Simulation - The Modem Cost-effective Way To

7/25/2019 Simulation - The Modem Cost-effective Way To

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International Journal of Mineral Processing,29 (1990) 249-265

Elsevier Science Publishers B.V., Amsterdam

249

S i m u l a t i o n t h e m o d e m c o s t e f fe c t i v e w a y to

s o l v e c r u s h e r c ir c u i t p r o c e s s i n g p r o b l e m s

R.P. King

Department of Metallurgy and Materials Engineering, Universityof Witwatersrand,

1 Jan SmutsAvenue, Johannesburg South Africa)

(Received April 11, 1989; accepted after revision January 30, 1990)

ABSTRACT

King, R.P., 1990. Simulat ion- he modern cost-effective way to solve crusher circuit processing prob-

lems. Int. J. Miner. Process., 29: 249-265.

Simulat ion is an effective technique for the improvement of crusher plant performance, and it is

now used routinely by some crusher manufacturers for both plan t design and trouble shooting. MOD-

SIM is probably the most versatile ore dressing-plantsimulator in general use in the mineral-process-

ing industry today. A case study using MODSIM applied to the crusher circuit of a major uran ium

producer is described in this paper. This study demonstrates the effectiveness of simulation to im-

prove plant performance when reliable and effective models of the unit operations are available.

The study was commissioned o investigate a 2000qon/h 4-stage crusher plant to identify a strategy

to increase production at a finer product size. After an intensive echnical audit on the plant , success-

ful simulation was achieved for the existing operating conditions. The simulator was then used to

identify the production bottlenecks and to establish plant modifications to meet the required produc-

tion objectives in a cost-effective manner.

I N T R O D U T I O N

Pl an t s i mu l a t i on tech n i q u e s are b ecom i n g i n creas i n g ly e f f ec t ive a n d th ere-

fore more f req u en t l y u sed as too l s to a s ses s an d i mp rove p l an t p er forman ce .

T h i s i s p ar t i cu l ar l y so wi th cru sh i n g p l an ts b ecau se th e u n i t op era t i on s o f

cru sh i n g an d screen i n g can b e d escr i b ed b y re l iab l e an d accu rate m od e l s . T h e

s tu d y rep orted h ere was u n d ertak en to e s tab l i sh cos t -e f f ec t i ve m od i f i ca t i on s

t o t h e f i n e c r u s h i n g p l a n t o f R o s s i n g U r a n i u m L t d . , a n d t h e a p p l i c a t i o n o f

s i m u l a t i o n t o a d d r e s s s o m e o f t h e p o s s i b i l i t i e s i s d e s c r i b e d . T h e s t u d y w a s

u n d e r t a k en b y a t e a m c o n s i s t in g o f p e r s o n n e l f r o m N o r d b e r g P t y ) L t d ., t h e

D e p a r t m e n t o f M e t a l l u r g y a n d M a t e r i a l s E n g i n e e r i n g o f t h e U n i v e r s i t y o f

W i tw a t e r sr a n d , a n d R o s s i n g U r a n i u m L t d .

T h e ob jec t i ves o f th e s tu d y were: 1 ) to in ves t i ga te an d es tab l ish a ll p roces s

an d op era t in g p arameters u n d er th e cu rren t op era t i n g con d i t i on s ; 2 ) to e s-

0301- 7516/90/$03.50 19 90 -- Elsevier Science Publishers B.V.


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25 0 R.P KING

t a b li s h t h e c o m p l e t e m a s s b a l a n c e a n d s iz e d i s t r i b u t i o n f l o w s h e e t f o r t h e p r e s-

e n t c o n f i g u r a t i o n a n d f o r t h e p l a n t u n d e r v a r i o u s p r o p o s e d a l t e r n a t i v e f lo w -

s h e e t c o n f i g u r a t i o n s ; ( 3 ) t o e s t i m a t e e n e r g y , s t e e l , a n d o t h e r c o s t r e d u c t i o n s

e x p e c t e d fr o m a n y p r o p o s e d p l a n t m o d i f i c a t io n s ; a n d ( 4 ) t o b a c k u p all p r o -

p o s al s b y b a s i c e n g i n e e r i n g i n f o r m a t i o n a n d d e t a i l e d f l o w s h e e t c al c u l at i o n s.

S i m u l a t i o n e f f e c t iv e l y a d d r e s s e s t h e s e c o n d a n d f o u r t h o f t h e se o b j e c t i v e s

a n d p r o v i d e s t h e n e c e s s a r y i n f o r m a t i o n t o p e r m i t t h e c a l c u l a t io n o f e n e r g y

a n d o t h e r c o s t s a v in g s to m e e t t h e t h i r d o f th e o b j e c t iv e s . N o r d b e r g I n c. o f

M i lw a u k e e , h a v e p i o n e e r e d t hi s a p p r o a c h a n d t h e i r C i r c u it A n a l ys is P r o g r a m

( C A P ) is n o w i n u s e w o r l d w i d e f or th e d e v e l o p m e n t a n d a n a ly s is o f c r u s h e r

c i rc u i ts . S i g n if i c a n t i m p r o v e m e n t s i n w o r k e r p r o o u c t i v i t y a n d t h e q u a l i t y o f

f l o w s h e e t d e s i g n h a v e b e e n r e p o r t e d ( O ' B r y a n , 1 9 8 7 ) . T h e a p p l i c a t i o n o f

s i m u l a t i o n t o c r u s h e r f l o w s h e e t d e s i g n h a s b e e n w e l l d e s c r i b e d b y M a g e -

r o w k s i a n d K a r r a ( 1 9 8 2 ) a n d t h e r e is n o d o u b t t h a t s i m u l a t i o n t e c h n i q u e s

w i l l p l a y a n e v e r - i n c r e a s i n g r o l e in t h e f u t u r e . T h i s s t u d y a f f o r d e d t h e o p p o r -

t u n i t y to u s e b o t h M O D S I M a n d C A P w i t h i n t h e co n t e x t o f a re a l m a j o r p l a n t

a n a ly s is . T h e a p p l i c a t i o n o f M O D S I M t o t h is p r o b l e m is d i s c u s s e d in d e t a i l

i n t h i s p a p e r . T h e f i r s t o b j e c t i v e w a s a d d r e s s e d b y u n d e r t a k i n g a d e t a i l e d

t e c h n ic a l a u d i t o n t h e p l a n t w h i c h in c l u d e d t h e m e a s u r e m e n t a n d r e c o r d in g

o f a ll r e l e v a n t e n g i n e e r i n g p a r a m e t e r s , t o g e t h e r w i t h t o n n a g e s a n d s iz e d is t ri -

b u t i o n s o f k e y p r o c e s s s t re a m s .

T h e m o s t i m p o r t a n t p l a n t i m p r o v e m e n t r e q u i r e d f r o m t h is s t u d y w a s t h e

r e d u c t i o n o f t h e f i n a l p r o d u c t s iz e f r o m 8 0 % p a s s i n g 10 .5 m m a s i n t h e e x i st -

i n g c i r c u i t to 8 0 % p a s s i n g 7 m m .

DATA COLLECTION

T h e d a t a c o l l e ct i on w a s u n d e r t a k e n o v e r a p e r i o d o f f iv e d a ys d u r i n g w h i c h

t h e p l a n t w a s o p e r a t e d s u n d e r c o n d i t i o n s c l o s e t o n o r m a l . P r o d u c t i o n w a s ,

h o w e v e r , in t e r r u p t e d t o p e r m i t t h e n e c e s s a r y s a m p l i n g to b e u n d e r t a k e n . G r e a t

c a r e w a s t a k e n t o e n s u r e t h a t a ll s a m p l e s w e r e r e p r e s e n t a t i v e o f n o r m a l o p e r -

a t i n g c o n d i t i o n s .

T h e k e y p ro c e s s v a r i a b le s m e a s u r e d w e r e t h e t o n n a g e s a n d s iz e d is t r ib u -

t i o n s i n t h o s e s t r e a m s t h a t w e r e d i a g n o s t ic o f t h e o p e r a t i o n o f e a c h o f t h e

u n i t s i n t h e p la n t . T h e s i z e d i s t r i b u t i o n s a n d t o n n a g e s w e r e m e a s u r e d b y s to p -

p i n g t h e a p p r o p r i a t e c o n v e y o r b e l ts i n th e p l a n t i n t h e p l a n t a n d c a r e f u ll y

c u t t i n g 1 -m s e c t io n s f r o m t h e b e l t lo a d . T o t a l m a s s a n d s iz e d i s tr i b u t i o n s o f

t h e se s a m p l e s w e r e d e t e r m i n e d i n t h e u s u a l w a y .

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s a m p l e s w e r e t a k e n a r e i d e n t i f i e d i n T a b l e I . W h e n n e c e s s a r y , fl o w o f m a t e r i a l

i n p o r t i o n s o f t h e p l a n t w a s s to p pe x i t o a l l o w t h e s a m p l i n g o f o n l y o n e o f t h e

p a r a ll e l s t r ea m s . F o r e x a m p l e , b o t h e a s t a n d w e s t s e c o n d a r y c r u s h e r p r o d u c t s


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1 0 0 7 6 .1 6 1 .1 6 9 .1 1 0 0 . 0 9 9 . 6 . . . . . . .

7 0 6 6 . 2 5 1 . 6 5 9 . 4 9 1 . 9 9 4 . 8 . . . . . . .

6 3 6 3 . 5 4 8 . 6 5 6 . 6 8 7 . 9 9 0 . 9 . . . . . . .

5 0 5 7 . 3 4 4 . 6 5 1 . 4 75 . 5 7 8 . 0 - - 1 0 0 . 0 . . . .

3 7 . 5 4 8 . 1 3 8 . 0 4 3 . 4 5 9 . 6 6 4 . 3 - - 9 9 . 7 1 0 0 . 0 1 0 0 . 0 1 0 0 . 0 -

2 5 4 0 . 5 3 3 . 0 3 7 . 0 4 8 . 9 5 2 . 3 1 0 0 . 0 - 9 3 . 6 9 4 . 4 9 9 . 5 9 9 . 0 -

1 9 3 5 . 1 2 9 . 8 3 2 . 6 4 2 . 9 4 7 . 3 9 9 . 6 1 0 0 . 0 8 0 . 7 8 1 . 4 9 5 . 2 9 6 . 5 1 0 0 . 0

1 2 . 7 2 9 . 4 2 5 . 6 2 7 . 6 3 5 . 6 4 0 . 0 9 7 . 5 9 9 . 3 5 5 .7 5 3 . 5 7 0 . 4 7 9 . 6 8 8 . 3

6 . 4 2 3 . 1 2 2 . 3 2 2 . 7 2 6 . 9 3 0 . 7 8 0 . 1 8 2 . 1 3 7 . 2 3 0 . 0 3 9 . 4 5 0 . 0 5 8 . 0

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h ) 7 1 8 1 5 8 0

were sampled on the convey or ind icated as s tream 35 in F ig . 1 . Only on e o f

the paral le l crusher l ines was op erated w hile loadin g the be lt for samp ling.

Crusher gaps were de termined by lead ing and w hen necessary gaps were

adjus ted to ensure un i form operat ion dur ing the ent ire the ent ire audi t pe -

r iod . Current drawn by the crusher m otors un der operating load as we l l as

under no- load condi t ions was de term ined from ex is ting p lant

ins trumentat ion .

Screen dim en sio ns and screen apertures were m easured by direct observa-

t ion . Screen v ibrat ion amp l i tudes and m ot ion s were recorded for each screen .

Sam ples o f s creen over f lows were taken by the m anu al lunge m etho d and are

con sequ ently less re l iable than the b e lt samples taken.

C o n v e y o r b e lt s p e e d s w e r e d e t e r min e d f r o m me a s u r e me n t s o f t h e d r iv e

drum d iameters and rotat ional speed .

Th e key operat ing var iables that were measu red are l is ted in Table II . Th e

mea sured s ize d i s tr ibut ions and tonn ages are g iven in Table I I I.

S I M U L A T I O N O F T H E E X I S T I N G F L O W S H E E T

M O D SIM is a mod ular s imu lator that can s im ulate any or dressing-p lant

f lowshee t. M ode ls are required for the d escr ipt ion o f the operat ion o f each

u n i t in t h e p la n t . F o r u se w i t h in M O D S I M a mo d e l mu s t b e c a p ab le o f a c-

cept ing as input the com ple te descr ipt ion of the feed to the u n i t and ca lcu lat -

ing the nature o f the produc t s tream in de ta i l su f f ic ient for the n eeds o f the

s imulat ion . T he parameters that descr ibed the s iz e and operat ing condi t ions


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o f e a c h u n i t m u s t b e s u p p l i e d t o t h e s i m u l a t o r . W h e n s i m u l a t i n g a n e x i s ti n g

p l a n t , t h e s e o p e r a t i n g p a r a m e t e r s m u s t m a t c h t h e v a l u e s a c t u a l l y s e t u p o n

t h e p l a n t .

F o r t h e R o s s i n g c r u s h e r c i rc u i t , m o d e l s w e r e r e q u i r e d f o r t h e s e g r e g a ti n g

a c t i o n o f t h e 1 0 0 0 -t o n c o a r s e o r e b i n , f o r t h e s t a n d a r d a n d s h o r t - h e a d c o n e

c r u s h e r s , a n d f o r t h e d o u b l e - a n d s i n g l e - d e c k s c r e e n s .

A m o d e l w a s d e v e l o p e d to d e s c r i b e t h e m e a s u r e d s e g r e g a t io n i n th e c o a r s e

o r e b i n b e c a u s e t h e s e g r e g a ti o n w a s t o o l a r g e t o b e i g n o r e d . T o w e f fe c ts w e r e

m o d e l l e d : th e u n e q u a l d i s c h a rg e r a te s c a u s e d b y v a r i a t io n s i n t h e o p e r a t i o n

o f t h e t w o a p r o n f e e d e r s u n d e r e a c h d i s c h a r g e a n d t h e t e n d e n c y o f c o a r s e r

p a r t i c l e s t o d i s c h a r g e p r e f e r e n t i a l l y t o t h e e a s t s i d e s t r e a m b e c a u s e o f s e g r e -

g a t i o n i n th e b i n . T h e m e a s u r e d f l o w r a te s a n d s iz e d i s tr i b u t o r s i n t h e p r o d -

u c ts p e r m i t t e d t h e d e v e l o p m e n t o f a s i m p l e e m p i r ic a l m o d e l . T h e f in e m a t e -

r i a l ( u p t o 1 0 m m ) s p l i t s i n d i r e c t p r o p o r t i o n t o t h e o v e r a l l m a s s f l o w s .

I n t e r m e d i a t e si ze s ( 1 0 m m t o 5 0 m m ) f a v o u r e d th e w e s t si d e t o t h e e x t e n t o f

2 0 % . L a r g e r s iz e s ( o v e r 5 0 m m ) f a v o u r e d t h e e a s t s i d e i n c r e a s in g l y a s si ze

i n c r e a s e d . T h e r e c o v e r y t o t h e w e s t s i d e d e c r e a s e d b y 7 . 2 % a s t h e s i z e i n -

c r e a s e d b y a f a c t o r o f 2 .

T h e m o d e l u s e d f o r t h e c o n e c r u s h e r s i s b a s e d o n t h e w e l l - k n o w n cl as s if i-

c a t io n a n d b r e a k a g e- z o n e d e v e l o p e d b y W h i t e n a t t h e J u l iu s K r u t t s c h n i t t

M i n e r a l R e s e a r c h C e n t r e ( W h i t e n , 1 97 3; W h i t e n e t a l., 1 9 7 9 ) . K a r r a ( 1 98 2 )

h a s d e m o n s t r a t e d t h a t t h is m o d e l c a n b e u s e d t o d e s c r ib e t h e o p e r a t i o n o f th e

s h o r t - h e a d c o n e c r u s h e r a s w e l l a s t h e s t a n d a r d c o n e c r u s h e r. T h e b e h a v i o u r

o f t h e c r u s h e r is m o d e l l e d t h r o u g h a c l a s s if i c a ti o n f u n c t i o n a n d a b r e a k a g e

f u n c t i o n . T h e c l a s s i f ic a t i o n fu n c t i o n d e f i n e s t h e c h a n c e t h a t a p a r t ic l e o f a

g i v e n s iz e w i ll a c t u a l ly b e c r u s h e d d u r i n g t h e n i p p i n g p e r i o d o f t h e c r u s h e r

c y c le . T h u s t h e f u n c t i o n C ( x ) i s t h e f r a c t i o n o f m a t e r i a l o f s iz e x t h a t w i l l b e

c r u s h e d d u r i n g a n i p . M a t e r i a l t h a t i s n o t c r u s h e d , i s p r e s u m e d t o b e d i s -

c h a r g e d d i re c t l y t h r o u g h t h e c r u s h e r i n t o t h e p r o d u c t s t r e a m . M a t e r i a l t h a t i s

c r u s h e d , p r o d u c e s a n e n t i r e s p e c t r u m o f p a rt i c le s i ze s. T h e s iz e d i s t r ib u t i o n

o f t h e p r o d u c t s o f b r e a k a g e i s d e s c r i b e d b y a b r e a k a g e f u n c t i o n B x , y ) w h i c h

is d e f i n e d t o b e t h e f r a c t i o n o f d a u g h t e r p a r ti c l e s s m a l l e r th a n s iz e x t h a t r e -

s u lt f r o m t h e b r e a k a g e o f p a rt i c le s o n s iz e y . T h e d a u g h t e r p a r t ic l e s a r e t h e m -

s e l v e s s u b j e c t t o f u r t h e r c l a s s i f i c a t io n t o s e l e c t t h o s e t h a t w i l l b e b r o k e n f u r-

t h e r d u r i n g s u b s e q u e n t c r u s h e r n i p s. T h e o p e r a t i o n o f t h e c r u s h e r c a n b e

c o m p l e t e l y d e s c r i b e d b y t h e c l a s s if i c a ti o n f u n c t i o n a n d t h e b r e a k a g e f u n c -

t io n . T h e f o r m s o f t h e s e f u n c t i o n s u s e d a r e g iv e n b y :

C x)

=0

= 1 k d

= 1 0

x ~ d ~

d l


7/17

SIMULATIONOF CRU SHER CIRC UIT PROCESSING PROBLEMS 255

a n d :

B ( x , y ) = G ( x / y ) l + ( 1 - G ) ( x / y ) n2

( 2 )

T h e p a r a m e t e r s i n t h e s e f u n c t i o n s m u s t b e r e l a te d t o t h e w a y t h e c r u s h e r i s

s e t u p . I n e q . 1, d l r e p r e s e n t s t h e s m a l l e st s iz e t h a t t h e c r u s h e r c a n n i p a n d

t h e r e f o r e b r e a k , w h i l e d2 re p r e s e n t s t h e l a rg e s t p a r ti c l e t h a t c a n p a s s t h r o u g h

t h e c r u s h e r d u r i n g t h e f u ll y o p e n p a r t o f t h e c y c l e , d l a n d dE a r e a f f e c t e d la r g e ly

b y t h e c l o s ed - s i d e s e t t in g o f t h e m a c h i n e . W h i t e n e t a l. ( 1 9 7 9 ) a n d K a r r a

( 1 9 8 2 ) h a v e f o u n d a l i n e a r d e p e n d e n c e b e t w e e n t h o s e v a r ia b l e s . C a r e f u l ex -

p e r i m e n t a t i o n b y W h i t e n e t a l. ( 1 9 7 9 ) h a s r e v e a l e d a w e a k i n v e rs e d e p e n -

d e n c e o f dE o n t h e f e e d r a t e t o t h e c r u s h e r , b u t o u r d a t a w e r e n o t s u f fi c ie n t ly

c o m p r e h e n s i v e t o r e v e a ls th i s e f fe c t. W e h a v e a c c o r d i n g l y m o d e l l e d d l a n d d E

b y :

d l = 0 . 6 5 3 C S S ( 3 )

dE = a C S S ( 4 )

T h e v a l u e o f a w a s f o u n d t o v a r y w i t h c r u s h e r t y p e , b e i n g c lo s e t o 1 .7 f o r t h e

s t a n d a r d c o n e c r u s h e r s u s e d a s s e c o n d a r i e s , a n d 3 .5 f o r t h e s h o r t - h e a d c o n e

c r u s h e r s u s e d i n t h e t e r t i a r y a n d q u a t e r n a r y s ta g es . A v a l u e o f n = 1 w a s u s e d

f o r t h e s t a n d a r d c o n e c r u s h e r s , a n d n = 3 fo r th e s h o r t - h e a d c r u s h e r s .

T h e p a r a m e t e r s i n t h e b r e a k a g e f u n c t i o n e q . 2 a r e a l s o m a c h i n e - s p e c i f i c , n l

a n d n2 w e r e f i x ed a t t h e v a l u e s s u g g e st e d b y W h i t e n e t al . ( 1 9 7 9 ) f o r th e

s t a n d a r d c o n e c r u s h e r a n d b y K a r r a ( 1 98 2 ) f o r t h e s h o r t - h e a d c r u s h e r . T h u s :

n , = 0 . 5 s t a n d a r d

= 0 . 5 1 8 s h o r t - h e a d

a n d :

n 2 =

4 .5 s t a n d a r d

= 2 . 4 7 5 s h o r t - h e a d

T h e p a r a m e t e r G r e p re s e n t s t h e f r a c t i o n a l p r o d u c t i o n o f fi n e s f r o m s in g le -

p a r t ic l e b r e a k a g e e v e n t s w i t h i n t h e c r u s h e r . T h e v a l u e o f t h i s p a r a m e t e r i s

a s s u m e d t o b e a f u n c t i o n o f t h e m a c h i n e t y p e a n d o f t h e o r e , b u t is a s s u m e d

t o b e i n d e p e n d e n t o f t h e c r u s h e r s e t ti n g .

V a l u es o f a a n d G w e r e f o u n d f o r e a c h c r u s h e r in t h e c i r cu i t t o m a t c h t h e

m e a s u r e d s i z e d i s t r i b u t i o n s i n t h e s t r e a m s t h a t w e r e s a m p l e d . N o s p e c i a l p a -

r a m e t e r e s t i m a t i o n p r o c e d u r e s w e r e u se d . T h e p a r a m e t e r s w e r e s i m p l y v a r ie d

u n t i l a g o o d f i t w a s o b t a i n e d w i t h t h e m e a s u r e d d a t a . M O D S I M d o e s n o t

o f fe r a n a u t o m a t i c p a r a m e t e r e s t i m a t i o n m o d e a l t h o u g h i ts c o m p a n i o n p ro -

g r a m M I C R O S I M I ~ d o e s

T h e v a l u e s u s e d a r e g i v e n b e l o w :


8/17

256 R.P. KING

S e c o n d a r y c r u s h e r s W e s t G = 0 . 1 5 , a = 1 .8

E a st G = 0 . 2 0 , a = l . 6

T e r t i a ry c r u sh e r s G = 0 . 3 2 , a = 3 . 5

Q u a t e r n a r y c r u s h e r s G = 0 . 3 2 , a = 3 .5

T h e s e p a r a m e t e r s a r e e n ti r e ly re a s o n a b le , a n d t h e c o r r e s p o n d e n c e b e t w e e n

t h e p r e d i c t e d s i ze d i s t ri b u t i o n s a n d t h o s e m e a s u r e d c a n b e s e e n in F i g. 2. T h e

a g r e e m e n t c a n b e c o n s i d e r e d t o b e v e r y sa t is f ac t o ry , a n d t h e c r u s h e r m o d e l

u s e d c a n b e r e g a r d e d a s r e li a b le .

T h e m o d e l u s e d t o d e s c r i b e th e o p e r a t i o n o f t h e s c r e e n s i n t h e p l a n t w a s

a d a p t e d f r o m a m o d e l d e s c r i b e d b y K a r r a ( 1 9 79 ) . T h i s i s a p r e d i c t i v e m o d e l

o f s c re e n b e h a v i o u r a n d is b a s e d o n t h e c o n v e n t i o n a l d e s c r ip t i o n o f s c re e n in g

b e h a v i o u r t h r o u g h a s et o f c a p a c it y f a c to r s w h i c h d e p e n d o n t h e t o n n a g e a n d

s iz e d i s tr i b u t i o n s o f t h e m a t e r i a l f e d to t h e s c r ee n a n d o n t h e n a t u r e o f th e

s c r e en i ts el f. K a r r a ' s m o d e l i s b a s e d o n c o n s i d e r a b l e o p e r a t i n g d a t a a n d w a s

d e v e l o p e d t o p r o v i d e a d e s c r i p t i o n o f s c r e e n in g b e h a v i o u r t h a t is a s c lo s e as

p o s s ib l e t o c o n v e n t i o n a l i n d u s t r ia l p r a c t ic e f o r t h e d e s i g n a n d a s s e s s m e n t o f

s c r e e n i n g p e r f o r m a n c e . C o n s e q u e n t l y , K a r r a ' s m o d e l c a n b e r e la t e d d i re c t ly

t o w e l l- e s ta b l is h e d in d u s t r i a l p r a c t ic e . T h e m o d e l c a n b e e v a l u a t e d u s i n g w e ll-

u n d e r s t o o d p r o c e d u r e s . K a r r a w a s a b le t o e s ta b l is h t h e p a r a m e t e r s i n t h e

m o d e l u s i ng th e a c c u m u l a t e d e x p e r i e n ce o f s c r ee n p e r f o r m a n c e a v a il ab le

w i t h i n h i s c o m p a n y . T h e m o d e l is c o n s i d e r e d t o b e r o b u s t a n d r e l ia b le a n d is

Z D / 1

' 0 . - / , / / , / ' / Z /

l

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: : : : :

, , ~ . . . . . . . .. . . . . .

=

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z ~ > - - 1

4 o

. .. .. . . , , < , , ~ v , . . . .. ..

, ~ p / o . . l < _ _ _ = = , . . . , s

c_ i < / / l i . + . . . . ~ . ~ / ~> ~ _ _ s l , . , , , , ,,7 I

X t ~ i ~ . . . .. .. .. * e : ~ v . . . . s = . , , , , 4

, . . ~ . . ; ' . ~ , , , . ~ + . . . .. . . .. . .. . . s t , . . , , , , I

2 0

~ t , , - = ' = ' ' - & ~ ~ s ~ ' e u a ]

~

~ S l : r i e u

3 i

I 0 E ] - - . - - S l P i l i 1

/

0 . . . . . . . . I

I

i O t O O t O

P a r t i c l e s i z e m m s

F i g. 2. S i m u l a t e d a n d m e a s u r e d s i ze d i s t ri b u t i o n s i n s e v e r a l s t r e a m s i n t h e p l a n t . T h e s t r e a m

n u m b e r s c o r r e s p o n d t o t h o s e i n F i g . 1. T h e s iz e d i s t r ib u t i o n s t h a t w e r e m e a s u r e d d u r i n g t h e

p l a n t a u d i t a re s h o w n b y m e a n s o f t h e p l o t t e d s y m b o l s . T h e c o r r e s p o n d e n c e b e tw e e n t h e

m e a s u r e d a n d s i m u l a t e d s i z e d i s t ri b u t i o n s i s g o o d .


9/17

SIMULATION OF CRUSHER CIRCUIT PROCESSING PROBLEMS 2 5 7

u s e d i n M O D S I M w i t h o u t c h a n g e . I t w a s f o u n d t o b e e n t i re l y s a ti s fa c to r y f o r

t h e p r e s e n t s t u d y a n d w a s v e r y e f f e c ti v e i n a l l o w i n g a u s e f u l c h a r a c t e r i z a t i o n

o f t h e b e h a v i o u r o f t h e s c r e e n s i n t h e R o s s i n g c i rc u i t .

A b r i e f d e s c r i p t io n o f t h e m o d e l i s g iv e n h e r e , a n d t h o s e a s p e ct s o f t h e m o d e l

t h a t c a n b e s p e ci al ly ex p l o i te d b y M O D S I M a r e h ig h l ig h t ed . T h e m o d e l i s

b a s e d o n t h e w e l l - k n o w n p r o c e d u r e f o r a s se s s in g t h e c a p a c i t y o f a v i b r a t in g

s c r e e n t h r o u g h t h e b a s i c c a p a c i t y f a c to r , A , w h i c h d e f i n e s t h e t o n n a g e o f u n -

d e r s i z e t h a t a p a r t i c u l a r s c r e e n c a n t r a n s m i t p e r u n i t s c r e e n s u r f ac e a r e a. T h i s

b a s i c f a c to r is i n c r e a s e d o r d e c r e a s e d d e p e n d i n g o n t h e n a t u r e o f t h e f e e d a n d

c o n d i t i o n s o n t h e s c r e en . A n u m b e r o f c ap a c i ty f a c to r s a l lo w f o r t h e a m o u n t

o f o v e r s i z e i n t h e f e e d ( f a c t o r B ) , t h e a m o u n t o f h a l f- s iz e in t h e f e e d ( f a c t o r

C ) , t h e c h e c k l o c a ti o n ( f a c to r D ) , w e t o r d ry s c re e n i n g ( f a c t o r E ) , a n d m a -

t e r i a l b u l k d e n s i t y ( f a c t o r F ) . T h e s e f a c to r s a ll h a v e a v a l u e o f u n i t y a t t h e

n o m i n a l s t a n d a r d o p e r a t i n g c o n d i t i o n a n d m o v e d o w n o r u p a s t h e s c r e e n

d u t y b e c o m e s m o r e o r l es s a r d u o u s .

T h u s t h e m o d e l m a k e s u s e o f a n i n d e x t h a t d e f in e s th e d u t y o f th e s c r e e n in

i ts p o s i t i o n i n t h e f lo w s h e e t . T h i s i n d e x w h i c h K a r r a d e s i g n a t e s a s K i s d e -

f i n e d a s:

t o n s o f u n d e r s iz e i n t h e f e e d / u n i t a r e a o f s c r ee n

K - A B C D E D 5 )

K a r r a g i v es f o r m u l a s f o r th e c a l c u l a t i o n o f e a c h o f t h e f a c to r s A t o F , a n d

t h e se a re p r o g r a m m e d i n t o th e M O D S I M s c re e n m o d e l . T h e s e f o r m u l a s r e-

l a te t h e f a c t o r s t o t h e p h y s i c a l c h a r a c te r i s ti c s o f t h e s c r e e n a n d t o t h e n a t u r e

o f t h e f e ed . T h u s K a r r a 's m o d e l c a n b e s e le c te d f o r u s e i n a M O D S I M s i m u -

l a t i o n o n l y i f t h e p h y s i c a l c h a r a c t e r is t i c s o f t h e s c r e e n h a v e b e e n c o m p l e t e l y

s p e c if ie d . M O D S I M s u p p l ie s a ll i n f o r m a t i o n a b o u t t h e f e e d f o r e v e r y s c r e e n

i n t h e c i r c u i t .

K a r r a h a s f o u n d t h a t t h e c a p a c i t y o f a s c r e e n i s r e d u c e d i f t h e r e i s a c o n s id -

e r a b l e q u a n t i t y o f n e a r - s iz e m a t e r i a l i n t h e f e e d . H e d e f i n e s a n a d d i t i o n a l

n e a r - s iz e c a p a c i t y f a c t o r G c a n d c a l c u l at e s i t f r o m

X . ~ o 5 1

G c = 0 . 9 7 5 ( 1 - 1 - - ~ / ( 6 )

w h e r e X n i s t h e p e r c e n t a g e o f n e ar - s iz e m a t e r i a l i n t h e f e e d . T h u s t h e t h e o r e t -

i c al a m o u n t o f u n d e r s i z e t h a t c a n b e t r a n s m i t t e d b y t h e s c r e e n is g iv e n b y:

T h = A . B . C . D . E . F . G X s c r e e n a r e a

A s c r e e n w i l l b e w e l l d e s i g n e d to h a n d l e i t s d u t y i n t h e c i r c u i t i f T h i s a p p r o x -

i m a t e l y e q u a l to t h e q u a n t i t y o f u n d e r s i z e i n t h e fe e d .

I n p r a c t i c e , n o t a l l o f th e u n d e r s i z e is t r a n s m i t t e d b e c a u s e o f v a r i o u s p h y s-

i c al f a c to r s t h a t i m p a i r t h e e f f i c i e n c y o f t h e s c r e e n . T h i s e f fe c t is d e s c r i b e d b y


10/17

258 k p KIN(;

t h e s c r e e n p a r t i t i o n f u n c t i o n . S e v e r a l s t a n d a r d f u n c t i o n a l f o r m s a r e a v a i l a b le

t o d e s c r i b e t h is e f f ec t , a n d K a r r a u s e s t h e f u n c t i o n :

P a r t i t i o n f a c t o r = 1 - e x p [ ( - 0 . 6 9 3 d / d s o ) 5.9 ] 7 )

T h e p a r a m e t e r t h a t w i l l d e t e r m i n e t h e s c r e e n i n g e f f i c i e n c y i s d s o . V a l u e s o f

d so s m a l l e r t h a n t h e s c r e e n m e s h s iz e w i ll le a d t o l o w e f f ic i e n c ie s , a n d v a l u e s

o f d s o g r e a t e r t h a n t h e m e s h s iz e g iv e h i g h e f f ic i e n c ie s .

T h e a c t u a l dso a c h i e v e d w i ll d e p e n d p r i m a r i l y o n t h e e f f e c ti v e t h r o u g h f a l l

a p e r t u r e o f t h e w i re m e s h u s e d o n t h e s c re e n . T h e t h r o u g h f a l l a p e r t u r e is in

t u r n r e l a t e d t o t h e a c t u a l m e s h s iz e , h, b y:

h-r = h + d w ) c o s O - d w ( 8 )

w h e r e 0 is t h e i n c l i n a t i o n a n g l e o f th e s c r e e n , a n d d w is t h e w i r e d i a m e t e r .

K a r r a ' s a n a l y s is o f e x p e r i m e n t a l d a t a f r o m a n e x t e n s i v e te s t p r o g r a m p r o -

d u c e d t h e f o ll o w i n g r e l a t i o n s h i p f o r t h e p r e d i c t i o n o f dso:

dso Gc

hv - K 0 148 (9 )

A f u r t h e r r e f i n e m e n t m u s t b e a d d e d t o K a r r a 's m o d e l b e fo r e it ca n b e u s e d

a s a g en e r a l s im u l a t i o n m o d e l f o r o p e r a t i n g s c r ee n s . K a r r a m a k e s n o a ll ow -

a n c e f o r th e p e r c e n t o p e n a r e a o f th e s c r ee n c l o t h u s e d . H i s f o r m u l a f o r t h e

c a l c u l a t io n o f c a p a c i t y A i s b a s e d o n i n d u s t r i a l li g h t - m e d i u m w o v e n w i r e m e s h .

F o r o t h e r s c r e e n c lo t h s a n d s u r fa c e s , A m u s t b e a d j u s t e d i n p r o p o r t i o n t o t h e

o p e n a r e a . T h e p e r c e n t o p e n a r e a f o r l ig h t - m e d i u m w i r e m e s h i s r e l a te d t o t h e

m e s h s iz e h b y :

O A = 2 1 . 5 l o g l 0 h + 1 01 .5 ( w i t h h i n m e t e r s ) ( 1 0 )

T h u s c a p a c i t y A m u s t b e a d j u s t e d t o:

A X a c t u a l % o p e n a r e a

O A

T h e m o d e l p r o v id e s a s i m u l a t io n o f th e a c tu a l p e r f o r m a n c e o f t h e s c r ee n i n

t h e c i rc u it . T h i s p e r f o r m a n c e c a n b e c o m p a r e d w i t h t h e d e s i g n c a p a c i ty o f t h e

s c r e en a n d t h e s c r e e n p e r f o r m a n c e e v a l u a t e d . I n p a r t ic u l a r , t h e a c t u a l o p e r -

a t i n g e f f ic i e n c y c a n b e c a l c u l a t e d f r o m :

S i m u l a t e d e f f ic i e n c y = t o n n a g e i n u n d e r f l o w

t o n n a g e o f u n d e r s i z e i n f e e d

T h e e f fe c t iv e u t i l i z a t io n o f th e s c r e e n a r e a c a n b e c a l c u l a t e d f r o m :

A r e a u t i l iz a t i o n f a c t o r = A U F

t o n n a g e o f u n d e r s iz e i n f e e d

t h e o r e t i c a l a b il it y o f t h e s c r e e n t o p a s s u n d e r s i z e


11/17

SIMULATIONOF CRUSHERCIRCU IT PROCESSINGPROBLEMS 259

A n A U F e q u a l t o u n i t y i n d i c a t e s t h a t t h e s c r e e n c a p a c i t y i s e x a c tl y b a l a n c e d

t o t h e r e q u i r e d d u t y . A U F ~< 1 i n d i c a t e s t h a t t h e s c r e e n i s u n d e r l o a d e d , w h i l e

A U F > I 1 i n d i c a t e s t h a t t h e s c r e e n i s o v e r l o a d e d .

1

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10 1

a r t i c l e s i z e m m s

A -- __St rsam 40

O - - __Stream 17

_____S t rea l l t

t 0

tO

F i g . 3 . T h e s i m u l a t e d a n d m e a s u r e d s iz e d i s t r ib u t i o n s i n t h e o v e r f lo w s tr e a m s f r o m t h e t o p

d e c k o f a t e r ti a r y s c r e e n ( s t r e a m 1 0 ) t h e l o w e r d e c k o f a t e r t i a r y s c r e e n ( s t r e a m 1 7 ) a n d t h e

o v e r f l o w f r o m t h e q u a t e r n a r y s c re e n s.

T A B L E I V

S i m u l a t e d ~ r f o r m a n c e o f cr u s h e rs i n t h e e x i s t in g fl o w s h e e t

U n i t D e s i g n S i m u l a t e d I n s t a ll e d M e a s u r e d S i m u l a t e d

t o n n a g e t o n n a g e n e t p o w e r n e t p o w e r n e t p o w e r

(kW) (kW) (kW)

Se c onda r y c r ushe r s :

W est 1000 1069 171 126 130

East 1000 935 158 136 167

T e ~ i a r y c r u s h e r s :

W e s t l 445 354 151 108 102

W e s t2 440 354 108 113

E a s t l 4 6 4 2 8 9 1 45 8 6 7 6

E a s t 2 4 5 0 2 8 9 9 6 8 4

Q u a t e r n a r y c r u s h e r s :

N o . l 3 9 0 2 3 5 1 58 3 4 4 7

No . 2 396 235 148 80 42


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260

TABLE V

Simulated performance of screens in the existing flowsheet

RP. KING

Unit

Simulated Simulated Calculated Simulated

tonnage tonnage to dso efficiency

(tons/h) underflow (mm) (%)

(tons/h)

Area

utilization

factor

Tertiary screens:

West top deck 534 317 34.9 82.7 1.60

lower deck 317 180 12.4 94.0 1.14

East top deck 468 293 35.6 84.0 1.40

lower deck 293 179 12.8 95.8 1.04

Quaternary screens 293 214 15.8 86.8 0.94

A particular advantage of the Karra screen model is that no free parameters

are required to be estimated from operating data. The adequacy of the model

for the screens in the Rossing plant can be judged by comparing the measured

and predicted size distributions in the screen overflow streams as shown in

Fig. 3. With the exception of the overflow from the lower deck of the second-

ary screens, the agreement is remarkably good.

A summary of the simulated behaviour of all of the units in the flowsheet

is given in Tables IV and V.

ASSESSMENT OF EXISTING F LOWSHEET OPERATION

The models used for the crushers and screens in the simulation required

very little tuning to achieve a very good match between the simulator output

and the observed behaviour of the plant. The models provide he necessary

information that is required to diagnose the plant bottlenecks and to suggest

modifications to enable the plant to meet its operating objective of 80% pass-

ing 7 mm in the final product. The simulation of the existing flowsheet pre-

dicted an 80% passing size of 10.4 mm against the measured value of 10.5

mm.

The summarized simulator data in Tables IV and V identify the important

operating characteristics immediately. The power drawn by each crusher was

calculated by the simulator using the known impact work index of the ore

(9kWh/ton) using formula:

P o w e r T W , I P ~ so - I F ~ s o )

where T= tonnage handled by the crusher, IV~ the impact work index,/'so the

80% passing size in the product from the crusher and Fso the ~ passing size

in the feed to the crusher. It is evident from Table IV that all the crushers in


13/17

S IMU LATION OF CRU S H ER CIR CU IT P ROCES S ING P ROBLEMS

261

t h e p l a n t a r e o p e r a t i n g a t o r w i t h i n t h e i r i n s t a l le d d e s i g n c a p a c it y . T h e s e c-

o n d a r y c r u s h e r s a r e w o r k i n g j u s t w i t h i n c a p a c i t y , t h e t e r t i a ri e s o n t h e e a s t

s i d e a t a b o u t 6 5 % o f c a p a c it y .

T a b l e V s h o w s t h a t t h e t e r t i a r y s c r e e n s a r e o v e r l o a d e d , p a r t ic u l a r l y o n t h e

u p p e r d e c k s . T h e c a l c u l a t e d a r e a u t i l i z a t i o n f a c t o r s a r e 1 .6 a n d 1 .4 o n th e t o p

d e c k s a n d t h i s i n d i c a t e s t h a t t h e s c r e e n s a r e b e i n g r e q u i r e d t o t r a n s m i t 6 0 %

m o r e m a t e r i a l t h a n t h e i r d e s i g n c a p a c i t y . S c r e e n i n g e f f ic i e n c ie s a r e r e l a t iv e l y

l ow . T h e l o w e r d e c k s a r e o p e r a t i n g i n a s li g ht ly o v e r l o a d e d c o n d i t i o n , b u t i n

s p i te o f t h is , t h e s i m u l a t e d e f f i c i e n c y i s q u i t e h i g h . H o w e v e r , t h e m e a s u r e d

s iz e d i s t r i b u t i o n o f t h e l o w e r d e c k o v e r f l o w , as s h o w n i n F i g . 3 , i n d i c a t e s s o m e

c a r r y o v e r o f u n d e r s i z e m a t e r i a l, a n d t h a t w o u l d b e c o n s i s t e n t w i t h t h e s i m -

u l a t e d o v e r l o a d e d c o n d i t i o n s .

T h e r e a s o n f o r t h e o v e r l o a d i n g o f t h e f r o n t e n d o f th e c i r c u i t is n o t d i f f i cu l t

t o s e e . T h e p l a n t f e e d o n t h e c o a r s e o r e r e c l a im c o n v e y o r h a s a la r ge q u a n t i t y

o f f in e m a t e r i a l w i t h a p r o x i m a t e l y 5 0 % s m a l l e r t h a n t h e c l o s e d - s id e s e tt in g o f

t h e s e c o n d a r y c r u s h e rs . A l l o f t h i s m a t e r i a l m u s t b e h a n d l e d b y th e s e c o n d a r y

c r u s h e r s a n d t h e t e r t i a r y s c r e e n s b e f o r e l e a v i n g t h e p l a n t i n t h e t e r t i a r y s c r e e n

u n d e r f l o w . A l l m a t e r i a l t h a t l e a v e s i n t h e t e r t i a r y s c r e e n u n d e r f l o w r e d u c e s

t h e l o a d o n t h e t e r t i a r y c r u s h e r s a n d t h e q u a t e r n a r y c i r c u i t . T h e c a l c u l a t e d

l o a d o n t h e q u a t e r n a r y c i r c u i t w a s f o u n d to b e 1 28 6 t o n s / h w i t h a c i r c u l a t in g

l o a d o f 3 7 % .

T w o s tr a te g ie s f o r t h e i m p r o v e m e n t o f p l a n t p e r f o r m a n c e i m m e d i a t e l y su g-

g e s t t h e m s e l v e s .

S T R A T E G I E S F O R I M P R O V E M E N T

Strategy A

I n c r e a s e t h e c i r c u l a t in g l o a d i n t h e q u a t e r n a r y c i r c u i t a n d u t i -

l iz e t h e e x i s ti n g q u a t e r n a r y s c r e e n i n g a n d c r u s h i n g c a p a c i t y m o r e e f fe c t iv e l y

t o p r o d u c e a f i n e p r o d u c t .

Strategy B I n s ta l l s e c o n d a r y s c r e e n s a h e a d o f th e s e c o n d a r y c r u s h e rs t o

r e m o v e f i na l p r o d u c t - s iz e m a t e r i a l b e f o r e i t e n te r s t h e c r u s h e r c i rc u i t a n d u t i-

l iz e t h e r e l e a s e d c r u s h i n g a n d s c r e e n i n g c a p a c i t y t o p r o d u c e a f i n e r p r o d u c t .

Strategy A

T h e c i r c u l a t in g lo a d i n t h e q u a t e r n a r y c i r c u i t is i n c r e a s e d i f t h e m e s h s iz e

o f t h e q u a t e r n a r y s c r e e n s i s d e c r e a s e d . E v e n m o d e s t i n c r e a s e s in t h e c i r c u l a t-

i n g l o a d l e a d t o a n o v e r l o a d c o n d i t i o n o n t h e q u a t e r n a r y s c r e e n s . T h i s e f f ec t

is s h o w n b y t h e s i m u l a t o r, a n d t h e p e r t i n e n t d a t a a r e s u m m a r i z e d i n T a b l e

V I i n l in e s 1, 2 a n d 3 , fo r s i m u l a t i o n s o f t h e e x i s t i n g f lo w s h e e t w i t h t h e q u a -

t e r n a r y s c r ee n m e s h r e d u c e d f r o m 2 0 m m t o 17.5 m m a n d 15.2 r a m . T h e

l a t te r c o n d i t i o n i n c r e a s e s t h e c i r c u l a t i n g l o a d f r o m 3 7 % t o 8 9 % , a n d t h e q u a -

t e r n a r y s c r e e n s a n d q u a t e r n a r y c r u s h e r s b e c o m e o v e r l o a d e d . I t i s n e c e s s a r y


14/17

262

FABLE VI

S i m u l a t i o n of effect of finer crushing in the quaternary c i r c u i t

R P KIN I

S i m u l a t i o n Quate rnary Quate rnary Circulat ing % - 7.41

Nr, screen crusher CSS load mm in final

aperture (ram ) (%) product

(mm)

Comments

1.1 20 8.17 and 8.6 37 63

2 17.5 8.17 and 8.6 56 68

3 15.2 8.17 and 8.6 89 74

4 20 6.5 28 66

5 17 6.5 40 72

6 15.2 6.5 48 75

7 15.2 6.5 45 74

Screens are overload ed

Screens and crushers

a r e overloaded

Screens are overloade d

No overloads

Screens are overloaded

No overloads.

Quaternary screens

i n c r e a s e d f r o m 6 to 8

~ E x i s ti n g f l o w s h e e t b a s e case.

t o r e d u c e t h e c l o s e d - s i d e s e t t in g o f t h e q u a t e r n a r y c r u s h e r s o t k e e p t h e q u a -

t e r n a r y c ir c u i t i n b a l a n c e , a n d t h e e f f e c t o f t h i s c a n b e s e e n i n r o w s 4 , 5 a n d 6

o f T a b l e V I . T o r e l ie v e t h e o v e r l o a d o n t h e q u a t e r n a r y s c r e e n s , a fu r th e r t w o

s c r e e n s c a n b e i n s t a l l e d i n t h e q u a t e r n a r y c i r c u i t , a n d a p r o d u c t h a v i n g 7 4

o f m a t e r i a l ~< 7 . 4 m m i s p r o d u c e d b y t h e c i r c u it .

Strategy

A m o d i f i e d c i r c u it h a v i n g a d d i t io n a l s e c o n d a r y s c r e e n i n g c a p a c i t y i n s ta l le d

i s s h o w n i n th e f lo w s h e e t i n F i g . 4 . T h e s e s c r e en s r e m o v e p r o d u c t - s i z e m a t e -

r i a l , a l l o w i n g t h e s e c o n d a r y c r u s h e r t o b e s e t f i n e r . T h e s e t t i n g s c h o s e n f o r

e a c h u n i t in t h e m o d i f i e d p l a n t a r e s u m m a r i z e d i n T a b l e V I I , a n d t h e s im u -

l at o r c o n f i r m e d t h a t n o u n i t w a s o v e r l o a d e d i n th e c i r cu it .

M O D S I M p r o v i d e s d e t a il e d o p er a t in g i n f o r m a t i o n o n t h e o p e r a t io n o f t h e

s c r e e n s s o t h a t i t i s e a s y t o s e l e c t s c r e e n s a p p r o p r i a t e t o t h e d u t y t o b e p e r -

f o r m e d . I n t h i s c a s e t w o p a i r s o f d o u b l e - d e c k s c r e e n s 6 . 1 m 2 . 1 3 m a r e r e -

q u i r e d , t h e a p e r t u r e s a n d o t h e r i n f o r m a t i o n a r e s p e c i f i e d i n T a b l e V I I . T h e

a p e r t u r e s w e r e c h o s e n t o b a l a n c e t h e l o a d o n e a c h d e c k s o t h a t t h e A U F i s

a p p r o x i m a t e l y e q u a l to 1 .0 fo r e a ch .

T h e a d d i t i o n o f t h e s e c o n d a r y s c r e e n s r e d u c e d t h e lo a d o n t h e q u a t e r n a r y

c i rc u it f r o m 1 2 8 6 to 1 1 8 6 t o n s / h , s o t h a t a p r o d u c t h a v i n g 75 ~ < 7 . 4 m m c a n

b e p r o d u c e d w i t h o u t a d d i t io n a l s c r e e n i n g c a p a c it y i n t h e q u a t e r n a r y c ir c u it .


15/17

S I M U L A T I O N O F C R U S H E R C I R C U I T P R O C E S S I N G P R O B L E M S 263

.7,

b

'X~ 0

,~ e '~

O

O *- '

~

a ~

o


16/17

2 6 4

T A B L E V I I

S e t ti n g s o f o p e r a t i n g p a r a m e t e r s i n m o d i f i e d f l o w s h e e t

RIL KING

U n i t T y p e

S e c o n d a r y D o u b l e - d e c k p o l y u r e t h a n e

s c r e e n s

Secondary 7-ft standard Symon s cone

c r u s h e r s c r u s h e r s

T e r t i a r y

s c r e e n s

D o u b l e - d e c k polyurethane

T e r t i a r y 7 - f i short-head

c r u s h e r s

T o p d e c k : 7 0 - m m s q u a r e o p e n i n g

5 0 - m m ribs

6 .1 m 2 . 1 3 m


L o w e r d e ck : 1 6 - m m s q u a r e

opening

1 2 - m m

ribs

6 .1 m x 2 . 1 3 m


C l o s e d - s i d e s e tt i ng : 3 5 m m

Topdeck: 1 5 - m m s q u a r e opening

1 0 - m m r ib s

6 .1 m X 2 . 1 3 m

18

inclination

L o w e r d e ck : 1 2 - m m s q u a r e

opening

8 - m m r i b s

6 . 1 m X 2 . 1 3 m

18 o

inclination

C l o s e d - s i d e s e t t i n g : 8 m m

Qu ater na ry 6b ingle-deck polyurethane 1 5 . 2 - m m s q u a r e opening

s c r e e n s 1 0 . 3 - m m r i b s

5 . 4 6 m 2 . 0 m

18

inclination

Quaternary

7 - ft s h o r t - h e a d

c r u s h e r s

C l o s e d - s i d e s e t ti n g : 6 .5 m m

D I S C U S S I O N

T h e m a i n o b s e r v a t io n t o b e m a d e f r o m t h e s i m u l a t i o n s i s t h a t t h e p r o d u c t

s i z e d i s t r ib u t i o n i s d e t e r m i n e d p r i m a r i l y b y t h e s e t u p o f t h e q u a t e r n a r y

c r u s h i n g c i r c u it . I t i s n e c e s s a r y t o u t i l i z e b o t h s c r e e n i n g a n d c r u s h e r c a p a c i ty

i n th i s s e c t i o n o f t h e p l a n t i n a n o p t i m a l f a s h i o n t o a c h i e v e t h e b e s t p r o d u c t.

T h e s i m u l a t i o n s i n d i c a t e t h a t t h is c a n b e d o n e b y a p p r o p ri a te c h o i c e o f m e s h

s i z e o n t h e q u a t e r n a r y s c r e e n s a n d s e t t i n g s i n t h e q u a t e r n a r y c r u s h e r s . T h e

i n t r o d u c t i o n o f a d d i t i o n a l s e c o n d a r y s c r e e n s h a s a p p a r e n t l y v e r y li tt le p o t e n

t ia l fo r i n c r e a s i n g t h e c a p a c i t y o f t h e p la n t . T h e r e d u c t i o n i n l o a d o n t h e q u a

t er n a r y c i r c u i t f r o m 1 2 8 6 t o 1 1 8 6 t o n s / h c a n n o t b e r e g a rd e d a s a v e ry a tt ra c

t i v e i n c e n t i v e f o r t h e i n t r o d u c t i o n o f f o u r l ar g e d o u b l e d e c k s c r e en s . I m p r o v e d


17/17

S IM U L A T I O N O F C R U S H E R C I R C U I T P R O C E S S IN G P R O B L E M S 265

p l a n t o p e r a t i o n s h o u l d b e s o u g h t f i rs t b y e x p l o i t i n g t h e c a p a c i t y o f t h e q u a -

t e r n a r y c i r c u i t t o t h e g r e a t e s t p o s s i b l e e x t e n t b e f o r e a d d i t i o n a l s e c o n d a r y

s c r e e n in g c a p a c i t y c a n b e c o n s i d e r e d .

S p a c e d o e s n o t p e r m i t a c o m p r e h e n s i v e p r e s e n t a t i o n o f a ll t h e d a t a o b -

t a i n e d f r o m M O D S I M , w h i c h i s ve r y v o l u m i n o u s . A c o m p l e t e se t o f d a t a

f r o m t h e s t u d y i s a v a i l a b l e in K i n g , 1 9 8 7 b a n d c .

A C K N O W LED G EM EN TS

T h e o p p o r t u n i t y t o p a r t i c i p a te i n t h is i m p o r t a n t p l a n t s t u d y w a s m a d e p o s -

s ib le b y R o s s i n g U r a n i u m a n d b y N o r d b e r g M a n u f a c t u r in g C o m p a n y . T h e

e x p e r t a s s i s t a n c e a n d c o - o p e r a t i o n o f t h e s e c o m p a n i e s is g r e a tl y a p p r e c i a t e d .

C o n t i n u i n g d e v e l o p m e n t o f m o d e l l in g a n d s i m u l a t io n t e c h n i q u e s h a s b e e n

m a d e p o s s ib l e b y a g r an t f r o m t h e F o u n d a t i o n f o r R e s e a r c h D e v e l o p m e n t .

R EF ER EN C ES

Karra, V .K., 1979. Deve lopment of a mod el for predicting the screening performan ce o f a vi-

brating screen. CIM Bull., April 1979, pp. 167-171.

Karra, V .K., 1982. A process performance m odel for cone crushers. Proc. 14th Int. M ining Congr.,

Toronto, III: 6.1-6.14.

King, R.P., 1986. A U ser 's Guide to M ODS IM. U niversi ty of the W itwatersrand, Department

of Metal lurgy and Materials Engineering, Johannesburg, R ept . G E N ?l/86 , 66 pp.

King, R.P., 1987a. MO DSIM : A Modular M ethod for the Design, Balancing and Simulation of

Ore D ressing Plant Flow sheets. U niversity o f the W itwatersrand, D epartment of Metallurgy

and M aterials Engineering, Johannesburg, Rept . GE N /2/8 3, 77 pp.

King, R.P., 1987b. The F ine Crushing Circuit of Rossing U ranium Ltd. Sim ulation o f the Ex-

isting Flowsheet. U niversity o f the W itwatersrand, D epartment of Me tallurgy and M aterials

Engineering, Johannesburg, Rept . G E N /8/8 7, 262 pp.

King, R.P., 1987c. The Fine C rushing Circuit of Rossing U ranium Ltd. Sim ulation o f M odified

Flowsheets. U niversity o f the W itwatersrand, D epartment o f M etallurgy and M aterials En-

gineering, Johannesburg, R ept ., G E N /13 /87 , 262 pp.

M agerowski, A .J. and Karra, V.K., 1982. Com puter-aided crushing circuit design. In: A.L. Mu-

lar and G.V. Jorgensen (Editors), Design and Installation o f Com m inution Circuits. Society

of M ining E ngineers, New York, N.Y., p. 288.

O'Bryan, K ., 1987. Crushing flowsheet simulation: increased productivity and improved flow-

sheet design. AP CO M 87. Proc. 20th Int. Sym p. Application of Com puters and M athematics

in the Mineral Industries, Vol. 2, Johannesburg, S AIM M , pp. 167-178.

Stange Wayne , 1989 . Strategies for m ore flexible sequential-mo dular simulation. In: A. W eiss

(E ditor), Proc. 21st Int. Sym p. Application of Com puters and O perations Resea rch in the

M inerals Industry. Society of Mining E ngineers, New York, N.Y., pp. 811-825.

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