Abstract: A pulverized fuel and air mixture is burnt in conditions giving relatively low NO.sub.x emissions by using a burner which has concentric passages for a primary air-fuel mixture and secondary and ternary air flows respectively. In the passage for the primary air-fuel mixture guide elements are provided at angularly spaced positions. The elements are arranged to deflect the flow in the passage and so produce regions of high fuel concentration. Downstream of the guide elements and adjacent the outlet of the passage flow disturbing members are provided in angularly spaced positions to modify the flow pattern of the air-fuel mixture at the passage outlet. The members assist stabilization of the flame front at the burner outlet and complement the action of the guide elements in promoting combustion conditions that lead to low NO.sub.x emissions.