Loss of Instrument Air
Anticipated Problems:
1. No oil burner can be taken in service. Oil guns, oil/steam valves will remain inoperative.
The igniter will not get advance.
2. If the unit is running only in oil, Boiler will trip. (AS HOTV/LOTV will close )
3. HAG/CAG/HAD/CAD will remain stay put , no mill can be taken in service. In case of a
running mill, temperature will not be controlled on auto. If a Mill trips , its hot air
gate will not close, which may cause fire hazard in the mill.
4. SH/RH spray Block valve will close on loss of IA. SH/RH Spray control valves will remain stay put but it may close due to leakage in cylinder & its associated assembly
5. SADC will remain stay put. If any mill or oil burner is taken out, the corresponding
elevation dampers will remain open. Any Particular SADC will open fully due to leakage in cylinder & its associated assembly.
6.Burner Tilt will remain stay put, hence no control of steam temperature can be done
through its operation. If there is leakage in power cylinder & its associated assembly and
power cylinder piston weight, Burner Tilt will go up.
7. Seal air fan / Scanner Fan discharge damper will remain stay put
8. Running BFPs re-circulation valves will open.
9. Vacuum pump inlet valve will start closing and condenser vacuum will start falling.
10. CEPs recirculation valve will get open.
11. GSC minimum recirculation valve is normally in closed condition but it will become full
open on loss of IA .This may reduce the condensate flow to deaerator.
12. Deaerator level control valves in operation will remain stay put. Deaerator level control valve will close if there is air leakage in pipeline.
13. Hotwell level control valves in operation :
Normal make up CV -- open
Emergency make up CV-- close
14. Main turbine seal steam supply & Leak off valve is of pneumatic type in Stage- 3.
These valves will remain stay put but in case of leakage from valve/actuator , it will close.
15. HP-LP Heaters alternate drip valves will open, normal drip will close
16. Deaerator overflow valve will open
17. TDBFP – A / B gland steam supply / dump valves will remain stay put
18. Low load control valve will be normally in closed condition during high load operation.
However, if load is less than 200 MW and it is in open condition, then it will remain stay put in that condition. But it will open fully if there is leakage in cylinder & its associated
assembly.
IMPORTANT POINTS AT A GLANCE:--
If total Loss of Instrument air occurs, the following points to be taken of utmost importance: ---
Steam temperatures
Condenser Vacuum
Drum level
Deaerator & Hotwell Level
Anticipated Problems:
1. No oil burner can be taken in service. Oil guns, oil/steam valves will remain inoperative.
The igniter will not get advance.
2. If the unit is running only in oil, Boiler will trip. (AS HOTV/LOTV will close )
3. HAG/CAG/HAD/CAD will remain stay put , no mill can be taken in service. In case of a
running mill, temperature will not be controlled on auto. If a Mill trips , its hot air
gate will not close, which may cause fire hazard in the mill.
4. SH/RH spray Block valve will close on loss of IA. SH/RH Spray control valves will remain stay put but it may close due to leakage in cylinder & its associated assembly
5. SADC will remain stay put. If any mill or oil burner is taken out, the corresponding
elevation dampers will remain open. Any Particular SADC will open fully due to leakage in cylinder & its associated assembly.
6.Burner Tilt will remain stay put, hence no control of steam temperature can be done
through its operation. If there is leakage in power cylinder & its associated assembly and
power cylinder piston weight, Burner Tilt will go up.
7. Seal air fan / Scanner Fan discharge damper will remain stay put
8. Running BFPs re-circulation valves will open.
9. Vacuum pump inlet valve will start closing and condenser vacuum will start falling.
10. CEPs recirculation valve will get open.
11. GSC minimum recirculation valve is normally in closed condition but it will become full
open on loss of IA .This may reduce the condensate flow to deaerator.
12. Deaerator level control valves in operation will remain stay put. Deaerator level control valve will close if there is air leakage in pipeline.
13. Hotwell level control valves in operation :
Normal make up CV -- open
Emergency make up CV-- close
14. Main turbine seal steam supply & Leak off valve is of pneumatic type in Stage- 3.
These valves will remain stay put but in case of leakage from valve/actuator , it will close.
15. HP-LP Heaters alternate drip valves will open, normal drip will close
16. Deaerator overflow valve will open
17. TDBFP – A / B gland steam supply / dump valves will remain stay put
18. Low load control valve will be normally in closed condition during high load operation.
However, if load is less than 200 MW and it is in open condition, then it will remain stay put in that condition. But it will open fully if there is leakage in cylinder & its associated
assembly.
IMPORTANT POINTS AT A GLANCE:--
If total Loss of Instrument air occurs, the following points to be taken of utmost importance: ---
Steam temperatures
Condenser Vacuum
Drum level
Deaerator & Hotwell Level
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