Publications

Other papers | 2015

The role of 1H-indene in product gas of biomass gasification

Kuba M, Kirnbauer F, Hofbauer H. The role of 1H-indene in product gas of biomass gasification. International Bioenergy Exhibition and Asian Bioenergy Conference 2015. October 2015, Shanghai, China.

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Peer reviewed papers | 2015

The Role of Leak Air in a Double-Wall Chimney

Lichtenegger K, Hebenstreit B, Pointner C, Schmidl C, Höftberger E. The role of leak air in a double-wall chimney. Heat Mass Transfer. 2015;51(6):787-94.

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In modern buildings with tight shells, often room-independent air supply is required for proper operation of biomass stoves. One possibility to arrange this supply is to use a double-wall chimney with flue gas leaving through the pipe and fresh air entering through the annular gap. A one-dimensional quasi-static model based on balance equations has been developed and compared with experimental data. Inclusion of leak air is crucial for reproduction of the experimental results. © 2014, Springer-Verlag Berlin Heidelberg.

Peer reviewed papers | 2016

The Virtual Biomass Grate Furnace - An Overall CFD Model for Biomass Combustion Plants

Ali Shiehnejadhesar, Ramin Mehrabian, Robert Scharler, Christoph Hochenauer. The Virtual Biomass Grate Furnace - An Overall CFD Model for Biomass Combustion Plants. 24rd European Biomass Conference & Exhibition (poster).

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This paper presents the virtual biomass grate furnace, which comprises of comprehensive CFD models of all relevant processes for the simulation of biomass grate furnaces. The models consist of a 3D packed bed model, a gas phase combustion model for laminar to highly turbulent flows and a model to account for the influence of the flue gas streaks arising from the fuel bed in the freeboard. The simulation results of a 20 kW underfeed stoker furnace show that the overall CFD model is able to provide valuable insight on the processes occurring in the packed bed and freeboard and their interactions.

Other papers | 2016

The wood pellet market in Austria: A structural market model analysis

Christa Kristöfel, Christoph Strasser, Erwin Schmid, Ulrich B. Morawetz, The wood pellet market in Austria: A structural market model analysis, Energy Policy, Volume 88, January 2016, Pages 402-412,

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Conference presentations and posters | 2010

Thermal Conversion of Biomass by Microwave Energy - First Results with Wood

Schrammel G, Paisler C, Krug H, Rauch R, Hofbauer H. Thermal Conversion of Biomass by Microwave Energy - First Results with Wood, 18th European Biomass Conference and Exhibiton 2010, 3rd-7th May 2010, Lyon, France. p 907-910.

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By using a microwave generator as energy source wood gets converted into three products: (1) condensate (“product oil”), (2) product gas and (3) charcoal (“material residue”). In this microwave-based specific kind of pyrolysis process wood is used as standard input material in order to have the possibility to compare the three generated products either with products of already established conventional pyrolysis processes [1] or other processes like gasification within thermo-chemical conversion [2]. Therefore, a discontinuous microwave apparatus of technical standard size (magnetron power: 6 kW, magnetron frequency: 2.45 GHz) is used.

Reports | 2019

Thermal Gasification of low-grade residuals for the production of valuable products and energy

Wagner K, Kuba M, Fuchs J, Müller S. Thermal Gasification of low-grade residuals for the production of valuable products and energy. Publishable final report. June 2019.

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Conference presentations and posters | 2014

Thermal simulation of a pellet boiler and a heat storage tank for future control strategies

Schnetzinger R, Musumarra I, Hebenstreit B, Lichtenegger K, Schwarz M, Höftberger E. Thermal simulation of a pellet boiler and a heat storage tank for future control strategies, 4th Central European Biomass Conference 2014, 15th-18th of January 2014, Graz, Austria.

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Peer reviewed papers | 2016

Thermal Stability of Bed Particle Layers on Naturally Occurring Minerals from Dual Fluid Bed Gasification of Woody Biomass

Kuba M, He H, Kirnbauer F, Skoglund N, Boström D, Öhman M, Hofbauer H. Thermal Stability of Bed Particle Layers on Naturally Occurring Minerals from Dual Fluid Bed Gasification of Woody Biomass. Energy & Fuels. 20 October 2016;30(10): 8277-8285.

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The use of biomass as feedstock for gasification is a promising way of producing not only electricity and heat but also fuels for transportation and synthetic chemicals. Dual fluid bed steam gasification has proven to be suitable for this purpose. Olivine is currently the most commonly used bed material in this process due to its good agglomeration performance and its catalytic effectiveness in the reduction of biomass tars. However as olivine contains heavy metals such as nickel and chromium no further usage of the nutrient-rich ash is possible and additional operational costs arise due to necessary disposal of the ash fractions. This paper investigates possible alternative bed materials and their suitability for dual fluid bed gasification systems focusing on the behavior of the naturally occurring minerals olivine, quartz and K-feldspar in terms of agglomeration and fractionation at typical temperatures. To this end samples of bed materials with layer formation on their particles were collected at the industrial biomass combined heat and power (CHP) plant in Senden, Germany, which uses olivine as the bed material and woody biomass as feedstock. The low cost logging residue feedstock contains mineral impurities such as quartz and K-feldspar which become mixed into the fluidized bed during operation. Using experimental analysis and thermochemical it was found that the layers on olivine and K-feldspar showed a significantly lower agglomeration tendency than quartz. Significant fractionation of particles or their layers could be detected for olivine and quartz, whereas K-feldspar layers were characterized by a higher stability. High catalytic activity is predicted for all three minerals once Ca-rich particle layers are fully developed. However quartz may be less active during the build-up of the layers due to lower amounts of Ca in the initial layer formation.
 

Conference presentations and posters | 2019

Thermal Trouble: Challenges in Optimization and Evaluation of Thermal Energy Systems

Lichtenegger K, Unterberger V, Stadler M, Zellinger M, Carreras F, Moser A. Thermal Trouble: Challenges in Optimization and Evaluation of Thermal Energy Systems. IAPE 2019 : International Conference on Innovative Applied Energy (oral presentation). March 2019.

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Other Publications | 2014

Thermo-chemical pre-treatment of brewers' spent grains

Gorter S, Rachbauer L, Scheidl S, Gabauer W, Ortner M, Bochmann G. Thermo-chemical pre-treatment of brewers' spent grains, 4th Central European Biomass Conference 2014, 15th-18th of January 2014, Graz, Austria.

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Peer reviewed papers | 2020

Thermochemical equilibrium study of ash transformation during combustion and gasification of sewage sludge mixtures with agricultural residues with focus on the phosphorus speciation

Hannl TK, Sefidari H, Kub M, Skoglund N, Öhmann M. Thermochemical equilibrium study of ash transformation during combustion and gasification of sewage sludge mixtures with agricultural residues with focus on the phosphorus speciation. Biomass Conversion and Biorefinery.2020

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The necessity of recycling anthropogenically used phosphorus to prevent aquatic eutrophication and decrease the economic dependency on mined phosphate ores encouraged recent research to identify potential alternative resource pools. One of these resource pools is the ash derived from the thermochemical conversion of sewage sludge. This ash is rich in phosphorus, although most of it is chemically associated in a way where it is not plant available. The aim of this work was to identify the P recovery potential of ashes from sewage sludge co-conversion processes with two types of agricultural residues, namely wheat straw (rich in K and Si) and sunflower husks (rich in K), employing thermodynamic equilibrium calculations. The results indicate that both the melting behavior and the formation of plant available phosphates can be enhanced by using these fuel blends in comparison with pure sewage sludge. This enhanced bioavailability of phosphates was mostly due to the predicted formation of K-bearing phosphates in the mixtures instead of Ca/Fe/Al phosphates in the pure sewage sludge ash. According to the calculations, gasification conditions could increase the degree of slag formation and enhance the volatilization of K in comparison with combustion conditions. Furthermore, the possibility of precipitating phosphates from ash melts could be shown. It is emphasized that the results of this theoretical study represent an idealized system since in practice, non-equilibrium influences such as kinetic limitations and formation of amorphous structures may be significant. However, applicability of thermodynamic calculations in the prediction of molten and solid phases may still guide experimental research to investigate the actual phosphate formation in the future.

Other papers | 2016

Thermochemische Behandlung eines niederkalorischen Reststoffes zur Gewinnung von Sekundärrohstoffen

Meirhofer M, Dißauer C, Strasser C, Kranner R, Wartha C. Thermochemische Behandlung eines niederkalorischen Reststoffes zur Gewinnung von Sekundärrohstoffen. e-nova 2016 (oral presentation). November 2016, Pinkafeld, Austria.

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Other papers | 2009

Thermodynamic equilibrium calculations concerning the removal of heavy metals from sewage sludge ash by chlorination

Fraissler G, Jöller M, Mattenberger H, Brunner T, Obernberger I. Thermodynamic equilibrium calculations concerning the removal of heavy metals from sewage sludge ash by chlorination. Chemical Engineering and Processing: Process Intensification. 2009;48(1):152-64.

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Peer reviewed papers | 2022

Thermodynamic Equilibrium Study on the Melting Tendency of the K-Ca-Mg-P-Si-O System with Relevance to Woody and Agricultural Biomass Ash Compositions

Falk J, Hannl TK, Skoglund N, Backman R, Öhman M. Thermodynamic Equilibrium Study on the Melting Tendency of the K-Ca-Mg-P-Si-O System with Relevance to Woody and Agricultural Biomass Ash Compositions. Energy and Fuels 7 July 2022.36(13):7035-7051.

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A major challenge in the combustion of biomass fuels is the heterogeneity of ash-forming elements, which may cause a wide range of ash-related problems. Understanding the melting tendency of the coarse ash fractions is necessary to mitigate agglomeration and slagging. This work aims to evaluate the melting tendency of the K-Ca-Mg-Si-P-O system by use of thermodynamic equilibrium calculations. The formation of condensed phases were systematically assessed in a combustion atmosphere, varying temperatures, and composition. Compositional ranges were based on fuel ash data extracted from the Phyllis 2 database. The speciation and degree of polymerization of phosphates, silicates, and melts were evaluated and indicated a systematic variation in composition. The melt fraction was predicted as a function of temperature and composition. The melting tendency was modeled for three systems, i.e., a P-dominated, a Si-dominated, and a mixed Si-P system. Four ratios between K2O, CaO, MgO, SiO2, and P2O5 were found to have a large effect on the melting tendency of the ash mixtures: the ratio between network formers (SiO2, P2O5), K2O to total network modifiers, CaO to CaO + MgO, and the ratio of network formers to total ash oxides. This modeling approach showed qualitative agreement with ash-related issues seen in previous lab-scale experiments in bubbling fluidized bed and fixed bed combustion. Practical implications of the results are discussed from the perspective of fuel design with the aim of preventing ash-related problems. This study presents a novel method of applying thermodynamic equilibrium calculations for a broad range of compositions and shows potential for predicting ash-related issues related to the melting of coarse ash fractions.

Conference presentations and posters | 2010

Thermogravimetric Analysis and Devolatilisation Kinetics of New Biomass Fuels

Moradi F, Brunner T, Obernberger I. Thermogravimetric Analysis and Devolatilisation Kinetics of New Biomass Fuels, 18th European Biomass Conference and Exhibition 2010, 3rd-7th of May 2010, Lyon, France. (visual presentation)

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Conference presentations and posters | 2019

Time-dependent catalytic activation of inactive k-feldspar by layer formation during fluidized bed conversion with residual fuels

Wagner C, Hammerl C, Kuba M, Hofbauer H. Time-dependent catalytic activation of inactive k-feldspar by layer formation during fluidized bed conversion with residual fuels. 27th European Biomass Conference & Exhibition (Poster). May 2019.

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Olivine is currently used as bed material in dual fluidized bed steam gasification due to its catalytic activity towards the water-gas-shift (WGS) reaction and tar reforming. However, olivine contains traces of heavy metals which necessitate an expensive disposal of the accruing ash. The study of alternative bed materials for DFB steam gasification is therefore of major importance. The activity of a bed material is one important factor when classifying its suitability. Several alternative bed materials like quartz and K-feldspar are non-active when fresh but become activated during operation by interaction with the ash by forming layers. The focus of this work was therefore to quantify the initial activation of K-feldspar over the first operational hours as exemplary inactive bed material. Bed material samples from fluidized bed combustion were collected during operation. The fuels used were bark, chicken manure and a bark/chicken manure mixture. The obtained samples were sieved to 200 – 250 µm and tested in a micro-scale test-rig regarding the WGS reaction. A time-dependent activation of K-feldspar was observed marking a first step in better understanding the activation of bed materials.

Conference presentations and posters | 2015

Time-resolved characterization of PM10 emissions from modern small scale biomass combustion units, including PAHs

Kistler M, Schmidl C, Cetintas EC, Padouvas E, Bauer H, Puxbaum H, Kasper-Giebl A. Time-resolved characterization of PM10 emissions from modern small scale biomass combustion units, including PAHs, 23rd European Biomass Conference 2015, 1st-4th of June 2015, Vienna, Austria. (visual presentation)

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Conference presentations and posters | 2014

Torrefied pellets – influence of torrefaction on pellet characteristics and combustion behaviour

Pointner C, Schmutzer-Roseneder I, Feldmeier S, Kristöfel C, Ehrig R, Schwabl M, Strasser C, Wörgetter M. Torrefied pellets – influence of torrefaction on pellet characteristics and combustion behavior, 4th Central European Biomass Conference 2014, 15th-18th of January 2014, Graz, Austria.

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Conference presentations and posters | 2014

Towards a Stochastic Cellular Automata Model of Log Wood Combustion

Lichtenegger K, Schappacher W, Hebenstreit B, Schmidl C, Höftberger E. Towards a Stochastic Cellular Automata Model of Log Wood Combustion. Journal of Physics: Conference Series. 2014:490:102015. (peer reviewed)

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Describing the combustion of log wood and others solid fuels with complex geometry, considerable water content and often heterogenous struture is a nontrivial task. Stochastic Cellular Automata models offer a promising approach for modelling such processes. Combustion models of this type exhibit several similarities to the well-known forest fire models, but there are also significant differences between those two types of models. These differences call for a detailed analysis and the development of supplementary modeling approaches. In this
article we define a qualitative two-dimensional model of burning log wood, discuss the most important differences to classical forest fire models and present some preliminary results.

Conference presentations and posters | 2019

Towards the in house production of enzymes using processing waste

Weiss R, Nyanhongo G, Ortner M, Guebitz G.Towards the in house production of enzymes using processing waste. 15th International Conference on Renewable Resources and Biorefineries, Toulouse, FRANCE. June 2019.

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Peer reviewed papers | 2016

Toxicological characterization of particulate emissions from straw, Miscanthus, and poplar pellet combustion in residential boilers

Kasurinen S, Jalava PI, Uski O, Happo MS, Brunner T, Mäki-Paakkanen J, Jokiniemi J, Obernberger I, Hirvonen MR. Toxicological characterization of particulate emissions from straw, Miscanthus, and poplar pellet combustion in residential boilers. Aerosol Science and Technology. 2 January 2016;50(1): 41-51.

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Wood pellets have been used in domestic heating appliances for three decades. However, because the share of renewable energy for heating will likely rise over the next several years, alternative biomass fuels, such as short-rotation coppice or energy crops, will be utilized. We tested particulate emissions from the combustion of standard softwood pellets and three alternative pellets (poplar, Miscanthus sp., and wheat straw) for their ability to induce inflammatory, cytotoxic, and genotoxic responses in a mouse macrophage cell line. Our results showed clear differences in the chemical composition of the emissions, which was reflected in the toxicological effects. Standard softwood and straw pellet combustion resulted in the lowest PM1 mass emissions. Miscanthus sp. and poplar combustion emissions were approximately three times higher. Emissions from the herbaceous biomass pellets contained higher amounts of chloride and organic carbon than the emissions from standard softwood pellet combustion. Additionally, the emissions of the poplar pellet combustion contained the highest concentration of metals. The emissions from the biomass alternatives caused significantly higher genotoxicity than the emissions from the standard softwood pellets. Moreover, straw pellet emissions caused higher inflammation than the other samples. Regarding cytotoxicity, the differences between the samples were smaller. Relative toxicity was generally highest for the poplar and Miscanthus sp. samples, as their emission factors were much higher. Thus, in addition to possible technical problems, alternative pellet materials may cause higher emissions and toxicity. The long-term use of alternative fuels in residential-scale appliances will require technological developments in both burners and filtration.

Peer reviewed papers | 2020

Transient CFD simulation of wood log combustion in stoves

Scharler R, Gruber T, Ehrenhöfer A, Kelz J, Mehrabian Bardar R, Bauer T, Hochenauer C, Anca-Couce A. Transient CFD simulation of wood log combustion in stoves. Renewable Energy 2020.145:651-662

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Wood log stoves are a common residential heating technology that produce comparably high pollutant emissions. Within this work, a detailed CFD model for transient wood log combustion in stoves was developed, as a basis for its optimization. A single particle conversion model previously developed by the authors for the combustion of thermally thick biomass particles, i.e. wood logs, was linked with CFD models for flow and turbulence, heat transfer and gas combustion. The sub-models were selected based on a sensitivity analysis and combined into an overall stove model, which was then validated by simulations of experiments with a typical wood log stove, including emission measurements. The comparison with experimental results shows a good accuracy regarding flue gas temperature as well as CO2 and O2 flue gas concentrations. Moreover, the characteristic behavior of CO emissions could be described, with higher emissions during the ignition and burnout phases. A reasonable accuracy is obtained for CO emissions except for the ignition phase, which can be attributed to model simplifications and the stochastic nature of stove operation. Concluding, the CFD model allows a transient simulation of a stove batch for the first time and hence, is a valuable tool for process optimization.

Conference presentations and posters | 2014

Transport Biofuels in Europe - A Vision for 2030

Wörgetter M. Transport Biofuels in Europe - A Vision for 2030, Fuels of the Future 2014, 20th-21st of January 2014, Berlin, Germany.

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Conference presentations and posters | 2010

Trends and opportunities of micro-CHP technologies based on biomass combustion

Obernberger I. Trends and opportunities of micro-CHP technologies based on biomass combustion, 18th European Biomass Conference and Exhibition 2010, 3rd-7th of May 2010, Lyon, France. p 1-9.

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Conference presentations and posters | 2011

Trennung heterogener Abfälle durch sensorgestützte Sortierung zur Optimierung materialspezifischer Abfallbehandlung

Pieber S, Ragossnig A, Sommer M, Meirhofer M, Curtis A, Pomberger R. Trennung heterogener Abfälle durch sensorgestützte Sortierung zur Optimierung materialspezifischer Abfallbehandlung, Waste-to-Resources 2011, 24th-27th of May 2011, Hannover, Germany.

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Peer reviewed papers | 2022

Trickle-Bed Bioreactors for Acetogenic H2/CO2 Conversion

Steger F, Ergal I, Daubek A, Loibl N, Rachbauer L, Fuchs W, Rittmann SKMR, Bochmann G. Trickle-Bed Bioreactors for Acetogenic H2/CO2 Conversion. Frontiers in Energy Research. 8 Apirl 2022.10;842284

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Acetic acid is an essential industrial building block and can be produced by acetogenic bacteria from molecular hydrogen (H2) and carbon dioxide (CO2). When gasses are supplied as substrates, bioreactor design plays an important role for their availability. Trickle-bed bioreactors (TBs) have an enhanced gas-to-liquid mass transfer and cells remain in the system by forming a biofilm on the carriers. So far, TBs have been investigated extensively for bio-methanation processes, whereas studies for their use in acetic acid production are rare. In this study, we evaluated the reproducibility of two parallel TBs for acetic acid production from H2:CO2 (= 70:30) by a mixed culture with a gas flow rate of 3.8 mL min−1 and a medium flow rate of 10 mL min−1. Additionally, the effect of glucose addition during the starting phase on the resulting products and microbial composition was investigated by setting up a third TB2. Partial medium exchanges to decrease the internal acetic acid concentration (AAC) combined with recycling of withdrawn cells had a positive impact on acetic acid production rates with maxima of around 1 g L−1 d−1 even at high AACs of 19–25 g L−1. Initial glucose addition resulted in the accumulation of unwanted butyric acid up to concentrations of 2.60 ± 0.64 g L−1. The maximum AAC of 40.84 g L−1 was obtained without initial glucose addition. The main families identified in the acetogenic TBs were Peptococcaceae, Ruminococcaceae, Planococcaceae, Enterobacteriaceae, Clostridiaceae, Lachnospiraceae, Dysgonomonadaceae and Tannerellaceae. We conclude that a TB is a viable solution for conversion of H2/CO2 to acetate using an anaerobic enrichment culture.

Other Publications | 2013

Two-Stage Anaerobic Digestion of Sugar Beet Pressed Pulp - Optimizing of reactor performance

Stoyanova E et al. Two-Stage Anaerobic Digestion of Sugar Beet Pressed Pulp - Optimizing of reactor performance, 13th World Congress on Anaerobic Digestion 2013, 25th-28th of June 2013, Santiago de Compostela, Spain. (peer reviewed) (visual presentation)

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Peer reviewed papers | 2016

Two-stage cultivation of N-rich and N–deprived Acutodesmus obliquus biomass: Influence of cultivation and dewatering methods on microalgal biomass used in anaerobic digestion

Gruber M, Nussbaumer M, Jerney J, Ludwig I, Zohar E, Lang I, Bochmann G, Schagerl M, Obbard JP, Fuchs W, Drosg B. Two-stage cultivation of N-rich and N–deprived Acutodesmus obliquus biomass: Influence of cultivation and dewatering methods on microalgal biomass used in anaerobic digestion. Algal Research. July 2016;17: 105-112.

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Peer reviewed papers | 2021

Ultra-low temperature water-gas shift reaction catalyzed by homogeneous Ru-complexes in a membrane reactor - membrane development and proof of concept

Logemann M, Wolf P, Loipersböck J, Schrade A, Wessling M, Haumann M. Ultra-low temperature water-gas shift reaction catalyzed by homogeneous Ru-complexes in a membrane reactor - membrane development and proof of concept. Catalysis Science and Technology. 2021.11(4):1558-1570. https://doi.org/10.1039/D0CY02111C

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A monolithic membrane reactor combining the supported ionic liquid-phase (SILP) catalyzed ultra-low temperature water–gas shift reaction (WGSR) with in situ product removal is presented. The SILP catalyst consists of the transition metal complex [Ru(CO)3Cl2]2 homogeneously dissolved in 1-butyl-2,3-dimethylimidazolium chloride [C4C1C1Im]Cl and supported on alumina pellets. These Ru-SILP pellets are deposited inside the channels of a silicon carbide monolith. The resulting monolithic catalyst is very active and stable in the WGSR in the temperature range between 120 and 160 °C, thereby making full use of the high equilibrium conversion at these conditions. A facilitated transport membrane was coated onto the smooth outside of the SiC monolith to allow preferential removal of CO2 compared to H2. The proof of this concept has been shown under industrially relevant conditions using a biogas feed. These results demonstrate, for the first time, the combination of homogeneous SILP catalyzed WGSR with enhanced in situ removal of one of the products (here: CO2) via facilitated transport membrane separation.

Conference presentations and posters | 2009

Unearthing waste`s potential for 100% renewable energy systems

Ragossnig A. Unearthing waste`s potential for 100% renewable energy systems. 5th SDEWES-conference 2009, 29th of September-3rd of October, Dubrovnik, Croatia.

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This paper focusses on the elaboration of the potential of the waste sector to contribute to the provision of 100% renewable energy systems. Waste is an abundant and locally available ressource and in many cases it is (at least partially) of biogenic origin, therefore pursuing political goals in waste management by energetic utilization of waste contributes towards achieving political goals in the energy as well as climate policy, too. However, it is shown based on the example of Austria that looking at energy systems on a national or international scale the waste sector is only able to contribute very little to the provision of the overall energy needed. It is different if one looks at specific energy systems in industrial sectors or on individual industrial sites. Here one must aknowledge that the energetic utilization of waste can have a high impact towards establishing renewable energy systems. Exemplarily this is shown by discussing the Austrian pulp & paper as well as the cement industry sector.

Peer reviewed papers | 2022

Unknown input observer design for linear time-invariant multivariable systems based on a new observer normal form

Niederwieser H, Tranninger M, Seeber R, Reichhartinger M. Unknown input observer design for linear time-invariant multivariable systems based on a new observer normal form. International Journal of Systems Science. 2022 Apr 6. https://doi.org/10.1080/00207721.2022.2046201

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In various applications in the field of control engineering, the estimation of the state variables of dynamic systems in the presence of unknown inputs plays an important role. Existing methods require the so-called observer matching condition to be satisfied, rely on the boundedness e variables or exhibit an increased observer order of at least twice the plant order. In this article, a novel observer normal form for strongly observable linear time-invariant multivariable systems is proposed. In contrast to classical normal forms, the proposed approach also takes the unknown inputs into account. The proposed observer normal form allows for the straightforward construction of a higher-order sliding mode observer, which ensures global convergence of the estimation error within finite time even in the presence of unknown bounded inputs. Its application is not restricted to systems which satisfy the aforementioned limitations of already existing unknown input observers. The proposed approach can be exploited for the reconstruction of unknown inputs with bounded derivative and robust state-feedback control, which is shown by means of a tutorial example. Numerical simulations confirm the effectiveness of the presented work.

Peer reviewed papers | 2022

Unknown Input Observer Design for Linear Time-Invariant Systems - A Unifying Framework

Tranninger M, Niederwieser H, Seeber R, Horn M. Unknown Input Observer Design for Linear Time-Invariant Systems - A Unifying Framework. International Journal of Robust and Nonlinear Control. 2022 Nov 18. https://doi.org/10.1002/rnc.6399

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This article presents a new observer design approach for linear time invariant multivariable systems subject to unknown inputs. The design is based on a transformation to the so-called special coordinate basis (SCB). This form reveals important system properties like invertability or the finite and infinite zero structure. Depending on the system's strong observability properties, the SCB allows for a straightforward unknown input observer design utilizing linear or nonlinear observers design techniques. The chosen observer design technique does not only depend on the system properties, but also on the desired convergence behavior of the observer. Hence, the proposed design procedure can be seen as a unifying framework for unknown input observer design.

Other Publications | 2009

Untersuchung der Fördercharakteristik von Schneckenförderern für eine Pelletabwurffeuerung

Ohnmacht, R. Untersuchung der Fördercharakteristik von Schneckenförderern für eine Pelletabwurffeuerung, Master Thesis, Technologische Universität Wien, Vienna, Austria, 2009.

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Other Publications | 2008

Untersuchung der Staubemissionen einer Prototyp Strohpelletsfeuerung, sowie Ermittlung des Potentials einer Emissionsreduktion durch einen Brennwertwärmetauscher mit Wäscher

Schwabl, M. Untersuchung der Staubemissionen einer Prototyp Strohpelletsfeuerung, sowie Ermittlung des Potentials einer Emissionsreduktion durch einen Brennwertwärmetauscher mit Wäscher, Master Thesis, Technische Universität Wien, Vienna, Austria, 2008.

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The primary energy consumption world-wide is rising constantly. Therefore it is necessary to open up renewable resources for energy production. Besides wood, the application of agricultural resources and residuals for energy production is possible, also within the range of small scale combustion units. These fuels still pose a challenge, concerning gaseous and particulate emissions. This work examines the application of straw pellets in a small scale combustion unit. Gaseous and particulate emissions, as well as the separation eciency of a secondary heat exchanger with scrubber were investigated. Compared with wood-like fuels a strong slagging of the combustion chamber could be determined. Gaseous emissions as NOx, SO2 and HCl, as well as the emission of particles were clearly higher than with combustions of wood. The gaseous emissions were below the considered limit value for other biogenous fuels after Art. 15 a B-VG 2007 [1]. The burnout of the gaseous phase, which can be evaluated by the emission of CO, was always good and comparable with the combustion of wood.
Using a secondary heat exchanger with scrubber (Hydrocube R of the company Schräder ) particulate emissions could be reduced by 20%. Element analysis of the particulate emissions as well as particle size measurements showed that primarily large particles were separated. A retrot of the Hydrocube R by an ionizing electrode increased the degree of separation on 60%. Besides the separation of particles, the Hydrocube R also reduced gaseous emissions like SO2 and HCl. The absorption of these components in the condensate phase caused a decrease of the pH value. Low ph value increased the corrosion of the Hydrocube R , what could be detected by rising concentrations on Fe, Ni and Cr in the condensate.

Other Publications | 2013

Untersuchung verschiedener Zugverhältnisse auf die Praxisrelevanz der Prüfung von Scheitholzöfen nach EN 13240

Stressler, H. Untersuchung verschiedener Zugverhältnisse auf die Praxisrelevanz der Prüfung von Scheitholzöfen nach EN 13240, Bachelor Thesis, FH Oberösterreich, Wels, Österreich, 2013.

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Other Publications | 2013

Untersuchung von Wirbelschichtbettmateralien mittels einer Kinetikapparatur

Yildiz, B. Determination of effects of different bed materials on steam reforming for tar reduction, Master Thesis, Vienna University of Technology, Vienna, Austria, 2013.

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Other papers | 2017

Upscaling and Operation of a Biomass Derived Fischer-Tropsch Pilot Plant Producing 1 Barrel Per Day

Loipersböck J, Weber G, Rauch R, Gruber H, Groß P, Hofbauer H. Upscaling and Operation of a Biomass Derived Fischer-Tropsch Pilot Plant Producing 1 Barrel Per Day. 25th European Biomass Conference & Exhibition (oral presentation). June 2017, Stockholm, Sweden.

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Peer reviewed papers | 2015

Use of Hazelnut's Pruning to Produce Biochar by Gasifier Small Scale Plant

Colantoni A, Longo L, Evic N, Gallucci F, Delfanti L. Use of Hazelnut‟s Pruning to Produce Biochar by Gasifier Small Scale Plant. International Journal of Renewable Energy Research. 2015;5(3):873-878.

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Biochar is the product of biomass pyrolysis and gasification. One of the possible application of this product is certainly in agronomic sector, as soil amendment. However biochar use in Italy is subordinated to insert this product in fertilizer list, which biochar could be commercialized with. The aim of this paper is to know the biochar from gasification process (using an Imbert downdraft prototype), in particular investigating its potentiality as soil amendment in terms of European and Italian regulations and in terms of physical and chemical characterizations.

Other papers | 2015

Validation of a Kinetic Model for the Catalyzed Water Gas Shift Reaction Applying a Fe/Cr Catalyst Processing Wood Gas from Biomass Steam Gasification

Kraussler M, Fail S, Plaza Quevedo A, Cortes Guerro JA, Rauch R, Hofbauer H. Validation of a Kinetic Model for the Catalyzed Water Gas Shift Reaction Applying a Fe/Cr Catalyst Processing Wood Gas from Biomass Steam Gasification. 23rd European Biomass Conference & Exhibition (Poster). June 2015, Vienna, Austria.

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Other papers | 2011

Validation of flow simulation and gas combustion sub-models for CFD-based prediction of NOx formation in biomass grate furnaces

Zahirović S, Scharler R, Kilpinen P, Obernberger I. Validation of flow simulation and gas combustion sub-models for the CFD-based prediction of NOx formation in biomass grate furnaces. Combustion Theory and Modelling. 2011;15(1):61-87.

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Other papers | 2010

Validation of flow simulation and gas combustion sub-models for CFD-based prediction of NOx formation in biomass grate furnaces

Zahirović S, Scharler R, Kilpinen P, Obernberger I. Validation of flow simulation and gas combustion sub-models for the CFD-based prediction of NOx formation in biomass grate furnaces. Combustion Theory and Modelling. 2011;15(1):61-87.

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While reasonably accurate in simulating gas phase combustion in biomass grate furnaces, CFD tools based on simple turbulence-chemistry interaction models and global reaction mechanisms have been shown to lack in reliability regarding the prediction of NOx formation. Coupling detailed NOx reaction kinetics with advanced turbulence-chemistry interaction models is a promising alternative, yet computationally inefficient for engineering purposes. In the present work, a model is proposed to overcome these difficulties. The model is based on the Realizable k-ε model for turbulence, Eddy Dissipation Concept for turbulence-chemistry interaction and the HK97 reactionmechanism. The assessment of the sub-models in terms of accuracy and computational effort was carried out on three laboratory-scale turbulent jet flames in comparison with the experimental data. Without taking NOx formation into account, the accuracy of turbulence modelling and turbulence-chemistry interaction modelling was systematically examined on Sandia Flame D and Sandia CO/H2/N2 Flame B to support the choice of the associated models. As revealed by the Large Eddy Simulations of the former flame, the shortcomings of turbulence modelling by the Reynolds averaged Navier-Stokes (RANS) approach considerably influence the prediction of the mixing-dominated combustion process. This reduced the sensitivity of the RANS results to the variations of turbulence-chemistry interaction models and combustion kinetics. Issues related to the NOx formation with a focus on fuel bound nitrogen sources were investigated on a NH3-doped syngas flame. The experimentally observed trend in NOx yield from NH3 was correctly reproduced by HK97, whereas the replacement of its combustion subset by that of a detailed reaction scheme led to a more accurate agreement, but at increased computational costs. Moreover, based on results of simulations with HK97, the main features of the local course of the NOx formation processes were identified by a detailed analysis of the interactions between the nitrogen chemistry and the underlying flow field. © 2011 Taylor & Francis.

Conference presentations and posters | 2020

Valorisation of industrial by-products from the pulp&paper and rendering industry

Ortner M, Valorisation of industrial by-products from the pulp&paper and rendering industry. 6th Central European Biomass Conference, 22-24 January 2020, Graz.

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Conference presentations and posters | 2010

Valorisation of low grade Biomass to substitute fossil Fuels in a thermal Power Plant

Kern S, Halwachs M, Hofbauer H, Kampichler G. Valorisation of low grade Biomass to substitute fossil Fuels in a thermal Power Plant, WasteEng 2010, 17th-19th of May 2010, Peking, China.

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Minimizing carbon dioxide emissions whereas keeping up the high living standard of today is only possible by increasing the efficiency of energy consumption and the change to a mix of renewable fuels. Huge amounts of unused biomass in terms of agricultural residues like straw, that is a cheap and local feedstock, are often available. But as a reason of the high amount of corrosive ash elements (K, Cl, S), the residues are not suitable for co-firing in a thermal power plant. Therefore the feedstock is converted by low temperature pyrolysis into pyrolysis gases and charcoal. The aim of this work is to obtain fundamentals for an advanced pyrolysis model approach by the results of the pilot plant for co-firing the pyrolysis gases in a thermal power plant. A 3 MW pyrolysis pilot plant is being operated since 2008. For the process, an externally heated rotary kiln reactor with a design fuel power of 3 MW is used. Several mass and energy balances have been calculated based on measured plant data for different operating points of the pilot plant. The high amount of pyrolysis oil in the gas has positive effects to the heating value of the pyrolysis gases. As a reason of that, cold gas efficiencies of more than 70 % are possible. Based on these results, a scale up to a next scale pyrolysis reactor with a capacity of 30 MWth fuel input is currently investigated.

Peer reviewed papers | 2016

Valorisation of slaughter house and deinking paper waste streams for the production of enzyme by Trichoderma reesei

Weiss R, Eischer A, Tadic T, Gritsch SM, Ortner M, Prall K, Neunteufel E, Putz RF, Guebitz GM, Nyanhongo GS. Valorisation of slaughter house and deinking paper waste streams for the production of enzyme by Trichoderma reesei. Journal of Cleaner Production. 2020;275:122882

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The study investigates for the first time the possibility of using carbon rich paper recovery sludge, and nitrogen rich meat processing industry waste as cultivation medium for the production of high value enzymes needed in the respective industries. The complex cellulose rich deinking sludge was able to support the growth of many industrially relevant enzyme producing microorganisms (Bacillus licheniformis, Candida cylindracea, Aspergillus oryzae, Trichoderma reesei) and of recombinant enzyme producers (Escherichia coli and Pichia pastoris). Further detailed studies with Trichoderma reesei as model organism demonstrated that the organism was able to grow optimally in the presence of 40gL-1 paper sludge as carbon source and 67.5 gL-1 pasteurised blood as nitrogen source substituted in Mandels medium. Under these conditions cellulase activities up to 28.1 nkat FPU were achieved. Anyhow, to achieve these results pretreatment of both waste streams is inevitable. In summary, this study provides the practical basis for a valorisation systems of paper industry waste to produce valuable enzymes to be used on-site in paper processing or for other purposes.

Peer reviewed papers | 2021

Valorisation of starch wastewater by anaerobic fermentation

Drosg B, Neubauer M, Marzynski M, Meixner K. Valorisation of starch wastewater by anaerobic fermentation. Applies Sciences (Switzerland). 2021.11(21):10482.

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Starch production is mainly focused on feedstocks such as corn, wheat and potato in the EU, whereas cassava, rice, and other feedstocks are utilised worldwide. In starch production, a high amount of wastewater is generated, which accumulates from different process steps such as washing, steeping, starch refining, saccharification and derivatisation. Valorisation of these wastewaters can help to improve the environmental impact as well as the economics of starch production. Anaerobic fermentation is a promising approach, and this review gives an overview of the different utilisation concepts outlined in the literature and the state of the technology. Among bioenergy recovery processes, biogas technology is widely applied at the industrial scale, whereas biohydrogen production is used at the research stage. Starch wastewater can also be used for the production of bulk chemicals such as acetone, ethanol, butanol or lactic acids by anaerobic microbes.

Other papers | 2012

Variation of Feedstock in a Dual Fluidized Bed Steam Gasifier ‐ Influence on Product Gas, Tar Content and Composition

Schmid JC, Wolfesberger U, Koppatz S, Pfeifer C, Hofbauer H. Variation of feedstock in a dual fluidized bed steam gasifier-influence on product gas, tar content, and composition. Environmental Progress and Sustainable Energy. 2012;31(2):205-15.

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A steam blown dual fluidized bed gasification plant was used to yield a nitrogen (N 2) free product gas (synthesis gas) from various biomass fuels. In addition to the variation of process parameters like temperature, steam to carbon ratio, fluidization rate, and the influence of different bed materials, various feedstock inputs affected the generation of the product gas. This study focuses on the gasification of different biomass feedstock. The variation of biomass implies wood chips, wood pellets, sewage sludge pellets, and straw pellets. The chosen evaluated experimental results are all gained from the uniformly operated "classical" 100 kW "DUAL FLUID" gasifier at Vienna University of Technology at constant gasification temperatures between 800°C and 810°C. In the "classical" design, the gasification reactor is a bubbling fluidized bed. The composition and ash melting behavior of each feedstock is displayed, as well as the ranges of the product gas compositions generated. Beside the main gaseous product gas components, typical content ranges of dust and char are highlighted. The content and composition of tar in the product gas is discussed. Further it is possible to present gravimetrical and gas chromatography coupled with mass spectrometry measured tar values. Not less than five significant component-groups of tar will also be outlined for each feedstock. © 2012 American Institute of Chemical Engineers (AIChE).

Peer reviewed papers | 2015

Ventilation of Carbon Monoxide from a Biomass Pellet Storage Tank - A Study of the Effects of Variation of Temperature and Cross-Ventilation on the Efficiency of Natural Ventilation

Emhofer W, Lichtenegger K, Haslinger W, Hofbauer H, Schmutzer-Roseneder I, Aigenbauer S, et al. Ventilation of carbon monoxide from a biomass pellet storage tank - A study of the effects of variation of temperature and cross-ventilation on the efficiency of natural ventilation. Ann Occup Hyg. 2015;59(1):79-90.

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Wood pellets have been reported to emit toxic gaseous emissions during transport and storage. Carbon monoxide (CO) emission, due to the high toxicity of the gas and the possibility of it being present at high levels, is the most imminent threat to be considered before entering a pellet storage facility. For small-scale (<30 tons storage capacity) residential pellet storage facilities, ventilation, preferably natural ventilation utilizing already existing openings, has become the most favored solution to overcome the problem of high CO concentrations. However, there is little knowledge on the ventilation rates that can be reached and thus on the effectiveness of such measures. The aim of the study was to investigate ventilation rates for a specific small-scale pellet storage system depending on characteristic temperature differences. Furthermore, the influence of the implementation of a chimney and the influence of cross-ventilation on the ventilation rates were investigated. The air exchange rates observed in the experiments ranged between close to zero and up to 8 m3h-1, depending largely on the existing temperature differences and the existence of cross-ventilation. The results demonstrate that implementing natural ventilation is a possible measure to enhance safety from CO emissions, but not one without limitations. © 2014 © The Author 2014. Published by Oxford University Press on behalf of the British Occupational Hygiene Society.

Conference presentations and posters | 2022

Vereinfachung von Absorptionskälteanlagen-Modellen

Wernhart MW, Rieberer R, Staudt S, Unterberger V, Gölles M. Vereinfachung von Absorptionskälteanlagen-Modellen. Deutsche Kälte- und Klimatagung 2022: DKV-Tagung 2022. 18. November 2022. Magdeburg, Germany.

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Conference presentations and posters | 2012

Vergleichsanalyse der Vergasung eines biogen und fossil angereicherten EBS

Sommer M, Ragoßnig AM, Kleinhappl M. Vergleichsanalyse der Vergasung eines biogen und fossil angereicherten EBS, DepoTech 2012, 6th-9th of October 2012, Leoben, Austria.

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Conference presentations and posters | 2012

Verwertung von Reststoffen aus der Lebensmittelproduktion zur Gewinnung von Prozessenergie.

Drosg B, Ortner M, Bochmann G. Verwertung von Reststoffen aus der Lebensmittelproduktion zur Gewinnung von Prozessenergie, Lebensmittel-Cluster Oberösterreich „ Strom - Wärme - Kälte - Wege zum energieeffizienteren Lebensmittelbetrieb“ 2012, 21th of March 2012, Linz, Austria.

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Conference presentations and posters | 2020

Virtual biomass combustion plant

Schulze K, Virtual biomass combustion plant. 6th Central European Biomass Conference, 22-24 January 2020, Graz.

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Other papers | 2017

Wasserstoff aus Biomasse - Stand der Technik und Perspektiven

Hofbauer H, Bosch K, Kraussler M. Wasserstoff aus Biomasse - Stand der Technik und Perspektiven. 5th Central European Biomass Conference (oral presentation). January 2017, Graz, Austria.

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Other Publications | 2023

Wastewater2Hydrogen

Biotechnological Hydrogen Production from Industrial Wastewater

Neubauer M, Pummer R, Neuhauser W, Bauer L, Fuchs W, Drosg B. Wastewater2Hydrogen. BEST Center Day. 28 June 2023

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Global hydrogen production is currently still based almost exclusively on fossil resources. A sustainable
hydrogen industry must be based on sustainable, renewable energy sources and resources.

Other papers | 2014

Wood Gas Processing To Generate Pure Hydrogen Suitable for PEM Fuel Cells

Fail S, Diaz N, Benedikt F, Kraussler M, Hinteregger J, Bosch K, et al. Wood gas processing to generate pure hydrogen suitable for PEM fuel cells. ACS Sustainable Chemistry and Engineering. 2014;2(12):2690-8.

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A test campaign was carried out to generate renewable hydrogen based on wood gas derived from the commercial biomass steam gasification plant in Oberwart, Austria. The implemented process consisted of four operation units: (I) catalyzed water-gas shift (WGS) reaction, (II) gas drying and cleaning in a wet scrubber, (III) hydrogen purification by pressure swing adsorption, and (IV) use of the generated biohydrogen (BioH2) in a proton exchange membrane (PEM) fuel cell. For almost 250 h, a reliable and continuous operation was achieved. A total of 560 (Ln dry basis (db))/h of wood gas were extracted to produce 280 (Ln db)/h of BioH2 with a purity of 99.97 vol %db. The catalyzed WGS reaction enabled a hydrogen recovery of 128% (nBioH2)/(nH2,wood gas) over the whole process chain. An extensive chemical analysis of the main gas components and trace components (sulfur, CxHy, and ammonia) was carried out. No PEM fuel cell poisons were measured in the generated BioH2. The only detectable impurities in the product were 0.02 vol %db of O2 and 0.01 vol %db of N2. © 2014 American Chemical Society.

Conference presentations and posters | 2010

Wooden Biofuels in Europe – Quantities and Corrosion Relevant Characteristics.

Schmidl C, Humel S, Haslinger W, Friedl G. Wooden Biofuels in Europe – Quantities and Corrosion Relevant Characteristics, 18th European Biomass Conference 2010, 3rd-7th of May 2010, Lyon, France. p 308-315.

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Other Publications | 2012

Zustandsschätzung einer Biomassefeuerungsanlage und deren modellbasierte Regelung

Seeber, R. Zustandsschätzung einer Biomassefeuerungsanlage und deren modellbasierte Regelung, Master Thesis, Technische Universität Graz, Graz, Austria, 2012.

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Die Verbrennung fester Biomasse gewinnt als nachhaltige Form der Energienutzung zunehmend an Bedeutung. Dabei stellt die Forderung nach einem schadstoffarmen Betrieb von Biomassefeuerungsanlagen bei möglichst hohem Wirkungsgrad eine Herausforderung an deren Regelung dar. Ziel dieser Arbeit ist die Untersuchung und Verbesserung eines existierenden, modellbasierten Regelungskonzepts, welches die Methode der Eingangs-Ausgangslinearisierung zur Regelung sowie einen Erweiterten Kalmanfilter zur Zustandsschätzung vorsieht. Die Arbeiten wurden in Kooperation mit dem Kompetenzzentrum Bioenergy 2020+ anhand einer Versuchsanlage (Flachschubrostfeuerung mit einer Kesselnennleistung von 180 kW) durchgeführt. Dabei lassen sich eine Reihe von Störeinflüssen identifizieren, unter anderem etwa die bei dieser Anlage besonders stark ausgeprägten Schwankungen des abgebauten Brennstoffs. Die geeignete Berücksichtigung dieser Störeinflüsse im Kalmanfilter durch Formfilter wird untersucht. Ebenso erfolgt die Modellierung von variablen Totzeiten und Sensordynamiken, die bei der Messung einzelner Größen auftreten, durch zusätzliche Sensormodelle. Auf Basis dieser Ergebnisse wird ein neuer Kalmanfilter vorgeschlagen und implementiert. Die auftretenden Störeinflüsse führen bei der exakt linearisierten Strecke zu einer Abweichung vom geforderten linearen Übertragungsverhalten. Daher wird auch der Regler dahingehend modifiziert, dass die vom Kalmanfilter rekonstruierten Störgrößen bei der Ermittlung des nichtlinearen Zustandsregelgesetzes verwendet werden. Das modifizierte Regelungskonzept wurde abschließend an der untersuchten Anlage implementiert und experimentell verifiziert. Dabei wurden gegenüber der ursprünglichen Regelung eine deutliche Verbesserung bei der Stabilisierung von Vorlauf- und Sekundärzonentemperatur sowie eine geringere Abweichung des Verbrennungsluftverhältnisses im Brennstoffbett vom vorgegebenen Sollwert erzielt.

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