Evaluation of Carbon Conversion/NOx Emissions from Full Scale Boilers Using CFD-Based Combustion Simulations

Laboratory-scale testing provides detailed analysis of potential NOx control technologies. Extrapolating these results to actual systems, however, often requires further testing at pilot and full-scale fumace sizes. Combustion simulations based on computational fluid dynamics (CFD) provide an avenue by which laboratory results can be evaluated under full-scale firing conditions without the expense of large-scale testing. To realistically simulate fumace behavior at multiple scales, however, the combustion simulations must accurately account for fuel parameters and the controlling physical processes (Le., time, temperature, mixing history, etc.). Furthermore, in many cases, the complex 3-dimensional representation of an actual furnace requires numerous empirical inputs, and/or a computer model that can not be readily used for design purposes or overall system performance calculations because of excessive complexity and computer processing time. This paper presents a summary of a 2-dimensional CFD based model and computational code that has been developed for the simulation of coal combustion in tangential fired commercial-scale furnaces. The primary objective of this work was to develop a simplified designer oriented model that incorporates the primary effects of time, temperature, and mixing. In addition, the paper presents examples of how this computaional code, using information derived in a drop tube furnace, can be used to accurately predict furnace outlet gas temperatures, % carbon in the fly ash, and NOx emissions in full-scale furnaces.