With many lube oil systems, it is common to cool the oil before it is pumped to the end user (engine, compressor, etc). However, for large centrifugal compressors, it is common to pump the lube oil hot, and cool the oil immediately before it enter the compressor. Since we know that cool oil extends the life of the lube oil pump, why would we do this?
Pumping hot lube oil and cooling it just before it enters the compressor is a common practice in large centrifugal compressors due to several reasons:
1. Thermal expansion control: When oil is heated, it tends to expand, which can cause differential thermal expansion issues within the pump and associated piping. By pumping hot oil, the thermal expansion is controlled and minimized. Cooling the oil just before it enters the compressor allows for a more stable and controlled operating condition.
2. Viscosity control: Heating the oil reduces its viscosity, making it easier to pump. This helps to improve the overall pump efficiency and reduce the load on the lube oil pump. However, it is important to cool the oil before it enters the compressor to restore its viscosity to the desired level. This ensures optimal lubrication and protection for the compressor components.
3. Oil film performance: Cooling the oil just before it enters the compressor helps to maintain a thin but effective lubricating film between the rotating and stationary components within the compressor. The cooler oil temperature allows for better lubrication and heat dissipation, thereby extending the life of the compressor.
4. Operational considerations: By cooling the oil just before entering the compressor, any potential contaminants or impurities that may have built up or entered the oil during the pumping process can be minimized or removed. This helps in maintaining a cleaner and higher-quality lubrication system, further enhancing the reliability and longevity of the compressor.
In summary, pumping hot oil and then cooling it just before it enters the compressor is done to control thermal expansion, maintain proper viscosity, ensure optimal lubrication, and improve operational reliability and efficiency of large centrifugal compressors.
The practice of pumping lube oil hot and cooling it just before it enters the compressor is commonly used for large centrifugal compressors. While it may seem counterintuitive since cool oil is known to extend the life of the lube oil pump, there are valid reasons for this approach.
The main objective of cooling the oil is to maintain the desired operating temperature within the compressor. Centrifugal compressors generate a significant amount of heat while in operation, due to high-speed rotation and compression of gases. If the oil is cooled prior to entering the compressor, it will absorb some of this heat, helping to maintain the temperature within safe limits.
By pumping the oil hot and cooling it just before it enters the compressor, several benefits can be achieved:
1. Heat dissipation: The hot oil acts as a coolant for the compressor during the initial stages, absorbing and carrying away some of the heat generated. This helps in preventing excessive heating of the compressor components and ensures optimal operating conditions.
2. Viscosity control: Lubricating oil generally has higher viscosity at lower temperatures. By pumping the oil hot, its viscosity decreases, allowing for smoother flow through the system. This helps in reducing pumping losses and improving overall system efficiency.
3. Thermal expansion compensation: When the oil is heated, it expands. By pumping the oil hot, any expansion that occurs is compensated for, ensuring that the oil is supplied at the desired flow rate and pressure to the compressor. This helps in maintaining proper lubrication and preventing potential damage to the compressor due to insufficient oil flow.
It's important to note that while hot oil can potentially reduce the lifespan of the lube oil pump, this is typically outweighed by the benefits mentioned above. Additionally, lube oil pumps for large centrifugal compressors are designed to handle the higher temperatures, and proper maintenance and monitoring systems are in place to ensure their reliable operation.
In summary, pumping the lube oil hot and cooling it just before it enters the compressor of large centrifugal compressors helps in dissipating heat, controlling viscosity, and compensating for thermal expansion. These benefits contribute to the safe and efficient operation of the compressor, outweighing any potential negative effects on the lube oil pump.