Comparison of Hydrodynamic Behaviour of Conical Fluidized Bed Risers with a Columnar Fluidized Bed Riser

Pressurized Circulating Fluidized Bed (PCFB) has earned appreciation in using low-grade coal for gasification and combustion applications because of its built-in capacity to capture sulphur and NOx. It becomes more attractive due to its compactness and elevated heat release rate. Whether the fluidized bed is used to separate or react, the key objective is to operate the bed at a flow rate that optimizes the application. Accurate models would help a great deal but modelling continues to challenge engineers and researchers even at a qualitative level. In this present investigation, numerical simulation is carried out in two conical risers and one columnar riser by considering coal as a bed inventory. The simulation is performed at a superficial velocity of 4 m/s for an inventory of 1 kg. The model k–e is used as a turbulence model. The simulation is performed to investigate the optimum parameters for the efficient use of the pressurized circulating fluidized bed. From the simulation, the variation of bed voidage, suspension density and pressure over the riser height are calculated at the operating pressure of 1, 2, 5 and 10 bar and results have been compared among the three risers. It is observed that pressure drop decreases up to a certain height and then increases with the height of the riser. Suspension density is also found to be decreasing with height. The pressure drop in the conical bed is found to be lower than that of columnar bed.