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  1. 1. UNIT 2 Boilers Dr S MuraliDr. S. Murali Professor & Head Department of Mechanical Engineering
  2. 2. Boiler is an apparatus to produce steam. – Thermal energy released by combustion of fuel is  d k h d i dused to make  steam at the desired temperature  and pressure.
  3. 3. Simple Boiler
  4. 4. Applications • The steam produced is used for: – Producing mechanical work by expanding it in  steam engine or steam turbine. H i h id i l d i d i l b ildi– Heating the residential and industrial buildings – Performing certain processes in the sugar mills,  h i l d t til i d t ichemical and textile industries.
  5. 5. Boiler Requirements • Safety.  Th b il h ld b f d ti– The boiler should be safe under operating  conditions. A ibilit• Accessibility.  – The various parts of the boiler should be accessible  f i d i tfor repair and maintenance. • Capacity.   – Should be capable of supplying steam according to  the requirements.
  6. 6. Boiler Requirements • Efficiency.   Sh ld b bl t b b i t f– Should be able to absorb a maximum amount of  heat produced due to burning of fuel in the  furnacefurnace. • Construction i l i t ti– simple in construction . • Cost  – Its initial cost and maintenance cost should be  low.
  7. 7. Boiler Requirements • Joints. Th b il h ld h j i t d t– The boiler should have no joints exposed to  flames. E f t ti• Ease of starting. – Should be capable of quick starting and loading.
  8. 8. Boiler Classification 1. According to the flow of water and hot gases  Fi t b ( k t b )a. Fire tube (or smoke tube)  Eg: Cochran, Lancashire and Locomotive boilers b Water tube boilersb. Water tube boilers Eg: babcock & Wilcox boiler, Sterling boiler . 2 A di t th i f th h ll2. According to the axis of the shell  a. Vertical boilers b. horizontal boilers c. Inclined
  9. 9. Boiler Classification 3. According to location or position of the  furnacefurnace.  a. Externally fired boilers.  ti l t b l l ti d th t h i b ilvertical tubular, locomotive and the scotch marine boilers b. internally fired boilers Cochran lancashireCochran, lancashire 4. According to the application  ia. stationery  b. mobile boilers. 
  10. 10. Boiler Classification 5. According to steam pressure  L (15 20b )a. Low (15 – 20bar) b. medium and (20 – 80bar) h h b l ( h b )c. high pressure boilers(more than 80 bar) a. Subcritical(less than 221 bar) b S iti l( th 221b )b. Supercritical(more than 221bar) 6. According to water circulation arrangement a. Natural Circulation Lancashire, babcock and wilcox boiler b d i l ib. Forced circulation Velox, lamont, benson boiler
  11. 11. Fire Tube boiler
  12. 12. advantages of fire tube boilers • Low cost Fl i f d d b• Fluctuations of steam demand can be met  easily • It is compact in size.
  13. 13. Simple Vertical boiler Capacity‐2500 kg/hr Pressure 7‐10 barPressure 7 10 bar
  14. 14. Cochran Boiler Salient features • The dome shape of the furnace  causes the hot gases to deflectcauses the hot gases to deflect  back and pass through the flue.  The un‐burnt fuel if any will also  be deflected backbe deflected back. • Spherical shape of the top of the  shell and the fire box gives higher  area by volume ratioarea by volume ratio. • It occupies comparatively less  floor area and is very compact. • It is well suited for small capacity• It is well suited for small capacity  requirements.
  15. 15. Cochran Boiler- features • very compact and requires minimum floor  areaarea • Any type of fuel can be used with this boiler • Well suited for small capacity requirements • gives about 70% thermal efficiency with coal g y firing and about 75% with oil firing
  16. 16. Cochran Boiler- features • Pressure Gauge W L l I di• Water Level Indicator • Safety Valve • Fusible Plug • Blow‐off CockBlow off Cock  • Steam Stop Valve  F d Ch k V l• Feed Check Valve
  17. 17. Cornish Boiler No. of Flue tubes one Diameter of Shell 1.25 to 1.75 m Length of shell 4 to 7m Max. Working Pressure 10.5 bar Steam Capacity 6500 kg/hr
  18. 18. Lancashire Boiler Di f Sh ll 2 3Diameter of Shell 2 to 3 m Length of shell 7to 9m Max. Working Pressure 16 bar Steam Capacity 9000 kg/hr Efficiency 50 to 60 %
  19. 19. Lancashire boiler • It is stationary fire tube, internally fired, horizontal, natural  circulation boiler.  hi i id l d b il b f i d i• This is a widely used boiler because of its good steaming  quality and its ability to burn coal of inferior quality.  • These boilers have a cylindrical shell 2 m in diameters and  l h fits length varies from 8 m to 10 m.  • It has two large internal flue tubes having diameter  between 80 cm to 100 cm in which the grate is situated.  • This boiler is set in brickwork forming external flue so that  the external part of the shell forms part of the heating  surface.
  20. 20. AdvantagesAdvantages • The feed pipe projecting into the boiler is perforated to  ensure uniform water distribution. • Its heating surface area per unit volume at the boiler is  considerably large. • Its maintenance is easy.Its maintenance is easy. • It is suitable where a large reserve of hot water is  needed. This boiler due to the large reserve capacity  can easily meet load fluctuationscan easily meet load fluctuations. • Super‐heater and economizer can be easily  incorporated into the system, therefore; overall  ffi i f h b il b id bl i defficiency of the boiler can be considerably increased  (80‐85%).
  22. 22. Locomotive boiler
  23. 23. LOCOMOTIVE BOILERLOCOMOTIVE BOILER Muhammad Fadhli Mustaffa & Ahmad Lutfi Mohayiddinff f y
  24. 24. LOCOMOTIVE BOILERLOCOMOTIVE BOILER • horizontal fire tube type mobile boiler.  • produce steam at a very high rate Therefore• produce steam at a very high rate. Therefore,  this boiler requires a large amount of heating  surface and large grate area to burn coal at asurface and large grate area to burn coal at a  rapid rate. In order to  provide the large  heating surface area, a large number of fire g , g tubes are setup  • heat transfer rate is increased by creating y g strong draught by means of steam jet.
  25. 25. AdvantagesAdvantages • Large rate of steam generation per square  metre of heating surface To some extent thismetre of heating surface. To some extent this  is due to the vibration caused by the motion. I i f f b i k k i l f d i• It is free from brickwork, special foundation  and chimney. This reduces the cost of  i ll iinstallation. • It is very compact. • The pressure of the steam is limited to about  20 bar.
  26. 26. Scotch Boiler Max. Working Pressure 17 barg Steam Capacity 1000 kg/hr
  27. 27. Water Tube Boiler
  28. 28. Merits Of Water Tube BoilersMerits Of Water Tube Boilers 1. Generation of steam is much quicker due to  small ratio of water content to steam content.  This also helps in reaching the steaming  temperature in short time. 2 Its evaporative capacity is considerably larger2. Its evaporative capacity is considerably larger  and the steam pressure range is also high‐200  bar. 3. Heating surfaces are more effective as the hot  gases travel at right angles to the direction of  water flowwater flow.
  29. 29. Merits Of Water Tube BoilersMerits Of Water Tube Boilers 4. The combustion efficiency is higher because  complete combustion of fuel is possible as the p p combustion space is much larger. 5 Th h l i h b il5. The thermal stresses in the boiler parts are  less as different parts of the boiler remain at  uniform temperature due to quick circulationuniform temperature due to quick circulation  of water. 6. The boiler can be easily transported and  erected as its different parts can be separated.
  30. 30. Merits Of Water Tube BoilersMerits Of Water Tube Boilers 7. Damage due to the bursting of water tube is  less serious. Therefore, water tube boilers are  sometimes called safety boilers. 8 All f h b b il il8. All parts of the water tube boilers are easily  accessible for cleaning, inspecting and  repairing.repairing. 9. The water tube boiler's furnace area can be  easily altered to meet the fuel requirements.
  31. 31. Demerits 1. It is less suitable for impure and sedimentary  water as a small deposit of scale may causewater, as a small deposit of scale may cause  the overheating and bursting of tube.  Therefore use of pure feed water is essentialTherefore, use of pure feed water is essential. 2. They require careful attention. The  i hi hmaintenance costs are higher. 3. Failure in feed water supply even for short  period is liable to make the boiler over‐ heated.
  32. 32. Water tube Vs Fire tube
  33. 33. Water tube Vs Fire tube
  34. 34. Water tube boilers classification 1. Horizontal straight tube boilers L it di l da. Longitudinal drum  b. Cross‐drum. 2. Bent tube boilers a. Two drum  b. Three drum c. Low head three drum  d. Four drum. 3. Cyclone fired boilersy
  36. 36. Features • The evaporative capacity of this boilers is high compared with  other boilers (20,000 to 40,000kg/hr). The operating pressure  lies between 11.5 to 17.5 bar. • The draught loss is minimum compared with other boilers. h d f b b l d l• The defective tubes can be replaced easily. • The entire boiler rests over an iron structure, independent of  brick work, so that the boiler may expand or contract freely.brick work, so that the boiler may expand or contract freely.  The brick walls which form the surroundings of the boiler are  only to enclose the furnace and the hot gases.
  37. 37. Stirling Boiler
  38. 38. High pressure Boilers
  39. 39. Lamont Boiler
  40. 40. Loeffler Boiler
  41. 41. Benson Boiler
  42. 42. Schmidt-Hartmann Boiler
  43. 43. Velox Boiler
  44. 44. Reference