The difference between axial fan and centrifugal fan

With the changes in China's metallurgical production, process, chemical industry, mining, and tunnels, it is necessary to constantly adjust the gas flow, pressure, temperature, etc.; many units still use the backward adjustment of the windshield or valve opening to adjust the gas Flow, pressure, temperature, etc. This is actually a way of artificially increasing resistance, and at the expense of wasting electricity and money to meet the requirements of process and operating conditions for gas flow regulation.

Fan classification Fan classification can be divided into centrifugal type, axial flow type, oblique flow type (mixed flow type) and cross flow type according to the direction of gas flow.

(1) Centrifugal fan. The air flow mainly enters the impeller of the fan and flows mainly in the radial direction. This kind of fan is made according to the principle of centrifugal action. The products include centrifugal fans, centrifugal blowers and centrifugal compressors.

(2) Axial fan. The air flow enters the impeller of the fan axially and flows approximately in an axial direction on the cylindrical surface. Such fans include axial flow fans, axial flow blowers, and axial flow compressors.

3 Centrifugal Fans Centrifugal fans consist of a housing, a main shaft, an impeller, a bearing transmission mechanism, and a motor. Chassis: made of steel plate is sturdy and reliable, can be divided into integral and semi-open type, semi-open type for easy maintenance. Impeller: It is composed of blades, curved front plate and flat plate rear plate. Rotor: Static balance and dynamic balance should be done to ensure stable rotation and good performance. Transmission part: It consists of main shaft, bearing box, rolling bearing and pulley (or coupling).

Centrifugal blower is essentially a variable flow constant pressure device. When the rotation speed is constant, the pressure-flow curve of the centrifugal fan should be a straight line. Due to internal losses, the actual characteristic curve is curved. The pressure generated in the centrifugal fan is greatly affected by changes in the intake air temperature or density. For a given intake air quantity, the pressure at which the maximum intake air temperature (lowest air density) produces is the lowest. For a given pressure and flow characteristic curve, there is a power vs. flow characteristic curve. When the blower operates at a constant speed At a given flow rate, the power required increases with decreasing inlet air temperature.

4 Axial flow fan The axial flow fan is the airflow in the same direction as the axis of the fan blade, such as an electric fan, and the fan of the external air conditioner is an axial flow fan. It is called "axial flow" because the gas flows parallel to the axis of the fan. Axial fans are usually used where there is a high flow requirement and a low pressure requirement. Axial fans fix the position and move the air.

5 Differences between centrifugal fans and axial fans (1) Centrifugal fans change the flow direction of the medium in the air duct, while the axial fan does not change the flow direction of the medium in the air duct.

(2) The former is more complex to install;

(3) The former motor and fan are generally connected through a belt to drive the rotating wheel, the latter motor is generally in the fan;

(4) The former is often installed at the inlet and outlet of air conditioning units, boiler drums, induced draft fans, etc. The latter is often installed in the air duct or in the front of the air duct outlet.

In addition, there is a diagonal flow (mixed flow) fan. The wind pressure coefficient is higher than the axial flow fan, and the flow coefficient is larger than that of the centrifugal fan. Fills the gap between the axial fan and the centrifugal fan. At the same time with the installation of simple and convenient features. Mixed-flow (or axial-flow) fans combine the characteristics of axial-flow and centrifugal fans, although they look more like conventional axial-flow fans. The curved plate-shaped blades are welded to the conical steel hub. The flow is changed by changing the blade angle in the upstream inlet housing of the impeller. The housing may have an open inlet, but more often it has a right-angled bent shape so that the motor can be placed outside the pipeline. The drain shell slowly expands to slow down the velocity of the air or gas flow and converts the kinetic energy to a useful static pressure.

6 Fan selection results According to a preliminary set of three working conditions of a company's steelmaking converter secondary dedusting system, through the selection of the parameters, the two options are shown in Table 1.

Option A (Axial flow type) uses an adjustable axial flow fan, each stove is equipped with a fan, the fan model is SAF37.5-23.7-1, the fan blade type is NA20, the fan diameter is 3758mm, the speed is 745r/ Min, the maximum shaft power of the fan is 3858kW.

Option B (double suction double support + frequency conversion) uses double-suction, double-branch centrifugal fans plus variable frequency control, taking into account the larger flow, each stove is equipped with 2 fans, the fan model is 1688AZ/1825/7, the fan diameter is 2928mm, The speed is 980r/min, and the maximum shaft power of a single fan is 2439.2kW.

7 Economic analysis Preliminary setting: The fan has a working period of 8000 hours in one year, of which working condition 1 is 2000 hours, working condition 2 to 3 is 3000 hours, working condition 4 to 6 is 3000 hours, and the axial fan is compared with the centrifugal type after calculation. The energy consumption of fans is about 5.2 million kW·h less. Calculated at 0.7 yuan per unit, the electricity bill can save about 3.6 million yuan in electricity consumption. The energy-saving effect is very considerable.

In summary, selecting an adjustable axial fan has many advantages over a centrifugal fan. At the same time meet the industrial requirements, select the adjustable blade axial fan.