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Available ONLINE www.visualsoftindia.com/vsrd/vsrdindex.html

VSRD-TNTJ, Vol. 2 (8), 2011, 382-389

____________________________

1Assistant Professor, Department of Mechanical Engineering, RSTM Nagpur University, Nagpur, Maharashtra, INDIA.2Professor, Department of Mechanical Engineering, SGB Amravati University, Amravati, Maharashtra, INDIA.3Principal, Department of Mechanical Engineering, RSTM Nagpur University, Nagpur, Maharashtra, INDIA.*Correspondence : [email protected]

RRREEE VVV III EEE WWW AAA RRRTTT III CCC LLL EEE

Design Considerations for

Pneumatic Conveying System : A Review1LP Dhole*,

2LB Bhuyar and

3GK Awari

ABSTRACT

Pneumatic conveying system is a conventional material handling system like belt conveyor or chain conveyor.

The main advantage of pneumatic conveying system is that material is transferred in close loop, thereby

preventing the environmental effect on the material and vice versa. In these paper different parameters like air

velocity, pressure, particle size and shape, distance to be conveyed, which govern the design of the system, are

described. The research work carried out on the pneumatic conveying system in the last decade considering

these parameters is also presented. No standard procedure is available for the design of pneumatic conveyingsystem. As the configuration of the system changes, variable involved also changes, and one has to change the

design considerations based on the applications. So there is wide scope for experimentation in the field of

pneumatic conveying system.

Keywords :Pneumatic Conveying, Venturi Feeder, Dilute Phase.

1. INTRODUCTION

Pneumatic conveying is a practical method for in-plant distribution of large amounts of dry powdered, granular,

and pelletized materials[1]. Based on the quantity of air used and pressure of the system, pneumatic conveying

system is divided in to two types viz. dense phase pneumatic conveying system and dilutes phase pneumatic

conveying system. In dilute phase conveying, solid particles are introduced into a fast flowing gas stream where

solids remain suspended. Such process systems operate at relatively low pressure and consequently are

comparatively inexpensive to install[1]

.

Dense-phase pneumatic conveying, is defined as the conveying of particles by air along a pipe which is filled

with particles atone or more cross-sections. There is much confusion over the use of the term dense-phase

conveying and, as a result, many different definitions have been proposed, based on the solid loading ratio,

pressure and quantity of air used[2]. Easiness in controlling and flexibility in installations are some of the

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LP Dhole et. al/ VSRD Technical & Non-Technical Journal Vol. 2 (8), 2011

Page 383 of 389

favourable features of pneumatics applications in many industrial and non-industrial fields. It has a wide range

of applications, with examples ranging from domestic vacuum cleaners to the transport of some powder

materials over several kilometers[3]

.

The industrial field where pneumatic conveying system is extensively used includes Chemical process industry,

Pharmaceutical industry, Mining industry, Agricultural industry, Mineral industry, and Food processing

industry. Virtually, all powders and granular materials can be transported using this method. . Murilo D.M.

Innocentini et al [27] experimentally investigated the dehulling process of cracked soybeans in 2008 and it has

been shown that the efficiency of the pneumatic device to remove hulls from the cracked soybean was very

high, with the recovery of meats with purity around 99%. In Ref. [4], a list of more than 380 different products,

which have been successfully conveyed pneumatically, is presented. It consists of very fine powders, as well as

the big crystals such as quartz rock of size 80 mm.

2.

EXPERIMENTAL ANALYSIS OF THE SYSTEM

The conveying potential of the system is of prime importance while selecting a pneumatic conveying system for

a particular application. Number of factors has a potential influence on material flow rate. They can be grouped

into three broad categories[28]

viz. those associated with the material required to be convey, the conveying

conditions and the pipeline geometry.

2.1.The Material To Convey

The factors required to considered related to material to be conveyed include mean particle size, particle size

distribution, particle shape, particle and bulk densities, particle volume fraction, air retention and permeability.

Decision of using pneumatic conveying system for particular material greatly depends on these properties.

2.2.The Conveying Conditions

Material conveying conditions that have a direct influence on material conveying potential include solids

loading ratio, conveying line pressure drop, and air flow rate or conveying air velocity. Of these conveying line

pressure drop is the only fully independent variable since both solids loading ratio and conveying air velocity

are additionally material dependent. Air velocity, pressure and solid loading ratio decide whether the system is

dense phase or dilute phase.

2.3.The Pipeline Geometry

The factors required to be considered related to pipeline geometry includes the length of the pipeline, the bore of

the pipe and the number of bends in the pipeline bend radius ratio. Power required operating the system

increases with the increase in pressure drop of the system. The pressure drop in the system depends on the

horizontal and vertical length of the system, bends in the pipeline. Whereas the quantity of air required increases

as the size of the pipeline increases.

These variables are generally required to be considered for the analysis of pneumatic conveying system. The

objective of the paper is to take the review of the research carried out in the field in the last decade considering

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all these variables. The different approaches and the models used for the analysis are also presented.

3. DESIGN PROCEDURE

There is no specific design procedure for the pneumatic conveying system. Sometimes it is also not possible to

categorize the particular system as dilute phase or dense phase. So many times one has to make the changes in

the generalized design procedure for the pneumatic conveying system or has to apply different methodology for

the design. Many researchers worked on the design procedure that can be adopted for the particular application.

Lot of experimental work has been carried out on the bulk transportation using pneumatic conveying system. R.

Pan and P.W. Wypych presented test design procedurefor low-velocity slug flow pneumatic conveying of bulk

solid materials with irregular-shaped materials like muesli, maize germ[5]

. Based on the particle properties and

data from a simple vertical test chamber, the pressure drop and slug velocity in low-velocity slug flow can be

predicted accurately by this method in large-scale systems.

Experimental analysis was carried out by Jens Reppenhagen, Arwed Schetzschen, and Joachim Werther[11]

to

find the optimum cyclone size with respect to the fines in pneumatic conveying systems. Two different design

aspects for cyclones were considered. The first aspect was to keep the product as free of fines as possible and

the second one was to minimize the cyclone loss rates. Besides the mechanisms of the true gas-solids separation,

the production of fines due to particle attrition was identified to affect these two aspects. A first approach of a

new design procedure was therefore provided, where an attrition model is implemented in a conventional

cyclone model.

P. Guiney, R. Pan), J.A. Chambers used Scale-up technology in low-velocity slug-flow pneumatic conveying

[13]

.The mechanisms involved at the boundaries were investigated. Based on the understood mechanisms, a small

and specific test rig was designed and built. As long as a sample of the conveyed product is tested in such test

rig, the boundaries for the product can be determined directly and accurately. Hence, by combining the

procedure for predicting the total pipeline pressure drop and the method for locating the boundaries, a simple

and reliable scale-up technology was presented for the design of low-velocity slug-flow pneumatic conveying

systems.

4. PRESSURE DROP

In 2002 experimental investigation of vertical pneumatic system by Grzegorz Dzido, Michal C Palica, Jerzy

Raczek[12]

shown that pressuredrop in the acceleration region can be predicted using the uniform flow model if

the proper value of the initial solid velocity is known. The equations for estimation of this value were proposed

and the correlations for drag force coefficient and friction factor that give the most accurate results were

selected.

Sean McNamara, Martin Straub[18]

investigated dense phase pneumatic conveying through simulation, using a

discrete element approach for the granular particles and a finite difference method for the pressurefield. Both

horizontal and vertical conveying were studied and compared. Studies of single plugs or slugs promise to give

insight into the performance of pneumatic conveying systems. Preliminary results indicate that the pressure

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drop is linearly related to the length of the plug. This indicates that the total pressure drop across a conveying

system is linearly proportional to the flux of granular material transported.

WANG Xiaofang, JIN Baosheng et al[24]

carried out computational study on the flow behavior of a gas-solid

injector by Eulerian approach. The gas phase was modeled with k- turbulent model and the particle phase was

modeled with kinetic theory of granular flow. The simulations by Eulerian two-fluid model (TFM) were

compared with the corresponding results by discrete element method (DEM) and experiments. It was showed

that TFM simulated results were in reasonable agreement with the experimental and DEM simulated results.

Based on TFM simulations, gas-solid flow pattern, gas velocity, particle velocity and the static pressureunder

different driving jet velocity, backpressureand convergent section angle were obtained. The results showed that

the time average axial gas velocity sharply decreased and then slightly increased to a constant value in the

horizontal conveying pipe. The time average axial particle velocity increased initially and then decreased, but in

the outlet region of the convergent section the particle velocity remarkably increased once more to the maximal

value. As a whole, the static pressuredistribution change trends were found to be independent on driving gasvelocity, backpressureand convergent section angle. However, the static pressure increased with increase of

convergent section angle and gas jet velocities. The difference of static pressureto backpressure increased with

increasing backpressure.

The characteristics of low-velocity conveying of particles having different hardness are experimentally

investigated by Yuji Tomita, Vijay Kumar Agarwal et al[25]

in a horizontal pipeline in terms of flow pattern and

pressuredrop to show that the slug flow can be classified into two types depending on the settling of particles

along the pipeline, and the period is small for slug flow without the settled layer, which is called solitary slug

flow. The pressure drop for soft particles was shown to be larger than that for hard particles. Experimentalresults were presented on horizontal fluidized-bed conveying of fine powders to show that air release from the

top surface of the conveying channel is an important factor for high mass flow rate of particles.

5. VELOCITY

Laboratory experiments and numerical simulations were carried out by R. Schallert, E. Levy[10]

to determine the

effect of two closely spaced elbows on roping behavior in a vertical pipe downstream of the second elbow. The

results show that the combination of elbows results in a stationary rope, which spirals around the inside of the

vertical pipe, adjacent to the pipe wall. The angular position of the rope, peak particle concentration, and particle

velocityin the rope was found to depend strongly on the length of the pipe connecting the two elbows.

Robert M. Carter, Yong Yana, and Stuart D. Cameron in 2005[15]

suggested a novel instrumentation system that

uses a combination of electrostatic and digital imaging sensors. An inferential approach was adopted for the

mass flow measurement of particles, velocity and volumetric concentration of particles being measured

independently. The velocityof particles was determined by cross correlating two signals derived from a pair of

electrostatic sensors and the volumetric concentration of particles was obtained using a novel digital imaging

sensor, which also provides particle size distribution data.

Anton Fuchs, Hubert Zangl, et al used Correlative-measurement technique [17] for the evaluation of the flow

velocity of bulk granular solids moving through the pneumatic conveyor pipes in both the dense and dilute

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phases. Flow velocities were recovered from the cross-correlation functions between the pairs of signals

produced by the noninvasive capacitive sensors placed in circular layers at a given distance on the conveyor

pipe. A random-data correlate architecture was suggested as a cost-effective solution for the real-time

computation of the multiple correlation functions that was used for the estimation of the cross-sectional

tomographic model of the flow-velocityprofile in the dilute phase.

Urmila Datta, Tomasz Dyakowski, and Saba Mylvaganam presented a technique[20]

developed to estimate the

velocitycomponents of two phase solid/gas flow using electrical capacitance tomography (ECT). The pixel-by-

pixel correlation method for consecutive frames in a given sensor plane was used to trace the particle velocity

profile in the transverse direction. The transverse movement of solid particles in slug flows has been reported

recently in the literature.

Evgeny Rabinovich and Haim Kalman carried out experimentation in 2007[21]

to measure pickup, critical and

wind threshold velocities of particulate solids in gases and in liquids. In 2008[22]

Evgeny Rabinovich and Haim

Kalman analyzed threshold velocities for fluidization and pneumatic conveying. It has been shown that how the

threshold velocities can be used to design of particle--fluid systems for particle size distribution. The analysis

provided practical guides for various engineering scenarios, such as selecting the appropriate fluidization

velocity for maximum fluidization and minimum entrainment and determining the conveying velocity in

pneumatic systems. In addition, the analysis provided a guide to determine whether the deposited layer of

particles at the pipe bottom is stationary or moving, for cases where the superficial velocityis smaller than the

saltation velocity.

K.S. Rajan, S.N. Srivastava et al[23]

carried out experimental study of thermal effectiveness in pneumatic

conveying heat exchanger. Gassolid interactions in pneumatic conveying were utilized to transfer heat between

gas and solid phases. Experiments on airsolid heat transfer were carried out in a specially designed vertical

pneumatic conveying test rig consisting of Galvanized Iron duct of 54 mm inner diameter and 2.2 m height,

using gypsum as the solid medium and hot air as gas medium. Thermal effectiveness of air was found to

increase with solids feed rate and decrease with air velocity. Thermal effectiveness of solids was found to

decrease with solids feed rate. An optimum air velocityhas found to exist at which the thermal effectiveness of

solids is maximum. The effect of particle size on thermal effectiveness of air and solid was found to be

predominant at higher solids feed rates. A dimensionless correlation has been developed for thermal

effectiveness of solid.

6. GAS SOLID FLOW

David J. Mason and Avi Levy[6]

investigated the effect of a bend on the distribution of particles in a pipe cross-

section and segregation in pneumatic conveying systems numerically. Also David J. Mason and Avi Levy[7]

compared the use of one-dimensional and a three-dimensional model to simulate the flow of a gassolids

mixture through a pipeline. The cost of using each of these models was presented in terms of the time taken to

produce a design and the amount of useful information obtained from the model.

N. Huber, M. Sommerfeld[8] presented the developments of Euler /Lagrange approach for the calculation of

dispersed gas-solid flows in pipe systems. The calculations include all important effects, such as, turbulence,

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two-way coupling, particle transverse lift forces, particle-wall collisions including wall roughness, and inter-

particle collisions.

Aimo Visa Poikolainen, Rautiainen, et al[9]

provided the experimental study of vertical pneumatic conveying.

This study was by using a one-dimensional equation system and experimental techniques to provide a

comprehensive description of vertical gassolid two-phase flow. The results from non-accelerating flow

experiments conducted with a riser tube of bore 192 mm and height 16.2 m using spherical glass beads of

average diameter 64 mm were presented.

S. Fokeera, S. Kingman et al. presented a review,[14]

on characterization of the cross sectional particle

concentration distribution in horizontal dilute flowconveying. It was the review and analysis of the results of

recent research that has been carried out on horizontal pneumatic conveying of materials in the dilute phase.

Many in-process applications require a detailed knowledge of the cross-sectional particle concentration

distribution and an insight into the research carried out in that field was reviewed. Tomography and

computational fluid dynamics (CFD) modelling were identified as the available tools for achieving the aims of

such a study and an overview of each was presented. The physical understanding and modelling of the cross

sectional distribution of particles in dilute SFPC was identified as a challenging area for future research.

Samy M. El-Behery, Mofreh H. Hamed et al.[26]

used CFD to examine airsolid flowin 180 curved duct. Gas

solid two-phase flow in 180 curved duct was simulated using a two-way coupling EulerianLagrangian

approach. Reynolds averaged NavierStokes equations (RANS) and four turbulence models namely; standard

k model, RNG (Renormalization Group) based k model, Low-Re k model and an extended version of the

standard k model were adopted. The effects of particle rotation and lift forces were included in the particle-

tracking model. The present predictions were compared with published experimental data for single-phase and

two-phase flows. The comparisons show that the RNG based k model predicts the flow behaviour better than

other models.

7. CONCLUSION

Despite the fact that there is a vast literature on the pneumatic conveying of solids is available, but still standard

method suitable for design of the pneumatic conveying system is not available till date. The different parameters

required to be considered for the design of pneumatic conveying system are air velocity, pressure drop, gas solid

flow, pressure drop, number of bends in the system, horizontal and vertical distance f the pipeline. Each of this

parameter in addition to the changes in the configuration forces to change the design procedure. The behaviour

of the system is unpredictable, so there is wide scope for the experimentation of the different configurations of

the system, which can use for specific application. Similarly behaviour of the particular parameter for the

particular system is also unpredictable. Therefore every application of the pneumatic conveying system is a

different problem; and thus provides a wide scope for researchers.

8. REFERENCES[1] F. Pon, K.K. Botros, P. Grabinski, B. Quaiattini, L. Motherwell. Experimental and Plant Data of Pneumatic

Conveying Characteristics of Seven Granular Polyethylene Resins in Horizontal and Vertical Pipes.

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Presentation at the AIChE Annual Meeting, Particle Technology Forum, Pneumatic Conveying November

7-12, 2004, Austin, Texas.

[2] Konrad, K. Dense-Phase Pneumatic Conveying: A Review. Powder Technology, 49 (1986) 1 35.

[3] Chandana Ratnayake. A Comprehensive Scaling Up Technique for Pneumatic Transport Systems,

Ph.D.Thesis Norwegian University of Sceince and Technology (NTNU), Porsgrunn, September 2005, 17-

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[4] AIR-TEC System: Official Website, http://www.air-tec.it/index_materialitrasp_uk.html

[5] Pan R., Wypych P.W. Pressure drop and slug velocity in low-velocity pneumatic conveying of bulk solids.

Powder Technology 94 (1997) 123- 132.

[6] Mason D. J., Levy Avi. The effect of a bend on the particle cross-section concentration and segregation in

pneumatic conveying systems. Powder Technology 98(1998) 95-103.

[7] Mason D. J., Levy Avi. A comparison of one-dimensional and three-dimensional models for the simulation

of gassolids transport systems. Applied Mathematical Modelling 22 (1998), 517532.

[8]

Huber N., Sommerfeld M. Modelling and numerical calculation of dilute-phase pneumatic conveying in

pipe systems. Powder Technology 99 (1998) 90-101.

[9] Rautiainen Aimo, Stewart Graeme, Poikolainen Visa, Sarkomaa Pertti. An experimental study of vertical

pneumatic conveying. Powder Technology 104 (1999) 139150.

[10]Schallert R., Levy E. Effect of a combination of two elbows on particle roping in pneumatic conveying.

Powder Technology 107 (2000) 226233.

[11]Reppenhagen Jens, Schetzschen Arwed, Werther Joachim. Find the optimum cyclone size with respect to

the fines in pneumatic conveying systems. Powder Technology 112 (2000) 251255.

[12]Dzido Grzegorz, Palica M. C, Raczek Jerzy. Investigations of the acceleration region in the vertical

pneumatic conveying. Powder Technology 127 (2002) 99 - 106.

[13]Guiney P., Pan R., Chambers J.A. Scale-up technology in low-velocity slug-flow pneumatic conveying.

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[14]Fokeer S., Kingman S., Lowndes I., Reynolds A. Characterisation of the cross sectional particle

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rate of particles in a pneumatic suspension using combined imaging and electrostatic sensors. Flow

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[16]Hidayat Muslikhin, Rasmuson Anders. Some aspects on gassolid flow in a U-bend: Numerical

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[17]Fuchs Anton, Zangl Hubert, Brasseur Georg, Petriu E. M., Fellow, IEEE. Flow-Velocity Measurement for

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[18]McNamara Sean, Straub Martin, and Zeller Florian. Simulations of Dense-phase Pneumatic Conveying.

Proceedings Issue: Behavior of Granular Media (2006).

[19]Hidayat Muslikhin, Rasmuson Anders. A computational investigation of non-isothermal gassolid flow in a

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U-bend. Powder Technology 175 (2007) 104114.

[20]Datta Urmila, Dyakowski Tomasz, Mylvaganama Saba. Estimation of particulate velocity components in

pneumatic transport using pixel based correlation with dual plane ECT. Chemical Engineering Journal 130

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[21]

Rabinovich Evgeny, Kalman Haim. Pickup, critical and wind threshold velocities of particles. Powder

Technology 176 (2007) 917.

[22]Kalman H., Rabinovich E. Analyzing threshold velocities for fluidization and pneumatic conveying.

Chemical Engineering Science 63 (2008) 3466-3473.

[23]Rajan K.S., Srivastava S.N., Pitchumani B., Dhasandhan K. Experimental study of thermal effectiveness in

pneumatic conveying heat exchanger. Applied Thermal Engineering 28 (2008) 19321941

[24]Xiaofang WANG, Baosheng JIN, Yuanquan XIONG and Wenqi ZHONG. Flow Behaviors of Gas-Solid

Injector by 3D Simulation with Kinetic Theory of Granular Flow. Chinese Journal of Chemical

Engineering, 16(6) 823-831 (2008)

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in horizontal pipe for coarse particles and fine powders. Particuology 6 (2008) 316321

[26]Samy M. El-Behery, Mofreh H. Hamed, M.A. El-Kadi, K.A. Ibrahim.CFD prediction of airsolid flow in

180 curved duct. Powder Technology 191 (2009) 130-142.

[27]Murilo D.M. Innocentini, Wellington S. Barizana, Maicon N.O. Alvesa, Reinaldo Pisani Jra. Pneumatic

separation of hulls and meats from cracked soybeans Food and bioproducts processing. Volume 87, Issue 4,

December 2009, Pages 237-246

[28]Mills David. Pneumatic Conveying Design Guide. Elsevier Butterworth-Heinemann, Burlington. 2004.

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