Air injection for nitrogen oxide reduction and improved product quality

A system for calcining a feed material, the system comprising:

• a rotary kiln rotating on a slightly inclined horizontal axis, the rotary kiln having a feed end and a discharge end wherein the feed material is introduced into the feed end and passes through the rotary kiln before exiting the discharge end;
• means for introducing combustible fuel and combustion air into the rotary kiln at the discharge end of the rotary kiln wherein the rotary kiln operates in a substoichiometric mode near the discharge end;
• means for introducing combustion air into the rotary kiln between the feed and discharge ends wherein combustion air is introduced in an amount creating an oxygen deficient atmosphere at the discharge end of the rotary kiln such that nitrogen oxide generation is lowered and sulfur is removed from the feed material;
• and
• wherein the combustion air completely combusts the combustible fuel prior to the combustible fuel exiting the rotary kiln.

A method for completely combusting combustible fuel added to a rotary kiln of a calcining system at a discharge end of the rotary kiln prior to the combustible fuel exiting a feed end of the rotary kiln, the rotary kiln rotating on a slightly inclined horizontal axis, the method comprising:

• introducing feed material into the rotary kiln through the feed end after the feed material has passed through a preheating/precalciner device positioned adjacent the feed end;
• introducing combustible fuel and combustion air into the rotary kiln at the discharge end through a burner located in a stationary hood positioned adjacent the discharge end of the rotary kiln, such that the rotary kiln operates in a substoichiometric mode near the discharge end;
• and
• introducing combustion air into the rotary kiln between the feed and discharge ends of the rotary kiln through at least one air nozzle wherein the air nozzles introduce combustion air in an amount that creates an oxygen deficient atmosphere in the rotary kiln such that nitrogen oxide generation is lowered and sulfur is removed from the feed material.

A method for calcining a feed material in a rotary kiln rotating on a slightly inclined horizontal axis, the method comprising:

• introducing the feed material into the rotary kiln through a feed end of the rotary kiln;
• introducing combustible fuel into the rotary kiln through a burner located in a stationary hood positioned adjacent a discharge end of the rotary kiln such that the combustible fuel travels through the rotary kiln towards the feed end of the rotary kiln and the rotary kiln operates in a substoichiometric mode near the discharge end;
• introducing combustion air into the rotary kiln through the discharge end of the rotary kiln;
• injecting combustion air into the rotary kiln between the feed and discharge ends of the rotary kiln through at least one air nozzle, wherein the combustion air injected by the air nozzles completely combusts the combustible fuel introduced by the burner before the combustible fuel exits the feed end of the rotary kiln as exhaust gas;
• and
• creating an oxygen deficient atmosphere at the discharge end of the rotary kiln wherein the oxygen deficient atmosphere lowers nitrogen oxide generation and aids in removing sulfur from the feed material being processed.