Development of European Ozonation Techniques - Advances in

Development of European Ozonation Techniques PAUL FRISON

Downloaded by AUBURN UNIV on September 12, 2017 | http://pubs.acs.org Publication Date: January 1, 1959 | doi: 10.1021/ba-1959-0021.ch058

Trailigaz, Paris, France

The historical development of European ozonators and ozone production are reviewed. The Otto, van der M a d e , a n d Siemens processes for generating ozone are described. Recent improvements a n d innovations are indicated. Two distinct operations are considered: conditioning of the air to be submitted to the electric discharge, a n d contact between the ozone a n d the water.

U u r i n g t h e first 20 y e a r s of t h i s c e n t u r y — t h a t i s , f r o m t h e b i r t h of t h e first i n d u s t r i a l o z o n a t o r s — c o n s i d e r a b l e i n t e r e s t w a s f o c u s e d o n ozone u t i l i z a t i o n . N u m e r o u s a n d d i v e r s i f i e d a p p l i c a t i o n s a p p e a r e d . N e a r l y a l l of t h e m l e d t o f a i l u r e a n d d i s a p p o i n t m e n t , w h i c h is n o t s u r p r i s i n g , c o n s i d e r i n g t h a t i n d u s t r i a l ozone p r o d u c t i o n a p p e a r e d t o o early i n a w o r l d w h i c h at that time was underdeveloped technologically. I n E u r o p e ozone w a s , a n d s t i l l i s , u s e d m e r e l y f o r t h e s t e r i l i z a t i o n of d r i n k i n g w a t e r . C o n s i d e r e d f r o m t h i s aspect, o z o n i z a t i o n c o m p r i s e s t h r e e d i s t i n c t o p e r a t i o n s : (1) ozone p r o d u c t i o n i n i t s e l f , (2) c o n d i t i o n i n g of t h e a i r t o be s u b m i t t e d t o t h e e l e c t r i c d i s c h a r g e , a n d (3) c o n t a c t b e t w e e n ozone a n d w a t e r .

Ozone

Generators

A l l i n d u s t r i a l ozone generators a r e b a s e d u p o n t h e p r i n c i p l e of t h e e l e c t r i c d i s charge t h r o u g h d i e l e c t r i c s w h i c h a c t as s t a b i l i z i n g resistances, c o u n t e r a c t i n g a n y i n crease o r l o c a l i z a t i o n of t h e d e n s i t y of t h e h i g h t e n s i o n d i s c h a r g e . T h e essential p r e s ence of s u c h d i e l e c t r i c s establishes e l e c t r i c a l c o n d i t i o n s u n d e r w h i c h t h e d i s c h a r g e t a k e s p l a c e , a t t h e same t i m e i n t r o d u c i n g a n e l e c t r i c a l c a p a c i t y effect a n d a l e a d i n g p o w e r f a c t o r of 0.4 t o 0.6. F r o m t h e e l e c t r i c a l p o i n t of v i e w , t h e r e f o r e , t h e o z o n a t o r a p p e a r s as a c o n d e n s e r w h i c h a l l o w s a r a t h e r s i g n i f i c a n t a m o u n t of e n e r g y t o pass t h r o u g h . A c c o r d i n g l y , t h e a l t e r n a t i n g e l e c t r i c a l s t r a i n s a p p l i e d t o t h e m o l e c u l a r s t r u c t u r e s of t h e d i e l e c t r i c s p r o duce h e a t t h r o u g h a d i s s i p a t i o n of e n e r g y , a n d t h e d i e l e c t r i c s h a v e t o be c o o l e d b y c o n duction or convection. I n o t h e r respects, t h e electrodes t h e m s e l v e s a r e s u b j e c t t o h e a t i n g . T h i s r e s u l t s i n F o u c a u l t ' s c u r r e n t s , i n a n e l e c t r o n i c e m i s s i o n o n t h e a c t i v e s u r f a c e of t h e electrodes, a n d finally i n a s e c o n d a r y h e a t i n g t h r o u g h c o n v e c t i o n , c o n d u c t i o n , a n d r a d i a t i o n , d u e t o t h e i m m e d i a t e v i c i n i t y of t h e d i e l e c t r i c s a n d t h e d i s c h a r g e itself. T h e r e f o r e , t h e electrodes c a n n o t b e t h e r m a l l y i n s u l a t e d f r o m t h e s y s t e m , a n d c o o l i n g m u s t b e p r o v i d e d . F o r o z o n a t o r electrodes a n d d i e l e c t r i c s , one of t h e f o u r a r r a n g e m e n t s s h o w n i n F i g u r e 1 c a n be a d o p t e d , i n w h i c h t h e d i s c h a r g e t a k e s p l a c e e i t h e r b e t w e e n t w o d i e l e c 443

OZONE CHEMISTRY AND TECHNOLOGY Advances in Chemistry; American Chemical Society: Washington, DC, 1959.

A D V A N C E S IN CHEMISTRY SERIES

444 ARRANGEMENT

A

ARRANGEMENT

Β

LA,

J Y Y Y Y m .

H

v, ARRANGEMENT C

ARRANGEMENT D

LJ


JMUL,

Η 6R0UN

E V

Figure

2

1.

3

Γ V,

Arrangement for ozonator charge

dis

E. Electrode V. Glass dielectric T. Transformer

tries or between

a dielectric a n d a bare electrode.

W i t h a n y of these

arrangements,

one of h i g h t e n s i o n poles c a n be g r o u n d e d . Two

dielectrics (arrangement A or C) are seldom used i n a c t u a l practice.

For

e q u a l d i s c h a r g e d e n s i t y , a n a p p l i e d t e n s i o n h i g h e r t h a n t h a t c o r r e s p o n d i n g t o a single d i e l e c t r i c a s s e m b l y is n e c e s s a r y .

T h e r e f o r e , t h e e n e r g y of t h e d i s c h a r g e w i t h t w o d i

e l e c t r i c s c a n o n l y b e less t h a n t h a t of t h e single d i e l e c t r i c a s s e m b l y .

The

double

d i e l e c t r i c ( a r r a n g e m e n t A), t h e o n l y one a p p l i e d i n d u s t r i a l l y w i t h success, p r o v i d e d a n o b v i o u s i n t e r e s t f o r a n e r a w h e n stainless steels w e r e u n k n o w n , because these d i e l e c t r i c s p r o t e c t e d t h e electrodes f r o m c o r r o s i o n d u e t o h i g h t e n s i o n d i s c h a r g e i n t h e a i r . O f t h e t w o assemblies possible w i t h one d i e l e c t r i c , a r r a n g e m e n t D h a s b e e n i n d u s t r i a l l y because of t h e p r a c t i c a l i m p o s s i b i l i t y of c o o l i n g t h e d i e l e c t r i c .

rejected Arrange

m e n t Β is t h e basis of t h e m o s t i n t e r e s t i n g of t h e a c c o m p l i s h m e n t s i n t h e m a t t e r of ozone p r o d u c t i o n . I n E u r o p e f r o m 1907 t o 1930, t h r e e o z o n e g e n e r a t i n g processes w e r e

successfully

s u b m i t t e d t o t h e test of i n d u s t r i a l a p p l i c a t i o n s : t h e O t t o , t h e V a n d e r M a d e , a n d S i e m e n s processes.

S i n c e 1930, t h e r e h a s b e e n a t e n d e n c y t o w a r d i m p r o v i n g t h e p r o

d u c t i o n e q u i p m e n t of these processes w i t h a v i e w t o r e d u c i n g i t s size a n d e l i m i n a t i n g c e r t a i n p r o d u c t i o n d r a w b a c k s , s u c h as t h e t o o f r e q u e n t b r e a k a g e of d i e l e c t r i c s . Otto Ozonators.

B e f o r e 1930, O t t o o z o n a t o r s , b u i l t a n d p u t i n t o use i n n u m e r o u s

m u n i c i p a l w a t e r t r e a t m e n t p l a n t s , w e r e of t h e flat e l e c t r o d e t y p e w i t h t w o d i e l e c t r i c s , a s s e m b l e d as i n a r r a n g e m e n t A, F i g u r e 1, a n d s u p p l i e d w i t h 5 0 0 - c y c l e

current.

A n o z o n a t o r c o m p r i s e d a c e r t a i n n u m b e r of i n d i v i d u a l l y p r o d u c i n g u n i t s g r o u p e d i n a n insulated enclosure, glazed o n t h e front a n d rear surfaces. trodes them.

T h e t w o outer

were hollow plates at g r o u n d p o t e n t i a l , cooled b y c i r c u l a t i n g water T h e high tension plate was water-cooled

isolated the high tension from

ground.

elec

through

b y t h e use of t w o w a t e r f a l l s w h i c h

F i g u r e 2 shows s u c h a n o z o n a t o r


with

five

445


FRISON—EUROPEAN O Z O N A T I O N TECHNIQUES

Figure 2.

Otto ozonator,

flat-electrode

type, with five ozonator elements

High tension electrode cooled with water

o z o n a t o r elements. O n e of t h e w a t e r f a l l devices c a n b e seen a t t h e t o p of t h e p h o t o graph. I n 1930 c e r t a i n s t r u c t u r a l m o d i f i c a t i o n s a p p e a r e d , w h i c h h a d l i t t l e effect o n p r o d u c t i o n efficiency. I n g e n e r a l , t h e y r e n d e r e d t h e o z o n a t o r s less b u l k y a n d c h e a p e r t o c o n s t r u c t . T h e o z o n e - p r o d u c i n g elements were g r o u p e d i n t h e m a n n e r of a filter press a n d were c a l l e d o z o n a t o r b l o c k s . E a c h b l o c k c o n t a i n e d one t o s i x elements. T h e p l a t e s , o r i g i n a l l y of cast i r o n , were n o w of A l p a x , a n a l l o y of a l u m i n u m a n d s i l i c o n . B a t t e r i e s of f o u r b l o c k s a r r a n g e d as s h o w n i n F i g u r e 3 p r o v i d e d g r e a t e r p r o d u c t i o n c a p a c i t y i n less space. T h e c o o l i n g a r r a n g e m e n t s r e m a i n e d s u b s t a n t i a l l y t h e same. I n 1938, t o e l i m i n a t e t h e h a n d i c a p s of c o o l i n g t h e h i g h t e n s i o n electrode w i t h w a t e r , t r a n s f o r m e r o i l w a s u s e d f o r c o o l i n g . I t w a s c i r c u l a t e d i n a closed c i r c u i t , w h i c h i n c l u d e d a p u m p a n d a water-cooled heat exchanger, a n d was conducted to a n d f r o m t h e h i g h t e n s i o n electrodes b y m e a n s of l o n g b o r o s i l i c a t e glass t u b e s . A l t h o u g h t h i s a r r a n g e m e n t e l i m i n a t e d e l e c t r i c a l losses c a u s e d b y t h e w a t e r f a l l s , t h e i m p r o v e m e n t w a s p a r t i a l l y offset b y t h e e l e c t r i c a l c o n s u m p t i o n of t h e c i r c u l a t i n g p u m p . F i g u r e 4 shows a n o z o n a t o r of t h i s t y p e . A t t h e e n d of W o r l d W a r I I , t h e use of 5 0 0 - c y c l e

current for supplying Otto




446

Figure 3 .

Otto ozonator with ozone-producing elements grouped in batteries of four blocks High tension electrode cooled with water

ozonators practically disappeared. Thenceforth they were designed to function at the normal distribution frequency of 50 cycles. About 1948, hollow plates of stamped and welded steel were introduced. While these reduced costs, it was difficult to achieve completely flat and parallel faces and plates which would not become deformed. These problems have not yet been solved satisfactorily, and this innovation cannot be considered successful because of more frequent dielectric breakage. In 1954, oil cooling was abandoned, largely because of the difficulty of keeping the circuits leak-tight. A block model ozonator was developed wherein the high tension

Figure 4 . High

tension

Otto ozonator

electrode cooled sulating oil

with

in-



447


electrode w a s c o o l e d o n l y b y r a d i a t i o n a n d c o n v e c t i o n of a i r w i t h i n t h e o z o n a t o r cage. T h e l o w t e n s i o n electrodes r e m a i n e d w a t e r - c o o l e d . T h e f i n a l d e v e l o p m e n t h a s been t h e a d o p t i o n i n t h i s l a t e s t design of a r r a n g e m e n t Β ( F i g u r e 1 ) , w h e r e b y t h e r e is o n l y one d i e l e c t r i c p e r d i s c h a r g e . A l s o , t h e d i electrics a r e t h i n n e r (2.6 m m . i n s t e a d of 2.5 t o 3.5 m m . ) , a n d t o l e r a n c e s a r e closer. E n e r g y y i e l d s of 18 w a t t - h o u r s p e r g r a m of ozone a r e a t t a i n e d ( c o n c e n t r a t i o n n o t specified). E v e n t h i s design h a s weaknesses: T h e h i g h t e n s i o n p l a t e of A l p a x is c o r r o d e d b y t h e a c t i o n of t h e d i s c h a r g e ; t h e l o w t e n s i o n steel p l a t e s a r e p r o n e t o c o o l i n g w a t e r c o r r o s i o n , a n d t h e i r l a c k of flatness increases d i e l e c t r i c f a i l u r e . V a n der M a d e Ozonators. D e r i v e d f r o m the original Siemens ozonator, the v a n d e r M a d e differs o n l y i n t h e i n g e n i o u s m e t h o d of r i g i d l y c e n t e r i n g t h e h i g h t e n s i o n electrodes. T h e s e t u b u l a r o z o n a t o r s , designed as i n a r r a n g e m e n t B, F i g u r e 1, h a v e u n d e r g o n e o n l y m i n o r m o d i f i c a t i o n s since t h e i r i n t r o d u c t i o n . A h o r i z o n t a l glass d i e l e c t r i c is s u r r o u n d e d b y c o o l i n g w a t e r , w h i c h serves as t h e g r o u n d e d electrode. T h e h i g h t e n s i o n electrode is s p a c e d c o n c e n t r i c a l l y w i t h i n t h e glass t u b e , l e a v i n g a n a n n u l a r d i s c h a r g e space. T h e m o r e recent m o d e l s a r e d i s t i n g u i s h e d f r o m t h e o l d e r m o d e l s ( p r i o r t o 1930) b y a c e n t r a l electrode of stainless steel i n s t e a d of a l u m i n u m , d i e l e c t r i c s of b o r o s i l i c a t e glass i n s t e a d of o r d i n a r y glass, a n i m p r o v e d m e t h o d of f i x i n g t h e d i e l e c t r i c t u b e s i n t o t h e e n d p l a t e s , a n d a change i n t h e e x t e r i o r shape of t h e h o u s i n g s f o r t h e u n i t s . Siemens Ozonators. T h e S i e m e n s o z o n a t o r , one of t h e f i r s t ozone g e n e r a t o r s c a p a b l e of successful i n d u s t r i a l a p p l i c a t i o n , h a s u n d e r g o n e n o t e c h n i c a l m o d i f i c a t i o n s since a b o u t 1933. I t i s s u p p l i e d b y a 10,000-cycle c u r r e n t . C u r i o u s l y , t h e g e n e r a t o r is v e r y s i m i l a r t o t h e v e n e r a b l e B e r t h e l o t o z o n a t o r . T h e basic g e n e r a t i n g c e l l i s of s e m i c r y s t a l glass of s p e c i a l c o m p o s i t i o n . I t is of t u b u l a r design w i t h t w o c o n c e n t r i c glass d i e l e c t r i c s a s s e m b l e d a c c o r d i n g t o a r r a n g e m e n t A, F i g u r e 1. T h e o u t e r glass t u b e is s u p p o r t e d v e r t i c a l l y i n a t a n k t h r o u g h w h i c h w a t e r c i r c u l a t e s . T h e w a t e r p l a y s a t t h e same t i m e t h e p a r t of a g r o u n d e d electrode a n d a m e a n s of c o o l i n g . T h e h i g h t e n sion electrode is l i k e w i s e of w a t e r , w h i c h is c i r c u l a t e d t h r o u g h t h e i n n e r glass t u b e . A n u m b e r of s u c h cells a r e a r r a n g e d i n p a r a l l e l . T h e c o o l i n g of t h e h i g h t e n s i o n electrodes is b y a m e a n s s i m i l a r t o t h a t of t h e first O t t o o z o n a t o r s , e x c e p t t h a t t h e b r e a k i n t h e h i g h t e n s i o n c i r c u i t is a c c o m p l i s h e d b y a r a i n of d r o p l e t s i n t o i n s u l a t i n g o i l i n s t e a d of a f a l l t h r o u g h a i r . T h i s o z o n a t o r , despite t h e q u a l i t i e s i t d i s p l a y e d a t t h e t i m e of i t s i n t r o d u c t i o n , h a s n o t b e e n v e r y successful. E x p e n s i v e because of t h e use of t h e 5 0 - t o 10,000-cycle c o n v e r t e r set, i t seems f r a g i l e a n d difficult t o o p e r a t e . O z o n o Ozonators. T h e s e g e n e r a t o r s , d e v e l o p e d b y t h e engineer N i c c o l i a b o u t 1936 f o r t h e O z o n o C o . of M i l a n , a r e d e r i v e d f r o m t h e O t t o p l a t e b l o c k - o z o n a t o r . T h e y differ i n details as w e l l as t h e f o l l o w i n g p o i n t s : T h e c o o l i n g p l a t e s a r e c i r c u l a r a n d m a d e of t h i n steel (0.5 m m . ) b y s t a m p i n g t w o h a l f - s h e l l s , u n i t e d b y c r i m p i n g , a n d m a d e t i g h t b y s o l d e r i n g . T h e d i e l e c t r i c s a r e of m i c a n i t e a n d a r e s p a c e d b y r a d i a l s t r i p s . T h e r e a r e s p e c i a l c h e c k - p l a t e s , e n s u r i n g a reasonable t i g h t e n i n g of t h e elements c o n s t i t u t i n g a b l o c k , a n d t h e m e t h o d of s u s p e n d i n g t h e p l a t e s a u t o m a t i c a l l y ensures t h e i r c e n t e r i n g . T h e o z o n a t o r is i n t h e f o r m of a desk. A c i r c u l a t i o n of i n s u l a t i n g o i l o p e r a t i n g b y m e a n s of a t h e r m o s i p h o n ensures t h e c o o l i n g of t h e electrodes w i t h o i l , w h i c h i n t u r n is c o o l e d b y w a t e r . T h e o z o n a t o r s operate o n 50-cycle current. T h e units are well constructed. I t is regrettable t h a t t h e y h a v e been s u p p l i e d w i t h a i r d r i e d b y c a l c i u m c h l o r i d e , w h i c h r e d u c e d t h e i r p r o d u c t i o n efficiency. T h e specific e n e r g y y i e l d s f o r these o z o n a t o r s h a v e n e v e r been made public. Conditioning

of A i r b e f o r e

Discharge

In G e r m a n y . P r i o r t o 1933, a l l i n d u s t r i a l o z o n a t o r s were s u p p l i e d w i t h a i r d r i e d b y c a l c i u m c h l o r i d e . I t w a s t h e S i e m e n s C o . w h i c h first used s i l i c a g e l . T h e d r y e r d e -

American Chemical Society

OZONE CHEMISTRY AND TECHNOLOGY LibrarySociety: Washington, DC, 1959. Advances in Chemistry; American Chemical



448

s i g n e d b y t h i s c o m p a n y w a s a c o n t i n u o u s - o p e r a t i o n t y p e w i t h t w o a d s o r p t i o n cells r e a c t i v a t e d i n closed c i r c u i t . T h e c h a n g i n g o v e r of t h e a i r s t r e a m s a t t h e t i m e of reactivation was ensured b y a solenoid valve, itself regulated b y a t i m e r w i t h a d justable electrical contacts. I n F r a n c e . I n 1938, t h e first s i l i c a g e l d r y e r a p p l i e d t o t h e O t t o process w a s p u t i n o p e r a t i o n . S i n c e t h e n , t h i s m e t h o d of d r y i n g h a s n o r m a l l y been u s e d i n a l l O t t o o z o n a t i o n p l a n t s , e x c e p t t h e S a i n t - M a u r p l a n t , w h i c h alone uses c o o l i n g . A f t e r 1952, O t t o o z o n a t i o n e q u i p m e n t u s e d t w o stages o f d r y i n g t o c o n d i t i o n t h e a i r : T h e first stage ensures t h e c o o l i n g of t h e a i r d o w n t o + 5 ° C . b y m e a n s of a h e a t e x c h a n g e r i m m e r s e d i n a b r i n e b a t h c o n t a i n i n g also t h e e v a p o r a t o r of t h e r e f r i g e r a t o r ; t h e second stage ensures t h e final d r y i n g b y p a s s i n g t h e a i r t h r o u g h s i l i c a g e l . O z o n e p l a n t s e s t a b l i s h e d a c c o r d i n g t o t h e v a n d e r M a d e processes use c a l c i u m c h l o r i d e as a d e h y d r a t i o n a g e n t . O n l y recently has silica gel d r y i n g been adopted. I n Switzerland. T h e v e r y fine ozone s t e r i l i z a t i o n p l a n t b u i l t a t B e r n e i n c l u d e s a n o v e l a i r - d r y i n g i n s t a l l a t i o n designed b y t h e C a r b a C o . , B e r n e . A f t e r p a s s i n g t h r o u g h a d u s t f i l t e r , t h e a i r i s c o m p r e s s e d t o 5 k g . p e r s q . c m . (71 p.s.i.), cooled i n a c i r c u l a t i n g water heat exchanger, t h e n cooled d o w n t o —30° to —40° C . i n a n e x c h a n g e r s e r v e d b y a r e f r i g e r a t o r b e f o r e e x p a n d i n g t o o p e r a t i n g p r e s s u r e . U n d e r these c o n d i t i o n s , t h e d r y n e s s a t t a i n e d i s a b o u t 3 0 m g . of w a t e r p e r k g . of d r y a i r ( d e w p o i n t , —60° F . ) . T h i s c o m p l e t e l y a u t o m a t i c i n s t a l l a t i o n operates w e l l , b u t seems m u c h t o o e x p e n s i v e t o r u n . T h e specific e l e c t r i c a l c o n s u m p t i o n i s 210 w a t t - h o u r s p e r c u b i c m e t e r of a i r , w h i c h b r i n g s t h e c o n s u m p t i o n f o r t h e o z o n a t e d a i r a t a c o n c e n t r a t i o n of 10 g r a m s p e r c u b i c m e t e r , t o 21 w a t t - h o u r s p e r g r a m of ozone. T h i s e l e c t r i c a l c o n s u m p t i o n i s m u c h h i g h e r t h a n t h a t necessary f o r t h e p r o d u c t i o n of ozone i t s e l f , a n d five t o s i x t i m e s higher t h a n that required for a d r y i n g system using activated a l u m i n a or silica gel. In Italy. T h e a i r - d r y i n g m e t h o d u s e d i n m o s t i n s t a l l a t i o n s of t h e O z o n o - N i c c o l i t y p e w a s a b s o r p t i o n b y c a l c i u m c h l o r i d e . T h e use of p o r o u s a d s o r b e n t s d i d n o t a p p e a r u n t i l a r o u n d 1938. Bringing

Ozone and Water

into

Contact

A f t e r t h e ozone i s p r o d u c e d , i t m u s t b e m a d e t o a c t u p o n t h e w a t e r . T h i s p r o b l e m , w h i c h i s a m a t t e r of b r i n g i n g l a r g e v o l u m e s of gases a n d l i q u i d s i n t o a d e q u a t e a n d c o n t i n u o u s c o n t a c t , h a s b e e n a p p r o a c h e d i n a v a r i e t y of w a y s . T w o m e t h o d s w e r e i n t r o d u c e d a b o u t 1930. O n e w a s d e v e l o p e d b y O t t o , t h e o t h e r b y V a n d e r M a d e .

Figure 5.

W a t e r pump a n d deep tower


449



A c c o r d i n g to t h e O t t o m e t h o d ( F i g u r e 5 ) , t h e ozonated a i r is aspirated b y a sort of w a t e r p u m p c a l l e d a n émulseur. T h e resulting emulsion is carried along a t i n c r e a s i n g p r e s s u r e t h r o u g h a v e r t i c a l t u b e , l'appendice de dissolution, t o t h e b o t t o m of a deep t o w e r , t h e colonne de self-contact, w h e r e i t rises a g a i n , f r e e i n g m y r i a d s o f fine b u b b l e s w h i c h p r o l o n g a n d i m p r o v e t h e c o n t a c t b e t w e e n w a t e r a n d gas. T h e d i s s o l v i n g a p p e n d i x , i m m e r s e d f o r i t s e n t i r e l e n g t h , releases t h e e m u l s i o n a t t h e base of t h e s e l f c o n t a c t c o l u m n b y m e a n s of a d i f f u s i n g b e l l , w h i c h i m p a r t s a c i r c u l a r m o v e m e n t t o the water entering t h e c o l u m n . T h e c o l u m n is c y l i n d r i c a l or prismatic, made of r e i n f o r c e d c o n c r e t e , w i t h a d e p t h of 5 m e t e r s ( 1 6 f e e t ) . T h e w a t e r leaves t h e c o l u m n o v e r a f w e i r a t t h e t o p a n d passes t h r o u g h a series of cascades c a l l e d a d e s a t u r a t o r , w h i c h r e m o v e s a n y d i s s o l v e d ozone. T h i s d e s a t u r a t i o n h a s been i n c o r p o r a t e d t o c o n f o r m t o t h e " R e c o m m a n d a t i o n s d u C o n s e i l Supérieur d ' H y g i è n e P u b l i q u e de F r a n c e de 1924," w h i c h s t i p u l a t e t h a t a f t e r treatment t h e water m u s t contain n o substance foreign t o i t s original composition. H o w e v e r , t o d a y t h e r e i s a t e n d e n c y t o w a r d e l i m i n a t i o n of f i n a l d e s a t u r a t i o n i n o r d e r t o m a i n t a i n t h e ozone i n c o n t a c t w i t h t h e w a t e r as l o n g as p o s s i b l e . T h e a p p a r a t u s u t i l i z e d i n t h e V a n d e r M a d e s y s t e m i s a c o l u m n of s u i t a b l y p r o t e c t e d steel i n s m a l l i n s t a l l a t i o n s , r e i n f o r c e d c o n c r e t e i n l a r g e ones. T h e c o l u m n i s d i v i d e d i n t o sections of h o r i z o n t a l p e r f o r a t e d c e l l u l o i d p l a t e s w i t h 0 . 7 - m m . holes. Both t h e w a t e r a n d a i r e n t e r a t t h e b o t t o m a n d pass u p w a r d t h r o u g h s e v e r a l o f these plates. T h i s m e t h o d provides good m i x i n g a n d allows utilization of l o w concentrations of ozone. A n o t h e r n o v e l c h a r a c t e r i s t i c of t h i s process is t h e r e c o v e r y of excess ozone at t h e t o p of t h e c o l u m n a n d i t s recycle t h r o u g h drier, ozonator, a n d piston-type compressor. B y use o f a v a r i a b l e speed c o m p r e s s o r , t h e q u a n t i t y o f ozone i n j e c t e d c a n be v a r i e d i n a c c o r d a n c e w i t h t h e q u a l i t y of t h e w a t e r . B e c a u s e of a n u m b e r of p r o b l e m s — e . g . , w e a k n e s s of t h e p e r f o r a t e d p l a t e s , t o o l o w a n ozone c o n c e n t r a t i o n , t o o l a r g e a v o l u m e of a i r , a n d c o s t l y m a i n t e n a n c e o f t h e c o m p r e s s o r a n d o t h e r e q u i p m e n t because of c o r r o s i v e a c t i o n of o z o n e — t h i s m e t h o d h a s been m o d i f i e d i n l a t e r i n s t a l l a t i o n s . T h e p e r f o r a t e d p l a t e s h a v e been e l i m i n a t e d , a n d t h e a i r is diffused t h r o u g h p l a s t i c diffusers. S t a i n l e s s steel r o t a r y , l i q u i d r i n g c o m p r e s s o r s a r e u s e d . I n s o m e cases, e v e n t h e O t t o m e t h o d of émulseur s a n d selfcontact columns is employed. C o n t a c t Processes Since 1 9 3 0 Chlorator Process. T h i s process uses a s m a l l c o n t a c t c o l u m n a n d i n j e c t o r , w h e r e b y a p o r t i o n of t h e w a t e r i s t r e a t e d t o dissolve a r e l a t i v e l y l a r g e a m o u n t of ozone. T h i s p o r t i o n is t h e n a d d e d t o t h e m a i n w a t e r s t r e a m . T h e success o f t h e m e t h o d r e q u i r e s a h i g h c o n c e n t r a t i o n of ozone ( 1 0 t o 2 0 g r a m s p e r c u b i c m e t e r ) a n d a s t a t i c p r e s s u r e of 0.6 t o 2.0 k g . p e r s q . c m . A n y w h e r e f r o m o n e h a l f t o one s i x t h o f t h e t o t a l w a t e r m a y be required i n t h e ozonized stream. T o r r i c e l l i Process. T h i s m i x i n g m e t h o d w a s d e v e l o p e d b y A l f r e d T o r r i c e l l i of B e r n e . I t s a d v a n t a g e s a r e t h e a b i l i t y t o d i s s o l v e m o r e ozone i n t h e w a t e r t h r o u g h h i g h e r pressures a n d i m p r o v e d c o n t a c t , a n d t o a t t a i n v i r t u a l l y c o m p l e t e a b s o r p t i o n of t h e ozone i n t h e w a t e r . T h e K e r a g Process. T h i s s y s t e m uses a h i g h - s p e e d a g i t a t o r of stainless steel, w h i c h r a p i d l y mixes the ozonized a i r a n d water i n t i m a t e l y . A f t e r m i x i n g , the waterozone passes i n t o a c o n t a c t b a s i n . T h e s e t h r e e s y s t e m s h a v e been i n t r o d u c e d o n l y r e c e n t l y , a n d t h e y a r e c o m p a r e d i n a p a p e r b y T o r r i c e l l i (1). Literature (1)

Cited

Torricelli, Alfred,

RECEIVED

ADVANCES

IN

CHEM.

for review June 19, 1957.

SER.

21, 453 ( 1 9 5 8 ) .

Accepted June 19, 1957.


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