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Emission from realistic utilization of wood pellet stove
Energy 68 (2014) 644e650
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Energy journal homepage: www.elsevier.com/locate/energy
Emission from realistic utilization of wood pellet stove G. Toscano a, D. Duca a, A. Amato b, A. Pizzi a, * a b
Dipartimento di Scienze Agrarie, Alimentari ed Ambientali (D3A), Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona (AN), Italy Dipartimento di Scienze della Vita e dell’Ambiente (DISVA), Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona (AN), Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 October 2013 Received in revised form 28 January 2014 Accepted 30 January 2014 Available online 20 February 2014
The Italian market of wood pellet and stoves is increasing quickly as, at the same time, the concerns about the particulate matter (PM) and gas emission products. Therefore, the assessment of their environmental impact is becoming an important issue. However, the emission factor from pellet stove measured according to technical standards does not provide representative data with respect to a real domestic utilization. This difference is a consequence of different operation and combustion conditions as well as the exclusion of unsteady state phases (e.g. ignition phase) from the standard measurement. In this study combustion tests were carried out simulating domestic utilization conditions of a pellet stove and a sampling methodology more representative of the real environmental impact of these devices. Higher concentration of PM, up to 72% more than those measured in steady state condition, was shown. A higher emission factor has been observed also for carbon monoxide (CO), total carbon (TC) and polycyclic aromatic hydrocarbons (PAHs) especially during unsteady combustion phases (e.g. ignition phase) which significantly affect the emission factor in particular when the pellet stove works for short time (less than 2 h). Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Wood pellet Combustion Pellet stove Particulate matter Polycyclic aromatic hydrocarbons Emission factor
1. Introduction There is an expanding market in the use of biomass [1], especially wood pellet that has become an important worldwide fuel during the recent years [2]. Total global consumption of wood pellets in 2011 was 14.4 million tonnes, from which about 80% were consumed in Europe [3]. In Italy the consumption of wood pellet has increased steadily over the last years, rising from 150 tonnes in 2001 [4] up to 1.4 million tonnes in 2010 [5,6] representing one of the most important market in Europe. In Italy wood pellets are predominantly used in residential applications such as boilers and stoves [2]. The prevailing pellet appliances in residential applications are pellet stoves and Italy has become the biggest pellet stove market in Europe, with an estimate of 700 000 units sold until 2009 [2,4]. Emission from residential wood combustion has been considered as a major contributor to ambient air pollution [7]. Household air pollution from incomplete combustion contains health-damaging pollutants such as carbon monoxide (CO),
* Corresponding author. E-mail addresses: [email protected] (G. Toscano), [email protected] (D. Duca), [email protected] (A. Amato), [email protected] (A. Pizzi). http://dx.doi.org/10.1016/j.energy.2014.01.108 0360-5442/Ó 2014 Elsevier Ltd. All rights reserved.
particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) [8]. Small domestic heating system (<35 kWth) are not regulated by national legislation [9], however, some administration are taking action. An example is Committee Resolution 1282/12 of Marche Region that prohibits the use of solid biomass domestic heating systems when they do not fulfill quality standards for emissions and pellet [10]. This measure is the consequence of an assessment carried out by the Marche Region organism based on the estimated regional pellet consumption and emission factors taken from national database INEMAR obtained by standard measurements [11]. Anyway, the assessment of the real emission factors for residential pellet heating systems is an important living matter because they are often different from measurement performed by technical standards, as stated by Win [7] which focuses on the CO and total organic carbon (TOC) parameters. There is a similar issue for PM determination, where the samplings are traditionally performed inside the chimney in hot (e.g. 150e200 C) raw flue gases. This approach suffers from several drawbacks such as: difficulty to fulfill a isokinetic sampling, especially in transient combustion conditions; incapability to determine condensable fraction of the particles, constituted of semi-volatile organic compounds (e.g. PAHs) [12]. In addition, standard measurements of emission factor for pellet stoves require steady state condition (SSC), defined as the stage in
G. Toscano et al. / Energy 68 (2014) 644e650
Abbreviations
645
Table 1 Experimental plan. Operating time/phase
CO PM PAH SSC USC IP Tgas DT DR TC EFPM EFPAH cPM/PAH QVDT Qmfuel HHV NHV Tx-y Tssc-y TEQ
carbon monoxide particulate matter polycyclic aromatic hydrocarbon steady state condition unsteady state condition ignition phase flue gas temperature dilution tunnel dilution ratio total carbon particulate matter emission factor polycyclic aromatic hydrocarbon emission factor concentration of PM/PAH measured in dilution tunnel volumetric gas flow in dilution tunnel (dry and normalized at 0 C) mass flow feeding pellet higher heating value net heating value combustion test of (x) hour operating time with (y) pellet type combustion test in steady state condition with (y) pellet type toxic equivalency
the flue gas when temperature does not change more than 5 K, in accordance to UNI EN technical standard [13]. SSC is quite different from a realistic utilization by domestic user, where the stove works also in unsteady state conditions (USC), associated to low combustion temperature [14] that produces significantly high emissions [7,15]. In particular, USC are represented by ignition, transient and shut-down phases. In most of the real cases, domestic users make an irregular utilization of the pellet stove and the short operating time determines different combustion conditions from the standard measurements. Moreover, settings of the pellet stove are not optimized for the pellet employed, further increasing the emission factor. Therefore, this study aims at determining the emission factor differences between realistic conditions, representative of typical domestic users, and emissions measured in laboratory at standard conditions. In order to better simulate the real environmental impact of domestic pellet stove, emissions were sampled using a dilution tunnel (DT) [16], evaluating two different pellets and several operating times. 2. Materials and methods 2.1. Appliance, fuels and experimental procedures Combustion tests were performed with a top-feed pellet stove (mod. 6000AV, Caminetti Montegrappa), representative of small household heating devices, whose power is in the range not yet regulated by the Italian law [9]. The device is the same used in a previous work [17]: the fuel storage is embedded in the stove and wood pellets are supplied by a small auger screw to the burner. This is a cast iron cup with holes on the bottom for the passage of the combustion air that is driven by an electric fan. The combustion starts by an electrical resistance. An heat exchanger, placed along the hot flue gases path, transfers the heat to a secondary air flow responsible for the heating of the room where the device is installed.
Pellet
Ignition phase 1h 2h 4h 6h SSC
A
B
TIP-A T1-A T2-A T4-A T6-A TSSC-A
TIP-B T1-B T2-B T4-B T6-B TSSC-B
The purpose of these experiments was to simulate a realistic domestic utilization of the pellet stove by a generic user. For this reason, tests were performed with heating device fired employing two different type of commercial pellets (pellet A and pellet B) and several operating times (1, 2, 4 and 6 h). Furthermore, ignition phase and SSC were evaluated to make a comparison. Every test condition was repeated for three time, resulting in overall 24 combustion experiments as reported in Table 1. During tests, the stove was operated at partial load (around 5.5 kWfuel) in order to reproduce a more realistic utilization of the stove, since the system is usually not operating at nominal power. The operating heating power was calculated from pellets mass flow and their net heating values (NHVs). Both pellets were analyzed before starting the tests following the European technical standards. The physicalechemical parameters taken into account in this study and their standard references are shown in Table 2. A scheme of the experimental set up for emission measurement is shown in Fig. 1. The gas temperature (Tgas), the draught and the composition of flue gases as oxygen (O2) and CO were monitored continuously in the chimney of the pellet stove by a gas analyzer (mod. Vario Plus, MRU). The analyzer filters and cools down a portion of flue gases, to remove dust and moisture respectively, before sending the gas to electrochemical cells. In order to simulate ambient dilution conditions of the flue gases a DT was used. This system, built according to Gaegauf project [18], allows to sample both particles and PAHs for USC phases [12] and to measure condensable fraction of PM [19]. All the flue gases exiting from the stove chimney were collected in a cowl with ambient air and cooled by means of dilution. The mean dilution ratios (DRs), defined as the volumetric flows ratio between the diluted gases in DT and the flue gases from the stove, were set changing the speed of the extraction fan and maintained within the range of 10e15 for all the tests. The by-pass valve was regulated for
Table 2 Physicalechemical characterization of wood pellet and standard methods references. Where not specified the values are expressed on dry basis. Parameter
Unit
Standard
Instrument
Moisture content
%a
UNI EN 14774-2:2010
Ash content
%
Carbon Hydrogen Nitrogen Oxygen Higher heating value (HHV) Net heating value (NHV)
%
UNI EN 14775:2010 UNI EN 15104:2011
Forced ventilation oven (mod. M120-VF, MPM ISTRUMENTS) Muffle furnace (mod. ZA, PREDERI VITTORIO & FIGLI). Elemental Analyzer (mod. 2400 Series II CHNS/O System, PERKIN ELMER)
a
MJ kg1
UNI EN 14918:2010
Isoperibolic calorimeter (mod. C2000 basic, IKA)
The percentage is a mass fraction of the sample as received.
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Fig. 1. Experimental setup: 1) pellet stove; 2) flue gas collection cowl; 3) by-pass valve; 4) dilution tunnel; 5) Pitot tube and thermocouple; 6) dust sampling port (for complete combustion cycle); 7) dust sampling port (for ignition phase); 8) gas analyzer; 9) extraction fan.
each test to reduce the influence of DT suction on pellet stove chimney draught. 2.2. PM measurement Two dust samplings were executed simultaneously for each test: the complete combustion cycle and the ignition phase. The first one is considered the interval between the start and the end of the combustion process, corresponding to beginning and ending of the CO emission respectively. The second one is associated with the first 20 min of the cycle, characterized by a high CO peak, from the start of the combustion up to a lower steady CO level. In addition, PM measurements were performed also in SSC, in order to make a comparison with a standard laboratory measurement. Before starting the sampling, the stove was run for 1 h at the fixed power in order to achieve stable conditions of the system. The samplings of total PM were performed isokinetically in DT by means of automatic samplers (mod. Isostack Basic, TECORA) connected with titanium probes which were equipped with quartz microfiber filters without binder (47 mm, MK-360, MUNKTELL). A Pitot tube and a thermocouple were placed inside the DT to measure the velocity of diluted gases in every moment and sampling flow was automatically regulated during the test. Before reaching the pump, sampled gases were dried by low temperature and silica gel, used as desiccant. The temperature of diluted flue gases at the sampling point was maintained below 35 C. After thermal conditioning, which is performed at 500 C for at least 4 h, the filters were equilibrated in the desiccator with silica gel as desiccant for 24 h at ambient temperature before and after sampling. The total mass sampled was determined weighing the filter with an analytical balance (mod. Wax 110, ORMA, accuracy 0.01 mg), thereafter the filter samples were analyzed for total carbon (TC) and PAHs content. After PM determination, filters with dust were stored in dark at 20 C to prevent photodegradation and/or volatilization phenomena. To evaluate the background concentration, several blanks were taken in the DT, which were subtracted from the measured amount.
2.3. PM analyses After PM determination dust sampled was analyzed to measure PAHs and TC content. For this purpose each sample filter with dust was cut exactly in half. 2.3.1. PAHs measurements To extract the PAHs from the particulate fraction, organic solvent extraction and ultrasounds have been used following method similar to that reported in Ref. [17]. Half filter was sonicated twice with 3 mL of dichloromethane (assay 99.5%, PANREAC). The product was filtered using a 0.2 mm regenerated cellulose filter (Phenex e RC, Phenomenex) and 0.05 mg of a deuterated internal standards was added. The compounds used as the internal standards were: naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysened12, and perylene-d12 (PAH-Mix 24, Dr. Ehrenstorfer GmbH). The solvent was evaporated by a low flow of nitrogen and 500 mL of hexane (assay 99.0%, PANREAC) were added. The extracts obtained were analyzed by GCeMS (mod. Clarus 600 S, PERKIN ELMER). To identify and quantify the 16 PAHs investigated (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b] Table 3 Results of physicalechemical characterization of wood pellets. Where not specified the values are expressed on dry basis. Parameter
Unit
Pellet A
Pellet B
Wood typea Moisture content Ash content Carbon Hydrogen Nitrogen Oxygen Higher heating value Net heating value
e %b % % % % % MJ kg1 MJ kg1
Beech 7.0 0.9 50.8 5.7 0.1 42.5 19.56 16.89
Spruce 6.8 0.2 50.8 7.0 0.1 42.0 19.44 16.58
a b
As declared by producer. The percentage is a mass fraction of the sample as received.
G. Toscano et al. / Energy 68 (2014) 644e650
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Fig. 2. Trend of Tgas (red), CO (black) and O2 (blue) for pellet A (T6-A) (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
Fig. 3. Trend of Tgas (red), CO (black) and O2 (blue) for pellet B (T6-B) (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno [1,2,3-cd]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]perylene) a standard mixture was used (PAH-Mix 9, Dr. Ehrenstorfer GmbH). The GCeMS was equipped with a cold on-column injector, a 0.53 mm ID pre-column and an Rxi 5 Sil-MS capillary column (30 m 0.32 mm ID 0.25 mm film thickness, RESTEK). The initial oven temperature of 55 C (2 min) was increased by 15 C min1 until 220 C, then by 2 C min1 until 240 C, and by 15 C min1 up to 300 C, where it was held for 15 min. The initial injector temperature of 60 C (2 min) was increased by 15 C min1 to 235 C, where it was held for 10 min, then by 15 C min1 to 305 C, where it was held until the end of the analysis. The transfer line and source temperatures were maintained at 280 and 230 C respectively. High purity helium at a constant flow of 1.5 mL min1 was used as carrier
gas. The mass selective detector was operated in Selected Ion-Full Ion (SIFI) mode: a Total Ion Current (TIC) acquisition was combined with a Selected Ion Monitoring (SIM) acquisitions. Analytes were identified in different ways: (i) by comparing total mass spectra with the National Institute of Standards and Technology (NIST) library; (ii) by comparing mass spectra with the mass spectra of pure PAHs; and (iii) by measuring the relative intensity of the qualifier fragments obtained in SIM mode. The target compounds were quantified in SIM mode. The toxicity of PAHs mixture was assessed as reported in a previous study [17] using the toxicity equivalency factors (TEF) [20] that assign to each single PAH a reference value for toxicity.
Table 4 Results of CO and Tgas for combustion tests. Tgas, C
CO; mg m3 n
Mean
Mean
Peak valuea
Pellet A T1-A T2-A T4-A T6-A TSSC-A
98.9 118.4 127.0 122.7 136.8
1000 844 758 897 811
5693 4228 3528 3897 3192
Pellet B T1-B T2-B T4-B T6-B TSSC-B
109.3 128.9 131.4 136.7 137.9
457 309 264 256 198
3327 2665 3605 2988 1120
a
Maximum of CO.
Fig. 4. EFPM versus operating time for pellet A combustion tests. EFPM for SSC are defined within two dotted lines. IP: ignition phase. Values with different letters are significantly different for p 0.05.
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Fig. 5. EFPM versus operating time for pellet B combustion tests. EFPM for SSC are defined within two dotted lines. IP: ignition phase. Values with different letters are significantly different for p 0.05.
2.3.2. TC measurement TC content was measured on sampled dust using a carbon analyzer equipped with a module for solids analysis (mod. TOCVCPH þ SSM-5000A, SHIMADZU) as reported in other works [21,22]. Half quartz filter was oxidized at 900 C with ultrapure oxygen (0.5 L min1 at 20 C). In these conditions all carbon was converted in carbon dioxide and quantified by infrared detector. Preliminary analyses were performed to determine the carbon content from carbonates on sampled particles, obtained following the same procedure for TC but at 250 C with the addition of phosphoric acid (assay 85.0%, BERND KRAFT GmbH). It was observed that the carbonate fraction was negligible. 2.4. Emission calculation The emission factors for PM (EFPM) and PAHs (EFPAH) were calculated in relation to the stove energy input as well as in relation to the amount of fuel used [23]. EFs were calculated using the equation below: EFPM/PAH ¼ (cPM/PAH$QVDT)/(Qmfuel$NHV) where cPM/PAH is the emission concentration of PM or PAH measured in DT, QVDT is the dry volumetric gas flow in DT normalized at 0 C, Qmfuel is the mass flow feeding pellet and NHV
Fig. 6. EFPAH versus operating time for pellet A combustion tests.
is the net heating value of the tested pellets. Qmfuel was determined for each pellet weighing the fuel supplied from the stove at the same device conditions of the experiments. One-way analysis of variance (ANOVA) was performed using Minitab. Means separation was achieved using Tukey test at the 0.05-probability level. 3. Results and discussion The analyses of the pellet used for combustion tests are shown in Table 3. The properties of the two pellets are in line with the pellet characteristic in the Italian market as reported in other study [2]. The main difference between the two biofuels concerns the ash content, resulting in 0.9% and 0.2% for pellets A and B respectively. With regard to gas emission analysis, the trends of CO in the combustion gases and their temperatures are shown in Figs. 2 and 3 for test with pellets A and B. For both products, high concentrations of CO are measured in ignition and shutdown phases. In each combustion cycle test the maximum CO value is always associated with the ignition phase, reaching concentration over to 5000 mg m3 n (Table 4). SSC begins after about 1 h of stove operation time as can be seen from the trend of the Tgas values. During this phase, CO shows a more steady trend with a less variability for pellet B than pellet A. This different behavior is a consequence of the not optimized setting of the combustion device just as occurs in a real domestic utilization where the user cannot choose the right setting of the
Table 5 Results of TC carried out on particulate emitted from combustion tests. Test
TC (%)
Pellet A TIP-A T1-A T2-A T4-A T6-A TSSC-A
40.5 33.4 26.3 24.7 23.5 23.1
Pellet B TIP-B T1-B T2-B T4-B T6-B TSSC-B
78.3 76.2 66.3 62.0 59.1 59.0
Fig. 7. EFPAH versus operating time for pellet B combustion tests.
G. Toscano et al. / Energy 68 (2014) 644e650 Table 6 Results for TEQ calculated for particulate emitted from combustion tests. Test
TEQ (mg MJ1)
Pellet A TIP-A T1-A T2-A T4-A T6-A TSSC-A
88.71 78.84 18.19 0.64 1.78 1.65
Pellet B TIP-B T1-B T2-B T4-B T6-B TSSC-B
68.59 41.70 11.10 3.87 4.07 3.75
device. The stove setting employed in this research context would seems more appropriate for the combustion of pellet B. In all the complete combustion cycle tests CO mean values tend to decrease with increasing in operating time, although they are always higher than those measured for TSSC. These results show that shorter operating time of the stove is more affected by the emission of products of incomplete combustion, mainly emitted during the ignition phase. More in particular, comparing the values of CO measured in 1 h stove operating time (T1-A and T1-B) and in TSSC there is a difference around 23% and 131% for test with pellets A and B respectively. With regard to the EFPMs, shown in Figs. 4 and 5, results for both pellets highlight that the highest values are reached during the ignition phase. Similarly to the CO trends, this parameter tends to decrease with increasing in stove operating time. Only after 6 h (T6A and T6-B) the EFPM is not significantly different from EFPM measured in the SSC. The interval defined by the two dotted lines represents the mean values plus and minus three times standard deviation. The differences between EFPM for 1 h stove operating time and SSC are 76 mg MJ1 for T1-A and 32 mg MJ1 for T1-B, corresponding to 72% and 53% more than EFPM in TSSC respectively. As considered for the trend of the CO, the high EFPM emission during the ignition phase affects the EFPM of the combustion cycle test even more with decreasing operating time. Also TC value (Table 5) tends to reduce with the increasing operating time and shows high value during the ignition phase. This result suggests, also considering the CO trend, that ignition phase and USC which occur during the first hour, are associated to low combustion efficiencies and poor oxidation of the fuel organic fraction. These conditions determine high emission of incomplete combustion products, i.e. CO, hydrocarbons and carbonaceous soot particles [19]. This is confirmed by PAHs results reported in Figs. 6 and 7 showing high emissions during ignition phase and short operating times. In particular, values of EFPAH for T1-A, T1-B are more of 10-times higher than EFPAH for TSSC-A and TSSC-B respectively. However, referring to the toxicity of PAHs expressed as TEQ, the values are significantly lower especially during the ignition phase (Table 6). Moreover, it can be seen a significant reduction of TEQ from 1 to 6 h operating time, corresponding to a value from 10 to 45-times lower for pellets B and A respectively. The TEQ reduction from 1 to 4 h operating is similar. Differences in combustion behavior and emission between pellets A and B depend in particular on the same stove settings applied to both pellet types. This condition usually occurs in real
649
utilization of the domestic stoves where the user cannot tune the device for each type of pellet. 4. Conclusions The paper shows that wood pellet stoves operating under realistic conditions produce significantly higher emissions than those measured in SSC according to technical standard requirements. In particular, referring to the EFPM, the emission increases up to 72% with respect to those measured during TSSC. This is caused by higher emissions produced during USC phases, in particular the ignition phase, associated to lower combustion efficiencies, characterized by low temperatures and very high level of CO and PAHs emission. These phases significantly affect the emission factor when the pellet stove works for short time. After 4 h operating time the emissions decrease at acceptable levels, as evident for TEQ. This aspect is very important because these pellet stoves with limited power are likely to be operated only for short time intervals. Therefore, in order to improve the evaluation of the environmental impact of wood pellet stoves, it would appear significant to carry out combustion tests not just following technical standard procedures, but also considering the complete combustion cycle for several operating times of the stove, setting measurements by DT, as outlined in this paper. References [1] Williams A, Jones JM, Ma L, Pourkashanian M. Pollutants from the combustion of solid biomass fuels. Prog Energy Combust 2012;38(2):113e37. [2] Toscano G, Riva G, Foppa Pedretti E, Corinaldesi F, Mengarelli C, Duca D. Investigation on wood pellet quality and relationship between ash content and the most important chemical elements. Biomass Bioenergy 2013;56(0): 317e22. [3] Mobini M, Sowlati T, Sokhansanj S. A simulation model for the design and analysis of wood pellet supply chains. Appl Energy 2013;111(0):1239e49. [4] Hiegl W, Janssen R. Development and promotion of a transparent European pellets market. Creation of a European real-time pellets atlas. Pellet market overview report EUROPE. Intelligent Energy Europe; 2009. [5] Goh CS, Junginger M, Cocchi M, Marchal D, Thrän D, Hennig C, et al. Wood pellet market and trade: a global perspective. Biofuel Bioprod Biorefin 2013;7(1):24e42. [6] Cocchi M, Nikolaisen L, Junginger M, Goh CS, Heinimö J, Bradley D, et al. Global wood pellet industry market and trade study. IEA Bioenergy; 2011. [7] Win KM, Persson T, Bales C. Particles and gaseous emissions from realistic operation of residential wood pellet heating systems. Atmos Environ 2012;59(0):320e7. [8] Commodore AA, Hartinger SM, Lanata CF, Mäusezahl D, Gil AI, Hall DB, et al. A pilot study characterizing real time exposures to particulate matter and carbon monoxide from cookstove related woodsmoke in rural Peru. Atmos Environ 2013;79(0):380e4. [9] DLgs 152. Norme in materia ambientale [Environmental Regulations]; 2006 [in Italian]. [10] Marche Region, 2012. Contingent measures for the reduction of pollutants in atmosphere air in the A municipalities Zone, referred to DACR 52/07. [11] ARPA Lombardia [Internet] INEMAR e INventario di EMissioni in ARia (Air Emission Inventory) [cited 2014 Jan 20]. Available from: http://www.inemar.eu. [12] Boman C, Nordin A, Westerholm R, Pettersson E. Evaluation of a constant volume sampling setup for residential biomass fired appliancesdinfluence of dilution conditions on particulate and PAH emissions. Biomass Bioenergy 2005;29(4):258e68. [13] UNI EN 14785:2006 (from EN 14785). Apparecchi per il riscaldamento domestico alimentati con pellet di legno e Requisiti e metodi di prova (Residential space heating appliances fired by wood pellets. Requirements and test methods). [14] Khan AA, de Jong W, Jansens PJ, Spliethoff H. Biomass combustion in fluidized bed boilers: potential problems and remedies. Fuel Process Technol 2009;90(1):21e50. [15] Persson T, Fiedler F, Nordlander S, Bales C, Paavilainen J. Validation of a dynamic model for wood pellet boilers and stoves. Appl Energy 2009;86(5): 645e56. [16] Wong CP, Chan TL, Leung CW. Characterisation of diesel exhaust particle number and size distributions using mini-dilution tunnel and ejectorediluter measurement techniques. Atmos Environ 2003;37(31):4435e46. [17] Riva G, Pedretti EF, Toscano G, Duca D, Pizzi A. Determination of polycyclic aromatic hydrocarbons in domestic pellet stove emissions. Biomass Bioenergy 2011;35(10):4261e7.
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[18] Gaegauf C, Griffin T. Vorschlag einer europäischen staubmessnorm für feststoff-feuerstätten Ausarbeitung und untersuchung eines typenprüf-messverfahrens für staubemissionen. Report No.: 101655. Bern (CH): Bundesamt für Energie (BFE); 2007. [19] Boman C, Er Pettersson, Westerholm R, Boström D, Nordin A. Stove performance and emission characteristics in residential wood log and pellet combustion, part 1: pellet stoves. Energy Fuels 2011;25(1):307e14. [20] Nisbet ICT, LaGoy PK. Toxic equivalency factors (TEFs) for polycyclic aromatic hydrocarbons (PAHs). Regul Toxicol Pharm 1992;16(3):290e300.
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Emission from realistic utilization of wood pellet stove G. Toscano a, D. Duca a, A. Amato b, A. Pizzi a, * a b
Dipartimento di Scienze Agrarie, Alimentari ed Ambientali (D3A), Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona (AN), Italy Dipartimento di Scienze della Vita e dell’Ambiente (DISVA), Università Politecnica delle Marche, Via Brecce Bianche, 60131 Ancona (AN), Italy
a r t i c l e i n f o
a b s t r a c t
Article history: Received 16 October 2013 Received in revised form 28 January 2014 Accepted 30 January 2014 Available online 20 February 2014
The Italian market of wood pellet and stoves is increasing quickly as, at the same time, the concerns about the particulate matter (PM) and gas emission products. Therefore, the assessment of their environmental impact is becoming an important issue. However, the emission factor from pellet stove measured according to technical standards does not provide representative data with respect to a real domestic utilization. This difference is a consequence of different operation and combustion conditions as well as the exclusion of unsteady state phases (e.g. ignition phase) from the standard measurement. In this study combustion tests were carried out simulating domestic utilization conditions of a pellet stove and a sampling methodology more representative of the real environmental impact of these devices. Higher concentration of PM, up to 72% more than those measured in steady state condition, was shown. A higher emission factor has been observed also for carbon monoxide (CO), total carbon (TC) and polycyclic aromatic hydrocarbons (PAHs) especially during unsteady combustion phases (e.g. ignition phase) which significantly affect the emission factor in particular when the pellet stove works for short time (less than 2 h). Ó 2014 Elsevier Ltd. All rights reserved.
Keywords: Wood pellet Combustion Pellet stove Particulate matter Polycyclic aromatic hydrocarbons Emission factor
1. Introduction There is an expanding market in the use of biomass [1], especially wood pellet that has become an important worldwide fuel during the recent years [2]. Total global consumption of wood pellets in 2011 was 14.4 million tonnes, from which about 80% were consumed in Europe [3]. In Italy the consumption of wood pellet has increased steadily over the last years, rising from 150 tonnes in 2001 [4] up to 1.4 million tonnes in 2010 [5,6] representing one of the most important market in Europe. In Italy wood pellets are predominantly used in residential applications such as boilers and stoves [2]. The prevailing pellet appliances in residential applications are pellet stoves and Italy has become the biggest pellet stove market in Europe, with an estimate of 700 000 units sold until 2009 [2,4]. Emission from residential wood combustion has been considered as a major contributor to ambient air pollution [7]. Household air pollution from incomplete combustion contains health-damaging pollutants such as carbon monoxide (CO),
* Corresponding author. E-mail addresses: [email protected] (G. Toscano), [email protected] (D. Duca), [email protected] (A. Amato), [email protected] (A. Pizzi). http://dx.doi.org/10.1016/j.energy.2014.01.108 0360-5442/Ó 2014 Elsevier Ltd. All rights reserved.
particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) [8]. Small domestic heating system (<35 kWth) are not regulated by national legislation [9], however, some administration are taking action. An example is Committee Resolution 1282/12 of Marche Region that prohibits the use of solid biomass domestic heating systems when they do not fulfill quality standards for emissions and pellet [10]. This measure is the consequence of an assessment carried out by the Marche Region organism based on the estimated regional pellet consumption and emission factors taken from national database INEMAR obtained by standard measurements [11]. Anyway, the assessment of the real emission factors for residential pellet heating systems is an important living matter because they are often different from measurement performed by technical standards, as stated by Win [7] which focuses on the CO and total organic carbon (TOC) parameters. There is a similar issue for PM determination, where the samplings are traditionally performed inside the chimney in hot (e.g. 150e200 C) raw flue gases. This approach suffers from several drawbacks such as: difficulty to fulfill a isokinetic sampling, especially in transient combustion conditions; incapability to determine condensable fraction of the particles, constituted of semi-volatile organic compounds (e.g. PAHs) [12]. In addition, standard measurements of emission factor for pellet stoves require steady state condition (SSC), defined as the stage in
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Abbreviations
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Table 1 Experimental plan. Operating time/phase
CO PM PAH SSC USC IP Tgas DT DR TC EFPM EFPAH cPM/PAH QVDT Qmfuel HHV NHV Tx-y Tssc-y TEQ
carbon monoxide particulate matter polycyclic aromatic hydrocarbon steady state condition unsteady state condition ignition phase flue gas temperature dilution tunnel dilution ratio total carbon particulate matter emission factor polycyclic aromatic hydrocarbon emission factor concentration of PM/PAH measured in dilution tunnel volumetric gas flow in dilution tunnel (dry and normalized at 0 C) mass flow feeding pellet higher heating value net heating value combustion test of (x) hour operating time with (y) pellet type combustion test in steady state condition with (y) pellet type toxic equivalency
the flue gas when temperature does not change more than 5 K, in accordance to UNI EN technical standard [13]. SSC is quite different from a realistic utilization by domestic user, where the stove works also in unsteady state conditions (USC), associated to low combustion temperature [14] that produces significantly high emissions [7,15]. In particular, USC are represented by ignition, transient and shut-down phases. In most of the real cases, domestic users make an irregular utilization of the pellet stove and the short operating time determines different combustion conditions from the standard measurements. Moreover, settings of the pellet stove are not optimized for the pellet employed, further increasing the emission factor. Therefore, this study aims at determining the emission factor differences between realistic conditions, representative of typical domestic users, and emissions measured in laboratory at standard conditions. In order to better simulate the real environmental impact of domestic pellet stove, emissions were sampled using a dilution tunnel (DT) [16], evaluating two different pellets and several operating times. 2. Materials and methods 2.1. Appliance, fuels and experimental procedures Combustion tests were performed with a top-feed pellet stove (mod. 6000AV, Caminetti Montegrappa), representative of small household heating devices, whose power is in the range not yet regulated by the Italian law [9]. The device is the same used in a previous work [17]: the fuel storage is embedded in the stove and wood pellets are supplied by a small auger screw to the burner. This is a cast iron cup with holes on the bottom for the passage of the combustion air that is driven by an electric fan. The combustion starts by an electrical resistance. An heat exchanger, placed along the hot flue gases path, transfers the heat to a secondary air flow responsible for the heating of the room where the device is installed.
Pellet
Ignition phase 1h 2h 4h 6h SSC
A
B
TIP-A T1-A T2-A T4-A T6-A TSSC-A
TIP-B T1-B T2-B T4-B T6-B TSSC-B
The purpose of these experiments was to simulate a realistic domestic utilization of the pellet stove by a generic user. For this reason, tests were performed with heating device fired employing two different type of commercial pellets (pellet A and pellet B) and several operating times (1, 2, 4 and 6 h). Furthermore, ignition phase and SSC were evaluated to make a comparison. Every test condition was repeated for three time, resulting in overall 24 combustion experiments as reported in Table 1. During tests, the stove was operated at partial load (around 5.5 kWfuel) in order to reproduce a more realistic utilization of the stove, since the system is usually not operating at nominal power. The operating heating power was calculated from pellets mass flow and their net heating values (NHVs). Both pellets were analyzed before starting the tests following the European technical standards. The physicalechemical parameters taken into account in this study and their standard references are shown in Table 2. A scheme of the experimental set up for emission measurement is shown in Fig. 1. The gas temperature (Tgas), the draught and the composition of flue gases as oxygen (O2) and CO were monitored continuously in the chimney of the pellet stove by a gas analyzer (mod. Vario Plus, MRU). The analyzer filters and cools down a portion of flue gases, to remove dust and moisture respectively, before sending the gas to electrochemical cells. In order to simulate ambient dilution conditions of the flue gases a DT was used. This system, built according to Gaegauf project [18], allows to sample both particles and PAHs for USC phases [12] and to measure condensable fraction of PM [19]. All the flue gases exiting from the stove chimney were collected in a cowl with ambient air and cooled by means of dilution. The mean dilution ratios (DRs), defined as the volumetric flows ratio between the diluted gases in DT and the flue gases from the stove, were set changing the speed of the extraction fan and maintained within the range of 10e15 for all the tests. The by-pass valve was regulated for
Table 2 Physicalechemical characterization of wood pellet and standard methods references. Where not specified the values are expressed on dry basis. Parameter
Unit
Standard
Instrument
Moisture content
%a
UNI EN 14774-2:2010
Ash content
%
Carbon Hydrogen Nitrogen Oxygen Higher heating value (HHV) Net heating value (NHV)
%
UNI EN 14775:2010 UNI EN 15104:2011
Forced ventilation oven (mod. M120-VF, MPM ISTRUMENTS) Muffle furnace (mod. ZA, PREDERI VITTORIO & FIGLI). Elemental Analyzer (mod. 2400 Series II CHNS/O System, PERKIN ELMER)
a
MJ kg1
UNI EN 14918:2010
Isoperibolic calorimeter (mod. C2000 basic, IKA)
The percentage is a mass fraction of the sample as received.
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Fig. 1. Experimental setup: 1) pellet stove; 2) flue gas collection cowl; 3) by-pass valve; 4) dilution tunnel; 5) Pitot tube and thermocouple; 6) dust sampling port (for complete combustion cycle); 7) dust sampling port (for ignition phase); 8) gas analyzer; 9) extraction fan.
each test to reduce the influence of DT suction on pellet stove chimney draught. 2.2. PM measurement Two dust samplings were executed simultaneously for each test: the complete combustion cycle and the ignition phase. The first one is considered the interval between the start and the end of the combustion process, corresponding to beginning and ending of the CO emission respectively. The second one is associated with the first 20 min of the cycle, characterized by a high CO peak, from the start of the combustion up to a lower steady CO level. In addition, PM measurements were performed also in SSC, in order to make a comparison with a standard laboratory measurement. Before starting the sampling, the stove was run for 1 h at the fixed power in order to achieve stable conditions of the system. The samplings of total PM were performed isokinetically in DT by means of automatic samplers (mod. Isostack Basic, TECORA) connected with titanium probes which were equipped with quartz microfiber filters without binder (47 mm, MK-360, MUNKTELL). A Pitot tube and a thermocouple were placed inside the DT to measure the velocity of diluted gases in every moment and sampling flow was automatically regulated during the test. Before reaching the pump, sampled gases were dried by low temperature and silica gel, used as desiccant. The temperature of diluted flue gases at the sampling point was maintained below 35 C. After thermal conditioning, which is performed at 500 C for at least 4 h, the filters were equilibrated in the desiccator with silica gel as desiccant for 24 h at ambient temperature before and after sampling. The total mass sampled was determined weighing the filter with an analytical balance (mod. Wax 110, ORMA, accuracy 0.01 mg), thereafter the filter samples were analyzed for total carbon (TC) and PAHs content. After PM determination, filters with dust were stored in dark at 20 C to prevent photodegradation and/or volatilization phenomena. To evaluate the background concentration, several blanks were taken in the DT, which were subtracted from the measured amount.
2.3. PM analyses After PM determination dust sampled was analyzed to measure PAHs and TC content. For this purpose each sample filter with dust was cut exactly in half. 2.3.1. PAHs measurements To extract the PAHs from the particulate fraction, organic solvent extraction and ultrasounds have been used following method similar to that reported in Ref. [17]. Half filter was sonicated twice with 3 mL of dichloromethane (assay 99.5%, PANREAC). The product was filtered using a 0.2 mm regenerated cellulose filter (Phenex e RC, Phenomenex) and 0.05 mg of a deuterated internal standards was added. The compounds used as the internal standards were: naphthalene-d8, acenaphthene-d10, phenanthrene-d10, chrysened12, and perylene-d12 (PAH-Mix 24, Dr. Ehrenstorfer GmbH). The solvent was evaporated by a low flow of nitrogen and 500 mL of hexane (assay 99.0%, PANREAC) were added. The extracts obtained were analyzed by GCeMS (mod. Clarus 600 S, PERKIN ELMER). To identify and quantify the 16 PAHs investigated (naphthalene, acenaphthylene, acenaphthene, fluorene, phenanthrene, anthracene, fluoranthene, pyrene, benzo[a]anthracene, chrysene, benzo[b] Table 3 Results of physicalechemical characterization of wood pellets. Where not specified the values are expressed on dry basis. Parameter
Unit
Pellet A
Pellet B
Wood typea Moisture content Ash content Carbon Hydrogen Nitrogen Oxygen Higher heating value Net heating value
e %b % % % % % MJ kg1 MJ kg1
Beech 7.0 0.9 50.8 5.7 0.1 42.5 19.56 16.89
Spruce 6.8 0.2 50.8 7.0 0.1 42.0 19.44 16.58
a b
As declared by producer. The percentage is a mass fraction of the sample as received.
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Fig. 2. Trend of Tgas (red), CO (black) and O2 (blue) for pellet A (T6-A) (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
Fig. 3. Trend of Tgas (red), CO (black) and O2 (blue) for pellet B (T6-B) (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).
fluoranthene, benzo[k]fluoranthene, benzo[a]pyrene, indeno [1,2,3-cd]pyrene, dibenzo[a,h]anthracene, benzo[g,h,i]perylene) a standard mixture was used (PAH-Mix 9, Dr. Ehrenstorfer GmbH). The GCeMS was equipped with a cold on-column injector, a 0.53 mm ID pre-column and an Rxi 5 Sil-MS capillary column (30 m 0.32 mm ID 0.25 mm film thickness, RESTEK). The initial oven temperature of 55 C (2 min) was increased by 15 C min1 until 220 C, then by 2 C min1 until 240 C, and by 15 C min1 up to 300 C, where it was held for 15 min. The initial injector temperature of 60 C (2 min) was increased by 15 C min1 to 235 C, where it was held for 10 min, then by 15 C min1 to 305 C, where it was held until the end of the analysis. The transfer line and source temperatures were maintained at 280 and 230 C respectively. High purity helium at a constant flow of 1.5 mL min1 was used as carrier
gas. The mass selective detector was operated in Selected Ion-Full Ion (SIFI) mode: a Total Ion Current (TIC) acquisition was combined with a Selected Ion Monitoring (SIM) acquisitions. Analytes were identified in different ways: (i) by comparing total mass spectra with the National Institute of Standards and Technology (NIST) library; (ii) by comparing mass spectra with the mass spectra of pure PAHs; and (iii) by measuring the relative intensity of the qualifier fragments obtained in SIM mode. The target compounds were quantified in SIM mode. The toxicity of PAHs mixture was assessed as reported in a previous study [17] using the toxicity equivalency factors (TEF) [20] that assign to each single PAH a reference value for toxicity.
Table 4 Results of CO and Tgas for combustion tests. Tgas, C
CO; mg m3 n
Mean
Mean
Peak valuea
Pellet A T1-A T2-A T4-A T6-A TSSC-A
98.9 118.4 127.0 122.7 136.8
1000 844 758 897 811
5693 4228 3528 3897 3192
Pellet B T1-B T2-B T4-B T6-B TSSC-B
109.3 128.9 131.4 136.7 137.9
457 309 264 256 198
3327 2665 3605 2988 1120
a
Maximum of CO.
Fig. 4. EFPM versus operating time for pellet A combustion tests. EFPM for SSC are defined within two dotted lines. IP: ignition phase. Values with different letters are significantly different for p 0.05.
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Fig. 5. EFPM versus operating time for pellet B combustion tests. EFPM for SSC are defined within two dotted lines. IP: ignition phase. Values with different letters are significantly different for p 0.05.
2.3.2. TC measurement TC content was measured on sampled dust using a carbon analyzer equipped with a module for solids analysis (mod. TOCVCPH þ SSM-5000A, SHIMADZU) as reported in other works [21,22]. Half quartz filter was oxidized at 900 C with ultrapure oxygen (0.5 L min1 at 20 C). In these conditions all carbon was converted in carbon dioxide and quantified by infrared detector. Preliminary analyses were performed to determine the carbon content from carbonates on sampled particles, obtained following the same procedure for TC but at 250 C with the addition of phosphoric acid (assay 85.0%, BERND KRAFT GmbH). It was observed that the carbonate fraction was negligible. 2.4. Emission calculation The emission factors for PM (EFPM) and PAHs (EFPAH) were calculated in relation to the stove energy input as well as in relation to the amount of fuel used [23]. EFs were calculated using the equation below: EFPM/PAH ¼ (cPM/PAH$QVDT)/(Qmfuel$NHV) where cPM/PAH is the emission concentration of PM or PAH measured in DT, QVDT is the dry volumetric gas flow in DT normalized at 0 C, Qmfuel is the mass flow feeding pellet and NHV
Fig. 6. EFPAH versus operating time for pellet A combustion tests.
is the net heating value of the tested pellets. Qmfuel was determined for each pellet weighing the fuel supplied from the stove at the same device conditions of the experiments. One-way analysis of variance (ANOVA) was performed using Minitab. Means separation was achieved using Tukey test at the 0.05-probability level. 3. Results and discussion The analyses of the pellet used for combustion tests are shown in Table 3. The properties of the two pellets are in line with the pellet characteristic in the Italian market as reported in other study [2]. The main difference between the two biofuels concerns the ash content, resulting in 0.9% and 0.2% for pellets A and B respectively. With regard to gas emission analysis, the trends of CO in the combustion gases and their temperatures are shown in Figs. 2 and 3 for test with pellets A and B. For both products, high concentrations of CO are measured in ignition and shutdown phases. In each combustion cycle test the maximum CO value is always associated with the ignition phase, reaching concentration over to 5000 mg m3 n (Table 4). SSC begins after about 1 h of stove operation time as can be seen from the trend of the Tgas values. During this phase, CO shows a more steady trend with a less variability for pellet B than pellet A. This different behavior is a consequence of the not optimized setting of the combustion device just as occurs in a real domestic utilization where the user cannot choose the right setting of the
Table 5 Results of TC carried out on particulate emitted from combustion tests. Test
TC (%)
Pellet A TIP-A T1-A T2-A T4-A T6-A TSSC-A
40.5 33.4 26.3 24.7 23.5 23.1
Pellet B TIP-B T1-B T2-B T4-B T6-B TSSC-B
78.3 76.2 66.3 62.0 59.1 59.0
Fig. 7. EFPAH versus operating time for pellet B combustion tests.
G. Toscano et al. / Energy 68 (2014) 644e650 Table 6 Results for TEQ calculated for particulate emitted from combustion tests. Test
TEQ (mg MJ1)
Pellet A TIP-A T1-A T2-A T4-A T6-A TSSC-A
88.71 78.84 18.19 0.64 1.78 1.65
Pellet B TIP-B T1-B T2-B T4-B T6-B TSSC-B
68.59 41.70 11.10 3.87 4.07 3.75
device. The stove setting employed in this research context would seems more appropriate for the combustion of pellet B. In all the complete combustion cycle tests CO mean values tend to decrease with increasing in operating time, although they are always higher than those measured for TSSC. These results show that shorter operating time of the stove is more affected by the emission of products of incomplete combustion, mainly emitted during the ignition phase. More in particular, comparing the values of CO measured in 1 h stove operating time (T1-A and T1-B) and in TSSC there is a difference around 23% and 131% for test with pellets A and B respectively. With regard to the EFPMs, shown in Figs. 4 and 5, results for both pellets highlight that the highest values are reached during the ignition phase. Similarly to the CO trends, this parameter tends to decrease with increasing in stove operating time. Only after 6 h (T6A and T6-B) the EFPM is not significantly different from EFPM measured in the SSC. The interval defined by the two dotted lines represents the mean values plus and minus three times standard deviation. The differences between EFPM for 1 h stove operating time and SSC are 76 mg MJ1 for T1-A and 32 mg MJ1 for T1-B, corresponding to 72% and 53% more than EFPM in TSSC respectively. As considered for the trend of the CO, the high EFPM emission during the ignition phase affects the EFPM of the combustion cycle test even more with decreasing operating time. Also TC value (Table 5) tends to reduce with the increasing operating time and shows high value during the ignition phase. This result suggests, also considering the CO trend, that ignition phase and USC which occur during the first hour, are associated to low combustion efficiencies and poor oxidation of the fuel organic fraction. These conditions determine high emission of incomplete combustion products, i.e. CO, hydrocarbons and carbonaceous soot particles [19]. This is confirmed by PAHs results reported in Figs. 6 and 7 showing high emissions during ignition phase and short operating times. In particular, values of EFPAH for T1-A, T1-B are more of 10-times higher than EFPAH for TSSC-A and TSSC-B respectively. However, referring to the toxicity of PAHs expressed as TEQ, the values are significantly lower especially during the ignition phase (Table 6). Moreover, it can be seen a significant reduction of TEQ from 1 to 6 h operating time, corresponding to a value from 10 to 45-times lower for pellets B and A respectively. The TEQ reduction from 1 to 4 h operating is similar. Differences in combustion behavior and emission between pellets A and B depend in particular on the same stove settings applied to both pellet types. This condition usually occurs in real
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utilization of the domestic stoves where the user cannot tune the device for each type of pellet. 4. Conclusions The paper shows that wood pellet stoves operating under realistic conditions produce significantly higher emissions than those measured in SSC according to technical standard requirements. In particular, referring to the EFPM, the emission increases up to 72% with respect to those measured during TSSC. This is caused by higher emissions produced during USC phases, in particular the ignition phase, associated to lower combustion efficiencies, characterized by low temperatures and very high level of CO and PAHs emission. These phases significantly affect the emission factor when the pellet stove works for short time. After 4 h operating time the emissions decrease at acceptable levels, as evident for TEQ. This aspect is very important because these pellet stoves with limited power are likely to be operated only for short time intervals. Therefore, in order to improve the evaluation of the environmental impact of wood pellet stoves, it would appear significant to carry out combustion tests not just following technical standard procedures, but also considering the complete combustion cycle for several operating times of the stove, setting measurements by DT, as outlined in this paper. References [1] Williams A, Jones JM, Ma L, Pourkashanian M. Pollutants from the combustion of solid biomass fuels. Prog Energy Combust 2012;38(2):113e37. [2] Toscano G, Riva G, Foppa Pedretti E, Corinaldesi F, Mengarelli C, Duca D. Investigation on wood pellet quality and relationship between ash content and the most important chemical elements. Biomass Bioenergy 2013;56(0): 317e22. [3] Mobini M, Sowlati T, Sokhansanj S. A simulation model for the design and analysis of wood pellet supply chains. Appl Energy 2013;111(0):1239e49. [4] Hiegl W, Janssen R. Development and promotion of a transparent European pellets market. Creation of a European real-time pellets atlas. Pellet market overview report EUROPE. Intelligent Energy Europe; 2009. [5] Goh CS, Junginger M, Cocchi M, Marchal D, Thrän D, Hennig C, et al. Wood pellet market and trade: a global perspective. Biofuel Bioprod Biorefin 2013;7(1):24e42. [6] Cocchi M, Nikolaisen L, Junginger M, Goh CS, Heinimö J, Bradley D, et al. Global wood pellet industry market and trade study. IEA Bioenergy; 2011. [7] Win KM, Persson T, Bales C. Particles and gaseous emissions from realistic operation of residential wood pellet heating systems. Atmos Environ 2012;59(0):320e7. [8] Commodore AA, Hartinger SM, Lanata CF, Mäusezahl D, Gil AI, Hall DB, et al. A pilot study characterizing real time exposures to particulate matter and carbon monoxide from cookstove related woodsmoke in rural Peru. Atmos Environ 2013;79(0):380e4. [9] DLgs 152. Norme in materia ambientale [Environmental Regulations]; 2006 [in Italian]. [10] Marche Region, 2012. Contingent measures for the reduction of pollutants in atmosphere air in the A municipalities Zone, referred to DACR 52/07. [11] ARPA Lombardia [Internet] INEMAR e INventario di EMissioni in ARia (Air Emission Inventory) [cited 2014 Jan 20]. Available from: http://www.inemar.eu. [12] Boman C, Nordin A, Westerholm R, Pettersson E. Evaluation of a constant volume sampling setup for residential biomass fired appliancesdinfluence of dilution conditions on particulate and PAH emissions. Biomass Bioenergy 2005;29(4):258e68. [13] UNI EN 14785:2006 (from EN 14785). Apparecchi per il riscaldamento domestico alimentati con pellet di legno e Requisiti e metodi di prova (Residential space heating appliances fired by wood pellets. Requirements and test methods). [14] Khan AA, de Jong W, Jansens PJ, Spliethoff H. Biomass combustion in fluidized bed boilers: potential problems and remedies. Fuel Process Technol 2009;90(1):21e50. [15] Persson T, Fiedler F, Nordlander S, Bales C, Paavilainen J. Validation of a dynamic model for wood pellet boilers and stoves. Appl Energy 2009;86(5): 645e56. [16] Wong CP, Chan TL, Leung CW. Characterisation of diesel exhaust particle number and size distributions using mini-dilution tunnel and ejectorediluter measurement techniques. Atmos Environ 2003;37(31):4435e46. [17] Riva G, Pedretti EF, Toscano G, Duca D, Pizzi A. Determination of polycyclic aromatic hydrocarbons in domestic pellet stove emissions. Biomass Bioenergy 2011;35(10):4261e7.
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