Co-firing beetle kill, or any dead woody biomass in coal-fired utility boilers is a method utilities are exploring to manage their carbon footprint and for the U.S. Forest Service to help maintain the health of our National Forests. This technology is being pursued by many groups as a viable power production alternative, with applications ranging from biomass / coal blends to complete biomass firing. Among the technological and economic hurdles for widespread application of this technology is the preparation and delivery of the biomass to the combustion hardware. Ideally, the biomass can be prepared in such a way that it can be utilized as a coal replacement. In this scenario, the biomass would be blended with coal on the coal pile and would travel through all of the conveying and milling equipment associated with the coal power station. It has been identified previously that the fibrous nature of raw wood materials does not behave well in a traditional coal bowl mills, reducing their performance and eventually plugging the system. However, it is possible to prepare woody biomass prior to mixing with coal using methods that break down the fibrous structure. An experimental program has been performed where 15% (wt.) blends of prepared biomass and Utah Bituminous Coal has been co-milled in a Combustion Engineering 312 Raymond Bowl mill. This paper will focus on elucidating the behavior of each of these fuels in the classifier of the bowl mill. A CFD model was constructed of the mill using Computational Particle Fluid Dynamics (CPFD) Barracuda software. Assumptions were made concerning the location and size distribution of the particles entrained at the active milling sites. The model was then tuned to replicate the observed behavior during experimentation. The predicted behavior of the wood and coal particles in the classifier was quantified and compared in order to understand the physical motivations for large (>300 miron) biomass particles escaping the classifier
展开▼
