A coal fire works through a process of combustion where the solid fuel heats up, releases gases, and then burns, primarily from the bottom up.
Understanding the Basics of Coal Combustion
Burning coal involves a chemical reaction with oxygen that releases heat and light. Unlike wood, which burns more uniformly, coal has a unique combustion process.
Key Stages of a Coal Fire
When you light coal, it doesn't instantly burst into flame. Several stages occur as the fire gets going:
- Heating and Drying: The coal is heated, and any moisture within it is driven off as steam.
- Volatile Matter Release: As the temperature increases, volatile organic compounds (coal gas) trapped within the coal are released. Coal contains coal gas which is released as it burns – producing a very nice flame effect. These gases ignite easily, creating the initial flames.
- Char Combustion: After the volatile matter burns off, the remaining solid material, primarily carbon (known as char), burns. This stage produces most of the heat and glows red.
The Direction of Burning
According to the reference, coal mainly burns from the bottom up. This is because the hot air and heat rise, preheating the coal above the burning layer, encouraging the combustion process to move upwards through the fuel bed.
Enhancing and Maintaining the Fire
Once a coal fire is established:
- It requires a steady supply of oxygen, usually drawn from beneath the grate.
- Regular stoking or stirring can help. Once the fire is established it responds well to a good stirring with the poker from above. Stirring breaks up clinkers (fused ash) and ensures oxygen can reach the burning coal efficiently.
- Adding fresh coal on top allows the heat from below to release more volatile gases, which then ignite.
| Stage | Description | Primary Output |
|---|---|---|
| Heating/Drying | Water vaporizes | Steam |
| Volatile Release | Coal gas is liberated and ignites | Flames, Heat |
| Char Combustion | Solid carbon burns | Heat, Glow (Embers) |
While coal is a powerful fuel, providing intense and long-lasting heat, its combustion releases significant amounts of pollutants, making it less environmentally friendly compared to other fuels.
