BOILERS AND THEIR CLASSIFICATION

DEFINITION

A boiler is a closed vessel in which fluid (generally water) is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications,^[1][2] including water heating, central heating, boiler-based power generation, cooking, and sanitation.

Working Principle of Boiler

The basic working principle of boiler is very very simple and easy to understand. The boiler is essentially a closed vessel inside which water is stored. Fuel (generally coal) is burnt in a furnace and hot gasses are produced. These hot gasses come in contact with water vessel where the heat of these hot gases transfer to the water and consequently steam is produced in the boiler.

Then this steam is piped to the turbine of the thermal power plant. There are many different types of boiler utilized for different purposes like running a production unit, sanitizing some area, sterilizing equipment, to warm up the surroundings etc.

contents

• 1 Heat sources
• 2 Materials
• 3 Energy
• 4 Boiler efficiency
  • 4.1 Input-Output Method (Direct method)
  • 4.2 Heat Loss Method (Indirect method)
• 5 Configurations
• 6 Safety
• 7 Superheated steam boiler
  • 7.1 Supercritical steam generator
• 8 Accessories
  • 8.1 Boiler fittings and accessories
  • 8.2 Steam accessories
  • 8.3 Combustion accessories
  • 8.4 Other essential items
• 9 Draught
• 10 See also
• 11 References
• 12 Further reading

  Heat  sources

  In a fossil fuel power plant using a steam cycle for power generation, the primary heat source will be combustion of coal, oil, or natural gas. In some cases byproduct fuel such as the carbon-monoxide rich off-gasses of a coke battery can be burned to heat a boiler; biofuels such as bagasse, where economically available, can also be used. In a nuclear power plant, boilers called steam generators are heated by the heat produced by nuclear fission. Where a large volume of hot gas is available from some process, a heat recovery steam generator or recovery boiler can use the heat to produce steam, with little or no extra fuel consumed; such a configuration is common in a combined cycle power plant where a gas turbine and a steam boiler are used. In whole cases the combustion product waste gases are separate from the working fluid of the steam cycle, making these systems examples of External combustion engines.

  Steam Boiler Efficiency

  The percentage of total heat exported by outlet steam in the total heat supplied by the fuel (coal) is called steam boiler efficiency.
  
  It includes thermal efficiency, combustion efficiency and fuel to steam efficiency. Steam boiler efficiency depends upon the size of the boiler used. typical efficiency of a steam boiler is 80% to 88%. Actually, there are some losses occur like incomplete combustion, radiating loss occurs from steam boiler surrounding wall, defective combustion gas etc. Hence, the efficiency of steam boiler gives this result. 

• TYPES OF BOILERS

• • Haycock and wagon top boilers.
  • Cylindrical fire-tube boiler.
  • Multi-tube boilers.
  • Solid fuel firing.
  • Firetube boiler.
  • Superheater.
  • Water-tube boiler.
  • Supercritical steam generator

• Haycock and wagon top boilers

  For the first Newcomen engine of 1712, the boiler was little more than large brewer's kettle installed beneath the power cylinder. Because the engine's power was derived from the vacuum produced by condensation of the steam, the requirement was for large volumes of steam at very low pressure hardly more than 1 psi (6.9 kPa) The whole boiler was set into brickwork which retained some heat. A voluminous coal fire was lit on a grate beneath the slightly dished pan which gave a very small heating surface; there was, therefore, a great deal of heat wasted up the chimney. In later models, notably by John Smeaton, the heating surface was considerably increased by making the gases heat the boiler sides, passing through a flue. Smeaton further lengthened the path of the gases by means of a spiral labyrinth flue beneath the boiler. These under-fired boilers were used in various forms throughout the 18th Century. Some were of round section (haycock). A longer version on a rectangular plan was developed around 1775 by Boulton and Watt (wagon top boiler). This is what is today known as a three-pass boiler, the fire heating the underside, the gases then passing through a central square-section tubular flue and finally around the boiler sides.

  Multi-tube boilers

  A significant breakthrough came in France in 1828 when Marc Seguin devised a two-pass boiler of which the second pass was formed by a bundle of multiple tubes. A similar design with natural induction used for marine purposes was the favoured Scotch marine boiler.

  Prior to the Rainhill trials of 1829 Henry Booth, treasurer of the Liverpool and Manchester Railway suggested to Stephenson, a scheme for a multi-tube one-pass horizontal boiler made up of two units: a firebox surrounded by water spaces and a boiler barrel consisting of two telescopic rings inside which were mounted 25 copper tubes; the tube bundle occupied much of the water space within the barrel and vastly improved heat transfer. Old George immediately communicated the scheme to his son Robert and this was the boiler used on Stephenson's Rocket, outright winner of the trial. The design formed the thought for all subsequent Stephensonian-built locomotives, being immediately haunted by other constructors.                 

     cylindrical fire-tube boiler

• An early proponent of the cylindrical form was British engineer John Blakey, who proposed his design in 1774.[1][2] Another early proponent was the American engineer, Oliver Evans, who rightly recognised that the cylindrical form was the simplest from the purpose of view of mechanical resistance and towards the top of the 18th Century began to include it into his projects.[citation needed] Probably inspired by the writings on Leupold's "high-pressure" engine scheme that appeared in encyclopaedic works from 1725, Evans favoured "strong steam" i.e. non-condensing engines during which the steam pressure alone drove the piston and was then exhausted to atmosphere. The advantage of strong steam as he saw it had been that more work might be done by smaller volumes of steam; this enabled all the components to be reduced in size and engines might be adapted to move and little installations. to the present end, he developed an extended cylindrical iron horizontal boiler into which was incorporated one fire tube, at one end of which was placed the hearth grate. The gas flow was then reversed into a passage or flue beneath the boiler barrel, then divided to return through side flues to hitch again at the chimney (Columbian engine boiler). Evans incorporated his cylindrical boiler into several engines, both stationary and mobile. thanks to space and weight considerations, the latter were one-pass exhausting directly from fire tube to the chimney. Another proponent of "strong steam" at that point was the Cornishman, Trevithick. His boilers worked at 40–50 psi (276–345 kPa) and were initially of hemispherical then cylindrical form. From 1804 onwards Trevithick produced a little two-pass or return flue boiler for semi-portable and locomotive engines. The Cornish boiler developed around 1812 by Trevithick was both stronger and more efficient than the straightforward boilers which preceded it. It consisted of a cylindrical cistern around 27 feet (8.2 m) long and seven feet (2.1 m) in diameter and had a coal fire grate placed at one end of one cylindrical tube abt three feet wide which passed longitudinally inside the tank. the hearth was tended from one end and therefore the hot gases from it travelled along the tube and out of the opposite end, to be circulated back along flues running along the surface than a 3rd time beneath the boiler barrel before being expelled into a chimney. This was later improved upon by another 3-pass boiler, the Lancashire boiler which had a pair of furnaces in separate tubes side-by-side. This was a crucial improvement since each furnace might be stoked at different times, allowing one to be cleaned while the opposite was operating.

  Railway locomotive boilers were usually of the 1-pass type, although in youth, 2-pass "return flue" boilers were common, especially with locomotives built by Timothy Hackworth.

• A fire-tube boiler is a type of boiler in which hot gases pass from a fire through one or (many) more tubes running through a sealed container of water. The heat of the gases is transferred through the walls of the tubes by thermal conduction, heating the water and ultimately creating steam. 

  types of fire tube boilers

  Cornish boiler

  Further information: Cornish boiler

  The earliest sort of fire-tube boiler was Richard Trevithick's "high-pressure" Cornish boiler. this is often an extended horizontal cylinder with one large flue containing the hearth. the hearth itself was on an iron grating placed across this flue, with a shallow ashpan beneath to gather the non-combustible residue. Although considered as low-pressure (perhaps 25 pounds per sq in (170 kPa)) today, the utilization of a cylindrical boiler shell permitted a better pressure than the sooner "haystack" boilers of Newcomen's day. because the furnace relied on natural draught (airflow), a tall chimney was required at the far end of the flue to encourage an honest supply of air (oxygen) to the hearth.

  For efficiency, the boiler was commonly encased beneath by a brick-built chamber. Flue gases were routed through this, outside the iron boiler shell, after passing through the fire-tube then to a chimney that was now placed at the front face of the boiler.

  Lancashire boiler in Germany

  The Lancashire boiler is analogous to the Cornish but has two large flues containing the fires. it had been the invention of William Fairbairn in 1844, from a theoretical consideration of the thermodynamics of more efficient boilers that led him to extend the furnace grate area relative to the quantity of water.

  Later developments added Galloway tubes (after their inventor, patented in 1848),[2] crosswise water tubes across the flue, thus increasing the heated area. As these are short tubes of huge diameter and therefore the boiler continues to use a comparatively low, this is often still not considered to be a water-tube boiler. The tubes are tapered, simply to form their installation through the flue easier.[

  Scotch marine boiler

  The Scotch marine boiler differs dramatically from its predecessors in employing a sizable amount of small-diameter tubes. this provides a far greater heating area for the quantity and weight. The furnace remains one large-diameter tube with the various small tubes arranged above it. they're connected together through a combustion chamber – an indoor volume contained entirely within the boiler shell – in order that the flow of flue gas through the firetubes is from back to front. an indoor smokebox covering the front of those tubes leads upwards to the chimney or funnel. Typical Scotch boilers had a pair of furnaces, larger ones had three. Above this size, like for giant steamships, it had been more usual to put in multiple boilers.

  Side-section of a Scotch marine boiler: the arrows show the direction of flue gas flow; the combustion chamber is on the proper, the smokebox on the left.

  Locomotive boiler

  A locomotive boiler has three main components: a double-walled firebox; a horizontal, cylindrical "boiler barrel" containing an outsized number of small flue-tubes; and a smokebox with chimney, for the exhaust gases. The boiler barrel contains larger flue-tubes to hold the superheater elements, where present. Forced draught is provided within the locomotive boiler by injecting exhausted steam back to the exhaust via a blast pipe within the smokebox.
  Locomotive-type boilers also are utilized in traction engines, steam rollers, portable engines and a few other steam road vehicles. The inherent strength of the boiler means it's used because the basis for the vehicle: all the opposite components, including the wheels, are mounted on brackets attached to the boiler. it's rare to seek out superheaters designed into this sort of boiler, and that they are generally much smaller (and simpler) than locomotive types.
  

  The locomotive-type boiler is additionally a characteristic of the overtype steam wagon, the steam-powered fore-runner of the truck. during this case, however, heavy girder frames structure the load-bearing chassis of the vehicle, and therefore the boiler is attached to the present. 

  Taper boiler

• Certain locomotive boilers are tapered from a bigger diameter at the firebox end to a smaller diameter at the smokebox end. This reduces weight and improves water circulation. Many later Great Western Railway and London, Midland and Scottish Railway locomotives were designed or modified to require taper boilers.

  Vertical fire-tube boiler

  A vertical fire-tube boiler (VFT), colloquially referred to as the "vertical boiler", features a vertical cylindrical shell, containing several vertical flue tubes.

• Horizontal return tubular boiler

  Horizontal Return Tubular boilers from the Staatsbad Bad Steben GmbH

  Horizontal return tubular boiler (HRT) features a horizontal cylindrical shell, containing several horizontal flue tubes, with the hearth located directly below the boiler's shell, usually within a brickwork setting

• • Admiralty-type direct tube boiler

• Extensively employed by Britain, before and within the youth of ironclads, the sole protected place was below the waterline, sometimes under an armoured deck, so to suit below short decks, the tubes weren't led back above the furnace but continued straight from it with keeping the combustion chamber in between the 2. Hence the name, and considerably reduced diameter, compared to the ever-present Scotch or return tube boiler. it had been not an excellent success and its use was being abandoned after the introduction of stronger side armouring – “the furnace crowns, being very near the water-level, are far more susceptible to overheating. Further, on account of the length of the boiler, for an equal angle of inclination, the effect on the water level is far greater. Finally, the unequal expansion of the varied parts of the boiler is more pronounced, especially at the highest and bottom, thanks to the increased ratio between the length and therefore the diameter of the boiler; the local strains also are more severe on account of the comparatively feeble circulation in long and low boilers.” of these also resulted during a shorter life. Also, an equivalent length of a combustion chamber was much less effective on an immediate tube than on a return tube boiler, a minimum of without baffling
• 
  

• Immersion fired boiler

• The immersion fired boiler may be a single-pass fire-tube boiler that was developed by Sellers Engineering within the 1940s. it's only firetubes, functioning as a furnace and combustion chamber also, with multiple burner nozzles injecting premixed air and gas struggling. It claims reduced thermal stresses and lacks refractory brickwork completely thanks to its construction.

• WATER TUBE BOILER

• A high-pressure water tube boiler[1] (also spelt water-tube and water tube) may be a sort of boiler during which water circulates in tubes heated externally by the hearth. Fuel is burned inside the furnace, creating hot gas which heats water within the steam-generating tubes. In smaller boilers, additional generating tubes are separate within the furnace, while larger utility boilers believe the water-filled tubes that structure the walls of the furnace to get steam.
• 
  
• The heated water then rises into the steam drum. Here, saturated steam is drawn off the highest of the drum. In some services, the steam will reenter the furnace through a superheater to become superheated. Superheated steam is defined as steam that's heated above the boiling point at a given pressure. Superheated steam may be a dry gas and thus wont to drive turbines since water droplets can severely damage turbine blades.
• 
  
• Cool water at rock bottom of the steam drum returns to the feedwater drum via large-bore 'downcomer tubes', where it pre-heats the feedwater supply. (In large utility boilers, the feedwater is supplied to the steam drum and therefore the downcomers supply water to the rock bottom of the waterfalls). to extend the economy of the boiler, exhaust gases also are wont to pre-heat the air blown into the furnace and warm the feedwater supply. Such water tube boilers in thermal power stations also are called steam generating units.

• WORKING PRINCIPLE
• The working rule of a water tube boiler is thermal siphoning (circulation of natural water). Basically, this sort of boiler includes two drums namely steam, lower or mud drum.
• 
  
• The water tube boiler diagram is shown below, and these two drums are associated via two tubes like downcomer and riser. At first, the water is supplied into the steam type drum with the assistance of a pump. Whenever the fuel is burned, then hot gases are going to be generated that are permitted to provide within the shell a part of the boiler. the recent gases which are produced by the fuel will replace heat by the water; the water gets become steam. Because, the water temperature increases, the concentration will increase automatically.
• 
  
• Clearly, the concentration of steam is going to be lesser than the water. Thus within the steam drum, the water, also as steam, gets divided obviously thanks to variation in concentration. Here the travelling of steam is going to be upward due to low concentration also as water will travel downward due to high concentration
• 
  
• The flow of predicament at the bottom of the steam drum is going to be supplied into mud drum via downcomer tube also on heat the water within the mud type drum. Whenever cooler supply water is initiated into steam type drum thanks to the high concentration of cool water, and it moves down within the downcomer type tube near the mud drum.
• 
  
• When transferring predicament from the mud type drum to steam type drum using riser tubes then it consequences within the normal water circulation within the water tube type boiler. As additional steam is generated within the boiler then the force within the drum enhances & the water system into the drum reduces which tend for decreasing the flow of steam. within the same way, when the assembly rate of steam reduces the force within the water-tube boiler reduces, & the water system into the boiler enhances which tends to reinforce the assembly rate. Like this, the water tube boiler controls the assembly of steam.

• The types of water tube boilers
• Simple Vertical Boiler
  Stirling Boiler
  Babcock and Wilcox Boilers
  

• 1) Simple Vertical Boiler

• This is one sort of water tube boiler. during this sort of boiler, the axis of direction is perpendicular with reference to the position. the main components of this boiler include ash pit, grate, feed check tap, fire hole, firebox, cross box, hand hole, fusible plug, water gage, cylindrical shell, steam space, manhole, pressure gage, steam stop tap, safety tap, chimney.
  
  In this sort of boiler, using the hearth hoke fuel is added into the grate which destroys by fire to get the nice and cosy gases. Ash pit is for collecting the ash which is converted from the fuel. Hot gases increase high and provide their heat toward the water within the cross box, then moves out using the chimney.
  
  When the water heats up and generates vapour as a result of water heating then collects at the boiler’s vapour space. Vapour is gathered until an assured force is conquered & vapour moves bent activate engine or turbine. These boilers are utilized in steam power-driven vehicles also as mobile machines like railway external-combustion engine, steam tractor, Steam shovels, and steam cranes.
• 

•  2) Stirling water tube Boiler

• The Stirling boiler is one sort of water tube boiler, used for generating steam (50,000 kg steam/hour and 60 kg /cm2 pressure) within the large area of the stationary plant. this sort of boiler consists of three steam drums also as 2 mud drums. The steam drums are located on the highest section of the boiler whereas mud drums are located on the bottom of the arrangement. The steam drums and dirt drums are connected through bent tube banks.

• When the tubes are turned then the mechanical pressures thanks to pipes extension throughout heating cannot influence the system. the 2 drums also as tubes are designed of steel which can support the entire system.
• 
  
• The arrangement of the Stirling boiler is enclosed with brickwork. Here, the arrangement of bricks will avoid the warmth dissipation within the surroundings
• 

•  3) Babcock and Wilcox Boilers

• This is a horizontal straight water tube boiler; it's a steam drum which is formed of steel. the 2 ends of the drum are related to a series of two end headers with short riser pipes. These are disposed at 15o0 angle to the horizontal axis of the steam drum. The disposed of the arrangement of tubes assists within the supply of water, and therefore the water level within the drum is indicated with a water level indicator.

• The fire door within the water boiler is going to be located at rock bottom and therefore the fuel is going to be supplied through this door and burns during a grate. The burning fuel will generate the recent gases that are forced within the grate to provide upward with baffle plates. At rock bottom of the water boiler, mud collector is found for removing the mud particles using blow down a cock. Therefore, endless water circulation from the steam drum toward the water tubes is maintained by convective currents due to the difference in concentration and it's called normal circulation.
• Thus, this is often all about water tube boiler design, working rule, and its types. From the above information finally, we will conclude that each one component of the water tube boilers is simply available for inspecting, repairing and cleaning. But they have a cautious concentration
• 

• DIFFERENCE BETWEEN FIRETUBE AND WATER TUBE BOILERS

• 1. the recent flue gases flow inside the tube and water has surrounded the tube. The water flow inside the tube and therefore the hot flue gases have surrounded the tube.
• 2. this is often heavy in weight. this is often light in weight.
• 3. this is often also called as internally fire tube boiler and This one is named an Externally Fire-tube boiler.
• 4. Here the pressure is restricted up to only 20 bar but within the water tube boiler the pressure around to 100 bar and more.
• 5. the speed of Steam generation is Lower. Why? because the pressure is restricted to only 20 bar. the speed of Steam generation is High. Why? because the pressure is restricted to 100 bar and more.
• 6. The explosion likelihood is that less during a fire tube boiler due to low. Here explosion likelihood is that more due to high.
• 7. the general efficiency is around 75 per cent. In the water tube, the general efficiency is around 90 per cent.
• 8. Efficiency is a smaller amount compared to the water tube. Efficiency is more.
• 9. Load fluctuations can't be handled. Load fluctuations are often handled easily.
• 10. The direction of water circulation isn't well defined during this boiler. The direction of water circulation during a water tube boiler is well defined.
• A definite path is provided for the circulation of water.
• 11. this is often not suitable for an outsized power station. it's used for the method industry. But it's suitable for the giant power station.
• 12. it's simple in design. it's complex in design.
• 13. A less skilled operator can work on this boiler. But here it requires a more skilled operator.
• 14. this is often having a coffee maintenance cost. But the Water tube boiler has High maintenance cost.
• 15. Fire Tube Boiler example:
• Cochran Boiler
• Cornish Boiler
• Locomotive Boiler
• Velcon Boiler
• Simple Vertical and
• Scotch Marine Boiler. Water Tube boiler example:
• Benson Boiler
• Lamont Boiler
• Babcock and Wilcox Boiler
• Lamont Boiler
• Loeffler boiler and
• Yarrow boiler.
• 16. A fire-tube boiler requires more floor area for a given output. The water-tube boiler requires less floor area for a given output.
• 17. The fire-tube boiler is bulky and difficult to move. But These (Water Tube Boiler) are light in weight, hence transportation isn't a drag.
•