(68b) Transient Reacting Flow Simulation of Biomass Combustion in a Pilot-Scale Circulating Fluidized Bed Combustor
The experimental basis for the simulations is the 50 kWth CFB combustor riser with a diameter of 0.15 m and a height of 5 m designed, built, and operated at CanmetENERGY in Ottawa, Canada. The MFiX-PIC model parameters for the simulation are tuned against cold flow experiments from Canmet using 9 kg of olivine sand as the inert bed material. It is shown that for the relatively coarse fluid meshes and large parcel sizes necessitated by the scale of the simulation, filter size dependent corrections to the drag law must be incorporated to ensure accuracy of the simulation results.
The validated cold-flow model is extended to simulate reacting flow with torrefied hardwood as the feedstock using an established reaction scheme from previous work. The effect of cooling air flow through heat exchanger tubes to maintain the bed temperature in the Canmet riser is represented by prescribing the heat flux across the tube surfaces in the simulation. The pressure and temperature profiles in the riser as well as the outlet gas compositions are compared against Canmetâs experiment and show satisfactory agreement. The simulations demonstrate the ability of MFiX-PIC to accurately capture the physics and chemistry of a circulating fluidized bed combustor at pilot plant scales, which can be further extended to industrial-scale systems. The detailed species information in the riser obtained from the simulation is also used to predict NOx formation based on a sub-grid model.