Advanced overfire air system for NOx control

摘要

An advanced overfire air system for NOx control designed for use in a firing system of the type that is particularly suited for use in fossil fuel-fired furnaces and a method of operating such a furnace which embodies an advanced overfire air system. The advanced overfire air system for NOx control includes multi-elevations of overfire air compartments consisting of a plurality of close coupled overfire air compartments (84, 86) and a plurality of separated overfire air compartments (94, 96, 98). The close coupled overfire air (84, 86) compartments are supported at a first elevation in the furnace (10) and the separated overfire air compartments (94, 96, 98) are supported at a second elevation in the furnace (10) so as to be spaced from but aligned with the close coupled overfire air compartments (84, 86). Overfire air is supplied (106, 92) to both the close coupled overfire air compartments (84, 86) and the separated overfire air compartments (94, 96, 98) such that there is a predetermined most favorable distribution of overfire air therebetween, such that the overfire (106) air exiting from the separated overfire air compartments (94, 96, 98) establishes a horizontal "spray" or "fan" distribution (124, 126, 128) of overfire air over the plan area of the furnace, and such that the overfire air (106) exits from the separated overfire air compartments (94, 96, 98) at velocities significantly higher than the velocities employed heretofore.