2. Coal Classification
• There are two main ways for classifying
coal - by rank and by type.
• Coal Rank
• Coal Types
• Coal Rank : The degree of 'metamorphisrn'
or coalification undergone by a coal, as it
matures from peat to anthracite
• This has an important bearing on its
physical and chemical properties, and is
referred to as the 'rank' of the coal.
3. Composition of Coals
• The natural constituents of coal can be divided into two
groups:
• (i) the organic fraction, which can be further subdivided
into microscopically identifiable macerals; and
• (ii) the inorganic fraction, which is commonly identified as
ash subsequent to combustion, but which may be isolated
in the form of mineral matter by low-temperature ashing
(LTA).
• The organic fraction can be further subdivided on the basis
of its rank or maturity.
4. Characteristics of Coal
• Sulfur Content : Coal with sulfur > 5% is not
recommended for combustion.
• Weatherability : Weathering or Slacking Index .
• An indication of size stability.
• Denotes the tendency to break on exposure to alternate wet
and dry periods.
• Weathering index is the percentage of coal passing through
a sieve having 170 mm2
openings.
• Grindability Index : A measure of relative ease of grinding
coals or the power required for grinding coals in a
pulverizer.
• G = 6.93 W + 13 -- W is the weight of sample passing
through 200 mesh size.
6. Theory of Oil Formation
• The most popular theory is known as the Organic Theory.
• This theory states that oil and gas have zoological origins.
• Small sea creatures from the days when the earth was mostly covered
in water died and settled to the bottom of the ocean floor.
• Layer upon layer of silt, sand and clay built up on top of them over
time.
• Through the process of decay, as well as ever increasing heat and
pressure, the former sea creatures were converted to oil and gas.
• Over millions of years, continuous pressure actually compressed those
layers of silt and clay into layers of rock.
• This is known as "reservoir rock".
• The temperature under the earth's surface increases the deeper you go
underground.
• At about 600
C, oil begins to form.
• Oil formation ceases at about 1500
C.
• Oil formed at lower temperatures (i.e. closer to the surface) is called
immature and is heavy.
10. Hydro carbon Chemistry & Classification of Crude Oils
• Paraffin based crudes (a waxy residue)
• Asphalt based crudes (an asphalt type
residue)
• Mixed type-based crudes ( a combination
residue)
• Components of Crude Oils.
• Paraffins (CnH(2n+2))
• Olefins
• Aromatics
• Ultimate Analysis
• C : 84 -- 87% ; H : 11 -- 16% ; O : 0.3 --
1.8% ; N : 0.1 -- 1.5% ; S : 0.1 -- 3%
11. petroleum refining : Basic refinery processes
• Functions of Refinery Units:
• (1) separating the many types of Hydrocarbon present in crude oils into
fractions of more closely related properties,
• (2) chemically converting the separated hydrocarbons into more
desirable reaction products, and
• (3) purifying the products of unwanted elements and compounds.
• Types of Distillation:
• Fractional Distillation
• Vacuum Distillation
• Super fractionation
• Thermal Cracking
• Catalytic Cracking
13. Boiling range, and molecule size for typical refinery
• BOILING RANGE # CARBON ATOMS
• Refinery Gas <25 o
C 3
• Gasoline 40-150 o
C 4-10
• Naptha 150-200 o
C 10-12
• Kerosene 200-300 o
C 12-16
• Diesel Fuel 300-400 o
C 16-25
• Residual Oil >400 o
C >25
14. Properties of Petroleum Derivatives
• Specific Gravity
• Calorific Value
• Viscosity
• Flash Point
• Fire Point
• Pour Point
• Volatility
• Ash content
• Carbon Residue
• Octane Number / Cetane Number / Performance Number
15. • Calorific Value:
• HCV (MJ/kg) = {51.916 - 8.792 * (SG)2
} * {1 - (M+A+S)} + 9.42 * S
• LCV = {46.392 - 8.792 * (SG)2
+ 3.187 *(SG)} * {1 - (M+A+S)} +
9.42 *S - 2.449 * M
• Flash Point: The temperature at which the oil must be heated under
prescribed conditions for sufficient vapour to be given off to form an
flammable mixture with air.
• Determines the type of blend
• indicates safe sotrage temperatures.
• Gasoline : 40o
C; Kerosene: 40o
C; Diesel Oile: 90 -- 95 o
C
• Fire Point: The temperature at which continuous flame is seen .
• Indication of fire risk.
16. • Viscosity: Kinematic viscosity (Centi Stokes) and Dynamic viscosity
(Centi Dynes).
• Design of burners/ IC engine injectors.
• Decreases with increasing temperature but becomes constant at 120o
C
• Heating of fuel helps in atomization.
• Maximum viscosity for easy atomization in commercial burners : 25
cStokes.
• For easy pumping 1200 cStokes.
• Diesel fules : Low viscosity causes exessive leakage.
• High viscosity produces coarse drops. -- results in formation of engine
deposits -- incomplete combustion.
• VISCOSITY IS NOT AN PROPORTIONATE PROPERTY.
17. Gaseous Fuels
• Can be easily piped into furnace -- no physical handling is required.
• Natural Gas -- True Fossil fuel
• Odorless and colorless
• Mainly CH4 + heavier HCs
• HHV = 55,000 kJ/kg.
• Manufactured Gases
• LPG -- light distillates of petroleum. -- Heavier than air!!!
• Stored and transported under pressure (0.4 -- 2 Mpa).
• SNG : Produced from coal by Hydrogenation -- cheap and clean..
• Pressurized Hydrogen at 9000
C is combined with coal to produce a
number of light HCs.
• Producer gas, Bio-gas, Water gas, Coke-oven gas etc….
