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  1. 1. Unit II Fuels and Lubricants 1 diesel coal LPG plastic Waste of plastic
  2. 2. Fuels Fuel is a combustible substance which on proper burning gives large amount of heat, which can be used economically for domestic and Industrial purposes. Examples are wood, coal, petrol Fuel + O2 Products + heat Reference Jain and Jain, 16th edition Page 55 2
  3. 3. Classification of fuels Reference Jain and Jain, 16th edition Page 55 3
  4. 4. Peat (decomposed vegetable matter ) Lignite (brown coal) Natural gas Coke 4
  5. 5. Characteristics of Good Fuel  Suitability: The fuel selected should be most suitable for the process. E.g., coke made out of bituminous coal is most suitable for blast furnace.  High Calorific value  Ignition Temperature: A good fuel should have moderate ignition temperature.  Moisture content: Should be low  Non combustible matter content  Velocity of combustion: It should be moderate  Nature of the products  Cost of fuel, Smoke, Control of the process
  6. 6. the amount of energy required to warm one gram of air-free water from 15 to 16 °C at standard atmospheric pressure. Experimental values of this calorie ranged from 4.1852 J to 4.1858 J. Fuels and Combustion Calorie: Kilocalorie: is equal to 1000 calories. This is the amount of energy required to warm one kilogram of air-free water from 15 to 16 °C at standard atmospheric pressure.. Units of heat 6
  7. 7. British Thermal Unit: the amount of heat required to raise the temperature of one pound (0.45359237 kilograms) of water through one degree Fahrenheit (60-61 °F). Experimental values of 1 B.Th.U.=252cal Fuels and Combustion Centigrade heat unit (C.H.U.) the amount of heat required to raise the temperature of one pound of water through one degree centigrade. 1Kcal=3.968B.Th.U=2.2C.H.U. Units of heat 7
  8. 8. CH4 + 2O2 CO2 + 2H2O steam is the total amount of energy produced, when unit mass/volume of the fuel has been burnt completely, and the products of combustion have been cooled to room temperature (15 ⁰C) Higher or gross calorific value: Fuels and Combustion Reference Jain and Jain, 16th edition Page 56 Cooled to 15 ⁰C and more energy is released in the process 8
  9. 9. is the net heat produced, when unit mass/volume of the fuel has been burnt completely and the products of combustion are permitted to escape. LCV=HCV – Latent heat of water formed =HCV – mass of hydrogen x 9 x Latent heat of steam Latent heat of steam at room temperature is 587kcal/Kg Fuels and Combustion Lower or net calorific value (LCV): Reference Jain and Jain, 16th edition Page 56 CH4 + 2O2 CO2 + 2H2O steam 9
  10. 10. Reference Jain and Jain, 16th edition Page 58 Bomb Calorimeter 10 O2 pressure is 25atm
  11. 11. 11 • Flame temperatures of magnesium and magnesium alloys can reach 3,100 °C (5,610 °F) • Beckmann thermometer can estimate temperature changes to 0.01 °C
  12. 12. Mass of fuel = x gm HCV of the fuel = L cal/gm Heat liberated by burning of x gm of fuel = xL cal (1) Mass of water in calorimeter = W gm Water equivalent of the calorimeter in gram = w Initial temperature of water in calorimeter = t1 Final temperature of water in calorimeter = t2 Heat absorbed by water and apparatus = (W+w)(t2-t1) (2) xL = (W+w)(t2-t1) from (1) and (2) Bomb Calorimeter L= (W+w)(t2-t1)/x cal/gm 12
  13. 13. LCV = L – 0.09H*587 cal/gm Corrections a) Fuse wire correction b) Acid correction, tA c) Cooling Correction, tC d) Cotton thread correction, tT (W+w)(t2-t1) x HCV or L= cal/g (W+w)(t2-t1+tC)-[tA+tF+tT] x L= cal/g Bomb Calorimeter 13
  14. 14. In a reaction the quantity of heat that raises the temperature of some substance/body by some amount, the same quantity of heat can simultaneously raise the same temperature of a certain mass of water. The mass of water is then termed as water equivalent. The amount of water which has the same heat capacity as that of the body/substance. body q t t Water Equivalent of Calorimeter: Bomb Calorimeter 14
  15. 15. Dulong’s formula Theoretical calculations of calorific value where C, H, O, S refer to % of carbon, hydrogen, oxygen and sulphur respectively. 1 100 8080*C + 34500(H- ) + 2240*S O 8 HCV = Kcal/kg LCV= HCV – 0.09*H*587 , kcal/kg 15
  16. 16. Numerical 1 Calculate the gross and net calorific values of coal having the following Compositions Carbon=85%, Hydrogen=8%, Nitrogen=2%, ash=4%, Sulphur= 1%, Latent heat of steam=587cal/g 1 100 8080*C + 34500(H - ) + 2240*S O 8 GCV or HCV = Kcal/kg 1 100 8080*85 + 34500(8 - ) + 2240*1 0 8 HCV = Kcal/kg HCV = 9650.4 kcal/kg NCV = HCV- 0.09*H*587 kcal/kg = 9650.4 - 0.09*8*587 = 9227.8 kcal/kg Reference Jain and Jain, 16th edition Page 99 16
  17. 17. Numerical 2 0.72g of a fuel containing 80% carbon, when burnt in bomb calorimeter, increased the temperature of water from 27.3 to 29.1 ⁰C. if the calorimeter Contains 250g of water and its water equivalent is 150g, calculate the HCV of the fuel. Give your answer in kJ/Kg. X=0.72g, W=250g, w=150g, t2=29.1 ⁰ C, t1=27.3 ⁰C (W+w)(t2-t1) x L= cal/g (250+150)(29.1-27.3) 0.72 HCV= cal/g HCV= 1000*4.2 J/g or kJ/kg =4200 kJ/kg Reference Jain and Jain, 16th edition Page 99 17
  18. 18. Coal Coal is a highly carbonaceous matter that has been formed as a result of alteration of vegetable matter (e.g. plants) under certain favorable conditions. It is chiefly composed of C, H, N and O, besides non-combustible inorganic matter Reference Jain and Jain, 16th edition Page 63 18
  19. 19. Cellulose lignin Constituents of wood 19
  20. 20. Classification of Coal Various types of coal commonly recognized on the basis of rank Or degree of alteration or coalification from the parent material, wood are: Wood Peat Lignite Bituminous coal Anthracite This progressive transformation of wood to anthracite results in 1. Decrease in moisture content 2. Decrease in H, N, O, and S content with a corresponding increase in C content 3. Decrease in volatile content 4. Increase in calorific value 5. Increase in hardness 20
  21. 21. Classification of Coal 1. Peat: is a fibrous jelly like mass. It is regarded as the first stage in the coalification of wood. It is uneconomical fuel, It may contain as much as 80-90% of water but on air-drying , it burns freely. Its calorific value is about 5400kcal/kg (on air-dry basis). 2. Lignite (brown coal): are soft brown colored variety of lowest rank coal which consists of vegetable matter decomposed more that in peat Lignite is compact in texture, containing 20-60% moisture and on air-drying, it breaks up into small pieces. The calorific value is about 6500-7100 kcal/kg 21
  22. 22. Classification of Coal 3. Bituminous coal: are pitch-black to dark-grey coals, which usually soil hands. They show a laminated structure of alternate very bright and dull layers. Its calorific value on ash-free basis is about 8000-8500Kcal/kg. 4. Anthracite: is the highest rank coal, containing highest percentage of carbon (92-98%) and has the lowest volatile matter and moisture contents. They are hardest of all kinds of coals, quite dense and lustrous in appearance. The calorific value is about is about 8600-8700 Kcal/kg 22
  23. 23. 1. Proximate analysis parameters include moisture, volatile matter, ash, and fixed carbon. It provides valuable information in assessing the quality of coal. Coal analysis 2. Ultimate analysis which is more comprehensive, is dependent on quantitative analysis of various elements present in the coal sample, such as carbon, hydrogen, sulfur, oxygen, and nitrogen Reference Jain and Jain, 16th edition Page 66 23
  24. 24. 1.1 Moisture is an important property of coal, as all coals are mined wet. Groundwater and other extraneous moisture is known as adventitious moisture and is readily evaporated. Moisture held within the coal itself is known as inherent moisture and is analyzed quantitatively. Percentage of moisture = Loss in weight Weight of coal taken * 100 (1) 1. Proximate analysis 1g of finely powdered air-dried coal sample is taken in a crucible and heated for 1hour inside a hot air oven maintained at 105- 110⁰C. The sample is then cooled in a desiccator and weighed. Loss in weight is reported as moisture Reference Jain and Jain, 16th edition Page 66 24
  25. 25. 1.2 Volatile matter in coal refers to the components of coal, except for moisture, which are liberated at high temperature in the absence of air. This is usually a mixture of short and long chain hydrocarbons, aromatic hydrocarbons and some sulfur The dried sample of coal in (1) is then covered with a lid and placed in an electric furnace (muffle furnace) , maintained at 925 ± 20 ⁰C. the crucible is then taken out of the oven after 7 minutes of heating. The crucible is first cooled in air then in desiccator and loss of weight is measured 1. Proximate analysis Reference Jain and Jain, 16th edition Page 66 % of volatile matter = Loss in weight due to removal of volatile matter *100 Weight of coal taken (2) 25
  26. 26. 1.3 Ash content of coal is the non-combustible residue left after coal is burnt. It represents the bulk mineral matter after carbon, oxygen, sulfur and water (including from clays) has been driven off during combustion. The residual coal in the crucible (2) is then heated without a lid in a muffle furnace at 700±50 ⁰C for 30 minutes. The crucible is taken out cooled in air first, then in desiccator and weighed. Heating, cooling and weighing is repeated till a constant weight is obtained. Percentage of ash = weight of ash left Weight of coal taken * 100 1. Proximate analysis Reference Jain and Jain, 16th edition Page 66 26
  27. 27. 1.4 Fixed carbon: The fixed carbon content of the coal is the carbon found in the material which is left after volatile materials are driven off. This differs from the ultimate carbon content of the coal because some carbon is lost in hydrocarbons with the volatiles. Fixed carbon is used as an estimate of the amount of coke that will be yielded from a sample of coal. Fixed carbon is determined by removing the mass of volatiles determined by the volatility test, above, from the original mass of the coal sample. Fixed carbon = 100 – % of (moisture + volatile matter + ash) 1. Proximate analysis Reference Jain and Jain, 16th edition Page 66 27
  28. 28. Importance of proximate analysis 1.1 Moisture: lowers the effective calorific value of the coal Quenches the fire in furnace Increase the transportation charges 1.2 Volatile matter: Large proportion of volatile matter escapes without burning Decreases the calorific value Increases the flame size 1.3 Ash: Useless, non combustible matter which reduces the calorific value of coal Causes hindrance to flow of air and heat, therby lowering the temperature It forms clinker, which block the interspaces of the grate. Increases the transportation charges Wear of furnace walls and burning apparatus 1.4 Fixed carbon: Higher the percentage of fixed carbon, greater is its calorific value and better the quality of coal. Reference Jain and Jain, 16th edition Page 66 28
  29. 29. 2. Ultimate analysis It involves the analysis of C, H, N, S, O and ash 2.1 Carbon and Hydrogen:. Reference Jain and Jain, 16th edition Page 67 29 Fig. Estimation of carbon and hydrogen
  30. 30. 2. Ultimate analysis It involves the analysis of C, H, N, S, O and ash 2.1 Carbon and Hydrogen: about 1-2g of accurately weighed coal sample is burnt in a current of oxygen in a combustion apparatus. C and H of the coal are converted CO2 and H2O respectively. The gaseous products of combustion are absorbed respectively in KOH and CaCl2 tubes of known weights. The increase in weights is measured and percentage of C and H is determined. Percentage of C = increase in weight of KOH tube * 12 * 100 Weight of coal sample taken * 44 Reference Jain and Jain, 16th edition Page 67 C + O2 CO2 12 44 2KOH + CO2 K2CO3 + H2O 30
  31. 31. Percentage of H = increase in weight of CaCl2 tube * 2 * 100 weight of coal sample taken * 18 2. Ultimate analysis Reference Jain and Jain, 16th edition Page 67 2.1 Hydrogen H2 + ½ O2 H2O CaCl2 + 7H2O CaCl2.7H2O 31
  32. 32. 2. Ultimate analysis 2.2 Nitrogen: Reference Jain and Jain, 16th edition Page 67 32 Fig. Estimation of nitrogen by Kjeldahl’s method
  33. 33. 2. Ultimate analysis 2.2 Nitrogen: About 1g of accurately weighed powdered coal is heated with concentrated H2SO4 along with K2SO4 (catalyst)in a long necked flask (called Kjeldahl’s flask). After the solution becomes clear, it is treated with excess KOH and the liberated ammonia is distilled over and absorbed in a known volume of standard acid solution. The unused acid is then determined by back titration with standard acid solution. The consumed acid is related to N in coal as follows Percentage of N = Volume of the acid used(ml) * Normality * 1.4 weight of coal sample taken Reference Jain and Jain, 16th edition Page 67 33
  34. 34. 34 2. Ultimate analysis Step1. The sample is first digested in strong sulphuric acid in the presence of catalyst 1. Nitrogenous organic compound + concH2SO4 (NH4)2SO4 2. (NH4)2SO4 + 2NaOH 2NH3 + Na2SO4 + 2H2O 3. NH3 + HCl NH4Cl + HCl (left back)
  35. 35. Ultimate analysis 2.3 Sulphur: is determined from the washings obtained from a known mass of coal, used in a bomb calorimeter for determination of a calorific value. During this determination, S is converted into sulphate. The washings are treated with barium chloride solution and barium sulphate is precipitated. This precipitate is filtered, washed and heated to a constant weight. Percentage of S = weight of BaSO4 obtained * 32 * 100 weight of coal sample taken * 233 2.4 Oxygen: it is obtained by difference Percentage of O = 100 - % of ( C + H + S + N + ash) Reference Jain and Jain, 16th edition Page 67 35
  36. 36. Importance of ultimate analysis Reference Jain and Jain, 16th edition Page 68 1. Carbon and Hydrogen: greater is the percentage of of C and H, better is the coal in quality and calorific value. Higher % of C reduces the size of the combustion chamber required. 2. Nitrogen: has no calorific value and hence its presence is undesirable. 3. Sulphur: contributes to calorific value nevertheless it is undesirable as its combustion products (acids from SO2 and SO3) have harmful effects of corroding the equipment's and also cause atmospheric pollution. 4. Oxygen: it decreases the calorific value and also results in low coking power. 36
  37. 37. Numerical 1 Calculate the weight and volume of air required for the combustion Of 3kg of Carbon. Weight of C= 3kg, or 3000g Moles of C = 3000/12 = 250 Moles of O2 required = 250 1 mole of gas at NTP = 22.4 litre Therefore 250 mole of gas = 250*22.4 litre of O2 Since O2 is only 21% by volume, so volume of air = 250*22.4*100/21 = 2.67E4 litre Weight of air required = 3*32/12*100/23 = 34.783kg Reference Jain and Jain, 16th edition Page 101 C + O2 CO2 37
  38. 38. Numerical2 Calculate the mass of the air needed for the complete combustion of 5kg of coal in which C=80%, H=15% and O=5% C=4kg, H=0.75kg, O=0.25kg H2 + 1/2O2 H2O Weight of oxygen required = [4*32/12] + [0.75*16/2] - 0.25 = 16.42kg mass of air required = 16.416*100/23 = 71.37kg C + O2 CO2 12 32 2 16 Mass percentage of oxygen in air is 23 Reference Jain and Jain, 16th edition Page 102 38
  39. 39. Numerical 3: A coal sample was found to contain: C=66.2%, H=4.2%, O=6.1%, N= 1.4%, S=2.9%, moisture=9.7% and ash =9.5% by weight. Calculate the quantity of dry products of combustion, if 1kg of coal coal is burnt with 25% excess air. 1kg of coal contains: C=662g, H=42g, O=61g, N=14g, S=29g, moisture=97g and ash=95g Minimum wt of O required for complete combustion of 1Kg coal = 662g X 32/12 + 42 X 16/2 + 29 X 32/32 - 61= 2069.3g Minimum weight of air required=2069.3 X 100/23 = 8997g Wt of CO2=662g X 44/12 = 2427.3g Wt of SO2=29g X 64/32 = 58.0g Wt of N2= Minimum amount of airX(125/100)X(77/100) + in coal =8997g X 125/100X77/100 + 14 = 8763.6g Weight of excess O=minimum wt of O2 X (25/100) =2069.3 X 25/100 =517.3g Total wt of dry products=2427.3+58.0+8763+517.3 = 11765.9g Reference Jain and Jain, 16th edition Page 103 39
  40. 40. Note: Do practice of numerical from the reference books given in your syllabus 40
  41. 41. Petroleum Petroleum or crude oil is a dark greenish-brown, viscous oil found in deep earth’s crust. It is mainly composed of various hydrocarbons (like paraffin, cycloparaffins, naphthalenes, olefins and aromatics), together with small amount of organic compounds containing oxygen, nitrogen and sulphur. The oil is usually found floating upon a layer of brine and has layer of gas on top of it. The average composition of crude oil is C=79.5 – 87.1%, H=11.5 - 14.8%, S=0.1-3.5%, N and O= 0.1 – 0.5%. Reference Jain and Jain, 16th edition Page 72 41
  42. 42. Petroleum Reference Jain and Jain, 16th edition Page 73 Crude oil 42
  43. 43. Crude oil: A mixture of hydrocarbons 43
  44. 44. Separation of crude oil into useful fractions C1-C4 C5-C9 C10-C16 C10-C18 C17-C30 44 C5-C7
  45. 45. Fractional distillation of crude oil 45
  46. 46. Abundance of different fractions in crude oil 46
  47. 47. Classification of petroleum 1. Paraffin-base type crude is mainly composed of saturated hydrocarbons from CH4 to C35H72 and a little of the naphthalenes and aromatics The hydrocarbons from C18H38 to C35H72 are semi-solids, called waxes. 2. Asphaltic-base type crude contains mainly cycloparaffins or naphthalenes with smaller amount of paraffin and aromatic hydrocarbons octane naphthalene 47
  48. 48. Classification of petroleum 3. Mixed-base type crude contains both paraffinic and asphaltic hydrocarbons and are generally rich in waxes Reference Jain and Jain, 16th edition Page 73 48
  49. 49. 1. Gasoline or petrol is obtained between 40-120 ⁰C and is mixture of hydrocarbons such as C5H12 (pentane) to C8H18 (octane). Its approximate composition is: C=84%, H=15%, N+S+O=1%. Its calorific value is about 11,250kcal/kg. It is volatile, inflammable and used as a fuel for internal combustion engines. Important fractions of petroleum Reference Jain and Jain, 16th edition Page 75 49
  50. 50. 2. Diesel oil is fraction obtained between 250-320 ⁰C and is a mixture of C15H32 to C18H38 hydrocarbons. Its density is 0.86 to 0.95. Its calorific value is about 11,000kcal/kg and is used as diesel engine fuel. Important fractions of petroleum Reference Jain and Jain, 16th edition Page 75 50
  51. 51. Important fractions of petroleum 3. Lubrication oil: the length of the hydrocarbon chain varies between 12 to 50 carbon atoms. The shorter chain oil have lower viscosity than the longer chain hydrocarbons. These are most widely used as lubricants because they are cheap and quite stable under service condition . However they possess poor oiliness as compared to that of animal and vegetable oils. The oiliness of petroleum oils can be increased by the addition of high molecular weights compounds like oleic acid, stearic acid etc. 51
  52. 52. Abundance of different fractions in crude oil Less in demand More in demand Conversion by cracking 52
  53. 53. Cracking: Synthetic petrol The decomposition of bigger hydrocarbons molecules into simpler, low boiling hydrocarbons of lower molecular weight. C10H22 C5H12 + C5H10 cracking pentane pentene B.p=174 ⁰C B.p=36 ⁰C 53
  54. 54. Cracking: 1. Thermal cracking: the heavy oil are subjected to high temperature (~500 ⁰C) and pressure (~100kg/cm2), when the bigger hydrocarbons molecules break down to give smaller molecules of the paraffin, olefins plus some hydrogen. Synthetic petrol 54 Thermal Cracking Catalytic Cracking
  55. 55. Cracking: 1. Thermal cracking may be carried either in liquid-phase or vapor-phase 1.a) Liquid phase thermal cracking: the heavy oil is cracked at a suitable temperature of 475-530 ⁰C and under a pressure of 100 kg/cm2. The cracked products are then separated in a fractionating column. The yield is 50-60 %. 1.b) Vapor-phase thermal cracking: the cracking oil is first vaporized and then cracked at about 600-650 ⁰C and under a low pressure of 10-20kg/cm2. this process is suitable for those oils which may be readily vaporized. It requires less time than liquid-phase method. Synthetic petrol 55
  56. 56. Cracking: 2. Catalytic cracking: A suitable catalyst like aluminum silicate, Al2(SiO3)2 or alumina (Al2O3) is used to break the high molecular weight hydrocarbons. The use of catalyst reduces the required temperature (420-450 ⁰C) and pressure (1-5kg/cm2) of the cracking. The yield of the petrol is higher and quality of the petrol produced is better. Synthetic petrol 56 Advantages of Catalytic cracking: • The yield of petrol is higher • Quality of petrol is better • A much lower pressure is needed • The product contains less amount of sulphur • The product contains higher fraction of aromatic thus better antiknock characteristics
  57. 57. Synthetic petrol 2.a) Fixed bed catalytic cracking Reference Jain and Jain, 16th edition Page 77 57 Cracking: Zircomium oxide catalyst
  58. 58. Synthetic petrol Fixed bed catalytic cracking: the oil vapors are heated to cracking temperatures (420-450 ⁰C) and then forced through a catalytic chamber (containing artificial clay mixed with Zirconium oxide) maintained at (425-450 ⁰C)and 1.5Kg/cm2 pressure. During their passage through the tower, about 40%of the charge is converted to gasoline and about 2-4% carbon is formed. The later gets adsorbed on the catalyst bed. The vapors produced are then passed through a fractionating column, where heavy oil fractions condense. The vapors are then led a cooler, where some of the gases are Condensed along-with gasoline and uncondensed gases move on. The gasoline containing some dissolved gases is then sent to a stabilized where the dissolved gases are removed and pure gasoline is obtained. 58
  59. 59. 1. Polymerization: the gases obtained as a by-product from cracking of heavy oils, etc., contains olefins (like ethylene, propene and butenes) and alkanes (such as methane, ethane, propane and butane). When this gaseous mixture is subjected to high pressure and high temperature, with or without the presence of catalyst, it polymerises to form higher hydrocarbons, resembling gasoline, called polymer gasoline CH3CH=CH2 + CH3CH2CH=CH2 CH2=CHCH2CH2CH(CH3)2 Pressure, heat And/or catalyst (propene) (butane-1) 5-methyl hexane-1 Synthetic petrol 59
  60. 60. 1. Thermal polymerization in which polymerization of cracked gases is carried out at 500-600 ⁰C and 70-350 kg/cm2 pressure. The product is gasoline and gas oil mixture, which are separated by fractionation. 2. Catalytic polymerization is carried out in presence of catalyst like phosphoric acid. In this case lower temperature of 150-200 ⁰C is employed. Products are gasoline and unpolymerized gas. The later is separated and recycled for polymerization. The polymerization is of two types: Synthetic petrol 60
  61. 61. 2. Fischer-Tropsh method: The Fischer–Tropsch process involves a series of chemical reactions that produce a variety of hydrocarbons, ideally having the formula (CnH(2n+2)). The more useful reactions produce alkanes as follows: (2n + 1) H2 + n CO → CnH(2n+2) + n H2O where n is typically 10-20. The formation of methane (n = 1) is unwanted. Most of the alkanes produced tend to be straight-chain, suitable as diesel fuel. In addition to alkane formation, competing reactions give small amounts of alkenes, as well as alcohols and other oxygenated hydrocarbons. 2n H2 + n CO → CnH2n + n H2O Synthetic petrol 61
  62. 62. 2. Fischer-Tropsh method: Reference Jain and Jain, 16th edition Page 78 Synthetic petrol Fe2O3 + H2S → Fe2S3 + 3H2O removal of H2S Fe2S3 + 4O2 → 2FeO + 3SO2↑ 4FeO + O2 → 2Fe2O3 regeneration of catalyst Fe2O3 Na2CO3 removes organic sulphur compounds 62 Pressure 5-25atm Temperature 200-300 ⁰C
  63. 63. Working: water gas (CO+H2) is mixed with H2 and purified by passing through Fe2O3 (to remove H2S) and then into mixture of Fe2O3.Na2CO3 (to remove organo sulphur compounds). The purified gas is then compressed (~5-25 atm) and then led through a convertor ( containing catalyst) maintained at about 200-300 ⁰C. A mixture of saturated and unsaturated hydrocarbons are formed. (2n + 1) H2 + n CO → CnH(2n+2) + n H2O 2n H2 + n CO → CnH2n + n H2O The reaction is exothermic, so out coming gaseous mixture is led to a cooler, where the liquid resembling to crude oil is obtained which is then fractionated to give gasoline and high boiling heavy oil Reference Jain and Jain, 16th edition Page 78 2. Fischer-Tropsh method: Synthetic petrol 63
  64. 64. 3. Bergius process Reference Jain and Jain, 16th edition Page 79 Synthetic petrol 64 Pressure 200-250 atm Temperature 450 ⁰C Yield of gasoline is ~60% of the coal dust used
  65. 65. 3. Bergius process The low ash coal is finely powdered and made into a paste with heavy oil and then a catalyst (composed of tin or nickel oleate) is incorporated. The whole is heated with H2 at 450 ⁰C and under a pressure of 200-250atm for about 1.5 hours, during which H2 combines with coal to form saturated hydrocarbons, which decompose at prevailing temperature and pressure to yield low boiling liquid hydrocarbons. The issuing gases are led to condenser , where a liquid resembling crude is obtained, which is then fractionated to give (1) gasoline, (2) middle oil, (3) heavy oil. The heavy oil is again used for making paste with fresh coal dust. The middle oil is hydrogenated in vapor phase in the presence of catalyst to yield more gasoline. The yield of gasoline is about 60% of the coal dust used. Synthetic petrol Reference Jain and Jain, 16th edition Page 78 65
  66. 66. Numerical: A petrol sample contains 84% Carbon and 16% hydrogen by weight. Its flue gas compositional data by volume is as under: CO2=12.1%, CO=1.1%, Oxygen=1.3%, Nitrogen=85.5%. Calculate weight of minimum air needed for complete combustion of 1Kg of petrol. 1kg of petrol; C=840g, H=160g C + O2 CO2 12 32 H2 + 1/2O2 H2O 2 16 Wt of oxygen needed=160*16/2=1280g Total=3520g weight of minimum air needed for complete combustion of 1Kg of petrol=3520*100/23 =15304g Reference Jain and Jain, 16th edition Page 107 Wt of oxygen needed= 840*32/12=2240g 66
  67. 67. 67 A car without lubricant will explode in less than 15 minutes Lubricants and lubrication
  68. 68. Lubricants and lubrication Lubricants: Any substance introduced between two moving/sliding surfaces with a view to reduce the frictional resistance between them, is known as lubricant. The main purpose of lubricant is to keep the sliding/moving surfaces apart. Lubrication: the process of reducing frictional resistance between moving /sliding surfaces by the introduction of lubricants in-between them. 68 Reference Jain and Jain, 16th edition Page 428
  69. 69. Function of lubricants: 1. It reduces surface deformation, wear and tear, because the direct contact between the rubbing surfaces is avoided 2. It reduces the loss of energy in the form of heat 3. It reduces expansion of metal by local frictional heat. 4. It avoids seizure of moving surfaces 5. It reduces running and maintenance cost of the machine 6. It also sometimes acts as a seal 7. It avoids unsmooth relative motion 69 Reference Jain and Jain, 16th edition Page 428
  70. 70. 70 Mechanism of lubrication 1. Fluid-film or thick-film or hydrodynamic lubrication: Reference Jain and Jain, 16th edition Page 428
  71. 71. 71
  72. 72. Mechanism of lubrication 1. Fluid-film or thick-film or hydrodynamic lubrication: The lubricant Film covers/fills the irregularities of the sliding/moving surfaces and Forms a thick layer (~1000Å) in-between them, so that there no direct contact between the material surfaces. This consequently reduces the wear. The resistance to movement is only due the internal resistance between the particles of the lubricant moving over each other. The lubricant chosen should have the minimum viscosity under working conditions and at the same time it should remain in place and separate the surfaces. Hydrocarbon oils (12-50 carbon atoms) are considered to be satisfactory lubricants for thick-film lubrication. In order to maintain the viscosity of the oil in all seasons of year, ordinary hydrocarbon lubricants are blended with selected long chain polymers 72
  73. 73. 73 Mechanism of lubrication 2. Boundary or thin-film lubrication: Reference Jain and Jain, 16th edition Page 429
  74. 74. Mechanism of lubrication 2. Thin film lubrication: this type of lubrication is preferred where a continuous film of lubricant can not persist . In such cases, the clearance space between the moving/sliding surfaces is lubricated by such a material which can get adsorbed on both the metallic surfaces by either physical or chemical forces. This adsorbed film helps to keep the metal surfaces away from each other at least up to a height of the peaks present on the surface. Vegetable and animal oils and their soaps can be used in this type of lubrication. Although these oils have good oiliness, they suffer from the disadvantage that they will break down at high temperatures. On the other hand, mineral oils are thermally stable and the addition of vegetable/animal oils to mineral oils, their oiliness can also be brought up. Graphite and molybdenum disulphide are also suitable for thin film lubrication 74
  75. 75. Mechanism of lubrication 3. Extreme pressure lubrication: when the moving/sliding surfaces are under very high pressure and speed, a high local temperature is attained under such conditions, liquid lubricants fails to stick and may decompose and even vaporize. To meet these extreme conditions, special additives are added to mineral oils. These are called extreme pressure additives. These additives form more durable films on metal surfaces. Important additives are organic compounds having active radicals or groups such as chlorine (as in chlorinated esters), sulphur (as in sulphurized oils) or phosphorous (as in tricrecylphosphate). These compounds reacts with metallic surfaces, at existing high temperatures, to form metallic chlorides, sulphides and phosphides. 75 Reference Jain and Jain, 16th edition Page 430
  76. 76. Classification of lubricants Lubricants can be broadly classified, on the basis of their physical state as follows: 1. Liquid lubricants and lubricating oils 2. Semi-solid lubricants or greases, 3. Solid lubricants 76
  77. 77. 1. Liquid lubricants and lubricating oils: liquid lubricants are further classified into three categories; a) animal and vegetable oils, b) Mineral or petroleum oils c) Blended oils Classification of lubricants 77
  78. 78. 1.a) animal and vegetable oils: animal oils are extracted from the crude fat and vegetable oils such as cotton seed oil and caster oils. These oils possess good oiliness and hence they can stick on metal surfaces effectively even under elevated temperatures and heavy loads. But they suffer from the disadvantages that they are costly, undergo easy oxidation to give gummy products and hydrolyze easily on contact with moist air or water. Hence they are only rarely used these days for lubrication. But they are still used as blending agents in petroleum based lubricants to get improved oiliness. 1. Liquid lubricants and lubricating oils Classification of lubricants 78
  79. 79. 1.b) Mineral or petroleum oils: these are basically lower molecular weight hydrocarbons with about 12 to 50 carbon atoms. As they are cheap, available in abundance and stable under service conditions, hence they are widely used. But the oiliness of mineral oils is less, so the addition of higher molecular weight compounds like oleic acid and stearic acid increases the oiliness of mineral oil. 1. Liquid lubricants and lubricating oils Classification of lubricants 79
  80. 80. 1.c) Blended oils: no single oil possesses all the properties required for a good lubricant and hence the addition of proper additives is essential to make perform well. Such additives added lubricating oils are called blended oils. Example: the addition of higher molecular weight compounds like oleic acid, stearic acid, palmitic acid, etc. or vegetables oil like coconut oil, castor oil, etc increases the oiliness of mineral oil. 1. Liquid lubricants and lubricating oils Classification of lubricants 80
  81. 81. Formulation of lubricants • Typically lubricants contain 90% base oil and less than 10% additives • Base : – most often petroleum fractions (called mineral oils) – vegetable oils or synthetic liquids such as hydrogenated polyolefins, esters, silicones, fluorocarbons are sometimes used as base oils 81
  82. 82. Formulation of lubricants • The primary function of the base fluid: – to lubricate and act as a carrier of additives • The function of additives: – to enhance an already existing property of the base fluid viscosity, viscosity index, pour point, oxidation resistance – to add a new property • cleaning/suspending ability, antiwear performance, corrosion control 82
  83. 83. Types of additives • Some additives impart new and useful properties to the lubricant • Some enhance properties already present • Some act to reduce the rate at which undesirable changes take place in the product during its service life 83
  84. 84. Typical additives • Friction modifiers • Anti-wear agents • Extreme-pressure additives • Anti-oxidation additives • Rust and corrosion inhibitors • Foam inhibitors • Oiliness agents • Detergents and dispersants • Alkaline agents • Pour point depressants (PPD) • Viscosity index improvers 84
  85. 85. 1) Oiliness carriers: the addition of higher molecular weight compounds like oleic acid, stearic acid, palmitic acid, etc. or vegetables oil like coconut oil, castor oil, etc increases the oiliness of mineral oil. 2) Extreme Pressure Additives: Under extreme pressure, a thick film of oil is difficult to maintain. High pressure additives contain materials which are either adsorbed on the metal surface or react chemically with the metal, producing a surface layer of low shear strength on the metal surface. Examples: fatty ester, acids, organic materials which contain sulphur,, organic chlorine compounds, organic phosophorous compounds etc. Additives in Blended oils 85
  86. 86. 3) Thickeners: such as polystyrene, polyesters etc., are materials of high molecular weight between 300 to 3000. They are added in lubricating oil to increase the viscosity Additives in Blended oils 86 polystyrene
  87. 87. 4) Antioxidants or inhibitors: when added to the oil retard oxidation of the oil by getting themselves preferentially oxidized. They are particularly added added in lubricants used for internal combustion engines. The antioxidants are aromatic phenols, or amino compounds. Additives in Blended oils 87
  88. 88. 5) Foam Inhibitors: Foaming of lubricants is a very undesirable effect - can cause enhanced oxidation by the intensive mixture with air Additives in Blended oils 88 Dimethylsilicones (dimethylsiloxanes)
  89. 89. 2.) semi-solid lubricants or grease: a semi-solid lubricant obtained by combining oil with thickening agents. Lubricating oil is the principal component and it can be either petroleum oil or a synthetic hydrocarbon of low to high viscosity. The thickeners consists primarily of special soaps of Li, Na, Ca, Ba, Al, etc. Non-soap thickeners include carbon black, silica gel, polyureas and other syntheic polymers, clays etc. Grease can support much heavier load at lower speed. Internal resistance of grease is much higher than that of lubricating oil; therefore it is better to use oil instead of grease. Compared to lubricating oils grease can not effectively dissipate heat from the bearings, so work at relatively lower temperature. 2. semi-solid lubricants or grease Classification of lubricants 89
  90. 90. 2.) Classification of grease: Greases are classified after the soap used in their manufacture. Important greases are 2.1 Calcium based greases or cup greases: are emulsions of petroleum oils with calcium soaps. They are prepared by adding calcium hydroxide to a hot oil. They are insoluble in water and are the cheapest 2.2 Soda base grease: are petroleum oils, thickened by mixing sodium soaps. They are not water resistant, because the sodium soap content is water soluble. However they can be used upto 175⁰C. They are suitable in ball bearings. 2. semi-solid lubricants or grease 90
  91. 91. 2.) Classification of grease: 2.3 Lithium based greases : are petroleum oils thickened by mixing lithium soaps. They are water resistant and suitable for use at low temperatures (<15⁰C). 2.4 Axle grease: are very cheap resin greases, prepared by adding lime to resin and fatty oils. The mixture is thoroughly mixed and allowed to stand, when grease floats as stiff mass. Fillers like talc and mica also added to them. They are water resistant. 2. semi-solid lubricants or grease 91
  92. 92. 3.) solid lubricants :they are preferred where (1) the operating conditions are such that a lubricating film cannot be secured by the use of lubricating oils or grease, (2) contamination of lubricating oil or grease is unacceptable, (3) the operating temperature or load is too high, even for grease to remain in position, (4) combustible lubricants must be avoided, they are used either in the dry powder from or with binders to make them stick firmly to the metal surface while in use. They are available as dispersions in non-volatile carriers like soaps, fats, waxes, etc and as soft metal films. The most common solid lubricants are graphite, molybdenum disulphide, tungten disulphide and zinc oxide. They can withstand temperatures up to 650 ⁰C and can be applied in continuously operating situations. They are also used as additives to mineral oils and greases in order to increase the load carrying capacity of the lubricant. Other solid lubricants in use are soapstone and mica. Classification of lubricants 92
  93. 93. 3.1 Graphite: It is the most widely used of all the solid lubricants and can be used either in the powdered form or in suspension. It is soapy to touch; non-flammable and stable upto a temperature of 375 ⁰C. Graphite has a plate like structure and the layers of graphite sheets are arranged one above the other and held together by van der Waal’s forces. These parallel layers which can easily slide one over other make graphite an effective lubricant. Also the layer of graphite has a tendency to absorb oil and to be wetted of it. Solid lubricants: examples 93
  94. 94. 3.2 Molybdenum disulphite: It has a sandwich like structure with a layer of molybdenum atoms in between two layers of sulphur atoms. Poor interlaminar attraction helps these layers to slide over one another easily. It is stable up to a temperature of 400 ⁰C. Solid lubricants: examples 94
  95. 95. Selection of lubricants: In selecting a lubricant for a particular job, the service condition requirements are to be related to the properties of the lubricant. The properties of a properly selected lubricant should not change under service conditions. The properties of a properly selected lubricant should not change under service conditions. Selection of a lubricant for a few typical jobs are illustrated as follows: 1. Lubricants for cutting tools: Cutting fluids are lubricants used in cutting, turning, and grinding of metals. The main functions of cutting fluids are: a) to cool the tool b) to cool the metal work-piece so as to prevent dimensional inaccuracies, c) to reduce power consumption by lubrication action, d) to improve surface finish Two situations can be there in cutting tool: Selection of lubricants 95
  96. 96. (1.a) For heavy cutting: the most effective lubricants are cutting oils. The cutting oils are essentially mineral oils of low viscosities containing additives like fatty oils, sulphurized fatty oils which by virtue of their polar groups attach themselves to the surface of continuously exposed fresh metals. (1.b) In light cutting: the most effective lubricants are oil-emulsions. Oil- emulsions have somewhat smaller lubricating effect than cutting oils, but they are more efficient as cooling media, due to high heat capacity of water, which is present in them as an external phase. Selection of lubricants 96
  97. 97. 2. Lubricants for internal combustion engines: In internal combustion engines, the lubricant is to be exposed to high temperatures. Therefore the lubricant should possess high viscosity index (i.e. low variation of viscosity with temperature) and high thermal stability. Petroleum oils containing additives, which impart high viscosity index and oxidation stability to them, are used as lubricants for internal combustion engines. Selection of lubricants 97
  98. 98. 3. Lubricants for gears: are subjected to extreme pressures. So they should possess good oiliness, ii) not to be removed by centrifugal force, iii) possess high resistance to oxidation, iv) have high load carrying capacity. Thick mineral oils containing extreme pressure additives are employed. Selection of lubricants 98
  99. 99. 4. Lubricants for transformers: The functions of the lubricating oil in the transformer are to insulate the windings and to carry away the heat generated. The oil must possess good dielectric properties, chemically inert and low viscosity. Highly refined mineral oils of high insulating quality, optimum oxidation resistance and chemical stability are employed. Selection of lubricants 99