Influence on the fluidization pattern of a freely bubbling fluidized bed with different modes of air supply

Abstract

Bubbling fluidized bed (BFB) reactors are extensively used in several process applications like gasification, pyrolysis, drying, and combustions due to their excellent mixing properties and good temperature control. The bubble dynamic and particle movement in the reactor is primarily responsible for uniform heat and mass transfer and mixing. The properties of bubbles in BFB are governed by the gas distribution inside the reactor or supply of the fluidizing gas. This work investigates the influence on the fluid dynamic behaviour of the BFB reactor at different fluidizing gas injection systems using the Computational Particle Fluid dynamic model. Three different modes of fluidizing gas injection include uniform injection, air injection via twenty-five nozzles, and air supply via side nozzles along the reactor height in a gasification reactor of 10.04 cm diameter. Air is used as the fluidizing gas and silica sand as the bed material. The CPFD model is developed in Barracuda Virtual reactor 20.01. The CPFD model is validated against the experimental data obtained from the Electrical Capacitance Tomography (ECT) sensors. The result depicts the better fluidization quality of the bed with uniform air supply as flow boundary and air injection via twenty-five nozzles located at the bottom of the reactor. With air injection via two side nozzles along the reactor height, the bed is fluidized with large bubbles and particle entrainment in the freeboard zone of the reactor. A method is proposed to improve the fluidization quality of the bed while using side nozzles as inlet flow Boundary Conditions (BC) for air injection. The proposed method includes addition of four nozzles along the reactor wall instead of two which improves the fluidization quality of the bed in terms of smaller size bubbles without particle entrainment in the freeboard region.