PPT ON BOILER NORMAL SHUT DOWN TO COLD

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Boiler Normal Shut Down to Cold   Presentation Transcript

1.Boiler Normal Shut Down to Cold  

2.Steps for normal shut down to cold
Shut Down Procedure:
  Turbine load reduction – To reduce the loading on turbine
  Pulveriser shut down – To reduce the loading  and take out the
     puveriser from service
   Load Reduction and HP/LP bypass operation
   Turbine on barring gear
  Shut down of air and flue gas system –
      To stop ID fan and air preheater
      To stop FD fans, scanner air fans
  Shut down of turbine side auxiliaries –
      To stop turbine lube oil pumps
      To stop control fluid pumps

3.Steps for normal shut down to cold
Shut down of condensate system –
   To stop the condensate pump which is in service
   To stop the make pump   
Shut down of circulation water system
   To stop the circulating water pump
Shut down of fuel oil system
   To stop the fuel oil pumps and associated system
Shut down of auxiliary steam system
   To isolate the 16 ata steam header

4.STEPS INVOLVED
 Gradually reduce load by reducing firing rate.
MS/HRH steam temperature and MS  pressure shall      be reduced at the rate permitted by the turbine but not exceeding the rate of saturated steam temp drip of 83°C/hr, rate of load drop may be about 2MW/min.
 Carefully monitor the turbine condition and adjust the load temp, pressure drop rates such that HP/IP rotor   differential expansion vibration etc are within the limit.

5.Load reduced to 160MW, take HP heaters out of service.
Load reduced to 150MW approximate parameter at turbine inlet are:
      M.S. pressure=120ks/cm2(g)
      M.S. temp=520 degree C
      RHS temp=520 Degree C

6.  While reducing the load  check that following condition are maintained:
     Drum level is maintained on auto.
     Check SH and RH steam temp are maintained at set point .
     Furnace draft is maintained.
     Check the boiler expansion and contraction.
 At 40% mill load  reduce the feeder speed to minimum and
   take upper elevation oil gun in service.
  When load on turbine is reduced to 100MW
     Temp=510°C
     Pressure=112kg/cm2
 At 100-90MW take out one BFP from service.

7. Continue reduce the firing rate ,thus temperature and pressure will drop with drop in load.
  At 40% load take next upper elevation oil gun in service and take heavy oil gun in service.
  Prepare to take next upper elevation mill out and reduce feeder speed to minimum and stop feeder.
 Stop the mill after cooling down to 44°C and completely evacuating it see the load  transferred on running mills.

8. Take heavy oil gun at lower elevation in service and take out next higher     mill from service when loading on mill is reduce to 40%.
 At 70MW load MS temp=490°C RH steam temp=490°C MS pressure=105kg/cm2
 Take drum level control on manual and control drum level.
 Stop one PA fan after transferring full load on running PA fan.
 Stop lube oil pumps of tripped PA fan motor and bearing after all bearing temp reduced.
 Stop one FD fan corresponding to PA tripped.
 Check furnace draft and air flow before stopping FD fan and reduce  load on this fan to minimum.
 Stop one ID fan corresponding to tripped FD fan . check furnace draft, transfer load from this ID fan to other and completely unload this ID fan before tripping it.
 Switch off supply of the ESP associated with tripped ID fan, carry out soot blowing of complete boiler.

9.  At unit load 30% reduce air flow to 30%. Flow below 30%check the secondary air damper set point.
Firing rate is reduced  further and when load on mill is reduce to 40%,reduce feeder speed minimum and finally stop the feeder. Cool down mill to 44°C and shut down it.
 When load is reduce to 40MW take low load feed control valve and isolate main feed control valve .
 Switch off the supply to the field of ESP .
 Unit at 25-30MW with H.O. firing and change over auxiliary electrical supply from UATs to station transformer.
 Stop PA fan, check that seal air fan trips on interlock.
 Reduce load on unit to 5-7 MW  
    MS pressure boiler =90ksc
    MS    temp=465°C
    RH steam temp=465°C

10.Trip the unit through MFT push buttons on FSSS console or through protections.
Check that boiler fire is completely out ,check that all the flame scanners sense no flame and check boiler  actually from peep hole and ensure that fire is completely out.
 Maintain 30% air flow and purge the boiler for at least five minute and check turbine bearing lubricating system.
Check that all the feeders and mills are off ,break the vacuum when turbine speed comes to zero.
 Individual burner HO, atomizing air and steam nozzle valves and Igniters valves are closed.
Check that Atemperation SH and RH isolating valve and its bypass valve are closed, close isolating valve of SH and Reheater spray control valves.
Open Reheater vents and close CBD valves.

11. Close boiler main steam stop valves and their bypass valves.
 Open MS line drains valves open CRH and HRH line drains.
 Shut down HO system
 Top up the drum level up to +180 mm ,stop BFP.
 Stop hydrazine dosing pumps, stop phosphates dosing pumps if it is in service.
 Do not stop AP Heaters till flue gas temp at APH inlet is less than 205°C,air flow through furnace shall be controlled to effect the desired cooling rate and it can be controlled by:
    air flow through boiler
    opening SHH valve
Boiler is to be forced cooled fast after shut down , keep ID fan and FD fan in service. Regulate  air flow to effect desired rate of cooling ,open starting vent valve.
 Bring up drum level to +180mm when it drops to –180mm, start BFP for toping up the level. Stop BFP after words.
Stop FD and ID fans when flue gas temp at APH inlet is reduced below 205°C and boiler is cooled.

12.If required stop APH otherwise keep them rotating , check that APH lube oil pump stop on  interlock when oil temp goes below 40°C.
When boiler water temp goes below 94°C, drain the boiler or preserve it according to the circumstances.