NOx Control by Combustion Modification
APTB has performed research and developed technologies for NOx reduction via combustion modification. Techniques such as low-excess air firing, staged combustion, flue gas recirculation, low NOx burners, and reburning have been applied to a wide range of combustion equipment including utility and industrial boilers, industrial process combustors, stationary engines, residential space heaters, and woodstoves. In-house projects include investigations of improved NOx reduction by injection of steam into the reburn zone, evaluations of advanced reburning techniques, and optimization of combustion/flue gas treatment hybrid NOx control techniques.
Reburning
                                       
Field studies include evaluation of reburning (fuel staging) on a 108 MW cyclone coal-fired utility boiler in Ohio and a 300 MW wall coal-fired wet-bottom utility boiler in the Ukraine. APTB is also working with EPA's Office of International Activities to demonstrate coal reburn technology on industrial boilers in Taiwan. This work will continue through 2001. Nitrous oxide (NOx) reductions of over 60% have been obtained using this technology. Reburning is a method of NOx control that uses hydrocarbon radicals to convert nitrogen oxide (NO) to nitrogen (N2) and carbon dioxide (CO2). Reburning is accomplished by diverting a portion of a boiler's fuel, typically 10-20%, to a point above the primary combustion zone where it is injected to create a fuel rich "reburn zone." The remaining combustion air is then injected above the reburn zone to provide the necessary burnout air.
Reburning can be applied to boilers that cannot use standard low NOx combustion modification techniques due to the need to maintain high furnace temperatures, such as wet bottom boilers. In many cases, reburning can be more economical than post combustion NOx controls that would otherwise be used in these instances.
Continuous Emission Monitors
APTB, EPA's National Risk Exposure Laboratory (NERL), and the U. S. Department of Energy (DOE) completed a series of tests to evaluate three different multi-metal continuous emission monitors (CEMs) which are under development. Seven metals plus a tracer metal were injected as an aqueous spray into the secondary combustion chamber of APTB's rotary kiln incinerator simulator (RKIS) research combustor. The facility was operated at carefully controlled conditions during the test period. Flyash from a coal-fired boiler was also injected to simulate the particulate loading expected in a real hazardous waste treatment environment. The CEMs and EPA Reference Method sampling probes were installed in the duct downstream from the secondary combustion chamber. Three different concentrations were injected to achieve a high-, medium-, and low-metals concentrations in the duct. The CEM instruments and participating developers are: Inductively Coupled Plasma, Atomic Emission Spectroscopy (ICP-AES); U. S. Department of Defense Naval Air Warfare Center; Laser Induced Breakdown Spectroscopy, Atomic Emission Spectroscopy (LIBS); Diagnostics Instrumentation and Analytical Laboratory (DIAL); Mississippi State University; and Laser Spark Spectroscopy (LASS), Sandia National Laboratories.
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