Patent ID: 7484955

Claim:
A method of adjusting air flow distribution in a cyclone furnace of the type having a plurality of cyclones, each cyclone having a barrel, an attached burner, primary, secondary and tertiary air flow dampers for controlling air flow to the barrel and burner, over-fire air flow dampers, a lighter scanner and a main flame scanner in order to minimize NOx while maintaining acceptable carbon monoxide emissions, unburned carbon loss, and reliable cyclone operation, the method comprising the steps of: (a) setting secondary air flow on each cyclone to a typical secondary air flow damper setting to provide equal secondary air flow to each cyclone; (b) setting all over-fire air flow dampers to a same air flow value; (c) closing the tertiary air flow damper; (d) adjusting the primary air flow dampers to 90-95% of a target sum of primary air flow and tertiary air flow as indicated by one or more flow measurement devices or the position of the primary air flow damper; (e) adjusting the tertiary air flow damper until a minimum tertiary air flow at which a balance of primary and tertiary air flow as indicated by flow measurement devices or the position of the primary and tertiary air flow dampers is achieved; (f) assessing cyclone performance by analyzing the flame scanner signals from the main flame scanner and lighter scanner and generating statistics indicative of whether operational characteristics of one or more cyclones is inside or outside of predetermined variance limits; (g) increasing primary air flow or secondary air flow as appropriate to eliminate instability indicated by some or all of statistics being outside of ± variance limits; (h) in the case of all cyclones indicating stable operation by reference to both main flame and scanner lighter signals, decreasing primary air flow on each cyclone until a minimum primary air flow is reached at which the main flame scanner signal begins to exhibit flame instability as indicated by statistics drifting toward variance limits, while maintaining tertiary air flow at minimum flow; (i) upon adjustment of the primary air flow to a minimum value needed to achieve stable operation, decreasing secondary air flow by closing the secondary air damper on each cyclone stepwise and simultaneously until a minimum secondary air flow is reached at which the lighter scanners begin to detect instability; (j) simultaneously increasing air flow to all overfire air ports equally to maintain excess air flow while decreasing secondary air flow to the cyclones to a value corresponding to a minimum secondary air flow and maximum degree of staging for each cyclone; and (k) adjusting the overfire air port dampers as needed to compensate for any O 2 or CO imbalances resulting from the adjustments made to the cyclones.