| OCR Text |
Show turn forms a toroidal vortex in the corner of the dome. The toroidal vortex mixes the incoming coal/air mixture with the hot combustion products thus providing for favourable ignition characteristics and promoting highly efficient, rapid and stable combustion. Jet impact and radial acceleration of the recirculating vortex flow in the upper dome is the primary mechanism that inertially separates particles from the combustion gases onto the slagging walls. A small amount of wall burning of larger char particles deposited on the walls with the ash mineral matter is expected. As the pertinent reacting flow field details inside the configuration shown in Figure (2) cannot be resolved adequately by simple, correlation based design methods of cut-and-try nature, the preliminary design process was aided considerably through the use of the three-dimensional analysis code. Due to conflicting requirements to achieve adequate carbon burn-out, while satisfying stringent NSPS criteria for emissions as well as several other design considerations, initial estimates for the required particle residence times for a variety of coals were obtained from a one-dimensional model(ll). Optimization of this tentative configuration and delineation of the operating envelope compatible with the design requirements was accomplished by exercising the three-dimensional code for select variations of: fuel/air injection velocity, injection angle, number of injectors, particle size distribution, combustor diameter and aspect ratio. Resulting predicted combustor performances were compared; performance was assessed in terms of the strength of the toroidal vortex produced and hence the implied stability of the flow field, coal particle residence time and fuel utilization. 9 |
