Boilers Exam Questions and
Answers 100% Verified
1) Which fire-tube boiler is most commonly used today? - ANSWER-The packaged
HRT boiler is most commonly used today. Manufacturers include Cleaver Brooks,
Kewanee, Hurst, etc.
1) Why are water-tube boilers used in large generating plants? - ANSWER-Water
tube boilers can be built for high pressures and high capacities, can be designed to
burn all fuels and can accept all heat recovery equipment.
What is the definition of boiler heating surface? - ANSWER-The ASME code defines
boiler heating surface as the parts of a boiler with water (wet steam) on one side
and the products of combustion on the other side. Measured on the side receiving
heat (hot gas side) and always expressed as square feet.
How is the heating surface of an HRT boiler calculated? - ANSWER-Heating surface
of an HRT boiler: ⅔ the area of the shell, the area of all the tubes and ⅔ the area of
the tube sheets minus the area of the tube holes.
How is the heating surface of a fire-tube calculated? A water-tube? - ANSWER-A fire
tube heating surface is determined by using the inside diameter times π
(circumference) times the length. A water tube is done the same way using the
outside diameter of the tube.
A fire-tube 3" o.d. has a wall thickness of 3/16 inch and a length of 14 '. What is the
heating surface? - ANSWER-3" - ⅜ = 2 ⅝" = 2.625 X π = 8.2466" = .687 X 14 = 9.62
ft2
How is the MAWP calculated? - ANSWER-MAWP = S X T X E
FXR
Where: S = tensile strength of material in psi (per inch of thickness)
T = thickness of material in inches
E = efficiency of joint.
, F = factor of safety
R = radius of drum in inches
What is the difference between super-heaters and re-heaters? - ANSWER-Both add
enthalpy to steam with the difference being that reheated steam has already done
some work in the turbine.
Name six (6) methods used to control super-heat temperature. - ANSWER-SH temp.
can be controlled by: attemperation/de-superheating, radiant/convection type super-
heaters in combination, separately fired burners, tilting burners, flue gas
recirculation, by-pass dampers and soot-blowers.
Why are radiant and convection super-heaters used in combination? - ANSWER-The
radiant super-heater has a decreasing temperature profile on a load increase and
the convection super-heater has a rising temperature profile on a load increase.
Used together, a flatter temperature profile is obtained.
Explain how you would justify the installation of an air pre-heater? - ANSWER-
Usually not practical below 1,000 BHP
Consider increased draft (larger fans)
Calculate heat savings (reduced heat loss out stack)
Consider dew point/sulfur content of fuel
Maintenance cost of added equipment.
Cost analysis/projected payback.
Explain the terms parallel flow and counter flow? - ANSWER-Parallel flow: Both fluids
flow in the same direction with the hot gas coming in contact with the coolest fluid.
Counter-flow: the flow of one of the working substances is opposite the flow of the
other substance. More heat is transferred in a counter-flow arrangement.
When are two (2) main steam stop valves required? - ANSWER-Two main steam stop
valves are required whenever a boiler is equipped with manhole(s) and is connected
to a common header with other boilers.
Answers 100% Verified
1) Which fire-tube boiler is most commonly used today? - ANSWER-The packaged
HRT boiler is most commonly used today. Manufacturers include Cleaver Brooks,
Kewanee, Hurst, etc.
1) Why are water-tube boilers used in large generating plants? - ANSWER-Water
tube boilers can be built for high pressures and high capacities, can be designed to
burn all fuels and can accept all heat recovery equipment.
What is the definition of boiler heating surface? - ANSWER-The ASME code defines
boiler heating surface as the parts of a boiler with water (wet steam) on one side
and the products of combustion on the other side. Measured on the side receiving
heat (hot gas side) and always expressed as square feet.
How is the heating surface of an HRT boiler calculated? - ANSWER-Heating surface
of an HRT boiler: ⅔ the area of the shell, the area of all the tubes and ⅔ the area of
the tube sheets minus the area of the tube holes.
How is the heating surface of a fire-tube calculated? A water-tube? - ANSWER-A fire
tube heating surface is determined by using the inside diameter times π
(circumference) times the length. A water tube is done the same way using the
outside diameter of the tube.
A fire-tube 3" o.d. has a wall thickness of 3/16 inch and a length of 14 '. What is the
heating surface? - ANSWER-3" - ⅜ = 2 ⅝" = 2.625 X π = 8.2466" = .687 X 14 = 9.62
ft2
How is the MAWP calculated? - ANSWER-MAWP = S X T X E
FXR
Where: S = tensile strength of material in psi (per inch of thickness)
T = thickness of material in inches
E = efficiency of joint.
, F = factor of safety
R = radius of drum in inches
What is the difference between super-heaters and re-heaters? - ANSWER-Both add
enthalpy to steam with the difference being that reheated steam has already done
some work in the turbine.
Name six (6) methods used to control super-heat temperature. - ANSWER-SH temp.
can be controlled by: attemperation/de-superheating, radiant/convection type super-
heaters in combination, separately fired burners, tilting burners, flue gas
recirculation, by-pass dampers and soot-blowers.
Why are radiant and convection super-heaters used in combination? - ANSWER-The
radiant super-heater has a decreasing temperature profile on a load increase and
the convection super-heater has a rising temperature profile on a load increase.
Used together, a flatter temperature profile is obtained.
Explain how you would justify the installation of an air pre-heater? - ANSWER-
Usually not practical below 1,000 BHP
Consider increased draft (larger fans)
Calculate heat savings (reduced heat loss out stack)
Consider dew point/sulfur content of fuel
Maintenance cost of added equipment.
Cost analysis/projected payback.
Explain the terms parallel flow and counter flow? - ANSWER-Parallel flow: Both fluids
flow in the same direction with the hot gas coming in contact with the coolest fluid.
Counter-flow: the flow of one of the working substances is opposite the flow of the
other substance. More heat is transferred in a counter-flow arrangement.
When are two (2) main steam stop valves required? - ANSWER-Two main steam stop
valves are required whenever a boiler is equipped with manhole(s) and is connected
to a common header with other boilers.
