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Govt. Polytechnic College For Girls Patiala

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1 Govt. Polytechnic College For Girls Patiala
Deptt. Of Applied Sciences Govt. Polytechnic College For Girls Patiala Presented By- Dr.Raman Rani Mittal M.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 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 chemicals by 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 CO kcal C + ½ O2 CO 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 + H – 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 & N2 with traces of CO2 comes out through the exit at the upper end of the of the producer and is named as Producer Gas.

24 Manufacture of Producer Gas
Distillation Zone 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 Now air entry is stopped & steam is passed to get water gas
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 CO 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-luminous blue 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 Coke is the residue left behind Coal Coal gas + Coke
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

42

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

51 Uses Mainly used as heating fuel As an illuminant Used to provide reducing atmosphere in metallurgical operations Also used as “town gas” for domestic purposes

52 5. OIL GAS Oil gas is a mixture of hydrocarbons
Prepared by thermal cracking of kerosene oil Kerosene oil consists of hydrocarbons ranging from C11H22to C16H34 C11H22 Thermal Cracking CH4 + C2H6 + C2H2+ C3H6 + C Kerosene Oil Tar Lower Hydrocarbons

53 Manufacture of Oil Gas Kerosene oil is allowed to fall drop wise on the bottom of the red hot cast iron retort heated in a furnace The oil on coming in contact with red hot bottom, immediately gets cracked into a number of lower gaseous hydrocarbons

54 The gaseous mixture emerge out through a bonnet which is fitted at the mouth of the retort with lead seal at one end & water seal at another end. Gaseous mixture goes to a hydraulic main, a tank containing water Tar gets condensed and is removed

55 The extent of cracking is tested time to time by withdrawing some gas samples through testing tap and examining its colour A good oil gas appears golden in colour

56 By proper adjustment of air supply, the gas of required colour can be obtained
The gas is finally stored over water in gas holders & is supplied wherever required The yield of the gas is about 40 to 50%

57 Manufacture of Oil Gas

58 Composition of Oil gas Composition of oil gas depends upon the nature of oil used. Approximate composition of the gas is given below : CH4 = 25 – 30% H2 = 50 – 60% CO = 10 – 15% CO2 = 3%

59 Calorific value Calorific value of the gas is about 4500 – 5400 kcal/m3 Uses of Oil gas Used as heating fuel in the laboratories of schools & colleges Used to improve the calorific value of water gas and mixture of water gas & oil gas is called carburetted water gas

60 6. Carburetted Water Gas Water gas enriched with oil gas is called carburetted water gas Manufacture : Oil gas is prepared in an auxiliary plant called carburettor A checker-work of fire-bricks is heated by burning a part of water gas Oil is sprayed over it

61 Oil undergoes thermal cracking & oil gas is produced
Water gas is passed through it The resulting carburetted water gas is passed through hydraulic main It is then passed into purifier with the help of exhaust fan followed by scrubbers to remove impurities

62 Manufacture of Carburetted Water Gas

63 Composition of Carburetted Water gas
Approximate composition of carburetted water gas is : CO = % H2 = % CO2 = % N2 = % Hydrocarbons = %

64 Properties of Carburetted water gas:
Burns with blue flame Poisonous in nature due to presence of carbon monoxide Uses : Used for industrial hydrogenation For manufacture of alcohol as a fuel in industrial preparation

65 7. Bio Gas Bio gas is produced by the degradation of biological matter by bacterial action (by anaerobic bacteria) in the absence of free oxygen The cheapest & easily obtainable biogas is gobar gas Gobar gas is produced by anaerobic fermentation of cattle dung

66 Manufacture of Gobar gas
The plant for gobar gas is a cylindrical tank made of bricks About 6m deep & 2m in diameter An iron gas holder is suspended upside down in the tank Diameter of gas holder is slightly less than tank

67 Gas holder is always kept in vertical position by a device
Animal waste is held in a side tank and is delivered to the tank through an inlet pipe Used animal waste is taken out in another side tank through an outlet pipe

68 To produce gobar gas, gobar ( or human excreta, poultry sweep, plant residue, leaves or any other biomass) is collected It is made into slurry with water & is put in the inlet tank The slurry slides down to the digester tank through the inlet pipe The level of the slurry rises in the tank It undergoes biological degradation by anaerobic bacteria in the absence of air

69 Gas so produced is collected in gas holder
Digested slurry (used ) is pushed to the outlet tank Digested slurry is dried partially which is an excellent manure for plants Gobar gas is easily prepared in summer because optimum temperature for fermentation is oC

70 Bio-gas Plant

71 Composition of Bio gas The average composition of bio gas is : Methane = 55% Carbon dioxide = 35% Hydrogen = 8% Nitrogen = 2% Before using, gobar gas is passed through KOH solution to absorb maximum of CO2

72 Properties of Bio gas It is colourless & odourless gas insoluble in water It burns with non-luminous blue flame and gives a temperature of 540oC It is non-poisnous in nature as it does not contain carbon monoxide Calorific value is about kcal/m3

73 Uses of Bio gas An excellent domestic fuel especially in villages where dung is available in plenty Gas can also be used for lighting and power purposes like running water pumps, chaff cutting machines Spent slurry is a richer manure than original dung

74 Advantages of gaseous fuels
Gaseous fuels can be transported through a pipe line to the place of use Can be lighted at a moment’s notice Calorific value is high Burn with high efficiency and a high temperature flame can be obtained in no time Do not produce any smoke or ash Burning can be easily controlled

75 Can be preheated by the heat of waste gases & hence their use is economical as far as heat is concerned Flame can be made oxidising, reducing by regulating the air supply. This is required in metallurgical operations Burn in slight excess of air

76 Disadvantages Large storage tanks are required for storing
Highly inflammable, hence risk of fire hazards are quite high Are usually suffocating Cost of production is quite high Great care is needed for storing & transportation

77 Thank You


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