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, SO_x, HCl, and NO_x 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.

Current international research results identify microalgae as a new and promising feedstock for the global energy supply chain. A novel concept to reduce costs and cover the need of water and nutrients is the combination of wastewater treatment and microalgae cultivation. In Austria in particular brewery and dairy effluents as well as municipal wastewater would be suitable for algae cultivation. Cultivation systems practical for the use of wastewater are High Rate Algal Ponds (open system, suspended culture), Algal Turf Scrubbers (open system, immobilized culture) and Photobioreactors (closed systems, suspended culture). The cultivation of microalgae in general and the special case of wastewater as nutrient source face a variety of challenges either concerning the accumulation of microalgal cells in wastewater (upstream process) or their removal and processing (downstream process). Taking a look at the whole production chain shows that for effluents of breweries, dairies
and smale-scale municipal wastewater no feasible concept for the combination of microalgae cultivation and wastewater treatment can be designed. A promising production concept for large-scale municipal wastewater treatment plants are HRAPs or biofilm production in ATS systems for energetic and material pathways. Various R&D challenges are to overcome to lead to an optimization and further development of technologies for combined wastewater treatment and microalgae cultivation in Austria.

An active condensation system for the heat recovery of biomass boilers is evaluated. The active condensation system utilizes the flue gas enthalpy exiting the boiler by combining a quench and a compression heat pump. The system is modelled by mass and energy balances. This study evaluates the operating costs, primary energy efficiency and greenhouse gas emissions on an Austrian data basis for four test cases. Two pellet boilers (10kW and 100kW) and two wood chip boilers (100kW and 10MW) are considered. The economic analysis shows a decrease in operating costs between 2% and 13%. Meanwhile the primary energy efficiency is increased by 3-21%. The greenhouse gas emissions in CO2 equivalents are calculated to 15.3-27.9kg MWh-1 based on an Austrian electricity mix. The payback time is evaluated on a net present value (NPV) method, showing a payback time of 2-12 years for the 10MW wood chip test case. © 2014 Elsevier Ltd.

Die europäische Technologie-Plattform für Heizen und Kühlen mit erneuerbaren Energien (RHC-Plattform, www.rhc-platform.org) fördert die Forschung und Entwicklung bei der Wärme- und Kälteproduktion aus erneuerbaren Energiequellen in der EU. Die verschiedenen Endanwendungen (Strom und/oder Bereitstellung von Wärme, Kraftstoff) setzen eine Verdoppelung der Biomassenutzung voraus, um die 20-20-20-Ziele der EU zu erreichen. Neue Ressourcen müssen erschlossen, mobilisiert und der Wirkungsgrad der Umwandlungsprozesse gesteigert werden. In Biomasse-Heizkraftwerken sowie Heizwerken werden derzeit mehr als ein Drittel des gesamten Biomasseaufkommens eingesetzt. Dies führt zu neuen, gemeinsamen Herausforderungen für den Strom- und Wärmesektor.
Das Biomasse-Panel der RHC-Plattform hat Schwerpunkte für Forschung und Entwicklung definiert, um bestimmte Kennzahlen für Biomassewertschöpfungsketten zu erreichen. Der vorliegende Beitrag stellt die Prioritäten für die Bestandteile der Wertschöpfungsketten vor, die relevant für den Strombereich sind:
a) nachhaltige und kosten-effiziente Biomasseversorgungsketten, b) thermisch behandelte Biomasse-Brennstoffe und c) hoch-effiziente KWK-Anlagen.
Herausforderungen für den Anlagenbetrieb sind Brennstoffflexibilität, Wirkungsgraderhöhung über den vollen Lastbereich, Betrieb mit variablen Brennstoffen und Qualitäten bei variablen Lastzuständen, höhere Betriebsparameter für Dampf und andere Wärmeträger, höhere Anlagenverfügbarkeit, Reduktion von unerwünschten gas- und partikelförmigen Emissionen und schließlich die Ascheverwertung.
 

Describing the combustion of log wood and others solid fuels with complex geometry, considerable water content and often heterogenous struture is a nontrivial task. Stochastic Cellular Automata models offer a promising approach for modelling such processes. Combustion models of this type exhibit several similarities to the well-known forest fire models, but there are also significant differences between those two types of models. These differences call for a detailed analysis and the development of supplementary modeling approaches. In this
article we define a qualitative two-dimensional model of burning log wood, discuss the most important differences to classical forest fire models and present some preliminary results.

A test campaign was carried out to generate renewable hydrogen based on wood gas derived from the commercial biomass steam gasification plant in Oberwart, Austria. The implemented process consisted of four operation units: (I) catalyzed water-gas shift (WGS) reaction, (II) gas drying and cleaning in a wet scrubber, (III) hydrogen purification by pressure swing adsorption, and (IV) use of the generated biohydrogen (BioH2) in a proton exchange membrane (PEM) fuel cell. For almost 250 h, a reliable and continuous operation was achieved. A total of 560 (Ln dry basis (db))/h of wood gas were extracted to produce 280 (Ln db)/h of BioH2 with a purity of 99.97 vol %db. The catalyzed WGS reaction enabled a hydrogen recovery of 128% (nBioH2)/(nH2,wood gas) over the whole process chain. An extensive chemical analysis of the main gas components and trace components (sulfur, CxHy, and ammonia) was carried out. No PEM fuel cell poisons were measured in the generated BioH2. The only detectable impurities in the product were 0.02 vol %db of O2 and 0.01 vol %db of N2. © 2014 American Chemical Society.

The results of experimental work to investigate the effects of air staging on emissions from energy crop combustion in small scale applications are presented. Five different biomass fuels (wood, willow, miscanthus, tall fescue and cocksfoot) were combusted in a small scale (35 kW) biomass boiler and three different tests looking at the effects of (1) air ratio in the primary combustion chamber (primary air ratio), (2) temperature in the primary combustion chamber, and (3) overall excess air ratio, on NO_x and particulate emissions were conducted. It was shown that by varying the primary air ratio, NO_x emission reductions of between 15% (wood) and 30% (Miscanthus) and PM₁ reductions of between 16% (cocksfoot) and 26% (wood) were possible. For all fuels, both NO_x and particulate emissions were minimised at a primary air ratio of 0.8. Particulate emissions from miscanthus increased with increasing temperature in the primary combustion chamber, NO_x emissions from Miscanthus and from willow also increased with temperature. Overall excess air ratio has no effect on emissions as no significant differences were found for any of the fuels. Emissions of particulates and oxides of nitrogen from a wide range of biomass feedstocks can be minimised by optimising the primary air ratio and by maintaining a temperature in the primary combustion chamber of approximately 900 °C.

Anaerobic digestion offers a good opportunity to degrade residues from breweries to biogas. To improve the anaerobic degradation process thermal pretreatment of brewers' spent grains (BSG) offers the opportunity to increase degradation rate and biogas yield. Aim of the work is to show the influence of the thermal pretreatment of BSG to anaerobic digestion. BSG were pretreated at different temperature levels from 100 to 200°C. The biogas production of thermally pretreated BSG lies between 30 and 40% higher than for untreated reference. The temperature of the pretreatment process has a significant influence on the degradation rate or gas yield, respectively. Up to a temperature of 160°C, the biogas yield rises. Temperatures over 160°C result in a slower degradation and decreasing biogas yield. Substrate with and without pretreatment gave a daily biogas yield of 430 and 389 Nm³ × kg^-1 VS, respectively. Batch analysis of the biochemical methane potential gives a total methane yield of 409.8 Nm3 CH₄ × kg^-1 VS of untreated brewers' spent grains and 467.6 Nm3 CH₄ × kg^-1 VS of the pretreated samples. For pretreatment energy balance estimation has been carried out. Without any heat recovery demand is higher than the energy surplus resulting from pretreatment of BSG. With energy recovery by heat exchanger the net energy yield could be increased to 38.87 kWh × kg^-1 FM or 8.81%. © 2015 American Institute of Chemical Engineers Environ Prog.

To gain reliable data for the development of an empirical model for the prediction of the local high temperature corrosion potential in biomass fired boilers, online corrosion probe measurements have been carried out. The measurements have been performed 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. Within the test runs the flue gas temperature at the corrosion probe has been varied between 625 °C and 880 °C, while the steel temperature has been varied between 450 °C and 550 °C to simulate typical current and future live steam temperatures of biomass fired steam boilers. To investigate the dependence on the flue gas velocity, variations from 2 m·s⁻¹ to 8 m·s⁻¹ have been considered. The empirical model developed fits the measured data sufficiently well. Therefore, the model has been applied within a Computational Fluid Dynamics (CFD) simulation of flue gas flow and heat transfer to estimate the local corrosion potential of a wood chips fired 38 MW steam boiler. Additionally to the actual state analysis two further simulations have been carried out to investigate the influence of enhanced steam temperatures and a change of the flow direction of the final superheater tube bundle from parallel to counter-flow on the local corrosion potential.

The direct combustion of the biomass is the most advanced and mature technology in the field of energetic biomass utilisation. The legislations on the amount of emitted pollutants and the plant efficiency of biomass combustion systems are continually being restricted. Therefore constant improvement of the plant efficiency and emission reduction is required Numerical modelling is gaining increasing importance for the development of biomass combustion technologies. In this paper an overview about the numerical modelling efforts deal with the most relevant phenomena in biomass grate firing systems is given. The numerical modelling results in a deeper understanding of the underlying processes in biomass combustion plants. Therefore, it leads to a faster and safer procedure of development of a new technology.

Biomass boilers used for residential heating and hot water supply are typically combined with a buffer storage and solar collectors. However, the annual utilization rates typically achieved with such systems are far below those theoretically possible, which is mainly because of the often poor quality of both the individual control of the components as well as the high-level control of the entire system. The control strategies typically applied consist of simple decou-pled control circuits with linear controllers, which cannot deal with the mostly nonlinear and coupled behaviour of the components and thus do not ensure their reasonable interaction. The most appropriate approach to address these challenges is the application of model-based control techniques. Within the paper an overview of mathematical models suitable for control purposes, a simple to implement load forecasting method as well as control strate-gies for both the individual components and the entire system are presented. Future chal-lenges for a practical implementation of this novel approach are discussed in the outlook sec-tion.

Industrial waste streams from brewing industries and distilleries provide a valuable but largely unused alternative substrate for biogas production by anaerobic digestion. High sulfur loads in the feed caused by acidic pretreatment to enhance bioavailability are responsible for H₂S formation during anaerobic digestion. Microbiological oxidation of H₂S provides an elegant technique to remove this toxic gas compound. Moreover, it allows for recovery of sulfuric acid, the final product of aerobic sulfide oxidation, as demonstrated in this study. Two-stage anaerobic digestion of brewer’s spent grains, the major byproduct in the brewing industry, allows for the release of up to 78% of total H₂S formed in the first pre-acidification stage. Desulfurization of such pre-acidification gas in continuous acidic biofiltration with immobilized sulfur-oxidizing bacteria resulted in a maximum H₂S elimination capacity of 473 g m^–3 h^–1 at an empty bed retention time of 91 s. Complete H₂S removal was achieved at inlet concentrations of up to 6363 ppm. The process was shown to be very robust, and even after an interruption of H₂S feeding for 10 days, excellent removal efficiency was immediately restored. A maximum sulfate production rate of 0.14 g L^–1 h^–1 was achieved, and a peak concentration of 4.18 g/L sulfuric acid was reached. Further experiments addressed the reduction of fresh water and chemicals to minimize process expenses. It was proven that up to 50% of mineral medium that is required in large amounts during microbiological desulfurization can be replaced by the liquid fraction of the digestate. The conducted study demonstrates the viability of microbial sulfur recovery with theoretical recovery rates of up to 44%.