Contact Section - Blowers - Lube Oil Systems
July 18, 2003

Introduction Oil Pumps Oil Filters Oil Piping Oil Reservoir Lube Oil Coolers Pressure Control Lube Oil Specification Lube Oil System Flushing Instrumentation

Associated Links Specification

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Introduction

Lube oil systems provide lubrication and cooling to the rotating parts and bearings of the blower, gear box and driver.  Lube oil systems for acid plant blowers are generally forced oil systems consisting of a main oil pump, standby oil pump, oil reservoir, duplex oil filters, oil coolers, instrumentation and piping.

Oil Pumps

Oil pumps are generally positive displacement gear type pumps.  On motor driven blowers, the main oil pump is generally driven off the low speed side of the gear box.  The auxiliary oil pump is generally electric motor driven.  A rundown oil pump is sometimes specified to ensure the bearings are supplied with oil when the plant and blower shutdowns due to a site electrical power failure.  The rundown oil pump will be motor driven with power supplied by a uninterruptible power supply (UPS).  Alternatively, the auxiliary motor driven oil pump can be supplied by the plant emergency power system.

During normal operation the main oil pump circulates oil from the reservoir, through the oil filters and to the bearings and gearbox.  In the event of a main oil pump failure the oil pressure will decrease and a low oil pressure switch will start the auxiliary oil pump. 

Oil Filters

Oil filters remove contaminates such as dirt, scale, etc. from the lube oil to prevent damage to the blower and driver bearings.  Two oil filters are generally specified with one operating and one standby.   Flow valves must enable the flow to be switched from one oil filter to the other without interruption in the flow of oil to the equipment.  The flow valves must also enable the off-line filter to be replaced without interrupting the operation of the blower.

Oil filters generally filter the oil down to a minimum of 25 µm.  Some manufacturer’s required filtration down to 10 µm.

Oil Piping

The oil piping supplied oil to the bearings and gear box and returns the oil to oil reservoir.  The oil supply piping downstream of the oil filters is generally stainless steel to avoid the formation of scale or rust which will damage the bearings.  Oil return piping can be carbon steel.

All new piping must be thoroughly cleaned and pickled prior to installation.   The piping is further cleaned when the oil system is flushed.

Oil Reservoir

The oil reservoir is a tank in which the oil returning from the bearings and gearbox collects and from which oil is pumped to the system.  The oil reservoir is generally an rectangular carbon steel tank sized for a minimum of 3 minutes retention time from the pump suction to the minimum operating level.

The oil reservoir should be equipped with a low point drain, level gauge, dip stick, vent, and access hole for cleanout and inspection. 

An immersion type electric oil heater is required to preheat the oil during initial start-up so the oil system is flushed with oil near its normal operating temperature.  An oil heater may also be required for operation in cold climates.  The oil heater is protected by a low oil level switch in the oil reservoir.

Lube Oil Coolers

Lube oil coolers are conventional shell and tube heat exchangers with water on the tube side and oil on the shell side.  Water is placed on the tube side for ease of cleaning.

The oil pressure on the cooler should be higher than the cooling water pressure to ensure that oil will leak into the water side and not vice versa.

Pressure Control

Pressure control in the oil supply header is generally maintained by a back pressure regulator type valve which returns a portion of the pump output back to the reservoir.  This allows the required oil flow and pressure to pass onto the system.

Lube Oil Specification

The oil used in lube oil systems must meet certain requirements in order to provide proper lubrication to the rotating parts of the machine.  Each equipment manufacturer will have specific requirements for the type and quality of oil required for their system.  Some vendors will specify a specific oil type and supplier while others will give general oil requirements/properties that must be satisfied and leave the selection of the specific oil up to the equipment owner.  The following are general oil requirements:

• Premium quality lubricant, typically known as a light turbine oil
• The oil should separate readily from water
• Minimum tendency to foam or emulsify when agitated
• High rust and oxidation resistance
• Minimum sludge, lacquer, varnish or resin-forming tendencies
• Flash point above 177°C (350°F)
• Viscosity:            
          1000 SSU @ 4.4°C (40°F)
        150 SSU @ 37.8°C (100°F)
           43 SSU @ 98.9°C (210°F)

The oil should meet the requirements of API Standard 614.

Lube Oil System Flushing 

All lube oil systems should be thoroughly flushed after initial installation and after major work on the system.  The importance of this step cannot be over-emphasized.  All dirt, rust, scale, weld slag, or other contaminants that have been introduced into the system during fabrication, transportation, storage, assembly must be removed by flushing the system.  In some cases mechanical cleaning, pickling and neutralization may be required to ensure a clean system.

Flushing should begin as soon as the system is assembles and oil can be circulated through the system.  Flushing should continue until inspection of the filters indicates that all contaminates have been removed.

The following provides general points to be consider for lube oil system flushing.  Vendor instructions for flushing should be followed.

• Inspect the system prior to filling with oil and remove any debris, dirt, etc. prior to filling with oil.
• Install clean filter elements.  Ensure there is are spare filters available to replace the filters used for flushing.
• Flushing oil is generally the same oil that will be used during normal operation.
• Bearings should be bypassed during the flushing procedure to avoid dirt entering the bearings.  Install jumper hoses from the supply side piping directly into the return oil piping.
• Fill the reservoir with oil through a fine mesh screen to prevent contaminants from the oil container from entering the system.
• The oil should be heated to its normal operating temperature.
• As the system is filled with oil, ensure that all air is vented from the system.  Periodically, check all vents an bleed off any accumulated air.
• Control valves and bypass should be flushed alternately.
• Check pressure gauges and flow sight glasses periodically to check for flow restrictions.
• Manually lift relief valves to flush valves are relief piping.
• Check filter pressure drops and clean filters as required.
• Continue oil circulation until there is no evidence of contaminants in the filters.

Instrumentation

Instrumentation is provided to control the oil system, to alarm at predetermined variations from normal conditions, and to trip the machinery when the abnormal conditions approach damaging values.  Pressure and temperature indicators, liquid level glasses and sight flow indicators provide operators with visual operating information necessary to manually correct for abnormalities in oil temperatures, filter fouling, low oil levels, etc.

Pressure

Lube oil pumps discharge	- Local gauge - Low pressure alarm (start auxiliary pump) - Low/low pressure trip (blower shutdown) - High pressure switch (blower start permissive)
Lube oil filters discharge	- Local gauge
Lube oil filter differential pressure	- Pressure switch

Temperature

 

Lube oil cooler outlet	- Local gauge and remote indication
Drains from each bearing	- Local gauge
Lube oil cooler inlet	- Local gauge and remote indication
Lube oil filter outlet	- High temperature switch - High/high temperature switch
Lube oil reservoir	- High temperature switch

Level

 

Lube Oil Reservoir

- Local level sightglass - Low level alarm - Low-low level alarm (shutdown oil heater)

Flow

 

Lube oil to each compressor bearing	- Local flow indicator
Lube oil to gear box	- Local flow indicator
Lube oil to driver	- Local flow indicator
Lube oil from compressor	- Local flow sight glass
Lube oil from gear box	- Local flow sight glass
Lube oil from motor	- Local flow sight glass