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PCDF inside the combustion chamber and on four boiler levels of a waste incineration plant
Chemosphere, Vol.20, Nos.lO-12, P r i n t e d in G r e a t B r i t a i n
SIMULTANEOUS CHAMBER
AND
pp 1 8 3 9 - 1 8 4 6 ,
SAMPLING
ON FOUR
1990
OF P C D D / P C D F
BOILER
LEVELS
0045-6535/90 $3.00 Pergamon Press plc
INSIDE
OF A WASTE
+ .00
THE COMBUSTION INCINERATION
PLANT
+ U.
Ddwel
* Goepfert,
, A.
Nottrodt
*, K.
Ballschmiter
Reimer & Partner, Bramfelder D - 2 0 0 0 H a m b u r g 60, W - G e r m a n y
**
StraBe
** U n i v e r s i t ~ t Ulm, A l b e r t - E i n s t e i n - A l l e e D - 7 9 0 0 Ulm, W - G e r m a n y
70,
ii
ABSTRACT At a MSWI (municipal solid waste incinerator) plant PCDD/PCDF samples (gasphase and p a r t i c u l a t e s ) were taken simultaneously by a s h o c k - f r e e z i n g method in the incinerator combustion chamber at approx. 800°C and in four sampling sections in the boiler at about 490°C ,370°C, 330°C and 270°C. In this way PCDD/PCDF-formation in the flow through the boiler was determined. Two data sets were evaluated. A considerable PCDD/PCDF-formation had occurred already at boiler temperatures of about 490°C; the highest concentration, however, was found at the end of the boiler at about 300°C. The accompanying measuring program of plant parameters made the calculation of the PCDD/PCDF mass flows possible, which allowed the inclusion of the PCDD/PCDF-content in the ESP dust in the mass flow calculations. KEYWORDS Waste
Incineration;
PCDD/PCDF
formations;
flue gas
sampling
INTRODUCTION W i t h i n t h e f r a m e w o r k of a PCDD/PCDF R / D - p r o g r a m at m u n i c i p a l s o l i d w a s t e incineration (MSWI) plants conceptionally presented in [i] a n d c a r r i e d o u t o v e r s e v e r a l y e a r s t h e f o l l o w i n g q u e s t i o n s w e r e p e r s u e d - H o w a r e PCDD/PCDF f o r m e d in M S W I s ? - A r e t h e r e s p e c i f i c a r e a s w i t h i n M W I s w h e r e PCDD/PCDF a r e preferably formed? - Are there specific operational conditions which influe n c e P C D D / P C D F f o r m a t i o n ? [2,3,4]. B a s e d o n t h e s e t a s k s a n d - as r e p o r t e d b e f o r e - s i m u l t a n e o u s PCDD/PCDF sampling inside the combustion chamber and the boiler outlet were performed at s e v e r a l p l a n t s . T h e r e s u l t s are s u m m a r i z e d in Fig. i. It s h o w s t h e r e s u l t s of t w o t e s t s e r i e s , n a m e l y r e l a t i v e l y l o w c o n c e n t r a t i o n s inside the combustion chamber and comparatively high concentrations at the boiler outlet particularly for the PCDF. These results support the hypothesis of a m a j o r PCDD/PCDF
formation
inside
the boiler.
+ P r e s e n t a d d r e s s : I n s t i t u t for G e w a s s e r s c h u t z G e i e r s t r a B e i, D - 2 0 0 0 H a m b u r g 60, W - G e r m a n y
1839
und Umgebungsdberwachung
-IGU-
1840
PCDD/PCDF-LEVELS SUM T4-CDD n
SUM PG-CDD B
SUM H6-CDD t ~
SUM HT-CDD
OCDD
MicrogrBm/t CARBON in C02 1500
PCDD 100(
50OO
4OOO
30OO
2000
1000
0 TEST-RUNI
TEST-RUNII
COMBUSTIONCHAMBER
TEST-RUNI
TEST-RUNII
BOILEROUTLET
Figure 1: COMBUSTION CHAMBER vs. BOILER OUTLET
Especially with a view to PCDD/PCDF answer the question where between these
reduction, two areas
a separate study should - combustion chamber and
boiler outlet - the formation of PCDD/PCDF takes place. To answer these q u e s t i o n s P C D D / P C D F a n d p o s s i b l e p r e c u r s o r s s u c h as c h l o r o b e n z e n e s and chlor o p h e n o l s w e r e s a m p l e d at a M S W I s i m u l t a n e o u s l y inside the combustion chamb e r a n d a t f o u r s e c t i o n s of t h e b o i l e r . T w o i d e n t i c a l t e s t r u n s w e r e u s e d t o o b t a i n d a t a o n t h e r e p e a t a b i l i t y b e t w e e n t w o s e r i e s of m e a s u r e m e n t s . F i r s t r e s u l t s w e r e r e p o r t e d a t t h e D i o x i n 88 m e e t i n g [5] w h e r e t h e s u m s and isomer-specific p a t t e r n of t h e P C D D a n d P C D F f o r m e d in t h e d i f f e r e n t parts from the combustion chamber to the boiler outlet were discussed. In this paper we will concentrate on the concentrations and particularly on the m a s s f l o w of P C D D a n d P C D F as a r e l e v a n t m e a s u r e of P C D D / P C D F f o r m a t i o n in a waste incineration plant.
1841
EXPERIMENTAL F i g u r e 2 s h o w s a s c h e m a t i c s k e t c h of the M S W I w h e r e this s t u d y was performed. The h o r i z o n t a l c o n s t r u c t i o n of the b o i l e r a l l o w e d the i n s t a l l a t i o n of n e c c e s s a r y s a m p l i n g ports, w h i c h are named " c o m b u s t i o n chamber" and "sampling sections 1 to 4". In addition, samples of b o i l e r ash from dust c o l l e c t o r s A, B, C, D and of dust from the e l e c t r o s t a t i c p r e c i p i t a t o r were taken. SAMPLING SECTIONS BOILER
i
1,
2,
37
SAMPLING:COMBUSTION I ,/~
\ \
~$~Z~PLANT 7
o
I
CROSS-SECTION
SEPARATED ESP ASH
SEPARATED BOILER ASH
Figure 2: The P C D D / P C D F - s a m p l i n g ~as c a r r l e d out s i m u l t a n e o u s l y at the five sampling locations with w a t e r - c o o l e d probes (Figure 3) [2,6] that have been d e v e l o p e d for this program.
@©©/LE#
PR©~E
PACKING QUARTZ
\,
TITANIUM _
/
PACKING /
/
12 GAS/DUST INLET
OUT
IN
COOLING WATER
1,5 - 6 m
/
[ -i
Figure 3:
1842
With these probes the effect of d i f f e r e n t c o m b u s t i o n gas t e m p e r a t u r e s on the i n t e g r i t y of the c o l l e c t e d sample at the five l o c a t i o n s was negligible. F o l l o w i n g this probe, a s t a n d a r d sampling t e c h n i q u e with c o l l e c t i o n of cond e n s a t e a n d c o l l e c t i o n in I m p i n g e r s was u s e d [6,7]. In s p i t e of d i f f i c u l t s a m p l i n g c o n d i t i o n s inside the c o m b u s t i o n c h a m b e r and at the other s a m p l i n g sections, a m u l t i - p o i n t sampling over the r e s p e c t i v e c r o s s - s e c t i o n s was carried out. S a m p l i n g was done by the IGU, Hamburg. The a n a l y s e s for P C D D / P C D F and f u r t h e r o r g a n i c s were done at the U n i v e r s i t y of Ulm. A m o d i f i e d s i m p l e s a m p l i n g t e c h n i q u e m e a n w h i l e has been d e v e l o p e d [8]. B e s i d e s P C D D / P C D F sampling, the i n c i n e r a t o r o p e r a t i n g c o n d i t i o n s , e.g. load, p r o c e s s t e m p e r a t u r e s etc., were r e c o r d e d and the s t a n d a r d c o n s t i t u e n t s of the flue gas b e h i n d the ESP and in the c o m b u s t i o n c h a m b e r , such as CO, CO , 02, HCl, S O were measured. These data showed that d u r i n g the two test runs c o m p a r a b l e operating conditions e x i s t e d in the M S W I . In a p r e v i o u s t e s t i n g program, in spite of d i f f i c u l t sampling conditions, r e p r o d u c a b l e results c o u l d be obtained. RESULTS Figure 4 s u m m a r i z e s the total PCDD/PCDF levels found at the five s a m p l i n g l o c a t i o n s " c o m b u s t i o n c h a m b e r " and " s a m p l i n g s e c t i o n s 1 to 4". The s h o w n l e v e l s are m i c r o g r a m s P C D D / P C D F per ton of c a r b o n in CO 2 to get a d i r e c t c o r r e l a t i o n of P C D D / P C D F formation to the c o m b u s t i o n process. The c o m p a r i s o n of the r e s u l t s of two independent test runs shows that, in spite of d i f f i c u l ties to keep a MWI plant at the same o p e r a t i o n a l conditions, a good r e p e a t a b i l i t y exists b e t w e e n the two data sets. As the lines of the graphs show, a f o r m a t i o n of P C D D / P C D F was d e t e c t e d in all l o c a t i o n s b e t w e e n the c o m b u s t i o n chamber and the b o i l e r outlet. The m a x i mum of P C D D / P C D F formation is not localized to t e m p e r a t u r e of about 300°C, as is s o m e t i m e s p o s t u l a t e d [9]. The highest increase in c o n c e n t r a t i o n s was found b e t w e e n b o i l e r s e c t i o n 1 and 2, c o v e r i n g the range of 490 to 370 °C. C o n s i d e r i n g the PDCF alone, a steady increase in c o n c e n t r a t i o n is found with a c o n s i d e r a b l e f o r m a t i o n in a t e m p e r a t u r e r a n g e b e t w e e n 800 and 490°C. In the case of the PCDD the increase is not as consistent. The c o n c e n t r a t i o n d e c r e a ses first b e t w e e n the c o m b u s t i o n chamber and the s a m p l i n g s e c t i o n 1 and than it increases up to the exit from the boiler. Both test runs show this p h e n o m e non, therefore, it is not c o n s i d e r e d as m e r e l y coincidental. It c o u l d be due to a n o n r e p r e s e n t a t i v e sampling, w h i c h may be a result of a d i v e r s i o n in the path of the gas stream before it reaches the s a m p l i n g s e c t i o n i. D i s c u s s i n g the individual h o m o l o g u e series of d i f f e r e n t levels of c h l o r i n a tion instead of total PCDD/PCDF we get the f o l l o w i n g results for PCDD (Figure 5). Both c h a r t s showing the two test-runs again d e m o n s t r a t e a good a g r e e m e n t b e t w e e n the two sets of data. The h o m o l o g u e d i s t r i b u t i o n of the P C D D i n s i d e the c o m b u s t i o n chamber differs d e f i n i t e l y from that at the s a m p l i n g s e c t i o n s 1 to 4 in the b o i l e r indicating a shift either in the c h e m i s t r y of PCDD formation or in the e q u i l i b r i u m of f o r m a t i o n and d e s t r u c t i o n [i0]. A l o w e r i n g of the c o n c e n t r a t i o n at section 1 can also be c l e a r l y seen. S t a r t i n g from s e c t i o n 1 a l e v e l l i n g of the h o m o l o g u e d i s t r i b u t i o n occurs. Figure 6 depicts the
1843
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r e s u l t s for the PCDF, a g a i n w i t h a r e m a r k a b l y c h a r a c t e r i s t i c distribution w i t h i n the c h l o r o h o m o l o g u e s in the c o m b u s t i o n chamber and the boiler. S t a r t i n g from section 1 up to s e c t i o n 4 the p a t t e r n s are similar. The pattern is char a c t e r i z e d by h i g h l e v e l s for the t e t r a c h l o r o - h o m o l o g u e s and low levels for the o c t a c h l o r o - h o m o l o g u e . The p a t t e r n s of d i s t r i b u t i o n are p r a c t i c a l l y identical for both test-runs. The c o r r e l a t i o n of the pattern of the c h l o r o h o m o l o g u e s of P C D D / P C D F to o r g a n o c h l o r i n e p r e c u r s o r s has been d i s c u s s e d in a p r e v i o u s paper [I0]. The m e a s u r e m e n t program was organized in s u c h a w a y t h a t m a s s f l o w s of P C D D / P C D F c o u l d a l s o be c a l c u l a t e d in the gas e m i s s i o n s , in the b o i l e r ash, and in the ESP dust. Thus it was p o s s i b l e to combine and c o m p a r e the PCDD/PCDF mass flows in t h e s e streams. F i g u r e 7 s h o w s the m a s s f l o w of the sums of PCDD/PCDF for b o t h t e s t - r u n s m e a s u r e d in m i l l i g r a m s per hour. The mass flows are shown for the c o m b u s t i o n c h a m b e r and the b o i l e r s a m p l i n g s e c t i o n s 1 to 4. Additionally, the P C D D / P C D F m a s s f l o w f o u n d v i a t h e d u s t of t h e E S P is i n c l u d e d . T h e m a s s f l o w of P C D D / P C D F found in the b o i l e r ash was negligible. The chart shows that c o n s i d e r a b l e d i f f e r e n c e s exist in the mass flow for PCDD and PCDF. C o n c e r n i n g the sum of PCDD, a jump of a b o u t a f a c t o r of 3 o c c u r s b e t w e e n s e c t i o n 4 of the b o i l e r and the ESP. A s i m i l a r i n c r e a se was not detected for the sum of PCDF. For e a c h t e s t run P C D D m a s s f l o ws of tetra-, h e x a - and o c t a - c h l o r o h o m o l o g u e s are s h o w n in F i g u r e 8. In this d i a g r a m v a l u e s d i f f e r i n g by s e v e r a l o r d e r s of m a g n i t u d e are s u m m a r i z e d on a l o g a r i t h m i c scale. B o t h test r u n s agree in that the i n c r e a s e of the tetras a m o u n t to about two orders of m a g n i tude from the c o m b u s t i o n c h a m b e r to b o i l e r section i, f o l l o w e d only by s m a l l e r increases g o i n g to the s e c t i o n s 2, 3 and 4. Levels an order of m a g n i t u d e lower can be d e t e c t e d in the ESP dust. The mass flow of the OCDD takes a d r a m a t i c a l ly d i f f e r e n t course. F i r s t l y a drop in the mass flow s t a r t i n g from the c o m b u s tion c h a m b e r to s e c t i o n 1 can be observed. Then a gradual i n c r e a s e to s e c t i o n 4 takes p l a c e f o l l o w e d by a d r a m a t i c rise in the ESP dust by about one o r d e r of m a g n i t u d e . T h e m a s s f l o w of t h e o t h e r c h l o r o h o m o l o g u e s are b e t w e e n t h e tetras and the OCDD, as shown for the hexas. Two c o n c l u s i o n s can be d r a w n from these results: A c o m p a r i s o n of the PCDD p a t t e r n found in b o i l e r section 4 w i t h that in ESP dust i n d i c a t e s a d r a s t i c s h i f t in basic c h e m i s t r y of PCDD f o r m a t i on and d e s t r u c t i o n as the m a x i m u m m o ve s from the tetras to the octa. F u r t h e r more, the mass flow of total PCDD increases, due to the p r e f e r e n t i a l f o r m a t i o n of the more c h l o r i n a t e d PCDD. Figure 9 shows that a s i m i l a r t r e nd for the mass flow line for PCDF as that found for PCDD. In the case of furans the mass flow of tetras rises even from the c o m b u s t i o n c h a m b e r to section i. Then it remains a p p r o x i m a t e l y c o n s t a n t up to the ESP w h e r e it d e c r e a s e s in the dust by about one o r d e r of magnitude. A reverse t r e n d in the line for octas in c o m p a r i s o n to the t e t r a s is indicated. An e l e m e n t a r y d i f f e r e n c e b e t w e e n d i o x i n s and furans is i n d i c a t e d in a d i f f e rence between tetra and octa homologues of t h e s e c o m p o u n d s at s a m p l i n g sections 2 to 4 amount,s to two orders of magnitude. A d e t a i l e d r e a c t i o n s c h e m e for the PCDD/PCDF f o r m a t i o n w h i c h can e x p l a i n the r e s u l t s r e p o r t e d here has been w o r k e d out [i0].
1845
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1846
CONCLUSIONS i. The highest total P C C D / P C D F c o n c e n t r a t i o n s were found at the exit of the boiler at a t e m p e r a t u r e of 270°C. 2. The P C D D / P C D F f o r m a t i o n o b s e r v e d in the tests is not c o n f i n e d to a temperature of about 300°C. The major f o r m a t i o n occurs in the temperature range 490-370°C. 3. The analysis of the P C D D / P C D F in the ESP input and the separated ESP dust shows a drastic s h i f t i n g from the tetras to the octas, indicating a difference in basic c h e m i s t r y going from the boiler to the ESP. 4. The mass flow of PCDD in the ESP ash is higher than the c o r r e s p o n d i n g ESP input flow, m a i n l y due to high octa levels. The study was s u p p o r t e d by the S t a p e l f e l d gGmbH, the M i n i s t r y for Science and T e c h n o l o g y and the U m w e l t b u n d e s a m t . REFERENCES [i] A. Nottrodt, K. B a l l s c h m i t e r et al.: "Emissionen von p o l y c h l o r i e r t e n D i b e n z o d i o x i n e n und p o l y c h l o r i e r t e n D i b e n z o f u r a n e n aus A b f a l l v e r b r e n nungsanlagen". MUll und Abfall, 11/84, 313-327 (1984). [2]
A. Nottrodt, U. D~wel, K. Ballschmiter: "Ursachen und M i n d e r u n g von P C D D / P C D F - E m i s s i o n e n bei M O l l v e r b r e n n u n g s a n l a g e n - Neue Untersuc h u n g s e r g e b n i s s e " . V D I - K o l l o q u i u m 5.5 bis 7.5.1987, V D I - B e r i c h t e Nr. 634, 595-634 (1987)
[3]
A. Nottrodt, U. DOwel, K. Ballschmiter: "Influence on formation of P C D D / P C D F im MWI plants - results of i n v e s t i g a t i o n s at several plants in the FRG", Chemosphere, 19, 309-316 (1988)
[4]
A. Nottrodt, U. DOwel, K. Ballschmiter: DIOXIN 89, September 17-22, 1989, T o r o n t o Canada, C h e m o s p h e r e in press.
[5]
K. Ballschmiter, R. Niemczyk, M. Swerev, W. Zoller, A. Nottrodt: "Organic C h e m i s t r y and F o r m a t i o n of P C D D / P C D F in MWI Plants: Influence of O p e r a t i o n a l P a r a m e t e r s on P C D D / P C D F Formation", DIOXIN 88, UMea, August 21-26, 1988.
[6]
U. DOwel, A. Nottrodt: "Probenahme von p o l y c h l o r i e r t e n D i b e n z o d i x i n e n und D i b e n z o f u r a n e n im H o c h t e m p e r a t u r b e r e i c h von M O l l v e r b r e n n u n g s a n lagen". V D I - K o m m i s s i o n R e i n h a l t u n g der Luft. Schriftenreihe, Band 8. M e 6 t e c h n i k in der M ~ l l v e r b r e n n u n g .
[7]
H. Hagenmeier, M. Kraft, S. Marklund, C. Rappe: "Studies towards Validated S a m p l i n g of PCDDs and PCDFs in Stack Gas", DIOXIN 1987, Las Vegas. C h e m o s p h e r e (1988)
[8]
A. Boenke, K. Ballschmiter: "A simple sampling t e c h n i q u e for organics in flue gas of i n c i n e r a t o r s and s i m i l a r gas streams", Fresenius Z. Anal. Chem. 334, 354-356 (1989).
[9]
L. Stieglitz, G. Zwick, J. Beck, H. Bautz, W. Roth:" Carbonaceons Particles in Fly Ash - A Source for the d e - n o v o - S y n t h e s i s of O r g a n o c h l o r o compounds", Chemosphere, 19, 283-290 (1989).
[i0] K. Ballschmiter, M. Swerev: " R e a c t i o n p a t h w a y s for the formation of p o l y c h l o r o d i b e n z o d i o x i n s (PCDD) and -furans (PCDF) in c o m b u s t i o n processes I", F r e s e n i u s Z. Anal. Chem. 328, 125-127 (1987). K. Ballschmiter, I. Braunmiller, R. Niemczyk, M. Swerev: "II. C h l o r o b e n zenes and C h l o r o p h e n o l s as P r e c u r s o r s in the F o r m a t i o n of Polychlorod i b e n z o d i o x i n s and - d i b e n z o f u r a n s in Flame Chemistry", C h e m o s p h e r e 17, 995-1005 (1988).
SIMULTANEOUS CHAMBER
AND
pp 1 8 3 9 - 1 8 4 6 ,
SAMPLING
ON FOUR
1990
OF P C D D / P C D F
BOILER
LEVELS
0045-6535/90 $3.00 Pergamon Press plc
INSIDE
OF A WASTE
+ .00
THE COMBUSTION INCINERATION
PLANT
+ U.
Ddwel
* Goepfert,
, A.
Nottrodt
*, K.
Ballschmiter
Reimer & Partner, Bramfelder D - 2 0 0 0 H a m b u r g 60, W - G e r m a n y
**
StraBe
** U n i v e r s i t ~ t Ulm, A l b e r t - E i n s t e i n - A l l e e D - 7 9 0 0 Ulm, W - G e r m a n y
70,
ii
ABSTRACT At a MSWI (municipal solid waste incinerator) plant PCDD/PCDF samples (gasphase and p a r t i c u l a t e s ) were taken simultaneously by a s h o c k - f r e e z i n g method in the incinerator combustion chamber at approx. 800°C and in four sampling sections in the boiler at about 490°C ,370°C, 330°C and 270°C. In this way PCDD/PCDF-formation in the flow through the boiler was determined. Two data sets were evaluated. A considerable PCDD/PCDF-formation had occurred already at boiler temperatures of about 490°C; the highest concentration, however, was found at the end of the boiler at about 300°C. The accompanying measuring program of plant parameters made the calculation of the PCDD/PCDF mass flows possible, which allowed the inclusion of the PCDD/PCDF-content in the ESP dust in the mass flow calculations. KEYWORDS Waste
Incineration;
PCDD/PCDF
formations;
flue gas
sampling
INTRODUCTION W i t h i n t h e f r a m e w o r k of a PCDD/PCDF R / D - p r o g r a m at m u n i c i p a l s o l i d w a s t e incineration (MSWI) plants conceptionally presented in [i] a n d c a r r i e d o u t o v e r s e v e r a l y e a r s t h e f o l l o w i n g q u e s t i o n s w e r e p e r s u e d - H o w a r e PCDD/PCDF f o r m e d in M S W I s ? - A r e t h e r e s p e c i f i c a r e a s w i t h i n M W I s w h e r e PCDD/PCDF a r e preferably formed? - Are there specific operational conditions which influe n c e P C D D / P C D F f o r m a t i o n ? [2,3,4]. B a s e d o n t h e s e t a s k s a n d - as r e p o r t e d b e f o r e - s i m u l t a n e o u s PCDD/PCDF sampling inside the combustion chamber and the boiler outlet were performed at s e v e r a l p l a n t s . T h e r e s u l t s are s u m m a r i z e d in Fig. i. It s h o w s t h e r e s u l t s of t w o t e s t s e r i e s , n a m e l y r e l a t i v e l y l o w c o n c e n t r a t i o n s inside the combustion chamber and comparatively high concentrations at the boiler outlet particularly for the PCDF. These results support the hypothesis of a m a j o r PCDD/PCDF
formation
inside
the boiler.
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und Umgebungsdberwachung
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Figure 1: COMBUSTION CHAMBER vs. BOILER OUTLET
Especially with a view to PCDD/PCDF answer the question where between these
reduction, two areas
a separate study should - combustion chamber and
boiler outlet - the formation of PCDD/PCDF takes place. To answer these q u e s t i o n s P C D D / P C D F a n d p o s s i b l e p r e c u r s o r s s u c h as c h l o r o b e n z e n e s and chlor o p h e n o l s w e r e s a m p l e d at a M S W I s i m u l t a n e o u s l y inside the combustion chamb e r a n d a t f o u r s e c t i o n s of t h e b o i l e r . T w o i d e n t i c a l t e s t r u n s w e r e u s e d t o o b t a i n d a t a o n t h e r e p e a t a b i l i t y b e t w e e n t w o s e r i e s of m e a s u r e m e n t s . F i r s t r e s u l t s w e r e r e p o r t e d a t t h e D i o x i n 88 m e e t i n g [5] w h e r e t h e s u m s and isomer-specific p a t t e r n of t h e P C D D a n d P C D F f o r m e d in t h e d i f f e r e n t parts from the combustion chamber to the boiler outlet were discussed. In this paper we will concentrate on the concentrations and particularly on the m a s s f l o w of P C D D a n d P C D F as a r e l e v a n t m e a s u r e of P C D D / P C D F f o r m a t i o n in a waste incineration plant.
1841
EXPERIMENTAL F i g u r e 2 s h o w s a s c h e m a t i c s k e t c h of the M S W I w h e r e this s t u d y was performed. The h o r i z o n t a l c o n s t r u c t i o n of the b o i l e r a l l o w e d the i n s t a l l a t i o n of n e c c e s s a r y s a m p l i n g ports, w h i c h are named " c o m b u s t i o n chamber" and "sampling sections 1 to 4". In addition, samples of b o i l e r ash from dust c o l l e c t o r s A, B, C, D and of dust from the e l e c t r o s t a t i c p r e c i p i t a t o r were taken. SAMPLING SECTIONS BOILER
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Figure 2: The P C D D / P C D F - s a m p l i n g ~as c a r r l e d out s i m u l t a n e o u s l y at the five sampling locations with w a t e r - c o o l e d probes (Figure 3) [2,6] that have been d e v e l o p e d for this program.
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1842
With these probes the effect of d i f f e r e n t c o m b u s t i o n gas t e m p e r a t u r e s on the i n t e g r i t y of the c o l l e c t e d sample at the five l o c a t i o n s was negligible. F o l l o w i n g this probe, a s t a n d a r d sampling t e c h n i q u e with c o l l e c t i o n of cond e n s a t e a n d c o l l e c t i o n in I m p i n g e r s was u s e d [6,7]. In s p i t e of d i f f i c u l t s a m p l i n g c o n d i t i o n s inside the c o m b u s t i o n c h a m b e r and at the other s a m p l i n g sections, a m u l t i - p o i n t sampling over the r e s p e c t i v e c r o s s - s e c t i o n s was carried out. S a m p l i n g was done by the IGU, Hamburg. The a n a l y s e s for P C D D / P C D F and f u r t h e r o r g a n i c s were done at the U n i v e r s i t y of Ulm. A m o d i f i e d s i m p l e s a m p l i n g t e c h n i q u e m e a n w h i l e has been d e v e l o p e d [8]. B e s i d e s P C D D / P C D F sampling, the i n c i n e r a t o r o p e r a t i n g c o n d i t i o n s , e.g. load, p r o c e s s t e m p e r a t u r e s etc., were r e c o r d e d and the s t a n d a r d c o n s t i t u e n t s of the flue gas b e h i n d the ESP and in the c o m b u s t i o n c h a m b e r , such as CO, CO , 02, HCl, S O were measured. These data showed that d u r i n g the two test runs c o m p a r a b l e operating conditions e x i s t e d in the M S W I . In a p r e v i o u s t e s t i n g program, in spite of d i f f i c u l t sampling conditions, r e p r o d u c a b l e results c o u l d be obtained. RESULTS Figure 4 s u m m a r i z e s the total PCDD/PCDF levels found at the five s a m p l i n g l o c a t i o n s " c o m b u s t i o n c h a m b e r " and " s a m p l i n g s e c t i o n s 1 to 4". The s h o w n l e v e l s are m i c r o g r a m s P C D D / P C D F per ton of c a r b o n in CO 2 to get a d i r e c t c o r r e l a t i o n of P C D D / P C D F formation to the c o m b u s t i o n process. The c o m p a r i s o n of the r e s u l t s of two independent test runs shows that, in spite of d i f f i c u l ties to keep a MWI plant at the same o p e r a t i o n a l conditions, a good r e p e a t a b i l i t y exists b e t w e e n the two data sets. As the lines of the graphs show, a f o r m a t i o n of P C D D / P C D F was d e t e c t e d in all l o c a t i o n s b e t w e e n the c o m b u s t i o n chamber and the b o i l e r outlet. The m a x i mum of P C D D / P C D F formation is not localized to t e m p e r a t u r e of about 300°C, as is s o m e t i m e s p o s t u l a t e d [9]. The highest increase in c o n c e n t r a t i o n s was found b e t w e e n b o i l e r s e c t i o n 1 and 2, c o v e r i n g the range of 490 to 370 °C. C o n s i d e r i n g the PDCF alone, a steady increase in c o n c e n t r a t i o n is found with a c o n s i d e r a b l e f o r m a t i o n in a t e m p e r a t u r e r a n g e b e t w e e n 800 and 490°C. In the case of the PCDD the increase is not as consistent. The c o n c e n t r a t i o n d e c r e a ses first b e t w e e n the c o m b u s t i o n chamber and the s a m p l i n g s e c t i o n 1 and than it increases up to the exit from the boiler. Both test runs show this p h e n o m e non, therefore, it is not c o n s i d e r e d as m e r e l y coincidental. It c o u l d be due to a n o n r e p r e s e n t a t i v e sampling, w h i c h may be a result of a d i v e r s i o n in the path of the gas stream before it reaches the s a m p l i n g s e c t i o n i. D i s c u s s i n g the individual h o m o l o g u e series of d i f f e r e n t levels of c h l o r i n a tion instead of total PCDD/PCDF we get the f o l l o w i n g results for PCDD (Figure 5). Both c h a r t s showing the two test-runs again d e m o n s t r a t e a good a g r e e m e n t b e t w e e n the two sets of data. The h o m o l o g u e d i s t r i b u t i o n of the P C D D i n s i d e the c o m b u s t i o n chamber differs d e f i n i t e l y from that at the s a m p l i n g s e c t i o n s 1 to 4 in the b o i l e r indicating a shift either in the c h e m i s t r y of PCDD formation or in the e q u i l i b r i u m of f o r m a t i o n and d e s t r u c t i o n [i0]. A l o w e r i n g of the c o n c e n t r a t i o n at section 1 can also be c l e a r l y seen. S t a r t i n g from s e c t i o n 1 a l e v e l l i n g of the h o m o l o g u e d i s t r i b u t i o n occurs. Figure 6 depicts the
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r e s u l t s for the PCDF, a g a i n w i t h a r e m a r k a b l y c h a r a c t e r i s t i c distribution w i t h i n the c h l o r o h o m o l o g u e s in the c o m b u s t i o n chamber and the boiler. S t a r t i n g from section 1 up to s e c t i o n 4 the p a t t e r n s are similar. The pattern is char a c t e r i z e d by h i g h l e v e l s for the t e t r a c h l o r o - h o m o l o g u e s and low levels for the o c t a c h l o r o - h o m o l o g u e . The p a t t e r n s of d i s t r i b u t i o n are p r a c t i c a l l y identical for both test-runs. The c o r r e l a t i o n of the pattern of the c h l o r o h o m o l o g u e s of P C D D / P C D F to o r g a n o c h l o r i n e p r e c u r s o r s has been d i s c u s s e d in a p r e v i o u s paper [I0]. The m e a s u r e m e n t program was organized in s u c h a w a y t h a t m a s s f l o w s of P C D D / P C D F c o u l d a l s o be c a l c u l a t e d in the gas e m i s s i o n s , in the b o i l e r ash, and in the ESP dust. Thus it was p o s s i b l e to combine and c o m p a r e the PCDD/PCDF mass flows in t h e s e streams. F i g u r e 7 s h o w s the m a s s f l o w of the sums of PCDD/PCDF for b o t h t e s t - r u n s m e a s u r e d in m i l l i g r a m s per hour. The mass flows are shown for the c o m b u s t i o n c h a m b e r and the b o i l e r s a m p l i n g s e c t i o n s 1 to 4. Additionally, the P C D D / P C D F m a s s f l o w f o u n d v i a t h e d u s t of t h e E S P is i n c l u d e d . T h e m a s s f l o w of P C D D / P C D F found in the b o i l e r ash was negligible. The chart shows that c o n s i d e r a b l e d i f f e r e n c e s exist in the mass flow for PCDD and PCDF. C o n c e r n i n g the sum of PCDD, a jump of a b o u t a f a c t o r of 3 o c c u r s b e t w e e n s e c t i o n 4 of the b o i l e r and the ESP. A s i m i l a r i n c r e a se was not detected for the sum of PCDF. For e a c h t e s t run P C D D m a s s f l o ws of tetra-, h e x a - and o c t a - c h l o r o h o m o l o g u e s are s h o w n in F i g u r e 8. In this d i a g r a m v a l u e s d i f f e r i n g by s e v e r a l o r d e r s of m a g n i t u d e are s u m m a r i z e d on a l o g a r i t h m i c scale. B o t h test r u n s agree in that the i n c r e a s e of the tetras a m o u n t to about two orders of m a g n i tude from the c o m b u s t i o n c h a m b e r to b o i l e r section i, f o l l o w e d only by s m a l l e r increases g o i n g to the s e c t i o n s 2, 3 and 4. Levels an order of m a g n i t u d e lower can be d e t e c t e d in the ESP dust. The mass flow of the OCDD takes a d r a m a t i c a l ly d i f f e r e n t course. F i r s t l y a drop in the mass flow s t a r t i n g from the c o m b u s tion c h a m b e r to s e c t i o n 1 can be observed. Then a gradual i n c r e a s e to s e c t i o n 4 takes p l a c e f o l l o w e d by a d r a m a t i c rise in the ESP dust by about one o r d e r of m a g n i t u d e . T h e m a s s f l o w of t h e o t h e r c h l o r o h o m o l o g u e s are b e t w e e n t h e tetras and the OCDD, as shown for the hexas. Two c o n c l u s i o n s can be d r a w n from these results: A c o m p a r i s o n of the PCDD p a t t e r n found in b o i l e r section 4 w i t h that in ESP dust i n d i c a t e s a d r a s t i c s h i f t in basic c h e m i s t r y of PCDD f o r m a t i on and d e s t r u c t i o n as the m a x i m u m m o ve s from the tetras to the octa. F u r t h e r more, the mass flow of total PCDD increases, due to the p r e f e r e n t i a l f o r m a t i o n of the more c h l o r i n a t e d PCDD. Figure 9 shows that a s i m i l a r t r e nd for the mass flow line for PCDF as that found for PCDD. In the case of furans the mass flow of tetras rises even from the c o m b u s t i o n c h a m b e r to section i. Then it remains a p p r o x i m a t e l y c o n s t a n t up to the ESP w h e r e it d e c r e a s e s in the dust by about one o r d e r of magnitude. A reverse t r e n d in the line for octas in c o m p a r i s o n to the t e t r a s is indicated. An e l e m e n t a r y d i f f e r e n c e b e t w e e n d i o x i n s and furans is i n d i c a t e d in a d i f f e rence between tetra and octa homologues of t h e s e c o m p o u n d s at s a m p l i n g sections 2 to 4 amount,s to two orders of magnitude. A d e t a i l e d r e a c t i o n s c h e m e for the PCDD/PCDF f o r m a t i o n w h i c h can e x p l a i n the r e s u l t s r e p o r t e d here has been w o r k e d out [i0].
1845
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CONCLUSIONS i. The highest total P C C D / P C D F c o n c e n t r a t i o n s were found at the exit of the boiler at a t e m p e r a t u r e of 270°C. 2. The P C D D / P C D F f o r m a t i o n o b s e r v e d in the tests is not c o n f i n e d to a temperature of about 300°C. The major f o r m a t i o n occurs in the temperature range 490-370°C. 3. The analysis of the P C D D / P C D F in the ESP input and the separated ESP dust shows a drastic s h i f t i n g from the tetras to the octas, indicating a difference in basic c h e m i s t r y going from the boiler to the ESP. 4. The mass flow of PCDD in the ESP ash is higher than the c o r r e s p o n d i n g ESP input flow, m a i n l y due to high octa levels. The study was s u p p o r t e d by the S t a p e l f e l d gGmbH, the M i n i s t r y for Science and T e c h n o l o g y and the U m w e l t b u n d e s a m t . REFERENCES [i] A. Nottrodt, K. B a l l s c h m i t e r et al.: "Emissionen von p o l y c h l o r i e r t e n D i b e n z o d i o x i n e n und p o l y c h l o r i e r t e n D i b e n z o f u r a n e n aus A b f a l l v e r b r e n nungsanlagen". MUll und Abfall, 11/84, 313-327 (1984). [2]
A. Nottrodt, U. D~wel, K. Ballschmiter: "Ursachen und M i n d e r u n g von P C D D / P C D F - E m i s s i o n e n bei M O l l v e r b r e n n u n g s a n l a g e n - Neue Untersuc h u n g s e r g e b n i s s e " . V D I - K o l l o q u i u m 5.5 bis 7.5.1987, V D I - B e r i c h t e Nr. 634, 595-634 (1987)
[3]
A. Nottrodt, U. DOwel, K. Ballschmiter: "Influence on formation of P C D D / P C D F im MWI plants - results of i n v e s t i g a t i o n s at several plants in the FRG", Chemosphere, 19, 309-316 (1988)
[4]
A. Nottrodt, U. DOwel, K. Ballschmiter: DIOXIN 89, September 17-22, 1989, T o r o n t o Canada, C h e m o s p h e r e in press.
[5]
K. Ballschmiter, R. Niemczyk, M. Swerev, W. Zoller, A. Nottrodt: "Organic C h e m i s t r y and F o r m a t i o n of P C D D / P C D F in MWI Plants: Influence of O p e r a t i o n a l P a r a m e t e r s on P C D D / P C D F Formation", DIOXIN 88, UMea, August 21-26, 1988.
[6]
U. DOwel, A. Nottrodt: "Probenahme von p o l y c h l o r i e r t e n D i b e n z o d i x i n e n und D i b e n z o f u r a n e n im H o c h t e m p e r a t u r b e r e i c h von M O l l v e r b r e n n u n g s a n lagen". V D I - K o m m i s s i o n R e i n h a l t u n g der Luft. Schriftenreihe, Band 8. M e 6 t e c h n i k in der M ~ l l v e r b r e n n u n g .
[7]
H. Hagenmeier, M. Kraft, S. Marklund, C. Rappe: "Studies towards Validated S a m p l i n g of PCDDs and PCDFs in Stack Gas", DIOXIN 1987, Las Vegas. C h e m o s p h e r e (1988)
[8]
A. Boenke, K. Ballschmiter: "A simple sampling t e c h n i q u e for organics in flue gas of i n c i n e r a t o r s and s i m i l a r gas streams", Fresenius Z. Anal. Chem. 334, 354-356 (1989).
[9]
L. Stieglitz, G. Zwick, J. Beck, H. Bautz, W. Roth:" Carbonaceons Particles in Fly Ash - A Source for the d e - n o v o - S y n t h e s i s of O r g a n o c h l o r o compounds", Chemosphere, 19, 283-290 (1989).
[i0] K. Ballschmiter, M. Swerev: " R e a c t i o n p a t h w a y s for the formation of p o l y c h l o r o d i b e n z o d i o x i n s (PCDD) and -furans (PCDF) in c o m b u s t i o n processes I", F r e s e n i u s Z. Anal. Chem. 328, 125-127 (1987). K. Ballschmiter, I. Braunmiller, R. Niemczyk, M. Swerev: "II. C h l o r o b e n zenes and C h l o r o p h e n o l s as P r e c u r s o r s in the F o r m a t i o n of Polychlorod i b e n z o d i o x i n s and - d i b e n z o f u r a n s in Flame Chemistry", C h e m o s p h e r e 17, 995-1005 (1988).