Centrifugal versus Reciprocating: General Comparative Advantage
Compressors are machine which is intended to compress a substance in gaseous state and from many types of compressors, centrifugal dan reciprocating type compressor is the most used.
Fig-1 Compressor type chart
The following comparison is in high level comparison without specifying value of operating condition on the comparison.
Advantages of centrifugal type compressor
- Reliability/Availability is high, compressor can achieve continuous run typically 3-5 years in clean service without spare.
- Machine is relatively small which requires less plot area for installation. It requires smaller foundation support but dynamic load should also be considered.
- Installation cost tend to lower due to smaller size and number to be installed. It may impact also to the lower cost.
- Maintenance cost is lower.
- Compressor has low vibration without pressure pulsation (on the operating region – above surge point). Flow control is continuous over relatively wide capacity range.
- Gearbox may not necessary in case Turbine driven which minimizing cost and increase reliability.
- There is no oil contamination in to process gas
Disadvantages of centrifugal type compressor
- Generally, has lower efficiency for the same flow rate and pressure ratio
- Compressor operation is not efficient below the surge point and therefore recycle is necessary.
- Sensitive to changes in gas properties, especially composition/molecular weight/density since the machine has head limitation.
- Not suitable for low molecular weight gases, as pressure ratio capability per stage is low it tends to require a large number of machine stages (issue in compressor stability as need more longer shaft)
Advantages of reciprocating type compressor
- It is suitable for low-capacity range which below economic range of centrifugal compressors.
- Suitable and economic for low molecular weight gas service (very high heads due to low molecular weight)
- Compressor is available in very high pressures
- Not sensitive to gas composition changes comparing to centrifugal compressors.
- Compressor can achieve 0 to 100% stepwise flow variation, via clearance pockets and valve unloaders.
- Higher overall efficiency, thus lower discharge temperature.
- Flow rate is not sensitive to discharge pressure changes.
Disadvantages of reciprocating type compressor
- Compressor is high vibration due to reciprocating forces, it needs large foundation masses and large plot plan
- Spare unit are required for continuous services, shorter continuous run primarily due to valve failure
- Maintenance costs is higher than centrifugal compressors. More frequent operator inspection is required
- Compressor is sensitive to solids carryover (due to use of rubbing parts) and sensitive to liquid carryover (due to destruction of the lubricant film)
- There will be oil contaminant in process gas on lubricated type machine