Industrial Gas Turbine

Week 8

2.16 – Lubricating Oil Specification2.17– Types of Lubricating Oil2.9 & 2.10 – Types of Journal Bearing.

Industrial Gas Turbine

2Learning Objective

Learning ObjectiveAt the end of this lesson, you should be able to:• Describe the specification of Gas Turbine Lubrication oil

System.• Describe the types of lubrication oil used on Gas Turbine.• State the types of bearing used on Gas Turbine without

mistake. • Describe the construction and operation of Journal Bearing.• State and sketch the types of Journal Bearings used on Gas

Turbine (at least 2 out of 3 types) without reference.• Describe the characteristic of elliptical type bearing and how

it was made.

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TermViscosity – a measure of the resistance of a liquid to flow at a specific temperature. Viscosity Index – a measure of how much the oil's viscosity changes as temperature changes.Low Pour Point – the effect of lowest temperature at which it will pour or flow under prescribed conditions.Flash Point – the effect of lowest temperature at which the oil gives off vapors which can ignite. Fire Point – the temperature at which it will continue to burn after ignition for at least 5 seconds.

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Term

Foaming – a substance that is formed by trapping many gas/air bubbles in the L.O.TBN (Total Base Number) – a measurement of the reserve alkalinity of an oil to neutralize acids.TAN (Total Acidic Number) – the measure of a lubricant's acidity.Volatility – it is a test to determines the evaporation loss of lubrication in high-temperature.

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2.16 - Specification for Gas Turbine Lubricating Oil System:

Anti-Wear

Low Pour Point

High Fire

Point

High Flash Point

High Viscosity

Index

HighTBN

High Oxidation

& Thermal Stability

High Carrying

Load Capacity

Foaming Resistanc

e

Volatility

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Principle of Lubrication - Video

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2.17 - Types of Lubricating oil used on Gas Turbine

Recommended Oil: Hydrocarbon/petroleum Base (Mineral Base) Oil

Three type of Viscosity Grade:

• Light Grade• Medium Grade• Heavy Grade

Three types of Liquid Oil used on

GT:• Mineral Oil• Semi-synthetic Oil• Fully-Synthetic Oil

Additives are added to enhance the physical and chemical properties of the lubricating oil.

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Comparison between Mineral & Synthetic Oil

Property Mineral Oil Synthetic Oil

Max. Temp in the presence of O2 150°C 210°C

Max. Temp in the absent of O2 200°C 250°C

Viscosity 0-140 145

Boundary Lubrication Good Good

Suitable material for seals Nitrile Rubber Nitrile Rubber

Resistance to attack by water Excellent Good

Note: Mineral Oil composed mainly alkenes (15-40carbon).

•Mineral Oil (Liquid Petrolatum) – It is a by product in the distillation of petroleum to produce gasoline. •Synthetic Oil – It provides superior mechanical and chemical properties than Mineral Oils because the chemical compound were artificially made from other compounds.

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Bearing used on Gas Turbine

There are two type of bearing used:A. Journal/sleeve Bearings – It is used to support

the Turbine Rotor weight as well as to support any dynamic forces resulting from rotor unbalance and gear tooth reactions.

B. Thrust Bearing – it is used to maintain the rotor-to-stator axial position.

Both of these main bearings and seals are incorporated in Two Housing; One at the inlet frame and the other at exhaust frame.

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2.9 - Journal Bearings• It consist of a Cylindrical shaft section (journal)

and a mating stationary shell (liner) which surrounds the shaft.

Journal Bearing for Big Propulsion

2.9 - Journal Bearings• In this bearing, it is filled-up with fluid lubricant

(lube oil) which act as the medium that supports the shaft and preventing metal to metal contact.

• Classified as Hydrodynamic in operation - which mean that their load supporting capability is derived from a thin oil film wedge.

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Operation of Journal Bearings• Wedge is formed as a result

of the relative motion between the journal and the liner.

• As shaft speedup, the oil film pressure increase, gives the oil in journal bearing dragged behind the pin until the oil film break through and separate the surface

• Which in turn, supports the bearing load.

Pin – The clearance space between the journal and the liner.

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1. Elliptical or two-lobe Bearings

Types of Journal Bearing

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2. Three-Lobe Bearings

Types of Journal Bearing

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3. Tilting-pad Bearings

Types of Journal Bearing

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Elliptical Type Journal Bearing• Non-cylindrical bores characteristic.• Design to improve shaft stability at high speed.• The extra clearance space increase the oil flow

and reduces the power loses, resulting in lower temperature rises in the bearing.

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How the Elliptical Bearing is made?• Two cylindrical halves brought together.

• Shims is placed at the horizontal split• Machining a cylindrical bore.• Removed shim• The two halves brought together.

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Recap• Describe the specification of Gas Turbine

Lubrication oil System.• Describe the types of lubrication oil used on Gas

Turbine.• State the types of bearing used on Gas Turbine

without mistake. • Describe the construction and operation of Journal

Bearing.• State and sketch the types of Journal Bearings used

on Gas Turbine (at least 2 out of 3 types) without reference.

• Describe the characteristic of elliptical type bearing and how it was made.

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