Fuels and Solid Fuels Overview

Fuels

• Fuels react with oxygen to produce heat
• Fuels contain combustible elements such as carbon, hydrogen, sulfur, etc.
• Fuels are classified according to their physical state (solid, liquid, or gas) and how they are obtained (naturally or manufactured).

Solid Fuels

• Wood is derived from tree trunks and branches
• Wood typically contains 15% moisture
• Its application as an engineering fuel is limited due to its low calorific value (4000-6400 Btu/lb)
• Coal is a highly carbonaceous solid fuel formed from prehistoric plants
• Coal contains carbon, hydrogen, oxygen, and non-combustible inorganic matter (ash)
• Coal Metamorphism: Stages of coal formation: peat, lignite, bituminous coal, anthracite
• With progressive transformation, carbon content increases, while moisture, volatile matter, and oxygen content decrease
• Coal's calorific value and hardness increase with each stage.

Analysis of Coals

• Proximate Analysis: Determines the percentages of volatile matter, fixed carbon, ash, and moisture in air-dried coal.
• Ultimate Analysis: Determines the percentages of carbon, hydrogen, oxygen, nitrogen, and sulfur in coal

Coke

• Coke is formed by carbonizing bituminous coal.

Calorific Value

• Gross Calorific Value (GCV) : Heat liberated during combustion of a unit mass of fuel, assuming all water produced is in liquid form
• Net Calorific Value (NCV): Heat liberated during combustion of a unit mass of fuel, assuming all water produced is in vapor form
• NCV is always less than GCV by the amount of heat needed to vaporize water.
• Dulong's Formula: Calculates calorific value from the chemical composition of fuel:
  • GCV = [8080C + 34500(H - O/8) + 2240S] kcal/kg
  • NCV = [GCV - 9(H)*587] kcal/kg
• Problem 1:
  • Coal composition: C=90%, O=3%, S=0.5%, N=0.5%, ash=2.5%
  • NCV = 8490.5 kcal/kg
  • Calculate H and GCV

Liquid Fuels

• Petroleum (crude oil) is a mixture of hydrocarbons, mainly paraffins, naphthenes, and aromatics
• Petroleum contains trace amounts of metals like silicon, iron, aluminum, calcium, magnesium, and nickel.
• It is formed from organic matter (marine sediments) transformed by anaerobic bacteria under pressure and heat over millions of years.

Classification of Petroleum

• Paraffin-base crude: Composed of saturated hydrocarbons up to C35H72, including waxes.
• Asphalt-base crude: Mainly contains naphthenes and cycloparaffins, with lower proportions of paraffins and aromatics.
• Mixed base crude: Contains both paraffin and asphalt-base compounds, but is rich in waxes.
  • Approximately 90% of current crude oil production falls into this category.

Petroleum Extraction

• Drilling: Wells drilled to reach oil reservoirs
• Hydrostatic Pressure: Oil is brought to the surface using the pressure of natural gas or by compressed air forced through a coaxial pipe system.
• Crude oil is sent to refineries for processing and refinement.