The theory behind diffusive flame burners is heating materials to elevated temperatures (irradiation); important flame volumes are required to ensure significant quantities of feedstock are heated. Diffusive flame burners are therefore applied to the front and side walls of the furnace.

These burners can be fed with both gaseous fuels with net calorific values inferior to 2000 kcal/Nm3 using Single Air Burners (SAB) and with high calorific values above 2000 kcal/Nm3 using Multi-Air Burners (MAB). Both burners can function using liquid fuels (light or heavy oils) or gaseous fuels simultaneously. Nitrogen monoxide and nitrogen dioxide emissions into the atmosphere are low. Carbon monoxide released into the atmosphere is zero even when preheated air is used above 500 °C; maximum flame temperature uniformity is fundamental for these burners reaching target temperatures.  NOx emissions remain below 200 mg/Nm3 @ 3% O2 (1250 °C furnace temperature) with standard burners, this value is below 100 mg/Nm3 with flameless burners.

Power and size are dimensioned according to requirements: power varies from 500 to 5000 kW. Diffusive flame burners are able to function either in the proportional control mode or in the on/off mode. Burners can also be equipped with an automatic flame control system using U.V. cells and with automatic pilot burners for cold start-up.