Power station at emergency condition meaning that the instrument values or parameters which show are not interlock to trip the equipment or unit of power station for safety but the situation is going to danger for operators and equipments. This situation fully under operators decision to take action to save the operator and equipment.
Pulverizer Fire
When a Pulverizer system fire is suspected, areas above, around and below the hazardous area should be evacuated of all personnel in accordance with plant emergency procedure.
The Pulverizer air/fuel ratio (Primary air flow and feeder speed) should not be changed in a direction that may increase air flow relative to fuel output.
Do not open Pulverizer with burning contents to fight fires.
Initiate an immediate mill emergency shutdown using the following special procedure:
1. Maintain the existing coal feed rate.
Changes to the air/coal ration that increase air flow or decrease coal flow make the fire more dangerous and should be avoided. Thus, it is highly recommended to maintain the existing coal feed rate until primary air flow is stopped.
2. Trip the mill on low air flow by stopping air flow (closing primary air isolation damper).
3. System logic must isolate the mill following the mill trip and steam inert for fire extinguished.
4. If the fire has been successfully extinguished, and housing temperature has cooled to room temperature, the mill may be opened for inspection.
5. Do not return the mill to service until all areas affected by the fire have been inspected and all debris and residual coal have been remove from the ill and primary air duct.
Coal Silo Fire.
A fire in the coal silo is very seriously and should not be neglected.
Burning fuel from the coal silo should not be fed to the feeder or pulverizer because it could cause fire damage in either of these.
A fire in the coal silo should be smothered with CO2 or steam.
Burner Line Fire.
Fires in burner lines are typically discover by observation of very high external surface temperatures. Blistering paint or even red-hot metal may be seen.
At mill in service, a fire in the burner line(s) will eventually burn itself out, once the flows of air and fuel stop.
At mill out of service, a fire in the burner line(s) will eventually burn itself out.
The outside of the burner line(s) may be hosed down with water to prevent damage to nearby cable trays, etc if required.
Warning, water sprayed on a hot burner line may flash to steam.
After the fire in the burner line(s) has burned itself out, each burner line will need to be visually inspected (internally and externally). Remove any debris and residual coal, and repair the burner line(s) as needed before the pulverizer is put back into service.
Air Heater Fire.
At the first evidence of fire from temperature indication or otherwise, inspection of the air heater should be made. If the temperature continues to rise or if fire is visible, the fans should be shutdown and water should be admitted to the heaters in sufficient quantities to quench the fire. Insure that all air preheater drain lines are open. Two-and-one-half-inch fire lines with at least one-inch nozzles should be used.
If it is possible to isolated the area of the fire, then stop air heater so that the water can be directed at the fire. On the other hand, if the fire is burning in several areas, continue to rotate the rotor as long as it will turn to be sure that the water contact the burning areas.
Do not be conservative with water quantities. If the fire has progresses to involve the metal, you will be dealing with temperature in the range of 1093oC to 2204oC. Large quantities of water are required to lower these temperatures. Do not attempt to smother the fire with foam, chemicals or steam, they are not effective.
Emergency Generator Shaft Seal.
The seal oil pressure at the shaft seals must be maintained at all time at a pressure of 50kPa above the hydrogen pressure in the generator casing, whether the generator is in operation or it rest. Before the turbine generator turns, seal oil must be supplied for lubrication.
The shaft sealing system includes an emergency seal oil pump (DC Power) which automatically supplies oil to the seals in case of failure of main pump or as result of other failures of the main seal oil supply.
In case DC power to the pump motor cannot be supplied, so pressure of shaft seal cannot be maintained, dissociate and shutdown the generator, release hydrogen gas in the generator casing through the vent pipe and lower the hydrogen gas pressure to atmospheric pressure.
Hydrogen gas may leak and explosive may potential result.
Generator Stator High Cooling Water Conductivity.
Failure of deionizer or failure of conductivity cell can make conductivity of stator cooling water high.
If the reading reaches 50µs/m, deionizer water flow can be increase.
If the reading reaches 990µs/m is very dangerous. This value indicates the maximum permissible conductivity, the generator should be tripped.
Emergency Steam Seal System.
To prevent air leakage into the turbine or steam blowout from the turbine glands, the following pressure ranges should be held in the steam seal header and the gland steam condenser.
The steam seal header pressure is held automatically by a motor operated pressure control valve.
The gland steam condenser pressure is manually adjusted by opening the exhaust fan outlet valve and is stable when the exhaust fan is in service. If the pressure deviates from the specified limit when the fan is in service, the exhaust fan outlet valve must be readjusted.
If the gland condenser exhaust fan is stopped, the turbine must be trip immediately to prevent the following:
1. Steam leakage from HP Turbine gland allows water to mix with lubrication oil, deteriorating the oil characteristic and allowing rust to develop on the turbine control device. Carbonized lube oil produced by hot steam at the tip of the oil deflector can cause rub or wear between stationary and rotating parts of turbine. In severe cases, vibration problems may occur.
2. Air leakage into the turbine may reduce condenser vacuum and lead to damage of the last stage bucket resulting from the increase in high temperature.
And also Exhaust Hood pressure and temperature limit.
Condenser Tube Leak.
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