introduction a fuel can be defined as a combustible substance, containing carbon as a main...

INTRODUCTION A fuel can be defined as a combustible substance, containing carbon as a main constituent, which on proper burning gives large amount of heat, which can be used economically for domestic & industrial purposes. E.g.: wood, charcoal, coal, kerosene, petrol, diesel etc. Fuel + O 2 Products + Heat

CLASSIFICATION OF FUEL Fuels are classified as Primary fuels Fuels which occur naturally such as coal, crude petroleum and natural gas. Coal and crude petroleum, formed from organic matter many millions of years ago, are referred to as fossil fuels. Secondary fuels Fuels which are derived from naturally occurring ones by a treatment process such as coke, gasoline, coal gas etc.

CLASSIFICATION OF FUELS FUEL Primary Fuels Solid Eg. Wood,peat Liquid Eg.crude oil Gas Eg.Natural gas Secondary fuels Solid EgCoke,charcoal Liquid Eg. Petrol,LPG Gas Eg.coal gas,water gas

CHARACTRISTICS OF A GOOD FUEL 1. High calorific value. 2. Moderate ignition temperature. 3. Low moisture content. 4. Low non-combustible matter content. 5. Moderate velocity of combustion. 6. Products of combustion. 7. Low cost. 8. Transportation. 9. Combustion should be easily controllable. 10. Efficiency.

CALORIFIC VALUE The calorific value of a fuel is defined as the quantity of heat (expressed in calories or kilo calories) liberated by the complete combustion of unit weight (1gm or 1kg) of the fuel in air or oxygen, with subsequent cooling of the products of combustion to the initial temperature of the fuel. Calorific value can be considered in a two ways: 1. Higher calorific value or Gross calorific value. 2. Lower calorific value or Net calorific value.

Higher calorific value or Gross calorific value. The gross calorific value refers to the heat evolved when the water produced by combustion is condensed as a liquid. Thus the gross calorific value is the quantity of heat liberated by the complete combustion of unit weight of the fuel with subsequent cooling of the products of combustion to the initial temperature of the fuel.

Lower calorific value or Net calorific value The net calorific value gives the heat liberated when water is in the form of steam or water vapour Under normal working conditions, water vapours produced during combustion are not condensed and escape as such along with the hot gases Hence lesser amount of heat is available, which is called Lower or net calorific value

Theoretical calculation of calorific value of fuel HCV = 1/100[8080 C + 34500 {H O/8 }+2240 S]kcal/kg LCV= [GCV-9H/100 x 587] =[GCV-0.09 x 587] kcal/kg where C, H, O, S refer to % of carbon, hydrogen, oxygen and sulphur respectively. Latent heat of steam=587kcal/kg

Analysis Of Coal And Its Significance The composition of coal varies widely according to source & age. hence its analysis is necessary to interpret the results from the point of view of classification, price fixation and industrial utilization of coal. In order to determine the quality of coal, it is subjected to the following two types of analysis: 1. Proximate analysis, 2. Ultimate analysis

Proximate analysis of coal Determines only fixed carbon, volatile matter, moisture and ash Useful to find out heating value (GCV) Simple analysis equipment Ultimate analysis of coal Determines all coal component elements: carbon, hydrogen, oxygen, sulphur, other Useful for furnace design Laboratory analysis

Proximate analysis Moisture content % of moisture in fuel (0.5 10%) Reduces heating value of fuel Weight loss from heated and then cooled powdered raw coal Volatile matter Methane, hydrocarbons, hydrogen, CO, other Typically 25-35% Easy ignition with high volatile matter Weight loss from heated then cooled crushed coal

Ash Impurity that will not burn (5-40%) Important for design of furnace Ash = residue after combustion Fixed carbon Fixed carbon = 100 (moisture + volatile matter + ash) Carbon + hydrogen, oxygen, sulphur, nitrogen residues Heat generator during combustion

Ultimate Analysis Determination of carbon &hydrogen

Significance: Higher the %of carbon, greater is the calorific value & better is the quality of coal. Lesser the % of hydrogen better is the quality of coal. % of C = increase in weight of KOH tube x 12 x 100 weight of coal taken x 44 % of H = increase in weight of CaCl2 tube x 2 x 100 weight of coal taken x 18

Determination of Nitrogen

Significance: Nitrogen is inert and incombustible gas &does not contribute any useful property. % of N = volume of acid used x Normality x 1.4 Weight of coal taken

Determination of Sulphur Coal is burnt in a bomb calorimeter in a current of oxygen. During burning sulphur present in coal is oxidized & converted in to sulphate. The ash formed is now extracted with dilute hydrochloric acid and the acid extract is heated with barium chloride solution to give a white precipitate of barium sulphate which is filtered, washed, dried and weighed. S SO 2 BaSO 4

Significance: Sulphur present in coal is harmful for use. oxidation products of sulphur have corrosive effect. hence the presence of sulphur in coal is undesirable. % of S = 32 x weight of BaSO4 x 100 233 x weight of coal

Liquid Fuels Petroleum (mineral oil) Petroleum is a natural product generated from organic material by physical & chemical process inside the earth. Carbon :79.5 to 87.1% Hydrogen : 11.5 to 14.8% Nitrogen + Oxygen : 0.1 to 0.5% Sulphur : 0.1 to 3.5%

Mining of Petroleum

Refining of Petroleum 1) Separation of water: The process of removing oil from water consists in allowing the crude to flow between two highly charged electrodes. The colloidal water droplets aggregates to form large drops, which separate out from oil. 2) Removal of harmful impurities: Electrical desalting and dehydration can be used. 3) Fractional distillation: It is a combination of distillation and rectification.

Cracking The process of composition of less volatile higher hydrocarbon molecules into more volatile simple hydrocarbon of lower molecular weight by the application of heat and catalyst is known as cracking. During the cracking process changes occurs as follows: 1. Size of molecules decreases & volatility increases. 2. A mixture of lower molecular weight hydrocarbon having lower boiling point will be formed. 3. Cyclisation may occur. 4. Straight chain hydrocarbon converted into branched chain hydrocarbon.

Types of cracking : Thermal cracking Liquid phase thermal cracking Vapour phase thermal cracking Catalytic cracking Fixed bed catalytic cracking Moving bed catalytic cracking

Thermal Cracking a) Liquid phase thermal cracking: heavy oil is cracked at 475 -530C and pressure of 100Kg/cm 2. The yield is 50-60% & octane rating of the petrol is 65-70. b) vapour phase thermal cracking: oil is first vaporized & then cracked at about 600- 650C &under a low pressure of 10- 20Kg/cm 2. This process is suitable for those oils which may be readily vaporized. It has poor stability than petrol.

Catalytic cracking

Moving bed catalytic cracking

Gasoline or petrol Gasoline is the most important liquid fuel derived from petroleum and is obtained between 40-120C. It is a mixture of hydrocarbon such as C 5 H 12 to C 8 H 18. Its approximate composition is C = 84% H = 15% N+S+O = 1% Its calorific value is 11250 kcal/kg.

Refining of gasoline Gasoline contains some undesirable straight chain hydrocarbons & sulphur compounds. And it has to be refined by chemical treatment. 1. Treatment with sulphuric acid: 2. Removal of sulphur compounds: 3. Stabilization of gasoline: 4. Addition of inhibitors

Characteristics of an ideal gasoline : 1) It must be a cheap and readily available. 2) It must burn clean &produce no corrosion. 3) It must have high calorific value. 4) It must be knock resistant. 5) It should mix readily with air.

Knocking Knocking is a term related to the internal combustion engine working on petrol.

Tendency to knock depend on: fuel air ratio, Design of engine, Speed of engine Shape of piston, location of spark plug & also upon running conditions. o Knocking results in the loss of efficiency of engine, causing fuel wastage and increased wear & tear of engine. o Straight chain>branched chain>olefins paraffins > cyclo paraffins >aromatic sparaffins

Octane value It expresses the knocking characteristics of a petrol. It is defined as the percentage by volume of iso- octane in a mixture of iso-octane and n-heptane which matches the knocking characteristics of fuel. n-heptane iso-octane (C 7 H 16 ) (C 8 H 18 ) knocks the most knocks the least poor anti-knock property good anti-knock property Octane no= 0 Octane no = 100

The octane number can be increased by addition of tetramethyl lead or diethyl ether. Oils having high octane number has a low cetane number. HydrocarbonOctane Number Benzene110 Toluene104 Cyclopentane82 Cyclohexane77 butene80

Cetane number In a diesel engine, the fuel is exploded not by a spark, but by the application of heat & pressure. The knocking characteristics of a diesel is expressed in terms of a cetane number. n- hexadecane 2- methyl naphthalene C 16 H 34 C 11 H 10 knocks the least knocks the most (least ignition delay) (higher ignition delay) Cetane no = 100 Cetane no = 0

The cetane number can be increased by addition of ethyl nitrite, ethyl nitrate. Oils having high cetane number has a low octane number. Compoundscetane Number Heptane56 Octane64 Decane77 Dodecane88 tetradecane96

Types of deisel engine Speed in r.p.mDiesel oil used having cetane number Uses Low speed100-150Heavy oil having cetane no.25 Ships Medium speed500-1500Medium oils having cetane no. 25-30 Tractors High speed1500-2000Light oils having cetane no. 45-50 Buses, trucks

Power alcohol It is used in internal combustion engine. It is not used as a prime fuel but only as an additive to motor fuels. Calorific value of 7000kcal/kg. Octane number is 90. Advantages i. On adding it increses the octane no of petrol. ii. Have lesser starting difficulties. iii. Absorbs traces of moisture.

Bio-diesel Chemically biodiesel is the methyl esters of long chain carboxylic acids. It is obtained from vegetable oil by the process transesterification. A molecule of oil is the triester of glycerol and three molecules of long chain carboxylic acids.this triester is converted into methyl esters of the fatty acids

Advantages of bio-diesel i. It is cheaper ii. Has high cetane number& high calorific value. iii. Regenerative & environment friendly. iv. Has lubricity. v. It does not give particulate and CO pollutants. vi. It is clen to use in diesel engine vii. Provides good market to vegetable oils & reduces our dependence for diesel on foreign countries.

Propellants An oxygen rich substance undergoes combustion in a definite & controlled manner, evolving a huge volume of gases It used in rockets, hence called as Rocket Propellants. Two types of propellants 1. Solid propellants. 2. Liquid propellants.

Characteristics of a good propellant 1. Should undergo combustion to produce low molecular weight products. 2. Should undergo combust steadily. 3. Should have low ignition delay. 4. Should have high density. 5. Should be stable at variable temperature. 6. Should be safe to transport.

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introduction a fuel can be defined as a combustible substance, containing carbon as a main...

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