Recap from previous week lesson:Purpose of Lubricating Oil Cooler -To take away the heat from the lubricating oil before recycle back to the system.The need of Oil Filter - To filter any Impurities and Particles. - Type of filter used is Duplex filter. - Type of Catridge used is Resin-impregnated pleated paper elements type. - The need of 2 filter is for backup purposes (1 standby & 1 running).The need of Protection Devices - To onitor the temperature & pressure of the Lubricating oil system. - The need of low pressure switch is to detect low lube oil pressure in the lube oil feed piping. - The need of high Temperature switch is to detect high lube oil temperature in the lube oil feedsystem.Describe inspection & maintenance procedure for Gas Turbine.
Viscosity - a measure of the resistance of a liquid to flow at a specific temperature. "thickness of L.O“Viscosity Index - a measure of how much the oil's viscosity changes as temperature changes such as; Viscosity become thin as temperature increase and thicken as temperature decrease.Low Pour Point – the effect of lowest temperature at which it will pour or flow under prescribed conditions which the oil easily to flow.Flash Point - the effect of lowest temperature at which the oil gives off vapors which can ignite. It is dangerous for the oil in GT to ignite and burn, so a high flash point is desirable.Fire Point - the temperature at which it will continue to burn after ignition for at least 5 seconds. At lower temperature, a substance will ignite, but vapor might not be produced to sustain the fire.
Foaming - a substance that is formed by trapping many gas/air bubbles in the L.O. (corrosion occur due to oxidation).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 service. The more oil vaporize, the thicker the oil become which contributing to poor circulation, reduced fuel economy, increased oil consumption, causing wear on bearings.
As previously mention, the Lubricating oil is primarily used for lubricating and cooling of the Main Bearings. It also used for Hydraulic Fluid to operate the accessories fitted with Gas Turbine.Why is it important to maintain the operating temperature of the main bearings?Refer back on the purpose of Lube oil Cooler (Topic 2.4)! During operation, L.O temperature rises due to coming in contact with the hot bearings. If this process continue the temperature will keep increasing , then the bearing may overheat and crack/damage.
Grades:Example of light Grade viscosity Oil; 29-36cSt(centistrokes) at a temperature of 38⁰C.Turbine oils usually use the ISO VG range 32, 46, and 68 (cSt at 40°C). Medium GradeMotor Oil Grades (just for share)The Society of Automotive Engineers(SAE) has established a numerical code system for grading motor oils according to their kinematic viscosity. SAE viscosity grading include the following: 0, 5, 10, 15, 20, 25, 30, 40, 50 or 60. Some of the numbers attached with the letter W, stand for "winter" or cold-start viscosity, at lower temperature.Viscosity is graded by measuring the time it takes for a standard amount of oil to flow through a standard orifice, at standard temperature. The longer it takes, the higher the viscosity, and thus higher SAE code.
Difference between Semi-synthetic and fully-synthetic: Semi synthetic (synthetic blends) - is a mixture of petroleum oil and synthetic oil (no more than 30%) . The advantage is that it has very small molecules that contribute to its "lubricity" (small molecules fit into little pits on the metal surface more easily). Trouble is, when things get hot, these little molecules are the first thing to burn up and turn to sludge!Advantage of Fully-synthetic:Better low and high temperature viscosity performance. Better chemical & shear stability.Decreased evaporative loss. Resistance to oxidation, thermal breakdown and oil sludge problems.Extended drain intervals with the environmental benefit of less oil waste. Improved fuel economy in certain engine configurations.Better lubrication on cold starts
Two cylindrical halves brought together so that their centers are displaced several mm from the bearing centre.Shims is placed at the horizontal split, then machining a cylindrical bore.Shim then removed, then two halves brought together to foam the elliptical bearing.
Industial gas turbine (week 8)
Industrial Gas Turbine Week 82.16 – Lubricating Oil Specification2.17– Types of Lubricating Oil2.9 & 2.10 – Types of Journal Bearing.
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.Learning Objective Industrial Gas Turbine 2
TermViscosity – a measure of the resistance of a liquid to flowat a specific temperature.Viscosity Index – a measure of how much the oilsviscosity changes as temperature changes.Low Pour Point – the effect of lowest temperature at whichit will pour or flow under prescribed conditions.Flash Point – the effect of lowest temperature at which theoil gives off vapors which can ignite.Fire Point – the temperature at which it will continue to burnafter ignition for at least 5 seconds. 3
TermFoaming – a substance that is formed by trapping manygas/air bubbles in the L.O.TBN (Total Base Number) – a measurement of the reservealkalinity of an oil to neutralize acids.TAN (Total Acidic Number) – the measure of a lubricantsacidity.Volatility – it is a test to determines the evaporation loss oflubrication in high-temperature. 4
2.16 - Specification for Gas Turbine Lubricating Oil System: High High High Low Oxidation HighAnti- High High Carrying Foaming Pour Fire Flash Viscosity & Load Resistance VolatilityWear Point Index TBN Thermal Capacity Point Point Stability 5
2.17 - Types of Lubricating oil used on Gas Turbine Three types of Liquid Three type of Oil used on GT: Viscosity Grade:• Mineral Oil • Light Grade• Semi-synthetic Oil • Medium Grade• Fully-Synthetic Oil • Heavy GradeAdditives are added to enhance the physical and chemicalproperties of the lubricating oil.Recommended Oil: Hydrocarbon/petroleum Base(Mineral Base) Oil 7
Comparison between Mineral & Synthetic Oil•Mineral Oil (Liquid Petrolatum) – It is a by product in thedistillation of petroleum to produce gasoline.•Synthetic Oil – It provides superior mechanical and chemicalproperties than Mineral Oils because the chemical compoundwere artificially made from other compounds. 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 GoodNote: Mineral Oil composed mainly alkenes (15-40carbon). 8
Bearing used on Gas TurbineThere 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 inTwo Housing; One at the inlet frame and the other atexhaust frame. 9
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 10
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.
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. 12
Types of Journal Bearing1. Elliptical or two-lobe Bearings 13
Types of Journal Bearing2. Three-Lobe Bearings 14
Types of Journal Bearing3. Tilting-pad Bearings 15
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. 16
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. 17
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. √ 18