DEPARTMENT OF FIRST YEAR ENGINEERING Academic Year 2017-18 ( Sem I )

1. Dr. D. Y. Patil Pratishthan’s DR. D. Y. PATIL INSTITUTE OF ENGINEERING, MANAGEMENT & RESEARCH DEPARTMENT OF FIRST YEAR ENGINEERING Academic Year 2017-18 ( Sem I ) Subject : Engineering Chemistry Name of faculty: Dr. MinazAlvi

2. FUELS AND COMBUSTION

3. FUEL: • “The combustible substance which on burning gives large amount of heat that can be used economically for domestic and industrial purposes”. Fuel + Oxygen  Products + Heat • Carbon - major constituent of fuel • Besides carbon, the fuels also contain elements like hydrogen, nitrogen, sulphur etc.

4. In the combustion (i.e. burning) process, these elements combine with oxygen to form their oxides such as CO2, H2O, SO2, NO2 etc. • These oxidation reactions also release large amount of heat.

5. CLASSIFICATIONOF FUELS:

6. CALORIFIC VALUE : • The capacity of any fuel to supply heat is measured in terms of calorific value. • Definition : “The total amount of heat liberated when a unit mass or unit volume of fuel is burnt completely at STP”.

7. Calorific value of any fuel can be given by two ways: 1. Gross Calorific Value (GCV) or Higher Calorific Value (HCV) 2. Net Calorific Value (NCV) or Lower Calorific Value (LCV)

8. 1. Gross Calorific Value (GCV) or Higher Calorific Value (HCV) : “It is the total amount of heat produced when one unit mass or unit volume of fuel is burnt completely (at STP)and the products of combustion are cooled to room temperature (i.e. 15°C)”.

9. 2.Net Calorific Value (NCV) or Lower Calorific Value (LCV) : “It is the total amount of heat produced when one unit mass or unit volume of fuel has been burned completely (at STP)and the products of combustion are allowed to escape to air”.

10. NCV/LCV is always smaller than GCV/HCV LCV =(GCV − Latent heat of water) =[GCV − (Mass of hydrogen  9  Latent heat of steam)] (Because one part by mass of hydrogen produces nine parts by mass of water.) (Mass of Hydrogen = % of Hydrogen/100) (LHC = 587 cal/gm or 2450 kJ/kg or 2.45 MJ/Kg) LCV = GCV – 0.09 x H x LHC

11. Units of Calorific Value: 1 cal/gm = 1 kcal/kg = 4.187 kj/kg

12. METHODS OF DETERMINATION OF CALORIFIC VALUE: • Bomb Calorimeter: Solid and Non volatile liquid fuel • Boys Gas Calorimeter: Volatile and Gaseous fuel • Principle • Construction • Working • Observations and Calculations

13. BOMB CALORIMETER: • It is used to determine calorific value of a solid or non-volatile liquid fuel. • Principle : “A known weight of solid or liquid fuel is burnt in a bomb calorimeter and liberated heat is absorbed by water”. OR “Heat liberated by burning of fuel is absorbed by water in calorimeter”.

14. Construction:

15. 1. Bomb Pot: • cylindrical stainless steel vessel / pot in which combustion of fuel takes place. • It is fitted with a lid consisting of two electrodes (stainless steel)and one inlet to pass oxygen. • One of the electrode is attached to ring which holds a crucible (nickel / stainless steel) containing fuel. • Two Magnesium wires in the form of loop are attached to both electrodes and loop touches the fuel sample.

16. 2. Calorimeter: • The bomb is placed in a copper calorimeter. • It contains known amount of water. • It consists of an electrically operated stirrer to maintain uniform temperature of water. • It is also provided with Beckmann’s thermometer which measures the temperature upto 0.010C.

17. 3. Insulating Cover / Chamber: • Calorimeter is surrounded by an air and water jacket to prevent loss of heat due to radiation. 4. Oxygen cylinder with pressure guaze

18. Working : • About one gram of a fuel is correctly weighed and taken in a crucible. • The crucible is placed on the ring. • A thin magnesium wire touching the fuel sample is then stretched across the electrodes. • Bomb lid is tightly fitted and oxygen gas is passed in bomb at 25 atm. pressure. • 10 ml distilled water is added to the bomb pot.

19. The bomb is then placed into copper calorimeter containing a known mass of water. • The stirrer is operated for 5 min. and initial temperature of water is noted as t1°C. • The electrodes are connected to battery (6 V) and current is passed for 5-10 sec. to ignite the fuel sample. • Due to burning of fuel sample, heat is liberated which is absorbed by water placed in calorimeter.

20. The maximum temperature of water is noted as t2°C. • Then, average rate of fall in temperature per minute(dt/min) and time (t) taken to reach initial temperature is noted. • Contents of the bomb pot is taken out to find out the amount of acids formed. (If fuel contains S and N, they get converted into NO3 and N2O5. These gases then get absorbed by distilled water in bomb pot and forms H2SO4 and HNO3 resp.)

21. Observations: (i) Mass of fuel sample = W gm. (ii) Mass of water in calorimeter = M gm. (iii) Water equivalent of calorimeter =m gm. (iv) Initial temperature of water = t1°C. (v) Final temperature of water = t2°C. (vi) Gross calorific Value (GCV) =L cal/gm

22. Calculations: Heat liberated by burning of fuel = Heat absorbed by water and calorimeter W  L = (M + m) (t2 − t1)  GCV or L = (M + m) (t2 − t1) cal/gm W

23. Net Calorific Value (NCV): (where, H is percentage of hydrogen in the fuel.) LCV = GCV – 0.09 x H x LHC

24. Corrections in Bomb Calorimeter: 1. Acid Correction (a) : If sulphur and nitrogen present in the fuel get converted into acids like H2SO4 and HNO3. (a) S + O2 SO2 2 SO2 + O2 + 2 H2O  2H2SO4 H = −144 kcal (b) 2 N2 + 5 O2 + 2 H2O  4HNO3 H = −57.16 kcal

25. Formation of above two acids are exothermic reactions. • Therefore, heat liberated due to such reactions must be subtracted from total GCV of fuel.

26. 2. Fuse wire Correction (f) : • The measured heat also includes the heat liberated by burning of fuse wire (Mg wire) • Therefore, heat liberated due to burning of fuse wire must be subtracted from total GCV.

27. 3. Cotton Thread Correction (c) : • Cotton thread is tied around the fuse wire and one end of thread is in contact with fuel so that, it catches fire first and helps for ignition of fuel. • Therefore, the heat liberated due to burning of cotton thread must be subtracted from total GCV.

28. 4. Cooling Correction (tC) : • If the time taken for the water in calorimeter to cool from the maximum temperature attained to the room temperature in ‘t’ minutes and the rate of cooling is dt/min., then the cooling correction = t·dt. • This should be added to the observed rise in temperature.

29. GCV or L = (M + m) (t2−t1+tC) – (a + f + c) W cal/gm • Then, the equation for accurate GCV is,

30. BOYS GAS CALORIMETER: • It is used to determine the calorific value of volatile liquid fuel and gaseous fuel. • Principle : “A known volume of liquid or gaseous fuel is burnt in a boys calorimeter and liberated heat is absorbed by cooling water circulated through the copper coil”. OR “Heat liberated by burning of fuel is absorbed by water in calorimeter”.

31. Construction:

32. 1. Gas Burner: • Known volume of gas is burnt at a pressure and at uniform rate of 3-4 lit./min. 2. Combustion Chamber/ Chimney: • Around the burner, there is a combustion chamber Chimney. • The inner and outer walls of the chamber are surrounded (or coiled) by copper tubes. • Water at constant rate enters the copper tube from the top of the chamber and moves down to the bottom. • Then goes up through the inner coil to exit at top.

33. 3. Thermometers: • Two thermometers T1 and T2 to record temperature of incoming and outgoing water respectively. 4. Insulating Cover / Annular Vessel: • Whole assembly is covered with an insulating cover/annular vessel to avoid loss of heat due to radiation.

34. Due to presence of hydrogen in fuel, steam formed is collected in beaker from bottom outlet. • There is a hole on top for exhaust gas.

35. Working : • The fuel sample is burnt at constant flow rate (10-15 min). • Cooling water is circulated at a constant rate. • Then processes of burning the gas and circulation of water at constant rate are continued for some time to establish steady conditions.

36. Steady conditions: constant gas flow rate, constant flow rate of water circulation, constant temperature of outgoing water. • When steady conditions are reached, then the observations are noted.

37. Observations : 1. Volume of gas burnt at STP in time ‘t’ = V m3. 2. Weight of cooling water circulated in time ‘t’ = W kg. 3. Temperature of the incoming water = t1°C. 4. Temperature of the outgoing water = t2°C. 5. Rise in temperature = (t2 − t1) °C. 6. Weight of steam condensed = m kg.

38. Calculations: Heat liberated by burning of fuel = Heat absorbed by water  GCV x V = W (t2 − t1)  GCV = W (t2 − t1) V kcal/m3

39. Net Calorific Value (NCV): • Weight of steam condensed per m3 of gas will be, m V kg/ m3 (V m3 = m kg, hence, 1 m3 = m/v kg/ m3 )  NCV = GCV – m x LHC V kcal/ m3

40. solid fuels: • Coal: • Coal is a highly carbon containing matter formed from vegetable matter (i.e. plants) buried in soil, under the effect of pressure, heat, action of aerobic and anaerobic bacteria for a long time. • It is mainly composed of C, H, N, O and some non-combustible inorganic matter. • Also contains considerable amounts of free and hygroscopic moisture and traces of sulphur, arsenic, phosphorous etc.

41. ANALYSIS OF COAL: • To decide the quality of coal • To determine the percentage of various constituents present in coal which directly affect the calorific value of coal. • To specify its use for particular purpose. • To calculate air requirement for complete combustion. • To decide price of coal.

42. Analysis of Coal Proximate Analysis % moisture, % volatile matter, % ash and % fixed carbon Ultimate Analysis • %C, %H, %S, %O, • % ash and % N

43. A. PROXIMATE ANALYSIS: a. Percentage of Moisture (M): • A known quantity of coal is taken in silica crucible. • It is then heated in an oven at 105 -110°C for 1 hour. • It is cooled in desiccator and then weighed.

44. The process of heating, cooling and weighing of crucible is repeated till constant weight is obtained. % of Moisture = Loss in weight / Weight (M) of coal taken x 100

45. b. Percentage Volatile Matter (V. M.): • A moisture-free coal from first experiment is covered with vented lid. • It is then heated in muffle furnace at 925-950°C for 7 minutes. • It is cooled in desiccator and then loss in weight is determined. % of Volatile Matter = Loss in weight / (V. M.) Weight of coal taken x 100

46. If fresh coal sample is taken for experiment 2, then loss in weight is due to moisture and volatile matter. • Hence, loss in weight due to volatile matter is calculated as, % of Volatile Matter = Loss in weight / (V. M.) Weight of coal taken x 100 - % of moisture

47. c. Percentage of Ash: • Ash is non-combustible inorganic matter in coal. • A coal from second experiment is heated without lid at 750°C for 30 minutes in muffle furnace. • It is cooled in desiccator and then weighed.

48. The process of heating, cooling and weighing of crucible is repeated till constant weight is obtained. % of Ash = Weight of ash / Weight of coal taken x 100

49. d. Percentage of Fixed Carbon: • It is obtained by subtracting the sum of the percentage of moisture, volatile matter and ash from 100. % of Carbon = 100 - % (M + V. M. + Ash)

50. Significance of Proximate Analysis : a. Moisture: • Increases ignition point of coal • Takes away heat • Decreases calorific value • Increases transportation cost • Difficulty in handling • A good quality of coal should contain low moisture content.