Flow characteristics and Shannon entropy analysis of dense-phase pneumatic conveying under high pressure

Experiments of dense-phase pneumatic conveying of pulverized coal using nitrogen are carded out in an experimental test facility with the conveying pressure up to 4. 0 MPa and the gas-solid ratio up to 450 kg/m^3. The influences of different conveying differential pressures, coal moisture contents, gas volume flow rates and superficial velocities on the solid-gas ratios are investigated. Shannon entropy analysis of pressure fluctuation time series is developed to reveal the flow characteristics. Through investigation of the distribution of the Shannon entropy under different conditions, the flow stability and the evolutional tendency of the Shannon entropy in different regimes and regime transition processes are discovered, and the relationship between the Shannon entropy and the flow regimes is also established. The results indicate that the solid-gas ratio and the Shannon entropy rise with the increase in conveying differential pressure. The solid-gas ratio and the Shannon entropy reveal preferable regularity with gas volume flow rates. The Shannon entropy is different for different flow regimes, and can be used to identify the flow regimes. Both mass flow rate and the Shannon entropy decrease with the increase in moisture contents. The Shannon entropy analysis is a feasible approach for researching the characteristics of flow regimes, flow stability and flow regime transitions in dense-phase pneumatic conveying under high pressure.

Electrostatic Charge Generation in Pneumatic Conveying Process: Effect of Particle Properties

One of the main concerns in particle pneumatic conveying process is the possibility of hazards for operation safety due to the electrostatic charge generation as a result of collisions between particles and the equipment wall. Indeed, the electrostatic discharge can occur in the equipment leading to fire or explosion. Simulation of these kinds of processes plays an important role in understanding the various aspects of the system in order to production loss prevention. This paper deals with the simulation of particle pneumatic conveying process inside an inclined tube using a particular method. In this method, the electrification of particles inside the tube is influenced by the vertical collision velocity against the tube wall. Simulation of the particle movements inside the tube, generation of electrostatic charges over the particle surfaces as well as the possibility of fire as a result of discharging the electrostatic energy are investigated. The possibility of fire is investigated by comparing the amount of electrostatic energy with minimum ignition energy (MIE) of the particles. The effect of particle properties including the size and mechanical ones in the simulation is studied. Finally, several solutions are proposed to manage the risk of fire and explosion. As results, the electrostatic energy (E) is beyond the MIE, and the electrostatic discharge can occur leading to explosion for the diameters more than 2 mm and also for elasticity constants lower than 140 MPa. Eventually, there is no hazard of fire and explosion, since all calculated electrostatic energy for the change of Particle Poisson’s ratio varying from 0.1 to 0.9 is less than the MIE value for the air flow rate of 10 m3/h.

Gas-Solid Flow Behavior in a Pneumatic Conveying System for Drying Applications: Coarse Particles Feeding with a Venturi Device

The feeding of coarse particles (>0.5 mm diameter) directly into a riser operating at positive pressure is important for drying and pre-heating applications. The presence of the feeding device can lead to heterogeneity of drying and heating, and is the main factor responsible for pressure loss in short conveying systems. However, there is a lack of information concerning the axial and radial distributions of coarse particles in this type of configuration, despite the recent advances when dealing with fine particles (FCC catalyst). The present work therefore investigates a vertical venturi feeder with the conveying system operating in dilute-phase regime with 1 mm spherical glass particles. Experimental assays revealed the behavior of the mass flow rate of solids in the system, and pressure measurements were made along the riser in order to evaluate the accuracy of simulations. Euler-Euler simulations provided close estimation of the experimental pressure drop and the pressure drop according to distance in the linear region. Simulation of the fluid dynamics in the riser showed that solids clusters were formed at low concentrations near the feeding device, reflecting heterogeneity in the solid phase volume fraction.

An investigation into flow mode transition and pressure fluctuations for fluidized dense-phase pneumatic conveying of fine powders

This paper presents the results of an ongoing investigation into the fluctuations of pressure signals due to solids-gas flows for dense-phase pneumatic conveying of fine powders. Pressure signals were obtained from pressure transducers installed along different locations of a pipeline for the fluidized dense-phase pneumatic conveying of fly ash （median particle diameter 30μm; particle density 2300 kg/m^3; loose- poured bulk density 700 kg/m^3） and white powder （median particle diameter 55 p.m; particle density 1600 kg/m^3 ; loose-poured bulk density 620 kg/m^3） from dilute to fluidized dense-phase. Standard deviation and Shannon entropy were employed to investigate the pressure signal fluctuations. It was found that there is an increase in the values of Shannon entropy and standard deviation for both of the prod- ucts along the flow direction through the straight pipe sections. However, both the Shannon entropy and standard deviation values tend to decrease after the flow through bend（s）, This result could be attributed to the deceleration of particles while flowing through the bends, resulting in dampened particle fluctua- tion and turbulence. Lower values of Shannon entropy in the early parts of the pipeline could be due to the non-suspension nature of flow （dense-phase）, i.e., there is a higher probability that the particles are concentrated toward the bottom of pipe, compared with dilute-phase or suspension flow （high velocity）, where the particles could be expected to be distributed homogenously throughout the pipe bore （as the flow is in suspension）. Changes in straight-pipe pneumatic conveying characteristics along the flow direction also indicate a change in the flow regime along the flow.

Flow characterization of high-pressure dense-phase pneumatic conveying of coal powder using multi-scale signal analysis

Flow characterization of high-pressure dense-phase pneumatic conveying of coal powder is not fully understood. To further reveal the dynamic behavior of coal particles in dense-phase pneumatic conveying pipelines, a method for the scale decomposition of particle motion based on empirical mode decompo- sition and Hurst analysis of experimental electrostatic signals is reported. This allows the multi-scale motion characteristics of single coal particles and particle clusters to be determined. Micro-, meso-, and macro-scale subsets were reconstructed, which reflected the different behaviors of the coal particles： specifically, dynamic features of the micro-scale subset represented features of single particle collisions and frictional interactions; dual ffactal characteristics of the meso-scale subset described the motion of coal particle clusters; and features of the macro-scale subset reflected persistent dynamic behavior of the entire pneumatic conveying system. Motion behavior of single particles and particle clusters could be respectively investigated by considering the relative energies of the micro- and meso-scale contributions to the electrostatic signal. This was verified both by theoretical analysis and experiment.

Experimental study on dense-phase pneumatic conveying of coal powder at high pressures

Clean utilization and conversion of coal resources is significant to China’s energy sustainable development.Entrained-flow coal gasification technology is an important method used for clean and efficient conversion of coal.The characteristics and stability of high-pressure dense-phase pneumatic conveying of pulverized coal is crucial to the safe and stable operation of dry-feed entrained-flow coal gasifiers.Dense-phase pneumatic conveying experiments were carried out using a high-volatile bituminous coal in pipes with diameters of 25,15 and 10 mm,respectively,and at back pressures of 1.0-4.0 MPag.The conveying characteristics and effects of operating and structure parameters were studied.Pressure drop models were established for horizontal and vertical upward conveying.The prediction uncertainty was within±30%for the horizontal conveying and±20%for the vertical upward conveying.The relative standard deviation of solid flow rate was proposed to explain conveying stability.The effect of operating parameters on conveying stability was systematically analyzed.The gas velocity-related criterion was proposed for stable conveying.

Dense-phase pneumatic conveying under pressure in horizontal pipeline

The gas/solid flow regime of dense-phase pneumatic conveying of pulverized coal under a pressure of 4.0 MPa in horizontal pipeline 10 mm in diameter, is monitored by electrical capacitance tomography （ECT） using 8 electrodes. To improve the accuracy of the capacitance measurement, an AC-based singlechannel capacitance measuring circuit was developed, and a modified iterative Landweber algorithm was used to reconstruct the image. A two-fluid model based on the kinetic theory of granular flow was used to study the three-dimensional steady-state flow behavior of dense-phase pneumatic conveying of pulverized coal.

Compact Pneumatic Pulse-Jet Pump with Venturi-Like Reverse Flow Diverter

A compact pneumatic pulse-jet pump with a Venturi-like reverse flow diverter,which consists of a nozzle and diffuser,is designed for lifting and transporting a hazardous fluid through a narrow mounting hole.The pumping performance for a liquid mixture or a liquid-solid mixture is examined in terms of the effects of liquid viscosity,particle mass concentration,lifting height,and compression pressure.Results reveal that the pumping performance of the compact pneumatic pulse-jet pump is controlled by jet inertia and the flow resistance of the riser tube positioned after the diffuser.The capacity of the compact pneumatic pulse-jet pump increases with compression pressure and decreases with liquid viscosity.However,even for a liquid mixture with a high viscosity of 7.38 mPa·s,a pumping capacity of 170.7 L·h-1 was observed.For a liquid mixture,two dimensionless indices of performance were found to be the ratio of Euler numbers Euout/EuDV and the suction factor q.As the liquid-solid mixture was lifted to elevation of 6.74 m by the compact pump,the particle size distributions of the liquid-solid mixture in the tank and from the riser tube outlet were determined by a particle size analyzer and found to coincide well.

Multi-scale analysis on the pulverized coal flow behaviors under high,pressure dense-phase pneumatic conveying

To deeply knowledge of the flow behaviors of pulverized coal particles in dense gas-solid two-phase flow,a multi-scale analysis method based on electrostatic sensor array is applied for the multi-scale characterization of flow behaviors of dense gas-solid flow.The experimental results indicate that:for steady flow,with the increment of conveying pressure difference,the individual particles increase and the particle clusters decrease,the individual particle distribution is always inhomogeneous but the particle cluster distribution tends to be more homogeneous over the cross-section of pipe,while the average flow behavior of pulverized coal particles is always in the relatively static state.For unsteady flow,the average flow behavior of pulverized coal particles is dynamic,and the flow behaviors of the multi-scale flow structures over the cross-section of pipe are all significantly inhomogeneous.Moreover,the effect of particle size on flow behavior of pulverized coal is also investigated and validated.

Experimental study of the blockage boundary for dense-phase pneumatic conveying of powders through a horizontal slit

The estimation of the blockage boundary for pneumatic conveying through a slit is of significant importance. In this paper, we investigate the characteristics for blockage of powder （48 gLm average diameter） through a horizontal slit （1.6 m × 0.05 m × 0.002 m）. The results show that the required critical solid mass flow rate increases as the superficial air velocity increases superficial air velocity. The solid loading ratio and superficial air velocity displayed a decreasing power law relationship. This finding agrees with existing theory and experimental results. However, a minimum inlet solid loading ratio exists. When the air velocity is greater than the corresponding air velocity of the minimum solid loading ratio, the solid loading ratio exhibits an increasing trend in power law. We also found that when the inlet conveying pressure increased, the critical solid mass flow rate required for blockage, the inlet solid loading ratio, and the minimum inlet solid loading ratio increased.

Validated scale-up procedure to predict blockage condition for fluidized dense-phase pneumatic conveying systems

This paper presents results of an ongoing investigation into modelling fluidized dense-phase pneumatic conveying of powders. For the reliable design of dense-phase pneumatic conveying systems, an accurate estimation of the blockage boundary condition or the minimum transport velocity requirement is of sig- nificant importance. The existing empirical models for fine powder conveying in fluidized dense-phase mode are either based on only a particular pipeline and product or have not been tested for their accuracy under a wide range of scale-up conditions. In this paper, a validated test design procedure has been devel- oped to accurately scale-up the blockage boundary with the help of a modelling format that employs solids loading ratio and Froude number at pipe inlet conditions using conveying data of two different samples of fly ash, electro-static precipitation （ESP） dust and cement （particle densities： 2197-3637 kgJm3; loose poured bulk densities： 634-1070kg/m3; median size： 7-30 l^m）. The developed models （in power func- tion format） have been used to predict the blockage boundary for larger diameter and longer pipelines （e.g. models based on 69 mm I.D. ~ 168 m long pipe have been scaled up to 105 mm I.D. and 554 m length）. The predicted blockage boundaries for the scale-up conditions were found to provide better accuracy compared to the existing models.

Numerical simulation of fluidized dense-phase pneumatic conveying of powders to develop improved model for solids friction factor

Accurate prediction of the solids friction factor through horizontal straight pipes is important for the reliable design of a pneumatic conveying system, but it is a challenging assignment to date because of the highly concentrated, turbulent, and complex nature of the gas-solids mixture. Power-station fly ash was transported through different pipeline configurations. Numerical simulation of the dense-phase pneumatic conveying systems for three different solids and two different air flow rates have shown that particle and actual gas velocities and the ratio of the two velocities increases in the flow direction, whereas the reverse trend was found to occur for the solids volumetric concentration. To develop a solids friction-factor model suitable for dense-phase flow, we modified an existing pure dilute-phase model by incorporating sub-models for particle and actual gas velocities and impact and solids friction factor. The solids friction-factor model was validated by using it for scale-up predictions for total pipeline pressure drops in longer and larger pipes and by comparing experimental and predicted pneumatic conveying characteristics for different solids flow rates. The accuracy of the prediction was compared with a recently developed two-layer-based model. We discussed the effect of incorporating the particle and actual gas velocity terms in the solids friction-factor model instead of superficial air velocity.

Experimental and numerical study of installing a dune model in a 90° bend in the horizontal-vertical pneumatic conveying system

In the pneumatic conveying process,particles move to the bend under the influence of inertia to form a particle rope,which will cause serious wear between the particles and the pipe wall,and then the dune model is designed and installed in the 90° bend to reduce energy consumption and wear in this study.Firstly,the minimum pressure drop velocity of particles transported by different size dune models was obtained through experimental study.Then the energy saving mechanism of the dune model is studied by CFD-DEM coupling.The experimental results show that the installation of the dune model reduces the minimum pressure drop velocity.The numerical simulation results show that the number of collisions between the particles and the tube wall in the vertical tube decreases after the installation of the dune model,which reduces the energy loss.Moreover,the increasing of tail size of the dune model is beneficial to the diffusion and acceleration of the particles in the vertical tube.

Depicting the role of gas–solid interactions on the hydrodynamics of converging pneumatic riser

The understanding of the flow characteristics and effect of gas–solid interactions in pneumatic risers is fundamental to investigate to ensure effective design cost-effective operation.Thus,to understand the effect of gas–solid interactions on the hydrodynamics of newly proposed conversing risers,this study mainly focused on predicting pressure drop in the dilute phase pneumatic conveying system.The experiments were conducted in a converging riser having a convergence angle of 0.2693°.Various solid particles such as sago,black mustard,and alumina have been considered to study the effect of particle sizes and density on the pressure drop.The experimental outcomes indicate that the total pressure drop increases with an increase in the solid density and gas mass flow rate.Moreover,smaller particle sizes are also increased the pressure drop.An empirical correlation is developed for the prediction of total pressure dropΔPTin converging pneumatic riser via dimensional analysis.All dependent variables such as particle and air density,drag force,acceleration due to gravity,the mass flow rate of air and particle,the diameter of particle and converging riser,the height of converging riser were considered to develop the empirical correlation.The established relationship is tested,and experimental data have been fitted for its validation.The estimated relative error of less than 0.05 proved the significance of the developed correlation.Hence,it can be stated that the established relationship is useful in studying the effects of various parameters on the pressure drop across the length of the conversing riser.

About the Change in Air Pressure in the Pipeline during the Pneumatic Transportation of Cotton

The article is devoted to the study of the issues of determining the patterns of changes in air pressure along the length of a pneumatic transmission pipeline for raw cotton at different flow parameters and different pipeline diameters. Theoretical studies have proved the reduction of static and total pressure along the line of pneumatic cotton transportation. The dependence of the pressure change on the diameter of the transport line and the aerodynamic drag of the pipeline is obtained. The results obtained are recommended for use in the design of raw cotton pneumatic transport systems.

Predicting the mode of flow in pneumatic conveying systems—A review

An initial prediction of the particulate mode of flow in pneumatic conveying systems is beneficial as this knowledge can provide clearer direction to the pneumatic conveying design process. There are three general categories of modes of flow, two dense flows： fluidised dense phase and plug flow, and dilute phase oniy. Detailed in this paper is a review of the commonly used and available techniques for predicting mode of flow. Two types of predictive charts were defined： basic particle parameter based （e.g. particle size and density） and air-particle parameter based （e.g. permeability and de-aeration）. The basic particle techniques were found to have strong and weak areas of predictive ability, on the basis of a comparison with data from materials with known mode of flow capability. It was found that there was only slight improvement in predictive ability when the particle density was replaced by loose-poured bulk density in the basic parameter techniques. The air-particle-parameter-based techniques also showed well-defined regions for mode of flow prediction though the data set used was smaller than that for the basic techniques. Also, it was found to be difficult to utilise de-aeration values from different researchers and subsequently, an air-particle-based technique was developed which does not require any de-aeration parameter in its assessment.

Determination of slug permeability factor for pressure drop prediction of slug flow pneumatic conveying

Current models for pressure drop prediction of slug flow pneumatic conveying in a horizontal pipeline system assume some type of steady state conditions for prediction, which limits their capability for increased predictive accuracy relative to experimental data. This is partly because of the nature of slug flow pneumatic conveying system, which, as a dynamic system, never becomes stable. By utilising conservation of mass （airflow）, a dynamic pressure analysis model is proposed on the basis of the derivative of the upstream pressure behaviour. The rate of air permeation through slug, one of the important factors in the conservation model, is expressed as a function of a slug permeability factor. Other factors such as slug velocity, slug length and the fraction of stationary layer were also considered. Several test materials were conveyed in single-slug tests to verify the proposed pressure drop model, showing good agreement between the model and experimental results.

Numerical study of coarse coal particle breakage in pneumatic conveying

Pneumatic conveying of coarse coal particles with various pipeline configurations and swirling intensities was investigated using a coupled computational fluid dynamics and discrete element method. A particle cluster agglomerated by the parallel-bond method was modeled to analyze the breakage of coarse coal particles. The numerical parameters, simulation conditions, and simulation results were experimentally validated. On analyzing total energy variation in the agglomerate during the breakage process, the results showed that downward fluctuation of the total particle energy was correlated with particle and wall col- lisions, and particle breakage showed a positive correlation with the energy difference. The correlation between the total energy variation of a particle cluster and particle breakage was also analyzed. Parti- cle integrity presented a fluctuating upward trend with pipe bend radius and increased with swirling number for most bend radii. The degree of particle breakage differed with pipeline bending direction and swirling intensity： in a horizontal bend, the bend radius and swirling intensity dominated the total energy variations： these effects were not observed in a vertical bend. The total energy of the particle cluster exiting a bend was generally positively correlated with the bend radius for all conditions and was independent of bending direction.

Energy loss at bends in the pneumatic conveying of fly ash

An accurate estimation of the total pressure drop of a pipeline is important to the reliable design of a pneumatic conveying system. The present paper presents results from an investigation into the modelling of the pressure drop at a bend in the pneumatic conveying of fly ash. Seven existing bend models were used （in conjunction with solids friction models for horizontal and vertical straight pipes, and initial acceleration losses） to predict the total pipeline pressure drop in conveying fly ash （median particle diameter： 30 }zm; particle density： 2300 kg/m^3; loose-poured bulk density： 700 kg/m3） in three test rigs （pipelines with dimensions of 69 mm inner diameter （I.D.） × 168 m length; 105 mm I.D. × 168 m length; 69 mm I.D. × 554 m length）. A comparison of the pneumatic conveying characteristics （PCC） predicted using the seven bend models and experimental results shows that the predicted total pipeline PCC and trends depend on the choice of bend model. While some models predict trends that agree with the experimental results, other models predicted greater bend pressure drops for the dense phase of fly ash than for the dilute phase. Models of Pan, R. （1992）. Improving scale-up procedures for the design of pneumatic conveying systems. Doctoral dissertation, University of Wollongong, Australia, Pan, R., ＆ Wypych, P.W. （1998）. Dilute and dense phase pneumatic conveying of fly ash. In Proceedings of the sixth International Conference on Bulk Materials Storage and Transportation （pp. 183-189）, Wollongong, NSW, Australia and Chambers, A.J., ＆ Marcus, R.D. （1986）. Pneumatic conveying calculations. In Proceedings of the second International Conference on Bulk Materials Storage and Transportation （pp. 49-52）, Wollongong, Australia reliably predicted the bend losses for systems conveying fly ash over a large range of air flows.

Characterization of the gas pulse frequency,amplitude and velocity in non-steady dense phase pneumatic conveying of powders

Current modelling techniques for the prediction of conveying line pressure drop in low velocity dense phase pneumatic conveying are largely based on steady state analyses. Work in this area has been on-going for many years with only marginal improvements in the accuracy of prediction being achieved. Experimental and theoretical investigations undertaken by the authors suggest that the flow mechanisms involved in dense phase conveying are dominated by transient effects rather than those of steady state and are possibly the principal reasons for the limited improvement in accuracy. This paper reports on investigations on the pressure fluctuation behaviour in dense phase pneumatic conveying of powders. The pressure behaviour of the gas flow in the top section of the pipeline was found to exhibit pulsatile oscillations. In particular, the pulse velocity showed variation in magnitude while the frequency of the oscillations rarely exceeded 5 Hz. A wavelet analysis using the Daubechie 4 wavelet found that the amplitude of the oscillations increased along the pipeline. Furthermore, there was significant variation in gas pulse amplitude for different types of particulate material.