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Conference contributions | 2014

Residential Wood Combustion (RWC) -Investigation of user behavior and operating conditions regarding stoves and their impact on emissions and efficiency

Reichert G, Schmidl C, Haslinger W, Moser W, Aigenbauer S, Figl F, Wöhler M. Residential Wood Combustion (RWC) -Investigation of user behavior and operating conditions regarding stoves and their impact on emissions and efficiency, 4th Central European Biomass Conference 2014, 15th-18th of January 2014, Graz, Austria.

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Contributions to trade journals | 2009

Results and Experiences of Long Term Tests of the Fischer Tropsch Synthesis at the Biomass CHP Güssing

Rauch R. Results and Experiences of Long Term Tests of the Fischer Tropsch Synthesis at the Biomass CHP Güssing, Kraftstoffe der Zukunft 2009, 7. Internationaler Fachkongress für Biokraftstoffe des BBE und der UFOP 2009, 30th of November–1st of December 2009, Berlin, Deutschland.

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Peer Reviewed Scientific Journals | 2020

Robust design of microgrids using a hybrid minimum investment optimization

Pecenak ZK, Stadler M, Mathiesen P, Fahy K, Kleissl J. Robust design of microgrids using a hybrid minimum investment optimization. Applied Energy. 2020;276:115400.

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Recently, researchers have begun to study hybrid approaches to Microgrid techno-economic planning, where a reduced model optimizes the DER selection and sizing is combined with a full model that optimizes operation and dispatch. Though providing significant computation time savings, these hybrid models are susceptible to infeasibilities, when the size of the DER is insufficient to meet the energy balance in the full model during macrogrid outages. In this work, a novel hybrid optimization framework is introduced, specifically designed for resilience to macrogrid outages. The framework solves the same optimization problem twice, where the second solution using full data is informed by the first solution using representative data to size and select DER. This framework includes a novel constraint on the state of charge for storage devices, which allows the representation of multiple repeated days of grid outage, despite a single 24-h profile being optimized in the representative model. Multiple approaches to the hybrid optimization are compared in terms of their computation time, optimality, and robustness against infeasibilities. Through a case study on three real Microgrid designs, we show that allowing optimizing the DER sizing in both stages of the hybrid design, dubbed minimum investment optimization (MIO), provides the greatest degree of optimality, guarantees robustness, and provides significant time savings over the benchmark optimization.


Conference contributions | 2014

Rolle und Potenzial der Bioenergie für die Wärmeversorgung der Zukunft

Haslinger W. Rolle und Potenzial der Bioenergie für die Wärmeversorgung der Zukunft, Technologiegespräche Alpbach 2014, 13th-29th of August 2014, Alpbach, Austria.

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Conference contributions | 2010

Rotary Kiln Pyrolysis First Results of a 3 MW Pilot Plant

Kern S, Halwachs M, Pröll T, Kampichler G. Rotary Kiln Pyrolysis First Results of a 3 MW Pilot Plant, 18th European Biomass Conference and Exhibiton 2010, 3th-7th May 2010, Lyon, France. p 950-955.

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A pyrolysis process can be used to split up the biomass in a volatile fraction poor in undesired substances (Cl, N, S,
Na and K) and a char fraction where these substances are concentrated. In this way cheap biomass can be used for cofiring in existing fossil fuel power stations without the danger of corrosion, deposition, and emission problems. The aim of the project is the development and demonstration of a biomass pretreatment process based on pyrolysis in the temperature range between 450-650 °C to split the energy in the biomass into volatiles with a low content of the above mentioned undesired compounds and char, where most of these pollutants are concentrated. The balance of the system can provide important results, such as the development of the product spectrum by a function of the operating parameters. Based on the results of the pilot plant a scale up to a capacity of 30 MWth fuel input and the connection with the coal fired power plant is currently investigated.


Contributions to trade journals | 2012

Rotary kiln pyrolysis of straw and fermentation residues in a 3 MW pilot plant – Influence of pyrolysis temperature on pyrolysis product performance

Kern S, Halwachs M, Kampichler G, Pfeifer C, Pröll T, Hofbauer H. Rotary kiln pyrolysis of straw and fermentation residues in a 3 MW pilot plant - Influence of pyrolysis temperature on pyrolysis product performance. J Anal Appl Pyrolysis. 2012;97:1-10.

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The idea of co-firing biomass in an already existing coal-fired power plant could play a major contribution in the reduction of carbon dioxide emissions. Huge amounts of unused biomass in terms of agricultural residues such as straw, which is a cheap and local feedstock, are often available. But due to the high amount of corrosive ash elements (K, Cl, etc.), the residues are usually not suitable for co-firing in a thermal power plant. Therefore, the feedstock is converted by low temperature pyrolysis into gaseous pyrolysis products and charcoal. A 3 MW pyrolysis pilot plant located next to a coal-fired power plant near Vienna was set up in 2008. For the process, an externally heated rotary kiln reactor with a design fuel power of 3 MW is used which can handle about 0.6-0.8 t/h straw. The aim is to investigate the fundamentals for scale-up to the desired size for co-firing in a coal-fired power plant. In addition to the desired fuel for the process, which is wheat straw, a testing series for DDGS was also performed. The high amount of pyrolysis oil in the gas had positive effects on the heating value of the pyrolysis gas. Chemical efficiencies of this pyrolysis pilot plant of up to 67% for pyrolysis temperatures between 450°C and 600°C can be reached. The focus of this work is set on the pyrolysis products and their behavior at different pyrolysis temperatures as well as the performance of the pyrolysis process. © 2012 Elsevier B.V.


Conference contributions | 2010

Rotary kiln pyrolysis- First results of a 3 MW pilot plant

Kern S, Halwachs M, Pröll T, Kampichler G. Rotary Kiln Pyrolysis First Results of a 3 MW Pilot Plant, IFC on IGCC and XtL 2010, 3rd-5th of May 2010, Dresden, Germany.

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A pyrolysis process can be used to split up the biomass in a volatile fraction poor in undesired substances (Cl, N, S,
Na and K) and a char fraction where these substances are concentrated. In this way cheap biomass can be used for cofiring in existing fossil fuel power stations without the danger of corrosion, deposition, and emission problems. The aim of the project is the development and demonstration of a biomass pretreatment process based on pyrolysis in the temperature range between 450-650 °C to split the energy in the biomass into volatiles with a low content of the above mentioned undesired compounds and char, where most of these pollutants are concentrated. The balance of the system can provide important results, such as the development of the product spectrum by a function of the operating parameters. Based on the results of the pilot plant a scale up to a capacity of 30 MWth fuel input and the connection with the coal fired power plant is currently investigated.


Contributions to trade journals | 2017

Rural electrification and capacity expansion with an integrated modeling approach

Hartvigsson E, Stadler M, Cardoso G. Rural electrification and capacity expansion with an integrated modeling approach. Renewable Energy by Elsevier. 2017.

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Peer Reviewed Scientific Journals | 2020

Scale-up methodology for automatic biomass furnaces

Barroso G, Nussbaumer T, Ulrich M, Reiterer T, Feldmeier S. Scale-up methodology for automatic biomass furnaces. Journal of the Energy Institute 2020.93:591-604.

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This work presents a methodology to perform the scale-up of a solid fuel furnace to a higher heat output with maintaining or improving the burn-out quality. As basis to derive the scale-up concept, an example of a 35 kW screw burner for biomass fuels is investigated. Based on the Pi-theorem, the relevant dimensionless parameters are derived and similarity rules for the scale-up are proposed as follows: As initial conditions, the height to diameter ratio of the combustion chamber, the mean Reynolds number in the combustion chamber and the mean square velocity through the combustion chamber shall be kept constant or in the case of the Reynolds number may also increase. Additionally the effective momentum flux ratio between the secondary air injected in the combustion chamber and the gases from the pyrolysis and gasification section also shall be kept constant to maintain the mixing conditions between combustible gases and secondary air. Finally the thermal surface load on the screw also shall be kept constant. The influence of different scale-up approaches on thermal surface load, gas velocity, pressure losses, Reynolds number and height-to-diameter ratio are compared and discussed and a scaling approach to increase the heat output from 35 kW to 150 kW is described. For a theoretical validation of the scale-up, CFD simulations are performed to investigate the predicted pollutant emissions and the pressure loss for the scaled 150 kW furnace.


Other Presentations | 2014

Scenedesmus obliquus as Source for Biogas: Anaerobic Digestion of Untreated and Pre-treated Biomass.

Gruber M, Zohar E, Jerney J, Bochmann G, Obbard JP, Schagerl M, Fuchs W, Drosg B. Scenedesmus obliquus as Source for Biogas: Anaerobic Digestion of Untreated and Pre-treated Biomass, 15. Tagung der Sektion Phykologie der DGB 2014, 23rd-26th of February 2014, Stralsund, Germany.

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Peer Reviewed Scientific Journals | 2014

Seeing about soil — management lessons from a simple model for renewable resources

Lichtenegger K, Schappacher W. Seeing about soil — management lessons from a simple model for renewable resources. International Journal of Modern Physics C. 2014;25(8).

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Employing an effective cellular automata model, we investigate and analyze the build-up and erosion of soil. Depending on the strategy employed for handling agricultural production, in many cases we find a critical dependence on the prescribed production target, with a sharp transition between stable production and complete breakdown of the system.

Strategies which are particularly well-suited for mimicking real-world management approaches can produce almost cyclic behavior, which can also either lead to sustainable production or to breakdown.

While designed to describe the dynamics of soil evolution, this model is quite general and may also be useful as a model for other renewable resources and may even be employed in other disciplines like psychology.


Peer Reviewed Scientific Journals | 2022

Self-Heating of Biochar during Postproduction Storage by O2 Chemisorption at Low Temperatures

Phounglamcheik A, Johnson N, Kienzl N, Strasser C, Umeki K. Self-Heating of Biochar during Postproduction Storage by O2 Chemisorption at Low Temperatures. Energies. 2022.15:380

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Biochar is attracting attention as an alternative carbon/fuel source to coal in the process industry and energy sector. However, it is prone to self-heating and often leads to spontaneous ignition and thermal runaway during storage, resulting in production loss and health risks. This study investigates biochar self-heating upon its contact with O2 at low temperatures, i.e., 50–300 °C. First, kinetic parameters of O2 adsorption and CO2 release were measured in a thermogravimetric analyzer using biochar produced from a pilot-scale pyrolysis process. Then, specific heat capacity and heat of reactions were measured in a differential scanning calorimeter. Finally, a one-dimensional transient model was developed to simulate self-heating in containers and gain insight into the influences of major parameters. The model showed a good agreement with experimental measurement in a closed metal container. It was observed that char temperature slowly increased from the initial temperature due to heat released during O2 adsorption. Thermal runaway, i.e., self-ignition, was observed in some cases even at the initial biochar temperature of ca. 200 °C. However, if O2 is not permeable through the container materials, the temperature starts decreasing after the consumption of O2 in the container. The simulation model was also applied to examine important factors related to self-heating. The results suggested that self-heating can be somewhat mitigated by decreasing the void fraction, reducing storage volume, and lowering the initial char temperature. This study demonstrated a robust way to estimate the cooling demands required in the biochar production process.


Conference contributions | 2011

Sensorbasierte Sortierung zur Erzeugung einer Deponiefraktion aus einer MBA-Schwerfraktion - Praxiserfahrungen und Vergleich verschiedener Aufbereitungsalternativen

Meirhofer M, Ragossnig A, Pieber S, Sommer M. Sensorbasierte Sortierung zur Erzeugung einer Deponiefraktion aus einer MBA-Schwerfraktion - Praxiserfahrungen und Vergleich verschiedener Aufbereitungsalternativen, Waste-to-Resources 2011, 24th-27th of May 2011, Hannover, Germany.

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The processing of heterogeneous waste is a major challenge for waste treatment equipment used in mechanical-biological (MB) waste treatment plants. This conference contribution focuses on the technical feasibility and efficiency of different technologies for the processing of a heavy waste fraction from a MB-plant which contains a high portion of high caloric components. The aim is to meet the requirements for waste to be landfilled in Austria. Also economic considerations with regard to the implementation of an additional separation step and the resulting changes in the waste routing are discussed. The processing technologies looked at comprise sensor-based sorting technologies (NIR, X-ray transmission) as well as traditional mechanical density separation technologies such as a jigger and cross-flow air classification.


Contributions to trade journals | 2010

Sewage Sludge Ash to phosphorus fertiliser (II): variables influencing heavy metal removal during thermochemical treatment

Mattenberger H, Fraissler G, Jöller M, Brunner T, Obernberger I, Herk P, et al. Sewage sludge ash to phosphorus fertiliser (II): Influences of ash and granulate type on heavy metal removal. Waste Manage. 2010;30(8-9):1622-33.

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Contributions to trade journals | 2008

Sewage Sludge Ash to phosphorus fertiliser: variables influencing heavy metal removal during thermochemical treatment

Mattenberger H, Fraissler G, Brunner T, Herk P, Hermann L, Obernberger I. Sewage sludge ash to phosphorus fertiliser: Variables influencing heavy metal removal during thermochemical treatment. Waste Manage. 2008;28(12):2709-22.

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Peer Reviewed Scientific Journals | 2015

Short term online corrosion measurements in biomass fired boilers. Part 1: Application of newly developed mass loss probe

Retschitzegger S, Gruber T, Brunner T, Obernberger I. Short term online corrosion measurements in biomass fired boilers. Part 1: Application of a newly developed mass loss probe. Fuel Process Technol 2015;137:148-156.

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Peer Reviewed Scientific Journals | 2016

Short term online corrosion measurements in biomass fired boilers. Part 2: Investigation of the corrosion behavior of three selected superheater steels for two biomass fuels

Retschitzegger, S., Gruber, T., Brunner, T., Obernberger, I. Short term online corrosion measurements in biomass fired boilers. Part 2: Investigation of the corrosion behavior of three selected superheater steels for two biomass fuels. Fuel Processing Technology. Volume 142, February 2016, Pages 59-70.

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The high temperature corrosion behavior of the boiler steels 13CrMo4-5 (1.7335), P91 (1.4903) and 1.4541 has been investigated during short-term test runs (~ 500 h) at a biomass fired grate furnace combined with a drop tube. For the test runs performed with 13CrMo4-5 and P91 chemically untreated wood chips have been used as fuel, whereas waste wood has been used for test runs with P91 and 1.4541. Online corrosion probes and a mass loss probe have been used applying a methodology developed in a previous study to correct for a measurement error occurring during short-term measurements with online corrosion probes (mass loss correction). Furthermore, deposit probe measurements have been performed to evaluate the deposit build-up rate and the chemical composition of deposits. SEM/EDX analyses of the corrosion probes have been performed subsequently to the test runs to gain information regarding the chemical composition and structure of the deposits as well as the corrosion layers.

The furnace has been operated at constant load to ensure constant combustion conditions. The flue gas temperature at the probes has been varied between 740 and 900 °C and the probe surface temperature has been varied between 400 and 560 °C in order to determine their influence on the corrosion rate.

General trends determined by the variation of these temperatures were similar for all boiler steels: the corrosion rate increased with increasing flue gas temperature and also with increasing probe surface temperature. For chemically untreated wood chips combustion at low flue gas temperatures (740 °C) the corrosion rates were comparable for 13CrMo4-5 and P91 at all probe surface temperatures. However, at flue gas temperatures of 800 °C and higher P91 showed better corrosion resistance than 13CrMo4-5. For waste wood combustion 1.4541 generally showed a better corrosion resistance than P91.

The mass loss correction of the measurement error occurring in the initial phase resulted in different errors of 55% for 13CrMo4-5 and 32% for P91 for chemically untreated wood chips. For waste wood the mass loss correction resulted in errors of 55% for P91 and 77% for 1.4541. The results from the mass loss determination for the waste wood test runs scattered stronger compared to the wood chips test runs. Therefore, the fits were not that accurate and the error margin was higher. However, the results outline that the mass loss correction is relevant in order to achieve a meaningful comparison of different short-term test runs using online corrosion probes.


Conference contributions | 2014

Sicherheit bei der Lagerung von Pellets

Emhofer W. Sicherheit bei der Lagerung von Pellets, Highlights der Energieforschung VIII - Erneuerbares Heizen und Kühlen 2014, 11th of July 2014, Vienna, Austria

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Peer Reviewed Scientific Journals | 2015

Simultaneous online determination of S, Cl, K, Na, Zn and Pb release from a single particle during biomass combustion Part 1: Experimental setup implementation and evaluation

Sommersacher P, Kienzl N, Brunner T, Obernberger I. Simultaneous online determination of S, Cl, K, Na, Zn and Pb release from a single particle during biomass combustion Part 1: Experimental setup implementation and evaluation. Energy and Fuels. 15 October 2015;29:6734-6746.

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The interest in experimental data regarding thermal fuel decomposition as well as the release behavior of ash-forming elements of biomass fuels for modeling and simulation purposes is continuously increasing. On the basis of combustion experiments with lab-scale reactors and single-particle reactors, integral release data regarding ash-forming vapors can be obtained, whereby the release is calculated on the basis of analysis data of the fuel and the ash residues. At the moment, almost no time-resolved release data of ash-forming elements from single particles exist. Therefore, a single-particle reactor was designed, which has been coupled to an inductively coupled plasma mass spectrometer (ICP-MS). This reactor can be used for targeted experiments in a temperature range of 250–1050 °C under inert, reducing, and oxidizing conditions. With this reactor, it is possible to simultaneously determine the surface and center temperatures of a biomass particle, weight loss of the particle, and flue gas composition. The reactor has been coupled to an ICP-MS through a gas stream that is sufficiently diluted with Ar. First performance tests with pure salts (KCl, NaCl, (NH4)2SO4, ZnCl2, and PbCl2) proved that relevant volatile ash-forming elements can be detected with the ICP-MS. For a further validation of the received signals, combustion tests with Miscanthus pellets have been carried out, whereby the controlled interruption of the experiments has also been investigated. These tests prove that with this system the simultaneous time-resolved determination of S, Cl, K, Na, Zn, and Pb is possible whereby the Cl signal can only be used with restrictions. On the basis of the determined release of ash-forming elements for the entire combustion experiment, a quantification/calibration of the measured intensities has been carried out. The data gained from these tests will provide deeper insights into release processes as well as form a relevant basis for release model development.


Peer Reviewed Scientific Journals | 2016

Simultaneous Online Determination of S, Cl, K, Na, Zn, and Pb Release from a Single Particle during Biomass Combustion. Part 2: Results from Test Runs with Spruce and Straw Pellets

Sommersacher P, Kienzl N, Brunner T, Obernberger I. Simultaneous Online Determination of S, Cl, K, Na, Zn, and Pb Release from a Single Particle during Biomass Combustion. Part 2: Results from Test Runs with Spruce and Straw Pellets. Energy and Fuels. 21 April 2016;30(4): 3428-3440.

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To gain better insight into inorganic element release processes, test runs with a specially designed single particle reactor connected with an inductively coupled plasma mass spectrometer (ICP-MS) have been performed. Relevant combustion related parameters such as mass loss during thermal degradation, temperature development of the particle (surface and center), and composition of released gases were recorded. By coupling the reactor to an ICP-MS, time-resolved release profiles of relevant aerosol forming elements (S, Cl, K, Na, Zn, and Pb) were determined. Targeted and controlled interruptions of the experiments (quenching) after a certain time were performed to validate reactor performance and reliability of the measurements. Test runs with softwood and straw pellets (8 mm in diameter and about 20 mm in length) were performed at reactor temperatures of 700, 850, and 1000 °C under oxidizing conditions (5.6 or 4.2 vol % O2). These test runs have revealed that the release ratios of volatile and semivolatile ash forming elements (S, Cl, K, Na, Zn, and Pb) generally increase as reactor temperatures rise. Moreover, regarding straw, higher Si and Al contents influence the release behavior of K, Na, Zn, and Pb. For K, existing release mechanisms proposed in the literature have been confirmed, and for Na it has been suggested that release mechanisms similar to K prevail. Especially during the starting phase of the experiment, a distinct temperature gradient exists from the surface to the center of the particle. Thus, different conversion phases occur in parallel in different layers of the particle, which has to be considered during the interpretation of the time-resolved release profiles of the main inorganic elements. Furthermore, transport limitations due to the occurrence of molten phases (especially for straw at reactor temperatures of 1000 °C) were obvious and could be directly derived from the online recorded release profiles. The targeted interruption of the ongoing decomposition process (quenching) provided an indication of the validity of the release profiles for S, K, Na, Zn, and Pb. Additionally, these experiments delivered valuable information regarding possible release mechanisms.


Conference Papers | 2020

Simultaneous state and fuel property estimation in biomass boilers - theory and practice

Zemann C, Gölles M, Horn M. Simultaneous state and fuel property estimation in biomass boilers - theory and practice. 1st Virtual IFAC World Congress. 2020.

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A key factor for the further distribution of biomass boilers in modern energy systems is the capability of changing the applied feedstock during normal plant operation. This is only possible with the application of advanced control strategies that utilize knowledge about the state variables and varying fuel properties. However, neither the state variables nor the fuel properties are measurable during plant operation and, thus, need to be estimated. This contribution presents a method for the simultaneous real-time estimation of the state variables and the fuel properties in fixed-bed biomass boilers which is a novel approach in the field of biomass boilers. The method bases on an Extended Kalman Filter using a nonlinear dynamic model and measurement data from the combustion process. The estimated variables are the masses of dry fuel and water in the fuel bed as well as the fuel's bulk density, water content, chemical composition and lower heating value. The proposed method is easy to implement and requires moderate computational effort which increases the potential of its application at actual biomass boilers. The proposed method is verified with simulation studies and by test runs performed at a representative small-scale fixed-bed biomass boiler. The estimation results show a good agreement with the actual values, demonstrating that the proposed method is capable of accurately estimating the biomass boiler's state variables and simultaneously its fuel properties. For this reason, the presented method is a key technology to ensure the further distribution of biomass boilers in modern energy systems.


Peer Reviewed Scientific Journals | 2020

Simultaneous state and fuel property estimation in biomass boilers - theory and practice

Zemann C, Gölles M, Horn M. Simultaneous state and fuel property estimation in biomass boilers - theory and practice. IFAC-PapersOnLine. 2020;53(2):12763-12770. https://doi.org/10.1016/j.ifacol.2020.12.1920

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A key factor for the further distribution of biomass boilers in modern energy systems is the capability of changing the applied feedstock during normal plant operation. This is only possible with the application of advanced control strategies that utilize knowledge about the state variables and varying fuel properties. However, neither the state variables nor the fuel properties are measurable during plant operation and, thus, need to be estimated. This contribution presents a method for the simultaneous real-time estimation of the state variables and the fuel properties in fixed-bed biomass boilers which is a novel approach in the field of biomass boilers. The method bases on an Extended Kalman Filter using a nonlinear dynamic model and measurement data from the combustion process. The estimated variables are the masses of dry fuel and water in the fuel bed as well as the fuel’s bulk density, water content, chemical composition and lower heating value. The proposed method is easy to implement and requires moderate computational effort which increases the potential of its application at actual biomass boilers. The proposed method is verified with simulation studies and by test runs performed at a representative small-scale fixed-bed biomass boiler. The estimation results show a good agreement with the actual values, demonstrating that the proposed method is capable of accurately estimating the biomass boiler’s state variables and simultaneously its fuel properties. For this reason, the presented method is a key technology to ensure the further distribution of biomass boilers in modern energy systems.


Peer Reviewed Scientific Journals | 2019

Single large wood log conversion in a stove: Experiments and modelling

Anca-Couce A, Caposciutti G, Gruber T, Kelz J, Bauer T, Hochenauer C, Scharler R. Single large wood log conversion in a stove: Experiments and modelling. Renewable Energy 2019.143:890-897.

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Natural draft wood log stoves for residential bioheat production are very popular due to the low fuel costs, the ecological aspect of a renewable energy source and the visual appeal of the flame. However, they have rather high pollutant emissions, specially of unburnt products. The description of large wood logs conversion in stoves needs to be improved to allow a process optimization which can reduce these emissions. The transient conversion of a single wood log in a stove is experimentally investigated with test runs quenching the log after defined time intervals and measuring the flue gas composition and temperatures in the log and stove. The experiments have been described with a volumetric single particle model, which predicts with good accuracy the log conversion until a time of around 30 min, when pyrolysis is almost ending. At that point, log fragmentation takes place and smaller fragments are detached from the log falling onto the bed of embers. Despite the increase in external surface area, char oxidation takes place at a moderate rate. This last stage of wood log conversion in a stove is the most challenging to model. Finally, preliminary recommendations are provided for reducing CO emissions in wood log stoves.


Peer Reviewed Scientific Journals | 2021

Single Pellet Combustion of Sewage Sludge and Agricultural Residues with a Focus on Phosphorus

Häggström G, Hannl TK, Hedayati A, Kuba M, Skoglund N, Öhman M. Single Pellet Combustion of Sewage Sludge and Agricultural Residues with a Focus on Phosphorus. Energy & Fuels. 8 June 2021.

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Recycling of phosphorus in combination with increased utilization of bioenergy can mitigate material and global warming challenges. In addition, co-combustion of different fuels can alleviate ash-related problems in thermal conversion of biomass. The aim of this study is to investigate the ash transformation reactions of mainly P in co-combustion of P-rich sewage sludge (SS) with K-rich sunflower husks (SH) and K- and Si-rich wheat straw (WS). Single pellets of 4 mixtures (10 and 30 wt % SS in WS and 15 and 40 wt % SS in SH) and pure SS were combusted in an electrically heated furnace at process temperatures relevant for fluidized bed combustion (800 and 950 °C). Collected ash fractions were analyzed by inductively coupled plasma techniques, ion chromatography, scanning electron microscopy–energy-dispersive X-ray spectroscopy, and X-ray diffraction. Thermodynamic equilibrium calculations were performed to interpret the results. Over 90% of K and P was found to be captured within the residual ash with 30–70% P in crystalline K-bearing phosphates for mixtures with low amounts of SS (WSS10 and SHS15). The significant share of K and P in the amorphous material could be important for P recovery. For the lower percentage mixtures of SS (WSS10 and SHS15), P in crystalline phases was mainly found in K-whitlockite and CaKPO4. For the higher percentage SS mixtures, most of P was found in whitlockites associated with Fe and Mg, and no crystalline phosphates containing K were detected. For P recovery, co-combustion of the lower SS mixtures is favorable, and they are suggested to be further studied concerning the suitability for plant growth.


Peer Reviewed Scientific Journals | 2022

Smart control of interconnected district heating networks on the example of “100% Renewable District Heating Leibnitz”

Kaisermayer V, Binder J, Muschick D, Beck G, Rosegger W, Horn M, Gölles M, Kelz J, Leusbrock I. Smart control of interconnected district heating networks on the example of “100% Renewable District Heating Leibnitz”. Smart Energy. 2022 Apr 7. 100069. https://doi.org/10.1016/j.segy.2022.100069

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District heating (DH) networks have the potential for intelligent integration and combination of renewable energy sources, waste heat, thermal energy storage, heat consumers, and coupling with other sectors. As cities and municipalities grow, so do the corresponding networks. This growth of district heating networks introduces the possibility of interconnecting them with neighbouring networks. Interconnecting formerly separated DH networks can result in many advantages concerning flexibility, overall efficiency, the share of renewable sources, and security of supply. Apart from the problem of hydraulically connecting the networks, the main challenge of interconnected DH systems is the coordination of multiple feed-in points. It can be faced with control concepts for the overall DH system which define optimal operation strategies. This paper presents two control approaches for interconnected DH networks that optimize the supply as well as the demand side to reduce CO2 emissions. On the supply side, an optimization-based energy management system defines operation strategies based on demand forecasts. On the demand side, the operation of consumer substations is influenced in favour of the supply using demand side management. The proposed approaches were tested both in simulation and in a real implementation on the DH network of Leibnitz, Austria. First results show a promising reduction of CO2 emissions by 35% and a fuel cost reduction of 7% due to better utilization of the production capacities of the overall DH system.