BURNER TECHNOLOGY FOR SINGLE DIGIT NOx EMISSIONS IN BOILER APPLICATIONS

The local air quality districts in the Los Angeles area were the first to implement restrictions to require that NOx emissions on natural gas fired boilers be reduced to single digit levels. Now additional states are being required to develop State Implementation Plans (SIPs) to address bringing into compliance the areas that do not meet the ozone standards set forth in the Clean Air Act Amendments of 1990. One of the most aggressive plans to date has been adopted by the Texas Natural Resource Conservation Commission (TNRCC) to address the Houston-Galveston area (HGA). This SIP plan will call for levels of NOx reduction that exceed what was done in the Los Angeles area in the early 1990's. Ultra low NOx emissions on boilers will be an integral part of meeting the compliance goals set forth in this plan by the 2007 deadline. The use of boiler burner technology that provides the lowest achievable emissions rate (LAER) will be one of the key factors to allow users to meet the proposed reductions. The reduction of NOx emissions into the sub-9 ppm range requires an understanding of the mechanisms that result in NOx formation. Several techniques exist to address these mechanisms, and to achieve ultra low NOx levels it is necessary to incorporate several of them into the complete system design. Since the lowering of NOx emissions limits in California in the early 1990's, new burner technology has been developed and applied to successfully meet these levels. However, many of the methods used for NOx reduction come with some price, either in terms of impact to system efficiency or increased operational costs. The continued emphasis for combustion companies is on optimization of these systems to increase operational flexibility and to minimize the impact on the overall system. As part of this optimization the development and implementation of new technologies is a key component. This paper will discuss the specific methods by which NOx is formed during clean (i.e. no fuel bound nitrogen) gas combustion in a boiler and the historical methods that have been applied to address them. The control of NOx emissions on both existing burners and new Low NOx burner designs will be discussed. The third section will cover the development and implementation of a burner designed specifically to meet the requirements of achieving sub-9 ppm NOx levels. The final section addresses some new technologies that are currently being developed …