OCR Text |
Show an "ordinary" burner in a "normal" furnace. For a specific burner in a particular furnace, it will be necessary to apply both a burner constant Qj to take account of burner characteristics such as size, load factor, amount of recirculation, single or multistage, type of flame, and a furnace constant Cf to take account of firebox conditions such as heat transfer, turndown/ mean temperature, dimensions. Since the only reliable way to obtain values for Cb and Cf is to take actual field measurements, a combined constant Q>f will usually be obtained unless several readings are available with similar burners in different furnaces or vice versa. For fuels that contain zero nitrogenous compounds only fixation need be considered. Fuel oases do not normally contain any nitrogenous compounds and any molecular nitrogen can be ignored, since all the NOx will be formed by fixation. Liquid fuels can be divided into four main groups: Petroleum crudes which range from .01 to 1% wt. organic nitrogen; petroleum residuals ranging from 0.20 to 2.50% wt. nitrogen; petroleum distillates ranging from 0.005 to 0.030% wt. nitrogen and liquid synfuels ranging from 0.10 to 4% wt. nitrogen. For these liquids, fuel NO will be in addition to fixation, and in most cases will provide the major portion of the NO. For estimating NOx from fuel nitrogen, read off the graph fig. 4, expected NOx vs. fuel bound nitrogen. Again it will be necessary to apply both a burner constant Kg to take account of burner characteristics such as reducing first stage, flame type, quantity of entrainment, vitiated air, and a furnace constant Kp to take account of firebox conditions such as loading, temperature, dimensions. As stated above Kgp will usually be obtained from field readings. 13/7 |