ARTICLE pubs.acs.org/est
Effect of Fuels and Domestic Heating Appliance Types on Emission Factors of Selected Organic Pollutants Michal Syc,*,† Jirí Horak,‡ Frantisek Hopan,‡ Kamil Krpec,‡ Tomas Tomsej,§ Tomas Ocelka,§ and Vladimír Pekarek† †
Environmental Process Engineering Laboratory, Institute of Chemical Process Fundamentals, Academy of Sciences of the Czech Republic, v. v. i., Rozvojova 135/2, 165 02 Prague 6 Suchdol, Czech Republic ‡ Energy Research Center, Technical University of Ostrava, Innovation for Efficiency and Environment, 17.listopadu 15/2172, 708 33 Ostrava, Czech Republic § Department of Hygienic Laboratories, Institute of Public Health Ostrava, Partyzanske namestí 7, 702 00 Ostrava, Czech Republic
bS Supporting Information ABSTRACT: This study reports on the first complex data set of emission factors (EFs) of selected pollutants from combustion of five fuel types (lignite, bituminous coal, spruce, beech, and maize) in six different domestic heating appliances of various combustion designs. The effect of fuel as well as the effect of boiler type was studied. In total, 46 combustion runs were performed, during which numerous EFs were measured, including the EFs of particulate matter (PM), carbon monoxide, polyaromatic hydrocarbons (PAH), hexachlorobenzene (HxCBz), polychlorinated dibenzo-p-dioxins and furans (PCDD/F), etc. The highest EFs of nonchlorinated pollutants were measured for old-type boilers with over-fire and under-fire designs and with manual stoking and natural draft. Emissions of the above-mentioned pollutants from modern-type boilers (automatic, downdraft) were 10 times lower or more. The decisive factor for emission rate of nonchlorinated pollutants was the type of appliance; the type of fuel plays only a minor role. Emissions of chlorinated pollutants were proportional mainly to the chlorine content in fuel, but the type of appliance also influenced the rate of emissions significantly. Surprisingly, higher EFs of PCDD/F from combustion of chlorinated bituminous coal were observed for modern-type boilers (downdraft, automatic) than for old-type ones. On the other hand, when bituminous coal was burned, higher emissions of HxCBz were found for old-type boilers than for modern-type ones.
’ INTRODUCTION Emissions from domestic heating appliances significantly add to total environmental pollution, which was proved by seasonal changes of polycyclic aromatic hydrocarbons (PAH) levels obtained by long-term monitoring programs.1 The participation of particular sources in total pollution varies depending on the emission inventory source.2 Breivik et al.2 have found out that, in Europe, 20 45% of PAH emissions and 18 30% of the emissions of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/F) come from domestic combustion. Quass et al.3 even assert that 30 35% of PCDD/Fs are produced in domestic combustion. Emission inventories use emission factors (EFs) to calculate the participation of individual sources in total emissions. However, the reported EF values of PCDD/Fs and other pollutants from domestic combustion differ widely. The EFs of PCDD/F, polychlorinated biphenyls (PCB), hexachlorobenzene (HxCBz), PAH, and particulate matter (PM) have been determined for a fireplace and a woodstove for oak and pine fuels.4 The resulting PCDD/F EFs were 19.1 87.7 ng international toxicity equivalents (I-TEQ)/GJ depending on fuel and combustion facility types. A significant effect of the combustion facility r 2011 American Chemical Society
age on the EF values has been reported, as well as the effect of the in- or stationary phase of the combustion period.5 For the tested facilities, the PCDD/F EFs varied from 100 to 700 ng World Health Organization toxicity equivalents (WHO-TEQ)/GJ in the case of woody biomass. Even though the effect of boiler operating conditions on pollutant formation has been investigated previously, the analyzed pollutants included only the PAH of persistent organic pollutants (POPs).6 Wevers et al.7 reported no effect of the combustion period or fuel age on the EFs from five tested stoves. The resulting EF values of PCDD/F were 2 89 ng I-TEQ/kg (i.e., approximately 100 5000 ng I-TEQ/GJ); the effect of the facility type was not investigated. Chimney emissions from 30 households were sampled for determination of real PCDD/F emission factors.8 The tested combustion facilities included stoves and boilers with a wide range of thermal input and facility age. The measured emission factors of PCDD/F were Received: May 27, 2011 Accepted: September 20, 2011 Revised: August 1, 2011 Published: September 20, 2011 9427
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Table 1. Ultimate and Proximate Analyses of Tested Fuelsa fuel properties
a
lignite (LI)
bituminous coal (BC)
beech logs (BL)
maize straw pellets (MP)
spruce logs (SL)
ash (wt %)
5.8
3.2
0.9
17.6
combustibles (wt %)
94.2
96.8
99.1
82.4
1.2 98.8
LHVb (MJ/kg)
26.3
32.8
17.3
14.7
18.1
carbon (wt %)
64.6
79.9
45.5
39.3
50.5
hydrogen (wt %)
5.28
4.45
5.65
4.92
5.98
nitrogen (wt %)
0.902
1.03
0.101
0.881
0.409
oxygen (wt %)
22.6
10.7
47.6
37.2
41.9
sulfur (wt %) chlorine (mg/kg)
0.854 40.0
0.720 1 620
0.243 58.0
0.144 1 170
0.0710 60.0
All on dry basis. b Lower heating value.
within 2 4500 ng I-TEQ/GJ depending on a tested facility, fuel, and/or an inappropriate operation of the facility. However, isokinetic sampling was not possible due to a low flue gas velocity in the chimney. Moreover, the EFs with respect to the boiler design and age were observed, but the study concentrated mainly on other pollutants than POPs.9 The EFs of PCDD/F, PCB, polychlorinated naphthalenes (PCN), PAH and PM for wood and coal burning were monitored in simulated open-fire domestic facilities that eliminated the effect of the combustion facility.10 The emissions of volatile organic compounds (VOC) and PAH for birch wood combustion in a wood stove were also quantified.11 Launhardt and Thoma12 published a complex study about the emissions of PCDD/F, polychlorinated phenols (PCPh), polychlorinated benzenes (PCBz), and PAH during combustion of five herbaceous and woody fuels in a modern automatic boiler. A possible effect of different dilution systems and filter media used for sampling on the EFs has been described as well.13 Numerous studies, besides the above-mentioned, have been conducted on this topic with varying results.14,15 Moreover, some studies mentioned the effect of facility design, but this effect has not been studied in detail yet. The majority of the studies particularly focus on the fuel effect. Therefore, this study focuses on the determination of both effects, the effect of the facility as well as the fuel. The EFs of some major pollutants [CO, total organic carbon (TOC), PM] and selected organic pollutants (PCDD/F, PCB, PAH, PCPh, PCBz) were determined for combustion of five different fuels in six combustion facilities with various combustion designs. The general aim of this study was to obtain complex and comparable data allowing identification of the above-mentioned influences. Furthermore, the obtained data enable us to particularize the emission inventories of the studied POPs and the estimation of emissions of new POPs such as pentachlorobenzene (PeCBz).
’ EXPERIMENTAL SECTION Fuels. Fuels were chosen according to their consumption in
domestic heating. Lignite (LI) is used in domestic combustion mainly in the Czech Republic and Poland.16 Bituminous coal (BC) from Poland was chosen due to its high Cl content and because of its high consumption therein. Three biomass fuels were tested as examples of the currently favored solid fuels for domestic heating. Beech logs (BL) were chosen for experiments as a hardwood sample, spruce logs (SL) as a softwood species, and maize straw pellets (MP) as a high Cl content herbaceous species. The results of the ultimate and proximate analyses of the
Table 2. Summary of Performed Runsa fuel
run
FFR
W
output
T
O2
(kg/h)
(wt %)
(kW)
(°C)
(vol. %)
B1, Over-Fire Boiler LI
1
8.1
27.5
21.6
235
11.3
LI
2 3
4.8
27.5
13.6
196
16.3
BC
4 6
2.9
2.41
16.1
234
12.5
BL
7 9
6.9
9.58
19.3
222
10.9
LI
10 11
5.7
22.6
182
10.7
BC
12 13
3.2
2.41
18.6
204
11.4
BL
14 16
6.2
9.58
18.2
163
12.5
LI
17 19
5.9
27.5
23.9
256
LI
20 22
3.7
26.4
15.4
167
12.0
26.4
13.3
B2, Under-Fire Boiler 27.5
B3, Automatic Under-Fire Boiler with Screw Conveyor
LI
23 25
1.9
BC
26 28
4.0
MP
29 31
5.1
LI
32 34
7.7
BL
35 37
9.8
SL
38 40
7.2
BL
41 43
8.7
BL
44 46
2.3
2.83 10.3
8.0
127
25.5
193
13.8
161
9.81
7.81 12.8
B4, Downdraft Boiler 27.5 9.58
33.4
305
28.9
260
10.6
6.83
23.1
224
10.5
29.7
261
B5, Downdraft Boiler 10.0 5.86
6.60
S6, S-Draft-type Stove 9.58
6.5
302
15.0
a
FFR, fuel feeding rate; W, fuel water content; output, measured according to EN 303-5; T, temperature at chimney outlet; O2, average O2 in chimney outlet.
tested fuels are shown in Table 1. The water content in the tested fuels is displayed in Table 2. Tested Facilities. The tested facilities represent the main designs of boilers used for domestic heating.17 For comparison, a classic S-draft type stove was used. Schemes of the tested facilities are shown in Figure 1; details about the facilities are given below. Boiler 1 is a hot water over-fire boiler with manual stoking and natural draft (see Figure 1a). The whole fuel batch is combusted at one time, and the operation of the facility is periodical. Primary air (P) is blown under the water-cooled fixed grate (1) through an automatic draft-regulating damper in the ash pit door 9428
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Figure 1. Schemes of tested combustion facilities.
(see Figure 1a). A secondary air (S) inlet into the gas combustion zone is in the fuel feeding door and can be manually regulated with a damper. The recommended fuels are coke, bituminous coal, and wood logs; lignite is also possible. Boiler 2 is an under-fire boiler with natural draft and manual stoking (see Figure 1b). The boiler can be divided into three parts: a fuel storage (1), a combustion chamber (2), and a gas flow chamber (3). Devolatilization and partial combustion occurs in a small part of fuel in the bottom of the fuel storage, while main combustion takes place in the follow-up combustion chamber. Primary air (P) is supplied through a damper in the fuel feeding door. Secondary air (S) is led through a channel to the combustion chamber; tertiary air is supplied sidewards to the combustion chamber as well. Rotary grates (4) are placed below the fuel storage and the combustion chamber. The recommended fuel is lignite, but other solid fuels can be used as well. Boiler 3 is a modern under-fire boiler (see Figure 1c) with forced draft and automatic stoking by a screw conveyor (1). The upper part of the boiler is a lamellate heat exchanger (2). The lower part is a combustion chamber formed by an iron grate (3), a ceramic heat reflector (4), a retort for fuel feeding (5), and an air mixing system (6). Primary air (P) is supplied by a fan (7) to the air mixing system. There is an ash chamber (8) situated under the combustion chamber. The recommended fuels are lignite and biomass pellets. Other solid fuels with required granulometry can be combusted as well. Boiler 4 is a modern downdraft boiler with manual stoking and forced draft by a draw-off fan (see Figure 1d). The boiler consists of two chambers; the upper one is for fuel storage (1) and the lower one is a combustion chamber (2). The chambers are divided by a special rotating burner (4). Primary air (P) is supplied to the combustion chamber from above through the batch of fuel and a special cast-iron grate (3). Secondary air (S) is supplied to the grate. The recommended fuels
are lignite, but wood logs and other solid fuels can be used as well. Boiler 5 is a modern downdraft boiler with manual stoking and forced draft by a draw-off fan. It has a similar construction to boiler 4 with larger chambers. It is for wood combustion only and has a stationary fire-clay grate. The recommended fuel is wood logs. Stove 6 is a modern S-draft stove with grate (1) and periodical combustion operation (see Figure 1e). Combustion Runs. Parameters of the realized combustion runs are summarized in Table 2. Thirty-nine combustion tests were performed according to the producer’s instructions (i.e., steady-state regime) and/or European standard EN 303-5. All combustion runs started with fuel ignition. After the ignition, the combustion process was conducted so that the nominal output of the boiler was reached immediately. The facility was operated under a steady-state regime for at least 2 h. Then, sampling of flue gases for off-line analyzed pollutants commenced. Boiler B1 and stove S6 are batch-operated facilities with combustion periods, therefore sampling of the flue gases started synchronously with the combustion period start and finished with the period end. The fuel batch for the measured combustion period was added onto a thin layer of burning fuel. Hence, the obtained EFs are not cold-start values. Boilers B2, B4, and B5 operate on fuel batch principles, however, due to their design there is no strictly binding combustion period. The B3 facility operates quasi-continuously. The sampling time for these four facilities was chosen to be about 6 h. The majority of the runs were triplicate in order to obtain robust and representative data. The “memory effect” has significant impact on the formation levels of some POPs. Therefore, the testing facility was mechanically cleaned up after triplicate runs with the same fuel and the same combustion facility, which effectively suppressed the effect of ash deposition inside the testing facility. 9429
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Environmental Science & Technology The stoking period and the size of the fuel batch influenced the emissions of the facilities operating with a combustion period, that is, B1 and S6. Both parameters were set in accordance with EN 303-5 (except runs 2 and 3) as follows: run 1 (one LI batch of 25 kg), runs 2 3 (stoking period 0.5 h, fuel batch 2.4 kg of LI), runs 4 6 (one 11.6 kg weight batch of BC), runs 7 9 (stoking period ca. 2 h, fuel batch 13.8 kg of BL), and runs 44 46 (stoking period ca. 45 min, fuel batch 1.8 kg). The effect of lower than nominal output was observed in B3. Runs 17 19 were performed with the nominal output of 23.9 kW (fuel feeding rate 5.9 kg/h, fan output 90%, screw conveyor on/ off 12/20 s). Runs 20 22 were performed with approximately 65% of the nominal output, that is, 15.4 kW (fuel feeding rate 3.7 kg/h, fan output 45%, screw conveyor on/off 6/23 s). Runs 23 25 were performed with the output of 8.0 kW, which is 33% of the nominal boiler output (fuel feeding rate 1.9 kg/h, fan output 7%, screw conveyor on/off 5/40 s). The design of the whole runs and the sampling was the same as mentioned above for the steady-state runs: the runs started with fuel ignition, subsequently the boiler was operated at intermittent state for ca. 1 2 h, then sampling of flue gases of off-line analyzed pollutants began. Testing Facility. The boilers and the stove were tested at a domestic combustion testing facility consisting of a balance, the tested boiler or stove, an isolated chimney system exhausting to a dilution tunnel hood, a dilution tunnel, and a fan. The testing facility was constructed on the principle of EPA Test Method 5G. More details and the scheme of the facility have been already published elsewhere.18,19 Analytical Procedures. Continuous measurements of CO and total organic carbon (TOC) were performed in the isolated chimney. Measurements of CO2 and O2 were performed simultaneously in the isolated chimney and the dilution tunnel. O2, CO, and CO2 were measured by an Advance Optima multigas analyzer in accordance with EN 15058 (CO), ISO 10396 (standard for sampling). The content of TOC was analyzed by a Multi-FID 100 (EN 12619). The particulate matter content was determined in the dilution tunnel in accordance with ISO 9096. Flue gases for determination of organic compounds were sampled isokinetically in the dilution tunnel according to EN 1948 (filtration condensation method). The determination of PCDD/F and DL-PCB was based on liquid liquid/Soxhlet extraction, followed by multistep cleanup (silica gel/alumina/ carbon) and gas chromatography (GC)/high-resolution mass spectrometry (HRMS) and GC/tandem mass spectrometry (MS/MS) analysis in according with EN 1948. For analysis of PAH and PCBz, aliquots of raw extracts were taken and analyzed after cleanup by HPLC with postcolumn fluorescence derivatization (FLD) and GC/MS/MS. The detailed analytical procedure can be found in Supporting Information. Calculation. Levels of some of the analytes were below detection limits; in such cases the detection limit values were used as a representative. The presented emission factors were related to fuel energy, that is, the EFs are based on the real lower heating values of the given fuels.
’ RESULTS AND DISCUSSION The results are subdivided into three groups. The first group consists of CO, TOC, PAH, and PM, i.e. nonchlorinated products of incomplete combustion. In the second group, there are PCBz as the main precursors of PCDD/F formation. And finally,
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the third part of discussion deals with the results of PCB and PCDD/F. Carbon Monoxide, Total Organic Carbon, Polycyclic Aromatic Hydrocarbons, and Particulate Matter. The obtained emission factors of PM, CO, TOC, and PAHs are depicted in Figure 2. A strong effect of boiler design on the EFs can be made out from the results. The most common indicator of combustion quality is the CO level. In both old-type boilers B1 and B2, the EFs of CO almost reached over 4 kg/GJ; the highest value of nearly 8 kg/GJ was observed during run 1. Similar values in the range 2.1 4.3 kg of CO/GJ had been measured for old-type boilers previously.8 The EFs of CO reached values in units of kilograms per gigajoule even for the modern boilers during combustion runs 29 31, 35 37, and 38 40, when inappropriate or substitute fuels were used. The results confirm that the excess amount of combustion air in flue gases deteriorates the quality of combustion and causes an increase in CO.9 The above-mentioned effect took place in modern boilers more significantly than old-type ones. The decrease of flue gas temperature in the chimney inlet with increased O2 was observed (see Table 2); this implies that deterioration of combustion was caused by a decrease of combustion temperature and/or by shortening of residence time in the postcombustion zones. The excess amount of combustion air (and O2) can be caused by use of substitute fuels for which the boilers were not designed, especially when they differ in energy density and devolatilization rate. Boiler B4 (concretely the combustion chamber size and the burner type) was designed for lignite combustion. Hence, in the case of BL combustion (runs 35 37), the EFs of CO increased 33 times in comparison with LI combustion (runs 32 34), and O2 concentration in flue gases rose from ca. 6.8 to 10.6 vol %. These high EFs are also given by the ratio of primary/secondary combustion air, which was set up for LI combustion on B4. The influence of primary to secondary air ratio is obvious also from the comparison of CO values obtained during runs 38 40 and 41 43 in B5. To minimize CO emissions, the change of the above-mentioned ratio is necessary in the case of substitution of hardwood for softwood. CO increase was also observed during runs 29 31 for B3; it was caused by deterioration of combustion due to formation of ash sinters on the retort. This had been reported previously for straw combustion in automatic residential boilers.5 The highest EFs of PM were measured for the over-fire boiler (B1), which seems to be logical due to its primitive design without any postcombustion zones or zones where particles can be separated from flue gases by means of gravitation (see Figure 1). Similarly, high EFs were found for the old-type boiler (B2) with the under-fire concept of combustion. The EFs of PM for B1 and B2 were higher by approximately 1 order of magnitude compared to the other four tested facilities. The lowest PM EFs were observed for both downdraft boilers (B4 and B5), provided the recommended fuels were burned. Among other things, the quality of combustion influenced the rate of PM emissions, because the PM is also formed by unburnt carbon residues. The influence of combustion quality was obvious for B4 where, surprisingly, 3.5 times lower emissions were measured from LI (runs 32 34) than from BL (35 37). The effect of ash content in fuel appeared mainly for both old-type boilers, more significantly for B1 than B2. The fuel ash content seems to be low in the case of modern boilers; the PM EFs are mainly predetermined by boiler design. Generally, the effect of a boiler on PM emissions is indisputable from our results, which is remarkable, as the effect of fireplaces or/and stoves on PM emissions had been considered small previously.20 9430
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Figure 2. Mean values of emission factors of CO, PM, TOC, and PAH with standard deviations. PAH is the sum of 10 polyaromatic hydrocarbons: fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b]fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, benzo[g,h,i]perylene, dibenzo[a, h]anthracene, and indeno[1,2,3-cd]pyrene.
Large differences between boilers were observed for PAH emissions. The EF values of PAH from B1 and B2 were higher by 1 2 orders of magnitude than those from the modern boilers. Contrary to the CO EFs, the PAH emission from S6 was comparable with that from the modern boilers. The lowest PAH EFs were observed for the modern automatic boiler, followed by both downdraft boilers. Inappropriate or substitute fuel combustion (runs 29 31, 35 37, and 38 40) in modern-type boilers caused approximately 10-fold increase of the PAH emission, but the EFs were still 1 order of magnitude lower than the EFs from the old-type boilers. The highest EFs of nonchlorinated pollutants were measured for the old-type boilers B1 and B2. The whole fuel batch burns at once in B1; that is, the boiler operates periodically depending on the stoking period. Therefore, the fuel batch size and the stoking period affected the quality of the combustion process and the emission levels significantly. This is evident from comparison of run 1 with runs 2 3. Lignite (ca. 25 kg) for the whole combustion period (set up according to EN 303-5) was added all at once for run 1. At first, the lignite devolatilization proceeded. The O2 in flue gases was decreasing to ca. 1.5 vol %. The CO was rising over 10 vol % during the first 25 min and stayed at the maximum values for the next 10 min. Subsequently, significant oxidation of the produced gases started and the CO values decreased. The cause
of such high emission values lies in the combination of the boiler design and the specific lignite properties. The characteristic features of B1 are a very poor quality of combustion given by poor mixing of the combustion air with local oxygen deficiency, a low combustion temperature (between 400 and 800 °C),21 and a nonhomogenous temperature field (so-called “cold wall effect”). The above-mentioned disadvantages were further multiplied by slow devolatilization of lignite.22 Moreover, the observed high values were measured during “hot starts”; the cold-start emission from B1 would have been even worse. Shortening of the stoking period to 0.5 h and changing of the fuel batch size to 2.4 kg led to 2 4 times lower EFs. Steadier operation and lower temperature fluctuation were the cause of that. Emissions from the combustion of BL and BC in B1 (runs 7 9 and 4 6) were 2 or more times lower than during run 1; however, the whole fuel batch was added at once as well. The above-mentioned disadvantages of B1 keep on holding true, but the lower EFs were caused by faster devolatilization of these fuels, so the fuel batch started to burn rapidly. The fuel devolatilization and combustion are taking place separately in the under-fire boiler B2. The drawbacks of B1, such as poor mixing of gases, a heterogeneous temperature field, and bad control of combustion, can be attributed to B2 as well. On the other hand, the effect of fuel devolatilization is partially suppressed by the boiler design. Hence, the EFs from LI were 9431
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Figure 3. Mean values of emission factors of PeCBz and HxCBz with standard deviations. Runs 1 3 of PCBz were not analyzed due to matrix effects. Run 32 34 were based on only two values.
comparable to the other fuels. The obtained EFs from B2 were at comparable or slightly lower levels than the emissions from B1. The lowest EFs were found for the modern automatic boiler B3 with well-managed combustion by means of quasi-continuous fuel stoking by a screw conveyor and an air forced draft. The temperature of combustion was also sufficiently high (950 1000 °C was measured in the flame under the heat reflector, 600 800 °C was measured in the inlet of the heat exchanger). It resulted into the lowest levels of nonchlorinated products of incomplete combustion. Similarly, B4 and B5 are of modern design and do not feature any of the old-type boilers’ drawbacks. The temperature in the combustion chamber reached 800 1000 °C; in the fuel storage chamber the temperatures ranged 200 400 °C, so a predried and partially devolatilized fuel was coming onto the grate. Polychlorinated Benzenes. The bituminous coal (BC) combustion in the old-type boilers (B1 and B2, runs 4 6 and 12 13) produced at least 2 orders of magnitude higher levels of HxCBz than the other tested fuel boiler combinations did. The high HxCBz EFs were given by high chlorine content in BC and also by the boiler design because the HxCBz was an absolutely prevailing homologue of PCBz. Conditions shifting competitive chlorination/ dechlorination reactions toward chlorination occurred in both oldtype boilers. High emissions of PCBz were also observed during BC combustion in the modern B3 (runs 26 28), but the homologue profile was quite opposite with domination of TeCBz. Therefore, HxCBz EFs more than 100 times lower than those from B1 were found. High PCBz EFs could be expected from MP combustion because of fuel chlorine content above 0.1 wt %, but surprisingly the emissions were comparable to the other fuels except for BC. On the contrary, a higher EF of HxCBz was observed unexpectedly during SL combustion in the downdraft boiler B5 (runs 38 40). A higher HxCBz EF was also found for BL for the B5 boiler. To promote chlorination toward higher chlorinated homologues is probably a characteristic feature of B5 because HxCBz was the dominant PCBz species there. Homologue profiles shifted toward the higherchlorinated ones were found also for PCDD/F on the B5. Generally, the EF of HxCBz from beech logs combustion was in the range 0.575 10.2 μg/GJ, at least 10 times higher than the previously found values for woody biomass.5 Comparable HxCBz EFs were measured during oak combustion in a woodstove.4 For lignite combustion, the HxCBz EFs were in the range 0.524 0.852
μg/GJ, that is, lower values than from woody biomass combustion. Unfortunately, the results from “the worst” boiler B1 are missing due to matrix effects during analyses. In the case of PeCBz, the highest EFs were also found for BC combustion. The EF values were in the range 96.8 230 μg/GJ depending on the boiler’s design. For the remaining fuels and boilers, the EFs of PeCBz were between 0.0890 and 1.88 μg/GJ. Generally, the fuel determines mainly the total amount of emitted PCBz, but the homologue profile can be strongly affected by the boiler design. It is obvious mostly from the results of the BC combustion. In the case of B1 and B2, the HxCBz formed approximately 90% of the PCBz, while for B3 it formed only approximately 7%. The resulting EFs of PeCBz and HxCBz are shown in Figure 3. Polychlorinated Biphenyls, Dibenzo-p-dioxins and Dibenzofurans. The EFs of PCB and PCDD/F are summarized in Figure 4. Similarly to their precursors, the highest PCDD/F EFs were found for the two high-chlorine fuels (BC and MP). Much lower EFs were found for lignite and woody biomass fuels. As expected, the chlorine content in fuel was decisive for the PCDD/ F emission rate. Moreover, during BC combustion the EF values varied approximately 16 times depending on the boiler, hence the influence of the boiler design was evident as well. Surprisingly, the two highest values of EFs of I-TEQ PCDD/F were measured for the modern B3 when BC and MP were combusted. The old-type boilers B1 and B2 (runs 4 6 and 12 13) emitted 7 and 16 times lower PCDD/F than the modern boiler B3 (runs 26 28) during BC combustion. The EFs of I-TEQ PCDD/F from LI combustion varied from 3.16 to 60.7 ng/GJ depending on the boiler: much lower EFs were found for the modern-type boilers than for the old-type ones (B1 and B2). A similar trend was found for the EFs from BL combustion. However, the width of EFs range was shorter: 3.48 to 24.7 ng I-TEQ (PCDD/F)/GJ. Surprisingly, the same value of I-TEQ PCDD/F EFs was found during run 1 and runs 2 3 in the B1, that is, the runs with a different fuel stoking period. The EFs of PAH, CO, and PM were 2 4 times higher in run 1, but the I-TEQ PCDD/F were the same and WHO-TEQ PCB were even lower in run 1. It means that the much worse combustion in B1 did not increase the emission of I-TEQ PCDD/F. Very interesting is the comparison of the results from both downdraft boilers. The BL combustion in B4 (primary designed for lignite) produced 2 times higher EFs 9432
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Figure 4. Emission factors of PCB and PCDD/F. PCB is the sum of PCBs 77, 81, 105, 114, 118, 123, 126, 156, 157, 167, 169, 170, 180, and 189. PCDD/ F is the sum of tetra- to octa-CDD/F. TEQ values were determined according to EN 1948.
than that in B5 (primary designed for wood). Again, it is welldocumented that the mere dimension of the combustion chamber can substantially influence the emissions because of the different energy density of each fuel and thus the different change of the temperature gradient inside the combustion chamber and the postcombustion zones. Very intriguing is the comparison of EFs for BC combustion with other fuels because of the opposite trend of boiler influence on the I-TEQ PCDD/F levels. For BC combustion, the highest EF of I-TEQ PCDD/F was found for B3 and the lowest for B1, whereas for lignite combustion the converse was found. No special effect of boilers or fuels on the homologue profiles of PCDD/F was found, with the notable exception of B5. For B5, a shift of PCDD/F homologue profiles toward higher-chlorinated ones was observed. The emission of WHO-TEQ PCB showed the same trends depending on the fuel and boiler as the emission of I-TEQ PCDD/F. The PCB contributed 5.3% to the total TEQ values on average, which was a 10 times higher contribution than found for fireplaces and the stove.4
’ ASSOCIATED CONTENT
bS
Supporting Information. Detailed analytical procedure for organic compounds, and eight tables of emission factors of PM, CO, TOC, PAH, PCBz, PCPh, PCB, and PCDD/F related
to fuel mass and also to fuel energy content (LHV). This material is available free of charge via the Internet at http://pubs.acs.org/.
’ AUTHOR INFORMATION Corresponding Author
*Telephone: + 420 220 390 261; fax: +420 220 920 661; e-mail:
[email protected].
’ ACKNOWLEDGMENT We gratefully acknowledge the financial support of the Ministry of the Environment of the Czech Republic (Project SP/1A2/116/07). ’ REFERENCES (1) Prevedouros, K.; Brorstr€ om-Lunden, E.; Halsall, C. J.; Jones, K. C.; Lee, R. G. M.; Sweetman, A. J. Seasonal and long-term trends in atmospheric PAH concentrations: evidence and implications. Environ. Pollut. 2004, 128, 17–27. (2) Breivik, K.; Vestreng, V.; Rozovskaya, O.; Pacyna, J. M. Atmospheric emissions of some POPs in Europe: a discussion of existing inventories and data needs. Environ. Sci. Policy. 2006, 9, 663–674. (3) Quass, U.; Fermann, M.; Br€oker, G. The European Dioxin Air Emission Inventory Project;Final Results. Chemosphere 2004, 54, 1319–1327. 9433
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