NOx Reduction and Burnout Optimisation Using an Aerodynamically Air Staged Burner and an Air Staged Precombustor Burner

Recently, a significant body of work has been undertaken at the IFRF to develop low-NOx pulverised-coal burners. The majority of the work has focused on the design and evaluation of internal air staged burners at the 2.5 MW semi-i~dustrial scale. Specific emphasis has been given to retrofitting the burner designs to wall-fired combustion units. Two burner concepts have been evaluated, an aerodynamically air staged burner (AASB) and an air staged precombustor burner (ASPB). The dominant design feature of all air-staged burners is the creation of a fuel-rich zone in which volatile coal-nitrogen species react to molecular N2 in prefernce to NOx. The two burners create this fuel rich zone in fundamentally different ways. The AASB relies on optimisation of the near-burner field aerodynamics whereas the ASPB utilises a prechamber operating under sub-stoichiometric conditions. Both burner were fired with a high volatile and a medium volatile bituminous coal. Relatively low NOx emissions and acceptable burnout levels were achieved for both coals, however a coal type dependence was observed. Results of the two burners have been compared to an externally air staged burner firing the same coals.