OCR Text |
Show AIR FUEL OXYGEN INJECTION LANCE Figure 2. Schematic of 0 2 lancing. Another variation of oxygen-enhanced combustion where the oxidizer contains significant amounts of N 2 is where the oxygen and air are separately injected through the burner with no premixing. In the Air Products' EZ-Fire® System [4], the oxidizer consists of a combination of air and high purity oxygen, as shown in Figure 3. The typical overall oxygen concentration in the combined oxidizer (if the air and oxygen were perfectly mixed together) for most industrial users of this technology is in the range of 35-45%. At this medium level of O E C , the dominate species in the overall oxidizer stream is still N2. This is one of the best places to operate as far as economics are concerned, but one of the worst for N O x formation, as will be discussed later. AIR FUEL OXYGEN Figure 3. Schematic of air-oxy/fuel burner. Other ways that significant amounts of N2 may be present in an oxygen-enhanced combustion system are through the fuel and through lower purity oxygen supply methods (see Figure 4). The amount of N 2 in, for example, natural gas fuel varies by location. In Europe, there are some natural gases, like Groningen in the Netherlands, that contain over 1 4 % N 2 [5]. In the U.S., some natural gases m a y contain as much as 1 7 % N 2 [6]. Organically-bound nitrogen may be present in fuels like coal, coke, and fuel oils. The amount of N 2 that may be in high purity oxygen supplies depends generally on the method that was used to produce the oxygen [7]. Cryogenic distillation methods commonly produce the highest purities (up to 99.9%), while adsorption systems such as V S A often produce purities in the 90-93%) 0 2 range. It is important to note that with adsorption separation systems, the impurity usually consists of approximately half argon and half N 2 which is important for determining its effects on N O x. 3 |