Steam Turbine Lube Oil And Control Oil System 2i702n

STEAM TURBINE LUBE OIL SYSTEM

By Moinuddin

CONTENTS    

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WHY LUB OIL SYSTEM IS NECESSARY COMPONENTS OF LUB OIL SYSTEM FLOW DIAGRAM OF LUB OIL SYSTEM FUNCTIONS OF INDIVIDUAL COMPONENTS OIL FLOW TO DIFFERENT BRANCHES PROTECTIONS

LUB OIL SYSTEM Steam turbine lube oil system is usually required to provide oil for trip-and-throttle valve, governor system, bearings. 

Oil Characteristics Physical & Chemical Properties CEI/ISO Viscocity class Kinematic Viscocity cSt at 40 deg C Flash Point Viscosity Index Neutalization Value Emulsion Test Pour Point

Test Method

Turbine speed (3000 rpm – 50Hz)

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32

ASTM D445

28.8 – 35.2

ASTM D92

180 deg C

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95 Minimum

ASTM D974

0.20 Max

ASTM D1401

45 Minutes Max

ASTM D97

-5 deg C Max

Oil Properties 

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Viscosity: The Viscosity of an oil is the measure of its resistance to flow. The kinematic viscosity of an oil is the measure of its resistance to flow under force of gravity action. Flash Point: The flash point of an oil is the lowest temperature at which sufficient vapors are given off to form an inflammable mixture with air that will burn momentarily when a small flame is applied. Neutralization value: The neutralization value (total acid number) is the quantity of base, expressed in milligrams of potassium hydroxide, that is required to neutralize all acidic constituents present in one gram of oil.

Oil Properties 

Emulsion test: This method describes a procedure for measuring the ability of oil and water to separate from each other. A 40 ml sample of oil and a 40 ml sample of distilled water are stirred for 5 minutes at 130 deg F in a graduated cylinder. The time required for the seperation of emulsion, thus formed is recorded.

Oil Properties 

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Oil Requirements: shalbe mineral oil of highest quality and uniformity. It shall conytain no grit, inorganic acid, alkali, water soap, asphalt, pitch, resinous substances, or any other substance which will interfere with the lubricating properties of the oil, or that will be detrimental to the oil or to the metals with which the oil will come in in service. Rust prevention: the oil shall be capable of preventing the formation of rust on steel parts bathed with oil, should small quantities of water enter the oil in the normal operation of steam turbine.

Oil Properties 

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Resistance to oxidation : for long service in steam turbine systems, the lubricating oil must have high resistance to oxidation to protect against the formation of sludge and in general to maintain all initial characteristics. Water – seperating ability: highly refined oils will separate from water more readily than oils which have been contaminated in service or which have begun to form insoluble sludge. Resistance to foaming: high quality turbine oils should have good resistance to foaming.

General information Oil Tank Capacity: 9500 Lt  Lube Oil Flow : 850 Lt/min  Working Temp : 50 deg C  Oil Header Pressure: 1.8 bar  Oil viscocity : 20.4CST @ 50 deg C  Oil Type : ISO VG 32 

MAIN & AUX OIL PUMP        

Two in numbers Specifications –Capacity- 1200 Lt/min Discharge pr- 6 bar Design Pr – 10 bar. Working temp: 15 – 70 deg C Speed - 1450 rpm Drive - A.C. Motor Motor power-30 KW

EMERGENCY OIL PUMP  

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Provided as back up protection Cuts in whenever there is AC failure or the pressure in the lubrication system falls less than 0.9 bar SpecificationsCapacity-850 Lt/min Discharge pr-4 bar Speed-1750 rpm Drive-D.C Motor Motor power- 11kw

DUPLEX FILTER        

Lubrication Oil Type : ISO VG 32 Fluid Viscocity : 10.2 Cst @ 70 deg C SpecificationsWorking Temp : 15 – 70/80 deg C Working PR : 5/10 bar. Delivery : min/ max – 800 / 930 Lt/min Filtration: 23 microns. Delta normal / max: 0.3 – 1.0/ 1.5 bar

FLOW CONTROL VALVE Fluid : Oil ISO VG 32  Sp Gravity at oper cond: 0.852 at 50 deg C  Oper Viscosity cst : 27.8 Cst @ 50 deg C  Control range : 1.5 to 2.5 bar.  Setting value : 1.8 bar 

LUBE OIL ACCUMULATOR         

Type : bladder Nominal capacity : 100 Lt Design pressure : 15 bar Test pressure : 22.5 bar Design temperature : 80 deg C Oil type : LUBE OIL ISO VG 32 Viscocity : 10.2 cSt at 70 deg C Operating temperature : -10 to +80 deg C Operating pressure : 9 bar

THERMOSTATIC VLAVE  

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Fluid : LUBE OIL ISO VG 46 Sp gravity @ operating cond : 0.875 Kg/ cdm Operating viscosity : 27.8 @ 50 deg C Flow : 900 Lt/min Temperature : 46 deg C Pressure @ normal flow : 4 kg/scm IN 3.62 kg/scm OUT Set point : 46 deg

SLC AOP Command goes to switch ON AOP When :SLC AOP IS ON and MOP trips OR Oil pressure < 1.3ksc 

SLC EOP EOP ON Command goes when  SLC EOP is on and Lub oil pressure< 0.9 bar 

MAIN OIL COOLERS 

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Purpose is to cool the oil , Water is inside the tube and oil flows in outer shell Maximum lubricating oil temperature at cooler outlet restricted to 47 deg Bearing metal temperature alarm- 90 deg shut down-120 deg Three way control valveElectrically driven & has the function of regulating lubricating oil temperature

CENTRIFUGE 

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Draws oil from turbine oil tank mainly DOT, after removing any water & entrained solid matter oil is returned back to oil tank Centrifuge does two functions: Clarification-Sludge separation in which the machine is used for separating off particles normally solid Purification-Liquid (oil) –Liquid (water)separating two intermixed liquids which are insoluble in each other & have different sp gravities. Solids with spgr higher than those of liquid can be separated of at the same time

MOT VAPOUR EXTRACTOR Mounted on top of main oil tank  Function is to produce slight negative pressure in main oil tank and in the bearing casing and thus draws off oil vapour  Oil vapour before exhausting to atm is ed through oil catcher 

MOT VAPOUR EXTRACTOR 

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Service : extraction and splitting air / oil fumes. Fliid : oil saturated air Capacity : 300 mc/h at 25 deg C Operation temperature : 40 deg C max Suction pressure : 175 mbar Filtering elements : coalescent cartridges Motor power : 2.2 kw

Protections 

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The minimum oil temperature value to start the oil pumps equal to 15°C The minimum oil temperature value to put in service the turning gear equal to 20 °C The minimum oil temperature value to running the turbine equal to 35°C Cooling water to oil heaters should be closed until the discharge lubricating oil temperature at turbine bearings inlet, reaches a value of  43-49°C

PROTECTIONS 

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During the operation, the normal oil temperature range should be around the following values : Lube oil temperature at bearings inlet  5052°C. The maximum allowed values should be 55°C. Bearing oil discharge temperatures should not exceed 85°C. Alarm at 80°C and trip at 85°C