Peer Reviewed Scientific Journals | 2019
NPK 2.0: Introducing tensor decompositions to the kinetic analysis of gas–solid reactions
Birkelbach F, Deutsch M, Flegkas S, Winter F, Werner A. NPK 2.0: Introducing tensor decompositions to the kinetic analysis of gas–solid reactions. Int J Chem Kinet. 2019;1–11.
A method for deriving kinetic models of gas–solid reactions for reactor and process design is presented. It is based on the nonparametric kinetics (NPK) method and resolves many of its shortcomings by applying tensor rank‐1 approximation methods. With this method, it is possible to derive kinetic models based on the general kinetic equation from any combination of experiments without additional a priori assumptions. The most notable improvements over the original method are that it is computationally much simpler and that it is not limited to two variables. Two algorithms for computing the rank‐1 approximation as well as a tailored initialization method are presented, and their performance is assessed. Formulae for the variance estimation of the solution values are derived to improve the accuracy of the model identification and to provide a tool for diagnosing the quality of the kinetic model. The methods effectiveness and performance are assessed by applying it to a simulated data set. A Matlab implementation is available as Supporting Information.
Conference Papers | 2015
Numerical modelling of biomass grate furnaces with a particle based model
Mehrabian R, Shiehnejadhesar A, Scharler R, Obernberger I. Numerical modelling of biomass grate furnaces with a particle based model, INFUB 10th European Conference on Industrial Furnace and Boilers 2015, 7th-10th of April 2015, Porto, Portugal.
Technical Reports | 2015
Nutrient recovery by biogas digestate processing
Drosg B, Fuchs W, Al Seadi T, Madsen M, Linke B. Nutrient recovery by biogas digestate processing. IEA Bioenergy (2015): 7-11
Conference contributions | 2009
Nutzungsgradsteigerung bei Pelletsfeuerungen
Friedl G. Nutzungsgradsteigerung bei Pelletsfeuerungen, 9. Industrieforum Pellets 2009, 7th-9th of October 2009, Stuttgart, Germany.
Reviewed Conference Papers | 2012
Odor, gaseous and PM 10 emissions from small scale combustion of wood types indigenous to central Europe
Kistler M, Schmidl C, Padouvas E, Giebl H, Lohninger J, Ellinger R, et al. Odor, gaseous and PM 10 emissions from small scale combustion of wood types indigenous to central Europe. Atmos Environ. 2012;51:86-93.
In this study, we investigated the emissions, including odor, from log wood stoves, burning wood types indigenous to mid-European countries such as Austria, Czech Republic, Hungary, Slovak Republic, Slovenia, Switzerland, as well as Baden-Württemberg and Bavaria (Germany) and South Tyrol (Italy). The investigations were performed with a modern, certified, 8 kW, manually fired log wood stove, and the results were compared to emissions from a modern 9 kW pellet stove. The examined wood types were deciduous species: black locust, black poplar, European hornbeam, European beech, pedunculate oak (also known as “common oak”), sessile oak, turkey oak and conifers: Austrian black pine, European larch, Norway spruce, Scots pine, silver fir, as well as hardwood briquettes. In addition, “garden biomass” such as pine cones, pine needles and dry leaves were burnt in the log wood stove. The pellet stove was fired with softwood pellets.
The composite average emission rates for log wood and briquettes were 2030 mg MJ−1 for CO; 89 mg MJ−1 for NOx, 311 mg MJ−1 for CxHy, 67 mg MJ−1 for particulate matter PM10 and average odor concentration was at 2430 OU m−3. CO, CxHy and PM10 emissions from pellets combustion were lower by factors of 10, 13 and 3, while considering NOx – comparable to the log wood emissions. Odor from pellets combustion was not detectable. CxHy and PM10 emissions from garden biomass (needles and leaves) burning were 10 times higher than for log wood, while CO and NOx rise only slightly. Odor levels ranged from not detectable (pellets) to around 19,000 OU m−3 (dry leaves). The odor concentration correlated with CO, CxHy and PM10. For log wood combustion average odor ranged from 536 OU m−3 for hornbeam to 5217 OU m−3 for fir, indicating a considerable influence of the wood type on odor concentration.
Conference contributions | 2014
Off-gassing – Safety issues related with harmful emissions from wood pellets
Emhofer W. Second International Workshop on Pellet Safety “Off-gassing – Safety issues related with harmful emissions from wood pellets”, 5th of May, Fügen, Austria, 2014.
Conference contributions | 2014
Off-gassing –Safety issues related with emissions from wood pellets along the pellet supply chain
Emhofer W, et al. Pellets Workshop ” Off-gassing –Safety issues related with emissions from wood pellets along the pellet supply chain” (held held during the Central European Biomass Conference 2014), 15th-18th of January, Graz, Austria, 2014.
Scientific Journals | 2020
Off-gassing reduction of stored wood pellets by adding acetylsalicylic acid
Sedlmayer I, Bauer-Emhofer W, Haslinger W, Hofbauer H, Schmidl C, Wopienka E. Off-gassing reduction of stored wood pellets by adding acetylsalicylic acid. Fuel Processing Technology 2020.198:106218.
During transportation and storage of wood pellets various gases are formed leading to toxic atmosphere. Various influencing factors and measures reducing off-gassing have already been investigated. The present study aims at applying an antioxidant, acetylsalicylic acid (ASA), to reduce off-gassing from wood pellets by lowering wood extractives oxidation. Therefore, acetylsalicylic acid was applied in industrial and laboratory pelletizing processes. Pine and spruce sawdust (ratio 1:1) were pelletized with adding 0-0.8% (m/m) ASA. Glass flasks measurements confirmed off-gassing reduction by adding ASA for all wood pellets investigated.The biggest effect was achieved by adding 0.8% (m/m) ASA in the industrial pelletizing experiments where the emission of volatile organic compounds (VOCtot) was reduced by 82% and a reduction of carbon monoxide (CO) and carbon dioxide (CO2) emissions by 70% and 51%, respectively, could be achieved. Even an addition of 0.05% (m/m) ASA led to off-gassing reduction by >10%. A six week storage experiment to investigate the long-term effectivity of ASA addition revealed, that antioxidant addition was effective in reducing CO-, CO2- and VOCtot-release, especially during the first four weeks of the storage experiment, after which time the relative reduction effect was significantly decreased.
Other Presentations | 2016
On site monitoring and dynamic simulation of a low energy house heated by a pellet boiler
Carlon E, Schwarz M, Prada A, Golicza L, Verma V, Baratieri M, Gasparella A, Haslinger W, Schmidl C. On site monitoring and dynamic simulation of a low energy house heated by a pellet boiler. 15 March 2016;116: 296-306.
Prefabricated low energy houses are becoming increasingly popular thanks to their low cost and high energy performance. Heating systems installed in these houses should be optimally designed and controlled, to ensure thermal comfort for the whole heating season.
This study presents the on-site monitoring and dynamic simulation of a low energy house heated by a pellet boiler via a floor heating system. The house combines a lightweight envelope, a heat distribution system with a high thermal inertia and a biomass-based heat supply. The one-year monitoring campaign allowed to closely investigate the system's response to the heat demand. Moreover, a coupled simulation of the house and its heating and hot water supply system was set-up, calibrated, and validated against measured indoor temperature profiles and energy consumptions. Root mean square deviations between simulated and measured indoor temperature were in the range 0.4–0.8 K, while simulated energy consumptions fulfilled the criteria of the ASHRAE 14-2002 Guideline. As monitoring data evidenced the importance of better managing the high thermal inertia of the floor heating system, two improved control strategies were tested in the simulation environment and evaluated in terms of thermal comfort, pellet consumption and efficiency of the pellet boiler.
Other Presentations | 2013
Online-Monitoring von Korrosionsvorgängen in Biomasse-befeuertenAnlagen
Bernsteiner, C. Online-Monitoring von Korrosionsvorgängen in Biomasse-befeuertenAnlagen, Master Thesis, Technische Universität Graz, Graz, Austria, 2013.
Für den ökonomisch und ökologisch effizienteren Betrieb von Dampfkesselanlagen ist die Untersuchung von Korrosionsvorgängen in Wärmetauschern, verursacht durch das Rauchgas aus einer Biomasse-Feuerung, notwendig. Daher wurden bei Bioenergy 2020+ kurzzeitige Korrosionsversuche im Umfang von 300h Betriebszeit an einem Wärmetauscherstahl 13CrMo4-5 mit einer ONLINE-Korrosionssonde der Firma Corrmoran GmbH für die Erstellung eines empirischen Korrosionsmodells durchgeführt. Als Brennstoffe dienten Waldhackgut, Weizenstrohpellets und Altholz. Die Messung benötigt eine Ionen leitende Deckschicht, die sich erst am Beginn des Versuchs aufbaut. Aufgrund der fehlenden Deckschicht wird daher zu Beginn der Messung der Korrosionsleitwert unterschätzt. Daraus ergeben sich systematische Messfehler. Ziel dieser Arbeit war die Eruierung des Zusammenhanges zwischen Messfehler und Versuchszeit. Dabei stellten sich zwei systematische Messfehler als relevant heraus: •Die Abzehrrate ist zum Korrosionsleitwert proportional. Daher wird die Abzehrrate während der Eingangsphase der Messung unterschätzt. •Die Abzehrrate berechnet sich aus dem Korrosionsleitwert, multipliziert mit einem Kalibrierungsfaktor. Dabei ergibt sich der Kalibrierungsfaktor aus dem Verhältnis des gesamten korrosionsbedingten Materialverlustes über die gesamte Versuchsdauer, dividiert durch den über denselben Zeitraum integrierten Korrosionsleitwert. Aufgrund des zu Beginn unterschätzten Korrosionsleitwertes wird der Kalibrierungsfaktor und somit die Abzehrrate, berechnet aus dem reproduzierbaren Signal, überschätzt. Die Literaturrecherche zeigte, dass die Kinetik bei der Hochtemperaturkorrosion bei konstant gehaltenen korrosionsrelevanten Parametern einen linearen, parabolischen oder paralinearen Verlauf einnehmen kann. Die kleinstmögliche Abzehrrate und somit der kleinstmögliche Korrosionsleitwert zu Beginn der Messung ergibt sich bei der Annahme eines linearen Verlaufs, welcher die möglicherweise erhöhten Abzehrraten der Initialkorrosion nicht mitberücksichtigt. Aus dieser Annahme konnte der kleinstmögliche Korrekturfaktor cmin berechnet werden. Dazu mussten die Daten bei konstant gehaltenen Parametern gefiltert und daraus der zeitlich integrierte Korrosionsleitwert PL,Messung gebildet werden. Das Verhältnis von PL,Messung mit einem über die gesamte Versuchszeit konstant angenommenen zeitlich integrierten Korrosionsleitwertes PL,linear ergibt den Korrekturfaktor, der multipliziert mit den ursprünglich bei gleichen Parametern bestimmten Abzehrraten eine neue Abzehrrate k(t)neu ergibt. Der Vergleich mit den Ergebnissen eines Langzeitversuches unter ähnlichen Betriebsbedingungen in einem Biomasse-Heizkraftwerk zeigte dadurch eine Verbesserung der Abweichung der Kurzzeitversuche von 125% auf 55%. Aufgrund der Parametervariationen sowie der Temperaturschwankungen, verursacht durch Ein- und Ausschaltvorgänge der Anlage, haben die bei konstanten Parametern bestimmten Korrekturfaktoren für die durchgeführten Versuche nur bedingt Gültigkeit. Daher wurde in einem weiteren Schritt ein Korrekturfaktor cmin,var bestimmt, welcher alle Daten der Versuchsserie berücksichtigt. Dazu wurde das Signal der Eingangsphase durch ein gleichlanges reproduzierbares Signal, gemessen unter denselben Bedingungen am Ende der Versuchsserien, ersetzt. Es ergibt sich aus dem Verhältnis der zeitlich integrierten Korrosionsleitwerte PL,Messung der Originalkurve zu PL,idealisiert des idealisierten Verlaufs der Korrekturfaktor cmin,var. Dieser hat aufgrund der Berücksichtigung aller gesammelten Daten für alle bei den Versuchen bestimmten Abzehrraten Gültigkeit. Durch cmin,var konnte eine Reduktion der Abweichung auf 110% erreicht werden. Diese wird auf die im Gegensatz zur Langzeitmessung im Biomasse-Heizkraftwerk unterschiedliche Versuchsmethode sowie auf den unbekannten Einfluss der möglicherweise erhöhten Abzehrraten der Initialkorrosion zurückgeführt.
Conference contributions | 2015
Operation and Efficiency of a Wood-Pellet Fired 5 KWel Stirling
Aigenbauer S, Schnetzinger R, Höftberger E, Schmidl C, Haslinger W. Operation and Efficiency of a Wood-Pellet Fired 5 KWel Stirling, 23rd European Biomass Conference 2015, 1st-4th of June 2015, Vienna, Austria. (visual presentation)
Conference contributions | 2013
Operation characteristics of a bulk catalyst in a test stand under similar conditions to a firewood stove
Wöhler M, et al. Operation characteristics of a bulk catalyst in a test stand under similar conditions to a firewood stove, Word Sustainable Energy Days next 2013, 27th-28th of February 2013, Wels, Austria.
Conference contributions | 2012
Operation Experience & Developments at Industrial Plants with Dual‐Fluid Gasification
Hofbauer H. Operation Experience & Developments at Industrial Plants with Dual‐Fluid Gasification, 20th European Biomass Conference 2012, 18th-22nd of June 2012, Milano, Italy.
Other Presentations | 2013
Optimierung des Emissionsverhaltens eines Ofens mittels primären und sekundären Maßnahmen am Beispiel des Scheitholzofens
Rieger, B. Optimierung des Emissionsverhaltens eines Ofens mittels primären und sekundären Maßnahmen am Beispiel des Scheitholzofens, Master Thesis, Fachochschule Technikum Wien, Vienna, Austria, 2013.
The use of biomass in manually charged room heating appliances to cover the domestic heating demand has traditionally been of a high percentage in the European Union. As a result of continued or even increased use of firewood stoves, the enhancement of available stoves is a declared objective of the European Union.
Therefore, an example-optimization of the firewood stove Stûv 16/78-in (available on the European market) was performed in preparation of this paper. There was a primary- and a secondary optimization carried out to quantify the potential of optimization. When optimizing, the gas and particulate emissions was considered. The operating behavior were measured and evaluated by performing combustion experiments on a specially designed test rig.
The primary optimization is divided into five sub-steps. Each Step was quantified by gas analysis. The achieved reduction of particulate emissions was measured before and after the entire primary optimization.
In comparison to the delivery condition it was possible to reduce the CO emissions to one quarter and the particulate emissions from 100 mg / mn³ to 39 mg / mn³ over the course of the primary optimization.
As a secondary optimization, a Catalyst was implemented. The used catalyst is a solid-state catalyst in the modification of a heterogeneous supported catalyst in the shape of honeycomb, which is marketed by Clariant International Ltd. under the name "EnviCat ® Longlife Plus". The catalytically active materials platinum and palladium are used.
After a strictly implemented primary optimizations, a further reduction to half of emissions was achieved by the integration of the catalyst even though a bypass of 20 % had to be integrated to ensure the operating safety.
Other Presentations | 2008
Optimierung einer biomassebefeuerten 10 kWth-Mikro-Kraft-Wärme-Kopplung mit Thermoelektrischem Generator
Lohr, M. Optimierung einer biomassebefeuerten 10 kWth-Mikro-Kraft-Wärme-Kopplung mit Thermoelektrischem Generator, Master Thesis, Fachhochschule Oberösterreich, Wels, Austria, 2008.
The availability of energy is important to our every day lives. Biomass-fuelled heating systems are comfortable and reach an efficiency form over 90 %. With a thermoelectric generator (TEG) it’s possible to convert a part of the heat directly into electrical power and so become self sufficient from electicity. The purpose of this thesis was to optimise an existing prototype of a combined heat and power (CHP) plant based on a pellet heating system and a thermoelectric generator. Balancing the energy flows, especially the losses, was also part of the thesis.
Tests with the prototype were done. Some with the originial prototype, some with additional insulation and some with preheating the combustion air. To examine the part load behaviour, tests were done at 10, 7 and 4 kW fuelheat input.
By insulating the TEG the performance rose from 153 W to 174 W. The insulation and the preheating of the combustion air from room temperature to 350 degree lead to an power output from 194 watt. All at 10 kW fuellheat input. Finally the following conclusions can be drawn: For the series product it is recommended to optimize the insulation of the TEG. As the preheating of the combustion air didn’t lead to the expected effects it should be left out.
Conference contributions | 2010
Optimisation of biomass grate furnaces with a new 3D packed bed combustion model - on example of a small-scale underfeed stoker furnace
Mehrabian R, Scharler R, Weissinger A, Obernberger I. Optimisation of biomass grate furnaces with a new 3D packed bed combustion model - on example of a small-scale underfeed stoker furnace, 18th European Biomass Conference and Exhibition 2010, 3rd-7th of May 2010, Lyon, France. p 1175-1183.
The design and optimisation of a biomass grate furnace requires accurate and efficient models for the
combustion process on the grate as well as the turbulent reactive flow in the combustion chamber. Computational Fluid Dynamics (CFD) have been successfully applied for gas phase combustion. However, no numerical models for the biomass packed bed combustion, which can be used as engineering design tools, are commercially available at present. This paper presents an innovative 3D CFD model for biomass packed bed combustion consisting of an Euler-Granular model for hydrodynamics of gas-particle multiphase flow and a thermally thin particle model for combustion of biomass particles. Modelling the particle trajectories and the thermal conversion of each particle in the bed constitutes the simulation of the entire bed combustion. The simulation of a small-scale underfeed stoker furnace of KWB has been successfully performed by the application of the new packed bed combustion model. The positions of the drying, pyrolysis and char burnout zones in the fuel bed as well as the temperature distribution among the particles seem to be plausible and could be confirmed by observations. Furthermore, a good qualitative agreement concerning the flue gas temperatures measured by thermocouples at different positions in the combustion chamber, and CO emissions measured at boiler outlet could be achieved. The new packed bed model provides the advantages of considering the release profiles of species and energy from the fuel bed close to reality and enables to consider the chemical compositions, size and physical properties of the fuel particles as well as the influence of primary air
distribution and grate motion on the particle trajectories.
Peer Reviewed Scientific Journals | 2017
Optimisation of continuous gas fermentation by immobilisation of acetate-producing Acetobacterium woodi
Steger, F, Rachbauer L, Windhagauer M, Montgomery LFR, Bochmann G. Optimisation of continuous gas fermentation by immobilisation of acetate-producing Acetobacterium woodi. Anaerobe. August 2017;46: 96-103
Other Publications | 2017
Optimisation of continuous gas fermentation by immobilisation of acetate-producing Acetobacterium woodii.
Steger, F, Rachbauer L, Windhagauer M, Montgomery LFR, Bochmann G. Optimisation of continuous gas fermentation by immobilisation of acetate-producing Acetobacterium woodii. Anaerobe. Available online 22 June 2017
Conference Papers | 2017
Optimisation of the post-consumer and demolition wood supply and value chain
Dißauer C, Kienzl N, Kunter A, Meirhofer M, Pointner C, Schwarzbauer P, Sommersacher P, Strasser C, Wellacher M. Optimisation of the post-consumer and demolition wood supply and value chain. 5th Central European Biomass Conference (Poster). January 2017, Graz, Austria.
Conference contributions | 2014
Optimising the heating system of a low energy house
Rimoldi M, Carlon E. Optimising the heating system of a low energy house, Word Sustainable Energy Days next 2014, 26th-28th of February 2014, Wels, Austria.
Other Presentations | 2019
Optimization Based Design and Control of Distributed Energy Resources and Microgrids
Stalder M, Optimization Based Design and Control of Distributed Energy Resources and Microgrids. LetsCluster, Lighthouse Summit in the heart of Europe: Smart Energy Generation - Management - Optimization, Smart Home / Building, Interface to the Smart Grid, Microgrids, Electric Grid of the Future, Sector Linking, Graz, Österreich, 25 - 27 März 2019
Peer Reviewed Scientific Journals | 2015
Optimization of a 50 MW bubbling fluidized bed biomass combustion chamber by means of computational particle fluid dynamics
Kraft S, Kuba M, Kirnbauer F, Bosch K, Hofbauer H. Optimization of a 50 MW bubbling fluidized bed biomass combustion chamber by means of computational particle fluid dynamics. Biomass and Bioenergy. 4 August 2015;89:31-39.
An efficient utilization of biomass fuels in power plants is often limited by the melting behavior of the biomass ash, which causes unplanned shutdowns of the plants. If the melting temperature of the ash is locally exceeded, deposits can form on the walls of the combustion chamber. In this paper, a bubbling fluidized bed combustion chamber with 50 MW biomass input is investigated that severely suffers deposit build-up in the freeboard during operation. The deposit layers affect the operation negatively in two ways: they act as an additional heat resistance in regions of heat extraction, and they can come off the wall and fall into the bed and negatively influence the fluidization behavior. To detect zones where ash melting can occur, the temperature distribution in the combustion chamber is calculated numerically using the commercial CPFD (computational particle fluid dynamics) code, Barracuda Version 15. Regions where the ash melting temperature is exceeded are compared with the fouling observed on the walls in the freeboard. The numerically predicted regions agree well with the observed location of the deposits on the walls. Next, the model is used to find an optimized operating point with fewer regions in which the ash melting temperature is exceeded. Therefore, three cases with different distributions of the inlet gas streams are simulated. The simulations show if the air inlet streams are moved from the freeboard to the necking area above the bed a more even temperature distribution is obtained over the combustion chamber. Hence, the areas where the ash melting temperatures are exceeded are reduced significantly and the formation of deposits in the optimized operational mode is much less likely.
Conference contributions | 2015
Outlook for the Project: Future Application and Development of the AshMelT methods
Schwabl M, Wopienka E. AshMelT Workshop “Outlook for the Project: Future Application and Development of the AshMelT methods” (held during de World Sustainable Energy Days 2015), 25th-27th of February, Wels, Austria, 2015.
Peer Reviewed Scientific Journals | 2017
Overcoming the bottlenecks of anaerobic digestion of olive mill solid waste by two-stage fermentation
Stoyanova E, Lundaa T, Bochmann G, Fuchs W. Overcoming the bottlenecks of anaerobic digestion of olive mill solid waste by two-stage fermentation. Environmental Technology (United Kingdom). 16 February 2017;38(4): 394-405.
Scientific Journals | 2019
Overview obstacle maps for obstacle‐aware navigation of autonomous drones
Pestana J, Maurer M, Muschick D, Hofer M, Fraundorfer F. Overview obstacle maps for obstacle-aware navigation of autonomous drones. Journal of Field Robotics 2019.
Achieving the autonomous deployment of aerial robots in unknown outdoor environments using only onboard computation is a challenging task. In this study, we have developed a solution to demonstrate the feasibility of autonomously deploying drones in unknown outdoor environments, with the main capability of providing an obstacle map of the area of interest in a short period of time. We focus on use cases where no obstacle maps are available beforehand, for instance, in search and rescue scenarios, and on increasing the autonomy of drones in such situations. Our vision‐based mapping approach consists of two separate steps. First, the drone performs an overview flight at a safe altitude acquiring overlapping nadir images, while creating a high‐quality sparse map of the environment by using a state‐of‐the‐art photogrammetry method. Second, this map is georeferenced, densified by fitting a mesh model and converted into an Octomap obstacle map, which can be continuously updated while performing a task of interest near the ground or in the vicinity of objects. The generation of the overview obstacle map is performed in almost real time on the onboard computer of the drone, a map of size is created in , therefore, with enough time remaining for the drone to execute other tasks inside the area of interest during the same flight. We evaluate quantitatively the accuracy of the acquired map and the characteristics of the planned trajectories. We further demonstrate experimentally the safe navigation of the drone in an area mapped with our proposed approach.