Boiler

In this slides we have discussed about boiler also condenser

1. UNIT II 12/31/2016 Jahangirabad institute of technology 1 By: Naphis ahmad Assistant professor JIT, Barabanki

2. STEAM GENERATOR OR BOILER 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. INTRODUCTION 12/31/2016 Jahangirabad institute of technology 2

3. BOILER PROPERTIES : ( i ) Safety. The boiler should be safe under operating conditions. (ii) Accessibility. The various parts of the boiler should be accessible for repair and maintenance. (iii) Capacity. Should be capable of supplying steam according to the requirements. 12/31/2016 Jahangirabad institute of technology 3

4. (iv) Efficiency. Should be able to absorb a maximum amount of heat produced due to burning of fuel in the furnace. (v) It should be simple in construction . (vi) Its initial cost and maintenance cost should be low. (vii) The boiler should have no joints exposed to flames. (viii) Should be capable of quick starting and loading. 12/31/2016 Jahangirabad institute of technology 4

5. Generate maximum steam. Light in weight and not occupy large space . Proper safety regulations. Cheaper in cost . Easy cope up with fluctuating demands of requirements. Easily accessible for inspection and repair. Requirements of a boiler 12/31/2016 Jahangirabad institute of technology 5

6. The source of heat for a boiler are : Wood Coal Diesel Natural Gas Nuclear Energy FUEL 12/31/2016 Jahangirabad institute of technology 6

7. Though there are many classifications of steam boilers, yet the following are important. ACCORDING TO THE CONTENTS IN THE TUBE: fire tube or smoke tube boiler water tube boiler. Classification Of Steam Boilers 12/31/2016 Jahangirabad institute of technology 7

8. FIRE – TUBE BOILERS 12/31/2016 Jahangirabad institute of technology 8

9. WATER TUBE BOILERS 3 12/31/2016 Jahangirabad institute of technology 9

10. ACCORGING TO POSITION OF FURNACE: Internally fired boilers Externally fired boilers ACCORDING TO AXIS OF FURNACE: Vertical boilers Horizontal boilers ACCORDING TO NUMBER OF TUBES: Single tube boilers Multi tube boilers 12/31/2016 Jahangirabad institute of technology 10

11. ACCORDING TO METHOD OF CIRCULATION OF WATER: Natural circulation boilers Forced circulation boilers ACCORDING TO THE USE Stationary boilers Mobile boilers 12/31/2016 Jahangirabad institute of technology 11

12. Following factors should be considered Quality of steam required Steam Generation rate Accessibility of repair and inspection Area Cost Erection facility Fuel and Water available FACTORS AFFACTING TO SELECTION OF BOILER 12/31/2016 Jahangirabad institute of technology 12

13. Boiler shell Combustion chamber Furnace Grate Heating surface Mounting Accessories COMPONENTS OF A BOILER 12/31/2016 Jahangirabad institute of technology 13

14. Pressure Gauge Water level indicator Safety valve Fusible plug Blow of cock Steam stop valve Feed check valve BOILER MOUNTINGS 12/31/2016 Jahangirabad institute of technology 14

15. Air preheater : It utilize the heat of exhaust gases. Economizer: Heat is used to raise the temperature of feed water supplied to the boiler. Steam super heater: Used to super heat the steam. Feed pump: Raise the pressure of water and force it into the boiler. Injector: Used to feed water in boilers. BOILER ACCESSORIES 12/31/2016 Jahangirabad institute of technology 15

16. SIMPLE VERTICLE BOILER 4 12/31/2016 Jahangirabad institute of technology 16

17. COCHRAN BOILER 5 12/31/2016 Jahangirabad institute of technology 17

18. Considered to be one of the most efficient type multi tubular boilers. Consists of external cylindrical shell and fire box. The shell and fire box both are hemispherical. The fire box and combustion chamber is connected through a short pipe. The flue gases from the combustion chamber flow to the smoke box through a number of smoke tubes. WORKING OF COCHRAN BOILER 12/31/2016 Jahangirabad institute of technology 18

19. The gases from the smoke box pass to the atmosphere through a chimney The external diameter of pipe is 62.5mm and are 165in number. Manhole is provided for cleaning . WORKING OF COCHRAN BOILER 12/31/2016 Jahangirabad institute of technology 19

20. LANCASHIRE BOILER 6 12/31/2016 Jahangirabad institute of technology 20

21. The boiler consists of a long cylindrical external shell (1) built of steel plates in sections riveted together. It has two large internal flue tubes (2). A fire grate (3) is also called furnace is provided at one end of the flue tubes on which solid fuel is burnt. At the end of the fire grate there is a brick arch (5) to deflect the flue gases upwards. The hot flue gases leaving internal flue tubes passes through the bottom tube(6). LANCASHIRE BOILER 12/31/2016 Jahangirabad institute of technology 21

22. These flue gases move to the front of the boiler where they divide and flow into side tube (7). The flue gases then enter the main flue (9) which leads them to chimney. The damper (8) is fitted at one side flues to control the draught and thus regulate the rate of generation of steam. A spring loaded safety valve (10) and stop valve (11) are mounted. LANCASHIRE BOILER 12/31/2016 Jahangirabad institute of technology 22

23. Locomotive boiler is a horizontal fire tube type mobile boiler. The main requirement of this boiler is that it should 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 a rapid rate. In order to provide the large heating surface area, a large number of fire tubes are setup and heat transfer rate is increased by creating strong draught by means of steam jet LOCOMOTIVE BOILER 12/31/2016 Jahangirabad institute of technology 23

24. LOCOMOTIVE BOILER 7 12/31/2016 Jahangirabad institute of technology 24

25. Large rate of steam generation per square metre of heating surface. To some extent this is due to the vibration caused by the motion. It is free from brickwork, special foundation and chimney. This reduces the cost of installation. It is very compact. The pressure of the steam is limited to about 20 bar. ADVANTAGES 12/31/2016 Jahangirabad institute of technology 25

26. BABCOCK AND WILCOX BOILER 8 12/31/2016 Jahangirabad institute of technology 26

27. This is an example of water tube boiler and is used in stationary and marine engine. The efficiency of this boiler is much greater than that of the fire tube boiler. This boiler is used when pressure is above 10bar and steam generating capacity is required higher then 7000kg/hr. 12/31/2016 Jahangirabad institute of technology 27

28. SAFETY MOUTINGS Safety valves (2 Nos ) Fusible plug Control mountings Water level indicator Pressure Gauge Blow of cock Steam stop valve Feed check valve Inspection Mountings Man hole Mud hole BOILER MOUNTINGS 12/31/2016 Jahangirabad institute of technology 28

29. Air preheater : It utilize the heat of exhaust gases. Economizer: Heat is used to raise the temperature of feed water supplied to the boiler. Steam super heater: Used to super heat the steam. Feed pump: Raise the pressure of water and force it into the boiler. Injector: Used to feed water in boilers. BOILER ACCESORIES 12/31/2016 Jahangirabad institute of technology 29

30. Air preheater BOILER ACCESORIES 9 12/31/2016 Jahangirabad institute of technology 30

31. Economizer BOILER ACCESORIES 10 12/31/2016 Jahangirabad institute of technology 31

32. Draught is defined as “the pressure difference (between absolute gas pressure at any point in a gas flow passage and the atmospheric air outside the boiler) required to maintain flow of air and exhaust gases through the boiler setting.” Function of draught: To supply required quantity of air to the boiler furnace for the combustion of fuel. To remove exhaust gases from the boiler passage to maintain flow of air and gases. To create pressure difference against pressure losses in the flow passage. To discharge the exhaust gases such that they will not be objectionable or injurious to the surroundings. Draught 12/31/2016 Jahangirabad institute of technology 32

33. Classification of Draught 12/31/2016 Jahangirabad institute of technology 33

34. It produces draught which required to force air and gases through the furnace, boiler accessories & setting. It carries the product of combustion to such a height that they will not be objectionable or injurious to surrounding. The chimney is vertical tabular structure build either of masonry concrete or steel. The draught produces by the chimney is due to density difference between the column of hot gases inside the chimney & cold air outside the chimney & also on the height of the chimney above the level of the furnace grate. The density difference depends on the temperature of flue gases passing in chimney & temperature of atmospheric air. Natural draught 12/31/2016 Jahangirabad institute of technology 34

35. Estimate the height & diameter of chimney Natural Draught Natural Draught = Difference of pressure due to cold air column and hot gas column 12/31/2016 Jahangirabad institute of technology 35

36. Suppose, T = Absolute Zero Temperature = 273 K = Density of air at absolute temperature = 1.293 T g = Temperature of hot gas = Density of hot gas Now from PV = m R T P = R T Density of air at temp. Tg   12/31/2016 Jahangirabad institute of technology 36

37. We know that (Where,   12/31/2016 Jahangirabad institute of technology 37

38. So, Density = Pressure of Hot Gases in Chimney at Grate level = g H Pressure due to Cold air (outside) column at Grade level   12/31/2016 Jahangirabad institute of technology 38

39. So, (Where, =1.293 * 273 = 353) Now, We Know that = m of gas   12/31/2016 Jahangirabad institute of technology 39

40. = mm of water Now, Hot Gas Velocity in Chimney (where h g = hot gas column h f = loss due to friction)   12/31/2016 Jahangirabad institute of technology 40

41. For max. discharge diff. w.r.t Tg & equate zero The condition for max. discharge will be   12/31/2016 Jahangirabad institute of technology 41

42. Where, T 2 = Temp. in artificial draught In Chimney draught, the efficiency if always less than 1%   Efficiency of Chimney 12/31/2016 Jahangirabad institute of technology 42

43. Chimney draught does not require any external power to produce draught. Simple in construction, less cost& has long life. No mechanical parts & hence maintenance cost is negligible. Chimney keeps flue gases at a high place in the atmosphere which prevents contamination of atmosphere & maintains the cleanliness. Advantages 12/31/2016 Jahangirabad institute of technology 43

44. The draught produced by chimney depends on height of chimney, atmospheric air tem & tem of flue gases leaving through the chimney. Hence in order to get appropriate draught at given height off chimney, the flue gases have to be discharged at comparatively high temp resulting in the reduction in overall efficiency of plant. The maximum pressure available for producing natural draught by chimney is hardly 10 to 20 mm of water. Draught created by chimney is dependent on atmospheric air &flue gases conditions, hence there is no flexibility to create more draught under peak load conditions because draught available is constant for given height of chimney. Due to low velocity of air, the mixing process of air & fuel is not proper & hence combustion is very poor. This increases the specific fuel combustion of boiler. Limitations 12/31/2016 Jahangirabad institute of technology 44

45. Steam super heater BOILER ACCESORIES 11 12/31/2016 Jahangirabad institute of technology 45

46. Evaporative capacity Equivalent evaporation Factor of evaporation Boiler efficiency BOILER PERFORMENCE 12/31/2016 Jahangirabad institute of technology 46

47. Ability to evaporate water. Generally it is expressed in terms of Kg of steam/hour Kg of steam /hour/area of heating surface Kg of steam/kg of fuel is fired 1. Evaporate capacity 12/31/2016 Jahangirabad institute of technology 47

48. It can be defined as the amount of water evaporated from water at 100 deg C to dry and saturated steam at 100 deg C. Simply it means that the capacity of boiler to generate same evaporation. 2. Equivalent evaporation 12/31/2016 Jahangirabad institute of technology 48

49. Ratio of heat received by 1kg water under working condition to that received by 1kg of water evaporated from and at 100deg C. Fc =h- h f / 2257 3. Factor of evaporation 12/31/2016 Jahangirabad institute of technology 49

50. Ratio of heat utilized to the heat supplied. Efficiency= ma ( h – hf )/c Where ma=mass of water actual evaporated to the system C= calorific value to the fuel hf =enthalpy of water at given feed temp. h=enthalpy of fuel. 4. Boiler efficiency 12/31/2016 Jahangirabad institute of technology 50

51. Condenser is a device in which steam is condensed to water at a pressure less than atmosphere. Condensation can be done by removing heat from exhaust steam using circulating cooling water. During condensation, the working substance changes its phase from vapour to liquid and rejects latent heat. The exhaust pressure in the condenser is maintaned nearly 7 to 8 kpa which corresponds to condensate temperature of nearly 313 kelvin. 12/31/2016 Jahangirabad institute of technology 51 Steam Condenser and it’s types Definition:

52. To reduce the turbine exhaust pressure so as to increase the specific output and hence increase the plant efficiency and decrease the specific steam consumption . To condense the exhaust steam from the turbine and reuse it as pure feed water in the boiler. Thus only make up water is required to compensate loss of water Enables removal of air and other non condensable gases from steam. Hence improved heat transfer. 12/31/2016 Jahangirabad institute of technology 52 Functions of Condenser :

53. Condenser Air Extraction Pump Condensate Extraction Pump Cooling Water Circulating Pump Hot Well Cooling Tower Make up Water Pump Boiler Feed Pump 12/31/2016 Jahangirabad institute of technology 53 Elements of Condensing Plant :

54. 12/31/2016 Jahangirabad institute of technology 54

55. It increases the work output per kg of steam supplied to the power plant. It also reduces the specific steam consumption, therefore reduces the size of power plant of given capacity. It improves the thermal efficiency of the power plant. It affects the saving in cost of water to be supplied to the boiler since the condensate is returned to the boiler. Cost of water softening plant is also reduced since pure feed water is available for the boiler. 12/31/2016 Jahangirabad institute of technology 55 Advantage of a Condenser

56. According to the type of flow : Parallel flow , Counter flow & Cross flow According to the Cooling Action: Jet Condensers or mixing type Low Level Parallel Flow Jet Condenser Low Level Counter Flow Jet Condenser High Level Jet Condenser Ejector Jet Condenser Surface Condensers or Non-mixing type Down Flow 2. Central Flow 3. Inverted Flow 4. Evaporative type 5. Regenerative type 12/31/2016 Jahangirabad institute of technology 56 Classification of Condensers:

57. In jet condensers exhaust steam and cooling water come in direct contact and mix up together. Thus, the final temperature of condensate and cooling water leaving the condenser is same. Such condensers are normally used for small power units. It can be used when cooling water is cheaply and easily available. These condensers are not usually employed since the Condensate collected can not be reused in boiler, because it contains impurities like dust, oil, metal particles etc in the condensate. 12/31/2016 Jahangirabad institute of technology 57 Jet Condensers

58. Exhaust steam and cooling water both flow in the same direction. Wet air pump is used to extract the mixture of condensate, air & coolant. This limits the vacuum created in the condenser up to 600 mm of Hg. 12/31/2016 Jahangirabad institute of technology 58 Low Level Parallel Flow Jet Condenser

59. The cooling water is supplied from the top of the condenser and steam from side of the condenser. The water flows in downward direction through a series of perforated trays. Steam gets condensed while it comes in contact with the falling water. The air pump always maintains the required vacuum in the condenser and induces the cooling water to be lifted into the condenser up to a height of 5.5m. The excess amounts of condensate from hot well flows into the cooling pond by an overflow pipe . 12/31/2016 Jahangirabad institute of technology 59 Low Level Counter Flow Jet Condenser:

60. Condenser shell is installed at height greater than that of atmospheric pressure in water column i.e. 10.33 m. A tall pipe more than 10.33m length is attached to the bottom of the condenser. This allows the condensate and coolant to be discharged from condenser under the gravity action; hence a condensate extraction pump is not required. The water from the hot well will not be able to rise into the condenser and flood the turbine due to vacuum pr. Maintained in condenser. 12/31/2016 Jahangirabad institute of technology 60 High Level Jet Condenser or Barometric jet condenser

61. In this cooling water enters from the top of the condenser at least under a head of 6m of water pressure with the help of a centrifugal pump and then it passes over a series of convergent nozzles and finally it leaves through a convergent divergent nozzle. The non return valve helps in preventing the rush of water from hot well to the engine in case the cooling water supply fails. Momentum of flowing water is used to remove the mixture of condensate & coolant from condenser without the use of any extraction pump. 12/31/2016 Jahangirabad institute of technology 61 Ejector Condenser:

62. Advantages: Simple in design & cheaper. Less floor area is required. Disadvantages: Condensate is not pure hence can not be reused. Low vacuum efficiency. 12/31/2016 Jahangirabad institute of technology 62 Advantages & Disadvantages of Jet Condensers:

63. In surface condenser, the exhaust steam and cooling water do not come in physical contact, rather they are separated by heat transfer wall. Hence condensate remains pure & can be reused. 12/31/2016 Jahangirabad institute of technology 63 Surface Condensers

64. Exhaust steam enters the top of condenser shell & flows downward over water tubes. Water tubes are double passed. The cold water flows in lower side first & then in upper side in the reverse direction, which enables the maximum heat transfer. 12/31/2016 Jahangirabad institute of technology 64 Down Flow Surface Condenser :

65. The steam flows radially inward The condensate is collected at the bottom of the shell from where it is taken out by the condensate extraction pump. The steam gets access to the entire periphery of tubes, and thus a large surface area for the hear transfer is available as compared to the down flow. 12/31/2016 Jahangirabad institute of technology 65 Central Flow Surface Condenser

66. The steam enters the bottom of the shell and air extraction pump connected at the top. Steam flows upward first and subsequently, returns to the bottom of the condenser. The condensate extraction pump is connected at the bottom of the shell to extract the condensate. 12/31/2016 Jahangirabad institute of technology 66 Inverted Flow Condenser:

67. The evaporation of some cooling water provides the cooling effect, thereby steam condenses. Steam to be condensed is passed through grilled tubes & cooling water is sprayed over outer surface of tubes. The evaporative condensers are most suitable for small plants, where supply of cold water is limited. 12/31/2016 Jahangirabad institute of technology 67 Evaporative Condenser:

68. Advantages: High vacuum efficiency. Pure condensate. Low quality cooling water can be used. It allows the expansion of steam through a higher pressure ratio. Disadvantages: Large amount of water is required. Construction is complicated. Costly maintenance and skilled workers. Large floor area. 12/31/2016 Jahangirabad institute of technology 68 Advantages & Disadvantages of Surface Condensers:

69. Comparison of Jet & Surface Condensers : Jet Condensers Surface Condensers Cooling water and steam are mixed up Requires small floor space The condensate cannot be used as feed water to boiler unless it is free from impurities More power is required for air pump Less power is required for water pump Requires less quantity of cooling water The condensing plant is simple Less suitable for high capacity plants due to low vacuum efficiency Cooling water & steam aren’t mixed up Requires large floor space The condensate can be used as feed water to boiler as it is not mixed with cooling water Less power is required for air pump More power is required for water pump Requires large quantity of cooling water The condensing plant is complicated More suitable for high capacity plants as vacuum efficiency is high 12/31/2016 Jahangirabad institute of technology 69

70. The ambient air leaks to the condenser chamber at the joints & glands which are internally under pressure lower than that of ambient. Another source of air is the dissolved air with feed water. The dissolved air in feed water enters into boiler and it travels with steam into condenser. Effects of Air Leakage: The presence of air lowers vacuum in the condenser. Thus back pressure of the plant increases, and consequently, the work output decreases. Air has very poor thermal conductivity. Hence, the rate of heat transfer from vapour to cooling medium is reduced. The presence of air in the condenser corrodes to the metal surfaces. Therefore, the life of condenser is reduced. 12/31/2016 Jahangirabad institute of technology 70 Sources of Air in the Condenser:

71. When the steam condenses in a closed vessel, the vapour phase of working substance changes to liquid phase, and thus its specific volume reduces to more than one thousand times . Due to change in specific volume, the absolute pressure in the condenser falls below atmospheric pressure and a high vacuum is created. This minimum pressure that can be attained depends on the temperature of condensate and air present in the condenser. The absolute pressure = Atmospheric pressure – Vacuum Gauge in the condenser Pressure 12/31/2016 Jahangirabad institute of technology 71 Vacuum Creation in Condenser:

72. Lowering the condenser pressure will increase the area enclosed by the cycle on a T-s diagram which indicates that the net work will increase. Thus, the thermal efficiency of the cycle will be increased Lowering the back pressure causes an increase in moisture content of steam leaving the turbine. Increase in moisture content of steam in low pressure stages, there is decrease in efficiency & erosion of blade may be a very serious problem and also the pump work required will be high. 12/31/2016 Jahangirabad institute of technology 72 Effect of Condenser Pressure on Rankine Efficiency: