FUNCTION
The main function of the PA FAN (Primary Air Fan) is to convey the fuel mainly coal to the furnace with Air Pressure created by the Fan. The pressure normally maintained by this Fan is around 1000mmWC to overcome the pressure drop in Pulverisers and Coal Pipe. The component in the below figure in 20. Normally one independent thermal power plant comprises of 2-PA Fans.
The two fans run in parallel operation and severe critical conditions arises which leads to plant trip when any one Fan trips. This topic is considered of two major critical issue that can be taken care of:
- ONE FAN TRIPS DURING A PARALLEL OPERATION
Problem:-
During a parallel operation of the Fans the header pressure is maintained by both the Fans. And when suddenly one fan trips, the header pressure drops with a transition, which is very much ahead of the transition operated in the normal operation mode. So the controller tuned for normal operation fails to maintain the desired set value. And this results in insufficient pressure in the header which was in use to convey the fuel (coal) to the furnace.
Solution:-
The normal operating controller to be suppressed by a direct demand setter for the running fan with transition higher than the transition loss occurred due to the tripped fan.
- UNSTABLE CONTROL OF PULVERISER HOT AIR DAMPER
Problem:-
Hot Air Damper operated to maintain the Pulveriser Inlet Air Flow which is based on coal flow requirement. But due to the usage of coal poor than the coal for which the system is designed, the coal requirement increased. This increase in coal demand generates a demand for more air flow, and this extra air requirement make the Hot Air Damper to operate on zone, which may be beyond the Air Flow controllable zone. Because this type of dampers is controllable for certain operating zone.
Solution:-
The known range Hot Air Damper to be checked. And the Header Pressure (discussed above) set value to be reduced if the Hot Air Damper tends to operate beyond the controllable zone.
Reference Books that can be followed:
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