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CO, NOx, PCDD/F and total particulate matter emissions from two small scale combustion appliances using agricultural biomass type test fuels Thomas Zeng, Justus von Sonntag, Nadja Weller, Andreas Pilz, Volker Lenz, and Michael Nelles Energy Fuels, Just Accepted Manuscript • Publication Date (Web): 20 Jun 2017 Downloaded from http://pubs.acs.org on June 21, 2017
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CO, NOx, PCDD/F and total particulate matter emissions from two small scale
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combustion appliances using agricultural biomass type test fuels
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Thomas Zeng a*; Justus von Sonntag a,b; Nadja Weller a; Andreas Pilz a; Volker Lenz a;
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Michael Nelles a,c
6 7 8 9 10 11
a
DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH, Torgauer Straße 116,
04347 Leipzig, Germany. b
Present address: Bubbles and Beyond GmbH, Karl-Heine-Straße 99, 04229 Leipzig,
Germany. c
Faculty of Agricultural and Environmental Sciences, Department of Waste and Resource
12
Management, University of Rostock, Justus-von-Liebig-Weg 6, 18059 Rostock, Germany.
13
* Corresponding author: phone: +49-341 2434-542, fax: +49-341 2434-133, e-mail:
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[email protected]
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Abstract
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In Germany, solid biomass fuels based on agricultural by-products are only used in marginal
19
amounts for small scale combustion. This is the consequence of several regulatory constraints,
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in particular requirements defined in the first ordinance of the German emission control act (1.
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BImSchV) including the mandatory utilization of dedicated licensed boilers for such fuels.
22
For the licensing, test fuels with defined fuel composition representing straw and cereal grain
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like fuels are demanded and strict emission thresholds have to be met both during type testing
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and during periodic chimney sweep measurements. To facilitate the market introduction of the
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first licensed boiler, agricultural biomass test fuels with characteristics being representative 1
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for the composition of these assortments were produced and utilized for combustion tests.
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Emission measurements (i.e. for CO, NOx, PCDD/F and total particulate matter) were
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performed by an accredited institute according to the relevant methods. It was demonstrated
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that test fuels with dedicated fuel composition can be produced in bench scale. The results
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prove that compliance with the strict emission thresholds of the 1. BImSchV in Germany can
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be realized even with challenging fuels if an appropriate boiler is combined with an efficient
32
dust separator. Accordingly, PCDD/F emission levels and toxicity almost as low as for wood
33
combustion were observed.
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Highlights
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For the first time, dedicated agricultural biomass type test fuels with characteristics
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representative for these non-woody biomass assortments were produced and employed for
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combustion tests and emission measurements which were performed by an accredited institute
39
according to the relevant methods.
40
The measurements during combustion tests with type test fuels verified compliance with the
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strict regulations of the 1. BImSchV for the combustion of agricultural fuels if an appropriate
42
boiler technology is combined with an efficient dust separator.
43 44
Keywords: straw, cereal grain, biomass, boiler, type test, emission, combustion, PCDD/F
45 46
Abbreviations
47
1. BImSchV: Erste Verordnung zur Durchführung des Bundes-Immissionsschutzgesetzes
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(first ordinance of the German emission control act); bld: below limit of detection; d.b.: dry
49
basis; DBFZ: DBFZ Deutsches Biomasseforschungszentrum gemeinnützige GmbH; DIN:
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Deutsches Institut für Normung e. V. (German standardization organization); DT: ash 2
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deformation temperature; EN: European standard; ENplus: wood pellets certification scheme
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ENplus; ESP: electrostatic precipitator; FF: fabric filter; FT: ash flow temperature; GHG:
53
greenhouse gas; HLMD: heat load control and measuring device; HPLC: high pressure liquid
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chromatography; HT: ash hemisphere temperature; I-TEQ: international toxic equivalent;
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ISO: International Organization for Standardization; LAI: Länderausschuss für
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Immissionsschutz (German federal committee for air pollution control); OCDD:
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octachlorodibenzodioxin; PCDD: polychlorinated dibenzodioxins; PCDD/F: polychlorinated
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dibenzodioxins and dibenzofurans; PCDF: polychlorinated dibenzofurans; Q: net calorific
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value; RF: reference fuel; SCR: selective catalytic reduction; SD: standard deviation; SNCR:
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selective non-catalytic reduction; SST: ash shrinkage temperature; STP: standard temperature
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and pressure; TF: test fuel; TPM: total particulate matter; uy,max: maximum measurement
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uncertainty; VDI: Verband der Deutschen Industrie (The Association of German Engineers);
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vol%: volume percent; VPAB8: Vollzugsempfehlung zur Prüfstandsmessung an Anlagen für
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Brennstoffe nach § 3 (1) Nr. 8 der 1. BImSchV (Recommendation for type tests for biomass
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fired boilers using fuels according to §3 (1) No. 8 of the 1. BImSchV); wt%: weight percent
66 67
1. Introduction
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There is a global consensus that the current ongoing climate change is a result of greenhouse
69
gas (GHG) emissions caused by human activity. 1 Accordingly, ambitious targets for global
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GHG reduction were set by the United Nations Climate Change Conference (Paris agreement)
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and ratified by 195 countries. 2 The long-term goal is to keep the increase in global average
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temperature to well below 2 K with respect to pre-industrial levels. 2 Consequently, Germany
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has to reduce GHG emissions until 2030 by 55 % and until 2040 by 70 % compared to the
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reference year 1990. 3 It is expected that a growing share in the energy mix will be provided
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by wind and solar power and that the heat demand for residential buildings will significantly 3
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decrease by 2050 (at least 40 %) based on a higher share of thermally well insulated
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buildings. 4 In the future, biomass could play an important role to compensate the fluctuating
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availability of wind and solar usage but as well to reduce GHG emissions and to secure
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energy supply. For a smart bioenergy in the heating sector, utilization of yet unexplored
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biomass residues and the application of efficient and low emission combustion technologies
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will be required. 5 In Germany, the generation of heat by using small scale appliances < 100
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kW is regulated by the first ordinance of the German emission control act (1. BImSchV)
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stating permitted fuels and emission thresholds. In this sector, wood fuels (i.e. log wood,
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wood chips and wood pellets) are the predominant biomass fuels. On local level, however,
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significant quantities of non-woody raw materials are available for heat production. 6 In the
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1.BImSchV, herbaceous biomass, i.e. straw, cereal whole plants, energy grains, grain
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processing residues, husks and similar assortments like miscanthus or hay are assigned to a
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specific class of biomass fuels, i.e. No. 8 fuels (according to §3 (1) No. 8 of the 1. BImSchV).
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7
For type testing and licensing of a dedicated boiler for such agricultural biomasses, strict
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emission thresholds for CO, NOx and PCDD/F have to be met. Furthermore, in contrast to
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woody biomasses, specific type test fuels are required. While there is consensus that high
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quality woody biomasses are close enough to each other in their combustion behavior to
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justify their classification as a single fuel class in the 1.BImSchV with no specific test fuel
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required, the case with herbaceous biomass is more complicated. Here it is well known that
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there is a wide span of fuel properties within the No. 8 fuels. Consequently, small scale
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combustion appliances can be operated well with low demanding representatives of the fuel
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class while utilization of more demanding fuels may result in high emission levels and
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operational problems. In Germany, this has caused considerable concern in the environmental
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protection bodies and the strict regulations and some uncertainties in the interpretation and
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implementation of these regulations so far hampered the use of unexplored agricultural by4
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products in small scale combustion appliances. The first obstacle is the insufficient definition
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of test fuel criteria since the DIN EN 303-5 only demands test fuels to be in accordance with
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the fuel requirements of the standard ISO 17225-6 for solid biofuels. 8,9 This bears the risk
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that test fuels with considerably better fuel properties than the average non-woody biomass
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could theoretically be used because DIN EN ISO 17225-6 only specifies upper limits for fuel
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properties. If such test fuels with better combustion and emission characteristics would be
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applied, the aim of boiler type tests according to DIN EN 303-5 could be undermined.
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Furthermore, high efforts and measurement costs (especially for PCDD/F) are expected in
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particular due to the regulatory need to test each boiler type with each possible fuel of No. 8
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group specified in the 1. BImSchV. Thus, licensed boilers are not available on the German
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market so far and appropriate guidelines for the boiler type tests were missing for several
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years after the last amendment of the 1. BImSchV in 2010. To overcome these constraints, the
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federal committee for air pollution control (Länderausschuss für Immissionsschutz, LAI) in
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Germany defined criteria for test fuels that must be used during boiler type tests. The LAI has
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published these criteria in the recommendation for type tests for biomass fired boilers using
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fuels according to § 3 (1) No. 8 of the 1. BImSchV (Vollzugsempfehlung zur
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Prüfstandsmessung an Anlagen für Brennstoffe nach § 3 (1) Nr. 8 der 1. BImSchV”, VPAB8).
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10
While the 1. BImSchV is rather general in its fuel definition, the VPAB8 specifies concrete
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biomass assortments that can be used as No. 8 fuels within three subgroups and demands test
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fuels with specifically defined characteristics for each of the three groups (Table 1):
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fuel group A: miscanthus, wheat straw, rye straw, barley straw, triticale straw, maize straw,
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linseed straw, spelt straw, hemp (fiber hemp and hemp straw) and flax,
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fuel group B: grains, cereal spilling, low quality cereal grains and bran (no rape or sunflowers
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seeds),
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fuel group AB: cereal whole plants, rape straw, landscape conservation hay, meadow hay, 5
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annual field grasses, maize spindles, sunflower straw, and hop.
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Licensing of a boiler for group A fuels would thus require the successful completion of the
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type testing with test fuel A (TF A). Accordingly, for licensing of a boiler for group B fuels,
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type testing would have to be performed with test fuel B (TF B) and for operation with group
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AB fuels both tests fuels have to be employed. VPAB8 lists minimum criteria rather than
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upper thresholds for certain characteristics of the test fuels (TF) in particular minimum
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content of ash, K, N and Cl as well as maximum ash deformation temperature (DT), Table 1.
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Net calorific value and water content are to be stated. The defined values were chosen so that
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the test fuels cover as far as possible the whole range of biomass composition for a certain
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fuel group and thus represent for all intents and purposes the worst critical fuel composition
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regarding the key fuel properties K, N, Cl and ash deformation temperature (DT). The
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successful type testing requires compliance with the emission thresholds defined by the 1.
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BImSchV (normalized to dry flue gas at standard temperature and pressure (STP) and related
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to 13 vol% O2) while operating with these test fuels: 7
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polychlorinated dibenzodioxins and dibenzofurans (PCDD/F): 0.1 ng/m³ (measured as
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2,3,7,8-polychlorinated dibenzodioxins and dibenzofurans which are stated as toxicological
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equivalents, I-TEQ),
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nitrogen oxides (NOx): 0.5 g/m3,
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carbon monoxide (CO): 0.25 g/m3.
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Additionally, periodic chimney sweep measurements are mandatory during full load boiler
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operation after installation. During these periodic chimney sweep measurements, emission
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thresholds of CO (0.4 g/m³) and total particulate matter (0.02 g/m³) have to be met. 7
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Published results for the combustion of non-woody biomass show that emission levels
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especially for NOx, PCDD/F and total particulate matter (TPM) are typically much higher
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compared to the use of high quality wood fuels during small scale combustion. 11–21 In some
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cases, the applicability of fuel pre-treatment such as leaching and mechanical dewatering 22–31,
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mixing with biomasses exhibiting less critical fuel composition (e.g. with wood, miscanthus
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or peat) 32–42 or adding of e.g. Al or Ca based additives 43,44 was demonstrated to be
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advantageous for emission reduction. In contrast, dust separators were scarcely applied during
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combustion of non-woody biomass fuels in small scale combustion appliances 45 and
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accordant standards for test methods for the determination of the efficiency of downstream
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dust separators 46 were just recently developed and published. The lack of suitable, approved
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agricultural biomass test fuels and uncertainties concerning their performance during type
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testing still hinders the licensing of the first boiler using agricultural fuels. The aim of this
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work is thus (i) to show a possible approach for the production of test fuels, (ii) to
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demonstrate that combustion of test fuels indeed would cause significantly higher emission
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levels than typical agricultural fuels and that the test fuel concept would thus be feasible and
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(iii) to prove that emission thresholds of 1. BImSchV can still be met by an appropriate
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combination of combustion technology with suitable secondary emission reduction measures.
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To reach this objective, combustion tests were conducted to identify feasible approaches for
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the production of type test fuels and to study the emission performance of these challenging
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test fuels. Consequently, the options to keep the strict emission thresholds for PCDD/F, CO,
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NOx and total particulate matter of the 1. BImSchV were investigated and challenges for the
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type testing will be highlighted. In this way, a successful type testing in Germany can help to
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overcome barriers for boiler type testing with non-woody biomass fuels and can be extended
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to type testing in other countries (especially in Europe).
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2 Experimental section
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2.1 Materials
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To identify appropriate raw materials for test fuel production, 13 raw materials for TF A and 7
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12 raw materials for TF B were purchased and analyzed. None of the raw materials fulfilled
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all criteria specified in the VPAB8, i.e. minimum content for ash, K, N, Cl and maximum ash
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deformation temperature (DT), thus showing that these criteria are indeed suitable to classify
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a fuel as “demanding”. Thus, for the production of the test fuels with the required properties
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(Table 1), mixtures of raw materials and additives had to be used. The following materials
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were employed for the test fuel production:
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wheat straw 1: Agrargenossenschaft Ilmtal e.G., Niedertrebra / Germany,
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wheat straw 2: GbR Klopfleisch, Niedertrebra / Germany,
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wheat grains: Thüringer Landesanstalt für Landwirtschaft, Dornburg / Germany,
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whole flour (type 1700): Aurora Mühlen GmbH, Hamburg / Germany,
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K2CO3: Overlack AG, Leipzig / Germany,
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CaCl2: CVM Chemie-Vertrieb GmbH & Co. KG, Magdeburg / Germany.
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Eventually, two test fuels, i.e. TF A1 and TF A2, were produced using a chaff cutter, of
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Hirlinger Landtechnik, for coarse grinding followed by fine grinding with a hammer mill of
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Netzsch-Condux Mahltechnik GmbH, type CHM 230/200. Mineral additives were used to
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reach the required TF A composition. For conditioning and admixing of the additives, a
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paddle mixer of Process Technologies GmbH, type RSX 550, was applied. Pelletizing was
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performed using a ring die press of Münch-Edelstahl GmbH, type RMP 250 with subsequent
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cooling and removing of fines < 3.15 mm. For the production of TF B1, wheat grains and
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bottom ash from the combustion of the very same wheat grain assortment was utilized. The
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bottom ash was ground using a Pulverisette 19 of Fritsch GmbH. Subsequently, the grinded
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bottom ash was admixed to the wheat grains by using the aforementioned paddle mixer. Since
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segregation turned out to be a serious issue, an additional fuel batch (i.e. TF B2) was
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produced using a granulation procedure with 35 wt% wheat flour and small amounts of water
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to ensure proper adhesion of the grain ash particles on the wheat grain surface. The required 8
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amount of additives of TF A production and grain ash for TF B production was calculated
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based on the average raw material composition. To compensate potential uncertainties from
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sampling, analysis and fuel production, a 10 % higher value than demanded by the VPAB8
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was targeted for the ash content and the elements K, N and Cl. As reference fuels (RF), wood
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pellets complying with ENplus class A1 47 (purchased from German Pellets GmbH, Torgau /
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Germany, RF WP), straw pellets produced from typical wheat straw (purchased from ABW
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Apoldaer Biomassewerk GmbH, Apolda / Germany, RF A) and wheat grains (purchased from
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TLL Thüringer Landesanstalt für Landwirtschaft, Jena / Germany, RF B) were used without
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any further fuel modification. RF A and RF B were employed to show whether typically
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available non-woody biomass fuels are characterized by lower emission levels compared to
211
the use of the test fuels with particularly challenging fuel characteristics. This is a crucial
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aspect to prove the applicability of the test fuel concept.
213 214
2.2 Combustion test benches
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As specified in the 1. BImSchV and the VPAB8, strict emission thresholds have to be met
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during type tests with dedicated test fuels according to DIN EN 303-5 both at full and part
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load. 7,9,10 However, since boiler operation with non-woody biomass fuels is typically at full
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load, emission measurements were performed only at this boiler operation state. Emission
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measurements during part load boiler operation were not within the scope of this work.
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Furthermore, for a boiler family with a nominal heat capacity < 100 kW and with the same
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constructional design, it is sufficient to perform type tests with the smallest and the largest
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boiler size of the boiler family if the ratio of the nominal heat output specified by the
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manufacturer of the largest to the smallest boiler is less than or equal to 2:1. 10 Thus,
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combustion tests were performed at full load using two boilers of the same boiler family from
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A.P. Bioenergietechnik, Hirschau / Germany with a nominal heat capacity of 49 kW 9
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(Ökotherm® Compact C0 boiler 1, located at laboratory of DBFZ) and 95 kW (Ökotherm®
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Compact C1L, boiler 2, located at head office of the boiler manufacturer). Both boilers are
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licensed according to DIN EN 303-5 for the operation with wood pellets and characterized by
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the same constructional design with a staged primary and secondary combustion air supply by
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two automatically adjusted air fans, Figure 1. The combustion chamber is water cooled and
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equipped with an ash slide enabling the combustion of ash rich fuels with increased slagging
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risk in the bottom ash. An electrostatic precipitator (ESP) which is officially certified in
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Germany was installed in the flue gas duct of boiler 1 to remove particulate matter from the
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flue gas. Furthermore, boiler 1 consists of a flue gas duct according to DIN EN 303-5
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upstream of the electrostatic precipitator and a flue gas duct according to DIN EN 13284-1
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(equivalent to the VDI 2066-1) downstream of the ESP. 9,48,49 Boiler 2 was equipped with an
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insulated fabric filter (FF) with a PTFE filter area of max. 12 m² suitable for a flue gas stream
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of up to 1600 m³/h and with a flue gas duct that complies with DIN EN 303-4. 50 Typically,
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the fabric filter was operated at roughly constant temperature < 150°C and flue gas humidity
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< 120 g/m³ STP during full load boiler operation. In both test benches, a chimney fan was
241
installed enabling continuous draught in the chimney.
242 243
2.3 Full load combustion tests
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Preliminary combustion tests were performed with each fuel to adjust boiler operation
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according to the specific requirements of the fuels aiming for (i) stable full load boiler
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operation at nominal heat output with (ii) low CO and NOx emissions, (iii) minimized slag
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formation in the bottom ash and (iv) sufficient ash removal into the ash pan. For requirement
248
(i), a heat load control and measuring device (HLMD) was installed to allow for boiler
249
operation at full load. The HLMD is equipped with resistance thermometer (Pt100 RM, type
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RL-10060, limiting deviation of 0.2 %) and a magneto-inductive flowmeter (Promag 53P, 10
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accuracy of 0.2 %) to continuously determine and adjust inlet and return temperature as well
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as the volume flow of water stream. Subsequently, these HLMD measurement results were
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used for calculation of the heat output of the boiler. To sufficiently fulfill requirements (ii),
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(iii) and (iv), adjustments of the primary and secondary air supply as well as fuel supply and
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operation of the ash slide were employed. The optimized boiler operation parameters were
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employed for further combustion tests. At stable boiler operation, emission data were
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recorded over a period of approximately 6 hours per combustion test without further
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adjustments in the boiler control. Typically, four combustion tests were performed for each
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fuel: three to determine three PCDD/F values and at least three NOx values and one further
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combustion test to measure TPM emissions. In all combustion tests O2 and CO emissions
261
were continuously recorded in parallel to acquire at least three mean values. Unless otherwise
262
stated, all gaseous and particulate emissions were normalized to dry flue gas at standard
263
temperature and pressure (STP) and related to 13 vol% O2. All emission values are stated
264
excluding measurement uncertainties. Maximum measurement uncertainties are stated
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separately where appropriate. When the boiler was completely cooled down, the bottom ash
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was removed and the primary and secondary combustion chamber and the heat exchanger
267
were cleaned thoroughly with an industrial vacuum cleaner. Polishing of adhering surface
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layers from the heat exchanger surface was avoided. Likewise, the dust separators were
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thoroughly cleaned prior to each combustion test.
270 271
2.4. Analysis and emission measurement methods
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For fuel analyses, samples were taken with regard to DIN EN 14778 and DIN EN 14780. 51,52
273
Cereal grains were stored in big bags. For sampling, a sample pipe according to DIN EN
274
14778 was introduced separately on five positions from the top of each big bag, i.e. at each
275
corner and in the middle, and was directed to the bottom of each big bag. 51 All samples were 11
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merged to a subsample representing each big bag. Furthermore, an overall merged sample
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representing the whole fuel batch was produced from all subsamples by dividing and
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homogenizing the subsamples of all big bags according to DIN EN 14780. 52 Fuel pellets
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were also stored in big bags. Sampling with the sample pipe was not feasible for pellets due to
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the stronger penetration resistance of this material. Thus, three samples with approx. 2.5 L
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each were manually taken on the upper right, middle and lower left of each big bag using a
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sample shovel. Subsequently, the three samples were merged to a subsample and thoroughly
283
mixed. An overall merged sample was produced from all subsamples by dividing and
284
homogenizing the subsamples of all big bags according to DIN EN 14780. 52 The fuel
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samples were analyzed according to the European standards for solid biofuels: water content,
286
net calorific value, ash content, ash melting behavior (SST, DT, HT and FT) and total content
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of sulfur and chlorine, major elements (i.e. Al, Ca, Mg, P, K, Si and Na, determined after
288
hydrofluoric digestion). 53 The analysis uncertainty for the relevant test fuel criteria (i.e. only
289
quantifiable parameters) are ±0.09 % for ash content, ±0.03 % for nitrogen, ±0.01 % for
290
chlorine and ±3 % for potassium. PCDD/F emission measurements were performed according
291
to DIN EN 1948-1 by an accredited institute applying a sampling time of 6 h during full load
292
boiler operation. 54,55 If the sampling time had to be reduced, e.g. due to higher dust
293
concentrations in the flue gas, measures according to VPAB8 were taken. 10 The average blank
294
value for PCDD/F of the boiler 1 test bench was 0.0008 ng I-TEQ/m³ and for the boiler 2 test
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bench 0.002 ng I-TEQ/m³. Values for PCDD/F congeners were set to zero if their analyzed
296
values were below the limit of detection (bld). Further emission measurements of CO and
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NOx were performed according to DIN EN 15058 and DIN EN 14792 respectively using a
298
Siemens Ultramat 23. 56,57 For both parameters, mean values for 30 min intervals were
299
calculated and subsequently used for the calculation of the overall mean value. TPM
300
emissions were measured by using the gravimetric method according to DIN EN 13284-1. 48 12
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For TPM sampling, the out stack method and an automatic isokinetic control unit ITES (Paul
302
Gothe GmbH) were employed. The sampling probe had a nozzle diameter of 8 mm and was
303
heated to 160 °C to avoid condensation of flue gas components. Sampling duration was at
304
least 30 minutes. The measurements were repeated at least twice for each combustion test. A
305
plane filter (Munktell MK360 with retention > 99.998 %, diameter 45 mm) was applied to
306
collect the particles. Prior to the measurement, the plane filter was pretreated by drying at 180
307
°C for at least 1 h and then cooled down to ambient temperature and conditioned in a
308
weighing chamber with constant temperature and humidity for at least 8 h. After the
309
measurement, the plane filter was dried at 160°C for at least 1 h, cooled down to ambient
310
temperature and conditioned in a weighing chamber with constant temperature and humidity
311
for 8 h. For total particle emissions in the flue gas > 50 mg/m³, a filter cartridge was applied
312
prior to the plane filter to remove coarse particles. The cartridge was cleaned with distilled
313
water and subsequently dried. Afterwards, the filter cartridge was stuffed with quartz wool so
314
that 2/3 of the cartridge volume was loaded followed by a manual densification of the quartz
315
wool to avoid channeling of unfiltered flue gas sample streams. Weighing of the filters and
316
cartridges before and after the measurement was performed three times for each filter or
317
cartridge on a balance (Kern, type ABT 220-5DM). The sampling probe was cleaned after
318
each combustion experiment with distilled water and acetone (HPLC grade) and subsequently
319
dried with pressurized oil free air. The obtained rinsing liquid was analyzed for residual mass
320
of the particles which was equally distributed to each TPM measurement of the combustion
321
experiment. The determination of the boiler efficiency was not within the scope of this work.
322 323
3. Results and discussion
324
3.1 Raw material selection
325
In Germany, the most important representative of the fuel group A is wheat straw. There are, 13
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326
however, many more possible candidates that could be used as raw materials for TF A. Based
327
on a literature review covering 55 references and a total number of 253 data sets, only 5 %
328
(i.e. 13 of the 253 data sets 58–62) match all test fuel A criteria specified in VPAB8. 10 The
329
required potassium and chlorine contents are rarely reached and in particular their
330
combination represents the most rigorous criteria. There is furthermore the risk that a fuel that
331
satisfies the potassium and chlorine criteria exceeds by far the ash content criterion of the
332
VPAB8. Consequently, a suitable strategy for the production of test fuel A may involve
333
blending of different raw materials accompanied by additive utilization for the compliance
334
with selected fuel criteria. As shown by leaching experiments, potassium and chlorine are
335
available in biomass fuels mostly in ionic form or precipitated as salts. 63,64 Thus, we expect a
336
low alteration of the combustion properties of test fuels with additives as compared to an
337
assortment naturally containing the required amount of potassium and chlorine. For the
338
acquisition of raw materials for the test fuel production, meeting the nitrogen content was a
339
prerequisite while a close match for the other criteria was anticipated. For TF B, the VPAB8
340
demands the utilization of grain-like test fuels rather than pellets. 10 Additive application is
341
thus hampered since the wax shell of the grain impedes with common agglomeration coating
342
techniques. 65 Therefore, a matching raw material composition would be even more
343
advantageous for test fuel B production. However, also in this case a literature review
344
covering 12 references and a total number of 52 data sets indicates a very low chance to
345
identify and purchase a matching raw material (only 2 %, i.e. 1 of the 52 data sets matches all
346
TF B criteria 66) since grains with a high nitrogen content are typically characterized by ash
347
contents below the requirement of the VPAB8. Thus, for TF B, wheat grains providing a close
348
match with required N, K and Cl content were acquired. The wheat grains exhibited only a
349
slightly too low potassium content and an insufficient ash content. The fuel properties were
350
adjusted by admixing grinded bottom ash from the combustion of the very same wheat grain 14
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enabling increased ash content similar to the fuel ash composition, Figure 2. Proper adhesion
352
of the grinded bottom ash on the grain was ensured by the application of a coating procedure
353
using whole flour and water as binding agent. Four test fuels were produced: TF A1, TF A2,
354
TF B1 and TF B2. The employed recipes are listed in Table 2.
355 356
3.2 Analysis of the produced test fuels
357
The results from fuel analysis are listed in Table 3. As expected, wood pellets (RF WP) are
358
characterized by N, K and Cl contents decisively below the criteria of VPAB8. In contrast, RF
359
A fulfills all criteria of VPAB8 except for chlorine content. The contents of K, N and ash are
360
above the thresholds given by VPAB8. A comparison with average values gained from Phyllis
361
database 67 for wheat straw (i.e. 95 samples, ash content: 7.1 wt% d.b. (n=77), DT: 891 °C
362
(n=14), nitrogen content: 0.68 wt% d.b. (n=65), chlorine content: 0.48 wt% d.b. (n=53) and
363
potassium content: 11,680 mg/kg d.b. (n=23)) highlight that RF A represent a typical wheat
364
straw. RF B only fulfills the criteria of VPAB8 for ash deformation temperature and chlorine
365
content. Though, available data sets for fuel properties of cereal grains and particularly wheat
366
grains are scarce, the comparison with literature data for wheat grains 58,66 (i.e. 7 samples, ash
367
content: 1.8 wt% d.b. (n=7), DT: 662 °C (n=3), nitrogen content: 2.4 wt% d.b. (n=7), chlorine
368
content: 0.04 wt% d.b. (n=7) and potassium content: 3589 mg/kg d.b. (n=7)) still indicates
369
that RF B represents a typical wheat grain. According to the results of the fuel analysis, the
370
criteria of the VPAB8 concerning the composition of the test fuel are generally satisfied by TF
371
A1 and TF A2. However, the employed strategy with KCl used as additive resulted in a fuel
372
composition of TF A1 exceeding the requirements of VPAB8 which may lead to unnecessarily
373
high total particulate and PCDD/F emission compared to thresholds specified for TF A.
374
Consequently, TF A2 was produced using K2CO3 instead of KCl and a higher proportion of
375
CaCl2. The fuel analysis reveals that all criteria of VPAB8 were met. A major advantage of TF 15
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376
A2 is that the critical content of K was adjusted well according to the required threshold of
377
10,000 mg/kg d.b. Based on the higher nitrogen content of the employed raw materials, TF
378
A2 is also characterized by a higher nitrogen content than TF A1 (section 3.1). Both TF A1
379
and TF A2 are characterized by ash contents significantly exceeding the requirements of
380
VPAB8. However, since the selected combustion appliances are able to handle fuels with ash
381
content up to 10 wt% d.b., no operational problems with regard to the ash removal into the
382
ash pan during combustion were expected. Addition of bottom ash to untreated wheat grains
383
(i.e. TF B1) for adaption of ash and potassium content did not lead to the desired change of
384
the fuel composition. Thresholds of VPAB8 were not kept possibly due to segregation effects,
385
Table 3. Thus, TF B2 was produced by using whole flour as binding agent to allow for proper
386
adhesion of the grinded ash particles on the surface of the wheat grains. This strategy proved
387
successful with TF B2 keeping the criteria of VPAB8.
388 389
3.3 Boiler performance
390
With RF WP a stable operation was observed in boiler 1 without any slagging tendencies in
391
the bottom ash, Figure 3. During the combustion of the other two reference fuels RF A and
392
RF B in boiler 1, severe slagging in the bottom ash especially for RF A was observed. This
393
could not be limited by boiler adjustments, e.g. adjusting excess (primary and secondary) air
394
ratio or frequency of the ash slide operation. Similar tendencies were observed for the test
395
fuels employed in boiler 1 and 2. However, the operation of the ash slide still guaranteed a
396
satisfactory ash removal and stable boiler operation which is characterized by average CO
397
emission levels below 250 mg/m³ (Table 4 and Table 5). Based on the low CO emission
398
levels, almost complete combustion and consequently low PAH emission levels can be
399
expected. 17,68–71 To further examine the boiler performance, the heat output was monitored
400
during the combustion tests. According to DIN EN 303-5 heat output should not exceed ±8 % 16
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during the whole combustion test. 9 For the full load combustion tests with RF WP, a deviation
402
of max. ±10 % from average heat output was recorded. In contrast, for the boiler operation with
403
the other non-woody biomass reference and test fuels, deviations were typically in the range of
404
±25 % from mean heat output which might be traced back to significant slag formation in the
405
bottom ash with enduring time of the combustion test. Accordingly, it was challenging to fulfill
406
the requirement of DIN EN 303-5 for continuous heat output of ±8 % for those fuels. 9
407
However, deviations from full load boiler operation did not lead to significant higher CO
408
emissions due to incomplete combustion, Table 4 and Table 5.
409 410
3.4 CO-, NOx and TPM emissions from the combustion in boiler 1
411
Reference and test fuels were both utilized for combustion tests in boiler 1. According to Table
412
4, emission thresholds for CO and NOx were complied with during combustion of the reference
413
and test fuels (except NOx for RF B). The results are in accordance with previous
414
measurements of other authors using boilers from the same manufacturer with woody and
415
non-woody biomass fuels. 29,72–75 With RF B, mean NOx emissions were measured that are
416
slightly higher than the required NOx emission threshold of 500 mg/m³. NOx formation is hardly
417
affected by the electrostatic precipitator (ESP) and pre-dominantly correlated with the nitrogen
418
content of the fuel. 76–81 Since it is not economically feasible to employ advanced fuel gas
419
cleaning systems like SCR, SNCR or flue gas recirculation in small scale combustion
420
appliances (< 100 kW), reduction of NOx emissions has to be achieved by staged air supply and
421
limitation of the oxygen availability in the ember bed. 76,79,82,83 Applying this strategy for TF B1
422
led to NOx emissions below the relevant emission threshold compared to the combustion of RF
423
B while CO emission levels for TF B1 remain typically below 60 mg/m³. In contrast, NOx
424
emission levels for the combustion of TF A1 and TF A2 as well as RF WP and RF A are not
425
critical with regard to the NOx emission threshold of 500 mg/m³ due to lower amount of 17
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426
nitrogen in the fuel. Higher CO emissions can be traced back to considerable slagging
427
tendencies in the bottom ash which might pre-dominantly be caused by the high potassium
428
content in the fuel. 84 Accordingly, steady state boiler operation on low emission levels is by far
429
more challenging using the test fuels. Consequently, keeping the emission thresholds requires
430
the interaction of the ash slide and the thorough adjustment of the fuel and combustion air
431
control parameters of the boiler. The application of the ESP enabled TPM emission levels < 20
432
mg/m³ during the combustion of RF WP, RF A and RF B. However, significantly higher TPM
433
emission levels were observed during the combustion of test fuels, i.e. 425 mg/m³ and 168
434
mg/m³ (before and after the ESP) for TF A1, 215 mg/m³ and 54 mg/m³ (before and after the
435
ESP) for TF A2 as well as 230 mg/m³ and 39 mg/m³ (before and after the ESP) for TF B1,
436
which is of course intended by the test fuel concept and their more challenging fuel
437
composition. However, the ESP did not reduce TPM emissions below the required TPM
438
emission threshold < 20 mg/m³ for the combustion of TF A1, TF A2 and TF B1.
439 440
3.5 CO-, NOx and TPM emissions from the combustion in boiler 2
441
For further evaluation of the emission and combustion behavior of the boiler family and to
442
further reduce TPM emissions especially during combustion of TF A1 and TF A2, additional
443
combustion tests were performed in boiler 2 which is combined with a fabric filter (FF). For
444
this, test fuels TF A1 and TF B2 were utilized. Preliminary combustion tests were performed
445
with each fuel to adjust boiler operation according to the requirements specified in section
446
2.3. According to Table 5, emission levels for CO, NOx and TPM are below the emission
447
thresholds specified in the 1. BImSchV. The comparison with boiler 1 indicates that both
448
boilers are characterized by a similar CO and NOx emission behavior. Utilization of a fabric
449
filter (FF) rather than an ESP significantly reduced TPM emissions < 10 mg/m³ both for TF A1
450
and TF B2 enabling to keep the TPM emission threshold specified in 1. BImSchV. 18
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451 452
3.6 PCDD/F emissions from the combustion in boiler 1 and boiler 2
453
In boiler 1, the emission threshold for PCDD/F was complied with for all employed fuels except
454
TF A1 and TF A2, Table 6. Clearly, the PCDD/F emission levels for RF A, RF B and TF B1
455
are lower compared to those measured during combustion tests with similar non-woody raw
456
materials such as straw, hay, triticale whole crop or reed canary-grass that showed comparable
457
combustion behavior and fuel qualities. During their combustion in the same boiler, however,
458
no dust precipitators were used and consequently higher PCDD/F emissions were measured.
459
72,74
Similarly, during the combustion of grass pellets in a different boiler setup
460
Chandrasekaran et al. also measured higher PCDD/F emissions despite significantly lower
461
chlorine contents between 0.04 and 0.08 wt% d.b. 14,17 Thus, effective dust separation seems
462
to substantially lower PCDD/F emission. PCDD/F emission levels from the combustion of TF
463
A1 and TF A2 in boiler 1 are significantly higher and correlate with elevated TPM emission
464
levels for those fuels which were measured after the ESP. During the combustion tests,
465
precipitation efficiencies of the ESP in the range 64 – 75 % for test fuels A and 83 – 90 % for
466
test fuels B (calculated based on the results for total particulate matter emissions listed in
467
Table 4) were measured which is lower than for precipitation of particles in the flue gas of
468
wood pellet combustion 85 but still a surprisingly good result for an ESP developed and
469
optimized for wood pellet and wood chip combustion. Nevertheless, TPM emissions in the
470
flue gas for the combustion of TF A1, TF A2 and TF B1 in boiler 1 are considerably above
471
emission thresholds. This may be attributed to the design of the ESP for the precipitation of
472
particles and particle concentrations from the flue gas of wood combustion. In contrast to
473
particulate matter arising from the combustion of woody biomass, particulate matter from
474
non-woody biomass fuel combustion contains a high share of inorganic salts. 86 This may also
475
affect PCDD/F formation during the combustion process since considerable amounts of 19
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Page 20 of 42
476
PCDD/F can be included in the fly ash. 87–89 Accordingly, PCDD/F emissions > 0.1 ng I-
477
TEQ/m³ were measured during the combustion of TF A1 and TF A2 while PCDD/F emission
478
levels for TF B1 were typically < 0.029 ng I-TEQ/m³ in boiler 1, Table 6 and Table S1. In
479
contrast, application of an efficient fabric filter to boiler 2 enabled both for low TPM
480
emissions and also PCDD/F emissions that can be in the range of the combustion of high
481
quality wood fuels, i.e. < 0.032 ng I-TEQ/m³ for TF A1 and < 0.012 ng I-TEQ/m³ for TF B2.
482
14,17,88,90,91
The homologue patterns of PCDD and PCDF emissions are typical for biomass
483
combustion processes 73,92–95 and independent from the used boiler, fuel and dust precipitator,
484
Figure 4. PCDF/PCDD ratios are in the range of 1.21 to 4.69 indicating that preferably furans
485
are formed. For all combustion tests, the highest amounts have been measured for the tetra
486
chlorinated compounds TCDD and TCDF that are characterized by highest toxicity (i.e.
487
highest I-TEQ equivalent). 96 The homologue patterns of PCDD and PCDF are decreasing
488
from TCDD to OCDD and from TCDF to OCDF respectively. Based on the results obtained
489
in the course of this study, it appears likely that toxicity levels almost as low as for wood
490
combustion can be achieved if a complete combustion is guaranteed and an appropriate
491
combination of a boiler and dust separator, i.e. boiler 2 with a FF (Table 6), are applied. Very
492
low TPM emission levels < 10 mg/m³ seem to be a good indicator for compliance with
493
PCDD/F emission thresholds.
494 495
4 Summary and conclusion
496
To facilitate the market introduction of the first licensed boiler for the use of agricultural
497
biomasses, test fuels with specified fuel composition were produced and utilized for
498
combustion tests. Since test fuel composition was intentionally critical, test fuels had to be
499
deliberately produced. In the case of the straw-like test fuel TF A, the most difficult parameter
500
was the high chlorine content. Mineral additives were necessary to successfully produce straw 20
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501
pellets with the required fuel properties. For TF B the required ash content proved most
502
difficult to achieve. A strategy employing biomass ash from cereal grain combustion together
503
with an agglomeration technique using whole flour and water as binder yielded TF B with the
504
desired fuel properties and the required segregation stability. Emission measurements (i.e. for
505
CO, NOx, PCDD/F and total particulate matter) performed by an accredited institute both with
506
the test fuels TF A and TF B and with typical fuels for the respective fuel class indicated that
507
the test fuels indeed showed more critical combustion and emission behavior than typical fuel
508
representatives. Thus, the test fuel concept is feasible with respect to the intention of the DIN
509
EN 303-5 and 1. BImSchV. For test fuel production on an industrial scale, raw material
510
selection, mixing and fuel sampling have to be optimized to ensure for precise compliance
511
with test fuel criteria. For the combustion tests with the test fuels substantial efforts had to be
512
made to adjust boiler parameters enabling steady boiler operation with minimum slagging in
513
the bottom ash and low emission levels for CO, NOx, total particulate matter and PCDD/F.
514
The results show that compliance with the strict emission thresholds of the 1. BImSchV in
515
Germany seem to be accomplishable even with challenging fuels if an appropriate boiler is
516
combined with an efficient dust separator, i.e. a fabric filter. Accordingly, PCDD/F emission
517
levels and toxicity almost as low as for wood combustion were observed. The combustion
518
tests have to be extended to verify sufficient boiler operation and low emission levels also
519
during part load boiler operation. With these results, licensing of boilers with a nominal heat
520
capacity < 100 kW using fuels specified in the first ordinance of the German emission control
521
act (i.e. according to §3 (1) No. 8 of the 1. BImSchV) would be possible for the first time
522
since the amendment of the 1. BImSchV in 2010.
523
5 Acknowledgements
524
The work presented here was funded under grant agreement number FKZ 22403112 of the
525
Agency for Renewable Resources (Fachagentur Nachwachsende Rohstoffe e.V., FNR) in the 21
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name of the German Federal Ministry of Food and Agriculture (BMEL) on the basis of a
527
resolution of the German Federal Parliament. The contribution of the industrial partner A.P.
528
Bioenergietechnik GmbH, Hischau / Germany is gratefully acknowledged.
Page 22 of 42
529 530
6 References
531
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(1) Intergovernmental panel on climate change (IPCC). Climate Change 2014, Synthesis Report: Summary for Policymakers; Geneva, Switzerland, 2015.
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Paris Agreement: Proposal by the President. Paris Climate Change Conference - November
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2015, COP 21; Paris, France, 2015.
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(3) Bundesministerium für Umwelt, Naturschutz und Reaktorsicherheit. Klimaschutzplan
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2050: Klimaschutzpolitische Grundsätze und Ziele der Bundesregierung; Berlin, Germany,
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(4) Bundesministerium für Verkehr, Bau und Stadtentwicklung. Bestandsaufnahme zur
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Energie- und Klimaschutzentwicklung - Monitor 2012 / Gebäude und Verkehr; Berlin,
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(5) Thrän, D. Smart Bioenergy Technologies and concepts for a more flexible bioenergy provision in future energy systems; Springer International Publishing, 2015. (6) Brosowski, A.; Adler, P.; Erdmann, G.; Stinner, W.; Thrän, D.; Mantau, U.
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Biomassepotenziale von Rest- und Abfallstoffen - Status Quo in Deutschland; Schriftenreihe
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specifications and classes - Part 6: Graded non-woody pellets; Beuth Verlag: Berlin,
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for solid fuels, manually and automatically stoked, nominal heat output of up to 500 kW -
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Terminology, requirements, testing and marking; Beuth Verlag: Berlin, Germany, 2012.
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(10) Bund/Länder-Arbeitsgemeinschaft für Immissionsschutz. Vollzugsempfehlung zur
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Behavior of Biomass Pellets Using a Burner Cup Developed for Ash-Rich Fuels. Energy
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Fuels 2014, 28, 1103–1110, DOI: 10.1021/ef402149j.
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(12) Chandrasekaran, S. R.; Sharma, B. K.; Hopke, P. K.; Rajagopalan, N. Combustion of
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Switchgrass in Biomass Home Heating Systems: Emissions and Ash Behavior. Energy Fuels
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Emissions from the Combustion of Biomass-Residue-Derived Fuels in a Small Residential
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Energy & Fuels
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deformation temperature). 10 fuel parameter ash content N K Cl DT
unit wt% d.b. wt% d.b. wt% d.b. wt% d.b. °C
test fuel (TF) TF A TF B >6.0 >2.0 >0.5 >2.0 >1.0 >0.5 >0.4 >0.05 0.4 >10,000 -
TF A1 10.9 7.7 16.9 710 895 1190 1255 45.3 5.6 0.7 0.75 0.19 13,727 68 3743 25,527 1173 193 1029
test fuels (TF) TF A2 criteria TF B* 9.4 8.0 >2.0 16.5 690 880 2.0 0.36 >0.05 0.09 10,750 >5000 162 5030 23,050 424 754 754 -
TF B1
TF B2
7.8 1.8 17.1 690 735 770 785 45.6 6.3 2.2 0.06 0.15 4770 4 410 227 1370 30 3840
8.4 2.1 16.6 660 720 760 780 46.0 6.9 2.4 0.09 0.3 5605 13 417 145 1690 106 4425
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Table 4. CO, NOx and total particulate matter emissions (TPM) during combustion of test
846
(TF) and reference fuels (RF) in boiler 1. Combustion tests with RF WP were performed
847
without ESP. All emissions are stated as mg/m3 (d.b., STP, 13 vol% O2).
RF WP NOx CO TPM (without ESP) RF A NOx CO TPM (after ESP) RF B NOx CO TPM (after ESP) TF A1 NOx CO TPM (before ESP) TPM (after ESP) TF A2 NOx CO TPM (before ESP) TPM (after ESP) TF B1 NOx CO TPM (before ESP) TPM (after ESP)
emission threshold
mean
SD
uy,max
max
min
n
500 250 20
107 174 20.0
0.788 83.6 0.000
11.5 28.1 0.70
108 319 20.0
106 38,9 20.0
3 20 3
500 250 20
268 135 13.0
11.9 95.9 3.00
20.0 23.1 0.90
277 355 16.0
261 36.2 10.0
3 26 3
500 250 20
505 62.1 14.7
18.6 61.5 2.89
10 11.0 3.00
527 248 18.0
493.5 11.2 13.0
3 39 3
500 250 20 20
269 207 425 168
29.0 93.0 43.2 80.0
4.00 37.5 20.0 116
319 490 480 322
233 50.3 370 84.0
6 73 6 13
500 250 20 20
300 125 215 54.0
32.3 56.1 7.07 8.49
4.00 3.00 7.00 4.00
343 209 220 60.0
255 46.6 210 48.0
9 9 2 2
500 250 20 20
388 52.8 230 38.8
37.5 66.7 54.8 19.1
4.00 4.86 8.00 3.00
447 350 310 66.0
349 13.1 190 24.0
9 43 4 4
848
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849
Table 5. CO, NOx and total particulate matter emissions (TPM) during combustion of the test
850
fuels in boiler 2. All emissions are stated as mg/m3 (d.b., STP, 13 vol% O2).
TF A1 NOx CO TPM (after FF)* TF B2 NOx CO TPM (after FF)**
emission threshold
mean
SD
uy,max
max
min
n
500 250 20
288 63.9 8.86
14.5 29.0 4.91
4.00 2.00 7.00
309 129 170
267 41.6 3.00
9 9 7
500 250 20
428 27.0 6.00
39.1 5.38 4.62
5.00 2.00 2.00
496 35.9 10.0
370 18.1 2.00
9 9 4
851
* Due to a malfunction of the TPM sampling probe, only one measurement was performed according to DIN EN 13284-1 by
852
an accredited institute. Six non-accredited TPM measurements were performed using a dust measuring device Wöhler, type
853
SM 500.
854
** TPM measurements were performed for all samples according to DIN EN 13284-1 by an accredited institute.
855 856
Table 6. PCDD/F emissions during combustion of the reference and test fuels in boiler 1
857
(with electrostatic precipitator, ESP) and boiler 2 (with fabric filter, FF). All emissions were
858
measured after the ESP and FF respectively. The emission threshold for polychlorinated
859
dibenzodioxins and dibenzofurans (PCDD/F) is 0.1 ng I-TEQ/m³ (d.b., STP, 13 vol% O2).
boiler
boiler 1
boiler 2
fuel RF WP RF A RF B TF A1 TF A2 TF B1 TF A1 TF B2
PCDD/F uy,max mean max min [ng I-TEQ/m³, d.b., STP, 13 vol% O2] 0.0002 0.005 0.008 0.002 0.0200 0.038 0.064 0.020 0.0200 0.062 0.075 0.042 0.0328 0.142 0.178 0.105 0.7980 1.78 3.19 0.639 0.0044 0.027 0.029 0.024 0.0071 0.023 0.032 0.019 0.0019 0.008 0.012 0.006
n 3 3 3 2 3 3 3 3
PCDF/PCDD ratio 2.64 3.75 4.69 4.24 1.21 2.46 3.22 1.38
860
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861 862
Figure 1.
863
864
Figure 2.
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Figure 3.
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Energy & Fuels
867 868
Figure 4.
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Supporting Information Table S1. Speciation of PCDD/F compounds during combustion of the reference and test fuels in boiler 1 (with electrostatic precipitator, ESP) and boiler 2 (with fabric filter, FF). All emissions were measured after the ESP and FF respectively. All values are stated as ng/m3 (d.b., STP). boiler fuel n 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 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 1,2,3,7,8,9-HxCDF 2,3,4,6,7,8-HxCDF 1,2,3,4,6,7,8-HpCDF 1,2,3,4,7,8,9-HpCDF OCDF
RF WP 3 6.7 x 10-04 9.7 x 10-04 2.3 x 10-04 3.0 x 10-04 3.0 x 10-04 bld bld 1.0 x 10-02 4.3 x 10-03 7.2 x 10-03 2.0 x 10-03 2.3 x 10-03 3.0 x 10-04 3.4 x 10-03 3.0 x 10-03 bld bld
RF A 3 7.3 x 10-03 1.0 x 10-02 5.8 x 10-03 8.4 x 10-03 4.0 x 10-03 2.7 x 10-02 1.9 x 10-02 7.3 x 10-02 3.0 x 10-02 4.2 x 10-02 2.4 x 10-02 2.2 x 10-02 5.2 x 10-03 1.7 x 10-02 3.6 x 10-02 3.5 x 10-03 8.8 x 10-03
boiler 1 RF B TF A1 3 2 -03 7.2 x 10 5.6 x 10-02 1.2 x 10-02 5.3 x 10-02 4.0 x 10-03 1.6 x 10-02 6.9 x 10-03 2.0 x 10-02 4.5 x 10-03 1.2 x 10-02 9.8 x 10-03 3.1 x 10-02 4.8 x 10-03 1.6 x 10-02 9.3 x 10-02 2.6 x 10-01 4.6 x 10-02 1.3 x 10-01 6.9 x 10-02 1.3 x 10-01 3.5 x 10-02 4.8 x 10-02 4.1 x 10-02 4.7 x 10-02 4.3 x 10-03 6.0 x 10-03 2.4 x 10-02 2.4 x 10-02 3.1 x 10-02 3.0 x 10-02 3.9 x 10-03 5.0 x 10-03 3.6 x 10-03 8.2 x 10-03
TF A2 3 2.2 x 10-01 1.4 x 10+00 2.1 x 10-01 2.1 x 10-01 2.0 x 10-01 4.7 x 10-01 2.0 x 10-01 1.4 x 10+00 1.5 x 10+00 2,4 x 10+00 1.5 x 10+00 1.8 x 10+00 3.1 x 10-01 1.3 x 10+00 2.2 x 10+00 2.8 x 10-01 4.5 x 10-01
TF B1 3 3.3 x 10-03 8.2 x 10-03 4.9 x 10-03 7.1 x 10-03 4.0 x 10-03 1.5 x 10-02 8.6 x 10-03 4.0 x 10-02 2.5 x 10-02 4.5 x 10-02 3.3 x 10-02 3.6 x 10-02 3.6 x 10-03 2.8 x 10-02 7.2 x 10-02 1.1 x 10-02 3.1 x 10-02
boiler 2 TF A1 TF B2 3 3 -03 3.0 x 10 1.5 x 10-03 3.4 x 10-03 2.9 x 10-03 1.8 x 10-03 1.3 x 10-03 2.7 x 10-03 2.3 x 10-03 1.8 x 10-03 1.4 x 10-03 1.3 x 10-02 5.3 x 10-03 2.3 x 10-02 5.1 x 10-03 2.2 x 10-02 8.8 x 10-03 1.2 x 10-02 4.1 x 10-03 2.4 x 10-02 5.9 x 10-03 8.9 x 10-03 2.0 x 10-03 1.1 x 10-02 2.4 x 10-03 1.2 x 10-03 7.7 x 10-04 9.9 x 10-03 2.0 x 0-03 1.5 x 10-02 2.7 x 10-03 3.1 x 10-03 7.3 x 10-04 1.2 x 10-02 5.9 x 10-03
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