[19

Europaisches Patentamt

European Patent Office

Office europeen des brevets © Publication number: 0 0 9 9 1 7 6

A 1

© EUROPEAN PATENT APPLICATION

© Application number: 83303227.9

© Date of filing: 03.06.83

© Int. CI.3: B 01 J 2 / 0 4 C 05 C 1/02, C 05 C 9 / 0 0

© Priority: 01.07.82 US 394297

© Date of publication of application: 25.01.84 Bulletin 84/4

© Designated Contracting States: BE DE FR GB IT NL

© Applicant: Lerner, Bernard J. 727 Orchard Hill Drive Pittsburgh Pennsylavania 15238(US)

© Inventor: Lerner, Bernard J. 727 Orchard Hill Drive Pittsburgh Pennsylavania 15238(US)

@ Representative: JENSEN & SON 8 Fulwood Place High Holborn London WC1V6HG(GB)

© Prilling.

The emission of fumes is suppressed from a prilling tower for producing prills of ammonium nitrate or urea by conducting particles from a spray of a melt of the material countercurrent through a stream of air. The spray of the material, as it leaves the prilling head is passed through a stagnant atmosphere of ammonia. In addition, the particles of the spray are coated with ammonia and their cooling by the countercurrent air stream is accelerated. To produce the ammonia atmosphere, a shroud (29) is provided about the spray nozzle or nozzles (21) into which gaseous ammonia is injected.

B a c k g r o u n d o f t h e I n v e n t i o n

T h i s i n v e n t i o n r e l a t e s to t he g r a n u l a t i o n o f

m a t e r i a l s and has n a r t i c u l a r r e l a t i o n s h i p to t h e f o r m a t i o n

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

s p h e r i c a l p a r t i c l e s of ammonium n i t r a t e and u r e a f rom m e l t s

of t h e s e m a t e r i a l s . The s p h e r i c a l p a r t i c l e s a r e c a l l e d

p r i l l s and t he f o r m a t i o n of p r i l l s f rom t he m e l t s i s c a l l e d

p r i l l i n g . P r i l l s of ammonium n i t r a t e and u r e a a r e u s e d f o r

a g r i c u l t u r a l f e r t i l i z e r . Ammonium n i t r a t e and u r e a a r e t h e

p r i n c i p a l t y p e s of n i t r o g e n f e r t i l i z e r in c u r r e n t l a r g e -

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

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

w i t h p r i l l i n g of ammonium n i t r a t e and u r e a to f o r m p r i l l s

w i t h r e s p e c t to w h i c h i t has u n i q u e a d v a n t a g e s . I t i s t o

be u n d e r s t o o d t h a t to t h e e x t e n t t h a t t h i s i n v e n t i o n i s

a d a p t a b l e to o t h e r m a t e r i a l s and in o t h e r a r e a s , s u c h a d a p -

t a t i o n i s w i t h i n t he s c o p e of e q u i v a l e n t s of t h i s a p p l i c a t i o n ,

and any p a t e n t wh ich may i s s u e on or as a r e s u l t t h e r e o f a s

s u c h e q u i v a l e n c e i s i n t e r p r e t e d and d e f i n e d in G r a v e r T a n k

& M a n u f a c t u r i n g Co. v. L i n d e A i r P r o d u c t s C o . , 70 S C t . 854

( 1 9 5 0 ) .

In c o n v e n t i o n a l f e r t i l i z e r p r i l l i n g o p e r a t i o n s ,

m o l t e n ammonium n i t r a t e or u r e a i s s p r a y e d c o u n t e r c u r r e n t t o

a s t r e a m of a i r in a r e l a t i v e l y t a l l empty t o w e r , and i s

c o o l e d by the a i r and s o l i d i f i e d and d r i e d so t h a t p r i l l s a r e

p r o d u c e d . The a i r may be f o r c e d t h r c u r h the t o w e r by f a n s ,

or n a t u r a l d r a f t may be e m p l o y e d to s e c u r e a d e q u a t e a i r

c o u n t e r f l o w . In some p r i l l i n g t o w e r s , a u x i l i a r y a i r may b e

l o c a l l y in c o n c u r r e n t f l o w w i t h t h e m o l t e n - p a r t i c l e f l o w ;

in t h i s c a s e t h e r e i s a l s o m a j o r a i r f l ow c o u n t e r c u r r e n t

to t he p a r t i c l e f l o w .

O t h e r m e t h o d s of g e n e r a t i n g s p h e r i c a l s o l i d

p a r t i c l e s i n c l u d e s p h e r o i d i z e r s , pan g r a n u l a t o r s a n d

f l u i d i z e d bed t e c h n i q u e s . In t h e s e l a t t e r m e t h o d s , l i q u i d

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

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

m o t i o n and a r e s i m u l t a n e o u s l y c o o l e d and d r i e d by e x p o s u r e

to an a i r s t r e a m .

S p r a y n o z z l e s of v a r i o u s t y p e s have b e e n u s e d t o

i n i t i a l l y form and d i s p e r s e t h e m o l t e n f e r t i l i z e r i n t o d r o p -

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

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

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

b u c k e t s , and v i b r a t i n g o r i f i c e p l a t e s . In a l l c a s e s , h o w e v e r ,

m o l t e n m a t e r i a l i s f e d to one or more such d i s p e r s i o n d e v i c e s ,

so a r r a n g e d as to d i s p e r s e t h e m o l t e n d r o p s more or l e s s

u n i f o r m l y o v e r t h e c r o s s - s e c t i o n a l a r e a of t h e p r i l l t o w e r .

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

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

n i t r a t e or u r e a g e n e r a t e s v i s i b l e fumes w h i c h a r e a s e r i o u s

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

in fume f o r m a t i o n i n c l u d e b o t h s i m p l e c o n d e n s a t i o n of t h e

s u b l i m e d v a p o r s on c o o l i n g , and t h e p o s s i b l e r e c o m b i n a t i o n

f rom the v a p o r p h a s e of t h e c h e m i c a l p r o d u c t s r e s u l t i n g f r o m

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

In an a r t i c l e e n t i t l e d , "Vapor P r e s s u r e of Ammonium

l J i t r a t e , " p u b l i s h e d in t h e J o u r n a l of C h e m i c a l and E n g i n e e r i n g

D a t a , Vol . 7, No. 2, p a g e s 2 2 7 - 2 2 8 , A p r i l 1 9 6 2 , J . D . B r a n d n e r ,

M.M. J u n k , J .W. L a w r e n c e and J. R o b i n s s u g g e s t e d t h a t b o t h

s o l i d and m o l t e n ammonium n i t r a t e v a p o r i z e p r i m a r i l y b y

d i s s o c i a t i o n i n t o ammonia and n i t r i c a c i d . T h i s r e a c t i o n

may b e r e v e r s i b l e and t h e t h e o r e t i c a l b a c k - r e a c t i o n t o

ammonium n i t r a t e f rom t h e c o o l e r v a p o r p h a s e may p o s s i b l y

f o r m a s u b m i c r o n a e r o s o l fume of ammonium n i t r a t e s o l i d s .

A p a r a l l e l r e a c t i o n may be w r i t t e n f o r t h e c a s e of u r e a

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

s o l u t i o n , to p o s s i b l e d i s s o c i a t i o n v a p o r p r o d u c t s of a m m o n i a

and o r g a n i c a c i d s s u c h as i s o c y a n u r i c a c i d . T h e s e a r e c o n -

j e c t u r a l m e c h a n i s m s of fume f o r m a t i o n , f o r m u l a t e d to e x p l a i n

t h e a p p a r e n t e x p o n e n t i a l i n c r e a s e in fume f o r m a t i o n w i t h i n -

c r e a s i n g t e m p e r a t u r e s . I t i s n o t i n t e n d e d t h a t t h e i r m e n t i o n

h e r e s h o u l d in any way a f f e c t t h i s a p p l i c a t i o n or a n y p a t e n t

w h i c h may i s s u e on or as a r e s u l t t h e r e o f .

In U.K. P a t e n t No. 1 , 2 0 8 , 8 5 0 , H .E . Todd d i s c l o s e s

t h e i n h i b i t i o n of fumes f r o m h o t ammonium n i t r a t e v a p o r b y

a d d i n g ammonia to t he a i r u s e d to c o o l a n d / o r d r y or s o l i d i f y

h o t s o l u t i o n s of ammonium n i t r a t e . Todd s t a t e s t h a t " t h e

d e s i r e d amount of ammonia i s i n j e c t e d i n t o t h e i n e r t g a s

s t r e a m b e f o r e t he gas c o n t a c t s t h e ammonium n i t r a t e . " B r a n d -

n e r , e t a l . t e a c h e s t h a t "by p a s s i n g ammonia w i t h n i t r o g e n

t h r o u g h a s a m p l e of ammonium n i t r a t e . . . w i t h b o t h s o l i d a n d

l i q u i d ammonium n i t r a t e , t h e w e i g h t l o s s p e r l i t e r of n i t r o -

gen p a s s e d t h r o u g h t h e s a m p l e i s r e d u c e d to a f r a c t i o n o f

i t s m a g n i t u d e in t he a b s e n c e of a m m o n i a . "

T h e d a t a p r e s e n t e d by Todd in U.K. P a t e n t No. 1 , 2 0 8 , 8 5 0

on ammonium n i t r a t e fume s u p p r e s s i o n by ammonia a d d i t i o n t o

a i r c o v e r s t he r a n g e of 220° F. to 2770 F. T h e s e d a t a w e r e

p r e s e n t e d in g r a p h i c a l form and show t h a t , at 2440 F . , a

c o n c e n t r a t i o n of 0 .083% by v o l u m e NH3 in a i r was r e q u i r e d

f o r fume s u p p r e s s i o n , w h i l e a t 2770 F. ammonium n i t r a t e

t e m p e r a t u r e , a 75% r e d u c t i o n in fume l e v e l r e q u i r e d a c o n -

c e n t r a t i o n of 0 .29% NH3 by v o l u m e in a i r . The t e m p e r a t u r e

r a n g e ( t o 277° F . ) c o v e r e d by t h e Todd d a t a i s no t c h a r a c t e r -

i s t i c or r e p r e s e n t a t i v e of t h e ammonium n i t r a t e p r i l l i n g

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

ium n i t r a t e and u r e a n o r m a l l y t a k e s p l a c e i n d u s t r i a l l y a t

t e m p e r a t u r e l e v e l s in e x c e s s of t h e m e l t i n g p o i n t s of t h e s e

m a t e r i a l s , w h i c h a r e 337° F. and 271° F . , r e s p e c t i v e l y .

I n d u s t r i a l p r i l l i n g t e m p e r a t u r e s f o r ammonium n i t r a t e a r e

g e n e r a l l y in t he r a n g e of 345° F. to 380° F . , and a t t h e s e

t e m p e r a t u r e s , t h e c o n c e n t r a t i o n of NH3 in a i r r e q u i r e d f o r

any s i g n i f i c a n t fume s u p p r e s s i o n b e c o m e s u n e c o n o m i c a l l y

l a r g e . For e x a m p l e , i t h a s b e e n e s t i m a t e d t h a t f o r a n

ammonium n i t r a t e t e m p e r a t u r e of 380° F. an NH3 c o n c e n t r a t i o n

of 1.5% w o u l d be r e q u i r e d f o r 80% fume s u p p r e s s i o n , and 6%

NH3 c o n c e n t r a t i o n f o r 90% s u p p r e s s i o n . For a t y p i c a l a m m o n -

ium n i t r a t e p r i l l i n g t o w e r p r o d u c i n g 1 0 0 0 t o n s / d a y o f p r i l l s ,

u s i n g 2 0 0 , 0 0 0 CFM of f o r c e d a i r f l o w , t h e 6% by v o l u m e N H 3

r e q u i r e m e n t i s e q u a l t o 17 t o n s / h r of NH3. To a v o i d l o s i n g

t h i s much NH3 to t h e e x h a u s t a i r , t he NH3 w o u l d have to b e

s c r u b b e d ou t of t h e e x h a u s t a i r . I f HNO3 s o l u t i o n i s u s e d

f o r a b s o r p t i o n , a m in imum of 6 3 . 2 t o n s of HNO3 p e r h o u r i s

n e e d e d to n e u t r a l i z e t h e NH3. T h i s w o u l d b e e q u i v a l e n t t o

m a n u f a c t u r i n g more t h a n 80 t o n s / h r of ammonium n i t r a t e i n

in t h e e x h a u s t a i r s c r u b b e r , or 1925 t o n s / d a y , w h i c h i s

a l m o s t d o u b l e t he a m o u n t of t h e i n i t i a l p l a n t c a p a c i t y . At

1.5% NH3 by v o l u m e , c o r r e s p o n d i n g to 80% fume s u p p r e s s i o n ,

8500 l b s / h r of NH3 w o u l d be n e e d e d , as w o u l d 1 5 . 8 t o n s o f

HNO3/hr f o r n e u t r a l i z a t i o n . I t i s t h e r e f o r e c l e a r t h a t t h e

N H 3 f e e d r a t e s and the a s s o c i a t e d s c r u b b i n g l o a d s and l i m i t s

t h a t a re n e e d e d to s u p p r e s s fume f o r m a t i o n in t h e p r i l l i n g

o p e r a t i o n by t h e m e t h o d of Todd a r e i m p r a c t i c a l and u n e c o n o -

mic at t e m p e r a t u r e s in e x c e s s of t h e p r i l l m a t e r i a l m e l t

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

s a r i l y u s e d in p r i l l i n g .

I t i s an o b j e c t of t h i s i n v e n t i o n to o v e r c o m e d r a w -

b a c k s and d i s a d v a n t a g e s of t h e a b o v e - d e s c r i b e d p r i o r a r t

and to p r o v i d e a p r a c t i c a l p r i l l i n g m e t h o d in whose p r a c t i c e

fumes s h a l l be s u p p r e s s e d e c o n o m i c a l l y by use of ammon ia i n

r e l a t i v e l y low q u a n t i t i e s . I t i s a l s o an o b j e c t of t h i s

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

and e c o n o m i c m e t h o d .

In a c c o r d a n c e w i t h t h i s i n v e n t i o n , a m e t h o d i s p r o -

v i d e d in whose p r a c t i c e t h e r e i s e s t a b l i s h e d and m a i n t a i n e d

a q u i e s c e n t z o n e of p u r e , or h i g h l y c o n c e n t r a t e d , NH3 d i r e c t -

ly b e l o w and in c o n t a c t w i t h t h e m o l t e n ammonium n i t r a t e o r

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

s p r a y , c a u s i n g t h e s p r a y p a r t i c l e s to be f o r m e d i n , a n d

i n i t i a l l y f a l l t h r o u g h an NH3, or N H 3 - r i c h , gas z o n e . T h i s

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

u n d e r t he s p r a y head by means of an o u t e r s h r o u d or b e l l

whose s k i r t e x t e n d s b e l o w and c o n t i g u o u s to t h e b o t t o m o f

t h e m o l t e n f e r t i l i z e r s p r a y n o z z l e or d i s p e r s i o n d e v i c e .

Ammonia gas or an a t m o s p h e r e e n r i c h e d in ammonia and c o n t a i n -

ing more t h a n 50% by v o l u m e a m m o n i a i s f ed to t h i s s h r o u d

or b e l l . A l t h o u g h any a m m o n i a - r i c h gas c o n t a i n i n g more t h a n

50% by v o l u m e may be e m p l o y e d , p a r t i c u l a r l y i f a w a s t e g a s

of t h i s c o m p o s i t i o n is a v a i l a b l e , i t i s p r e f e r a b l e to u s e

ammonia gas of 95 to 100% ammon ia c o n c e n t r a t i o n . Gas s t r e a m s

of t he l a t t e r c o m p o s i t i o n a r e n o r m a l l y a v a i l a b l e in a f e r t i -

l i z e r p l a n t a t s u p e r - a t m o s p h e r i c p r e s s u r e s , or a l t e r n a t e l y ,

a r e e a s i l y g e n e r a t e d f rom l i q u i d a m m o n i a . B e c a u s e a m m o n i a

is l e s s d e n s e t h a n a i r , t h e s h r o u d i n g of t h e m o l t e n m a t e r i a l

s p r a y n o z z l e p r o v i d e s f o r t h e e s t a b l i s h m e n t of t h e d e s i r e d

s t a b l e zone of r e l a t i v e l y q u i e s c e n t ammonia by t r a p p i n g t h e

ammonia u n d e r t h e s h r o u d by r e a s o n of d e n s i t y d i f f e r e n t i a l

r e l a t i v e to t h e a i r o u t s i d e t h e s h r o u d . A d d i t i o n a l l y , t h e

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

t h e m o l t e n p r i l l and t h i s a u g m e n t s t h e i n h e r e n t m o l e c u l a r

w e i g h t g a s d e n s i t y d i f f e r e n c e r e l a t i v e to a i r . The a m m o n i a

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

s p r a y n o z z l e w h e r e t h e h o t t e s t m a t e r i a l i s e m i t t e d and i s

t h u s h e a t e d to a h i g h e r d e g r e e t h a n t h e a i r b e l o w or o u t s i d e

t h e s h r o u d .

In some p r i l l i n g t o w e r s , a p l u r a l i t y of s p r a y

n o z z l e s or d i s p e r s i o n d e v i c e s , as many as 20 or m o r e , may b e

p r o v i d e d . In s u c h t o w e r s , a s i n g l e s h r o u d may be p r o v i d e d

f o r t h e a s s e m b l y of s p r a y n o z z l e s or d i s p e r s i o n d e v i c e s , o r

s e v e r a l s h r o u d s may be p r o v i d e d , e a c h f o r s e v e r a l of t h e

s p r a y n o z z l e s or d i s p e r s i o n d e v i c e s . A s i n g l e s h r o u d i s

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

s p r a y n o z z l e or d i s p e r s i o n d e v i c e .

W h e t h e r fume f o r m a t i o n o c c u r s b e c a u s e of d i s s o c i a t i o n /

r e c o m b i n a t i o n , v a p o r p r e s s u r e , s u b l i m a t i o n / c o n d e n s a t i o n , o r

o t h e r m e c h a n i s m s , t he t e n d a n c e to form fumes i n c r e a s e s w i t h

i n c r e a s i n g t e m p e r a t u r e . By w h a t e v e r s u p p r e s s i o n m e c h a n i s m ,

e x p o s u r e of t he h o t t e s t ammonium n i t r a t e or u r e a m e l t t o

t h e p u r e or e n r i c h e d a m m o n i a a t m o s p h e r e c o m p l e t e l y s u p p r e s s e s

fume f o r m a t i o n at t h i s z o n e . The q u a n t i t y of ammonia r e -

q u i r e d f o r a c c o m p l i s h i n g t o t a l fume s u p p r e s s i o n by use o f

a t r a p p e d q u i e s c e n t a t m o s p h e r e i s s m a l l c o m p a r e d to t he f l o w

of c o u n t e r c u r r e n t c o o l i n g p r i l l t o w e r a i r . I t i s a l s o s m a l l

r e l a t i v e to t h e amoun t of ammonia r e q u i r e d f o r t h e a i r d i l u -

t i o n m e t h o d of Todd . The l a t t e r m e t h o d p r e s e n t s a d i l u t e d

l o w - c o n c e n t r a t i o n gas s t r e a m u n i f o r m l y to t h e s p r a y o v e r i t s

e n t i r e d r o p p a t h in t h e p r i l l t o w e r , o v e r w h i c h t h e s p r a y

t e m p e r a t u r e v a r i e s f rom m o l t e n l i q u i d t e m p e r a t u r e s as h i g h

as 3 8 0 ° F . a t t h e s p r a y h e a d e r to 200° F. at t he b o t t o m o f

t h e t o w e r . I t has b e e n r e a l i z e d in a r r i v i n g at t h i s i n v e n t i o n

t h a t b e c a u s e t h e a m m o n i a - a i r c o n c e n t r a t i o n r e q u i r e m e n t s f o r

fume s u p p r e s s i o n v a r y w i t h s p r a y t e m p e r a t u r e , w i t h t h e m a x i -

mum ammonia c o n c e n t r a t i o n s b e i n g r e q u i r e d f o r t h e h o t t e s t

s p r a y , T o d d ' s a i r d i l u t i o n m e t h o d u s e s u n e d o n o m i c a l a n d

e x c e s s i v e a m o u n t s of ammonia to a c h i e v e s u p p r e s s i o n f o r t h e

h o t t e s t top p o r t i o n of t he t o w e r . A l t e r n a t e l y , T o d d ' s

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

a v e r a g e ammon ia c o n c e n t r a t i o n s w h i c h i n h i b i t fume f o r m a t i o n

.in t h e l o w e r and c o o l e r p o r t i o n of t h e p r i l l t o w e r , bu t n o t

a t t h e h o t t e r u p p e r r e g i o n s .

In t h e p r a c t i c e of t h i s i n v e n t i o n , t h e h o t t e s t

s p r a y is e x p o s e d to t h e h i g h e s t a m m o n i a c o n c e n t r a t i o n . I n

f a l l i n g t h r o u g h and out of t h e t r a p p e d zone of a m m o n i a

c r e a t e d by t h e m e t h o d of t h i s i n v e n t i o n , t h e s p r a y p a r t i c l e s

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

a m m o n i a . The p a r t i c l e s a re t h u s " c o a t e d " or e n v e l o p e d b y

a g a s e o u s s u r f a c e l a y e r of a m m o n i a . T h i s p e n o m e n o n i s

s i m i l a r to t h a t e n c o u n t e r e d in h i r h - d i v i n g i n t o w a t e r , w h e r e i n

t he d i v e r on e n t e r i n g the w a t e r c a r r i e s w i t h him an e n t r a i n e d

l a y e r of a i r . The c o n c e n t r a t i o n of ammonia in t h e l a m i n a r

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

o n l y by t h e m o l e c u l a r d i f f u s i o n of ammonia i n t o t h e s u r r o u n -

d i n g a i r z o n e , w h i c h i s a s l o w p r o c e s s , and by c o n v e c t i v e

h e a t t r a n s f e r . H o w e v e r , as t h e s p r a y c o o l s , t h e a m m o n i a

c o n c e n t r a t i o n r e q u i r e d f o r fume s u p p r e s s i o n d e c r e a s e s , s o

t h e two e f f e c t s of l o s s of ammonia w i t h d i s t a n c e of f a l l o f

s p r a y and d e c r e a s i n g t e m p e r a t u r e s e r v e to c o u n t e r b a l a n c e

e a c h o t h e r . The a c c e l e r a t i o n of t he c o o l i n g of t h e s p r a y

i s an a d d i t i o n a l a d v a n t a g e of t h e i n v e n t i o n .

B r i e f D e s c r i t i o n o f D r a w i n g s

F o r a b e t t e r u n d e r s t a n d i n g of t h i s i n v e n t i o n , b o t h

as to i t s o r g a n i z a t i o n and as to i t s m e t h o d of o p e r a t i o n ,

t o g e t h e r w i t h a d d i t i o n a l o b j e c t s and a d v a n t a g e s t h e r e o f ,

r e f e r e n c e i s made to t h e f o l l o w i n g d e s c r i p t i o n , t a k e n i n

c o n n e c t i o n w i t h t h e a c c o m p a n y i n g d r a w i n g s , in w h i c h :

F i g . 1 i s a d i a g r a m m a t i c v i ew s h o w i n g a p r i l l i n g

t o w e r in a c c o r d a n c e w i t h t h i s i n v e n t i o n w h i c h i s u s e d in t h e

p r a c t i c e of t h i s i n v e n t i o n a n d c o n s t i t u t e s an e m b o d i m e n t o f

t h i s i n v e n t i o n ;

F i g . 2 i s a f r a g m e n t a l d i a g r a m m a t i c v i e w i l l u s t r a -

t i n g t h e o p e r a t i o n of t h e p r i l l i n g head or s p r a y n o z z l e f o r

t h e m o l t e n m a t e r i a l in t h e p r a c t i c e of t h i s i n v e n t i o n ;

F i g . 3 i s a f r a g m e n t a l v i e w of t h e p o r t i o n of t h e

p r i l l i n g t o w e r shown in F i g . 1, in t h e c i r c l e i n o f F i g . 1 ,

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

F i g . 4 i s a f r a g m e n t a l v iew s h o w i n g , in t he r e c -

t a n g l e IV of F i g . 3, t he r e l a t i o n s h i p b e t w e e n t h e a m m o n i a

g a s , m o l t e n f e r t i l i z e r s p r a y and a i r :

F i g s . 5 and 6 a r e d i a g r a m m a t i c v i e w s s h o w i n g s h r o u d s

wh ich a r e u s a b l e in t he p r a c t i c e of t h i s i n v e n t i o n ;

P i g . 6 is a d i a g r a m m a t i c p l a n v i ew of a p r i l l i n g

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

c a r r y i n g ou t s t u d i e s on t h i s i n v e n t i o n ; a n d

F i g . 7 i s a d i a g r a m m a t i c v i e w s h o w i n g t h e m a n n e r

in w h i c h ammonia was s u p p l i e d t o t h e s h r o u d s of t h e p r i l l i n g

t o w e r s of F i g . 7 when t h i s s t u d y was c a r r i e d o u t .

D e t a i l e d D e s c r i p t i o n o f I n v e n t i o n

The a p p a r a t u s 10 shown in F i g . 1 i n c l u d e s a v e r t i c a l

p r i l l i n g t o w e r 11. The t o w e r 11 i s an e l o n g a t e d member o f

c i r c u l a r or r e c t a n g u l a r t r a n s v e r s e c r o s s - s e c t i o n c o m p o s e d o f

a l u m i n u m ( f o r NH4NO3) or c o n c r e t e or o t h e r s u i t a b l e m a t e r i a l .

A c o n c r e t e t o w e r may be l i n e d w i t h a l u m i n u m i f t h e p r i l l i n g

m a t e r i a l in t h e t o w e r i s c o r r o s i v e . The t o w e r 11 h a s a b a s e

13 and is open at t h e t o p , b u t h a s a s u p e r s t r u c t u r e 1 5 .

Above t he t o p , a p l u r a l i t y of s c r u b b e r s 17 a r e p r o v i d e d .

The e x h a u s t f rom the t o w e r 11 f l o w s i n t o t h e s c r u b b e r s

t h r o u g h l i q u i d r a i n s h i e l d s 18 w h i c h p r e v e n t s l i q u i d f r o m

r u n n i n g b a c k i n t o t h e t o w e r . The s c r u b b e d gas p a s s e s i n t o

t h e a t m o s p h e r e t h r o u g h m i s t e l i m i n a t o r 20. A l t e r n a t e l y , t h e

t o w e r 11 may be p r o v i d e d w i t h a t op and a c o n d u c t o r may b e

p r o v i d e d to c o n d u c t t he e x h a u s t to s c r u b b e r s a t t h e g r o u n d

or to a l o w e r l e v e l .

P r i l l i n g h e a d s or n o z z l e s 21 f o r p r o d u c i n g a s p r a y

a r e s u s p e n d e d n e a r t he top of t o w e r 11. The p r i l l i n g h e a d s

21 a re c o n n e c t e d to a l i n e or c o n d u c t o r 23 t h r o u g h w h i c h

m o l t e n ammonium n i t r a t e or u r e a i s s u p p l i e d . The m e l t i s

p r o j e c t e d d o w n w a r d l y t h r o u g h e a c h p r i l l i n g head 21 in a

s p r a y 25 which may have g e n e r a l l y c o n i c a l s h a p e of c r o s s -

s e c t i o n d e p e n d i n g on t he c o n f i g u r a t i o n or o p e r a t i o n of t h e

p r i l l i n g head 21 and w i t h t h e p r i l l i n g head a t t he a p e x .

S t r i c t l y , t h e c o n f i g u r a t i o n has t h e s h a p e of a f r u s t r u m o f

a cone (o r of a p y r a m i d ) w i t h t h e p l a n e 27 of d r o p f o r m a t i o n

of t h e p r i l l i n g h e a d , w h i c h may be c a l l e d the d i s p e r s i o n

p l a n e , d e f i n i n g t h e b a s e of s m a l l e s t a r e a f rom w h i c h t h e

s p r a y d i v e r g e s . The s p r a y s p r e a d s ou t i n t o t h e p r i l l i n g

t o w e r 11. A c o n i c a l s h r o u d 29 e x t e n d s f rom e a c h p r i l l i n g

h e a d 21 w i t h t h e h e a d a t t h e a p e x . The j o i n t 31 ( F i g . 3 )

b e t w e e n t h e p r i l l i n g h e a d 21 and t h e s h r o u d 29 i s s e a l e d

g a s t i g h t . In l i e u of b e i n g c o n i c a l , t h e s h r o u d may h a v e

t h e form of a b e l l 3 3 ( F i g . 5) or i t may be f l a r e d as t h e

s h r o u d 35 shown in o u t l i n e in F i g . 6. The i n n e r s u r f a c e o f

t h e s h r o u d 29, 33 , 35 m u s t d i v e r g e f rom t h e p r i l l i n g h e a d

in s u c h m a n n e r t h a t i t i s n o t c o n t a c t e d by t h e s p r a y 2 5 .

F o r e x a m p l e , t h e s o l i d a n g l e of t h e c o n i c a l s h r o u d 29 m u s t

be a t l e a s t so g r e a t t h a t t h e i n n e r s u r f a c e of t h i s s h r o u d

i s p a r a l l e l to t h e l i n e s of f l o w of t h e s p r a y .

The s h r o u d 29 has an i n l e t 37 to w h i c h a g a s l i n e

or gas c o n d u c t o r 39 i s c o n n e c t e d . Ammonia , e i t h e r i n r e l a -

t i v e l y p u r e f o r m or m i x e d in h i g h c o n c e n t r a t i o n in a g a s ,

s u c h as a i r , i s i n j e c t e d i n t o t h e s h r o u d t h r o u g h t h e l i n e 3 9

and i n l e t 3 7 .

The a p p a r a t u s 10 a l s o i n c l u d e s f a c i l i t i e s f o r i n -

j e c t i n g a s t r e a m of a i r i n t o t h e l o w e r p a r t of p r i l l i n g

t o w e r 11. T h i s may be a c c o m p l i s h e d by f o r c e d d r a f t , i n d u c e d

d r a f t or c o m b i n a t i o n t h e r e o f . Ai r may be f o r c e d i n t o t h e

t o w e r 11 by f a n s 41 t h r o u g h l o u v e r s ( n o t s h o w n ) . The s c r u b -

b e r s 17 a r e p r o v i d e d w i t h f a n s 42 to c o m p e n s a t e f o r s c r u b b e r

s y s t e m p r e s s u r e d r o p a n d , in some c a s e s , to p r o v i d e f o r

i n d u c e d d r a f t f o r t he p r i l l i n g t o w e r 11. In e i t h e r e v e n t ,

t he p a r t i c l e s in t h e f e r t i l i z e r s p r a y 25 f l o w c o u n t e r c u r r e n t

to t he a i r and a r e c o o l e d by t he a i r .

The ammonia wh ich f l o w s i n t o t h e s h r o u d 29, b e c a u s e

i t is l i g h t e r t h a n a i r , r i s e s in t he s h r o u d p r o d u c i n g a s t a g -

n a n t a t m o s p h e r e of ammonia 43 ( F i g . 4) w i t h i n t h e s h r o u d .

The p a r t i c l e s 45, as t h e y l e a v e t he p r i l l i n g head 21, a n d

a r e at t h e i r h i g h e s t t e m p e r a t u r e , p a s s t h r o u g h t h i s a t m o s -

p h e r e 43. I t has b e e n f o u n d t h a t t h e ammon ia has t h e e f f e c t

of s u p p r e s s i n g t h e f o r m a t i o n of f u m e s . In a d d i t i o n , t h e

p a r t i c l e s of t h e s p r a y , as t h e y l e a v e t h e i n t e r f a c e 47 b e t w e e n

t h e ammonia and t h e u p w a r d l y f l o w i n g a i r , a r e c o a t e d w i t h a

l a y e r 49 of a m m o n i a . T h i s c o a t i n g c o n t r i b u t e s to t h e c o n t i n -

ued s u p p r e s s i o n of fumes and in a d d i t i o n , has t h e u n i q u e

a d v a n t a g e of a c c e l e r a t i n g t h e c o o l i n g of t h e p a r t i c l e s s o

t h a t t h e y a r e c o n v e r t e d i n t o p r i l l s . The p r i l l s a r e d e p o s i -

t e d on c o n v e y o r 51 and r e m o v e d f rom t h e t o w e r 1 1 .

As has b e e n s t a t e d , e a c h s h r o u d 29 s u r r o u n d i n g t h e

p r i l l i n g h e a d mus t be j o i n e d g a s - t i g h t to t h e h e a d , to r e t a i n

t h e l i g h t e r - t h a n - a i r ammonia g a s . E a c h s h r o u d mus t p r o j e c t

b e l o w the p l a n e 27 of d r o p f o r m a t i o n to p r o v i d e a m i n i m a l

ammonia gas l a y e r c o n t a c t t h i c k n e s s . The r e q u i r e d v e r t i c a l

d e p t h of a s h r o u d v a r i e s w i t h t h e t y p e of t h e a s s o c i a t e d

p r i l l i n g h e a d , bu t in g e n e r a l , a t r a p p e d ammonia zone t h i c k -

n e s s be low t h e p l a n e 27 of d r o p f r o m a t i o n of f rom 25 to 70%

of t he l a r g e s t d i a m e t e r of t h e s h r o u d may be e m p l o y e d . I n

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

ammonia zone d e p t h of f rom 6 to 18 i n c h e s b e l o w the p l a t e

i s p r e f e r r e d f o r a s h r o u d 29 h a v i n g a maximum d i a m e t e r o f

2 6 . 7 5 i n c h e s . The l i m i t on t h e o b t a i n a b l e d e p t h of t h e

a m m o n i a zone be low t h e p l a n e 27 of d rop f o r m a t i o n i s d i c t a t e d

p r i m a r i l y by t he s o l i d s p r a y a n g l e and t he n e c e s s i t y of e l e -

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

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

w a l l i s p r e f e r a b l y f l a r e d ( F i g . 6) or b e l l - s h a p e d ( F i g . 5 )

to a v o i d i n t e r f e r i n g w i t h t h e s p r a y , w h i l e s t i l l p r o v i d i n g

f o r t h e s t a g n a n t ammon ia zone r e q u i r e d b e l o w t he p l a n e 2 7 .

W h i l e t h e d e e p e s t s t a g n a n t a m m o n i a zone i s p r e f e r r e d , t h e r e

i s a p r a c t i c a l g e o m e t r i c a l l i m i t on t h i s d e p t h f o r a c o n i c a l ,

f l a r e d or b e l l - s h a p e d p r i l l i n g h e a d . The b o t t o m d i a m e t e r o f

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

ammon ia l a y e r , and t h e r e f o r e b l o c k s an i n c r e a s i n g p r o p o r t i o n

of t h e f r e e a i r f l o w c r o s s - s e c t i o n a l a r e a of t h e t o w e r . F o r

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

r e s t r i c t e d f l o w a r e a u n o c c u p i e d by t h e s h r o u d i n d u c e s a

v e n t u r i e f f e c t a r o u n d t h e s h r o u d s , w h i c h t e n d s to a s p i r a t e

t h e a m m o n i a ou t f rom w i t h i n t h e s h r o u d s . At c o n v e n t i o n a l

p r i l l t o w e r l i n e a r a i r v e l o c i t i e s of f rom 3 to 10 f e e t / s e c o n d ,

s i g n i f i c a n t v e n t u r i e f f e c t s w o u l d n o t o c c u r b e l o w a b o u t 5 0 - 7 5 %

r e d u c t i o n of empty t o w e r f r e e f l o w a r e a . H o w e v e r , i n c r e a s i n g

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

t h e l o c a l a i r v e l o c i t y and t h e ammonia z o n e a r e a s u b j e c t t o

a i r i m p a c t i o n and d i s t u r b a n c e , so t h a t i t i s p r e f e r a b l e t o

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

s p r a y a n g l e and p r e f e r r e d r a n g e of s t a g n a n t ammonia z o n e

t h i c k n e s s .

The ammonia t r a p p e d u n d e r a s h r o u d 29 s u r r o u n d i n g

a p r i l l i n g head i s l o s t to t h e s u r r o u n d i n g a i r by s e v e r a l

m e c h a n i s m s . T h e s e i n c l u d e v o l u m e t r i c d i s p l a c e m e n t by t h e

s p r a y , b o u n d a r y l a y e r c o a t i n g of t he p a r t i c l e s of t h e s p r a y

l e a v i n g t he q u i e s c e n t ammonia z o n e , and a i r i m p a c t i o n o n

t h e s h r o u d o p e n i n g . The a m o u n t s of ammonia l o s t by m e a n s

of t h e f i r s t two m e c h a n i s m s may be d i r e c t l y e s t i m a t e d . F o r

an ammonium n i t r a t e p r i l l r a t e of 1 0 0 , 0 0 0 p o u n d s p e r h o u r ,

w h e r e t he n i t r a t e has a s p e c i f i c g r a v i t y of 1 . 4 3 , t he d i s -

p l a c e m e n t vo lume of t h e p a r t i c l e s of s p r a y w o u l d be 1 1 2 1

c u b i c f e e t p e r h o u r . Fo r an a s s u m e d 180° F. a m m o n i a - g a s

t e m p e r a t u r e in t h e s h r o u d , t h i s d i s p l a c e d v o l u m e is e q u a l

to 862 s t a n d a r d c u b i c f e e t p e r h o u r , or 4 0 . 8 p o u n d s p e r h o u r ,

of a m m o n i a .

The c o n s u m p t i o n of a m m o n i a due to b o u n d a r y l a y e r

c o a t i n g of t he s p r a y p a r t i c l e s may be e s t i m a t e d f o r t h e s a m e

1 0 0 , 0 0 0 p o u n d s p e r h o u r p r o d u c t i o n r a t e . For a 2 0 0 , 0 0 CFM

r a t e of a i r f l o w in a 400 s q u a r e f o o t c r o s s - s e c t i o n a l a r e a

p r i l l t o w e r , t he l i n e a r a i r v e l o c i t y i s 500 f e e t p e r m i n u t e .

N e g l e c t i n g t he p a r t i c l e f a l l v e l o c i t y and a s s u m i n g an a v e r a g e

p a r t i c l e s i z e of 5 / 6 4 i n c h , t h e R e y n o l d s n u m b e r c o r r e s p o n d i n g

to t h i s p a r t i c l e s i z e , and a i r p r o p e r t i e s at an a v e r a g e o f

1150 F . , i s 228 . T h i s R e y n o l d s n u m b e r f o r a s p h e r e i s in t h e

l a m i n a r - t o - t u r b u l e n t f l o w t r a n s i t i o n z o n e , b u t a d d i n g on t h e

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

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

t h i c k n e s s of a p p r o x i m a t e l y 0 .2 mm may be e s t i m a t e d , a c c o r d i n g

to W.L. McCabe and J . C . S m i t h , " U n i t o p e r a t i o n s o f C h e m i c a l

E n g i n e e r i n g , " page 61 , T h i r d E d i t i o n , McGraw H i l l Book C o m p a n y ,

New Y o r k , 1956 . For t h e 5 / 6 4 i n c h d i a m e t e r p a r t i c l e s , a t

1 0 0 , 0 0 0 p o u n d s pe r h o u r , t h e r e w i l l be 7 .76 x 109 p a r t i c l e s /

h o u r . At 0 .2 mm b o u n d a r y l a y e r t h i c k n e s s , e ach p r i l l has a

b o u n d a r y l a y e r vo lume of 1 . 0 6 1 x 10 -7 c u b i c f e e t , and t h e

t o t a l v o l u m e pe r h o u r of ammonia c o n t a i n e d in t h i s b o u n d a r y

v o l u m e i s :

I f a mean b o u n d a r y l a y e r t e m p e r a t u r e of 150° F .

i s a s s u m e d , t h i s ammonia c o n s u m p t i o n r a t e i s e q u a l to 6 6 4

s t a n d a r d c u b i c f e e t pe r h o u r , or 3 1 . 4 p o u n d s p e r h o u r o f

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

c o a t i n g r e q u i r e m e n t s f o r 1 0 0 , 0 0 0 p o u n d s p e r h o u r p r o d u c t i o n

t o t a l s o n l y 7 2 . 2 p o u n d s p e r h o u r .

I t i s n o t f e a s i b l e to e s t i m a t e t h e ammonia l o s s e s

c a u s e d by a i r i m p a c t i o n on t h e o p e n s h r o u d 29 , b u t a t e s t

r u n of t h e m e t h o d of t h i s i n v e n t i o n a t a b o u t 5 4 , 0 0 0 p o u n d s

p e r h o u r on a c o m m e r c i a l p r i l l t o w e r , u s i n g o n l y two s h r o u d e d

p r i l l i n g h e a d s , showed t h a t an ammon ia r a t e of a b o u t 7 2

p o u n d s p e r h o u r were r e q u i r e d as a s h r o u d f e e d f o r fume s u p -

p r e s s i o n . T h i s wou ld i n d i c a t e t h a t , a t 1 0 0 , 0 0 0 p o u n d s p e r

h o u r p r o d u c t i o n r a t e , a t o t a l of 133 p o u n d s p e r h o u r w o u l d

be r e q u i r e d in t h e s h r o u d . T h e r e f o r e , t h e ammon ia l o s t t o

a i r i m p a c t i o n and t u r b u l e n c e m a y b e t a k e n a s a p p r o x i m a t e l y

e q u a l to t h e t o t a l of v o l u m e t r i c d i s p l a c e m e n t l o s s e s a n d

b o u n d a r y l a y e r c o a t i n g r e q u i r e m e n t s . The i n d i c a t e d r a t e o f

133 p o u n d s p e r h o u r ammonia u s a g e a t 1 0 0 , 0 0 0 p o u n d s p e r h o u r

ammonium n i t r a t e p r o d u c t i o n r a t e i s o n l y 2 . 6 7 p o u n d s o f

ammonia p e r t o n of p r o d u c t i o n .

As has been s t a t e d , a n o t h e r b e n e f i t of i m p a r t i n g

an a m m o n i a b o u n d a r y l a y e r to t h e p a r t i c l e s of t h e s p r a y a s

c o m p a r e d to an a i r b o u n d a r y i s a s i g n i f i c a n t i n c r e a s e in t h e

c o o l i n g r a t e of t he p a r t i c l e s , w i t h a c o n s e q u e n t i n c r e a s e i n

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

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

c o a t i n g of t he p a r t i c l e s in the p r a c t i c e of t h i s i n v e n t i o n ,

and no t f rom the t e c h n i q u e of ammonia a d d i t i o n to t he a i r

s t r e a m as t a u g h t by t h e p r i o r a r t . In t h e p r a c t i c e of t h i s

i n v e n t i o n , t he a i r b o u n d a r y l a y e r is r e p l a c e d by an a m m o n i a

b o u n d a r y l a y e r , and a c o m p a r i s o n of the r e s u l t i n g r e s p e c t i v e

h e a t t r a n s f e r c o e f f i c i e n t s i n d i c a t e s a p o t e n t i a l 27% a d v a n -

t a g e in c o o l i n g f o r t he a m m o n i a - c o a t i n g m e t h o d . T h i s g a i n

may be e s t i m a t e d f rom t h e f o l l o w i n g c a l c u l a t i o n s .

The f u n d a m e n t a l e q u a t i o n f o r t h e c o n v e c t i v e h e a t

t r a n s f e r c o e f f i c i e n t f rom a s p h e r e to a gas i s g i v e n b y

A.C. C a r s l o w and J . C . J a e g e r , " C o n d u c t i o n o f H e a t i n S o l i d s , "

pp. 2 3 4 - 2 4 1 , O x f o r d U n i v e r s i t y P r e s s ( 1 9 5 9 ) a s :

whe re h c = c o n v e c t i v e h e a t t r a n s f e r c o e f f i c i e n t

k = h e a t c a p a c i t y of g a s

D = s p h e r i c a l p a r t i c l e d i a m e t e r

Pr = P r a n d t l n u m b e r

µ = gas v i s c o s i t y

ρ = gas d e n s i t y

Δ ρ = gas d e n s i t y d i f f e r e n c e , b o u n d a r y l a y e r t e m p e r a t u r e v s . b u l k gas t e m p e r a t u r e

A s s u m i n g an i n i t i a l p a r t i c l e s u r f a c e t e m p e r a t u r e o f

350° F. and s u b s t i t u t i n g t h e p h y s i c a l p r o p e r t i e s of a m m o n i a

and a i r , r e s p e c t i v e l y , t h e r a t i o of ( h ) N H 3 t o ( h c ) a i r

r e d u c e s t o :

a n d

T h e r e i s t h e n a p o t e n t i a l i n c r e a s e of 27% in t h e

h e a t - t r a n s f e r r a t e f rom t he p a r t i c l e w i t h an a m m o n i a - g a s

b o u n d a r y l a y e r as c o m p a r e d to an a i r b o u n d a r y l a y e r .

The e x h a u s t gas f rom t he p r i l l i n g t o w e r 11 i n c l u d e s

a m m o n i a . The l o s s of t he ammonia u sed f o r fume s u p p r e s s i o n

to t h e a t m o s p h e r e , e v e n a t t h e r e d u c e d r a t e s c a l l e d f o r b y

t h e p r a c t i c e of t h i s i n v e n t i o n , i s e c o n o m i c a l l y and e n v i r o n -

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

t h i s a d d e d a m m o n i a be r e m o v e d f rom t h e t o w e r e x h a u s t a i r

and r e c o v e r e d . T h i s i s a c c o m p l i s h e d by s c r u b b e r s 17. A

p r o c e d u r e w h i c h i s s u g g e s t e d i s to r e c o v e r t h e ammonia b y

o n c e - t h r o u g h w a t e r w a s h . T h i s i s n o t an e f f e c t i v e or d e s i r -

a b l e m e t h o d b e c a u s e i t i s t h e n n e c e s s a r y to t r e a t t h e s c r u b b e r

e f f l u e n t s t r e a m p r i o r to d i s p o s a l or to use t h e d i l u t e a m m o n i a

s t r e a m in t h e p l a n t p r o c e s s . The d i l u t e ammonia e x h a u s t w a s h

l i q u o r c a n n o t be r e c y c l e d t h r o u g h t he s c r u b b e r s 17 b e c a u s e

t h e ammonia s o l u t i o n b a c k p r e s s u r e i n c r e a s e s as t h e a m m o n i a

c o n c e n t r a t i o n i n c r e a s e s , and t he a b s o r p t i o n of ammonia c e a s e s

when t h e s o l u t i o n a m m o n i a v a p o r - p r e s s u r e a p p r o a c h e s t h e p a r -

t i a l p r e s s u r e of a m m o n i a in t h e a i r l e a v i n g t h e t o w e r .

An a l t e r n a t e m e t h o d of s c r u b b i n g ou t t h e a m m o n i a

in t h e c a s e of ammonium n i t r a t e or u r e a p r i l l t o w e r s i s t o

u s e a d i l u t e s o l u t i o n of a n o n - v o l a t i l e a c i d as t h e a m m o n i a -

a b s o r b i n g l i q u o r . T h i s a s s u r e s t h a t t he s o l u t i o n h a s z e r o

ammon ia b a c k p r e s s u r e and m a x i m i z e s t h e a b s o r p t i o n d r i v i n g

f o r c e , g i v i n g r a p i d and c o m p l e t e ammonia r e m o v a l in a v e r y

c o m p a c t s c r u b b i n g d e v i c e , such as a s i m p l e s p r a y s c r u b b e r .

Among t h e n o n - v o l a t i l e a c i d s t h a t may be u s e d a r e

p h o s p h o r i c , s u l f u r i c , n i t r i c and t h e l i k e . O x i d i z a b l e a c i d s ,

s u c h as o r g a n i c a c i d s , a r e h a z a r d o u s in an ammonium n i t r a t e

p l a n t and t h e i r u se would t h e r e f o r e no t be p r a c t i c a l . I t

is a d v a n t a g e o u s to use an a c i d , such as HNO3, w h i c h i s

n o r m a l l y made in t h e p l a n t p r o d u c t i o n s e q u e n c e and w h i c h ,

on r e a c t i o n w i t h a m m o n i a , y i e l d s a c o m p o u n d w h i c h is t h e

same as t he end p l a n t p r o d u c t . T h e r e f o r e , n i t r i c a c i d i s

t h e p r e f e r r e d a b s o r p t i o n a c i d in t h e ammonium n i t r a t e p r i l l

t o w e r c a s e .

The r e m o v a l of the ammonia f rom t h e e x h a u s t a n d

i t s c o n v e r s i o n i n t o a u s e f u l c o m p o u n d i s shown in F i g . 1 .

The e x h a u s t gas f l o w s t h r o u g h c o n d u c t o r 16 i n t o t h e l o w e r

r e g i o n s of t h e s c r u b b e r s 17 and i s c o n d u c t e d u p w a r d l y . T h e

e x h a u s t gas i s c o n t a c t e d d i r e c t l y by a r e a c t a n t w h i c h i s

s u p p l i e d t h r o u g h c o n d u c t o r 53 to s p r a y h e a d s 55 as d i s c l o s e d

in L e r n e r P a t e n t 3 , 8 9 5 , 9 2 6 . The l i q u i d s o l u t i o n w h i c h c o n -

t a c t s t h e ammonia f i r s t a b s o r b s t he a m m o n i a . The a m m o n i a

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

w i t h t he f r e e r e a c t a n t a c i d in t h e s o l u t i o n . A z e r o b a c k -

p r e s s u r e of ammonia f rom the s o l u t i o n i s t h u s a c h i e v e d .

The r e a c t a n t c o n v e r t s t h e a b s o r b e d ammonia i n t o a s t a b l e

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

ammonium n i t r a t e , t h e r e a c t a n t i s n i t r i c a c i d as shown i n

F i g . 1. The n i t r i c a c i d s o l u t i o n i s s p r a y e d c o u n t e r c u r r e n t l y

on t h e e x h a u s t gas a b s o r b i n g and c o n v e r t i n g the ammonia i n

t h e e x h a u s t i n t o ammonium n i t r a t e . The ammonium n i t r a t e i s

in s o l u t i o n and i s s u p p l i e d t h r o u g h c o n d u c t o r 57 to r e c y c l e

t a n k 59 c o n t a i n i n g t he ammonium n i t r a t e s o l u t i o n . M a k e - u p

w a t e r to r e p l e n i s h t h e w a t e r in t a n k 5° i s s u p p l i e d t h r o u g h

c o n d u c t o r 61. The f l o w t h r o u g h c o n d u c t o r 61 is c o n t r o l l e d

by f l o w s w i t c h 63. The l i q u i d in t h e r e c y c l e t a n k 50 i s

r e c y c l e d by pump 65 t h r o u g h c o n d u c t o r F7. The c o n c e n t r a t i o n

of ammonium n i t r a t e in r e c y c l e t a n k 59 is m o n i t o r e d . When

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

69 i s o p e n e d and t h e ammonium n i t r a t e i s t r a n s f e r r e d to a

p r o d u c t r e c o v e r y f a c i l i t y t h r o u g h b lowdown c o n d u c t o r 7 1 .

An a d v a n t a g e of u s i n g a d i l u t e n i t r i c a c i d s o l u t i o n

to a b s o r b a m m o n i a f rom ammonium n i t r a t e p r i l l t o w e r e x h a u s t

a i r , p r a c t i c i n g t h i s i n v e n t i o n , i s t h a t ammonium n i t r a t e i s

c o n t i n u o u s l y f o r m e d in t h e s c r u b b i n g l i q u o r , and t he s o l u -

t i o n i s r e c y c l e d t h r o u g h s c r u b b e r s 17 u n t i l a d e s i r e d d o n -

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

t h i s c o n c e n t r a t i o n i s r e c o v e r e d t h r o u g h b l o w d o w n c o n d u c t o r 7 1 .

To m i n i m i z e d o w n s t r e a m e n e r g y r e q u i r e m e n t s f o r c o n c e n t r a t i o n

of d i l u t e a m m o n i u m - n i t r a t e s o l u t i o n s c r u b b e r b l o w d o w n , i t i s

d e s i r a b l e t h a t t y p i c a l l y a m in imum c o n c e n t r a t i o n of 20%

ammonium n i t r a t e be m a i n t a i n e d in t h e r e c y d l e t a n k 59. R e -

c y c l e c o n c e n t r a t i o n s of more t h a n 60% by w e i g h t a m m o n i u m

n i t r a t e h a v e b e e n a c h i e v e d in t e s t s on an i n d u s t r i a l p r i l l

t o w e r s c r u b b e r , bu t o p e r a t i o n a t c o n c e n t r a t i o n s g r e a t e r t h a n

60% by w e i g h t i s u n d e s i r a b l e b e c a u s e of t h e d a n g e r of f r e e z -

i n g t h e s o l u t i o n i n t h e l i n e s i f t h e a m b i e n t e x h a u s t a i r w e t -

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

i n g p o i n t .

N i t r i c a c i d i s c o n t i n u o u s l y added t h r o u g h c o n d u c t o r

53 to t h e r e c y c l e l i q u o r to m a i n t a i n s c r u b b e r r e c y c l e s o l u -

t i o n a c i d i t y as a m m o n i a i s a b s o r b e d f rom t h e e x h a u s t a i r .

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

a i r l e a v i n g t h e p r i l l t o w e r and e n t e r i n g t h e s c r u b b e r , i t i s

a d v a n t a g e o u s to use c o n c e n t r a t e d a c i d , of a b o u t 53% n i t r i c

a c i d by w e i g h t , to m a i n t a i n t h e r e c y c l e s o l u t i o n a c i d i t y .

I f t o o d i l u t e an a c i d i s u s e d , t h e w a t e r b e i n g a d d e d w i t h t h e

a c i d may Le g r e a t e r t h a n the e v a p o r a t i o n r a t e , so t h a t t h e

r e c y c l e s o l u t i o n a m m o n i u m - n i t r a t e c o n c e n t r a t i o n w i l l not b e

m a i n t a i n a b l e a t the d e s i r e d c o n c e n t r a t i o n l e v e l of 20% o r

a b o v e . F u r t h e r , 50-60% i s t h e a p p r o x i m a t e n i t r i c a c i d c o n -

c e n t r a t i o n g e n e r a l l y a v a i l a b l e in an a m m o n i u m - n i t r a t e p l a n t

o p e r a t i o n . The p r i m e d i s a d v a n t a g e o f a d d i n g r e l a t i v e l y c o n -

c e n t r a t e d n i t r i c a c i d to t h e s c r u b b e r r e c y c l e l i q u o r i s t h e

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

in t h e s c r u b b e r . N i t r i c a c i d c o n c e n t r a t i o n s a b o v e a b o u t

2-5% by w e i g h t may h a v e s u f f i c i e n t n i t r i c - a c i d or n i t r i c -

o x i d e v a p o r p r e s s u r e s to g e n e r a t e fume v i a a v a p o r - p h a s e

r e a c t i o n w i t h t h e g a s e o u s ammon ia in t h e p r i l l t o w e r e x h a u s t

a i r . I t has b e e n d i s c o v e r e d t h a t s e c o n d a r y fume f o r m a t i o n

in t h e s c r u b b e r can be a v o i d e d by u s i n g a v e r y h i g h l i q u i d /

gas s c r u b b i n g r a t i o , in t h e r a n g e of 5 -25 g a l l o n s of r e c y c l e

l i q u o r p e r 1000 ACFM ( a c t u a l c u b i c f e e t pe r m i n u t e ) of a i r ,

and p r e f e r a b l y in t h e r a n g e of 1 0 - 1 5 GPM/1000 CF. In t h i s

way, a d i l u t i o n " s i n k ' ' i s p r o v i d e d f o r t he a c i d , w h i c h r e -

d u c e s t h e c o n c e n t r a t i o n e n t e r i n g t h e s c r u b b e r s 17 , and c o n -

t a c t i n g t he a m m o n i a / a i r m i x t u r e , t o l e v e l s w h e r e t h e v a p o r

p r e s s u r e of t he a c i d i s n e g l i g i b l y s m a l l . I t i s d e s i r a b l e

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

to l e s s t h a n 2% by w e i g h t , and p r e f e r a b l y l e s s t h a n 0.4% b y

w e i g h t . F o r a m a x i m u m ammonia u s a g e of 300 l b / h r in a 1 0 0 0

t o n / d a y , 2 0 0 , 0 0 0 ACFM p r i l l t o w e r , t he a c i d r e q u i r e m e n t i s

2097 l b s / h r of 53% HNO3. To d i l u t e t h i s a c i d to 0 . 4 % , i t

must be mixed w i t h 2 7 , 9 4 2 l b / h r of d i l u t i o n l i q u o r , o r

r o u g h l y , 555 GPM of a d d i t i o n a l n o n - a c i d s o l u t i o n . At t h e

minimum 5 g a l l o n s r e c y c l e / 1 0 0 0 CF of s c u r b b e r o p e r a t i o n ,

r e c y c l e p r o v i d e s 1000 GPM o f d i l u t i o n l i o u o r . T h i s d i l u t i o n

i s a b o u t t w i c e t h a t of t h i s m i n i m u m , and s e c o n d a r y f u m e

f o r m a t i o n i s a v o i d e d .

In t h e a p p l i c a t i o n of t h e m e t h o d of t h i s i n v e n t i o n

to u r e a p r i l l t o w e r s and t h e l i k e , t h e n o n - v o l a t i l e d i l u t e

a c i d s o l u t i o n s w h i c h may be u s e d in t h e ammonia a b s o r b e r s

a r e i n o r g a n i c a c i d s s u c h as p h o s p h o r i c , s u l f u r i c and n i t r i c ,

and o r g a n i c a c i d s s u c h as c i t r i c , o x a l i c and s i m i l a r n o n -

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

To r e c y c l e s c r u b b e r s o l u t i o n b l o w d o w n b a c k t o t h e

u r e a - f o r m i n g p r o c e s s , i t w o u l d be d e s i r a b l e to g e n e r a t e

ammonium b i c a r b o n a t e in t h e ammon ia a b s o r p t i o n s c r u b b e r . T h i s

w o u l d r e q u i r e t h e use of c a r b o n i c a c i d as t h e a b s o r b i n g a c i d ;

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

t h e u r e a f l o w s h e e t and w o u l d be o b j e c t i o n a b l e . The s c r u b b e r

r e c y c l e l i q u o r b l o w d o w n r e s u l t i n g f rom t h e ' u s e of a c i d s

o t h e r t h a n c a r b o n i c , s u c h as p h o s p h o r i c , n i t r i c or s u l f u r i c ,

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

or m a r k e t e d in l i q u i d f o r m .

B e c a u s e of v a p o r p r e s s u r e c o n s i d e r a t i o n s , i t i s

n o t u s u a l l y p r a c t i c a l to s c r u b ammon ia f rom u r e a p r i l l t o w e r

e x h a u s t a i r w i t h r e c y c l e ammonium b i c a r b o n a t e / c a r b o n i c a c i d

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

a m m o n i a , i . e . , s o l u t i o n b a c k p r e s s u r e , can be r e d u c e d b e l o w

t h e n o r m a l a i r p a r t i a l p r e s s u r e r a n g e of ammonia in t h e

p r a c t i c e of t h i s i n v e n t i o n ( 0 . 1 to 1 . 0 mm Hg) o n l y by t h e

use of s o l u t i o n s h a v i n g a h i g h C02 to NH3 r a t i o , and t h u s

e x c e s s i v e l y h i g h C02 v a p o r p r e s s u r e s . W h i l e i t i s p o s s i b l e

to g e n e r a t e s u c h s c r u b s o l u t i o n s , t he C02 l o s s e s would b e

u n e c o n o m i c a l l y l a r g e . I t i s mos t p r a c t i c a b l e to r e m o v e t h e

ammon ia w i t h p h o s p h o r i c a c i d and r e c o v e r t h e ammonia a s

ammonium p h o s p h a t e . The p h o s p h o r i c a c i d is s o r a v e d i n t o

t h e s c r u b b e r s 17 and the ammonjum p h o s p h a t e i s p a s s e d

t h r o u g h a r e c y c l e t a n k s i m i l a r l y to t he ammonium n i t r a t e

and n i t r i c a c i d in t h e a p p a r a t u s shown in F i g . 1 .

P r e l i m i n a r y t e s t s of t h i s i n v e n t i o n were c o n d u c t e d

in a f a c i l i t y 81 ( F i g . 7) f o r c o m m e r c i a l g e n e r a t i o n of a m m o n -

ium n i t r a t e p r i l l s of a g r i c u l t u r a l f e r t i l i z e r . The f a c i l i t y

81 i n c l u d e s 3 b a y s , 83, 85, 87, w i t h two p r i l l i n g n o z z l e s

in e a c h bay . The t e s t s were c o n d u c t e d w i t h t h e n o z z l e s 89

and 90 in t h e c e n t r a l bay 8 5 .

The p r i l l i n g head c o n n e c t o r 91 ( F i g . 8) of e a c h

n o z z l e 89 and 90 was p r o v i d e d w i t h a s h r o u d 93. The p e r p e n -

d i c u l a r d i s t a n c e b e t w e e n t h e p l a n e 92 of m e l t d r o p f o r m a t i o n

of t h e p r i l l i n g head 91 and t h e p l a n e d e f i n e d by t he r im o f

t h e s h r o u d was a b o u t 12 i n c h e s . The s h r o u d f l a r e d ou t f r o m

t h e p l a n e 92 and t h e n e x t e n d e d at an a n g l e of a b o u t 60° t o

t h e h o r i z o n t a l . L i q u i d ammonia ( s o u r c e no t shown) was v a p o r -

i z e d by v a p o r i z e r 95 and s u p p l i e d to t h e i n l e t f i x t u r e 9 7

of t h e s h r o u d 93 of n o z z l e s 89 and 90 t h r o u g h a h e a d e r 9 9 ,

a n e e d l e v a l v e 101 , a r o t a m e t e r 103 and a f l e x i b l e h o s e 1 0 5

( F i g . 8 ) . The c e n t e r of t h e i n l e t f i x t u r e 97 was a b o u t 4

i n c h e s b e l o w t he p l a n e 92 of m e l t d r o p f o r m a t i o n . T h e

s h r o u d 93 a t t a c h e d to p r i l l i n g head c o n n e c t o r 91 was s i m i -

l a r l y s u p p l i e d t h r o u g h a b r a n c h c h a n n e l 107 ( F i g . 7) c o n -

n e c t e d to t h e h e a d e r 99 t h r o u g h a T - j o i n t 1 0 9 .

P r i l l s of ammonium n i t r a t e were p r o d u c e d w h i l e t h e

t e s t was c o n d u c t e d . The p r i l l i n g t e m p e r a t u r e was 345° F .

Abou t 80 g a l l o n s p e r m i n u t e or a b o u t 689 t o n s of p r i l l s p e r

day were p r o d u c e d . The ammonia was s u p p l i e d i n i t i a l l y a t

t h e r a t e of 20 p o u n d s p e r h o u r . At t h i s r a t e . u n m i s t a k a b l e

s u p p r e s s i o n of f u m i n g was o b s e r v e d , bu t t he o p a c i t y m e a s u r e d

was a b o u t 70%. F o u r h u n d r e d p o u n d s p e r h o u r of ammonia w a s

i n t r o d u c e d at t he b a s e of t h e p r i l l i n g t o w e r . R e d u c t i o n

of o p a c i t y to a b o u t 50% was t h e n n o t e d . Wi th t he s u p p l y o f

a m m o n i a at 400 p o u n d s p e r h o u r a t t h e b a s e of t he t o w e r ,

t h e s u p p l y of ammonia to t h e s h r o u d s 93 was r a i s e d to 7 4

p o u n d s pe r h o u r . R e d u c t i o n of o p a c i t y to 10% was o b s e r v e d .

W i t h t h e r a t e of f e e d of ammon ia to t h e s h r o u d s 93 a t 74

p o u n d s p e r h o u r , t h e s u p p l y of 400 p o u n d s p e r h o u r of a m m o n i a

t o t h e ba se of t h e t o w e r was d i s c o n t i n u e d . O p a c i t y o f 4 0 %

was o b s e r v e d . S c h e d u l e d p r o d u c t i o n of p r i l l s c o m p e l l e d t h e

t e s t s to be t e m p o r a r i l y d i s c o n t i n u e d .

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

t h i s i n v e n t i o n . The a d d i t i o n of 400 p o u n d s p e r h o u r o f

a m m o n i a as t a u g h t by Todd r e d u c e s t h e o p a c i t y o n l y f rom 70%

t o 50% w h i l e f e e d i n g 20 p o u n d s p e r h o u r t o t h e s h r o u d s . By

i n c r e a s i n g t he f e e d to t h e s h r o u d s by o n l y 54 p o u n d s p e r

h o u r , t h e o p a c i t y i s r e d u c e d by 40%. D i s c o n t i n u a t i o n o f

t h e 400 p o u n d s p e r h o u r and r e l i a n c e o n l y on t h e 7 0 p o u n d s

p e r h o u r in t h e s h r o u d s , g a v e an o p a c i t y of 40%; 10% l o w e r

t h a n t h a t p r o d u c e d by t h e 400 p o u n d s p e r h o u r as t a u g h t b y

T o d d .

Whi le p r e f e r r e d e m b o d i m e n t s of t h i s i n v e n t i o n h a v e

b e e n d i s c l o s e d h e r e i n , many m o d i f i c a t i o n s of t h e s e e m b o d i -

m e n t s a r e f e a s i b l e . T h i s i n v e n t i o n i s n o t to be r e s t r i c t e d ,

e x c e p t i n s o f a r as i s n e c e s s i t a t e d by t h e s p i r i t of t he p r i o r

a r t .

1. The m e t h o d of o p e r a t i n g a p r i l l i n g t o w e r

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

of ammonium n i t r a t e and u r e a , t h e s a i d m e t h o d i n c l u d i n g i n -

j e c t i n g a s p r a y of a m e l t of s a i d m a t e r i a l at a f i r s t p o s i t i o n

of s a i d t o w e r , i n t r o d u c i n g a s t r e a m of a i r at s e c o n d p o s i t i o n

of s a i d t o w e r d i s p l a c e d f rom s a i d f i r s t p o s i t i o n , c o n d u c t i n g

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

s a i d s p r a y and to p r o d u c e p r i l l s , and r e m o v i n g s a i d p r i l l s

f rom s a i d t o w e r , t h e s a i d m e t h o d b e i n g c h a r a c t e r i z e d by t h a t

t h e s p r a y i s m a i n t a i n e d in an a t m o s p h e r e of g a s e o u s a m m o n i a

. a s i t e n t e r s t h e t o w e r to s u p p r e s s t h e e m i s s i o n of fumes f r o m

t h e t o w e r .

2. The m e t h o d of c l a i m 1 w h e r e i n t h e s p r a y p a s s e s

t h r o u g h a s t a g n a n t a t m o s p h e r e of ammonia in t he r e g i o n w h e r e

i t e n t e r s t h e t o w e r .

3. The m e t h o d of c l a i m 1 w h e r e i n t h e a i r w h i c h

c o n t a c t s t h e s p r a y , on l e a v i n g t h e t o w e r , c a r r i e s ammonia w i t h

i t :and w h e r e i n t h e a m m o n i a - c o n t a i n i n g a i r i s t r e a t e d w i t h o n e

of t h e c l a s s of a c i d s c o n s i s t i n g of p h o s p h o r i c a c i d , s u l f u r i c

a c i d , n i t r i c a c i d , and c a r b o n i c a c i d to r e m o v e t h e a m m o n i a

f rom s a i d a i r by f o r m i n g a s a l t of a m m o n i a .

4. The m e t h o d of c l a i m 1 w h e r e i n t h e s p r a y i s

c o m p o s e d of u r e a and t h e a i r w h i c h c o n t a c t s t h e s p r a y , o n

l e a v i n g the t o w e r , c a r r i e s ammon ia w i t h i t a n d w h e r e i n t h e

a m m o n i a - c o n t a i n i n g a i r is t r e a t e d w i t h one of the c l a s s o f

a c i d s c o n s i s t i n g of p h o s p h o r i c a c i d , s u l f u r i c a c i d , n i t r i c

a c i d , and n o n - v o l a t i l e o r g a n i c a c i d s s u c h as c i t r i c a c i d a n d

o x a l i c a c i d to r e m o v e the a m m o n i a f rom s a i d a i r by c o n v e r t i n g

t he ammonia i n t o a s a l t .

5. The m e t h o d o f o p e r a t i n g a p r i l l i n g t o w e r t o

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

ammonium n i t r a t e and u r e a , t h e s a i d m e t h o d i n c l u d i n g i n j e c -

t i n g a s p r a y of a m e l t a t a f i r s t p o s i t i o n of s a i d t o w e r ,

i n t r o d u c i n g a s t r e a m of a i r i n t o s a i d t o w e r in a s e c o n d

p o s i t i o n of s a i d t o w e r d i s p l a c e d f rom s a i d f i r s t p o s i t i o n ,

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

s p r a y and to p r o d u c e p r i l l s , and r e m o v i n g s a i d p r i l l s f r o m

s a i d t o w e r , t h e s a i d m e t h o d b e i n g c h a r a c t e r i z e d by t h a t t h e

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

e n t e r s a i d s t r e a m of a i r so t h a t t h e c o o l i n g of s a i d p a r t i c l e s

by s a i d a i r i s a c c e l e r a t e d .

6. A p p a r a t u s f o r p r o d u c i n g p r i l l s of one or m o r e

of t h e c l a s s of m a t e r i a l s c o n s i s t i n g of ammonium n i t r a t e a n d

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

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

m e l t of s a i d m a t e r i a l a t s a i d f i r s t p o s i t i o n , m e a n s p r o d u c i n g

an a t m o s p h e r e c o n t a i n i n g ammon ia a b o u t s a i d s p r a y - p r o d u c i n g

m e a n s w h e r e b y s a i d s p r a y p a s s e s t h r o u g h s a i d a t m o s p h e r e a s

i t i s e m i t t e d by s a i d s p r a y - p r o d u c i n g m e a n s , m e a n s , c o n n e c t e d

t o s a i d t o w e r , f o r p r o d u c i n g a s t r e a m of a i r in s a i d t o w e r ,

s a i d a i r f l o w i n g f rom a s e c o n d p o s i t i o n in s a i d t o w e r , s a i d

s p r a y b e i n g d i r e c t e d to f l o w f rom s a i d f i r s t p o s i t i o n to s a i d

s e c o n d p o s i t i o n t h r o u g h s a i d s t r e a m of a i r so t h a t s a i d s p r a y

i s c o o l e d and p r i l l s of s a i d m a t e r i a l a r e p r o d u c e d , and m e a n s

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

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

s a i d s p r a y - p r o d u c i n g means so as to s u p p r e s s t h e e m i s s i o n o f

f u m e s f r o m s a i d t o w e r .

7. The a p p a r a t u s of c l a i m 6 w h e r e i n t h e a m m o n i a -

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

s a i d s p r a y - p r o d u c i n g means and m e a n s , c o n n e c t e d to s a i d

s h r o u d , f o r s u p p l y i n g ammonia t h e r e t o .

8. The a p p a r a t u s of c l a i m 7 w h e r e i n t he s h r o u d i s

s h a p e d so t h a t i t i s n o t i m p i n g e d by t h e s p r a y .

9. The a p p a r a t u s of c l a i m 8 w h e r e i n t h e s h r o u d i s

of c o n i c a l s h a p e d i v e r g i n g f rom t he s p r a y - p r o d u c i n g m e a n s

in t he d i r e c t i o n f rom w h i c h t h e s t r e a m of a i r f l o w s .

10. The a p p a r a t u s of c l a i m 8 w h e r e i n t h e s h r o u d i s

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

d i r e c t i o n f rom w h i c h t h e s t r e a m of a i r f l o w s .

11. The a p p a r a t u s of c l a i m 8 w h e r e i n t h e s h r o u d

f l a r e s t o w a r d s t h e d i r e c t i o n f rom w h i c h t h e s t r e a m of a i r

f l o w s .

12. The a p p a r a t u s of c l a i m 6 i n c l u d i n g s c r u b b e r

means c o n n e c t e d to s a i d t o w e r f o r r e m o v i n g t h e ammonia f r o m

t h e gas e m i t t e d f r o m s a i d t o w e r .

13. The a p p a r a t u s of c l a i m 12 w h e r e i n . t h e s c r u b b e r

means i n c l u d e s a s c r u b b e r and m e a n s , c o n n e c t e d to s a i d s c r u b b e r ,

f o r d e r i v i n g f rom s a i d s c r u b b e r an ammonium c o m p o u n d t h e r e b y

r e c l a i m i n g t h e p r e d o m i n a n t p o r t i o n of t h e a m m o n i a c o n t a i n e d

in t he gas e m i t t e d f r o m t h e t o w e r .

14. The a p p a r a t u s of c l a i m 13 w h e r e i n t h e p r i l l s

p r o d u c e d by t h e t o w e r a r e c o m p o s e d of ammonium n i t r a t e a n d

t he ammonium compound d e r i v e d from t he s c r u b b e r i s a l s o

ammonium n i t r a t e .

15. The a p p a r a t u s of c l a i m 13 w h e r e i n t h e p r i l l s

p r o d u c e d by t h e t o w e r a re c o m p o s e d of u r e a and t h e a m m o n i u m

compound d e r i v e d f rom the s c r u b b e r is ammonium p h o s p h a t e .

16. The m e t h o d of s u p p r e s s i n g t h e f o r m a t i o n o f

fumes f rom a p r i l l i n g t o w e r p r o d u c i n g p r i l l s of one of t h e

c l a s s c o n s i s t i n g of ammonium n i t r a t e and u r e a by i n j e c t i n g

l i q u i d m e l t of n i t r a t e or t h e u r e a , as t h e c a s e may b e , n e a r

t he t o p of t h e p r i l l i n g t o w e r t h r o u g h a p r i l l i n g head t h e r e -

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

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

a i r , t h e s a i d m e t h o d c o m p r i s i n g i n j e c t i n g ammonia gas in t h e

r e g i o n a d j a c e n t t o and a b o u t t h e p r i l l i n g h e a d to p r o d u c e a n

a t m o s p h e r e of ammonia a b o u t t h e p r i l l i n g h e a d and c o n d u c t i n g

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

t h r o u g h t h e r e m a i n d e r of t h e t o w e r , t h e r e b y s u p p r e s s i n g t h e

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

17. The m e t h o d of c l a i m 15 i n c l u d i n g s h r o u d i n g t h e

p r i l l i n g h e a d and c o n t i n u o u s l y i n j e c t i n g t h e ammonia i n t o t h e

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

head w h i c h i s c o n t i n u o u s l y r e n e w e d .

18. A p p a r a t u s , in whose o p e r a t i o n fumes a r e s u p -

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

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

c o n n e c t e d to s a i d p r i l l i n g h e a d , f o r i n j e c t i n g i n t o s a i d

p r i l l i n g h e a d a m e l t of t h e m a t e r i a l of w h i c h t h e p r i l l s a r e

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

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

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

t e d to s a i d s h r o u d f o r i n j e c t i n g i n t o s a i d s h r o u d a gas w h i c h

s u p p r e s s e s f u m e s f rom the t o w e r , means f o r i n j e c t i n g a s t r e a m

of a i r i n t o s a i d t o w e r in c o u n t e r f l o w r e l a t i o n s h i p to t h e

s p r a y to c o o l t h e s p r a y and to c o n v e r t t h e s p r a y p a r t i c l e s

i n t o p r i l l s and means f o r c o l l e c t i n g t h e p r i l l s .

19. The a p p a r a t u s of c l a i m 17 i n c l u d i n g a s c r u b b e r ,

m e a n s , c o n v i c t i n g s a i d s c r u b b e r to s a i d t o w e r , so t h a t t h e

gas e m i t t e d f rom s a i d s h r o u d p a s s e s t h r o u g h s a i d s c r u b b e r ,

and m e a n s , c o n n e c t e d to s a i d s c r u b b e r , f o r s u p p l y i n g t o

s a i d s c r u b b e r , in c o u n t e r f l o w r e l a t i o n s h i p to s a i d g a s , a

l i q u i d r e a c t i o n w i t h s a i d gas f o r a b s o r b i n g s a i d g a s .

20. The m e t h o d of c l a i m 18 w h e r e i n t h e m a t e r i a l i s

ammonium n i t r a t e , t h e gas i s ammonia and t h e l i q u i d i s n i t r i c

a c i d and w h e r e b y , r e c o v e r a b l e ammonium n i t r a t e i s d e r i v e d

f r o m t h e a m m o n i a .