Numerical investigation of 3-D transient combusting flow in a 1.2MWth pilot power plant

Abstract

As industrial Circulating Fluidized bed Combustors (CFBCs) tend to be scaled up, numerous design and operating problems emerge. At the same time uncertainties which concern hydrodynamics, combustion and pollutants formation mechanisms, come in to sight. Along with experience, CFD analysis can play crucial role providing further insight on the complex multiphase combusting flow occurring in CFBCs. This work aims to present a methodology for CFBCs comprehensive modeling, taking into consideration the coupling of hydrodynamics - heat transfer - chemical phenomena that take place in the bed. A combination of acceptable accuracy with high computational efficiency was also an objective. For this purpose, a simple combustion mechanism was integrated in an isothermal model and applied on a 1.2 MWth pilot plant. In this comprehensive model gas, inert-material and fuel are taken into consideration, as three discrete, pure eulerian phases. Solids inventory in the riser as well as temperature of the bed were predicted with satisfactory accuracy. Moreover, major chemical components as O2 and CO2 concentrations were predicted along the bed with acceptable accuracy. Concluding, the developed CFD model is capable of efficiently modeling a CFBC. However in order to further increase total accuracy, the need for improved closure equations for the set of Partial Differential Equations solved was made obvious. Finally, the computational cost for such modeling was found extremely high but not prohibitive for large scale CFBC simulations.