Auxiliary Boilers Flashcards
- List eight mountings that are found on auxiliary marine boilers. (16)
Boiler gauge glass. Safety valve Blow down valve Boiler feed check John Willison IAMI Revision 24 Drum vent valve. Pressure gauge connection Main stop valve Water sampling valve Scum valve
- List EIGHT mountings which must be present on auxiliary marine boilers. (16)
Boiler gauge glass. Safety valve Blow down valve Boiler feed check Drum vent valve. Pressure gauge connection Main stop valve Water sampling valve Scum valve
- a) State four possible reasons for the boiler feed pump failing to maintain the water level in an auxiliary boiler.
b) Upon rectification of the fault in Q a) describe the start up sequence of the boiler.
a) Feed filter tank empty.
Tube failure.
Problem with pump i.e. coupling failed key failure.
Boiler water controller fail shut.
b) Stop the burner.
When restoring the normal water level ensure that you feed with hot feed water to avoid thermal shocking.
Shut the stop valve to ensure not feeding steam to the system.
Start the burner on low fire on auto and keep on low fire until the steam pressure returns to normal.
- a) State TWO consequences of not treating the waterin a boiler. (4)
b) Outline TWO tests which are carried out on boiler water. (12)
a) Failure to control the recommended level for the water can lead to increased chance of water becoming acidic, or the dissolved solids increasing to level that could lead to tube blockage reduction of water circulation.
b) Total Alkalinity:
This test gives the alkalinity due to all salts in the water.
Use the sample from ‘P’ Alkalinity and add 5 drops of total alkalinity indicator and the solution should go clear. Add sulphuric acid N/10 until pink. Convert ml in burette to ppm using chart and chemically treat using manufactures guidance.
Chlorides:
This test measures the amount of chloride in the water.
Fill the plastic vial to 10ml and add 3 drops of phenolphthalein to neutralise the sample. Add N/10 until turns clear and add one more drop, add 6 drops of potassium chromate to turn yellow. Add silver nitrate N/10 until orange. Drops of silver nitrate x 10 = ppm chloride.
- a) State the effect on auxiliary boiler operation in the event of the following alarm condition:
John Willison IAMI Revision 25
i) High water level; (2)
ii) Low water level; (2)
iii) Extra-low or low-low water level. (2)
b) Describe the procedure for blowing down a low-pressure boiler gauge glass. (8) c) How often should a low-pressure boiler gauge glass be blown down? (2)
a)
i) May need to stop feed pump.
ii) May need to start feed pump.
iii) Burner must be stopped to identify problem.
b) Close off cocks ‘S’ and ‘W’ and open drain ‘D’. Make sure both water and steam cocks are holding.
Open cock ‘W’ and blow through. Make sure that water is coming out and cock ‘W’ is clear. Close water cock.
Open cock ‘S’ and blow through. Make sure that steam is coming out and cock ‘S’ is clear. Close steam cock.
Close drain ‘D’.
Open water cock ‘W’ and check water level rises in the glass.
Open steam cock ‘S’ for showing boiler water level.
c) Once a day.
- With the aid of simple sketches describe the procedure for blowing through a boiler gauge glass.
- Close off cocks ‘S’ and ‘W’ and open drain ‘D’. Make sure
both water and steam cocks are holding. - Open cock ‘W’ and blow through. Make sure that water is
coming out and cock ‘W’ is clear. Close water cock. - Open cock ‘S’ and blow through. Make sure that steam is
coming out and cock ‘S’ is clear. Close steam cock. - Close drain ‘D’.
- Open water cock ‘W’ and check water level rises in the
glass. - Open steam cock ‘S’ for showing boiler water level.
a) Explain the sequence of events that occur on pressing the start button of an automatically controlled oil fired package steam boiler.
John Willison IAMI Revision 26
b) State three reasons why the boiler in Q a) would automatically shut down during the starting sequence (6)
a) The burner force draught fan will run to purge the combustion space
Upon successful purge and correct air-pressure, the ignition spark is started
The diesel oil pilot flame solenoid valve is opened and pilot flame ignited
The main burner fuel solenoid is opened once a pilot flame is detected, and burner ignition commences, the pilot flame now extinguishes after a time delay
If no flame after 5 seconds, the main burner and pilot burner fuel supplies are cut and the boiler locked out
The air register dampers and burner fuel supply adjusted to achieve the correct firing rate. b) Low-Low Water Level
Flame Fail
High Water Level
Low Fuel Oil Pressure
- State FOUR tests which are required for boiler water, giving a reason for EACH test (16).
Phenol Alkalinity to keep the water neutral not alkaline or acidic.
Chloride to monitor and control the concentration of chloride salts within boiler water, indicating the ingress of salt water from coolers.
Total Dissolved Solids, to monitor and control the amount of solids within boiler water that gradually build up overtime. These would otherwise cause foaming within the boiler water and carry over that would damage steam plant severely.
PH to monitor and control the chemical concentration of boiler water preventing acidic and caustic corrosion.
Water Hardness, to monitor and control the levels of calcium and magnesium salts within feed water, that would otherwise damage boiler surfaces.
- State four circumstances under which the fuel supply to the burners of an auxiliary boiler would be automatically cut off, giving a reason why each circumstance requires the fuel to be cut off.
Low-Low water level, to prevent permanent thermal damage to the heat transfer surfaces of the boiler risking a possible boiler drum rupture.
Flame Fail, so that un-burnt does not flood the combustion space filling it with explosive gasses. High water level, so that carry over does not occur damaging steam plant and systems. Low fuel oil pressure, a reduced fuel pressure leads to poor and unstable combustion.
- List four safety or alarm devices fitted to an automatically controlled auxiliary boiler indicating how each of these devices may be tested. (16)
High Water Level, using the manual feed valve slowly over - fill the boiler until the alarm sounds and the feed pumps cut-off.
Low fuel oil temperature - turn off the fuel oil heaters and allow the fuel to cool tripping the burners.
Low-low water level - blow the boiler down until the alarm sounds followed but the tripping of the burners.
Ignition failure - isolate the ignition transformer and begin start sequence, the burner will lock out after purge.
- State the possible cause, and outline the remedial action that should be taking when each of the following faults occur during starting up of an automatic package boiler.
a) The boiler starts and the fan runs with the control dampers correctly positioned, the boiler then locks out before purging is completed; (4)
b) The boiler purges correctly, but the ignitors fail to spark and the boiler locks out; (4) c) The boiler purges correctly, the ignitors spark, but the boiler fails to light up and locks out; (4)
d) The boiler flame flashes up but after about 5 seconds the automatic control locks the boiler out. (4)
a) Low air pressure. Action check that the fan is running and no obstruction to the air flow check the pressure sensor is operational
b) Check the igniter tips clean clearance are correct and the high voltage supply is operational. c) Check the burner tip is clean, fuel is being supplied ok and solenoid valve opens ok. d) Check flame condition and fuel and air ration is correct.
- With reference to auxiliary boilers:
a) Explain how scale forms on the heating surfaces; (8)
b) State two reasons why scale is undesirable; (4)
c) State how scale builds up is prevented from forming in steam boilers. (4)
a) The bicarbonates of calcium and magnesium are decomposed by heat and come out of the solution as scale forming carbonates.
High concentrations of calcium and magnesium salts within hard water.
Scale forms as carbonates adhere to heated surfaces due to “coming out of suspension” Due to the scale covering of scale heat increases and the process intensifies.
b) Reduction in heat transfer efficiency.
Local overheating of boiler tubes and damage.
c) By keeping the hardness salts in suspension in the solution to prevent scale formation. By stopping any suspended salts and impurities from sticking to the heat transfer surfaces.
- a) The name given to the water level indicators mounted on a boiler. (2) b) State why at least two of the items stated in Q (a) are fitted.
c) List FIVE boiler mountings which are subject to survey, other than those stated in Q(a).
a) Water Level Gauge Glass
b) To enable the level of boiler water to be monitored in the event of glass failure To allow the water level to be monitored in the event of severe roll
c) Pressure Gauge Connections
Boiler Vent Cock
Main Steam Stop Valve
Safety Valves
Blow Down valve connection
- With reference to an auxiliary boiler, state for EACH of the following circumstances the action to be taken, giving a reason for EACH action;
a) no water level visible in gauge glass; (4)
b) safety valve lifting; (4)
c) excessive smoking during firing; (4)
d) excessively high chloride content of boiler water. (4)
a) If water level has not yet dropped completely out of the sight glass, water may be put into the boiler. If water drops completely out of sight glass, check another sight glass. If both have no water visible, don’t add water until the boiler is cold enough to prevent any possible damage due to rapid cooling of overheated plate.
b) Excessive boiler pressure of steam can occur due to the steam outlet valve being shut off. You would check the boiler steam outlet valve, if on manual change to auto and if auto isn’t working shut down the boiler.
c) Too much fuel, not enough air or cold oil. Check the oil temperature, check the flame colour, if orange increase until primrose yellow.
d) Blow down frequently.
Reduce the boiler load to minimum.
If highly contaminant shut down and completely and wash out.
Trace and fine out the fault and remedied.
