Drawbacks such as low over-fire air(OFA) coverage in the whole furnace cross section

weak mixing between OFA and the flue gas

and the high NOx emission occur in the conventional wall-firing boiler with single stage OFA.Thus

two-stage OFA was experimentally studied by taking the supercritical 2×600 MW units boiler of first phase project in Guodian Bengbu Power Generation Co.

Ltd.as the object.Results show that

setting two-stage OFA not only can increase the total OFA volume so as to decrease the NOx emission by about 20%

but also can improve the boiler combustion efficiency because staggered arrangement of two layers of OFA nozzles expands the airflow coverage in the furnace cross section

and enhances the mixing between the OFA and flue gas

enabling the unburnt matter fully combust within limited height.