PERFORMANCE OF ZIGZAG AIR CLASSIFIERS AT LOW PARTICLE CONCENTRATIONS:

A Study of the Effect of Stage Geometry Variations

M.M.G.SENDEN Eindhoven University of Technology

Eindhoven, The Netherlands

ABSTRACT

The separation performance of zigzag air clas­sifiers with angles between the sections of 90 deg., 120 deg. and 150 deg. has been studied at low particle concentrations, both with respect to the single stage behavior of particles and to the inter­action between the stages. The influence of stage geometry on the single stage behavior has been explained, based on an analysis of the air flow pattern and the particle trajectories. The exchange of particles between the stages has been described by a stochastic one-step-memory model which re­lates multistage performance to single stage characteristics.

LIST OF SYMBOLS

dt - channel depth (see Table 1) I Rf = amplification factor of the single stage

separation efficiency for falling particles as defmed in Eq. 1

I Rr = amplification factor of the single stage separation efficiency for rising particles as defmed in Eq. 1

= section length (see Table 1) Pf = probability of a particle to return to the

next higher stage after having arrived at a stage in the falling stream

Pr = probability of a particle to continue its rise to the next higher stage after having arrived at a stage in the rising stream

351

SOf = single stage separation efficiency for fall­ing particles as defined in Eq. 1 .

Sor = single stage separation efficiency for rising particles as defmed in Eq. 1

SR = multistage separation efficiency as defin­ed by Eq. 1

vf = superficial air velocity based on the hor-izontal empty cross section

vfx = vf for which 1-Pf or I-Pr equals x percent

v;50 = vf for which <I>R = 0.5 We = channel width (see Table 1)

= angle between the sections (see Table 1) <I>R - fraction of identical particles from the

feed that end up in the bottom product

I NTRODUCTI ON

In the last decade, a number of separation processes have been developed to isolate useful single waste components or fractions from munic­ipal refuse. The separation is usually realized by a combination of techniques such as sieving and gravitational air classification. In Europe, air clas­sifiers of the zigzag type are often chosen [1-3] .

A zigzag air classifier consists of a number of sections with a rectangular cross section connected to each other at a fixed angle to create a zigzag shaped channel. Particles are fed to the column via a rotary valve. They are classified with respect to their falling behavior in the channel in which an air stream is flOwing upwards. Fig. 1 shows the

geometry

1], cross section

_ soliel ,artIcles

• air FlOW pattern

�mainair

protrud edge -

FIG:1 GEOMETRY OF THE ZIGZAG AIR CLAS­SIFIER, THE AIR FLOW PATTERN AND THE

DOMINANT PARTICLE STREAMS

particular geometry of the zigzag channel and the air flow pattern induced by it. In the channel two

distinct particle streams exist:

1. a stream of particles carried upwards by the upflowing air current; and

2. a stream of particles moving downwards

along the lower wall of each section.

At each junction of two sections, i.e., at each

stage, the particles of both streams are subjected

to a renewed classification. At the edges protrud­

ing into the channel, the upwards flowing air stream separates from the wall. In general, it does not reattach before the next higher junction of two sections. A separation region of turbulent air is thereby created. In that region the falling parti­cles descend along the lower section wall. They enter the main air flow again at the protruding edge where relatively high local air velocities exist. The falling particles may pass over the main

air flow and continue their way down, or they may be deflected to such an extent that they are carried upwards again by the main air flow. At a

junction, rising particles may either be carried up­

wards further by the main air flow or fly out of

that flow and start falling down in the turbulent air separation region.

The separation performance of a zigzag air clas­

sifier is determined by the particle behavior at a

single stage on the one hand and by the interaction

between the stages on the other hand. Empirical

studies concerning the influence of the channel

geometry on the performance of zigzag classifiers

have been presented by Fastov et al. [4] and Worrell [5] . Their presentation of the overall

separation results does not allow for discrimination between single stage particle behavior and the

interaction between the stages. In this study both

the single stage behavior of the particles and the

interaction between the stages were studied for zigzag channels with an angle a between the sec­tions of 90 deg. and 120 deg. respectively. The study has been extended to 0:= 150 deg. and to

other channel depths for a = 90 deg. and a = 120

deg. For those geometries, however, merely the

multistage performance was studied.

SINGLE STAGE BEHAVIOR OF THE

PARTICLES IN THE 90 DEG. AND 120 DEG.

ZIGZAG AIR CLASSIFIER OF STANDARD

DEPTH

EXPERIMENTAL SET-UP AND PROCEDURES

The single stage behavior of the particles was

measured at very low particle concentrations in­side the classifier to enable the analysis of particle motions by video recording. The flat side walls of

the classifiers were made of glass for this purpose.

Figure 2 shows the experimental set-up. Data on

the standard geometries are given in Table 1. In its standard geometry the channel has a standard

depth � for which the edges protruding into the channel are vertically in line.

Identical particles were used at all individual

experiments. For each type of particles the in­fluence of the superficial air velocity vf on the

single-and multistage process outcome was meas­

ured at low particle concentrations. The drawback of this procedure is that the results are limited to

process conditions for which particle-particle

interactions are negligible. Data on the particle properties are given in Table 2. Relatively large,

flat particles were used to simulate the character of paper and plastic foil to be separated from mixed municipal waste.

RESULTS OF THE EXPERIMENTS

At each value of the superficial air velocity the motions of 100 - 200 identical particles at a stage were analyzed. Identical particles entering a stage

may subsequently leave this stage either in an up­ward direction or in a downward direction. This uncertainty in the results is caused by variations

in the entry conditions of those identical particles at a stage, by variations in their flying behavior at the air velocity that is applied and by possible contacts between the particles and the classifier

wall. Taking the horizontal planes situated half way between any section as the stage boundaries,

352

parti Feed

•

au

1

air to blower

tt

cyclone

B

top '---' product

o-t-glass shields

4

zig zag channel

bottom '---' product

FIG.2 EXPERIMENTAL SET-UP OF THE ZIGZAG AIR CLASSIFIERS

TABLE 1 GEOMETRIC DIMENSIONS OF THE STAGES FOR THE ZIGZAG AIR CLASSIFIERS OF STANDARD

DEPTH

� \ )

Ls

, j -'( A - -

I I I I , i " I I A' ---- --I I

't---I 1 I I r'" -� I Cit f I I I I

"

dt Ls

We

... dt 1 --

--I I I A !I. I

90· 120· 180·

14.14 10 8.1B

20 20 20 20 20 20

DIIliENSIONS IN elll STANDAftD DEPTH:

-r dt = Ls cos ( a/2)

W · C

j

353

four possible transition modes can be defined for the particles:

Pf - the probability of a particle to return to the next higher stage after having arrived at a stage in the falling stream

I-Pf = the probability of a particle to continue its fall to the next lower stage after having arrived at a stage in the falling stream

Pr = the probability of a particle to continue its rise to the next higher stage after hav­ing arrived at a stage in the rising stream

I-Pr = the probability of a particle to return to the next lower stage after having arrived at a stage in the rising stream

This expression of single stage particle behavior by transition probabilities is illustrated in· Fig. 3. The experimentally determined dependence of these transition probabilities on the superficial air velocity vf is shown in Figs. 4 and 5. The superficial

•

air velocity has been made dimensionless by divid-ing it by vfx' i.e. the value of vf for which I-pc and I-Pf are x percent respectively. It is seen from Figs. 4 and 5 that the transition probabilities for identical particles at the same superficial air veloc­ity depend on the direction from which the parti­cles entered the stage, i.e. Pr =1= Pro This is caused by the considerable differences in the entry condi­tions and in the classification process itself for identical particles entering a stage from different directions. The resemblance of the dependence of Pr and Pf on vf for the various model particles indicates a similar behavior of the various types of model particles. The steepness of the I-Pr (Vf/Vf50) and the I-Pf (vf/vf50) curves, i.e. the sensitivity of Pr and P!" to vf' is a measure for the

id

stage boundary

I-P

• I

stage boundary

f i-I I-P r

FIG.3 SINGLE STAGE PARTICLE BEHAVIOR EXPRESSED BY TRANSITION PROBABILITIES

". 0 ,

I-P I r .B

.B

.4

.2

. 4

• 0 * *

particles A2 Al 82 C

".0 ".2 1A 1.B - V f/ Vf75 -

t 1.0 "\-,t*\ ----'----'-��-'---'---'--' '-----' --''--'-' ---'-�-'--'-_'___1 I-Pc '0'\ 900

·B \ '\, , ' part icIes

.6 -

.2

'.;" * 'q', • A2

,*" AI 0"*'0 0 � �. * 82 '- ' .

---* � * c -* g ""-.-0 ....... --!. - --0-- --"t- * ---

.6 .B .,.0 1.2 .,A 1.6 "S 2 0 2.2

FIG. 4 l-Pr AND l-Pf AS FUNCTION OF iif/Vf FOR THE 90 DEG. ZIGZAG AIR CLASSIFIER dF

STANDARD DEPTH

particles vf75 (l-Prl vf50 (l-pfl - Al 1 .45 1 .30 vfx A2 1 .58 1 .23 (m/sl B2 2.57 2.22

C 1 .37 1.1 3

.6

1.0

.6

. 4 -

.2

* c .6 .B '\D U! ".4 "S 1.8 20

- Vr/Vr50 -..

.. c

* .6 .6 1.0 1.2 "A 1.6 1.B 2.0

- vrl Vrso •

FIG. 5 l-p AND l-Pf AS FUNCTION OF vf/vf FOR THE 126 DEG. ZIGZAG AIR CLASSIFIER �F

STANDARD DEPTH.

particles l-p r l-Pf - A2 1 .64 1.52 vf50 B2 2.67 2.58 (m/sl C 1 .48 1 .00

TABLE 2 DATA ON THE PARTICLES USED IN THE EXPERIMENTS

Material dimensions surface density type

density code

(g/m2) (kg/m3)

lx! 2 square em 100 826 Al

• thickness: 0.0121 p�eces em

of 2 2x2 em paper 100 826 A2 thickness: 0.0121 em

2x2 2 em

thickness: 0.034 em 280 824 B2

porous mean diameter: - 29 C polystyrene 0.45 em

spheres

354

FIG. 6 AIR FLOW PATTERN IN THE 90 DEG. ZIGZAG AIR CLASSIFIER OF STANDARD DEPTH AT

vf = 1.65 m/s

efficiency of the single stage separation [6]. From

Figs. 4 and 5 it can be concluded that for the model particles given in Table 2 the single stage separation efficiency at low particle concentrations

is higher for the 120 deg. zigzag air classifier of standard depth than for the 90 deg. zigzag air clas­sifier of standard depth.

EXPLANATION OF THE DIFF ERENCES IN

SINGLE STAGE BEHAVIOR OF THE

PARTICLES IN THE 90 D EG. AND 120 D EG.

ZIGZAG AIR CLASSIFIER OF STANDARD

DEPTH

Experimental information on the local air velocity pattern and the influence of the channel

geometry on it should be the starting point for the

explanation of particle trajectories of which PI and Pc represent the overall outcome. The air flow pat­

tern in empty zigzag channels was visualized by

free floating, helium filled soap bubbles that were

illuminated through a light slit. By means of dark

field photography the illuminated soap bubbles

were registered as a light track. The visualized air

flow patterns for the 90 deg. and 120 deg. zigzag

air classifiers are given in Figs. 6 and 7. To quantify

the observations of the air flow visualization experi-

355

FIG. 7 AIR FLOW PATTERN IN THE 1 20 DEG. ZIGZAG AIR CLASSIFIER OF STANDARD DEPTH

AT v f=2 m/s

ments, local air velocity measurements have been carried out by hot fIlm anemometry. The scalar value and the orientation of the local air velocity, including the turbulent fluctuations of them, were measured by means of a single hot fIlm sensor in a vertical plane situated between and parallel to the flat side walls of the classifier. Complete results were presented elsewhere [6] .

Both in the 90 deg. and 120 deg. zigzag air classifier a zone of high and upwards directed local air velocities exists, the direction of which is relatively well defined. This "main air flow" takes up a larger part of the channel depth dt in the 120 deg. zigzag air classifier than in the 90 deg. zigzag air classifier as can be seen from Figs. 6 and 7. In the main air flow of the 120 deg. zigzag air clas­sifier of standard depth the local air velocity is relatively well directed and its scalar value varies only moderately. In the 90 deg. zigzag air clas­sifier of standard depth the local air velocity strongly varies over the main flow channel. At the protruding edge the local air velocity is 4 - 5 times the value of the superficial air velocity. Over a horizontal distance of 1/4 dt from the edge point, the velocity drops by a factor of 2.5 while the orientational and scalar fluctuations of the air velocity increase by a factor of 3.

The main air flow separates from the classifier wall at the protruding edge. In both geometries the flow does not reattach itself to the lower wall of the section before the next higher stage. The upper boundary of this separation region is form­ed by turbulent eddies breaking away from the main, upwards directed air flow. In the 90 deg. zigzag air classifier the separation region of the air is more voluminous. The geometry of the separa­tion region, together with the high local air veloc­ities at its boundary at the main air flow, induce a reverse flow in this region of the 90 deg. zigzag air classifier. This was not observed in the 120 deg. zigzag air classifier.

It will be clear that the differences in the air flow patterns for both geometries will have their impact on the entry-positions and -velocities of particles at a stage and self evidently on the single stage classification itself. It was observed in the 120 deg. zigzag air classifier that the rising particles arrive at the junction of two sections fairly uni­formly distributed over the depth of the main air flow channel, while their mean entry velocity does not depend strongly on their entry position. In the 90 deg. zigzag air classifier of standard depth the

fraction of rising particles per unit of depth and the mean entry velocity of them strongly vary over the depth of the main air flow channel.

The downward motion of particles descending in the separation region of the air flow was observ­ed to be not a simple sliding motion. In the 90 deg. zigzag air classifier the downward directed particle velocities were observed to be higher than in the 120 deg. zigzag air classifier which for comparable air velocities and identical particles is in contradic­tion to the values expected for a simple sliding motion [6].

Particle trajectories were calculated from the information about the air velocity pattern and the variations in entry conditions of the particles. The complete results of the trajectory calculations were discussed in [6] . Here the discussion will be confmed to the essential differences between both geometries as reflected by the I-Pr (vf/vfx) rela­tions shown in Figs. 4 and 5. In the standard 90 deg. zigzag air classifier the rising probability Pr does not exceed the value of 0.5 over the range of superficial air velocities in which Pf increases from o to 0.9. Above Pr = 0.4 the sensitivity of Pr to vf becomes small. The low value of Pr and the insen­sitivity of Pr to vf at higher values of vf in this classifier is caused by the fact that the rising parti­cles collide with the upper section wall at an angle of impact that is about perpendicular to that wall. A large part of the kinetic energy of the particles is lost in the collision with the wall and cannot be used for the continuation of their upward motion. The outcome of the collision depends on stochastic factors such as the orientation of the particle after the collision and the instantaneous scalar value and direction of the local air velocity. The local air velocities around the part of the upper wall against which' rising particles collide are subject to con­siderable variations. An increase of vf of 50 percent above vf/Vf75 = 1.3 hardly influences the overall outcome of the collisions of the rising particles.

In the standard 120 deg. zigzag air classifier the angle of iinpact for colliding particles at higher values of vf is such that they retain a part of the kinetic energy after their collision and continue their upward motion. The local air velocities at the collision points are subject to less variation than in the standard 90 deg. zigzag air classifier and directed upwards. The rising probability Pr can, therefore, reach higher values than in the standard 90 deg. zigzag air classifier and its sensi­tivi ty to v f is larger.

356

MULTISTAGE SEPARATION PERFORMANCE

OF THE 90 DEG. AND 120 DEG. ZIGZAG AIR

C LASSIFIER OF STANDARD DEPTH

The multistage zigzag air classifiers of which the stage geometry is given in Table 1 consist of 11 stages including the top and bottom exit. The experimental set·up was shown in Fig. 2. Identical particles were fed into the column half way be­tween the central stage and the next higher stage where they were separated into a top fraction that left the column at the top exit and a bottom frac­tion that left the column at the bottom exit. The performance of the classifiers was studied by measuring the fraction of identical particles that end up in the bottom product <PR as a function of the superficial air velocity vf' Results of the experiments are shown in Fig. 8. vf has been made dimensionless by dividing it by v[50' i.e., the value of vf for which <PR = 0.5. The multistage separa­tion efficiency is described here by the steepness of the separation function <PR (vrIV[50) at vfIV[50 = 1. It proved to be slightly better for the 120 deg. zigzag air classifier of standard depth than for the 90 deg. zigzag air classifier of standard depth. This inequality in separation efficiency is caused by differences in single stage efficiencies on the one hand and by different interaction between the stages on the other hand. The mathematical

1.0

.8 90'

.8

.7 • 7

*

1200 -* 900 -* '(50 'f50 * .R .R

• A2 1.158 • A2 1.BO * 82 ..... 8 * 82 Rosa m/s

.1 * C 1.RBI5 *c ".31 .1

.8 ...... 8

FIG.8 "'R (iili;50) for the 90 DEG. AND 120 DEG. ZIGZAG AIR CLASSIFIER OF STANDARD

DEPTH

357

formulation of this interrelation is [6] :

where:

--d (vr/v;50) _ __ * vf - vf50

(Eq. 1)

- multistage separation 'efficiency' described by the steepness of the <PR -curve at - -* vr = vf50'

-

= single stage separation "efficiency" for falling particles described by the steepness of the Pf -relation at v f = v;50'

--

= single stage separation 'efficiency' for rising particles

. descri�ed �r the steepness of the

Pr -relatlOn at vf = vf50.

-

p* r = 'amplification factor' which expresses the

amplification of the single stage separation efficiency for rising particles .

a<PR (Pr * , Pf) -apf p[

= "amplification factor" which expresses the amplification of the single stage separation efficiency for falling particles.

Pf * and p. * are the values of Pf and Pr respectively

for vr = vf50. The experiments in the multistage zigzag air classifier yield numerical data on SR' while experiments on the single stage behavior of the particles give the information for Sof and Sor' The amplification of the single stage performance, as expressed by IRr and IRf, is the result of the interaction between the stages of rising and descending particles.

A one-step-memory model was develop,ed for the mathematical description of the interaction between the stages [7] . This model relates <l>R to Pr and Pr with, as the main parameter, the total number of stages and the position of the feed-stage. An example of the results of this model is given in Fig. 9 which shows lines of constant <l>R as a function of Pr and Pr for I I stages and central feeding. The increase of the amplicifation factors IRr and IRr is visible from Fig. 9 by the narrowing of the bundle of iso-<I>R -lines, i.e., by an increase of the sensitivity of <l>R to changes in Pr and Pr' For a combination of high Prvalues and low Pr -values <l>R becomes very sensitive to changes in Pr and Pr and consequently IRJ and IRf are high. This is caused by the fact that the particle exchange be­tween the rising and falling particle streams is then high and particles pass over the stages many times. Figure 9 also gives the Pr -Pf combinations found for the standard 90 deg. and 120 deg. zigzag air classifier. It is seen from this figure that the Pf-Pr combinations of the standard 90 deg. zigzag air classifier are such that the interaction level between the stages is higher than in the standard 120 deg. zipzag air classifier. This indicates a favorable ratio of multistage to single stage separation perform­ance. However, this higher interaction level be­tween the stages of the standard 90 deg. classifier proved to be insufficient to compensate for its lower single stage efficiency and to achieve the same multistage efficiency as in the standard 120 deg. zigzag air classifier. The interaction between the stages directly influences the mean number of stages passed by the particles during their stay in the classifier and it consequently codetermines

+ Pf I

0

:

.Il

/ /

/ ./ /

/ /

"'R'

-P -­r

model classifier particles 0 AI I A2 90' � B2 90' • A2 120' • B2 120'

FIG. 9 RELATION BETWEEN �R AND Pr AND Pf SHOWN BY LINES OF CONSTANT �R-VALUE.

LOCATION OF THE EXPERIMENTAL (Pr' Pf)-COMBINATIONS FOR THE 90 DEG.

AND 12'0 DEG. ZIGZAG AIR CLASSIFIER OF STANDARD DEPTH

their mean residence time. At a constant value of the particle concentration, the latter quantity is inversely proportional to the potential through­put capacity of the classifier. This means that the large degree of particle exchange between the stages in the standard 90 deg. zigzag air classifier will cause undesirable, long, mean residence times of the particles and consequently may reduce its potential throughput capacity. Experiments with our model particles indeed showed that the resi­dence times of the particles in the standard 90 deg. zigzag air classifier at low particle concentrations are about 2 - 3 times higher than in the standard 120 deg. zigzag air classifier. This fact does not favor the standard 90 deg. zigzag air classifier.

MU L TISTAGE SEPARATION PER FORMANCE

OF THE 150 DEG. ZIGZAG AIR CLASSIFIER

OF STANDARD DEPTH AND THE 90 DEG.

AND 120 DEG. ZIGZAG AIR CLASSIFIERS OF

01 FFERENT DEPTHS

The discrete, multistage character that exists in the standard 90 deg. and 120 deg. zigzag air clas­sifier did not clearly exist in the standard 150 deg. zigzag air classifier. No distinct rising and falling particle streams were observed. The particles move over "any horizontal cross section of the channel. At small particle concentrations the separation performance � of this apparatus is extremely good, as shown in Table 3. The price for this high separation efficiency is a high mean residence time of the particles, as can also be seen from Table 3. The results for other channel depths of the 90 deg. and 120 deg. zigzag air classifier have been sum­marized in Table 3 also. The table shows the value of v;50' the steepness of the separation function as expressed by �, and some characteristic mean residence times of the particles. The following re­marks can be made:

1. Increasing the channel depth beyond its standard value does not improve the separation efficiency of the 90 deg. and 120 deg. zigzag air classifier. An increase of the channel depth might be justified for the 90 deg. zigzag air classifier be­cause of the fact that the residence time of the particles seems to decrease considerably.

2. Decreasing the channel depth to below its standard value tends to raise the separation effi­ciency. For the 90 deg. zigzag air classifier this is accompanied by a reduction of the mean residence time of the particles. For the 120 deg. zigzag air classifier decreasing the channel depth to below its

358

TABLE 3 RESULTS FOR VARIOUS CHANNEL GEOMETRIES OF THE MULTISTAGE ZIGZAG AIR CLASSIFIER

channel model -* mean vf5 0 d<iJ R particles residence time ex d�pth SR = d (v /vf5 0) �fsO (em) (m/s) (s)

1200 5 .2 Al 1.72

10 A2 1.56

15 .1 A2 1.49

1200 5.2 B1* 3.00

10 B2 2.56

15 .1 B2 2.40

900 9.8 A2 1.46

14.1 A2 1.60

20.3 A2 1.04

14.1 B2 2.80

1500 5.1 Al 1.42

* Bl: paper particles: 1x1xO.034 cm

standard value causes an increase of the mean resi­dence time of the particles.

It should be recalled that these observations were made at small particle concentrations at which particle-particle interactions are excluded. The same holds for conclusions that were drawn with respect to the performances of the 90 deg. and 120 deg. zigzag air classifiers of standard depth.

REFERENCES

[1] Colon, F. J. and Kruijdenberg, H., "The Mechan­ical Separation of Municipal Refuse into Useful Compo­nents and Their Application as Raw Materials in Indus­try," Proc. First World Recycling Congress, March 6-8, 1978, Basel, pp. 3.15.i-3. 15. ix.

[2] Hoberg, H. and Schulz, E., "Das Aachener Ver- .

3 • ,

-7.4 25.4 for <iJR - 0.5 1

-6.2 14.2 for <iJR - 0.5 4

-6 .2 18.7 for <iJR - 0.5 0 -

-9.0 14.7 for <iJR - 0.44

-6.0 7 for <iJR - 0.22

-3.9 7.6 for <iJR - 0.54 -

-6.9 17.3 for <iJR - 0.55

-4.1 30 for <iJR - 0.235

-2.6 6.5 for <iJR - 0.64 -

-4.0 21 for <iJR - 0.64

-28.0 5 5 for <iJR - 0.50

280 g/m 2

fahren zur Hausmtillaufbereitung," Aufbereitungstechnik,

No. 1, 1977, pp. 1-5. [3] Cederholm, C., "Paper Fiber Recovery System,"

Flakt Engineering, Vol. 2, No.2, April 1978. [4] Fastov, B. N., et al., "Testing of the Zigzag Clas­

sifier for Granulated Materials," Khimicheskoe i

Neftyanoe Mashinostroenie, No.5, May 1975, pp. 44-45, Plenum Publ. Co. 1976, UDC 621.928.6.001 .5.

[5] Worrell, W. A., "Testing and Evaluation of Three Air Classifier Throat Designs," report from Department of Civil Engineering, 1978, Duke University, Durham, North Carolina.

[6] Senden, M. M. G., "Stochastic Models for Individ­ual Particle Behavior in Straight and Zigzag Air Clas­sifiers," Ph. D. Thesis, March 1 979, Ei ndhoven University of Technology, Eindhoven, Holland.

[7] Senden, M. M. G. and Tels, M., "A Stochastic Model of Multistage Separation in Zigzag Air Classifiers,"

Journal of Powder and Bulk Solids Technology, Vol. 2, No. 1, 1978, pp. 16-35.

Key Words

Classification

Design

Refuse

Separating

Separator

Solid

359