Experimental Study on Solid Discharge Rate from a Nonmechanical Solid Feeding System

Abstract

A nonmechanical solid feeding device uses aeration gas in combination with its geometrical shape to cause particulate solids to flow through it. Serious erosion of moving parts, high solid flow rate requirement, and high operating temperature preclude the use of mechanical solid feeders. A nonmechanical solid feeding system was designed and developed in the Chemical Engineering Division of Bhabha Atomic Research Centre for continuous solid addition to the fluidized bed. The controlled continuous solid addition fulfills various purposes − maintain proper particle size distribution inside fluidized bed, provide make up for entrained solids, and supply solid reactant where solids are consumed in reaction. A solid circulation vessel which works on the principle of compartmented fluidized bed was the heart of this solid feeding system. It consists of two compartments (main and riser), and the compartments were connected through an orifice. Solid discharge rate from solid circulation vessel was regulated by adjusting the fluidizing air flow rates to main and riser compartments and solid level in the main compartment. Theoretical and experimental investigations were carried out to evaluate performance characteristics of solid circulation vessel. Experimental results showed that a wide range of solid discharge rate (6−80 kg/h) could be achieved by changing aeration rates of two compartments and fluidized solid level in the main compartment. The experimental data were used to develop a correlation between solid mass flow rate through an orifice and pressure drop across an orifice. A mathematical model was also developed to predict the solid discharge rate from solid circulation vessel for a range of operating parameters.