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

Solids Deposition in Low Velocity Slug Flow Pneumatic Conveying Systems

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.

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

The conveying characteristics of powder material transport are investigated for a pilot-scale pneumatic conveyor. The experimental system is a closed-loop, dense-phase pneumatic transport system, incorporating an auxiliary air-assisted conveying line. Powder materials, such as cement, fly ash, pulverized coal and rawmeal have been conveyed and their suitability to conveyed in the dense phase is investigated. The air supply is achieved through axial and annular nozzles, in addition to an air supply through the solids feeding device, namely the blowtank. From a secondary pipeline, which runs parallel to the main conveying line, air is injected into the conveying pipeline at regular intervals. The power consumed in supplying compressed air through the different nozzles is evaluated and the effect of the phase density on the air supply through these nozzles is also estimated. A large number of experiments are carried out to identify the optimum combinations, such that the air mass flow rates and supply line pressures of air are low, resulting in less power consumption. Useful conclusions are drawn for design and layout of the auxiliary air-assisted pneumatic conveying system.

S. Sivakumar

Papers

Experimental investigation of a dense-phase pneumatic transport system