Analysis of Gas-Solids Feeding and Slug Formation in Low-Velocity Pneumatic Conveying

Gas and solids feeding is a key operation in pneumatic conveying of particulate materials. This article presents an analysis of the interfacing effects between a nozzle gas supplier, a rotary valve solids feeder with dropout box, and the pipeline of a pneumatic conveying test rig for low-velocity dense-phase flow. Experiments were carried out to examine the flow pattern of slugs in different combinations of gas flow conditions and solids loading ratios. The effect of gas and solids feeding on the formation of slugs is analyzed by using both experimental data and computer-modeled results. Solids accumulation and sliding motion at the bottom of the dropout box and near the entrance of the downstream pipe, which happen prior to the bulk motion in the form of a slug, are found important in determining the size of a slug. Gas retention and pressure buildup characteristics in the feed section are also found crucial in influencing the flow patterns of slugs.     

An Experimental Technique for the Analysis of Slug Flows in Pneumatic Pipelines Using Pressure Measurements

An experimental technique has been developed to measure the flow characteristics of slugs in dense phase pneumatic conveying using pressure measurements. This method is based on the unique characteristics of slug flows in pipes, i.e., an axial pressure fluctuation along the pipeline and a pressure difference in the radial direction at the back of a slug. Standard differential pressure transducers were used in this study and the influence of the finite response time of these transducers was considered. Experiments were conducted over a range of gas-solids flow conditions and experimental data were analyzed to describe the behavior of solids slugs through pipes. The calculated slug velocity and length using axial pressure measurements were confirmed by video recordings, and the synthesis between axial and radial pressure signals showed reasonable agreement in flow pattern analysis. This relatively simple measuring technique has been found effective in detecting solids slugs traveling through horizontal pipes and will distinguish various flow regimes. It provides a useful and easily applied tool for system optimizing and benchmarking in industrial applications.     

An Experimental Technique for the Analysis of Slug Flows in Pneumatic Pipelines Using Pressure Measurements

An experimental technique has been developed to measure the flow characteristics of slugs in dense phase pneumatic conveying using pressure measurements. This method is based on the unique characteristics of slug flows in pipes, i.e., an axial pressure fluctuation along the pipeline and a pressure difference in the radial direction at the back of a slug. Standard differential pressure transducers were used in this study and the influence of the finite response time of these transducers was considered. Experiments were conducted over a range of gas-solids flow conditions and experimental data were analyzed to describe the behavior of solids slugs through pipes. The calculated slug velocity and length using axial pressure measurements were confirmed by video recordings, and the synthesis between axial and radial pressure signals showed reasonable agreement in flow pattern analysis. This relatively simple measuring technique has been found effective in detecting solids slugs traveling through horizontal pipes and will distinguish various flow regimes. It provides a useful and easily applied tool for system optimizing and benchmarking in industrial applications.     

HYDRODYNAMICS OF FLUIDIZATION EFFECT OF PRESSURE

One of the largest concerns when using fluidized beds to commercialize many chemical processes, such as gasification of coal, is scale-up. We believe this is due to the absence of an experimentally verified hydrodynamic theory that can describe the complicated transient gas and solid motion in a fluid bed. During the past few years several organizations began to develop hydrodynamic computer models that promise to be predictive in many respects.

Our present computer model calculates the pressure, the void fraction and the velocities of a single size solid and of the gas. Computed time averaged porosity distributions in two dimensional beds with a Jet at atmospheric pressure agreed with our measurements without the use of any fitted parameters. Photographically determined bubble sizes compared well with the predicted sizes. Calculated gas velocity distributions also agreed with the experimental values measured at westinghouse in a semi-circular bed with a Jet.

In this paper the results of our measurements of time averaged porosities in a steel bed at elevated pressures are compared to our model predictions. We also show that the computed Jet penetrations are close to those reported by IGT in their high pressure fluidized bed. Our calculations also show that the amplitudes of pressure oscillations are much smaller at elevated pressures than at atmospheric pressure. In this sense, the fluidization is smoother at high pressures. An analytical examination of the equations of change in terms of a linearized hyperbolic diffusion equation supports this observation.