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 single-channel 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.     

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 C_ε3. 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.     

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.     

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.     

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 μm;particle density:2300 kg/m~3;loose-poured bulk density:700 kg/m~3) 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.     

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 μm; particle density: 2300 kg/m³; 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.     

Investigation of influence of coal properties on dense-phase pneumatic conveying at high pressure

Experiments of dense-phase pneumatic conveying of pulverized coal using nitrogen were carried out in a test facility at pressures of up to 3.7 MPa to study the effects of coal type, particle size and moisture content on flow characteristics. The Jenike shear test and scanning electron microscopy (SEM) were employed to provide a better understanding of effects of the material properties on flow characteristics. Two kinds of pulverized coals, Yanzhou and Datong, with similar particle size, moisture content and density, were used in the test. Pressure drop increases with increasing the particle size at similar solid–gas ratio, superficial velocity and pressure in the receiving hopper, and pressure drops through different test sections decrease firstly and then rise with increasing the conveying velocity for the same particle size, mass flow rate and pressure in the receiving hopper. The flowability of pulverized coal decreases with increasing the moisture content in the range from 3.24% to 8.18%. Unconfined yield strength (UYS) increases and flow function (FF) decreases with increasing the moisture content. Results of the shearing tests are consistent with the results of the conveying study. Pressure drops through different test sections are discussed and analyzed.     

Experimental investigation into transient pressure pulses during pneumatic conveying of fine powders using Shannon entropy

This paper presents the results of an ongoing investigation into transient pressure pulses using Shannon entropy. Pressure fluctuations (produced by gas–solid two-phase flow during fluidized dense-phase conveying) are recorded by pressure transducers installed at strategic locations along a pipeline. This work validates previous work on identifying the flow mode from pressure signals (Mittal, Mallick, & Wypych, 2014). Two different powders, namely fly ash (median particle diameter 45 μm, particle density 1950 kg/m³, loosely poured bulk density 950 kg/m³) and cement (median particle diameter 15 μm, particle density 3060 kg/m³, loosely poured bulk density 1070 kg/m³), are conveyed through different pipelines (51 mm I.D. × 70 m length and 63 mm I.D. × 24 m length). The transient nature of pressure fluctuations (instead of steady-state behavior) is considered in investigating flow characteristics. Shannon entropy is found to increase along straight pipe sections for both solids and both pipelines. However, Shannon entropy decreases after a bend. A comparison of Shannon entropy among different ranges of superficial air velocity reveals that high Shannon entropy corresponds to very low velocities (i.e. 3–5 m/s) and very high velocities (i.e. 11–14 m/s) while low Shannon entropy corresponds to mid-range velocities (i.e. 6–8 m/s).     

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 2300kg/m~3;loosepoured bulk density 700kg/m~3) and white powder(median particle diameter 55 u.m;particle density1600kg/m~3;loose-poured bulk density 620kg/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 products 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 fluctuation 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.     

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 30 μm; particle density 2300 kg/m³; loose-poured bulk density 700 kg/m³) and white powder (median particle diameter 55 μm; particle density 1600 kg/m³; loose-poured bulk density 620 kg/m³) 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 products 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 fluctuation 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.     

Wavelike motion of particulate slugs in a horizontal pneumatic pipeline

In the pneumatic transport of polyethylene pellets in the horizontal pipeline, wavelike slugs which resemble solitary waves in an open channel are observed in a settled layer of the particles when a superficial air velocity is smaller than the saltation velocity by Zenz and those transport characteristics such as travelling velocity, length, period of appearance and pressure drop are measured. It is found that the pressure drop by the wavelike slug is estimated by the Ergun equation for the fixed bed.     

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(approximately100 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 experimental 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.     

Spectral element modelling and analysis of a pipeline conveying internal unsteady fluid

In this paper, a spectral element model is developed for the uniform straight pipelines conveying internal unsteady fluid. Four coupled pipe-dynamics equations are derived first by using the Hamilton's principle and the principles of fluid mechanics. The transverse displacement, the axial displacement, the fluid pressure and the fluid velocity are all considered as the dependent variables. The coupled pipe-dynamics equations are then linearized about the steady-state values of the fluid pressure and velocity. As the final step, the spectral element model represented by the exact dynamic stiffness matrix, which is often called spectral element matrix, is formulated by using the frequency-domain solutions of the linearized pipe-dynamics equations. The fast Fourier transform (FFT)-based spectral dynamic analyses are conducted to evaluate the accuracy of the present spectral element model and also to investigate the structural dynamic characteristics and the internal fluid transients of an example pipeline system.     

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 collisions, 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. Particle 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.     

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 only.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.     

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.     

An analytic solution of dense two-phase flow in a vertical pipeline

According to a mathematical model for dense two-phase flows presented in theprevious paper,a dense two-phase flow in a vertical pipeline is analytically solved,and theanalytic expressions of velocity of each continuous phase and dispersed phase arerespectively derived The results show that when the drag force between two phases dependslinearly on their relative velocity,the relative velocity profile in the pipeline coincides withDarcy’s law except for the thin layer region near the pipeline wall,and that the theoreticalassumptions in the dense two-phase flow theory mentioned are reasonable.     

DEM investigation on conveying of non-spherical particles in a screw conveyor

Screw conveyors are extensively used in modern industry such as metallurgy, architecture and pharmaceutical due to their high-efficiency in the transportation of granular materials. And substantial efforts have been devoted to the study of the screw conveyors. Numerical method is an effective way to study screw conveyor. However, previous studies have mainly focused in the regime of spherical particles while the in-depth investigations for non-spherical particles that should be the most encountered in practical applications are still limited. In view of the above situations, discrete element method (DEM), which has been widely accepted in simulating the discrete systems, is utilized to investigate the conveying process of non-spherical particles in a horizontal screw conveyor, with particles being modeled by super-ellipsoids. In addition, a wear model called SIEM (Shear Impact Energy Model) is incorporated into DEM to predict the wear of screw conveyor. The DEM simulation results demonstrate that the particle shape is influential for the flow behaviors of particles and the wear of conveyor. The conveying performance evaluated quantitatively of both mass flow rate and power consumption is subsequently obtained to investigate the effect of sphericity of particle with different operation parameters. Moreover, particle collision frequency and collision energy consumption are acquired to investigate the possible particle breakage between particles and screw blade. The comparisons between particle–particle collision and particle–wall collision reveal that particles with large shape index have more possibility to be damaged in particle–wall impingement.     

Pressure drop prediction with a modified frictional-kinetic model for alumina in bypass pneumatic conveying system

A new frictional-kinetic model is proposed and modified for pressure drop prediction of alumina in a bypass pneumatic conveying system. This new model is based on the conventional Johnson–Jackson frictional-kinetic model. The critical value of solids volume fraction and maximum packing limit are modified based on the fluidized bulk density and tapped bulk density, respectively. In addition, an offset solid volume fraction is introduced into the frictional pressure model as well as into the radial distribution functions which represents the correction factors to modify the probability of collisions between particles when solid phase becomes excessively dense. For the application of the model, computational fluid dynamics (CFD) simulations were conducted by using kinetic theory, conventional frictional-kinetic model and modified frictional-kinetic model. The simulation results were then compared with the experimental results. It was found that the modified frictional-kinetic model showed the largest improvement on pressure drop prediction results compared with results obtained from applying the kinetic theory and the conventional frictional-kinetic model, especially for denser flows with low air mass flow rates and high solid loading ratios (SLR). In addition, the solids volume investigation of CFD simulations shows a strong comparison to the actual flow conditions in the pipe, as transient slug type flow of alumina is observed.     

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 μm 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.