Effect of particle degradation on electrostatic sensor measurements and flow characteristics in dilute pneumatic conveying

Vigorous particle collisions and mechanical processes occurring during high-velocity pneumatic conveying often lead to particle degradation. The resulting particle size reduction and particle number increase will impact on the flow characteristics, and subsequently affect the electrostatic type of flow measurements. This study investigates this phenomenon using both experimental and numerical methods. Particle degradation was induced experimentally by recursively conveying the fillite material within a pneumatic pipeline. The associated particle size reduction was monitored. Three electrostatic sensors were embedded along the pipeline to monitor the flow. The results indicated a decreasing trend in the electrostatic sensor outputs with decreasing particle size, which suggested the attenuation of the flow velocity fluctuation. This trend was more apparent at higher conveying velocities, which suggested that more severe particle degradation occurred under these conditions. Coupled computational fluid dynamics and discrete element methods (CFD–DEM) analysis was used to qualitatively validate these experimental results. The numerical results suggested that smaller particles exhibited lower flow velocity fluctuations, which was consistent with the observed experimental results. These findings provide important information for the accurate application of electrostatic measurement devices in pneumatic conveyors

Breakage characteristics of granulated food products for prediction of attrition during lean-phase pneumatic conveying

Pneumatic conveying is utilised in a variety of industries to convey food products exhibiting diverse handling characteristics. Attrition of particles caused by this conveying process can result in a number of undesirable outcomes such as loss in product quality or issues in subsequent handling processes. The ability to predict the breakage behaviour of particulate materials is desirable in both new system design and resolving issues in existing plants. This work considers two different particulate materials (Salt and Golden Breadcrumbs) across a range of particle sizes, and quantifies their breakage behaviour under varying impact conditions. Narrow size fractions of each material was degraded; material retained on 250 µm and 355 µm sieves for salt, and 500µm, 710µm and 1000 µm sieves for Golden Breadcrumbs. Velocity was found to be the most influential factor with respect to particle attrition. The results from the narrow size fraction tests were superimposed to form a simulated full size distribution breakage behaviour, which was then compared to the experimentally determined behaviour. A good agreement was found, however the proportion of material predicted for size fractions smaller than 355 µm for Golden Breadcrumbs and 180 µm for Salt was under-predicted. Recommendations for increasing accuracy of the prediction method are given

Numerical study of pneumatic conveying of powders

The dense phase mode may be advantageous over the dilute phase mode, for some pneumatic conveying problems, because it causes less erosion of the pipeline, less attrition of the material, requires less dust collection and is effective even for smaller pipe diameters. The objective of this study is to numerically determine the parameters that govern the formation slugs in dense phase conveying. The distributed Lagrange multiplier/fictitious domain method (Glowinski et al. 1998 and Singh et al. 2000) is used to perform direct simulations of the motion of solid and gas phases in pipes with rectangular cross-sections. In this approach the exact governing equations are solved at scales finer than the particle size and no ad hoc two-phase flow model is used. Simulations are started by placing a particle slug in the flow. Several cases were simulated to understand the role of gravity, the particle density and the strength of applied pressure gradient in the formation and destruction of slugs. When the applied pressure gradient is increased the slugs become more compact, their velocity in the flow direction increases and they remain intact for longer time durations. A reduction in the pressure gradient, on the other hand, causes the particle velocity to decrease and consequently they sediment and simply roll on the bottom. The reduced gravity causes the slug to disintegrate and the center of mass of the slug moves upwards against gravity. The increased viscosity of the fluid, for a fixed pressure gradient, causes the particle to settle on the bottom of the channel under gravity

Particle Attrition Mechanisms, their characterisation, and application to horizontal lean phase pneumatic conveying systems: A review

Understanding particle attrition is vital to the optimisation of a wide range of industrial processes. Lean phase pneumatic conveying is one such process, whereby the high energy particle impacts can cause undesirable loss in product quality or change in bulk behaviour. The attrition process is resolved into a material function and a process function; the combination of these functions dictates the attrition mechanism present, and the magnitude of failure observed. Subsequently, the forces applied to the particles are examined within the context of lean phase pneumatic conveying. Finally, empirical and numerical models are reviewed along with comments on experimental method. To summarise some of the findings of this review: the requirement of standardised test equipment is recognised in order to compare the wide variety of particulate materials under comparable loading conditions; stronger correlation between the results obtained from different particle attrition test methods is required; and finally, seldom are the manufacturing conditions (where applicable) linked to the particulate attrition behaviour

A model to predict the lifetime of pneumatic conveyor bends

Bursts in pneumatic conveyor pipelines in industrial processes are a well-known hindrance to the smooth operation of any plant. Unanticipated stoppages can have serious financial implications for any company using pneumatic conveying technology, and health and safety factors are also paramount. This thesis describes an attempt to enable improved prediction of bend-wear and bend lifetime, so that more cost-effective survey work can be undertaken in anticipation of bursts. This work delivers a tool that allows bend lifetime prediction to be made according to: the bend geometry and material; the material conveyed and its rate of transportation; and bend wall thickness. Firstly, a computational model based on the coupling of CFD and particle tracking techniques is created in order to encompass the mechanics of the erosion process. This erosion process is assumed to be dominated by impact damage, and predictions of bend lifetime are made using empirical erosion algorithms gleaned from laboratory experiments, commercial CFD code (PHOENICS, and GENTRA its particle tracking sister code), and custom erosion modelling code that employs a three-dimensional toroidal geometry. Secondly, matrices of predictions are built up using the mathematical modelling technology mentioned above. These predictions are collated behind a friendly interface to produce a far more accessible piece of PC software that an engineer can employ quickly and easily. More general bend-life predictions are interpolated from this fundamental dataset using behaviours established in the course of this work, according to the particular conveying conditions input by the user. Predictions in the desktop tool are calibrated to actual bend lives as established by experimentation on a full-scale pneumatic conveyor. This experimental work was an integral part of this EPSRC-funded project, and allows some estimation of error magnitude in the predictive tool

APPLICATION OF BREAKAGE MATRIX APPROACH TO PREDICT INADVERTENT DEGRADATION DURING HANDLING AND PROCESSING OF PARTICULATE MATERIALS

Many process industries deal with particulate materials, often in the form of bulk mixtures with considerable variations in particle size and shape. Degradation (breakage) of particles during transport, handling and processing presents a serious handling problem – improved understanding of degradation processes is a highly desirable aim. When bulk assemblies are dense-phase in nature, degradation of particles is likely to be significantly influenced by the presence of surrounding particles. Quantifying such influence allows better modeling and predictive capability. Techniques involving matrix equations are potentially useful modelling tools, already successfully used in predicting degradation of (lean-phase) assemblies, where the influence of particles on each other is probably negligible. The motivation of this research is to pioneer use of breakage matrix techniques as more versatile tools to predict degradation in dense-phase assemblies (significant interacting mixture breakage conditions). The principal issue with the breakage matrix approach is the amount of necessary data and the difficulty in obtaining that data, particularly when there is intra-mixture influence as described above. A technique is pioneered, based on experimental data obtained from compression and impact tests of mixtures of assemblies, by which breakage matrices can be calculated from only the input and output particle size distributions for a degradation process. The results reveal that the degree of intra-mixture influence can be quantified by recourse to fairly straightforward analytical expressions of coefficient of interaction, and indicate ways in which breakage matrices can be inferred from scarce available data. The results show that the breakage matrix approach to be a more promising tool for modeling and predicting interacting and non-interacting mixture degradation than has been appreciated to date. The significance of the semi-empirical correlations established for interacting and noninteracting mixtures could further be demonstrated in industrial applications such as through systematic sampling in pneumatic conveyors and in silo filling and discharge. Industrial field data could further be compared with the results of controlled experiments in model compaction, attrition and shear cells demonstrated in the thesis to pave the way for an universal approach.</p

Computational modeling of multiphase fibrous flows for simulation based engineering design

This dissertation develops a modeling framework for predicting the behavior of fibrous bulk solids in pneumatic conveyance systems that are currently not possible with conventional computational models. The developed framework allows designers to computationally predict flow characteristics of fibrous bulk solids, which impacts pneumatic conveyance system performance. These performance characteristics include air and fibrous bulk solids velocity profiles, fibrous bulk solids concentrations, pressure loss, and general system behavior. The motivation for this research is to expand the capabilities of computational models within in the engineering design process, rather than relying solely on generalized experimental correlations and previous design experience. This framework incorporates the primary characteristics of fibrous biomass-based bulk solids including low density, large characteristic length, and non-spherical shape. The main features of the developed modeling framework are (1) the effects of the particle drag on the flowing air and (2) the resistive effects of the interconnected fibers between the particles. The models are implemented within a commercially available CFD solver package with user-defined functions. Velocity profiles, bulk solids concentration, and air pressure are modeled with the differential conservation equations for mass and momentum based on the Eulerian-Eulerian multiphase modeling approach. The inter-particle and the particle-air interactions result in momentum exchanges, and these exchanges are incorporated into the model through a series of externally defined user functions that account for the momentum exchange due to drag of the particles and the resistance of the connected fibers. These user-defined functions allow the user to set a series of parameters specific to the transported bulk solids and to the loading conditions. The model is applied to two specific studies, which include (1) cotton-air flow through a positive pressure pneumatic conveyance system and (2) biomass-air flow through a negative pressure (vacuum) conveyance system. The model parameters are chosen to match existing experimental data obtained from their corresponding lab tests

Experimental quantification and modelling of attrition of infant formulae during pneumatic conveying

Infant formula is often produced as an agglomerated powder using a spray drying process. Pneumatic conveying is commonly used for transporting this product within a manufacturing plant. The transient mechanical loads imposed by this process cause some of the agglomerates to disintegrate, which has implications for key quality characteristics of the formula including bulk density and wettability. This thesis used both experimental and modelling approaches to investigate this breakage during conveying. One set of conveying trials had the objective of establishing relationships between the geometry and operating conditions of the conveying system and the resulting changes in bulk properties of the infant formula upon conveying. A modular stainless steel pneumatic conveying rig was constructed for these trials. The mode of conveying and air velocity had a statistically-significant effect on bulk density at a 95% level, while mode of conveying was the only factor which significantly influenced D[4,3] or wettability. A separate set of conveying experiments investigated the effect of infant formula composition, rather than the pneumatic conveying parameters, and also assessed the relationships between the mechanical responses of individual agglomerates of four infant formulae and their compositions. The bulk densities before conveying, and the forces and strains at failure of individual agglomerates, were related to the protein content. The force at failure and stiffness of individual agglomerates were strongly correlated, and generally increased with increasing protein to fat ratio while the strain at failure decreased. Two models of breakage were developed at different scales; the first was a detailed discrete element model of a single agglomerate. This was calibrated using a novel approach based on Taguchi methods which was shown to have considerable advantages over basic parameter studies which are widely used. The data obtained using this model compared well to experimental results for quasi-static uniaxial compression of individual agglomerates. The model also gave adequate results for dynamic loading simulations. A probabilistic model of pneumatic conveying was also developed; this was suitable for predicting breakage in large populations of agglomerates and was highly versatile: parts of the model could easily be substituted by the researcher according to their specific requirements

A Comparative Study of Induced and Transferred Charges for Mass Flow Rate Measurement of Pneumatically Conveyed Particles

In-line measurement of the mass flow rate of solids in pneumatic conveying pipelines is essential for the efficient and optimized operation of many industrial processes. This paper presents a comparative study of using induced and transferred charges from non-intrusive electrodes exposed to the particle flow for mass flow rate measurement. A novel signal conditioning circuit, which consists of a current sense amplifier and a charge amplifier, is designed to convert the induced and transferred charges into two separate voltage signals. Empirical measurement models that relate the particle velocity, the root-mean-square (r.m.s) magnitude of the induced charge signal and the slope of the transferred charge signal to the mass flow rate are proposed. Experiments were undertaken using electrodes of different widths and under different mass flow rate and particle velocity conditions. Results obtained show that both the r.m.s magnitude of the induced charge signal and the slope of the transferred charge signal increase with the mass flow rate and the velocity of particles. In general, the measurement results using the induced and transferred charges from either the narrow or the wide electrode are similar. However, the method based on the transferred charge is less reliable due to confined sensing area and electrode charging by particles adhered to the electrode surface

Simulation of a new pipe design for erosion reduction in curves

Pneumatically conveyed particles are commonly responsible for triggering the erosion process by impacts on the wall. Those impacts result from the fluid-particle interaction and understanding its mechanisms is the key to mitigate the erosion damage in engineering applications. In general, erosion due to particle impingement, which can occur in a variety of practical cases, is often the key factor in pipeline failure. Parts such as elbows, for instance, are particularly prone to erosion issues. In the first part of this thesis, the Unsteady Reynolds Averaged Navier-Stokes (URANS) equations are combined with a stochastic Lagrangian particle tracking scheme considering all relevant elementary processes (drag and lift forces, particle rotation, inter-particle collisions, particle-wall interactions, coupling between phases) to numerically predict the erosion phenomenon on a 90 elbow pipe. After a detailed validation of the erosion model based on the experimental data of Solnordal et al. (2015), several cases regarding the wall roughness and static and dynamic coefficients of friction are analysed to elucidate the nature of the erosive process. For such analysis, more fundamental variables related to particle-wall interactions (impact velocity, impact angle, impact frequency) were used to scrutinize the basic erosion mechanisms. Finally, to prove the importance of inter-particle collision on elbow erosion, different mass loadings are additionally simulated. Especially for the high mass loading cases, interesting results about the role of the inter-particle collisions on elbow erosion are enlightened. In a second step, we propose a novel pipe wall design in order to reduce the erosion on a 90 elbow. This design consists of twisting the pipe wall along the flow streamwise direction. Basically, such configuration generates a swirling motion of the flow upstream of the elbow and consequently re-disperse the transported particles, preventing them to focus on a single point at the elbow. Based on a four-way coupled simulation, the simulations were run for the new pipe wall design. To understand the nature of the erosive process on the new pipe wall design, the above-mentioned variables regarding the particle-wall interaction were evaluated. In general, it was found that the changes in the multiphase flow promoted by the twisted pipe wall are effective for reducing elbow erosion. The numerical simulations reveal that the pipeline equipped with a twisted pipe wall reduces the peak of erosion depth up to 33% on the elbow when compared to the conventional pipe.Tese (Doutorado)Partículas transportadas pneumaticamente são comumente responsáveis por desencadear o processo de erosão por impactos na parede. Esses impactos resultam da interação fluido-partícula e a compreensão de seus mecanismos é a chave para mitigar os danos causados pela erosão em aplicações de engenharia. Em geral, a erosão causada por impacto de partículas, que pode ocorrer em uma variedade de casos práticos, é frequentemente o fator principal na falha de tubulações. Acessórios como cotovelos, por exemplo, são particularmente propensos a problemas de erosão. Na primeira parte desta tese, as equações médias de Reynolds transiente (URANS) são combinadas com um modelo lagrangeano estocástico de rastreamento de partículas considerando todos os processos elementares relevantes (forças de arrasto e sustentação, rotação das partículas, colisões entre partículas, interações partícula-parede, acoplamento entre as fases) para predizer numericamente o fenômeno erosivo em um cotovelo de 90 . Após uma validação detalhada do modelo de erosão com base nos resultados experimentais de Solnordal et al. (2015), vários outros casos com diferentes rugosidades na parede e coeficientes de atrito estático e dinâmico são apresentados para elucidar a natureza do processo erosivo. Para tal análise, foram utilizadas variáveis mais fundamentais e que estão relacionadas às interações partículaparede (velocidade de impacto, ângulo de impacto, frequência de impacto) para examinar os mecanismos básicos de erosão. Finalmente, para provar a importância da colisão entre partículas na erosão do cotovelo, diferentes cargas mássicas são simuladas. Especialmente para os casos com carga mássica elevada, resultados interessantes sobre a importância das colisões entre partículas na erosão do cotovelo são abordados. Em uma segunda etapa, propomos um novo design para a parede da tubulação com o intuito de reduzir a erosão no cotovelo de 90 . Esta concepção consiste em torcer a parede do tubo ao longo do sentido principal do escoamento. Basicamente, tal configuração gera a rotação do fluido a montante do cotovelo e, consequentemente, re-dispersa as partículas transportadas, evitando que se concentrem diretamente em um único ponto no cotovelo. Com base em simulações com quatro vias de acoplamento, simulações são feitas para a configuração proposta. Para compreender a natureza do processo erosivo na nova geometria, as variáveis relativas as interações partícula-parede que foram mencionadas anteriormente também foram avaliadas. Em geral, verificou-se que as alterações no escoamento multifásico promovidas pela parede torcida são efetivas na redução da erosão no cotovelo. As simulações numéricas revelam que a tubulação equipada com o tubo torcido reduz o pico de profundidade de erosão no cotovelo em até 33% quando comparado ao tubo convencional