8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 1/27

Click to edit Master subtitle style

  11

Fuels and Combustion

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 2/27

  22

Recommended Books

1. Fuels and Combustion; M.L. Smith & K.W. Stinson

2. Fuels and Fuel Technology ; W. Francis & M.C. Peters

3. Fuel – Solid , Liquid and Gaseous; J.S.S. Brame & J.G.King

4. Hydrocarbon Fuels;  E.M. Goodger 

5. Coal Conversion Processes;  Stanley & Lee

6. Fuel Testing: Laboratory Methods in FuelTechnology;  G.W. Himus

7. Methods of Analysis of Fuels and Oils;  J.R.Campbell

8. Element of fuel , furnaces and combustion

9. O.P Gupta.

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 3/27

  33

Fuel

l A substance which produce heat

either by combustion or by nuclear 

fission / fusion

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 4/27

  44

Classification of Fuels

l Fuels can be classified as solid, liquidand gaseous fuels.

l Solid fuels : wood, coal, charcoal (50% to 95%

carbon) and cokeLiquid fuels : petrol, kerosene,diesel, alcohol etcGaseous fuels : methane, propane,

butane, hydrogen, coal gas, gobar gasetc

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 5/27

  55

Classification of Fuels

l Primary Fuels: Naturally occurring

e.g. coal, wood, natural gas

l Secondary Fuels: Which are derivedfrom primary fuels e.g. kerosene, coke etc

l Naturally occurring

l Artificially prepared

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 6/27

  66

Combustion

l Combustion is the conversion of asubstance (called a fuel) into chemicalcompounds known as products of 

combustion by combination with anoxidizer .

l The combustion process is an exothermic 

chemical reaction, i.e., a reaction thatreleases energy.

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 7/27  77

Combustion

l Combustion or burning is a complex

sequence of exothermic chemical

reactions between a fuel (usually ahydrocarbon) and an oxidant

accompanied by the production of heat

or both heat and light

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 8/27  88

Combustion

l Fuel + Oxidizer  => Products of combustion + Energy

l Fuel ?

l Oxidizer ?

l Products of Combustion ?

l Incomplete Combustion ?

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 9/27  99

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 10/27

  1010

Fundamental Definitions

l Calorific value

  Amount of heat librated by the combustion of unitquantity of fuel. kcal/ kg , kcal / m3 

l Gross Calorific Value (G.C.V) or HCV

  heating value measurement in which the productwater vapour is allowed to condense

l Net Calorific Value (N.C.V) or LCV

  heating value in which the water remains a vapor 

and does not yield its heat of vaporization

l HHV = LHV + (mwater /mfuel ) water  ʎ

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 11/27

  1111

l Flash Point

  The lowest temperature at which a liquid fuelgives enough vapours in air which produce a

momentary flash when exposed to a flame l Firepoint

The lowest temperature at which a liquid fuelvapours in air produces a continuous flame when

exposed to a flame 

Fundamental Definitions

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 12/27

  1212

l Density

l Specific gravity

l Viscosity

l Pour Point

l Carbon Residue

 

Fundamental Definitions

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 13/27

  1313

Theoretical Flame Temperature:

  It is the temperature attained by theproducts of combustion of fuel whenthere is no loss of heat to thesurroundings

Flue Gas: It is the gaseous product of combustion of fuel

Fundamental Definitions

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 14/27

  1414

Coal

l Origin of Coal

Coal has been formed by the partialdecay of plant materials accumulated

million of years ago and further altered bythe action of heat and pressurel In situ Theory: coal occupies the same

site where the orignal palnts grewl Drift Theory: plants were uprooted and

drifted by rivers to get deposited

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 15/27

  1515

Coal classification

• Peat :

• Lignite: soft coal and the youngest

• sub-bituminous

• Bituminous:

• Anthracite: hard and geologically theoldest composed mainly of carbon

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 16/27

 

Types

l  As geological processes apply pressure to deadbiotic material over time, under suitable conditions it istransformed successively into

l Peat, considered to be a precursor of coal, has

industrial importance as a fuel in some regions, for example, Ireland and Finland. In its dehydrated form,peat is a highly effective absorbent for fuel and oil spillson land and water 

l

Lignite, also referred to as brown coal, is the lowestrank of coal and used almost exclusively as fuel for electric power generation.

l Jet is a compact form of lignite that is sometimes polished andhas been used as an ornamental stone since the Iron Age

1616

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 17/27

 

Jet

l Jet is a geological material and isconsidered to be a minor gemstone. Jetis not considered a true mineral, but

rather a mineraloid as it has an organicorigin, being derived from decayingwood under extreme pressure.

1717

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 18/27

 

Sub-bituminous coal

l Sub-bituminous coal, whose properties range fromthose of lignite to those of bituminous coal are usedprimarily as fuel for steam-electric power generation. Additionally, it is an important source of light

aromatic hydrocarbons for the chemical synthesis industry.

l Bituminous coal, dense mineral, black but sometimesdark brown, often with well-defined bands of bright anddull material, used primarily as fuel in steam-electricpower generation, with substantial quantities also usedfor heat and power applications in manufacturing and tomake coke

1818

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 19/27

 

l  Anthracite, the highest rank; a harder, glossy, black coalused primarily for residential and commercialspace heating.

l Graphite, technically the highest rank, but difficult to

ignite and is not so commonly used as fuel: it is mostlyused in pencils and, when powdered, as a lubricant.

1919

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 20/27

  2020

Coal 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, etc• Useful for furnace design (e.g flame temperature,

flue duct design)

• Laboratory analysis

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 21/27

  2121

Proximate analysis

l Moisture Content :

Ø Moisture in coal must be transported,handled and stored

Ø Since it replaces combustible matter, itdecreases the heat content per kg of coal

Ø  Aids radiation heat transfer 

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 22/27

  2222

Proximate analysis

l  Volatile Matter:

Ø Consist of CH4, hydrocarbons, H2 and CO,and incombustible gases like CO2 and N2

Ø Proportionately increases flame length, andhelps in easier ignition of coal

Ø Sets minimum limit on the furnace height

and volume

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 23/27

  2323

Proximate analysis

Ash Content :

•  Ash is an impurity that will not burn

• Reduces handling and burning capacity.

• Increases handling costs.•  Affects combustion efficiency and boiler 

efficiency

• Causes clinkering

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 24/27

  2424

Proximate analysis

l  Fixed carbon:

Ø Solid fuel left in the furnace after volatilematter is removed

Ø consists mostly of carbon

Ø may contains some H2, O2, S and N2

Ø gives a rough estimate of heating value

of coal

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 25/27

 

l Pyrolysis is usually the first chemical reaction that occurs in theburning of many solid organic fuels, like wood, cloth, and paper,and also of some kinds of plastic.

l In a wood fire, the visible flames are not due to combustion of thewood itself, but rather of the gases released by its pyrolysis;

l whereas the flame-less burning of embers is the combustion of the solid residue (charcoal) left behind by it.

l Thus, the pyrolysis of common materials like wood, plastic, andclothing is extremely important for fire safety and fire-fighting.

2525

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 26/27

 

l In practice it is not possible to achieve acompletely oxygen-free atmosphere. Becausesome oxygen is present in any pyrolysissystem, a small amount of oxidation occurs.The word is coined from the Greek-derivedelements  pyr "fire" and lysis "separating".

2626

8/3/2019 Lect 1intro to Fuel Engg

http://slidepdf.com/reader/full/lect-1intro-to-fuel-engg 27/27

l Pyrolysis has been used since ancient times for turning wood intocharcoal in an industrial scale. Besides wood, the process canalso use sawdust and other wood waste products.

l Charcoal is obtained by heating wood until its complete pyrolysis(carbonization) occurs, leaving only carbon and inorganic ash.

l In many parts of the world, charcoal is still produced semi-industrially, by burning a pile of wood that has been mostlycovered with mud or bricks.

l The heat generated by burning part of the wood and the volatileby products pyrolyzes the rest of the pile. The limited supply of 

oxygen prevents the charcoal from burning too.l  A more modern alternative is to heat the wood in an airtight metal

vessel, which is much less polluting and allows the volatileproducts to be condensed.

2727