On reciprocating piston compressors and centrifugal compressors in the selection of CNG equipment
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There is a wellhead gas treatment project with a wellhead pressure of 0.5 MPa and a flow rate of 15,500 Nm3/h. The exhaust pressure varies depending on whether the gas is used for power generation or sold; it is either 4 MPa or 25 MPa. The current plan involves using 6 piston compressors, which are capable of compressing the gas to either 4 MPa or 25 MPa. I would like to ask: Given the advantages of centrifugal compressors, such as their high flow rate and the ability to achieve a maximum discharge pressure of up to 60 MPa, why aren’t they chosen as compressors for CNG? If a centrifugal compressor is chosen as the CNG compressor, the number of units required can be significantly reduced. Moreover, centrifugal compressors have few vulnerable components, which helps to cut maintenance costs considerably. But why not choose it?
Answering my own question: After consulting experienced professionals, it is possible to use a centrifugal compressor, but the moisture content in the medium compressed by the centrifuge must not be too high; if the moisture level is high, dehydration is necessary first. I wonder if this statement is correct? Please ask an expert to provide another interpretation
This post was last edited by foolloof on 2017-12-13 11:12. So, adding several separators could also solve the problem, right?
The pressure of centrifuges in a two-stage series configuration is around 12 only, so it’s not possible to use them for CNG in the left and rear sections. Moreover, two-stage series centrifuges are already very expensive
Theoretically, centrifugal compressors can be compressed to 25 MP, but it is difficult to compress from 0.5 MP to 25 MP; the compression ratio is too high, which imposes strict requirements on the design of the equipment’s structure and the materials used, resulting in high costs.
The experienced technician you consulted is not qualified; although centrifugal compressors have a high flow rate, they cannot cope with large variations in pressure. The discharge pressure is related to the speed of rotation, rather than to the back pressure. The working principle of a centrifugal compressor is to increase the speed of the gas within the impeller, which can reach over 300 meters per second; thereafter, energy is converted in the diffuser, resulting in a decrease in speed and an increase in pressure.