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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 .
T h e e x i s t in g p la n t f l o w s h e e t i s s h o w n i n F ig . l , a n d t h e s t r e a m s f r o m w h i c h
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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f r o m
2 & 3
1 5 0 8 8 . 3 8 1 . 7 8 5 . 2 1 0 0 . 0 . . . . . . .
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
4 . 7 2 0 . 8 2 0 . 0 2 0 . 4 2 4 . 2 2 7 . 5 7 1 . 2 7 3 . 2 2 9 . 4 2 5 . 6 3 3 . 1 4 3 . 0 5 0 . 6
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t o n s / + 3 5 2 + 7 2 4
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
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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 :
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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
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c_ i < / / l i . + . . . . ~ . ~ / ~> ~ _ _ s l , . , , , , ,,7 I
X t ~ i ~ . . . .. .. .. * e : ~ v . . . . s = . , , , , 4
, . . ~ . . ; ' . ~ , , , . ~ + . . . .. . . .. . .. . . s t , . . , , , , I
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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 .
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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
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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
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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 .
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t 0
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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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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
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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
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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 .
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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
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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
1 8 i n c l i n a t i o n
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
1 8 i n c l i n a t i o n
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
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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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