CN107345777B - Method for Determining Optimal Operation Plan of Variable Frequency and Angle of Cooling Tower Semi-regulating Fans in a Year - Google Patents

Abstract

The method for determining the annual frequency-variable-angle optimal operation scheme of the semi-regulating fan of the cooling tower belongs to the field of energy-saving technology of industrial systems. Cooling towers require ventilation; with the goal of the lowest energy consumption, set the number of different types of blade installation angles for the whole year, and use the method of hourly variable frequency and variable speed to make the air volume of the fan equal to the air volume required by the cooling tower, and calculate and determine the optimal operation plan of variable frequency and variable angle; Considering the cost of fan angle adjustment and frequency converter, compare the total cost of several variable frequency and variable angle optimization operation schemes for cooling tower fans with different blade installation angles throughout the year, and determine the optimal annual variable frequency and variable angle operation based on the principle of the lowest total cost The plan includes the hourly frequency conversion of the fan, the number of blade installation angles operated throughout the year, the value of each blade installation angle and the time point of the angle change. The annual frequency-variable-angle optimal operation scheme of the fan of the cooling tower determined by the invention has remarkable energy-saving effect.

Description

Method for Determining Optimal Operation Plan of Variable Frequency and Angle of Cooling Tower Semi-regulating Fans in a Year

technical field

The invention belongs to the technical field of energy saving of industrial systems, and relates to an annual frequency-variable-angle optimization operation plan for a semi-adjustable fan of a cooling tower equipped with a frequency conversion device. The method of determining the optimal operation scheme of the semi-regulating fan of the cooling tower with variable frequency and variable angle for the whole year on the premise of cooling requirements and the goal of saving the total cost of fan operation.

Background technique

Energy is an important basis for the development of the national economy. Due to serious energy waste, energy shortage has become a stumbling block to my country's economic development. Energy conservation and consumption reduction is one of the important tasks of my country's current economic development.

Circulating cooling water systems are widely used in metallurgy, electric power, steel, petrochemical and other industrial sectors, with high energy consumption. Among them, the cooling tower cools the circulating water through fan forced ventilation, and the fan consumes a lot of electric energy. At present, there are many studies on the energy saving of water pump units in the circulating cooling water system and the form of cooling towers, and the research on energy saving of fans in cooling towers is ignored. The current practice is to select cooling tower fans and blade installation angles according to the ventilation volume design required for the most unfavorable environmental conditions throughout the year, and the fans operate under the maximum ventilation volume design conditions for many years. In fact, in winter and spring-autumn transitional seasons, the minimum ventilation rate required by the cooling tower to meet the cooling and heat transfer is far lower than the design maximum ventilation rate. The ventilation operation mode causes serious energy waste, and the cooling tower fan has great potential for energy saving.

Contents of the invention

The purpose of the present invention is to overcome the shortcomings of excessive cooling and serious waste of energy due to the cooling tower fan operating according to the design maximum annual ventilation volume throughout the year, and propose a cooling tower semi-adjustable fan annual variable frequency and angle optimization operation scheme The determination method includes the number of blade installation angles, the value of each blade installation angle and the time point of the angle change under the premise of hourly frequency conversion and speed change, and the timely optimization of the fan blade installation angle of the cooling tower to save the annual fan cost. operation and maintenance costs.

In order to achieve the above object, the present invention provides a method for accurately determining the optimal operation scheme of the cooling tower semi-regulated fan based on the hourly variable frequency variable angle optimization operation scheme, including the following steps:

A. Calculate the total resistance P _Z and total resistance S of cooling tower ventilation.

Taking the counter-flow cooling tower as an example, each part of the tower consists of the air inlet, the air guide device, the airflow turning before entering the water spray device, the water spray filler, the support beam of the water spray device, the water distribution device, the water eliminator, and the inlet of the air cylinder ring beam. , Composed of the diffuser section at the outlet of the air duct. Among them, the water spray packing resistance is calculated as follows

A＝(A ₁ q ² +A ₂ q+A ₃ )×9.81 (2)

m＝m ₁ q ² +m ₂ q+m ₃ (3)

P _tl = A·ρV ^m (4)

In the formula, P _tl is the resistance of the water-spraying packing, Pa; V is the average air velocity of the packing section, m/s; Q is the total water flow rate, m ³ /h; F is the area of the water-spraying packing area, m ² ; q is the spraying water density, m ³ /(m ² h); A and m are the resistance coefficients of different fillers, which are obtained from Table 3 in "Thermal and Resistance Performance Analysis of Cooling Tower Plastic Spraying Fillings"; A ₁ , A _{2 . _ _ _}

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

In the formula, P is the total ventilation resistance of the cooling tower, m air column; S is the total resistance, h ² /(10 ⁸ ·m ⁵ ); G is the ventilation volume of the cooling tower, ten thousand m ³ /h; i is each The number of components; n is the total number of components in the cooling tower; ξ _i , v _i , F _i are the local resistance coefficient, cross-sectional air velocity m/s, and cross-sectional area m ² of each component in the cooling tower, respectively.

B. Calculate and determine the actual working point parameters of different blade installation angles when the fan is working in the cooling tower: flow G _j , wind pressure P _j , power N _j and efficiency η _j .

The performance curve of the cooling tower fan is provided by the equipment manufacturer. The wind pressure performance curve of the fan at the jth blade installation angle can be fitted by the equation:

In the formula, j is the number of the installation angle of the fan blade; m is the number of the set fan blade installation angle; P _j is the wind pressure at the _jth blade installation angle of the fan, m gas column; The air volume at a blade installation angle, ten thousand m ³ /h; A _j , B _j , C _j , D _j are constants.

The power performance curve of the cooling tower fan at the jth blade installation angle can be fitted by the following equation:

In the formula, N _j is the power of the fan at the jth blade installation angle, kW; A _j ', B _j ', C _j ', D _j ' are constants.

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

P = SG ² (10)

For the j-th blade installation angle of the fan, the j-th formula and formula (10) of the simultaneous equation (8) are solved to obtain the fan operating air volume G _j and wind pressure P _j (j=1) at the j-th blade installation angle of the cooling tower fan , 2, 3,..., m), a total of 2m quantities.

Substitute the obtained air volumes G _j of the m blade installation angles of the fan in the cooling tower into the power performance curve equation (9) of the fan corresponding to the blade installation angle, and calculate the m power N _j , and calculate the fan according to the formula (11). Efficiency η _fj of m blade installation angles

The m efficiencies η _fj calculated by formula (11) are fitted into the fan air volume-efficiency curve and the air volume-blade installation angle curve:

η _fj ＝η _fj (G) (11')

β _j = β _j (G) (11')

In the formula, η _fj is the jth blade installation angle β _j of the fan, that is, the efficiency when the air volume is G _j , and Fig. 1 shows the relationship between the fan efficiency and the blade installation angle of the fitted cooling tower fan at the rated speed variable angle operating point curve.

C. Calculation and determination of the minimum ventilation required by the cooling tower under different environmental conditions.

When the cooling equipment needs to remove heat and the cooling water flow rate is constant, the lower the ambient temperature and the lower the humidity, the smaller the minimum ventilation required by the cooling tower of the circulating cooling water system, and reducing the ventilation means that the cooling tower fan runs energy saving. The minimum ventilation required for cooling towers is determined by:

First, calculate the air saturated water vapor pressure P” and the relative humidity of the air respectively The apparent density ρ' of moist air, the moisture content of air x, the specific enthalpy of moist air h and the value of saturated air enthalpy h";

Secondly, the thermal calculation of the counterflow cooling tower is carried out, and the characteristic number of the filler is calculated:

Ω _n '=Bλ ^k (12)

In the formula, Ω _n ' is the characteristic number of the working packing of the counterflow cooling tower (dimensionless); B and k are the experimental constants of the water spraying packing, which are found in Table 2 in "Analysis of Thermal and Resistance Performance of Plastic Water Sprinkling Fillings of Cooling Towers"; λ is the mass ratio of the air (calculated as dry air) entering the packing to the water entering the packing, kg(DA)/kg.

Using the enthalpy difference method, the cooling number of the cooling tower:

In the formula, Ω _n is the cooling number of the counterflow cooling tower (dimensionless); K is the coefficient of heat taken away by the evaporated water (K<1.0, dimensionless); C _w is the specific heat of water, kJ/(kg·℃ ), taking 4.1868kJ/(kg °C); h” is the specific enthalpy of saturated air, that is, the specific enthalpy of heat release when the air temperature is the water vapor partial pressure reaches the saturation state temperature t, kJ/kg (DA); h is the humidity Air specific enthalpy, kJ/kg(DA); dt is the water temperature difference between the inlet water and the outlet water of the micro-element packing, ℃; t ₁ is the water temperature in the tower (℃); _{t 2} is the water temperature in the tower (℃); Heat of vaporization of water at filler water temperature, kJ/kg.

The calculation of the cooling number should adopt the multi-stage Simpson base decomposition method, as follows:

Δt=t ₁ -t ₂ (18)

δt=Δt/n=(t ₁ -t ₂ )/n (19)

δh=△h/n=(h ₁ -h ₂ )/n (20)

In the formula, n is the number of segments; They are the saturated air enthalpy when the corresponding water temperature is t ₁ -δt, t ₁ -2δt, t ₁ -(n-1)δt, kJ/kg(DA); h" ₁ and h" ₂ are the temperature of water entering and leaving the tower respectively enthalpy of saturated air, kJ/kg(DA); h ₁ and h ₂ are the specific enthalpy of humid air entering and leaving the tower, kJ/kg(DA); h _m is the average specific enthalpy of humid air in the tower, kJ/kg( DA); Δt is the water temperature difference between entering and leaving the tower, ℃; δt is the water temperature difference between equal segments, ℃; Δh is the air enthalpy difference between entering and leaving the tower, kJ/kg(DA); δh is the enthalpy difference between equal segments, kJ/kg (DA).

When the calculation accuracy is not high and Δt<15°C, the following simplified calculation can be used:

In the formula, h" _m is the saturated air enthalpy when the corresponding water temperature is t _m , kJ/kg(DA).

As shown in Figure 2, the cooling task curve represents the cooling number required for the cooling tower to complete the design conditions of the cooling tower when a different air-water ratio λ is given; the performance curve of the filler represents the cooling capacity of the cooling tower. Under the same air-to-water ratio, the cooling task of the cooling tower is equal to the cooling capacity, that is, when Ω _n '=Ω _n , it is the working point of the cooling tower.

According to different environmental conditions, on the premise of satisfying the cooling capacity, the temperature of the inlet and outlet water can be controlled, and the corresponding air-water ratio λ required at the working point of the cooling tower can be obtained through trial calculation. This patent adopts a method of continuous approximation for trial calculation, as shown in FIG. 3 .

Given a cooling tower with an air-water ratio λ ₁ , take a number of different outlet water temperatures t ₂ , and calculate a number of corresponding cooling numbers Ω _n according to the above formulas (12) to (21), and fit them as shown in Figure 3 The quadratic curve; according to this λ ₁ , the cooling characteristic number (Ω _n ') ₁ of the water spraying filler in the actual operation of the cooling tower is obtained, and the cooling tower cooling number (Ω _n ) ₁ is equal to the cooling characteristic number of the water spraying filler (Ω _n ' ) ₁ , the cooling tower outlet water temperature (t ₂ ) ₁ corresponding to the equilibrium point can be obtained from the curve, and the inlet water temperature (t ₁ ) ₁ can be obtained according to the specified water temperature difference between the inlet and outlet towers, and the (t ₁ ) ₁ is generally not the required inlet water temperature, the problem now becomes: given the inlet water temperature t ₁ * and the temperature difference between inlet and outlet water, it is required to obtain the corresponding air-water ratio λ*, and use the following method to solve it.

As shown in Figure 4, for a certain cooling tower packing system, if there is a gas-water ratio λ, the above-mentioned series of formulas can be used to calculate a corresponding water temperature t ₁ entering the tower, t ₁ is a function of λ, and the functional relationship is as shown in Figure 4 Curve ATB, let the point T on the curve ATB be the required coordinates (λ*, t ₁ *), λ* cannot be obtained directly from t ₁ *, and iterative calculation is used to solve it by point-by-point approximation: known The curve ATB decreases monotonously. On the curve ATB, two points A and B with a lower and higher air-water ratio are taken, and the values of the air-water ratio are λ _A and λ _B respectively. Suppose the required inlet water temperature t _1A >t ₁ *> t _1B , use the air-water ratio λ _A , λ _B to calculate the temperature t _1A and t _1B of the water entering the tower respectively, and determine the two points A and B on the curve ATB. The equation AB of the straight line passing through the two points A and B is obtained as:

Substitute t ₁ =t ₁ * into formula (22), and obtain the air-water ratio λ _C of the corresponding point C' by linear interpolation

Use λ _C to calculate the actual inlet water temperature t _1C of the balance point C on the curve ATB through formulas (12) to (21), and compare whether the calculated value t _1C of the inlet water temperature meets the requirement of a given accuracy of 0.01, and if it does not meet the accuracy requirements , use the same method to obtain the equation of a straight line passing through two points AC, and substitute t ₁ =t ₁ * into the equation of a straight line at two points AC, linear interpolation to obtain the air-water ratio λ _D of the corresponding point D', and then use λ _D Calculate and obtain the actual water temperature t _1D of the equilibrium point D on the curve ATB, check whether t _1D meets the accuracy requirements, ... until the nth iterative calculation, the point N on the curve infinitely approaches the point T, and satisfies the formula (24) until

|t _1N -t ₁ *|≤0.01 (24)

This method can quickly iteratively approximate the air-water ratio λ* corresponding to the solution t ₁ * on the curve ATB.

In the circulating water system with constant water volume operation, the corresponding ventilation volume under different environmental conditions can be obtained:

G _k = λ _k · Q · ρ _W /(ρ _k · 10000) (k=1, 2, 3, ..., z) (25)

In the formula, G _k is the ventilation volume under the kth environmental condition, ten thousand ^m3 /h; ρk is the air density under the _kth environmental condition, kg/ ^m3 ; _ρw is the density of circulating water, kg/m ³ ; λ _k is the mass ratio of the air (calculated as dry air) fed into the filler to the water fed into the filler under the kth environmental working condition, kg(DA)/kg; z is the number of different environmental working conditions .

D. Calculation and determination of the frequency-variable-angle optimal operation scheme for cooling tower semi-regulated fans with different blade installation angles throughout the year and hourly variable frequency variable speed.

Since the fan model, rated speed and blade installation angle are selected according to the most unfavorable environmental conditions of the year—the required maximum ventilation in summer, and because the ambient temperature is lower than that in the hottest period of summer most of the time throughout the year, the cooling tower The required minimum ventilation is drastically reduced and there are also large ambient temperature differences throughout the day. Taking the maximum value of the minimum ventilation required by the cooling tower at all times in a week as the required ventilation of the cooling tower in that week, the required ventilation of a cooling tower in a typical year by week is shown in Figure 5; for any hour, take the The maximum value of the minimum ventilation required by the cooling tower at all times in an hour is used as the required ventilation of the cooling tower for that hour. The change law of the required ventilation in a typical day is shown in Figure 6. Therefore, if the fan of the cooling tower operates at the rated speed and the installation angle of the blades, it is easy to produce supercooling phenomenon, resulting in energy waste.

Considering that most of the fan blades used in cooling towers are semi-adjustable, adjusting the blades requires a certain amount of work and cost, and adjusting the blade installation angle will have a certain impact on the normal application of the cooling tower. Therefore, the fan blades should not be adjusted frequently. It can only be adjusted several times in a year; while the cooling tower fan adopts frequency conversion speed regulation operation, in addition to the initial investment of frequency converter equipment, only need to turn the knob to achieve frequency conversion, easy to achieve multiple and automatic frequency conversion adjustment, will not increase costs, so adopt Hourly frequency conversion adjustment, that is, the cooling tower chooses different fan blade installation angles in different periods of the year-weeks, so that the rated speed of the fan during this period is equal to the maximum value of the minimum air volume required by the cooling tower during this period, Select different speeds at different times of the day, so that the air volume of the fan in this hour is equal to the air volume required by the cooling tower in that hour, and aim at the minimum fan power per hour, so as to realize the optimal operation of the cooling tower fan with variable frequency and variable angle, and reduce the fan energy. consumption purpose.

The fan implements frequency conversion optimization operation. Considering safety, only the speed is reduced, not increased. Figure 7 shows the relationship between the air volume, efficiency and blade installation angle of a typical cooling tower fan. Under the condition of constant speed, the actual operating point of the cooling tower fan, one blade installation angle corresponds to one air volume and one fan efficiency, and the curve has four peaks They are marked as A, B, C, and D respectively, and are divided into 5 sections with 4 peaks as the boundary. In the first section of the curve from the left, as the blade installation angle increases, the fan efficiency becomes higher and higher to the highest efficiency point A. In this section, under the premise of meeting the minimum air volume required by the cooling tower, the fan should be operated at a larger blade installation angle as much as possible to maximize the efficiency of the fan, and the air volume will be reduced to the minimum air volume required by the cooling tower through frequency conversion and speed reduction. , keep the operating conditions similar to the highest efficiency point, and the operating efficiency is the highest; in the second section of the AB curve, as the blade installation angle increases, the fan efficiency first decreases sharply and then increases to the second peak B, and the horizontal line is drawn through point B Intersect the second section of the curve at point B'. In the range of curve AB', because it is a monotonous decreasing curve, as the blade installation angle increases, the efficiency of the fan decreases. Therefore, under the premise of meeting the minimum air volume required by the cooling tower, the fan The blade installation angle should be as small as possible; in the curve BB' section, the fans at points B and B' have the highest efficiency. Under the premise of meeting the minimum air volume required by the cooling tower, select the fan blade installation angle at point B, and then reduce the speed by frequency conversion Reduce the air volume to the minimum air volume required by the cooling tower; the third to fifth curves BC, CD, and the right curve of point D have the same trend as the AB' section, and the efficiency of the fan decreases with the increase of the blade installation angle. Therefore, under the premise of meeting the minimum air volume required by the cooling tower, the installation angle of the fan blades should be as small as possible.

To sum up, if the minimum air volume required by the cooling tower is on the left side of point A on the curve in Figure 7, the fan blade installation angle should be adjusted to point A; if the required minimum air volume is located in section B'B, the fan blade installation angle should be adjusted to Adjust to point B, and then reduce the fan flow to the minimum air volume required by the cooling tower through frequency conversion and speed reduction respectively; The minimum air volume determines the corresponding blade installation angle on the curve to implement operation, without the need for frequency conversion speed regulation.

The cooling tower fan operates with variable frequency and speed regulation, and the input power of the frequency converter is

In the formula, N _bj is the input power of the inverter, kW; ρ is the air density, kg/m ³ ; g is the acceleration of gravity, m/s ² ; η _c is the transmission efficiency of the fan; η _bpj is the installation angle of the jth blade Drive efficiency during operation.

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

η _bp =Aδ ² +Bδ+C (27)

In the formula, η _bp is the frequency conversion efficiency of the inverter; δ is the speed ratio; A, B, and C are constants.

When the minimum ventilation required by the cooling tower is on the left side of point A and BB' in Figure 7, adjust the installation angle of the fan blades to point A and point B respectively to maximize the efficiency of the fan, and then use frequency conversion to reduce the speed to reach the required Air volume. As shown in Figure 8, point A in the figure is the point A with the highest fan efficiency in Figure 7. Taking the required minimum ventilation volume on the left side of point A as an example, adjust the installation angle of the fan blades to the angle of point A, using Frequency conversion and speed reduction, so that the operating point of the fan moves down to the left along the parabola of the similar operating condition, so that the air volume of the new operating condition point of the fan is equal to the required ventilation volume of the cooling tower in this hour. The new operating condition is similar to the original operating condition A, and the fan efficiency remains unchanged. On the premise of meeting the required ventilation volume of the cooling tower, the ventilation volume of the fan is reduced, the operating efficiency is improved, and the purpose of energy saving is achieved.

When the fan is running at reduced speed, the speed ratio is generally limited to between 0.6 and 1. It can be considered that the efficiency of the similar operating point after the speed reduction is equal to that before the speed reduction. Assuming that the speed ratio of point A1 in Figure 8 is δ _{A1 =} 0.6, The air volume is G _A1 , the power is N _A1 , the efficiency of the fan is η _fA1 , η _fA1 = η _fA = η _{f max} ; if the cooling tower requires a ventilation volume of G _A2 , G _A2 <G _A1 , consider the frequency conversion speed regulation of the fan at A ₂ Point operation, because δ _A2 <0.6, η _fA2 <η _fA1 , but η _fA2 drops very little compared with η _fA1 , in addition, compared with A ₁ point, A ₂ point motor efficiency η _emA2 , transmission efficiency η _cA2 and inverter efficiency η _bpA2 changes very little, and because the air volume at point A2 is significantly smaller _than that at point A1, the shaft power at points with similar operating conditions of the fan is proportional to the cube _of the air volume, so the shaft power N _A2 at point _A2 is significantly smaller _than that at point A1 Shaft power N _A1 , according to _formula (26), the input power N _bA2 of the inverter at point A2 is significantly smaller _than the input power N _bA1 of the inverter at point A1, and the fan speed should be adjusted by frequency conversion to run at point A2.

Weeks are used as the unit of time throughout the year. Assume that during a certain period of several weeks to tens of weeks, the fan operates at a blade installation angle. It is required that the operating air volume of the fan at the rated speed during this period is equal to that of the cooling tower during this period. The maximum value of ventilation required in each week, set the fan blade installation angle β _tw , the rated speed air volume G _tw and the fan efficiency η _ftw in this week, on this basis, carry out frequency conversion every hour, and the frequency conversion efficiency of each hour is

In the formula, η _bpth is the inverter efficiency of the fan running in the t _h hour; G _th is the air volume of the fan running in the t _h hour, 10,000 m ³ /h, and its value is equal to the required ventilation volume of the cooling tower in this hour; G _tw is the cooling tower in the t h hour The air volume at the rated speed when the fan blade installation angle of t _w is β _tw , 10,000 m ³ /h.

The efficiency of the motor under load for each hour of the day is

In the formula, η _emth is the efficiency of the supporting motor for the fan operation in the t _h hour; η _N is the rated efficiency of the motor; β _th is the load rate of the motor in the t _h hour; k is the ratio of the fixed loss coefficient of the motor to the variable loss coefficient. The size of k: 2 for 2-pole asynchronous motors; 1 for 4-pole and 6-pole asynchronous motors; 0.5 for 8-pole and above asynchronous motors. According to Table 1 in "Calculation of Efficiency and Power Factor of Asynchronous Motor Under Any Load", the value of b can be obtained.

Energy consumption of fan system in week t _w :

In the formula, A _tw is the energy consumption of the fan system on week t _w , kW h; ρ _th is the air density in hour t _h , kg/m ³ ; P _th is the operating wind pressure of the fan in hour t _h , m gas column; η _ftw is the operating efficiency of the fan in the t _wth week.

Assuming that the required ventilation volume of the cooling tower changes in the same hourly manner in week t _w , the annual energy consumption and energy cost of the cooling tower fan are as follows:

Y _z =A _z ·y (33)

In the formula, A _z is the power consumption of the cooling tower fan for the whole year, kW·h; t _w is the number of running weeks in the whole year; T is the number of running weeks in the whole year, and the continuous running is counted as 52 weeks; Y _z is the cooling The annual energy cost of the tower fan, yuan; y is the unit price of electricity, yuan/(kW·h).

The blades of large fans are semi-adjustable. Manually adjusting the blade installation angle requires a certain amount of cost. When determining the optimal operation plan of the fan with variable angle and frequency conversion, the cost of adjusting the blade installation angle should be considered.

The fan implements hourly frequency conversion operation. When the number of installed angles of the fan blades is fixed throughout the year, the time point of changing the angle is different, and the annual power consumption of the fan is also different. The time point of the annual fan angle change is used as a variable , and list the calculation formula of the annual fan operation power consumption, and calculate the annual fan operation power consumption A _z minimum value of the fan blade installation angle and the corresponding optimal blade installation angle and variable by optimizing iterative calculation corner time point.

Programming to optimize iterative calculation, first input the air volume, wind pressure, power and efficiency of the operating point of the cooling tower fan at the rated speed and variable angle operation, and then the required air volume and corresponding air density for each week of the cooling tower under the environmental conditions throughout the year Input, take the operation of two kinds of fan blade installation angles throughout the year as an example, start the trial generation from the adjustable minimum blade installation angle of the fan, set the angle step length of 0.1°, and take the minimum ventilation required by the cooling tower at all times in a week The maximum value is taken as the required ventilation volume of the cooling tower in this week. Compare whether the air volume corresponding to the two kinds of blade installation angles of the trial generation meets the required ventilation volume of each week. If it is not satisfied, run at another fan blade installation angle. After determining the fan blade installation angle for weekly operation throughout the year, the frequency conversion per hour is used to make the fan operating air volume equal to the ventilation volume required by the cooling tower for that hour.

The frequency and speed of the fan are changed every hour every day. Although the energy consumption of the fan decreases after the speed change, the energy consumption of the inverter increases after the frequency conversion. Therefore, it is necessary to compare the input power of the inverter before and after the frequency conversion. If the input power of the inverter increases after the frequency conversion , indicating that the reduced power of the fan is not enough to compensate for the increased power of the inverter, and it should not be operated with variable frequency and variable speed in this hour.

Use this method to calculate the annual fan operation energy consumption and energy costs; then try to replace the installation angle of the fan blades according to the step length again, use the above method to recalculate the annual fan operation energy consumption and energy costs, and install all the fan blades After all the trials of angles are completed, the scheme of the minimum annual fan operation energy consumption and energy cost is obtained by comparison, and the optimal blade installation angle and angle-changing time point for the operation of the two blade installation angles of the fan are obtained.

Changing the annual number of blade installation angles of the wind turbine and re-optimizing the calculation, the optimal operation plan of the fan with variable frequency and variable angles for the annual blade installation angles is obtained.

Calculate and formulate the air volume expression required for each week of the cooling tower under the annual environmental conditions corresponding to Figure 5

G _r =G _r (t _w ) (34)

Scheme 1 One kind of blade installation angle throughout the year, frequency conversion optimization operation every hour every day

The required ventilation volume of the cooling tower for each week in a year is shown in the histogram in Figure 9. On the premise of meeting the maximum required ventilation volume of the cooling tower G _max throughout the year, one blade installation angle β ₁ for the fan’s annual operation is set, and the rated The efficiency of the rotating speed fan is η _f1 and the air volume is G ₁ , which can meet the requirements of G ₁ ≥ G _r . The fan operates at variable frequency and speed every hour at this blade installation angle. After frequency conversion, the air volume of the fan is equal to the ventilation volume required by the cooling tower for each hour. Referring to the relationship curve between fan efficiency and blade installation angle in Fig. 1, aiming at the lowest total energy consumption of fan operation throughout the year, determine the optimal blade installation angle for the annual operation of one blade installation angle of the fan.

The total energy consumption of the fan operation throughout the year is

With the goal of minimizing the total energy consumption of the fan in the whole year, formula (35) is programmed and calculated to determine the optimal rated speed operating air volume and corresponding blade installation angle throughout the year, so as to minimize the total operating cost.

Option 2: 2 kinds of blade installation angles throughout the year, frequency conversion optimization operation every hour every day

As shown in Figure 10, the fan of this scheme uses two kinds of blade installation angles throughout the year to operate with frequency conversion every hour to ensure the ventilation volume of the most unfavorable environmental conditions throughout the year, and set the optimal blade installation for the fan to operate at two blade installation angles throughout the year The angles are β ₁ and β ₂ respectively, the rated speed and air volume of the fans are G ₁ and G ₂ respectively, assuming that β ₁ ≥ β ₂ , G ₁ ≥ G ₂ , and the efficiency of the fans are η _f1 and η _f2 respectively, the annual T weeks There are three stages: from the 1st week to the t2th _small week and from the t2th _big week to the Tth week, reduce the installation angle of the fan blades to β ₂ , and the air volume is G ₂ to meet the requirements of G ₂ ≥ G _r . The fan in the first stage starts to operate with frequency conversion every hour at the rated speed and air volume G ₂ ; from the t _{2 small} + 1 week to the t _{2 large} - 1 week, increase the fan blade installation angle to β ₁ , and the air volume G ₁ can meet G ₂ ≤ G _r ≤ G ₁ requirement, during this time period the fan starts to run at the rated speed G ₁ with variable frequency per hour. Determine the blade installation angle of the fan for weekly operation, and implement variable frequency and variable speed operation for the fan every hour every day. The total energy consumption of the fan for the whole year is

The goal is to minimize the total energy consumption of the fan in the whole year, and the rated speed air volume G ₁ and G ₂ at the cut-off point of the fan blade angle change time are the variables. For different air volume G ₁ and G ₂ values, the programming formula (36) can Select the values of G ₁ and G ₂ with the smallest energy consumption to obtain the corresponding blade installation angles β ₁ , β ₂ and the time point t 2 of the angle change time point t _{2 is small} , t _{2 is large} , and the frequency conversion of the fan with two blade installation angles throughout the year is obtained Variable angle optimization operation plan.

Scheme 3 Three kinds of blade installation angles throughout the year, frequency conversion optimization operation every hour every day

As shown in Figure 11, this scheme considers the operation of three kinds of blade installation angles β ₁ , β ₂ , β ₃ throughout the year, corresponding to the efficiency η _f1 , η _f2 , η _f3 of the rated speed of the fan, and the air volume G ₁ , G ₂ , G ₃ , let β ₁ ≥β ₂ ≥β ₃ , G ₁ ≥G ₂ ≥G ₃ . Divide the annual T week into five sections: from the first week to the _t3th week and from _{the t3rd} week to the Tth week, the fan operates at the blade installation angle β3, and the air volume G3 corresponding to the rated speed can _{satisfy G3≥G} The requirement of _r , during this time period, the fan starts to operate with frequency conversion every hour from the air volume G ₃ ; from the t3th _small +1 week to the t2th _small week and from the t2th _large week to the t3th _large -1 week, the fan is installed at the blade installation angle β ₂ operation, the air volume G ₂ corresponding to the rated speed can meet the requirements of G ₃ ≤ G _r ≤ G ₂ , and the fan starts to operate at variable frequency every hour from the air volume G ₂ during this time period; the t _{2 small} + 1 week to the t _{2 large} -1 Weekly, the fan operates at the blade installation angle β ₁ , and the air volume G ₁ corresponding to the rated speed can meet the requirements of G ₂ ≤ G _r ≤ G _1. During this time period, the fan starts to operate with frequency conversion every hour from the air volume G ₁ . Determine the blade installation angle of the fan for weekly operation, and implement frequency conversion every hour every day. The total energy consumption of the fan operation throughout the year is

With the goal of the lowest total energy consumption of the fan in the whole year, and the rated speed air volume G ₁ , G ₂ , G ₃ at the cut-off point of the fan blade angle change time as the variable, for different air volume G ₁ , G ₂ , G ₃ values, program Calculate the energy consumption of formula (37), select the values of G ₁ , G ₂ , and G ₃ with the smallest energy consumption, and obtain the corresponding blade installation angles β ₁ , β ₂ , β ₃ and the time points of variable angle t ₃ and t ₂ , t _{2 is large} , t _{3 is large} , and the optimal operation scheme of fan with variable frequency and variable angle for three kinds of blade installation angles is obtained throughout the year.

Option 4 Four kinds of blade installation angles throughout the year, frequency conversion optimization operation every hour every day

As shown in Figure 12, this scheme adopts four fan blade installation angles throughout the year to operate. According to the method of scheme 2 and scheme 3, the calculation formula of the total energy consumption of the fan in the whole year is listed, and the total energy consumption of the fan in the whole year is the minimum The goal is to program and calculate the solution to determine the optimal fan blade installation angles β ₁ , β ₂ , β ₃ , β ₄ , the corresponding rated speed air volumes G ₁ , G ₂ , G ₃ , G ₄ and the corresponding strain angle time points. The same method can be used to find out the optimal operation scheme of cooling tower fans with variable frequency and variable angles for 5 types, 6 types... blade installation angles throughout the year.

E. Cost comparison of frequency-variable-angle optimal operation plan for cooling tower semi-regulating fans with different blade installation angles per hour and annual optimal frequency-variable-angle operation plan.

The cooling tower fan has different blade installation angles throughout the year, and the cost of frequency conversion and angle adjustment optimization operation plan for hourly frequency conversion includes operating energy costs and angle adjustment costs. Compared with non-frequency conversion, the initial equipment cost of the frequency converter is increased.

Option 1 is based on a blade installation angle for a whole year and operates with variable frequency every hour every day. There is no cost for angle adjustment. There is an initial cost for frequency converter for frequency conversion operation, and no cost for frequency converter adjustment. Therefore, the total annual cost of cooling tower fan operation is equal to the energy cost of fan operation and The sum of the initial equipment costs of the frequency converter.

Plans 2 to 4 are based on different blade installation angles throughout the year and operate with frequency conversion every hour every day. The angle adjustment cost is calculated according to the number of angle changes in the operation plan. Frequency conversion operation has frequency converter equipment costs, so the cooling tower fan annual total The cost is equal to the sum of fan operation energy cost, angle adjustment cost and frequency converter initial equipment cost apportionment.

Finally, compare the equipment operating energy costs and total operating costs of the six schemes of the original annual design blade installation angle operation scheme of the fan, the annual cooling tower maximum required ventilation blade installation angle operation scheme, and schemes 1 to 4, and finally determine The scheme with the least total cost is the optimum operation scheme with variable frequency and variable angle.

Description of drawings

Figure 1 is a graph showing the relationship between the fan efficiency and the blade installation angle at the operating point of the cooling tower fan at the rated speed variable angle operation.

Figure 2 shows the cooling task curve and filler performance curve of the cooling tower.

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

Fig. 4 is a diagram of the iterative approximation method for calculating the equilibrium point of the cooling tower.

Figure 5 is a graph showing the required ventilation for cooling towers by week in a typical year.

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

Fig. 7 is a diagram of the determination method of the variable frequency and variable speed optimal operation scheme when the cooling tower semi-regulated fan has different blade installation angles.

Figure 8 is a diagram for determining the variable speed ratio of the cooling tower semi-regulated fan with variable frequency and variable speed for optimal operation.

Fig. 9 is a diagram of fan air volume and blade installation angle for one kind of blade installation angle in a year, every hour of frequency conversion optimization operation scheme.

Figure 10 is a diagram of fan air volume and blade installation angle for the daily and hourly frequency conversion optimization operation scheme of two kinds of blade installation angles throughout the year.

Figure 11 is a diagram of fan air volume and blade installation angle for the daily and hourly frequency conversion optimization operation scheme of three kinds of blade installation angles throughout the year.

Figure 12 is a diagram of fan air volume and blade installation angle for the four kinds of blade installation angles throughout the year for the daily and hourly frequency conversion optimization operation scheme.

Fig. 13 is a graph showing the air volume and wind pressure, air volume and power performance curves of the LF-42 fan according to the embodiment of the present invention.

Fig. 14 is a graph showing the relationship between the blade installation angle and the air volume of the cooling tower fan operating at variable angle according to the embodiment of the present invention.

Fig. 15 is a graph showing the relationship between the air pressure and the air volume of the cooling tower fan in the embodiment of the present invention when the fan operates at a variable angle at a rated speed.

Fig. 16 is a graph showing the relationship between the operating efficiency and the air volume of the cooling tower fan according to the embodiment of the present invention.

Fig. 17 is a diagram of fan air volume and blade installation angle of the typical annual variable frequency variable angle optimization operation scheme 3 of this embodiment.

Fig. 18 is a diagram of the speed ratio diagram of frequency conversion operation for each hour in a typical day of the third frequency conversion angle optimization operation scheme of this embodiment.

Detailed ways

The technical scheme of the present invention is adopted below, and the present invention will be further described in conjunction with the drawings and embodiments, but this embodiment should not be construed as a limitation of the present invention.

There is a LDCM-800SC cooling tower in the first workshop of a chemical factory, the local atmospheric pressure is 754mmHg, the density is 1.13kg/m ³ , and the cooling water flow rate is 800m ^3/ h. Fan model LF-42, semi-regulated, equipped with three-phase asynchronous motor Y180L-4, rated power 22kW, rated current 43A, motor efficiency 90%, speed 1470r/min, equipped with VFD220CP43B-21 special inverter for fan and water pump. The cooling tower is equipped with LJ3 type reducer, its efficiency is 92%. The unit price of local electricity is 0.6 yuan/(kW·h).

The original operation plan is: the fan operates at a blade installation angle of 13° throughout the year, the operating air volume is 453,769 m ³ /h, the operating power is 18.4877kW, the input power of the motor is 21.88kW, the total annual operating power consumption is 191144kW·h, the total energy The cost is 114,686 yuan.

A. Calculate the total resistance P _Z and total resistance S of cooling tower ventilation.

Known LDCM-800SC cooling tower body structure: packing area 46m ² , air inlet area 46m ² , length of air guiding device 3m; net ventilation area of sprinkler device 41m ² , net ventilation area of water distribution device 43m ² , water collection The net ventilation area of the device is 43m ² , the inlet area of the air duct is 26m ² , the throat area of the air duct is 14.12m ² , the outlet area of the air duct is 25.53m ² . The gradual expansion angle is 60°.

In this example, 1.0m oblique ladder wave spray filler is selected, and the spray water density q is 17kg/(m ² h) from formula (1); it can be obtained from Table 3 in "Thermal and Resistance Performance Analysis of Cooling Tower Plastic Water Sprinkler Filling" It is found that A ₁ , A ₂ , and A ₃ are 0.00054, 0.02372, and 0.38310 respectively, and m ₁ , m ₂ , and m ₃ are 0.00422, -0.12560, and 2.9710, respectively. Substituting into formula (2) and formula (3), A=9.2449, m = 2.05538; Calculate the resistance of the water spray filler from formula (4):

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

According to the cross-sectional area and resistance coefficient of each component in the cooling tower, the velocity v _i of each section can be obtained from formula (5), and substituted into formula (6) to obtain the total ventilation resistance of the cooling tower:

Substitute the total resistance P _z of the cooling tower into formula (7) to get the total resistance

B. Calculate and determine the actual working point parameters of different blade installation angles when the fan is working in the cooling tower: flow G _j , wind pressure P _j and efficiency η _j .

Fig. 13 is the air volume and wind pressure, air volume and power performance curve of the LF-42 fan used in the cooling tower of the embodiment of the present invention, obtained by fitting, the coefficient A ₁₃ of the 13° blade installation angle air volume-wind pressure performance curve equation, B ₁₃ , C ₁₃ , and D ₁₃ are -0.000069, 0.0057, -0.4205, and 24.4712 respectively, which are substituted into formula (8), and the equation of the air volume-wind pressure performance curve at the blade installation angle of 13° is obtained as

P ₁₃ ＝-0.000069G ³ +0.0057G ² -0.4205G+24.4712

Through fitting, the coefficients A ₁₃ ', B ₁₃ ', C ₁₃ ', and D ₁₃ ' of the 13° blade installation angle air volume-power performance curve equation are 0.0005, -0.0723, 3.1266, and -24.1831 respectively, which are substituted into the formula ( 9), the air volume-power performance curve equation of the blade installation angle of 13° is obtained as

N ₁₃ =0.0005G ³ -0.0723G ² +3.1266G-24.1831

Substituting the total impedance S of the cooling tower into formula (10), the required pressure performance curve equation of the cooling tower is obtained:

P=0.00514G ²

The intersection point of the required pressure performance curve and the fan air volume-wind pressure performance curve is the working point of the fan. The simultaneous equations are solved to obtain the actual operating point flow G=453,769 m ³ /h, the wind pressure P=10.6742m air column, and the power N=18.4877kW at the blade installation angle of 13°.

Use the above method to fit the performance curves of the other blade installation angles of the fan, from 2° to 22°, fit a curve at an interval of 0.1°, a total of 201 air volume-wind pressure performance curve equations, respectively, the required pressure performance curve equation (10), 201 operating point parameters are obtained by solving, as shown in Fig. 14 and Fig. 15.

Substitute the obtained air volumes G _j of 201 blade installation angles of the fan in the cooling tower into the power performance curve equation (9) of the fan corresponding to the blade installation angle, and calculate 201 power N _j , and calculate the fan according to formula (11). The efficiency η _fj at 201 blade installation angles is shown in Figure 16.

C. Calculation and determination of the minimum ventilation required by the cooling tower under different environmental conditions.

Taking an environmental working condition as an example, the calculation is as follows:

Environmental conditions: Atmospheric pressure 100.56kPa, dry bulb temperature: 27°C, wet bulb temperature: 25°C, according to equipment cooling requirements, the maximum temperature of the water entering the tower is 45°C, and the temperature difference between the water entering and leaving the tower is 10°C. The partial pressures of saturated water vapor corresponding to 27°C and 25°C are P _d ”=3.5631kPa, P _s ”=3.1655kPa respectively, and the relative air humidity is The apparent density of humid air is ρ=1.1569kg/m ³ , and the moisture content of air is x=0.0193kg/kg (DA).

As shown in Figure 2, when the cooling task curve of the cooling tower intersects the filler performance curve, that is, when Ω _n '=Ω _n under the same air-water ratio, it is the working point of the cooling tower. In order to obtain the equilibrium operating point of the cooling tower, a trial calculation is carried out. First, 3 sets of data are taken: (1) t ₁ =46°C, t ₂ =36°C, t _m =41°C, λ=0.39kg(DA)/kg; ( 2) t ₁ =47°C, t ₂ =37°C, t _m =42°C, λ=0.39kg(DA)/kg; (3) t ₁ =48°C, t ₂ =38°C, t _m =43°C , λ=0.39kg(DA)/kg. Taking the first set of data as an example, the calculation is as follows:

The enthalpy of humid air entering the tower is calculated as h ₁ =76.362kJ/kg(DA), and the relevant data are substituted into formula (14) to obtain the heat coefficient taken away by the evaporated water as

According to formula (16), the enthalpy of wet air exiting the tower is

According to formula (17), the average enthalpy of humid air in the tower is

The partial pressures of saturated water vapor corresponding to t ₁ , t ₂ , and t _m are P _t1 ”=10.0832kPa, P _t2 ”=5.939kPa, P _tm ”=7.776kPa, and the corresponding specific enthalpy of saturated air is h ₁ ”= 225.4689 kJ/kg (DA), h ₂ ″=136.4071 kJ/kg (DA), h _m ″=175.5128 kJ/kg (DA).

Substituting into formula (21), the cooling number of the cooling tower is

According to the above method, the other two sets of data are calculated, and the calculation is shown in Table 1:

Table 1 λ=0.39kg(DA)/kg Calculation data table of balance point A

After finishing, (1) t ₂ =36°C, Ω _n =1.0503; (2) t ₂ =37°C, Ω _n =0.8606; (3) t ₂ =38°C, Ω _n =0.7258. Through these three sets of data, as shown in Figure 3, the fitting curve:

Choose the 1.0m inclined ladder wave water spray filler, check the B and k coefficients from Table 2 in "Thermal and Resistance Performance Analysis of Cooling Tower Plastic Water Spray Filler", and substitute them into the formula (12) to get the filler characteristic number as

Ω _n '=Bλ ^k ＝1.60×0.39 ^0.64 ＝0.8758

In order to satisfy that the cooling number Ω _n is equal to the characteristic number Ω _n ', set Ω _n =Ω _n ', and the equilibrium point t ₂ =36.9078°C. Therefore, the equilibrium point A is obtained, and the coordinates are (0.39, 46.9078).

Then take 3 sets of data of λ=0.49kg(DA)/kg, (1) t ₁ =43°C, t ₂ =33°C, t _m =38°C, λ=0.49kg(DA)/kg; (2) t ₁ =44°C, t ₂ =34°C, t _m =39°C, λ=0.49kg(DA)/kg; (3) t ₁ =45°C, t ₂ =35°C, t _m =40°C, λ = 0.49 kg(DA)/kg. Recalculate according to the above process, and the specific calculation is shown in Table 2:

Table 2 Calculation data table of λ＝0.49kg(DA)/kg balance point B

After finishing, (1) t ₂ =33°C, Ω _n =1.4689; (2) t ₂ =34°C, Ω _n =1.1625; (3) t ₂ =35°C, Ω _n =0.9566. Through these three sets of data, as shown in Figure 3, the fitting curve:

Substituting into formula (12), the filler characteristic number is Ω _n '=Bλ ^k =1.60×0.49 ^0.64 =1.0136. Let Ω _n =Ω _n ', the equilibrium point t ₂ =34.6691°C. Therefore, another equilibrium point B is obtained, and the coordinates are (0.49, 44.6691).

As shown in Figure 4, the balance points A and B are connected in a linear form, and the equation of the line is t _1AB = -22.387λ+55.63873.

Control the water temperature entering the tower to a maximum of 45°C, and the temperature of the water entering the tower at the final approach point is t ₁ * = 45°C, let t ₁ * = t _1AB = 45°C, substitute the linear equation into formula (22), and solve the formula (23 )C' point λ _C' = 0.4752kg(DA)/kg, C' point is obtained according to the linear change of two points A and B, in turn, according to λ _C' = 0.4752kg(DA)/kg, use the above method to re- Calculate the water temperature t ₂ of the outlet water at point C of the equilibrium point on the curve = 34.9708°C, then the temperature of the water entering the tower t ₁ = 44.9708°C, so the coordinates of point C are (0.4752, 44.9708), which is substituted into formula (24), |t _1C -t ₁ *|＝0.0292>0.01, the accuracy does not meet the requirements, it is necessary to continue the iterative calculation; compare the positions of the points on the curve, the required balance point T is located between the nearest points A and C, list the AC linear equation, and use t ₁ * = 45°C is substituted, and the abscissa of point _D ' obtained is λ _D' = 0.4739kg(DA)/kg, and then recalculated according to the above method to obtain the equilibrium point D on the curve The outlet water temperature at point t ₂ =35.0037°C, the coordinates of point D are (0.4739, 45.0037), substituted into formula (24), |t _1D -t ₁ *|=0.0037<0.01, the accuracy meets the requirements, and substituted into formula (25) to get Calculate the ventilation rate for the working condition:

G _k ＝λ _k · Q · ρ _w /(ρ _k · 10000)＝0.4739×800×1000/1.1569＝327,634 million m ³ /h

According to the above method, calculate the minimum ventilation rate required by the cooling tower under the environmental working conditions at different times throughout the year.

D. Calculation and determination of the frequency conversion and angle optimization operation scheme of the semi-regulating fan of the cooling tower with different blade installation angles and frequency conversion per hour throughout the year.

In this embodiment, the fan adopts frequency conversion operation every day and every hour throughout the year, and solves and determines the optimal operation scheme of frequency conversion and variable angle with different blade installation angles throughout the year.

In this embodiment, an asynchronous motor is selected, and the relationship between the inverter efficiency and the transmission ratio δ is fitted according to the formula (27):

η _bp =-0.0266δ ² +0.0992δ+0.9054

Scheme 1 One kind of blade installation angle throughout the year, frequency conversion optimization operation every hour every day

As shown in Figure 9, under the premise of satisfying the annual maximum air volume G _max = 412,454 m ³ /h, with the goal of minimizing the total energy consumption of the fan in the whole year, it is calculated that the optimal blade installation angle of the fan is 10.1°, namely At point B in Figure 7, the rated speed of the fan is 419,791 m ³ /h, and the efficiency of the fan is 80.73%. The fan is operated with frequency conversion every hour every day, so that the air volume of the fan is equal to the air volume required by the cooling tower per hour. In the trial calculation, if the input power of the inverter increases after frequency conversion, it will run without frequency change for that hour. Substituting into formula (35), the total energy consumption of the fan in the whole year is A _z =48289kW·h.

Option 2: 2 kinds of blade installation angles throughout the year, frequency conversion optimization operation every hour every day

As shown in Figure 10, the fan of this scheme selects two kinds of blade installation angles for the whole year to operate with frequency conversion every hour, with the goal of minimizing the total energy consumption of the fan in the whole year, and the two optimal blade installation angles for the operation of the fan are calculated to be 10.1 ° and 6°. From the 1st week to the 22nd week and from the 38th week to the 52nd week, the fan operates at a blade installation angle of 6°, which is point A in Figure 7. The rated speed of the fan is 359,505 m ³ /h, and the fan efficiency is 88.85%. For the required air volume of the cooling tower in the second time period, the fan starts to operate with frequency conversion from the air volume of 359,505 m ³ /h; from the 23rd week to the 37th week, the fan operates at a blade installation angle of 10.1°, and the rated speed of the fan is 419,791 m ³ /h h, the efficiency of the fan is 80.73%, which meets the required air volume of the cooling tower during this period, and the fan starts to operate with frequency conversion from the air volume of 419,791 m ³ /h. Substituting into formula (36), the annual total energy consumption of fan operation A _z =46796kW·h.

Scheme 3 Three kinds of blade installation angles throughout the year, frequency conversion optimization operation every hour every day

As shown in Figure 11, the fan in this scheme uses three kinds of blade installation angles throughout the year to operate with variable frequency every hour. With the goal of minimizing the total energy consumption of the fan in the whole year, the three optimal blade installation angles for the operation of the fan are calculated to be 10.1° and 6.8° respectively. ° and 6°. As shown in Figure 17, from the 1st week to the 22nd week and from the 38th week to the 52nd week, the fan operates at a blade installation angle of 6°, the air volume of the fan is 359,505 m ³ /h, and the efficiency of the fan is 88.85%. Frequency conversion operation; in the 23rd and 37th weeks, the fan operates at a blade installation angle of 6.8°, the fan air volume is 370,575 m ³ /h, the fan efficiency is 83.60%, and the fan starts to operate with frequency conversion at this air volume; from the 24th week to the 36th week In operation, the fan operates at a blade installation angle of 10.1°, the air volume of the fan is 419,791 m ³ /h, the efficiency of the fan is 80.73%, and the fan starts to operate with frequency conversion at this air volume. Figure 18 shows the fan frequency and speed ratios for each hour of the day in the 27th week. Substituting into formula (37), the total energy consumption of fan operation for the whole year is calculated as A _z =46675kW·h.

Option 4 Four kinds of blade installation angles throughout the year, frequency conversion optimization operation every hour every day

As shown in Figure 12, the fan of this scheme adopts 4 kinds of blade installation angles throughout the year to operate with frequency conversion every hour, with the goal of minimizing the total energy consumption of the fan in the whole year, programming and trial calculation are used to solve the problem, and the 4 optimal blade installation angles of the fan are determined to be 10.1°, 7.5°, 6.8° and 6°, from the 1st week to the 22nd week and from the 38th week to the 52nd week, the fan operates at a blade installation angle of 6°, the air volume of the fan is 359,505 m ³ /h, and the efficiency of the fan is 88.85%. This air volume starts to operate with frequency conversion; in the 23rd and 37th weeks, the fan operates at a blade installation angle of 6.8°, the air volume of the fan is 370,575 m ³ /h, and the efficiency of the fan is 83.60%, and the fan starts to operate with frequency conversion at this air volume; the 24th week And in the 36th week, the fan operates at a blade installation angle of 7.5°, the air volume of the fan is 380,542 m ³ /h, and the efficiency of the fan is 81.13%. The installation angle is running, the air volume of the fan is 419,791 m ³ /h, the efficiency of the fan is 80.73%, and the fan starts to operate with frequency conversion at this air volume. The calculated annual total energy consumption of the fans is A _z =44323kW·h.

E. Cost comparison of frequency-variable-angle optimal operation scheme with frequency-variable frequency-variable-angle-variable frequency-variable hourly frequency-variable frequency-variable-angle fan for cooling tower semi-regulated fans throughout the year and determination of optimal frequency-variable angle variable-frequency optimal operation scheme for the whole year.

The semi-adjustable fan used in the cooling tower of this embodiment has a blade installation angle range of 2° to 22°, which is applied to the cooling tower of this embodiment. The highest efficiency point is at 6°. The number of blade installation angles used by the cooling tower fans throughout the year is different. The cost of several aspects of the frequency conversion and variable angle optimization operation scheme is also different. For the original operation scheme of the fan, the installation angle scheme of the fan blade is determined according to the maximum annual ventilation volume of the cooling tower, and the scheme 1 to scheme 4. A total of 6 schemes of frequency conversion per hour The running energy consumption, energy consumption cost, angle adjustment cost, frequency converter cost and total cost are compared. Among them, the unit price of electricity is calculated as 0.6 yuan/(kW h), and the cost of semi-adjustable fan angle adjustment is 1,000 yuan once; the selected VFD220CP43B The initial investment cost of -21 type inverter for fan and water pump is 4,500 yuan, the service life is 10 years, the residual value is 500 yuan, and the cost of the inverter allocated to each year is 400 yuan.

Table 3 Comparison of the annual cost of the cooling tower fan 6° blade installation angle with the highest efficiency when the frequency-variable-angle optimization operation scheme is shown in Table 3

As shown in Table 3, for each hourly frequency conversion operation scheme, the optimal operating blade installation angle and running time of cooling tower fans are determined according to the lowest operating energy consumption; The total cost of device cost allocation is the lowest, and the optimal variable frequency and variable angle operation scheme is determined.

Compared with the original plan, the installation angle of the blades is adjusted to 9.6° of the maximum air volume required by the cooling tower throughout the year, and the annual energy cost is saved by 17.36%; plan 1 to plan 4 adopt hourly frequency conversion optimization operation, and the energy cost saving rate reaches 75% Left and right, the energy saving effect is very good; with the increase in the number of blade installation angles used throughout the year, the energy cost of frequency conversion and variable angle operation decreases slightly. Considering the increase in angle adjustment costs, the total cost gradually increases with the increase in the number of angle adjustments Big, so, plan 1: An optimal operation plan with an optimal blade installation angle of 10.1° and frequency conversion per hour throughout the year is the best annual operation plan for cooling tower fans with variable frequency and angle. Compared with the original plan, the total cost Save 74.39%.

If the angle adjustment costs of Scheme 2 to Scheme 4 are reduced to 800, 1600, and 2400 yuan respectively, the total annual expenses are 29261, 30001, and 30784 yuan respectively. Scheme 2—the two kinds of blade installation angle schemes are optimal frequency conversion and angle adjustment optimization. Run the program and save 74.49% of the total cost for the year.

Claims (3)

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.