Auxiliary Steam System In Thermal Power Plant 513416

Auxiliary Steam System 26 December 2013

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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 lines depending on load on the turbine sources may be:  Main steam line through pr and temp reducing valves  CRH 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 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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Uses of Auxiliary Steam on Turbine side • 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.

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Uses of Auxiliary Steam on Boiler side • 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.

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AUX STEAM HEADER

29/14

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Flange, Stud & Rotor Heating 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 and measuring instruments for steam inlet, outlet, and drains. • The flanges and studs are heated with live steam bled from pipelines 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 the width 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 50°C. The temperature of outside flange surface should never exceed that measured with a thermocouple at a maximum depth inside the flange. • The difference between the flange and stud temperature should not exceed 20°C and the stud temperature should never be more than that of the flange. • When starting the turbine from cold or hot (temperature of metal of the upper half of the HP- casing being up to 250°C, heating of flanges and 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 ts, it is necessary to first supply steam for heating flanges and only then 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 steam is supplied at a higher temperature then that of the turbine casing at the front sealing till it comes under control.

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THANK YOU

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