Hydraulic-binder rotary-furnace operation

A method of operating a rotary furnace for the production of a hydraulic binder, comprising the steps of:

• providing a furnace having a substantially cylindrical shape with a longitudinal axis which is inclined with respect to the horizontal, an upper end, a lower end and a substantially cylindrical wall, the length of the furnace being at least 9 times the diameter of the furnace, and preferably from 9 to 40 times the diameter of the furnace, the furnace comprising a burner assembly at its lower end;
• rotating the furnace around the longitudinal axis;
• feeding a material to be pyroprocessed to the furnace at its upper end, the material to be pyroprocessed thereby traveling downwards through the furnace under the effect of gravity and being pyroprocessed in the furnace by heat generated by combustion of a main fuel in the furnace and leaving the furnace at its lower end as pyroprocessed material;
• transferring the pyroprocessed material from the furnace to an air-cooled material cooler, to produce cooled pyroprocessed material and hot air;
• injecting the main fuel and primary combustion oxidizer into the furnace with the burner assembly so as to generate partial combustion of the main fuel with the primary combustion oxidizer, a flame generated by combustion of the main fuel with the primary and secondary oxidizer being directed substantially parallel to the longitudinal axis of the furnace;
• feeding hot air from the material cooler to the furnace at its lower end as secondary oxidizer so as to substantially complete combustion of the main fuel;
• evacuating flue gas from the upper end of the furnace;
• and
• varying a longitudinal temperature profile within the furnace during furnace operation by injecting, into the furnace, at least one fluid other than the main fuel, the primary oxidizer and the secondary oxidizer, wherein the variation of the longitudinal temperature profile is achieved by continuously or discontinuously varying at least one injection parameter of the fluid injection into the furnace.