Models for Representation of Fuels

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Models for Representation of Fuels

• P M V Subbarao
• Professor
• Mechanical Engineering Department

Characterization of Natural Resources for Better
Design.
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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.

• Low rank coals, such as lignite and
  sub-bituminous coals, are typically softer,
  friable materials with a dull, earthy appearance
  they are characterised by high moisture levels
  and a low carbon content, and hence a low energy
  content.
• Higher rank coals are typically harder and
  stronger and often have a black vitreous lustre.

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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.

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Characteristics of Coal

• Sulfur Content Coal with sulfur gt 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.

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• Burning Characteristics of Coal
• Free burning coals and Caking Coals.
• Caking index -- Pulverulent, sintered, weakly
  caked, caked and strongly caked.
• Ash Fusion temperature -- The temperature where
  the ash becomes very plastic.
• Design of ash handling system. -- Stoker furnace
  cannot use low ash fusion temperature coals.
• Dirtiness of furnace walls.

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Formation of Oils Gas
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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 600C, 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.

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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(2n2))
• Olefins
• Aromatics
• Ultimate Analysis
• C 84 -- 87 H 11 -- 16 O 0.3 -- 1.8
  N 0.1 -- 1.5 S 0.1 -- 3

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Product contents of Crude oils
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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

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Boiling range, and molecule size for typical
refinery

• BOILING RANGE CARBON ATOMS
• Refinery Gas lt25 oC 3
• Gasoline 40-150 oC 4-10
• Naptha 150-200 oC 10-12
• Kerosene 200-300 oC 12-16
• Diesel Fuel 300-400 oC 16-25
• Residual Oil gt400 oC gt25

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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

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Specific Gravity

• Specific Gravity (Weight of fuel/unit
  volume)/(weight of water/unit volume at 15oC)
• API Gravity 141.5/(SG15.6/15.6oC) - 131.5
• Significance of SG Origin of the fuel Combustion
  characteristics
• A high API G Paraffin fuel with good ignition
  quality low c/H ratio.
• A high API G aromatic asphaltic fuel with poor
  combustion characteristics
• APT G lt 10 Difficult or impossible to
  separate-out water and solid.
• Good quality paraffin straight run fuels 35 --
  40 (API G)
• Aromatic fules 27 -- 30

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• Calorific Value
• HCV (MJ/kg) 51.916 - 8.792 (SG)2 1 -
  (MAS) 9.42 S
• LCV 46.392 - 8.792 (SG)2 3.187 (SG) 1
  - (MAS) 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 40oC Kerosene 40oC Diesel Oile 90
  -- 95 oC
• Fire Point The temperature at which continuous
  flame is seen .
• Indication of fire risk.

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• Ash content Amount of totally non combustible
  products. Contaminants such as dirt, sand, rust
  and scales.
• Solid ash forming compounds can cause
• Severe abrasive wear in IC enginescylinder
  liners.
• High temperature slagging in fire tubes and super
  heater tubes.
• Blade deposition on gas turbine blades.

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• Viscosity Kinematic viscosity (Centi Stokes) and
  Dynamic viscosity (Centi Dynes).
• Design of burners/ IC engine injectors.
• Decreases with increasing temperature but becomes
  constant at 120oC
• 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.

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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 9000C is combined with
  coal to produce a number of light HCs.
• Producer gas, Bio-gas, Water gas, Coke-oven gas
  etc.

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Analysis of Fuel

• Proximate Analysis Ultimate Analysis.
• Proximate analysis - to determine the moisture,
  ash, volatiles matter and fixed carbon
• Ultimate or elementary analysis - to determine
  the elemental composition of the fuel
• The Energy content -- CFRI Formulae --
• Low Moisture Coal(M lt 2 ) -- CV (Kcal/kg) 71.7
  FC 75.6 (VM-0.1 A) - 60 M
• High Moisture Coal(M gt 2) -- CV(kcal.kg) 85.6
  100 - (1.1AM) - 60 M
• Where, M, A, FC and VM denote moister, ash ,
  fixed carbon and Volatile mater (all in percent),
  respectively.

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Fuel Model
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Ash Model