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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 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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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.


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.


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.


Peer Reviewed Scientific Journals | 2019

Layer Formation on Feldspar Bed Particles during Indirect Gasification of Wood Part 1: K-Feldspar

Faust R, Hannl T K, Berdugo Vilches T, Kuba M, Öhmann M, Seemann M C, Knutsson P Layer Formation on Feldspar Bed Particles during Indirect Gasification of Wood Part 1: K-Feldspar.Energy&Fuels 2019.33:8:7321-7332

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The choice of bed material for biomass gasification plays a crucial role for the overall efficiency of the process. Olivine is the material conventionally used for biomass gasification due to the observed activity of olivine toward cracking of unwanted tars. Despite its catalytic activity, olivine contains high levels of chromium, which complicates the deposition of used bed material. Feldspar has shown the same activity as olivine when used as a bed material in biomass gasification. As opposed to olivine, feldspar does not contain environmentally hazardous compounds, which makes it a preferred alternative for further applications. The interaction of bed material and ash heavily influences the properties of the bed material. In the present study interactions between feldspar and main ash compounds of woody biomass in an indirect gasification system were investigated. Bed material samples were collected at different time intervals and analyzed with SEM-EDS and XRD. The obtained analysis results were then compared to thermodynamic models. The performed study was divided in two parts: in part 1 (the present paper), K-rich feldspar was investigated, whereas Na-rich feldspar is presented in part 2 of the study (DOI: 10.1021/acs.energyfuels.9b01291). From the material analysis performed, it can be seen that, as a result of the bed materials’ interactions with the formed ash compounds, the latter were first deposited on the surface of the K-feldspar particles and later resulted in the formation of Ca- and Mg-rich layers. The Ca enriched in the layers further reacted with the feldspar, which led to its diffusion into the particles and the formation of CaSiO3 and KAlSiO4. Contrary to Ca, Mg did not react with the feldspar and remained on the surface of the particles, where it was found as Mg- or Ca-Mg-silicates. As a result of the described interactions, layer separation was noted after 51 h with an outer Mg-rich layer and an inner Ca-rich layer. Due to the development of the Ca- and Mg-rich layers and the bed material–ash interactions, crack formation was observed on the particles’ surfaces.


Scientific Journals | 2019

Layer Formation on Feldspar Bed Particles during Indirect Gasification of Wood. 1. K-Feldspar

Faust R, Hannl TK, Berdugo Vilches T Kuba M, Öhman M, Seemann M, Knutsson P. Layer Formation on Feldspar Bed Particles during Indirect Gasification of Wood. 1. K-Feldspar. Energy and Fuels 2019.33:7321-7332.

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The choice of bed material for biomass gasification plays a crucial role for the overall efficiency of the process. Olivine is the material conventionally used for biomass gasification due to the observed activity of olivine toward cracking of unwanted tars. Despite its catalytic activity, olivine contains high levels of chromium, which complicates the deposition of used bed material. Feldspar has shown the same activity as olivine when used as a bed material in biomass gasification. As opposed to olivine, feldspar does not contain environmentally hazardous compounds, which makes it a preferred alternative for further applications. The interaction of bed material and ash heavily influences the properties of the bed material. In the present study interactions between feldspar and main ash compounds of woody biomass in an indirect gasification system were investigated. Bed material samples were collected at different time intervals and analyzed with SEM-EDS and XRD. The obtained analysis results were then compared to thermodynamic models. The performed study was divided in two parts: in part 1 (the present paper), K-rich feldspar was investigated, whereas Na-rich feldspar is presented in part 2 of the study (DOI: 10.1021/acs.energyfuels.9b01291). From the material analysis performed, it can be seen that, as a result of the bed materials’ interactions with the formed ash compounds, the latter were first deposited on the surface of the K-feldspar particles and later resulted in the formation of Ca- and Mg-rich layers. The Ca enriched in the layers further reacted with the feldspar, which led to its diffusion into the particles and the formation of CaSiO3 and KAlSiO4. Contrary to Ca, Mg did not react with the feldspar and remained on the surface of the particles, where it was found as Mg- or Ca-Mg-silicates. As a result of the described interactions, layer separation was noted after 51 h with an outer Mg-rich layer and an inner Ca-rich layer. Due to the development of the Ca- and Mg-rich layers and the bed material–ash interactions, crack formation was observed on the particles’ surfaces.


Scientific Journals | 2019

Layer Formation on Feldspar Bed Particles during Indirect Gasification of Wood. 2. Na-Feldspar

Hannl TK, Faust R, Kuba M, Knutsson P, Berdugo Vilches T, Seemann MC, Öhman M. Layer Formation on Feldspar Bed Particles during Indirect Gasification of Wood Part 2: Na-Feldspar. Energy and Fuels 2019.33:7333-7346.

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Selecting a suitable bed material for the thermochemical conversion of a specific feedstock in a fluidized bed system requires identification of the characteristics of potential bed materials. An essential part of these characteristics is the interaction of the bed material with feedstock ash in a fluidized bed, which leads to layer formation and morphology changes. For this purpose, the interaction of feldspar bed material with the main ash-forming elements in wood ash (Ca, K, Mg, Si) in an indirect gasification system was analyzed using SEM-EDS, XRD, and thermodynamic modeling. In part 1 of this work (DOI: 10.1021/acs.energyfuels.9b01291), the layer formation on K-feldspar dominated by Ca reaction and ash deposition was investigated. The aim of this second part of the work was to determine the time-dependent layer formation on Na-feldspar and compare the results with the findings for K-feldspar. Interaction of Na-feldspar with ash-derived elements resulted in different layers on Na-feldspar: K reaction layers, where K replaced Na and Si shares decreased; Ca reaction layers, where Ca enriched and reacted with the Na-feldspar; and ash deposition layers, where wood ash elements accumulated on the surface. Ca reaction layers were formed first and became continuous on the surface before K reaction layers and ash deposition layers were detected. Cracks and crack layer formation in the Na-feldspar particles were found after several days of operation. The layer compositions and growth rates indicate that the diffusion of Ca and K plays an essential role in the formation of Ca reaction and K reaction layers. The reaction with Ca and the crack formation coincide with the interaction previously found for quartz and K-feldspar. In contrast to K-feldspar, Na-feldspar showed high potential for reaction with K. The findings indicate that the reaction of Na-feldspar with ash-derived K makes Na-feldspar a less stable bed material than K-feldspar during the thermochemical conversion of K-rich feedstocks in a fluidized bed system.


Scientific Journals | 2019

Layer formation on K-feldspar in fluidized bed combustion and gasification of bark and chicken manure

Wagner K, Häggström G, Mauerhofer AM, Kuba M, Skoglund N, Öhman M, Hofbauer H. Layer formation on K-feldspar in fluidized bed combustion and gasification of bark and chicken manure. Biomass and Bioenergy 2019.127:105251.

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Understanding layer formation on bed materials used in fluidized beds is a key step for advances in the application of alternative fuels. Layers can be responsible for agglomeration-caused shut-downs but they can also improve the gas composition in fluidized bed gasification. Layers were observed on K-feldspar (KAlSi3O8) impurities originating from the combined heat and power plant Senden which applies the dual fluidized bed (DFB) steam gasification technology. Pure K-feldspar was therefore considered as alternative bed material in DFB steam gasification. Focusing on the interactions between fuel ash and bed material, K-feldspar was tested in combustion and DFB steam gasification atmospheres using different fuels, namely Ca-rich bark, Ca- and P-rich chicken manure, and an admixture of chicken manure to bark. The bed particle layers formed on the bed material surface were characterized using combined scanning electron microscopy and energy-dispersive X-ray spectroscopy; area mappings and line scans were carried out for all samples. The obtained data show no essential influence of operational mode on the layer-formation process. During the combustion and DFB steam gasification of Ca-rich bark, a layer rich in Ca formed while K was diffusing out of the layer. The use of Ca- and P-rich chicken manure inhibited the diffusion of K, and a layer rich in Ca and P formed. The addition of P to bark via chicken manure also changed the underlying layer-formation processes to reflect the same processes as observed for pure chicken manure.


Scientific Journals | 2019

Mathematical model of Fischer-Tropsch synthesis using variable alpha-parameter to predict product distribution.

Filip L, Zámostný P, Rauch R. Mathematical model of Fischer-Tropsch synthesis using variable alpha-parameter to predict product distribution. Fuel 2019;243:603-609.

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A mathematical model was developed based on data obtained on Fischer-Tropsch (FT) laboratory scale unit operated in steady state, belonging to BIOENERGY 2020+ GmbH, Austria to demonstrate alpha-parameter dependence on carbon number. The lab-scale unit processed the synthesis gas, obtained by the gasification of biomass (woodchips), to produce liquid fuels for transportation applications. The FT reaction took place in a slurry reactor filled with dispersed cobalt-based catalyst. The products were then separated by partial condensation depending on their boiling points. The final output of the FT laboratory scale unit comprised three product streams – wax, diesel and naphtha. The reaction and separation of products were simulated in Aspen Plus software. The mathematical model used kinetic description based on power-law rate equations. The modeled product selectivity was controlled using an alpha-parameter of the Anderson-Schulz-Flory distribution. Because of the significant deviation of products spectrum from typical Anderson-Schulz-Flory distribution, a modified description of reaction selectivity was developed. The description introduces variable alpha-parameter, dependent on number of carbon atoms in the reacting molecule. The mathematical model developed using MATLAB software considered the production of aliphatic paraffins having a number of carbon atoms from C1 to C60. The mathematical model of simulated lab-scale unit comprised an ideally mixed reactor RCSTR and three FLASH2 separators for the separation of desired products. The results from mathematical model were validated by a comparison with experimental results from FT lab-scale unit. The modified polynomial dependency of alpha-parameter on carbon number showed significantly better description of composition and amounts of FT products, especially for wax stream where the description using constant alpha led to enormous deviations. Such better prediction of composition and amounts of acquired products is important for evaluating efficiency of further upgrading the FT products to liquid fuel.


Peer Reviewed Scientific Journals | 2019

New experimental evaluation strategies regarding slag prediction of solid biofuels in pellet boilers

Schön C, Feldmeier S, Hartmann H, Schwabl M, Dahl J, Rathbauer J, Vega-Nieva D, Boman C, Öhman M, Burvall J. New experimental evaluation strategies regarding slag prediction of solid biofuels in pellet boilers. Energy & Fuels. 2019.33:11985-11995

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Pellet boilers and pellet stoves are widely used for heat production. But in most cases, only specific wood pellets with a low ash content are approved due to the increased risk of slagging and limited deashing capacity. The ash fusion test (AFT), according to prCEN/TS 15370-1, is currently the only standard method for the prediction of slagging. This method is not feasible for all biomass fuel types, since sometimes the characteristic temperatures cannot be determined or the characteristic shapes do not occur for temperature determination. Furthermore, the method is costly and requires complex instrumental infrastructure. Hence, a demand for more expressive or more rapid methods to characterize slag formation potential of fuels is often claimed. Based on a literature study, four such laboratory test methods were chosen, partly adapted, and then experimentally investigated. These methods included thermal treatment of the fuel itself or the ashes of the fuel and were the rapid slag test, CIEMAT, the slag analyzer, and the newly developed pellet ash and slag sieving assessment (PASSA) method. Method performance was practically assessed using 14 different biomass fuel pellets, which were mainly from different assortments of wood, but also herbaceous or other nonwoody fuels. The results from the tests with these four alternative methods were evaluated by comparing to both results from standard AFT and results from full-scale combustion tests performed over a maximum of 24 h. Seven different pellet boilers were assessed, of which one boiler was used to apply all 14 test fuels. According to the granulometric ash analysis (i.e., the ratio of >1 mm-fraction toward total ash formed), the sensitivity of the new test methods to depict slagging phenomena at a suitable level of differentiation was assessed. Satisfactory conformity of the boiler ash assessment (reference) was found for both, the slag analyzer and the PASSA method. The latter may, in particular, be seen as a promising and relatively simple low-input procedure, which can provide more real-life oriented test results for fixed-bed combustion. The standardized AFT could, however, not sufficiently predict the degree of slag actually formed in the reference boiler, particularly when only wood fuels are regarded.


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.

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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.


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

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Peer Reviewed 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.

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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 urn:x-wiley:15564959:media:rob21863:rob21863-math-0001 is created in urn:x-wiley:15564959:media:rob21863:rob21863-math-0002, 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.


Peer Reviewed Scientific Journals | 2019

Photoautotrophic production of poly-hydroxybutyrate – First detailed cost estimations

Panuschka S, Drosg B, Ellersdorfer M, Meixner K, Fritz I. Photoautotrophic production of poly-hydroxybutyrate – First detailed cost estimations. Algal Research 2019.41:101558.

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Political, economic and ecological reasons have recently been leading to efforts to replace fossil hydrocarbons and their products in a sustainable way. In order to replace fossil-based polymers, photoautotrophically produced polyhydroxybutryrates (PHBs), which are intracellular carbon storage products of nutrient-deprived microorganisms, seem to be a promising, biobased and biodegradable alternative. Although laboratory and pilot scale experiments have already been performed, no economic evaluation has been carried out so far. Consequently, valid claims on PHB production costs and the influence of different parameters, such as intracellular PHB-content, choice of cultivation system or location, cannot be made. In this study potential demonstration plants, equipped with different photoautotrophic cultivation systems and located at two sites, were designed to identify key parameters for a successful economic realization and implementation. Material and energy balances were determined to reveal specific PHB production costs for four different scenarios. Raw material and operating supply costs, expenditures for plant construction and operation as well as product amounts were determined using literature data for specified results from laboratory and pilot scale experiments. The lowest calculated PHB production price (24 € kg−1) accomplished in a thin-layer-system plant located in Southern Europe with 60% PHB-content of the produced biomass is significantly higher than the current market price of heterotrophically produced PHB. The most important cost factors in all scenarios are cultivation and harvesting costs accounting for 62 to 72% of the total specific production costs, followed by maintenance costs with a cost share of 11 to 14%. Therefore, the choice of a suitable cultivation system is the key driving factor for an economic PHB-production due to the currently high investment costs for photosynthetic biomass production systems. Specific production costs for a Southern compared to a Central European location amount to almost half of the costs.


Peer Reviewed Scientific Journals | 2019

Planning and implementation of bankable microgrids

Stadler M, Nasle A. Planning and implementation of bankable microgrids. The Electricity Journal 2019. 32:24-29.

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Currently, many Microgrid projects remain financially uncertain and not bankable for institutional investors due to major challenges in existing planning and design methods that require multiple, complex steps and software tools.

Existing techniques treat every Microgrid project as a unique system, resulting in expensive, non-standardized approaches and implementations which cannot be compared. That is, it is not possible to correlate the results from different planning methods performed by different project developers and/or engineering companies.

This very expensive individual process cannot guarantee financial revenue streams, cannot be reliably audited, impedes pooling of multiple Microgrid projects into a financial asset class, nor does it allow for wide-spread and attractive Microgrid and Distributed Energy Resource projects deployment.

Thus, a reliable, integrated, and streamlined process is needed that guides the Microgrid developer and engineer through conceptual design, engineering, detailed electrical design, implementation, and operation in a standardized and data driven approach, creating reliable results and financial indicators that can be audited and repeated by investors and financers.

This article describes the steps and methods involved in creating bankable Microgrids by relying on an integrated Microgrid planning software approach that unifies proven technologies and tested planning methods, researched and developed by the United States National Laboratory System as well as the US Department of Energy, to reduce design times.


Other Presentations | 2019

Primäre und sekundäre Verbesserungen an einem Biomassekessel für Agrarbrennstoffe

Zemann C, Kelz J, Muschick D, Retschitzegger S, Gölles M. Primäre und sekundäre Verbesserungen an einem Biomassekessel für Agrarbrennstoffe. 10. Fachgespräch: Partikelabscheider in häuslichen Feuerungen. 20. März 2019 (2019). [online]. (Tagungsreader, 15). Leipzig: DBFZ. 168 S.

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ie Biomasseverbrennung spielt eine zentrale Rolle bei der Bereitstellung von Wärme aus erneuerbaren Energieträgern. Konventionelle Biomasse-Brennstoffe werden jedoch aufgrund einer steigenden Anzahl stofflicher Verwertungsmöglichkeiten, wie z.B. der Umwandlung in Chemikalien, teurer und schwieriger zugänglich. Agrarbrennstoffe, die bisher nur selten oder gar nicht in Biomasse-Kleinfeuerungen eingesetzt wurden, stellen eine vielversprechende Alternative zu konventionellen Brennstoffen dar. Diese Agrarbrennstoffe, wie zum Beispiel Kurzumtrieb, Maisspindeln oder Stroh sind kostengünstig und in ausreichender Menge vorhanden. Der Einsatz von Agrarbrennstoffen in konventionellen Biomasse-Kleinfeuerungen ist jedoch aufgrund stark variierender Brennstoffeigenschaften mit erhöhten Anforderungen an das Verbrennungssystem verbunden. Erhöhte N, S, Cl, Alkalimetall- und Aschegehalte sowie niedrigere Aschenschmelzpunkte können zu aschebedingten Problemen (Ascheschmelze, Ascheablagerung und Korrosion) sowie erhöhten Konzentrationen von gasförmigen (CO, NOx, HCl und SOx) und partikelförmigen Emissionen bei der Verbrennung führen.

Ziel der in diesem Beitrag präsentierten Arbeiten war die Erhöhung die Brennstoffflexibilität einer handelsüblichen Biomasse-Kleinfeuerung um damit eine Verbrennung von Agrarbrennstoffen mit niedrigen Schadstoffemissionen und einem hohen Wirkungsgrad zu ermöglichen. Hierzu wurde eine modellbasierte Regelung entwickelt, welche insbesondere eine gezielte Einstellung des Luftverhältnisses in der Primärverbrennungszone ermöglicht und damit das Risiko der Ascheschmelze reduziert und Schadstoffmissionen verringert. Soft-Sensoren bestimmen relevante Brennstoffeigenschaften während des Betriebs, welche von der modellbasierten Regelung zur automatischen Anpassung an geänderte Brennstoffeigenschaften genutzt werden. Die modellbasierte Regelung wurde um eine CO-lambda-Optimierung ergänzt, welche auf Basis von Messwerten des Restsauerstoffgehalts und der CO-Emissionen den Wirkungsgrad der Verbrennung maximiert und gleichzeitig die Schadstoffemissionen verringert. Zur weiteren Verringerung von partikelförmigen Schadstoffemissionen wurde ein am Markt verfügbarer Elektrofilter adaptiert und nach dem Wärmeübertrager der Biomasse-Kleinfeuerung angebracht.

Dieses Verbrennungssystem wurde durch umfassende Testläufe mit begleitenden Emissionsmessungen sowie Brennstoff-, Staub- und Ascheanalysen bewertet. Der Einsatz der modellbasierten Regelung führte zu einem stabileren Betrieb bei allen Leistungen und für alle Brennstoffe. Der Elektrofilter zeigte sehr zufriedenstellende Abscheidegrade für alle untersuchten Brennstoffe und Anlagenleistungen. Dadurch konnte die Brennstoffflexibilität der handelsüblichen Biomasse-Kleinfeuerung erhöht und die Verbrennung von Agrarbrennstoffen ermöglicht werden.

 


Scientific Journals | 2019

Real-life emission factor assessment for biomass heating appliances at a field measurement campaign in Styria, Austria

Sturmlechner R, Schmidl C, Carlon E, Reichert G, Stressler H, Klauser F, Kelz J, Schwabl M, Kirchsteiger B, Kasper-Giebl A, Höftberger E, Haslinger W. Real-life emission factor assessment for biomass heating appliances at a field measurement campaign in Styria, Austria. WIT Transactions on Ecology and the Environment 2019.236:221-231

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Biomass combustion is a major contributor to ambient air pollution. Thus, knowing the real-life emissions of biomass heating systems is crucial. Within the project Clean Air by biomass a field measurement campaign was conducted. 15 biomass heating appliances were tested in households at the end user according to their usual operation. Emission factors for gaseous and particulate emissions, as well as for the genotoxic and carcinogenic substance benzo(a)pyrene, were evaluated and compared to current proposed European and Austrian emission factors used for emission inventories. Moreover, the shares of particles and benzo(a)pyrene in hot and cooled flue gas were determined. Results showed a high variability of emissions in the field. Highest values and ranges occurred for room heaters (TSPtotal: 226 mg/MJ). Biomass boilers showed clearly lower emission factors (TSPtotal: 184 mg/MJ) in the field than room heaters and also than the proposed European and Austrian emission factors, in many cases. Emission factors for tiled stoves showed a similar trend (TSPtotal: 67 mg/MJ). The share of condensable particles in the flue gas was remarkable. Especially benzo(a)pyrene was found mostly in the condensable fraction of the particles.