Over-fire air control system for a pulverized solid fuel furnace

摘要

An over-fire air control system for a pulverized fuel furnace, in which a burner assembly is provided for discharging a fuel/primary air mixture along with secondary air to combust the fuel. The amount of primary air and secondary air discharge is controlled to achieve incomplete combustion, and an overfire air port is provided through which additional air is discharged to complete the combustion. The overfire air port receives two streams of air, one high in volume and low in velocity and the other low in volume and high in velocity. Dampers are provided for controlling the air streams to achieve optimum quantifies and velocities of the air. According to one embodiment, a source of one of the air streams is the primary air portion of the fuel/primary air mixture applied to the burner assembly. As a result, the formation of nitrous oxides are reduced and fairly precise air fuel ratios can be maintained despite variations in the quality of the fuel and the pressure and amount of primary air.