Auxiliary Steam common Header Charging

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Auxiliary Steam common Header Charging

SYSTEM DESCRIPTION :

Aux steam system includes four  ways of steam source: 
  • Start-up boiler or aux boiler,(If it is available in plant )
  • Low-temperature reheated steam supply 
  • Main steam steam supply line
  • Near by unit common header


In normal, each unit aux steam is supplied by CRH steam.
There is interconnection between aux steam headers of all units and also connected to start-up aux boiler. 

Parameters of aux steam are:
Aux steam pressure normal range: 8-12 kg/cm2
Aux steam normal temperature: 300-350 deg C.
Initial conditions

  • Aux boiler is running
  • hot boxed-up condition
  • station APRDS
Pre Checks & Charging Procedure:

 Ensure that Auxiliary Boiler is ready for Aux Steam header charging from aux. boiler.
Generally temperature maintain before charging from  aux boiler between range is 180 to 300 deg C and pressure is 4 to 5 Kg/cm2
All the way from Auxiliary boiler MS stop valve to Start up steam line’s all drain valves should be open.
Auxiliary Steam common header drain valve should be open to atmosphere.

 Following MOVs should be in closed condition initially:
                      i.        Start up steam  (Open in case of cold startup of aux boiler for aux steam requirement)
                     ii.        Main Steam to Aux. steam header MOV & CV
                    iii.        CRH to Aux. steam header   MOVs and CV
                   iv.        Aux steam to Gland sealing 
                    v.        Aux steam to Soot blower/fuel atomizing 
                   vi.        Aux. steam to Mill fire fighting

 Aux steam header to Aux steam common header can be kept open.
Ensure that all the temperature and pressure measuring gauges are healthy.
Each attemperating or pressure reducing valve should be closed.
Steam Charging:

  1. Ensure all the drains related to aux steam system charging are open.
  2. Light-up the aux boiler. Ensure aux steam header is lined up for warm-up.
  3. Open MS equalizing valve first to warm the line if aux boiler is running already for FOPH requirement. Keep observations for any water hammering in the line.
  4. Ensure the aux steam system piping temperature is increasing. Open MS stop valve up to 5 to 10% intermittently after observing steam from all the line drains. Throttle MS stop valve if hammering is noticed wait for complete warm up.
  5. Open start up steam MOV to 10-20% intermittently for initial warm up. Then open this MOV to 100% at a rate of 5-10% each time careful observation for line hammering. Ensure proper warm up of Aux steam common header (i.e. steam is coming from its drain).
  6. Now close/throttle Aux steam common header drain and put trap in service after getting standard temperature. Maintain Aux steam common header temperature/pressure from Aux Boiler.
Aus steam Switchover from Aux Boiler to #3 MS line:
  1. At MS temperature (>350degC) and pressure (>25 Kg/cm2 ) Aux steam header can be charged from MS line.
  2. Normalize/line-up the MS to Aux steam header attemperation system.
  3. Open the drain valve in MS to Aux steam header line and open MS to Aux steam header MIV. Then open upstream MOV of MS to Aux steam header to 100% slowly (keeping water hammering in mind).
  4. Then open the pressure control valve to 5-8%.
  5. After warm up close the drain valve and maintain the required header pressure and temperature while closing/stopping the Aux steam to Aux steam common header by opening CV of MS to Aux steam header.

Aux steam Switchover from MS line to CRH:

  1. When CRH temperature is greater than 300 degC and pressure is greater than 20 Kg/cm2, the aux steam header can be charged from CRH line.
  2. Open the drain valve of CRH to Aux steam header line. First open both the MIVs of main and by-pass line then open both the MOVs of main and by-pass line intermittently keeping water hammering in mind. Close the drain valve after proper warm-up of the line.
  3. Now start charging the Aux steam header via CRH by opening the control valves while closing the MS to Aux steam header CV keeping Aux steam header pressure/temperature constant.
  4. Close the drain valve after proper warm-up of the line.

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