Working principle of centrifugal blower

The working principle of centrifugal blower is similar to that of centrifugal fan, except that the air compression process is usually carried out under the action of centrifugal force through several working impellers (or stages). The blower has a rotor that rotates at a high speed. The blades on the rotor drive the air to move at a high speed. The centrifugal force makes the air flow to the fan outlet along the involute in the involute shaped casing. The high-speed air flow has a certain air pressure. The fresh air is replenished from the center of the casing.

The working principle of single-stage high-speed centrifugal fan is: the prime mover drives the impeller to rotate at a high speed through the shaft. The air flow enters the high-speed rotating impeller from the inlet axial direction and becomes radial flow, which is accelerated, and then enters the diffuser chamber to change the flow direction and decelerate. This decelerating effect converts the kinetic energy in the high-speed rotating air flow into pressure energy (potential energy), so that the fan outlet maintains a stable pressure.

Theoretically, the pressure flow characteristic curve of the centrifugal blower is a straight line. However, due to the friction resistance and other losses inside the blower, the actual pressure and flow characteristic curve decreases gently with the increase of the flow, and the corresponding power flow curve of the centrifugal blower rises with the increase of the flow. When the fan operates at a constant speed, the operating point of the fan will move along the pressure flow characteristic curve. The operating point of the fan depends not only on its own performance, but also on the characteristics of the system. When the resistance of the pipe network increases, the pipeline performance curve will become steeper. The basic principle of fan regulation is to obtain the required working conditions by changing the performance curve of the fan itself or the characteristic curve of the external pipe network.

Principle and characteristics of frequency conversion regulation

With the continuous development of science and technology, AC motor speed regulation technology is widely used. Through a new generation of fully controlled electronic components, the frequency converter is used to change the speed of the AC motor to control the fan flow, which can greatly reduce the energy loss caused by the previous mechanical way of regulating the flow. Energy saving principle of frequency conversion regulation:

It can be seen that when the speed is reduced to half of the original rated speed, the flow, pressure and shaft power at the corresponding operating point are reduced to the original 1/2, 1/4 and 1/8 respectively, which is the reason why the frequency conversion adjustment mode can greatly save power. According to the characteristics of frequency conversion regulation, in the sewage treatment process, the aeration tank always maintains a normal liquid level of 5m. The blower is required to conduct a wide range of flow regulation under the condition that the outlet pressure is constant. When the regulation depth is large, the air pressure will drop too much to meet the process requirements. When the adjustment depth is small, it does not show the advantages of energy saving, but makes the device complex and one-time investment increased.

Regulating principle and characteristics of inlet guide vane

The inlet guide vane regulating device is to install a group of guide vanes with adjustable angle - inlet guide vanes near the suction inlet of the blower, which is used to make the air flow rotate before entering the impeller, causing twisting speed. The guide vane can rotate around its own axis. Each angle of blade rotation means changing a guide vane installation angle, so that the direction of air flow entering the fan impeller changes accordingly.

Principle of inlet guide vane regulating air volume

When guide vane installation angle θ= At 0 °, the guide vane basically has no effect on the inlet air flow, and the air flow will flow into the impeller blade in a radial direction. When θ> At 0 °, the inlet guide vane will deflect the absolute velocity of the air flow inlet along the circumferential velocity direction θ At the same time, it has a certain throttling effect on the speed of the air inlet. This pre rotation and throttling effect will lead to the decline of the fan performance curve, thus changing the operating conditions and realizing the flow regulation of the fan. Energy saving principle of inlet guide vane regulation.

When the installation angle of inlet guide vane is changed from θ 1=0 ° increases to θ 2 or θ 3, the operating condition point moves from M1 to M2 or M3; The flow decreases from Q1 to Q2 or Q3; The shaft power is reduced from P ′ 1 to P ′ 2 or P ′ 3. The area represented by the section line is the power saved by the inlet guide vane compared with the throttling regulation. The depth of the aeration tank is fixed. When the outlet pressure of the blower is kept constant, the blower adjusts the flow. That is, when H=constant and Q=variable, the characteristic curve of the pipe network is approximate to a horizontal straight line. The blower uses inlet guide vanes for adjustment. It is not necessary to change the characteristic curve of the pipe network. The pressure flow performance curve of the fan can be changed by changing the opening and closing angle of the guide vanes, The change of flow is realized by moving the operating point to the new changed fan characteristic curve.

The centrifugal fan adopts the inlet guide vane adjustment mode, which can achieve high efficiency and a wide performance range during partial load operation. Under the condition of keeping the outlet pressure constant, the working flow can vary from 50% to 100% of the rated flow. The greater the adjustment depth, the more work saved. If the flow is reduced to 60% of the rated flow, the power saved by the inlet guide vane mode is up to 17% more than that by the inlet throttling mode. In addition, it is relatively simple in structure, reliable in operation, convenient in maintenance and management, and low in initial investment. Therefore, the blower adopts the inlet guide vane to adjust the flow, which is obviously the best adjustment mode.