OCR Text |
Show C2) OPERABILITY - Achieve or exceed raw UL TRALOW NOx™ Theory gas burner range of operation so that production would never be limited by the NOx reduction equipment C3) RELIABILITY - Achieve or exceed raw gas burner design for trouble free operation. Eliminate any possibility of flash back and minimize the potential for internal fouling of the gas gun or risers which can cause flame impingement problems and high NOx formation. C4) MAINTAINABILITY - Achieve or exceed raw gas burner capabilities for on line maintenance. All guns, risers and burner parts must be 100% maintainable during heater operation. Burner tile design must not be more complex or a cause of additional maintenance. The commercial acceptance goals were extremely important, based on the critical role that all direct fired heaters play in the production and profitability of processing plants. The IT-McGill research team knew that if goals C 1 through C4 could not be achieved and conclusively demonstrated, alternative existing technologies would be selected for NOx reduction projects. Acceptable technologies at the time were as follows; A) Selective catalytic reduction (SCR) B) Chemical/additive injection C) External flue gas recirculation (FGR) (one or two fan systems) All existing technologies were expensive, required external equipment, rotating equipment, complicated instrumentation and safety monitoring systems. The external flue gas recirculation system had additional drawbacks in that it operated near the stability limits of the fuel/air and flue gas mixture. In spite of the drawbacks to external flue gas recirculation it unquestionably reduced flame temperature and NOx production. 2 The IT-McGill research team recognized that the economic and certain operational drawbacks of external flue gas recirculation could be eliminated by utilizing the flue gas already present in the firebox or radiant section of heaters and boilers. The now familiar phrase "natural flue gas recirculation system" originated at the IT-McGill test facility based on this revolutionary idea and concept. Utilization of natural flue gas recirculation in the NOx reduction process is incorporated in the pending IT-McGill concept patent. Three fundamental questions still needed to be answered; 1) What was the temperature of the naturally recirculating flue gas at various locations in the firebox? 2) How much flue gas was associated with each temperature gradient? 3) What was the most effective way to utilize natural flue gas recirculation in the NOx reduction process? In order to answer questions 1 and 2 above the IT-McGill research team developed a computer program to calculate the temperature and tlow rate of the naturally recirculating flue gas at any location (roof, side, end, or floor) of a tirebox. The IT-McGill natural flue gas recircu·lation program was developed and the results were analyzed from June of 1988 until February of 1989. The data presented in the Appendix are from this early research work. Based on the computer modeling, it was determined that for all firing configurations (up, down or horizontally) the quantities and temperatures of the naturally recirculated flue gas were in a range that would reduce the production of NOx. In February of 1989 a commitment was made by IT-McGill management to construct a test heater to prove the theory of NOx reduction by utilizing natural flue gas recirculation. |