176 Questions
What is the definition of a watertube boiler according to the ABMA?
A boiler in which the tubes contain water and steam, the heat being applied to the outside surface
What was a limitation of early watertube boilers?
The use of straight tubes restricted the location of heat transfer surface
What advance in technology allowed boiler manufacturers to confidently install bent tubes?
Advances in water treatment technology
What was the result of using bent tubes in watertube boilers?
A reduction in the amount of refractory brickwork
What replaced riveted construction in watertube boilers?
Welded construction
What were the benefits of the development of modern watertube boilers?
They became increasingly safe to operate
Where is most steam produced in a watertube boiler?
In the tubes exposed to direct radiant heat of the furnace
What is the purpose of the internal feedwater pipe in a steam drum?
To raise the feedwater temperature to near the boiler saturation temperature
At what pressure does natural circulation become inadequate in a watertube boiler?
12.5 MPa
What is the purpose of the continuous blowdown pipe in a steam boiler?
To maintain proper dissolved solids levels
What determines the sophistication of the steam separating equipment required in a boiler?
The degree of dryness required
What is the main difference between the fluid in the downcomers and the fluid in the risers?
Density
What is the purpose of the chemical feed pipe in a steam boiler?
To introduce chemicals to the boiler to prevent scale formation and corrosion
Why do internal feedwater pipes discharge close to the downcomers?
To promote proper water circulation
What is the term for the condition that can occur when high concentrations of dissolved solids are present in a boiler?
Foaming
What is the purpose of the steam drum in a watertube boiler?
To separate the steam from the water
What is the main difference between watertube boilers and firetube boilers in terms of the location of water and heat?
Watertube boilers have water on the inside of the tubes and heat on the outside, while firetube boilers have heat on the inside and water on the outside.
What is one of the advantages of watertube boilers over firetube boilers?
They can be brought to operating pressure and temperature quicker.
What is a disadvantage of watertube boilers compared to firetube boilers?
They have less water content and therefore must be tuned to respond quickly to changes in steam pressure.
What is the primary purpose of the bent tube design in watertube boilers?
To allow optimal placement of superheaters, reheaters, and other heat transfer components.
What is the purpose of the risers in a watertube boiler?
To transfer water or water/steam mixture between the steam drum and the mud drum.
What is the purpose of the downcomers in a watertube boiler?
To feed water to the furnace area.
Why do watertube boilers require higher quality water than firetube boilers?
Because they are more prone to corrosion and scaling.
What is the purpose of the water-cooled furnace in a watertube boiler?
To absorb more radiant heat from the fire.
What is the main difference between the boilers shown in Figures 1 and 2?
One is a packaged two-drum watertube boiler and the other is a once-through steam generator.
What is the result of the density difference between water and steam in a watertube boiler?
The denser water in the downcomers forces the less dense water/steam mixture upward through the risers.
What is the primary function of baffles in watertube boilers?
To separate the water in the steam drum from the two-phase steam/water mixture
What is the main difference between firetube and watertube boilers in terms of steam separation?
Firetube boilers have less need for steam separation equipment
How does a dry pipe separate steam from water?
By forcing the steam to make sharp turns
What is the purpose of a centrifugal (cyclone) separator?
To further dry the steam by separating water particles
What is the function of the chevron plates in a chevron dryer?
To force the steam to change direction and drop entrained water particles
What is the term 'setting' used to describe in modern boilers?
The walls that form the boiler and furnace enclosure
Why do firetube boilers have less need for steam separation equipment?
Because they have larger shells and more room in the steam space
What is the primary purpose of a steam separator?
To separate the steam from water
What is the advantage of using waterwalls in modern boilers?
They improve heat transfer, decrease heat loss, and reduce the need for insulation and refractory
Where are chevron dryers often situated in a boiler?
Directly below the steam outlet
What is the primary purpose of a watertube boiler furnace?
To produce a certain maximum amount of steam
What type of boilers are designed to accommodate single burners, multiple burners, fluidized beds, and stokers?
Watertube boilers
What is the purpose of refractory-lined tubes in fluidized bed boilers?
To withstand high temperatures
What is the function of the steam drum in a watertube boiler?
To separate water and steam
What type of construction is characteristic of watertube boiler furnaces?
Waterwall
What is the purpose of the bent tubes in a watertube boiler?
To form a water-cooled furnace
What is the primary difference between A, D, and O-type boilers?
The shape of the tubes and drums
What is the function of the downcomers in a watertube boiler?
To return water to the mud drum
Why is the back wall of a D-type boiler often protected by refractory?
To protect it from radiant and convection heat
What is the purpose of the castable refractory lining the furnace floor in a watertube boiler?
To shield the mud drum from radiant heat
What is the purpose of the induced draft (ID) fan in an air heater?
To draw out the cooler flue gases
What is the characteristic of a natural circulation steam generating unit?
It uses only natural convection currents to circulate the boiler water
At what pressure is there no difference in density between steam and water?
22 090 kPa
What is the purpose of the air heater in the sub-critical, natural circulation power boiler?
To heat the air
What is the characteristic of a radiant steam generating unit?
It has a steam drum but no boiler bank
What is the purpose of the external downcomer in the sub-critical, natural circulation power boiler?
To enhance positive water circulation
What is the primary function of a steam generating unit?
To produce high-pressure, high-temperature steam
What is the purpose of the boiler section in a steam generating unit?
To extract heat from flue gas and transfer it to water
What is the main producer of steam in a steam generating unit?
Water walls
What is the purpose of superheaters in a steam generating unit?
To increase the temperature of steam above its saturation temperature
What is the primary function of the reheater in a steam generating unit?
To reheat the steam after it has performed work in the turbine
What is the purpose of reheaters in a steam generating unit?
To reheat exhaust steam from the high or medium-pressure turbine stages
What is the result of steam passing through turbine stages?
The pressure and temperature of steam decrease
What type of heat exchanger is a regenerative air heater?
Rotating wheel with corrugated metal plates
What is the direction of fluid flow in the steam generating unit compared to the direction of flue gas flow?
The opposite direction
What is the purpose of the economizer in a steam generating unit?
To preheat the feedwater before it enters the boiler
What is the benefit of using superheated steam in a steam generating unit?
It increases the amount of energy that can be extracted from each kilogram of steam
What is the purpose of the economizer in a steam generating unit?
To transfer heat from the flue gas to the feedwater
What is the benefit of using an air heater in a steam generating unit?
It improves the combustion efficiency of the fuel
What is the purpose of the air heater in a steam generating unit?
To extract heat from flue gas and transfer it to air
What is the order of heat transfer components in the flue gas flow?
Radiant superheater, convection superheater, reheater, economizer
What is the primary difference between a boiler and a steam generating unit?
A boiler is a single heat exchanger, while a steam generating unit consists of multiple heat exchangers
What type of heat exchanger is a recuperative air heater?
Simple shell-and-tube heat exchanger
What is the purpose of the steam drum in a steam generating unit?
To separate the steam from the water
What is the direction of the flue gas flow in the steam generating unit?
From the furnace to the stack
What is the benefit of the cross-counter flow design of the heat transfer components?
It improves the efficiency of the heat transfer process
What is the primary reason why early watertube boilers were less efficient than modern ones?
Straight tubes restricted heat transfer surface
What is the significance of bent tube technology in modern watertube boilers?
It permitted boilers to increase in size
What is the result of advances in water treatment technology in watertube boiler design?
Reduced need for refractory brickwork
What is the role of combustion gases in watertube boilers?
They transfer heat to the boiler water
What is the significance of codes in the development of watertube boilers?
They standardized design calculations and construction methods
What is the result of the development of welding methods in watertube boiler construction?
Stronger boilers
What is a major consequence of watertube boilers having less water content compared to firetube boilers of the same steaming capacity?
They can be brought to operating pressure and temperature quicker.
What is the primary reason why natural circulation is not sufficient for high-pressure boilers?
The density of steam and water becomes too similar
What is the primary reason why watertube boilers are more complex to design and construct than firetube boilers?
They need to accommodate higher steam pressures and temperatures.
What is the primary purpose of the bent tubes in watertube boilers?
To allow for optimal placement of superheaters and reheaters.
What is the purpose of the internal feedwater pipe in a steam drum?
To raise the feedwater temperature to near the boiler saturation temperature
Why are watertube boilers used in the oil and gas industry, pulp and paper industry, and electric power industry?
They can accommodate extremely high pressures and temperatures.
Why are steam separating equipment and chemical feed piping often located near each other in a steam drum?
To allow the chemicals to mix with the feedwater and circulate throughout the boiler
What is the primary function of baffles in watertube boilers?
To direct cooler inlet water to the downcomers
What is the primary reason why watertube boilers require higher quality water than firetube boilers?
They operate at higher temperatures and pressures.
What is the primary function of the continuous blowdown pipe in a steam boiler?
To remove dissolved solids from the boiler water
What is the primary benefit of watertube boilers having better water circulation compared to firetube boilers?
They can respond more quickly to changes in steam pressure.
Why do watertube boilers typically have a higher heat transfer rate than firetube boilers?
Because radiant heat transfer occurs at a greater rate than convective heat transfer
What is the purpose of the dry pipe in steam separation?
To separate the water from the steam by making sharp turns
What is the term for the condition that can occur when high concentrations of dissolved solids are present in a boiler?
Foaming
What is the primary purpose of the risers in a watertube boiler?
To allow for the circulation of steam and water between the drums.
What type of separators are used in larger plants to further dry the steam?
Cyclone separators
What is the primary disadvantage of watertube boilers compared to firetube boilers in terms of maintenance and repair?
They are more difficult to repair and maintain.
What is the primary purpose of the risers in a watertube boiler?
To produce steam in the boiler
What is the purpose of the chevron plates in a chevron dryer?
To force the steam to rapidly change direction
What is the term used to describe the walls that form the boiler and furnace enclosure?
Setting
Why do steam drums and mud drums have internal mechanisms such as feedwater, blowdown, and chemical feed piping?
To facilitate proper circulation and removal of dissolved solids
What is the primary reason why watertube boilers are more flexible in design than firetube boilers?
They have a more modular design.
What is the advantage of using waterwalls in modern boilers?
They improve heat transfer and reduce heat loss
What is the primary consequence of the density difference between water and steam in a watertube boiler?
It forces the less dense water/steam mixture upward through the risers.
What is the primary advantage of using internal feedwater piping in a steam boiler?
It prevents thermal shock and promotes proper water circulation
What is the purpose of the centrifugal force in a cyclone separator?
To fling water and entrained water particles to the outside of the separator
What is the primary function of the steam separating equipment in a steam drum?
To separate the steam from the steam/water mixture
What is the characteristic of the steam generated in larger plants?
It is dry and contains very little water
What is the purpose of the rectangular opening in a cyclone separator?
To allow water and steam to enter the separator
What is the result of the water and entrained water particles impinging on the surfaces of the chevron plates?
They drop back to the boiler water
What is the primary reason for the design of watertube boiler furnaces to accommodate single burners, multiple burners, fluidized beds, and stokers?
To accommodate different fuel types and combustion setups
What is the purpose of the water-cooled furnace in a watertube boiler?
To protect the mud drum from radiant heat
Why do watertube boilers need larger furnaces to accommodate the combustion air requirements?
To ensure the velocity of the combustion products is not so great that combustion continues outside of the furnace
What is the primary difference between A, D, and O-type boilers?
The shape of the tubes and drums
What is the purpose of the castable refractory lining the furnace floor in a watertube boiler?
To protect the mud drum from radiant heat
What is the primary function of the steam generating unit's auxiliary equipment?
To handle fuel, draft, and ash removal
What is the characteristic of a watertube boiler furnace?
It is internally fired
Why do fluidized bed boilers need very tall furnaces and refractory-lined tubes?
To accommodate the specific combustion requirements of fluidized bed boilers
What is the purpose of the boiler section in a steam generating unit?
To convert water to steam
What is the primary reason for the design of watertube boilers to produce a certain maximum amount of steam?
To ensure the furnace has adequate volume to burn the amount of fuel needed to produce the steam
What is the primary difference between a primary and secondary superheater?
The order in which they receive steam from the steam drum
What is the result of the density difference between water and steam in a steam generating unit?
Natural circulation becomes inadequate
What is the purpose of the bent tube design in watertube boilers?
To accommodate the burners that penetrate the waterwall
What is the primary advantage of watertube boilers over firetube boilers?
They offer more design flexibility
What is the primary purpose of the reheater in a steam generating unit?
To minimize the chance of condensation in the low-pressure turbine
What is the characteristic of a steam generating unit with a reheater?
It reduces the chance of condensation in the low-pressure turbine
What is the primary reason why heat leaving through a chimney represents a loss in efficiency?
It is wasteful of fuel and money
What is the purpose of the economizer in a steam generating unit?
To extract heat from the flue gases
What is the primary benefit of using superheated steam in a steam generating unit?
It increases the overall plant efficiency
What is the primary function of the air heater in a steam generating unit?
To transfer heat to the air
What is the primary purpose of the air heater in Figure 14?
To heat the air for combustion
What is the characteristic of a sub-critical steam generating unit?
It operates at pressures below the critical pressure of water and steam
What is the purpose of the external downcomer in Figure 14?
To completely shield the downcomer from the heat of combustion
What is the difference between a natural circulation and a forced circulation steam generating unit?
The method of circulating boiler water
At what pressure is there no difference in density between steam and water?
22 090 kPa
What is the purpose of the induced draft (ID) fan in the air heater?
To discharge the flue gases up the chimney
What is the primary reason for the placement of the economizer inlet at the location where the flue gas is the coolest?
To reduce the thermal shock of relatively cool water entering the hot steam drum
What is the primary difference between the flow of water/steam and the flow of flue gases in the heat transfer components?
The flow of one is always counter to the flow of the other
What is the primary function of the wheel in a regenerative air heater?
To transfer heat from the flue gas to the combustion air
What is the primary benefit of preheating the combustion air in the air heater?
It improves the combustion efficiency and assists in the burning of most fuels
What is the primary purpose of the radiant superheater and the reheater in the steam generating unit?
To heat the steam to a higher temperature
What is the primary direction of fluid flow in the steam generating unit compared to the direction of flue gas flow?
Opposite direction
What is the primary function of the cross-counter flow design in the heat transfer components?
To maximize the heat transfer between the fluids
What is the primary purpose of the windbox in the steam generating unit?
To mix the combustion air with the fuel
What is the primary reason for the placement of the superheaters in the steam generating unit?
To heat the steam to a higher temperature after it leaves the steam drum
What is the primary function of the forced draft (FD) fan in the steam generating unit?
To draw in combustion air from the atmosphere
At what pressure is forced circulation required for boilers?
20 MPa
What is the characteristic of a supercritical steam generating unit?
It does not have steam or mud drums
What is the flow of feedwater in a supercritical steam generating unit?
It flows through the economizer, waterwall section, convection superheater, and radiant superheater
What is the term for the pressure at which the density of water and steam is equal?
Critical pressure
What is the characteristic of an once-through steam generator (OTSG)?
It does not have a steam drum and uses forced circulation
What is the advantage of using forced circulation in boilers above 12.5 MPa?
It is advantageous for efficiency or design reasons
What is the characteristic of steam produced in an OTSG?
Wet and low-pressure
What is the primary function of the in-bed tubes in an FBC steam generator?
To absorb radiant heat and heat conducted directly from the bed particles
What is the advantage of FBC steam generating units in terms of emissions?
Lower furnace temperatures reduce NOX production
What is the purpose of the fluidizing air nozzles in an FBC boiler?
To provide combustion air to the bed
What is the characteristic of a circulating fluidized bed boiler?
The flue gas carries burning fuel through the boiler to the dust collector
What is the primary advantage of OTSGs over natural circulation boilers?
No internal recirculation
What is the purpose of the refractory in an FBC boiler?
To protect the boiler walls from heat
What is the primary reason for the use of FBC steam generating units?
Suitability for a wide range of fuels
What is the characteristic of the burning bed in an FBC steam generator?
It behaves like a suspended fluid
What is the purpose of the limestone in an FBC steam generator?
To reduce SOX emissions
What is the minimum pressure above which forced circulation is required in boilers?
20 MPa
What is the characteristic of a supercritical steam generating unit?
It does not have steam or mud drums
In a supercritical steam generating unit, where does the feedwater flow from?
Economizer to the waterwall section
What is the term used to describe the pressure at which the density of water and steam is equal?
Critical pressure
What is the advantage of using forced circulation in boilers above 12.5 MPa?
Increased efficiency
What type of steam generator is a supercritical steam generating unit?
Once-through steam generator (OTSG)
What is the primary advantage of the bubbling bed FBC boiler over the circulating fluidized bed boiler?
Easier control of combustion at low firing rates
What is the primary reason why OTSGs do not require steam drums?
The entire mass of water entering is turned to steam
What is the primary function of the in-bed tubes in an FBC steam generator?
To absorb radiant heat from the burning bed
What is the primary advantage of fluidized bed combustion steam generators over other steam generating units?
Suitability for a wide range of fuels
What is the primary purpose of the refractory in an FBC boiler?
To protect the boiler from the high temperatures of the burning bed
What is the primary characteristic of the burning bed in an FBC steam generator?
It behaves like a suspended fluid
What is the primary benefit of the wet steam produced by an OTSG?
It carries dissolved solids and feedwater impurities away from the boiler
What is the primary purpose of the limestone added directly to the bed in an FBC steam generator?
To reduce SOX emissions
What is the primary difference between a bubbling bed FBC boiler and a circulating fluidized bed boiler?
The way the burning bed is maintained
What is the primary benefit of the high recirculation rate in natural circulation boilers?
It improves the steam quality
Learn about the definition, features, and functionality of watertube boilers, as identified by the American Boiler Manufacturing Association (ABMA). Understand how heat is transferred from combustion gases to water within the tubes. Discover the evolution of watertube boilers from less efficient early designs.
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