CN107345777B

CN107345777B - Method for determining annual frequency conversion variable angle optimization operation scheme of half-regulation fan of cooling tower

Info

Publication number: CN107345777B
Application number: CN201710546566.8A
Authority: CN
Inventors: 仇宝云; 陆霞; 罗翌; 冯晓莉; 有力
Original assignee: Yangzhou University
Current assignee: Yangzhou University
Priority date: 2017-07-06
Filing date: 2017-07-06
Publication date: 2019-12-17
Anticipated expiration: 2037-07-06
Also published as: CN107345777A

Abstract

A method for determining a year-round frequency conversion variable angle optimization operation scheme of a half-regulation fan of a cooling tower belongs to the technical field of industrial system energy conservation, and calculates the total ventilation resistance of the cooling tower; calculating and determining the operating parameters of different blade installation angles of a fan in the cooling tower, and calculating and determining the ventilation quantity required by the cooling tower in each week all the year around; setting different numbers of blade installation angles in annual operation by taking the lowest energy consumption as a target, and calculating and determining a variable-frequency variable-angle optimized operation scheme by adopting a method of enabling the air quantity of a fan to be equal to the air quantity required by a cooling tower through variable-frequency and variable-speed every hour; and (3) considering the fan angle modulation and frequency converter cost, comparing the total cost of a plurality of frequency conversion angle conversion optimization operation schemes of different blade installation angle numbers of the cooling tower fan all the year around, and determining the optimal all-year frequency conversion angle conversion operation scheme by using the lowest total cost as a principle, wherein the optimal all-year frequency conversion angle conversion operation scheme comprises the frequency conversion of the fan per hour, the blade installation angle number of all-year around operation, the installation angle numerical value of each blade and the angle conversion time point. The annual frequency-conversion angle-change optimal operation scheme of the cooling tower fan determined by the invention has obvious energy-saving effect.

Description

method for determining annual frequency conversion variable angle optimization operation scheme of half-regulation fan of cooling tower

Technical Field

The invention belongs to the technical field of energy conservation of industrial systems, and relates to an annual frequency conversion and angle change optimization operation scheme of a cooling tower half-regulation fan with a frequency conversion device, in particular to a method for determining the annual frequency conversion and angle change optimization operation scheme of the cooling tower half-regulation fan, which aims to meet the cooling requirement on water and save the total cost of fan operation according to the minimum ventilation quantity required by the cooling tower at different periods all the year around.

Background

energy is an important basis for national economic development, energy shortage becomes a tragus stone for economic development of China due to serious energy waste, and energy conservation and consumption reduction are one of the important tasks of the current economic development of China.

The circulating cooling water system is distributed in the industrial departments of metallurgy, electric power, steel, petrochemical industry and the like, and has high energy consumption, wherein the cooling tower cools circulating water through forced ventilation of a fan, and the fan needs to consume a large amount of electric energy. At present, the energy conservation of a water pump unit and the form of a cooling tower in a circulating cooling water system are researched more, and the research on the energy conservation of a fan in the cooling tower is neglected. The method comprises the following steps of designing and selecting a fan and a blade installation angle of a cooling tower according to the ventilation required by the worst environment working condition all the year around, and operating the fan under the working condition of the designed maximum ventilation all the year around. In fact, the minimum ventilation quantity required by the cooling tower to meet the requirement of cold quantity heat exchange in winter and spring and autumn transition seasons is far lower than the designed maximum ventilation quantity, the overcooling ventilation operation mode of the cooling tower fan which operates at fixed blade installation angle and fixed rotating speed all the year round causes serious energy waste, and the cooling tower fan has huge energy-saving potential.

Disclosure of Invention

The invention aims to overcome the defect that the annual maximum required ventilation quantity of a fan of a cooling tower is designed to generate excessive cooling and cause serious energy waste, and provides a method for determining an annual frequency-conversion variable-angle optimized operation scheme of a half-regulation fan of the cooling tower.

In order to achieve the aim, the invention provides a method for accurately determining an angle-variable optimal operation scheme of a cooling tower half-adjusting fan based on frequency conversion per hour, which comprises the following steps:

A. Calculating total ventilation resistance P of cooling tower_ZAnd the total impedance S.

Taking a counter-flow cooling tower as an example, each part in the tower consists of an air inlet, an air guide device, an air flow turning part before entering a water spraying device, a water spraying filler, a water spraying device supporting beam, a water distribution device, a water collector, an air cylinder ring beam inlet and an air cylinder outlet diffusion section. Wherein, the resistance of the water spraying filler is calculated as follows

A＝(A₁q²+A₂q+A₃)×9.81 (2)

m＝m₁q²+m₂q+m₃ (3)

P_tl＝A·ρV^m (4)

In the formula, P_tlThe resistance of the water spraying filler is Pa; v is the average air velocity of the section of the filler, m/s; q is the total water flow, m³H; f is the area of the water spraying filler zone, m²(ii) a q is the density of the water spray, m³/(m²H); A. m is the resistance coefficient of different fillers, and is obtained by table 3 in the analysis of thermal and resistance properties of plastic water-spraying fillers of cooling towers; a. the₁、A₂、A₃、m₁、m₂、m₃The coefficient, which is related to the type and height of the plastic water-pouring filler, can be found from the related data.

Total ventilation resistance P and total ventilation resistance S of the cooling tower are respectively

In the formula, P is total ventilation resistance of the cooling tower, and m is an air column; s is the total impedance, h²/(10⁸·m⁵) (ii) a G is the ventilation of the cooling tower, ten thousand meters³H; i is the number of each component in the cooling tower; n is the total number of all components in the cooling tower; xi_i、v_i、F_iRespectively is the local resistance coefficient, the air speed of the section m/s and the area of the section m of each component in the cooling tower²。

B. Calculating and determining actual working point parameters of different blade mounting angles when the fan works in the cooling tower: flow rate G_jWind pressure P_jPower N_jAnd efficiency η_j。

The performance curve of the cooling tower fan is provided by an equipment manufacturer, and the wind pressure performance curve of the fan at the jth blade installation angle can be fit by an equation as follows:

in the formula, j is the number of the fan blade installation angle; m is the number of the set fan blade installation angles; p_jThe wind pressure and the m air column when the jth blade of the fan is installed at an angle are set; g_jThe air quantity is ten thousand meters when the jth blade of the fan is arranged at an angle³/h；A_j、B_j、C_j、D_jIs a constant.

The power performance curve of the cooling tower fan at the jth blade mounting angle can be fit by an equation as follows:

In the formula, N_jThe power is kW when the jth blade of the fan is installed at an angle; a. the_j’、B_j’、C_j’、D_j' is a constant.

According to the structure of the cooling tower and the type of the filler, the pressure performance curve equation for determining the requirement of the cooling tower can be expressed as follows:

P＝SG² (10)

Solving the jth blade mounting angle of the fan and the jth formula and the formula (10) of the simultaneous equation (8) to obtain the fan operation air volume G at the jth blade mounting angle of the cooling tower fan_jAnd wind pressure P_j(j ═ 1, 2, 3, …, m), amounting to 2 m.

The obtained wind quantity G of the m blade installation angles of the fan in the cooling tower_jRespectively substituting into the equation (9) of the power performance curve of the corresponding blade installation angle of the fan, and calculating to obtain m powers N_jCalculating the efficiency eta of the installation angle of m blades of the air blower according to the formula (11)_fj

M efficiencies η calculated by equation (11)_fjThe air quantity-efficiency curve and the air quantity-blade of the fan are synthesizedinstallation angle curve:

η_fj＝η_fj(G) (11’)

β_j＝β_j(G) (11’)

In the formula eta_fjMounting angle beta for jth blade of fan_jI.e. the air volume is G_jThe time efficiency is shown in fig. 1, which is a fitted relationship curve between the fan efficiency and the blade installation angle of the cooling tower fan at the rated rotating speed variable-angle operation working point.

C. And calculating and determining the minimum ventilation quantity required by the cooling tower under different environmental conditions.

Under the condition that the heat quantity and the cooling water flow quantity of the cooled equipment need to be removed are fixed, the lower the environmental temperature is, the smaller the humidity is, the smaller the minimum ventilation quantity needed by the cooling tower of the circulating cooling water system is, and the reduction of the ventilation quantity means that the fan of the cooling tower is operated to save energy. The minimum ventilation required for the cooling tower is determined by the following method:

Firstly, the saturated water vapor pressure P' of the air and the relative humidity of the air are respectively calculatedApparent density of wet air ρ', air moisture content x, specific enthalpy of wet air h, and value of saturated air enthalpy h ";

Secondly, performing thermodynamic calculation on the counter-flow cooling tower, and calculating the characteristic number of the filler:

Ω_n'＝Bλ^k (12)

in the formula, omega_n' is the characteristic number (dimensionless) of the working filler of the counter-flow cooling tower; B. k is an experimental constant of the water spraying filler, and is obtained by table 2 in cooling tower plastic water spraying filler thermal and resistance performance analysis; λ is the mass ratio of air (in dry air) entering the packing to water entering the packing, kg (DA)/kg.

By adopting an enthalpy difference method, the cooling number of the cooling tower is as follows:

In the formula, omega_nThe cooling number (dimensionless) for the operating characteristics of the counter-flow cooling tower; k is the coefficient of heat removal of the evaporated water volume (K)<1.0, dimensionless); c_wTaking 4.1868kJ/(kg DEG C), which is the specific heat of water, and kJ/(kg DEG C); h' is saturated air specific enthalpy, namely specific enthalpy of heat release when the air temperature is that the water vapor partial pressure reaches saturated state temperature t, kJ/kg (DA); h is the specific enthalpy of humid air, kJ/kg (DA); dt is the water temperature difference between the inlet water and the outlet water of the infinitesimal filler, and is DEG C; t is t₁The water temperature (DEG C) entering the tower; t is t₂The temperature of water leaving the tower (DEG C); r is_t2kJ/kg is the heat of vaporization of water at the water temperature of the filler.

The number of cooling cycles is preferably calculated by the multistage Simpson's base decomposition method, as follows:

△t＝t₁-t₂ (18)

δt＝△t/n＝(t₁-t₂)/n (19)

δh＝△h/n＝(h₁-h₂)/n (20)

Wherein n is the number of segments;Respectively corresponding to water temperature t₁-δt、t₁-2δt、t₁Saturated air enthalpy at (n-1) δ t, kJ/kg (DA); h'₁、h"₂Respectively the saturated air enthalpy at the water temperature of the inlet and outlet columns, kJ/kg (DA))；h₁、h₂Specific enthalpy, kJ/kg (DA), of the moist air entering and leaving the column, respectively; h is_mIs the average specific enthalpy of the humid air in the column, kJ/kg (DA); delta t is the temperature difference of water entering and leaving the tower; δ t is the water temperature difference of equal segments, DEG C; delta h is the enthalpy difference of air entering and leaving the tower, kJ/kg (DA); δ h is the enthalpy difference of the iso-segments, kJ/kg (DA).

When the requirement on the calculation precision is not high and the delta t is less than 15 ℃, the following simplified calculation can be used:

In the formula, h "_mCorresponding to a water temperature of t_mSaturated air enthalpy, kJ/kg (DA).

As shown in fig. 2, the cooling duty curve represents the number of cooling cycles that the cooling tower needs to have to meet the design conditions of the cooling tower when different gas-water ratios λ are given; the performance curve of the packing represents the cooling capacity of the cooling tower. When the same gas-water ratio is adopted, the cooling task of the cooling tower is equal to the cooling capacity, namely omega_n’＝Ω_nand is the working point of the cooling tower.

According to different environmental conditions, on the premise of meeting the cold quantity, the temperature of inlet and outlet water is controlled, and the corresponding air-water ratio lambda required by the working point of the cooling tower can be obtained through trial calculation. The patent adopts a continuous approximation method for trial calculation, as shown in fig. 3.

Setting a gas-water ratio lambda of the cooling tower₁Taking a plurality of different water temperatures t out of the tower₂A plurality of corresponding cooling numbers omega are calculated according to the above equations (12) to (21)_nfitting a quadratic curve as in fig. 3; according to this lambda₁Calculating the cooling characteristic number (omega) of the trickle filler in the actual operation of the cooling tower_n’)₁Satisfy the cooling number (omega) of the cooling tower_n)₁Equal to the cooling characteristic number (omega) of the water spraying filler_n’)₁Under the premise of (a), the outlet water temperature (t) of the cooling tower corresponding to the equilibrium point is obtained from the curve₂)₁The temperature (t) of the inlet water is determined from the difference between the inlet water and the outlet water₁)₁And then (t) is₁)₁The desired water temperature in the column is not generally needed, and the problems now become: knowing the temperature t of the water entering the tower₁And the temperature difference between water entering and leaving the tower requires the corresponding gas-water ratio lambda, and the method is used for solving.

Referring to FIG. 4, for a given cooling tower fill system, with a gas-to-water ratio λ, a corresponding tower inlet water temperature t can be calculated using the above-mentioned series of equations₁，t₁Is a function of λ, and the function relationship is shown as curve ATB in FIG. 4, and point T on curve ATB is the coordinate (λ, T) to be solved₁λ) cannot directly pass t₁Solving by adopting an iterative computation point-by-point approximation method: knowing that the curve ATB decreases monotonically, two points A, B of lower gas-water ratio and higher gas-water ratio are taken on the curve ATB, and the values of the gas-water ratios are lambda respectively_A、λ_BSetting the required water temperature t_1A>t₁*>t_1BAir-water ratio lambda_A、λ_BRespectively calculating the water temperature t of the inlet tower_1A、t_1BTwo points a and B on the curve ATB are determined, and the equation AB of the straight line passing through A, B is determined as:

Will t₁＝t₁Substituting formula (22), linear interpolation to obtain gas-water ratio lambda of corresponding C' point_C

By λ_CCalculating the actual tower inlet water temperature t of the balance point C on the curve ATB through the formulas (12) to (21)_1CComparing the calculated value t of the water temperature entering the tower_1CIf the requirement of given precision 0.01 is met, the equation of a straight line passing through two points AC is solved by the same method, and t is calculated₁＝t₁Substituting the linear equation of the AC two points, and linearly interpolating to obtain the gas-water ratio lambda of the corresponding D' point_DReuse λ_DCalculating and solving the actual tower inlet water temperature t of the balance point D on the curve ATB_1DCheck t_1DWhether or not to meet the requirement of precision… … until the nth iteration calculation, the point N on the curve approaches the point T infinitely and the formula (24) is satisfied

|t_1N－t₁*|≤0.01 (24)

The method can quickly iterate to approximate the solution t on the curve ATB₁The corresponding gas-water ratio lambda.

In the circulating water system of the fixed water volume operation, can obtain the ventilation volume that corresponds under the different environment operating mode:

G_k＝λ_k·Q·ρ_W/(ρ_k·10000) (k＝1，2，3，…，z) (25)

In the formula, G_kIs the ventilation volume under the k environmental condition of ten thousand meters³/h；ρ_kis the air density in kg/m under the k environmental condition³；ρ_wIs the density of the circulating water, kg/m³；λ_kthe mass ratio of air (calculated by dry air) entering the filler to water entering the filler under the k environmental working condition is kg (DA)/kg; z is the number of different environment working conditions.

D. And (3) calculating and determining a frequency conversion variable angle optimized operation scheme of frequency conversion variable speed per hour for different blade installation angle numbers of the cooling tower half-adjusting fan all the year round.

The model of the fan, the rated rotating speed and the installation angle of the blades are selected according to the maximum ventilation quantity required in summer, which is the most unfavorable environmental working condition of the whole year, and the minimum ventilation quantity required by the cooling tower is greatly reduced compared with the hottest period in summer due to the lower environmental temperature in most of the whole year, and the large environmental temperature difference is generated in one day. Taking the maximum value of the minimum ventilation quantity required by the cooling tower at all times in a week as the required ventilation quantity of the cooling tower in the week, wherein the required ventilation quantity of a certain cooling tower according to the times of the week in a typical year is shown in FIG. 5; for any hour, taking the maximum value of the minimum ventilation quantity required by the cooling tower at all times of the hour as the ventilation quantity required by the cooling tower in the hour, the change rule of the ventilation quantity required in a typical day is shown in fig. 6. Therefore, the cooling tower fan is easy to generate supercooling phenomenon when running according to the rated rotating speed and the blade installation angle, and energy waste is caused.

Considering that most of fan blades adopted by the existing cooling tower are half-adjustable, certain workload and cost are needed for adjusting the blades, and the adjustment of the mounting angles of the blades has certain influence on the normal application of the cooling tower, so that the fan blades are not suitable for frequent adjustment and can be adjusted only for a plurality of times in one year; the cooling tower fan adopts frequency conversion speed regulation operation, except for the initial investment of frequency converter equipment, the frequency conversion is realized only by rotating a knob, multiple times of automatic frequency conversion regulation are easy to realize, and the cost is not increased.

the fan implements frequency conversion optimization operation, only reduces the speed and does not increase the speed in consideration of safety. FIG. 7 is a relationship between the air volume and efficiency of a typical cooling tower fan and the blade installation angle, in the case of constant speed, the actual operation operating point of the cooling tower fan, one blade installation angle corresponding to one air volume and one fan efficiency, 4 peak values of the curve are respectively marked as A, B, C, D, the curve is divided into 5 segments by taking 4 peak values as boundaries, in the first segment of the curve with the left number, the fan efficiency is higher and higher to the highest efficiency point A along with the increase of the blade installation angle, the segment enables the fan to operate at a larger blade installation angle as much as possible on the premise of meeting the minimum air volume required by the cooling tower, the fan efficiency is highest, the air volume is reduced to the minimum air volume required by the cooling tower through frequency conversion and speed reduction, the operation condition is kept similar to the highest efficiency point, and the operation efficiency is highest; the second section of curve AB is a monotone decreasing curve, and the efficiency of the fan is reduced along with the increase of the minimum air quantity required by the cooling tower on the premise of meeting the requirement of the minimum air quantity of the cooling tower, so that the fan blade installation angle is as small as possible; in a curve BB 'section, the fan efficiency of a point B, B' is highest, on the premise of meeting the minimum air quantity required by the cooling tower, the fan blade installation angle of the point B is selected, and then the air quantity is reduced to the minimum air quantity required by the cooling tower through frequency conversion and speed reduction; the right curves of points BC, CD and D of the third section to the fifth section of curves have the same change trend as the section AB', and the fan efficiency is reduced along with the increase of the blade installation angle, so that the fan blade installation angle is as small as possible on the premise of meeting the minimum air quantity required by the cooling tower.

In summary, if the minimum air volume required by the cooling tower is located on the left side of the point a of the curve in fig. 7, the mounting angle of the fan blade should be adjusted to the point a, if the minimum air volume required is located on the section B' B, the mounting angle of the fan blade should be adjusted to the point B, and then the flow of the fan is reduced to the minimum air volume required by the cooling tower through frequency conversion and speed reduction respectively; if the minimum air quantity required by the cooling tower is positioned on the right side of the AB' section or the B point of the curve of figure 7, the corresponding blade installation angle is directly determined on the curve according to the minimum air quantity required to implement operation without frequency conversion and speed regulation.

The frequency converter has the input power of the cooling tower fan with the frequency conversion and speed regulation operation

In the formula, N_bjInputting power, kW, for the frequency converter; rho is air density, kg/m³(ii) a g is the acceleration of gravity, m/s²；η_cThe transmission efficiency of the fan; eta_bpjThe frequency converter efficiency when operating for the jth blade setting angle.

The frequency conversion efficiency of the frequency converter is related to the speed ratio, and can be expressed as:

η_bp＝Aδ²+Bδ+C (27)

In the formula eta_bpthe frequency conversion efficiency of the frequency converter is obtained; delta is a transmission ratio; A. b, C is a constant.

When the minimum ventilation quantity required by the cooling tower is on the left side of the point A and on the BB' section in the graph 7, the mounting angle of the fan blade is adjusted to the point A and the point B respectively, the efficiency of the fan is enabled to be the highest, and then the required air quantity is achieved by adopting frequency conversion and speed reduction. As shown in fig. 8, point a in the figure is point a of the highest efficiency of the fan in fig. 7, taking the required minimum ventilation amount on the left side of point a as an example, the installation angle of the fan blade is adjusted to the angle of point a, and the variable-frequency speed reduction is adopted, so that the operating point of the fan moves downwards and leftwards along the parabola of the similar operating condition, the air quantity of the new operating point of the fan is equal to the ventilation amount required by the cooling tower in the hour, the new operating condition is similar to the original operating condition a, the fan efficiency is kept unchanged, on the premise of meeting the ventilation amount required by the cooling tower, the ventilation amount of the fan is reduced, the operating efficiency is improved, and the purpose of.

The fan operates at a reduced speed, the speed ratio is generally limited to be 0.6-1, the efficiency of a similar working condition point after the reduced speed is considered to be equal to that before the reduced speed, and the efficiency is set as A in the graph of fig. 8₁Point speed ratio of delta_A1Air quantity G is 0.6 ═ G_A1With a power of N_A1Efficiency of fan is eta_fA1，η_fA1＝η_fA＝η_{f max}(ii) a If the cooling tower needs to be ventilated with the ventilation quantity G_A2，G_A2<G_A1Considering the frequency conversion and speed regulation of the fan at A₂Point operation due to delta_A2<0.6，η_fA2<η_fA1But eta_fA2Comparison eta_fA1Little drop, in addition, with A₁Point by point comparison, A₂Point motor efficiency eta_emA2Transmission efficiency eta_cA2And frequency converter efficiency eta_bpA2Little change due to A₂the point air volume is obviously less than A₁The point air quantity and the axial power of the fan similar working condition point are in direct proportion to the third power of the air quantity, so A₂Axial power N of a point_A2Is significantly less than A₁Axial power N of a point_A1As shown in equation (26), the input power N of the frequency converter at point A2_bA2Is significantly less than A₁Input power N of point frequency converter_bA1The rotating speed of the fan is adjusted to be A by frequency conversion₂The point is operated.

Taking weeks as a time unit all year round, assuming that a fan operates at a blade installation angle in a period of a certain period of time from weeks to tens of weeks, requiring that the operating air volume of the fan at a rated rotating speed in the period is equal to the maximum value of the ventilation volume required by each week of a cooling tower in the period, and setting the blade installation angle beta of the fan at the period_twRated speed and wind volume G_twAnd fan efficiency η_ftwOn the basis of the frequency conversion efficiency of each hour, the frequency conversion efficiency of each hour is

in the formula eta_bpthIs at the t_hThe efficiency of a frequency converter for hourly fan operation; g_thIs at the t_hTen thousand meters of operating air quantity of hourly fan³A value of/h equal to the hourly cooling tower required draft; g_twIs at the t_wthe installation angle of the blade of the peripheral fan is beta_twAir quantity at rated speed of rotation, ten thousand m³/h。

The motor efficiency under load of each hour during a day is

In the formula eta_emthIs at the t_hthe hourly fan runs the efficiency of a matched motor; eta_NRated efficiency for the motor; beta is a_thIs at the t_hMotor load rate in hours; k is the ratio of the motor fixed loss factor to the variable loss factor. The size of k: the 2-pole asynchronous motor is 2; the number of the 4-pole and 6-pole asynchronous motors is 1; the number of 8 poles and above is 0.5. The b value is found from table 1 in "calculation of efficiency and power factor of asynchronous motor under any load".

T th_wThe weekly fan system consumes energy in one day:

In the formula, A_twIs the t th of the fan system_wenergy consumption of one day of the week, kW.h; rho_thIs at the t_hHourly air Density, kg/m³；P_thIs at the t_hThe wind pressure and the m air columns are generated when the fan operates for hours; eta_ftwIs at the t_wOperating efficiency of the circulating fan.

Let t_wThe ventilation quantity required by the cooling tower every day in the week is the same according to the change rule of hours, and then the annual operation energy consumption and energy cost of the fan of the cooling tower are as follows:

Y_z＝A_z·y (33)

In the formula, A_zThe power consumption for the annual operation of the cooling tower fan is kW.h; t is t_wThe number of times of year-round operation; t is the number of operating weeks in the whole year, and the continuous operation is counted by 52 weeks for one year; y is_zThe annual energy cost of the cooling tower fan is high; and y is the unit price of the electric charge, yuan/(kW & h).

the large fan blade is in a semi-adjusting type, the installation angle of the blade is manually adjusted, certain cost is needed, and the cost for adjusting the installation angle of the blade is considered when the fan variable-angle variable-frequency optimized operation scheme is determined.

The method comprises the steps that frequency conversion operation is carried out on a fan per hour, under the condition that the mounting angles of blades of the fan in operation all the year round are constant, the time points of angle change are different, the power consumption of the fan in operation all the year round is different, the time points of angle change of the fan all the year round are used as variables, a calculation formula of the power consumption of the fan in operation all the year round is listed, and the power consumption A of the fan in operation of the fan of the mounting angles of the blades of the fan all the year round is calculated_zMinimum value and its corresponding optimal blade setting angle and variable angle time point.

programming to optimize iterative calculation, inputting the wind quantity, wind pressure, power and efficiency of the rated rotating speed and angle-variable operation working point of the fan of the cooling tower, inputting the required wind quantity and corresponding air density of the cooling tower in each week and each hour under the working condition of the annual environment, taking 2 fan blade installation angles operating all the year round as an example, starting trial generation from the minimum blade installation angle of the adjustable fan, setting an angle step of 0.1 degrees, taking the maximum value of the minimum ventilation quantity required by the cooling tower at all the moments in a week as the ventilation quantity required by the cooling tower in the week, comparing whether the air quantity corresponding to the 2 fan blade installation angles of the trial generation meets the ventilation quantity required by each week, if so, the cycle is operated at such a fan blade setting angle and, if not, at another fan blade setting angle, after the mounting angle of the fan blade which operates every week all the year is determined, the operating air quantity of the fan is equal to the ventilation quantity required by the cooling tower in the hour through frequency conversion every hour.

The frequency conversion and speed change of the fan are carried out every hour every day, although the energy consumption of the fan is reduced after the speed change, the energy consumption of the frequency converter is increased after the frequency conversion, so that the input power of the frequency converter before and after the frequency conversion needs to be compared, if the input power of the frequency converter is increased after the frequency conversion and speed change, the reduced power of the fan is not enough to compensate the increased power of the frequency converter, and the frequency conversion and speed change operation is not required in the hour.

The method is used for operating and calculating the annual fan operation energy consumption and energy cost; and then replacing the fan blade installation angle by the step length again, calculating the annual fan operation energy consumption and energy cost again by the method, comparing the minimum annual fan operation energy consumption and energy cost scheme after all the fan blade installation angles are replaced by steps, and obtaining the optimal blade installation angle and the angle change time point of 2 fan blade installation angle operations.

And changing the annual blade mounting angle number of the fan to carry out optimization calculation again to obtain a fan frequency conversion angle change optimization operation scheme of various annual blade mounting angle numbers.

Calculating and drawing up an expression for the air quantity required by each week of the cooling tower under the annual environmental working condition corresponding to the graph of 5

G_r＝G_r(t_w) (34)

Scheme I, 1 blade installation angle in whole year is changed frequency and optimized to operate every hour every day

The ventilation required by the cooling tower in each week in a year is shown in the bar chart of FIG. 9, and the maximum ventilation required by the cooling tower G in the year is satisfied_maxOn the premise of setting 1 blade installation angle beta of the annual running of the fan₁Rated speed fan efficiency of eta_f1The air quantity is G₁Can satisfy G₁≥G_rThe fan is onThe blade mounting angle is operated in a frequency-changing and speed-changing mode every day, and the air quantity of a fan after frequency conversion is equal to the ventilation quantity required by the cooling tower in each hour. Referring to a relation curve of the fan efficiency and the blade mounting angle in fig. 1, the optimal blade mounting angle for 1 type of blade mounting angle operation of the fan all the year is determined by taking the lowest total energy consumption of the fan operation all the year around as a target.

The total energy consumption of the annual fan operation is

And (3) aiming at the minimum total energy consumption of the annual operation of the fan, performing trial calculation on a programming sequence of the formula (35), and solving and determining the annual optimal rated rotating speed operation air volume and the corresponding blade installation angle to minimize the total operation cost.

scheme two, 2 blade mounting angles all year round and frequency conversion optimization operation every hour

As shown in figure 10, the fan adopts 2 blade mounting angles in the whole year to operate in a variable frequency mode every hour, the ventilation quantity of the worst environment working condition in the whole year is ensured, and the optimal blade mounting angles of the fan in the whole year operation with the 2 blade mounting angles are set to be beta respectively₁、β₂The rated rotational speed and the rated air quantity of the fan are respectively G₁、G₂Is provided with beta₁≥β₂，G₁≥G₂The fan efficiency is eta respectively_f1、η_f2Dividing the whole year T week into three sections: in week 1 to t_{2 small}Week and t_{2 is large}Turning down the installation angle of the fan blade to beta from the second to the Tth week₂The air quantity is G₂Can satisfy G₂≥G_rThe fan in the two time periods has rated rotating speed and air quantity G₂Starting frequency conversion operation every hour; at the t th_{2 small}+1 week to t_{2 is large}1 week, increase the fan blade setting angle to beta₁The air quantity is G₁can satisfy G₂≤G_r≤G₁At a rated speed G of the fan during the period₁Hourly variable frequency operation was started. Determining the blade installation angle of the fan in operation every week, carrying out frequency-conversion and speed-change operation on the fan every hour every day, and the total energy consumption of the fan in operation all the year around is

The wind quantity G of the rated rotating speed of the fan blade at the variable angle time demarcation point is used as the target of the lowest total annual operating energy consumption of the fan₁、G₂As variable, for different air quantities G₁、G₂Value, program order calculation formula (36) energy consumption, selecting G with minimum energy consumption₁、G₂Value, to obtain the corresponding blade installation angle beta₁、β₂And a variable angle time point t_{2 small}、t_{2 is large}And obtaining the annual fan frequency-conversion angle-changing optimized operation scheme with 2 blade mounting angles.

Scheme three-year-round 3-blade installation angles per day and per hour variable frequency optimized operation

As shown in FIG. 11, the present solution considers 3 blade setting angles β all year round₁、β₂、β₃Operating efficiency eta respectively corresponding to rated speed of fan_f1、η_f2、η_f3Air volume G₁、G₂、G₃Is provided with beta₁≥β₂≥β₃，G₁≥G₂≥G₃. Dividing the whole year T into five sections: week 1 to t_{3 small}Week and t_{3 is large}From the week to the Tth week, the fan is installed at a blade installation angle beta₃operation, air quantity G corresponding to rated speed₃Can satisfy G₃≥G_rThe secondary air volume G of the fan in the time period₃Starting frequency conversion operation every hour; t th_{3 small}+1 week to t_{2 small}Week and t_{2 is large}Week to t_{3 is large}1 week, fan blade setting angle β₂Operation, air quantity G corresponding to rated speed₂Can satisfy G₃≤G_r≤G₂The secondary air volume G of the fan in the time period₂Starting frequency conversion operation every hour; t th_{2 small}+1 week to t_{2 is large}1 week, fan blade setting angle β₁Operation, air quantity G corresponding to rated speed₁Can satisfy G₂≤G_r≤G₁The secondary air volume G of the fan in the time period₁At the beginning of every hourThe time-varying frequency operates. The blade installation angle of the fan in operation every week is determined, and frequency conversion every hour every day is implemented. The total energy consumption of the annual fan operation is

The wind quantity G of the rated rotating speed of the fan blade at the variable angle time demarcation point is used as the target of the lowest total annual operating energy consumption of the fan₁、G₂、G₃As variable, for different air quantities G₁、G₂、G₃Value, program order calculation formula (37) energy consumption, selecting G with minimum energy consumption₁、G₂、G₃Value, to obtain the corresponding blade installation angle beta₁、β₂、β₃And a variable angle time point t_{3 small}、t_{2 small}、t_{2 is large}、t_{3 is large}And obtaining a fan frequency conversion angle-changing optimized operation scheme of 3 blade mounting angles all the year round.

four-year-round 4-blade installation angles of the scheme are subjected to frequency conversion operation optimization every hour every day

As shown in fig. 12, the method adopts 4 fan blade installation angles operating all the year around, lists the total energy consumption calculation formula of the fan operating all the year around according to the methods of the second scheme and the third scheme, and determines the optimal fan blade installation angle beta by using the minimum total energy consumption of the fan operating all the year around as the target to perform programmed calculation and solution₁、β₂、β₃、β₄Corresponding rated rotational speed air volume G₁、G₂、G₃、G₄And corresponding to the transformation angle time point. The frequency conversion angle-changing optimization operation scheme of the cooling tower fan with 5 and 6 … … blade installation angles can be obtained by the same method all the year round.

E. And comparing the cost of the frequency conversion variable-angle optimized operation scheme for frequency conversion of the annual different blade installation angle numbers of the half-adjusting fan of the cooling tower per hour with the annual optimal frequency conversion variable-angle operation scheme.

The frequency conversion and angle conversion optimization operation scheme cost of frequency conversion of the fan of the cooling tower in different blade installation angle numbers per hour all the year comprises operation energy cost and angle modulation cost, and compared with the non-frequency conversion, the cost of the initial equipment of the frequency converter is increased.

The scheme one year round is based on that the blade installation angle is operated in a frequency conversion mode every hour every day, no angle modulation cost is provided, the frequency conversion operation has the initial cost of a frequency converter, the frequency converter adjustment does not need the cost, and therefore the total annual operation cost of a cooling tower fan is equal to the sum of the operation energy cost of the fan and the initial equipment cost of the frequency converter.

And the schemes two to four are all frequency conversion operation based on different blade installation angle numbers every day and every hour all year around, the angle modulation cost is accumulated and calculated according to the angle conversion times of the operation scheme, and the frequency conversion operation has the frequency converter equipment cost, so that the total annual cost of the cooling tower fan is equal to the sum of the fan operation energy cost, the angle modulation cost and the frequency converter initial equipment cost.

Finally, comparing the equipment operation energy cost and the total operation cost of 6 schemes including the original annual blade installation angle operation scheme of the fan, the annual cooling tower maximum ventilation quantity required blade installation angle operation scheme and the first to fourth schemes, and finally determining the scheme with the minimum total cost as the optimal variable-frequency variable-angle optimal operation scheme.

Drawings

FIG. 1 is a diagram of fan efficiency and blade installation angle at a rated speed variable angle operating point of a cooling tower fan.

FIG. 2 is a graph of cooling duty curves and packing performance for a cooling tower.

FIG. 3 is a graph showing the relationship between the cooling rate of the cooling tower and the temperature of the water leaving the tower.

FIG. 4 is a diagram of a cooling tower equilibrium point calculation iterative approximation method.

FIG. 5 is a chart of typical annual cooling tower weekly ventilation requirements.

FIG. 6 is a graph of the required hourly ventilation for a typical day for a cooling tower.

FIG. 7 is a diagram of a method for determining an optimal operation scheme of variable frequency and variable speed when the mounting angles of different blades of a half-adjusting fan of a cooling tower are adjusted.

FIG. 8 is a diagram for determining the optimal operation speed ratio of the cooling tower half-adjusting fan during variable frequency and variable speed operation.

FIG. 9 is a graph of fan air volume and blade setting angle for a frequency-conversion optimized operation scheme of 1 blade setting angle per hour per day throughout the year.

FIG. 10 is a graph of fan air volume versus blade setting angle for 2 blade setting angles per day per hour of the year round for a variable frequency optimized operating scheme.

FIG. 11 is a graph of fan air volume and blade setting angle for a variable frequency optimized operating scheme of 3 blade setting angles per hour per day throughout the year.

FIG. 12 is a graph of fan air volume versus blade setting angle for a 4 blade setting angles per day per hour frequency conversion optimized operating scheme throughout the year.

Fig. 13 is a graph showing the performance of the LF-42 type fan according to the embodiment of the present invention.

FIG. 14 is a graph showing the relationship between the mounting angle of the variable angle blades of the cooling tower fan and the air flow rate according to the embodiment of the present invention.

FIG. 15 is a graph showing the relationship between the rated rotational speed and the angular operation wind pressure and the wind quantity of the cooling tower fan according to the embodiment of the present invention.

FIG. 16 is a graph showing the relationship between the rated rotational speed and the angular operation efficiency of the cooling tower fan and the air volume according to the embodiment of the present invention.

fig. 17 is a diagram of fan air volume and blade installation angle for a third exemplary year variable frequency variable angle optimized operation scheme according to this embodiment.

Fig. 18 is a gear ratio diagram of variable frequency operation in each hour of a typical day according to the third variable frequency and variable angle optimized operation scheme of the embodiment.

Detailed Description

The following uses the technical solutions of the present invention to further describe the present invention with reference to the accompanying drawings and embodiments, but the present invention should not be construed as being limited thereto.

One workshop of a chemical plant has 1 LDCM-800SC type cooling tower, local atmospheric pressure 754mmHg, density 1.13kg/m³Cooling water flow rate of 800m^3/h. The model of the fan LF-42 is half-regulated, is matched with a three-phase asynchronous motor Y180L-4, the rated power is 22kW, the rated current is 43A, the motor efficiency is 90 percent, the rotating speed is 1470r/min, and is matched with a special frequency converter for a VFD220CP43B-21 type fan water pump. The cooling tower was equipped with a model LJ3 reducer, which was 92% efficient. The unit price of the local electric charge is 0.6 yuan/(kW h).

The original operation scheme is as follows: the fan operates at 13-degree blade installation angle all the year round, and the operation air quantity is45.3769 km in ten thousand³The operating power is 18.4877kW, the input power of the motor is 21.88kW, the total annual operating power consumption is 191144 kW.h, and the total energy cost is 114686 yuan.

The tower structure of the known LDCM-800SC cooling tower is as follows: packing area 46m²Air inlet area 46m²The length of the air guide device is 3 m; net ventilation area 41m for water drenching device²Water distribution device net ventilation area 43m²And the net ventilation area of the water collector is 43m²26m of air duct inlet area²Throat area of wind tube is 14.12m²Area of outlet of air duct 25.53m²The water spraying filler is in an inclined trapezoidal wave shape, the taper angle of the inlet of the air duct is 120 degrees, and the taper angle of the outlet of the air duct is 60 degrees.

In this example, a 1.0m gradient water-spraying packing was selected, and the water-spraying density q obtained from the formula (1) was 17 kg/(m)²H); a can be found from Table 3 in analysis of thermal and resistance properties of Plastic packing for Cooling Tower₁、A₂、A₃0.00054, 0.02372, 0.38310, m respectively₁、m₂、m₃0.00422, -0.12560 and 2.9710 respectively, and substituting the formula (2) and the formula (3) to obtain A-9.2449, m-2.05538; calculating the resistance of the water spraying filler according to the formula (4):

P_tl＝A·ρV^m＝9.2449×1.13×2.86^2.05538＝90.57Pa

The velocity v of each section can be obtained from the equation (5) based on the sectional area and the coefficient of resistance of each component in the cooling tower_iAnd substituting the formula (6) to obtain the total ventilation resistance of the cooling tower:

total resistance P of cooling tower_zTotal impedance of formula (7)

B. Calculating and determining different blades of fan in cooling towerActual working point parameters of the installation angle: flow rate G_jWind pressure P_jAnd efficiency η_j。

FIG. 13 is a graph of the curves of the air volume and the air pressure, the air volume and the power performance of the LF-42 type fan adopted in the cooling tower of the embodiment of the present invention, which is obtained by fitting, and the coefficient A of the 13-degree blade installation angle air volume-air pressure performance curve equation₁₃、B₁₃、C₁₃、D₁₃Respectively-0.000069, 0.0057, -0.4205 and 24.4712, and the formula (8) is substituted to obtain a 13-degree blade installation angle air volume-air pressure performance curve equation of

P₁₃＝-0.000069G³+0.0057G²-0.4205G+24.4712

Obtaining a coefficient A of an air volume-power performance curve equation of the 13-degree blade installation angle through fitting₁₃’、B₁₃’、C₁₃’、D₁₃' are respectively 0.0005, -0.0723, 3.1266 and-24.1831, and are substituted into the formula (9) to obtain the 13-degree blade installation angle air volume-power performance curve equation of

N₁₃＝0.0005G³-0.0723G²+3.1266G-24.1831

And (3) substituting the total impedance S of the cooling tower into an equation (10) to obtain a pressure performance curve equation required by the cooling tower:

P＝0.00514G²

The intersection point of the required pressure performance curve and the air quantity-air pressure performance curve of the fan is the working point of the fan. The flow G of the actual operation working point of the 13-degree blade mounting angle obtained by solving the simultaneous equation is 45.3769 ten thousand meters³And h, wind pressure P is 10.6742m, and power N is 18.4877 kW.

The performance curves of the installation angles of other blades of the fan are fitted by the method, one curve is fitted at intervals of 0.1 degrees from 2 degrees to 22 degrees, 201 wind volume-wind pressure performance curve equations are totally combined to respectively obtain a required pressure performance curve equation (10), and 201 working point parameters are obtained by solving, as shown in fig. 14 and 15.

The obtained wind volume G of 201 blade installation angles of the fan in the cooling tower_jRespectively substituting into the equation (9) of the power performance curve of the corresponding blade installation angle of the fan, and calculating to obtain 201 powers N_jCalculating the efficiency eta at the time of setting the 201 blades of the fan according to the equation (11)_fjAs shown in fig. 16.

Taking an environmental condition as an example, the following is calculated:

Environmental conditions are as follows: atmospheric pressure 100.56kPa, dry-bulb temperature: 27 ℃, wet bulb temperature: at 25 ℃, according to the cooling requirement of the equipment, the maximum temperature of water entering the tower is controlled to be 45 ℃, and the temperature difference between water entering the tower and water leaving the tower is 10 ℃. The saturated water vapor partial pressures at 27 ℃ and 25 ℃ are respectively P_d”＝3.5631kPa、P_s"═ 3.1655kPa, air relative humidity wasThe apparent density of the wet air is rho 1.1569kg/m³The air moisture content x is 0.0193kg/kg (da).

As shown in FIG. 2, when the cooling duty curve of the cooling tower intersects with the packing performance curve, i.e. omega is in the same gas-water ratio_n’＝Ω_nand is the working point of the cooling tower. In order to obtain the balance working point of the cooling tower, trial calculation is carried out, and 3 groups of data are taken: (1) t is t₁＝46℃，t₂＝36℃，t_m＝41℃，λ＝0.39kg(DA)/kg；(2)t₁＝47℃，t₂＝37℃，t_m＝42℃，λ＝0.39kg(DA)/kg；(3)t₁＝48℃，t₂＝38℃，t_m43 ℃ and λ 0.39kg (da)/kg. Taking the first set of data as an example, the following is calculated:

The enthalpy of the wet air entering the tower is calculated to be h₁76.362kJ/kg (DA), the coefficient of heat taken away by substituting the relevant data into formula (14) to obtain the amount of evaporated water is

The enthalpy of the wet air in the tower obtained from the formula (16) is

The average enthalpy of the wet air in the column obtained from formula (17) is

t₁、t₂、t_mCorresponding partial pressures of saturated water vapor of P_t1”＝10.0832kPa、P_t2”＝5.939kPa、P_tm"═ 7.776kPa, the corresponding saturated air specific enthalpies are h respectively₁”＝225.4689kJ/kg(DA)、h₂”＝136.4071kJ/kg(DA)、h_m”＝175.5128kJ/kg(DA)。

Obtaining the cooling number of the cooling tower of formula (21)

Two additional sets of data were calculated according to the method described above, the calculations being shown in table 1:

TABLE 1 λ 0.39kg (DA)/kg balance point A calculation data Table

Finishing to obtain (1) t₂＝36℃,Ω_n＝1.0503；(2)t₂＝37℃,Ω_n＝0.8606；(3)t₂＝38℃,Ω_n0.7258. From this 3 sets of data, as in fig. 3, a curve was fitted:

Selecting 1.0m inclined gradient wave water spraying filler, finding B, k coefficient by table 2 in cooling tower plastic water spraying filler thermal and resistance performance analysis, substituting formula (12) to obtain filler characteristic number

Ω_n'＝Bλ^k＝1.60×0.39^0.64＝0.8758

To satisfy the cooling number omega_nIs equal to characteristic number omega_n’，Let omega_n＝Ω_n', solution of equilibrium point t₂36.9078 ℃. Therefore, the balance point A is obtained with coordinates of (0.39, 46.9078).

Taking 3 groups of data with lambda being 0.49kg (DA)/kg, (1) t₁＝43℃，t₂＝33℃，t_m＝38℃，λ＝0.49kg(DA)/kg；(2)t₁＝44℃，t₂＝34℃，t_m＝39℃，λ＝0.49kg(DA)/kg；(3)t₁＝45℃，t₂＝35℃，t_mλ 0.49kg (da)/kg at 40 ℃. Recalculating according to the above procedure, the specific calculation is shown in table 2:

TABLE 2 data sheet for the calculation of the lambda 0.49kg (DA)/kg balance point B

Finishing to obtain (1) t₂＝33℃,Ω_n＝1.4689；(2)t₂＝34℃,Ω_n＝1.1625；(3)t₂＝35℃,Ω_n0.9566. From this 3 sets of data, as in fig. 3, a curve was fitted:

The filling material with the characteristic number of omega obtained by substituting formula (12)_n'＝Bλ^k＝1.60×0.49^0.641.0136. Let omega_n＝Ω_n', solution of equilibrium point t₂34.6691 ℃. So another balance point B is obtained with coordinates (0.49, 44.6691).

FIG. 4 shows a line connecting the equilibrium points A, B, where the equation for the straight line is t_1AB＝﹣22.387λ+55.63873。

The maximum temperature of the water entering the tower is controlled to be 45 ℃, and the temperature of the water entering the tower at the final approach point is t₁1 ═ 45 ℃, let t₁*＝t_1ABSubstituting the linear equation into the equation (22) at 45 deg.C to obtain the C' point λ of the equation (23)_C’0.4752kg (DA)/kg, point C' was determined as a linear change of A, B points, in turn as λ_C’0.4752kg (DA)/kg were recalculated on the curve using the method described aboveWater temperature t out of tower at balance point C₂When the temperature is 34.9708 ℃, the water temperature t is the temperature of the water entering the tower₁44.9708 deg.C, so that the coordinates of point C are (0.4752, 44.9708), and the formula (24) or | t_1C-t₁*|＝0.0292>0.01, the precision does not meet the requirement, and iterative calculation needs to be continued; comparing the positions of the points on the curve, the desired point of equilibrium T is located between the nearest points A, C, the AC line equation is set forth and T is used₁Substituting at 45 deg.C to obtain the abscissa of point D' as lambda_D’0.4739kg (DA)/kg, further expressed as lambda_DThe temperature t of the water taken out of the tower at the point D of the equilibrium point on the curve is obtained by recalculating the temperature t of the water taken out of the tower by the method₂35.0037 deg.C, D point coordinate of (0.4739, 45.0037), substitution formula (24), | t_1D-t₁*|＝0.0037<0.01, the precision meets the requirement, and the formula (25) is replaced to obtain the ventilation quantity of the calculation working condition:

G_k＝λ_k·Q·ρ_w/(ρ_k10000) ═ 0.4739 × 800 × 1000/1.1569 ═ 32.7634 km³/h

And calculating the minimum ventilation quantity required by the cooling tower under the environmental working conditions at different time all the year around according to the method.

D. And (3) calculating and determining a frequency conversion variable angle optimized operation scheme of frequency conversion of the annual different blade installation angle numbers of the half-adjusting fan of the cooling tower per hour.

In the embodiment, the fan is subjected to frequency conversion operation every hour all year round, and the frequency conversion and angle conversion optimization operation scheme for determining the number of the installation angles of the different blades all year round is solved.

In the embodiment, an asynchronous motor is selected, and the relation between the efficiency of the frequency converter and the speed ratio delta is obtained by fitting an equation according to a formula (27)

η_bp＝-0.0266δ²+0.0992δ+0.9054

As shown in FIG. 9, the maximum air volume G is satisfied all the year round_max41.2454 km³On the premise of h, the aim of minimizing the total energy consumption of the fan in operation all the year round is to tentatively calculate that the mounting angle of the fan at the optimum blade all the year round is 10.1 degrees, namely the point B in figure 7, and the rated rotating speed and the rated air quantity of the fan are 41.9791 ten thousand m³And h, the efficiency of the fan is 80.73%, and the fan is subjected to frequency conversion operation every hour every day, so that the air quantity of the fan is equal to the air quantity required by the cooling tower every hour. In trial calculation, if the input power of the frequency converter is increased after frequency conversion, the frequency conversion is not carried out in the hour. The formula (35) is replaced, and the total annual fan operation energy consumption is A_z＝48289kW·h。

As shown in fig. 10, the fan in the scheme adopts frequency conversion operation per hour under 2 blade installation angles all the year around, and 2 optimal blade installation angles of the fan in operation are calculated by trial to be 10.1 degrees and 6 degrees respectively with the aim of minimizing total energy consumption of the fan in operation all the year around. In the 1 st to 22 nd weeks and the 38 th to 52 th weeks, the fan operates at a blade installation angle of 6 degrees, namely, at the point A in FIG. 7, the rated speed and the rated air quantity of the fan are 35.9505 ten thousand meters³The efficiency of the fan is 88.85 percent, the required air quantity of the cooling tower in the two time periods is met, and the fan is 35.9505 ten thousand meters³The air volume begins to operate in a variable frequency mode; in the 23 rd week to the 37 th week, the fan operates at a blade installation angle of 10.1 degrees, and the rated rotating speed and the air quantity of the fan are 41.9791 km³The efficiency of the fan is 80.73 percent, the required air quantity of the cooling tower in the time period is met, and the fan is 41.9791 ten thousand meters³And the air volume per hour starts to operate in a variable frequency mode. Formula (36) is substituted, and total energy consumption A of annual fan operation_z＝46796kW·h。

As shown in fig. 11, the fan in the scheme selects 3 blade installation angles for operation in the year round per hour in a variable frequency mode, and the 3 optimal blade installation angles for operation of the fan are calculated by trial to be 10.1 degrees, 6.8 degrees and 6 degrees respectively with the aim of minimizing the total energy consumption for the operation of the fan in the year round. As shown in FIG. 17, the fans operated at the blade installation angle of 6 degrees from the 1 st week to the 22 nd week and from the 38 th week to the 52 th week, and the fan air volume was 35.9505 km³The fan efficiency is 88.85 percent, and the fan starts to operate in a frequency conversion mode according to the air quantity; in 23 rd week and 37 th week, the fan operates at a blade installation angle of 6.8 degrees, and the air volume of the fan is 37.0575 km³The efficiency of the fan is 83.60 percent, and the fan starts to operate in a frequency conversion mode according to the air quantity; operating 24 th to 36 th weeks, operating the fan at a blade mounting angle of 10.1 degrees, and windThe machine air volume is 41.9791 ten thousand meters³and h, the fan efficiency is 80.73%, and the fan starts to operate in a variable frequency mode according to the air quantity. The variable-frequency variable-speed ratio of the fan at each hour of the day of week 27 is shown in fig. 18. Substituting formula (37), calculating to obtain total annual fan operation energy consumption A_z＝46675kW·h。

As shown in fig. 12, the fan of the present scheme adopts frequency conversion operation of 4 blade mounting angles per hour all the year around, and with the goal of minimum total energy consumption of the fan operating all the year around, programming trial calculation is performed to solve, it is determined that the 4 optimal blade mounting angles of the fan are 10.1 °, 7.5 °, 6.8 °, and 6 °, 1 st to 22 nd and 38 th to 52 th weeks, the fan operates at a blade mounting angle of 6 °, and the air volume of the fan is 35.9505 km³The fan efficiency is 88.85 percent, and the fan starts to operate in a frequency conversion mode according to the air quantity; in 23 rd week and 37 th week, the fan operates at a blade installation angle of 6.8 degrees, and the air volume of the fan is 37.0575 km³The efficiency of the fan is 83.60 percent, and the fan starts to operate in a frequency conversion mode according to the air quantity; in the 24 th week and the 36 th week, the fan operates at a blade mounting angle of 7.5 degrees, and the air volume of the fan is 38.0542 km³the fan efficiency is 81.13%, and the fan starts to operate in a variable frequency mode according to the air quantity; in the 25 th week to the 35 th week, the fan operates at a blade installation angle of 10.1 degrees, and the air volume of the fan is 41.9791 km³And h, the fan efficiency is 80.73%, and the fan starts to operate in a variable frequency mode according to the air quantity. Calculating to obtain total annual fan operation energy consumption A_z＝44323kW·h。

E. And comparing the cost of the frequency conversion variable-angle optimized operation scheme for frequency conversion of the annual different blade installation angle numbers of the half-adjusting fan of the cooling tower per hour with the annual optimal frequency conversion variable-angle optimized operation scheme.

The half-regulation fan selected for the cooling tower of the embodiment has a blade installation angle range of 2-22 degrees, is applied to the cooling tower of the embodiment, has the highest efficiency point of 6 degrees, has different blade installation angles adopted by the fan of the cooling tower all the year round, has different expenses in various aspects of the frequency conversion angle-changing optimization operation scheme, and compares the original operation scheme of the fan, the annual operation energy consumption, the energy consumption expense, the angle regulation expense, the frequency converter expense and the total expense of 6 schemes of the fan blade installation angle scheme, the frequency conversion of four per hour from the first scheme to the second scheme according to the maximum air volume required by the cooling tower, wherein the electricity cost is calculated according to 0.6 yuan/(kW.h), and the half-regulation fan angle regulation once needs 1000 yuan; the initial investment cost of the special frequency converter for the VFD220CP43B-21 type fan water pump is 4500 yuan, the service life is 10 years, the residual value is 500 yuan, the cost of the frequency converter distributed to each year is 400 yuan, and the scheme cost is shown in Table 3.

TABLE 3 annual cost comparison of the best efficiency time-varying variable-angle optimized operating scheme for the 6-degree blade installation angle of the cooling tower fan in this embodiment

As shown in table 3, for each hourly variable frequency operation scheme, the size and the operation time of the optimal operation blade installation angle of the cooling tower fan are determined according to the lowest operation energy consumption; and for all operation schemes, determining the optimal frequency conversion and angle conversion operation scheme according to the lowest total cost comprising the fan operation energy cost, the angle modulation cost and the frequency converter cost.

Compared with the original scheme, the mounting angle of the blade is adjusted to 9.6 degrees of the maximum air quantity required by the cooling tower all the year around, and the energy cost is saved by 17.36 percent all the year around; the first scheme to the fourth scheme adopt frequency conversion optimization operation per hour, the energy cost saving rate reaches about 75%, and the energy-saving effect is good; along with the increase of the number of the installation angles of the blades adopted all the year round, the cost of the variable-frequency variable-angle operation energy is slightly reduced, and considering the increase of the angle adjusting cost, the total cost is gradually increased along with the increase of the angle adjusting times, so that the first scheme is as follows: the annual optimal blade installation angle is 10.1 degrees, and the hourly frequency conversion is optimized, the annual optimal frequency conversion and angle conversion operation scheme is the annual optimal frequency conversion and angle conversion operation scheme of the cooling tower fan, and compared with the original scheme, the total cost is saved by 74.39%.

If the angle adjusting cost of the scheme two to the scheme four is respectively reduced to 800 yuan, 1600 yuan and 2400 yuan, the annual total cost is respectively 29261 yuan, 30001 yuan and 30784 yuan, the scheme two-2 blade installation angle schemes are the optimal variable-frequency variable-angle optimal operation scheme, and the annual total cost is saved by 74.49%.

Claims

1. The method for determining the annual frequency conversion variable angle optimized operation scheme of the half-regulating fan of the cooling tower is characterized by comprising the following steps of:

Step A: calculating total ventilation resistance P and total ventilation resistance S of the cooling tower;

And B: calculating and determining actual working point parameters of different blade mounting angles when the fan works in the cooling tower: flow rate G_jWind pressure P_jPower N_jAnd efficiency η_j；

And C: calculating and determining the minimum ventilation quantity required by the cooling tower under different environmental working conditions;

Step D: calculating and determining a frequency conversion variable angle optimized operation scheme of frequency conversion variable speed per hour for different blade installation angle numbers of a cooling tower half-adjusting fan all the year round;

Step E: calculating and comparing the cost of a frequency conversion variable angle optimization operation scheme of frequency conversion variable speed per hour for different blade installation angle numbers of a cooling tower half-adjusting fan all the year around, and determining an optimal frequency conversion variable angle optimization operation scheme all the year around;

In the step A, the solving process of the total ventilation resistance P and the total ventilation resistance S of the cooling tower is as follows:

Taking a counter-flow cooling tower as an example, each part in the tower consists of an air inlet, an air guide device, an air flow turning part before entering a water spraying device, a water spraying filler, a water spraying device supporting beam, a water distribution device, a water collector, an air cylinder ring beam inlet and an air cylinder outlet diffusion section, wherein the resistance of the water spraying filler is P_tl＝A·ρV^mWherein P is_tlIs the resistance of the water spraying filler, Pa; v is the average air velocity of the section of the filler, m/s; A. m is the resistance coefficient of the filler; solving formula for solving total resistance P, m gas column and P of cooling tower by accumulating resistance of each partSolving formula of total impedance SWherein i is the local resistance number of each part in the tower, xi_iIs the local resistance coefficient of each part of the cooling tower, v_iThe average flow velocity of air in each section of the tower is rho is the air density, kg/m³G is the acceleration of gravity, m/s²G is the ventilation of the cooling tower, ten thousand meters³/h；

And B, determining the air volume G of actual working points of different blade mounting angles when the fan works in the cooling tower_jWind pressure P_jPower N_jAnd efficiency η_jThe solution process of (2) is as follows:

The wind pressure performance curve equation of the cooling tower fan isWherein P is_jIs the wind pressure of the fan, m air columns; and D, simultaneously establishing a wind pressure performance curve equation of the fan and the cooling tower required pressure performance curve equation determined in the step ASolving to obtain the operation air volume G when the jth blade mounting angle of the fan is obtained_jAnd wind pressure P_j(j ═ 1, 2, 3, …, m), where j is the fan blade setting angle number, m is the number of set fan blade setting angles, A_j、B_j、C_j、D_jIs a constant; the obtained blower air volume G_jRespectively substituting into the fan power performance curve equation of the corresponding blade installation anglecalculating the operating power N of the fan at the mounting angles of m blades in the cooling tower_jIn which N is_jIs the fan power, kW; a. the_j’、B_j’、C_j’、D_j' is a constant; the air quantity G of the installation angles of m blades of the fan_jWind pressure P_jAnd power N_jAre respectively substituted intoComputingObtaining the efficiency eta of the installation angle of m blades of the fan in the cooling tower_fjG is_j～η_fjFitting a relation curve eta of working efficiency and air quantity of a fan in a cooling tower_fj＝η_fj(G) And the relation curve beta of the blade installation angle and the air volume_j＝β_j(G)；

And C, calculating and determining the minimum ventilation quantity required by the cooling tower under different environment working conditions according to the following solving process:

(1) Respectively calculating the saturated water vapor pressure P' and the relative humidity of air according to different environmental conditions all the year aroundApparent density of wet air ρ', air moisture content x, specific enthalpy of wet air h, and value of saturated air enthalpy h ";

(2) Calculating the thermodynamic calculation of the cooling tower by an enthalpy difference method, and establishing a packing characteristic number equation omega of the cooling tower_n'＝Bλ^kAnd cooling number equation of cooling towerWherein B, k is the experimental constant of the water spraying filler; λ is the mass ratio of air (in dry air) entering the packing to water entering the packing, kg (DA)/kg; omega_nThe cooling number (dimensionless) for the operating characteristics of the counter-flow cooling tower; k is the coefficient of heat removal of the evaporated water volume (K)<1.0, dimensionless); c_wTaking 4.1868kJ/(kg DEG C), which is the specific heat of water, and kJ/(kg DEG C); h' is saturated air specific enthalpy, namely specific enthalpy of heat release when the air temperature is that the water vapor partial pressure reaches saturated state temperature t, kJ/kg (DA); h is the specific enthalpy of humid air, kJ/kg (DA); dt is the water temperature difference between the inlet water and the outlet water of the infinitesimal filler, and is DEG C; t is t₁The water temperature entering the tower is DEG C; t is t₂The water temperature at the outlet of the tower is DEG C; when omega is higher than_n’＝Ω_nThen, the air-water ratio lambda of the cooling tower under the actual environment working condition is obtained through solving, a linear iterative approximation method is adopted in the numerical calculation process until the error is within the allowable range, and finally t is obtained₁The gas-water ratio of the corresponding balance point, the method can quickly approach to obtain the final solution;

(3) According to step (2) at a given t₁Calculating the determined air-water ratio of the balance working point of the cooling tower under the actual environment working condition, and the minimum fan air volume G required by the cooling tower_k＝λ_k·Q·ρ_w/(ρ_k10000) in which G_kThe minimum ventilation required by the cooling tower under the k environmental condition, Q is the total water flow, m³/h，ρ_kIs the air density, rho, in the k-th ambient condition_wis the density, lambda, of the circulating water_kCalculating the determined gas-water ratio of the inlet filler under the k environmental condition, namely the mass ratio of air to water, for the step (2);

D, calculating and determining a frequency conversion variable angle optimization operation scheme of the annual different blade installation angle numbers of the cooling tower half-adjusting fan for frequency conversion and speed change per hour according to the following steps:

(1) For the t th year, the time unit is week_wC, calculating the maximum value G of the minimum ventilation quantity required by the cooling tower at all the time points in the determined week_twDetermining the rated rotating speed air quantity G of the peripheral fan as the required ventilation quantity of the week according to the last two formulas of the step B_twCorresponding blade setting angle beta_twand fan efficiency η_ftwFor the t th week_htaking the maximum value of the minimum ventilation quantity required by the cooling tower at all the moments of the hour as the required ventilation quantity G of the cooling tower in the hour_thRequires G_tw≥G_thT th, t_hThe hourly frequency conversion is carried out, so that the running air quantity of the fan is equal to the hourly required ventilation quantity G of the cooling tower_thT of the week_hThe frequency conversion efficiency of the hour isWherein eta_bpthIs at the t_hHourly fan frequency converter efficiency, G_thIs the t th of the fan_wDay of the week t_hHourly air flow, G_twIs the t th of the fan_wSetting the air volume of the blade at the installation angle rated rotating speed; A. b, C is a constant;

(2) T th_hThe efficiency of the motor matched with the operation of the hourly fan isWhereinWherein eta_NFor rated efficiency of the motor, beta_thIs at the t_hThe motor load factor in hours, k is the ratio of the fixed loss coefficient and the variable loss coefficient of the motor; t th_wThe weekly fan system has the one-day energy consumption ofWherein A is_twIs the t th of the fan system_wEnergy consumption of a certain day of the week, ρ_thIs at the t_hHourly air density, P_thIs at the t_hHourly fan operating wind pressure, η_ftwIs at the t_wEfficiency of operation of the peripheral fan, η_cIs at the t_wTransmission efficiency of peripheral fan and motor, eta_emthIs at the t_hThe hourly fan runs the efficiency of a matched motor;

(3) Let t_wThe air volume required by the cooling tower in each day of the week is the same according to the change rule of hours, and the annual operation energy consumption of the fan of the cooling tower isThe annual energy cost is Y_z＝A_zY, wherein A_zFor the annual running power consumption of the cooling tower fan, t_wis operated for the whole year, T is the number of the whole year operation weeks, Y_zY represents the unit price of electricity charge for the total annual energy charge;

(4) Calculating and determining the change rule of the air quantity required by the cooling tower along with time under the working condition of the actual environment all year round by using an equation G_r＝G_r(t_w) Represents; setting the number of installing angles of blades of the fan in the annual operation, implementing the frequency conversion operation per hour, listing the calculation formula of the annual operation power consumption of the fan, and meeting the requirement of the operation air volume G of the fan_th≥G_rOn the premise of taking the minimum operation energy consumption as a target, taking the annual angle change time point of the fan as a variable and calculating through optimization iterationCalculating to obtain the fan operation power consumption A of the installation angle number of the blade of the fan all the year_zThe minimum value and the corresponding optimal blade installation angle and the angle-changing time point thereof; the annual blade mounting angle number of the fan is changed to carry out optimization calculation again, and the frequency conversion and angle change optimization operation scheme of the fan with various blade mounting angle numbers required all the year is obtained as follows:

The first scheme is as follows: annual 1-type blade mounting angle per day hourly frequency conversion optimized operation

the ventilation quantity needed by the cooling tower in one year is different along with different time environments, and the rated rotating speed and the air quantity of the fan meet the maximum ventilation quantity G needed by the cooling tower all the year around_maxOn the premise of setting 1 blade installation angle beta of the annual running of the fan₁rated speed fan efficiency of eta_f1The air quantity is G₁≥G_maxCan satisfy G₁≥G_rThe fan operates at the blade mounting angle in a frequency-variable and speed-variable mode every hour every day, the air quantity of the fan after frequency conversion is equal to the ventilation quantity required by the cooling tower in each hour, and the total annual fan operation energy consumption isSubstituting the relation between the fan efficiency and the blade mounting angle, programming and calculating by taking the minimum total energy consumption of the annual fan operation as a target, solving and determining the annual optimal rated speed operation air quantity and the corresponding blade mounting angle, and minimizing the total operation cost;

Scheme II: annual 2-type blade mounting angle per hour-per-day variable-frequency optimized operation

According to the scheme, 2 blade mounting angles of the fan in the whole year are selected for variable-frequency operation every hour, the ventilation quantity of the worst environment working condition of the whole year is ensured, and the optimal blade mounting angles of the fan in the whole year operation of the 2 blade mounting angles are set to be beta respectively₁、β₂The rated rotational speed and the rated air quantity of the fan are respectively G₁、G₂Is provided with beta₁≥β₂，G₁≥G₂The fan efficiency is eta respectively_f1、η_f2Dividing the whole year T week into three sections: in week 1 to t_{2 small}Week and t_{2 is large}Turning down the installation angle of the fan blade to beta from the second to the Tth week₂The air quantity isG₂can satisfy G₂≥G_rThe fan in the two time periods has rated rotating speed and air quantity G₂Starting to operate at variable frequency and variable speed every hour; at the t th_{2 small}+1 week to t_{2 is large}1 week, increase the fan blade setting angle to beta₁The air quantity is G₁Can satisfy G₁≥G_r≥G₂At a rated speed G of the fan during the period₁Starting to operate at variable frequency and variable speed every hour; determining the blade installation angle of the fan in operation every week, carrying out frequency-conversion and speed-change operation on the fan every hour every day, and the total energy consumption of the fan in operation all the year around is

The wind quantity G of the rated rotating speed of the fan blade at the variable angle time demarcation point is used as the target of the lowest total annual operating energy consumption of the fan₁、G₂As variable, for different air quantities G₁、G₂value, programming calculation, solving for G with minimum energy consumption₁、G₂Value, to obtain the corresponding blade installation angle beta₁、β₂And a variable angle time point t_{2 small}、t_{2 is large}Obtaining a fan frequency conversion angle-changing optimized operation scheme of 2 blade mounting angles all the year round;

The third scheme is as follows: annual 3-type blade mounting angle per hour-per-day variable-frequency optimized operation

The scheme considers the installation angles beta of 3 blades all the year round₁、β₂、β₃Operating efficiency eta respectively corresponding to rated speed of fan_f1、η_f2、η_f3Air volume G₁、G₂、G₃Is provided with beta₁≥β₂≥β₃，G₁≥G₂≥G₃(ii) a Dividing the whole year T into five sections: week 1 to t_{3 small}Week and t_{3 is large}From the week to the Tth week, the fan is installed at a blade installation angle beta₃Operation, air quantity G corresponding to rated speed₃Can satisfy G₃≥G_rthe secondary air volume G of the fan in the time period₃Starting frequency conversion operation every hour; t th_{3 small}+1 week tot_{2 small}Week and t_{2 is large}week to t_{3 is large}1 week, fan blade setting angle β₂Operation, air quantity G corresponding to rated speed₂Can satisfy G₃≤G_r≤G₂The secondary air volume G of the fan in the time period₂Starting frequency conversion operation every hour; t th_{2 small}+1 week to t_{2 is large}1 week, fan blade setting angle β₁operation, air quantity G corresponding to rated speed₁Can satisfy G₂≤G_r≤G₁The secondary air volume G of the fan in the time period₁Starting frequency conversion operation every hour; determining the blade installation angle of the fan in operation every week, and implementing fan frequency conversion every hour every day; the total energy consumption of the annual fan operation is

The wind quantity G of the rated rotating speed of the fan blade at the variable angle time demarcation point is used as the target of the lowest total annual operating energy consumption of the fan₁、G₂、G₃As variable, for different air quantities G₁、G₂、G₃Value, programmed calculation, and G with minimum energy consumption₁、G₂、G₃Value, to obtain the corresponding blade installation angle beta₁、β₂、β₃And a variable angle time point t_{3 small}、t_{2 small}、t_{2 is large}、t_{3 is large}Obtaining a fan frequency conversion angle-changing optimized operation scheme of 3 blade mounting angles all the year round;

And the scheme is as follows: 4 blade installation angles in the whole year are changed in frequency and optimized to operate every hour every day

The scheme adopts 4 fan blade installation angles to operate all the year around, lists the total annual operation energy consumption calculation formula of the fan according to the method of the scheme II and the scheme III, takes the minimum total annual operation energy consumption of the fan as a target, performs programmed calculation and solution, and determines the optimal fan blade installation angle beta₁、β₂、β₃、β₄Corresponding rated rotational speed air volume G₁、G₂、G₃、G₄and corresponding to the time point of the angle change;

The frequency conversion variable-angle optimization operation scheme of the cooling tower fan for determining 5, 6 and more blade mounting angles all year around can be solved by the same method.

2. The method for determining the annual frequency conversion and angle change optimized operation scheme of the half-regulation fan of the cooling tower as claimed in claim 1, wherein the fan operation power consumption A for setting the blade installation angle number for the annual fan through the optimized iterative computation in the step (4) in the step D_zThe solving method of the minimum value and the corresponding optimal blade installation angle and the variable angle time point thereof is as follows:

Programming to carry out optimization iterative calculation, firstly inputting the air volume, the air pressure, the power and the efficiency of a rated rotating speed variable-angle operation working point of a fan of a cooling tower, then inputting the air volume required by each week of the cooling tower under different environmental working conditions all the year around and the corresponding air density, taking the operation of 2 fan blade installation angles all the year around as an example, starting a trial generation from the adjustable minimum blade installation angle of the fan, setting an angle step of 0.1 degrees, taking the maximum value of the minimum ventilation required by the cooling tower at all the moment in one week as the required ventilation of the cooling tower all the week, comparing whether the air volume corresponding to the 2 fan blade installation angles of the trial generation meets the ventilation required by each week, if so, operating the week under the fan blade installation angle of the fan, if not, operating under the other fan blade installation angle, after determining the fan blade installation angle operated all the year around, carrying out frequency conversion per hour, the running air quantity of the fan is equal to the ventilation quantity required by the cooling tower in the hour; the frequency conversion and speed change of the fan are carried out every hour every day, although the energy consumption of the fan is reduced after the speed change, the energy consumption of the frequency converter is increased after the frequency conversion, so that the input power of the frequency converter before and after the frequency conversion needs to be compared, if the input power of the frequency converter is increased after the frequency conversion and speed change, the reduced power of the fan is not enough to compensate the increased power of the frequency converter, and the frequency conversion and speed change operation is not required in the hour;

Fan operation power consumption A for setting blade installation angle number by utilizing annual fan_zthe minimum value and the corresponding optimal blade installation angle and the solving method of the variable angle time point thereof are operated to calculate the annual fan operation energy consumption and energy cost, and thenAnd (3) newly replacing the fan blade installation angle according to the step length, recalculating the annual fan operation energy consumption and energy cost, comparing to obtain the minimum annual fan operation energy consumption and energy cost scheme after all the fan blade installation angles are completely replaced, and obtaining the optimal blade installation angle and the angle-variable time point of 2 fan blade installation angle operations.

3. The method for determining the annual frequency conversion and angle change optimized operation scheme of the cooling tower half-adjusting fan according to claim 1, is characterized in that: e, comparing the cost of the frequency conversion variable angle optimization operation scheme of the annual variable frequency speed change of different blade installation angle numbers of the cooling tower half-adjusting fan, and determining the annual optimal frequency conversion variable angle operation scheme as follows:

The cost of the frequency conversion and angle conversion optimized operation scheme of the hourly frequency conversion and speed conversion of the number of different blade installation angles of the cooling tower fan all the year round comprises the operation energy consumption cost and the angle modulation cost, and compared with the non-frequency conversion, the cost of the initial equipment of the frequency converter is increased; accumulating and calculating angle adjusting cost according to the angle changing times of the operation scheme; the original operation scheme refers to an operation scheme that the fan operates according to the rated rotating speed and the designed blade installation angle all the year around, and the improved operation scheme refers to an operation scheme that the fan operates according to the rated rotating speed and the maximum required ventilation quantity of the cooling tower all the year around; and finally, comparing annual energy consumption, angle modulation and total cost of additional equipment sharing of 6 schemes including the original operation scheme, the improved operation scheme and the first scheme, the second scheme, the third scheme and the fourth scheme, wherein the annual energy cost of the first scheme to the fourth scheme is obtained by optimized calculation in the step D, and the annual optimal variable-frequency variable-angle operation scheme of the half-regulation fan of the cooling tower is finally determined on the basis of the minimum total cost.