Power Engineering 2A3 Questions With Complete Solutions
One boiler horsepower is equal to how many kW - (ANSWER)9.809kW
This is still the common measure of capacity for small boilers, where large boiler capacity is given in the
number of kg of steam per hour.
What are the definitions of boiler, steam generator and steam generating unit? - (ANSWER)Boiler -
strictly speaking are the elements in which the change of state from water to steam takes place.
Steam generator - embraces the many combinations of heating surfaces, such as water walls,
superheaters, reheaters, economizers, and air heaters.
Steam generating units - consists of a steam generator and its associated equipment, including fuel
burning, ash removal, and draft systems.
What are the three general methods of calculating the output rating of a boiler? - (ANSWER)1) One
square meter of heating surface equals 10 kW. Where a computation is to be made of a curved surface,
the surface having the greater radius shall be taken.
2)Where electric power is used as the heat source, the boiler rating shall be the maximum kilowatt
rating of the heating element. The actual output will be somewhat less.
3) Where neither of the above determinations are applicable, an hourly output of 36 MJ is equivalent to
10 kW. This is the calculation employed in determining the heat balance of a steam plant.
Steam generators are often rated in terms of - (ANSWER)maximum continuous steam output in kg/hr at
design temperature and pressure. The kg/hr rating at the stop valves must include reheater sections of
steam generating units.
Steam generators supplying steam to turbo-alternators are often rated in - (ANSWER)megawatts,
because the energy supplied to the turbines is converted to electrical power. This is not an accurate
measure of the energy output because the turbine and generator efficiencies are not considered.
,Power Engineering 2A3 Questions With Complete Solutions
What are the standard conditions for comparing boilers/equivalent evaporation? - (ANSWER)The
amount of heat necessary to convert 1 kg of water at 100 ℃ into 1 kg of 100% dry steam at 101.325 kPa
and 100 ℃
What is the factor of evaporation? - (ANSWER)The ratio between the heat taken per kg of steam under
actual conditions and the heat taken in evaporating 1 kg of dry steam at 100 ℃
What are the 5 fundamental requirements, or objectives, for boiler design? - (ANSWER)- Efficiency
- Reliability
- Cost
- Serviceability
- Safety
When looking at boiler design, which components will be influenced due to the type of fuel being used?
- (ANSWER)- The furnace size or heating surface
- The placement of the heating surface
- The equipment needed to prepare and burn the fuel
- The size and type of heat recovery equipment
- The fuel gas treatment devices
What is the most common type of solid fuel that is burned? - (ANSWER)Pulverized coal
For the same output, which furnace must be the largest for gas, oil or coal? - (ANSWER)The coal
furnaces must be larger, but the velocities of the combustion gases must be slower. The combustion
process is slower, because the solid coal releases volatile matter which is then oxidized.
What are the differences in furnace size needed for the different types of coal? - (ANSWER)High-slagging
lignite coal will require a larger furnace volume than volatile bituminous or subbituminous coal.
Medium-sized furnaces are specified for low-slagging types of lignite coal.
,Power Engineering 2A3 Questions With Complete Solutions
What are the design parameters used for oil-fired furnaces? - (ANSWER)- The time needed to
completely combust the fuel
- The need to limit furnace wall temperatures
Oil fired furnaces have higher heat release rates per unit volume (compared to coal), as no extra size is
built in for ash control. The result is heat absorption rates can been seen on metal temperatures and
circulation.
Gas fired furnace designs - (ANSWER)They are similar to the design of oil firing, except that gas firing
results in lower localized heat absorption rates, which means the furnace temperature is more uniform
than with oil. Therefore, the furnace can be slightly smaller in volume than an oil-fired furnace.
Define circulation ratio - (ANSWER)The amount of water circulated in a boiler usually exceeds the
amount of steam being generated. If 10 kg of steam-water mixture is circulated for each kg of steam
generated, the circulation ratio is 10:1.
What is top dryness? - (ANSWER)The percentage of steam, by mass, in the steam water mixture at the
top of a riser tube, where heating ceases is called top dryness.
It varies with design but normally runs from about 5% to 20%.
What happens if "top dryness" is excessive? - (ANSWER)If the percentage of steam in the mixture
becomes excessive, a condition is reached in which a film of steam exists at the inner surfaces of the
boiler tubes. This condition is unacceptable in superheaters as these tubes are exposed to higher
temperature radiant heat and the steam will not cool the tube metal as much as the steam-water
mixture will.
What is mass flow? - (ANSWER)It refers to the mass of fluid mixture in kg/hr passing through the tube. It
is affected by velocity, density, specific heat, conductivity, fluid viscosity, tube diameter, and internal
tube surface.
, Power Engineering 2A3 Questions With Complete Solutions
What are some of the factors in flow resistance? - (ANSWER)- Mass flow
- Tube diameter
- Fluid velocity
- Viscosity
At what pressure is forced circulation usually preferred at? - (ANSWER)Boilers operating at above 12 400
- 14 000 kPa
What are some of the advantages of forced circulation? - (ANSWER)Due to the positive flow, smaller
diameter tubes can be used with the benefits of lower cost, less mass, thinner tube walls with reduced
thermal stresses, and heat transfer rates are improved.
Another advantage is that the layout is more flexible and there is no need for a high head to produce
circulation.
This flexibility allows the heating surfaces to be arranged with less baffling and fewer gas passes,
resulting in lower fan power requirements.
These boilers can be started up more quickly and enables it to adjust to load changes more rapidly.
What are the two general classes of forced circulation boilers? - (ANSWER)- Controlled circulation or
recirculating boilers
- Once-through boilers
What kind of pumps are generally used in a large controlled circulation boiler? How many stages do they
usually need? - (ANSWER)There may be several pumps used in a large boiler, but they are usually
vertical centrifugal pumps driven by constant speed motors.
Single stage pumps are generally adequate as the pump may only be required to develop a head of
about 275 kPa. This head is only over and above the pump suction which may be 14 000 kPa or more.
Due to this high pressure water, which is at or near saturation temperature, the pumps must have
One boiler horsepower is equal to how many kW - (ANSWER)9.809kW
This is still the common measure of capacity for small boilers, where large boiler capacity is given in the
number of kg of steam per hour.
What are the definitions of boiler, steam generator and steam generating unit? - (ANSWER)Boiler -
strictly speaking are the elements in which the change of state from water to steam takes place.
Steam generator - embraces the many combinations of heating surfaces, such as water walls,
superheaters, reheaters, economizers, and air heaters.
Steam generating units - consists of a steam generator and its associated equipment, including fuel
burning, ash removal, and draft systems.
What are the three general methods of calculating the output rating of a boiler? - (ANSWER)1) One
square meter of heating surface equals 10 kW. Where a computation is to be made of a curved surface,
the surface having the greater radius shall be taken.
2)Where electric power is used as the heat source, the boiler rating shall be the maximum kilowatt
rating of the heating element. The actual output will be somewhat less.
3) Where neither of the above determinations are applicable, an hourly output of 36 MJ is equivalent to
10 kW. This is the calculation employed in determining the heat balance of a steam plant.
Steam generators are often rated in terms of - (ANSWER)maximum continuous steam output in kg/hr at
design temperature and pressure. The kg/hr rating at the stop valves must include reheater sections of
steam generating units.
Steam generators supplying steam to turbo-alternators are often rated in - (ANSWER)megawatts,
because the energy supplied to the turbines is converted to electrical power. This is not an accurate
measure of the energy output because the turbine and generator efficiencies are not considered.
,Power Engineering 2A3 Questions With Complete Solutions
What are the standard conditions for comparing boilers/equivalent evaporation? - (ANSWER)The
amount of heat necessary to convert 1 kg of water at 100 ℃ into 1 kg of 100% dry steam at 101.325 kPa
and 100 ℃
What is the factor of evaporation? - (ANSWER)The ratio between the heat taken per kg of steam under
actual conditions and the heat taken in evaporating 1 kg of dry steam at 100 ℃
What are the 5 fundamental requirements, or objectives, for boiler design? - (ANSWER)- Efficiency
- Reliability
- Cost
- Serviceability
- Safety
When looking at boiler design, which components will be influenced due to the type of fuel being used?
- (ANSWER)- The furnace size or heating surface
- The placement of the heating surface
- The equipment needed to prepare and burn the fuel
- The size and type of heat recovery equipment
- The fuel gas treatment devices
What is the most common type of solid fuel that is burned? - (ANSWER)Pulverized coal
For the same output, which furnace must be the largest for gas, oil or coal? - (ANSWER)The coal
furnaces must be larger, but the velocities of the combustion gases must be slower. The combustion
process is slower, because the solid coal releases volatile matter which is then oxidized.
What are the differences in furnace size needed for the different types of coal? - (ANSWER)High-slagging
lignite coal will require a larger furnace volume than volatile bituminous or subbituminous coal.
Medium-sized furnaces are specified for low-slagging types of lignite coal.
,Power Engineering 2A3 Questions With Complete Solutions
What are the design parameters used for oil-fired furnaces? - (ANSWER)- The time needed to
completely combust the fuel
- The need to limit furnace wall temperatures
Oil fired furnaces have higher heat release rates per unit volume (compared to coal), as no extra size is
built in for ash control. The result is heat absorption rates can been seen on metal temperatures and
circulation.
Gas fired furnace designs - (ANSWER)They are similar to the design of oil firing, except that gas firing
results in lower localized heat absorption rates, which means the furnace temperature is more uniform
than with oil. Therefore, the furnace can be slightly smaller in volume than an oil-fired furnace.
Define circulation ratio - (ANSWER)The amount of water circulated in a boiler usually exceeds the
amount of steam being generated. If 10 kg of steam-water mixture is circulated for each kg of steam
generated, the circulation ratio is 10:1.
What is top dryness? - (ANSWER)The percentage of steam, by mass, in the steam water mixture at the
top of a riser tube, where heating ceases is called top dryness.
It varies with design but normally runs from about 5% to 20%.
What happens if "top dryness" is excessive? - (ANSWER)If the percentage of steam in the mixture
becomes excessive, a condition is reached in which a film of steam exists at the inner surfaces of the
boiler tubes. This condition is unacceptable in superheaters as these tubes are exposed to higher
temperature radiant heat and the steam will not cool the tube metal as much as the steam-water
mixture will.
What is mass flow? - (ANSWER)It refers to the mass of fluid mixture in kg/hr passing through the tube. It
is affected by velocity, density, specific heat, conductivity, fluid viscosity, tube diameter, and internal
tube surface.
, Power Engineering 2A3 Questions With Complete Solutions
What are some of the factors in flow resistance? - (ANSWER)- Mass flow
- Tube diameter
- Fluid velocity
- Viscosity
At what pressure is forced circulation usually preferred at? - (ANSWER)Boilers operating at above 12 400
- 14 000 kPa
What are some of the advantages of forced circulation? - (ANSWER)Due to the positive flow, smaller
diameter tubes can be used with the benefits of lower cost, less mass, thinner tube walls with reduced
thermal stresses, and heat transfer rates are improved.
Another advantage is that the layout is more flexible and there is no need for a high head to produce
circulation.
This flexibility allows the heating surfaces to be arranged with less baffling and fewer gas passes,
resulting in lower fan power requirements.
These boilers can be started up more quickly and enables it to adjust to load changes more rapidly.
What are the two general classes of forced circulation boilers? - (ANSWER)- Controlled circulation or
recirculating boilers
- Once-through boilers
What kind of pumps are generally used in a large controlled circulation boiler? How many stages do they
usually need? - (ANSWER)There may be several pumps used in a large boiler, but they are usually
vertical centrifugal pumps driven by constant speed motors.
Single stage pumps are generally adequate as the pump may only be required to develop a head of
about 275 kPa. This head is only over and above the pump suction which may be 14 000 kPa or more.
Due to this high pressure water, which is at or near saturation temperature, the pumps must have
