Thomas Nussbaumer

Lucerne University of Applied Sciences and Arts, Luzern, Lucerne, Switzerland

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Publications (17)14.37 Total impact

  • Thomas Nussbaumer · Martin Kiener · Pascal Horat
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    ABSTRACT: Grate boilers are often applied for solid biofuels with high ash and moisture content in typical applications from 0.5 MW to 25 MW, and often operated at part load for heating applications. The paper presents measures to optimize the fluid dynamics to improve the combustion and to extend the part load capability. Thereto, special interest is given to the secondary air injection described as jets in cross flow (JICF) and the momentum flux ratio MR. For the situation in channel cross flows, the effective momentum flux ratio MReff is introduced. Different air injections are investigated by computational fluid dynamics (CFD) and validated by model experiments with particle image velocimetry (PIV) and image analysis. It is shown, that optimum conditions are achieved for MReff between 0.1 and 0.2 with 50% penetration depth for single-sided air injections. For opposite air-injections, as commonly applied in combustion chambers, higher MReff are also applicable. The most promising concepts are implemented in a 1.2 MW boiler and experimentally validated. The results show that the combustion quality, described by carbon monoxide (CO), can be improved by a factor of 4, compared to the reference case with already low emissions. Further, the boiler can be operated at lower excess air ratio, enabling an efficiency increase. By implementation of the presented measures, a stable operation from 30% load to full load can be achieved with CO emissions < 15 mg mn−3 at an oxygen volume fraction of 11% and at an excess air ratio of 1.8.
    Biomass and Bioenergy 05/2015; 76. DOI:10.1016/j.biombioe.2015.02.033 · 3.41 Impact Factor
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    ABSTRACT: Primary emissions from a log wood burner and a pellet boiler were characterized by online measurements of the organic aerosol (OA) using a high-resolution time-of-flight aerosol mass spectrometer (HR-TOF-AMS) and of black carbon (BC). The OA and BC concentrations measured during the burning cycle of the log wood burner, batch wise fueled with wood logs, were highly variable and generally dominated by BC. The emissions of the pellet burner had, besides inorganic material, a high fraction of OA and a minor contribution of BC. However, during artificially induced poor burning BC was the dominating species with ∼80% of the measured mass. The elemental O:C ratio of the OA was generally found in the range of 0.2-0.5 during the startup phase or after reloading of the log wood burner. During the burnout or smoldering phase, O:C ratios increased up to 1.6-1.7, which is similar to the ratios found for the pellet boiler during stable burning conditions and higher than the O:C ratios observed for highly aged ambient OA. The organic emissions of both burners have a very similar H:C ratio at a given O:C ratio and therefore fall on the same line in the Van Krevelen diagram.
    Environmental Science & Technology 09/2012; 46(20):11418-25. DOI:10.1021/es301654w · 5.48 Impact Factor
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    ABSTRACT: This study reports the potential toxicological impact of particles produced during biomass combustion by an automatic pellet boiler and a traditional logwood stove under various combustion conditions using a novel profluorescent nitroxide probe, BPEAnit. This probe is weakly fluorescent but yields strong fluorescence emission upon radical trapping or redox activity. Samples were collected by bubbling aerosol through an impinger containing BPEAnit solution, followed by fluorescence measurement. The fluorescence of BPEAnit was measured for particles produced during various combustion phases: at the beginning of burning (cold start), stable combustion after refilling with the fuel (warm start), and poor burning conditions. For particles produced by the logwood stove under cold-start conditions, significantly higher amounts of reactive species per unit of particulate mass were observed compared to emissions produced during a warm start. In addition, sampling of logwood burning emissions after passing through a thermodenuder at 250 degrees C resulted in an 80-100% reduction of the fluorescence signal of the BPEAnit probe, indicating that the majority of reactive species were semivolatile. Moreover, the amount of reactive species showed a strong correlation with the amount of particulate organic material. This indicates the importance of semivolatile organics in particle-related toxicity. Particle emissions from the pellet boiler, although of similar mass concentration, were not observed to lead to an increase in fluorescence signal during any of the combustion phases.
    Environmental Science & Technology 09/2010; 44(17):6601-7. DOI:10.1021/es100963y · 5.48 Impact Factor
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    Thomas Nussbaumer · Adrian Lauber
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    ABSTRACT: The particles from biomass combustion are collected in a laboratory electrostatic precipitator (ESP). Three different combustion regimes are maintained by a modified pellet boiler, i.e., high temperature and sufficient oxygen, high temperature and local lack of oxygen, and low temperature. The resulting particles are classified as salts, soot, and condensable organic compounds (COC) based on the particle type expected from the theory of particle formation. The chemical and electrical properties are analysed and confirm the classification: While salts exhibit a low carbon content, soot and COC are high in carbon. Soot and COC can be distinguished by significantly different molar C/H-ratio being 6.44 for soot and 1.24 for COC. The electrical conductivity, which is a key parameter for the precipitation and dust layer built-up in the ESP, is measured at different temperatures and humidities. Significant differences in conductivity are found for salts, soot, and COC, and in addition, a strong influence of the humidity of the flue gas is observed. Salt is confirmed to be ideal for ESP, while soot reveals high conductivity leading to re-entrainment of agglomerated particles, and COC exhibit low conductivity leading to back-corona which can be limiting at low humidity. The presented particle properties can be applied as guideline for ESP design and operation.
  • AAAR 28th Annual Conference; 10/2009
  • European Aerosol Conference; 09/2009
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    N. K. Meyer · Lauber A · Nussbaumer T · Burtscher H
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    ABSTRACT: The efficiency of an electrostatic precipitator (ESP) for reducing wood combustion emissions was investigated. Real-time measurements were conducted by directly reading the change in frequency of the tapered element in a Thermo Scientific 1400a TEOM. These measurements have been shown to be influenced by the charge on the aerosols reaching the tapered element such that the TEOM overestimates mass concentration. This electrostatic effect was crosschecked with particle mass concentration and particle number concentration measurements where no influence was observed. Placing a radioactive neutraliser prior to the TEOM leads to agreement between observed ESP efficiencies as measured by both the TEOM, mass filters and a CPC.
    01/2009; DOI:10.5194/amt-2-81-2009
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    ABSTRACT: Die Bereitstellung von End- bzw. Nutzenergie aus biogenen Festbrennstoffen erfolgt entweder direkt durch Verbrennung oder durch eine vorherige Umwandlung in entsprechende Sekundärenergieträger, wobei thermo-chemische, physikalisch-chemische oder bio-chemische Verfahren zum Einsatz kommen können. Im Folgenden werden die physikalischen und chemischen Grundlagen der thermo-chemischen Umwandlungsverfahren dargestellt; ihnen liegen letztlich vergleichbare Mechanismen zugrunde. Zuvor werden jedoch die wesentlichen Brennstoffeigenschaften definiert und zusammenfassend dargestellt.
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    ABSTRACT: Since biomass combustion is related to high emissions of particulate matter (PM), the International Energy Agency (IEA) Bioenergy Task 32 is promoting the implementation of technical measures for PM reduction. As a basis to set priorities and as a guideline for future regulations, emission factors from different types of combustion are of interest. The target of the present study is to collect and critically discuss emission factors from residential wood combustion in the IEA member countries. The reported results on emission factors from manual wood combustion devices exhibit huge ranges from less than 20 mg/MJ under ideal conditions up to more than 5 000 mg/MJ under poor conditions. Hence ideal operation is regarded as a major target for the future. Furthermore, the implementation of heat storage tanks is identified as an important need for log wood boilers. Since different PM measurements are applied, the influence of the sampling method, i.e., hot filter probe, quenching, and dilution tunnel, is discussed. Measurements reveal that the mass on solid particles and condensables need to be distinguished. Under poor combustion conditions, the mass of condensables can exceed the mass of solid particles and should be considered to evaluate the impact of wood combustion on the ambient air quality.
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    Rolf Frischknecht · Matthias Stucki · Thomas Nussbaumer
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    N Klippel · T Nussbaumer
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    ABSTRACT: The aim of the present investigation is to assess the health relevance of different combustion particles, i.e.: Diesel soot, particulate emissions from a quasi complete combustion of wood in an automatic wood boiler, consisting mainly of inorganic matter such as salts, and particulate matter from an incomplete combustion of wood in a badly operated wood stove. In addition, the range of variability of particle emissions and size distributions from different types of residential wood combustion and of different operation modes of wood stoves was determined. Particles and condensates were sampled in the flue gas and the total particle mass and the particle size distributions were analysed. The samples were used for biological tests on cell toxicity and on chromosome defects with lung cells from the chinese hamster. In addition, polycyclic aromatic hydrocarbons (PAH) were analysed. The results show, that Diesel soot exhibits a medium level of toxicity and chromosome defects, while particles from the automatic wood combustion exhibits app. 5 times lower toxicity. However, soot from the badly operated wood stove exhibits app. 15 times higher toxicity and chromosome defects than Diesel soot and app. 20 times higher levels of PAH. The highest toxicities are found for condensable matter from the wood stove.
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    Anna Doberer · Thomas Nussbaumer
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    ABSTRACT: Different recent investigations of PM 10 revealed that biomass burning is an underestimated source of soot in the ambient air (Prévôt et al, 2006): secondary organic aerosols and condensable compounds may significantly contribute to the total organic mass found in PM 10 in the ambient air (Robinson, 2007; Tsigaridis and Kanakidou, 2007). Furthermore, investigations on pollutant emissions from residential wood combustion (RWC) show that these emissions are strongly influenced by the type of operation and that emission factors may vary in a wide range (Nussbaumer, 2008). The aims of the present investigation are: • To investigate the range of pollutant emissions as a function of different types of operation. This information is used to estimate real-life emissions in comparison to emissions expected from type-tests. • To calculate emission factors (emissions per fuel amount used) which consider all phases of a burning cycle. • To estimate the additional contribution of condensable compounds to PM 10 in the ambient air. • The relevance of carbon monoxide (CO) as a tracer for unburned particulate matter and other pollutants is investigated, since CO analysis can be easily applied in practice and is currently used for emission limit values for RWC in Switzerland. For this purpose the emissions of different wood combustion devices were measured during start-up, stationary combustion, and burnout. The filling degree, the fuel moisture, the air supply and other parameters were varied. Flue gas composition, including CO, VOC, O 2 , CO 2 , and NO X was determined as well as the mass of solid particles in the chimney at 160°C according to VDI 2066. In addition, mass concentration of condensable compounds was measured at 0°C according to EPA standards. Particle number concentration and particle size distribution were analysed by electric and optical methods, i.e., SMPS and OPC.
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    T. Nussbaumer · N. Klippel · M. Oser
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    ABSTRACT: Biomass combustion exhibits relatively high particle emissions smaller 10 microns (PM 10). Under optimized conditions, these particles consist mainly of salts from ash constituents. Under poor combustion conditions, organic particulate matter is emitted additionally. The aim of the present project is to compare indicators for health effects of different types of combustion particles, i.e., mainly inorganic particles from optimized wood combustion, particles from wood burnt at incomplete combustion, and Diesel soot. The present paper presents different effects on cytotoxicity of particles during in-vitro tests of V79 lung cells of the Chinese hamster. For this purpose, particle emissions from an automatic wood furnace and from a Diesel engine were sampled on plane filters. The particles were extracted and added to the cell medium to test the respective toxicity. First tests reveal cytotoxic reactions for both types of particles, i.e., Diesel soot and mainly inorganic wood particles emitted during optimized combustion conditions. For a comparison, the cell survival rate was determined for both particle species as a function of particle mass concentration in the cell medium. The result reveals a significantly higher cytotoxicity for Diesel soot than for wood particles from optimized combustion, based on the same particle mass concentration.
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    ABSTRACT: Für biogene Festbrennstoffe (z. B. Holz, Stroh) hat die direkte Verbrennung in Feuerungen bis heute die weitaus größte Bedeutung unter den Energiewandlungsprozessen und -verfahren. Verbrennungsanlagen werden eingesetzt zur Produktion von Wärme, die genutzt werden kann als Sekundärenergie (z. B. Dampf, der dann weiter in elektrische Energie umgewandelt werden kann), als Endenergie (z. B. Fernwärme) oder als Nutzenergie (z. B. Strahlungswärme eines Kachelofens). Unter einer Verbrennung wird dabei hier die Oxidation eines Brennstoffs unter Energiefreisetzung verstanden. Dabei entstehen Abgase und Asche. Vor diesem Hintergrund werden im Folgenden die mit der direkten thermischen Umwandlung biogener Festbrennstoffe zusammenhängenden Aspekte diskutiert. Der Schwerpunkt liegt dabei auf der Darstellung der Feuerungsanlagentechnik. Auch wird auf die Techniken für die Abgasreinigung eingegangen. Zusätzlich werden die Möglichkeiten einer Stromerzeugung bzw. einer Kraft-Wärme-Kopplung (KWK) diskutiert. Zuvor werden jedoch spezielle Anforderungen und Besonderheiten erläutert.
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    Thomas Nussbaumer
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    Martin Kiener · Thomas Nussbaumer
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    ABSTRACT: Grate boilers are widely applied for biomass combustion and achieve high combustion quality in good operation conditions. However, uneven fuel distribution such as e.g. uncovered grate sections can occur due to part load operation or changing fuel properties. Uncovered grate sections influence the flow conditions and are assumed to cause increased emissions from incomplete combustion such as carbon monoxide (CO). The objective of this investi-gation is to analyse the influence of the grate coverage on the flue gas emissions by experiments and CFD modelling. Experiments are performed on a 1.2 MW moving grate boiler. The grate coverage is varied by different primary air settings. To identify the grate coverage and to derive gas profiles for the CFD calculations, pyrolysis gas measur-ements (CO, CO 2 , CH 4 , H 2 , O 2 and H 2 O) above the grate with an oil cooled sampling probe are performed. Flue gas analysis is performed with use of CO as indicator for the combustion quality. Experiments and CFD modelling confirm a relevant influence of the grate coverage on the combustion quality. With increasing uncovered area at the end of the grate, CO emissions increase. A change from an ideally covered grate with 80% coverage and CO emissions of 25 mg/m 3 at 11 vol.-% O 2 to a highly uncovered grate with 40% coverage, a CO increase by a factor of 2.5 is found in experiments. CFD modelling predicts an increase by a factor of 3.9. Hence modelling is qualitatively validated by experiments and uneven fuel distribution is confirmed as a source of increased emissions. Measures to reduce emissions due to uncovered grates are discussed.
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    Anna Doberer · Jürgen Good · Thomas Nussbaumer