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Anca-Couce A.,University of Graz | Obernberger I.,University of Graz | Obernberger I.,BIOS BIOENERGIESYSTEME GmbH
Fuel | Year: 2016

A detailed pyrolysis kinetic scheme is applied in this work for biomass torrefaction, with a focus on hardwood and softwood. The scheme includes secondary charring reactions, relevant for particles of a certain thickness, and sugar formation is avoided due to the catalytic effect of alkali metals in biomass. The release of acetic acid from hardwood and softwood hemicellulose is also considered. Representative initial compositions of hardwood and softwood are proposed in order to correctly predict mass loss in pyrolysis and torrefaction micro-TGA experiments. The predictions for product composition are validated with torrefaction batch experiments conducted in a lab-scale reactor with beech and spruce. The scheme predicts with good accuracy the yields of permanent gases and the main groups in which the condensable species are classified. The amount of secondary charring reactions is higher in the lab-scale than in the micro-TGA experiments, due to the higher particle size. The main discrepancies can be explained by the limitations of the scheme: reactive drying is not included and xylan is considered as representative for hemicellulose, which leads to deviations in the predictions of some products from softwood, e.g. furans. A more precise description of hemicellulose from softwood would include a hemicellulose reaction scheme based on glucomannan. © 2015 Elsevier Ltd. Source

Obernberger I.,BIOS BIOENERGIESYSTEME GmbH | Obernberger I.,Bioenergy 2020+ GmbH | Obernberger I.,University of Graz
Energy and Fuels | Year: 2014

Because of an increasing interest in the utilization of new and in terms of combustion-related properties rather unknown biomass fuels in heat and power production, advanced fuel characterization tools are gaining rising interest. Currently, ongoing research and development (R&D) focuses on a better and more precise description of the combustion properties of specific biomass fuels by applying new/advanced analysis methods and modeling tools. These novel characterization methods cover combustion tests in specially designed lab reactors, special fuel indices for biomass fuels, and the dedicated application of high-temperature equilibrium calculations. In this paper, a strategy is presented how the information gained from different advanced fuel characterization methods can be combined to characterize a fuel regarding its combustion behavior in a novel way. By means of this strategy, relevant qualitative and quantitative information regarding the ash-melting behavior, aerosol, SOx, HCl, and NOx emissions to be expected, and high-temperature corrosion risks can be gained. In addition, the approach can also be used for the evaluation of additives and fuel blending as measures to improve specific combustion properties. The results show that a much better and clearer picture about the combustion properties of a specific biomass fuel can be provided than by conventional approaches (such as wet chemical analysis or other standardized methods). The results can be used for the preliminary design of plants as well as for evaluation of the applicability of a specific technology for a certain biomass fuel or fuel spectrum. Moreover, they can be applied in combination with computational fluid dynamics (CFD) simulations for the detailed design and evaluation of furnaces and boilers. © 2014 American Chemical Society. Source

Blank M.,University of Graz | Blank M.,BIOS BIOENERGIESYSTEME GmbH | Krassnigg A.,University of Graz
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2011

Using a well-established effective interaction in a rainbow-ladder truncation model of QCD, we fix the remaining model parameter to the bottomonium ground-state spectrum in a covariant Bethe-Salpeter equation approach and find surprisingly good agreement with the available experimental data including the 2- Υ(1D) state. Furthermore, we investigate the consequences of such a fit for charmonium and light-quark ground states. © 2011 American Physical Society. Source

Gruber T.,Bioenergy 2020+ GmbH | Gruber T.,University of Graz | Schulze K.,Bioenergy 2020+ GmbH | Scharler R.,Bioenergy 2020+ GmbH | And 4 more authors.
Fuel | Year: 2015

High-temperature corrosion in biomass fired boilers is still an insufficiently explored phenomenon which causes unscheduled plant shutdowns and hence, economical problems. To investigate the high-temperature corrosion and deposit formation behaviour of superheater tube bundles, online corrosion probe as well as deposit probe measurements have been carried out in a specially designed fixed bed/drop tube reactor in order to simulate a superheater boiler tube under well-controlled conditions. The investigated boiler steel 13CrMo4-5 is commonly used as steel for superheater tube bundles in biomass fired boilers. Forest wood chips and quality sorted waste wood (A1-A2 according to German standards) as relevant fuels have been selected to investigate the influence on the deposit formation and corrosion behaviour. The following influencing parameter variations have been performed during the test campaigns: flue gas temperature between 650 and 880°C, steel temperature between 450 and 550°C and flue gas velocity between 2 and 8 m/s. One focus of the work presented is the detailed investigation of the structure and the chemical composition of the deposits formed as well as of the corrosion products. A further goal of the work presented was the development of an empirical model which can be used within CFD simulations of flow and heat transfer to calculate and evaluate the local corrosion potential of biomass fired plants already at the planning stage. The corrosion probe measurements show a clear dependency on the parameters investigated and the empirical function developed reproduces the measured corrosion behaviour sufficiently accurate. Since the additional calculation time within the CFD simulation is negligible the model represents a helpful tool for plant designers to estimate whether high-temperature corrosion is of relevance for a certain plant or not, when using fuels with similar compositions and the steel 13CrMo4-5. © 2014 Elsevier Ltd. All rights reserved. Source

Mandl C.,University of Graz | Obernberger I.,University of Graz | Obernberger I.,BIOS BIOENERGIESYSTEME GmbH | Biedermann F.,BIOS BIOENERGIESYSTEME GmbH
Fuel | Year: 2010

This paper presents a one-dimensional steady state mathematical model for the simulation of a small scale fixed-bed gasifier. The model is based on a set of differential equations describing the entire gasification process of softwood pellets and is solved by a two step iterative method. The main features of the model are: homogeneous and heterogeneous combustion and gasification reactions, one-step global pyrolysis kinetics and drying, heat and mass transfer in the solid and gas phases as well as between phases, heat loss, particle movement and shrinkage within the bed. The pyrolysis model has been improved by partially cracking primary tar into lighter gases according to experimental data. The model is used to simulate a laboratory scale fixed-bed updraft gasifier. Good agreement is achieved between prediction and measurements for the axial temperature profiles and the composition of the producer gas. Moreover, results are presented for different air to fuel ratios and varying power inputs. The gasification process is improved by increasing the power input of the gasifier as a result of higher temperatures. Furthermore, a higher air to fuel ratio lowers the efficiency of the gasification process. © 2010 Elsevier Ltd. All rights reserved. Source

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