Real time flow rate measurements and characterization of gas-solid flows is desirable in many process applications utilizing solids transport. To date, limited methods for non-intrusive measurement of solid circulation rate exist and even fewer exist for the imaging of these flows, particularly at high temperatures. The Ohio State University (OSU) has been developing electrical capacitance volume tomography (ECVT) sensors, measurement techniques, and processing algorithms for imaging multi-phase flows. ECVT is a noninvasive 3-D imaging technology capable of providing real time images of multi-phase flow systems. The ECVT sensor consists of an array of capacitance sensor plates designed to externally fit around the sensing domain. Capacitance measurements from all possible plate pairings are taken by sequentially applying a voltage between each electrode pair. The permittivity distribution of dielectric material within the sensing domain can be derived from the measured capacitance values through the Poisson equation. The solution can be quickly estimated using one of many reconstruction techniques including but not limited to: iterative linear back projection, multicriteria optimization image reconstruction technique, and the Hopfield neural network model. Thus, ECVT is able to provide real time, high fidelity imaging of the internal multiphase flow.
In this study, ECVT technology was utilized and developed to study flow characteristics of gas-solid systems found in circulating fluidized bed systems including packed moving bed and fluidized bed regimes. Algorithms and techniques were developed to extract solid circulation rate, linear velocity of solids, and 3-D imaging of flow patterns. Additionally, the ability of the ECVT sensor to detect small variations in solids packing was studied. Flow rate and velocity measurements were calculated using cross correlation and peak matching techniques. Data measurement and analysis techniques of both the raw sensor data and reconstructed 3-D images will be discussed. Experiments at elevated temperatures were also conducted to examine temperature effects and to confirm the ECVT concept at high temperatures.