OCR Text |
Show of delaying mixing with coal is to create a Type 1 flame with the fuel jets penetrating through the IRZ. The flame width (and length) is most easily controlled by changing the quar1 exit angle. The greater the quar1 angle the larger the flame diameter and the shorter the flame length. The flame length is also controlled by the fuel and air mixing rate. NOx EMISSIONS Natural Gas Fuel Natural gas NOx emissions result from thermal NOx, and lower NOx emi ss ions can be achi eved by 1 oweri ng the f1 arne temperature. The most commonly used method of lowering NOx emission with natural gas is flue gas recirculation (FGR) The NOx emissions without FGR are primarily dependent on the burner design and the heat re 1 ease rate (MW/M2). Other factors can a 1 so be important, inc 1 udi ng the excess ai r, the rat i 0 of the burner size to the furnace diameter, air preheat temperature, etc. Oi 1 Fue 1 NOx emissions from an oil fuel can result from both thermal effects and fuel bound nitrogen. The relative importance of the fuel nitrogen NOx component is dependent on the nitrogen content of the oil. For low levels of fuel nitrogen, the conversion to NOx is high, about 50%. Higher levels of fuel nitrogen give lower conversion percentages to NOx. Air staging is one method that can be used to decrease NOx emissions from oil flames containing fuel nitrogen. Another NOx reduction method that can be used when using high momentum atomizers is directing the spray angle to control the fuel and air mixing. If the fuel can be devo1ati1ized and ignited primarily in the recirculation zone, a fuel-rich low NOx region is created. A burner schematic showing an example of this technique is shown in Figure 2. -6- |