Three-stage low NOx burner for burning solid, liquid and gaseous fuels

A low Nox burner comprising ducts for the primary, secondary and tertiary air, arranged coaxially around its longitudinal axis, for supplying primary, secondary and tertiary air, respectively to a combustion chamber, means for accumulation of the air, means to give vorticity to the primary, secondary and tertiary air installed in the respective ducts, fuel supply means arranged within said ducts to inject the fuel into said combustion chamber, said means for giving vorticity to the secondary air comprising an axial swirler for the secondary air, formed by a plurality of blades each of which is made up of a fixed part and a mobile part connected to actuator means capable of angularly displacing said mobile part to give an air duct outlet angle between 30.degree. and 60.degree. , and ,means for giving vorticity to the tertiary air comprising an axial swirler for the tertiary air, in the shape of a cone and with fixed blades, a passage being formed on the tertiary air duct to feed the secondary air and the tertiary air.