Auxiliary Steam System
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Transcript of Auxiliary Steam System
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Auxiliary SteamSystemhttp://studygalaxy.com/
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Presentation outlineSources of Aux steam supply
PRDS Station
Uses of Aux steam
Flange and stud heating
Rotor heating
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SOURCES Auxiliary boiler.
Station PRDS header (from other running units)
Under unit running condition Steam for turbine auxiliary
steam header is normally taken from extraction linesdepending on load on the turbine sources may be:
Main steam line through pr and temp reducing valves
CRH line
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PRDS StationIt Consists of Set of pressure reducing cum control valves
Set of temp reducing (spray) valves
For maintaining desired pressure and temp.
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PRDS Header For a 210 MW Thermal Power Unit using coal as
basic fuel, auxiliary steam is one of the important
systems. The current practice is to have two
different headers:- Turbine Auxiliary Steam Header
Boiler Auxiliary Header
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To turbine gland seal header.
To ejector system of condenser (main as well as
starting ejector).
to Deaerator as pegging steam
For flange & stud heating.
Interconnection to station PRDS header for
supplying aux steam to other units.
Uses of Auxiliary Steam
on Turbine side
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Burner atomisation,cleaning, scavenging
SCAPH charging during cold start up
Regenerative air heater sooth blowing.
Off Sites:
HFO station: Fuel oil system heating fuel, oil
storage tanks, pipelines, fuel oil heaters.
Uses of Auxiliary Steam
on Boiler side
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AUX STEAM HEADER
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Flange and Stud heating Used for quick starting of turbine from warm or cold start.
Helps in reducing the temperature difference of the metal toreduce thermal stress.
The device consists of jackets welded to side walls of casingflanges and special piping complete with fittings andmeasuring instruments for steam inlet, outlet, and drains.
The flanges and studs are heated with live steam bled frompipelines before main stop valve (ESV).
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Flange and Stud heating The headers, supplying steam to the flanges and studs, are
provided with safety valves and pressure gauges for
regulating pressure in the headers.
To check the temperature difference of the metal across thewidth of casing and between flanges and studs of the
casing, thermocouples have been provided.
Careful check of the metal temp. is required during heating
process.
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Flange and Stud heating The temperature difference across the width of the casing flange should
be within 50C. The temperature of outside flange surface should neverexceed that measured with a thermocouple at a maximum depthinside the flange.
The difference between the flange and stud temperature should not
exceed 20C and the stud temperature should never be more thanthat of the flange.
When starting the turbine from cold or hot (temperature of metal ofthe upper half of the HP- casing being up to 250C, heating of flangesand studs is permitted provided differential expansion of the rotor is
positive and not less than 1 mm.
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Flange and Stud heatingIt is not permitted to operate the flange heating device:
If the differential expansion of rotor is less than 1 mm.
If the differential expansion indicating and recording
instruments are either out of order or disconnected. In order to maintain proper tightening of flange joints, it is
necessary to first supply steam for heating flanges and onlythen after some time to studs.
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Rotor Heating In case the contraction of HP rotor reaches 0.8 mm
and that of IP rotor 1.5 mm. fresh steam is supplied
to the front sealing of HP & IP turbines. In order to
control the contractions of HP & IP rotor the steamis supplied at a higher temperature then that of the
turbine casing at the front sealing till it comes under
control.
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