A centrifugal compressor is an air pump used for industrial or commercial processes, such as refrigeration or air conditioning, dust collection, and pneumatic conveying. Centrifugal compressors use a rotating impeller to move a fluid, such as gas, liquid, or molten material, through a tube at high pressure.
By increasing the velocity of the flow of fluid through the tube, the pressure of that fluid increases. Centrifugal compressors consist of an outer case and rotating shaft, mounted on bearings and supported by shaft seals. Fluid enters near the shaft and reaches high pressure as it is forced through the tubes.
Adequate lubrication of compressors and centrifugal pumps is necessary for the uninterrupted operation of oil and gas refineries. When examining the design of machine equipment, less more attention is given to flow, pressure, and construction materials lubricant application and protection.
Compressor Lubricating Oil System
Dynamic compressors have a few key components that require a coolant or lubricant: gears, bearings, and seals. The compressor lubrication oil system is designed for the application of automatic lubrication of a centrifugal compressor or pump as part of a refrigeration system. The control system delivers the required oil quantity and lubricates the components as per the calculation made by the control algorithm.
The lubrication system begins with an oil filter that removes large contaminants. The filter is located after the oil pump to protect the pump from damage if there are any particles in the oil that could cause damage to the pump. Oil is then forced through the system by the oil pump to an accumulator when inlet system pressure drops below atmospheric pressure, back to an inlet filter when inlet system pressure increases above atmospheric pressure, and out to the Nozzle when inlet system pressure remains constant. The flow rate is proportional to the volume flow at low inlet pressures, and it is proportional to the square of flow at outlet pressures.
Lubrication Best Practices
The key to successful lubrication practices for centrifugal compressors and pumps is selecting the correct lubricants and maintaining their quality through the application life cycle. From oils and greases to fluid gels, additives, coatings, and other additive packages, choosing the right lubricant for the compressor and pumps is crucial to maintaining its operation and function.
Modern compressor and pump systems rely on regular lubrication to operate without problems and achieve optimal operating efficiency. There are two key points to achieve this using lubrication best practices:
- Replacing oil whenever the compressor or pump is refueled
- Using an oil-resistant lubricator to avoid introducing water into the system
Most centrifugal compressors are best served by premium grade turbine oils ISO viscosity grades of 32 or 46. It should be noted, however, that there are many different types of compressors, and manufacturers will likely recommend lubricants that have been tested and proven at controlled user facilities.
The compressor lubricant should satisfy the following needs:
- Stays functional for long without a need for changeout
- Provides excellent protection against rust and corrosion
- Contains additives (molybdenum disulfide, graphite, zinc dithiophosphate) that allow them to withstand contact with water much better than standard lubricants.
- Prevents acidity, sludge, and deposit formation
- Provides easy filterability without depleting additives
All in all, the compressor lubricants should be formulated using high-quality synthetic base oils, advanced additive technology to ensure excellent thermal stability, oxidation resistance, antiwear protection, cleanliness reduction to improve critical service intervals, and improved seal life.