Non-invasive investigation of the cross-sectional solids distribution in CFB risers by X-ray computed tomography

We apply X-ray computed tomography for non-invasive investigation of the distribution of solids over the cross-section of a pilot plant scale circulating fluidized bed riser and present a novel method to derive volumetric solids concentrations from tomographic raw data. In this, the elimination of low-energetic radiation from the incident X-ray spectrum plays an essential role to avoid detrimental beam hardening effects, which are caused by the pipe material and the fluidized solids. The presented technique is applied for quantitative analysis of the radial solids concentration distribution in a gas-solid circulating fluidized bed riser. The examined operating range covers mean solids concentrations between 2.7 vol% and 37.2 vol% whilst the superficial gas velocity is varied between 1.5 m s(-1) and 6.0 m s(-1). The high spatial resolution of the measured data permits evaluation of the influence of the overall solids holdup and the superficial gas velocity on the radial solids concentration profile. Comparison of the cross-section averaged solids concentrations obtained by X-ray computed tomography with those inferred from differential pressure measurements confirms the high accuracy of the applied method. Based on a comprehensive set of measurement data a model is developed that allows for the prediction of the radial solids concentration distribution in vertical gas-solid upflow. (C) 2016 Elsevier B.V. All rights reserved.