Solid Wastes and Residues - American Chemical Society

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Activated C a r b o n and F u e l f r o m Sewage Solids

Downloaded by UNIV OF CALIFORNIA SANTA BARBARA on April 3, 2018 | https://pubs.acs.org Publication Date: June 1, 1978 | doi: 10.1021/bk-1978-0076.ch012

JOHN E. SIGLER 2839 Tabago Place, Costa Mesa,CA92626

Under a NASA development program for a source of carbon for i n s u l a t i o n , Marshall Humphrey of Jet Propulsion Labs, (1) Pasadena, Ca., conceived a new process for t r e a t i n g wastewater. A f t e r bench t e s t i n g , a trailer mounted unit was brought to the County Sanit a t i o n D i s t r i c t s of Orange County, C a l i f o r n i a . After t e s t i n g t h i s 10,000 gallon per day unit plus some tests on reactors i n Belle Meade, New Jersey, Springf i e l d , Ohio and L o u i s v i l l e , Kentucky, the Sanitation D i s t r i c t s decided the system had enough promise to j u s t i f y a p i l o t plant scale t e s t . Much of t h i s j u s t i f i c a t i o n was the elimination of a sludge disposal problem with which all present wastewater treatment systems are confronted. With the approval of the C a l i f o r n i a State Water Resources Control Board, the Environmental Protection Agency, and the Sanitation D i s t r i c t s Board of Directors, a p i l o t plant was b u i l t and operated to obtain data for design of a full scale p l a n t . The one m i l l i o n gallon a day (MGD) size was considered an intermediate step between the .01 MGD trailer mounted unit and the full plant size of 175 MGD. Process Description Hydraulics. The treatment system i s a two-stage counter-current adsorption process using activated carbon produced from the sewage s o l i d s . The flow diagram i n F i g . 3 i l l u s t r a t e s the 0-8412-0434-9/78/47-076-241$05.00/0 © 1978 American Chemical Society Jones and Radding; Solid Wastes and Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1978.


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Figure 1.

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AND

RESIDUES

A 10,000 gallon/day demonstration plant—trailer mounted

Jones and Radding; Solid Wastes and Residues ACS Symposium Series; American Chemical Society: Washington, DC, 1978.


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Activated Carbon and Fuel

Figure 2.

The 1 MGD pilot plant


243


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c o u n t e r - c u r r e n t movement o f t h e carbon w i t h r e s p e c t t o the wastewater. F r e s h carbon i s added b e f o r e the s e c ondary c l a r i f i e r where t h e a c t i o n i s e s s e n t i a l l y a d s o r p t i o n o f d i s s o l v e d o r g a n i c s on t h e c a r b o n . The p a r t i a l l y used carbon i s removed from t h e secondary c l a r i f i e r and mixed w i t h t h e i n c o m i n g wastewater. In the p r i m a r y s t a g e t h e a c t i o n o f t h e carbon i s as a s e t t l i n g a i d but some a d s o r p t i o n a l s o o c c u r s . Chemi c a l a d d i t i o n s o f F e r r i c C h o l o r d e and polymers were used t o a i d t h e s e d i m e n t a t i o n i n t h e c l a r i f i e r s . A sand f i l t e r was i n s t a l l e d on t h e e f f l u e n t but the main t h r u s t o f t h e work was d i r e c t e d toward obt a i n i n g a s a t i s f a c t o r y e f f l u e n t from t h e s e c o n d a r y clarifier. M i x i n g o f t h e carbon w i t h t h e wastewater b e f o r e each c l a r i f i e r was a c c o m p l i s h e d i n two s t e p s a 2 minute f a s t mix and a 1 5 minute slow mix. 3

S o l i d s Dewatering and D r y i n g .

While t h e s o l i d s removed from t h e s e c o n d a r y s t a g e were r e t u r n e d t o t h e p r i m a r y s t a g e ^ s o l i d s from t h e p r i m a r y s t a g e were removed from t h e h y d r u a l i c system. These s o l i d s a r e o f a m i x t u r e o f a c t i v a t e d carbon and sewage s o l i d s i n about a 5 t o 3 r a t i o . The s l u d g e s o l i d s removed from t h e c l a r i f i e r were about 1 0 $ d r y s o l i d s . S t o r i n g and d e c a n t i n g i n c r e a s e d the s o l i d s c o n t e n t t o about 1 5 $ b e f o r e f e e d i n g t o t h e f i l t e r press. The f i l t e r p r e s s r e g u l a r l y produced cakes which were g r e a t e r t h a n 5 0 $ s o l i d s c o n t e n t . F u r t h e r d r y i n g was a c c o m p l i s h e d i n a f l a s h d r y e r which can produce s o l i d s w i t h o n l y 2 o r 3 $ m o i s t u r e ^ but t h e p r o d u c t i s d u s t y and f l u f f y . At 1 0 to 1 5 $ moisture content^ the product i s i n a b e t t e r c o n d i t i o n for feeding t o the reactor. Reactor.

The r e a c t o r used was an i n d i r e c t l y f i r e d , r o t a r y k i l n known as a c a l c i n e r . The tube was 3 0 i n c h e s i n d i a m e t e r and had a h o t zone o f 3 0 f e e t . This i s a s t a n d a r d u n i t as manufactured by Combustion E n g i n e e r i n g except t h e tube was o f ^ i n c h I n c o n e l 6lJ p l a t e r o l l e d and welded t o shape. F i f t e e n burners> d i v i d e d i n t o 3 zones f o r tempe r a t u r e c o n t r o l ^ were used t o s u p p l y the heat t o t h g reactor. The most common temperature used was l 6 0 0 F i n a l l t h r e e zones but some runs were made w i t h a



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temperature p r o f i l e o f 1 1 0 0 - 1 3 5 0 - 1 5 0 0 ° F from f e e d t o p r o d u c t end. Feed was d e p o s i t e d w e l l i n t o the f i r s t zone by a screw f e e d e r which a l s o m a i n t a i n e d a gas s e a l . Product d i s c h a r g e d from t h e tube i n t o an end b e l l and then t h r o u g h a r o t a r y v a l v e which m a i n t a i n e d t h e s e a l on t h e d i s c h a r g e end. Three t h i n g s were t o be a c c o m p l i s h e d i n t h e r e actor. 1. Complete t h e d r y i n g o f t h e f e e d . 2. P y r o l y z e t h e sewage s o l i d s . 3. A c t i v a t e t h e carbon w i t h superheated steam. Superheated steam was f e d i n t o the l a s t zone o f the tube t o a c c o m p l i s h t h e a c t i v a t i o n and r e a c t i v a t i o n of t h e carbon. I t was g e n e r a l l y a c c e p t e d t h a t t h e p y r o l y s i s gas was e v o l v e d i n t h e c e n t e r s e c t i o n o f the r e a c t o r w h i l e t h e d r y i n g was accomplished i n t h e f e e d end zone. Naturally,, a i r was e x c l u d e d from t h e r e a c t o r tube by t h e use o f r o t a r y s e a l s connected t o b e l l o w s on each end. A l l gas was taken from t h e r e a c t o r a t t h e f e e d end and washed i n a s p r a y s c r u b b e r t o remove any p a r t i c l e s c a r r i e d from the r e a c t o r . I t was o r i g i n a l l y i n t e n d e d t h a t t h i s gas be used t o f i r e t h e f l a s h d r y e r . However,, a few days o p e r a t i o n proved t h e f l a s h d r y e r c o u l d o p e r a t e u s i n g t h e hot s t a c k gases from t h e r e a c t o r . The next l o g i c a l p l a c e t o use t h i s gas was t h e r e a c t o r f i r e b o x but t h e p i l o t p l a n t was n o t plumbed t o a l l o w t h i s usage. A f t e r c l e a n i n g ^ t h e gas was compressed> metered, a n a l y z e d ^ and f l a r e d . Mi s c. Equipment.

An a f t e r b u r n e r t r a i n c o n s i s t i n g o f an a f t e r b u r ner^ p r e - c o o l e r ^ v e n t u r i s c r u b b e r ^ and f a n were i n s t a l l e d on the exhaust l i n e from t h e f l a s h d r y e r . However^ t h e v e n t u r i s c r u b b e r performed w e l l enough t o meet t h e a i r q u a l i t y s t a n d a r d s so t h e a f t e r b u r n e r and p r e - c o o l e r were n o t o p e r a t e d . D i s c h a r g e o f d r y carbon from t h e r e a c t o r i s conveyed t o a quench t a n k where i t i s c o o l e d and s l u r r i e d w i t h water f o r t r a n s p o r t i n g back t o the carbon feed tanks. Pyrolysis

Reactor

Reactor Operating C o n d i t i o n .


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W h i l e numerous p r o f i l e s were used throughout t h e p i l o t p l a n t o p e r a t i o n ^ t h e most runs wege made w i t h the t e m p e r a t u r e s c o n t r o l l e d around ΐβΟΟ F i n a l l t h r e e zones o f t h e f i r e b o x . This allows the r e a c t o r t o es t a b l i s h i t s own l e n g t h s n e c e s s a r y t o a c c o m p l i s h t h e d r y i n g ^ p y r o l y s i s and a c t i v a t i o n . A r o t a t i o n a l speed o f 1 . 6 rpm gave a r e s i d e n c e time i n the r e a c t o r o f about 4 0 minutes. Steam was superheated e x t e r n a l l y t o about 9 0 0 ° F and f e d a t r a t e s o f 2 0 ^ 5 0 ^ and 7 5 pounds p e r hour. D e s c r i p t i o n o f Feed t o R e a c t o r .

The r e a c t o r feed was a d r i e d cake which was about 5 p a r t s o f used r e a c t o r p r o d u c t and 3 p a r t s o f sewage solids. The f e e d s had m o i s t u r e c o n t e n t s o f 1 t o 6 $ . Analysis

o f Feeds

on Dry B a s i s

Ash

29-45$

V o l a t i l e Organics F i x e d Carbon

12-21$ 37-58$

Feed r a t e s were v a r i e d d r y f e e d p e r hour.

from 2 2 0 t o 4 8 0 pounds o f

Reactor Products.

The d r y s o l i d s d i s c h a r g e d from the r e a c t o r worked up t o an a s h c o n t e n t around 5 0 $ i n t h e l a s t r u n s . This ash content i s n e c e s s a r i l y a f u n c t i o n of the ash l o s s e s i n t h e system as a whole as w e l l as the r e a c t o r operating conditions. The a c t i v i t y o f t h e carbon^ as measured by t h e i o d i n e number^ f i n a l l y s t a b a l i z e d i n t h e range o f 3 0 0 to 3 5 0 mg o f i o d i n e p e r gram o f c a r b o n . A b e t t e r measure o f a c t i v i t y o f t h e carbon f o r use on t h i s p r o c e s s i s an e q u i l i b r i u m curve where t h e removal o f t h e a c t u a l contaminants i s measured. Figure 4 i s a p l o t of s e v e r a l of these isotherms comparing r e a c t o r p r o d u c t s w i t h commercial c a r b o n s . The carbons produced i n 1976 tended t o match Nuchar w h i l e t h e l a t e s t carbons o f Aug. 77 matched Calgon PC but were n o t as good as Calgon RB i n a d s o r b i n g T0C from sewages. A f t e r water washing^ p y r o l y s i s gas had t h e following analysis: Constituent $ V/V H 38-46 2



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Figure 3. Flow schematic of activated carbon treatment system

EQUILIBRIUM DATA 1-0. //!. / /

Calgon

Calgon

' ////

RB-7 J 11 I / // P C

/~~f

Nuchar 8/20/77-

/

η / //

19 76

2 12 Hi•hi -H 2/22 -11/26 -11/24 I

Figure 4. Equilibrium plots of total organic carbon adsorption of commercial carbons and re actor products

.01 10 100 TOTAL ORGANIC CARBON mg/L

Q

w.40f CO CO

io.30[

GAS PRODUCED STEAM R A T E S kg/hr

S

o23 • 34 /_ ο

O-20J Ο

GM

.20 .30 VOLATILES/GM

.40 ASHLESS FEED

Figure 5. Gas production of the reactor com pared with volatile matter fed at various rates of steam addition. > Λ

American Uliemical Sociaty Library

Jones and Radding; Solid Wastes Residues 41W 1£th Si MandW ACS Symposium Series; American Chemical Society: Washington, DC, 1978.

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10-22

17-27


4-8

T h i s gas had a c a l c u l a t e d n e t h e a t i n g v a l u e o f 3 0 0 - 4 0 0 BTU/ft^. A comparision o f the v o l a t i l e matter f e d t o the r e a c t o r v s . the p y r o l y s i s gas produced shows t h a t ; except a t t h e lowest steam r a t e s ; t h e v o l a t i l e s i n t h e f e e d a r e accounted f o r i n t h e p y r o l y s i s g a s . Material

Balances.

Around t h e r e a c t o r ; m a t e r i a l b a l a n c e s were run i d e a l l y on an 8 hour b a s i s when p o s s i b l e . The b e s t checks on the i n p u t v s . t h e o u t p u t were found when t h e ash b a l a n c e was c o n s i d e r e d . However^ a check on t h e e n t i r e system showed t h e p r o c e s s has a c t u a l l y gained 1 , 0 0 0 pounds i n f i x e d c a r bon i n t h e system over a 3 0 day p e r i o d o f s u s t a i n e d operation. T h i s i s t h e i m p o r t a n t f a c t s i n c e even w i t h the l o s s e s i n h e r e n t t o any p i l o t s c a l e o p e r a t i o n ; t h e system produced enough a c t i v a t e d carbon t o s u s t a i n t h e system as a whole. Energy B a l a n c e .

The p i l o t p l a n t d i d n o t a c t u a l l y produce enough gas f o r t h e r e a c t o r t o s u s t a i n i t s e l f . There were s e v e r a l reasons f o r t h i s which c o u l d n o t be c o r r e c t e d i n t h e time a l l o t e d . The b u r n e r s s u p p l i e d w i t h t h e r e a c t o r were s i z e d so t h a t t h e excess a i r used i n the combustion c o u l d not be reduced below 1 2 0 $ . T h i s meant e x c e s s i v e heat l o s s e s i n t h e s t a c k gases. The i n s u l a t i o n f o r t h e r e a c t o r f i r e b o x was des i g n e d i n a p e r i o d when energy was cheap. These l o s s e s w i l l have t o be s u b s t a n t i a l l y reduced i n t h i s p e r i o d o f energy c o n s e r v a t i o n . F o r example; t h e r e a c t o r r u n n i n g a t temperature b u t w i t h no l o a d r e q u i r e d 1 5 0 0 t o 1 7 0 0 c u b i c f e e t p e r hour o f n a t u r a l g a s . When o p e r a t i n g ; t h e gas consumption was i n the range o f 1 7 0 0 t o 2 0 0 0 c u b i c f e e t p e r hour. A n o t h e r a r e a o f energy s a v i n g can be found i n t h e d e w a t e r i n g by t h e f i l t e r p r e s s . Some s m a l l s c a l e t e s t i n g showed t h a t t h e use o f h i g h e r p r e s s u r e s w i t h a



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change i n c l o t h s c o u l d produce cakes i n the range o f 5 8 to 6 0 $ s o l i d s . In t h i s range an i n c r e a s e from 5 0 $ s o l i d s t o 6 0 $ s o l i d s means a r e d u c t i o n of 1 / 3 o f a pound o f water t o be removed p e r pound o f d r y s o l i d s or a r e d u c t i o n i n d r y i n g l o a d o f 3 3 $ . While the system was a c t u a l l y s e l f - s u s t a i n i n g i n a m a t e r i a l sense^ t h e r e were s t i l l l o s s e s o f f i x e d carbon. These l o s s e s o f carbon r e p r e s e n t energy which c o u l d be r e c o v e r e d i n a water-gas type r e a c t i o n . When the above energy c o n s e r v a t i o n measures a r e c a l c u l a t e d , the r e a c t o r system t h e n becomes s e l f - s u s t a i n i n g on a energy b a s i s . R e a c t o r Damage.

The r e a c t o r s u s t a i n e d damage i n two d i s t i n c t areas. The f i r s t developed i n the b e l l o w s a t t a c h e d t o the s e a l s n e a r each end of the r o t a t i n g t u b e . Changing the m a t e r i a l s o f c o n s t r u c t i o n from 3 0 4 s t a i n l e s s s t e e l y t o 6 0 1 I n c o n e l j t o 3 1 6 s t a i n l e s s s t e e l was not the answer. A c o a t i n g of Dow C o r n i n g S i l a s t i c 8 3 4 was the o n l y temporary measure t h a t c o u l d p r e v e n t the p i n h o l i n g and f a i l u r e o f t h e s e b e l l o w s . The second f a i l u r e was i n the r e a c t o r tube when a weld i n the c e n t e r o f the 3 f i r i n g zone f a i l e d . There was e v i d e n c e o f s u l f i d e a t t a c k i n t h i s weld material. In I n c o n e l 6 1 7 the weld m a t e r i a l i s a c t u a l l y the m a t e r i a l i t s e l f puddled w i t h an i n e r t gas arc. T h i s means the weld i s e s s e n t i a l l y a c a s t mat e r i a l whereas the p l a t e s are a r o l l e d m a t e r i a l . A r e a s o f p i t s were found i n s i d e the tube^ away from the welds> which showed e v i d e n c e o f s u l f i d e a t t a c k of the m e t a l . The r e p a i r was a c c o m p l i s h e d by c u t t i n g out bad a r e a s and r e p l a c i n g e n t i r e s e c t i o n s of the tube w i t h new m a t e r i a l . The s m a l l e r spots were ground and r e f i l l e d w i t h new weld m a t e r i a l . A f t e r 6 weeks of ope r a t i o n the r e p a i r e d a r e a s showed no s i g n s of a t t a c k . Comparisions W i t h Other Systems Cost e s t i m a t e s were made,, by our c o n s u l t i n g eng i n e e r s ^ f o r a 1 0 MGD s i z e d p l a n t f o r the A c t i v a t e d Carbon system compared w i t h A c t i v a t e d Sludge and Trickling Filters. These are shown i n F i g u r e 8 . The c o n s t r u c t i o n c o s t s match t r i c k l i n g f i l t e r s and are about 1 2 $ l e s s than a c t i v a t e d s l u d g e . Since a m u l t i p l e h e a r t h f u r n a c e i s a known s u b s t i t u t e f o r the c a l c i n e r as the reactor,, a c o s t e s t i m a t e was made



250

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Figure 6.

Construction $

O&M $/MG Energy $/MG

Figure 8.

Failed weld of reactor tube

COMPARISONS ACTS ACT.SL

COSTS

0

A N D RESIDUES

Pitting damage of Bellows Seal on reactor

Figure 7.

1

WASTES

14.4(Kii ) n

16.3

TR. FT. 144

15.6(Hearth)

212

260

37.30(50%cake)61.26

180

25.44

24.30(60%cake)

Comparison of cost estimates at a 10-MGD plant size


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on t h a t system as w e l l . The 0 & M c o s t s a r e "between t h e a c t i v a t e d s l u d g e and t h e t r i c k l i n g f i l t e r c o s t s . Energy c o s t s a r e s e n s i t i v e t o t h e d r y n e s s o f t h e cake i n t h e a c t i v a t e d c a r b o n system b u t c a n be t h e l o w e s t o f t h e t h r e e . B o t h t h e a c t i v a t e d s l u d g e and t h e t r i c k l i n g f i l t e r systems r e c e i v e d c r e d i t f o r gas t h a t c o u l d be gene r a t e d from d i g e s t i o n o f sewage s o l i d s . D i f f e r e n t e f f l u e n t s were used i n t h e systems e v a l u a t e d f o r c o m p a r i s o n . These a r e t a b u l a t e d below. ACTS Effluent SS mg/1 BOD mg/1 Grease mg/1

25 50

8

ACTS Sludge

25 25

7

Trickling Filter 40 50

10

I t s h o u l d be n o t e d t h a t t h e BOD o f t h e c a r b o n system does n o t match t h e e f f l u e n t from a c t i v a t e d s l u d g e a t t h e p r e s e n t s t a t e o f t h e a r t . More work w i l l have t o be done on r e a c t o r o p e r a t i n g c o n d i t i o n s t o produce a c a r b o n w h i c h w i l l remove more o f t h e BOD from w a s t e w a t e r . A complete r e p o r t o f a l l o p e r a t i o n a l d a t a has been p u b l i s h e d . (2_) Literature 1.

2.

MARCH

Cited

Humphrey, M.F., et al, "Carbon Wastewater T r e a t ment P r o c e s s . " Paper p r e s e n t e d a t Intersociety Conference on E n v i r o n m e n t a l Systems, Seattle, W a s h i n g t o n , July 2 9 - A u g . 1, 1974. " A c t i v a t e d Carbon Treatment System for M u n i c i p a l Treatment S y s t e m s . " County Saintation Districts of Orange C o u n t y , California, November, 1977. 3,

1978.


Solid Wastes and Residues - American Chemical Society

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