Figure FDA0003370096440000041
in the formula, HbptThe unit is the lift of the circulating water pump under the current working condition; h1t、H2tRespectively sucking a front pool water level and a cooling tower water distribution well water feeding level by a circulating water pump under the current working condition;
(iii) the lift of the circulating water pump under the power frequency is as follows:
Figure FDA0003370096440000042
in the formula (f)gpThe power frequency is 50 Hz;
(iv) determining the corresponding circulating water pump flow G according to a circulating water pump flow-lift performance curve H-Q under the power frequency of the circulating water pumpwgp；
(v) Determining the frequency conversion frequency lower flow G corresponding to the circulating water pump power frequency lower flowwbp；
Figure FDA0003370096440000043
(vi) Judgment of abs (G)wT-Gwbp) Whether the water flow rate is less than 0.01, if so, the circulating water flow rate of the circulating water pump under the current operating frequency is GwTThe lift is HbptEntering step (vii); if not, set GwT＝Gwbp(iii) returning to step (ii) for recalculation;
(vii) determining the flow G of the circulating water pump under the frequency conversion frequencywTCorresponding shaft power Pwbp(ii) a Firstly, determining the flow G of the circulating water pump according to a circulating water pump flow-shaft power curve P-Q under the power frequency of the circulating water pumpwgpLower corresponding shaft power Pwgp(ii) a Shaft power P at variable frequencywbpComprises the following steps:
Figure FDA0003370096440000044
the power consumed by the circulating water pump at this time is as follows:
Figure FDA0003370096440000045
in the formula, Ppbp、PwbpRespectively the consumed electric power and the shaft power under the variable frequency of the circulating water pump, and the unit kW is; etaM、ηfcRespectively circulating water pump motor efficiency and frequency converterEfficiency, unit%, corresponding design values were taken.
7. The method of determining according to claim 6, wherein the change in the cooling tower effluent temperature is determined by:
i) when the circulating water pump keeps the original frequency, the temperature t of the dry bulb is determined according to the environmenta0And wet bulb temperature ta1Temperature t of air at outlet of water towera2Condition, calculating the air density rho entering the towert1Air density rho out of the towert2Average density of air entering and leaving tower rhotmAnd difference in tower entry and exit air density Δ ρt；
ii) when the circulating water pump keeps the original frequency, determining the current operation load and the water-air ratio under the dry environment wet bulb temperature condition, and solving the tower inlet air flow Ga(ii) a Calculated using the formula:
Figure FDA0003370096440000051
Figure FDA0003370096440000052
in the formula, hta1、hta2Respectively corresponding to the ambient wet bulb temperature ta1And the temperature t of the air at the outlet of the water towera2The enthalpy value of the saturated humid air is kJ/kg; cwTaking 4.182kJ/(kg. ℃) as the specific heat capacity of circulating water; rwabThe water-gas ratio is obtained; gwbpThe circulating water flow rate determined when the original frequency is kept for the circulating water pump is in unit kg/s;
iii) assuming an increase of Δ f in the operating frequency of the circulating water pumpbpAir flow of the rear inlet tower is Ga', calculating the air enthalpy value h of the tower by adopting the following formulata2′；
Figure FDA0003370096440000053
According to the calculated enthalpy value h of the air out of the towerta2', determining the temperature t of the air at the outlet of the water towera2'; the density of air entering the tower is still rhot1Value, calculating the tower air density rhot2', average density of air entering and leaving tower rhotm', and difference in tower entry and tower exit air density Δ ρt′；
Calculating the density difference delta rho of the water tower with equal air resistance and suction forcec', calculated as:
Figure FDA0003370096440000054
in the formula, Gwbp' increase the running frequency of the circulating water pump by delta fbpThe corresponding circulating water flow rate in unit kg/s is calculated according to the new variable frequency f'bpSolving is carried out, f 'is taken'bp＝fbp+Δfbp；
iv) repeating the presumption of four-intake tower air flow Ga', four sets of corresponding density differences Δ ρ are obtainedt' difference in value and density Deltarhoc' numerical value; delta ρ 'is plotted on the abscissa of the air flow rate and on the ordinate of the density difference't-Ga'Curve and Δ ρ'c-Ga' Curve, intersection abscissa G of two curvesa0' i.e. increasing the required circulating water pump operation frequency by delta fbpThe corresponding air flow value entering the tower;
v) calculating the increase delta f of the running frequency of the circulating water pumpbpThe latter new water-gas ratio value;
Figure FDA0003370096440000061
vi) Cooling Tower characteristic Ω obtained in Water Tower testp＝C×(Rwa)-mCalculating the increase delta f of the running frequency of the circulating water pumpbpLate new water-to-air ratio value Rwab' time corresponding to new cooling tower cooling number omegap′；
vii) calculatingIncrease of running frequency of circulating water pump by delta fbpThe temperature rise value of the new cooling tower; according to the following formula:
Figure FDA0003370096440000062
viii) ambient wet bulb temperature ta1New water-to-air ratio Rwab', New Cooling Tower temperature rise Δ tw', calculate Cooling amplitude height value Δ t 'satisfying New Cooling Tower Cooling number'fg(ii) a Amplitude by delta t'fg＝t′w1-ta1Calculating; the specific method comprises the following steps:
suppose a certain high value Δ t'fgThen the water tower outlet water temperature t 'can be solved'w1＝Δt′fg+ta1Water inlet temperature t 'of water tower'w2＝Δtw′+t′w1Combined ambient wet bulb temperature ta1New water-to-air ratio Rwab', the cooling number omega of the cooling tower can be solvedpg′；
If ABS (omega)p′-Ωpg') is less than or equal to 0.001, then the amplitude value delta t ' is assumed 'fgThe final water tower outlet water temperature is t 'according to the required amplitude'w1＝Δt′fg+ta1；
If ABS (omega)p′-Ωpg′)>0.001, then assume again amplitude height value Δ t'fgThe foregoing calculation is repeated.
8. The determination method according to claim 7, wherein the change in the condenser pressure is determined by:
1) determining the heat exchange coefficient of a condenser when the circulating water pump operates at the original frequency under the conditions of the current operation load of the unit and the environmental wet bulb temperature;
calculating the heat load of the condenser under the current operation condition:
QT＝Gwbp·Cw·(t2T-t1T)
calculating the heat exchange coefficient of the condenser under the current operating condition:
Figure FDA0003370096440000071
in the formula: qTkW for the condenser running heat load; kTFor circulating water pump operating frequency fbpTotal heat transfer coefficient of condenser, W/(m)2Deg.c); a is condenser area, m2；tsTFor condenser pressure pctThe corresponding saturation temperature in units; t is t2TThe outlet temperature of the circulating water of the condenser is unit ℃; t is t1TThe inlet temperature of the circulating water of the condenser is unit ℃; gwbpFor circulating water pump operating frequency fbpThe flow rate of circulating water is t/h; cwTaking 4.182kJ/(kg. ℃) as the specific heat capacity of circulating water;
2) determining the circulating water flow of the condenser as Gwbp', the inlet water temperature of the circulating water of the condenser is t1T′(t′1T＝t′w1) Condenser pressure; the method comprises the following steps:
total heat transfer coefficient K after flow change of condensert' is:
Figure FDA0003370096440000072
in the formula, betatIs a performance correction coefficient beta of the circulating water inlet temperature of the condenser when the primary variable frequency of the circulating water pump is operated'tThe performance correction coefficient of the inlet water temperature of the circulating water of the condenser when the circulating water pump changes the frequency and operates; calculating the performance correction coefficient according to the actual circulating water inlet temperature and a method specified by an HEI standard;
the new condenser pressure value is calculated according to the following formula:
Figure FDA0003370096440000073
Figure FDA0003370096440000074
pct′＝f(tct′)
in the formula: p is a radical ofct' increase the running frequency of the circulating water pump by delta fbpThe corresponding new condenser pressure, kPa; t is tct' increase the running frequency of the circulating water pump by delta fbpThe corresponding new condenser saturation temperature value is DEG C; x is the logarithmic mean temperature difference coefficient after the overall heat transfer coefficient is corrected; kt' is the overall heat transfer coefficient after the flow of the condenser is changed; formula pct′＝f(tct') obtaining the corresponding saturation pressure according to the saturation temperature of the steam; the parameter with the prime sign in the formula is increased by delta f corresponding to the running frequency of the circulating water pumpbpThe latter variation parameter.
9. The method for determining the power consumption rate of the unit according to claim 8, wherein the unit power supply coal consumption rate increase value is determined by the following method:
1) determining the influence of the pressure change of the condenser on the change of the coal consumption of the unit for power generation; the method comprises the following steps:
circulating water pump frequency increase Δ fbpThe pressure increment of the condenser is as follows:
Δpct＝p′ct-pct
when the generating power of the unit is not changed, the increasing amount of the coal consumption caused by the increase of the pressure of the condenser is as follows:
Figure FDA0003370096440000081
in the formula, K is a correction coefficient of the change of the backpressure of the unit on the change of the heat rate of the unit, and is obtained according to a unit correction curve provided by a steam turbine manufacturer, wherein the unit%/kPa and K are positive values; pGThe unit is the power of the unit under the current working condition, namely kW; Δ pctIncreasing the frequency of the circulating water pump by delta fbpIncreasing the pressure of the condenser in unit of kPa; delta BGFor power generation caused by increased pressure of condenserThe coal consumption is increased, and the unit t/h is increased; bfAccording to the power generation coal consumption and load function b provided by the power plant for the power generation coal consumption rate under the current working condition of the unitf＝f(PG) Obtaining a unit g/kWh;
2) the net power supply coal consumption rate increase value of the computer set is as follows:
the unit power supply coal consumption rate under the original operation condition is as follows:
Figure FDA0003370096440000082
circulating water pump frequency increase Δ fbpThe unit power supply coal consumption rate is changed into:
Figure FDA0003370096440000083
in the formula, bgAnd bg' increase of delta f for original operation condition of unit and frequency of circulating water pump respectivelybpThe later unit supplies power to coal consumption rate, unit g/kWh;
3) calculating the frequency increase deltaf of the circulating water pumpbpTime-dependent unit power supply coal consumption rate increase value delta bg：
Δbg＝bg′-bg。
10. Determination method according to claim 9, characterised in that the increase Δ f according to the circulating water pump frequency is madebpThe method for determining the optimized operation mode of the increment value of the coal consumption rate of the power supply of the unit specifically comprises the following steps:
in the direction of increasing the frequency of the circulating water pump, if the frequency of the circulating water pump increases for the first time by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgIf the value is negative, the frequency of the circulating water pump is increased by delta fbpIn order to optimize the operation mode, the optimization is continuously carried out towards the direction of increasing the frequency of the circulating water pump; increasing the frequency of the circulating water pump by delta fbpThe parameters obtained later include the running frequency of the newly obtained circulating water pump, the power of the unit, the pressure of the condenser, the flow rate of the circulating water and the circulationThe power consumption of the water circulating pump is used as an initial parameter and is recalculated; when the frequency of the nth circulating water pump is increased by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgWhen the frequency is positive, the frequency of the (n-1) th circulating water pump is increased by delta fbpThe rear state is an optimized operation mode;
in the direction of increasing the frequency of the circulating water pump, if the frequency of the circulating water pump increases for the first time by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgIf the frequency is positive, the original running frequency of the circulating water pump is in an optimized running mode, and optimization is carried out in the direction of reducing the frequency of the circulating water pump;
in the direction of reducing the frequency of the circulating water pump, if the frequency of the circulating water pump is reduced for the first time by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgIf the value is negative, the frequency of the circulating water pump is reduced by delta fbpIn order to optimize the operation mode, the optimization is continuously carried out in the direction of reducing the frequency of the circulating water pump; reducing the frequency of the circulating water pump by delta fbpThe parameters obtained later comprise newly obtained running frequency of the circulating water pump, unit power, condenser pressure, circulating water flow and circulating water pump consumed power which are used as initial parameters, and the initial parameters are recalculated; when the frequency of the m-th circulating water pump is reduced by delta fbpCoal consumption rate increase value delta b of power supply of rear unitgWhen the frequency is positive, the frequency of the m-1 th circulating water pump is reduced by delta fbpThe rear state is an optimized operation mode; if the frequency of the j (j is less than or equal to m) th circulating water pump is reduced by delta fbpThe circulating water flow in the obtained parameters is lower than the minimum circulating water flow corresponding to the minimum pressure difference of the inlet and the outlet of the condenser when the condenser rubber ball cleaning system is put into operation or the frequency of the circulating water pump is lower than the minimum frequency operation limit value when the circulating water pump is in variable frequency operation, and the frequency of the circulating water pump is reduced by delta f for the (j-1) th timebpThe rear state is an optimized operation mode.
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JPS57115679A (en) * 1981-01-09 1982-07-19 Toshiba Corp Adjusting device of degree of vacuum in condenser
US20050132735A1 (en) * 2003-12-17 2005-06-23 Yu Chen Transcritical vapor compression optimization through maximization of heating capacity
KR101512273B1 (en) * 2014-08-20 2015-04-14 코넥스파워 주식회사 Steam turbine condenser optimizing system and the method thereof
CN205895562U (en) * 2015-12-25 2017-01-18 唐文魁 High -efficient energy -saving control device of refrigeration cycle water pump
CN112228329A (en) * 2020-10-22 2021-01-15 西安热工研究院有限公司 System, device and method for automatically optimizing and adjusting running frequency of circulating water pump
CN113340127A (en) * 2021-05-27 2021-09-03 苏州西热节能环保技术有限公司 Method for optimizing generator set cold end system with counter-flow mechanical ventilation cooling tower

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS57115679A (en) * 1981-01-09 1982-07-19 Toshiba Corp Adjusting device of degree of vacuum in condenser
US20050132735A1 (en) * 2003-12-17 2005-06-23 Yu Chen Transcritical vapor compression optimization through maximization of heating capacity
KR101512273B1 (en) * 2014-08-20 2015-04-14 코넥스파워 주식회사 Steam turbine condenser optimizing system and the method thereof
CN205895562U (en) * 2015-12-25 2017-01-18 唐文魁 High -efficient energy -saving control device of refrigeration cycle water pump
CN112228329A (en) * 2020-10-22 2021-01-15 西安热工研究院有限公司 System, device and method for automatically optimizing and adjusting running frequency of circulating water pump
CN113340127A (en) * 2021-05-27 2021-09-03 苏州西热节能环保技术有限公司 Method for optimizing generator set cold end system with counter-flow mechanical ventilation cooling tower

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