The functions of the isolation gas and sealing gas in MRC centrifugal compressors
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Please explain the functions and principles of the isolation air and sealing air in Shaanxi Blower MRC centrifugal compressors, as well as the key points to note during the startup and shutdown of the MRC. Thank you
The function of the isolation gas is to prevent the lubricating oil in the centrifuge’s bearings from leaking to the chamber side or the sealed side, thereby avoiding contamination of the compressed gas and the chamber. Nitrogen is commonly used as the isolation gas; therefore, it must be introduced before the oil circulation starts ； And it must stop after parking is completed and the cranking is finished; please pay close attention to these two time points. Sealing gas is the medium gas that prevents excessive leakage of process gas from within the chamber and forms an air film between the stationary and rotating rings. Nitrogen is used as the sealing gas before starting the compressor, while process gas is used after it has started running. As for different compressor manufacturers, the principle of dry gas sealing remains the same.
Is there a first-stage and a second-stage seal gas? Leaking gas? Are there any requirements for gas pressure? By how much should the pressure of the isolation gas be higher than the oil pressure? What are the risks of it being too high or too low?
In this regard, the main categories of seals used for sealing purposes are single-face seals, double-face seals, and tandem seals. The primary and secondary sealing gases you mentioned are used in a tandem sealing structure. Gas leakage is only a minor leak from the gas film between the stationary and rotating rings. There are certainly requirements regarding gas pressure; the specific value depends on the specifications set by the compressor manufacturer. The isolation gas pressure needs to be slightly higher than the oil pressure – at least about 1.5 kilograms higher, in my opinion, to ensure proper functionality. If the pressure of the isolation gas is too low, it is first not possible to prevent lubricant from leaking into the cylinder or toward the dry gas seal, thereby contaminating other components of the compressor – after all, it is an oil-free seal. Just a reminder: it seems that there’s no such thing as a chain shutdown due to the isolation gas in dry gas seals; I’ve never seen a shutdown occur because of the isolation gas·······
Generally, the pressure of the isolation gas and the sealing gas is between 0.4–0.6 MPa, with slight variations in these values. There is no exact figure for how much the air pressure is higher than the oil pressure, as the structures and stress-bearing cross-sections are not identical.