Environ. Sci. Technol. 2004, 38, 4734-4738
Polychlorinated Dibenzo-p-dioxin/ Polychlorinated Dibenzofuran Releases into the Atmosphere from the Use of Secondary Fuels in Cement Kilns during Clinker Formation E S T E B A N A B A D , K A R E L L M A R T IÄ N E Z , JOSEP CAIXACH, AND JOSEP RIVERA* Mass Spectrometry Laboratory, Department of Ecotechnologies, IIQAB-CSIC, Jordi Girona 18-26, 08034 Barcelona, Spain
The aim of this study was to evaluate the influence of using waste materials, such as tires or meat meal, as a secondary fuel during clinker production on the polychlorinated dibenzo-p-dioxin (PCDD)/polychlorinated dibenzofuran (PCDF) emission levels to the atmosphere. For this purpose, three different cement plants in Spain were chosen to conduct the project in different sampling episodes. Different materials were separately evaluated in each plant: the first plant included the addition of meat meal in the kiln, the second plant used rejected tires, and the third plant used a mixture of both. In all cases, PCDD/F emission values remained below the limit established by the European Union Directive of 0.1 ng I-TEQ/Nm3, with values ranging from 0.001 to 0.042 ng I-TEQ/Nm3. The major contribution to total TEQ in the majority of cases came from 2,3,7,8-tetrachlorodibenzofuran owing to its relatively higher levels and 2,3,4,7,8-pentachlorodibenzofuran because of its TEF of 0.5. The remaining 15 toxic congeners collectively provided only a minor contribution to TEQ. Furthermore, no marked differences were found compared with reported data obtained from Spanish cement kiln plants using conventional fuel. This fact indicates that the addition of used tires or meat meals had no effect on PCDD/ PCDF emission levels.
1. Introduction Waste management is a current topic of discussion worldwide; however, no fully satisfactory definitive solution has been proposed. Minimization, reutilization, recycling, landfill disposal, composting, and a variety of combustion processes are common practices being attempted for implementation and consolidation in this difficult task. Moreover, the best solution must be healthy and environmentally friendly and, in many cases, is highly dependent on the time and place. Experience shows that no proposal should be accepted or rejected before the procedure has been extensively assessed. In recent years, the use of certain waste materials to provide some of the energy requirements for industrial processes has grown significantly, one of the most notable * Corresponding author phone: 34-93-400.61.67; fax: 34-93204.59.04; e-mail:
[email protected]. 4734
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being secondary fuels in cement kiln plants. Cement production involves heating the raw materials at very high temperatures in a rotary kiln to induce chemical reactions that produce a fused material called clinker. Combustion of primary fuels, mainly fossils such as coal and petroleum coke, is commonly used to attain high temperatures required to form cement. Nevertheless, the operating conditions achieved in cement kilns offer an attractive technology for combusting wastes including those classified as hazardous and the socalled alternative, additional, supplementary, or secondary fuels since in many cases an energy output similar to that of fossil fuels can easily be obtained. Furthermore, inherent conditions of the cement kiln mimic those of hazardous waste incineration. For instance, the gas residence time in the kiln is more than 3 s while the temperature exceeds 1500 °C, and destruction of organic compounds can be assumed. Some typical wastes commonly involved in cement formation are waste oils, spent organic solvents, sludges, meat meals, and automobile tires. It is well-known that combustion processes also imply the formation and release into the atmosphere of minor amounts of unwanted byproducts resulting from incomplete combustion. In many cases, these products such as polychlorinated dibenzo-p-dioxins (PCDDs) and dibenzofurans (PCDFs) may be highly toxic (1, 2). As a result, stringent regulations, mainly governing stack gas emissions, have been enforced in recent years in an attempt to reduce the emissions of pollutants into the air (3). To our knowledge, only a few papers on the use of waste in cement kilns have been published, and no particular attention has been paid to the evaluation of the releases into the atmosphere following the use of secondary fuels during clinker manufacture. Furthermore, the reports focused mainly on the elaboration of atmospheric emission inventories (4-10). Interesting data were reported by Fiedler et al. regarding the first results from stationary source emission in Thailand. In that paper, results from the evaluation of PCDD/F emission from cement kilns, with and without the use of tires and liquid waste, revealed concentrations far below the 0.1 ng I-TEQ/Nm3 limit. Results of the PCDD/PCDF emission measurements of 16 cement clinker kilns operating (suspension preheater kilns and Lepol kilns) in Germany were reported by Schneider et al. in 1996. The study included both plants using raw material alone and those using secondary fuels. In all cases, air pollution control systems (APCSs) were based on the use of an electrostatic precipitator (ESP). The operating plants revealed an average concentration of 0.02 ng I-TEQ/Nm3 (12). More data on the analysis of PCDDs/PCDFs and dioxinlike PCBs revealed emission values from cement kilns around 0.0016 ng WHO-TEQ/Nm3, with a minor PCB contribution of 0.0002 ng WHO-TEQ/Nm3 (13). Data reported from 5 different sites in the U.K. as part of the compliance monitoring survey undertaken by the U.K. Environmental Agency yielded 14 individual measurements. No comments were provided on the type of process or APCS. Nevertheless, the results revealed average values of 0.058 ng I-TEQ/Nm3 (n ) 14) (7). Similarly, French experience on the use of secondary fuels in cement plants was also reported. PCDD/F emission values from 40 measurements collected in cement plants using meat meal as a secondary fuel were compared to those obtained from 22 measurements taken in plants using fossil fuels with no notable differences (14). Preliminary data on PCDD/PCDF emission from cement kiln plants operating in Spain had already been reported in 10.1021/es049641a CCC: $27.50
2004 American Chemical Society Published on Web 08/10/2004
FIGURE 1. Diagram of a cement kiln plant examined in this study. the framework of the Spanish Dioxin Inventory. Provided data refer to 20 cement plants, 18 of which operate with a dry process and 2 more use wet processes; in all cases fossil fuels were used as primary fuels. Results ranged from 0.0006 to 0.0472 ng I-TEQ/Nm3 with an average value of 0.007 ng I-TEQ/Nm3 (n ) 20) (5). The potential impact of clinker plants was also evaluated in the surroundings of two different cement kiln plants in Spain. In particular, temporal variations of both PCDD/F and heavy metals in two environmental matrixes such as soils and herbages were studied. From the findings obtained in both studies, no relevant influence on the neighborhood was observed (15, 16). This work presents the results of the studies conducted to evaluate PCDD/PCDF emissions into the atmosphere at three Spanish cement kiln plants using secondary fuels in clinker production. In particular, two different types of waste materials (meat meal and used tires) and a mixture of both were separately evaluated in duplicate in several sampling campaigns. In all cases, operating conditions included dry processes, and the APCSs were based on the use of fabric filters (FFs) in two plants and an ESP in the third plant. Current practices complying with the minimum requirements indicated in well-accepted procedures, such as EN-1948:1996, were fulfilled for the analyses (17).
2. Materials and Methods 2.1. Sampling Strategy. A measurement program was undertaken in two sampling campaigns at three different plants in Spain. In all cases, clinker was formed in a dry process. All plants presented a state-of-the-art configuration with a preheater consisting of a vertical tower containing a series of cyclone-type vessels depending on the plant. A diagram of a typical cement kiln plant and some operating condition details are shown in Figure 1. In particular, in plant 1, the tower contained five cyclonetype vessels. Raw materials were fed into the kiln at the cold end at 230 Mg/h; meanwhile, conventional fuel, mainly petroleum coke, at a dosage of 15.6 Mg/h, was combined with meat meal at a dosage ranging from 1.6 to 2 Mg/h, which signifies 4.8-6% thermal substitution. Injection of waste materials was performed in the calciner and the main burner (highest temperature zone). In this case, the APCS devices consisted of fabric filters. In plant 2, raw materials were injected at a dosage of 100 Mg/h at the top of a tower with four cyclone-type vessels. In this case, combustion conditions included a mixture of conventional fuel, petroleum
coke at 8.5 Mg/h, and used automobile tires at a dosage of 1 Mg/h representing 9.4% thermal substitution. Used tires were previously crushed and injected in the precalciner. The APCS in plant 2 also consisted of fabric filters. Finally, plant 3 presented a dry process with a tower containing four cyclone-type vessels. Raw materials were fed into the kiln at a dosage of 110-125 Mg/h. Conventional fuel was combined with both residues, used tires and meat meal, at a dosage of 0.7-1.2 Mg/h for tires and between 0.6 and 0.7 Mg/h for meat meal, with a total thermal substitution of 13-14%. The final configuration of the plant included an ESP as an APCS device. The operating conditions, sampling schedules, and proportions of conventional fuel and waste materials are summarized in Table 1. For gaseous matrixes, sampling was made with a stack gas sampler of the filter/condenser method, fulfilling the minimum requirements described in EN-1948:1996 part 1, as extensively documented in previous studies (18, 19). 2.2. Extraction and Cleanup. Prior to the extraction process, samples were spiked with labeled PCDD/PCDF standards described in the EN-1948 methods. Analytes were removed from XAD-2 and the filter by Soxhlet extraction using toluene for 24 h. The toluene extracts were then transferred to n-hexane and rotary-concentrated prior to the cleanup process. The cleanup procedure was based on the use of the Power Prep system (FMS Inc., Boston, MA). The automated system cleanup employs multilayer silica, basic alumina, and PX-21 carbon adsorbents (FMS Inc.). The n-hexane extracts were loaded and pumped through individual sets of multilayer silica followed by a basic alumina column with n-hexane. Interferences were eliminated with n-hexane/dichloromethane (98:2). PCDDs/PCDFs were then eluted from the alumina column and transferred to the PX-21 carbon column with a mixture of n-hexane/dichloromethane (1:1). Finally, interferences were eluted with 12 mL of ethyl acetate/toluene (1:1) in the forward direction, and PCDDs/PCDFs were collected from the carbon column in the reverse direction. All solvents, acetone, dichloromethane, toluene, n-hexane, and ethyl acetate, for organic trace analysis were purchased from Merck (Germany) (20). 2.3. Instrumental Analysis. Purified extracts were analyzed by HRGC-HRMS on a GC 8000 series gas chromatograph (Carlo Erba Instruments, Milan, Italy) coupled to an Autospec Ultima mass spectrometer (Micromass, Manchester, U.K.), using a positive electron ionization (EI+) source and operating in the SIM mode at resolving power of 10000. Chromatographic separation was achieved with a DB-5 (J&W Scientific, California) fused-silica capillary column (60 m × 0.25 mm i.d., 0.25 µm film thickness) with helium as carrier gas in the splitless injection mode (1-2 µL). The temperature program was 140 °C (1 min) to 200 °C (1 min) at 20 °C/min, then at 3 °C/min to 300 °C, and hold isothermally for 20 min at 300 °C. Confirmatory analyses were performed by using polar GC capillary columns such as a J&W DB-DIOXIN GC column (21). 2.4. Quality-Control Criteria. Quality criteria were based on the applications of quality control (QC) and quality assurance (QA) measures such as analysis of a blank sample covering the complete analytical procedure, analysis of certified reference materials, or participation in intercalibration exercises as a current quality policy of the Laboratory of Dioxins, which have been reported in previous works (19).
3. Results and Discussion In this study, the use of waste materials as a secondary fuel during the formation of clinker in several Spanish cement kilns was evaluated. Three different plants, coded plant 1, plant 2, and plant 3, were selected for the project. Owing to the complexity and cost of the study, two different sampling VOL. 38, NO. 18, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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TABLE 1. Operating Conditions and Sampling Schedule for Assessment of the Use of Waste Materials as Secondary Fuels in a Cement Kiln Plant type of process preheater raw material dosage (Mg/h) conventional fuel primary fuel dosage (Mg/h) secondary fuel secondary fuel dosage (Mg/h) feeding point percentage thermal substitution APCS first campaign second campaign
plant 1
plant 2
plant 3
dry process five cyclone-type vessels 230 coke pretroleum 15.6 meat meal 1.6-2 calciner 4.8-6 fabric filters 05/15/2002 03/26/2003
dry process four cyclone-type vessels 100 coke pretroleum 8.5 used tires 1 preheater 9.4 fabric filters 07/16/2002 12/11/2002
dry process four cyclone-type vessels 110-125 coke pretroleum 5.7-7.8 mixed meat meal and used tires 15.6 calciner and preheater 13-14 electrostatic precipitator 09/13/2002 07/17/2003
TABLE 2. PCDD/PCDF Concentrations (pg/Nm3) of Emission Samples Collected in Cement Kilns Using Secondary Fuelsa plant 1, meat meal
plant 2, used tires
plant 3, used tires plus meat meal
compound
first campaign
second campaign
first campaign
second campaign
first campaign
second campaign
2,3,7,8-TCDF 1,2,3,7,8-PeCDF 2,3,4,7,8-PeCDF 1,2,3,4,7,8-HxCDF 1,2,3,6,7,8-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,7,8,9-HxCDF 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF 2,3,7,8-TCDD 1,2,3,7,8-PeCDD 1,2,3,4,7,8-HxCDD 1,2,3,6,7,8-HxCDD 1,2,3,7,8,9-HxCDD 1,2,3,4,6,7,8-HpCDD OCDD total TCDF total TCDD total PeCDF total PeCDD total HxCDF total HxCDD total HpCDF total HpCDD total I-TEQ (ng/Nm3)
33.97 4.42 6.36 8.35 3.89 6.15 NQ (3.33) 12.61 4.47 14.49 NQ (0.90) NQ (1.16) NQ (2.74) NQ (2.33) NQ (2.59) 8.19 20.15 193.02 30.87 43.52 3.25 36.16 5.70 24.59 36.06 0.009
6.62 0.89 1.20 1.79 0.56 0.85 NQ (0.13) 1.80 0.84 0.00 NQ (0.03) NQ (0.06) NQ (0.11) 0.55 N. Q.(0,11) 3.44 7.74 34.78 0.17 7.35 0.61 5.00 0l67 2.64 5.86 0.002
32.50 5.11 15.80 43.48 19.08 23.46 NQ (4.58) 50.24 8.99 22.36 0.93 3.02 4.65 7.43 10.62 33.22 47.48 141.12 53.14 102.05 67.14 151.51 99.33 85.00 66.64 0.026
8.47 12.38 38.71 36.30 28.95 37.79 13.98 96.38 18.85 76.16 NQ (0.98) 10.36 6.22 8.57 5.70 45.43 85.00 81.34 59.54 216.57 80.01 265.96 120.16 141.16 95.56 0.042
49.11 3.07 29.24 4.13 1.66 3.16 NQ (0.91) 2.07 NQ (0.93) 2.11 NQ (1.78) NQ (0.93) NQ (0.94) NQ (0.90) NQ (0.99) 1.65 4.01 1780.69 17.83 203.11 9.50 22.95 4.79 3.98 2.05 0.021
8.06 1.45 4.85 1.26 0.93 3.17 1.35 5.96 3.19 19.03 NQ (0.091) 0.73 0.32 0.90 0.62 7.06 13.92 132.62 3.26 29.48 8.41 12.48 22.06 17.79 14.34 0.005
a
In parentheses are given the quantification limits. NQ ) nonquantifiable.
campaigns were designed to obtain two values from each experiment. Two different types of waste materials, used tires and meat meal, were assessed since they are the most abundant and accessible candidates for use in cement kilns in Spain. In plant 1, the addition of meat meal as a supplementary fuel in combination with conventional fuel consisting of petroleum coke in the previously indicated proportions was assessed. Likewise, plant 2 employed used tires together with conventional fuel. Finally, in plant 3, the experiments consisted of the addition of a mixture of used tires and meat meal, respectively, as described in previous sections. Thus, two sampling campaigns in three different plants yielded a total of six sampling collection episodes. Summarized data including congeners and total PCDD/ PCDF concentrations are shown in Table 2. In general terms, the results expressed in TEQ were far below the limit of 0.1 ng I-TEQ/Nm3 established by the European Union Directive (3), with values ranging from 0.002 to 0.042 I-TEQ/Nm3 with an average value and median of 0.017 and 0.014 ng I-TEQ/ 4736
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Nm3 (n ) 6), respectively. Moreover, the results are consistent with those reported in the literature. Cement clinker kilns operating in Germany revealed an average concentration of 0.02 ng I-TEQ/Nm3 (12). Data on the analysis of PCDDs/ PCDFs and dioxin-like PCBs revealed emission values from cement kilns around 0.0016 ng WHO-TEQ/Nm3, where PCBs had only a minor contribution of 0.0002 ng WHO-TEQ/Nm3 (13). Data from the U.K. revealed average values of 0.058 ng I-TEQ/Nm3 (n ) 14) and median values of 0.032 ng I-TEQ/ Nm3 (n ) 14) (7). PCDD/PCDF concentrations between 0.0003 and 0.0029 ng I-TEQ/Nm3 were reported from Thailand in cement plants burning hazardous liquid wastes and tires, respectively. It is remarkable that no significant differences were observed when the use of secondary fuels was compared with data obtained under normal conditions without the use of secondary fuels, with mean values between 0.0008 and 0.0105 ng I-TEQ/Nm3 (6). Taking into account these findings, our data were compared with previous results obtained from emission samples collected in cement plants not using
FIGURE 2. Congener distribution of 2,3,7,8-PCDDs/PCDFs (pg/Nm3) in cement kilns using secondary fuels. secondary fuels during clinker formation. Thus, emission data collected between 2000 and 2001 from 20 Spanish cement plants covering more than 29 kilns yielded over 40 measurements submitted to the Spanish Dioxin Inventory. In summary, overall results revealed values from 0.001 to 0.054 ng I-TEQ/Nm3 (22). Statistics were calculated by the Kruskal-Wallis tests which compares medians within each group (23), with the P value being greater than 0.05 (0.13). Therefore, no statistically significant differences were found among the medians at the 95% confidence interval levels. Conventional analysis of congeners and their distribution, commonly called chemical fingerprint analysis, is widely used as an important tool to link the presence of these contaminants to a specific source. A representative congener-specific concentration profile of the 2,3,7,8-chloro-substituted PCDDs/ PCDFs is shown in Figure 2. The results presented a similar combustion byproduct profile with a notable presence of PCDFs (mainly tetrachorodibenzofuran (TCDF), pentachlorodibenzofuran (PeCDF), and hexachlorodibenzofuran (HxCDF) followed by heptachlorodibenzo-p-dioxin (HpCDD) and octachlorodibenzo-p-dioxin (OCDD)) compared to PCDDs (18, 19). In contrast, a remarkable particularity was the presence of 2,3,7,8-TCDF in a significant number of samples as occurs in emissions from kilns operating without the addition of secondary fuels (5). Unfortunately, owing to the low number of samples, this hypothesis could not be statistically corroborated at the 95% confidence level. In terms of TEQ, an analogous situation was found when TEQ profiles were compared. In all cases, the major contribution stemmed from the 2,3,7,8-TCDF and the 2,3,4,7,8PeCDF with the other congeners remaining in a minor proportion. As an example, Figure 3 shows the relative
FIGURE 3. Congener distribution of 2,3,7,8-PCDDs/PCDFs (in TEQ values) in cement kilns using secondary fuels. contribution of each congener expressed as TEQ values for all species studied. The emission of polychlorinated dibenzo-p-dioxins and dibenzofurans was evaluated in cement kiln plants operating under normal conditions and using secondary fuels. In all cases, the emitted PCDD/F concentrations were consistent with those reported in the literature and complied with the present EU Directives limit for PCDD/PCDF emission. Moreover, no statistical differences were found between data obtained from the use of conventional fuel alone and those obtained from the use of secondary fuels. Therefore, from these findings it can be concluded that the addition of used VOL. 38, NO. 18, 2004 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
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tires or meat meal had no effect on emission results in keeping conditions.
Acknowledgments This project was carried out in the framework of a collaboration between OFICIEMEN and the Spanish Council for Scientific Research (CSIC). We thank Marina Romay, Asier Otxoa de Eribe, and Pedro Mora from OFICEMEN for encouragement in the elaboration of this study, Dr. Albert Manich for comments on statistics, and Eric Jover and Nuria Garcı´a for comments and critiques. We also thank Ms. M. G. Martrat and Mr. M. A. Adrados for excellent work in sample preparation (extraction and FMS purification) and J. Saulo´ for HRGC-HRMS analysis.
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(10) UNEP. Standardized Toolkit for Identification and Quantification of Dioxin and Furan Releases; UNEP Chemicals: Geneva, Switzerland, January 2001, 2003; http://www.chem.unep.ch/ pops/newlayout/repdocs.html. (11) Fiedler, H.; Chareonsong, P.; Mayer, J.; Hartenstein, H. U. Organohalogen Compd. 2002, 59, 211. (12) Kuhlmann, K.; Schneider, M.; Su ¨ llenbo¨hmer, F. Organohalogen Compd. 1996, 27, 78. (13) Luthardt, P.; Mayer, J.; Fuchs, J. Chemosphere 2002, 46, 1303. (14) Capmas, A. ATILH, 2003. The French Cement Industry experience in the use of waste fuels. 5th Colloquia of managers and technicians of cement plants, Sevilla, February 2003. (15) Schuhmacher, M.; Agramunt, M. C.; Bocio, A.; Domingo, J. L.; de Kok H. A. M. Environ. Int. 2003, 29, 415. (16) Schuhmacher, M.; Agramunt, M. C.; Bocio, A.; Domingo, J. L.; de Kok, H. A. M. Chemosphere 2002, 48, 209. (17) European Standard, Stationary source emissions- Determination of the mass concentration of PCDDs/PCDFs; EN-1948-1,2,3:1996; European Committee for Standardization: Brussels, 1996. (18) Abad, E.; Caixach, J.; Rivera, J. Chemosphere 2003, 50, 1175. (19) Abad, E.; Adrados, M. A.; Caixach, J.; Rivera, J. Environ. Sci. Technol. 2002, 36, 92. (20) Abad, E.; Caixach, J.; Rivera, J. J. Chromatogr., A 2000, 893, 383. (21) Abad, E.; Caixach, J.; Rivera, J. J. Chromatogr., A 1997, 786, 125. (22) OFICEMEN. www.oficimen.es, 2003. (23) Siegel, S. Non-parametric statistics for the behavioural sciences; MacGraw Hill Book Co., Inc.: London, 1956.
Received for review March 8, 2004. Revised manuscript received June 14, 2004. Accepted June 15, 2004. ES049641A
