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Power engineering 5th class final exam questions and answers
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Power engineering 5th class final exam questions and answers
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5th Class Power EngineeringAssignment 3 questions and
answers
Explain the conditions required and actions that must be attempted
before a boiler start up can be attempted - answer Make sure the
boiler has a valid inspection certificate, make sure no foreign
matter, such as tools or rags, is left behind, clean the boiler
chemically, make sure the firing equipment is ready for startup
Describe the automatic start-up sequence of a gas fired boiler fitted
with a draft fan or blower. Also describe how the boiler is warmed
up after starting from cold - answer On gas-fired boilers with a
standing pilot, open the pilot valve and light the the pilot. Follow
the lightning instructions given on the instruction plate attached to
the burner mandifold or automatic valve. When the pilot is lit and
burning satisfactorily, open the stop valve in the fuel line to the
main burner. It's warmed up from cold to warm slowly to prevent
uneven expansion and thermal shock
Describe the automatic shutdown sequence of a gas fired boiler -
answer Reset all limit switches, such as low water, which would
have been tripped or opened during shut down, check the boiler
control switch is in the off position
List three reasons why ignition may not occur during the startup
sequence of a boiler and explain each - answer Flame scanners if
they don't detect the fire in your furnace the boiler will cut off gas
supply. Broken electrode will cause the pilot not to light at all.
Faulty pilot ignition cable if your boiler does not seem to be
attempting to ignite, check to ensure it has any power, and if not,
inspect the fuse box to see if any fuse has tripped
,Describe two reasons why a high/ low fire burner might stay on low
fire - answer The modulating control may be malfunctioning, the
igniter is defective
Describe four reasons why a burner shutdown may occur during
firing - answer Too much air in the system, excessively high boiler
firing rate, opening burner fuel valves before ignition is established,
purging the furnace before light-off
Explain step by step, the general preparations required for starting
up a hot water heating boiler after a lengthy shut-down - answer
Heat up a cold boiler slowly as to avoid thermal shock and uneven
expansion, because this leads to boiler leakage and costly repairs.
Should any abnormal condition occur immediately shut down the
boiler and close the stop valves in the fuel lines. Identify the
problem before restarting the boiler.
Describe how would you start up of a hot water boiler with a
standing pilot - answer First set the gas valve to the pilot. Position
hold down the bypass button to let gas into pilot. Keep holding the
button down and use a lighter to insert a flame over the pilot
Describe two conditions that, while appearing abnormal, will
disappear after a hot water heating boiler heats up - answer 1.
Slight Smoking- When a cold- fired boiler is started up, the operator
may notice that during the first part of the warm-up period to the
stack will smoke slightly. This is normal since the furnace
temperature is not enough yet to vaporize the incoming fuel oil
immediately and completely. If the stack is smoking heavily and the
burner nozzle is known to be clean, adjust the air damper to obtain
the proper fuel- air ratio.
2. condensation- When a cold gas fired boiler is started up,
condensation will run out of the drain in the colour of the reversing
chamber
Describe the cause of uneven expansion and what the effects of
uneven expansion are - answer When the burner is lit in a cold fire
, tube boiler, the furnace and the first pass of the fire tubes will heat
up rapidly. This heat is not readily carried off by the water
surrounding the tubes since proper circulation has not been
established and as a result, the metal temperature will rise
considerably. In hot water boiler with forced circulation, the metal
temperature will not rise to the same extent.
Define "thermal Shock" - answer When metal is subjected to a
sudden change in temperature, the temperature change will not be
even throughout the metal. Expansion and contraction will not be
equal in all parts of the metal. This causes strong internal stresses
in the metal, called "thermal shock"
Explain the problems which may arise by operating a gas-fired hot
water heating boiler below a temperature of 77 C (170F) - answer
Are avoided to prevent flue gas condensation
What is the recommended operating pressure of hot water heating
system that has a safety relief valve set to 827 Kpa (120 psi) -
answer The operating pressure should not exceed 620 kpa (90 psi).
The reason for this recommendation is that a large pressure
differential will assure tight closing of the valve
State the advantage of having a stack thermometer - answer To
check the temperature of the flue gases
Explain the importance of maintaining up to date records of boiler
stack temperatures during normal operations plant operation. -
answer By keeping a log of the stack temperature, a gradual
increase in temperature will tell the operator that the heating
surfaces are fouling up and that the heat transfer, and thus the
boiler efficiency, is dropping. Cleaning may be required
Describe the results of excessive scale and soot in a boiler - answer
Spot deposits on the fireside caused by improper combustion or
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