A numerical and experimental investigation of a retrofitted industrial boiler firing dry micronized coal.

摘要

The hypothesis addressed in this investigation was that the combustion of micronized coal in a retrofitted industrial boiler (5,300 kW) can be predicted by the solution of the conservation equations of mass, momentum and energy along with the appropriate constitutive equations, solved iteratively by a commercially available Computational Fluid Dynamics Code (CFD). An experimental test matrix was set up for three low-NO{dollar}rmsb{lcub}x{rcub}{dollar} pulverized-coal swirl burners (A, B and C). The combustion environment of the boiler was characterized for each burner by measurements of gas temperature, velocity, particle number density, size distribution and speed. The measurements were used to assess the accuracy of the predictions from the CFD modeling, which was carried out with two goals in mind. The first goal was to model each burner separately and, as such, examine the fluid mechanics and performance of each burner in a two-dimensional axi-symmetric geometry. The second goal was to model the boiler with the burner used as a source of mass, momentum and energy in a three-dimensional geometry. The predictions obtained from the mathematical modeling were then compared with the experimental measurements to investigate the thesis hypothesis and were judged in terms of the overall trends, and absolute accuracies. Employing a flow classification scheme, the flow types associated with the three low NO{dollar}rmsb{lcub}x{rcub}{dollar} pulverized coal were categorized. The impact of the Internal Recirculation Zone (IRZ) in flame stability and NO{dollar}rmsb{lcub}x{rcub}{dollar} reduction was discussed within the context of the combustion aerodynamics of each burner. The intensity of the IRZ, particle trajectories and finally flow Type (I, II and III) were concluded to be the key concepts that allowed the combustion aerodynamics of the swirling two phase flow of air and coal to be analyzed for the three burners.