9.5 What is important to know about incineration?

Incineration is the thermochemical process that provides the most significant volume reduction. The combustion process between 800 and 1000°C produces ash, heat, and flue gases. The residual ash is usually less than 4% of the dewatered sludge volume fed to incineration.

Temperature

While incineration occurs at temperatures between 800 and 1000°C, the optimum range is 850 to 980°C. Temperatures below 850°C can result in odour emissions, and ash sintering can occur at temperatures above 950°C. The reached temperature will depend on the energy content and quantity of sludge/biosolids and the amount of available combustion air.

Oxygen

Sludge incineration destroys organic substances and pathogenic organisms through combustion obtained in the presence of excess oxygen. While the heating value of sludge/biosolids is relevant for all thermochemical processes, it has a critical role in the incineration process.

Heating Value

The heating value of sludge impacts the combustion efficiency and the amount of heat generated during burning. Sludge with a higher heating value is more efficient in incineration as it produces more heat when burned, contributing to better energy recovery, and potentially reducing the need for external energy sources. The heating value also influences the combustion temperature, residence time, and emissions control in incineration, affecting the overall process efficiency and environmental impact.

Dry Matter Content

Organic sludge incineration is only energy-autonomous when solids concentration is higher than 35%. Sludge that has only been dewatered may have solids between 20 and 30% and may still be burned with additional fuels. An increased solids concentration not only reduces the requirement for fuel but also the required operating time. Furthermore, it increases the processing capacity.

For further information, please click on the Materials tab at the top of the page.