1. If Drum level becomes very low i.e. 25% then ID fan Trips and Emergency cap opens
2. This is to protect the Boiler tubes. At low Drum level, heat flux input has to be cut off, to protect the Boiler tubes, otherwise starvation takes place.
3. If PCC out let temperature rises to 1050 deg C then ID fan damper becomes Zero and Emergency Cap opens.
4. This protection is incorporatedto protect the Boiler tubes from overheating.
5. If all BFPs trip then ID fan damper becomes Zero and Emergency cap opens.
6. When all running BFPs Trip, then Drum level falls drastically. To protect the Boiler from starvation heat flux input should be cut off.
7. If Deaerator level becomes very low i.e.25% then All BFPs Trip.
8. Running of BFPs at Low Deaerator Level is harmful for the Pump.
9. If Ash Silo level is high, all ash handling systems stop.
10. When ash Silo is at high level then conveying more ash from ash handling systems results line blockage of ash conveying line. To prevent this, it is better to stop the systems and unload ash from Ash Silo.
11. Boiler Main steam stop valve will not open if by-pass MOV of MSSV is in close condition.
12. This protection is to avoid line hammering due to presence of condensate in main steam line and to prevent carry over of condensate towards Turbine side.
13. Boiler Feed Water MOV will not open if by-pass MOV of Feed water MOV is in close condition.
14. If feed water is empty in Economizer and in the pipe line after Feed water MOV, then by opening Feed water MOV directly without opening FW by-pass, MOV will lead to overloading of BFP, resulting BFP Trip.
15. ESP trips, if Ash Hopper level is high.
16. ESP has high voltage. Ash has presence of combustibles.
17. This protection is to safeguard ESP at Ash Hopper level high.
18. ESP can not be charged without starting of Purge Air Blower.
20. This is to Seal the ESP by the air from Purge Air Blower before charging it.
22. ESP can not be charged till flue gas inlet temperature reaches 160 deg C.
23. This is to avoid deposition of moisture and oil content influe gas on ESP.
1. Decrease in Drum level
a. Tripping of Feed Pump
If Boiler feed Pump trips then Feed water supply to Boiler interrupts and leads to lowering of Drum level. If this has happened then ensure that the auto stand-by Boiler feed pump has started in Auto mode. If the auto stand-by Boiler Feed pump has failed to start in Auto mode then start the Boiler feed pump manually otherwise Boiler will suffer from starvation and ultimately it will lead to Boiler trip to protect the Boiler.
b. Tube failure in Economizer
If Boiler Economizer tube fails then water supply to Boiler Drum will be affected. This leads to decrease in drum level and Feed Control valve will open more to compensate the Drum level to Normal water level, which leads to overloading of Boiler Feed pump.
Observe the steam flow and feed water flow. If feed water demand to drum is increasing then observe any sound from the furnace. If tube has failed inside boiler then hissing sound comes and it can be noticed from outside. Simultaneously check the smoke from the chimney. If it is of white colour then tube failure in side the furnace is confirmed.
c. Unit getting into Island mode
When Unit comes to Island mode, it follows the load connected to the Generator. Suppose Unit is generating more power than the Unit load and exporting to Grid.
At the time of Islanding, Generator will follow the load connected in this Unit and the Governing Control Valves would close according to load and allow the steam to pass through Turbine. The surplus amount of steam will remain in Boiler which increases the Drum pressure. This drum pressure will exert a downward thrust to the drum level and it decreases drastically.
d. Whether CBD valve, EBD valve or IBD valve opened?
If any operating personnel has opened any of these valves without proper reason or intimation then also drum level decreases rapidly. Ensure first then close the valve or regulate it observing the drum level.
2. INCREASE IN DRUM LEVEL
a. Whether Cold start-up in Boiler is in progress?
During Cold start-up when water temperature reaches 900 C then formation of bubble starts. This is known as swelling phenomenon. If this is the case then blow down has to be given to maintain the drum level at Normal water level.
b. Whether Instrument air compressor tripped and air lock unit at feed control station failed?
If Instrument air compressor trips, then air lock unit of control valve at feed control station keeps the control valve at a position at which it was, before supply of instrument air. This is known as stay put condition. If air lock unit fails to keep the feed station control valve at stay put condition, then when supply of instrument air fails, it leads to 100% opening of control valve. If this happens, start the instrument air compressor as early as possible and regulate the feed station control valve.
c. Whether Start-up vent has opened or safety valve popped up?
By opening start-up vent, when Boiler is in steaming condition, supply of steam to Turbine Drum level increases rapidly due to release of pressure in drum. If the steam demand in TG has reduced to a large extent then it results Boiler drum pressure rise quickly and at that instant drum level falls rapidly. When start-up vent is operated to release the surplus steam or safety valve pops up, then drum level increases rapidly. In this case at first ensure for what reason the pressure in Boiler has increased. If drum level is increasing drastically then give blow down to regulate it. Because at higher side drum level, the steam quality will be affected and carry over of water particles to super heaters and turbine will take place, which is very much harmful.
d. Whether Start-up vent has opened or safety valve popped up? Continued….
Operation should not be carried out when Boiler is in loaded condition. Donot close the Feed Control valve fully if drum level rises because if the control valve is closed completely, the feed water in Economizer tubes, which was passing to Drum, will became steam due to heat in flue gas and when feed water supply through Economizer will be again established through Feed control valve then hammering in Economizer tubes due to presence of steam. This may lead to Economizer tube failure. After ensuring the reason, close the start-up vent and dump the surplus steam in Condenser. Ensure that the safety valve has been reset in its position and no passing is observed.
e. Whether drum level transmitter is malfunctioning?
If drum level transmitter is malfunctioning then observe the level in hydrastep and immediately inform shift in charge and instrument personnel about this.
f. Whether rapid heat supply to Boiler?
If heat supply to Boiler will be increased suddenly with a huge amount then it affects the drum level and it swells. To avoid this regulate the heat input supply in a gradual loading manner. Sudden and huge amount of heat supply will overheat the grain structure of the tubes and it suffers from fatigue. In course of time tube fails.
g. Whether stand-by Boiler Feed Pump has started?
When stand-by Boiler feed water pump has started with running Boiler feed water pump, then Drum level increases because at that opening in Boiler feed Control valve when feed water pressure increases, more feed water flows to drum due to that opening of control valve and leads to increase in drum level. This case normally happens during scheduled Equipment change over of Boiler feed water pump. At first the stand-by feed water pump is started and discharge valve of the respective feed water pump is opened. After that the previously running Boiler feed pump is stopped. Ensure whether it is a scheduled equipment change over.
h. Whether TG has come to Island mode?
If TG has come to Island mode then Boiler pressure increases as there is a cut off steam demand as Generator has to follow the load, connected to it in this unit. If unit was exporting the power to Grid then the surplus power will be reduced at that instant,
which the Governor of the TG set will follow. It closes the control valve and steam pressure rises in Boiler accordingly. Ensure that the unit is running under Island mode. Open the start up vent to release the pressure. Ensure that the Safety valve has popped up or not. If popped up then it has reset properly or not. Observe the drum level during this operation. Observe the Dump control valve is functioning properly or not. If it is responding properly then try to supply steam to condenser by closing start-up vent after ensuring that Boiler pressure has reduced and safety valve has reset.
h. Whether TG tripped?
If turbine trips then steam demand in Turbine will cut off and resulting Boiler pressure rise. Ensure Dump circuit is healthy. Open the Control valve of dump and close the start-up vent after ensuring that the safety valve reset.
i. Whether any Cooling water pump in TG has tripped?
When Cooling water pump in TG for Condenser condensate cooling trips then the vacuum in condenser drops quickly and at that instant if the auto stand-by pump fails to start then the load set point at Generator has to be reduced with immediate effect. Otherwise the TG will trip due to low vacuum. When load set point at Generator decreased suddenly then Boiler pressure increases. In this case communicate with the TG operator and open start-up vent and lower the Load set point. Try to start the Main cooling water pump manually. After restoration of cooling water pump divert the steam from start-up vent by closing it to the dump circuit and normalize the load of Generator.
3. Decrease in Boiler Steam Pressure
a. Whether flue gas inlet temperature has reduced?
If flue gas inlet temperature reduces then it steam generation reduces in Boiler and pressure drops. This has to be observed very carefully and the generator Load set point has to be lowered, otherwise the TG will trip when the Main steam pressure becomes low.
b. Whether more steam demand at TG end?
If the unit is running at low load as steam generation in Boiler is low. If as a mal operation Load set point at Generator is given more than steam generation then Boiler pressure decreases. and TG is running with low load set point. Unit is importing power from Grid. If unit came to Island mode then the Generator will follow the load which is connected to it and load set point at Generator increases than the steam generation in Boiler. So Boiler pressure decreases. As we can not change the load set point of Generator by putting lower set point value, Load on the Generator has to be lowered by cutting off the load connected to it. Choose the less important load connected to Generator and cut off it as quickly as possible otherwise the unit will suffer from Black out condition due to TG trip at Main steam pressure low and Grid power is unavailable.
The same case happens when the steam generation in Boiler is low
c. Whether superheater tube failed?
If superheater tube fails then Boiler steam pressure decreases. Observe steam flow and feed water flow. If steam flow is at lowering trend and feed water flow is at increasing trend then it indicates that tube has failed. If the tube failure has occurred in side the furnace then white smoke comes out from chimney. When steam pressure decreases then reduce the Generator set point accordingly to avoid TG trip at main steam pressure low and ensure whether tube has failed or not. If tube has failed then Boiler shut down has to be taken to replace the failed tube with a new tube.
d. Whether ID fan damper has closed to zero position?
This case happens when flue gas temperature at Post Combustion Chamber reaches 10500 C. Flue gas flow to Boiler cut off when ID damper closes. It means heat supply to Boiler has cut off. It results in less steam generation. So when ID damper closes due to high PCC temperature, immediate load reduction has to be carried out in Generator to avoid TG trip due to Main steam pressure low.
e. Whether hand lever of Safety valve has been operated?
If any person has operated the hand lever of safety valve without proper communication with the operating personnel for sometime then Boiler steam pressure decreases and drum level increases.
4. INCREASE IN MAIN STEAM TEMPERATURE
a. Whether Boiler is loaded with huge amount of heat suddenly?
Main steam temperature rises if flue gas temperature at Boiler inlet rises suddenly. As superheaters are located at convection zone, therefore when flue gas temperature rises, it increases the superheater temperature. If attemperator control valve fails to control the main steam temperature then TG will trip due to main steam temperature going high. In order to avoid such a situation, if main steam temperature rises due to rise in flue gas temperature, then immediately attemperator control valve has to be taken to manual mode and attemperation should be increased. Also communicate with the kiln personnel about the sudden rise in flue gas temperature.
b. Whether Soot Blowing is in progress?
During soot blowing, steam temperature rises because more steam is required for soot blowing and heat input to the Boiler has been increased by opening the ID fan damper. So during soot blowing, main steam temperature has to be observed carefully. If attemperator control valve fails to control the rise in main steam temperature in auto mode, then it has to be controlled taking it to manual mode.
c. Whether Attemperation control valve is in manual mode or wrong value command input by the operator?
Normally it happens when there is a high fluctuation in main steam temperature. The attemperation control valve fails to control the temperature in Auto mode. So the concerned operator has to take the attemperation control valve to manual mode to control the temperature. But if he forgets to put this control valve in Auto mode after stabilization of main steam temperature, then it will remain in manual mode and during more heat input from Kiln, the main steam temperature would rise. Also sometimes operator puts wrong value command for attemperation control valve opening from control station in manual mode, which would result in increase in main steam temperature.
d. Whether forget to open before and after isolation valves of attemperation Control valve?
This situation comes during cold start-up of Boiler, if the inspection and checking was not done properly by the operation personnel. During initial period, this thing cannot be noticed but at the time of main steam temperature rise by opening attemperation control valve flow of water cannot be established as before and after isolation valves are in close condition. So care has to be taken for proper inspection and checking before start-up.
5. DECREASE IN MAIN STEAM TEMPERATURE
a. Whether inlet flue gas temperature has dropped?
If flue gas inlet temperature drops due to problem in Kiln side then main steam temperature decreases. So if main steam temperature is in decreasing trend then first observe the flue gas inlet temperature to Boiler.
b. Whether Load set point is given in Generator more than the Steam generation?
If Load set point in Generator is given more than the steam generation in Boiler then main steam pressure decreases and also the main steam temperature decreases
c. Whether valve sheet of Attemperation control valve is eroded?
This situation comes during Low Load operation of Boiler. If heat input to Boiler is low, then steam generation reduces and also the power generation. At that time, feed water passes due to eroded valve sheet of attemperation control valve and decreases main steam temperature.
d. Whether ID damper has become Zero due to PCC outlet temperature High?
When Post Combustion Chamber temperature increases more than 10500C, opening of ID damper becomes Zero. At that time heat supply to Boiler from Kiln stops suddenly. So it results in rapid decrease in main steam temperature. If this situation arrives, then attemperation control valve has to be taken to Manual mode from Auto mode and decreasing main steam temperature has to be controlled.
6. FURNACE DRAUGHT TOWARDS POSITIVE SIDE
a. Whether tube failure has occurred in side furnace?
In furnace, the draught is maintained at negative side to carry out the hot flue gas, ash and other suspended particles from kiln to chimney through ID fan. If Boiler tube fails inside furnace then draught goes towards positive side. As steam density is higher than air density. Also it adds an additional load on ID fan. So ID fan takes more current in this situation.
b. Whether draught transmitter is showing wrong value?
This can be known if other draught transmitters in flue gas path are showing right value and one of these is showing erratic value. This problem should be brought to the notice to shift in charge and instrumentation personnel.
7. LONG RETRACTABLE SOOT BLOWER IS NOT AT ITS ORIGINAL POSITION
a. Whether Long Retractable soot blower’s chain has broken during Soot Blowing operation?
If chain breaks at intermediate position of lancer tube during soot blowing by LRSB, then motor will be unable to retract it to the original position i.e. home position. Check the position of lancer tube, when soot blowing operation is in progress and chain has broken. In this situation, donot cut off steam flow through lancer tube. It is because it is situated in high heat zone i.e. at convection zone. As steam acts as a coolant, it will take the heat added to the lancer tube and will protect the lancer tube from over heating and bending. The lancer tube has to be drawn out manually. After ensuring that it has been drawn to its home position, steam through the lancer tube can be cut off and chain maintenance work can be carried out.
b. Whether home position limit switch is malfunctioning?
This may happen after completion of soot blowing by Long Retractable Soot Blower. The limit switch at home position may not give home position feed back of the LRSB due to malfunction. If this case happens then immediately the position of the lancer tube has to be checked. Limit switch at home position has to be rectified by Instrumentation department.
c. HAMMERING OF MAIN STEAM LINE DURING CHARGING.
Usually main steam line hammering occurs if the condensate present in that line is not properly drained out and pipe line is in cold condition. If huge amount of steam is allowed to pass through that pipe line then line hammering takes place which is very much harmful for the pipe line. So to avoid this case happening always open the drain of the pipe line. Observe the condensate is drained properly from that pipe line. After completion of condensate draining, warm-up the pipe line with very less quantity of steam. Gradually increase the pipe line temperature. After confirmation that the line is properly heated, more steam flow can be allowed.
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