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Show Finally, the effect of burner design and operation must be discussed. Although coal quality can affect the NOx emissions, burner parameters usually predominate. This follows from the difficulty in creating the environment dictated by fundamental studies into actual burners and flames. In pulverized-coal, low-NOx burners, the design should lead to the creation of an oxygen-lean zone in which the volatile N2 species can react to N2 instead of NOx. However, burnout can be significantly reduced if the fuel-rich zone is too large or the temperature is too low. Therefore, the oxygen-lean and oxygen-rich regions must be optimized by the burner design and operation. Additionally, the yield of volatile matter is coal dependant, and this affects the optimum amount of oxygen in any zone. Thus, no single burner design and operation conditions will be the optimum for all coals. Changes in burner design can affect peak temperature, and the local conditions that the coals are exposed to. This topic is the subject of many publications. This paper will not focus on this subject. Rather, data from two experimental burners has been studied with the main parameter varied being the coal combusted. 3 EXPERIMENTAL A number of low-NOx pulverized-coal burner concepts have been tested at the IFRF, but two will be discussed in this paper. These burners are displayed in Figure 2. The externally air staged burner (EASB) was the first concept tested [1, 20]. It involved the creation of a oxygen lean zone by the injection of some of the combustion air through tertiary air ports. The main combustion air or secondary air was swirled to create the well-known internal recirculation zone (IRZ) which stabilizes the flame and controls the flame properties. The second burner concept was an internally or aerodynamically air staged burner (AASB). In this design, the tertiary air ports were removed to make retrofit easier [2, 21, 22]. The reaction of nitrogen species in a fuel rich zone was accomplished by optimization of coal particle trajectories in relation to the IRZ. Proper control of the near-field aerodynamics of the swirling secondary air was the key to this optimization. Both of the burners were tested at the 2.5 MW scale in the furnace shown in Figure 3. The furnace is 6 by 2.5 by 2.5 m and is brick lined. Heat is extracted by water cooling through pipes located along the furnace wall. The input conditions for the flames varied considerably. In 5 |