Boiler Types and Examples: Water Tube Boiler
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Questions and Answers

What is the purpose of the inclined water tubes in a Babcock and Wilcox boiler?

  • To direct the flow of hot gases between the tubes
  • To ensure proper circulation of water through the boiler (correct)
  • To facilitate efficient cleaning and inspection of the tubes
  • To increase the angle of inclination to 30°

    • What is the angle of inclination of the water tubes to the horizontal in a Babcock and Wilcox boiler?

  • 40°
  • 5°
  • 25°
  • 15° (correct)

    • Why are water tube boilers preferred for pressures above 10 bar and capacities exceeding 7000 kg of steam per hour?

  • To improve fuel combustion
  • To reduce maintenance costs
  • For ease of transportation
  • Due to their higher efficiency (correct)

    • What is the function of the feed valve in a Babcock and Wilcox boiler?

    <p>To fill the drum and inclined tubes with water</p> Signup and view all the answers

    How does the water circulate through a Babcock and Wilcox boiler?

    <p>From the uptake header to the downtake header</p> Signup and view all the answers

    Where does the steam collect in a Babcock and Wilcox boiler?

    <p>Steam space of the drum</p> Signup and view all the answers

    What is the purpose of the superheater tubes in a boiler?

    <p>To heat the steam further</p> Signup and view all the answers

    How does a Babcock Wilcox water tube boiler with cross drum differ from a longitudinal drum boiler?

    <p>In the number of connecting tubes allowed</p> Signup and view all the answers

    What is the main function of the mud drum in a Stirling water tube boiler?

    <p>To remove impurities and mud particles</p> Signup and view all the answers

    Why is a baffle provided at the mud drum in a Stirling water tube boiler?

    <p>To deflect pure water and impurities in different directions</p> Signup and view all the answers

    What is the purpose of the fire brick arch in a fire tube boiler?

    <p>To help in combustion and prevent chilling of the furnace</p> Signup and view all the answers

    How are the steam drums and mud drum supported in a Stirling water tube boiler?

    <p>By steel beams independent of the brickwork</p> Signup and view all the answers

    Why is a babcock Wilcox water tube boiler preferred for large central power stations?

    <p>For its high steaming capacities and pressure</p> Signup and view all the answers

    What is a common characteristic of both Babcock Wilcox and Stirling water tube boilers?

    <p>They have two upper drums known as steam drums</p> Signup and view all the answers

    What can be inferred about fire tube boilers from the text?

    <p>Their cylindrical shell is filled with water</p> Signup and view all the answers

    What happens when the blow off cock is used in a water tube boiler?

    <p>Impurities are blown out</p> Signup and view all the answers

    What is the purpose of Sugden's superheater in a Lancashire boiler?

    <p>To increase the temperature of the steam</p> Signup and view all the answers

    How are the 'U' tubes attached in Sugden's superheater?

    <p>Welded to the headers</p> Signup and view all the answers

    In Sugden's superheater, how many tubes are generally carried by one pair of headers?

    <p>40 tubes</p> Signup and view all the answers

    How is the path of gases controlled in Sugden's superheater?

    <p>By operating the damper with a hand wheel</p> Signup and view all the answers

    What happens when the steam is passed through the superheater of a Lancashire boiler?

    <p>Valve V1 is closed and valves V2 and V3 are opened</p> Signup and view all the answers

    What is the main function of a steam separator in a boiler system?

    <p>To remove water droplets from steam</p> Signup and view all the answers

    What is the primary purpose of hand holes provided at the ends of each cross tube in a boiler?

    <p>To give access for cleaning the tubes</p> Signup and view all the answers

    In a vertical boiler, what is the function of a manhole?

    <p>To clean the interior of the boiler and chimney</p> Signup and view all the answers

    Why is a Cochran boiler considered to be self-contained and easily transportable?

    <p>Because it has a seamless construction and compact design</p> Signup and view all the answers

    What is the purpose of a blow off cock in a Cornish boiler?

    <p>To clean sediments collected at the bottom of the boiler</p> Signup and view all the answers

    In a Lancashire boiler, why are there multiple rings of cylindrical form constructed inside the shell?

    <p>To create channels for flow of hot gases</p> Signup and view all the answers

    Which boiler mounting is primarily responsible for controlling the water level in a Cochran boiler?

    <p>Water level gauge</p> Signup and view all the answers

    What does the hemispherical shape of the crown in a Cochran boiler primarily help with?

    <p>Providing maximum volume for steam space</p> Signup and view all the answers

    Why are flue tubes used in Cochran boilers?

    <p>To direct combustion gases through horizontal fire tubes</p> Signup and view all the answers

    What is the main reason for having two large tubes placed inside the cylindrical shell of a Lancashire boiler?

    <p>To increase heating efficiency by providing more surface area</p> Signup and view all the answers

    What is the purpose of having fusible plug as one of the mountings in a Cornish boiler?

    <p>To prevent damage due to overheating by melting at high temperatures</p> Signup and view all the answers

    What is the function of the arch of fire bricks in a locomotive boiler?

    <p>To heat up the walls of the fire box</p> Signup and view all the answers

    In a locomotive boiler, where is the coal introduced for burning?

    <p>Into the grate at the bottom of the fire box</p> Signup and view all the answers

    What is the purpose of a steam dome in a locomotive boiler?

    <p>To direct steam through a steam pipe</p> Signup and view all the answers

    What is the main function of dampers in a locomotive boiler?

    <p>To control the flow of air to the grate</p> Signup and view all the answers

    Why is natural draught not achievable in a locomotive boiler without artificial arrangements?

    <p>The requirement of a very high chimney</p> Signup and view all the answers

    What is one of the demerits associated with locomotive boilers?

    <p>Corrosion and scale formation in water legs</p> Signup and view all the answers

    In a locomotive boiler, what happens to the hot gases generated from burning coal?

    <p>They go through a series of fire tubes</p> Signup and view all the answers

    What component prevents entry of burning coal and ashes into furnace tubes?

    <p>Brickwork fire bridge at back of gate</p> Signup and view all the answers

    Why are some dampers fitted at both ends of an ash pit in a locomotive boiler?

    <p>To control air flow to the grate evenly</p> Signup and view all the answers

    What is a distinctive feature of locomotive boilers compared to other types?

    <p>Requirement for artificial draught mechanisms</p> Signup and view all the answers

    What is the main difference between a single-acting pump and a double-acting pump?

    <p>The side of the piston that displaces water</p> Signup and view all the answers

    In a duplex direct-acting steam pump, how are the slide valves in each cylinder operated?

    <p>By the crosshead on the piston rod of the opposite cylinder</p> Signup and view all the answers

    What is the purpose of an injector in a boiler system?

    <p>To increase the pressure and velocity of the feed water</p> Signup and view all the answers

    Why is an injector commonly used for vertical and locomotive boilers?

    <p>To save space in boiler installations</p> Signup and view all the answers

    What type of pumps are rotary feed pumps, and how are they commonly powered?

    <p>Centrifugal pumps powered by a small steam turbine or electric motor</p> Signup and view all the answers

    What role does an economiser play in a boiler system?

    <p>Utilizing waste heat to heat feed water</p> Signup and view all the answers

    What distinguishes an independent type economiser from an integral type economiser?

    <p>Location relative to the boiler setting</p> Signup and view all the answers

    What is a unique advantage of using an injector for feeding water into a boiler?

    <p>Simplicity in design</p> Signup and view all the answers

    Why can an injector not be employed in large capacity high pressure boilers?

    <p>Space constraints</p> Signup and view all the answers

    What feature allows an economiser to enhance thermal efficiency in a boiler system?

    <p>Utilization of waste heat from flue gases</p> Signup and view all the answers

    What is the most popular type of boiler for steaming capacities up to about 1000 kg/h and a pressure of about 17 bar?

    <p>Scotch boiler</p> Signup and view all the answers

    Why are shell boilers considerably cheaper than water tube boilers for steam applications that require less than about 30000 kg of steam per hour?

    <p>They are easier to transport</p> Signup and view all the answers

    What factor influences the choice between water tube boilers and shell boilers according to the text?

    <p>Output capacity</p> Signup and view all the answers

    In high pressure boilers, what is the main method used for water circulation?

    <p>Forced circulation</p> Signup and view all the answers

    How does the arrangement of tubing in high pressure boilers help improve efficiency?

    <p>By reducing pressure loss</p> Signup and view all the answers

    What feature distinguishes high pressure boilers used for power generation from other types of boilers?

    <p>Improved heating efficiency</p> Signup and view all the answers

    What is a limitation of using natural circulation in high pressure boilers?

    <p>Applicable only to sub-critical boilers</p> Signup and view all the answers

    Why are water tube boilers generally preferred over shell boilers for high pressure and high output applications?

    <p>&quot;&quot;Smaller diameter pressure parts&quot;</p> Signup and view all the answers

    What distinguishes high pressure boilers employed for power generation from other types in terms of steam temperature?

    <p>Higher steam temperature</p> Signup and view all the answers

    What is the primary function of an economiser in a boiler system?

    <p>To heat the water by transferring heat through the surfaces of pipes</p> Signup and view all the answers

    In a boiler system, what is the purpose of an air preheater?

    <p>To increase the temperature of air before it enters the furnace</p> Signup and view all the answers

    What advantage does superheated steam provide in a steam plant?

    <p>Erosion of turbine blades is eliminated</p> Signup and view all the answers

    Why are superheaters located in the path of furnace gases in a boiler system?

    <p>To recover heat from the hot gases</p> Signup and view all the answers

    What is the purpose of having a blow-off cock in a boiler system?

    <p>To remove sediments deposited in the bottom boxes</p> Signup and view all the answers

    Which part of a boiler system is responsible for increasing air temperature before it enters the furnace?

    <p>Air preheater</p> Signup and view all the answers

    What is one advantage of using an economiser in a boiler system as described in the text?

    <p>Reducing stresses due to unequal expansion</p> Signup and view all the answers

    In a boiler system, what is the primary function of a superheater?

    <p>To increase temperature above steam's saturation point</p> Signup and view all the answers

    Why are radiantsuperheaters used where high superheat temperature is required?

    <p>To receive heat from burning fuel through radiant process</p> Signup and view all the answers

    What part of a boiler system helps to maintain a clean external pipe surface for better heat transfer?

    <p>Scrapers S</p> Signup and view all the answers

    Why is it important to use pumps in high-pressure boilers?

    <p>To ensure positive circulation of water</p> Signup and view all the answers

    What is the primary purpose of using small diameter tubes in large numbers in high-pressure boilers?

    <p>To increase the rate of heat release</p> Signup and view all the answers

    How does pressurised combustion impact the operation of high-pressure boilers?

    <p>It increases the rate of firing of fuel</p> Signup and view all the answers

    What is one advantage of the Lamont boiler over the Loeffler boiler?

    <p>Deposits less salt and sediment in water tubes</p> Signup and view all the answers

    Why does a Loeffler boiler prevent the flow of water into boiler tubes?

    <p>To enhance heat transfer efficiency</p> Signup and view all the answers

    What is a significant advantage of Loeffler boilers over directly heated boilers?

    <p>Can carry higher salt concentrations</p> Signup and view all the answers

    Why are accessories necessary for steam boilers?

    <p>For proper operation and efficiency improvement</p> Signup and view all the answers

    Why is a reciprocating pump used as a feed pump in boilers?

    <p>To deliver feed water to the boiler</p> Signup and view all the answers

    What distinguishes a double-acting pump from a single-acting pump?

    <p>A double-acting pump displaces water in two directions</p> Signup and view all the answers

    What is the function of a rotary pump in a boiler system?

    <p>To deliver feed water to the boiler</p> Signup and view all the answers

    Study Notes

    Water Tube Boilers

    • Water tube boilers are used when pressure above 10 bar and capacity in excess of 7000 kg of steam per hour is required.
    • They have two types: Horizontal straight tube (Babcock and Wilcox) and Bent tube boiler.

    Babcock and Wilcox Boiler

    • It is an example of horizontal straight tube boiler.
    • It consists of a drum connected to a series of front end and rear end headers by short riser tubes.
    • To these headers are connected a series of inclined water tubes of solid drawn mild steel.
    • A feed valve is provided to fill the drum and inclined tubes with water.
    • The water flows through the inclined tubes via downtake header and goes back into the shell in the form of water and steam via uptake header.

    Stirling Boiler

    • It is an example of bent tube boiler.
    • It consists of two upper drums known as steam drums and a lower drum known as mud or water drum.
    • The steam drums are connected to mud drum by bank of bent tubes.
    • The steam and water space of the steam drums are interconnected with each other, so that balance of water and steam may be obtained.
    • Manhole at one end of each drum is provided for carrying out cleaning operation.

    Fire Tube Boilers

    • The various fire tube boilers are described as follows:
      • Simple vertical boiler
      • Cochran boiler
      • Cornish boiler
      • Lancashire boiler

    Simple Vertical Boiler

    • It consists of a cylindrical shell, the greater portion of which is full of water and remaining is the steam space.
    • At the bottom of the fire box is grate on which fuel is burnt and the ash from it falls in the ash pit.
    • The fire box is provided with two cross tubes.
    • It is self-contained and can be transported easily.

    Cochran Boiler

    • It is one of the best types of vertical multi-tubular boiler.
    • It consists of a cylindrical shell with a dome shaped top where the space is provided for steam.
    • The rate of production in not exceed 2500 kg/h and pressure 7.5 to 10 bar.

    Cornish Boiler

    • It consists of a cylindrical shell with flat ends through which passes a smaller flue tube containing the furnace.
    • The products of combustion pass from the fire grate forward over the brickwork bridge to the end of the furnace tube.
    • It is still used in some industries.

    Lancashire Boiler

    • It is reliable, has simplicity of design, ease of operation and less operating and maintenance costs.
    • It is commonly used in sugar-mills and textile industries where along with the power steam and steam for the process work is also needed.

    Boiler Accessories

    • Economiser: increases the temperature of the feed water, increases the evaporative capacity of the boiler, and increases the overall efficiency of the plant.
    • Air Preheater: increases the temperature of air before it enters the furnace, accelerates the combustion and facilitates the burning of coal.
    • Superheater: increases the temperature of the steam above its saturation point, reduces the steam consumption of the engine or turbine, and increases the efficiency of the steam plant.
    • Steam Separator: separates the steam from the water and removes any impurities from the steam.### High Pressure Boilers
    • In high pressure boilers, pumps are used to maintain forced circulation of water through the tubes of the boiler, ensuring positive circulation and increasing evaporative capacity.
    • The use of small diameter tubes in large numbers and multiple circuits increases the efficiency of heat utilisation.
    • Pressurised combustion is used to increase the rate of firing of fuel and heat release.
    • Compactness of high pressure boilers reduces the required floor space.
    • The high velocity of water through the tubes eliminates the tendency of scale formation.
    • Uniform heating of all parts reduces the danger of overheating and thermal stress.

    Lamont Boiler

    • The Lamont boiler works on forced circulation, maintained by a centrifugal pump driven by a steam turbine using steam from the boiler.
    • An electrically driven pump is also fitted for emergency situations.
    • The boiler can generate 45 to 50 tonnes of superheated steam at a pressure of 130 bar and a temperature of 500°C.

    Loeffler Boiler

    • The Loeffler boiler solves the problem of salt and sediment deposition on the inner surfaces of the water tubes by preventing the flow of water into the boiler tubes.
    • The boiler uses forced circulation and evaporates feed water by means of superheated steam from the superheater.
    • The boiler can carry higher salt concentrations and is more compact than indirectly heated boilers with natural circulation.
    • Loeffler boilers with a capacity of 100 tonnes/h and operating at 140 bar have been commissioned.

    Boiler Mounting and Accessories

    • Accessories are auxiliary plants required for steam boilers to operate efficiently.
    • Feed pumps are used to deliver feed water to the boiler, with two types: reciprocating and rotary pumps.

    Feed Pumps

    • Reciprocating pumps consist of a pump cylinder and a piston, with two types: single-acting and double-acting.
    • The reciprocating pump may not be suitable for high overloads due to overheating.
    • Rotary pumps are of centrifugal type and are commonly run by a small steam turbine or an electric motor.

    Scotch Boiler

    • The Scotch type marine boiler is a popular boiler for steaming capacities up to 1000 kg/h and pressure of about 17 bar.
    • It consists of a cylindrical shell with one to four cylindrical, corrugated steel furnaces.
    • The furnaces are internally fired and surrounded by water, with a combustion chamber located at the back end.

    High Pressure Boilers

    • High pressure boilers are preferred for high pressure and high output applications.
    • Unique features of high pressure boilers include:
      • Forced circulation of water using pumps.
      • Type of tubing, including partial systems and multiple sets.
      • Improved methods of heating, such as evaporation above critical pressure, mixing of superheated steam, and increasing water velocity.
    • Advantages of high pressure boilers include:
      • Increased evaporative capacity.
      • Compactness.
      • Reduced danger of overheating.
      • Improved heat transfer.

    Injector

    • An injector is a device used to feed water into the boiler, commonly employed for vertical and locomotive boilers.
    • It uses steam pressure to increase the pressure and velocity of the feed water.
    • Advantages of an injector include:
      • Low initial cost.
      • Simplicity.
      • Compactness.
      • Absence of dynamic parts.
      • High thermal efficiency.
    • Disadvantages of an injector include:
      • Low pumping efficiency.
      • Inability to force very hot water.
      • Irregularity of operation under extreme variation in steam pressure.

    Economiser

    • An economiser is a device that utilises the waste heat of the flue gases to heat the feed water.
    • There are two types of economisers: independent and integral.
    • The independent type is installed in a chamber apart from the boiler setting, while the integral type is part of the boiler heating surface.
    • Advantages of an economiser include:
      • Increased efficiency.
      • Reduced fuel consumption.
      • Compactness.

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    Description

    Learn about water tube boilers, specifically the Babcock and Wilcox boiler which is an example of a horizontal straight tube boiler. Understand the types of water tube boilers used in different capacities and purposes.

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