DEVELOPMENT OF A TOTAL CLOSED WATER SYSTEM FOR A D E I N K I N G PLANT

Milos Krofta , P.E., Ph.D., P re s iden t Krof t a Engineering Corporation, Lenox, MA 01240 USA

Lawrence K. Wang, P.E., Ph.D., Manager LenOX I n s t i t u t e f o r Research Inc. , Lenox, MA 01240 USA

ABSTRACT

Waste paper is recycled as pulp f o r reproduct ion of papers o r boards. The pulp con ta in ing secondary f i b e r s needs t o be p u r i f i e d i n a deinking p l a n t . A t o t a l c l o s e d water system has now been developed f o r water reclamation i n deinking p l a n t s . The pulp with inks is f i r s t processed wi th a foaming u n i t (Foamer) and then a washing u n i t (Stock Washer). The waste water is c l a r i f i e d by a d i s so lved a i r f l o t a t i o n c l a r i f i e r (Suprace l l ) f o r water reclamation. A f r a c t i o n a t o r (Spray F i l t e r ) is a d d i t i o n a l l y used f o r recovery of long f i b e r s from washing water. The s ludge is thickened on a th i ckene r (Twin Wirepress) . The newly developed water reclamation and deinking system i n I t a l y is highly e f f i c i e n t and c o s t - e f f e c t i v e . For academic and engineer ing c o n t r i b u t i o n s s p e c i a l emphasis is placed on t h e design of i nd iv idua l t reatment u n i t s and t h e e n t i r e deinking/reclamation system. [Key Words1 Innovation, Water Reclamation, Zero Discharge, Waste Paper, Pulp, Deinking, Secondary F ibe r s , F l o t a t i o n , Dissolved A i r F l o t a t i o n , Dispersed A i r F l o t a t i o n , Stock Washer, Spray F i l t e r , Thickening

INTRODUCTION

Since 1965 Krof t a Engineering Corporation, Lenox, MA, has been developing equipment f o r reuse of wastepaper and water reclamation i n deinking processes .

High raw ma te r i a l p r i c e s , combined wi th high energy c o s t s and p rogres s ive ly s t ronge r e f f l u e n t p o l l u t i o n c o n t r o l are making wastepaper deinking always more economically f e a s i b l e and c l o s i n g of t h e deinking water systems imperative.

Un t i l r ecen t ly wastepaper was used exc lus ive ly f o r t h e lowgrade boards or f o r m u l t i p l e l a y e r board a s i n t e r n a l gray f i l l e r . In t h e near f u t u r e , it is expected t h a t more and more wastepaper recovered from municipal s o l i d waste treatment p l a n t s w i l l be used f o r t h i s purpose and more p r i n t e d wastepaper w i l l i nc rease i n va lue a s a raw m a t e r i a l f o r b e t t e r grades of paper, i f t h e deinking technology is s u f f i c i e n t l y developed.

P resen t ly t h e b u l k of wastepaper deinking is concentrated on newsprint waste deinking. The reasons are: (a) The d a i l y c o l l e c t i o n of ove r i s sues provides f o r a s teady raw ma te r i a l flow; and (b) The requirements f o r degree of b r i g h t n e s s f o r newsprint is n o t t o o high.

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The next group of present wastepaper deinking 1s cons iderably smaller and used f o r t h e product ion of t i s s u e papers. The genera l t r end toward always h igher and higher b r igh tness and s o f t n e s s of t i s s u e paper p l aces cons iderable demand f o r a continuous improvement of the deinking technology . With cons iderable d i s t ance fo l lows t h e deinking of p r i n t e d books wi th a very high b a s i c va lue of t h e o r i g i n a l paper f i b e r but wi th a l s o very high demand on c l e a n l i n e s s and br ightness .

For decades two p r i n c i p a l deinking systems have been competing: (a) Foam f l o t a t i o n deinking, e x t r a c t i n g ink by foam. - Mineral f i l l e r and paper f i n e s a r e mainly recovered t h e r e f o r e t h e y i e l d is h igh b u t t h e phys ica l s t r e n g t h of t h e deinked s tock i s poor; and (b) Washing deinking where ink , mineral f i l l e r and f i b e r f i n e s are washed ou t a t high d i l u t i o n and a papermaking f i b e r of good q u a l i t y is obta ined wi th s a c r i f i c e of lower y i e l d .

Both above systems a r e p r e f e r e n t i a l f o r c e r t a i n wastepaper grades and f i n a l uses of deinked s tock without much f l e x i b i l i t y t o a d j u s t t o d i f f e r e n t wastepaper grades o r d i f f e r e n t f i n a l usage.

D E S I G N OF I N D I V I D U A L D E I N K I N G AND WATER RECLAMATION FACILITIES

I n order t o ob ta in t h e maximum of deinking e f f i c i e n c y , Krofta Engineering Corporat ion has incorpora ted both systems and o p e r a t e s wi th f i r s t foaming (Krofta Foamer; F igu re 1) and then washing (Krofta Stockwasher; F igure 2) and o b t a i n s a c losed water system wi th c l a r i f y i n g t h e washwater wi th a d isso lved a i r f l o t a t i o n c l a r i f i e r (Krof ta Suprace l l ; F igu re 3 ) . A f r a c t i o n a t o r (Krof t a Spray F i l t e r ; F igure 4 ) is a d d i t i o n a l l y used f o r recovery of longer f i b e r s from washing water . The s ludge is thickened on a twin wire p r e s s (Krof ta Twin-Wirepress; F igure 5).

The combination of both p r i n c i p l e s of foaming and washing was made p o s s i b l e without r a i s i n g t h e i n s t a l l a t i o n c o s t of t h e deinking p l a n t by using advanced methods f o r foaming and washing.

Xro f t a Foamer -- iSDerSed A i r F l o t a t i o n Deinkina C e l l ,

Krofta Foamer uses t h e p r i n c i p l e t h a t foam e x t r a c t i o n is propor t iona l t o t h e su r face area and no t t h e volume of t h e foaming machine. Therefore a l a r g e su r face wi th a low depth (80 c m ) is used and l a r g e amounts of foam a r e e a s i l y produced i n a n inexpensive foaming tank.

The Foamer is s p e c i f i c a l l y designed f o r deinking of waste paper. It removes ink from waste paper by producing foam a r t i f i c i a l l y . T h i s foam c o l l e c t s ink and when t h e foam is e x t r a c t e d , t h e ink is separa ted from t h e waste paper. The cons t ruc t ion of t h e Foamer is designed f o r low power and space requirements as w e l l as f o r s imple ope ra t ion and low equipment cos t . The f r o t h (foam) removes ink

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F r e f e r e n t i a l l y and t h e subsequent washing can be made i n

As shown i n F igu re I, t h e Foamer is composed of a shallow tank 111 with a f eed w e l l [ 2 1 where t h e waste paper s l u r r y e n t e r s w i th approximately 4% bone dry consis tency. The paper s l u r r y is d i l u t e d a t t h e en t r ance with recycled c l a r i f i e d water t o approximately 0.8% cons i s t ency and some foaming chemicals a r e added a t t h e same spot . A r e c y c l e pump E31 f eeds an e j e c t o r [ 4 1 t h a t d i scha rges t a n g e n t i a l l y i n t o t h e tank [11 c r e a t i n g a c i r c u l a r movement of s tock i n t h e tank. With a blower [51 a i r is added i n t o t h e e j e c t o r a t low pressure. This a i r is d i spe r sed i n t h e e j e c t o r and e n t e r s i n t o t h e tank, producing a l a r g e amount of foam t h a t t rave ls on t h e t o p of t h e c i r c u l a t i n g s tock. The foam is cont inuously c o l l e c t e d by t h e foam c o l l e c t o r [61 and e x t r a c t e d i n t o t h e foam s u c t i o n tank 171, where a s u c t i o n blower holds a l i g h t vacuum. The foam c o l l a p s e s i n t h e foam s u c t i o n tank and is e x t r a c t e d cont inuously by a water l ock and discharged i n t o t h e s ludge c o l l e c t i o n tank. The cleaned s t o c k is discharged i n t h e c e n t e r of t h e tank [11 a t t h e bottom opening and overflows t h e t e l e s c o p i c a d j u s t a b l e weir [ 8 1 . From t h e r e it is pumped t o t h e c l e a n e r s and t o t h e Krofta Stock Washer.

Stock Washer

Krofta Stock Washer is a n improvement of t h e t r a d i t i o n a l s i d e h i l l washer by having a n u p h i l l slowly moving s c r e e n and m u l t i p l e dams f o r t h e downflowing s tock. A t r i p l e washing is e f f e c t e d i n t h e same space a s a conventional s i n g l e s i d e h i l l screen. The sc reen is cont inuously cleaned and a p r e s s e x t r a c t s a d d i t i o n a l mineral f i l l e r from t h e s tock.

With t r i p l e washing wi th recycled c l a r i f i e d water , a high degree of b r i g h t n e s s is ob ta inab le , p a r t i c u l a r l y a f t e r t h e removal of t h e ink i n t h e Krofta Foamer. With m u l t i p l e washing it is f u r t h e r p o s s i b l e t o c o n t r o l t h e washing ou t of t h e f i l l e r and f i n e s from t h e f u r n i s h .

A s shown i n Figure 2 , t h e Krofta Stock Washer has a n i n c l i n e d upward moving s c r e e n 111 t h a t r e t u r n s back t o t h e bottom thickening drum 121. The s tock t o be washed and thickened e n t e r s on t o p [31 with a consis tency of 0.6 - 1 .0%. Flowing down over t h e upper part of t h e screen, t h e s tock is p a r t i a l l y dewatered and accumulates a t t h e f i r s t c r o s s b a r r i e r [ 4 1 . The p a r t i a l l y thickened s t o c k is d i l u t e d wi th recycled c l a r i f i e d water and overf lows t o t h e second b a r r i e r [51. P a r t i a l l y thickened s t o c k is t h e r e d i l u t e d again, overflows t h e b a r r i e r and f lows and rolls down t h e s c r e e n and t h e s t a t i o n a r y i n c l i n e d board [61 u n t i l it e n t e r s i n t o t h e n i p between t h e r e t u r n i n g s c r e e n and t h e drum. The s tock is pressed by t h e sc reen on t h e drum. The s c r e e n wraps around t h e drum and t h i c k e n s t h e s tock t o high consis tency. A p r e s s 181 squeezes t h e deinked s t o c k t o higher consis tency 9 - 14%. A t r a n s v e r s e l y mounted r o t a t i n g screw e x t r a c t s t h e thickened s t o c k and d i scha rges i t a t t h e s i d e 171.

ewer s t a g e s o r can r e s u l t i n a b r i g h t e r pulp.

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The e f f l u e n t from t h e t h r e e th ickening phases is s e p a r a t e l y c o l l e c t e d and discharged i n t o t h e Krofta Spray F i l t e r f o r f u r t h e r f i b e r recovery. The e f f l u e n t from t h e Spray F i l t e r is f i n a l l y discharged i n t o Krofta Supracell f o r water t rea tment and reclamation.

Kro f t a Supra c e l l -- A D i s so lved A i r F1 o t a t i o n C l a r i f i e y

Progress ive ly f o r l a r g e i n s t a l l a t i o n s a s e p a r a t e Suprace l l c l a r i f i e r is i n s t a l l e d on t h e a l k a l i n e pulper -ex t rac tor l o o p for recovery of chemicals and hea t .

F igure 3 shows t h e Suprace l l design. The i n l e t 18 and 1 1 1 , o u t l e t [ 2 1 , and s ludge removal mechanisms [61 are contained i n t h e c e n t r a l r o t a t i n g sec t ion . This s e c t i o n and t h e s p i r a l scoop [61 r o t a t e around t h e tank a t a speed synchronized wi th t h e flow. Waste water, f i r s t pass ing through t h e a i r d i s so lv ing tube , is re l eased through a r o t a r y j o i n t [51 i n t h e cen te r of t h e tank. It then passes i n t o t h e d i s t r i b u t i o n duct [111 t h a t moves forward wi th t h e same v e l o c i t y as t h e incoming water thus c r e a t i n g "Zero Veloci ty" . The f l o t a t i o n processes t a k e p l ace i n t h i s qu ie scen t state. The pa ten ted S p i r a l Scoop [61 t a k e s up t h e f l o a t e d s ludge , pouring it i n t o t h e s t a t i o n a r y cen te r s e c t i o n where i t is discharged by g r a v i t y f o r d i sposa l . C l a r i f i e d water is removed by e x t r a c t i o n p ipes [91 which a re a t t ached t o t h e moving c e n t e r s ec t ion . The c l a r i f i e d water which normally con ta ins less than 30 mg/l of suspended s o l i d s is recyc led i n t h e process f o r reuse.

Wiper b lades a t t ached t o t h e moving d i s t r i b u t i o n duct s c rape t h e bottom and t h e s i d e s of t h e tank [41 and d ischarge s e t t l e d s ludge i n t o t h e b u i l t - i n sump [31, f o r p e r i o d i c purging. The v a r i a b l e speed gear motor 1101 d r i v e s t h e r o t a t i n g elements and scoop [61. Electrical c u r r e n t f o r t h e gear motor f eeds from a ro t a ry contac t 151 mounted on t h e c e n t r a l s h a f t .

The u s e of Krofta Suprace l l f o r wastewater t reatment and water rec lamat ion has been f u l l y demonstrated (1-10).

Sprav F i l te l ;

The Krof ta Spary F i l t e r , shown i n F igure 4 , is s p e c i f i c a l l y designed f o r t h e f r a c t i o n a t i o n of e f f l u e n t s conta in ing from 20 - 5000 mg/l of suspended s o l i d s . A f i n e mesh c l o t h wi th openings from 74 t o 500 microns is used as t h e f i l t e r media, e i t h e r t o s e p a r a t e long f i b e r s from c l ay and f i l l e r or as s a f e t y f i l t e r f o r showers using c l a r i f i e d water. The Spray F i l t e r meets t h e need f o r a high thruput u n i t which can handle wide v a r i a t i o n s i n s o l i d s conten t . It is equipped wi th a c leaning shower which g r e a t l y reduces t h e need t o remove t h e c l o t h for cleaning. All p a r t s i n con tac t wi th t h e water a re b u i l t of 304 s t a i n l e s s steel. The access door has a p l e x i g l a s s window. All bearings s u r f a c e s are made of corrosion-proof p l a s t i c ma te r i a l s .

Twin Wirepress

The Twin Wirepress, shown i n F igure 5 , is designed f o r

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sludge thickening, and dewatering.

In ope ra t ion , t h e s ludge is f e d by pump from t h e s ludge tank t o t h e v e r t i c a l f l o c c u l a t i o n compartment on t o p of t h e p r e s s and composed of a d j u s t a b l e undulated p l a t e s . F loccu la t ing chemicals a r e f e d i n along wi th t h e sludge.

The f l o c c u l a t e d s ludge l e a v e s t h e f l o c c u l a t i n g compartment a t t h e bottom and e n t e r s t h e v e r t i c a l mixing compartment where m u l t i p l e h o r i z o n t a l p l a t e s g e n t l y a g i t a t e t h e sludge.

The wire coming out of t h e mixing department is i n c l i n e d upwards and t h e f i r s t dewatering t a k e s place. Then t h e wire with t h e s ludge t u r n s downward i n t o t h e wedgeshaped compartment - composed of two wires - which squeeze t h e sludge between them.

The two wires wi th t h e s ludge sandwiched between them, run wrapped f o r ha l f t u r n around t h e l a r g e p e r f o r a t e d drum which is l o c a t e d a t t h e lower side of t h e p re s s . After l e a v i n g t h e drum, t h e double wires move up around s e v e r a l r o l l e r s f o r f u r t h e r dewatering. The r o l l e r s have p rogres s ive ly smaller diameter f o r b e t t e r dewatering.

A t t h e t o p of t h e p r e s s , t h e two wires sepa ra t e . Each has i t s own rubber-covered pickup r o l l with a s c rape r f o r s ludge discharge i n t o a hopper.

The two wires have ind iv idua l wire guiding dev ices (pneumatically operated) and manually-operated t e n s i o n rolls. Each wire has a shower with shower water c o l l e c t i n g pan.

The Krofta Twin Wirepress has a capac i ty of approximately 1 0 TPD of bone dry s ludge per 3 f t . 3 in . (1 .0 m) wire width. This r e f e r s t o primary papermil l s ludge with adequate chemical cond i t ione r . The i n l e t consis tency is 1.5 - 4.0% and t h e d i scha rge has a dryness of 30 - 35%.

D E S I G N OF COMPLETE SEMI-INDUSTRIAL D E I N K I N G PLANT I N ITALY

Wastepaper deinking is a complex procedure and cannot be demonstrated and t e s t e d s u f f i c i e n t l y on a l a b o r a t o r y s c a l e .

Krofta I t a l i a S.A. with t h e cooperat ion of Krofta Engineering Corporat ion, Lenox, MA i n USA, and t h e Lenox I n s t i t u t e f o r Research Inc. , has e r e c t e d a complete deinking p l a n t for a capac i ty of 5 TPD. This i n s t a l l a t i o n is l o c a t e d a t t h e Papermill C a r t i e r a d i Vidardo, approximately 3 5 km ( 2 2 miles) from t h e c i t y of Milano, I t a l y .

This i n s t a l l a t i o n is completely sepa ra t ed from o the r papermil l ope ra t ions .

The i n t e n t is t o g ive t o p o t e n t i a l customers who a r e i n t e r e s t e d i n i n s t a l l i n g a deinking p l a n t t h e p o s s i b i l i t y t o br ing t h e i r wastepaper and t o determine a11 t h e f a c t o r s and resu l t s of t h e deinking procedures.

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Following such semi - indus t r i a l tests it can be determined: ( a ) The obtained q u a l i t y of t h e deinked s tock ( b r i g h t n e s s , c l e a n l i n e s s , mineral f i l l e r s and f i n e s con ten t ) ; (b) Yield and f i b e r and f i l l e r l o s s under d i f f e r e n t procedures; ( C ) Consumption of chemicals, power, water and h e a t ; (d) S p e c i f i c capac i ty of equipment (pumping t i m e , chemicals a c t i n g t i m e , foaming product ion, c l ean ing requirements , stockwashing parameters, recycled water c l a r i f i c a t i o n requirements, etc.) ; (e) Overa l l economic a spec t of t h e deinking; ( f ) S p e c i f i c design of t h e deinking p l a n t and t h e i n d i v i d u a l machines capaci ty .

The semi - indus t r i a l deinking p l a n t can be u s e f u l l y operated a l s o by chemical companies manufacturing s p e c i a l chemicals f o r deinking a p p l i c a t i o n i n order t o e v a l u a t e t h e performance of t h e new chemicals.

S u f f i c i e n t amounts of deinked s tock can be produced i n order t o make paper s h e e t s on small paper machines and t o e l a b o r a t e t h e combination of t h e s tock wi th o the r raw materials . The deinking p l a n t was designed with a maximum of v e r s a t i l i t y , al lowing d i f f e r e n t combinations of t h e deinking process .

It can ope ra t e with foaming and washing toge the r o r only with foaming o r with washing.

Each phase can be operated by repeated r ecyc l ing if d e s i red . Figures 6 , 7 and 8 show t h e composition of t h e Semi-Industr ia l Deinking P l a n t .

Loadina P1 atform I1 1 and PulPer [2L

The Loading Platform [ll is f o r accumulation of t h e waste paper b a l e s and s c a l e s f o r measuring and f eed ing i n t o t h e Pulper E21 with a volume of 3 m3. The a g i t a t o r has a h o r i z o n t a l s h a f t and a pe r fo ra t ed p l a t e with 8 mm ho le s passing t h e pulped s tock. The consis tency is kept , depending on t h e requirements, from 3 - 6% bone dry, having 90 - 180 kg of dry waste paper f o r each batch. The pulping time is 20 - 30 minutes. Including loading and discharging t i m e , each batch con ta ins approximately 45 minutes r e s u l t i n g i n a maximum load of 5.7 MT/24h.

Addition of chemicals u sua l ly is made fol lowing a r e c i p e i n t h e pulper t o o b t a i n t h e r equ i r ed chemical r eac t ions : (a ) Sapon i f i ca t ion of o i l s combining t h e p r i n t i n g inks ; (b) Dispersion of ink p a r t i c l e s i n t o a c o l l o i d a l s t a t e ; (c) S u r f a c t a n t a c t i o n t o c o l l e c t ink on foam; (d) Detergents f o r s e p a r a t i o n of colored pigments with t h e r e s i d u a l s of t h e s a p o n i f i c a t i o n with t h e water hardness; (e) Oxydation f o r bleaching purpose; and ( f ) Steam f o r keeping t h e s tock temperature a t approximately 60 deg res s C.

U e n s i t v Cleaner [3L

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;t is . for t h e s e p a r a t i o n of coa r se impur i t i e s . Such i m p u r i t i e s should be e x t r a c t e d ahead of def i b e r i n g a c t i o n for easier e l imina t ion . - s tock Chest is provided with slow running ver t ical a g i t a t o r . Required s t o r a g e of t h e s tock is approximately one hour. I f required, a d d i t i o n a l steam hea t ing can be provided i n t h e ches t s .

Deflaker I51

Deflaker is used a f t e r t h e s tockches t s o r between t h e two s tockches t s i n order t o f i n e l y s e p a r a t e a l l f i b e r bundles.

fleadbox I71

The headbox over t h e Foamer is used f o r metering t h e s tock t o t h e continuous o p e r a t i o n of t h e success ive p l an t . C l a r i f i e d water is recycled t o d i l u t e t h e s tock t o a cons i s t ency required f o r f u r t h e r processing. The consis tency can be set between 0.8 - 1.8%. Addit ional foaming agen t s may be added cont inuously a t t h e po in t of d i 1 u t ion.

K r o f t a Foamer I81

The Foamer ope ra t e s with d i spe r sed a i r producing l a r g e amounts of foam (See Figure 1).

The Foam e x t r a c t i o n is p ropor t iona l t o t h e foaming s u r f a c e and no t t h e depth of t h e foaming tank. Therefore t h e Krofta Foamer ope ra t e s w i th only 80 c m water depth.

A very f i n e d i s p e r s i o n of a i r is e s s e n t i a l and wi th Foamers m u l t i p l e i n j e c t o r s a f i n e bubble foam is created. A r ecyc l ing pump feeds t h e second inne r c i rc le of t h e i n j e c t o r nozz le s wi th t h e s tock a l r eady foamed i n t h e ou te r circle. The s tock is i n t h i s way s u b j e c t t o m u l t i p l e foaming wi th l a r g e amounts of foam.

The nozz le s - in j ec to r s provide a c i r c u l a r movement i n t h e foaming tank t h a t can be ad jus t ed by r egu la t ing t h e flow, a i r a d d i t i o n and d i r e c t i o n of t h e nozzles. The s tock cleaned by foaming is discharged i n t h e c e n t e r a t t h e bottom of t h e Foamer.

If d e s i r e d , t h e s tock can be passed s e v e r a l times through t h e foamer.

The c o n s t r u c t i o n of t h e Foamer i s very simple and low c o s t f a b r i c a t i o n i n s t a i n l e s s steel i f poss ib l e . The foaming tank is open and al lows easy supe rv i s ion , obse rva t ion and cleaning.

The foam is sucked by r a d i a l foam a s p i r a t o r and passed i n t o a cyclone where i t is a d d i t i o n a l l y co l l apsed by spraywater.

The a i r a s p i r a t e d by t h e foam a s p i r a t o r keeps t h e room am

c lean .

Because of t h e l a r g e su r face and low volume t h e r e t e n t i o n t i m e i n t h e Foamer is low (5-10 minutes) .

Cvclon [91

The cyclon is f o r Foam e x t r a c t i o n and co l laps ing , and d ischarges co l lapsed foam d i r e c t l y i n t o t h e s ludge compartment [151.

Vibra t ina Screen [l O l

The v i b r a t i n g sc reen is used t o a d d i t i o n a l l y sc reen t h e foamed s tock and e l imina te coarser impur i t i e s . A l t e rna te ly t h e v i b r a t i n g sc reen can a l s o be used ahead of t h e Foamer, sc reening s tock before foaming. The rejects a re f e d i n t o t h e s ludge tank.

T r i c l ean and Elu t r i c o n e [ l l L

They are suppl ied by Bi rd Company and used f o r a d d i t i o n a l e l imina t ion of l i g h t and heavy contaminants. The c l e a n l i n e s s of t h e deinked s tock is as important as t h e b r igh tness and removal of t h e ink and t h e r e f o r e t h e KrOfta Deinking P lan t is provided wi th a l l p re sen t ly a v a i l a b l e s tock c leaning devices .

Xro f t a S tock Washer Llu Krof ta Stock Washer is i l l u s t r a t e d i n F igure 2. As it is known, t h e foaming e x t r a c t s only ink p a r t i c l e s over 20 micron s i z e and t h e rest of t h e c o l l o i d a l d i sso lved ink p a r t i c l e s are ex t r ac t ed by washing.

Krofta Stock Washer ope ra t e s similar t o a mul t ip l e s i d e h i l l sc reen , combined wi th a th ickener and p res s . No f i l t e r i n g f i b e r m a t is formed and t h e s tock r o l l s over t h e upwards moving p l a s t i c wire sc reen i n t h r e e sec t ions . A t each s e c t i o n t h e s tock can be d i l u t e d and t h e washing process improved.

The Stock Washer g ives a wide p o s s i b l e v a r i a t i o n of t h e washing process . I f t h e f i n e s and f i l l e r should no t be removed and c o l l o i d a l ink only, then t h e washing is done i n one s e c t i o n only and t h e Stock Washer ope ra t e s as a th ickener without forming a m a t .

The outgoing cons is tency of t h e deinked s tock from t h e Stock Washer is 9 - 14% bone dry. The water used f o r washing is t h e r e f o r e t h e water coming wi th t h e d i l u t e d s tock i n t o t h e Stock Washer.

If mineral f i l l e r and f i n e s should be removed by deinking of magazine coated waste paper wi th high ash conten t , then t h e m u l t i p l e washing takes e f f e c t and t h e o r i g i n a l s tock wi th 20 or more percent ash content can be reduced t o some 3 - 5% ash conten t . This is p a r t i c u l a r l y important f o r some t i s s u e manufacturing opera t ion .

888

K r o _ f f a a v F i l t e r 1 1 3 1

Krofta Spray F i l t e r is a f r a c t i o n a t o r t o recover longe r f i b e r s from t h e Stock Washer e f f l u e n t . such e f f l u e n t is sprayed through a f i n e mesh sc reen (100-200 micron). Longer f i b e r s a re recovered and added t o t h e deinked s tock. A t l a r g e r i n s t a l l a t i o n s t h e f i b e r recovery is of cons ide rab le economical importance.

The Stock Washer does not form a mat and t h e r e f o r e washes ou t t h e c o l l o d i a l ink p a r t i c l e s and mineral f i l l e r and f i n e s , f a r b e t t e r t han any drum th i ckene r or d i s c f i l t e r t h a t always forms a mat and r e t a i n s c o l l o i d a l ink i n t h e s tock. However a t t h e same time some longer f i b e r s escape and such f i b e r s a r e recovered with t h e Krofta Spray F i l t e r t h a t is a r a t h e r inexpensive machine.

Kro f t a SuDracel l C l a r i f i e r [14L

The Krofta Suprace l l C l a r i f i e r i s i l l u s t r a t e d i n Figure 3 . The Suprace l l is widely used i n many of t h e l a r g e s t deinking p l a n t s over t h e world and i s an e s s e n t i a l p a r t of such deinking i n s t a l l a t i o n s . With t h e Suprace l l a l l Stock Washer e f f l u e n t is c l a r i f i e d and recycled. There is no excess water l eav ing t h e deinking p l a n t . A makeup water is requ i r ed a s t h e waste paper e n t e r s w i th only 1 0 % moisture and t h e deinked s tock is discharged wi th 90% moisture. Some water is l o s t a l s o with t h e sludge. In general we can c a l c u l a t e t h a t i f sludge is thickened t o 20% and s ludge water recycled, t h e t o t a l water consumption f o r t h e deinking p l a n t is approximately 1 0 l /kg.

Because of high r ecyc l ing of t h e c l a r i f i e d water , t h e h e a t c o s t s a r e low and t h e ope ra t ing temperature can be kept high.

C l a r i f i e d Water Tank [l 5 1

. .

The C l a r i f i e d Water Tank is an e s s e n t i a l p a r t of t h e deinking p l a n t . The va luab le high temperature c l a r i f i e d water m u s t be s t o r e d t o be a v a i l a b l e t o f eed t h e pulper i n t h e batch process . Also change i n t h e washing and foaming d i l u t i o n r e q u i r e promptly a v a i l a b l e c l a r i f i e d warm water.

Additional r e fe rences f o r t h e t o t a l c losed water systems i n m i l l s can be found elsewhere (11-17).

REFERENCES

1. Krofta, M., L. K. Wang, D. B a r r i s and J. Janas, "Treatment of P i t t s f i e l d Raw Water f o r Drinking Water Production by Innovat ive Process Systems, 'I U.S. Dept. of Commerce, National Technical Information Se rv ice , Sp r ing f i e ld , VA., Report No. PB82-118795, 87 p., Feb. 1981.

2 . Krofta, M . , D. G u s s and L, K. Wang, "Improved B io log ica l Treatment w i th a Secondary F l o t a t i o n C l a r i f i e r ", C i v i l Ena i n e e r i n s f o r Pra c t i c i u Desiqn Enain ' e era I VOI.. 2 , p. 307-3241 1983.

889

(NTIS-PB82-154196)

Wang, L. K., " I n v e s t i g a t i o n and Design . of A D e n i t r i f i c a t i o n F i l t e r " , C i v i l Engineering f Or t

, Vole 3 , p. 347-362, 1984. (NTIS-PB82-199803)

Krofta! M. and L. K. Wang, "Design of Dissolved A i r F l o t a t i o n Systems f o r I n d u s t r i a l Pretreatment and Municipal Wastewater Treatment--Design and Energy Considerat ions" , American m- Enaineers. Na t i o n a l C onference, Houston, Texas, March 27-31, 1983 3 0 pages. (NTIS-PB83-232868)

Krofta , M. and L. K. Wang, "Design of Dissolved A i r F l o t a t i o n Systems f o r I n d u s t r i a l Pretreatment and Municipal Wastewater Treatment--Case History of P r a c t i c a l A p p l ica ti ons " , American I n s t i t u t e of C h c ' 0 o e ce, Houston, Texas, March 27-31, 1983 , 25 pages.

Krofta , M. , L. K. Wang, B. C. Wu and C. C. J. Bien, "Recent Advances i n Titanium Dioxide Recovery, F i l l e r Re ten t ion and White Water Treatment", U.S. Dept. of Commerce, Nat ional Technical Information Se rv ice , Technical Report No. PB83-219543, 39 p., June 1983.

Krofta , M., L. K. Wang, L . Kurylko and A. E. Thayer, "Pretreatment and Ozonation of Cooling Tower Water, P a r t I", U.S. Dept. of Commerce, National Technical Information Se rv ice , S p r i n g f i e l d , VA, Report PB84-192053, 34 p., A p r i l , 1983.

Krofta , M. , L. K. Wang, L. Kurylko and A. E. Thayer, "Pretreatment and Ozonation of Cooling Tower Water, P a r t II", U.S. Dept. of Commerce, National Technical Information Se rv ice , S p r i n g f i e l d , VA, Report

Wang, L. K. , D. Barris, P. Milne, B. C. Wu and J. Hollen, "Removal of Extremely High Color from Water Containing Trihalomethane Precursor by F l o t a t i o n and F i l t r a t i o n " , U. S. Dept. of Commerce, National Technical Information Se rv ice , S p r i n g f i e l d , VA, Technical Report No. PB83-240374, 11 p., A p r i l 1982.

Wan9 , L. K * I "Design of Innovat ive F l o t a t i o n - F i l t r a t i o n Wastewater Treatment Systems f o r A Nickel-Chromium P l a t i n g P lan t " , U.S. Dept. of Commerce, Nat ional Technical Information Se rv ice , S p r i n g f i e l d , VA., 50 p., Jan. 1984.

Krofta , M., "Closed water C i r c u i t s i n Board M i l l s " , WochenBlatt Fur PaDier f&r ika t ion, No. 99: pp. 781-784, (1971).

Brecht, W., " I n v e s t i g a t i o n of Closed Water Systems i n Another Waste Paper Processing Plant" , HWhenEAatt FUL

( NTIS-PB8 3 - 23 2 85 0 1

PB84-192046, 29 P., August, 1983.

Paaierfabrikation, NO. 101: pp. 113-119, (1973) 890

3 .

4.

5.

6.

7 .

8.

9.

10.

11.

12.

13. Dalpke, H. L., "Special D i f f i c u l t i e s w i th E n t i r e l y Closed Water C i r c u i t s " , D a s Pap iec, (June): pp.

14. S t r e e k i n , L. E., "Water Reuse i n a Paper Reprocessing P l a n t , EPA-600/2-76-232, (October 1976) .

15. Springer , A. M., "The R e l a t i o n between Process Water Q u a l i t y C h a r a c t e r i s t i c s and Its Reuse P o t e n t i a l i n Combination Board M i l l s " , W B u l l e t i n , No. 282, (September 1975) .

16. Ladmiral, D., "La S o c i e t e D e s Usines Royeres Supprime Sa P o l l u t i o n A Uzerche", H'Eau e t L' Environment, ( June ) : pp. 8-12, (1975).

17. GUSS, D. B., "Closed Water Systems i n M i l l s Using Secondary Fiber ", secondarv F i b e r s C onf erenc e, Nov. 1977.

236-240, (1975) .

891

a3 W N

F i g u r e 1. K r o f t a F o a m e r - - D i s p e r s e d A i r F l o t a t i o n D e i n k i n q C e l l

m co m

W UJ a

1 ROTATING CENTER SECTION 2 CLARIFIED WATER OUTLET 3 SETTLED SLUDGE SUMP A DlAMETERofSUPRACELL 4 SETTLED SLUDGE OUTLET B DEPTHofSUPRACELLTANK 5 R O T A R Y CONTACT C DEPTH of SUPRACELLTANKwithBOTTOM SUPPORT 6 SPIRAL SCOOP D M I N I M U M O V E R A L L HElGHTofSUPRACELL 7 FLOATED SLUDGE OUTLET 8 UNCLARlFlED WATER INLET 9 CLARIFIED WATER EXTRACTION PIPES

10 GEAR MOTOR 11 DISTRIBUTION DUCT

Figure 3. Krofta Supracell--Dissolved Air F l o t a t i o n C l a r i f i e r

W W m

F i g u r e 4. Spray F i l t e r F i g u r e 5. Twin Wirepress

C Y C L O N

03 m

I I I I i i i i L.-.

H O M O G E N I Z A T O R S C R E E N ;

1 T R IC 1 E ANS b f

<KRoFTA) C L A R l f I t R

14 i

f -.

I I '

E L U T R I C O N E

r'-'--

C L A R I F I I O W A T E R T A N K S T O C K W A S H E R

_._._ C L A R I F I E D WATER STOCK

W H I T E WATER

- -_- - S L U D G E 6 REJECT

F i g u r e 6 . Flow D i a g r a m of A S e m i - I n d u s t r i a l D e i n k i n g P l a n t U s i n g T o t a l Closed Water S y s t e m

h m W

I

10 11 12

Figure 8. Over V i e w of A Semi-Industrial Deinking Plant in Italy