Deptt . Of Applied Sciences Govt. Polytechnic College For Girls Patiala Presented By-

1. Deptt. Of Applied Sciences Govt. Polytechnic College For Girls Patiala Presented By- Dr.RamanRaniMittalM.Sc.,M.Phil.,Ph.D. (Chemistry)

2. Gaseous Fuels

3. Contents • Natural Gas • Producer Gas • Water Gas • Coal Gas • Oil Gas • Carburetted Water Gas • Bio Gas • Advantages of gaseous fuels

4. FUELS Fuel is a combustible substance chiefly containing carbon, which on burning produces large amount of heat that can be used economically for domestic and industrial purposes. Fuel + O2 Products + Heat

5. Classification of Fuels Fuels have been classified according to their (i) Occurrence or preparation (ii) Physical state On the basis of their occurrence, fuels may be of two types (a) Natural fuels or primary fuels (b) Artificial or secondary fuels

6. Natural Fuels Fuels which are found in nature as such are called natural fuels. Examples- wood, peat, coal, petroleum, natural gas etc. • Artificial Fuels Fuels which are prepared artificially from primary fuels are called artificial fuels. These fuels are derived from naturally occurring fuels by further chemical processing so these are called secondary fuels. Coke, petrol, kerosene oil, coal gas.

7. On the basis of their physical state, fuels are of three types: • Solid fuels • Liquid fuels • Gaseous fuels • SOLID FUELS • Natural solid fuels- wood, peat, lignite, bituminous coal & anthracite coal. • Artificial solid fuels- wood charcoal, coke.

8. 2. LIQUID FUELS • Natural liquid fuels- Crude petroleum • Artificial liquid fuels- Various fractions of petroleum such as petrol, diesel, kerosene oil, coal tar & alcohol etc. 3.GASEOUS FUELS • Natural gaseous fuels- Natural gas or marsh gas. • Artificial gaseous fuels- Producer gas, water gas, coal gas & blast furnace gas etc.

9. 1. Natural Gas • The naturally occurring gaseous fuel is known as natural gas. • It is formed by decomposition of organic matter • It is obtained from wells dug in the oil-bearing regions

10. Before use, the natural gas is purified to remove objectionable impurities such as water, dust, grit, H2S, CO2, N2 and higher hydrocarbons which can be easily liquified. • It is a very cheap & convenient fuel.

11. Composition Methane (CH4) = 70-90% Ethane (C2H6) = 5-10% Hydrogen = 3% CO & CO2 = rest Calorific value 12000-14000 kcal/m3

12. Uses of Natural Gas • It is an excellent domestic fuel and can be conveyed over large distances in pipelines • It has been used in the manufacture of a large number of chemicalsby synthetic processes

13. Natural gas is also used as raw material for the manufacture of carbon black ( a filler for rubber) and hydrogen (used in ammonia synthesis) • Synthetic proteins (used as animal feed) is obtained by microbiological fermentation of methane

14. 2. PRODUCER GAS • Producer gas is a mixture of carbon monoxide and nitrogen (CO + N2). • It is produced by passing air mixed with little steam over a red hot coke bed maintained at a temperature of about 1100oC. • Its calorific value is very low. • Among all gaseous fuels, producer gas is the cheapest.

15. Manufacture of Producer Gas • The furnace used at for the manufacture of producer gas is known as gas producer. • It consists of a steel vessel which is lined inside with refractory bricks • It is about 3 m in diameter and 4 m in height

16. It is provided with a cup and cone feeder at the top • Producer gas comes out from an exit near the top. • At the base, it has inlet for passing air and steam • Moreover, at the base it has an exit for the removal of ash formed.

17. Manufacture of Producer Gas

18. Reactions in Gas Producer The gas production reactions can be divided into four zones : • Ash zone • Combustion zone • Reduction zone • Distillation zone

19. (1).Ash zone • It is the lowest zone & contains mainly of ash and hence, is known as ash zone. • The ash protects the grate of the producer from the intense heat of combustion • The temperature of supplied air and steam is increased as they pass through this zone

20. (2) Combustion zone • This zone is next to the ash zone • It is also known as oxidation zone • Here carbon burns and forms CO & CO2 C + O2 CO2 + 97 kcal C + ½ O2 CO + 29.5 kcal • Temperature of this zone is about 1100oC

21. (3) Reduction Zone • In this zone carbon dioxide and steam combines with red-hot coke and liberates free H2 & CO. CO2 + C 2 CO – 36 kcal C + H2O CO + H2 – 29 kcal C + 2H2O CO2 + 2H2 – 19 kcal All these reactions are endothermic, so temperature falls to 1000oC

22. (4) Distillation Zone • Temperature of this zone is about 400-800oC • The incoming coal is heated by the outgoing hot gases • In the way the volatile matter present in the coal vaporises and mixes with the outgoing gases

23. Nitrogen remains unaffected throughout the process. • Thus a mixture of CO & N2with traces of CO2 comes out through the exit at the upper end of the of the producer and is named as Producer Gas.

24. DistillationZone Secondary Reduction Zone Primary Reduction Zone Oxidation Zone Ash Zone Manufacture of Producer Gas

25. Composition of Producer Gas The average composition of producer gas is : Carbon monoxide (CO) = 30% Nitrogen (N2) = 55% Carbon dioxide (CO2) = 3% Hydrogen (H2) = 12%

26. Properties of Producer gas • Burns with a blue flame • Poisonous in nature due to presence of CO • Calorific value is about 1300 kcal / m3 • Calorific value is lowest of all gaseous fuels • In spite of its lowest calorific value, this gas is the cheapest gaseous fuel per unit heat.

27. Uses of Producer gas • It is used for heating open hearth furnaces in the manufacture of steel and glass • It is used for heating muffle furnaces and retorts in the manufacture of coke and coal gas • It is used as a reducing agent in certain metallurgical operations

28. 3. Water gas • Water gas is a mixture of combustible gases (CO & H2) • It contains little amount of non-combustible gases (CO2 & N2) • It can be prepared by passing alternatively steam and air through a bed of red hot coke or coal maintained at about 900 to 1000oC.

29. Manufacture of Water Gas • A water gas generator is a cylindrical vessel made of steel • It is about 4m in height and 3m wide • Lined inside with refractory bricks • At the top, it has cup & cone feeder for adding coke

30. Water gas outlet is provided near the top • At the base, it is provided with inlet pipes for passing air & steam • At the bottom, it has an arrangement for taking out ash formed

31. Manufacture of Water Gas

32. Reactions Step I. • First of all, steam is passed • Steam reacts with red hot coke (coal) at 1000oC C + H2O CO + H2 - 29kcal (endothermic) water gas • CO and H2 (water gas) is formed • The above reaction is endothermic • Hence, the temperature of the bed falls below 1000oC

33. Step II. • To raise the temperature of coke bed to 1000oC , steam supply is cut off and air is blown in • Coke burns in air C + O2 CO2 + 97 kcal 2C + O2 2CO + 59 kcal • As both the reactions are exothermic, so temperature of the bed rises to 1000oC • Now air entry is stopped & steam is passed to get water gas (exothermic)

34. In modern gas plants steam & air are blown alternatively. • The period of steam blow (cold blow) is about 4min while period of air blow (hot blow) is of 1 min • The durations of these periods is adjusted in such a way to get maximum yield of water gas

35. Composition of Water Gas The average composition of water gas is: Carbon monoxide = 44% Hydrogen = 48% Carbon dioxide = 4% Nitrogen = 4%

36. Properties of Water Gas • Water gas burns with non-luminousblue flame & hence is called blue water gas • The temperature of the flame reaches up to 1200o

37. Due to presence of CO, it is poisonous gas • Calorific value is about 2800 kcal/m3 • When mixed with hydrocarbons , it is called carburetted water gas

38. Uses of Water Gas • Water gas is a good heating fuel because of high calorific value • A good source of hydrogen on commercial scale • Used in manufacture of methyl alcohol

39. Used for welding purposes • When mixed with hydrocarbons , it is called carburetted water gas. It is used for heating & lighting purposes.

40. 4. Coal Gas • It is obtained by destructive distillation of coal • Coal used should be rich in volatile matter (30 to 40%) • The process is carried out in horizontal or vertical closed iron or silica retorts at 1350o C

41. The gaseous product obtained is a mixture of several combustible gases & is known as coal gas • Coke is the residue left behind Coal Coal gas + Coke Destructive Distillation

43. Manufacture of coal gas • The plant consists of vertical silica retort having airtight hopper at the top • The retort is heated to about 1350oC by the combustion of preheated producer gas and air mixture • Coal rich in volatile matter is fed to the retort through hopper which decomposes on heating

44. The gases so produced as a result of decomposition of coal are allowed to pass through a hydraulic main to a big water cooled condensers • Tar and ammonia get condensed & collected in two separate layers in a tar well below the condensers

45. The gases are then led to a scrubber under pressure with the help of exhaust pump where they are scrubbed with water to remove last portions of tar & ammonia • The hot gases are chilled by passing them through empty tower sprayed with jets of high pressure water where naphthalene is removed

46. Coal gases are then passed through another scrubber containing creosote oil • Benzene, toluene & other aromatic compounds are dissolved in oil • Gases are then passed through purifier containing trays of hydrated iron oxide & lime

47. Impurities like H2S, CS2, CO2 and HCN etc get removed • Purified coal gas is then collected in the gas holder over water from where it is supplied

48. Manufacture of Coal Gas

49. Composition of Coal gas The approximate composition of coal gas is: Methane = 32% Hydrogen = 47% Carbon monoxide = 7% Acetylene (C2H2) = 2% Ethylene (C2H4) = 3% Nitrogen (N2) = 4% Carbon dioxide (CO2) = 1% Other hydrocarbons = 4%

50. Properties • Colourless gas with a characteristic odour • Lighter than air • Slightly soluble in water • Burns with long smoky flame • Poisonous in nature • Calorific value is about 5000 kcal/m3