SIMPLE, SINGLE STAGE STEAM TURBINE

FUNCTIONS OF LUBRICANTSTo entirely separate the two working surfaces in order to reduce the static and dynamic friction to a minimum in order to prevent wear.

To remove the heat generated within bearing or from the outside source.

To protect the metal against corrosion. Ensure no or minimal under crown deposits and prevent hot corrosion. Maintain proper alkalinity and environment to protect from cold corrosion.

To remove the contaminants and ensure cleanliness of engine components. Handle un-burnt fuel particles and suspended solids in fuel.

To dampen the noise of sliding surfaces and knocks of gas loads on rolling bearings by maintaining proper lubrication.

FUNCTIONS OF LUBRICANTS (CONTD.-1)To act as a sealant and prevent leakage of fuel oil from fuel pumps and prevent blow-by from combustion space.

To handle variety of fuel quality with variable wax, asphaltenes, sulphur, sodium and vanadium contents.

Ability to perform under high stress level.

TBN stability under high stress

Ability to perform under different operating conditions of continuous/standby.

REQUIREMENTS OF LUBRICANTSThe basic function is to separate the two moving surfaces and thereby eliminate friction and wear.

A good lubricant should possess high thermal conductivity so that it can quickly and efficiently dissipate the frictional heat generated due to shearing of lubricant.

The lubricant should be inert so that it does not initiate corrosion of bearing material and should provide high degree of protection from corrosion against environment.

They should be cheap and easily available.

Their physical and chemical properties should remain same.

REQUIREMENTS OF LUBRICANTS (CONTD.-1)They should be available in wide range of viscosity.

Their operational range should be wide enough to cover majority of applications.

They should have economical service life and should be resistant to oxidation.

They should be miscible with various chemicals used as additives to provide special property for specific application.

They should be compatible with materials of seals/glands.

They should be non toxic.

TYPES OF LUBRICATIONHydrodynamic or full film lubricationIt is said to exist when the moving surfaces are separated completely by the pressure of continuous layer of lubricant.

Boundary or thin film lubricationIt is said to exist when operating conditions are such that it is not possible to establish a full fluid film. In this condition some degree of metal to metal contact will occur.

Partial full fluid film lubricationThis may be an intermediate condition between boundary and hydrodynamic lubrication.

TYPES OF LUBRICATION (CONTD.-1)Hydrostatic lubricationIt is a form of hydrodynamic lubrication where pressure within the oil film is not self generated but is supplied externally by the pressure pump.

Elastohydrodynamic lubricationThis applies to a point or line contact which occurs in rolling or sliding contact bearings or meshing gear teeth. In this condition hydrodynamic lubrication does not fully apply but thin film lubrication limits metal to metal contact. Metals are subjected to elastic deformation and lubricant is subjected to high pressure.SUITABLE LUBRICANTS FOR STEAM TURBINESENERGOL THB 68, 100 (FROM BP MARINE)Energol THB is recommended for marine steam turbines and reduction gears. It is also suitable for use in turbo-chargers. Additionally Energol THB may be used for general lubrication. MAIN PERFORMANCE FEATURES High oxidation stability for extended service life Rust inhibited Good demulsification properties Good anti-foam and air release properties Energol THB is fully approved by major marine steam turbine manufacturers world-wide.

LUBRICATION OF STEAM TURBINEModern trend of steam turbine lubrication is by pressure system which reduces size of gravity tank, length of piping and reduction in oil quantity leading to considerable economy.

A safeguard must be provided to ensure that the bearings are not run out in the event of oil pump failure. With gravity system, this is simple as the oil from gravity tank will flow until turbine comes to rest.

With pressure system, an auxiliary pump could start automatically, but this would not be satisfactory in the event of total electrical blackout.

A small gravity tank at a lower level may prove to be a better and safer arrangement.

GRAVITY LUBRICATION SYSTEM

GRAVITY LUBRICATION SYSTEM (CONTINUED)Oil is drawn from the sump via a suction/magnetic filter by pump and discharged via filter and cooler to pressure distribution piping.

Some amount of oil is continuously fed to gravity tanks which keep overflowing to sump, thus keeping the gravity tanks filled up at all the time.

In the event of pump failure, standby pump will automatically take over. In case of blackout, oil will flow to the distribution points through non return valve at 1.7 bar pressure for about three minutes as emergency supply. Usual supply pressure being 3.1 bar

Oil inlet temperature is maintained at about 46.5oC10PRESSURE LUBRICATION SYSTEM

PRESSURE LUBRICATION SYSTEM (CONTINUED)Oil is drawn up from sump by independent pumps.

When turbine is started, attached pump starts building up pressure and independents pumps are cut off.

A small gravity tank in the top of gear case is kept always full.

When turbine is stopped then one of the two independent pumps will start automatically.

In the event of a black out when turbine RPM reduces, gravity tank supplies oil through non return valve for about 30 minutes till then operator can start auxiliary pump or stop the machinery,