9.4 What different burning methods exist?
Burning or thermochemical conversion processes comprise incineration, gasification, and pyrolysis. A typical flame can be used to describe these three methods as they resemble the different zones of a flame.
The pyrolysis zone occurs at the lowest region of the flame, where the temperature is relatively low. In this zone, organic materials undergo thermal decomposition due to the heat but without oxygen supply. Pyrolysis will break down the organic compounds into simpler molecules such as gases, volatile organic compounds, and solid char.
The middle region of the flame represents the gasification zone. In this zone, the pyrolysis products partially oxidise with limited oxygen. Gases like carbon monoxide, hydrogen and methane are formed.
In the upper region of the flame combustion or incineration takes place. The flame has sufficient oxygen available for the complete combustion of gases generated in the pyrolysis and gasification zones. Complete combustion of gases occurs producing heat, water vapor, carbon dioxide and ash.
The following table summarizes and compares essential parameters for incineration, pyrolysis and gasification.
| Parameter | Incineration | Pyrolysis | Gasification |
|---|---|---|---|
| Temperature | 800 – 1000°C | 300 – 900°C | 700 – 1000°C |
| Process conditions | Excess air/oxygen required | No oxygen | Partial oxygen supply |
| Main Products | Ash Heat Flue gas | Char Oil Syngas | Syngas Char Tar |
| Harmful substances | Heavy metals: mainly in the solid fraction and traces in the gas fraction | ||
Let’s delve in and learn more about the different burning methods.
