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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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Energy & Fuels

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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

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Management, University of Rostock, Justus-von-Liebig-Weg 6, 18059 Rostock, Germany.

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* 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

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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.

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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

ACS Paragon Plus Environment

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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

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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

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according to the relevant methods.

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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

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boiler technology is combined with an efficient dust separator.

43 44

Keywords: straw, cereal grain, biomass, boiler, type test, emission, combustion, PCDD/F

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Abbreviations

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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:

50

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:

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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

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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

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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.

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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

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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

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(i), a heat load control and measuring device (HLMD) was installed to allow for boiler

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operation at full load. The HLMD is equipped with resistance thermometer (Pt100 RM, type

250

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

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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

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temperature and pressure (STP) and related to 13 vol% O2. All emission values are stated

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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

266

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

268

layers from the heat exchanger surface was avoided. Likewise, the dust separators were

269

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

280

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

282

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

287

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

295

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

297

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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301

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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Page 14 of 42

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


Page 15 of 42

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Energy & Fuels

351

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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Page 16 of 42

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


Page 17 of 42

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Energy & Fuels

401

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


Energy & Fuels

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Page 18 of 42

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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Energy & Fuels

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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Energy & Fuels

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


Energy & Fuels

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526

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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(2) United Nations Framework Convention on Climate Change (UNFCCC). Adoption of the

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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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Germany, 2013.

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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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Germany, 2014.

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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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822

Figure Captions

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Figure 1. Schematic description of the small scale combustion appliance (Ökotherm®

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Thoma. Investigation on organic pollutants from a domestic heating system using various

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Figure 2. Picture of (a) untreated wheat grains, (b) TF B1, (c) TF B2.

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Figure 3. Pictures of the bottom ash after combustion tests in boiler 1.

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Figure 4. Homologue patterns of PCDD (upper section) and PCDF emissions (lower section)

830

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are stated as average of three values as well as their minimum and maximum values.

832

34


Page 35 of 42

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Energy & Fuels

833

Tables

834

Table 1. Criteria for TF A and TF B specified in the VPAB8 (d.b.: dry basis, DT: ash

835

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

36


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Energy & Fuels

845

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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Page 38 of 42

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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Energy & Fuels

861 862

Figure 1.

863

864

Figure 2.

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Page 40 of 42

865 866

Figure 3.

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Energy & Fuels

867 868

Figure 4.

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Energy & Fuels

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Page 42 of 42

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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F and total particulate matter ... - ACS Publications

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