Pilot-scale studies on the effect of bromine addition on the emissions of chlorinated organic combustion by-products

Waste Management 22 (2002) 381–389 www.elsevier.com/locate/wasman

Pilot-scale studies on the effect of bromine addition on the emissions of chlorinated organic combustion by-products P.M. Lemieux*, E.S. Stewart, J.V. Ryan US Environmental Protection Agency, Office of Research and Development, National Risk Management Research Laboratory, Research Triangle Park, NC 27711, USA

Abstract The addition of brominated organic compounds to the feed of a pilot-scale incinerator burning chlorinated waste has been found previously, under some circumstances, to enhance emissions of volatile and semivolatile organic chlorinated products of incomplete combustion (PICs) including polychlorinated dibenzo-p-dioxins and polychlorinated dibenzofurans (PCDDs/Fs). This phenomenon appears to be sensitive to temperature and combustion conditions. This paper reports on a study to evaluate the emissions of organic combustion by-products while varying amounts of bromine (Br) and chlorine (Cl) are being fed into a pilot-scale incinerator burning surrogate waste materials. The surrogate waste was fed at a constant molar halogen input rate, with varying Br/Cl molar ratios. In these tests, an approximately 30% decrease in the total PCDD/F concentrations due to the addition of Br was observed. This decrease appears to be a decrease only in the chlorinated dioxin and furan species; other halogenated dioxins and furans were formed instead. PCDD/F homologue distribution shifted towards the higher chlorinated species. Perhalogenated or nearly perhalogenated mixed bromo-chloro furans were also observed in quantities that could potentially account for the observed decrease in PCDDs/Fs. This research illustrates the need for careful trial burn planning if Br will be present in the facility’s feedstock during normal operation. Published by Elsevier Science Ltd.

1. Introduction Concern from both the public and the US Environmental Protection Agency (EPA) has been directed at the formation and control of PCDDs/Fs from combustion systems. These classes of chemical compounds are believed to be carcinogenic and have been implicated in other potential health effects, such as endocrine disruption (Okey et al., 1994). Br, although not nearly as ubiquitous as Cl in combustion systems, undergoes a similar set of reactions as Cl, and has the potential to form a similar class of compounds, polybrominated dibenzo-pdioxins and dibenzofurans (PBDDs/Fs). There are an additional 5020 congeners of the mixed bromo-chloro dioxins and furans; PXDDs/Fs (X=Cl, Br). The toxicity of PBDDs/Fs is comparable to that of their chlorinated analogs (Nagao et al., 1990; Mennear and Lee, 1994). However, there are only a limited amount of

* Corresponding author. Tel.: +1-919-541-0962; fax: +1-919-5410554. E-mail address: [email protected] (P.M. Lemieux). 0956-053X/02/$ - see front matter Published by Elsevier Science Ltd. PII: S0956-053X(02)00020-X

data on emissions of brominated compounds from incinerators, and most of the data in the literature were generated in laboratory experiments (Wellington Laboratories, 1984). As more and more discarded consumer electronics equipment, which frequently contains brominated flame retardants, enters the waste stream, understanding the impact of the presence of Br on combustion emissions becomes important. The combustion chemistry of brominated compounds has generally not been the subject of extensive systematic investigation. During their combustion, simple brominated hydrocarbons, such as bromoform (CHBr3), can undergo complex reactions that result in the formation of brominated alkenes, aromatics, and other PBDD/F precursors. It is already known that CHBr3’s chlorinated analog, chloroform (CHCl3), forms chlorinated benzenes through a mechanism of three-center elimination of hydrogen chloride (HCl) to produce CCl2 radicals which can then enter into a number of molecular growth schemes (Taylor et al., 1991). Other chlorinated radicals such as C2Cl3 and chlorinated alkynes such as C2Cl2 may be very important as well. Proper destruction of chlorinated compounds is largely dependent on a

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sufficient source of hydrogen (H) available to participate in the key process shown in Eq. (1). H
þ O2 <¼> OH þ O


ð1Þ

Without sufficient amounts of H, Cl will be available to attack organic molecules (Tsang, 1990). Carbonchlorine bond formation processes are expected to be important in systems where the ratios between H and Cl are low. Since brominated flame retardants work by scavenging the H radicals (Blum and Ames, 1977) from organic species (R) as shown in Eq. (2). RBr þ H
<¼> HBr þ R


ð2Þ

The resulting pool of hydroxyl (OH) radicals is reduced in a system containing Br. In addition to these radical scavenging reactions that Br undergoes, a host of bromo-organic combustion reactions occur that are analogous to the chloro-organic reactions. The US EPA has performed pilot-scale investigations into the interaction between Br and Cl and its influence on emissions of volatile organic PICs and PCDDs/Fs (Lemieux et al., 1996; Ryan et al., 1996; Lemieux and Ryan, 1998a,b). Br has been shown to influence emissions of chlorinated organics; however, the phenomenon appears to be sensitive to temperature and local stoichiometry (e.g. mixing). The purpose of the current study is to further investigate the effects of Br on emissions of PCDDs/Fs and other organic PICs.

2. Experimental Experiments were performed on EPA’s Rotary Kiln Incinerator Simulator (RKIS), a 73-kW (250,000-Btu/h) pilot-scale simulator with a 73-kW secondary combustion chamber (SCC). The RKIS is shown in Fig. 1. After exiting the SCC, the flue gases pass through a long horizontal duct, where organic species are sampled. Gases then pass through a flue gas cleaning system (FGCS) consisting of an afterburner, spray quench, baghouse, and wet scrubber. The long horizontal duct provides several seconds of gasphase residence time during which the PCDD/F formation reactions can occur. During these experiments the temperature profile in the duct was maintained at a constant level. Note that the Duct 7 thermocouple (TC) shown in Fig. 1 is not on the same run of ducting as Ducts 5 and 6 TCs, but on another vertical run leading up to the FGCS manifold. The RKIS was fired with natural gas in the primary burner, and a mixture of natural gas and surrogate waste in the SCC. Liquid surrogate waste mixtures of methylene chloride (CH2Cl2, MeCl2) and methylene bromide (CH2Br2, MeBr2) were atomized directly into the afterburner (along with the burner’s natural gas fuel) as shown in Fig. 1. Air flowing at a rate of 0.42 scm/h (standard cubic meters per hour) (15 scfh (standard cubic feet per hour)) was used to atomize the liquid. Reactive surfaces in the gas phase to allow for the heterogeneous reactions that form PCDDs/Fs were provided by injecting 1 g/min of flyash collected from a coal-fired utility boiler into the transition section

Fig. 1. Rotary kiln incinerator simulator.

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between the kiln and the SCC using a K-Tron gravimetric screw feeder and an air eductor. This provided gas-phase particulate matter (PM) loadings of approximately 35 mg/dscm, which is near the upper PM loading allowable for facilities operating under a Resource Conservation and Recovery Act (RCRA) permit. The flyash was analyzed for catalytic metals and other key components, and was found to have the following concentrations, all in mg/g: copper (Cu): 169; aluminum (Al): 92,800; silicon (Si): 256,000; and iron (Fe): 41,500. Continuous emission monitors (CEMs) provided simultaneous measurement of oxygen (O2), carbon dioxide (CO2), carbon monoxide (CO), and nitric oxide (NO) at two locations. A Perkin–Elmer MCS100 provided continuous measurement of water (H2O) and hydrogen chloride (HCl) in the duct, as well as providing a backup CO2 measurement. Volatile organic PIC emissions were measured using an on-line gas chromatograph system (OLGC) (Ryan et al., 1998) that contains a heated sample delivery unit, a purge-and-trap sample concentrating device, and the GC analytical unit. The sample concentrating device was a Tekmar LSC-2000 thermal desorption unit that had been modified to accommodate the collection of combustion samples directly. The GC analytical unit was a HP 5890 series II GC equipped with both a flame ionization detector (FID) and an electron capture detector (ECD). The effluent of the column is split (ratio 9:1, respectively) to deliver the sample to both the FID and ECD simultaneously. A computer data station processed and integrated detector responses as well as controlled system operations. A total of 25 individual volatile organic PICs can be quantified at concentration levels at or near 1 ppbv. The ECD was not operational during these tests (due to a broken splitter) so all OLGC data reported in this paper are based only on FID measurements. Separate volatile organic PIC emissions that were collected using the volatile organic sampling train (VOST) (EPA Test Method 0030, 1986) and Tedlar bags (EPA Test Method 0040, 1994) concurred with the OLGC samples. These samples were analyzed by GC/ low-resolution mass spectrometry (LRMS) to confirm OLGC target analytes, as well as tentatively identify additional unknown PICs present in the emissions. Semivolatile and nonvolatile organics, including PXDD/Fs, were collected using the EPA Modified Method 5 (MM5) train as described in EPA Test Method 23, (1991). Each sample train was spiked with several presample surrogate standards for quality control purposes. The collected samples were sequentially Soxhlet extracted with methylene chloride and then toluene. The toluene sample extracts were analyzed by GC/LRMS for PCDDs/Fs and PXDDs/Fs as described by EPA Method 23 with minor modifications (e.g. to include the mono-tri isomers). Analyses included the 17 2,3,7,8-

383

substituted isomers for International Toxic Equivalency (I-TEQ) determination as well as mono-octa CDD/F totals. Samples were also screened for PXDDs/Fs by analyzing the toluene extracts by LRMS in the total ion mode. As analytical standards for mixed bromochloro PXDDs/Fs are virtually nonexistent, tentative identifications were based on ion extractions of characteristic PXDD/F ion patterns. PXDDs/Fs were quantified based on response factors from similar PCDDs/Fs. A statistical experimental design was generated using the Br/Cl molar ratio in the feed, SCC O2 concentration, and temperature as the primary variables of interest. Total halogen molar input rate was constant over the entire test series. Changes in the SCC O2 concentration and temperature were affected by changing the flow rates of the primary burner combustion air at levels between 2000 and 4000 scfh (56.6 and 113.2 scm/h), primary burner fuel at levels between 150 and 200 scfh (4.2 and 5.7 scm/h), and the afterburner fuel between 150 and 180 scfh (4.2 and 5.1 scm/h). The afterburner combustion air flow rate was determined so that the burner stoichiometric ratio of the afterburner would be 1.0 prior to introduction of any dopant. The baseline test conditions were defined as: main air4000 scfh (113.2 scm/h); main gas200 scfh (5.7 scm/h); afterburner air1500 scfh (42.5 scm/h); and afterburner gas150 scfh (4.2 scm/h). The Br/Cl molar ratio was varied between 0 (pure MeCl2 feed) and 0.1 (91.2 vol.% MeCl2; 9.8 vol.% MeBr2) for most tests. One additional test each was performed with Br/Cl=0.2 and 0.5. The liquid feed rate was 25 ml/min for the tests with Br/Cl=0, and determined in such a way for other conditions as to match the halogen input rate of 25 ml/min of MeCl2. Table 1 lists the designated test conditions. For each run, after the RKIS was equilibrated at the desired operating temperature and stack O2 concentration, the flyash feed was initiated at 1 g/min, the liquid feed was initiated at a rate of 25 ml/min, and the system was allowed to operate for 5–10 min, until the CEM readings in the duct stabilized. At that point, the samples for volatile organic compounds (VOCs), semivolatile organic compounds (SVOCs), and PCDDs/Fs were acquired.

3. Results The continuously measured data from the CEMs and the thermocouples are shown in Table 2. For the most part, the runs showed good agreement with each other, particularly with temperatures, although there were slight variations. HCl concentrations showed some variations from run to run, and the SCC Exit temperature for the 26 February 2001 run was slightly lower than on other days. The RKIS has a large amount of thermal inertia, and it requires 2–3 days to achieve thermal equilibrium. Sometimes temporary burner outages occurred

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Table 1 Table of RKIS test conditions Condition

Kiln air (scm/h)

Kiln gas (scm/h)

SCC air (scm/h)

SCC gas (scm/h)

0 (Baseline) 1 2 3 4 5 6 7 8

113 57 57 113 57 57 113 113 113

5.7 4.2 4.2 4.2 5.7 5.7 5.7 4.2 5.7

42 42 51 42 42 51 51 51 54

4.2 4.2 5.1 4.2 4.2 5.1 5.1 5.1 4.2

Table 2 Continuously measured data Date

6/9/00 7/13/00 7/14/00 7/27/00 8/3/00 8/4/00 8/8/00 8/9/00 8/16/00 8/18/00 2/26/01 2/28/01 3/7/01 3/14/01 3/16/01 3/21/01 4/11/01 4/13/01 4/17/01 4/19/01 5/2/01 5/7/01 5/9/01 a

Test Br/Cl Duct Duct Duct Duct Duct SCC SCC Kiln SCC SCC SCC Duct 1 Duct 3 Duct 4 Duct 5 Duct 6 Duct 7 ( C) ( C) ( C) ( C) ( C) condition Molar O2 CO2 CO H2O HCI O2 CO exit Mix Mid exit ( C) ratio (%) (%) (ppm) (%) (ppm) (%) (ppm) ( C) ( C) ( C) ( C) 0 4 0 1 2 3 7 5 6 0 0 0 4 3 5 1 0 2 7 6 0 8 0

0 0 0 0 0 0 0 0 0 0 0.1 0.1 0.1 0.1 0.1 0.1 0.5 0.1 0.2 0.1 0.1 0.1 0

13.2 10.3 13.1 11.5 12.1 14.4 13.8 10.2 12.9 12.8 15.0 na 11.5 14.6 10.2 11.8 13.5 12.2 14.1 13.6 13.4 14.0 14.2

4.9 6.7 5.0 6.0 5.5 4.2 4.5 6.7 5.1 5.2 3.9 4.4 6.1 4.1 6.7 5.7 4.8 5.6 4.3 4.9 4.9 4.6 4.4

15 18 18 14 13 62 24 14 14 14 38 na 19 158 21 33 24 23 59 14 24 22 22

10.8 12.6 10.3 11.8 11.3 9.0 9.4 12.7 10.5 10.4 2.9 9.1 10.8 7.6 12.1 10.6 9.8 11.1 7.6 9.0 9.7 9.3 9.8

3837 4744 2580 4570 3977 2575 2950 2924 3049 3106 2075 2039 1803 1749 2749 2752 1442 2617 1463 2006 2097 2156 2886

11.7 6.4 10.8 11.0 11.1 13.5 12.4 8.8 11.1 11.1 na 11.8 9.4 12.7 8.3 10.0 11.7 10.2 12.2 11.5 11.6 11.7 11.8

5.4 7.5 5.8 5.9 5.8 4.4 4.9 7.0 5.8 5.7 na 5.4 6.6 4.6 7.5 6.4 5.6 6.4 5.0 5.7 5.5 5.5 5.5

781 893 791 827 741 648 661 914 787 807 758 768 897 619 906 808 776 778 659 763 775 807 785

440 823 753 805 797 677 716 867 780 789 762 739 811 653 859 778 761 781 726 782 753 765 747

784 837 787 823 802 725 757 874 822 831 762 766 808 682 837 781 784 804 761 815 782 803 800

naa 686 645 674 650 588 602 717 678 699 532 619 659 535 669 623 643 654 619 672 638 665 659

574 573 572 572 568 539 554 602 599 604 558 560 562 508 581 547 581 574 567 608 579 595 595

378 335 360 348 357 356 368 368 392 391 362 362 340 337 357 338 379 359 377 400 380 388 389

239 336 361 344 355 354 365 364 388 387 358 359 336 334 353 334 377 356 374 398 377 na na

322 282 310 291 301 305 315 308 335 333 308 309 283 289 299 284 326 304 325 346 327 336 336

301 258 289 268 278 284 300 290 318 315 292 292 265 275 280 267 308 284 308 326 309 315 316

250 218 246 238 250 256 266 253 280 274 246 246 221 233 237 225 260 242 263 277 263 269 268

na–not available.

due to unrelated testing elsewhere in the laboratory, and the RKIS cooled down, which resulted in slightly lower gas temperatures on some days. In addition, the manifold pressure of the gases entering the FGCS has a large influence on the rate of air leakage into the RKIS, which can influence temperatures and gas-phase species concentrations. This manifold pressure sometimes fluctuated to the point of forcing the RKIS operators to manually change the draft damper position in order to maintain a static pressure in the main rotary kiln chamber of 0.25 kPa (0.05 in. w.c. (inches water column)) over the course of a day. On 26 February 2001, neither the CEMs measuring the SCC exit conditions nor the MCS100 analyzer was operational. On 28 February 2001, the CEMs measuring the duct conditions were not operational, so the duct CO2 data were reported using the measurements from the MCS100 analyzer.

To calculate emissions of organic pollutants, all concentrations were corrected to 12% CO2. The authors believe that, since the measured O2 concentrations in the duct were fairly high, slight errors in the measured O2 concentration would create larger errors in the corrected pollutant concentrations, so CO2 was used to correct for dilution. Fig. 2 shows a representative sample of the volatile organic PIC data taken at the baseline conditions with the OLGC. Note that some brominated target analytes (bromobenzene in particular) were present even on runs where no Br was being fed. Combustion blanks (samples taken when no organic feed was present and only natural gas was being fired) showed low (10 mg/m3) concentrations of chloromethane; also observed in the blanks were low (10 mg/ m3) concentrations of bromobenzene, which increased

P.M. Lemieux et al. / Waste Management 22 (2002) 381–389

385

Fig. 3. Total PCDD/F vs Br/Cl ratio (corrected to 12% CO2).

Fig. 2. Volatile organic PICs (concentrations corrected to 12% CO2). Note: multiple bars reflect concentrations of duplicate runs at the same operating conditions.

when the MeCl2 feed was initiated, probably due to reactions of wall deposits with the HCl, which was at approximately 2000 ppm while feeding MeCl2. This observation led the authors to believe that Br salts from previous tests have deposited on refractory parts of the interior of the RKIS facility, making it difficult to get a ‘‘clean’’ combustion blank, in spite of several weeks of operation at high temperature prior to initiation of this test series. Bromobenzene increased to very high concentrations when MeBr2 was in the feed. When the brominated and chlorinated organics were being fed, significant amounts of bromomethane were measured, which were not present when only chlorinated organics were being fed. Emissions of chlorobenzene dropped significantly with the addition of the MeBr2 in the feed, although dichlorobenzene emissions did not change significantly. Benzene emissions increased somewhat during the runs where MeBr2 was being fed. Table 3 lists the PCDD/F data by homologue group, as total PCDDs, total PCDFs, total PCDD/F, the contribution of PCDDs/Fs to the International Toxic Equivalency (I-TEQ) values, and the I-TEQ values. The ratio between Total PCDD/F and I-TEQ was approximately 100. This differs from the ratio found in municipal waste combustors (approximately 50) and cement kilns burning hazardous waste (about 200) (Rigo et al., 1996). Plotting the total PCDD/F emissions of each set of RKIS conditions at a given Br/Cl ratio yields Fig. 3 (note that conditions 7 and 8 were not included in Fig. 3 because runs at both Br/Cl ratios did not exist for those conditions). For the purposes of Fig. 3, results were averaged where duplicate or triplicate measurements

were made, with the exception of the Br/Cl=0.1 baseline run on 26 February 2001. The 26 February 2001 run showed considerably higher emissions, both in terms of total PCDDs/Fs and in terms of the I-TEQ, than the runs with no Br addition; however, the 28 February 2001 run, which was nominally a repeat of the 26 February 2001 run, showed similar emissions to the runs without Br addition. It is possible that some effect due to residues remaining behind in the RKIS ductwork was observed on the 26 February 2001 run. Due to concerns about contamination of the facility with Br, all of the runs with Br/Cl=0 were run first, with the Br/ Cl=0.1 runs being performed later. An unrelated test series was performed on the RKIS during the JanuaryFebruary 2001 time frame (between the Br/Cl=0 and Br/Cl=0.1 test series), which could have produced reactive deposits on the ductwork. There was a consistent reduction in the emissions of PCDDs/Fs when Br was present in the system. The difference between the results at different Br/Cl ratios varied based on the combustion conditions in the RKIS. A more detailed statistical analysis is planned for the data set in order to understand this observation more fully. This suggests that, for these experimental conditions and dopant injection method, the presence of Br resulted in a decrease in measured chlorinated dioxins and furans. One possible explanation for this is that there were fewer dioxins and furans formed (both chlorinated and otherwise). Another possible explanation is that other PXDDs/Fs were formed that were not fully chlorinated. Both of these possibilities will be discussed. First, the homologue groups and isomer patterns were examined to see if any changes occurred due to the addition of Br. A plot of the mass fraction of each homologue group versus the total mass of PCDDs/Fs is shown in Fig. 4 for the baseline tests. The homologue pattern showed a distribution strongly favoring the

386

Table 3 PCDD/F data (ng/dscm at 12% CO2) MCDD DCDD TrCDD TeCDD PCDD HxCDD HpCDD OCDD MCDF DCDF TrCDF TeCDF PCDF HxCDF HpCDF OCDF PCDD PCDF Total PCDD PCDF PCDD+ PCDD+ I-TEQ I-TEQ PCDF PCDF I-TEQ

6/9/00 7/13/00 7/14/00 7/27/00 8/3/00 8/4/00 8/8/00 8/9/00 8/16/00 8/18/00 2/26/01 2/28/01 3/7/01 3/14/01 3/16/01 3/21/01 4/11/01 4/13/01 4/17/01 4/19/01 5/2/01 5/7/01 5/9/01

NDa ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND

a

ND ND ND ND ND ND ND ND ND ND 9.6 ND ND ND ND ND ND ND ND ND ND ND ND

ND, not detected.

ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND

ND ND 1.7 3.3 ND ND 5.0 1.5 ND ND 18.2 ND ND ND ND ND ND ND 3.1 ND ND ND ND

0.5 ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND

1.7 ND ND 1.2 1.4 2.7 1.8 ND ND ND 8.6 ND ND ND ND ND ND 2.4 ND ND ND ND ND

3.8 7.7 4.0 4.6 4.4 5.0 3.4 2.4 5.2 10.0 21.3 7.0 4.8 ND 2.4 3.3 ND 3.6 1.8 3.9 4.6 ND 3.6

6.4 14.6 4.8 6.6 4.1 6.4 3.8 3.3 6.4 8.2 36.6 9.5 7.8 ND 4.1 6.2 2.8 5.2 1.7 3.8 3.8 4.6 6.2

ND ND 2.8 ND ND ND ND ND ND ND ND ND ND ND ND ND 1.8 1.0 ND ND ND ND ND

ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND

ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND ND

16.9 19.6 10.7 10.0 9.9 10.0 6.9 9.7 5.9 ND ND ND ND ND ND ND ND ND ND 12.4 4.5 4.2 15.2

8.0 3.8 11.0 11.6 ND ND 11.2 7.8 12.3 16.0 31.7 ND ND ND 4.6 ND ND ND 3.8 45.4 5.2 ND 24.1

28.2 57.5 30.5 33.4 26.2 25.3 24.4 19.9 22.8 35.7 98.7 43.7 30.4 13.3 18.3 18.6 7.6 26.5 15.1 67.1 23.3 15.5 34.4

72.8 125.8 56.9 78.7 49.3 82.9 38.5 33.1 56.4 66.9 228.2 83.1 58.6 24.9 33.3 35.0 10.4 32.3 16.7 47.1 21.1 17.8 44.4

137.1 176.9 72.6 104.3 54.3 118.0 52.0 39.1 94.4 95.3 266.7 86.7 52.5 17.0 29.5 29.7 8.5 21.3 6.8 13.7 8.7 7.0 42.0

12.4 22.2 10.5 15.7 9.8 14.1 13.9 7.2 11.6 18.2 94.3 16.5 12.6 ND 6.5 9.5 2.8 11.3 6.6 7.7 8.4 4.6 9.9

263.2 383.5 184.6 238.0 139.8 236.2 132.9 105.9 195.6 219.7 625.2 213.6 141.5 55.3 85.7 83.3 28.3 81.1 42.3 185.6 62.8 44.4 160.2

275.6 405.8 195.1 253.7 149.6 250.3 146.8 113.1 207.2 237.9 719.5 230.1 154.2 55.3 92.2 92.8 31.1 92.3 49.0 193.3 71.2 49.0 170.0

0.062 0.059 0.029 0.035 0.034 0.040 0.025 0.017 0.040 0.072 0.155 0.049 0.036 0.000 0.018 0.024 0.003 0.025 0.011 0.024 0.027 0.005 0.028

1.85 2.61 1.87 2.15 1.20 1.64 1.48 1.30 1.93 2.69 6.75 1.90 1.49 0.58 1.12 0.91 0.32 1.21 0.52 3.25 0.87 0.69 2.29

1.91 2.67 1.89 2.19 1.24 1.68 1.51 1.32 1.97 2.77 6.90 1.95 1.53 0.58 1.13 0.93 0.32 1.23 0.53 3.27 0.90 0.69 2.32

P.M. Lemieux et al. / Waste Management 22 (2002) 381–389

Date

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387

Fig. 4. Homologue distribution vs. Br/Cl ratio. Note: multiple bars reflect concentrations of duplicate runs at the same operating conditions.

furans over the dioxins, with the distribution favoring the higher chlorinated species. There is an apparent shift farther upward in the relative degree of chlorination as the Br is added. In particular, the amount of penta- and lower-chlorinated furans is much lower with the added Br, and the relative amount of HpCDD and OCDD is somewhat higher with the additional Br. Fig. 5 shows the relative distribution of the toxic PCDD/F isomers that are used to calculate I-TEQ. The distributions look very similar, with the singular exception of OCDD, which appears to be marginally higher with Br/Cl=0.1. To investigate the hypothesis that other PXDDs/Fs were formed that were not fully chlorinated, analyses were performed to look for the fully brominated PBDDs/Fs and the mixed bromo-chloro PXDDs/Fs. No PBDDs/Fs were detected in the samples; however, this is not surprising due to limitations of the GC/MS equipment. Due to some aspect of the experimental conditions, the flyash catalyst, or the feed that was used, the purely chlorinated PCDDs/Fs were shifted towards the higher chlorinated congeners. It would be consistent to assume that the lower-substituted brominated species would be present in low concentrations, possibly below the instrument’s detection limit, and the higher brominated species would exceed the maximum molecular weight that the GC/MS can analyze. However, in addition to the PCDDs/Fs, several mixed bromo-chloro furan homologues were also detected. Due to the lack of analytical standards, it was not possible to identify what halogen substitution pattern these PXDFs possessed, but the homologue groups were determined from ion fragmentation patterns on the mass spectrometer, and quantitations were based on response factors of HpCDF (for the hepta-substituted PXDF) and OCDF (for the octa-substituted PXDF). Three PXDF homologues were identified: hexachloro-monobromodibenzofuran, pentachloro-dibromo-dibenzofuran, and

Fig. 5. Isomer pattern vs Br/Cl ratio. Note: multiple bars reflect concentrations of duplicate runs at the same operating conditions.

heptachloro-monobromo-dibenzofuran. Concentrations of the partially brominated dibenzofurans were approximately 50–35% of the concentrations of the fully chlorinated dibenzofurans. It is interesting to note that the PXDFs that were identified were perhalogenated or nearly perhalogenated, which is somewhat counterintuitive, given the steric hindrances that might be expected in substituting the larger Br atom around a fully halogenated dibenzofuran. Table 4 lists the PXDD/F concentrations that were measured as well as those of the chlorinated HpCDF and OCDF so that their relative concentrations can be seen. To explore how the relative amounts of PXDFs changed as a function of experimental conditions, the ratio between each of the species from Table 4 (including the purely chlorinated HpCDF and OCDF) and the total PCDF was plotted for the various run conditions. Fig. 6 shows the results. The PXDFs as a fraction of total PCDF tended to cluster together as a function of Br/Cl ratio. With Br/Cl=0, there were no mixed bromo-chloro furans measured at all. The runs with Br/ Cl=0.1 all showed remarkably similar trends of the concentrations of the PXDFs relative to the fully chlorinated furans. As higher Br/Cl ratios were imposed on the system, the concentrations of the mixed bromochloro furans increased to levels above the purely chlorinated species. These observations strongly support the hypothesis that the presence of Br produces other compounds of concern that are not usually looked for in stack gases. Since the quantitation of the PXDF species was based only on a relative response factor to its nearest fully chlorinated analog, it was not possible to conclusively determine whether the reduction in PCDD/ F emissions due to the presence of Br was quantitatively offset by the formation of PXDDs/Fs; however, it does

388

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Fig. 6. Ratio between PXDF homologues and total PCDF (note unlabeled lines reflect experiments performed at Br/Cl=0.1). Table 4 PXDDs/Fs (ng/dscm at 12% CO2) Date

HpCDF

HxCIMBrDF

PeCIDiBrDF

TeCITriBrDF

OCDF

HpCIMBrDF

HxCIDiBrDF

2/26/01 2/28/01 3/7/01 3/14/01 3/16/01 3/21/01 4/11/01 4/13/01 4/17/01

228.0 83.4 58.3 24.8 33.4 35.0 10.6 32.5 16.6

81.4 11.8 18.8 9.1 9.2 12.5 14.2 12.0 10.2

16.3 1.8 3.0 ND 2.1 3.8 11.8 3.4 3.8

1.5 NDa ND ND ND ND ND ND ND

266.5 87.0 52.4 17.4 29.2 30.0 8.3 21.4 6.4

63.7 7.3 9.9 4.1 5.7 7.5 7.1 6.0 2.6

5.9 ND ND ND 0.7 ND 1.2 ND ND

a

ND, not detected.

qualitatively appear that some or most of the difference in emissions of PCDDs/Fs at Br/Cl=0 and 0.1 can be accounted for by the formation of PXDDs/Fs.

4. Conclusions Experiments were performed on the pilot-scale RKIS facility to understand the impact of adding small amounts of Br on emissions of chlorinated organics. Based on these tests, the following observations were made:
The homologue distribution strongly favored the furans over the dioxins.


The lower chlorinated homologue groups were found only in trace amounts.
There was an apparent shift in the homologue distribution favoring the higher chlorinated PCDDs/ Fs even more by the addition of small amounts of Br, although it was not an obvious shift because the homologue distribution was already favoring the higher chlorinated homologues.
The isomeric distribution of the toxic PCDD/F isomers did not significantly change by the addition of Br.
The predominant non-PCDD/F organic PICs present in the flue gas shifted from chlorobenzene to bromobenzene by the addition of Br. Benzene

P.M. Lemieux et al. / Waste Management 22 (2002) 381–389

was present in moderate concentrations in both cases, although benzene emissions were considerably higher with the Br addition. Dichlorobenzenes did not significantly change with the addition of Br.
For these test conditions, using this combination of feed materials, the addition of Br resulted in a reduction of emissions of PCDDs/Fs. This reduction appears to be the result of the formation of partially brominated PXDDs/Fs.
The PXDFs that were measured appeared to be emitted at a fixed fraction of their fully chlorinated furan analogs. The ratio between the PXDF and the chlorinated analog appears to be a function solely of the Br/Cl molar ratio.
This research illustrates the need for careful trial burn planning if Br will be present in the facility’s feedstock during normal operation.

Acknowledgements The authors would like to thank Chris Winterrowd, John Foley, Bill Preston, and Dennis Tabor of ARCADIS Geraghty & Miller, Inc. for their aid in performing the sampling and analytical activities for these tests. The authors would also like to thank Marc Calvi and Chris Pressley of EPA/APPCD for maintaining the combustor and associated equipment operational throughout the tests. References Blum, A., Ames, B.N., 1977. Flame-retardant additives as possible cancer hazards. Science 195, 17–23. EPA Test Method 0030, Volatile Organic Sampling Train. In: Test Methods for Evaluating Solid Waste, Volume II, SW-846 (NTIS PB88–239223). Environmental Protection Agency, Office of Solid Waste and Emergency Response, Washington, DC, September 1986. EPA Test Method 23, Determination of Polychlorinated Dibenzo-pdioxins and Polychlorinated Dibenzofurans from Stationary Sour-

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ces. In: Code of Federal Regulations, Title 40, Part 60, Appendix A, U.S. Government Printing Office, Washington, DC, July 1991. EPA Test Method 0040, Sampling of Principal Organic Hazardous Constituents from Combustion Sources Using Tedlar Bags. In: Test Methods for Evaluating Solid Waste, Volume II, SW-846 (NTIS PB88–239223). Environmental Protection Agency, Office of Solid Waste, Washington, DC, August 1994. Lemieux, P.M., Ryan, J.V., 1998a. Enhanced formation of chlorinated PICs by the addition of bromine. Combust. Sci. and Tech. 134 (1– 6), 367–387. Lemieux, P.M., Ryan, J.V., 1998b. Enhanced formation of dioxins and furans from combustion devices by addition of trace quantities of bromine. Waste Management 18, 361–370. Lemieux, P.M., Ryan, J.V., Lutes, C., Bruce, K. Interactions Between Bromine and Chlorine in a Pilot-Scale Hazardous Waste Incinerator, in Proceedings of International Conference on Incineration and Thermal Treatment Technologies, Savannah, GA, 6–10 May, 1996. Mennear, J.H., Lee, C.C., 1994. Polybrominated dibenzo-p-dioxins and dibenzofurans: literature review and health assessment. Environmental Health Perspectives Supplements 102 (1), 265–274. Nagao, T., Neubert, D., Lo¨ser, E., 1990. Comparative studies on the induction of ethoxy resorufin o-deethylase by 2,3,7,8-TCDD and 2,3,7,8-TBrDD. Chemosphere 20, 1189–1192. Okey, A.B., Riddick, D., Harper, P., 1994. The Ah receptor: mediator of the toxicity of 2,3,7,8-TCDD and related compounds. Toxicology Letters 70, 1–22. Rigo, G.H., Chandler, A.J., Lanier, W.S., 1996. The relationship between chlorine in waste streams and dioxin emissions from Waste Combustor Stacks. ASME Research Report CRTD 36. Ryan, J.V., Lemieux, P.M., Preston, W.T., 1998. Near-real-time measurement of trace volatile organic compounds from combustion processes using an on-line gas chromatograph. Waste Management 18, 403–410. Ryan, J.V., Lemieux, P.M., Lutes, C., Tabor, D. Development of PIC target analyte list for hazardous waste incineration processes. In: Proceedings of International Conference on Incineration and Thermal Treatment Technologies, Savannah, GA, 6–10 May 1996. Taylor, P.H., Dellinger, B., Tirey, D.A., 1991. Oxidative pyrolysis of CH 2 Cl 2, CHCl 3, and CCl 4- I: incineration implications. International Journal of Chemical Kinetics 23, 1051. Tsang, W., 1990. Mechanisms for the formation and destruction of chlorinated organic products of incomplete combustion. Combust. Sci. and Tech. 74, 99–116. Wellington Laboratories, Polybromodibenzo-p-dioxins and Furans, Their Mixed Bromo/Chloro Analogues: A Review of the Literature on Sources, Methods of Analysis, Environmental Distribution, and Toxicities, Ontario Ministry of the Environment Report 96–02403, April 1984, Toronto, Ontario, Canada.