F emissions from a fluidized bed incinerator

Chemosphere, Voi.23, Nos.8-10, Printed in Great Britain

pp 1491-1500,

1991

0045-6535/91 $3.00 + 0.00 PerBamon Press plc

I N F L U E N C E OF OPERATING PARAMETERS AND FUEL TYPE

ON PCDD/F EMISSIONS FROM A FLUIDIZED BED INCINERATOR D. Lenoir a., A. Kaune a, O. Hutzinger a, G. Mfitzenich b, and K. Horch o a Chair of Ecological Chemistry and Geochemistry, University of Bayreuth, W-8580 Bayreuth, FRG b Deutsche Babcock Anlagen AG, W-4150 Krefeld 11, FRG * Corresponding author, present address: GSF-Forschungszentrum for Umwelt und Gesundheit, Ingolst/idter LandstraBe 1, W-8042 Neuherberg, FRG

ABSTRACT The influence of operating parameters and different fuel types on PCDD/F emissions was studied in a fluidized bed incinerator. Under conditions of incomplete combustion, CO concentration in the flue gas was positively, and 02 concentration was negatively correlated with total PCDD/F emissions. Low O2, high CO, and high C concentrations in the flue gas shifted the distribution pattern of PCDD/F to lower chlorinated homologues. Under normal operating conditions, high fluidized bed temperatures, low freeboard temperatures, and high O 2 values increased PCDD/F levels. PCDD/F emissions did not depend on the HCI concentration in the flue gas. The investigated fuel types varied in their chlorine content which, in some experiments, was increased by adding NaC1 or polyvinylchloride (PVC). Only the addition of 3 % PVC to polyethylene resulted in an increase in PCDD/F concentrations. Apart from this single experiment, no effect of fuel type on PCDD/F emissions was observed. High water contents of refuse derived fuel did not affect total PCDD/F concentrations, but reduced the furans to dioxins ratio and led to a shift to lower chlorinated homologues. KEYWORDS Fluidized bed incinerator, fly ash, operating parameters, PCDD, PCDF, RDF, PE, PVC INTRODUCTION Polychlorinated dibenzo-p-dioxin (PCDD) and dibenzofuran (PCDF) emissions from waste incinerators can be reduced by further improvements of flue gas cleaning systems, optimization of incineration conditions, and removal of waste substances which particularly favor PCDD/F formation. Reports about the influence of incineration conditions and waste type on PCDD/F concentrations are often contradictory. This is due to different types of incinerators, the high variability encountered in incineration experiments, and the often limited number of experiments which do not permit statistically significant conclusions. In this investigation, we studied the influence of operating parameters and different fuels in a fluidized bed incinerator. The data were statistically evaluated whenever possible.

1491

1492

EXPERIMENTAL Incineration experiments were conducted in the fluidized bed incinerator of the Deutsche Babcock Anlagen AG in Krefeld, FRG. A scheme of this pilot plant was presented by Lenoir et al. (1990). The investigated fuel types were refuse derived fuel (RDF), RDF plus 3 %, 5 %, 10 %, and 15 % lime, RDF + 2 % plastic containing decabromodiphenyl ether as flame retardant, a 1:1 mixture of RDF and polyethylene (PE), pure PE, PE + 2 % NaCI, PE + 3 % polyvinylchloride (PVC), wood chips, cellulose fiber, cellulose fiber + 2 % NaCI, and cellulose fiber + 2 % NaCI + 0.5 % PVC. The chlorine concentration of the fuel was 0.009 g/g for RDF, 0.002 g/g for wood chips and cellulose fiber, and 10-4 g/g for PE. RDF contained about 0.05 g water/g. In two experiments, water was added to RDF to give water contents of 0.20 and 0.25 g/g. Burning 40 kg of fuel per hour yielded approximately 260 m 3 of flue gas (standard conditions, 0 °C, 1013 hPa), containing about 5 kg of particulate material. When burning PE, the particulate material resulted from the quartz sand previously added to the PE. The particulate material was separated and collected in two fly ash fractions. Coarse fly ash (about 4 kg/h) had an average particle diameter of 100/~m and was separated by mass, while fine fly ash, with an average diameter of 10 #m, was separated by a fabric filter. Fine fly ash generation was about 1 kg/h. Before sampling coarse and fine fly ash from RDF combustion, about 24 h of burning under constant conditions were performed to equilibrate the incinerator. Fly ash was treated with hydrochloric acid, Soxhlet extracted with toluene for 48 h, and the extract was cleaned up using open column liquid chromatography. G C / M S analyses were performed on a Hewlett Packard 5890 GC/5970 MSD, using a 25 m Ultra 2 fused silica column (0.2 mm i. d., crosslinked, 0.33/~m film thickness, Hewlett Packard). The carrier gas was helium. Analysis parameters: splitless injector and interface temperatures 280 °C, ion source temperature 200 °C, temperature program: 100 °C 2 min isothermal, 20 °C/min to 180 °C, 5 °C/min to 320 °C. The internal standard mixture which was added prior to Soxhlet extraction contained one isomer each for tetra- to octachlorinated dibenzo-p-dioxins and dibenzofurans and was used for quantification. Fly ash concentrations of PCDD/F (#g/kg) and of organic carbon (C, g/kg) were converted to concentrations in flue gas (#g/m 3 for PCDD/F, and g/m 3 for organic carbon) utilizing the equation concentration in flue gas =

concentration in fly ash x mass flow of fly ash (kg/h) flow of flue gas (m3/h)

In two experiments, the stack gas, from which coarse and fine fly ash had been removed, was sampled isokinetically at 100 °C using a glass fiber filter and two cartridges (70 mm i. d.) in series, each filled with 30 g XAD-2 resin (Lenoir et al. 1989). Sample preparation for the glass fiber filter and XAD-2 resin were the same as for fly ash samples with the exception of acidic digestion. To examine a possible alteration of the homologue distribution pattern, incinerator operating parameters were correlated with absolute and relative homologue concentrations. The absolute concentrations are expressed in #g/m 3, while the dimensionless relative homologue concentrations are defined as the ratios of dioxin homologue concentrations to PCDD and the ratios of furan homologue concentrations to PCDF. If there is no change in the homologue distribution pattern, these ratios should not depend on operating parameters even if total P C D D / F emission and the furans to dioxins ratio are dependent on these parameters. However, from correlation analyses using either the relative or the absolute homologue concentrations, roughly the same conclusions had to be drawn. This particularly applies for part of the data (data set No. 1, see below). RESULTS The two experiments in which coarse and fine fly ash, as well as the stack gas, were sampled show that both fly ash fractions contained 26 and 8 1 % of the tonil P C D D / F concentration in the flue gas (Table 1). The remaining fraction of P C D D / F was either in the gas phase or adsorbed on particles smaller than 10 #m in diameter, which were not

1493

retained by the fabric filter. The large difference between 25 and 81% of P C D D / F adsorbed on coarse and fine fly ash may be attributed to the difference in the sampled stack gas volumes (126 and 1.6 m 3, respectively). The following statements about the influence of incinerator operating conditions and fuel types on P C D D / F emission might have to be modified if the total P C D D / F concentration in the flue gas, rather than the P C D D / F fraction attributed to coarse and fine fly ash, had been considered. TABLE 1.

Distribution of P C D D / F between fly ash of different size and gas phase. Fuel type

PCDD/F PCDD/F PCDD/F PCDD/F

RDF (/~g/m3) (%) adsorbed on coarse fly ash adsorbed on fine fly ash collected by glass fiber filter adsorbed on XAD-2 resin

Sum TABLE 2.

0.8 2.0 4.34 3.77

7 18 40 35

10.91

100

RDF + 3 % lime (#g/m 3) (%) 1.0 7.9 1.92

9 72 18

0.14 10.96

1 100

Reproducibility of P C D D / F measurements in 4 experiments (incineration of RDF). Variable

Mean

Standard deviation

Coefficient of variation

PCDD/F CO

(/~g/m3) (mg/m 3)

1.59 45

0.07 10

0.04 0.22

O2 C HCI

(%) (g/m 3) (mg/m 3)

6.1 0.17 320

0.1 0.04 90

0.02 0.24 0.28

Bed temperature (°C) Freeboard temperature (°C)

810 946

3 4

0.004 0.004

P C D D / F results were reproducible under similar incineration parameters (Table 2). The standard deviation of P C D D / F measurements was in the range of -+ 4 % of the mean, when the standard deviation of incinerator operating parameters was in the range of -+ 28 % of the mean. Apart from the experiments described in Table 2, operating parameters varied extremely. For example, the CO content in the flue gas varied about 3 orders of magnitude. The variation of operating parameters was very large during the first 9 experiments (data set No. 1) and smaller in the remaining 44 experiments (data set No. 2). P C D D / F levels were generally higher for data set No. 1 (mean _+ standard deviation = 39 _+ 15/~g/m 3, range 22.51-73.37 #g/m 3) than for data set No. 2 (4.8 -+ 6.4 #g/m 3, median 2.94 /~g/m3, range 0.54-31.97/~g/m3). The furans to dioxins ratio was 3.7 _+ 1.2 for data set No. 2 and thus similar to the ratio of 3.2 _+ 1.2 given by Pitea et al. (1989). However, the furans to dioxins ratio of data set No. 1 (6.6 -+ 2.4) was significantly higher (level of significance a = 0.01). For these reasons, we considered the two groups of experiments separately. This procedure is also justified by the fact that the concentrations of CO, O 2, and C, and freeboard temperature values of the entire data set were not normally distributed and could not be normalized by transformation. However, values of data set No. 1 met the criterion of normal distribution which is required for regression analyses and computation of Pearson correlation coefficients, and values of data set No. 2 could be normalized by logarithmic transformation (variables P C D D / F and CO) or square root transformation (HCI). For C concentrations and freeboard temperatures (due to bimodal frequency distribution) no transformation was found to be satisfactorily approximated by the normal distribution. In these cases, rather than calculating the Pearson correlation coefficient, the nonparametric Spearman correlation coefficient was determined.

1494

Influence of Incinerator Operating Parameters on PCDD/F Emissions In data set No. 1 a significant correlation existed for P C D D / F v e r s u s CO concentration in the flue gas (Table 3). For the negative correlation coefficient between PCDD/F and 0 2 a significance of a = 0.06 was computed which usually led to the rejection of the hypothesis of correlation. Combustion temperatures and the C concentration in the flue gas exhibited no relationship to total P C D D / F values. CO, 0 2, and C concentrations in the flue gas were significantly correlated with levels of CI4DD, CI4DF, and CI5DF. Another significant correlation existed between CIsDD and C concentration in the flue gas. In conclusion, an incomplete burning of the fuel was responsible for increased P C D D / F values and a shift to lower chlorinated homologues. The incomplete combustion was indicated by high CO and low O 2 concentrations in the flue gas. As far as the pattern change is concerned, the flue gas C concentration was also a good indicator, although this variable had no influence on total PCDD/F emissions. In contrast to the experiments of data set No. 1, which were characterized by incomplete burning, experiments of data set No. 2 were conducted under normal operating conditions. Decreasing the fluidized bed temperature and increasing the freeboard temperature decreased PCDD/F emissions and the furans to dioxins ratio. The significant correlations of freeboard temperature versus CIaDF and O 2 versus some of the homologue concentrations were related to the dependence on total P C D D / F emissions and did not indicate a shift in the distribution pattern. This could be seen from the relative homologue concentrations, which were not significantly dependent on freeboard temperatures and 0 2 values. Besides very low O 2 concentrations indicating incomplete burning, very high values have also been shown to favor PCDD/F formation (Martin and Zahlten 1989, Hagenmaier 1987, Vogg 1987, Nottrodt et al. 1989, Manscher et al. 1990). The highly significant positive correlation for O 2 values above 6 % shown in Figure 2 supports this finding. It could also be conf'wrned that the C concentration did not affect total PCDD/F levels (Martin and Zahlten 1989, Manscher et al. 1990). However, C concentration affected emissions of CITDD and CIsDF. The dependence of P C D D / F on CO values (Sierig 1989, Manscher et al. 1990, Boscak 1990, Kilgroe 1990) was only true above a threshold value of approximately 250 mg/m 3 (data set No. 1). Lower CO values had no significant influence on PCDD/F levels (data set No. 2). When injecting HCI in hydrocarbon flames or flue gases from hydrocarbon combustion, De Fr6 and Rymen (1989) found an exponential relationsfiip between the HCI and the generated PCDD/F concentrations. Also Manscher et al. (1990) stated that P C D D / F emissions increased by 14 % when HC1 was doubled in the range of 100 to 1000 mg/m 3. Despite these findings, but in agreement with Stelzner and Greiner (1989), Figure 4 reveals no significant relation between total P C D D / F emissions and HCI concentration. However, HCI concentration in the flue gas was found to have a significant inverse correlation with emissions of CI4DD, CIsDD, and C14DF. Two possible explanations may account for these results. A high HCI concentration may either make dechlorination of higher chlorinated PCDD/F less favorable or may lead to chlorination of lower chlorinated homologues. The latter was expected by De Fr6 and Rymen (1989), but not found in their experiments. Production of higher chlorinated PCDD through chlorine substitution reaction of 1,2,3,4-C14DD with HCI has been proven by Eiceman and Rghei (1982). The chlorination was independent of HCI concentration between 1 and 50 % by volume (equivalent to 16-800 g/m 3 under standard conditions), but these HC1 concentrations were much higher than in our experiments. Either the less favorable dechlorination of higher chlorinated homologues or the chlorination of lower chlorinated homologues with increasing HC1 content yields smaller amounts of the lower chlorinated species. This was statistically significant for C14DD, CIsDD, and C14DF. On the other hand, an increase of higher chlorinated homologues was not significant. For PCDD, this may be due to the higher concentrations of higher chlorinated compared to lower chlorinated homologues. Therefore, the higher chlorinated homologues produced by chlorination had a smaller percentage of those originally present and thus did not have a strong influence on total levels of highly chlorinated PCDD.

1495

TABLE 3.

Pearson correlation coefficients for data set No. 1 (n = 9). The range of values is given in parentheses. §, *, **, *** indicate significance at t~ = 0.06, 0.05, 0.01, and 0.001, respectively. Values not marked with an asterisk are insignificant. T = temperature. CO (444-3261 mg/m3)

02 (2.7-8.2%)

C (0.31-1.05g/m3)

HC1 (not measured)

TBed (717-928°C)

TFreeboard (871-994°C)

PCDD/F

0.705 *

-0.649 §

Furans to dioxins ratio

0.239

-0.190

0.451

0.004

0.066

-0.040

-0.119

-0.086

CI4DD

0.807 **

-0.802 **

0.829 **

-0.100

0.317

CIsDD

0.637

-0.616

0.872 **

-0.038

0.353

C16DD

0.392

-0.522

0.488

-0.011

0.330

Cl7DD

0.564

-0.369

0.328

0.229

-0.118

CIsDD

0.150

0.517

-0.254

-0.162

CI4DF

0.716 *

-0.895 **

0.762 *

-0.076

0.424

CIsDF

0.748 *

-0.875 **

0.708 *

-0.032

0.425

CI6DF

0.585

-0.444

0.173

0.323

-0.211

CITDF CI8DF

0.237 0.219

-0.015 -0.450

0.020 -0.022

-0.195 -0.372

-0.222 0.279

0.622

0.247

-0.163

-0.573

-0.262 0.039

-0.470 0.373

CO

0.096

-0.709 *

O2 C Bed temperature

TABLE 4.

0.037

Pearson correlation coefficients and Spearman correlation coefficients (italicized) for data set No. 2 (n = 44 with the exception of HCI concentration for which n = 40). Plots are shown in Figures 1 to 6. log CO (2-212 mg/m3)

02 (6-11%)

C (0.01-0.87g/m3)

HC1 (10--1129mg/m3)

TBed (798-841 °C)

TFreeboar d (886-975°C)

log P C D D / F

-0.100

0.495 ***

0.222

--0.010

0.371 *

-0.299 *

Furans to dioxins ratio

-0.188

0.266

0.101

-0.368 *

0.477 **

-0.362 *

log C14DD

-0.024

-0.019

-0.222

- 0 . 6 1 2 ***

log C15DD log CI6DD

-0.084

0.148

-0.059

-0.400 *

0.258

O. 1 1 7

log CITDD log CIsDD log C14DF

-0.038 0.031 -0.173

0.278 0.265 0.317 *

0.342 *

0. 084

-0. 4 7 0 **

log C15DF

-0.055

0.281

0.141

-0.199

0.179

-0.165

log C16DF

-0.009

0.297 §

O. 192

-0.081

0.158

-0.205

log C17DF log CI8DF

-0.052 -0.087

0.314 * 0.395 **

0.243

0.023 0.148

0.231 0.273

-0.199

0.426 **

-0.426 **

--0.164

log CO 02 C

HCI Bed temperature

0.044

O.2 4 0

0.529 ***

-0.192

0.200

0.053

0.041

-0.166

-0.008

-0. 032

0.023

0.079

-0.237

O.2 1 7

0.070

-0. 079

0.202

-0.160

0.443 ** -0.086 0.364 *

-0.300 * 0.365 * 0.096 -0.131

- 0 . 3 9 2 ** 0.444 ** - 0 . 6 2 8 *** - 0 . 6 9 8 *** -0. 055 -0.223

1496

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FIGURE 1. Plot of P C D D / F versus CO concentration in

FIGURE 2. Plot of P C D D / F versus oxygen concentration

flue gas. r = -0.100 (not significant).

in flue gas. r = 0.495 ***

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FIGURE 3. Plot of P C D D / F versus C concentration in

FIGURE 4. Plot of P C D D / F versus HC1 concentration

flue gas. Spearman correlation coefficient r = 0.222 (not

from combustion of R D F ( + ) , R D F + 3 % (x), 5 % (o), 10 % (*), 15 % lime (*), R D F + PE (u), PE (a), Cellu-

significant).

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1497

In addition to correlation analysis, multiple linear regression analysis was employed to data sets No. 1 and 2 and to metal and chlorine concentrations of fly ash (see below). By doing so, the variance explained (r 2) was only improved to a negligible degree since in most cases the independent variables were intercorrelated. Hence, the results are not presented. Apart from incinerator operating conditions, the catalytic activity of fly ash metals for PCDD/F formation was indicated by significant correlation coefficients (Table 5). However, PCDD/F did not depend on the chlorine concentration of fly ash, as could be found by Vogg et al. (1989).

TABLE 5.

Correlation coefficients for PCDD/F versus metal and chlorine concentrations of fly ash (n = 12). The range for P C D D / F concentration was 5.1-1093/~g/kg, the range for metal and chlorine concentrations is given in parentheses.

Variable Range (mg/kg)

log Hg log Pb log Cr (0.05-4.6) (261-4033) (97-557)

log Cd (2-166)

log Zn log Ni (854-7218) (93-182)

Cu log CI (467-3866) (1200-54300)

log PCDD/F

0.807 **

0.665 *

0.647 *

0.603 *

0.682 *

0.679 *

0.635 *

0.282

Influence of Fuel Type on PCDD/F Emissions The lack of relationship between PCDD/F and HCI levels described above indicates that the chlorine of the fuel, from which HCI is formed, had no influence on PCDD/F emissions. Indeed, burning RDF with 0.09 g chlorine/g, wood chips with 0.002 g Cl/g, and PE with 10-4 g Cl/g led to about the same PCDD/F emissions (Table 6). Emission from combustion of cellulose fiber with the same chlorine content as the wood chips was lower than the mean values, but within the standard deviation of values for the other fuels. Adding NaCI to PE and to cellulose fiber, and adding 0.5 % PVC to cellulose fiber did not increase PCDD/F concentrations. However, addition of 3 % PVC to PE increased PCDD/F levels by a factor of 3 compared to the mean value for pure PE combustion. This statement lacks statistical significance, since the treatment was not repeated, but it is one of the few experiments where an influence of larger amounts of PVC on P C D D / F emissions was observed in waste incinerators. Conversely, it has frequently been published that the addition of PVC to municipal waste and waste paper did not increase PCDD/F emissions (Giugliano et al. 1989, Jager and Wilken 1989, Martin and Zahlten 1989, Sierig 1989, Stelzner and Greiner 1989). Nevertheless, in laboratory experiments PCDD/F were formed during burning of PVC (Theisen et al. 1989) and PVC-cable coatings (Christmann et al. 1989). PVC is also suspected to be responsible for PCDD/F emissions from metal reclamation plants. Our results from combustion of wood chips do not agree with those given by Aittola et al. (1989, 1990), who could not detect any P C D D / F when wood chips alone were burned in a gasifier and a grate fired power plant. Additionally, data by Jager and Wilken (1989) and Sierig (1989), showing reduction of PCDD/F due to addition of lime, could not be confirmed. Values A, B and C (Table 6) were excluded from interpreting the effect of fuel type, because, according to the v-test (Dyck 1980), A and B were identified as extreme values not belonging to the parent population (0t = 0.01). The v-test was not applicable to experiments burning RDF + 10 % lime since there were only two observations. Nevertheless, C was also believed to be an extreme value due its similarity to A and B and therefore excluded from discussion. However, A, B and C demonstrate the high variability sometimes encountered in technical scale combustion experiments and stress the need for repetitions rather than single experiments to obtain reliable results.

1498

TABLE 6.

Influence of fuel type on P C D D / F emissions.

Fuel type

PCDD/F (/Jg/m 3)

CO ( m g / m 3)

RDF (n=17)

3.2 - 1.5

44 _+ 46

RDF + 3 % lime ( n = 2 )

8.9

11-16

RDF+5%lime(n=9) RDF + 10 % lime

2.5 + 1.7 3.03

50_+ 50 84

RDF + 15 % lime

4.25

retarded plastic R D F / P E 1:1

02 (%) 8.6 _+ 1.5

C (g/m 3)

HC1 ( m g / m 3)

Bed Freeboard temperature (°C)

0.30 _+ 0.09

520 _+ 310

820 -+ 10

920 _+ 20

0.28-0.20

190-270

820-837

921-895

9.1 + 1.3 7.9

0.30_+ 0.07 0.28

500_+ 150 255

810-+ 10 815

920_+ 30 955

2

9.9

0.71

100

827

888

2.22 4.45

96 30

9.3 6.9

0.40 0.11

295

818 826

910 953

PE ( n = 3 )

2.7 + 1.4

21 _+ 12

8.5 + 0.6

0.022 _+ 0.007

817 -+ 6

950 _+ 20

PE + 2 % NaCI

0.75

5

7.2

0.010

257

835

975

PE + 3 % PVC Cellulose fiber (C. f.)

8.01 1.71

55 15

9.0 8.9

0.067 0.35

120 140

821 812

958 901

C. f. + 2 % NaCl

1.75

15

9.3

0.40

50

803

890

1.79

14

8.9

0.17

50

801

897

2.81

7

10.5

0.050

13

824

969

10.5

RDF + 2 % flame

10-74

C.f. + 2 % N a C 1 + 0.5 % PVC Wood chips

The following measurements yielded extreme values of P C D D / F and were excluded from interpretation (see text). A) RDF

24.32

14

10.2

0.87

827

807

887

B) RDF + 5 % lime

31.97

12

10.5

0.53

280

841

900

C) RDF + 10 % lime

24.01

18

9.4

0.38

264

835

886

Influence of Water Content of RDF on PCDD/F Emissions Five experiments using RDF with 0.05 g water/g were compared to two experiments, in which RDF with water contents of 0.20 and 0.25 g/g was employed (Table 7). These experiments were performed under similar incineration conditions and revealed no effect of the investigated RDF water contents on total P C D D / F concentrations in the flue gas. To allow an analysis of variance, the two experiments with water contents of 0.20 and 0.25 g/g were combined into one group, whereas the five experiments with 0.05 g water/g formed a second group. As a result, total P C D D / F concentrations were not significantly different for both groups. Vogg et al. (1989) found increasing P C D D / F concentrations when the water content of RDF was increased from 0.24 to 0.39 g/g. In conclusion, these data and those reported above possibly indicate that total P C D D / F concentrations are only affected above a certain threshold value of water content of fuel. This threshold value seems to be in the range of 0.20 to 0.25 g water/g RDF. However, this conclusion only applies to total P C D D / F concentrations. For a high water content (0.20 to 0.25 g/g) compared to a low one (0.05 g/g), the furans to dioxins ratio was significantly lower, and the concentrations of PCDD, CIsDD, C15DD, C14DD, and C15DF were significantly higher. Therefore, a high moisture content of RDF favored the formation of dioxins and of lower chlorinated homologues. The latter has also been documented by Boscak (1990). In laboratory experiments (Stieglitz et al. 1990), the presence of water vapor had the same effects as the water content of RDF in our experiments. Compared to a dry atmosphere, water vapor favored the synthesis of dioxins and the dechlorination of higher chlorinated congeners. Since we did not perform isomer specific measurements, it can not be concluded whether or not the shift to lower chlorinated P C D D / F was also accompanied by a significant increase in toxicity equivalents.

1499

TABLE 7.

P C D D / F concentrations in flue gas and operating parameters at low (0.05 g/g) and high water content of RDF (0.20 and 0.25 g/g). * and ** indicate that the difference between low and high water content is statistically significant (a = 0.05 and 0.01, respectively). Water content of RDF (g/g) 0.05 (n = 5) 0.20 P C D D / F (/~g/m3) Furans to dioxins ratio *

CI4DD (#g/m 3) ** C15DD (/~g/m3) * CI6DD (/;g/m 3) CI7DD (/~g/m3) CIsDD (/zg/m3) * PCDD (/~g/m3) * C14DF (#g/m 3) C15DF (#g/m 3) ** CI6DF (#g/m 3) CI7DF (#g/m 3) CIsDF (#g/m 3) PCDF (/~g/m3)

02 (%) CO (mg/m 3) C (g/m3) * Bed temperature (°C) Freeboard temperature (*C)

36 7.2 0.029 0.16 1.0 1.9 1.2 4.3

_+ 10 _+ 1.7 +-+ -+ + _+ -+

0.005 0.06 0.3 0.6 0.3 0.7

1.4 1.9 11.8 13.0 3.3 31

_+ 0.8 -+ 0.4 _+ 5.7 + 5.1 -+ 1.1 _+ 10

6.8 980 0.49 820 930

-+ 1.0 _+ 740 _ 0.14 + 80 -+ 53

33.45 2.8 0.11 0.48 3.16 3.43 1.65 8.83

0.25 33.06 4.6 0.083 0.31 1.35 2.27 1.90 5.91

3.35 3.45 7.79 7.37 2.66 24.62

2.39 5.29 10.07 7.93 27.15

5.86 1553 0.78 796 951

6.7 1748 0.85 820 923

1.47

ACKNOWLEDGEMENTS The financial support of the BMFT (Bundesministerium ftir Forschung und Technologie, Project No. 1450434-4) and the technical assistance of Ms. H. Spreter and Ms. E. Helld6rfer are gratefully acknowledged. We thank K. Froese for reviewing the manuscript. REFERENCES Aittola; J.-P., S. Viinikainen, and J. Roivainen (1989): The Emission of PCDD/PCDF's and Related Compounds from Co-Combustion of RDF with Peat and Wood Chips. Chemosphere 19, 353-359. Aittola, J.-P., M. Wihersaari, and J. Kartano (1990): The Emission of PCDD/PCDF's, Related Compounds and Heavy Metals from Combustion of MSW with Wood Chips in a Gasifier. In: O. Hutzlnger and H. Fiedler (ed.): Organohalogen Compounds3, 21-26. Boscak, V. (1990): Use of Incinerator Exit Gas Temperature and CO-Content as Surrogate for PCDD/F Emissions. In: O. Hutzinger and H. Fiedler (ed.): OrganohalogenCompounds 3, 39-42. Christmann, W., D. Kasiske, K. D. Kl6ppel, H. Partscht, and W. Rotard (1989): Combustion of Polyvinylchloride An Important Source for the Formation of PCDD/PCDF. Chemosphere 19, 387-392. De Fr6, R. and T. Rymen (1989): PCDD and PCDF Formation from Hydrocarbon Combustion in the Presence of Hydrogen Chloride. Chemosphere 19, 331-336.

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