pieces drop of f a belt t amount of l i g h t t r a n s a l i g h t beam is i n t e r r u p

BASIC PRINCIPLES OF MATERIALS SEPARATION

P. Aarne Vesi l ind Department of C i v i l and Environmental Engineering Duke Universi ty Durham, North Caro l ina

Environmental eng inee r ing is i n g r e a t p a r t a search f a processing of h igh ly heterogeneous m a t e r i a l s i n t o pure components; a decrease in entropy. In t h i s ques t , soue a r e i n v a r i a b l y sepa ra t ed from o t h e r ma te r i a l s : s e t t l e a b l e from sewage, aluminum cans from r e f u s e , s u l f u r dioxide f r gases--the l i s t is almost end le s s . I n a l l cases, however, p r i n c i p l e s governing the s e p a r a t i o n process are similar, be r a t i o n a l l y analyzed in gene ra l terms. I n t h i s paper, t sepa ra t ion of materials is considered f i r s t as a binary pr then with more than one product, and f i n a l l y as a series b opera t ions each of which acts as a m a t e r i a l s se

Separat ion sc ience i s an evo lv ing f i e l d in en engineer ing, as a t t e s t e d t o by a number of conte ( 1 ) ( 2 ) ( 3 ) Although much of t h i 8 work can b e c l a s epa ra t ion s c i e n c e , t h e r e have been few a t t empt s f i e l d of s e p a r a t i o n nomenclature. A secondary o paper is thus t o sugges t a framework f o r unifying nomenclature used t o descr ibe va r ious s e p a r a t i o n proces common t o t h e waste t reatment profess ion .

BINARY SEPARATION

The o b j e c t i v e of a binary materials s e p a r a t o r is feed material i n t o two d i f f e r e n t components by exp lo d i f f e r e n c e i n the m a t e r i a l p r o p e r t i e s . For example, i s necessary t o design a device which w i l l separa te broken g l a s s i n t o two c a t e g o r i e s , t r a n s p a r e n t and op resource recovery p l a n t s , such a device would separa

ELEC

u Figure 1. Simple Dei \

Clear G l a e

gate not gate sepa

T

f l i n t g l a s s ( c l e a t ) from the a m b e r o r brown g lass .

e x p l o i t . t e l l the machine how t o d i v z t h e i n d i v i d u a l p a r t i c l e s f eed stream. In t h e case of the g l a s s , the code should be t ransparency and t h i s can be used i n the design of t s e p a r a t i n g system, such as perhaps i n Figure I= h the

F i r s t , i t i s necessa ry t o decide what m a t e r i a l propert This becomes the code, o r a s i g n a l which can be

is pu l l ed t o the k n t e r r u p t the l i g h t

a c t i v a t e d by the s3 a t i n g the ma te r i a l i s simple device il.

switching; reading a pro1 s igna l t o achieve a sepal pr inc ip le of coding and II

of environmental enginee .. Materials separa t ion w

mistakes. It cannot be a i accurately sense i f the and with even the most sa devices, mistakes w i l l oa i n a box f u l l of t ranspan The measure of how w e l l tt two parameters: recovery

Consider a binary sepre two components x and y ar stream 1 and y goes t o p r the y mistakenly ends up comes out a t 2. The e is defined a s

201

I.

zER Rietema Eff ic iency

Aluminum cans, no. lmin

Steel cans, no. lmin

Total Product i n feed Stream 1

Product Stream 2

300 270

100 0

30

100

The recovery and p u r i t y are c a l c u l a t e d as

270

xRal. cansl 300 m - x 100 90%

270 x 100 = 100% I-

1 270 + O "al. cans

I n many engineer ing s t u d i e s , i t is very inconvenient t o have two parameters which descr ibe the performance of a u n i t operation. For example, the performance of two competing a i r c l a s s i f i e r s used f o r producing refuse-derived f u e l may be advert ised as follows:

XRorgani cs "organics

A i r C l a s s i f i e r 1 90

Air C l a s s i f i e r 2 93

92

87

It is d i f f i c u l t t o s t a t e which is the b e t t e r device. Accordingly, a number of s ingle-value parameters have been suggested. For a b ina ry s e p a r a t o r two suggest ions are: ( 4 ) ( 5

Worrell-Stessel E f f i c i ency %E = [ . 2] x 100

112

0 yo ws X

X 1 y1

0 yo Rietema Ef f i c i ency %ER = I y- - - I x 100

203

For the second ai11

XI

Clearly the f i r s t In many unit og

the objective is 11 stream, the latteii materials. Such ti

input (the feed) ti

product and the 0::

reasonable nomencll engineering, is t c c is extracted from

204

4 12

206

worrell-Stessel and Rietema e f f i c i e n c i e s are

X

X 22 33 X X 11 - , -

x20 x30 no

I n the above polynary s e p a r a t o r , i t has been assumed that t h e feed has E components and t h a t t h e s e p a r a t i o n process has 1 product streams. were Figure 4 .

A more genera l condi t ion would be if these product streams f o r a feed wi th 1. components, as shown i n

The e q u a t i o n s f o r recovery, p u r i t y

Figure 4. A Polynary Separa tor w i t h m Product S t r e a m and p Matertials.

207

Although the d i f f e r r use dens i ty as the ,,

In t h i s case, a BY jud ic ious ly choo, plast ic can be made,

The easiest sepal plast ics (PVC and P!, This can be done us , most l i k e l y p l a i n uti

each must be separatl s p l i t t i n g of PE and somewhat easier by B

ent i re process t r a i n

f loa1

PVC 1.313 PS 1.055 PE 0.916 PP 0.901

sim

Figure 5 . A Proce:: of Plas:

Suppose ins tead oU removed f i r s t , resulll this a better choice

208

a m and t meral

plast ic Symbol Quant i ty Densifjy ( t o n s ) Wcm 1

polyvinylchloride (Pvc) 4 polystyrene (PS polyethylene (PE) 1

1

1 polypropylene (PP)

1.313 1.055 0.916 0.901

Although the d i f f e rences are smal l , i t s t i l l might be poss ib le t o use dens i ty a s t he e. BY jud ic ious ly choosing a proper f l u i d dens i ty , a piece of p las t ic can be made t o s i n k o r f l o a t .

The e a s i e s t s epa ra t ion is the removal of the two heavy p las t ics (PVC and PS) from the two l i g h t e r ones (PE and PP). T h i s can be done us ing a f l u i d wi th a dens i ty of 1.0 m g / l , o r most l i k e l y p l a i n w a t e r . Following t h i s s t e p , the two streams each must be sepa ra t ed f u r t h e r . The t r i c k i e s t s epa ra t ion , the s p l i t t i n g of PE and PP, must be done wi th great care, and is made somewhat easier by a l r eady having removed the PVC and PS. The e n t i r e process t r a i n is shown in Figure 5 .

In t h i s case, a f l o a t / s i n k appara tus can be used as a switch.

f loot

PVC 1.313 PS 1.055 ~

PE 0.916 PP 0.901

sink

“0°’ I-- PP 0.901

p =0.908 P E a PP 0.916 a 0.90 I

sink PE 0.916

PS 1.055

PVC 1,313 sink

Figure 5 . A Process Tra in f o r the Separa t ion of Four Types of Plast ics by Float /Sink.

Suppose i n s t e a d of the process t r a i n i n Figure 5 the PVC is removed f i r s t , r e s u l t i n g in the process shown i n Figure 6. IS this a better choice of the process?

209

o s s i b l e t zing the

ure 7.

The two separa tors 11 and b a r e t o s e p a r a t e the incoming materials and y , with x t o e x i t from s e p a r a t o r 5 and y from s e p a r a t o r a.

Separator a t a k e s out x but a l s o removes some of the unwanted y from t h e feed stream. it r e j e c t s (xo-xl) amount of x and (yo-yl amount of y.

3 We now def ine a new t e r m , c a l l e d a s p l i t , f , such t h a t

= f r a c t i o n of component x not removed ( r e j e c t e d ) a t u n i t ope ra t ion 5. xa

Thus f o r a given m a t e r i a l a t a u n i t ope ra t ion ,

pnity] . = [.uaz;ity ] (feed) ( r e j e c t )

With r e fe rence t o Figure 7 f o r u n i t ope ra t ion 5,

0 . fxa = x - x

Yo - f = Yo - Y 1

0 1 X

Ya

and a t u n i t ope ra t ion b,

(xo - xl) . fxb = (xo - x1 - x2)

This a r r a y can be w r i t t e n i n ma t r ix n o t a t i o n , which is in t h i s case j u s t a convenient method of keeping t r a c k of the information. In mat r ix n o t a t i o n ,

X f x a fxb (xo-xl> (xo-x1-x2)

f f (Yo-Y1) (Yo-Y1-Y2)

- -

YO Yb Y a

21 1

Figure 8 . A Process Tra in f o r Separa t ing Glass, Ferrous and Organics (RDF) from Refuse.

S e t t i n g t h i s up i n mat r ix n o t a t i o n , and c a l c u l a t i n g the f r a c t i o n of a component e n t e r i n g the u n i t opera t ion not r e s u l t s i n the fol lowing:

&

u-c

m

r(

4J r( m

& U

Glass

Ferrous

Organics

212

A ques t ion of orden: trommel screen be plaa: process t r a i n shown i m and a trolmoel screen, recovery and p u r i t y of!

Using again the mat:

Glass

Ferrous

Organics

U 01

8 2

10 1.0)

10 . 0.1.

80 0.91

The product matr ix is a s p l i t wi th the reject.

In t h i s second case,

XRorganics i n a..

reject . It i s now poss ib le t o c a l c u l a t e some of the parameters of

, f f ic iency. clean f u e l ; the e x t r a c t from the a i r c l a s s i f i e r . The o v e r a l l system has a recovery and p u r i t y of

Suppose, f o r example, i t is important t o produce a

= - 60 8o x 100 = 75% %Roragnics i n a.c.

XP organ ic s i n a.c. - 6o

60 + 1 + 0 x 100 = 98%

A quest ion of o rde r arises, and a suggest ion is made t h a t the trommel sc reen be placed behind the a i r c l a s s i f i e r , producing a process t r a i n shown i n which inc ludes a magnet, an a i r c l a s s i f i e r and a trommel screen , i n t h a t order. recovery and p u r i t y of the re fuse de r ived f u e l ?

What would be the expected

Using again t h e matr ix nota t ion : $4

d

Glass I

w

B 11.0 B

I lo 5 1.01

Ferrous 10 0.11 0 0.9 = 1.1 0 0 I

Organics 180 i ’ 10.93 0.08 0.871 174 6 51

The product ma t r ix is c a l c u l a t e d , a s before , by mult iplying the s p l i t wi th the reject.

In t h i s second case, the recovery and p u r i t y are

- - - ( 7 4 - 6, x 100 = 85% XRorganics i n a.c. 80

(74-6) %P organ ic s E (10-5) + (0) + (74 -6 ) x 100 = 93%

213

It is seen t h a t the swi tch of the u n i t opera t ions result- higher recovery, but a lower product pur i ty . The choice process t r a i n of course depends on the f u e l requirements, p u r i t y is adequate, then t h e increased recovery would wa use of the second materials separa t ion t r a i n .

CONCLUSIONS T , g - m ~ ~ O G Y OF RECOVERY s MARDOUS WASTE I N Pus'II I N D ~ ~ ~ R I E S I N PENNSyLvAN

Separat ion science is a c e n t r a l core of environmental engineer ing. I n t h i s paper , some of t h e p r i n c i p l e s of se sc ience a r e d iscussed , and examples presented. J u s t as t profess ion adopted t h e i d e a of r e a c t o r s and r e a c t o r k i n e t present a c e n t r a l framework f o r d e s c r i b i n g many u n i t oper separa t ion sc ience should become a used and u s e f u l t o o l fo i n s t r u c t i o n and design.

REFERENCES

1. Lee, H. L, En. N. L ight foot , J. F. G., Reis, and M. D. Waissbluth, "Systematic Descr ip t ion and Development of Separat ion Processes , " i n Recent Developments i n The p l a s t i c s and SYnE Separat ion Science, N. N. L i ( E d . ) v o l . 3 A , p . 1-69, ,,umber of n o t i f i e r s and P r e s s Inc., Cleveland, Ohio, (1977). sylvania. The purpose C:

of- the-ar t of hazardous In t roduct ion t o Separa t ion Science, John Wiley & Sons, synthet ics i n d u s t r i e s ar

t h e i r waste management New York, (1973). 3. King, C. J., Separa t ion Processes , M c G r a w - H i l l , New York, on recovery, recyc l ing ,

i d e n t i f i c a t i o n Of industt category and a s-ary 4. Pei rce , J. J., R. I. S t e s s e l and P. A. Ves i l ind ,

"Quantifying the performance of n-Way Separa tors , " and cur ren t management H Resources and Conservat ion, 10, p. 243-247 (1983). look a t only hazardous U

5. Rietma, K., "On the E f f i c i e n c y i n Separa t ing Mixtures res idua ls were found t o of Two Const i tuents , " Chemical Engineer ing Science, discussed i n t h i s Paper.. 7, p 89-96 (1957). from packaging t h a t end

6. Tony, P.R., "Extent of Separat ion: On U n i f i c a t i o n of the study. It however, i s = of Chemical Separat ion," AIChE Symposium S e r i e s , n. 120, s t u d i e s have d e a l t .

7. Berthourex, B. M. and D. F. Rudd, S t r a t e g y f o r P o l l u t i o n Control, John Wiley L Sons, New York 1977. Hasselriis, F., Unit Operat ions i n Resource Recovery, B u t t e m o r t h s , Woburn, MA, (1983).

c. A. cole , Professor off S. A. Kressin, Reseau Pennsylvania S t a t e Um Middletown, PA

2. Karger, Be L., L. R. Snyder, and C. Horvath,

p. 89-94 (1972). The p l a s t i c s and SYnE

t h r e e segments: mOnOmen processing (1) . The relate t o the organic Cfi The polymer manufacturen resins and the converton f i l m s , e tc . Frequent ly in tegra ted a t t h e Same 1 occur together . The Po1

*Based on a f i n a l r e E i n Recycle, Reuse, and and Synthe t ics I n d u s t r i e t h e Off ice of Toxic and Park, PA and supported It Environmental Resources ..

214