Steam boilers presentation slide_Ris.pptx

this slide is about boilers

1. Steam Boilers

2. Book Reference 2

3. Introduction 5 A steam generator or steam boilers is, usually, a closed vessel made of steel. Its function is to transfer the heat produced by the combustion of fuel (solid, liquid or gaseous) to the water and ultimately to generate steam. Use: To rotate turbine Cotton mills, Sugar factories etc. To produced hot water

4. Important terms 6 Boiler Shell: It is made of steel plates bent into cylindrical form and pivoted or welded together. A boiler shell should have sufficient capacity to contain water and steam. Combustion chamber: It is the space, generally below the boiler shell, meant for burning fuel in order to produce steam. Grate: It is a platform, in the combustion chamber, upon which fuel is burnt. Furnace: It is the space, above the grate and below the boiler shell, in which the fuel is actually burnt.

5. Important terms 7 Heating Surface: It is the part of boiler surface, which is exposed to the fire. Mountings: These are the fittings which are mounted on the boiler for its proper functioning. Such as water level indicator, pressure gauge, safety valve ete. Accessories: These are the devices, which form an integral part of the boiler, but are not mounted on it. Such as superheater, economiser, feed pump etc.

6. Essentials of a good steam boilers 8 Maximum quantity of steam with minimum fuel consumption Economical to install Able to meet the fluctuation of load Capable of quick starting Light in weight Occupy a small space Joints should be few and accessible for inspection Tubes should not accumulate soot or water deposit Comply with safety regulation

7. Selection of a steam boilers 9 The selection of type and size of steam boiler depends upon the following factors: Power required Rate of steam generation Geographical position Fuel and water available Type of fuel Probable permanency of the station Probable load factor

8. Classification of steam boilers 10 According to the contents in the tube: Fire tube boiler (ii) Water tube boiler According to the position of the furnace: Internally fired boiler (ii) Externally fired boiler According to the axis of the shell: Vertical boiler (ii) Horizontal boiler According to the number of tubes: Single tube boiler (ii) Multitubular boiler According to the method of circulation of water and steam: Natural circulation boiler (ii) Forced circulation boiler

9. Classification of steam boilers 11 According to the use: Stationary boiler (ii) Mobile boiler According to the source of heat: Solid fuel boiler Liquid fuel boiler Gaseous fuel boiler Hot waste gases boiler Electrical or nuclear fuel energy etc.

10. Simple vertical boiler 12

11. Simple vertical boiler 13

12. Locomotive boiler 14

13. Locomotive boiler 15

14. La- Mont boiler 16

15. Comparison between water tube and fire tube boiler Water tube boiler Fire tube boiler Water circulates inside the tube which are surrounded by hot gases Hot gases from furnace pass through the tube which are surrounded by water Generates steam upto 164 bar pressure Generates steam upto 24.5 bar pressure Generates steam upto 450 tonnes per hour Generates steam upto 9 tonnes per hour Overall efficiency with economiser 90% Overall efficiency with economiser 75% Preferred for wide fluctuating loads Not preferred for wide fluctuating loads High operating cost Low operating cost More bursting chance Less bursting chance Suitable for large power plant Not suitable for large power plant 17

16. Boiler Mountings and Accessories

17. Mountings These are the fittings which are mounted on the boiler for its proper and safe functioning. 19 - They are: Water level indicator Pressure gauge Safety valve Stop valve Blow off cock Feed check valve Fusible plug

18. Water level indicator 20 -

19. Pressure gauge 21 -

20. Pressure gauge 22 -

21. Safety valve 23 -

22. Safety valve 24 -

23. Steam stop valve 25 - Functions: To control the flow of steam from the boiler to the main steam valve To shut off the steam completely when required

24. Blow off cock 26 - Functions: To empty the boiler whenever required To discharge the mud, scale or sediments which are accumulated at the bottom of the boiler

25. Feed check valve 27 -

26. Feed check valve 28 -

27. Fusible plug 29 -

28. Fusible plug 30 -

29. Boiler Accessories 31 - These are the devices, which form an integral part of the boiler, but are not mounted on it. They are: Feed pump Superheater Economiser Air preheater

30. Schematic diagram of boiler 32 -

31. Feed pump 33 - In boiler, the water is continuously converted into steam which is used by the engine. Thus we need a feed pump to deliver the water to the boiler. A feed pump may be centrifugal or reciprocating type. The pressure of the feed water is 20% more than the boiler shell in order to deliver the water to the boiler.

32. Superheater 34 - Its purpose is to increase the temperature of saturated steam without rising its pressure. It is placed in the path of hot flue gases from the furnace. The heat given up by these flue gases, is used in superheating the steam

33. Economiser 35 - An economiser is a device used to heat feed water by utilizing the heat in the exhaust flue gases before leaving through the chimney. Advantages: 15 to 20% of coal saving Steam rising capacity is increased Formation of scale is prevented Reduced cost

34. Air preheater 36 - Air preheater is used to recover the heat from the exhaust flue gases. It is installed between the economiser and outlet of the chimney. The air is required for the purpose of combustion is drawn through the air preheater where its temperature is raised. Advantages: It gives higher furnace temperature It increases of about 2% in the boiler efficiency It results in better combustion It enables a low grade fuel to be burnt with less air.

35. Performance of steam boilers

36. Evaporation capacity 38 It is defined as the amount of water evaporated or steam produced in kg/h. It is also expressed in kg/kg of fuel burnt or kg/h/m² of heating surface.

37. Equivalent Evaporation It is the amount of water evaporated from feed water at 100° C and formed into dry and saturated steam at 100° C at normal atmospheric pressure. It is usually written as “from and at 100° C”. Equivalent evaporation “from and at 100° C”, The value of latent heat of water is 2257 KJ/Kg 39

38. Equivalent Evaporation 40 Let, t 1 = Temperature of feed water in °C h f1 = Enthalpy or sensible heat of feed water in KJ/Kg of steam corresponding to t 1 (from steam table) h= Enthalpy or total heat of steam in KJ/Kg of steam corresponding to a given working pressure (from steam table) = h f + x*h fg = h f + h fg = h g = h g + c p * (t sup - t) (For wet steam) (For dry saturated steam) (For superheated steam)

39. Equivalent Evaporation Let, m e = mass of water actually evaporated or steam produced in kg/h or kg/kg of fuel burnt. We know the heat is required to evaporate 1kg of water =h- h f1 So, the total heat is required to evaporate m e kg of water = m e (h- h f1 ) Equivalent evaporation “from and at 100° C”, The term is know as factor of evaporation . It is denoted by F e 41

40. Boiler Efficiency It is defined as the ratio of heat actually used in producing steam to the heat liberated in the furnace. It is also known as thermal efficiency of the boiler. Mathematically, boiler efficiency or thermal efficiency, Where, C = Calorific value of fuel in KJ/kg of fuel. If m s = Total mass of water evaporated into steam in Kg m f = Mass of fuel used in Kg 42

41. = Example 15.1: A boiler evaporates 3.6 kg of water per kg of coal into dry saturated steam at 10 bar. The temperature of feed water is 32° C. Find the equivalent evaporation “from and at 100° C” as well as the factor of evaporation. Solution: Given, m e = 3.6 Kg/Kg of coal; P= 10 bar; t 1 = 32° C From steam table, corresponding to a feed water temperature of 32° C, we find that h f1 =134 KJ/Kg And corresponding to steam pressure of 10 bar, we find that h= h g =2776.2 KJ/Kg (For dry saturated steam) So, the equivalent evaporation “from and at 100° C” = 3.6(2776.2-134)/2257= 4.2 Kg/Kg of coal. Factor of evaporation, F e = (2776.2-134)/2257= 1.17 43

42. Try yourself example 15.2, 15.3, 15.4, 15.5 44

43. Thanks to all