Thomas Nussbaumer

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

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Publications (26)24.75 Total impact

  • Jorge Martinez-Garcia · Thomas Nussbaumer
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    ABSTRACT: A one dimensional transient model for simulating the conversion of solid biomass fuels in grate boilers is presented. The model considers drying, pyrolysis, and char oxidation, gas flow through the pore space of the bed, conductive, convective and radiative heat transfer, and shrinkage of the fuel bed. It allows to study the influence of fuel properties and operating parameters on the solid fuel conversion, the resulting grate coverage, and the gas profiles. Experimental results from a 1.2 MW grate boiler at optimum conditions are used to adjust the moving bed velocity in the model. Calculations with increased fuel humidity then result in a prolonged drying time and unburnt carbon in the ash. Adopted model runs further reveal that ideal conditions can be recovered either by increasing the excess air, by air pre-heating, or by reducing the boiler capacity. Hence the model is useful to predict the influence of parameters on the fuel conversion, to evaluate measures for combustion optimisation, and to develop control strategies.
    No preview · Article · Aug 2015 · Combustion Science and Technology
  • 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.
    No preview · Article · May 2015 · Biomass and Bioenergy
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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.
    No preview · Article · Sep 2012 · Environmental Science & Technology
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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.
    Full-text · Article · Sep 2010 · Environmental Science & Technology
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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.
    Full-text · Article · Apr 2010

  • No preview · Conference Paper · Oct 2009

  • No preview · Conference Paper · Sep 2009
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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.
    No preview · Article · Jan 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.
    No preview · Article · Jan 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.
    Full-text · Article · Jan 2009
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    Thomas Nussbaumer
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    ABSTRACT: Since biomass is the only carbon-based renewable fuel, its application becomes more and more important for climate protection. Among the thermochemical conversion technologies (i.e., combustion, gasification, and pyrolysis), combustion is the only proven technology for heat and power production. Biomass combustion systems are available in the size range from a few kW up to more than 100 MW. The efficiency for heat production is considerably high and heat from biomass is economically feasible. Commercial power production is based on steam cycles. The specific cost and efficiency of steam plants is interesting at large scale applications. Hence co-combustion of biomass with coal is promising, as it combines high efficiency with reasonable transport distances for the biomass. However, biomass combustion is related to significant pollutant formation and hence needs to be improved. To develop measures for emission reduction, the specific fuel properties need to be considered. It is shown that pollutant formation occurs due to two reasons:  (1) Incomplete combustion can lead to high emissions of unburnt pollutants such as CO, soot, and PAH. Although improvements to reduce these emissions have been achieved by optimized furnace design including modeling, there is still a relevant potential of further optimization. (2) Pollutants such as NOX and particles are formed as a result of fuel constituents such as N, K, Cl, Ca, Na, Mg, P, and S. Hence biomass furnaces exhibit relatively high emissions of NOX and submicron particles. Air staging and fuel staging have been developed as primary measures for NOX reduction that offer a potential of 50% to 80% reduction. Primary measures for particle reduction are not yet safely known. However, a new approach with extensively reduced primary air is presented that may lead to new furnace designs with reduced particle emissions. Furthermore, assisting efforts for optimized plant operation are needed to guarantee low emissions and high efficiency under real-world conditions.
    Preview · Article · Sep 2003 · Energy & Fuels
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    Christian Bruch · Bernhard Peters · Thomas Nussbaumer
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    ABSTRACT: A computer model describing the conversion of wood under packed-bed conditions is presented. The packed bed is considered to be an arrangement of a finite number of particles, typically sized between 5 and 25 mm, with a void space left between them. Each particle is undergoing a thermal conversion process, which is described by a one-dimensional and transient model.Within the single-particle model, heating, drying, pyrolysis, gasification and combustion are considered, whereby each particle exchanges energy due to conduction and radiation with its neighbours. Because of the one-dimensional discretization of the particles, heat transfer and mass transfer is taken into account explicitly. Therefore, no macrokinetic data are needed within the model. For ease of implementation and access, kinetic data and property data are stored in a database. The global conversion of the packed bed is represented by the contributions of single particles, where each particle is coupled to the surrounding gas phase by heat and mass transfer. For gas phase flow through the porous bed, the conservation equations for mass, momentum and energy are solved on a Cartesian mesh by a Finite Volume method.Experiments have been performed to validate the single particle model for the conversion of beech wood during pyrolysis and char combustion. Agreement between experimental and predictions obtained by the model is very satisfactory. However, for wet wood, changes in structure seem to enhance the heat transfer to the solid which is not yet covered in the model.
    Full-text · Article · Apr 2003 · Fuel
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    ABSTRACT: The objective of this study is to measure the heat-up and the drying of a packed bed consisting of large wood particles as encountered in furnaces and to compare the predictions of a particle resolved approach to measurements. Within the experiments both single particle and packed bed measurements for the drying of wood were carried out. For both cases the samples as single particles and as a packed bed were exposed to a gas stream its temperature ranging from T=443 to . The temperatures and the mass loss due to drying were recorded during the experiments and the heat transfer properties were correlated with earlier findings.Within the present contribution a packed bed is considered as an ensemble of a finite number of particles. The heat-up and drying process of each particle is described by one-dimensional and transient conservation equations for mass and energy. Applying this model to all particles of a packed bed forms the entire packed bed process as a sum of individual particle processes. The arrangement of particles within the bed defines a solid phase and a void space between the particles. The flow through the void space of a packed bed is modelled as a flow through a porous media taking into account interaction between the solid and the gaseous phase by heat and mass transfer. A comparison between measurements and predictions of drying models yielded satisfactory agreement only for the constant evaporation temperature model. Furthermore, the results show, that a particle resolved approach is better suited than a continuum mechanic approach to describe packed bed processes since this approach omits additional empirical correlations for a packed bed.
    Full-text · Article · Oct 2002 · Biomass and Bioenergy
  • H. Hofbauer · M. Kaltschmitt · T. Nussbaumer

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  • R. Haberl · L. Konersmann · E. Frank · J. Good · T. 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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    Marc-André Baillifard · Ernesto Casartelli · Thomas Nussbaumer
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    ABSTRACT: Biomass combustion is characterised by a multi step process consisting of an initial conversion of the solid fuel to gaseous compounds prior to the consecutive gas phase reactions. At combustion temperatures above 850°C, the quality of the gas phase oxidation strongly depends on the mixing quality between combustible gases and combustion air. Hence optimising the combustion chamber geometry to improve mixing and flow conditions offers a significant potential for pollutant reduction and efficiency improvement. This work shows how this optimisation can be achieved using small scale model experiments. The design process of the scaled model is presented, as well as different measurement techniques. Tracer particles are used to get a qualitative insight on the flow behaviour in the combustion chamber. The velocity in the scaled model is then measured using hot wire anemometry. Further, the mixing quality is assessed using particle tracers which are introduced in one of the flow, and by measuring their local concentration in a section of the combustion chamber. A laser is used to illuminate a planar section of the combustion chamber, and the particle concentration is recorded using a camera. This method is used to assess the mixing efficiency of two different secondary air injection configurations. In addition, the experimental results are compared with CFD calculations. Good agreement of experiment and CFD is found thus enabling a validation of critical flow regimes to improve the reliability of CFD applications.
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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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    Rolf Frischknecht · Matthias Stucki · Thomas Nussbaumer

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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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