Choosing the right fan is an important condition to ensure the normal and economical operation of the ventilation system. The so-called correct selection mainly refers to the selection of fans for different purposes according to the nature and purpose of the gas being transported; the selected fan must meet the air volume required by the system, and the wind pressure must be able to overcome the resistance of the system, and in the highest efficiency or economic use Within work.
Choosing the right fan is an important condition to ensure the normal and economical operation of the ventilation system. The so-called correct selection mainly refers to the selection of fans for different purposes according to the nature and purpose of the gas being transported; the selected fan must meet the air volume required by the system, and the wind pressure must be able to overcome the resistance of the system, and in the highest efficiency or economic use range Within work. The specific selection methods and steps are as follows:
1. Depending on the nature of the gas being transported, fans for different uses are selected. For example, when transporting clean air, or when the dust-containing gas has passed through the purification, and the dust concentration does not exceed 150mg / m3, the general ventilation can be selected; for the transmission of corrosive gases, an anticorrosive fan must be used; when transporting flammable, For explosive gas or dusty gas, use explosion-proof or dust exhaust fan. However, when selecting a specific fan model and specification, it must be determined according to the performance table or characteristic curve chart on a certain type of product sample.
2. Considering that the pipe system may leak air, some resistance calculations are not very accurate. For reliable operation, the selected air volume and air pressure should be greater than the calculated air volume and air pressure of the ventilation and dust removal system, that is,
Air volume: L ′ = KLL (1)
Wind pressure: H ′ = KHH (2)
Where L ′, H ′ —— selected air volume and air pressure;
L, H——Calculated air volume and wind pressure of ventilation and dust removal system;
KL——additional coefficient of air volume, dust removal system KL = 1.1 to 1.15;
KH—— additional coefficient of wind pressure, dust removal system KH = 1.15 ～ 1.2.
3． According to the selected air volume L ′ and wind pressure H ′, the type of the fan is selected on the fan product sample to determine the machine number, speed and motor power of the fan. In order to facilitate the takeover and installation, it is also necessary to select a suitable fan outlet location and transmission method. The operating point of the selected fan should be within the economic range, preferably to the right of the highest efficiency point.
4． The fan sample shows the performance parameters of the fan under standard conditions (atmospheric pressure of 1.013 × 105 Pa, temperature of 20 ° C, and relative humidity of 50%). If the actual operating status is not the standard status, the actual performance of the fan Will change (except for air volume). Therefore, when selecting a fan, the parameters in the actual operating state should be converted into the parameters in the standard state, and the conversion relationship is as follows:
Pa (3)
kW (4)
Where Hb, Nb, ρb, pb, tb-wind pressure, power, air density, gas pressure and temperature of the fan in the standard state (or specified state), that is, the data listed on the fan sample;
H ′, N ′, ρ, p, t——wind pressure, power, air density, gas pressure and temperature of the fan under the working conditions.
In the fan sample, the performance parameters of some boiler induced draft fans are obtained according to the gas temperature of 200 ° C or 240 ° C. When converting, the tb in equations (3) and (4) should be substituted by 200 ° C or 240 ° C. .
5． Unless any one of the fans can not meet the requirements, or the wind pressure and air volume of the fans are required to vary greatly during use, you should try to avoid using two or more fans in parallel or in series. Because two or more fans work together, each fan plays a worse role than when used alone.
6. In recent years, due to the continuous improvement of the structure of fans in China, the efficiency of fans has been continuously improved, and the noise has been continuously reduced. Some new types of fans are gradually replacing some old fans. In order to save energy and reduce noise hazards, a new type of fan with high efficiency and low noise should be selected as much as possible on the premise of meeting the required air volume and pressure.