| OCR Text |
Show F'uel --- --- --- Flue The ideal dilute oxygen combustion (DOC) process can be envisioned to occur as follows (see Fig. 1). The oxidant is injected into the furnace and mixes with the present combustion products (e.g., CO2, H20, 02) to generate a Oxidant high-temperature, dilute-oxygen ( - 2-10 % O2 Fig. 1. Schematic diagram of the dilute oxygen combustion (DOC) concept. vol. wet) atmosphere distributed uniformly throughout the furnace volume. Care is exercised in that the injected oxidant does not directly mix with the fuel which would result in high-temperature combustion. Note that the fuel and oxidant streams potentially can be injected from opposite sides of a furnace. Upon entering the furnace, the fuel jet entrains the high-temperature, dilute-oxygen furnace gas and combustion proceeds (fuel reaction zone). Since the fuel jet is reacting with a dilute-oxygen oxidant, low flame temperatures prevail, thus curtailing thermal NOx formation. This process has similarities to flue gas recirculation (FGR) techniques; however, dilution is achieved using the natural aspirating characteristics of p~~bulent jets. Note that it is important for the furnace gas temperature to be sufficiently high ~ote combustion (above the auto-ignition temperature). be dilute oxygen combustion burner system has been demonstrated to a limited extent IIJ temperature furnace applications and has been patented [1]. However, a more comprehensive evaluation of the DOC system is needed to augment its applicability in the commercial environment. Consequently, a fundamental and applied research effort pertaining to the DOC system has been pursued. The fundamental issues explored include the mass entrainment and flame lift-off characteristics of a fuel jet in a high-temperature oxidant. Knowledge of th :e quantities are needed to develop a burner design that results in ultra-low emissions and stable combustion. In addition, several laboratory-scale furnace tests (185 kW (0.6 MMBtu/h)} were undertaken to primarily assess the NOx and CO emissions associated with the DOC burner system. The furnace tests involved varying the burner geometric arrangement, the furnace temperature and the furnace nitrogen content and recording the effect of these variations on pollutant emissions. TL _ lNICAL SURVEY Prior to presenting the experimental details and the results, previous work related to the pertinent aspects of this study are detailed. 1\ .40SS Entrainment Mass entrainment rates of jets have importance in a variety of practical devices. For example many burner designs for commercial furnaces rely on the jet t s entrainment characteristics to develop a stable, low-emissions combustion event. Hence, a complete understanding of jet entrainment can enhance the development of state-of-the-art burners. Entrainment phenomena have been a robust topic of research because of its importance in a variel . of arenas. Examples of research include fundamental jet studies [2-4], turbulent flame 2 |
