Topic 6.3 Notes – Fuel Types and Uses

What Fuels Are and How Their Uses Differ

A fuel is any material that stores chemical energy and releases usable energy when it is burned or otherwise converted.

Two useful categories show up right away:

• Direct fuels are burned with little processing.
  • Firewood and peat fit here.
• Processed fuels are made from or separated out of raw resources.
  • Charcoal is made from wood.
  • Refined petroleum products are made from crude oil.

What makes one fuel better than another depends on a few things:

• Energy content
  More energy per mass or volume means more useful power or heat.
• Moisture content
  Wet fuels waste energy evaporating water, so they usually burn less efficiently.
• Carbon content and composition
  This affects heat output and emissions.
• Ignition, storage, and transport
  A fuel might burn well but still be inconvenient to move or store.
• Accessibility and cost
  A fuel people can easily get often gets used even if it is lower quality.
• Intended use
  Cooking, home heating, electricity generation, transportation, and industry all need different fuel traits.

The main idea is simple. The “best” fuel depends on the job and the infrastructure available.

Major Fuel Types and Their Common Uses

Wood fuels

• Firewood is wood burned directly.
  • Common for cooking and heating, especially in developing countries and rural areas.
  • It is widely used because it is accessible and needs little technology.
  • It often has lower efficiency because moisture and incomplete combustion reduce useful heat.
• Charcoal is a carbon-rich fuel made by heating wood in low oxygen.
  • Burns hotter and with less smoke at the point of use than firewood.
  • It is more compact and easier to store and transport.
  • Used for cooking and for jobs needing concentrated heat.
  • Important exam trap: charcoal is processed wood, not coal.

Peat

• Peat is partially decomposed organic material from waterlogged places such as bogs.
• It can be dried and burned for heating or cooking.
• It is a low-quality fuel because it has high moisture and lower energy content.
• Another common trap: peat is a precursor to coal, but it is not one of the three coal grades.

Coal types

Coal forms in a progression as burial, heat, and pressure increase. The diagram below traces that change from peat into lignite and then higher-grade coals.

1. Peat
2. Lignite
3. Bituminous coal
4. Anthracite

Coal formation and increasing coal rank

Across that sequence, carbon concentration and energy content increase, and moisture decreases.

• Lignite
  • Lowest-grade coal
  • High moisture, lower carbon, lower energy
  • Often used near mining sites for electricity generation
• Bituminous coal
  • Intermediate-to-high-grade coal
  • More energy and less moisture than lignite
  • Major fuel for electricity generation and industrial heating
• Anthracite
  • Highest-grade coal
  • Highest carbon concentration and heat content
  • Burns hotter and relatively more cleanly than lower-grade coal

Natural gas

• Natural gas is mostly methane.
• It is the cleanest-burning fossil fuel.
• Used for cooking, space and water heating, industrial heat, electricity generation, and some transportation.
• Delivered by pipeline or stored as compressed or liquefied gas.

Petroleum fuels

• Crude oil is a raw mixture of hydrocarbons.
• It is refined into specialized fuels such as:
  • gasoline
  • diesel fuel
  • jet fuel
  • heating oil
  • liquefied petroleum gases such as propane
• Petroleum works especially well for transportation because liquid fuels are energy-dense and easy to store in tanks.

Tar Sands and Specialized Petroleum Products

Tar sands are a mixture of clay, sand, water, and bitumen.

• Bitumen is a thick, viscous hydrocarbon material.
• It must be separated and processed before use.
• Tar sands are an unconventional petroleum resource.
• They are not pure crude oil and not a finished fuel.

Refined petroleum products have specialized uses:

• Gasoline for spark-ignition motor vehicles
• Diesel for trucks, buses, heavy equipment, ships, and generators
• Jet fuel for turbine aircraft
• Heating oil for furnaces and boilers
• Propane for cooking, heating, and some vehicles

Matching Fuels to Uses

Here’s the pattern APES wants you to recognize:

Why these patterns happen:

• Solids like coal work well in large stationary facilities.
• Gases like natural gas work well where pipelines or storage systems exist.
• Liquids from petroleum dominate transportation because they are portable and energy dense.

How Cogeneration Increases Efficiency

Cogeneration, or combined heat and power, uses one fuel source to produce both electricity and useful heat.

The diagram below shows the basic idea. Instead of letting the exhaust heat leave the system, a CHP plant captures it and uses it.

1. Fuel is burned.
2. The system generates electricity.
3. Waste heat is captured instead of released.
4. That heat is used for steam, hot water, space heating, or industrial processes.

Combined heat and power system

Why it matters:

• It increases overall efficiency
• It reduces the need for separate fuel use for heat and electricity
• It can lower costs and emissions

Cogeneration can use natural gas, coal, petroleum products, or biomass. It works best where there is a steady nearby heat demand, like hospitals, factories, campuses, and district-heating systems.