MS/HRH TEMPERATURE RISING/FALLING FAST

MS TEMPERATURE RISING FAST

Likely causes

·         Inadequate spray due to malfunctioning of spray control valves.

·         Excess airflow.

·         Burner tilt stuck in up position

·         Leakage in the spray line.

·         Low feed water temperature.

·         Boiler firing raised in top elevation

·         Heavy furnace slagging

·         Spray isolation valve in close condition

Plant response

·         MS temperature high alarm will appear.

·         Spray control valves will go for further opening.

·         If temperature is very high, turbine will trip.

Parameters of concern/Adverse effects

·         MS/RH temperatures

·         MS temp at turbine inlet

·         HP exhaust temperature.

·         Spray quantity/ FCV differential pressure.

·         Tilt position

·         Metal temp. raise above design value will reduce tube life drastically

Immediate expected or desirable operator action

·         Make burner tilt fully down

·         Take MS spray control to manual & raise spray quantity

·         Reduce firing in top elevation

·         If rate of pressure rise is more, then pick up load if margin is there.

·         Reduce airflow based on the O2 percentage.

·         Check spray station is properly lined up

Final correction activity

·         Start soot blowing, if slagging is more

·         Restore back the temp controls in auto if it has been taken in manual

·         Check for any malfunction of spray control valves & isolate such type of valve.

·         Burner tilt can be kept horizontal.

9. RH TEMPERATURE RISING FAST

Likely causes

·         Inadequate spray due to malfunctioning of spray control valves.

·         Excess airflow.

·         Burner tilt stuck in up position

·         Leakage in the spray line.

·         Low feed water temperature.

·         Boiler firing raised in top elevation

·         Heavy furnace slagging

·         HP exhaust temp is high

·         Spray isolation valve in close condition

Plant response

·         RH temperature high alarm will appear.

·         Amount of spray will rise.

·         Turbine will trip if RH temp reaches very high

Parameters of concern/Adverse effects

·         RH temperatures

·         RH temp at turbine inlet

·         HP exhaust temperature.

·         Spray quantity/ FCV differential pressure.

·         Tilt position

·         Metal temp raise above design value will reduce tube life drastically

Immediate expected or desirable operator action

·         Make burner tilt fully down

·         Take RH spray control to manual & raise spray quantity

·         Reduce firing in top elevation

·         If rate of pressure rise is more, then pick up load if margin is there.

·         Reduce airflow based on the O2 percentage.

·         Check spray station is properly lined up

·         Check HP exhaust temp is normal

Final correction activity

·         Start soot blowing if furnace slagging is there.

·         Keep the burner tilt in horizontal condition.

·         Restore back the control in auto if it has been taken in manual.

10. MS TEMPERATURE FALLING FAST

Likely causes

·         Tripping of mill

·         Sudden boiler pressure drop

·         Malfunctioning of spray control valves.

·         Spray station passing

·         Less air flow

·         Burner tilt fully down

·         High feed water temperature

·         Soot deposits on SH tubes

Plant response

·         MS temperature low alarm will appear.

·         Turbine will  trip if  MS  temp goes  very low.

Parameters of concern/Adverse effects

·         Ms temp

·         Spray quantity

·         Burner tilt

Immediate expected or desirable operator action

·         Close the spray control valves by taking it into manual.

·         Make burner tilt upward.

·         Check airflow &Rise if necessary.

·         Increase firing in top elevation

·         Reduce turbine load if pressure is dropping

·         Close spray station Block valve/ isolation valve if control valve is passing.

Final correction activity

·         Start LRSB operation

·         Observe for improvement in temperature.

·         Restore back the controls in auto (spray control)

·         Check for any malfunction of control valve & isolate it.

11. RH TEMPERATURE FALLING FAST

Likely causes

·         Tripping of mill

·         Sudden boiler pressure drop

·         Malfunctioning of spray control valves.

·         Spray station passing

·         Less air flow

·         Burner tilt fully down

·         High feed water temperature

·         Soot deposits on RH tubes

Plant response

·         RH temperature low alarm will appear.

Parameters of concern/Adverse effects

·         RH temp

·         Spray quantity

·         Burner tilt

·         Load

Immediate expected or desirable operator action

·         Close the spray control valves by taking it into manual

·         Make burner tilt upward

·         Check airflow &Rise if necessary

·         Increase firing in top elevation

·         Reduce turbine load if pressure is dropping

·         Close spray station Block valve/ isolation valve if control valve is passing.

Final correction activity

·         Start LRSB operation

·         Observe for improvement in temperature.

·         Restore back the controls in auto (spray control)

·         Check for any malfunction of control valve & isolate it.

AIR-PREHEATER MOTOR TRIPS/ AIR MOTOR DOES NOT START

AIR-PREHEATER MOTOR TRIPS/ AIR MOTOR DOES NOT START:

LIKELY CAUSES
·         Motor may trip on overload.
·         Power supply to the motor failed.
·         Air motor failure or solenoid failure
·         No compressed air available.
·         Lube oil system fail.
·         Some foreign material fallen on the APH & got stuck.
·         Seal of the APH has got disturbed.

PLANT RESPONSE

·         Rapid fall of hot air temperature on one side.
·         Rapid rise of gas temperature of stopped APH.
·         Possibility of deformation of APH.
·         Alarm at ECP/ DCS electrical motor stop- appears.
·         Furnace draft will fluctuate due to ingress of cold FD air.
·         Mill temp will drop as a result of drop in hot PA temperature.

OPERATOR ACTIONS

·         Reduce boiler/generator load to 60% MCR gradually.
·         Attempt for starting the electric motor, if the power has resumed or after resetting the over load.
·         If the air motor has not started because of air solenoid problem open the bypass valve of the solenoid.
·         Isolate affected air heater on the gas side first if all the attempts of starting the air motor or electric motor has failed. (Keep watch on draft)
·         Isolate the affected APH at airside (keep watch on total airflow)
·         Try to rotate air heater manually.
·         Maintain generator load depending upon the parameters of the running AH.
·         Watch hot air temperatures to mills
·         Cut in oil burners, when load is reduced.
·         Reduce corex to minimum.
·         Checks lube oil system & restore lubrication.

PARAMETERS OF CONCERN

·         Flue gas temp at APH I/L & O/L.
·         Furnace draft.
·         Mill o/l temp / hot PA temperature
       Secondary air temperature.

220V DC system

220V DC system:

• The 220V DC system supplies direct current as source of operating power for control, signaling, relays, tripping and closing of switchgears,  emergency motors of most important auxiliary systems
• Under normal conditions of station generation, the storage battery units are kept floating in DC bus bars by means of the chargers (also known as float chargers)
• The charger of each Battery unit,which is a rectifier with AC input, is normally made to take all DC requirements of the Power station without allowing the battery to discharge. This is achieved by maintaining the DC output voltage of battery charger a few volts higher than the voltage of battery.
• With this, the charger besides meeting all the DC requirements of the power station, supplies a few hundred milliamps of direct current to the battery to compensate the loss in the capacity of the battery due to action between the plates of the cell.
• The complete AC power system failure in a power station is known as emergency situation. DC battery units are designed to supply station DC loads for an emergency period of one hour
•  In case of AC mains failure the full battery of 115 cells will supply the load ie 230 volts. If the emergency lasts for one hour with an appropriate load of 450 Amps, then battery will supply the load for one hour when its end voltage will drop down to 1.75 volts per cell ie 201 volts.

Float and Boost Charging of Batteries:

Float charging:

• Float charging is used where the battery rarely gets discharged
• A typical application where float charging can be used would consist of the float charger, battery and the load in parallel
• During normal operation, the load draws the power from the charger.  When the supply to the charger is interrupted, thebattery steps in.
• Float charging of a battery involves charging the battery at a reduced voltage
• This reduced voltage reduces the possibility of overcharging
• The Float charger ensures that the battery is always in the charged condition and is therefore considered "floating"
• The Float charger starts by applying a charging voltage to the battery.  As the battery gets charged, its charging current reduces gradually.  The float charger senses the reduction in charging current and reduces the charging voltage
• If the battery gets drained, the float charger will again increase the charging voltage and process continues.  Float chargers can be connected indefinitely to the batteries.

Boost charging:

• Boost charging involves a high current for short period of time to charge the battery.  It is generally if the battery has been discharged heavily.  Boost charge enables the quick charging of depleted batteries.
• For instance, a two volt lead acid battery which has been discharged will initially be boost charged with a charging voltage of around 2.35-2.4 volts.  However, as the battery voltage rises, the charger will switch over to the float charge mode with a float voltage of 2.25 volts.
• Most battery chargers come equipped with provisions for both boost and float charging.

Generator Air Tightness Test

Generator Air Tightness Test

• Period Of Test= 24 Hrs without a Break
• Air Pressure Drop (Allowed in 24 Hrs) : <=0.15 ksc
• Air Test Pressure = 3.5 ksc
• All LLDs Drain Closed.
• Ensure Seal Oil system in Operation
• Seal Oil DP >1.5 ksc
• AS Seal Oil Pr>4.5 ksc, start H2S Seal Oil system
• H2 Cooler Isolated
• PW in Winding is in filled condition, Winding Isolated. PW also kept Isolated.
• PW Tank at Atmospheric Pressure
• Ensure availability of  Instrument air and Bleed Out moisture from it by keeping it open till 
• Connect flexible air hose with the gas plant through the coupling and ensure no air leakage is there 
• The filling is to be done by opening the valves in the normal H2 filling line where as the valve from H2 rack side will remain closed.
• Once the air filling is commenced the test record data sheet 
• The air valve is to be opened full.
• While pressurising the LLD / Seal oil DP / Seal oil parameters are to be recorded as per the enclosed sheet.
• The generator casing is to be pressurised with instrument air up to pressure of 3.5 ksc.
• The approximate time to attain rated pressure will be around 7- 8 hrs 
• Record the time when the pressure has reached at 3.5 ksc at the special gauge fixed in the gas rack 
• Stop the air filling and shut off the valve when the test pressure has been reached (3.5bar) and then disconnect the air hose from the system to avoid further pressurisation of the system. 
• Once the rated pressure has been attained, the test can be commenced. 
• Once the test is commenced the test record data sheet is to be filled at hourly basisfor continuous 24 hrs. No break is allowed. 
• During test ensure the LLD‘s are not getting oil 
• If a pressure increase was observed in the primary water tank, a leak of the primary water system with in the generator would be expected and must be located and attended 
• If an air loss higher than 0.15 bar/ 24 hrs, a search for leakages must be made.
• Suspected areas should be brushed with Diprol or other foaming solution. The formation of bubbles (foam) indicates a leak. 
• Attend the leakages and then repeat the test until satisfactory results are obtained.
• If a satisfactory tightness is established the generator may be filled with CO2 and subsequently with H2 as per normal operation practice. 
• After the test is declared complete, the air is to be depressurised and the system is to be normalised 
• After completion of the test, the electrical purity meter system should be calibrated with pure CO2 and H2 
• Normalise the primary water coolers and take the primary water system into service.
• Normalise the all-4 hydrogen coolers 
• Then the generator may be filled with CO2 and subsequently with H2 as per normal procedure.   
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Seal Oil system Charging

Pre – start checks 

(For air side seal oil PPS)

1. Turbine lube oil system is in service.
2. Seal oil storage tanks level is normal ( low level alarm not persisting )
3. Ensure that following valves are open :----

• Shut off valve from seal oil storage tank at oil canal.
• Shut off valves before seal oil Pumps ( air side )
• Shut off valves after seal oil Pumps ( air side )
• Shut of valves before and after DPR valves
• Shut of valve before float valve in oil inlet to seal oil tank.
• Shut off valve after float valve in oil drain line from SOT
• Shut off valves after flow indicators of air side, H2 side and ring relief seal oil at 8.5 m rack.
• Air side and H2 side seal oil signal to pr. Equalizing valve at 8.5 m rack.

4. Ensure venting of air side seal oil cooler and filters.
5. Ensure cooling water is available for seal oil coolers.
6. Ensure root valves of all instruments are open at “O” m & 8.5 m
7. Ensure interconnecting valve to H2 side seal oil system is close.
8. Gen. Brg. Exhaust fan is in service.
9. By pass valve of float valve in oil drain line from SOT is close.

Pre – start checks 

(For H₂ side seal oil Pumps)

1. Air side seal oil circuit is in operation.
2. Air side seal oil pr. > 4.5 Ksc at 8.5 m.
3. Seal oil Tanks level is adequate.
4. Ensure that following valves are open

• H₂ side seal oil Pump suction valve.
• H₂ side seal oil Pump discharge value.
• Manual isolating value after DPR valve
• Isolating valve before H₂ side seal oil cooler.

5. Ensure proper venting of H₂ side seal oil coolers and filters.
6. Ensure cooling water is available for seal oil coolers.
7. Ensure that manual isolating valve in H₂ side seal oil Pump discharge header for seal oil storage tank is close. 

ROUTINE CHECKS FOR SEAL OIL SYSTEM

1. Air side and H₂ side seal oil pumps discharge pr. is ( 10  1) Ksc
2. Air side and H₂ side seal oil temp in the range of 35 to 40C
3. Air side and H₂ side seal oil filters are not chocked.
4. SOT level is normal
5. Inter connecting valve between H₂ side and Air side seal oil circuits is close.Inter connecting valve in between DPR valves is close
6. Stand-by pump is lined up and not rotating in reverse direction.
7. Seal oil flow and pressure is adequate in air side, H₂ side and ring relief supply line at 8.5 m rack.
8. Air side seal oil / H₂ gas differential pr. is 1.3 to 2 Ksc
9. H₂ side and air side seal oil DP at seals is 10-20 mbar.
10. Gen. Brg. Vapour exhaust fan is running and ensure vapour is coming out to atmosphere.
11. Ensure no oil in LLD ( Liquid Level Detector)
12. By-pass valve of float in oil drain line from SOT is close.