Low NO.sub.x short flame burner with control of primary air/fuel ratio for NO.sub.x reduction

A method of operating a pulverized coal burner to control a primary air to pulverized coal ratio and minimize NO.sub.x production from the burner, the burner including a nozzle pipe having an inlet for receiving a pulverized coal plus primary air mixture and an outlet for discharging same, a hollow plug extending axially in the nozzle pipe and defining an annular space between the hollow plug and the nozzle for conveying the pulverized coal plus primary air mixture therethrough, and a burner barrel positioned around the nozzle pipe defining at least one annular secondary air passage around the nozzle pipe, comprising the steps of:

• determining a coal flow rate being provided to the burner, in lb/hr;
• determining a percent volatile matter content in the coal being burned;
• and
• supplying core air to the inside of the hollow plug so that it is mixed with the pulverized coal plus primary air mixture at an outlet end of the burner to establish a desired primary air to pulverized coal ratio for combustion to minimize NO.sub.x production from the burner, the amount of core air supplied lying within a range defined approximately by the following Upper and Lower core air flow rates:
• upper core air flow rate (lb/hr)=1.5.times.coal flow rate (lb/hr).times.(percent volatile matter content/100)
• lower core air flow rate (lb/hr)=0.9.times.coal flow rate (lb/hr).times.(percent volatile matter content/100).