Answer MEP Question 45

Q. An Auxiliary boiler is periodically unattended and equipped with alarms to cover low water level, high steam pressure, and air and flame failure. 

A. State why and how fuel the burners are automatically cut off under alarm conditions of water level, steam pressure, air and flame failure. 

B. Describe how and when each of the above alarms is tested without endangering the boiler.

A. State why and how fuel the burner is automatically cut off under alarm conditions of water level, steam pressure, air and flame failure. 

Water level

Steam pressure:

- Steam pressure is the main controlling parameter and the controller will adjust fuel to maintain this at a set level.

- If steam pressure reaches the set point the boiler will cut off and firing stops. 

- If for any reason the steam pressure continue to rise above the set pressure the master controller will immediately activate the closure of fuel shut off valve to stop firing and activate an High Steam pressure alarm, 

- The trip is provided to avoid over pressurizing of steam drum which will eventually cause the safety valve will act. Pressure build u above boiler safe working pressure may lead to rupture of water tubes or even explosion.

Air and flame failure:

- Air failure will cause improper combustion and poor atomization which is not good for an ideal stoichiometric combustion.

- Failure of atomizing air or secondary air also results in un burn fuel accumulation and other consequential failures. 

- Flame failure is one of the most dangerous scenarios where if the burner doesn't cut off the fuel, the fuel will continue to spray inside which is more dangerous situation.

-Hence, a flame eye is constantly monitoring the flame and if the flame failure occurs for any reason, the flame eye immediately trips and shuts off the fuel valve and rises a "flame failure alarm".

B Describe how and when each of the above alarms is tested without endangering the boiler:

Testing of water level alarms: 

To test the Low-Low water level

- Shut valve #1 and valve #2 and open valve #3.

- Steam side and water side is isolated and the water inside is completely drained causing the float to drop Which activates the bottom magnetic switch which initiates the Low-Low water level trip.

To test the Low water level & High Water level with Feed pump stop

High & High-High water level

- Close valve #2 & Open valve #5

- First high level alarm is triggered, and then Hi-Hi alarm is triggered and stops the feed pump.

Lo & Lo-Lo water level & Burner trip

- Close valve # 3 & Open valve # 4

- First Low water level alarm is triggered, and then Lo-Lo alarm is triggered and shuts down the fuel to boiler.

Steam Pressure

 Ona steady steam demand day, preferably a sea day, Inform watch keepers and obtain permission from C/E.

- Start the boiler in Manual firing mode and increase the fuel modulation slowly to maximum, the boiler will start to increase the pressure past the operating pressure and when it reaches High steam pressure set point level the High steam pressure alarm is raised and the boiler is shut down.

- Some ships C/E might prefer to avoid pressing up the boiler, but simply adjust the setting on the master high steam pressure cut off and trigger the alarm.

Flame Failure

- Start the boiler is normal ‘Auto’ mode. .

- When the boiler is firing well just remove the flame eye sensor out, it should trigger the alarm and cut off the fuel to the boiler and cause a trip,