OCR Text |
Show on the fuel/oxygen ratio, temperature and turbulence level in the local environment in which the nitrogen is released from the coal. Increased consumption of coal in recent years has resulted in a greater interest to improve energy utilization and reduce NO pollutant emissions from these systems. Abatement of these pollutants can be accomplished most economically by controlling their formation during the combustion process rather than through post-cleanup processes. 1,2 Control of NOx during combustion processes has been achieved through such methods as air and fuel staging, low-NO x burners or product gas recirculation, all of which aim to reduce NO x formation through control of the local temperature and fuel/air ratio. Computer simulations of combustion systems can give insights into the phenomena occurring inside combustion and flow systems, and can be used as design and analysis tools to improve efficiency and reduce pollutant emissions. A model for NOx pollutant formation and destruction has been developed and reported previously. 3-6 This model has been applied as part of a comprehensive combustion code to a small-scale utility boiler to demonstrate application of the pollutant model for prediction of observed trends. A brief discussion of the comprehensive model and the NOx pollutant model will be given. This will be followed by discussion of the experimental tests and comparisons of predicted NO pollutant emissions with the observed trends. Comprehensive Combustion Model For prediction of the NOx pollutant formation process, the comprehensive model must adequately predict the particle heat-up, ignition, and provide an adequate description of nitrogen release from the reacting coal and char particles. This involves adequately predicting the general flow and heat transfer characteristics of the coal furnace. Comprehensive combustion models include the various submodels of the physical processes occurring in combustion systems, including gaseous fluid dynamics, homogeneous gas phase reactions, radiative and convective heat 2 |