Boiler Emergencies

Procedures during the following emergency conditions1. Boiler Explosions2. Boiler Implosions3. Low Water Level4. High Water Level5. Boiler Tube Leaks6. Master Fuel Trip7. Reheater Protection Trip

Other boiler emergenciesAir preheater fires/tripping of APH ( one fan operation)Coal mill explosions ( may lead to boiler trip)Loss of furnace sealLoss of scan supply of any elevationLoss of instrument airLoss of cooling water to scaffold doorBending of long retractable soot blower / furnace probe

Boiler EmergenciesEmergency boiler procedures : A) Boiler explosions a. Causes 1. Furnace explosions can be caused by an accumulation of unburned

fuel in the furnace due to incomplete combustion, loss of ignition, or fuel valve leakage.

2. With a mixture of unburned fuel with air in explosive proportions, and the application of heat sufficient enough to raise the temperature of the mixture to the ignition point, explosions can occur.

3. The accumulated fuel is ignited resulting in a greater than normal pressure increase.

4. The fuel may enter the furnace in the unburned state in a number of ways, for instance:

a) Through leaky main fuel or ignition fuel inlet valves on idle wind box/burner compartments.

Boiler Emergenciesb) If the fires are extinguished and the if the fuel is not shutoff promptly.c) If the fuel is not burning as rapidly as rapidly as it is entering the furnace.d) In starting up, if difficulty is experienced in establishing ignition. b. Prevention 1) During start-ups maintain a high air flow (up to 30% of full load air flow) to ensure an air rich furnace atmosphere and prevent accumulation

of explosive mixtures.2) Be sure that the main fuel and ignition fuel inlet valves on idle fuel

compartments or burners are closed tightly and do not leak. It is advisable to remove idle oil guns from the guide pipes, to avoid dripping.

3) Watch the fires so that the fuel may be shut off without delay if extinguished unexpectedly. If the fires are lost, trip all main and ignition fuel immediately. Close all trip and fuel shut off valves. Purge the furnace at least for 5 minutes after shut down with 30% (minimum) air flow.

Boiler Emergencies4) When a boiler has been idle, purge the furnace before putting igniters in service. Be sure that the warm up fuel firing rate is high enough to produce a flame not easily extinguished.5)Always use an associated igniter to light off a main oil or gas nozzle.6) Regularly check proper function of FSSS or BMS (interlocks, trips)B) Boiler Implosions : Destructive negative pressure.a. Causes 1) Tripping or sudden loss of fuel results in mass temperature reduction

resulting in rapid decrease in furnace pressure.2) Rapid evacuation of heated gases by ID fans.3) Failure of fan controls.b. Prevention1) The air flow to the furnace must be maintained at its pre trip value

and must not be prevented from increasing by following natural fan curves; but positive control action to increase air flow is not allowed.

Boiler Emergencies – water levels2) The flow of combustion products from a furnace must be reduced as quickly as possible following a unit trip.3) If the removal of fuel from the furnace can be over a 5 to 10 seconds period (rather than instantaneously) there will be a reduction in the magnitude of a furnace pressure excursion that follows a unit trip.4) Further prevention of implosion can be accomplished by keeping protective control systems in proper working order and well tuned.C. Low Water Level a. Causes 1. Control failure 2. BFP failure 3. Tube leaksb. Action 1) Compare indication.

Boiler Emergencies- water levels2) If the water level falls out of sight in the water gauge, due to failure of the feed water supply or neglect of the operator, except in cases of momentary fluctuations that might occur with extraordinary changes in load, appropriate action should be taken at once to trip the fuel. Any decision to continue to operate, even if only for a short time at a reduced rating, would have to be made by someone in authority who is thoroughly familiar with the circumstances that led to the emergency and positively certain that the water level can be restored immediately without damaging the boiler. In the absence of such a decision : a) Trip all fuel immediately.b) Shut off all steam discharged from the unit( trip turbine, steam driven

auxiliaries etc.)c) Simultaneously, if feed water has become available and the operator is

assured that no pressure parts have been damaged, gradually reduce the flow of feed water to the boiler by manual regulation. This will avoid quenching of hot pressure parts with relatively cold water. The feed water regulating valve should be closed completely when all the steam flow from the unit has ceased.

Boiler Emergencies-water levelsd) Maintain a high air flow at first to hasten the cooling process.e) If pressure parts damage is suspected, reduce the main steam pressure gradually by opening the super heater startup drain. Open the drum vents when the pressure drops below 1.75 bar. As the boiler cools, reduce the air flow. Shut down the fans as soon as the unit is cool enough for a man to enter. Drain the boiler when the drum metal temperature is 93C. Determine the cause of low water and examine the boiler for the effects of possible overheating such as leaks and distortion of pressure parts.D. High Water Level :Water impingement may cause turbine damage.a. Causes1) Feedwater control malfunction2) Operator errorb. Action1) Abnormally high water level should be avoided as it may lead to

carryover and even priming. If the water level rises above rises above the recommended normal operating range proceed as follows

Boiler Emergencies-water levelsa) Reduce the water level immediately by opening the intermittent

blowdown valves. b) Reduce the steam rate, if necessary, and place feedwater control on manual.2) If priming should occur, as indicated by rapid fluctuations in outlet steam temperatures in outlet steam temperature, proceed as follows:a) Reduce the steaming rate.b) If the water level is abnormally high, reduce the level by opening the

intermittent blowdown valves and place feedwater control on manual.

c) Investigate the water condition (alkalinity and solids)d) Investigate the condition of the drum internals as soon as an

opportunity is afforded.

Boiler Emergency-Tube failure

Boiler tube failures : Operating a boiler with a known tube leak is not recommended. Steam or water escaping from a small leak can cut other tubes by impingement and set up a chain reaction of tube failures. By the loss of water or steam, a tube failure can alter boiler circulation or flow and result in other circuits being overheated. A tube leak can also cause loss of ignition and, if reignition occurs, a furnace explosion. An investigation of tube failure is very important so that the conditions causing the tube failure can be eliminated and future failures prevented.The investigation should include a visual inspection of the failed tube. In some cases a laboratory analysis or consideration of background information leading up to the tube failure is required. This information should include the location of the failure, the length of time the unit has been in operation, load conditions, start up and shutdown conditions, and feed water treatment.

Boiler Emergencies-tube leaks5. Tube Leaksa. Indications of the tube leaks are 1) Feedwater flow greater than steam flow2) Excessive desuperheater flow3) Wetted insulation of water running down casing with no apparent

cause.4) Excessive make up.5) Noise from the boiler (Acoustic noise level indicators)b. Action6) Furnace tube leaks a) The action taken is dependant on the size and location of the tube

leak 1) A large leak may extinguish fire or cause loss of drum level. 2) A medium size leak may force an immediate shut down.

Boiler Emergencies-tube leaks3) A small leak may allow continued operation after considering its consequences on continued operation.b) If at all possible locate the leakc) In the vent of failure of one or more water carrying tubes, the best method of shutting down the unit will be dictated by the size of the failure, the ability to maintain normal water level and the demands for the service of the unit.d) The following instructions regarding tube failures are of general nature. It must be understood that conditions may arise which will require exercise of judgment by the operators.e) In case of a leak or tube failure which does not involve a serious drain on the feedwater supply, the water level should be maintained and the unit taken out of service in the normal manner.f) If the tube failure results in a loss of water so great that the water level cannot be maintained with the feedwater supply available, use the method outlined below. 1) Trip all fuel

Boiler Emergencies-tube leaks 2) Shut off feedwater to the boiler. 3) Maintain only enough air flow to carry the escaping steam up the stack. 4) Leave the fans in service until pressure is off the unit. g) After the unit has cooled enough to permit a man enter it, make a thorough inspection of pressure parts for any indication of damage resulting from loss of water level. After the necessary repairs have been made, apply a hydrostatic test and obtain the approval of the proper authorities before putting the unit back in service.2) Economizer Tubesa) An economizer tube leak can be detected by sound and/ or increased

make up water requirements. The leak should be detected at the earliest possible time and the unit shutdown in the normal manner.

b) Water leaks in the economizer can cause considerable erosion damage to the adjacent tubes. Water carried over from economizer tube leak may cause plugging of hoppers and airheaters.

Boiler Emergencies-tube leaks3) Super heater Tubes a) A small leak in a superheater element should be investigated at the earliest possible time, and the unit should be shut down in a normal manner. Steam leaks in the superheater can cause considerable erosion damage to the adjacent tubes. Any decision to continue operation with leaks should be made this in mind.b) A major superheater tube failure may require an emergency unit shutdown.6. Master Fuel Tripa) Under conditions requiring a master fuel trip through normal interlocks

or operators action (manual trip), all fuel should be tripped instantaneously.

b) The following steps should be taken immediately following an emergency fuel trip.

1) Maintain the unit air flow at the pre-trip value for at least 5 minutes to purge the system.

2) Check to ensure that all the fuel nozzles shut off valves are closed.

Boiler Emergencies-tube leaks

3) If all auxiliary power sources are lost during a trip, upon restoration of power, start the ID and FD fans and purge the furnace for five minutes.

Other boiler emergenciesAir preheater fires/tripping of APH ( one fan operation)Coal mill explosions ( may lead to boiler trip)Loss of furnace sealLoss of scan supply of any elevationLoss of instrument airLoss of cooling water to scaffold doorBending of long retractable soot blower / furnace probe

Reheater Protection Boiler will trip when any one or more of the following conditions occur : 1. Turbine Tripped or Gen CB open and HP or LP Bypass valves opening < 2% then after 5 sec of Time delay. 2. Turbine working (control valves >2 %) and Load shedding relay actuated and if HP or LP Bypass opening is < 2 %, Reheat protection will act after 10 sec. delay. 3. If Turbine is not working (HP or IP control valves < 2%) and boiler working (No. contact of loss all fuel arming relay from FSSS) and HP or LP Bypass valves < 2 % with a time delay of 5 Sec. Reheat Protection will act. Arming of Reheat Protection -Once HP & LP Bypass are open 2 % and steam flow increases beyond 200T/hr Reheater protection will be armed .

BOILER TRIP CausesWith the exception of the operator push button trip, following conditions will automatically generate Master Fuel Trip (MFT)• Loss Of All ID Fans•Loss Of All FD Fans•Less Than Two Circulating Pumps Running•Circulating Δp Less Than 0.6 Bar•Drum Level Low-low (-330 mm).•Furnace Pressure More Than 330 Mmwc Or Less Than -250 Mmwc•Loss Of All Fuel•Air Flow Less Than 30%•Turbine Trip•Reheater Protection Trip •Unit Flame Failure•Loss Of Unit Logic Power•Emergency Push Button.Cause of trip system : The first boiler trip command that causes a MFT will illuminate the appropriate indicator in the cause of trip section on the console insert. Any successive boiler trip commands to the other indicators are blocked. There will be only one indicator that will be glowing

Turbine protections1. LOW VACUUM

( Hyd trip > 0.3 bar, electrical trip > 0.3bar)

2. HIGH AXIAL SHIFT

( 1.0 mm)

3. OVERSPEEDING OF TURBINE

( Mechanical Trip3330 rpm, electrical trip >3330 rpm)

4. MAIN OIL TANK LEVEL LL( fire protection 2)

( 1030 mm from top)

5. C. F. TANK LEVEL LL( fire protection 1) ( -115 mm )6. LOW LUBE PRESSURE( A 4.8 bar,T 2.2 bar)

7. CONTROL OIL PRESSURE( T 3.5 bar)

8.TURBINE REMOTE PUSH BUTTON TRIP 9.FIRE PROTECTION 1 & 2(PUSH BUTTON)10.BOILER TRIP LEADING TO TURBINE TRIP11.GENERATOR TRIP LEADING TO TURBINE TRIP

Turbine protections

TURBINE ADVISORY TRIP

1. HIGH SHAFT VIBRATION / ECCENTRICITY

( A 120mic,T 200 mic)

2. HIGH BEARING VIBRATION

( A 35 mic,T 45mic)

3. HIGH BEARING METAL TEMPERATURE

( A 90C,T 120C)

4. HIGH DIFFERENTIAL EXPANSION

(HP -3/5mm,IP -2/7mm,LP -3/30mm)

5. HIGH/LOW MAIN STEAM TEMPERATURE

6.HIGH DRUM LEVEL

BOILER TRIP A “boiler trip’ command stops all fuel inputs by tripping all of the pulverizers and feeders and closing all heavy oil nozzle valves on all elevations. There are two separate “boiler trip” commands in this unit. Both “no boiler trip” command signals must be established before a furnace purge cycle can be initiated. A “boiler trip” command will establish a “master fuel trip” memory signal. This is indicated by the (red) “ MFT TRIP” light being on and the (green) “MFT RESET” light being off. When a “master fuel trip” memory signals established (red, “MFT TRIP” light is on), The following events occur: 1. The (red) “MFT A TRIP” and MFT B TRIP” lights come on and the associated (green) “MFTA RESET” and “MFT B RESET” lights go off. 2. The Data Logger receives a “MFT A TRIPPED” AND MFT B TRIPPED” SIGNALS.

3. The “boiler load greater than 30 %” memory signal is removed. When the “master fuel trip” memory signal is established (red, “MFT A TRIP” or MFT B TRIP” LIGHT IS ON), the following events occur: 4. Both of the (red ) “BOILER TRIP” light come on and the “PUSH TO PURGE” AND “PURGING” light are “armed”. 5. The PULV MODE (green) “MANUAL” light comes on, if it was off. 6. All pulverizers are tripped as indicated by the PULV START PERMITS (white) “NO PULV TRIP” lights going off. 7. A five minute counting period is started. Five minutes latter, all cold air dampers are opened to the “100 % pulverizer air flow position”. 8.The “permit to start P.A. fans” signal is removed. 9. The “oil elevation trip” memory signal is established at all oil elevations. 10. If all heavy fuel oil nozzle valves are not closed, the heavy fuel oil trip valve is closed. The heavy fuel oil trip valve can then be reopened after all heavy fuel oil nozzle valves are closed and the heavy fuel oil recirculation valve is opened.

11. A five second counting period is started. Five seconds later, the “loss of fuel trip arming” signal is removed. 12. The CAUSE OF TRIP memories cannot be reset. 13. All feeders are shutdown. 14. The upper and lower fuel air dampers are opened. 15. The auxiliary air control is transferred to MANUAL control and all auxiliary air dampers are opened. 16. The primary air (P.A.) fans are tripped. 17. The “feed forward to furnace draft control” signal is established for thirty seconds if the following conditions are satisfied: A. The unit critical power is available for more than six seconds ANDB. The “loss of fuel trip arming” signal is established. When this signal is established, item “B” is no longer required to keep this signal established. Thirty seconds later, the “feed forward to furnace draft control” signal is removed. 18. The furnace pressure recorder changes to a higher speed for thirty seconds.

When the thirty second counting period expires, the furnace pressure Recorder will remain at the higher speed if a “high furnace pressure alarm” or a “low furnace pressure alarm” signal is established. When both of these signals do not exist for more than thirty seconds, the furnace pressure recorder reverts to its original speed. The recorder will revert to the higher speed if either of these signals are established. A “boiler trip signal is established if any of the following conditions exist: 19. Loss of ACS power for more than two seconds. 20 Loss of customer’s 220 VDC Battery power for more than 2 ) seconds. 21. Loss of unit critical power for more than two seconds. 22. A “simulator trip” signal exists. 23. The water drum level is “low” for more than ten seconds. 24. The water drum level is high” for more than ten seconds. 25 All boiler feed pumps are off. 26. “Inadequate water wall circulation” signal exists.

27. All I.D. (Induced Draft) fans are off. 28. ALL F.D. (Forced Draft) fans are off. 29. The air flow is less than 30 % before the boiler load exceeds 30 %. 30. The deaerator level is “low-low”. 31. At least two of the three pressure switches indicate a “high furnace pressure trip” condition. 32. At least two of the three pressure switches indicate a “low furnace pressure trip” condition. 33. Both BOILER TRIP (emergency) push buttons are depressed simultaneously. 34. All feeders are off and loss of power exists at the elevation that is in service. 35. A loss of reheat protection occurs. 36 A “loss of fuel trip” signal is established (see Note below). Note : The “loss of fuel trip” signal becomes “armed” when the first oil elevation that is placed in service has at least three of the four heavy oil nozzle valves proven fully open (OIL VALVE COR (green) “CLOSED” lights are off).

After the “loss of fuel trip” signal is “armed”, a “loss of fuel trip” signal will be established if all of the following conditions occur simultaneously: A. At all coal elevation, the feeder is off or loss of elevation power exists. This condition exists for more than two seconds AND At all four oil elevations all oil nozzle valves are closed or an “elevation trip” signal is established at the associated oil elevation. The “loss of fuel trip” signal is proven established when the Data Logger receives a “LOSS OF ALL FUEL TRIP” signal. B. At all coal elevations, the feeder is off or loss of elevation power exists. This condition exists for more than two seconds. AND The heavy fuel oil trip valve is not fully open AND At all four oil elevations, all oil nozzle valves are closed. When the “master fuel trip” memory signal exists for more than five seconds the “loss of fuel trip arming” memory signal is removed.

The Data Logger’s “LOSS OF ALL FUEL TRIP” signal will remain established if item B above is satisfied. When the heavy oil trip valve is proven fully open (for oil recalculation), this signal is removed. 37. A “unit flame failure” signal is established (see Note below). NOTE : During light off and before any feeder is “proven” for more than two seconds, the “fireball” flame scanners do not take part in the overall flame failure protection systems. When any feeder is “proven” for more than two seconds, the system automatically changes from flame failure protection of an individual fuel nozzle to a “FIREBALL” supervision of the furnace. The system is designed to initiate a “boiler trip” when any feeder is “proven for more than two seconds and all five fireball flame scanner elevations vote “no flame” simultaneously.After any feeder is “proven” for more than two seconds, the UNIT FLAME FAILURE (amber) “ARMED” light comes on. After this light is on, a “unit flame failure “signal is established when all five UNIT FLAME FAILURE (amber) “GH” and “FG” and “DF” and “BC” and “AB” lights are all on simultaneously.

This is indicated when the Data Logger receives a “FLAME FAILURE TRIP” signal. This signal causes a “master fuel trip” memory signal to be established (both (red) “BOILER TRIP” lights come on). When each fireball flame scanner elevation votes “no flame”, the associated UNIT FLAME FAILURE (amber) light comes on at the associated fireball flame scanner elevation. Listed below are the conditions that will cause this (amber)light to be illuminated for the various fireball flame scanner elevations. Elevation “AB”: 1. Feeder A is off or loss of elevation A power and Feeder B is off or loss of elevation B power. This condition exists for more than two seconds. OR2. At elevation AB, less than three of the four heavy fuel oil nozzle valves are fully open or fuel flow is not adequate at the associated oil nozzle valve or elevation AB power is not available for more than two seconds and less than two of the four “fireball” flame scanners indicate flame on elevation “AB” OR

3.At elevation AB, less than three of the four heavy fuel oil nozzle valves are fully open or fuel flow is not adequate at the associated oil nozzle valve or elevation AB power is not available for more than two seconds and any elevation AB heavy fuel oil nozzle valve is not closed or elevation AB power is not available for more than 2 seconds. Elevation BC:1. Feeder B is off or loss of elevation B power and Feeder C is off or loss of elevation C power. This condition exists for more than two seconds. 2. Less than two of the four “fireball” flame scanners indicate flame on elevation “BC”. Elevation “DE”: 1. Feeder D is off or loss of elevation D power and Feeder E is off or loss of elevation E power. This condition exists for more than two seconds. 2. Less than two of the four “fireball” flame scanners indicate flame on elevation “DE”.

Elevation “FG”: 1. Feeder F is off or loss of elevation F power and Feeder G is off or loss of elevation G power. This condition exists for more than two seconds. 2. Less than two of the four “fireball” flame scanners indicate flame on elevation “FG”. 3. One elevation GH, any heavy fuel oil nozzle valve is not closed or elevation GH power is not available for more than two seconds. Elevation “GH”:1. Feeder G is off or loss of elevation G power and Feeder H is off or loss of elevation H power. This condition exists for more than two seconds. OR 2. At elevation GH, less than three of the four heavy fuel oil nozzle valves are fully open or fuel flow is not adequate at the associated oil nozzle valve or elevation GH power is not available for more than two seconds and less than two of the four “fireball” flame scanners indicate flame on elevation “GH” OR

3. At elevation GH, less than three of the four heavy fuel oil nozzle valves are fully open or fuel flow is not adequate at the associated oil nozzle valve or elevation GH power is not available for more than two seconds and any elevation GH heavy fuel oil nozzle valve is not closed or elevation GH power is not available for more than 2 seconds. CAUSE OF TRIP SYSTEM A “Cause of Trip” system has been incorporated which allows the Operator to determine the cause of a master fuel trip which was initiated by a boiler trip command. The boiler trip commands that can cause a “master fuel trip” memory signal to be established . The first boiler trip command that causes a master fuel trip (both (red) “BOILER TRIP” lights come on), will illuminate the appropriate indicator in the CAUSE OF TRIP section on the console insert. The Data Logger will also receive a corresponding signal. Any successive boiler trip commands to the other indicators are blocked. There will be only one indicator that is illuminated.

When the furnace purge cycle is successfully completed (PURGE CYCLE (yellow) “PURGE COMPLETE” light is on) and a “ no master fuel trip” memory signal is established (both (red) “BOILER TRIP” lights are off), all CAUSE OF TRIP memories are reset and there are no illuminated indicators. POST PURGE EXCURSION PROTECTION A post purge excursion circuit has been designed into the Furnace Safeguard Supervisory System. It operates as described below: 1. During the Furnace Purge Cycle, the following conditions are satisfied: A. The mode permit is satisfied B. All heavy fuel oil nozzle valves are closed C. The heavy fuel oil trip valve is closed, D. All pulverizers are off E. All feeders are off F. All flame scanners (discriminating and fireball) indicate no flame G. Air flow is greater than 30 %

2. When all of these conditions are satisfied simultaneously, a five minute counting period is started. After the five minute counting period expires, the following events will occur: A. A “post purge time expired” memory signal is established and a “post purge fan trip” signal is established if a “high or low furnace pressure trip” signal is established. This is indicated when the Data Logger receives a “FURNACE PRESSURE HIGH” or a “FURNACE PRESSURE LOW” signal. The “post purge fan trip” signal is proven established if the Data Logger receives “POST PURGE FAN TRIP” signal. If this signal is established, the I.D. and F.D. fans are tripped. B. The “open upper fuel air dampers” memory signal is removed, closing the upper fuel air dampers. Simultaneously, a thirty second counting period is started. When the thirty second counting period expires, the “open lower fuel air dampers” memory signal is removed, closing the lower fuel air dampers. Simultaneously, a five second counting period is started.

When the five second counting period expires, the auxiliary air dampers are now released from manual to the auxiliary air control system and the “open auxiliary air dampers” signal is removed. When any heavy fuel oil elevation has at least three of the four oil nozzle valves fully open, the “post purge time expired” memory signal is removed which will now prevent the “post purge fan trip” signal from being established. When the heavy oil trip valve is moved form the closed position (for oil recalculation), the five minute counting period is reset.