Chapter 27
In Situ Radio Frequency Heating Process for Decontamination of Soil 1
1
1
2
3
H. Dev , P. Condorelli , J . Bridges , C. Rogers , and D. Downey 1
2
IIT Research Institute, Chicago, IL 60616 U.S. Environmental Protection Agency, Cincinnati, OH 45268 Headquarters, Air Force Engineering Services Center, Tyndall Air Force Base, FL 32403 3
In-situ radio frequency (RF) heating is accomplished by inserting tubular electrodes into boreholes, or by laying horizontal electrodes over the surface of the soil, and connecting them to a source of electromagnetic (EM) energy in the frequency range of 6 to 13 MHz. An overview of the RF heating techniques is presented. Experiments were performed on 75 g batches of sandy soil to determine the feasibility of removing chlorinated hydrocarbons. Tetrachloroethylene was selected as a simulant. Soil containing 9.28 and 957 ppm tetrachloroethylene was heated for four hours in a temperature range of 90° and 130°C. It was demonstrated that under these conditions 95% of the contaminant can be removed from soil. Radio Frequency (RF) in-situ heating is an electromagnetic (EM) technique originally developed and demonstrated by Krstansky et al. (1) for in-situ thermal processing of hydrocarbonaceous earth formations for resource recovery. This technique uses EM energy in the radio frequency band for rapid in-situ heating of earth and mineral formations. The mechanism of absorption and conversion of EM energy to heat is similar to that of a microwave oven, except that the frequency is lower and the scale of operation is much larger. In-situ RF heating to 200°-400°C of large blocks of earth from 35 cu ft (1.0 cu m) to 660 cu ft (25 cu m) in size has been demonstrated in field tests (1) • A sustained average heating rate of O.8°-l.0°C/hr was achieved in these tests. The purpose of this paper is to present the results of laboratory studies performed to determine the feasibility of using RF heating techniques to decontaminate soils containing hazardous chemicals such as chlorinated hydrocarbons, benzene, and toluene. The occurrence of numerous large uncontrolled sites of contaminated soil containing the above-mentioned chemicals is well documented and previously reported in the literature (2-6). In-situ RF heating offers two alternatives for decontaminating soil. These alternatives are: (1) thermal decontamination of soil
0097-6156/87/0338-0332$06.00/0 © 1987 American Chemical Society
27.
DEV
ET
AL.
In Situ Radio Frequency Heating Process
333
by v a p o r i z a t i o n a n d r e c o v e r y o f c o n t a m i n a n t s , and ( 2 ) i n - s i t u RF heat treatment i n c o n j u n c t i o n w i t h the a p p l i c a t i o n of a c h e m i c a l d e c h l o r i n a t i n g a g e n t f o r c o n t a m i n a n t s s u c h as PCB. In a l t e r n a t i v e ( 1 ) t h e c o n t a m i n a n t s w i l l be v a p o r i z e d , d i s t i l l e d , o r steam-stripped f r o m t h e s o i l and r e c o v e r e d a t t h e s u r f a c e . I n a l t e r n a t i v e ( 2 ) RF h e a t i n g o f t h e s o i l w i l l be u s e d t o i m p r o v e t h e r a t e o f r e a c t i o n b e t w e e n t h e c o n t a m i n a n t and t h e a p p l i e d r e a g e n t . In a d d i t i o n , the h e a t i n g c a n be u s e d t o c o n d i t i o n t h e s o i l by r e m o v i n g t h e m o i s t u r e e i t h e r before or a f t e r reagent a p p l i c a t i o n . Thermal Decontamination of
Soil
C h l o r i n a t e d o r g a n i c contaminants are found at v a r i o u s s i t e s of i n t e r e s t t o t h e U.S. A i r Force. Among t h e s e c o n t a m i n a n t s a r e compounds s u c h a s t e t r a c h l o r o e t h y l e n e , d i c h l o r o e t h a n e , trichloroe t h y l e n e , c h l o r o b e n z e n e , b e n z e n e , t o l u e n e , and c o m p o n e n t s o f JP-4 jet f u e l . T h e s e m a t e r i a l s h a v e a b o i l i n g r a n g e o f 80° t o 232°C., h a v e s u b s t a n t i a l v a p o r - p r e s s u r e a t 100°C., and c a n be s t e a m d i s t i l l e d i f p r e s e n t i n ' e x c e s s of t h e i r s o l u b i l i t y l i m i t . To e s t a b l i s h t h e f e a s i b i l i t y of thermal recovery of such chemical c o n t a m i n a n t s , t e t r a c h l o r o e t h y l e n e (120.8°C., n b p ) was s e l e c t e d as a r e p r e s e n t a t i v e contaminant. Uncontaminated ( c l e a n ) sandy s o i l from the v i c i n i t y of a w a s t e s i t e was s p i k e d w i t h t e t r a c h l o r o e t h y l e n e and u s e d i n recovery experiments. Experimental Procedure. A l a r g e amount o f s a n d y s o i l was o b t a i n e d f r o m t h e field. A p p r o x i m a t e l y 1000 g o f t h i s s o i l was p l a c e d i n a l a r g e g l a s s j a r and t u m b l e d o v e r n i g h t . A s o i l s a m p l e was a n a l y z e d for c h l o r i n a t e d s o l v e n t s by e x t r a c t i o n i n a N i e l s o n - K r y g e r (7) steam d i s t i l l a t i o n a p p a r a t u s f o l l o w e d by a n a l y s i s o f t h e e x t r a c t on a g a s c h r o m a t o g r a p h (GC) e q u i p p e d w i t h an e l e c t r o n c a p t u r e ( E C ) detector. When i t was v e r i f i e d t h a t t h e s o i l d i d n o t c o n t a i n a n y c h l o r i n a t e d s o l v e n t s , t h e m o i s t u r e c o n t e n t o f t h e s o i l was a d j u s t e d t o 5 o r 10%. The c l e a n m o i s t s o i l was p r e p a r e d f o r e x p e r i m e n t s by p l a c i n g i t i n t h e 500 ml r o u n d b o t t o m f l a s k and s p i k i n g i t w i t h a s o l u t i o n o f t e t r a c h l o r o e t h y l e n e t o a c o n c e n t r a t i o n o f e i t h e r 9.28 o r 957.3 ppm. The f l a s k was s e a l e d and r o t a t e d i n an i c e b a t h f o r 3 h r t o h o m o g e n i z e t h e s o i l and t h e s p i k e by t u m b l i n g . A t t h e end o f t h i s t u m b l i n g p e r i o d , t h e f l a s k was a t t a c h e d t o a w a t e r - c o o l e d s o l v e n t recovery condenser. The s i d e l e g o f t h e c o n d e n s e r was p l a c e d i n a c h i l l e d r e c e i v e r c o n t a i n i n g a p p r o x i m a t e l y 10 ml o f p e s t i c i d e g r a d e hexane. A T e n a x t r a p was p l a c e d on t h e g a s o u t l e t p o r t o f t h e condenser to t r a p uncondensed vapors. The s o i l was h e a t e d w i t h a h e a t i n g m a n t l e t o t h e d e s i r e d f i n a l t e m p e r a t u r e and m a i n t a i n e d a t t h a t t e m p e r a t u r e f o r 4 h r . At the erd o f t h i s t i m e , t h e h e a t i n g m a n t l e was r e m o v e d a n d t h e f l a s k was c o o l e d t o room t e m p e r a t u r e . The c o n d e n s e r was w a s h e d w i t h h y d r o c a r b o n - f r e e w a t e r and h e x a n e . These washings were combined w i t h the d i s t i l l a t e . The T e n a x t r a p was a l s o w a s h e d w i t h p e s t i c i d e g r a d e h e x a n e and t h e w a s h i n g s w e r e c o m b i n e d w i t h t h e distillate. The d i s t i l l a t e a n d w a s h i n g s w e r e d r i e d by p a s s i n g t h r o u g h a b e d o f anhydrous sodium s u l f a t e . The d r i e d d i s t i l l a t e a n d w a s h i n g s w e r e
334
SOLVING HAZARDOUS WASTE PROBLEMS
b r o u g h t u p t o v o l u m e w i t h h e x a n e i n a 100 m l v o l u m e t r i c f l a s k a n d a n a l y z e d f o r t e t r a c h l o r o e t h y l e n e o n a H e w l e t t P a c k a r d 5 8 4 0 GC equipped w i t h a N i EC d e t e c t o r . The g l a s s f l a s k c o n t a i n i n g t h e t r e a t e d s o i l was a t t a c h e d t o t h e N i e l s o n - K r y g e r d i s t i l l a t i o n head t o d e t e r m i n e the r e s i d u a l tetrachloroethylene. T h e amount o f t e t r a c h l o r o e t h y l e n e e x t r a c t e d b y t h i s p r o c e d u r e was c o r r e c t e d f o r t h e e x t r a c t i o n e f f i c i e n c y . T h e e x t r a c t i o n e f f i c i e n c y o f t e t r a c h l o r o e t h y l e n e f r o m s a n d y s o i l was determined by e x t r a c t i o n o f s o i l spiked a t nine l e v e l s i n t h e c o n c e n t r a t i o n r a n g e o f O.1 t o 1 1 9 0 ppm. T h e a v e r a g e e x t r a c t i o n e f f i c i e n c y b a s e d o n a l l n i n e s a m p l e s was 9 7 . 1 % w i t h a s t a n d a r d d e v i a t i o n o f ±4.3. Results, The r e s u l t s o f d e c o n t a m i n a t i o n e x p e r i m e n t s a r e summarized i n T a b l e s I and I I . The r e s u l t s o f a l l h i g h concentrat i o n e x p e r i m e n t s ( T a b l e I ) show t h a t t h e a v e r a g e r e c o v e r y was 9 6 . 6 % w i t h a s t a n d a r d d e v i a t i o n o f ±2.O. The r e s u l t s were not a f f e c t e d s i g n i f i c a n t l y b y v a r y i n g t h e t e m p e r a t u r e i n t h e r a n g e o f 90° t o 130°C. S i m i l a r l y , r e c o v e r y was n o t a f f e c t e d b y v a r y i n g s o i l m o i s t u r e i n t h e r a n g e o f 5.7 t o 9.85 w t % . S i m i l a r r e s u l t s were o b t a i n e d when s o i l c o n t a i n i n g 9.28 ppm t e t r a c h l o r o e t h y l e n e a n d a p p r o x i m a t e l y 5.7% m o i s t u r e was t r e a t e d a t 90° a n d 100°C ( T a b l e I I ) . The a v e r a g e r e c o v e r y o f t e t r a c h l o r o e t h y l e n e i n f i v e e x p e r i m e n t s u s i n g 9.28 ppm t e t r a c h l o r o e t h y l e n e a n d a p p r o x i m a t e l y 5 . 7 % m o i s t u r e a t 90° a n d 100°C was 9 5 % w i t h a s t a n d a r d d e v i a t i o n o f ± 1 . 5 . The r e s u l t s show t h a t s u b s t a n t i a l r e c o v e r y o f t e t r a c h l o r o e t h y l e n e f r o m s o i l i s f e a s i b l e i n t h e t e m p e r a t u r e r a n g e o f 90° t o 130°C. C o n s i d e r i n g t h e d a t a shown i n T a b l e s I a n d I I , a n d e x t r a p o l a t i n g t h e r e s u l t o b t a i n e d a t a c o n c e n t r a t i o n o f 9 5 7 . 3 ppm h e a t e d t o 130°C., i t may a l s o b e s t a t e d t h a t t h e r e i s n o s i g n i f i c a n t d i f f e r e n c e b e t w e e n t h e amount o f t e t r a c h l o r o e t h y l e n e r e c o v e r e d when t h e s o i l i s h e a t e d t o 90° a n d when i t i s h e a t e d t o 130°C. 6 3
Table I.
Init ial Moisture, %
Thermal Recovery of Tetrachloroethylene from S o i l (containing 957.3 ppm)
Temp., °C
Time, hr
Residual Concentration, ppm
Recovery, % O.4
5.9
21
4.00
1089*
5.7
90
4.00
58.4
94.2
5.7
90
4.10
52.0
94.9
5.7
101
3.55
29.1
97.1
5.7
101
3.62
18.4
98.2
5.7
101
4.02
56.3
94.5
5.7
131
3.75
20.6
98.0
9.85
89
4.00
1.6
99.8
9.85
102
3.50
25.0
97.6
•^Initial concentration: of experimental error.
992 ppm.
Difference
i s w i t h i n the
bounds
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Table I I .
Initial Moisture, %
Thermal Recovery of Tetrachloroethylene from S o i l (containing 9.28 ppm)
Temp., °C
5.9 5.7
21 89
O.3
9690* 242
97.5
499 461
94.9 95.3
635 525
93.5 94.7
3.73 3.58 3.72
5.7
101
3.45
I n i t i a l concentration: of experimental error.
Recovery, %
4.0 4.07
99 100
90
Residual Concentration, ppb
Time, hr
5.7 5.7 5.7
Principles
335
In Situ Radio Frequency Heating Process
9.92
ppm.
Difference is within the bounds
of Radio Frequency Heating
The term radio frequency (RF) generally refers to the frequencies used in wireless communications. These frequencies can be as low as 45 Hz or extend well above 10 GHz. The frequencies primarily used for radio frequency, d i e l e c t r i c , or microwave heating range from 6.78 MHz to 2.45 GHz. The principles of RF heating are similar to those of a microwave oven, except that the frequency of operation is different and the size of the application i s much larger. In these systems, the temperature r i s e occurs as a result of ohmic or d i e l e c t r i c heating mechanisms. Ohmic heating arises from an ionic current or conduction current that flows in the material in response to the applied elect r i c f i e l d . D i e l e c t r i c heating results from the physical d i s t o r t i o n of the atomic or molecular structure of polar materials in response to an applied e l e c t r i c f i e l d . Since the applied AC e l e c t r i c f i e l d changes rapidly, the alternating physical d i s t o r t i o n dissipates mechanical energy that i s translated into thermal energy in the material. The d i e l e c t r i c properties of s o i l determine the amount of RF power that can be dissipated in the s o i l . These properties are the r e l a t i v e d i e l e c t r i c constant (e ) and the loss-tangent. The losstangent, tan 6, is defined as a/(joe e where a is the apparent conductivity, oj i s the frequency of the applied e l e c t r i c f i e l d , radians/sec, and e i s the permittivity of free space which equals 8.85 x 10" Farads/meter. A l l the d i e l e c t r i c properties are a function of s o i l temperature, the frequency of the applied f i e l d , and the composition of the s o i l . The amount of RF power dissipated in the s o i l i s d i r e c t l y related to the frequency of the applied e l e c t r i c f i e l d , to the square of the amplitude, to the relative d i e l e c t r i c constant, and to the loss-tangent (8). The depth of penetration of the electromagnetic energy i s measured by i t s skin depth. Skin depth i s defined as the distance from the power source at which the amplitude of the EM wave f a l l s to 0
Q
12
r
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SOLVING HAZARDOUS WASTE PROBLEMS
37% o f i t s i n i t i a l a m p l i t u d e ( 8 ) . Skin depth i s i n v e r s e l y r e l a t e d t o t h e s q u a r e r o o t o f f r e q u e n c y , a p p a r e n t AC c o n d u c t i v i t y , o r t h e loss-tangent. The d i e l e c t r i c p a r a m e t e r s d e t e r m i n e t h e d e p t h o f p e n e t r a t i o n o f EM f i e l d s i n t o t h e s o i l f o r a g i v e n o p e r a t i n g f r e q u e n c y . I f the d e p t h o f p e n e t r a t i o n i s s m a l l compared t o t h a t needed, o n l y t h e volume n e a r e s t the e n e r g y s o u r c e would be h e a t e d i n i t i a l i y . This s u g g e s t s t h a t f o r a n y r e a s o n a b l e volume, as low a f r e q u e n c y as p o s s i b l e s h o u l d be c h o s e n . On t h e o t h e r h a n d , i f t o o l o w a frequency i s chosen, very l i t t l e energy a b s o r p t i o n w i l l occur f o r an acceptable l e v e l of e l e c t r i c f i e l d . W h i l e t h e e l e c t r i c f i e l d c a n be i n c r e a s e d , e l e c t r i c a l breakdown, corona d i s c h a r g e , o r other undesirable e f f e c t s canresult. Thus, t h e r e i s , an optimum range w h e r e i n a s u i t a b l e f r e q u e n c y c a n be c h o s e n f o r a g i v e n volume o f m a t e r i a l and a g i v e n set o f d i e l e c t r i c parameters. I n - S i t u RF H e a t i n g
Systems
A f u l l y o p e r a t i o n a l i n - s i t u RF h e a t i n g s y s t e m f o r d e c o n t a m i n a t i o n r e q u i r e s the development and t e s t i n g o f a t l e a s t f o u r major subsystems. T h e s e a r e : ( 1 ) RF e n e r g y d e p o s i t i o n e l e c t r o d e a r r a y ; ( 2 ) RF p o w e r g e n e r a t i o n , t r a n s m i s s i o n , m o n i t o r i n g a n d c o n t r o l s y s t e m ; (3) vapor b a r r i e r and containment system; and (4) gas and l i q u i d condensate h a n d l i n g and treatment system. Among t h e s u b - s y s t e m s m e n t i o n e d a b o v e , t h e d e s i g n o f t h e e l e c t r o d e a r r a y ( a l s o c a l l e d the e x c i t e r a r r a y ) i s the c r i t i c a l f a c t o r that w i l l determine the design requirements and c o n s t r a i n t s f o r the other three sub-systems. Previous attempts (9-12) t o use e l e c t r i c a l energy f o r h e a t i n g e a r t h f o r m a t i o n s were aimed a t r e s o u r c e r e c o v e r y from h y d r o c a r bonaceous d e p o s i t s . Simple techniques such as burying e l e c t r i c a l h e a t i n g e l e m e n t s o r a p a i r o f e l e c t r o d e s t o w h i c h 60 c y c l e s AC p o w e r i s a p p l i e d were not s u c c e s s f u l f o r two main r e a s o n s : ( 1 ) n o n u n i f o r m h e a t i n g l e d t o unacceptable l e v e l s o f energy i n e f f i c i e n c y ; and ( 2 ) h e a t i n g b e y o n d t h e b o i l i n g p o i n t o f f r e e w a t e r was n o t p o s s i b l e . To o v e r c o m e t h e t e m p e r a t u r e l i m i t a t i o n i m p o s e d b y 60 Hz h e a t i n g , antennas r a d i a t i n g very h i g h f r e q u e n c y o r microwaves have been considered (9). Though t h e s e methods p r o v i d e r a p i d v o l u m e t r i c h e a t i n g even above the b o i l i n g p o i n t o f f r e e m o i s t u r e , they s u f f e r from i n e f f i c i e n t u s e o f the a p p l i e d energy. To o v e r c o m e t h e s e l i m i t a t i o n s , i t i s n e c e s s a r y t o u s e b o u n d w a v e e x c i t e r s a s o p p o s e d t o t h e r a d i a t e d wave h o r n s o r a n t e n n a s p r e v i o u s l y used. The bound-wave e x c i t e r s a r e d e s i g n e d t o f u l l y c o n t a i n t h e EM r a d i a t i o n w i t h i n a d e f i n e d v o l u m e o f s o i l . There a r e two b a s i c t y p e s o f b o u n d - w a v e e x c i t e r a r r a y s . These are the t r i p l a t e l i n e and the f r i n g i n g - f i e l d t r a n s m i s s i o n l i n e . Triplate Line. The t r i p l a t e t r a n s m i s s i o n l i n e i s t h e r e c t a n g u l a r a n a l o g u e o f t h e more f a m i l i a r c y l i n d r i c a l c o a x i a l c a b l e s . T h e t r i p l a t e l i n e i s formed by a f u l l y e n c l o s e d r e c t a n g u l a r c a v i t y i n w h i c h a c e n t r a l p l a n a r c o n d u c t o r has been i n s e r t e d p a r a l l e l t o t h e l a r g e s i d e s o f the c a v i t y . C l e a r l y emplacement o f s o l i d m e t a l p l a t e s that e n c l o s e a r e c t a n g u l a r c a v i t y below the s o i l s u r f a c e i s impractical. T h i s p r o b l e m h a s b e e n r e s o l v e d (1, 1 3 ) b y s i m u l a t i n g the f u l l y contained r e c t a n g u l a r c a v i t y by i n s e r t i n g an a r r a y o f
27.
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ET AL.
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e l e c t r o d e s i n t o bore-holes d r i l l e d through the s o i l . The e l e c t r o d e s a r e i n s e r t e d i n t h r e e p a r a l l e l r o w s t h a t r e p r e s e n t t h e two o u t e r w a l l s and t h e c e n t r a l c o n d u c t o r o f t h e f u l l y c o n t a i n e d r e c t a n g u l a r triplate. I t h a s b e e n d e m o n s t r a t e d (1, H ) that through a p p r o p r i a t e s e l e c t i o n o f t h e r o w - s p a c i n g and t h e s p a c i n g o f t h e e l e c t r o d e s w i t h i n e a c h row, i t i s p o s s i b l e t o f u l l y c o n t a i n t h e a p p l i e d e l e c t r o m a g n e t i c f i e l d w i t h i n t h e two o u t e r r o w s o f e l e c t r o d e s . The t r i p l a t e l i n e i s s u i t a b l e f o r t h o s e s o i l d e c o n t a m i n a t i o n a p p l i c a t i o n s w h e r e t h e c o n t a m i n a n t s h a v e p e n e t r a t e d more t h a n t h r e e f e e t b e l o w t h e s u r f a c e and f o r c o n t a m i n a n t s t h a t r e q u i r e t r e a t m e n t t e m p e r a t u r e s i n e x c e s s o f 130° t o 150°C. F i g u r e 1 i l l u s t r a t e s a c o n c e p t u a l d e s i g n o f s u c h an a r r a y t h a t i s c o v e r e d by a v a p o r b a r r i e r t o c o n t a i n and c o l l e c t g a s e s and v a p o r s as t h e y r i s e f r o m t h e s u r f a c e o f t h e s o i l . A triplate line was t e s t e d b y K r s t a n s k y e t a l . (I) b y h e a t i n g 660 c u f t o f a t a r s a n d f o r m a t i o n t o 200°C t o a n a v e r a g e d e p t h o f 14.7 f t . Fringing-Field Line. T h i s c o n c e p t makes u s e o f t h e f r i n g i n g f i e l d s or leakage f i e l d s that e x i s t near a transmission l i n e . F i g u r e 2 i l l u s t r a t e s a s c h e m a t i c d i a g r a m showing rows o f h o r i z o n t a l e l e c t r o d e s placed over the s u r f a c e of the s o i l . Fringing f i e l d s are f o r m e d a r o u n d t h e e l e c t r o d e s when t h e y a r e e n e r g i z e d . T h u s EM e n e r g y i s f i r s t a b s o r b e d by t h e m o i s t l a y e r s o f s o i l n e a r e s t t h e electrodes. As t h e m o i s t u r e i s d r i v e n o u t o f t h e s o i l , t h e e n e r g y i s s e l e c t i v e l y absorbed at g r e a t e r depths. The h e a t i n g z o n e i s e v e n t u a l l y r e s t r i c t e d because of the e x p o n e n t i a l f a l l - o f f of the f i e l d s i n t o the s o i l . A 1:3 s c a l e m o d e l o f a s i n g l e e l e c t r o d e f r o m t h e f r i n g i n g - f i e l d l i n e shown i n F i g u r e 2 was made a n d t e s t e d ( 1 4 ) . The r e s u l t s o f t h i s t e s t show t h a t t h e f r i n g i n g f i e l d l i n e i s s u i t a b l e f o r t h e treatment of s o i l s i n which the depth of contaminant p e n e t r a t i o n i s l e s s t h a n t h r e e f e e t and where t h e r e q u i r e d t r e a t m e n t t e m p e r a t u r e s do n o t e x c e e d 130°C. A d d i t i o n a l d e v e l o p m e n t a n d t e s t i n g i s , however, necessary to f u l l y e x p l o r e the l i m i t a t i o n s of the f r i n g i n g f i e l d l i n e s , a n d i n p a r t i c u l a r , t o d e t e r m i n e ways t o i m p r o v e t h e penetration depth. Cost
Estimate
P r e l i m i n a r y cost estimates f o r t r e a t i n g contaminated s o i l u s i n g the t r i - p l a t e e x c i t e r h a v e b e e n r e p o r t e d (14)« I t was e s t i m a t e d t h a t the c o s t o f t r e a t i n g s o i l c o n t a i n i n g 12.1% m o i s t u r e t o a t e m p e r a t u r e o f 170°C was $ 4 2 / t o n . T h i s e s t i m a t e was b a s e d o n t h e t r e a t m e n t o f a 3 - a c r e s i t e t o a d e p t h o f 8 f t b y t h e p r o g r e s s i v e h e a t i n g o f a 96 x 96 x 8 f t m o d u l e . I t was e s t i m a t e d t h a t t h e 3 - a c r e s i t e c a n be t r e a t e d i n one y e a r . A p p r o p r i a t e p i l o t and f i e l d t e s t s c u r r e n t l y i n the p l a n n i n g phase w i l l v a l i d a t e o p e r a t i n g and economic parameters. Conclusions L a b o r a t o r y - s c a l e s t u d i e s h a v e shown t h a t 9 5 % o f t h e t e t r a c h l o r o e t h y l e n e p r e s e n t i n s o i l c a n be r e c o v e r e d by h e a t i n g t o a t e m p e r a t u r e r a n g e o f 90° t o 130°C f o r 4 - h r . A d d i t i o n a l experiments are n e c e s s a r y to d e t e r m i n e whether s i m i l a r r e c o v e r y e f f i c i e n c i e s can be s u s t a i n e d o v e r d e e p s o i l b e d s . The RF h e a t i n g t e c h n i q u e s h a v e
SOLVING HAZARDOUS WASTE PROBLEMS
338
Vapor
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In Situ Radio Frequency Heating Process
339
been t e s t e d on hydrocarbonaceous e a r t h f o r m a t i o n s i n t h e temperature r a n g e o f 2 0 0 C t o 4 0 0 °C. A p p r o p r i a t e f i e l d a n d p i l o t t e s t s a r e necessary t ov a l i d a t e the t e c h n i c a l f e a s i b i l i t y and the cost p a r a m e t e r s o f u s i n g t h e i n s i t u RF h e a t i n g m e t h o d s f o r s o i l decontamination. Acknowledgment T h i s w o r k was s u p p o r t e d b y t h e U.S. E P A , U S A F , a n d I I T R e s e a r c h I n s t i t u t e t h r o u g h a U.S. E P A c o - o p e r a t i v e a g r e e m e n t C R - 8 1 1 5 2 9 - 0 1 - O . Literature 1.
2. 3. 4. 5.
6.
7. 8.
9.
10. 11. 12. 13. 14.
Cited
Krstansky, J., et al. "RF Heating of Utah Tar Sands"; IIT Research Institute: Chicago, 1982; Final Report, IITRI E06482. Barnhart, Benjamin J. Environmental Science Technology 1979, 12, 1132-6. Murray, C. Chemical & Engineering News 1979, 57, 12-16. Rogers, C. J. Proc. 8th Annual EPA Symposium on the Treatment of Hazardous Waste, 1983, p. 197. "Solid Waste Facts - A Statistical Handbook," U.S. Environmental Protection Agency, Office of Public Awareness, 1978. "Everybody's Problem: Hazardous Waste," U.S. Environmental Protection Agency, Office of Water and Waste Management, 1980. Onuska, F. I; Terry, K. A. Analytical Chemistry 1985, 57, 801-5. Dev, H., J. Bridges, and Clark, D. "Radio Frequency Enhanced Decontamination of Soils Contaminated with Halogenated Hydrocarbons, Interim Report"; IIT Research Institute; Chicago, 1985; IITRI C06600. Abernathy, E. R. 1974 Annual Technical Meeting of the Petroleum Society of CIM, Calgary, Alberta, 1974, paper 374007. Flock, D. L; Tharin, A. J. Journal of Canadian Petroleum Technology 1975, 14, 17. Ljungstrom, F. Teknisk Tidskrift 1951, 81, 33. Salomonsson, G. Tidskrift För Tekniski-Vetenskaplig För Skning 1953, 24, 118. Sresty, G. C.; Dev, H.; Snow, R. H.; Bridges, J. E. SPE Reservoir Engineering 1986, I, 85. Dev, H. Proc. 12th Annual Research Symposium, 1986, p. 402. EPA/600/9-86/022.
R E C E I V E D December 5, 1986
