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Show VWs Presented at the 1998 Joint American/Japanese Flame Research Committee International Symposium Environmental Control of Combustion Processes: Innovative Technology Towards the 21st Century Maui. Hawaii. October 11-15. 1998. FUEL-LEAN GAS REBURN (FLGR™) TECHNOLOGY FOR ACHIEVING NOx EMISSIONS COMPLIANCE: APPLICATION TO A TANGENTIALLY-FIRED BOILER Richard D. Frederiksen, Werner J.A. Dahm and Gretar Tryggvason NGB Technologies, Inc. 2600 Roseland, Suite 100 Ann Arbor, MI 48103-2135 USA Bernard P. Breen, Roger Glickert and Joseph A. Urich Energy Systems Associates 564 Washington Avenue Pittsburgh, PA 15106 USA John M. Pratapas and Robert V. Serauskas Gas Research Institute 8600 West Bryn Mawr Avenue Chicago, IL 60631-3505 USA The application of fuel-lean gas reburn (FLGR) technology for NOx emissions reduction from a tangentially-fired coal-burning utility boiler is described. Design of the FLGR system involved a combination of prior field experience with the technology in other utility boiler designs, together with advanced LIM-based simulations of the injected gas mixing and reaction processes within the boiler. Parametric simulations were conducted to determine an initial FLGR system design for the boiler. Initial testing of the system performance showed higher than expected CO emissions at all boiler loads. The origin of these elevated CO levels was traced to interactions between the injected gas and the coal burnout process that are specific to tangentially-fired boiler designs employing close-coupled overfire air. Modifications to the original FLGR system were developed that led to reduced interactions and thus to significantly lower CO emissions. 1. INTRODUCTION Gas reburn can provide an important option for reducing emissions to meet regulatory levels in large installations such as utility boilers and waste incinerators, as well as in high temperature industrial process furnaces. The chemical kinetics involved in gas reburn are well understood. Natural gas injected into hot furnace gases forms hydrocarbon radicals which react with N O to form HCN. The H C N then undergoes a further series of reactions involving NO to form N2. However, if the H CN instead reacts with 02, it can reform NO. Consequently, effective removal of N O can be accomplished via gas injection to promote CH radical formation, and subsequent mixing of the resulting C H radicals with N O in the furnace gases under sufficiently oxygen-depleted conditions to avoid the N O reforming reactions. The gas reburn principle can be implemented in several ways. The traditional approach involves overall fuel-rich gas reburn. NOx-containing furnace gases enter a |