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Show ABSTRACT AFRC90 Paper #32 ADVANCED NON-CATALYTIC POST COMBUSTION NOX CONTROL / 5fl ~ S. L. Chen, R. K. Lyon, W. R. Seeker Energy and Environmental Research Corporation 18 Mason, Irvine, California 92718 The effectiveness of combustion modifications, including staged combustion and reburning, for the control of nitrogen oxide emissions from coal or oil fired combustors is most often limited by problems due to carbon burnout or flame impingement. This paper presents new data on the use of selective reducing agents, such as ammonium sulfate, suggesting that a hybrid control scheme is possible which uses combustion modification to provide those conditions which optimize the selective reduction process. Very low emission levels appear possible that can presently only be achieved by catalytic reduction. INTRODUCTION Combustion of fossil fuels, especially coals and heavy oils, produces significant amount of NO~ which ultimately participate in the formation of smog and fCid rain. l,~mbustion modification concepts including staged combustion and reburning have been effective in achieving up to 60 percent NOx reductions. D~wnstream i~ection of selective reducing agents, particularly ammonia and urea, can produce significant additional reductions. However, the temperature window over which these reagents are effective is relatively narrow. This paper summarizes the results of a study which was undertaken to investigate the possibility of positive synergism between the injection of various selective reducing agents, such as ammonia, and more conventional combustion modifications. The experimental studies were conducted in a 25 kWt refractory lined tunnel furnace. The work focused on the importance of reaction temperature, local stoichiometric satio, and the composition of the selective reducing agent. Cyanuric acid, urea, ammonium sulfate, and ammonia gas were considered as selective reducing agents. Fuel rich and fuel lean conditions were included in a temperature range of 600 to 1300·C. These studies were subsequently supported with testing in a 3.0 MWt pilot scale facility and with kinetic modeling. EXPERIMENTAL The bench scale experiments were conducted in~ 15.2 centimeter diameter by 2.4 meter long refractory lined tunnel furnace. All data reported here are for natural gas firing in a 15 kWt premixed burner. The oxidant was air and ammonia was added to the naturar gas to provide the desired level of post-flame NO. The NO values, along with all other concentrations, are reported on a dry bas is, corrected for d i 1 ut i on to 0.0 percent O2. The temperature was decl ining at a rate of 225·C/s throughout the region of interest in this study. When the furnace was operated to simulate staged combustion, the gases from the first stage, normally fuel rich, were mixed with burnout air via a radial injector positioned on the furnace axis. The temperatures reported for the staging location are those of the furnace gas immediately after the staging air has been added and mixed. When the furnace was operated to simulate reburning, the reburning fuels were injected with 1 |
