Fuel Technology Notes

Unit-IV: Fuel Technology

Definition of Fuel
  • A fuel is a combustible carbonaceous material, either naturally occurring or artificially manufactured.
  • It serves as a source of heat, light, and raw material in some cases.
Classification of Fuels

1. Based on Origin

  • Primary Fuels: Naturally occurring fuels like wood, coal, crude oil, natural gas, peat, lignite, anthracite.
  • Secondary Fuels: Derivatives of primary fuels that require chemical processing, e.g., charcoal, coke, producer gas, petrol, diesel.

2. Based on Physical State

  • Solid Fuels: E.g., Coal, wood, coke.
  • Liquid Fuels: E.g., Crude oil, petrol, diesel.
  • Gaseous Fuels: E.g., Natural gas, coal gas.
Liquid Fuels

Importance: Commonly used for commercial and domestic purposes as they are derived from crude oil (primary fuel).

Advantages
  • Higher calorific value per unit mass compared to solid fuels.
  • Burns cleanly without dust, ash, or clinkers.
  • Easier to extinguish fires by stopping fuel supply.
  • Easy to transport and store without loss.
  • Minimal heat loss in chimneys; requires less air for combustion.
Disadvantages
  • Higher cost than solid fuels.
  • Requires special storage tanks.
  • Higher risk of fire hazards.
  • Odor issues.
  • Needs specialized burners for efficient combustion.
Petroleum (Crude Oil)
  • Dark liquid composed mainly of hydrocarbons with impurities.
  • Average composition:
    • Carbon (C): 79.5% - 87.1%
    • Hydrogen (H): 11.5% - 14.8%
    • Sulfur (S): 0.1% - 3.5%
    • Nitrogen & Oxygen: 0.1% - 0.5%
Refining of Petroleum
  • Definition: The process of removing impurities from crude oil and separating it into various fractions based on boiling points.
Stages of Refining
  1. Removal of solid impurities: Allow crude oil to settle, then centrifuge.
  2. Removal of water: Use Cottrell’s process with charged electrodes.
  3. Removal of harmful impurities: Treat with copper oxide to remove sulfur.
  4. Fractional Distillation:
    • Crude oil is heated to about 400°C, vaporized, and passed through a cooling tower to condense at different levels.
    • Collect fractions based on boiling points.
Fractions and Applications
  • Uncondensed gases (Below 300°C): LPG
  • Petroleum ether (30-70°C): Solvent
  • Gasoline (40-120°C): Motor fuel
  • Naphtha (120-180°C): Dry cleaning solvent
  • Kerosene (180-250°C): Domestic and jet fuel
  • Diesel oil (250-320°C): Diesel engine fuel
  • Heavy oil (320-400°C): Lubricating oil, petroleum jelly
  • Residual products (Above 400°C): Asphalt, petroleum coke
Synthesis of Petrol

Methods:

  1. Fischer-Tropsch Method: Uses water gas (CO + H2) catalyzed at 200-300°C.
    • Reaction:
      $n ext{CO} + 2n ext{H}2 ightarrow ext{C}n ext{H}{2n} + n ext{H}2 ext{O}$
  2. Bergius Process: Converts coal into hydrocarbons using hydrogen at high temperatures and pressures.
Gaseous Fuels
  • Include natural gas, water gas, producer gas, bio gas, LPG.
Advantages
  • Easily transported through pipelines
  • High heat contents
  • Clean burning, no smoke or ash
  • Easily controlled combustion
Disadvantages
  • Requires large storage tanks
  • High fire hazard risks

Natural Gas Composition: Primarily methane, it may vary from dry to rich gas based on its hydrocarbon content. Calorific value: 12000 - 14000 kcal/m³.

Combustion and Knocking
  • Knocking: A phenomenon where the fuel-air mixture ignites prematurely, reducing engine efficiency.
  • Chemical Structure Influence:
    • Order of knocking tendency: Straight-chain paraffins > Branched-chain > Olefins > Cyclo-paraffins > Aromatics
    • Good fuel should minimize knocking.
Antiknocking Agents
  • Added to petrol to prevent knocking, e.g., TEL (Tetraethyl lead), MTBE (Methyl Tertiary Butyl Ether).
  • Lead Issues: Mechanical damage, pollution, catalyst poisoning.
Calorific Value
  • Definition: Heat released when a unit mass of fuel is combusted.
    • Higher Calorific Value (HCV) included latent heat of steam.
    • Lower Calorific Value (LCV) excludes latent heat.
Determination of Calorific Value
  • Bomb Calorimeter Method: Calculates heat absorbed by water from combusting fuel.
  • Calculations: Use mass, temperature rise, specific heat, water equivalent.
Example Calculations
  1. Calculation of GCV based on initial and final temperatures of water.
  2. Calculate calorific values from mass properties and temperature changes of fuel samples.
  3. Problems involving GCV and NCV determinations using provided formulas and results.
Summary
  • Fuels are vital energy sources classified into primary/secondary, solid/liquid/gaseous.
  • Liquid fuels, petroleum, and synthetic processes are crucial for energy generation, efficiency, and environmental considerations in their use.