Experimental investigation of a dense-phase pneumatic transport system

Solids deposition in low-velocity slug flow pneumatic conveying

Abstract: Solids deposition in the horizontal pipeline of a pneumatic conveying system was studied both mathematically and experimentally. Mathematically modelled results using the coupled discrete element method (DEM) and computational fluid dynamics (CFD) approach have demonstrated an intensive exchange of particles between the stationary layer (deposited particles) and the moving slug and a variation of solids concentration and pressure and velocity distributions across the slug. Slug flows were also visualised experimentally through a glass section and analysed by a high-speed video camera. The amount of particle deposition in the pipeline after a conveying was calculated by controlling the solids feeding rate using a rotary valve and by monitoring the solids flow out of the system using dynamic load cells. Experimentally generated data have quantitatively shown a tendency of more solids deposition with lower gas mass flow rate in slug flows except that, below a certain amount of solids mass flow rate, the deposition becomes independent of gas flow rate.

Solids Deposition in Low Velocity Slug Flow Pneumatic Conveying Systems

Abstract: Solids deposition in the horizontal pipeline of a pneumatic conveying system was studied both mathematically and experimentally. Mathematically modelled results using the coupled discrete element method (DEM) and computational fluid dynamics (CFD) approach have demonstrated an intensive exchange of particles between the stationary layer (deposited particles) and the moving slug and a variation of solids concentration and pressure and velocity distributions across the slug. Slug flows were also visualised experimentally through a glass section and analysed by a high-speed video camera. The amount of particle deposition in the pipeline after a conveying was calculated by controlling the solids feeding rate using a rotary valve and by monitoring the solids flow out of the system using dynamic load cells. Experimentally generated data have quantitatively shown a tendency of more solids deposition with lower gas mass flow rate in slug flows except that, below a certain amount of solids mass flow rate, the deposition becomes independent of gas flow rate.

Physical mechanisms involved in the transport of slugs during horizontal pneumatic conveying

Abstract: In dense phase pneumatic conveying, only relatively small amounts of gas are used to transport large volumes of material. Because the complex physical mechanisms involved in the transport of high particle concentrations in a gas phase have still not been fully understood, the design of low velocity pneumatic conveying systems still remains a problem. This work focuses on the identification and description of the main physical mechanisms involved in horizontal slug flow pneumatic conveying. In particular, experimental investigations were carried out on slugs of granular material with respect to velocity, pressure profile, porosity and internal stress states. The results obtained lead to better comprehension of slug formation and stability. Besides, existing models for the prediction of the pressure loss in slug flow pneumatic conveying are reviewed and compared. Based on both experimental results and theoretical investigations, a new approach based on kinetic theory is proposed to predict the pressure loss and allow more reliable design of slug flow pneumatic conveying systems.

Types of gas fluidization

Abstract: The behaviour of solids fluidized by gases falls into four clearly recognizable groups, characterized by density difference (ϱs–ϱf) and mean particle size. The most easily recognizable features of the groups are: powders in group A exhibit dense phase expansion after minimum fluidization and prior to the commenment of bubbling; those in group B bubble at the minimum fluidization velocity; those in group C are difficult to fluidize at all and those in group D can form stable spouted beds. A numerical criterion which distinguishes between groups A and B has been devised and agrees well with published data. Generalizations concerning powders within a group can be made with reasonable confidence but conclusions drawn from observations made on a powder in one group should not in general be used to predict the behaviour of a powder in another group.

Dense-phase pneumatic conveying: A review

Abstract: In the last twenty years, several commercial systems for dense-phase pneumatic conveying have been developed. However, despite an extensive literature, the subject is very confusing, particularly for the beginner. This paper gives an introduction to, and a review of, dense-phase pneumatic conveying (defined here as the conveying of particles by air along a pipe which is filled with particles at one or more cross-sections). Firstly, the advantages, disadvantages and proposed definitions of dense-phase pneumatic conveying are discussed, then previous published work is reviewed. This review focuses on: horizontal and vertical conveying, the use of phase diagrams, choking and the suitability of powders for dense-phase conveying, and the pressure drop required to move a plug through a pipeline as a function of plug length. (Note: A plug is a length of bulk solids that occupies the full cross-section of the pipeline.) After that, some photographs of the observed flow patterns are described and discussed. This is followed by a brief description of a theoretical model for horizontal plug conveying and, finally, by conclusions and suggestions for further work.

Reduction of Power Consumption in Pneumatic Conveying of Granular Materials through a Pipeline

Abstract: Pneumatic conveying of granular materials generally requires a great deal of power consumption in spite of its excellent advantages which are not obtainable with other transport methods. The purpose of this study is to examine the behavior of pneumatic conveying systems from both theoretical and experimental perspectives and find out an optimum way of reducing power consumption. It is concluded that the application of vibration to pipes or bends is effective for this purpose. In addition several improvements to obtain economic conditions are discussed.