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.

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.

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.

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.

PNEUMATIC CONVEYING OF BIOMASS PARTICLES:A REVIEW

Processes involving biomass are of growing interest, but handling and conveying biomass particles are challenging due to the unusual physical properties of biomass particles. This paper reviews recent work on pneumatic conveying of biomass particles, especially agricultural particles and pulp fibres. Experimental work has been mainly carried out to determine a range of parameters, such as pressure drop, particle velocity, flow regime and electrostatic charging for both horizontal and vertical conveying. Models ranging from empirical to CFD models are also being developed. Difficulties in representing turbulence and interactions among biomass particles and between the particles and fluid have so far limited the success of advanced modeling. Further work is needed to improve understanding of multiphase biomass pneumatic conveying and to assist in the development of biomass energy and conversion processes.

CFD-DEM simulation of the pneumatic conveying of fine particles through a horizontal slit

Fine particles play a significant role in many industrial processes. To study the dynamic behavior of fine particle and their deposition in rock fractures, the pneumatic conveying of fine particles （approximately 100 μm in diameter） through a small-scale horizontal slit （0.41 m × 0.025 m） was studied, which is useful for the sealing technology of underground gas drainage in coal mining production. The CFD-DEM method was adopted to model the gas-particle two-phase flow; the gas phase was treated as a continuum and modeled using computational fluid dynamics （CFD）, particle motion and collisions were simulated using the DEM code.Then, the bulk movement of fine particles through a small-scale horizontal slit was explored numerically, and the flow patterns were further investigated by visual inspection. The simulation results indicated that stratified flow or dune flow can be observed at low gas velocities. For intermediate gas velocities, the flow patterns showed pulsation phenomena, and dune flow reappeared in the tail section. Moreover, periodic flow regimes with alternating thick and sparse stream structures were observed at a high gas velocity. The simulation results of the bulk movement of fine particles were in good agreement with the experimental findings, which were obtained by video-imaging experiments. Furthermore, the calculated pressure drop versus gas velocity profile was investigated and compared with relative experi- mental findings, and the results showed good agreement. Furthermore, the particle velocity vectors and voidage distribution were numerically simulated. Selected stimulation results are presented and provide a reference for the further study of fine particles.

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.

CFD-DEM simulation of turbulence modulation in horizontal pneumatic conveying

A study is presented to evaluate the capabilities of the standard k–ε turbulence model and the k–ε turbulence model with added source terms in predicting the experimentally measured turbulence modulation due to the presence of particles in horizontal pneumatic conveying, in the context of a CFD–DEM Eulerian–Lagrangian simulation. Experiments were performed using a 6.5-m long, 0.075-m diameter horizontal pipe in conjunction with a laser Doppler anemometry （LDA） system. Spherical glass beads with two sizes, 1.5 and 2 mm, were used. Simulations were performed using the commercial discrete element method software EDEM, coupled with the computational fluid dynamics package FLUENT. Hybrid source terms were added to the conventional k–ε turbulence model to take into account the influence of the dispersed phase on the carrier phase turbulence intensity. The simulation results showed that the turbulence modulation depends strongly on the model parameter Cε3. Both the standard k–ε turbulence model and the k–ε turbulence model with the hybrid source terms could predict the gas phase turbulence intensity trend only generally. A noticeable discrepancy in all cases between simulation and experimental results was observed, particularly for the regions close to the pipe wall. It was also observed that in some cases the addition of the source terms to the k–ε turbulence model did not improve the simulation results when compared with those of the standard k–ε turbulence model. Nonetheless, in the lower part of the pipe where particle loading was greater due to gravitational effects, the model with added source terms performed somewhat better.

Experimental Study on Wavy-Flow Pneumatic Conveying in Horizontal Pipe

Low-velocity pneumatic conveying systems have been developed to meet the requirement of low operation costs and have been widely used in chemical and process industries. However, the understanding of the mechanism is limited. This paper reports an experimental study on a slug-flow pneumatic conveying. Electrical capacitance tomography has been used to visualize plug shape and identify the flow pattern. Comparison was made between the experimental data of pressure drop with existed models.

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.