Control of Nitrogen Oxide Emissions in Gas-Fired Heaters -- The Retrofit Experience

Clean air legislation in the United States will continue to mandate reductions in the quantities of nitrogen oxides emitted by process heaters and boilers in petroleum refineries. Already, significant controls are required for such units operating in Southern California. The South Coast Air Quality Management District, responsible for maintaining clean air in that region, currently requires the most stringent controls for nitrogen oxides anywhere in the United States. A significant aspect of these regulations is that they apply to existing heaters and boilers and not new units. Retrofitting existing units to reduce their emissions subject to various other constraints is often a challenging task for the engineer and designer. It is also a subject that has not received adequate exposure in the literature, where most discussion is limited to technology applicability in new designs. This paper describes the various constraints faced by designers in applying present NOx reduction technology to process fired heaters. It includes actual examples of the successful implementation of these technologies.