Effect of oxidizing honeycomb catalysts integrated in a firewood

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Effect of oxidizing honeycomb catalysts integrated in a firewood roomheater on gaseous and particulate emissions, including PAHs Franziska Klauser, Christoph Schmidl, Gabriel Reichert, Elisa Carlon, Magdalena Kistler, Manuel Schwabl, Walter Haslinger, and Anneliese Kasper-Giebl Energy Fuels, Just Accepted Manuscript • DOI: 10.1021/acs.energyfuels.8b02336 • Publication Date (Web): 11 Oct 2018 Downloaded from http://pubs.acs.org on October 12, 2018

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Effect of oxidizing honeycomb catalysts integrated in a firewood roomheater on gaseous and particulate emissions, including PAHs Franziska Klauser†, ‡, Christoph Schmidl†*, Gabriel Reichert†, Elisa Carlon†, Magdalena Kistler‡, Manuel Schwabl†, Walter Haslinger†§, Anne Kasper-Giebl‡ †

‡

BIOENERGY 2020+ GmbH, Inffeldgasse 21b, 8010 Graz, AUSTRIA

Institute of Chemical Technologies and Analytics, Vienna University of Technology, Getreidemarkt 9, 1060 Vienna, AUSTRIA

§

Luleå Univesity of Technology, Energy Engineering, Division for Energy Science, 97187 Luleå, Sweden [email protected]

ACS Paragon Plus Environment

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ABSTRACT:

Residential wood combustion is linked with a significant extent of emissions of polycyclic aromatic hydrocarbons (PAHs), which represent highly toxic, semi-volatile pollutants. The use of catalysts reveals an effective measure to reduce emissions, especially gaseous flue gas compounds (carbon monoxide - CO and organic gaseous compounds - OGC). Their effect on toxicologically relevant PAHs is not clarified yet. In this work, the impact of two commercially available oxidizing Platinum/Palladium catalysts with either metallic or ceramic honeycomb carriers was examined under real life operating conditions of a firewood roomheater. The catalytic effect on CO and OGC, total suspended particles (TSP), total carbon (TC), elemental carbon (EC), organic carbon (OC) and 19 different PAHs including 16 EPA PAHs (PAHs defined by the Environmental Protection Agency as priority pollutants) was evaluated by parallel measurements of catalytically treated and untreated flue gas from firewood combustion. The metallic catalyst, having a 3.5 times higher reaction surface than the ceramic catalyst, leads to a more pronounced impact. Both types, the ceramic and the metallic catalyst, led to distinct reductions of CO (-69%, -88%) and OGC (-27%, -39%). In the test with the metallic catalyst, TSP increased (+17%) and PAHs were clearly reduced (-63%). This reduction was exclusively related to the higher molecular weight PAHs, like the particularly toxic Benzo(a)pyrene. Carbonaceous fractions (TC, EC and OC) were not affected significantly. The toxicity of emissions arising from EPA PAHs can be clearly reduced by catalytic treatment. Moreover, the increase of TSP opens new questions, which must be clarified before the investigated catalysts are recommended as suitable secondary measure for emission abatement.


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ABBREVIATIONS Ace

Acenaphthene

Acy

Acenaphthylene

Anth

Anthracene

BaA

Benz(a)anthracene

BaP

Benzo(a)pyrene

BbF

Benzo(b)fluoranthene

BeP

Benzo(e)pyrene

BghiP

Benzo(g,h,i)perylene

BjF

Benzo(j)fluoranthene

BkF

Benzo(k)fluoranthene

Chr

Chrysene

CO

Carbon monoxide

DBA

Dibenz(a,h)anthracene

EC

Fla

Elemental carbon Polycyclic aromatic hydrocarbons classified as priority pollutants by the United States Environmental Protection Agency Fluoranthene

Flu

Fluorene

HMW PAHs

High molecular weight PAHs (4-, 5- and 6-ring PAHs)

IcdPyr

Indeno(1,2,3-cd)pyrene

LMW PAHs

Low molecular weight PAHs (2- and 3-ring PAHs)

Naph

Naphthalene

OC

Organic carbon

OGC

Organic gaseous compounds

PAHs

Polycyclic aromatic hydrocarbons

Per

Perylene

Phe

Phenanthrene

PM

Particulate matter

PM10/2.5/1

Particulate matter with an aerodynamic diameter below 10, 2.5 or 1 µm

Pyr

Pyrene

ƩPAHs

Sum of determined PAHs

EPA PAHs


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TC

Total carbon

testC

Test run with ceramic catalyst and dummy

testM

Test run with metallic catalyst and dummy

testV

Validation test with no catalyst and no dummy

TSP

Total suspended particles

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1

INTRODUCTION Residential wood combustion for heat production is considered as a major source of

atmospheric contaminants throughout Europe

1–4

and worldwide

5,6.

Carbon monoxide (CO),

organic gaseous compounds (OGC), particulate matter (PM) and polycyclic aromatic hydrocarbons (PAHs) are among the pollutants emitted during biomass combustion. These substances are of major interest, because of their negative influence on human health

7,8.

In a

recent study, combustion of woody biomass was assessed to be the largest source of organic aerosols in Europe 9. Among the emissions from biomass heating, PAHs have recently received increasing attention, because of their genotoxic and carcinogenic properties, which have been thoroughly investigated 7,8,10–12. PAHs comprise several hundreds of substances, which contain at least two connected benzene rings in their chemical structure 13. Benzo(a)pyrene (BaP) is one of the most toxic compounds in this group

7,10,14.

It belongs to the 16 priority pollutant polycyclic

aromatic hydrocarbons defined by the US Environmental Protection Agency (EPA-PAHs) and is commonly defined as the guiding substance among PAHs

13,15,16.

Since 2013, in the European

Union the limit value for BaP concentration in the ambient air is set to a yearly average value of 1 ng m-3 17. Several reports show that in rural regions, where industry and traffic have a minor impact, this threshold is exceeded regularly because of higher values during the heating season 2,18–21.

This indicates the high contribution of woody biomass combustion to PAH pollution.

Due to the relevance of biomass as climate friendly fuel, it is important to identify effective mitigation strategies to reduce emissions from the combustion process of this renewable and sustainable resource for energy. Besides the optimization of combustion

22,23

(e.g. primary

measures for emission mitigation), numerous recently published studies focused on flue gas cleaning by secondary measures

24–31.

Catalytic converters, either used as retrofit or integrated


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systems, have been identified as an effective approach for the reduction of gaseous emissions (CO and OGC)

25,26,30–33.

Reduction efficiencies of up to 95% for CO and 60% for OGC have

been reported 26. Although the effectiveness of various catalysts has been demonstrated, the impact on toxicologically relevant pollutants, like PM or compounds in the PM like PAHs, are still unclear. In emission measurements PM is usually reported as total suspended particles (TSP). In some studies with either integrated or retrofitted catalysts a reduction of TSP was indicated

26,31,33.

Bindig et al. (2011) 28 evaluated a firewood roomheater retrofitted with an oxidative noble-metal catalyst. They observed that TSP, elemental carbon (EC) and organic carbon (OC) emissions were not significantly affected by this catalyst. Zhang et al. (2011)34 measured a clear reduction of PAHs (>90%) in the flue gas of coal combustion by a Palladium (Pd) catalyst. In the work of Kaivosoja et al. (2012)

29

the authors carried out combustion tests with a sauna stove retrofitted

with a Platinum/Palladium (Pt/Pd) catalyst and observed that PAHs (15 different PAHs) were reduced (-24%) by the treatment. They also analyzed the impact on polychlorinated dibenzo(p)dioxines and -furanes and found out that they clearly increased in tests with the catalyst. Fine et al. (2001)

35

tested a Pt/Pd catalyst integrated in a firewood roomheater using

two different wood fuels. PM and OC emissions were either reduced or remained constant in the two conducted tests. However, the EC and PAH concentration (12 different PAHs as compounds of TSP) increased when treating the flue gas with the catalyst. Altogether, the impact of catalysts on TSP and PAHs observed in previous studies are inconsistent. Tests were conducted at different combustion conditions with different types of catalysts, either integrated or used as retrofit solutions. Furthermore, measurements were carried out with different methods (for instance, TSP were sampled either in hot 26,33 or diluted flue gas


6

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31).

In most studies the chemical impact of the catalytic layer and the physical impact of the

catalyst carrier material on the flue gas composition were not distinguished for the catalyst evaluation

29,30,34–36.

In many studies, catalyst evaluations were accomplished by comparing

results of consecutive combustion tests with and without catalysts29,30,35,36. Hence, variations of combustion conditions, which are typical during firewood combustion, could not be considered and might be ascribed to the catalytic effects. Therefore, a special tailored test device (DemoCat) which enables the exclusive determination of the chemical conversion potential of the integrated catalyst has been developed. Effects of the carrier material of the catalysts or effects due to varying combustion conditions can be clearly distinguished from the catalytic effect. Since the health relevance of TSP emissions depends on their concentration, size distribution and composition, the catalytic influence of all factors on TSP must be clarified before a catalyst is recommended as detoxifying agent. Therefore, the objective of this study is the evaluation of the effect of two commercially available Pt/Pd-catalysts on gaseous and particulate emissions under typical real life operating conditions. A special test device (DemoCat) enables synchronous measurements of flue gas either with or without catalytic treatment at identical flow conditions. In detail, the catalytic impact on the emissions of CO, OGC, TSP, TC, EC, OC and 19 different PAHs, including 16 EPA PAHs, was determined. The focus is set on the mass and composition of PM emissions with a special concern on the toxicologically highly relevant PAHs. A comprehensive evaluation of measurement uncertainties allows a clear identification of the effects of the catalyst.


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EXPERIMENTAL SECTION

2.1

Fuel

Combustion tests were conducted using beech firewood (“Fagus sylvatica”). Fuel properties and chemical composition are presented in Table 1. The logs were cut to a length of 0.33 m and were delivered in May 2017. For the ignition batches, kindling material of spruce wood (“Picea abies”) with moisture content below 12% was used. Both, the fuel and the kindling material were delivered by a regional firewood producer located in Lower Austria 37. The firewood was covered and stored outside until the combustion tests in June and July 2017.

2.2

Catalysts

Two catalysts, EnviCat® LongLife Plus Ceramic and EnviCat® LongLife Plus Metal, manufactured by Clariant International Ltd are used (Figure 1). The catalysts have the same noble metal coating, but different honeycomb carriers and different active surfaces. The carriers consist of mullite ceramic (ceramic catalyst) and brazed stainless steel (metallic catalyst). The coating contains a washcoat of aluminium oxide (Al2O3), on which platinum (Pt) and palladium (Pd) as catalytic active elements are applied. The metallic catalyst has a cross-section area of 0.0158 x 0.059 m and a depth of 0.049 m, while the ceramic catalyst has a cross-section of 0.162 x 0.063 m and a depth of 0.051 m. The main difference between both types of catalysts is the cell density which is more than three times higher at the metallic catalyst (50 cpsi correspond 7.75 cells cm-2) compared to the ceramic catalyst (16 cpsi, corresponds 2.48 cells cm-2). Consequently, the reaction surface of the metallic catalyst (0.554 m2) is 3.5 times higher than the


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reaction surface of the ceramic catalyst (0.158 m2) 26. A detailed description of the two catalysts is given in a previous study of Reichert et al. 26.

2.3

DemoCat test facility

The tests were carried out with a special tailored test facility, the so called “DemoCat”. The DemoCat test facility consists of a firewood roomheater (10 kW/ DIN EN 13240:2005

38),

an

adapted post combustion chamber and a flue gas line with two parallel streams, which enables flue gas measurements under equal operating conditions of catalytically treated and untreated flue gas. At the inlet of the post combustion chamber, the flue gas is divided into two equal streams. One stream flows through a coated catalyst, while the other stream flows through a noncoated dummy (Figure 2). The post combustion chamber is equipped with parallel measurements for pressure drops and temperatures up- and downstream the catalyst. The flue gas line is equipped with parallel temperature sensors and parallel ducts for flue gas (O2, CO2, CO and OGC) and particulate matter (TSP) measurement and pressure transmitters for draught control. By this parallel measurement the catalytic effect can be evaluated simultaneously. For example, primary effects or varying combustion conditions affect both compartments of the flue gas line and thus do not have an impact on the catalytic change in emissions. A more detailed description of the experimental set-up is provided by Reichert et al. (2018) 26. Technical data of the used measurement equipment, installed in the DemoCat, is presented in the Supporting Information SI 1. Equal flow conditions of the separate sections were checked before the test series and revealed good accordance as presented in the Supporting Information SI 2. Moreover, Figure 6 indicates that the pressure drop in the different compartments in all conducted tests are similar,


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confirming the similar pressure and flow conditions on the catalyst and dummy side during the tests.

2.4

Emission measurements

Gaseous flue gas compounds (O2, CO2, CO and OGC) were determined online with the measurement equipment presented in the Supporting Information SI 1. In the parallel measurement sections, equipment of the same type or at least of the same measurement principle and the same measuruement range was used. TSP, TC, EC, OC and PAHs were measured discontinuously. TSP was sampled after dilution at temperatures below 313 K on quartz fibre filters. The sampling method was adapted from the “Dilution Method” in ISO 11338-1:2003

39

and specified for the requirements of quantitative

BaP sampling as recently presented by Klauser et al. (2018) 40. After gravimetric determination of TSP concentrations, aliquots of the filter samples were used for further analysis of TC, EC, OC and 19 different PAHs. TC, EC and OC were determined by a thermal-optical method. The analysis were carried out using circular filter punches with 5 mm diameter using a SUNSET Lab OC-EC Aerosol Analyzer using EUSAAR2 protocol in the transmission mode 41. 19 PAHs were determined with a method, which bases on EN 15549:2008 42, designed for the determination of PAHs from ambient aerosol samples. These 19 PAHs are Naphthalene (Naph), Acenaphthylene (Acy), Acenaphthene (Ace), Fluorene (Flu), Phenanthrene (Phe), Anthracene (Anth), Fluoranthene (Fla), Pyrene (Pyr), Benz(a)anthracene (BaA), Chrysene (Chr), Benzo(b)fluoranthene

(BbF),

Benzo(j)fluoranthene

(BjF),

Benzo(k)fluoranthene

(BkF),

Benzo(e)pyrene (BeP), Benzo(a)pyrene (BaP), Perylene (Per), Indeno(1,2,3-cd)pyrene (IcdPyr), Benzo(g,h,i)perylene

(BghiP)

and

Dibenz(a,h)anthracene

(DBA).

Fluoranthenes

(Benzo(b)fluoranthene and Benzo(k)fluoranthene) showed insufficient resolution in retention


10

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time (>50% of peak height) and thus are given as sum (Bb/kF). Benzo(j)fluoranthene was identified in the samples and was semi-quantified using the calibration curve of next placed peak: Benzo(e)pyrene. Details on discontinuous emission measurements are presented in the Supporting Information SI 3.

2.5

Testing procedure

Three combustion tests were carried out. The first was a validation test (testV), in which neither catalysts nor dummies were used. The validation test was conducted in order to confirm the comparability of the test equipment in the two compartments of the test facility. In the following tests (testC and testM), the separate compartments of the post combustion chamber were equipped with a catalyst on the left side and a dummy on the right side. The dummies have the same carrier material and dimensions as the respective catalysts but are not coated with a catalytic layer (Figure 1). In testC the ceramic catalyst (left side) and the ceramic dummy (right side) were positioned in the post combustion chamber. In testM the metallic catalyst (left side) and the metallic dummy (right side) were applied (Figure 2). The comparison of the change in emissions (see Equation 4 in section 2.6) achieved with catalysts and dummies allows to identify the effect of the catalytic layer, excluding primary effects like increased residence time and different flow conditions in the primary combustion zone induced by the pressure drop over the catalyst. All three tests comprised seven consecutive batches, i.e. one ignition batch and six nominal load batches. The flue gas compounds CO, OGC, O2 and CO2 were measured continuously during the whole test runs. TSP samples were taken in batches 1, 3, 5 and 7, allowing filter changes during batches 2, 4 and 6. Consequently, one measurement of TSP concentrations at the


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ignition batch and three measurements in full load operation were available. The measurement of gaseous compounds started before the ignition batch and ended after the last batch. TSP sampling started before ignition or recharging of the respective batch and ended before the next recharging. For the ignition batch six beech logs (each having a mass of 0.415 kg and length of 0.33 m) were placed crosswise in three layers into the combustion chamber (Figure 3a). Additionally, 0.5 kg of kindling material (spruce) was positioned crosswise in three layers on the top of the beech logs. Two starting aids consisting of wood shavings were put in the middle layer of the kindling material (Figure 3b). For batch 2 to 7, two beech logs, each 1.1 kg, were positioned in parallel to the door of the combustion chamber (Figure 3c). After Opening the combustion chamber door for recharching, the glows were stoked, logs were put into the combustion chamber and the door was immediately closed again. The combustion air supply of the DemoCat facility is provided in three different streams which are primary, secondary and window purge air, and can be adjusted manually

26.

At the start of the test, the

dampers regulating primary and secondary combustion air were completely open (100%), and the damper adapting window purge air was half open (50%). After the second batch the damper regulating primary combustion air supply was reduced to 75% of full scale. This reflects the normal combustion procedure in the field. The flue gas draught was constantly controlled to 12 Pa underpressure during the whole test duration.

2.6

Data Evaluation

In the first step data of continuously measured parameters (CO, OGC and O2) were harmonized according to their logging and averaging intervals as described in Supporting Information SI 4.


12

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Emissions of CO, OGC, TSP, TC, EC and OC are expressed in mg m-3 at standard temperature and pressure (STP; 273.15 K, 1013 hPa) and are referred to a 13% O2 volume fraction in dry flue gas. To shorten the description, concentration values are always expressed as “STP, 13% O2”. PAHs are given in µg m-3 at STP and 13% O2. CO and OGC concentrations of each batch are calculated according to DIN EN 13240:2005

38

and CEN/TS 15883:2010

43

respectively.

Concentrations of these compounds are given as means over the combustion time of each batch (from opening the door until the consecutive opening). Overall emissions for whole test runs are calculated as mean values over the whole test duration (from batch 1 to 7). In contrast, overall emissions of discontinuously measured parameters (TSP, EC, OC and PAHs) are calculated from batches 1, 3, 5 and 7. The mass of the sample collected over each batch is related to the extracted volume of the flue gas to determine the mass concentration values per batch (e.g. mg m-3 STP, 13% O2 for TSP). Overall emissions of discontinuously determined parameters are calculated by dividing the total masses of pollutants collected at batches 1, 3, 5 and 7 by the total volume of flue gas sampled at batches 1, 3, 5 and 7 (Equation 1). The mean O2 concentration of batches 1, 3, 5 and 7 (𝑐𝑂2) is calculated according to Equation 2 by taking a volume weighted average and is used to refer the measured concentration to 13% O2 (Equation 3). In Equation 1-3 𝑐𝑥, 𝑆𝑇𝑃 is the concentration of the emission component 𝑥 (e.g. TSP) over the whole test run [mg m-3 at STP], 𝑚𝑥, 𝑏𝑡𝑖 is the sampled mass of 𝑥 in batch i [mg], 𝑉𝑏𝑡𝑖,𝑆𝑇𝑃 is the sampled flue gas volume of batch i [m3 at STP], 𝑐𝑂2,𝑆𝑇𝑃 is the mean O2 concentration of the whole test run [v v-1], 𝑐𝑂2, 𝑏𝑡𝑖 is the mean O2 concentration of batch i [v v-1], 𝑐𝑥,𝑆𝑇𝑃,13%𝑂2 is the mean concentration of emission component 𝑥 at STP, referred to 13% O2 [mg m-3 at STP].


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𝑐𝑥, 𝑆𝑇𝑃 =

Page 14 of 44

∑𝑖 = 1,3,5,7 𝑚𝑥,𝑏𝑡𝑖 ∑𝑖 = 1,3,5,7 𝑉𝑏𝑡𝑖,𝑆𝑇𝑃

Equation 1: Calculation of mass concentration of discontinuously measured emission parameters for the whole test run.

𝑐𝑂2,𝑆𝑇𝑃 =

∑𝑖 = 1,3,5,7 (𝑐𝑂2,𝑏𝑡𝑖 ∗ 𝑉𝑏𝑡𝑖,𝑆𝑇𝑃) ∑𝑖 = 1,3,5,7 𝑉𝑏𝑡𝑖,𝑆𝑇𝑃

Equation 2: Calculation of mean O2 concentration of the whole test run (for referring discontinuously measured parameters to standardized O2 concentration).

𝑐𝑥,𝑆𝑇𝑃,13%𝑂2 = 𝑐𝑥, 𝑆𝑇𝑃 ∗

0,21 ― 0,13 0,21 ― 𝑐𝑂2,𝑆𝑇𝑃

Equation 3: Calculation for referring emission concentration to standardized O2 concentration of 13%. The catalytic change in emissions from the tests with catalysts are calculated according to Equation 4. The change in emissions is negative in case of emission reduction and positive in case of emission increase. 𝑐𝑥,𝑆𝑇𝑃,13%𝑂2,

𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡

specifies the concentration of parameter 𝑥 after a

catalytic treatment of the flue gas and 𝑐𝑥,𝑆𝑇𝑃,13%𝑂2, 𝑑𝑢𝑚𝑚𝑦 expresses the concentration when no catalytic conversion takes place. 𝑐ℎ𝑎𝑛𝑔𝑒 𝑖𝑛 𝑒𝑚𝑖𝑠𝑠𝑖𝑜𝑛𝑠 (%) =

𝑐𝑥,𝑆𝑇𝑃,13%𝑂2, 𝑐𝑎𝑡𝑎𝑙𝑦𝑠𝑡 ― 𝑐𝑥,𝑆𝑇𝑃,13%𝑂2, 𝑐𝑥,𝑆𝑇𝑃,13%𝑂2, 𝑑𝑢𝑚𝑚𝑦

𝑑𝑢𝑚𝑚𝑦

∗ 100

Equation 4: Calculation of change in emissions. Some results were tested for a significant difference, as noted in section 4, with a two-tailed ttest. A p-value of

Effect of oxidizing honeycomb catalysts integrated in a firewood

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