How to choose a suitable negative pressure fan to cool the plant is an important condition to ensure the normal and economic operation of the ventilation system. The so-called correct choice mainly refers to the selection of the fan according to the nature and use of the gas to be transported; the selected fan should meet the required air volume of the system, and the wind pressure should overcome the resistance of the system, and the efficiency is the highest or the economic use range. Working inside. The specific selection methods and steps are as follows:
1. Depending on the nature of the gas being transported, fans of different uses are used. For example, when the clean air is delivered, or the dust-containing gas has been purified, the dust concentration is not more than 150mg/m3, and the general ventilation can be used. For the corrosive gas, the anti-corrosion fan should be used; Explosion-proof or dust-exhausting fans should be used for explosive or dusty gases. However, when selecting a specific fan model and specification, it must be determined based on the performance table or characteristic graph on a certain type of product sample.
2. Considering that the pipeline system may leak air, some resistance calculations are not accurate. For reliable operation, the selected air volume and wind pressure should be greater than the calculated air volume and wind pressure of the ventilation dust removal system, ie the air volume: L'=KLL (1)
Wind pressure: H'=KHH (2)
L', H' in the formula - the air volume and wind pressure used for selection;
L, H—calculated air volume and wind pressure of the ventilation and dust removal system;
KL - air volume additional coefficient, dust removal system KL = 1.1 ~ 1.15;
KH——wind pressure additional coefficient, dust removal system KH=1.15～1.2.
3. According to the selected air volume L' 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 the appropriate fan outlet position and transmission mode. The operating point of the selected fan should be within the economic range, preferably at the right side of the highest efficiency point.
4. The performance parameters of the fan in the standard state (atmospheric pressure is 1.013×105 Pa, temperature is 20 °C, relative humidity is 50%), if the actual operating state is not the standard state, the actual performance of the fan It will change (except for air volume). Therefore, when selecting a fan, the parameters in the actual operating state should be converted to the parameters in the standard state. The conversion relationship is as follows:
Pa (3)
kW (4)
Where Hb, Nb, Ïb, pb, tb are the wind pressure, power, air density, gas pressure and temperature of the fan in the standard state (or specified state), ie the data listed on the fan sample;
H', N', Ï, p, t - wind pressure, power, air density, gas pressure and temperature of the fan under working conditions.
On the negative pressure fan sample, some boiler induced draft fan performance parameters are obtained according to the gas temperature of 200 ° C or 240 ° C, the conversion of the tb in the formula (3), (4) should be 200 ° C or 240 °C substitution.
5. Unless you choose any one of the fans can not meet the requirements, or when the wind pressure and air volume of the fan are required to change the amplitude of the large air conditioner, you should avoid using two or more fans in parallel or in series. When two or more fans work together, each fan will perform worse than its own.
6. In recent years, due to the continuous improvement of the structure of wind turbines in China, the efficiency of wind turbines has been continuously improved, and noise has been continuously reduced. Some new types of wind turbines are gradually replacing some old wind turbines. In order to save energy and reduce noise hazard, new wind turbines with high efficiency and low noise should be selected as far as possible to meet the required air volume and wind pressure. For example, the new Lauyt water-cooled fan and environmentally-friendly air conditioner are used.
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