Chap 1 - Steam Boiler PPT.pdf

1 Steam Boilers  Steam Boilers Definition of a Boiler Boiler is defined as a closed metallic vessel in which the water is converted into steam above the atmospheric pressure by the application of heat generated by the combustion of fuels. Function of a Boiler The f...

1 Steam Boilers  Steam Boilers Definition of a Boiler Boiler is defined as a closed metallic vessel in which the water is converted into steam above the atmospheric pressure by the application of heat generated by the combustion of fuels. Function of a Boiler The function of a boiler is to generate & supply the steam at the required constant pressure with its quality either dry, wet or superheated. Department of Mechanical & Industrial Engineering, MIT. Manipal 2  Classification of Boilers 1. According to the axis of the shell: a. Horizontal boiler b. Vertical boiler c. Inclined boiler 2. According to the application a. Stationary boiler b. Mobile boiler 3. According to the location of the furnace a. Internally fired boiler Furnace SHELL b. Externally fired boiler SHELL Furnace Department of Mechanical & Industrial Engineering, MIT. Manipal 3 4. According to the type of fuel used a. Solid fueled boiler b. Liquid fueled boiler c. Gaseous fueled boiler 5. According to the method of circulation of water a. Natural circulation boiler (circulation of water due to difference in temperature) b. Forced circulation boiler (pumps are used) 6. According to the flow of water and flue gases a. Fire tube boilers b. Water tube boilers Department of Mechanical & Industrial Engineering, MIT. Manipal 4  Fire Tube Boiler In the fire tube boilers, the hot flue gases produced by the combustion of fuels are led through a nest of tubes around which the water circulates. Example: Lancashire boiler. Ref: http://www.icym.edu.my/v13/about- us/our-news/general/1194-fire-tube- boiler.html Department of Mechanical & Industrial Engineering, MIT. Manipal 5 Locomotive boiler (Fire Tube Boiler) Department of Mechanical & Industrial Engineering, MIT. Manipal 6  Water Tube Boiler: In the water tube boilers, the water flows through the tubes while the hot gases produced by the combustion of the fuels pass around them externally Example: Babcock and Wilcox Boiler Department of Mechanical & Industrial Engineering, MIT. Manipal 7  Babcock & Wilcox boiler (Water tube boiler) It is a horizontal, stationary, externally fired, natural circulation, water tube boiler. By using this boiler, we can get steam up to a pressure of 75 – 80 bar. Application: It is widely used in thermal power stations. Department of Mechanical & Industrial Engineering, MIT. Manipal 8  Babcock and Wilcox boiler Department of Mechanical & Industrial Engineering, MIT. Manipal 9  Babcock and Wilcox boiler A: Water tubes B: Uptake header C: Down take header D: Boiler drum E: Steel Caps F: Mud Box G: Dampers H: Doors J: Chain grate stoker K: Furnace door L: ‘T’ tube M: Lower junction box N: Upper junction box. O: Stop valve connection P: Stop valve, Q: Safety valve, R: Water-level indicator, S: Super heater, T: Pressure gauge, V: Feed check valve, W: Baffles, X: Blow off valve Department of Mechanical & Industrial Engineering, MIT. Manipal 10  Water circuit in the boiler Department of Mechanical & Industrial Engineering, MIT. Manipal 11  Path of flue gases Department of Mechanical & Industrial Engineering, MIT. Manipal 12  Superheating of the steam Department of Mechanical & Industrial Engineering, MIT. Manipal 13  Advantages of Water Tube Boilers over Fire Tube Boilers 1. Rapid steam generation 2. Generation of steam at higher pressures 3. Higher steam generation capacity 4. Sediment deposition is less 5. Suitable for any type of fuel 6. Occupies less space per unit power generation 7. Easy maintenance. Department of Mechanical & Industrial Engineering, MIT. Manipal 14  Disadvantages of Water Tube Boilers over Fire Tube Boilers Not suitable for mobile application Treatment (Filtering/Softening) of water is necessary High initial cost Department of Mechanical & Industrial Engineering, MIT. Manipal 15  Differences / Comparison between Fire tube and Water tube boilers Particulars Fire tube Water tube Flow of water & Hot gases inside Water inside the hot gases the tubes and tubes and hot water outside the gases outside the tubes tubes Mode of firing Internally fired Externally fired Operating Low High pressure (Up to 15 bar) ( Up to 75 bar) Rate of steam Low High production Department of Mechanical & Industrial Engineering, MIT. Manipal 16  Differences / Comparison Particulars Fire tube Water tube Suitable for Ideally suitable for Applications chemical & sugar power generation industries & not for plants. power generation Safety Safe, due to low Not safe, due to pressure high pressure Treatment of Not essential Essential water Shell diameter Large for given Small for given capacity capacity Department of Mechanical & Industrial Engineering, MIT. Manipal 17  Boiler Mountings and Accessories Mountings are mandatory and are required: To have complete control over the steam generation, Measurement of some of the important steam properties, To provide safety to the boiler. They are mounted directly on the boiler and become an integral part of the same. Department of Mechanical & Industrial Engineering, MIT. Manipal 18  Boiler Mountings ❑ Water level indicators ❑ Pressure gauge ❑ Safety valves ❑ Steam stop valve ❑ Blow-off valve ❑ Feed check valve ❑ Fusible plug ❑ Manhole & Mud Box Department of Mechanical & Industrial Engineering, MIT. Manipal 19  Functions of Boiler Mountings Water Level Indicator: It is used to indicate the level of water inside the boiler drum, and thereby guide the boiler attendant to maintain a constant level of water in the boiler drum. Pressure Gauge: It is used to indicate the pressure of steam inside the boiler drum. Department of Mechanical & Industrial Engineering, MIT. Manipal 20  Functions of Boiler Mountings Safety Valve : The function of the safety valve is to Safety Stop Valve Valve prevent the steam pressure in the boiler from exceeding a certain predetermined value. Steam Stop Valve: It is used to regulate the flow of steam from the boiler drum to the steam pipe or from one steam pipe to another. Department of Mechanical & Industrial Engineering, MIT. Manipal 21  Steam Stop Valve Hand wheel Department of Mechanical & Industrial Engineering, MIT. Manipal 22 Blow off Valve: The function of the blow off valve is to remove the sediments collected at the bottom of the boiler periodically while in operation & also to empty water from the Blow off Valve boiler for periodical cleaning and maintenance. Department of Mechanical & Industrial Engineering, MIT. Manipal 23  Feed Check Valve: It is a non return valve and performs the dual function of regulating the flow of water to the boiler when the level of water inside the boiler drum falls and prevents the return flow of water from the boiler drum when the feed pump stops or in the event of failure of feed pump. Department of Mechanical & Industrial Engineering, MIT. Manipal 24 Fusible Plug: It is used to extinguish the fire in the furnace of the boiler when the water level falls too much below the normal level. It protects the boiler against damage due to over heating caused by low water level. Normal condition Brass Overheated condition Fusible alloy (Tin) Ref: https://www.youtube.com/watch?v=fVIu4-IPyY8 Department of Mechanical & Industrial Engineering, MIT. Manipal 25 Manhole: It is an opening in the boiler shell through which a person can go in for periodic inspection and cleaning. It is elliptical in shape. Oval shaped Manhole Plate Department of Mechanical & Industrial Engineering, MIT. Manipal 26  BOILER ACCESSORIES ❑They are used to improve the efficiency of the boiler and hence the steam power plant. ❑They are not mandatory and are not mounted directly on the boiler. The essential boiler accessories are: 1. Economizer 2. Air-preheater 3. Superheater 4. Steam separator 5. Steam trap Department of Mechanical & Industrial Engineering, MIT. Manipal 27  Functions of Boiler Accessories Economizer: The function of the economizer is to increase the temperature of feed water. It is a device in which the waste heat of the flue gases is utilized for preheating the feed water thereby increasing its sensible heat. Department of Mechanical & Industrial Engineering, MIT. Manipal 28  Functions of Boiler Accessories Air preheater: ❑It is a accessory which is used for preheating the air supplied to the furnace of the boiler. ❑It uses the waste heat of the flue gases for preheating the air, which accelerates the combustion process of the fuel thereby improving the boiler Air pre-heater efficiency. Atmospheric air entry Pre-heated air supply to boiler furnace Department of Mechanical & Industrial Engineering, MIT. Manipal 29  Functions of Boiler Accessories Super heater: It is used to increase the temperature of the steam beyond the saturation temperature thereby increasing its enthalpy. It is fitted outside the boiler drum. Generally it uses the same heat source of the boiler. Department of Mechanical & Industrial Engineering, MIT. Manipal 30  Steam Trap It is a device which is used to drain off the condensed water accumulating in the steam pipe lines by ensuring no escape of pressure steam out of it. steam condensate steam condensate to removed be removed Ref: https://www.tlv.com/global/TI/steam- theory/mechanical-steam-traps.html Department of Mechanical & Industrial Engineering, MIT. Manipal 31  Steam Seperator It separates the entrained water droplets from the steam flowing in the pipe lines. It is installed very close to the turbine room. Entrained water droplets not Steam trap removed by steam trap Ref: https://www.tlv.com/global/TI/steam- theory/mechanical-steam-traps.html Department of Mechanical & Industrial Engineering, MIT. Manipal 32  Steam seperator Department of Mechanical & Industrial Engineering, MIT. Manipal 33  Differences between Boiler mountings & Accessories Boiler mountings Boiler accessories They are mandatory They are optional They are related to proper They are related to efficiency & functioning, maintenance and economy of the boilers. safety of the boilers. They are not fitted directly on the They are fitted directly on the boiler drum boiler drum. They are also used to measure They are used to improve some some of the important properties of the important properties Department of Mechanical & Industrial Engineering, MIT. Manipal 34