GARY WORKS EXPERIENCE WITH DUST CONTROL AT NUMIBER 3 SINTER PLANT
T. A. Young, Jr.
A s s i s t a n t S u p e r i n t e n d e n t , S i n t e r Department, Gary Works
United S t a t e s S t e e l Corporation
Number 3 S i n t e r P l a n t , which c n n s i s t s of t h r e e l a r g e s t r a n d s , was b u i l t i n t h e l a t e
1 9 5 0 ' s . A s i n most s i n t e r p l a n t s c o n s t r u c t e d d u r i n g t h i s p e r i o d , d e d u s t i n g f a c i l i t i e s
were provided i n t h e f o u r primary a r e a s of d u s t g e n e r a t i o n :
(See F i g u r e No. 1 )
1.
2.
3.
4.
Exhaust Gas System
S i n t e r Machine Discharge Area
Screening S t a t i o n
S i n t e r Load Out Bins
Area 1
The windboxes a r e connected t o "St' o r multicone mechanical t y p e c o l l e . c t o r s b e f o r e
e n t e r i n g t h e e x h a u s t gas main. An i n t e r m e d i a t e dynamic d u s t c o l l e c t o r i s l o c a t e d i n t h e
main, a f t e r t h e windboxes. The secondary gas c l e a n e r i s an e l e c t r o s t a t i c d r y p r e c i p i t a t o r
between t h e end of t h e main and t h e induced d r a f t f a n . The e n t i r e system does an adequate
job of c l e a n i n g t h e exhaust g a s e s , w i t h r o u t i n e maintenance of e l e c t r o d e s , r e c t i f i e r s ,
r a p p e r s , and wear a r e a s , t o p r o t e c t t h e f a n and t o p r e v e n t a community problem.
Very l i t t l e more need b e s a i d about t h i s system, u n l e s s i t would b e t h a t t h e h i g h e r
t h e s i n t e r b a s i c i t y , t h e l e s s e f f i c i e n t t h e p r e c i p i t a t o r . I t appears that. w i t h super
f l u x s i n t e r , l a r g e r p r e c i p i t a t o r s may be needed t o m a i n t a i n a c l e a n d i s c h a r g e s t a c k .
Area 2
There were seven independent c o l l e c t o r systems i n t h e d i s c h a r g e a r e a of t h e t h r e e
s t r a n d s . They were designed t o dedust t h e s i n t e r machine d i s c h a r g e s , h o t v i b r o f e e d e r s ,
h o t f i n e s h a n d l i n g systems, c o o l e r c h u t e s , s i n t e r d i s c h a r g e f e e d e r s , and two s i n t e r cnnveyor j u n c t i o n s .
Area 3
Two covered
I n t h e s c r e e n i n g s t a t i o n a r e a t h e r e were t h r e e c o l l e c t o r system:;.
twenty-two t r a n s f e r c h u t e s and t h i r t e e n conveyors i n t h e s c r e e n i n g s t a t i o n . The t h i r d
system took c a r e of t h e t r a n s f e r c h u t e s of t h e s i n t e r f i n e s conveyors from t h e s c r e e n i n g
s t a t i o n and s h u t t l e conveyor o v e r t h e t h r e e cold r e t u r n s s t o r a g e b i n s .
Area 4
One s y s t e m was i n s t a l l e d i n t h e s i n t e r l o a d o u t b i n s a r e a . The two t r a n s f e r c h u t e s
were hooded and t h e t o p s of t h e e i g h t s t o r a g e b i n s were s e a l e d and e a c h p r o v i d e d w i t h
a suction pick up point.
A l l t h e c o l l e c t o r s i n a r e a s two, t h r e e , and f o u r (See F i g u r e No. 1 ) were of t h e
m u l t i p l e t u b e c y c l o n e d e s i g n , which o p e r a t e under n e g a t i v e p r e s s u r e a t a p r e s s u r e d r o p
o f between 2 and 2 . 7 5 i n c h e s of water. The c o l l e c t e d d r y d u s t w a s removed from t h e
bottom of t h e h o p p e r s by a screw conveyor. I n some of t h e s y s t e m s , a s m a l l amount of
w a t e r was added i n t h e s c r e w f e e d e r t o minimize r e - d u s t i n g i n p r o c e s s .
The e l e v e n s e p a r a t e d e d u s t i n g s y s t e m s i n s t a l l e d , proved t o b e i n a d e q u a t e f o r t h e
job t h e y were a t t e m p t i n g t o perform. The atmosphere i n t h e p l a n t w a s d u s t y and s o w a s
t h e d i s c h a r g e from t h e s t a c k s . A f t e r a d e t a i l e d i n v e s t i g a t i o n o f t h e problem by o u r
I n d u s t r i a l Hygiene D i v i s i o n , t h e f o l l o w i n g c o n c l u s i o n s were r e a c h e d :
1.
The s y s t e m s d e d u s t e d o n l y t w o - t h i r d s of t h e j u n c t i o n p o i n t s where d u s t i s
generated i n t o the a i r .
2.
The c a p a c i t i e s o f t h e v a r i o u s d u s t e x h a u s t s y s t e m s were c o n s i d e r a b l y lower
t h a n i n d i c a t e d i n t h e d e s i g n drawings. T h e r e f o r e , i n a d e q u a t e d u s t c o n t r o l
r e s u l t e d a t many of t h e p i c k up p o i n t s . The most s e v e r e example was t h e s y s t e m
d e s i g n e d t o d e d u s t t h e s i n t e r machine d i s c h a r g e , h o t s i n t e r v i b r o f e e d e r s , and
h o t f i n e s h a n d l i n g system. The s y s t e m moved o n l y a p p r o x i m a t e l y t h i r t y - f i v e
p e r c e n t (35%) of t h e a i r r e q u i r e d t o do t h e j o b p r o p e r l y .
3.
The d r y m u l t i p l e t u b e c y c l o n e c o l l e c t o r s were a p p r o x i m a t e l y s i x t y - f i v e p e r c e n t
(65%) e f f i c i e n t f o r t h e d u s t t h e y were a t t e m p t i n g t o c o l l e c t . T h i s means
t h i r t y - f i v e p e r c e n t (35%) of t h e a i r b o r n e d u s t w a s n o t c o l l e c t e d , b u t e x h a u s t e d
i n t o t h e atmosphere.
4.
The method of d i s p o s a l of c o l l e c t e d d u s t was n o t a d e q u a t e . I t was found t h a t
a s c r e w f e e d e r c a n n o t b e used t o mix w a t e r and d u s t . The w a t e r and d u s t mix
a c t s l i k e a g r i n d i n g compound and wears t h e s c r e w o u t i n j u s t a few weeks. I n
o r d e r t o keep t h e s c r e w f e e d e r s i n o p e r a t i o n , t h e y had t o b e o p e r a t e d d r y .
T h i s meant a p o r t i o n o f t h e c o l l e c t e d d u s t w a s e n t r a i n e d a t t h e p o i n t where i t
was d i s c h a r g e d o n t o t h e conveyor and a t e a c h j u n c t i o n f o l l o w i n g t h i s p o i n t .
5.
This w a s due t o t h e
The s i n t e r machine b u i l d i n g was found t o b e " a i r bound".
v e r y l a r g e volumes o f a i r e x h a u s t e d by t h e d e d u s t i n g s y s t e m s and t h e s i n t e r
machine i n d u c e d d r a f t f a n s . The r o o f v e n t i l a t i n g s y s t e m was i n a d e q u a t e t o make
up t h e e x h a u s t e d a i r . To make up t h e a i r d e f i c i e n c y , a l l windows were opened
and a d d i t i o n a l o p e n i n g s were made i n t h e s i d e of t h e b u i l d i n g . These o p e n i n g s
were e f f e c t i v e i n warm w e a t h e r , b u t c a u s e d e x c e s s i v e l y c o l d t e m p e r a t u r e s d u r i n g
the winter inside the building.
T h i s b u i l d i n g h o u s e s t h e mixing d i s c s and s i n t e r mix c o n v e y o r s , which h a n d l e
w e t m a t e r i a l . S e v e r e damage t o t h e equipment and e x t e n s i v e d e l a y s were i n c u r r e d as t h e m a t e r i a l f r o z e on conveyor p u l l e y s , c h u t e s , and mixing d i s c s due
t o below f r e e z i n g a i r b e i n g drawn i n t o t h e b u i l d i n g t o r e p l a c e a i r b e i n g exhaus ted
.
How c o u l d s u c h a n i n a d e q u a t e d e d u s t i n g s y s t e m b e d e s i g n e d and i n s t a l l e d ? A f t e r
a n a l y z i n g t h e s i t u a t i o n , t h e p r i m a r y answer would b e t h e l a c k of e x p e r i e n c e by t h e
c o n t r a c t o r i n t h e d e s i g n of t h e d u s t c o n t r o l v e n t i l a t i o n s y s t e m s i n a t t e m p t i n g t o d e d u s t
a l a r g e t h r e e s t r a n d s i n t e r p l a n t of more advanced d e s i g n . So, a d e f i n i t e p l a n of
a c t i o n had t o b e d e v e l o p e d f o r remedying t h e s e c a n d i t i o n s .
A f t e r c o n s u l t i n g w i t h Dust C o n t r o l Equipment M a n u f a c t u r e r s , ~ e s e a r c h ]and I n d u s t r i a l
Hygiene p e r s o n n e l and v i s i t i n g s e v e r a l B e n e f i c i a t i o n P l a n t s , i t was d e c i d e d t o r e d e s i g n
t h e d u s t c o n t r o l v e n t i l a t i o n s y s t e m , t o i n s t a l l a "wet" w a t e r s p r a y s y s t e m on t h e s i n t e r
p r o d u c t and f i n e s a r e a 3 and 4 , and t o i n s t a l l bag c o l l e c t o r s i n t h e d u s t e x h a u s t systems
i n area 2.
(See F i g u r e No. 1 ) I t was f e l t t h a t b o t h i n - p l a n t and community f u g i t i v e
d u s t c o u l d b e c o n t r o l l e d by t h e s e systems i f p r o p e r l y d e s i g n e d .
Wet Water Spray System
B e f o r e a t t e m p t i n g t o d i s c u s s t h e w a t e r s p r a y system, i t s h o u l d b e p o i n t e d o u t t h a t
v e n t i l a t i o n i s n e a r l y u n i v e r s a l l y a d a p t a b l e t o d u s t c o n t r o l problems, whereas s p r a y
systems have a somewhat l i m i t e d a r e a of a p p l i c a t i o n . C e r t a i n l y , s p r a y s have no a p p l i c a t i o n s where (1) t h e l i b e r a t e d d u s t i s h i g h l y t o x i c o r h a z a r d o u s , ( 2 ) t h e d u s t and
w a t e r a r e n o t c o m p a t i b l e , ( 3 ) t h e d u s t o r p r o c e s s i s a t e l e v a t e d t e m p e r a t u r e , and ( 4 )
t h e equipment o r p r o c e s s p r e c l u d e s t h e h a n d l i n g of any e x c e s s w a t e r .
The b a s i c t e c h n i q u e of a wet w a t e r s y s t e m i s t h e c o n t r o l l e d a p p l i c a t i o n of s m a l l
amounts of w a t e r s o l u t i o n a t s t r a t e g i c p o i n t s t o p r e v e n t t h e d u s t i n t h e s i n t e r from
becoming a i r b o r n e . The key t o e f f e c t i v e d u s t c o n t r o l i s t h e w e t t i n g a g e n t added t o t h e
w a t e r . I t i s u s u a l l y a s o l u t i o n of o r g a n i c s o l v e n t s , s u r f a c e a c t i v e a g e n t s , and s t a b i l i z e r s , which r e s e m b l e s a l i q u i d household d e t e r g e n t . When d i l u t e d w i t h w a t e r , 1 p a r t
t o 1 , 0 0 0 - 2,500 p a r t s w a t e r , depending on t h e p r o d u c t , t h e r e s u l t i n g s o l u t i o n h a s a
s u r f a c e t e n s i o n which i s o n l y a f r a c t i o n t h a t of w a t e r . T h i s e n a b l e s t h e w a t e r t o
b e t t e r wet t h e s i n t e r and p r e v e n t t h e l i b e r a t i o n of f i n e d u s t i n t o t h e a i r . The u s e of
t h e s e p r o d u c t s do n o t c o n s t i t u t e any h a z a r d t o p e r s o n n e l .
The equipment needed f o r a wet w a t e r s y s t e m i s r e l a t i v e l y s i m p l e and i n e x p e n s i v e
p r o v i d e d t h e r e i s a n a d e q u a t e s u p p l y of w a t e r , I t would i n c l u d e t h e f o l l o w i n g : (See
F i g u r e No. 2)
1.
Storage tank f o r wetting agent.
s t a l l a t i o n .)
(Could b e a 55 g a l l o n drum on a s m a l l i n -
2.
P r o p o r t i o n i n g pump and mixing c o n t a i n e r .
3.
S o l u t i o n ( w a t e r ) pump.
4.
Pipe l i n e t o d e s i r e d l o c a t i o n s .
5.
S o l e n o i d v a l v e s and l i m i t s w i t c h e s .
6.
S t r a i n e r f o r i n l e t w a t e r and e a c h s p r a y l o c a t i o n .
7.
Heat t r a c i n g o f l i n e s , i f l o c a t e d i n a f r e e z i n g a r e a .
Description
A pump house (See F i g u r e No. 3) w a s e r e c t e d on t h e ground which h o u s e s a 5 , 0 0 0 .
g a l l o n s t a i n l e s s s t e e l w e t t i n g a g e n t s t o r a g e t a n k , p r o p o r t i o n i n g and mixing c o n t a i n e r
The pumps a r e d r i v e n by twenty h o r s e
and two c e n t r i f u g a l pumps (one used f o r s t a n d - b y ) .
power motors and a r e r a t e d a t e i g h t y g a l l o n s p e r m i n u t e a t a p r e s s u r e of one hundred and
twenty p s i . The pump s e r v i c e s t h i r t y - s i x s p r a y h e a d e r s (each h e a d e r h a s from two t o
s i x s p r a y s ) a t e i g h t e e n (18) j u n c t i o n p o i n t s from t h e c o o l e r s t o t h e S i n t e r S t o r a g e B i n s .
The j u n c t i o n s covered i n c l u d e t h e s i n t e r , c o l d r e t u r n s , and h e a r t h l a y e r s y s t e m s . A l l
p i p e l i n e s a r e e l e c t r i c a l l y o r s t e a m h e a t t r a c e d and i n s u l a t e d . A s t r a i n e r i s l o c a t e d
i n t h e i n l e t w a t e r l i n e t o t h e pump s t a t i o n and s m a l l i n d i v i d u a l f i l t e r s a r e l o c a t e d a t
each j u n c t i o n p o i n t .
The s p r a y s a t each l o c a t i o n a r e a u t o m a t i c a l l y c o n t r o l l e d by a l i m i t s w i t c h and
s o l e n o i d v a l v e . I f t h e conveyor b e l t s t o p s , t h e s p r a y s s h u t o f f . I n c a s e a conveyor
i s r u n n i n g l i g h t , t h e s p r a y s w i l l n o t t u r n on u n t i l a n a d e q u a t e l o a d i s d e t e c t e d . I n
a d d i t i o n , depending on t h e amount of s o l u t i o n needed, i n d i v i d u a l s o l e n o i d v a l v e s a t
each header can b e t u r n e d on o r o f f manually from a remote c o n t r o l s t a t i o n .
Maintenance and O p e r a t i n g Problems
Maintenance: Routine maintenance i s accomplished primarily by t h e e q u i v a l e n t of one
m i l l w r i g h t , e i g h t (81, h o u r s p e r day, s e v e n days a week. H i s job f u n c t i o n s a r e i n s p e c t i o n
and minor r e p a i r s t o t h e f o l l o w i n g equipment:
1. Clean f i l t e r ' s a t each j u n c t i o n a t l e a t once p e r week.
2 . D a i l y check and c l e a n o r change a t o m i z i n g s p r a y n o z z l e s when n e c e s s a r y .
3 . I n s p e c t s p r o p o r t i o n i n g mechanism d a i l y .
4 . Packs main pump when n e c e s s a r y .
5. A d j u s t under b e l t c o n t r o l s w i t c h e s when n e c e s s a r y .
6 . R e p o r t s any unusual i r r e g u l a r i t i e s of system.
O c c a s i o n a l l y , t h e r e i s need f o r a d d i t i o n a l maintenance p e r s o n n e l t o r e p l a c e f r o z e n
l i n e s , when h e a t t r a c i n g f a i l s o r when t h e e l e c t r i c a l system does n o t f u n c t i o n p r o p e r l y .
G e n e r a l l y , t h e r e i s v e r y l i t t l e down time on t h e s p r a y s and t h e R and M i s c o n s i d e r e d
minor.
Operating:
The o p e r a t i n g problems f a l l i n t o f i v e c a t e g o r i e s :
1. Carry back from conveyors.
2 . Hot s i n t e r .
3 . Condensate.
4. Cold s c r e e n b l i n d i n g .
5 . Algae.
The f i n e w e t d u s t a d h e r i n g t o t h e conveyor b e l t caused e x c e s s " c a r r y back" of
m a t e r i a l which, i n a few d a y s , b u r i e d t h e r e t u r n r o l l e r s . Conventional b e l t s c r a p e r s
were n o t a d e q u a t e . Too many s p r a y s were b e i n g used a t t i m e s , t o t h e e x t e n t t h a t t h e
w a t e r s o l u t i o n was r u n n i n g o f f t h e s i n t e r o n t o t h e conveyor b e l t . G e n e r a l l y , t h i s
s i t u a t i o n h a s been remedied through a p e r s o n n e l t r a i n i n g and follow-up program, and
b e t t e r c o o l i n g of t h e s i n t e r .
S i n t e r t e m p e r a t u r e i s a n i m p o r t a n t f a c t o r i n t h e e f f e c t i v e n e s s of t h e s p r a y system
i n s u p p r e s s i n g a i r b o r n e - d u s t . A t s i n t e r t e m p e r a t u r e s o v e r 200°F, t h e d u s t s u p p r e s s i o n
system i s n o t e f f e c t i v e s i n c e t h e s i n t e r immediately d r y s a f t e r a p p l i c a t i o n . It i s
n e c e s s a r y t o m a i n t a i n s i n t e r t e m p e r a t u r e s a s low a s p r a c t i c a l i n o r d e r t o r e d u c e t h e
amount of w a t e r u s e d , and l e s s e n t h e e v a p o r a t i o n of w a t e r and w e t t i n g a g e n t . S i n t e r
t e m p e r a t u r e s were o r i g i n a l l y i n e x c e s s of 150 d e g r e e s F a h r e n h e i t a t normal o p e r a t i o n ,
which meant t h a t t h e s p r a y s were b e i n g u t i l i z e d f o r c o o l i n g a s w e l l a s d u s t s u p p r e s s i o n .
Cooler f a n c a p a c i t y was i n c r e a s e d s o t h a t p r e s e n t l y , t h e s i n t e r t e m p e r a t u r e d u r i n g normal
o p e r a t i o n i s 120°F o r l e s s .
During t h e w i n t e r months and humid w e a t h e r , e x c e s s i v e condensate developed i n t h e
unheated S c r e e n i n g S t a t i o n . Condensation i s caused b e c a u s e steam g i v e n o f f by t h e wet
s i n t e r r a i s e s t h e humidity above t h e dew p o i n t . T h i s problem h a s been g r e a t l y reduced
by t h e i n s t a l l a t i o n of t h r e e steam c o i l u n i t h e a t e r s t o r a i s e t h e ambient a i r t e m p e r a t u r e
and f o u r f i f t y - f o u r i n c h a x i a l flow e x h a u s t f a n s , r a t e d a t 63,000 CFM e a c h , t o e x h a u s t
t h e steam.
Because of t h e wet s i n t e r and c o n d e n s a t i o n , t h e a l l o y s t e e l c a s t s c r e e n p l a t e s
plugged. T h i s was of c o n s i d e r a b l e concern because i t i n c r e a s e d t h e " f i n e s " i n t h e
p r o d u c t t o t h e B l a s t Furnaces. The s c r e e n s were c l e a n e d "once p e r t u r n " (each e i g h t
h o u r s ) w i t h an a i r o p e r a t e d w e l d e r ' s c h i p p i n g hammer i n o r d e r t o m a i n t a i n p r o p e r s i z e
f o r t h e b l a s t f u r n a c e s . However, i t was a d i f f i c u l t and l a b o r consuming job.
Eventually,
by r e p l a c i n g t h e c a s t s c r e e n p l a t e s w i t h w i r e t y p e s c r e e n s , t h i s problem was r e s o l v e d .
Algae
During c o o l w e a t h e r , t h e a l g a e i n t h e l a k e w a t e r g e n e r a l l y a r e n o t a problem because
t h e y a r e n o t a c t i v e i n c o o l w a t e r . However, d u r i n g t h e summer months, when t h e w a t e r
warms u p , t h e "slimy j e l l y - l i k e " a l g a e p l u g up t h e f i l t e r s and n o z z l e s . Algae t h r i v e
on w e t t i n g a g e n t s ; b u t , t h e a d d i t i o n of a b i o c i d e s o l u t i o n t o t h e p r o p o r t i o n i n g t a n k f o r
a few h o u r s e a c h week d u r i n g t h e summer k i l l s t h e a l g a e a n d , i n e f f e c t , c l e a n s t h e f i l t e r s
and n o z z l e s and e l i m i n a t e s any s e r i o u s p l u g g i n g .
O p e r a t i n g Data
P r e s e n t r e c o r d s show t h a t twenty-five t o t h i r t y g a l l o n s of w e t t i n g a g e n t a r e consumed
p e r day. The r a t i o of w e t t i n g a g e n t t o w a t e r i s one t o t w e n t y - f i v e hundred ( 1 t o 2500).
The l a s t a i r samples t a k e n i n t h e l o c a t i o n s where s p r a y s were i n s t a l l e d , showed
t h a t d u s t c o n t a m i n a t i o n l e v e l s i n e i g h t y p e r c e n t of t h e l o c a t i o n s were below t h e a c c e p t e d
l i m i t of twenty m i l l i o n p a r t i c l e s p e r c u b i c f o o t of a i r f o r a working enviornment.
These samples were t a k e n b e f o r e improved c o o l i n g . P r e s e n t v i s u a l o b s e r v a t i o n s i n d i c a t e
t h a t a t l e a s t n i n e t y - f i v e p e r c e n t of t h e l o c a t i o n s a r e now w i t h i n t h e a c c e p t a b l e l i m i t .
Dust Exhaust V e n t i l a t i n g Systems
Description
For t h e d i s c h a r g e a r e a ( a r e a 2) (See F i g u r e No. 1 ) t h e h o t d u s t y l o c a t i o n i n a
s i n t e r p l a n t , a F i l t e r Bag House was e r e c t e d , n o r t h o f t h e c o o l e r s f o r each of t h e t h r e e
s t r a n d s . There a r e 1 8 p i c k up p o i n t s f o r each machine t h a t i n c l u d e t h e v i b r o f e e d e r s ,
h o t f i n e s h a n d l i n g system, and conveyors i n t h e a r e a t h a t h a n d l e s i n t e r mix p l u s h o t f i n e s
and r e c y c l e d d u s t .
Dust s e p a r a t i o n from a i r i s accomplished by p u l l i n g t h e d u s t l a d e n a i r i n t o t h e
e x h a u s t hoods a t v a r i o u s d u s t s o u r c e s and conveying i t through t h e d u c t system t o a bag
c o l l e c t o r c o n s i s t i n g o f e i g h t hundred and e i g h t y f i b e r g l a s s bags w i t h a n induced d r a f t
f a n . The bags a r e hung i n groups of e i g h t y - e i g h t i n t e n s e p a r a t e s e a l e d compartments
i n p a r a l l e l rows of f i v e each. D i r t y a i r e n t e r s t h e bags v i a e n t r y plenums (See F i g u r e
No. 4) a l o n g each s i d e of t h e "bag house" s t r u c t u r e and t h e n through s e p a r a t e hoppers
(where l a r g e r p a r t i c l e s of d u s t d r o p o u t ) l o c a t e d under each compartment. Clean a i r
l e a v e s t h e top of e a c h compartment and e n t e r s t h e c l e a n a i r plenum (through Valve B on
F i g u r e No. 4) which i n t u r n goes t o t h e I . D . f a n and o u t t h e d i s c h a r g e s t a c k t o t h e
atmosphere.
Each s e t of e i g h t y - e i g h t bags i s dumped o r c l e a n e d a t one hour and twenty minute
i n t e r v a l s . C l e a n i n g one compartment a t a time l e a v e s n i n e compartments o r seven hundred
and ninety-two bags s t i l l i n o p e r a t i o n and m a i n t a i n s a c l e a n d i s c h a r g e s t a c k a t a l l t i m e s .
I n t h e c l e a n i n g c y c l e , t h e a i r f l o w i s r e v e r s e d by c l o s i n g a n e l e c t r i c a l l y o r a i r o p e r a t e d
b u t t e r f l y v a l v e (Valve B on F i g u r e No. 4) i n t h e o u t l e t t o t h e c l e a n a i r plenum on t o p
and opening a s i m i l a r v a l v e (Valve A on F i g u r e No. 4) which a l l o w s a t m o s p h e r i c a i r t o
flow i n t o t h e compartment. The p r o c e d u r e r e v e r s e s t h e p r e s s u r e from i n s i d e t h e bag t o
t h e o u t s i d e , t h u s c o l l a p s i n g t h e bag and d i s l o d g i n g t h e d u s t c o a t i n g i n s i d e , p e r m i t t i n g
i t t o f a l l t o t h e hoppers below. The i n l e t and o u t l e t v a l v e s (A and B) a r e opened and
c l o s e d g r a d u a l l y t h e r e b y r e d u c i n g t h e p o s s i b i l i t y of mechanical damage t o t h e b a g s .
Dust from t h e hopper below t h e bags i s d i s c h a r g e d through a r u b b e r d r i b b l e v a l v e t o
a twenty-four i n c h wide, covered conveyor b e l t . The d u s t i s conveyed t o a n e i g h t c u b i c
f o o t hopper from which i t i s f e d d r y t h r o u g h a s c r e w f e e d e r t o a c e n t r i f u g a l d u s t w e t t e r .
The damp d u s t i s t h e n d i s c h a r g e d from t h e w e t t e r t o a s i n t e r mix conveyor below.
A t t h i s p o i n t , l e t u s c o n s i d e r t h e f o u r key components i n d e s i g n i n g a v e n t i l a t i n g
system.
Hoods (See F i g u r e No. 5) The hood d e s i g n i s t h e most i m p o r t a n t p a r t o f a s y s t e m t o cont r o l t h e d u s t a t t h e s o u r c e . The hood must e n c l o s e a s t i g h t l y a s p o s s i b l e t h e a r e a of
d u s t g e n e r a t i o n and b e d e s i g n e d t o p r o v i d e a movement of a i r o v e r t h e whole e n c l o s e d
a r e a . A i r f l o w t h r o u g h t h e hood s h o u l d b e o n l y enough t o move t h e v e r y f i n e d u s t . L a r g e r
p a r t i c l e s s e t t l e r a p i d l y and a r e n o t c o n s i d e r e d i m p o r t a n t .
-
Duct Work
The p u r p o s e o f t h e d u e t work i s t o t r a n s p o r t t h e d u s t - l a d e n a i r from t h e hood
t o t h e "bag house".
Duct d e s i g n s h o u l d b e a s s t r e a m l i n e d a s p o s s i b l e t o r e d u c e p r e s s u r e
l o s s e s . A minimum v e l o c i t y of 3,500 f e e t p e r m i n u t e s h o u l d b e m a i n t a i n e d t o p r e v e n t
s e t t l i n g of d u s t i n t h e d u c t .
C o l l e c t o r - The f u n c t i o n of a d u s t c o l l e c t o r i s t o remove d u s t p a r t i c l e s from t h e c o l l e c t e d
a i r s o t h a t t h e e f f l u e n t i n t h e d i s c h a r g e . s t a c k w i l l conform t o a i r p o l l u t i o n s t a n d a r d s
o r o r d i n a n c e s . However, u n l e s s t h e d u s t e x h a u s t s y s t e m i s p r o p e r l y d e s i g n e d t h e c o l l e c t o r
c a n n o t , by i t s e l f , b e e f f e c t i v e . It can o n l y c l e a n t h e a i r d e l i v e r e d t o i t . E x p e r i e n c e
a t Gary d e m o n s t r a t e s t h a t t h e f i l t e r bag d r y c o l l e c t o r i s v e r y e f f i c i e n t i n p e r f o r m i n g
t h i s function.
~ ~ ~ l i c a t of
i o "Bag
n
Houses" u s i n g s p e c i a l h i g h t e m p e r a t u r e r e s i s t a n t c l o t h a r e l i m i t e d
t o . c o n d i t i o n s where t h e t e m p e r a t u r e o f t h e g a s i s below 5 0 0 ' ~ and t h e m o i s t u r e l e v e l i s
s u c h t h a t no c o n d e n s a t i o n t a k e s p l a c e i n t h e s y s t e m . Temperature l i m i t a t i o n of f a b r i c s
c o n t r o l t h e maximum a i r t e m p e r a t u r e . F i b e r g l a s s w i l l w i t h s t a n d up t o f i v e hundred d e g r e e s
F a h r e n h e i t . O t h e r f a b r i c s a r e a v a i l a b l e f o r low t e m p e r a t u r e a p p l i c a t i o n .
G e n e r a l l y , t h e lower t h e a i r t o c l o t h r a t i o , t h e more e f f e c t i v e t h e c o l l e c t o r . A t
no time s h o u l d t h e r a t i o b e g r e a t e r t h a n 3.0 c u b i c f e e t of g a s p e r m i n u t e t o one s q u a r e
f o o t of c l o t h .
Improper a i r . d i s t r i b u t i o n through t h e bags h a s b e e n t h e c a u s e of many bag house
f a i l u r e s . Equal d i s t r i b u t i o n i s i m p o r t a n t s o t h a t e a c h b a g c a n b e a r i t s d e s i g n e d s h a r e
of t h e l o a d . Unequal d i s t r i b u t i o n c a u s e s p r e m a t u r e f a i l u r e o f a f f e c t e d b a g s b e c a u s e of
a b r a s i o n by h i g h v e l o c i t y d u s t . C o n s i d e r a b l e a t t e n t i o n s h o u l d b e g i v e n t o t h i s f a c t o r
d u r i n g d e s i g n , even t o t h e e x t e n t o f b u i l d i n g a model.
Fan and Motor - I f t h e f a n i s l o c a t e d on t h e c l e a n a i r s i d e of t h e d u s t c o l l e c t o r , a
v e r y e f f i c i e n t t y p e f a n c a n b e u t i l i z e d . Fan and motor s h o u l d b e s i z e d t o p r o v i d e d e s i g n
a i r f l o w a t a l l p i c k up p o i n t s and overcome a l l s y s t e m r e s i s t a n c e w i t h a n a l l o w a n c e of
20% ( o v e r d e s i g n ) f o r d e s i g n v a r i a b i l i t y o r f a c t o r o f s a f e t y .
Design and O p e r a t i n g Data
Volume of a i r :
Suction :
P r e s s u r e drop a c r o s s bags:
Number of h o p p e r s i n . c o l l e c t o r :
Bags p e r hopper:
T o t a l number of b a g s :
Bag S i z e :
Diameter :
Length :
Type bag :
Estimated l i f e of bag:
Bag p e r m e a b i l i t y :
172,000 CFM a t 2 5 5 ' ~
1 2 i n c h e s of w a t e r
4 inches of water
10
88
880
11-1/2 i n c h e s
32 f e e t 2-114 i n c h e s
Fiberglass
1 2 months - a c t u a l 1 7 months
1 2 t o 20 CFM/Sq. F t . of c l o t h
A i r to cloth ratio
A i r to cloth ratio
cleaning :
A i r temperature:
-
normal:
o n e compartment
T h e o r e t i c a l Design e f f i c i e n c y :
2.17 CFM/Sq. F t . o f c l o t h
2.41 CM/Sq. F t . of c l o t h
1 7 5 d e g r e e s F a h r e n h e i t t o 300 d e g r e e s Fahrenheit.
Excess of 99.0 p e r c e n t
Maintenance
Once a f a b r i c bag c o l l e c t o r i s p u t i n t o o p e r a t i o n , t h e key t o k e e p i n g i t r u n n i n g
p r o p e r l y i s r o u t i n e i n s p e c t i o n and maintenance of t h e bags. A manometer i s l o c a t e d a t
each compartment t o measure t h e p r e s s u r e d r o p a c r o s s t h e b a g s . An e x c e s s i v e l y h i g h o r
low r e a d i n g i n d i c a t e s a f a u l t i n t h e c l e a n i n g s y s t e m f o r a p a r t i c u l a r compartment.
Immediate s t e p s s h o u l d b e t a k e n t o c o r r e c t t h e i r r e g u l a r i t y .
R o u t i n e v i s u a l i n s p e c t i o n of t h e bags a r e made e a c h week d u r i n g t h e s i n t e r machine
s c h e d u l e d down t u r n . They a r e i n s p e c t e d f o r s m a l l h o l e s and wear, t e n s i o n , and t i g h t n e s s
of clamps a t b o t h e n d s . Bag t e n s i o n i s v e r y i m p o r t a n t f o r e f f i c i e n t c l e a n i n g of t h e a i r ,
dumping of t h e b a g s , and bag l i f e .
Not enough t e n s i o n c a u s e s e x c e s s f l a p p i n g and c r e a s i n g d u r i n g t h e dumping c y c l e .
The bag l i f e w i l l b e g r e a t l y i m p a i r e d by "super c l e a n i n g " of t h e bottom s e c t i o n . I n
a d d i t i o n , t h e c r u s t b u i l t up i n s i d e t h e bag i n t h e upper s e c t i o n may n o t b e b r o k e n which
w i l l c a u s e poor e f f i c i e n c y of t h e bag.
I f t h e bags a r e too t i g h t , t h e f a b r i c w i l l b e
s t r e s s e d and c a u s e p r e m a t u r e f a i l u r e . A l s o , v e r y poor c l e a n i n g w i l l b e o b t a i n e d b e c a u s e
t h e r e i s n o t enough f l e x i n g .
The p r o p e r t e n s i o n i s j u s t enough t o form s e v e r a l small c r e v i c e s s o t h a t t h e bag
p e r i p h e r y t a k e s t h e s h a p e of a s t a r d u r i n g t h e c l e a n i n g c y c l e . A t Gary, we a r e u s i n g
f i b e r g l a s s bags t o c o l l e c t h o t s i n t e r d u s t , u t i l i z i n g a t e n s i o n of 80 l b s . / s q . i n c h .
T h i s p o i n t i s s t r e s s e d b e c a u s e , depending on t h e f a b r i c , weave, and t y p e of d u s t , i t
c o u l d r a n g e from 30 t o 120 l b s . / s q . i n c h .
Whenever e x p e c t e d l i f e of t h e b a g s h a s been r e a c h e d and s i g n s of wear s t a r t t o
d e v e l o p i n s e v e r a l of t h e b a g s , Garys' p r a c t i c e i s t o s t a r t changing a l l of them, one
compartment a t a t i m e . T h i s t a k e s a p p r o x i m a t e l y e i g h t weeks, w i t h t h r e e q u a l i f i e d pers o n n e l working a normal work week. By f o l l o w i n g t h i s p r o c e d u r e , i t i s n o t l i k e l y t h a t
a l l t h e b a g s w i l l f a i l a t t h e same t i m e , making t h e c o l l e c t o r i n o p e r a t i v e .
A f a c i l i t y (See F i g u r e No. 6 ) t h a t o p e r a t e s c o n t i n u o u s l y i s n o t maintenance f r e e .
T h e r e a r e many e l e c t r i c a l and m e c h a n i c a l components t o m a i n t a i n i n a n a u t o m a t i c system.
Of p r i m a r y c o n c e r n i s t h e p r o p e r f u n c t i o n i n g of t h e i n l e t and o u t l e t b u t t e r f l y v a l v e s
and t i m e r t h a t c o n t r o l s t h e v a l v e s . I n a d d i t i o n , t h e e n t i r e s y s t e m must b e m a i n t a i n e d
a s t i g h t a s p o s s i b l e by r e p l a c i n g seals and p a t c h i n g h o l e s i n d u c t s when n e c e s s a r y .
T h i s month, A p r i l , 1971, t h e f i r s t c o l l e c t o r h a s been i n o p e r a t i o n f o r f o u r and
one-half y e a r s w i t h o u t any major f a i l u r e s . The environment i s c l e a n and t h e d i s c h a r g e
s t a c k h a s no "plume".
The second s y s t e m s t a r t e d i n J u l y of 1968 and t h e t h i r d i n February
of 1969.
Make-up A i r
1
A s mentioned e a r l i e r , i n any l a r g e e x h a u s t a i r s y s t e m i t i s v e r y i m p o r t a n t t h a t
more a i r i s n o t t a k e n o u t of a b u i l d i n g t h a n c a n b e s u p p l i e d . A common m i s c o n c e p t i o n i n
b u i l d i n g d e s i g n f o r a n e x h a u s t g a s p r o c e s s s u c h as a s i n t e r machine o r a d u s t e x h a u s t
s y s t e m , i s t h a t enough a i r w i l l i n f i l t r a t e from windows and d o o r s and c r a c k s i n t h e
building.
(At o u r No. 3 S i n t e r i n g P l a n t , n e a r l y two m i l l i o n CFM a r e removed from t h e
b u i l d i n g by t h e t h r e e s i n t e r machines induced d r a f t f a n s and t h e t h r e e d u s t c o l l e c t o r
I n t h e d e s i g n of s u c h a s y s t e m , c o n s i d e r a t i o n must b e g i v e n f o r a d e q u a t e "make
fans.)
up" a i r p r o p e r l y d i s t r i b u t e d . The e f f e c t i v e n e s s of t h e e x h a u s t g a s s y s t e m may b e re-
duced i f t h i s i s n o t done. We have t a k e n some s t e p s t o c o r r e c t t h e s u p p l y a i r d e f i c i e n c y
problem and a d d i t i o n a l measures a r e c o n t e m p l a t e d .
Summary
1.
I n a s i n t e r i n g p l a n t , a w e l l designed d u s t c o n t r o l system coupled w i t h e f f i c i e n t
c o l l e c t o r s a r e n e c e s s a r y f o r i n d u s t r i a l h y g i e n e p u r p o s e s , community r e l a t i o n s
and p r o t e c t i o n of equipment.
2.
Before s e l e c t i n g a d u s t c o n t r o l s y s t e m , t h e f o l l o w i n g s h o u l d b e c o n s i d e r e d ! t y p e
and s i z e of d u s t , t e m p e r a t u r e of m a t e r i a l o r g a s , e f f i c i e n c y , i n p l a n t a n d / o r
community problems, and government c o n t r o l s . I n a d d i t i o n , i t would b e a d v i s a b l e
t o c o n s u l t w i t h e x p e r t s and v i s i t o t h e r p l a n t s making t h e same p r o d u c t and h a v i n g
related dust control f a c i l i t i e s .
3.
Wet w a t e r s p r a y s a r e most e f f e c t i v e when t h e t e m p e r a t u r e of t h e m a t e r i a l i s
above f r e e z i n g and below 120 d e g r e e s F a h r e n h e i t . Excess w a t e r s o l u t i o n c a u s e s
clean-up problems b e c a u s e of carry-back of f i n e m a t e r i a l under t h e conveyor
belt return idlers.
4.
F i l t e r bag c o l l e c t o r s a r e one of t h e most e f f i c i e n t t y p e a i r c l e a n e r s . However,
t h e y s h o u l d n o t b e used i f t h e h u m i d i t y c o u l d exceed t h e dew p o i n t o r i f t h e a i r
t e m p e r a t u r e exceeds 500 d e g r e e s F a h r e n h e i t . M o i s t u r e c r e a t e s build-up and s e a l s
t h e bags and d u c t s . Bag f a b r i c s w i l l n o t t a k e t e m p e r a t u r e s o v e r 500 d e g r e e s
Fahrenheit.
5.
The p o s s i b i l i t y t h a t "make-up" a i r may b e needed f o r a l a r g e v e n t i l a t i n g e x h a u s t
gas system should not b e overlooked.
References
1. I n d u s t r i a l Hygiene H e a l t h S e r v i c e s , U n i t e d S t a t e s S t e e l , Survey R e p o r t , "Wetting
Agents f o r S i n t e r P l a n t Dust C o n t r o l " , September, 1964.
2. subcommittee, United S t a t e s S t e e l O p e r a t i n g Committee, S i n t e r i n g , "Dust C o n t r o l
S p e c i f i c a t i o n s and Recommendations f o r Ore B e n e f i c i a t i o n P l a n t s " , September 1, 1960.
3. U n i t e d S t a t e s S t e e l C o r p o r a t i o n , Gary S t e e l Works, Gary, I n d i a n a , "Operating
I n s t r u c t i o n s f o r F a b r i c Type Dust C o l l e c t o r f o r #1 S i n t e r Machine Dust C o l l e c t i o n System
a t S i n t e r i n g P l a n t No. 3", American B r i d g e D i v i s i o n Order Numbers C-8400-09, Gary S t e e l
Works Order No. 154-86162-56.
4 . United S t a t e s S t e e l C o r p o r a t i o n , ARL R e f e r e n c e Number 30.008-006, "Performance
T e s t of Bag House Dust C o l l e c t o r a t Gary Works, No. 3 S i n t e r P l a n t " , March 21, 1967.
.
Figure 1
Figure 4
Figure 2
Figure 5
Figure 3
Figure 6
WET W A T E R
SPRAY SYSTEM