Mechanical
Which of the following is the correct classification of boilers based on the position of water and hot gases?
- Fire-tube and water-tube boilers
- Horizontal and vertical boilers only
- High-pressure and low-pressure boilers only
- Stationary and portable boilers only
Explanation:
- In a fire-tube boiler, hot flue gases flow through tubes surrounded by water. In a water-tube boiler, water flows through tubes surrounded by hot gases.
In a fire-tube boiler, the hot flue gases flow through:
- Inside the tubes
- Outside the tubes
- Inside the water drum only
- Inside the steam drum only
Explanation:
- Fire-tube boilers carry hot combustion gases through tubes, while water surrounds the tubes and receives heat.
In a water-tube boiler, water flows through:
- Inside the tubes
- Outside the tubes only
- Inside the furnace only
- Inside the chimney
Explanation:
- Water-tube boilers circulate water inside tubes exposed to hot gases. This arrangement allows high-pressure steam generation.
Which type of boiler is generally more suitable for high-pressure steam generation?
- Water-tube boiler
- Fire-tube boiler
- Simple vertical boiler
- Cochran boiler
Explanation:
- Water-tube boilers are commonly used for high-pressure and high-capacity steam generation because the small water content and tube arrangement permit higher pressures and rapid steam generation.
Which of the following is an example of a fire-tube boiler?
- Cochran boiler
- Babcock and Wilcox boiler
- LaMont boiler
- Benson boiler
Explanation:
- The Cochran boiler is a vertical, multi-tubular fire-tube boiler. Babcock and Wilcox, LaMont and Benson are water-tube boilers.
Which of the following is a water-tube boiler?
- Babcock and Wilcox boiler
- Cochran boiler
- Locomotive boiler
- Cornish boiler
Explanation:
- The Babcock and Wilcox boiler is a well-known water-tube boiler in which water circulates through inclined tubes heated externally by hot gases.
Which type of boiler generally has a higher rate of steam generation?
- Water-tube boiler
- Fire-tube boiler
- Simple vertical boiler
- Cornish boiler
Explanation:
- Water-tube boilers generally provide higher steam-generation rates because of their larger heating surface and better circulation, making them suitable for large power plants.
Which boiler contains a relatively larger quantity of water?
- Fire-tube boiler
- Water-tube boiler
- Benson boiler
- LaMont boiler
Explanation:
- Fire-tube boilers generally contain a larger quantity of water compared with water-tube boilers of similar capacity. This gives them greater stored energy but makes rapid pressure changes less desirable.
Which boiler generally responds more rapidly to changes in steam demand?
- Water-tube boiler
- Fire-tube boiler
- Cornish boiler
- Simple vertical boiler
Explanation:
- Water-tube boilers contain less water and have efficient heat transfer, allowing them to respond rapidly to changes in load.
Which boiler is generally safer for very high-pressure operation?
- Water-tube boiler
- Fire-tube boiler
- Cornish boiler
- Simple vertical boiler
Explanation:
- In a water-tube boiler, water is contained in relatively small-diameter tubes. Therefore, the amount of high-pressure water stored in each tube is comparatively small, reducing the severity of a failure compared with a large fire-tube shell.
What is the main function of a boiler?
- To convert water into steam by supplying heat
- To convert steam into water
- To compress steam
- To cool combustion gases
Explanation:
- A boiler is a pressure vessel in which water receives heat from combustion or another heat source and is converted into steam.
Which boiler classification is based on the pressure of steam generated?
- Low-pressure, medium-pressure and high-pressure boilers
- Fire-tube and water-tube boilers
- Horizontal and vertical boilers
- Internally and externally fired boilers only
Explanation:
- Boilers can be classified according to operating pressure. Other classifications are based on tube contents, axis, firing arrangement, circulation and method of heat supply.
Which classification divides boilers according to the axis of the boiler shell?
- Horizontal, vertical and inclined boilers
- Fire-tube and water-tube boilers
- High-pressure and low-pressure boilers
- Natural and forced circulation boilers
Explanation:
- Based on the axis of the boiler shell, boilers may be classified as horizontal, vertical or inclined.
A boiler in which the furnace is located inside the boiler shell is called:
- Internally fired boiler
- Externally fired boiler
- Water-tube boiler
- Forced-circulation boiler
Explanation:
- In an internally fired boiler, the furnace is located within the boiler shell. In an externally fired boiler, the furnace is outside the main boiler shell.
Which of the following is an example of an internally fired boiler?
- Cochran boiler
- Babcock and Wilcox boiler
- Stirling boiler
- Benson boiler
Explanation:
- The Cochran boiler is an internally fired vertical fire-tube boiler. Its furnace is located within the boiler shell.
Which type of circulation occurs due to the density difference between hot and cold water?
- Natural circulation
- Forced circulation
- Mechanical circulation
- Vacuum circulation
Explanation:
- In natural-circulation boilers, circulation occurs because heated water/steam-water mixture has a lower density than relatively cooler water. This density difference creates circulation.
Which device is used to force water circulation in a forced-circulation boiler?
- A circulating pump
- Safety valve
- Steam stop valve
- Fusible plug
Explanation:
- A forced-circulation boiler uses a pump to maintain water circulation through the heating tubes.
Which of the following is generally an advantage of a water-tube boiler?
- High-pressure steam generation
- Very large water storage
- Very simple construction in all cases
- Very low initial cost for large power plants
Explanation:
- Water-tube boilers are particularly suitable for high-pressure, high-capacity steam generation. Their construction and accessories are generally more complex than those of simple fire-tube boilers.
Which of the following is generally an advantage of a fire-tube boiler?
- Simple construction and operation
- Very high-pressure operation for all designs
- Extremely rapid steam generation in all cases
- Very low water content
Explanation:
- Fire-tube boilers are comparatively simple in construction and operation and are commonly used for low-to-medium pressure applications.
Which type of boiler generally requires more careful water treatment because water circulates through small tubes?
- Water-tube boiler
- Fire-tube boiler
- Cornish boiler only
- Locomotive boiler only
Explanation:
- Water-tube boilers have relatively small water passages. Scale formation can seriously restrict heat transfer and circulation, so proper feed-water treatment is particularly important.
What is meant by the specification of a boiler?
- A statement of important operating and performance parameters of the boiler
- Only the weight of the boiler
- Only the dimensions of the furnace
- Only the type of fuel used
Explanation:
- Boiler specifications describe important parameters such as steam-generating capacity, operating pressure, steam temperature, heating surface, fuel consumption and efficiency, depending on the application.
Boiler capacity is commonly expressed in terms of:
- Mass of steam generated per unit time
- Mass of fuel stored
- Volume of furnace only
- Mass of boiler shell only
Explanation:
- Boiler capacity is commonly stated as the amount of steam generated per unit time, such as kg/h or tonnes/h.
What does the term steam-generating capacity indicate?
- The amount of steam generated per unit time
- The total water stored in the boiler
- The volume of the furnace
- The pressure inside the chimney
Explanation:
- Steam-generating capacity indicates the rate at which the boiler produces steam under specified operating conditions.
What is the function of boiler fittings?
- To ensure safe and proper operation of the boiler
- To increase fuel moisture
- To replace the furnace completely
- To reduce boiler pressure to atmospheric pressure continuously
Explanation:
- Boiler fittings are essential devices mounted on the boiler for safety, control and proper operation.
Which of the following is a boiler fitting?
- Safety valve
- Economiser
- Superheater
- Air preheater
Explanation:
- A safety valve is a boiler fitting because it protects the boiler against excessive pressure. Economiser, superheater and air preheater are generally classified as boiler accessories.
Which device protects a boiler against excessive steam pressure?
- Safety valve
- Economiser
- Superheater
- Feed pump
Explanation:
- The safety valve automatically releases steam when boiler pressure rises above the set safe limit, preventing dangerous overpressure.
Which boiler fitting indicates the water level inside the boiler?
- Water level indicator
- Safety valve
- Steam stop valve
- Blow-off cock
Explanation:
- The water level indicator, commonly called a gauge glass, allows the operator to observe the water level inside the boiler.
What is the main function of a pressure gauge fitted to a boiler?
- To indicate the pressure of steam inside the boiler
- To indicate water level
- To control fuel flow automatically
- To measure chimney temperature only
Explanation:
- The pressure gauge indicates the steam pressure in the boiler and helps the operator monitor operating conditions.
Which fitting is used to completely or partially drain water from a boiler?
- Blow-off cock
- Safety valve
- Steam stop valve
- Pressure gauge
Explanation:
- The blow-off cock is used for draining the boiler and can also assist in removing sludge and concentrated impurities from the boiler water.
What is the function of a steam stop valve?
- To control and stop the flow of steam from the boiler to the steam pipe
- To indicate water level
- To remove ash from the furnace
- To heat feed water
Explanation:
- The steam stop valve controls the outlet of steam from the boiler and can isolate the boiler from the steam main.
Which boiler fitting prevents the boiler from operating with an excessively low water level?
- Low-water safety device / low-water alarm and trip
- Steam stop valve
- Pressure gauge
- Economiser
Explanation:
- Low water level can expose heating surfaces and cause overheating or serious boiler damage. Low-water protection systems warn or shut down the burner/feed system depending on the design.
Which device is used to feed water into the boiler?
- Feed check valve
- Safety valve
- Fusible plug
- Steam stop valve
Explanation:
- The feed check valve admits feed water into the boiler and prevents reverse flow from the boiler toward the feed system.
What is the main function of a fusible plug?
- To protect the furnace crown or heating surface from overheating due to low water level
- To increase steam pressure continuously
- To measure steam temperature
- To increase fuel flow
Explanation:
- A fusible plug contains a low-melting-point material. When excessive temperature occurs due to inadequate water coverage, the material melts and releases water/steam toward the furnace to provide warning and protection.
Which of the following is a boiler accessory rather than a boiler fitting?
- Economiser
- Safety valve
- Water level indicator
- Pressure gauge
Explanation:
- An economiser is a boiler accessory used to improve efficiency by recovering heat from flue gases to preheat feed water. Safety valve, water level indicator and pressure gauge are fittings.
What is the main purpose of an economiser?
- To preheat feed water using heat from flue gases
- To cool steam before entering the turbine
- To reduce boiler pressure
- To remove dissolved gases from feed water only
Explanation:
- An economiser transfers waste heat from outgoing flue gases to the incoming feed water, reducing the heat required in the boiler and improving overall efficiency.
Which boiler accessory is used to superheat saturated steam?
- Superheater
- Economiser
- Air preheater
- Feed pump
Explanation:
- A superheater raises the temperature of steam above its saturation temperature at the corresponding pressure. Superheated steam is generally preferred for steam turbines because it reduces moisture during expansion.
What is the main function of an air preheater?
- To preheat combustion air using heat recovered from flue gases
- To preheat feed water
- To condense steam
- To reduce steam pressure
Explanation:
- An air preheater transfers heat from flue gases to the incoming combustion air. Preheated air improves combustion and can increase boiler efficiency.
Which accessory improves boiler efficiency by recovering heat from flue gases to heat feed water?
- Economiser
- Superheater
- Air preheater
- Steam separator
Explanation:
- The economiser uses waste heat from flue gases to raise feed-water temperature before the water enters the boiler.
Which accessory improves the quality of steam by removing suspended water droplets?
- Steam separator
- Economiser
- Air preheater
- Feed pump
Explanation:
- A steam separator removes entrained water droplets from wet steam, producing drier steam for downstream equipment.
Which device is used to remove dissolved gases, especially oxygen, from boiler feed water?
- Deaerator
- Economiser
- Superheater
- Safety valve
Explanation:
- A deaerator removes dissolved gases such as oxygen and carbon dioxide from feed water. Removing oxygen helps reduce corrosion in boiler and feed-water systems.
Which type of boiler is generally preferred for large-capacity power generation?
- Water-tube boiler
- Small fire-tube boiler
- Simple vertical boiler
- Cornish boiler
Explanation:
- Large power plants require high steam generation rates and high operating pressures, for which water-tube boilers are generally more suitable.
Which statement correctly compares fire-tube and water-tube boilers?
- Fire-tube boilers carry hot gases through tubes, whereas water-tube boilers carry water through tubes
- Both always carry water outside the tubes only
- Fire-tube boilers always operate at higher pressure than water-tube boilers
- Water-tube boilers cannot produce superheated steam
Explanation:
- The fundamental difference is the fluid flowing inside the tubes. Hot gases flow inside tubes in fire-tube boilers, while water flows inside tubes in water-tube boilers.
Which type of boiler generally has a lower risk associated with the stored energy of high-pressure water?
- Water-tube boiler
- Large fire-tube boiler
- Cornish boiler
- Simple vertical boiler
Explanation:
- Water-tube boilers contain relatively small quantities of water within their high-pressure tubes, so the stored energy associated with high-pressure water is generally lower than in large fire-tube shells at comparable high-pressure service.
Which boiler type generally has easier access for inspection of the large water space?
- Fire-tube boiler
- Water-tube boiler
- Benson boiler
- LaMont boiler
Explanation:
- Fire-tube boilers generally have a comparatively large water space within the shell, making their basic construction and inspection relatively simple.
Which of the following is NOT normally classified as a boiler fitting?
- Economiser
- Safety valve
- Pressure gauge
- Water level indicator
Explanation:
- An economiser is normally considered a boiler accessory. Boiler fittings such as safety valves, pressure gauges and water-level indicators are necessary for safe operation and control.
Which of the following is NOT normally a boiler accessory?
- Safety valve
- Economiser
- Superheater
- Air preheater
Explanation:
- The safety valve is a boiler fitting, while economisers, superheaters and air preheaters are commonly classified as boiler accessories.
Which boiler component increases the temperature of steam without adding moisture?
- Superheater
- Economiser
- Feed check valve
- Blow-off cock
Explanation:
- A superheater adds sensible heat to saturated or nearly dry steam and converts it into superheated steam, increasing its temperature above the saturation temperature.
Why is superheated steam commonly used in steam turbines?
- It reduces the moisture content during expansion and helps reduce turbine blade erosion
- It always eliminates the need for a condenser
- It reduces the boiler pressure to zero
- It prevents all heat losses
Explanation:
- Superheating increases the initial steam temperature and generally produces drier steam at the turbine exhaust, reducing the harmful effects of excessive moisture on turbine blades.
Which boiler is characterized by a large number of small-diameter water tubes exposed to hot gases?
- Water-tube boiler
- Fire-tube boiler
- Cornish boiler
- Locomotive boiler
Explanation:
- Water-tube boilers use tubes containing water, with hot combustion gases flowing around the tubes. The arrangement provides a large heat-transfer surface and is suitable for high-pressure operation.
Which statement about fire-tube boilers is correct?
- They generally have simple construction and are suitable for low-to-medium pressure applications
- They are always used for ultra-high-pressure power generation
- Water flows inside the fire tubes
- They always have lower water content than water-tube boilers
Explanation:
- Fire-tube boilers are generally simple and are widely used for low-to-medium pressure steam generation. Their tubes carry hot gases while water surrounds them.
Which statement about water-tube boilers is correct?
- They are suitable for high-pressure and high-capacity steam generation
- Hot gases flow inside water tubes
- They always contain a large quantity of stored water
- They cannot be used in power plants
Explanation:
- Water-tube boilers are widely used in power plants because they can produce large quantities of high-pressure steam with comparatively rapid response to load changes.
What is the primary purpose of a boiler safety valve?
- To prevent excessive pressure from developing in the boiler
- To increase the boiler pressure above the design pressure
- To measure water level
- To preheat feed water
Explanation:
- The safety valve opens automatically when pressure reaches its set value, releasing steam and protecting the boiler against dangerous overpressure.
Which device provides a visual indication of boiler water level?
- Gauge glass
- Pressure gauge
- Safety valve
- Economiser
Explanation:
- The gauge glass or water-level indicator provides a direct visual indication of the water level in the boiler.
Which boiler accessory uses waste heat to increase the temperature of combustion air?
- Air preheater
- Economiser
- Superheater
- Feed check valve
Explanation:
- An air preheater transfers heat from hot flue gases to incoming combustion air, improving combustion conditions and reducing stack heat losses.
Which accessory uses waste heat to increase the temperature of feed water?
- Economiser
- Air preheater
- Superheater
- Safety valve
Explanation:
- The economiser recovers heat from flue gases and transfers it to feed water before it enters the boiler.
Which component is used to remove sludge from the bottom of a boiler?
- Blow-off cock
- Superheater
- Economiser
- Air preheater
Explanation:
- The blow-off arrangement permits water and accumulated sludge or concentrated impurities to be discharged from the boiler.
Which type of boiler generally requires a smaller foundation for a given large steam-generating capacity?
- Water-tube boiler
- Large fire-tube boiler
- Cornish boiler
- Simple vertical boiler
Explanation:
- Water-tube boilers can provide high steam-generating capacity with a comparatively compact arrangement, making them suitable for large industrial and power-generation installations.
Which boiler type generally has a comparatively higher initial cost for large installations because of its complex construction?
- Water-tube boiler
- Simple fire-tube boiler
- Cornish boiler
- Simple vertical boiler
Explanation:
- Water-tube boilers have complex tube arrangements, drums, circulation systems and accessories, so their initial cost is generally higher than that of simple fire-tube boilers.
Which boiler type generally requires comparatively skilled operation and maintenance?
- Water-tube boiler
- Simple fire-tube boiler
- Cornish boiler
- Simple vertical boiler
Explanation:
- Water-tube boilers have more complex circulation, control, water-treatment and pressure systems. Therefore, skilled operation and maintenance are generally required.
Which of the following combinations is correctly matched?
- Cochran — Fire-tube boiler
- Babcock and Wilcox — Fire-tube boiler
- Benson — Fire-tube boiler
- LaMont — Fire-tube boiler
Explanation:
- Cochran is a fire-tube boiler, whereas Babcock and Wilcox, Benson and LaMont are water-tube boilers.
Which of the following combinations is correctly matched?
- Babcock and Wilcox — Water-tube boiler
- Cochran — Water-tube boiler
- Cornish — Water-tube boiler
- Locomotive — Water-tube boiler
Explanation:
- Babcock and Wilcox is a well-known water-tube boiler. Cochran, Cornish and locomotive boilers are fire-tube types.
Which factor is particularly important for preventing scale formation in water-tube boilers?
- Proper feed-water treatment
- Increasing chimney height only
- Reducing steam temperature to zero
- Increasing fuel moisture
Explanation:
- Scale deposits on water-tube surfaces reduce heat transfer and can cause tube overheating. Proper feed-water treatment helps control scale-forming impurities.
Which boiler component is directly associated with controlling the pressure of steam leaving the boiler?
- Steam stop valve
- Fusible plug
- Gauge glass
- Economiser
Explanation:
- The steam stop valve controls or isolates the steam flow from the boiler to the main steam line. It is not the primary device for regulating boiler pressure itself; pressure is controlled through the operating system and steam demand.
Which parameter is most directly used to specify the maximum allowable pressure of a boiler?
- Design or working pressure
- Fuel calorific value only
- Furnace volume only
- Chimney height only
Explanation:
- The boiler specification includes its allowable operating/design pressure, which determines the pressure for which the pressure-containing components are designed and operated.
Why is a water-tube boiler preferred for very high steam pressures?
- High-pressure water is confined mainly within relatively small-diameter tubes
- It stores an extremely large quantity of high-pressure water
- It has no heating surface
- It does not require feed water
Explanation:
- The small-diameter tubes can withstand high pressure effectively, while the comparatively low water content reduces the stored energy associated with high-pressure water.
Which type of boiler is generally more suitable where compact steam-generation equipment is required for high pressure and high capacity?
- Water-tube boiler
- Large simple fire-tube boiler
- Cornish boiler
- Simple vertical boiler
Explanation:
- Water-tube boilers can be arranged compactly while providing high steam-generation rates and high operating pressures, making them suitable for large industrial and power applications.
What is the main difference between a boiler fitting and a boiler accessory?
- Fittings are mainly required for safe/control operation, while accessories generally improve performance or efficiency
- Fittings always increase efficiency, while accessories always reduce efficiency
- There is no difference between them
- Accessories are used only for decoration
Explanation:
- Boiler fittings are essential for safe operation, control and monitoring, such as safety valves, pressure gauges and water-level indicators. Accessories improve efficiency, steam quality or performance, such as economisers, superheaters and air preheaters.