Effect of the annulus aeration on annulus leakage and particle circulation in a three-phase spout-fluid bed with a draft tube

Abstract

Abstract The distribution of flow between the annulus and the draft tube sections of a liquid spout-fluid bed with a draft tube was analyzed in the presence of air flow through the annulus using a tracer response technique. The responses of the tracer injections prove that part of the flow originating from the annulus liquid inlet leaks into the draft tube when any amount of annulus liquid inlet flow is present and this annulus leakage increases when air flow is introduced into the annulus. This finding extends the recently acquired knowledge about the annulus leakage and cross flow in the entrance region below the draft tube in liquid spout-fluid beds to three phase spout-fluid beds with a draft tube where the annulus is aerated. The experimental system studied consisted of a semi-circular column of 80 mm diameter equipped with a semi-circular draft tube of 20 mm diameter. Liquid and air flows coexisted in the annulus. The liquid velocities were well above the minimum fluidization velocity and the particles were glass beads of 3 mm diameter. Experimentally determined values of the superficial annulus and draft tube liquid velocities from the tracer response analyses together with the experimental draft tube pressure gradients were used as input into Grbavcic et al.'s [Z.B. Grbavcic, R.V. Garic, D.V. Vukovic, Dz.E. Hadzismajlovic, H. Littman III, M.H. Morgan, S.Dj. Jovanovic, Hydrodynamic modeling of vertical liquid–solids flow. Powder Technol. 72, (1992)183–191] variational model for vertical non-accelerating liquid–solids flow to calculate the draft tube voidage and the particle mass flux assuming an air free draft tube. Results indicate that annulus aeration lowers the particle mass flux in this particular column geometry.