Studies On Suspension Dense Phase Pneumatic Conveying And Its Numerical Simulation

Pneumatic conveying, which uses flowing gas to transport solid particles through a pipeline, is an important operation in a significant number of chemical and process industries for transporting materials such as flour, granular chemicals, cement, soda, plastics chips, coal etc. Pneumatic conveying may be differentiated into several categories such as, dilute phase conveying, suspension dense-phase (a gas-particle suspension conveying with high loading of particles) and slug flow depending on particle properties, mass flow rate and conveying velocity.An essential concern of pneumatic conveying transport system designer relates to the determination of the minimum conveying velocity necessary to minimize the energy losses during conveying and the product granulation and equipment erosion. These conditions force us to operate with the lowest velocities. On the other hand, in order to avoid flow instability phenomena, the conveying velocity must be sufficient. The suspension dense phase conveying in the saltation velocity (also called the optimal economic velocity) can obtain the steady and continuous gas-particle flow while minimizing the energy losses.In suspension dense phase pneumatic conveying, the Reynolds number for the gas flow based on the pipe diameter and the particle concentration is high, gas-particle, particle-particle and particle-wall interactions play an important role for suspension dense phase pneumatic conveying systems, the flows of both phases are, therefore, expected to be turbulent, so gas-particle two-phase flows in dense phase suspension pneumatic conveying system is a complicated nonlinear dynamics system. A detailed understanding of the behavior of particles is important for design, optimization, and operation of the systems. The main approaches used to study suspension dense phase are experimental approach. Being limited in measuring technique and experimental condition, the experimental approach cannot provide the flow mechanics of both gas and particles. The numerical approaches can handle turbulent gas-particle two-phase flows thoroughly, however, few studies on suspension dense phase pneumatic conveying by using this numerical method are found.In this thesis, the status of the developments in experiments and theories related to phase diagrams, flow pattern, gas and particle velocity distribution, particle concentration distribution and model of pressure drop in the pneumatic conveying are reviewed and analyzed. Based on the analysis, the contents and objectives of this paper are presented. The main points of this thesis are as follows:The suspension dense-phase conveying pilot experiments are carried out in Equipment Institute ofJinling Petroleum Chemical Corporation. The pressure loss is measured and the conveying stabilityand flow pattern is analyzed according to signals of gas pressure undulation inside the pipe. Theresults provide qualitative and quantitative bases for comparison of numerical simulation results.Based on the principal turbulence theory of the gas dynamics and kinetic theory of granular flow, atwo-dimensional and a three-dimensional gas-particle two-fluid flow model are developed in pneumatic conveying system, and relevant numerical algorithm and a computational code are obtained. Both models make it possible to calculate the macroscopic behaviors (such as effective pressure, effective viscosity, the shear viscosity) of the solid phase.The verification of the models is carried out by experimental data and literature data with wide range of experimental condition for both vertical pneumatic conveying pipe and for horizontal pneumatic conveying pipe. The predicted flow parameters, such as particle velocity and gas velocity distribution, pressure drop, saltation velocity, particle concentration etc. are in agreement with experimental data. This shows that the models are with good predictability and reliability.The effects of factors such as gas velocity, solid flux, particle size, particle density, diameter of pipe an specularity factor on pressure drop, saltation velocity...