Why: For removing all combustibles from the boiler furnace and replacing them with air to prevent any explosive mixture from remaining in the furnace prior to light up…
When: After a Master Fuel Trip has occurred
How:
A. Ensuring that a predetermined set of fuel and air related permissive conditions are satisfied which shall include
- All fuel valves (Shut-off valves, oil valves) closed
- Either of one FD Fan & ID Fan running
- All Mills and Feeders stopped and Mill discharge valves closed
- All PA Fans stopped and PA to Mill inlet dampers closed
- All scanners sense no flame
- Air flow is not less than 25% - 35 % (multiple burner boilers) of full load air flow
- 4 out of 6 secondary air dampers at Purge position
- No MFT conditions present
- MFT relay tripped
Now the Boiler is Ready for Purge
B. Initiate Boiler Purge
- Dampers are initiated to move to Purge position (air flow 30 to 80 T/hr)
- 5 minute purge timer triggers
- Boiler purge in progress is indicated
- After 5 minutes has elapsed the Purge process is complete and the boiler is ready for firing If any of the condition mentioned in ‘A’ fails during purging process, purging is interrupted and the timer resets…