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Reviewed Conference Papers | 2019

Co-Simulation of an Energy Management System for Future City District Energy Systems

Moser AGC, Muschick D, Gölles M, Lerch W, Schranzhofer H, Nageler PJ et al. Co-Simulation of an Energy Management System for Future City District Energy Systems. In Proceedings of the International Conference on Innovative Applied Energy. 2019.

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The continuous increase of (volatile) renewable energy production and the development of energy-efficient buildings have led to a transformation of city districts’ energy systems. Their complexity has increased significantly due to the coupling of the different energy sectors like heating, cooling and electricity. Such complex multi-energy systems can be operated more efficiently and reliably if knowledge of their specific components (in terms of mathematical models) as well as knowledge of weather forecasts is incorporated in a high-level controller, which is typically referred to as an Energy Management System (EMS). However, still little comprehensive information on the costs and the practical advantages of such systems is available. For this reason, a simulation environment to estimate the real costs and advantages of the use of such an EMS is required. Consequently, this work focuses on the development of an EMS for future city districts’ energy systems and the development of a co-simulation environment in order to demonstrate the benefits of the use of the developed EMS in comparison to a conventional control strategy. The co-simulation is implemented with the aid of the co-simulation platform Building Controls Virtual Test Bed (BCVTB) and consists of the following parts: a non-linear, thermoelectric model and a control block containing either the conventional control strategy or the EMS. The thermoelectric model is built up using the well-established simulation tools TRNSYS and IDA-ICE, simulating the energy hub of the city district and the districts’ buildings, respectively. The control block is simulated using MATLAB, where IBM ILOG CPLEX is used for solving the resulting mixed-integer linear program (MILP) of the EMS. Finally, an economic model for financial (and ecological) assessment of the operation is simulated with the aid of the software package Dymola. To put the developed EMS and the co-simulation into practise a case study based on a new city district in Graz, Austria, which is currently in the planning stage, is carried out. The integration of the responsible planners and investors in the modelling process guarantees the models’ practical applicability. In the case study the performance of the originally planned conventional control strategy is compared with the performance of the developed EMS using annual simulations with a simulation time step of 1 minute, and a 24 hour prediction horizon and a 15 minute time step for the EMS. For a more robust and realistic comparison both control strategies are simulated for different scenarios considering current and future (2060) climate conditions, medium and high energy demands (load), ideal and real load prediction methods and varying import prices for electricity from the electricity grid. The results show that the use of the developed EMS strategy results in reduced annual total costs (considering operational and investment costs of additionally suggested distributed energy resources) in comparison to the conventional control strategy. Furthermore, the annual CO2-emissions could be reduced by increasing the self-consumption of the installed (renewable) energy resources and thus decreasing the necessary energy imports from the electricity and the heating grid.


Conference contributions | 2019

Co-Simulation of an Energy Management System for Future City District Energy Systems (Presentation)

Moser AGC, Muschick D, Gölles M, Lerch W, Schranzhofer H, Nageler PJ et al. Co-Simulation of an Energy Management System for Future City District Energy Systems. International Conference on Innovative Applied Energy. 2019. (Oral presentation, 15.03.2019.)

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Slides of the talk "Co-Simulation of an Energy Management System for Future City District Energy Systems"


Scientific Journals | 2019

Cultivation of the microalga Eustigmatos magnus in different photobioreactor geometries and subsequent anaerobic digestion of pre-treated biomass

Gruber-Brunhumer MR, Schöberl A, Zohar E, Koenigsberger S, Bochmann G, Uher B, Lang I, Schagerl M, Fuchs W, Drosg B. Cultivation of the microalga Eustigmatos magnus in different photobioreactor geometries and subsequent anaerobic digestion of pre-treated biomass. Biomass and Bioenergy 2019.105303.

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Microalgal biomass as a feedstock for biogas production is linked to the parameters biomass productivity and biogas yield. Besides an easy-to-use strain for anaerobic digestion, the photobioreactor (PBR) design is important. A microalgae strain selection revealed Eustigmatos magnus (SAG 36.89) as the most promising strain yielding an average of 100 mg total suspended solids (TSS) L−1 day−1. The strain was tested in cost-effective sleevebag-PBR-systems of 10 cm, 20 cm and 30 cm diameter facing the light from the front or laterally. Highest mean productivity on a volumetric basis was measured in PBRs with the lowest diameter (104 and 117 mg L−1 day−1. The highest productivity per m−2 was achieved in 10 cm PBRs with front light configuration (9.35 g TSS m−2 day−1). The lateral light configuration of 10 cm PBRs had positive aspects such as the lowest mean water demand to produce 1 kg TSS (481 L−1 kg−1) and the lowest mean energy demand for medium separation of 1 kg TSS (106 Wh). The concentrated microalgal biomass was then subjected to ultrasonication and thermal pre-treatment (90 °C and 120 °C) and tested in BMP tests. Mesophilic anaerobic mono-digestion of untreated microalgae biomass led to a methane (CH4) yield of 343 L−1 kg−1 volatile solids (VS). Thermal pre-treatment at 120 °C resulted in significantly increased CH4 yields of 430 L−1 kg−1 VS. As thermal pre-treatment can be easily installed nearby a biogas plant it could be an interesting option for AD of microalgal biomass with only little investment.


Conference contributions | 2019

Customizing biomass as reducing agent in blast furnace steelmaking – preliminary results

Strasser C, Kienzl N, Martini S, Dißauer C, Deutsch R. Customizing biomass as reducing agent in blast furnace steelmaking – preliminary results. 27th European Biomass Conference & Exhibition (Poster). May 2019.

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The reduction of greenhouse gas emission is an important issue for steel industry. One possibility is to use biomass-based reducing agents, also called bioreducers, to replace a least partly the fossil reducer agents. To produce bioreducer we treated woody biomass in a lab-scale muffle furnace, we performed grinding experiments with a ball mill, we analyzed the particle size distribution with laser diffraction and we used a rotating device, the revolution powder analyzer, for flow behavior investigations. Our preliminary results show that treatment temperatures >250 oC bring adequate increased calorific value and improved grindability. For a certain treatment temperature the particle size distribution and as well the flow behavior shows similarities to lignite.


Conference contributions | 2019

Decomposition of tars in dual fluidized bed gasification – mechanisms of formation and decomposition in long-term operation

Umeki K, Priscak J, Kuba M. Decomposition of tars in dual fluidized bed gasification – mechanisms of formation and decomposition in long-term operation. ICPS 2019.

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Conference contributions | 2019

Development of a New Method for Investigation of the Ash Melting Behavior in the Fluidized Bed Conversion Processes

Priscak J, Kuba M, Hofbauer H. Development of a New Method for Investigation of the Ash Melting Behavior in the Fluidized Bed Conversion Processes. ICPS 2019.

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Peer Reviewed Scientific Journals | 2019

Double-cropping systems based on rye, maize and sorghum: Impact of variety and harvesting time on biomass and biogas yield

Wannasek L, Ortner M, Kaul HP, Amon B, Amon T. Double-cropping systems based on rye, maize and sorghum: Impact of variety and harvesting time on biomass and biogas yield. European Journal of Agronomy 2019.110:125934

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Climate change affects the frequency and intensity of extreme weather, the results of which include production losses and climate-induced crop productivity fluctuations.

Double-cropping systems (DCSs) have been suggested as a way to increase biomass-production while simultaneously delivering environmental benefits. In a three-year field-test, two DCSs based on maize and sorghum as the main crop and rye as the preceding winter crop were compared with each other and compared with 2 single-cropping systems (SCSs) of maize or sorghum; there were comparisons of growth dynamics, optimal harvesting and growing time as well as biomass and methane yield. In addition, the impact of variety and harvest time on the winter rye optimal biomass yield was studied.

The experiments clearly showed the superiority of the DCS over the SCS. Within the DCS, the rye/sorghum combination achieved significantly higher biomass yields compared to those of the rye/maize combination. The highest dry matter biomass yield was achieved during year 1 at 27.5 ± 2.4 t∙ha−1, during which winter rye contributed 8.3 ± 0.7 t∙ha−1 and sorghum contributed 19.2 ± 1.8 t∙ha−1. At the experimental location, which is influenced by a Pannonia climate (hot and dry), the rye/sorghum DCS was able to obtain average methane yields per hectare, 9300 m3, whereas the rye/maize combination reached 7400 m3. In contrast, the rye, maize and sorghum SCSs achieved methane yields of 4800, 6100 and 6500 m3 ha−1, respectively. The study revealed that the winter rye and sorghum DCS is a promising strategy to counteract climate change and thus guarantee crop yield stability.


Peer Reviewed Scientific Journals | 2019

Effects of partial maize silage substitution with microalgae on viscosity and biogas yields in continuous AD trials

Gruber-Brunhumer MR, Montgomery LFR, Nussbaumer M, Schoepp T, Zohar E, Muccio M, Ludwig I, Bochmann G, Fuchs W, Drosg B. Effects of partial maize silage substitution with microalgae on viscosity and biogas yields in continuous AD trials. Journal of Biotechnology 2019;295:80-89.

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The microalga Acutodesmus obliquus was investigated as a feedstock in semi-continuously fed anaerobic digestion trials, where A. obliquus was co-digested with pig slurry and maize silage. Maize silage was substituted by both 10% and 20% untreated, and 20% ultrasonicated microalgae biomass on a VS (volatile solids) basis. The substitution of maize silage with 20% of either ultrasonicated and untreated microalgae led to significantly lower biogas yields, i.e., 560 dm³ kg−1 VScorr in the reference compared to 516 and 509 dm³ kg-1VScorr for untreated and ultrasonicated microalgae substitution. Further, the viscosities in the different reactors were measured at an OLR of 3.5 g VS dm-3 d-1. However, all treatments with microalgae resulted in significantly lower viscosities. While the mean viscosity reached 0.503 Pa s in the reference reactor, mean viscosities were 53% lower in reactors where maize was substituted by 20% microalgae, i.e. 0.239 Pa s, at a constant rotation speed of 30 rpm. Reactors where maize was substituted by 20% ultrasonicated microalgae had a 32% lower viscosity, for 10% microalgae substitution a decrease of 8% was measured. Decreased viscosities have beneficial effect on the bioprocess and the economy in biogas plants. Nonetheless, with regard to other parameters, no positive effect on biogas yields by partial substitution with microalgae biomass was found. The application of microalgae may be an interesting option in anaerobic digestion when fibrous or lignocellulosic substances lead to high viscosities of the digested slurries. High production costs remain the bottleneck for making microalgae an interesting feedstock.


Scientific Journals | 2019

Efficient Multi-Year Economic Energy Planning in Microgrids

Pecenak Z, Stadler M, Fahy K, Efficient Multi-Year Economic Energy Planning in Microgrids. Applied Energy 2019;225.

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With energy systems, the problem of economic planning is decisive in the design of a low carbon and resilient future grid. Although several tools to solve the problem already exist in literature and industry, most tools only consider a single “typical year” while providing investment decisions that last around a quarter of a century. In this paper, we introduce why such an approach is limited and derive two approaches to correct this. The first approach, the Forward-Looking model, assumes perfect knowledge and makes investment decisions based on the full planning horizon. The second novel approach, the Adaptive method, solves the optimization problem in single year iterations, making incremental investment decisions that are dependant on previous years, with only knowledge of the current year. Comparing the two approaches on a realistic microgrid, we find little difference in investment decisions (maximum 21% difference in total cost over 20 years), but large differences in optimization time (up to 12000% time difference). We close the paper by discussing implications of forecasting errors on the microgrid planning process, concluding that the Adaptive approach is a suitable choice.


Conference contributions | 2019

Evaluation of analytical methods for assessing biomass gasification producer gas quality for solid oxide fuel cell (SOFC) operation

Martini S, Lagler J, Tsiotsias T, Kienzl N, Anca-Couce A. Evaluation of analytical methods for assessing biomass gasification producer gas quality for solid oxide fuel cell (SOFC) operation. 27th European Biomass Conference & Exhibition (Poster). May 2019.

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The efficient and flexible conversion of solid biomass into energetic products will be an essential part of a future renewable, independent and reliable energy providing system. The main objective of the project Bio-CCHP is the development of a novel tri-generation system, including biomass gasification, gas cleaning, a Solid Oxide Fuel Cell (SOFC) and a cooling machine with the aim to produce electricity, heat and cold (CCHP), maximizing the efficiency and flexibility of the system. However, the employment of biomass derived product gas as fuel gas for SOFC is facing new challenges for gas quality assurance. For the evaluation of required dry high temperature gas cleaning processes the applied methods of gas characterization have to be accurate and reliable. Therefore, a comprehensive evaluation of analytical methods for the detection of SOFC harmful compounds is conducted within the ongoing project. First results of online and offline sampling and analysis methods employed at air- and steam-operated gasifiers are shown in this paper.


Conference contributions | 2019

Evaluation of methane emissions from different Austrian biogas plants using harmonised methods including an open-path technology

Wechselberger V, Huber-Humber M, Meixner K, Knoll L, Hrad M. Evaluation of methane emissions from different Austrian biogas plants using harmonised methods including an open-path technology. 17th International Waste Management and Landfill Symposium, Calgari Italy. Sep 2019.

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Although the number of studies investigating the contribution of anaerobic digestion facilities to greenhouse gas (GHG) emissions has increased during the last decade, reliable data with respect to gaseous process losses from these management practices, particularly at commercial scale, is scarce (Liebetrau et al., 2013, Reinelt et al., 2017, Hrad et al., 2015). The dynamic and fugitive nature of methane emissions, changing operating conditions, and different as well as not standardised measurement approaches compromise the precise quantification of the overall emissions from full-scale biogas plants. However, reliable and verifiable emission data from biogas or biomethane facilities are required in order to optimise and improve the plant-specific process efficiency as well as future technology developments. In addition, precise and comprehensive measurement data from full-scale waste treatment facilities are needed for more accurate emission factors (EFs) estimates, which are required for annual reporting according to the Intergovernmental Panel on Climate Change (IPCC) guidelines (IPCC, 2006).
Within the European project “EvEmBi - Evaluation and reduction of different biogas plant concepts” (2018-2021, funded within the 11th ERA-NET bioenergy call) 15 partners from 5 European countries evaluate the existing technologies at biogas plants regarding their methane EFs and develop emission reduction strategies, respectively. The focus of the Austrian research group within this project is the evaluation of Austrian bio-waste plants.
In a first step, emissions from single sources as well as overall plant emissions are quantified. For the latter, the Austrian team uses an open-path technology (Open-Path Tunable-Diode-Laser-Spectroscopy) together with meteorological data (ultra-sonic anemometer) and inverse dispersion modelling (Backward Lagrangian Model). In order to determine comparable EFs, the applied methodologies are based on a measurement guideline developed in the previous project “MetHarmo – European harmonization of method to quantify methane emissions from biogas plants” (funded within the 9th ERA-NET bioenergy call). In addition, the determined EFs of the individual plant concepts are transferred to EFs of the entire plant inventory of the particular countries. For that, a model for EF quantification is used which is based on statistical information on the emissions from different plant components as well as on the distribution of certain technologies present in the participating countries. Furthermore, for the particular biogas plants emission reduction strategies are developed, implemented and verified.
In this presentation, the harmonised approach, first emission results from the Austrian measurement campaigns as well as emission reduction strategies are presented.


Conference Papers | 2019

Evaluation of the Operational Behaviour of Fixed-bed Biomass Gasifiers - A Novel Approach for Steady-state Analysis

Hollenstein C, Zemann C, Antolini D, Patuzzi F, Martini S, Baratieri M, Gölles M. Evaluation of the Operational Behaviour of Fixed-bed Biomass Gasifiers - A Novel Approach for Steady-state Analysis. Proceedings of the 27th European Biomass Conference and Exhibition, Vols. 27-30 May 2019, pp. 849-860, 2019.

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Assessing the operational behaviour of biomass gasification systems is a crucial basis for further improvements in terms of operational behaviour and robustness in order to increase the technologies’ operational and economic viability. However, in most fixed-bed biomass gasification systems not all parameters required for the assessment can be measured directly. Typically, unknown parameters are determined by using as many balance equations as parameters have to be determined neglecting the additional information provided by other available but not chosen balance equations. Thus, these approaches do not incorporate all measurement data available resulting in a lack of reliability in their results. A detailed analysis of these approaches emphasises that even small deviations in the measurement data can lead to significant deviations in the calculated parameters, demonstrating that individual choices of equations can be highly sensitive regarding measurement uncertainties.

Therefore, an adjusted weighted least squares approach is developed utilizing an overdetermined system of equations incorporating all balance equations simultaneously. Thus, all measurement data available is taken into account, minimizing the influences of measurement uncertainties on the determined parameters. A comprehensive analysis shows that this approach is less sensitive to measurement uncertainties, allowing for a more reliable and accurate assessment of fixed-bed biomass gasifiers.

Keywords: fixed-bed, gasification, mass balance, performance assessment


Peer Reviewed Scientific Journals | 2019

Experimental investigation on biomass shrinking and swelling behaviour: Particles pyrolysis and wood logs combustion

Caposciutti G, Almuina-Villar H, Dieguez-Alonso A, Gruber T, Kelz J, Desideri U, Hochenauer C, Scharler R, Anca-Couce A. Experimental investigation on biomass shrinking and swelling behaviour: Particles pyrolysis and wood logs combustion. Biomass and Bioenergy 2019;123:1-13.

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Biomass is a suitable energy source to reduce the carbon footprint and increase the use of renewable energy. However, the biomass exploitation is still slowed by many technical issues. In most practical applications, such as gasification or combustion devices, it is important to predict the fuel physical behavior in order to determine the emissions and heat release profile as well as for modeling and design purposes. Within this paper, the study of the dimensional evolution of a biomass fuel (beech wood) in pyrolysis and combustion processes were carried out with the use of the image analysis tool. Sizes from 15 mm to 300 mm characteristic length range were employed in the experiments and the collected data were related to the mass loss and temperature evolution of the biomass particle. It was found that for all the fuel sizes employed a similar volume reduction (60%–66%) was obtained at the end of pyrolysis. However, for the small particles with minor intra-particle gradients shrinkage took place mainly at the end of conversion, while for bigger particles the size variation patter was more linear. Furthermore, swelling was detected in the pyrolysis experiments, and it was higher for a bigger particle size, while cracking and fragmentation phenomena was observed for large wood logs combustion in the stove.


Studien | 2019

Factsheet Staubemissionen

Schwarz M, Strasser C. Factsheet Staubemissionen. 2019

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Zum Erreichen der Ziele der österreichischen Klimastrategie leisten Biomassefeuerungen einen entscheidenden Beitrag. Um dabei die Luftgüte nicht außer Acht zu lassen, wird in diesem Factsheet der aktuelle und zukünftige Status (bis 2050) von Staubemissionen in Österreich basierend auf Literaturdaten und eigenen Messungen dargelegt, und der aktuelle Kenntnisstand zu Emissionen aus Biomasse-Kleinfeuerungen zusammengefasst.


Technical Reports | 2019

Fischer-Tropsch products from biomass-derived syngas and renewable hydrogen

Gruber H, Groß P, Rauch R, Reichhold A, Zweiler R, Aichernig C, Müller S, Ataimisch N, Hofbauer H. Fischer-Tropsch products from biomass-derived syngas and renewable hydrogen. 2019.

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Global climate change will make it necessary to transform transportation and mobility away from what we know now towards a sustainable, flexible, and dynamic sector. A severe reduction of fossil-based CO2 emissions in all energy-consuming sectors will be necessary to keep global warming below 2 °C above preindustrial levels. Thus, long-distance transportation will have to increase the share of renewable fuel consumed until alternative powertrains are ready to step in. Additionally, it is predicted that the share of renewables in the power generation sector grows worldwide. Thus, the need to store the excess electricity produced by fluctuating renewable sources is going to grow alike. The “Winddiesel” technology enables the integrative use of excess electricity combined with biomass-based fuel production. Surplus electricity can be converted to H2 via electrolysis in a first step. The fluctuating H2 source is combined with biomass-derived CO-rich syngas from gasification of lignocellulosic feedstock. Fischer-Tropsch synthesis converts the syngas to renewable hydrocarbons. This research article summarizes the experiments performed and presents new insights regarding the effects of load changes on the Fischer-Tropsch synthesis. Long-term campaigns were carried out, and performance-indicating parameters such as per-pass CO conversion, product distribution, and productivity were evaluated. The experiments showed that integrating renewable H2 into a biomass-to-liquid Fischer-Tropsch concept could increase the productivity while product distribution remains almost the same. Furthermore, the economic assessment performed indicates good preconditions towards commercialization of the proposed system.


Conference Papers | 2019

Ganzheitliche Planung dezentraler Energiekonzepte durch mathematische Optimierung

Liedtke P, Stadler M, Zellinger M, Hengl F. Ganzheitliche Planung dezentraler Energiekonzepte durch mathematische Optimierung. e-nova Konferenz 2019.

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Kernthema dieses Beitrags ist die ganzheitliche Konzeption von Mikronetze, die sich auf die Reduzierung von Kosten und CO2-Emissionen konzentriert. Mikronetze, oder auch Microgrids, ermöglichen die koordinierte Energieerzeugung von dezentralen Energieressourcen, die Speicherungen der produzierten Energie und ein Lastmanagement zum Ausgleich von Wärme-, Kälte- und Elektrizitätsdienstleistungen. Mikronetze können vom breiteren Versorgungsnetz getrennt werden, können diverse Dienstleistungen erbringen und/oder selbst Energie erzeugen sowie in Überschusszeiten speichern und bei Bedarf wieder Kosten- oder Stabilitäts-orientiert freigeben.
Die mathematische Optimierung dient als unvoreingenommene Alternative für eine gesamtheitliche Planung von dezentralen Energietechnologien. Dieses Kriterium wird bei einer Kosten- oder CO2-Reduktion vor allem dann essentiell, wenn vielfältigen Kombinationen von Technologien und Kapazitäten möglich sind. Modernste Ansätze betrachten jedoch einen quasistatischen Aufbau unter Verwendung linearisierte Modelle und Mixed Integer Linear Optimization (MILP), wobei dynamische Effekte vernachlässigt werden. Unter Berücksichtigung von Lasten, geografischen, ökonomisch-ökologischen und tariflichen Daten sind mathematische Optimierungsalgorithmen in der Lage, verschiedene Anwendungsfälle zu beurteilen, wobei Effekte wie Vorwärmung, Sollwertänderungen oder kurzfristige Sonnenschwankungen unberücksichtigt bleiben. Dies bedeutet, dass die in quasistatischen Ansätzen verwendete Wärme- und Strombilanzen ungenau sein können (eventuell können physikalische Randbedingungen sogar verletzt werden, was zu suboptimalen Ergebnissen bei der Planung führen würde).
Die Notwendigkeit besteht quasistatische Optimierung mit einer weiteren Modellierungsart zu vergleichen und die Auswirkungen auf traditionelle quasistatische Ansätze, wie sie in DER-CAM oder ReOpt eingesetzt werden, aufzudecken. Um Abweichungen - bestehend aus dynamischen oder sogar Rebound Effekten - zu erkennen, werden mit TRNSYS Gebäude- und Anlagensimulationen für eine geplante Siedlungsanlage erstellt und ein Energiekonzept mit dem mathematischen Optimierungsprogramm OptEnGrid berechnet. Der Ansatz wird für vier Doppelhäuser und ein Mehrfamilienhaus getestet. Die Gebäude werden in TRNSYS simuliert und bieten thermische Lastdaten für den Referenzfall. Auch die Stromerzeugung mit PV-Modellen und der elektrische Verbrauch mit synthetischen Lastprofilen sind sowohl in der Optimierung als auch in der Simulation beteiligt. In der elektrischen Stromerzeugung zeigt die mathematische Optimierung bereits eine Abweichung von mehr als 5% auf Jahresbasis zur TRNSYS-Simulation. Ergebnisse im thermischen Energiebereich folgen nach weiterer Auswertung.


Conference contributions | 2019

GHG emission reduction costs of various technologies in the heating and mobility sectors

Strasser C, Schwarz M, Sturmlechner R, GHG emission reduction costs of various technologies in the heating and mobility sectors. 27th European Biomass Conference & Exhibition (Poster). May 2019.

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Peer Reviewed Scientific Journals | 2019

High Utilization of Humidified Ammonia and Methane in Solid Oxide Fuel Cells: An Experimental Study of Performance and Stability

Stöckl B, Preininger M, Subotic V, Gaber C, Seidl M, Sommersacher P, Schröttner H, Hochenauer C. High Utilization of Humidified Ammonia and Methane in Solid Oxide Fuel Cells: An Experimental Study of Performance and Stability. Journal of The Electrochemical Society 2019.166:F774-F783.

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Wastewater contains high amounts of unused energy in the form of dissolved ammonia, which can easily be converted into gaseous humidified ammonia via membrane distillation, thus providing a potential fuel for solid oxide fuel cells. This study presents comprehensive investigations of the use of humidified ammonia as the primary fuel component in high-fuel utilization conditions. For these investigations, large planar anode- and electrolyte-supported solid oxide single cells were operated at the respective appropriate temperatures, 800°C and 850°C. Fueled with ammonia, both cells exhibited excellent ammonia conversion ( > 99.5%) in addition to excellent performance output and fuel utilization. In 100 h stability tests performed at 80% fuel utilization, the cells exhibited stable performance, despite scanning electron microscopy analyzes revealing partial impairments to the nickel parts of both cells due to the formation and subsequent decomposition of nickel nitride. This study also demonstrates that methane is a perfect additional fuel component for humidified ammonia streams, as steam supports the internal reforming of methane. Alternating and direct current as well as electrochemical impedance measurements with a variety of ammonia/steam/methane/nitrogen fuel mixtures were used to evaluate the performance potential of the cells, and proved their stability over 48 h in highly polarized conditions.


Scientific Journals | 2019

Implementation and long term experiences with a continuous hygienisation process in food industry – A case study

Wöss D, Ortner M, Mensik J, Kirchmayr R, Schumergruber A, Pröll T. Implementation and long term experiences with a continuous hygienisation process in food industry – A case study. Chemical Engineering and Processing - Process Intensification 2019;137:100-107.

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A three tonne/hour batch-type hygienisation process for animal waste was replaced by a fully continuous process including heat integration. The plant is embedded into a pig abattoir including an anaerobic digestion (biogas) plant and gas-engine-based combined heat and power (CHP) production. Pre-heating is done in a series of four tube bundle apparatuses with heat transferred from the hot treated animal waste leaving the hygienisation plant. A closed water loop is used for heat transfer in this heat recovery arrangement. After pre-heating, the feed passes a second series of four tube bundles operated with heat from the biogas CHP plant in order to meet a target temperature of 72 °C at the inlet of the continuous hygienisation section. The material leaving the tube section is finally cooled in a series of four tube bundles and provides heat for pre-heating the feed before it is directed into the biogas plant. The process was started up in 2011 and monitoring results are be presented from 2011 to 2016. With the implementation of the continuous process, energy consumption of the hygienisation step was reduced by 64% for thermal and by 69% for electric energy.


Conference Papers | 2019

Increased economic efficiency of dual fluidized bed plants via model-based control

Nigitz T, Gölles M, Aichernig C, Schneider S, Hofbauer H, Horn M. Increased economic efficiency of dual fluidized bed plants via model-based control. In 27th European Biomass Conference and Exhibition. 2019. p. 533 - 538 https://doi.org/10.5071/27thEUBCE2019-2BO.6.5

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Sustainable technologies can hardly compete with fossil-based technologies in terms of economic efficiency. One sustainable technology with special relevance due to its wide range of application and industrial readiness is biomass gasification using a dual fluidized bed (DFB). The economic challenges of a DFB gasification plant are addressed without constructional measures by adapting a current control strategy. This paper proposes a model-based control strategy aiming for increased economic efficiency of a DFB gasification plant considering exemplarily the “HGA Senden” in Ulm, Germany. A process analysis reveals high potential for improvement at the current control strategy for the synchronization of product gas production and utilization. A significant surplus of product gas is burned in an auxiliary boiler just for synchronization, and regular manual adjustments by the plant operators at the fuel feed are necessary. The model-based control strategy synchronizes by actuating the auxiliary boiler and the fuel feed simultaneously. The model-based control strategy is experimentally validated for over one month at the “HGA Senden” proofing a significant increase in economic efficiency. So, the economic efficiency of this technology for the sustainable production of energy and products is increased by model-based control.


Conference contributions | 2019

Influence of fuel ash and bed material on the water-gas-shift equilibrium in DFB steam gasification

Fürsatz K, Fuchs J, Bartik A, Kuba M, Hofbauer H. Influence of fuel ash and bed material on the water-gas-shift equilibrium in DFB steam gasification. ICPS 2019.

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The bed material chosen for dual fluidized bed steam gasification has an important effect on the performance of gasification. Depending on their characteristics and properties, bed materials can have either a higher or lower catalytic activity, which influences the product gas composition as well as the tar content in the product gas. More catalytically active bed materials, like limestone and olivine, improve the quality of the product gas by e.g. promoting the water-gas-shift reaction and tar reforming reaction. The layers formed on the bed material are another aspect influencing the product gas composition. These layers are formed by the interaction of bed material and fuel ash. The deviation from the water-gas-shift equilibrium was chosen to quantify the effect of several bed materials and ash layers on the catalytic activity. The bed materials tested were K-feldspar, limestone, and activated olivine, while the used fuels were softwood, chicken manure, a bark – chicken manure mixture, and a bark –straw – chicken manure mixture. The performed experiments showed that an increased catalytic activity can be achieved by either using a catalytically active bed materials or ash-rich fuels.

 


Peer Reviewed Scientific Journals | 2019

Input data reduction for microgrid sizing and energy cost modeling: Representative days and demand charges

Fahy K, Stadler M, Pecenak ZK, Kleissl J. Input data reduction for microgrid sizing and energy cost modeling: Representative days and demand charges. Journal of Renewable and Sustainable Energy. 2019.11:065301

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Computational time in optimization models scales with the number of time steps. To save time, solver time resolution can be reduced and input data can be down-sampled into representative periods such as one or a few representative days per month. However, such data reduction can come at the expense of solution accuracy. In this work, the impact of reduction of input data is systematically isolated considering an optimization which solves an energy system using representative days. A new data reduction method aggregates annual hourly demand data into representative days which preserve demand peaks in the original profiles. The proposed data reduction approach is tested on a real energy system and real annual hourly demand data where the system is optimized to minimize total annual costs. Compared to the full-resolution optimization of the energy system, the total annual energy cost error is found to be equal or less than 0.22% when peaks in customer demand are preserved. Errors are significantly larger for reduction methods that do not preserve peak demand. Solar photovoltaic data reduction effects are also analyzed. This paper demonstrates a need for data reduction methods which consider demand peaks explicitly.

 


Scientific Journals | 2019

Interrelation of Volatile Organic Compounds and Sensory Properties of Alternative and Torrefied Wood Pellets

Poellinger-Zierler B, Sedlmayer I, Reinisch C, Hofbauer H, Schmidl C, Kolb LP, Wopienka E, Leitner E, Siegmund B. Interrelation of Volatile Organic Compounds and Sensory Properties of Alternative and Torrefied Wood Pellets. energy & fuels 2019.33:5270-5281.

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The increasing demand for wood pellets on the market, which is caused by their excellent combustion properties, inspires the production as well as the utilization of alternative biomass pellets as fuel. However, the emission of volatile organic compounds gives pellet materials a distinct odor or off-odor, which is directly perceived by the end user. Thus, there is an urgent need for knowledge about the emitted volatile organic compounds and their potential formation pathways as well as their contributions to odor properties of the pellets. In this study, pellets made of biomass energy crops (i.e., straw or miscanthus), byproducts from the food industry (i.e., rapeseed, grapevine, or DDGS (dried distillers grains with solubles from beer production)), or eucalyptus, as well as torrefied pinewood and torrefied sprucewood were investigated with respect to the emitted volatile compounds and their possible impact on the pellet odor. Headspace solid-phase microextraction in combination with gas chromatography–mass spectrometry was used to enrich, separate, and identify the compounds. Techniques used in sensory science were applied to obtain information about the odor properties of the samples. A total of 59 volatile compounds (acids, aldehydes and ketones, alcohols, terpenes, heterocyclic compounds, and phenolic compounds) were identified with different compound ratios in the investigated materials. The use of multivariate statistical data analysis provided deep insight into product–compound interrelation. For pellets produced from bioenergy crops, as well as from byproducts from the food industry, the sensory properties of the pellets reflected the odor properties of the raw material. With respect to the volatiles from torrefied pellets, those volatiles that are formed during the torrefaction procedure dominate the odor of the torrefied pellets covering the genuine odor of the utilized wood. The results of this work serve as a substantiated basis for future production of pellets from alternative raw materials.


Technical Reports | 2019

Langzeitvalidierung eines neuen Ansatzes zur CO-Lambda-Optimierung

Zemann C, Gölles M. Langzeitvalidierung eines neuen Ansatzes zur CO-Lambda-Optimierung. 2019.

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Scientific Journals | 2019

Layer formation mechanism of K-feldspar in bubbling fluidized bed combustion of phosphorus-lean and phosphorus-rich residual biomass.

Wagner K, Häggström G, Skoglund N, Priscak J, Kuba M, Öhman M, Hofbauer H. Layer formation mechanism of K-feldspar in bubbling fluidized bed combustion of phosphorus-lean and phosphorus-rich residual biomass. Applied Energy 2019.248:545-554.

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The use of phosphorus-rich fuels in fluidized bed combustion is one probable way to support both heat and power production and phosphorus recovery. Ash is accumulated in the bed during combustion and interacts with the bed material to form layers and/or agglomerates, possibly removing phosphorus from the bed ash fraction. To further deepen the knowledge about the difference in the mechanisms behind the ash chemistry of phosphorus-lean and phosphorus-rich fuels, experiments in a 5 kW bench-scale-fluidized bed test-rig with K-feldspar as the bed material were conducted with bark, wheat straw, chicken manure, and chicken manure admixtures to bark and straw. Bed material samples were collected and studied for layer formation and agglomeration phenomena by scanning electron microscopy combined with energy dispersive X-ray spectrometry. The admixture of phosphorus-rich chicken manure to bark changed the layer formation mechanism, shifting the chemistry to the formation of phosphates rather than silicates. The admixture of chicken manure to straw reduced the ash melting and agglomeration risk, making it possible to increase the time until defluidization of the fluidized bed occurred. The results also highlight that an increased ash content does not necessarily lead to more ash melting related problems if the ash melting temperature is high enough.