5th Class Power Engineering Assignment
3
Explain the conditions required and actions that must be attempted before a boiler start up can
be attempted - ANS 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 - ANS 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 - ANS 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 - ANS 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 - ANS The
modulating control may be malfunctioning, the igniter is defective
Describe four reasons why a burner shutdown may occur during firing - ANS 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 - ANS 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 - ANS 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 - ANS 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 - ANS
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" - ANS 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) - ANS 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) - ANS 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 - ANS 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. - ANS 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 - ANS Spot deposits on the
fireside caused by improper combustion or scale and sludge deposits caused by insufficient or
improper water treatment will foul up the heating surfaces and reduce heat transfer
3
Explain the conditions required and actions that must be attempted before a boiler start up can
be attempted - ANS 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 - ANS 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 - ANS 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 - ANS 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 - ANS The
modulating control may be malfunctioning, the igniter is defective
Describe four reasons why a burner shutdown may occur during firing - ANS 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 - ANS 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 - ANS 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 - ANS 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 - ANS
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" - ANS 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) - ANS 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) - ANS 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 - ANS 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. - ANS 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 - ANS Spot deposits on the
fireside caused by improper combustion or scale and sludge deposits caused by insufficient or
improper water treatment will foul up the heating surfaces and reduce heat transfer
