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Show '---- percentages can exceed 50 % (see sketch of model ULW and ULS in Appendix for reference). Flue gas products enter the throat of the burner through holes which are at least 1" in diameter. This eliminates any possibility of fouling by the products of combustion. After careful review of the commercial acceptance goals and objectives by the IT-McGill research team, the only method that would meet the design criteria was inerting the flame. The other two methods caused concerns not only in repeatability of NOx emissions, but also in the areas of safety, operability, reliability, and maintainability. A test burner was created for operation with natural flue gas recirculation. In order to inert the flame, a venturi system was designed which utilized low pressure steam as a driving medium and injected flue gas into the primary zone of the burner. Testing continued through July and in August 1989, It-McGill achieved all its goals - a natural flue gas recirculation system was operating with consistent and repeatable NOx numbers below 20ppmv. Computer modeling and performance of multi-burner applications "The system approach" The development of ULTRA LOW NOX™ and natural flue gas recirculation technology has been greatly aided by computer modeling. Theory did predict actual performance for the important parameters of flue gas quantity and temperature. However, the test heater was a single burner installation at 5.0MM BTU/HR heat release. Almost all operating heaters are multi-burner heaters with 10.0MM BTU/HR or greater heat release. (Note: this scale up has been accomplished and all recent ULTRA LOW NOX™ projects have been multi-burner applications in excess of 10.OMM BTU/HR heat release per burner.) In order to predict the effects of scale up and 4 multi-burner applications, IT-McGill developed a NOx prediction program for the SRGR model (staged fuel burner) and the family of ULTRALOW NOx™ Burners ULB, ULW, and ULS models. The latest version of the IT-McGill NOx prediction program incorporates the original natural flue gas recirculation program plus the ability to analyze the .effects of the flame burst and radiant to convection section load shifts. Flame burst analysis and load shifts Mr. Eli Talmor, in his book "Combustion Hot Spot Analysis for Fired Process Heaters" developed a method for predicting the peak flux rate and location in the firebox. The analysis is based on multi-burner systems with burners at any location (roof, end, side, or floor) of the firebox. IT-McGill has incorporated the predictive methods of Talmor in order to account for the macroscopic production of NOx. The IT-McGill NOx prediction program addresses the reality that the combustion process can not be separated from or considered isolated from the mechanisms of heat transfer. Specifically, this refers to the ability of a flame burst to radiate energy at a given rate/temperature to a given surrounding. NOx production is time and temperature dependent, but time and temperature must be analyzed at both the microscopic and macroscopic level. Traditional NOx prediction is based on a microscopic analysis which is the basis of theoretical adiabatic flame temperature calculations for a given fuel, air, and inert mixture. The predicted NOx is then adjusted either upwards or downwards based on the firebox temperature. This old method of predicting NOx did, at least, acknowledge that there was more to NOx production than the adiabatic flame temperature. It was also very inaccurate by today's standards. Predictive inaccuracies of + 10ppmv at the lOOppmv level can be tolerated. Predictive inaccuracies of + 10ppmv at 25ppmv can be the |