The progress of air pressure in centrifugal compressor is accomplished by impeller rotation and diffuser expansion. According to the exhaust pressure, it can be divided into three categories: centrifugal fan, whose air pressure is in the range of 10-15 kPa or less; centrifugal blower, whose air pressure is in the range of 15-350 kPa; centrifugal compressor, whose air pressure is above 350 kPa.
(1) Outlet throttling adjustment, that is, adjusting the opening of the adjusting valve at the outlet of the compressor to change the pipeline performance curve, change the working point of the compressor and stop flow adjustment. The adjustment method of export throttling is to increase the outlet resistance artificially to regulate the flow, which is not economical. Especially when the performance curve of the compressor is steeper and the flow (or pressure) of the adjustment is larger, the shortcomings of this adjustment method are more prominent. At present, in addition to the use of fans and small blowers, this method is seldom used by the compressor.
(2) Import throttle conditioning, which installs a conditioning valve on the inlet pipe of the compressor and regulates the intake pressure through the inlet conditioning valve. The reduction of intake pressure directly affects the exhaust pressure of the compressor, which makes the performance curve of the compressor move down. Therefore, the result of import adjustment is to change the performance curve of the compressor in practice to achieve the purpose of regulating the flow rate. Compared with the export throttling method, the import throttling method is more economical. According to the introduction of related materials, the stop test of a compressor shows that the power of import throttling is about 4-5% less than that of export throttling in the range of 60-80% fluidity change. So this is a simple and commonly used method of conditioning. However, there are still some throttling losses and some effects on the efficiency of the compressor after the change of working conditions. The import throttling method has another advantage: closing the small import valve will move the performance curve of the compressor to the small flow area, so it can make the compressor work in a smaller flow condition, and it is not easy to form surge.
(3) Change the speed adjustment. When the speed of the compressor changes, its performance curve also has corresponding changes, so this method can be used to change the operating point to meet the consumer conditioning requirements. The energy head of the centrifugal compressor is approximately proportional to n2, so a considerable range of adjustment can be obtained by adjusting the rotational speed. Variable speed conditioning does not cause additional losses, but the new working point after conditioning may not necessarily lead to some reduction in efficiency. Therefore, from the perspective of energy conservation, this is an economic conditioning method. Changing the speed adjustment method does not need to change the structure of the compressor itself, but only considers the strength of the rotor, the critical speed and the life of the bearing after increasing the speed. But this method requires that the driver must be adjustable.