Introduction To Boiler, Waste Heat Boiler.pptx

1. Boiler Definition
2. Types, application of boilers
3. Furnace Classification
4. Boiler Mountings and Accessories

1. Introduction to Boiler 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 1

2. Boiler/Steam Generator A steam generator or boiler is usually a closed vessel made of steel . Its function is to transfer the heat produced by the combustion of fuel to water and ultimately to generate steam at  a  desired pressure and temperature . Steam Boiler " means any closed vessel exceeding 22.76 litres which is used exclusively for generating steam under pressure and includes any mountings and other fittings attached to such vessel which is wholly or partly under pressure when steam is shut off. ( Indian Boiler Act. 1923 ) Open vessels , generating steam at atmospheric pressure are not considered to be boiler 2 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

3. Before going into the design phase we need to understand different options available for the boiler: . Boiler Classificaion 1. According to Relative Passage of water and hot gases: Water Tube Boiler : A boiler in which the water flows through some small tubes which are surrounded by hot combustion gases, e.g., Babcock and Wilcox , Stirling , Benson boilers, etc. Fire-tube Boiler : The hot combustion gases pass through the boiler tubes , which are surrounded by water, e.g., Lancashire, Cochran , locomotive boilers, etc. 2. According to Water Circulation Arrangement: Natural Circulation: Water circulates in the boiler due to density difference of hot and water, e.g., Babcock and Wilcox boilers , Lancashire boilers, Cochran , locomotive boilers, etc. Forced Circulation: A water pump forces the water along its path, therefore, the steam generation rate increases, Eg : Benson, La Mont , Velox boilers, etc.

4. 3. According to the Use: Stationary Boiler: For power plants or processes steam in plants. Portable Boiler: Small mobile units and used for temporary uses at the sites. Locomotive: Produce steam to drive railway engines. Marine Boiler: Used on ships 4. According to Position of the Boilers: Horizontal Inclined Vertical boilers 5. According to the Location of Furnace Internally fired: The furnace is located inside the boiler shell, e.g., Cochran , Lancashire boilers, etc. Externally fired: The furnace is located outside the boiler shell, e.g., Babcock and Wilcox , Stirling boilers, etc.

5. 6. According to Pressure of steam generated Low-pressure boiler : Boiler pressure is about 15-20 bar (process heating). Medium-pressure boiler: Boiler pressure 20-80 bars (for power generation or combined use of power generation and process heating). High pressure boiler: Boiler pressure of more than 80 bars (for power generation). Sub-critical boiler: Boiler pressure which is less than the critical pressure (220 bars for water ) , it is called as a subcritical boiler. Supercritical boiler: Boiler pressure is greater than the critical pressure around 220-280 bars, 540 C for water. Ultra Supercritical boiler: These boilers provide steam at a pressure greater than the critical pressure ( 300 bar, 600 C ) for water. 7. According to fuel used in the boiler Solid fuel boiler Liquid fuel boiler Gaseous fuel boiler Electric boiler

6. Boilers that are encountered frequently: Fire Tube Boiler Water Tube Packaged Boiler Package Boiler Tubeless Boiler Electric Boiler Stoker Fired Boiler Pulverized Fuel Boiler Fluidized Bed (FBC) Boiler Waste Heat Boiler Recovery Boiler Thermal Oil Boiler (Hydronics Boiler) 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 6

7. Fire Tube Boiler In fire-tube boilers, combustion gases pass through the inside of the tubes with water surrounding the outside of the tubes. The advantages of a fire-tube boiler are its simple construction and less rigid water treatment requirements . 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 7

8. Fire Tube Boiler ©Md. Abu Daud, Lec . Dept. of ME, BAUST 18-Sep-24 8

9. Water Tube Boiler In a water-tube boiler, the water is inside the tubes and combustion gases pass around the outside of the tubes. The advantages of a water-tube boiler are: Lower unit weight-per-pound of steam generated Less time required to raise steam pressure , Greater flexibility for responding to load changes Ability to operate at high rates of steam generation. 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 9

10. Water Tube Boiler Water-tube boilers are: Are available in sizes far greater than a fire-tube design , up to several million pounds-per-hour of steam Are able to handle higher pressures up to 5,000 psig Have the ability to reach very high temperatures Disadvantages of water-tube boilers include: High initial capital cost Cleaning is more difficult due to the design No commonality between tubes Physical size may be an issue 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 10

11. Difference Between Firetube and Watertube 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 11 Sl. Fire tube boiler Water tube boiler 1 In Fire-tube boilers hot flue gases pass through tubes and water surrounds them. In Water-tube boilers water passes through tubes and hot flue gasses surround them. 2 These are operated at low pressures up to 20 bar . The working pressure is high enough , up to 250 bar in super critical  boilers . 3 The rate of steam generation and quality of steam are low, therefore, not suitable for power generation . The rate of steam generation and quality of steam are better and suitable for power generation . 4 Overall efficiency: up to 75%. Overall efficiency with an economizer: 90%. 5 Even less skill operators are sufficient for efficient operation. Skilled operators are required for operation. 6 The treatment of feed water is not very essential , as overheating due to scale formation cannot burst thick shell. Treatment of feed water is very essential as small scale deposits inside the tubes can cause overheating and bursting. 7 Used in process industry . Used in large power plants .

12. Packaged Boiler Small self-contained boiler Used as: hot water boilers, utility boilers and process steam producers . Packaged boilers can be both water tube and fire tube boilers . Packaged boilers can only be used with oil and gas as fuel without separate preparation devices. 12 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

13. Stoker Fired Boiler Uses both suspension and grate burning for solid fuel like coal Coal fed continuously over burning coal bed . Coal fines burn in suspension and larger coal pieces burn on grate Spreader and moving grate increase the combustion efficiency 13 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

14. Pulverized Fired Boiler (PF) 14 The PCF technology has enabled the increase of boiler unit size from 100 MW in the 1950's to far over 1000 MW . Thermal cycle efficiencies ranging from 34 to 37% while removing up to 97% of the combined, uncontrolled air pollution emissions ( SOx and NOx) control. ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

15. Fluidizied Bed Boiler (FB) 15 A fluidized bed based on a layer of sand or a sand-like media , where the fuel is introduced into and combusted. The combustion air blows through the sand layer from an opening in the bottom of the boiler. ©Md. Abu Daud , Lec . Dept. of ME, BAUST 18-Sep-24

16. Bubbling Fluidizied Bed Boiler (BFB) Greater fuel flexibility over PCF High combustion efficiency Low NOx emission Control of SOx emission by desulfurization during combustion Wide range of acceptable fuel particle sizes 16 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

17. Circulating Fluidizied Bed Boiler (CFB) Velocity of air is high, so the medium sized particles are carried out of the combustor. Carried away particles are captured by a cyclone installed in the outlet of combustor and sent back to the bottom part of the combustor to combust unburned particles. Higher combustion efficiency Lower NOx emission Quicker response to load Changes 18-Sep-24 ©Md. Abu Daud , Lec . Dept. of ME, BAUST 17

18. Electric Boiler An electric steam boiler steam is generated using electricity , rather than through the combustion of a fuel source. Such boilers are used to generate steam in many applications for example laundries , food processing and hospitals . Electric boilers have smaller carbon footprints than their traditional cousins Capacity 5-1500 kg/ hr @ 0-40 Bar 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18

19. Waste Heat Boiler 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 19

20. Boiler Systems 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 20

21. Water Treatment System 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 21

22. Chemical Feed System 22 Chemical feed system : To minimize the corrosion of all materials within the steam/water cycle To minimize deposition of corrosion product or other impurities within the cycle Use antifoam, neutralizing amines, scale dissolver etc.. Major Components: Chemical storage tanks Mixing and dilution tanks Dosing pump Pipe work and double insulation valves Drain and wash down for spillage ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

23. Fuel Supply System ©Md. Abu Daud, Lec. Dept. of ME, BAUST 23 Consist of various group of devices that consist of control valve, solenoid valve, gas regulator, fuel pump etc. 18-Sep-24

24. Air Supply System About 10 times more air is required for full combustion of fuel An efficient air supply system is necessary for wide control, stable combustion and the better possible emission Blower/Compressor drive air flow Both the performance and emission is significantly affected by air supplied 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 24

25. Flue Gas System Starting from the combustor/furnace to the stack, the flus gas system consists of: Burner Evaporator Super heater Economizer/ Air Preheater Performance of flue gas system depends on various factors such as: Combustion efficiency and completeness (Air fuel ratio and draft) Heat transfer surface condition (Fouling, Shoot formation) 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 25

26. Flue Gas System 26 Various performance improvement schemes for flue gas system are available such as Overfire Air Technology Staggered combustion technique FGR system ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

27. Steam System 18-Sep-24 27 Consists of steam pipe, headers , valves (Flow and Pressure Regulating), Steam Trap etc. Insulation of steam pipe is crucial Local formation of water droplet may lead to corrosion in the equipment ©Md. Abu Daud, Lec. Dept. of ME, BAUST

28. Blow Down System As water is boiled, sediments settles down the boiler while scum rises to the surface . The purpose of boiler blow down is to control solids in the boiler water (TDS). Blow down protects from severe scaling or corrosion problems Two types: Continuous and Intermittent. A continuous blow down uses a calibrated valve and a blow down tap near the boiler water surface. This is an optional feature usually used in large bolier . All steam boilers must include a means for intermittent blow down as standard equipment. The frequency and duration of manual intermittent blow down depends on the TDS level of feed water, boiler water and boiler pressure and usually done in routine basis. In automatic intermittent blow down system, the conductivity and pH of the boiler water is measured continuously and blow down is accomplished accordingly Blow down recovery system increases the boiler efficiency 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 28

29. Boiler Mountings BOILER MOUNTINGS are the components generally mounted on the surface of the boiler to ensure safety during operation. These are the essential parts of the boiler, without which the boiler operation is not possible . The following are the important mountings of the boiler: Water Level Indicator Pressure gauge Safety Valves Steam stop valve Blow off cock Low Water Cut Off Switch (LWCO) Feed Check valve 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 29

30. Boiler Mountings Water Level Indicator The water level indicator is needed to ascertain the water level of a boiler. Two water level indicators should be fitted for each boiler in such a place that the water level can be constantly seen. 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 30

31. Boiler Mountings Pressure Gauge A pressure gauge is an instrument by means of which the pressure exerted inside a boiler can be measured. 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 31 Bourden’s pressure gauge with water filled U-tube siphon attachment

32. Boiler Mountings Safety Valve The safety valve (pressure relief valve) is used in a boiler to relieve the pressure of steam when it is above the pressure of steam when it is above the working pressure. As per boiler regulation two safety valves are required to be fitted in each boiler. . 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 32

33. Boiler Mountings Low Water Cut Off Switch LWCOs are installed in boilers as a safety device to shut down the boiler/burner in the event of loss of water in the system. 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 33

34. Boiler Mountings Steam Stop Valve The function of the stop valve or junction valve is to regulate the flow of steam from the boiler to the main steam pipe. To shut off the steam completely when required. 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 34

35. Boiler Mountings Feed Check Valve The feed check valve is used to control the supply of water to the boiler and to prevent the backflow of water from the boiler when the pump pressure is less or the pump is stopped. 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 35

36. Boiler Mountings Blow-off Cock The blow-off cock has two main functions: It may empty the boiler when necessary for cleaning, inspection and repair. It may discharge a portion of water when the boiler is in operation to blow out mud, scale or sediments periodically. 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 36

37. Boiler Accessories These are those devices which are installed with a boiler and its neighboring area to increase the efficiency of the boiler. These are not the essential part of the boiler and thus without installing these devices, the boiler operation can be accomplished though at a lower efficiency. Economiser Air pre heater Super heater Feed water pump Injector Pressure reducing valve Steam drier or separator Steam trap 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 37

38. Boiler Accessories 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 38 Economiser Used to recover some heat being carrying by exhaust flue gases. Heat recovered is utilized in raising the temperature of the feed water . Feed water at raised temperature is supplied to the boiler, thus less heat is required for conversion into steam .

39. 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 39 Advantages The temperature range between various parts of the boiler is reduced which results in reduction of stresses due to unequal expansion . If the boiler is fed with cold water it may result in chilling the boiler metal . Hot fed water checks it. Evaporative capacity of the boiler is increased. Overall efficiency of the plant is increased. Economiser

40. Waste Heat Boiler 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 40

41. Boiler Accessories Air Preheater Used to recover heat from the exhaust flue gases that rises the combustion air temperature Installed in between the economizer and chimney . Advantages Gives higher furnace temperature which results more heat transfer thus increase evaporative capacity . Approximately boiler efficiency increases about 2% for each 30-35 ° C rise in air temperature. 18-Sep-24 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 41

42. Boiler Accessories 42 Super heater Super heater is used for stationary boiler. The function of the super heater is to convert dry saturated steam into super heated at the desired temperature ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

43. Boiler Accessories 43 Boiler feed pumps are multistage radial flow pumps that feed water in the boiler against the boiler pressure ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

44. Boiler Accessories 44 Injector : function of the injector is the same as that of feed pump i.e.; to deliver feed water to boiler under pressure. Pressure reducing valve : the function of the pressure reducing valve is to maintain constant pressure on its delivery side of the valve irrespective of fluctuating demand of steam from the boiler. Steam Separator/Trap : the function of the steam separator/trap is to separate water particles from steam system ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

45. Boiler Capacity Evaporation or equivalent evaporation per hour may be taken as a measure of boiler capacity. It is generally measured in tons or kg per hour . Boiler load - the capacity of a steam boiler - is often rated as boiler horse powers, lbs of steam delivered per hour, or BTU. 45 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

46. Boiler Capacity Boiler Horsepower -  BHP : The Boiler Horsepower (BHP) is the amount of energy required to produce  34.5 pounds  of steam per hour or 15.65 k g of steam per hour at a temperature of  212 o F (100 o C) , with feedwater at 212 o F. A BHP is equivalent to  33,475 BTU/ hr or 9.81 kW and it should be noted that a boiler horsepower is  13.1547 times a normal horsepower. 46 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

47. Boiler Capacity Example - Boiler Horsepower to lbs of Steam Conversion 200 hp × 34.5 =  6900   lbs of steam per hour Lbs of steam can be converted to hp by dividing lbs steam per hour by 34.5 Example - Lbs of Steam to Boiler Horsepower Conversion 5000 lbs of steam / 34.5 =  145   hp boiler 47 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

48. Factors to be considered for selection of a boiler The working pressure and quality of steam required Steam generation rate Floor area available Accessibility for repair and inspection Comparative initial cost Erection facilities The probable load variation The fuel and water available Operating and maintenance costs 48 ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24

49. Assignment-01 49 A descriptive report on “Boiler Manufacturing Scenario in Bangladesh” mentioning all the details from manufacture to maintenance. ©Md. Abu Daud, Lec. Dept. of ME, BAUST 18-Sep-24