Scaleup and hydrodynamics study of gas-solid spouted beds.

摘要

A thorough understanding of the complex flow structure of gas-solid spouted bed is crucial for design, scale-up and performance. Advanced gas-solid optical probes were developed and used to evaluate different hydrodynamic parameters of spouted beds. These optical probes measure solids concentration, velocity and their time series fluctuations. Since solids concentration needs to be converted to solids holdup through calibration, for meaningful interpretation of results, a novel calibration method was proposed (which is inexpensive and reliable compared to the current reported methods) and validated in the present study. The reported dimensionless groups approach of spouted bed scale-up was assessed and was found that the two different spouted beds were not hydrodynamically similar. Hence, a new scale-up methodology based on maintaining similar or close radial profiles of gas holdup was proposed, assessed and validated. CFD was used after it was validated as an enabling tool to facilitate the implementation of the newly developed scale-up methodology by identifying the new conditions for maintaining radial profiles of gas holdup while scaling up. It can also be implemented to quantify the effect of various variables on their hydrodynamic parameters. Gamma Ray Densitometry (GRD), a non-invasive radioisotope based technique, was developed and demonstrated to montior on-line the conditions for the scale-up, flow regime and spouted beds operation. The solids holdup in spout region increases with axial height due to movement of solids from the annulus region. However, solids velocity in the spout region decreases with axial height. In the annulus region the solids move downward as a loose packed bed and the solids velocity and holdup do not change with axial height. Using factorial design of experiments it was found that solids density, static bed height, particle diameter, superficial gas velocity and gas inlet diameter had significant effect on the identification of spout diameter. Flow regimes in spouted bed were determined with the help of optical probes, pressure transducers and GRD. It was found that the range of stable spouting regime is higher in 0.152 m beds and the range of stable spouting decreases in the 0.076 m beds. The newly developed non-invasive radioisotope technique (GRD) was able to successfully identify different flow regimes and their transition velocities besides scale-up conditions and operation.