Auxiliary Steam System in Thermal Power Plant.ppt

8/13/2019 Auxiliary Steam System in Thermal Power Plant.ppt

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26 December 2013 PMI Revision 00 1

Auxiliary SteamSystem


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Presentation outline

Sources 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 valvesCRH line


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PRDS Station

It 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 asbasic fuel, auxiliary steam is one of the importantsystems. 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 Steamon 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 Steamon Boiler side


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AUX STEAM HEADER

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Flange, Stud RotorHeating System


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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 to

reduce thermal stress. The device consists of jackets welded to side walls of casing

flanges 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 forregulating pressure in the headers.

To check the temperature difference of the metal across thewidth of casing and between flanges and studs of thecasing, thermocouples have been provided.

Careful check of the metal temp. is required during heatingprocess.


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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 notexceed 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 heating

It 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 suppliedto 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 theturbine casing at the front sealing till it comes undercontrol.


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THANK YOU

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Auxiliary Steam System in Thermal Power Plant.ppt

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