Effect of over-Fire Air Velocity on the Aerodynamic Characteristics in a Cold Model of an Arch-Fired Boiler with New over-Fire Air Arrangement

Abstract

A new over-fire air (OFA) program is proposed for Foster Wheeler (FW) type arch-fired boiler: the OFA nozzles are setting on arches near the furnace center and emitting OFA flow into the furnace at an inclined angle. Cold airflow experiments were conducted to determine the effect of the OFA velocity on the aerodynamic field in a small-scale furnace modeled for a 660-MWe arch-fired boiler. As the OFA velocity increases, the penetration depth of the OFA flow increases and the turning point of the OFA flow moves to the furnace center. At the same time, the vertical velocity of arch-injected airflow reduced faster because of the attracted effect of the OFA flow with higher velocity. When the OFA velocity is 22.39m/s (corresponding to 30m/s in the actual boiler), the OFA flow could penetrate to the furnace center and mix with the upflowing gas completely, while the arch-injected airflow have sufficient travel distance and enough residence time in the lower furnace. Thus, considering the penetration depth of arch-injected flow and the OFA flow, an OFA velocity of 22.39m/s recommended according to the present work.