Destruction of Dioxin Contamination by Pyrolysis Techniques - ACS

Chapter 24

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 1, 2015 | http://pubs.acs.org Publication Date: April 24, 1987 | doi: 10.1021/bk-1987-0338.ch024

Destruction of Dioxin Contamination by Pyrolysis Techniques 1

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Jimmy Boyd , H. D. Williams , R. W. Thomas , and T. L . Stoddart 1

J. M . Huber Corporation, P.O. Box 283, Borger, TX 79008 EG&G Idaho, P.O. Box 1625, Idaho Falls, ID 83401 Headquarters, Air Force Engineering Services Center, Research & Development Directorate, Environics Division, Environmental Engineering Branch, Tyndall Air Force Base, F L 32403 2

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The J. M. Huber Corporation Advanced Electric Reactor (AER) pyrolysis process was field-demonstrated in a proof-of-principle test to show that dioxins in contaminated soil could be destroyed to less than 1 ppb. Testing was conducted at a former Herbicide Orange storage site at the Naval Battalion Construction Center (NCBC) in Gulfport, MS, during June 1985. Sample analysis of treated soil shows total isomer classes of tetra-, penta-, and hexapolychlorinated dibenzo-p-dioxins and tetra-, penta-, and hexapolychlorinated dibenzofurans to be less than 0.12 ppb. Herbicide compounds 2,4-D and 2,4,5-T and 2,4-di and 2,4,5/2,4,6trichlorophenol compounds in the soil feedstock were also destroyed in the treated soil to levels below detectability. NCBC treated soil meets the Environmental Protection Agency delisting characteristic requirements. Lead and zinc are enriched in the baghouse material, which suggests that the process can be used for recovery of inorganic materials from contaminated soils that volatilize at the AER operating temperature. Test results clearly demonstrate the extremely high destruction capabilities of the AER process. Dioxin contamination of soils has occurred throughout the world. Herbicide Orange (HO), primarily composed of two compounds, 2,4-D (2,4-dichlorophenoxyacetic acid) and 2,4,5-T (2,4,5-trichlorophenoxyacetic acid) and various esters of these two compounds, was sprayed

0097-6156/87/0338-0299$06.00/0 © 1987 American Chemical Society

In Solving Hazardous Waste Problems; Exner, J.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


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SOLVING HAZARDOUS WASTE PROBLEMS

a s a d e f o l i a n t i n V i e t n a m d u r i n g t h e 1960s a n d a t E g l i n A i r F o r c e B a s e , F L , b e t w e e n 1 9 6 2 a n d 1 9 7 0 ( 1 , 2 ) . 2,4,5-T w a s s u b s e q u e n t l y i d e n t i f i e d as t e r a t o g e n i c i n mice and r a t s , w i t h t e t r a c h l o r o d i b e n z o p - d i o x i n (2,3,7,8-TCDD) shown t o be t h e t o x i c c o n t a i n m e n t ( 3 , 4 ) . D u r i n g t h e e a r l y 1970s, unpaved roads and r i d i n g a r e n a s i n Times B e a c h , MO, w e r e s p r a y e d w i t h s a l v a g e o i l b e l i e v e d t o h a v e b e e n m i x e d w i t h w a s t e m a t e r i a l c o n t a i n i n g 2,3,7,8-TCDD i n h i g h c o n c e n t r a t i o n s (5). I n 1976, a n e x p l o s i o n i n a t r i c h l o r o p h e n o l p r o d u c t i o n p l a n t a t S e v e s o , I t a l y , c a u s e d s i g n i f i c a n t 2,3,7,8-TCDD c o n t a m i n a t i o n t o t h e s u r r o u n d i n g a r e a ( 6 ) . D i o x i n s have a l s o been i d e n t i f i e d a s combust i o n products r e l e a s e d from m u n i c i p a l and i n d u s t r i a l i n c i n e r a t o r s through the combustion o f c h l o r i n a t e d precursors present i n t h e f u e l o r b y r e a c t i o n o f o r g a n i c compounds w i t h i n o r g a n i c c h l o r i n e b o t h present i n the fuel (7-12). Through l o n g - t e r m r e l e a s e , these i n c i n e r a t o r e m i s s i o n s o f d i o x i n s c a n c o n t a m i n a t e downwind s o i l s t o r e a c h l e v e l s o f concern t o the public health. Exposure from d i o x i n c o n t a m i n a t e d s o i l c o n d i t i o n s a s shown i n t h e s e e x a m p l e s may p l a c e the p u b l i c h e a l t h a t r i s k . The U.S. E n v i r o n m e n t a l P r o t e c t i o n A g e n c y ( E P A ) p r e s e n t l y h a s n o l i m i t s on d i o x i n contamination l e v e l s i n s o i l . After studyingthe r i s k s , h o w e v e r , t h e C e n t e r s f o r D i s e a s e C o n t r o l ( C D C ) o f t h e U.S. D e p a r t m e n t o f H e a l t h a n d Human S e r v i c e s i n A t l a n t a , GA, h a s c o n c l u d e d t h a t r e s i d u a l s o i l c o n t a m i n a t i o n l e v e l s a t o r above 1 ppb o f 2,3,7,8TCDD i n r e s i d e n t i a l a r e a s c a n n o t b e c o n s i d e r e d s a f e a n d r e p r e s e n t a l e v e l o f c o n c e r n ( 5 ) . U n i f o r m c o n t a m i n a t i o n l e v e l s a r e a s s u m e d . CDC a l s o recommends l o w l e v e l s f o r p a s t u r e l a n d s b e c a u s e o f f o o d c h a i n accumulation. H o w e v e r , CDC c o n c l u d e s t h a t , i n c e r t a i n c o m m e r c i a l a r e a s , h i g h e r l e v e l s i n s o i l s may r e p r e s e n t a n a c c e p t a b l e r i s k t o n o n o c c u p a t i o n a l l y exposed i n d i v i d u a l s , b u t t h a t l e v e l has n o t been defined. I n S e p t e m b e r 1 9 8 3 , t h e J . M. H u b e r C o r p o r a t i o n o f B o r g e r , T X , embarked on a program t o demonstrate t h e c a p a b i l i t y o f t h e Advanced E l e c t r i c R e a c t o r ( A E R ) t o d e t o x i f y 2,3,7,8-TCDD c o n t a m i n a t e d s o i l . This program a l s o i n c l u d e s t h e treatment o f s o i l s contaminated w i t h p o l y c h l o r i n a t e d b i p h e n y l s (PCBs), carbon t e t r a c h l o r i d e , and o c t a c h l o r o d i b e n z o - p - d i o x i n (OCDD). A f i e l d d e m o n s t r a t i o n o f 2,3,7,8TCDD c o n t a m i n a t e d s o i l a t a f o r m e r HO s t o r a g e s i t e a t t h e N a v a l C o n s t r u c t i o n B a t t a l i o n C e n t e r (NCBC) i n G u l f p o r t , MS, r e p r e s e n t s a continuation o f this demonstration process. T h i s t e s t i n g was p e r formed t o demonstrate i n n o v a t i v e t e c h n o l o g i e s as p a r t o f t h e A i r F o r c e E n v i r o n m e n t a l R e s t o r a t i o n P r o g r a m f o r f o r m e r HO s i t e s . A spec i f i c g o a l o f t h i s t e c h n o l o g y t e s t i n g was t o r e d u c e t h e t o t a l c o n c e n t r a t i o n o f a l l i s o m e r s o f t e t r a - , p e n t a - , a n d hexa-CDD a n d r e s p e c t i v e isomers o f c h l o r o d i b e n z o f u r a n s t o l e s s than 1 ppb. Method AER P r o c e s s . T h e AER e m p l o y s a new t e c h n o l o g y t o r a p i d l y h e a t m a t e r i a l t o a p p r o x i m a t e l y 2200°C., u s i n g i n t e n s e t h e r m a l r a d i a t i o n i n t h e n e a r i n f r a r e d r e g i o n ( F i g u r e 1 ) . The r e a c t i o n s , w h i c h c a n b e g a s eous, l i q u i d , o r s o l i d , a r e i s o l a t e d from t h e r e a c t o r core w a l l s by means o f a g a s e o u s b l a n k e t f o r m e d b y f l o w i n g n i t r o g e n r a d i a l l y i n w a r d through t h e porous core w a l l s . Carbon e l e c t r o d e s a r e heated and, i n t u r n , heat t h e r e a c t o r core t o incandescence so t h a t the heat t r a n s fer i s accomplished by thermal r a d i a t i v e c o u p l i n g from t h e core t o


Destruction of Dioxin Contamination by Pyrolysis


BOYD ET AL.

Figure

1.

Advanced E l e c t r i c

Reactor.



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the feed m a t e r i a l s . The o n l y f e e d s t r e a m s t o t h e r e a c t o r a r e t h e s o l i d , l i q u i d , o r gaseous wastes and the n i t r o g e n b l a n k e t gas. D e s t r u c t i o n i s accomplished by p y r o l y s i s r a t h e r than o x i d a t i o n ; t h e r e f o r e , t y p i c a l products and by-products produced by i n c i n e r a t i o n such as carbon monoxide, carbon d i o x i d e , and oxides o f n i t r o g e n are not formed i n s i g n i f i c a n t c o n c e n t r a t i o n s . The p r i n c i p a l p r o d u c t s f r o m s o i l - a f f i x e d TCDD u s i n g t h e H u b e r p r o c e s s a r e h y d r o g e n , c h l o r i n e , h y d r o c h l o r i c a c i d , elemental carbon, and granular f r e e - f l o w i n g soil material. F i g u r e 2 i s a s i m p l i f i e d p r o c e s s d i a g r a m o f t h e AER p r o c e s s f o r s o l i d hazardous waste d e s t r u c t i o n . The s o l i d f e e d steam i s i n t r o d u c e d a t t h e t o p o f t h e r e a c t o r b y means o f a m e t e r e d s c r e w f e e d e r c o n n e c t i n g the a i r t i g h t feed hopper t o the r e a c t o r . Nitrogen i s i n t r o d u c e d p r i m a r i l y a t two p o i n t s i n the r e a c t o r a n n u l u s . The s o l i d f e e d passes t h r o u g h the r e a c t o r where p y r o l y s i s o c c u r s a t temperat u r e s b e t w e e n 1900 a n d 2500°C. A f t e r l e a v i n g t h e r e a c t o r , t h e product gas and waste s o l i d s pass through a p o s t r e a c t o r treatment zone (PRTZ). T h e PRTZ p r o v i d e s f o r a d d i t i o n a l r e s i d e n c e t i m e b u t p r i m a r i l y c o o l s t h e g a s t o l e s s t h a n 550°C b e f o r e d o w n s t r e a m p a r t i c u l a t e cleanup. S o l i d s e x i t i n g t h e PRTZ a r e c o l l e c t e d i n a s o l i d s c o l l e c t i o n b i n t h a t i s s e a l e d t o the atmosphere. Any e n t r a i n e d s o l i d s i n the p r o d u c t g a s a r e removed a s the gases e n t e r a baghouse. Any r e s i d u a l o r g a n i c s and c h l o r i n e a r e removed by p a s s i n g the p r o d u c t g a s t h r o u g h a c t i v a t e d c a r b o n beds (or a c a u s t i c s c r u b b e r , i f n e c e s s a r y ) j u s t upstream o f the process s t a c k . The c l e a n p r o d u c t g a s , composed a l m o s t e n t i r e l y o f n i t r o g e n (some m o i s t u r e ) , i s t h e n e m i t t e d t o t h e atmosphere through the process s t a c k . An i n t e g r a l p a r t o f t h e A E R d e s i g n i s t o e n s u r e s a f e t y o f p e r s o n n e l a n d t h e e n v i r o n m e n t when p r o c e s s i n g h a z a r d o u s w a s t e s . F o r e x a m p l e , i f e l e c t r i c a l power t o t h e p r o c e s s i s i n t e r r u p t e d , t h e m o t o r - d r i v e n screw f e e d e r stops f e e d i n g s o l i d s , and w i t h i n one t o two s e c o n d s , a l l s o l i d s a r e p u r g e d f r o m t h e r e a c t o r b y g r a v i t y f l o w . The l a r g e amount o f t h e r m a l i n e r t i a , i n p r o p o r t i o n t o t h e f e e d r a t e , ensures continued waste d e s t r u c t i o n and safe c l e a r i n g o f feed from the r e a c t o r . To p r o t e c t t h e e l e c t r o d e s a n d m a i n t a i n a n o n c o m b u s t i b l e environment, n i t r o g e n purge t o the r e a c t o r remains u n t i l the r e a c t o r temperature i s approximately 100°C. T h e AER i s a l s o e q u i p p e d w i t h an a u t o m a t i c t r i p t o c u t e l e c t r i c a l power i n the e v e n t o f e l e c t r o d e failure. H u b e r m a i n t a i n s t w o f u l l y e q u i p p e d AERs (AER3 a n d A E R 1 2 ) . T h e A E R 3 , w h i c h w a s u s e d f o r t h e NCBC t e s t a n d i s t h e s m a l l e r r e a c t o r , h a s a n i n s i d e c o r e d i a m e t e r o f 7.6 cm, w i t h a h e a t e d l e n g t h o f 91.4 cm. T h e u n i t , i n s t a l l e d i n a t r a i l e r f o r m o b i l i t y , i s u s e d f o r proof-of-concept experiments and o n s i t e demonstrations. The A E R 1 2 , w h i c h i s o f p i l o t / c o m m e r c i a l s c a l e ( a 30.5-cm c o r e d i a m e t e r w i t h a h e a t e d l e n g t h o f 365.8 cm), i s u s e d f o r r e s e a r c h s u c h a s s c a l e - u p d e s i g n , process e n g i n e e r i n g , economic s t u d i e s , and technology demonstrations. Site Conditions. T h e i n d i g e n o u s s o i l a t NCBC i s s a n d t o s a n d y l o a m , i n t e r m i x e d w i t h some c l a y . T h e HO s t o r a g e s i t e w a s s t a b i l i z e d w i t h P o r t l a n d cement a p p r o x i m a t e l y 30 y e a r s ago. Since that time, a d d i t i o n a l f i l l m a t e r i a l s , i n c l u d i n g s h e l l , r o c k , a s p h a l t , and t a r , were


Destruction of Dioxin Contamination by Pyrolysis


BOYD ET AL.

Feedstock

Dioxin-contaminated soil, etc. in airtight ' hopper

-Metered screw feeder

Gaseous effluent (clean N ) 2

N L

2

Electricity

Electric reactor

High-temperature destruction

Process stack

n Post-reactor treatment zone

Solids collection bin

Baghouse

Activated carbon beds

Particulate removal

Residual organics and CI removal

Clean soil

Figure

2.

Simplified

AER P r o c e s s

Diagram.



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a d d e d t o t h e s t o r a g e a r e a , p r o v i d i n g a c o v e r r a n g i n g u p t o 10 cm over the c e m e n t - s t a b i l i z e d s o i l . Before the demonstration t e s t i n g , a surface and subsurface s o i l s a m p l i n g p r o g r a m was c o n d u c t e d t o c h a r a c t e r i z e t h e s t o r a g e a r e a c o n ditions. A t t h e s o i l s u r f a c e , a maximum i n d i c a t e d h o t s p o t c o n c e n t r a t i o n o f 2,3,7,8-TCDD w a s f o u n d t o b e 6 4 6 p p b . H o w e v e r , t h e maximum i n d i c a t e d 2,3,7,8-TCDD c o n c e n t r a t i o n w a s 9 9 8 p p b , f o u n d i n t h e s u b s u r f a c e i n t h e 1 5 - c m - t h i c k c e m e n t - s t a b i l i z e d s o i l . The 2,3,7,8-TCDD c o n c e n t r a t i o n i n t h e s o i l b e n e a t h t h e c e m e n t - s t a b i l i z e d s o i l d e c r e a s e d t o a v a l u e

Destruction of Dioxin Contamination by Pyrolysis Techniques - ACS

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