The working principle of centrifugal blower
The working principle of centrifugal blower is similar to that of centrifugal ventilator, except that the compressive process of air is usually carried out by several working impeller (or several level) under the action of centrifugal force. A high-speed rotation of the rotor, the fan is on the rotor blade drive air high-speed movement, centrifugal force makes the air within the involute in the shape of a chassis, along the involute flow fan outlet, high-speed airflow have a certain air pressure. The new air is replenished by the center of the shell.
Working principle of single stage high speed centrifugal fan is: engine by high speed rotation shaft to drive the impeller, axial airflow by imports after entering the high-speed rotating impeller into radial flow is accelerated, and then into the cavity expansion pressure, change flow direction and reduction, the reduction effect will be in the high speed rotating airflow with kinetic energy into pressure energy (potential energy), make the fan exports stable pressure.
In theory, the characteristic curve of pressure and flow of centrifugal blower is a straight line, but the fan is internal friction losses, such as the actual pressure and flow characteristic curve along with the increase of traffic and gently falling, the corresponding power of centrifugal fan - flow curve rises along with the increase of flow rate. When the fan is running at constant speed, the operating point of the fan will move along the pressure - flow characteristic curve. The operating point of the fan is not only dependent on its own performance, but also depends on the characteristics of the system. When the pipe network resistance increases, the pipeline performance curve will get 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.
The principle and characteristics of frequency conversion control
With the development of science and technology, ac motor speed regulation is widely adopted. By a new generation of all type of electronic components, with a frequency converter to change the way of ac motor speed fan flow rate control, can greatly reduce the energy loss that causes way past mechanical control flow. Energy saving principle of frequency conversion adjustment:
Known, when the rotation speed reduced to half of the rated speed, the corresponding point of the flow, pressure and shaft power down to the original 1/2, 1/4, 1/8, this is the reason why inverter control methods can greatly saving electricity. Based on frequency conversion adjustment of the properties, in the wastewater treatment process, aeration tank always maintain the normal level, 5 m for blower under the condition of the outlet pressure constant, for a wide range of flow control, when adjusting the depth is larger, will decrease the wind pressure is too big, can't meet the technological requirements. When the adjustment depth is less than an hour, it can not show the advantage of energy saving. Instead, it makes the device complex and the one-time investment increases. Therefore, it is obviously improper to adopt the variable frequency modulation method to keep the aeration tank of the project in the condition of 5m liquid level.
Principle and characteristics of inlet guide blade adjustment
Inlet guide vane adjusting device is installed near the entrance of the blower suction a set of adjustable guide vane Angle of guide vane - import, its role is to make the air before entering the impeller rotation, distortion caused by speed. The guide blade can rotate around its own axis, and each Angle of the blade means the transformation of a guide blade installation Angle, so that the flow direction of the fan impeller changes accordingly.
Principle of regulating air volume of imported guide blade
When the guide blade installation Angle theta = 0 °, basically no vanes on imported air, air to the radial flow impeller blades. When theta > 0 °, will make the air inlet guide vane imported absolute speed along the circumference direction deflection Angle of theta, at the same time, the speed of imported gas throttling effect to a certain extent, the prewhirl and throttling fan performance curve will lead to decline, so that the operation point of change, realize the fan flow control. Energy saving principle of imported guide blade adjustment.
When install the inlet guide vane Angle by theta. 1 = 0 ° increase to 2 or theta. Theta 3, operation condition point by M1 to M2 or M3. Flow from Q1 to Q2 or Q3; The shaft power is reduced by P '1 to P' 2 or P '3. The area of the profile is the power saved by the inlet guide blade. In this project, the depth of the aeration tank is fixed, blower under the condition of the outlet pressure constant, which can adjust the flow, or H = constant, Q = variables, pipeline characteristic curve similar to straight and level of blower imported guide blade adjustment, need not by change of pipeline characteristic curve, but by changing the Angle of the guide vane opening and closing, change the pressure - flow performance curve of the fan, the change of the flow point by point moved to the new change of the fan characteristic curve method.
Centrifugal fan with regulating mode, inlet guide vane at partial load operation can obtain high efficiency and wide performance range, under the condition of the outlet pressure constant, work flow can change within 50% ~ 100% of the rated flow range. The greater the adjustment, the more the province. When the flow rate is reduced to 60% of the rated flow, the imported guide blade saves 17% more power than the imported throttling method. In addition, its structure is relatively simple, the operation is reliable, the maintenance management is convenient, the initial investment is low. Therefore, in this project, the blower adopts the inlet guide blade regulating flow, which is obviously the best mode.