The detailed ash transformation process during the combustion of agricultural biomass containing moderate to high amounts of P was studied in entrained flow conditions. The selected fuels were grass and brewer’s spent grain (BSG) containing a moderate and high amount of P in the fuel, respectively. The experiments were conducted in a lab-scale drop tube furnace at 1200 and 1450 °C. The residual chars, ashes, and particulate matter (PM) were collected and analyzed by scanning electron microscopy-energy-dispersive X-ray spectroscopy (SEM-EDS), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES) and ion chromatography (IC), and CHN-analysis. Additionally, the obtained results were interpreted through thermodynamic equilibrium calculations (TECs). For both fuels, P was primarily identified in the residual coarse ash (>1 μm) fractions. In contrast, a minor to moderate amount of fuel inherent P was detected in the fine particulate (<1 μm) fraction at 1200 and 1450 °C, respectively. For grass, the retained P in the residual coarse ash fractions was mainly identified as amorphous K–Ca–Mg-rich phosphosilicate melt. These phosphosilicates were most likely formed through the initial formation of molten K-rich silicates, with subsequent incorporation of Ca, P, and Mg. For BSG, a P–Si-rich fuel with moderate to minor amounts of Ca, Mg, and K, most P was retained in a Ca–Mg-rich phosphosilicate melt, likely originating from phytate-derived Ca–Mg phosphates interacting with fuel-inherent Si-rich particles. The results obtained from this study could be used to address the ash-related challenges and potential P-recovery routes during pulverized fuel combustion of P-containing biomass.

As the iron and steel industry needs to cut its CO2 emissions drastically, much effort has been put into establishing new—less greenhouse-gas-intensive—production lines fueled by hydrogen and electricity. Blast furnaces, as a central element of hot iron production, are expected to lose importance, at least in European production strategies. Yet, blast furnaces could play a significant role in the transitional phase, as they allow for the implementation of another CO2-reducing fuel, carbonized wood reducing agents, as a substitute for coal in auxiliary injection systems, which are currently widely used. Wood carbonization yields vastly differing fuel types depending on the severity of the treatment process, mainly its peak temperature. The goal of this study is to define the lowest treatment temperature, i.e., torrefaction temperature, which results in a biogenic reducing agent readily employable in existing coal injection systems, focusing on their conveying properties. Samples of different treatment temperatures ranging from 285 to 340 °C were produced and compared to injection coal regarding their chemical and mechanical properties. The critical conveyability in a standard dense-phase pneumatic conveying system was demonstrated with a sample of pilot-scale high-temperature torrefaction.

This work investigates the chemical looping combustion (CLC) and chemical looping hydrogen (CLH) production processes of synthetic ilmenite at three relevant length scales: reactor, particle and reaction. Focusing on reduction with hydrogen, part I analyzed the reaction scale for CLC using thermogravimetric analysis (TGA). Complementary fixed bed reactor experiments for reduction and oxidation using pellets (CLC, CLH) and TGA experiments using powders or pellets (CLH) were now added. All measurements were used to develop a consistent multiscale model. Particle and reactor scales were described by one-dimensional volumetric models. The required complexity of the reaction model differed from case to case. Kinetic modeling for oxidations in the reactor was trivial, since gaseous reactants were fully consumed. Reductions with hydrogen, however, were more intricate. Considering the influence of equilibrium on the reactivity was crucial for CLH. The reduction for CLC was faster and even more complex. We novelly demonstrated how kinetics, originally derived only from TGA with powders, were not directly applicable to larger scales when underlying phenomena had been neglected. In order to overcome these limitations and achieve better consistency, equilibrium effects and the gas availability above the sample during TGA had to be considered. The suitability of the synthetic ilmenite for CLC and CLH was discussed based on the findings in this work.

After years of development of the dual fluidized bed gasification process with woody biomass, new challenges arise with a wider range of feedstocks, such as agricultural residues or waste fractions, gaining importance. This work presents the results from the operation of a 1 MW advanced dual fluidized bed (aDFB) gasifier at the Syngas Platform Vienna, with cashew shells (CS) as feedstock and pure olivine or olivine mixed with 33% limestone as the bed material. Two operation points, different in their main process parameters, with CS as feedstock were performed for a minimum of 16 h. Due to the high calorific value (22.7 MJ/kg dry) and high content of volatile components (81.7 wt % dry), CS are well suited for gasification. During the operation, a product gas with a H2/CO ratio of 1.93–2.29 was produced, which suits the use of the syngas as input for Fischer–Tropsch synthesis. Due to the low ash softening temperature of CS of about 840 °C, determined in ash fusion tests and predicted by thermodynamic equilibrium calculations, the operating temperature in the gasifier was kept below 820 °C in the first operation point with around 20 h of runtime. Bed material samples after the operation revealed the formation of agglomerates, which were analyzed by SEM and EDS for their morphology and composition. During the second operation point, temperatures in the gasifier were increased to 870 °C for 16 h, while no agglomeration tendencies were observed. Both operations did not show changes in fluidization behavior compared to operations with wood chips (WC). The evaluated key performance indicators were compared to aDFB steam gasification of WC as the reference.

This study explores AnMBR technology as a promising method for treating wastewater from the meat-processing industry by analysing its characteristics and impact under continuous feeding. The solids were retained, utilising an ultrafiltration membrane with a pore size of 0.2 µm, and the efficacy of reducing the organic load was evaluated. Although the COD removal rate decreased from 100% at an OLR of 0.71 g/(L*d) to 73% at an OLR of 2.2 g/(L*d), maximum methane yields were achieved at the highest OLR, 292.9 Nm3/t (COD) and 397.8 Nm3/t (VS) per loaded organics and 353.1 Nm3/t (COD) and 518.7 Nm3/t (VS) per removed organics. An analysis of the microbial community was performed at the end of the experiment to assess the effects of the process and the substrate on its composition. The AnMBR system effectively converts meat-processing wastewater into biogas, maintaining high yields and reducing the loss of dissolved methane in the permeate, thanks to a temperature of 37 °C and high salt levels. AnMBR enables rapid start-up, efficient COD removal, and high biogas yields, making it suitable for treating industrial wastewater with high organic loads, enhancing biogas production, and reducing methane loss. Challenges such as high salt and phosphate levels present opportunities for a wider use in nutrient recovery and water reclamation.

Aqueous phase reforming (APR) has been proposed during the last years as a promising technology to produce renewable hydrogen from carbon-laden water fractions. However, only small-scale set-ups have been used for the investigation so far, leading to a gap in technological knowledge. In this work, a multi-component mixture representative of wastewater from lignin-rich hydrothermal liquefaction (HTL) was evaluated at two different scales: a lab-scale facility (30–60 mL/h) to optimize the reaction conditions and, for the first time, a pilot-scale unit (max. 44 L/h) to validate the results. On lab scale, the influence of reaction temperature, weight hourly space velocity and feed concentration on the process performance was investigated using a response surface methodology (RSM) approach via Box-Behnken design. It was found out that temperature was the most important variable to model the reactants conversion, carbon conversion to gas and hydrogen yield, with a significant agreement between the experimental and predicted values in the design space. At pilot scale, the influence of temperature and pressure as well as catalyst stability were investigated. Furthermore, stable operation was demonstrated in a continuous 100 h experiment. A maximum hydrogen yield of 58% and carbon conversion to gas of 54% were achieved at 547 K, 10 g/L organics concentration and 60 mL/gcat‧h. Overall, this study allowed to increase the understanding of APR at the highest technology readiness level available so far, paving the way towards its implementation on industrial scale.

The advanced dual fluidized bed steam gasification technology allows the generation of a medium-calorific product gas from various feedstocks. Thereby, biogenic residues, municipal and industrial wastes e.g., sewage sludge or rejects from pulp and paper industry can be utilised. This paper presents the development step of this technology from pilot to demonstration plant scale i.e. the step from technology readiness level 4 to 6. The newly erected demonstration plant at the Syngas Platform Vienna is designed for 1 MWth fuel input power and incorporates a counter current column as the upper part of the gasification. This design choice already resulted in an improvement of product gas quality in pilot scale. By comparing the data gathered from multiple years of 100 kWth pilot scale testing at TU Wien with first results from the new demonstration plant via mass and energy balance simulation, fluidisation regimes and temperature and pressure profiles, the success of the scale-up of the reactor design is proven. The first full load operation achieved a conversion of 1 MW fuel input power into 769 kW product gas power. This translates to 256 kg/h dry biomass being converted into 245 Nm3/h of dry product gas. Although first experiments with the reference feedstock high-grade wood chips showed good reproducibility of the results achieved in pilot scale, challenges still remain. The expected product gas composition was different compared to pilot scale results, as the volume share of hydrogen was lower and the relative content of carbon monoxide and carbon dioxide inverted. While the results show an important intermediate step in the process development, the challenges of improving product gas quality and increasing overall conversion efficiency remain to be tackled.

Poly(3-hydroxybutyrate) (PHB) is a biobased and biodegradable polymer with properties comparable to polypropylene and therefore has the potential to replace conventional plastics. PHB is intracellularly accumulated by prokaryotic organisms. For the cells PHB functions manly as carbon and energy source, but all possible functions of PHB are still not known. Synechocystis (cyanobacteria) accumulates PHB using light as energy and CO2 as carbon source. The main trigger for PHB accumulation in cyanobacteria is nitrogen and phosphorous depletion with simultaneous surplus of carbon and energy. For the above reasons, obtaining knowledge about external factors influencing PHB accumulation is of highest interest. This study compares the effect of continuous light exposure and day/night (16/8 h) cycles on selected physiology parameters of three Synechocystis strains. We show that continuous illumination at moderate light intensities leads to an increased PHB accumulation in Synechocystis salina CCALA 192 (max. 14.2% CDW – cell dry weight) compared to day/night cycles (3.7% CDW). In addition to PHB content, glycogen and cell size increased, while cell density and cell viability decreased. The results offer new approaches for further studies to gain deeper insights into the role of PHB in cyanobacteria to obtain bioplastics in a more sustainable and environmentally friendly way.

Green hydrogen is central to the energy transition, but its production often requires expensive materials and poses environmental risks due to the perfluorinated substances used in electrolysis. This study introduces a transformative approach to green hydrogen production via chemical looping, utilizing an iron-based oxygen carrier with yttrium-stabilized zirconium oxide (YSZ). A significant innovation is the replacement of Al2O3 with SiO2 as an inert support pellet, enhancing process efficiency and reducing CO2 contamination by minimizing carbon deposition by up to 700%. The major findings include achieving a remarkable hydrogen purity of 99.994% without the need for additional purification methods. The Fe-YSZ oxygen carrier possesses a significantly higher pore volume of 323 mm³/g and pore surface area of 18.3 m²/g, increasing the pore volume in the iron matrix by up to 50%, further improving efficiency. The catalytic system exhibits a unique self-cleaning effect, substantially reducing CO2 contamination. Fe-YSZ-SiO2 demonstrated CO2 contamination levels below 100 ppm, which is particularly noteworthy. This research advances our understanding of chemical looping mechanisms and offers practical, sustainable solutions for green hydrogen production, highlighting the crucial synergy between support pellets and oxygen carriers. These findings underscore the potential of chemical looping hydrogen (CLH) technology for use in efficient and environmentally friendly hydrogen production, contributing to the transition to cleaner energy sources.

Bioeconomy strategies promote higher shares of biomass products in material and energy sectors. Deploying by-products from sawmills is therefore of major interest. This study aims at analyzing market characteristics and implications of bioeconomy strategies by combining three methods: First, an econometric supply and demand model for sawmill by-products (SBP) was estimated based on data from 2001 to 2020. Second, the model was used to analyze a reference and a bioeconomy scenario. Third, a use case was analyzed dealing with the integration of wood gasification and BioSNG (Synthetic Natural Gas) production into Austrian flows of SBP. The results indicate that SBP supply reacts unit-elastic to sawnwood exports, while both supply and demand respond inelastic to SBP prices. Demand is positively inelastic related to SBP as input in panel and pellet production. In a bioeconomy scenario, long-term supply would exceed demand, resulting in additional SBP to be used for gasification. A 100 MW BioSNG plant converting these SBP could provide 528 MWh BioSNG per year. This is a 11 % share of the Austrian target value of 5 TWh green gas.

This study investigates the detailed ash transformation process during the combustion of rice husks in entrained flow conditions. The experiments were conducted in a lab-scale drop tube furnace at 1200 and 1450 °C in pyrolysis/devolatilization (using N2) and combustion (using air) conditions. The detailed ash transformation process during the different fuel conversion stages in combustion (i.e., devolatilization and char combustion) was investigated by comparing the results obtained in the pyrolysis/devolatilization experiments with the combustion experiments. The resulting residual chars, ashes, and particulate matter (PM) were collected and characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM–EDS), X-ray diffraction (XRD), inductively coupled plasma atomic emission spectroscopy (ICP-AES), ion chromatography (IC), and CHN analyses. Furthermore, the obtained results were interpreted via thermodynamic equilibrium calculations (TECs). For all investigated conditions, Si, Ca, and Mg were retained entirely in the coarse ash and char fractions (>1 μm). Meanwhile, K and P were found in coarse ash/char fractions and fine particulate fractions (<1 μm). A moderate, at 1200 °C, to high share, at 1450 °C, of the detected K and P was found in the fine particle fractions after combustion. The majority (>95%) of the detected S and Cl were volatilized during the experiments. The study showed an accumulation of minor ash-forming elements (i.e., K, Ca, Mg, P) on the inner part of rice husk chars, initiating melt formation during the char combustion stage. The identified melt at 1200 °C after combustion was rich in Si with minor amounts of K, Ca, Mg, and P. The share of molten ashes was increased at 1450 °C compared to that at 1200 °C. Overall, the results presented in this work reveal detailed insights into the ash transformation processes taking place in different parts of the fuel during the combustion of rice husks in entrained flow conditions.

Torf ist ein breit etablierter und quantitativ wichtiger Inhaltsstoff von Substratmischungen für den
Gartenbau. Den guten gartenbaulichen Eigenschaften stehen allerdings ökologische Bedenken
gegenüber. Torf entsteht in Moorgebieten, welche als Kohlenstoffsenken fungieren. Das
bedeutet, dass Kohlendioxid (CO2) über tausende Jahre aus der Atmosphäre gebunden und als
Torf langfristig im Boden gespeichert wird. Beim Abbau von Torf sowie bei dessen Nutzung wird
dieses CO2 freigesetzt, wodurch Torfabbau und -nutzung einen relevanten Einfluss auf das Klima
haben können (ähnlich wie bei der Verwendung fossiler Energieträger). Global betrachtet
speichern Moore etwa doppelt so viel Kohlenstoff wie die gesamte Biomasse der Wälder (Global
2000 2023). In Österreich spielt der Torfabbau eine relativ geringe Rolle, jedoch werden jährlich
mehr als 100.000 t Torf für den Gartenbau importiert (Statistik Austria 2023). Durch den Verzicht
von Torfprodukten und die Umstellung auf Torfersatzstoffe im Gartenbau sollen Treibhausgas-
Emissionen aus dem Abbau des Torfes, aber auch aus dessen gartenbaulicher Nutzung,
reduziert und Moorgebiete bewahrt werden (BMLRT 2022).

The present study investigates how three different silicate-based bed materials behave in bubbling fluidized bed combustion of a model agricultural residue with respect to ash composition, namely barley straw. Quartz, natural K-feldspar, and olivine were all used in combustion at 700 °C, and the resulting layer formation and bed agglomeration characteristics were determined. Based on this, a general reaction model for bed ash from agricultural residues was proposed, taking into account the reactivity of the different silicates investigated towards the main ash-forming elements K, Ca, and Si. The proposed reaction model links bed material interaction with K-rich bed ash to the degree of polymerization of the silicate bed material, where addition reactions occur in systems with high polymerization, predominately in quartz, and substitution reactions dominate for depolymerized silicates such as K-feldspar and olivine.

Green Carbon Liquids - staged condensation from lab-scale pyrolysis; Green Gas - Green Heat for Industrie from Biogenic Waste; Biohydrogen - Implementation of Dark Fermentation for Industrial Wastewater Treatment; Effects of the climate crisis and pesticide use on fatty acida in the food web; Syngas production from biogenic residues and waste via advanced dual fluidized bed gasification; New developments in gas cleaning for the production of C-based products and fuels via gasification; Advancements in Fischer-Tropsch synthesis using a slurry bubble column reactor; Biofuels - a crucial part of decarbinisation; Speed-Up Algorithms for advanced simulations; Multiscale modeling of metal oxide and biomass conversion for chemical looping processes; Multiscale modeling of metal oxide and biomass conversion for chemical looping processes; Model-Based Control of the Generated Steam Mass Flow in a Fluidized-Bed Waste Incineration Plant; Modular, predictive, optimization-based supervisory control of multi-energy systems; Monitoring of a Renewable Flow Battery; Use cases of optimally planned multi-energy systems with OptEnGrid: hotel resort and renewable energy communities; Optimal Design of Multi-Energy Systems using OptEnGrid; Sustainability assessment: mere obligation or a key to success; 

The main aim of biomass utilization in a future, sustainable energy and resource system must be to cover everything which cannot be covered by other sustainable sources. Among being a sustainable carbon source, this must be providing controllable technologies in order to compensate for the volatility of most renewable energy sources as well as the demands among the different sectors. However, most of the existing technologies currently in the market and those in research are not able to provide this flexibility, since their concepts and in particular their control strategies were not designed for highly flexible operation. Thus, new and more advanced control strategies, able to handle strongly varying operating conditions (fuel variations, load modulation, etc.) automatically, and ensuring an optimal interaction of all the production units, storages and consumers on system level, have to be developed. In the paper, a general discussion of the requirements and the state-of-the-art is given, and specific approaches on technological and system level are presented, and their potential regarding flexibility provision is evaluated based on industrial applications, clearly showing the high potential of flexibility provision to multi-energy systems by bioenergy through model-based control.

In this work, the fate of the ash-forming elements during bubbling fluidized bed combustion and gasification of P-rich sewage sludge (SS) and mixtures with either Si-K-rich wheat straw (WS) or K-Ca-rich sunflower husks (SH) were investigated. The focus of the study was assessing the feasibility of using fuel blends in fluidized bed systems and potential P recovery from the resulting ashes. The used fuels were pure SS and mixtures including 90 wt.% WS (WSS) and 85 wt.% SH (SHS). The analyzed operating conditions were combustion (930–960 °C, λ: 1.2–1.5) and gasification (780–810 °C, λ: 0.4–0.7) in a 5 kW bench-scale reactor. Residual ash and char fractions were collected from different parts of the 5 kW bubbling fluidized bed (bed, cyclone, filter) and analyzed by CHN, SEM/EDS, XRD, and ICP-AES.

The conversion of the fuel mixtures achieved a steady state under the used process conditions except for the combustion of WSS, which led to the formation of large bed agglomerates with the bed material. The morphology of ash samples after combustion showed that SS fuel pellets mostly maintained their integrity during the experiment. In contrast, the ash and char particles from fuel mixtures were fragmented, and larger quantities were found in the cyclone, the filter, or on interior reactor surfaces. The fate of P was dominated by crystalline Ca-dominated whitlockites in all ash fractions, partially including K for the fuel mixtures SHS and WSS. 76–81 % of ingoing P was found in the bed residue after combustion and gasification of the SS-fuel. After conversion of the fuel mixtures SHS and WSS, the share was lower at 22–48 %, with larger shares of P in the entrained fractions (25–34 %). The quantity of identified crystalline compounds was lower after gasification than combustion, likely due to the limited interaction of ash-forming elements in the residual CHN matrix. Altogether, the results show that fuel mixtures of sewage sludge with agricultural residues could expand the fuel feedstock and enable P recovery. This may be used in the fuel and process design of upscaled fluidized bed processes or systems employing both combustion and gasification.

Integrating thermoelectric generators (TEGs) with photovoltaic (PV) devices presents an effective strategy to enhance the power generation of PV cells, thus substantially contributing to the widespread adoption of solar energy. By harnessing both photon and heat energy from sunlight, this integration maximizes energy capture and improves overall system efficiency, thereby advancing the feasibility and scalability of solar energy generation. This article provides a timely review of the advances and challenges in hybrid photovoltaic-thermoelectric generator (PV-TEG) technology, covering fundamentals, the impact of thermal, contact, and load resistance on performance, various integration options (such as hybrid PV-TEG systems with spectral splitters, phase change materials, and thermal systems), thermal management, feasibility, economic and environmental aspects, and long-term efficiency improvements. Following a detailed analysis and review of extensive progress, PV-TEG systems demonstrate higher efficiency across diverse environmental conditions compared to standalone PV devices. Finally, we address constraints, propose potential remedies, and point out future directions in the field.

Polyhydroxyalkanoates (PHA) are a promising bio-based alternative to traditional plastics derived from petroleum. Cyanobacteria are photosynthetic organisms that produce PHA from CO2 and sunlight, which can potentially reduce production costs and environmental footprint in comparison to heterotrophic bacteria cultures because (1) they utilize inorganic carbon sources for growth and (2) they do not require intensive aeration for oxygenation. Moreover, supplementing precursors such as propionate, acetate, valerate, etc., can be used to obtain various copolymers with plastic customizable properties in comparison to the classical homopolymers, such as polyhydroxybutyrate, PHB. This critical review covers the latest advances in PHA production, including recent discoveries in the metabolism interplay between PHA and glycogen production, and new insights into cultivation strategies that enhance PHA accumulation, and purification processes. This review also addresses the challenges and suggests potential solutions for a viable industrial PHAs production process.

Reliable experimental data and models are required to better understand and design chemical looping processes with oxygen carrier materials like ilmenite. A dubious variability of suggested kinetics for similar oxygen carrier materials has been presented in the literature. Part I of this work focuses on thermogravimetric analysis (TGA) of gas–solid kinetics and addresses several of its challenges, which are possible reasons behind such deviations. The reduction of synthetic ilmenite (60 mass% Fe2O3 ＋40 mass% TiO2) powder with H2 in a TGA system was investigated for this purpose.
Multiple steps were necessary to overcome mass transfer limitations during the measurements: (i) small sample masses down to 1.6 mg, (ii) high gas flow rates, (iii) a suitable sample carrier and (iv) proper sample dispersion on the sample carrier. Three types of sample carriers (crucible, basket and plate) were tested; the plate showed the best performance overall. It was alarming that an exemplary increase in sample mass from 1.6 to 3 mg, which was still significantly lower than all other studies reviewed, already introduced a noticeable influence of diffusion. Isothermal (650–950 °C, 17–50 vol% H2) and nonisothermal parameter studies were conducted and yielded vastly different isoconversional activation energies. A computational fluid dynamics (CFD) study of the TGA system suggested considerable axial dispersion of H2 influencing the initial conversion period.
These findings help to assess the reliability of kinetic studies and guide towards diffusion-free, kinetic measurements. The results will be used for model development in part II.

Chemical looping combustion has the potential to be an efficient and low-cost technology capable of contributing to the reduction of the atmospheric concentration of CO2 in order to reach the 1.5/2 °C goal and mitigate climate change. In this process, a metal oxide is used as oxygen carrier in a dual fluidized bed to generate clean CO2 via combustion of biomass. Most commonly, natural ores or synthetic materials are used as oxygen carrier whereas both must meet special requirements for the conversion of solid fuels. Synthetic oxygen carriers are characterized by higher reactivity at the expense of higher costs versus the lower-cost natural ores. To determine the viability of both possibilities, a techno-economic comparison of a synthetic material based on manganese, iron, and copper to the natural ore ilmenite was conducted. The synthetic oxygen carrier was characterized and tested in a pilot plant, where high combustion efficiencies up to 98.4% and carbon capture rates up to 98.5% were reached. The techno-economic assessment resulted in CO2 capture costs of 75 and 40 €/tCO2 for the synthetic and natural ore route respectively, whereas a sensitivity analysis showed the high impact of production costs and attrition rates of the synthetic material. The synthetic oxygen carrier could break even with the natural ore in case of lower production costs and attrition rates, which could be reached by adapting the production process and recycling material. By comparison to state-of-the-art technologies, it is demonstrated that both routes are viable and the capture cost of CO2 could be reduced by implementing the chemical looping combustion technology.

Various single particle models to describe the conversion of porous solids with gaseous reactants are available in the literature. It is, therefore, not obvious which models should be selected for specific problems and applications. This work focuses on two popular types of particle models: the volumetric model (VM) and the layer model (LM). Different variations of the layer model were considered: the standard layer model, which is similar to common shrinking core models, and an extended layer model, which solves inherent problems of the shrinking core approach by replacing surface reactions with volumetric reactions. For the first time, all these models were benchmarked together regarding prediction quality and computational cost for relevant applications: gasification and oxidation of biochar, reduction of nickel oxide and oxidation of magnetite. These cases covered a wide range of Thiele moduli and Biot numbers. The volumetric model reliably predicted the conversion for all cases considered. Its computational effort was, however, significantly higher than for the layer models. Suitable reactions kinetics in combination with heat of reaction and pore diameters were integral to prediction accuracy. Char oxidation, having a high Thiele modulus, could be described suitably by the standard layer model and the extended layer model, when it accounted for the residual ash layer. Char gasification and nickel oxide reduction had moderate Thiele moduli, rendering the standard layer model unsuitable in the general case. The extended layer model overcomes these limitations due to its volumetric reaction approach. All layer models showed inferior temperature predictions for biochar gasification and magnetite oxidation owing to their lower spatial resolution compared to the volumetric model. Additional, possible problems for layer models were addressed.

Biofuels are crucial for reducing emissions in the transport sector, contributing significantly to the objectives of the Fit for 55 package and climate neutrality goals. This role is anticipated to grow in the future as advanced biofuels become increasingly accessible. This expansion will be driven by the full commercial-scale development of technologies, processes, and value chains, supported by ambitious policies and sector-specific targets that will encourage their deployment.

Bioenergy retrofitting may be a short-term strategy to promote the transition from first-generation to advanced bioethanol, as it could improve the cost-competitiveness of the latter. In addition, this strategy could also extend the operational lifetime of first-generation ethanol plants, whose production is restricted by the current European renewable energy regulations. Therefore, this work evaluates two retrofitting scenarios of an existing corn-based first-generation ethanol facility located in Spain from an economic and environmental perspective. In the first case (scenario 1), advanced bioethanol was produced using industrial waste streams included in the Renewable Energy Directive II. The second approach (scenario 2) involves the integration of second-generation technology into the existing first-generation facility. The economic analysis shows that scenario 1 presents a low capital expenditure (CAPEX, €100,000), as it only requires the installation of an industrial waste storage tank. Although, in terms of net present value (NPV), the CAPEX of scenario 2 is higher. It obtains better profitability reaching an NPV of approximately €25,610,000. The environmental assessment identified natural gas consumption as the main contributor to the overall score of the global warming impact category. Consequently, the increased energy demand of the retrofit scenarios, mainly linked to second-generation technology, has a negative impact in terms of greenhouse gas emissions. Therefore, a key aspect to improve the environmental performance of these scenarios would be the replacement of natural gas with a more sustainable alternative, such as bio-based gases.

Bioenergy retrofitting may be a short-term strategy to promote the transition from first-generation to advanced bioethanol, as it could improve the cost-competitiveness of the latter. In addition, this strategy could also extend the operational lifetime of first-generation ethanol plants, whose production is restricted by the current European renewable energy regulations. Therefore, this work evaluates two retrofitting scenarios of an existing corn-based first-generation ethanol facility located in Spain from an economic and environmental perspective. In the first case (scenario 1), advanced bioethanol was produced using industrial waste streams included in the Renewable Energy Directive II. The second approach (scenario 2) involves the integration of second-generation technology into the existing first-generation facility. The economic analysis shows that scenario 1 presents a low capital expenditure (CAPEX, €100,000), as it only requires the installation of an industrial waste storage tank. Although, in terms of net present value (NPV), the CAPEX of scenario 2 is higher. It obtains better profitability reaching an NPV of approximately €25,610,000. The environmental assessment identified natural gas consumption as the main contributor to the overall score of the global warming impact category. Consequently, the increased energy demand of the retrofit scenarios, mainly linked to second-generation technology, has a negative impact in terms of greenhouse gas emissions. Therefore, a key aspect to improve the environmental performance of these scenarios would be the replacement of natural gas with a more sustainable alternative, such as bio-based gases.

Solar thermal plants have proven to be a successful player in providing heat for district heating networks. However, to ensure the efficient operation of such plants and to achieve optimal coordination with other heat generation units, thorough monitoring, quality control, and system control are required. These tasks strongly depend on accessible and reliable measurement data, which are often unavailable.

Thus, this report focuses on efficient data gathering, storage, distribution, and validation, covering data
management topics- from sensor selection to permanent data storage. The report is mainly targeted at system designers and plant operators, aiming to provide checklists and recommendations on these topics.

The report considers a general solar district heating plant, as depicted by IEA SHC Task 55  – including a collector field, heat storage, and heating center (including a biomass boiler, heat pump, and other auxiliary heating) up to the interface to the district heating network. The topics are described on a summary level of detail while referring the reader to individual articles in case more information is needed. In addition, research groups may use this report to get an overview of data management in the solar-thermal field and identify related work.

The work consists of five sections: The Required Data section lists recommended measurements and discusses meta information required to interpret the data successfully. The Data Gathering section provides recommendations for data logging – e.g., sampling rate, encoding, and formatting. The Data-Distribution section shows proven examples of architectures for collecting and distributing data. Furthermore, the Data Storage section describes what data storage technologies (e.g., CSV files or relational databases) are currently used. The section also discusses the experiences, advantages, and challenges of the respective technologies. Finally, the Data Validation section lists common data-validation procedures that can be applied to solar-thermal data and links to open-source implementations where available.

Industry is not only a big primary emitter of CO2 itself, but also a big consumer of electricity with a share of about 43% of electricity consumption in Austria in 2023. Therefore, providing the future electrical grid with storage capacities will be a big opportunity for industrial facilities, as industry has a unique capability of load management due to its diversity compared to households or other services. While major scientific projects have investigated this potential, there is a lack of incentives for industrial plants at various levels to foster the balancing of electricity supply.

In this paper we provide an overview regarding the state of research and the obstacles we need to overcome to close the implementation gap. We expand the state-of-the-art approach of assessing flexibility potentials by not only incorporating technical but also economic and organizational key performance indicators. With the proposed novel assessment strategy, we bridge the gap between top down and bottom-up approaches, aiming to facilitate practical and economically viable demand response measures in energy-intensive industrial processes. Our methodology is demonstrated through a case study based on real life industry application, with results validated against literature and expert discussions.

The increasing share of volatile energy sources as well as variable demands provide challenges for the electrical power grid. To counteract these instabilities a balance between supply and demand needs to be established. In industrial processes, this can be achieved by coordinating the energy production with local storage and demand. Specifically, the optimized scheduling of batch production processes can avoid peak loads. A holistic approach for the control of industrial energy systems and production processes is needed to use this flexibility. This contribution presents an extension to a modular framework for optimization-based, predictive supervisory control of multi-energy systems providing the possibility to incorporate batch production processes, and a first study showing that shifting production processes can result in a more resource- and cost-efficient process.

In dual fluidized bed (DFB) gasification, the solids circulation rate is critical as it determines the amount of char and heat transported between the interconnected reactors. In DFB plants, multiple control inputs are typically available to control the solids circulation rate, resulting in an over-actuated system. We propose a modeling and control method based on Gaussian process regression, a technique that provides a measure of confidence in the model prediction. The availability of redundant control inputs is resolved by explicitly incorporating the prediction confidence information into the control algorithm to drive the process in regions of low model uncertainty. To address plant-model mismatches, a disturbance model is employed, and an extended Kalman filter is used to estimate both system and disturbance states, enabling offset-free tracking of constant references. Modeling and closed-loop simulation results for both a 100 kW and a 1 MW DFB gasification plant demonstrate the applicability of the method to different plants. Experimental results are presented for the 100 kW plant, demonstrating the successful control of the circulation rate by the proposed algorithm.

Absorption heat pumping devices (AHPDs, comprising heat pumps and chillers) can provide heating and cooling in a resource-efficient manner. However, their perceived complexity has limited their widespread application. This contribution shows how mathematical models, systematically capturing this complexity, can be used for model-based control of AHPDs (on the device-level for model-predictive or state feedback control and on the system-level for optimisation-based energy management systems) to facilitate their integration into energy systems, and discusses an exemplary application to solar cooling systems.

Die saubere und effiziente Verbrennung von Müll stellt, insbesondere aufgrund der typischerweise stark inhomogenen Brennstoffzusammensetzung, eine große Herausforderung dar. Eine effektive Maßnahme dieser Problematik zu begegnen, ist der Einsatz geeigneter Methoden zur Prozessregelung. In diesem Artikel wird daher eine neue Methode zur modellbasierten Regelung des produzierten Dampfmassenstromes in einer Wirbelschichtmüllverbrennungsanlage vorgestellt. Diese beinhaltet als Herzstück einen Softsensor, welcher den Rauchgasmassenstrom aus vorhandenen Messgrößen online schätzt. Durch die zusätzliche Kenntnis dieser wichtigen Prozessgröße kann die Regelgüte deutlich verbessert werden. Zusätzlich zeigt sich eine stabilisierende Wirkung auf die Reaktorkopftemperatur, wodurch die thermische Belastung des Schamotts verringert werden kann.

The present study examines the applicability of reaction kinetic mechanisms for predicting NOX emissions from biomass furnaces. These mechanisms are essential for numerical optimization of new innovative combustion technologies and therefore must be computationally affordable and provide reasonable accuracy in predicting NOX emissions. The selection of a suitable mechanism from literature is the goal of this work. The numerical investigations carried out utilized chemical reaction kinetic simulations with continuous stirred tank reactor networks. First, the predictions of a detailed benchmark mechanism are compared to experimental data and analyzed with regard to temperature, air-to-fuel equivalence ratio, residence time and producer gas composition. Then, various hybrid and reduced mechanisms are compared with the benchmark mechanism. The investigation showed a good agreement on the trends of NOX emissions from the detailed mechanism and measurements. The detailed mechanism can therefore be employed to find optimal operation windows in terms of temperature, air-to-fuel equivalence ratio and residence time. Benchmarking of the hybrid and reduced mechanisms showed large differences between the mechanisms. In conclusion, only one reduced mechanism is considered suitable for application in a full-scale 3D CFD simulation, which will be investigated in future studies.

Heat is still the largest energy end-use, accounting for about 50% of global final energy consumption in 2022 and contributing to 40% of global carbon dioxide (CO2) emissions. Regarding the heat supply of buildings, district heating plays an important role and is well-established in many countries. However, most of the district heating networks worldwide are still operated with supply temperatures of 70-120°C (medium-high temperature) often produced by caloric power plants. Solar district heating (SDH) systems can be a valuable alternative to decarbonize these systems. How this can be done most efficiently is investigated within the task 68 Efficient Solar District Heating Systems of the International Energy Agency (IEA) from the technology cooperation program – solar heating and cooling (SHC). This contribution presents the latest results of the task regarding comparison of different collector technologies, important digitalization aspects, analysis of available funding schemes and latest efficient SHD installations.

The chemical looping hydrogen (CLH) production process typically uses iron-based oxygen carrier materials and can provide hydrogen with high purity. Chemical looping is particularly attractive when renewable fuels like syngas from biomass gasifiers are used. This work provides a novel assessment of the possible thermodynamic and kinetic limitations for iron-based oxygen carriers in CLH fueled by biomass-based syngas, with a detailed study employing synthetic ilmenite (Fe2O3 + TiO2). Its phase diagram with H2/H2O- or CO/CO2-mixtures was compared to the typical Baur–Glaessner diagram for iron oxides. Thermogravimetric analyses underlined the necessity to consider TiO2 as a chemically active component for this material, in contrast to the common simplification of inert support materials. The validated phase diagram predicted stringent fuel limitations concerning H2O- or CO2-contents. This was confirmed by feeding a real biomass-based syngas, provided by a lab-scale gasifier, to a fixed bed CLH reactor. It was demonstrated for the H2/H2O-system that removing the oxidizing agent from the feed gas helps to overcome these limitations. Kinetic limitations within the thermodynamic boundaries were investigated using a recently published multiscale model for the H2/H2O-system. The influence of the fuel’s reduction potential on reaction rates was explored to formulate simple, kinetic design criteria. A significant retardation of conversion rate in the vicinity of the equilibrium was indicated, effectively narrowing the feasible composition range. Recommendations for the application of biomass-based syngas with iron-based oxygen carrier materials were provided.

This article presents a general representation of the characteristic polynomial of the dynamic matrix for multivariable systems in Luenberger’s canonical forms. The characteristic polynomial is given by means of the determinant of a polynomial matrix of substantially lower order. Therein, the polynomial coefficients of the single elements are the coefficients of the corresponding blocks of the dynamic matrix. The proposed representation of the characteristic polynomial can be helpful for the design of state-feedback controllers and state observers which is demonstrated by a numerical example.

Pore size distribution is a key parameter in the performance of biobased pyrolytic char in novel applications. In industrial-scale production, the size of feedstock particles typically exceeds a few millimeters. For such particle sizes, it is a challenge to tailor the final properties of the char based only on the process conditions (experimental and modeling-wise). Pyrolysis studies of single particles larger than a few millimeters provide data sets useful for modeling and optimization of the process. Part 1 of this research focused on the pyrolysis of single particles of beech wood, secondary cracking, and its effect on the char porous texture. It contains a quantitative assessment of the effects of five conversion temperatures (from 300 to 840 °C) and two particle dimensions (Ø8 × 10 mm and Ø8 × 16 mm) on the composition of the pyrolysis vapors and pore morphology of the char. Results from real-time temperature and mass changes are presented along with release profiles of 15 vapor constituents measured by infrared spectroscopy. Furthermore, characterization of the collected bio-oil (using GC-MS/FID) and the textural hierarchical structured char (through N2 and CO2 adsorption, Hg porosimetry, and scanning electron microscopy (SEM)) was performed. Cracking of vapors above 500 °C was compound-specific. The polyaromatic hydrocarbons (PAHs) yield, between 680 and 840 °C, increased 5 times for 10 mm particles and 9 times for 16 mm ones. Besides temperature, PAH yield was suspected to correlate with particle length and PAHs/soot deposition in the micropores. Results showed that the macropores accounted for over 80% of the total pore volume, regardless of the temperature and particle length. Increasing the particle length by 60% caused a reduction in the specific surface area (ca. 15% at 840 °C) of the resulting char, mainly due to a reduction in microporosity. Based on the findings, the production conditions for a specific char application are suggested. The obtained data will be used in Part 2 of this research, devoted to subsequent CFD modeling of the process.

The prediction of the structural properties of biobased carbonaceous materials of pyrolytic origin (chars) with only base feedstock properties and process conditions still poses a challenge that hinders char tailoring for novel applications. CFD modeling of single biomass particle conversion can help solve this issue since it allows for the quantification of relations between parameters that are difficult to measure. A model for char tailoring must include a validated representation of the structural changes coupled to all other relevant phenomena occurring during conversion. Part 2 of this study focuses on finding the description of the mentioned aspects to achieve the highest precision of prediction of the structural changes in char by a CFD model. The investigation in Part 2 is composed of three cases focused on accurate description and prediction of (1) bulk density and porosity, (2) secondary vapor reactions on yields and soot formation, and (3) permeability, as well as the outflux and conversion of evolved vapors. The experimental results from Part 1 and the literature data were used to find appropriate descriptions of phenomena and assess the accuracy of the model. The model results indicate that for both particle lengths (10 and 16 mm), a high accuracy of prediction of base structural parameters was achieved. The average prediction error for temperatures between 400 and 840 °C of bulk density was 31 ± 15 kg/m3, and the porosity was 1.8 ± 1.1 vol %. The results also show a low error in the prediction of bulk product yields (dry basis) over the mentioned temperature range, which were: for char 2.8 ± 1.1 wt %, for the condensable fraction 6.5 ± 3.3 wt %, and for the pyrolysis gas 4.1 ± 1.9 wt %. The distribution of secondary char formation was found to be nonuniform below 500 °C. The changes in permeability had a minor influence on the vapor outflux but a non-negligible effect on the soot formation, especially at 840 °C. The results indicate a need for further improvement of the primary degradation model to increase the accuracy of the effect of soot formation on the char structure.

Emissions from wood-burning stoves contribute to local air pollution. However, it is difficult to determine the real emissions from such stoves, especially due to unknown user behaviour, which can have a large impact on emissions. In this study, the low-cost emission reduction measure “user training” was evaluated to determine its emission reduction potential on firewood stoves. Two sets of tests were carried out. First, a field measurement campaign was conducted in Styria (Austria) with four wood stoves, where gaseous and particulate emissions were measured before and after a user training on optimised heating behaviour (e.g. ignition mode, fuel properties and placement in the combustion chamber, air supply). Gaseous emissions (carbon monoxide – CO, organic gaseous compounds – OGC) were measured continuously, while particulates were measured in batches, in undiluted and hot as well as in diluted and cooled flue gas in parallel with a specific field measurement setup. In addition, particle filters were analysed to quantify the concentration of the carcinogenic compound benzo(a)pyrene (BaP). Second, user training workshops were conducted. These tests had a simple measurement setup in order to increase the number of tests. Thus, only CO emissions were evaluated.

The results show that real life emissions in the field are high and have a high variability compared to laboratory tests and official type test results. However, user training showed a significant reduction of CO, OGC, TSP and BaP emissions of 42%, 57%, 45% and 76% (median), respectively. In addition, TSPsum (sum of hot and cooled particle emission samples) emissions decreased by 39% (median) after user training. The relative reduction rates of all batches show that the highest emission reduction potential was identified for BaP, with a reduction rate of up to 97%. The results of the workshop tests confirmed the high variability in user behavior and the range for the emission reduction potentials, with a median CO reduction of 41%.

The emission reduction potential of the user training measure is comparable to state-of-the-art technological measures such as electrostatic precipitators and catalysts. However, these measures are costly and require a high level of technical sophistication. User training, on the other hand, is relatively cheap, easy to implement and suitable for all users. Of course, there is some risk that trained end-users will revert to their old habits, leading to higher emissions again. Therefore, regular training may be necessary to maintain the higher level of performance. As we did not assess this aspect in our work, further research would be needed to prove this theory.

Retrofitting buildings with predictive control strategies can reduce their energy demand and improve thermal comfort by considering their thermal inertia and future weather conditions. A key challenge is minimizing additional infrastructure, such as sensors and actuators, while ensuring user comfort at all times. This study focuses on retrofitting with intelligent software, incorporating the users’ feedback directly into the control loop. We propose a predictive control strategy using an optimization-based energy management system (EMS) to control thermal zones in an office building. It uses a physically motivated grey-box model to predict and adjust thermal demand, with individual zones modelled using an RC-approach and parameter estimation handled by an unscented Kalman filter (UKF). This reduces deployment effort as the parameters are learned from historical data. The objective function ensures user comfort, penalizes undesirable behaviour and minimizes heating and cooling costs. An internal comfort model, automatically calibrated with user feedback by another UKF, further improves system performance. The practical case study is an office building at the ”Innovation District Inffeld”. Operation of the system for one year yielded significant results compared to conventional control. Thermal comfort was improved by 12% and thermal energy consumption for heating and cooling was reduced by about 35%.

Pyrolyse ist ein althergebrachtes Verfahren, das bereits vor Jahrtausenden zur Herstellung von Kohle praktiziert wurde. Bestrebungen nach Unabhängigkeit von fossilen Ressourcen und klimaneutralen sowie kreislaufwirtschaftlichen Wertschöpfungsketten, führen aktuell zu deutlich steigendem Interesse an dieser Technologie. Durch vielseitige verfahrenstechnische Ausgestaltungsmöglichkeiten stellt die Pyrolyse eine potenzielle Schlüsseltechnologie für verschiedene zum Teil hoch spezifische Anwendungen für stoffliche und energetische Prozessketten dar. Diese Vielfalt an Möglichkeiten resultiert jedoch gleichzeitig in einer hohen Komplexität, die es erschwert einen Überblick über angebotene Anlagen zu bekommen.

Ziel dieser Studie ist es, Informationen vielfältiger Systeme in eine vergleichbare Form zu bringen und dadurch eine Übersicht für Interessierte zu ermöglichen. Der Aufwand der Informationsbeschaffung als initialer Schritt für Umsetzungen soll dadurch reduziert werden. Hierdurch soll zur Realisierung regionaler Pyrolyseprojekte als Bestandteil kreislaufwirtschaftlicher Stoffnutzungskonzepte beigetragen werden.

Phytoremediation is the use of vegetation for the in situ treatment of contaminated environments. After plants have been used for phytoremediation of soils, their biomass can be used for example as value-added products or converted by thermochemical processes. Large-scale application of pyrolysis technology for phytoremediation biomass requires accurate predictive kinetic models and a characterization of the toxicity of the materials produced. The pyrolysis of industrial hemp (Cannabis sativa L.) was investigated on a laboratory scale by varying the process conditions and accurately modelled by considering four pseudo-components with first reaction order. The average value of the coefficients of determination is 0.9980. Biomass and biochar were characterized and the main components of the gas phase were monitored. We found Cd, Pb, and Zn in the roots, although in lower amounts than in the soil. Especially the leaves and stems showed negligible traces of these elements, so that these parts can be used directly, even if the hemp was grown on the polluted soil. After pyrolysis, the concentration of pollutants in the solid fraction decreased, which could be attributed to the reduction of metal oxides (or salts) to elemental form and subsequent evaporation. This pyrolysis process has the potential to treat heavy metal-rich biomass, with gas phase purification via condensation, yielding agricultural-grade biochar, CO-rich gas and a highly concentrated heavy metal stream in absorbent material.

A dried dairy processing sludge (sludge from wastewater treatment of an effluent from a milk processing plant) was pyrolysed in a single-particle reactor at different temperatures from 400 °C to 900 °C. NH₃ and HCN were measured online and offline by means of FTIR as well as by cumulative sampling in impinger bottles (in 0.05 M H₂SO₄ and 1 M NaOH, respectively) and analysed by photometric method. NO and NO₂ were measured online using a nitric oxide analyser while N₂O was measured by FTIR. Nitrogen (N) in the sludge and in the remaining char, char-N, was determined. Moreover, tar content in pyrolysis gas was measured and tar-N was determined. The results with respect to N mass balance closure are discussed. The different measurements techniques are compared. For pyrolysis at 520 ℃ and 700 ℃ nitrogen in the gas phase was mainly contained as N₂ (36 % and 40 % respectively), followed by NH₃ (15 % and 18 %), tar-N (10 % and 9 %), HCN (1 % and 3 %), NO (1 %) and NO₂ (0.2 %). The dairy processing sludge has very specific properties with organic-N present predominantly as proteins and a high content of inherent Ca. These characteristics affected the distribution of N. The amount of char-N was higher while the amount of tar-N lower than for sewage sludge from literature, at comparable pyrolysis temperature.

First experiments with biogenic residues and a plastic-rich rejects and woody biomass blend were conducted in an advanced 1 MW dual fluidized bed steam gasification demonstration plant at the Syngas Platform Vienna. Wood chips, bark, forest residues, and the plastic-rich rejects and woody biomass blend were tested and the tar composition was analyzed upstream and downstream of the upper gasification reactor, which is designed as a high-temperature column with countercurrent flow of catalytic material. Each feedstock was gasified with olivine as bed material in demonstration scale and is compared to the gasification of softwood pellets with olivine and limestone in pilot scale. A reduction in tar content was observed after countercurrent column for all feedstocks. However, a shift in tar species occurred. While styrene, phenol, and 1H-indene were predominant upstream, naphthalene and polycyclic aromatic hydrocarbons (PAHs) were the prevailing tar species downstream the countercurrent column. Hence, an increase of i.e. anthracene, fluoranthene, and pyrene from the upstream concentration was observed. For pyrene, up to twice the initial concentration was measured. This recombination to PAHs was observed for all feedstocks in demonstration- and pilot-scale. The only exception occurred with limestone as bed material, characterized by a higher catalytic activity in comparison to the typically used olivine. In the perspective of the integrated product gas cleaning, tar with higher temperature of condensation are separated more efficiently in the installed scrubbing unit. Hence, the recombination facilitates an overall decline of tar content after the gas cleaning.

Sustainable liquid biofuels are fundamental for decarbonizing the transportation
sector. Biofuels offer a viable, economical, and environmentally sustainable alternative
to fossil fuels, serving as a bridge to future mobility solutions like electromobility and
hydrogen, which have longer development timelines. They improve air quality, public
health, and contribute to agricultural and economic development, enhancing energy
diversification, security, and leveraging each country's comparative advantages. The
main challenges for the continued development of biofuels are the absence of an
international standard, coordination and certification methodologies, lack of regulations
in some countries and the subsidies to fossil fuels. The authors of this policy brief
recommend that the G20 and the international community strengthen regulatory
frameworks for sustainable biofuel use in land transportation, standardize and harmonize
GHG reduction standards and certification mechanisms, and develop common regional
and national policies to advance the production and consumption of new biofuels for
sectors such as aviation and maritime transportation. An analysis1 of biofuels
implementation in emerging markets of Africa, Asia, and Latin America shows that
meeting 25% blending targets requires only 1–7.8% of their total land area, achieving
substantial GHG reductions. Favorable climatic conditions for biomass production in
these countries and the low greenhouse gas impact of international freight underscore the
benefits of global biofuel trade, highlighting the urgent need for widespread adoption to
accelerate decarbonization efforts.

A drastic reduction in the consumption of fossil resources and efficient use are key factors in limiting the further progression of climate change. Cascading use and recycling of residues in the sense of bioeconomy and circular economy are essential. Thermochemical or microbiological conversion can produce various intermediates and endproducts (e.g. biochar, basic chemicals, bioenergy) from biogenic residues. Implemented decentrally, such concepts can reduce transportation efforts, increase the degree of self-sufficiency with raw materials, increase regional added value creation and close (preferably regional) material and energy cycles.

In modern waste management, the energetic utilization of waste is an important key technology. On the one hand, it allows the waste to be disposed of in an environmentally friendly manner and, on the other hand, makes it possible to reduce the use of other controversial energy sources, such as nuclear fission or fossil fuels. However, the efficient and clean incineration of waste is a challenging task due to the strong inhomogeneity of the waste.

The Alpine Region is characterized by a high density of biomass processing and conversion plants. Alps4GreenC sets the scene for transnational utilization of biomass residues in biochar-based value chains. The project aims at:

• Researching opportunities for conversion of biomass residues with focus on biochar production.
• Increasing awareness of citizens, plant owners, policy makers and all involved stakeholders.
• Establishing connection and coordination among Austria, Italy and Slovenia.

Anaerobic acidification of pressed sugar beet pulp (PSBP) is a promising strategy for the transition towards a circular economy. In this work, volatile fatty acids were produced by anaerobic acidification of PSBP and subsequently converted to mcl-polyhydroxyalkanoates. The results point to mesophilic acidification as superior to thermophilic one. At the same time, the pH regulated at the value of 6.0 showed a decisive advantage over both the pH of 7.0 and the lack of pH regulation. Furthermore, the conditions with a hydraulic retention time (HRT) of 10 days significantly outperformed those with an HRT of 6 days. The best-performing process (mesophilic, pH controlled at 6, HRT of 10 days) was successfully scaled up to a 250 L reactor, reaching a volatile fatty acid (VFA) concentration of up to 27.8 g L-1. Finally, the produced VFA were investigated as feedstock for mcl-PHA producers, Pseudomonas citronellolis and Pseudomonas putida. Both strains grew and produced PHA successfully, with P. citronellolis reaching a biomass of 15.6 g L-1 with 38% of mcl-PHA, while P. putida grew to 15.2 g L-1 with a polymer content of 31%. This study proves that acidified PSBP is a valuable feedstock for mcl-PHA production and an important approach to developing biorefineries.

Buildings with floor heating or thermally activated building structures offer significant potential for shifting the thermal load and thus reduce peak demand for heating or cooling. This potential can be realised with the help of model predictive control (MPC) methods, provided that sufficiently descriptive mathematical models of the thermal characteristics of the individual thermal zones exist. Creating these by hand is infeasible for larger numbers of zones; instead, they must be identified automatically based on measurement data. In this paper an approach is presented that allows automatically identifying thermal models usable in MPC. The results show that the identified zone models are sufficiently accurate for the use in an MPC, with a mean average error below 1.5K for the prediction of the zone temperatures. The identified zone models are then used in a distributed optimisation scheme that coordinates the individual zones and buildings of a city quarter to best support an energy hub by flattening the overall load profile. In a preliminary simulation study carried out for buildings with floor heating, the operating costs for heating in a winter month were reduced by approximately 9%. Therefore, it can be concluded that the proposed approach has a clear economic benefit.

The Area Automation and Control at BEST - Bioenergy and Sustainable Technologies GmbH focuses on the optimal operation of sustainable biorefinery and renewable energy systems, the optimal interaction of different technologies and systems and the highly automated operation management
by new digital services.

Char originating from biomass can be used as a sustainable carbon additive in the production of polymer compounds with enhanced characteristics.

Over the last decades the general interest in recycling and upcycling technologies heavily grew and in the agricultural sector, it is not different. Lal estimated already in 2005 that 3,8 billion tons of crop residues alone are produced annually
worldwide.

With respect to the climate objectives Chemical Looping (CL) processes constitute a promising alternative to traditional thermochemical conversion routes. Through the application of solid materials, so-called oxygen carriers (OC), instead of air as oxygen supply, CO2 can be easily separated from the flue gas. By this, biomass can be used for hydrogen production (Chemical Looping Hydrogen, CLH) or it can be burnt without CO2 emissions (Chemical Looping Combustion, CLC).

Absorption heat pumping devices (AHPDs, comprising absorption heat pumps and chillers) are devices that use thermal energy instead of electricity to generate heating and cooling, thereby facilitating the use of waste heat and renewable energy sources such as solar or geothermal energy. Despite this benefit, widespread use of AHPDs is still limited. One reason for this is partly unsatisfactory control performance under varying operating conditions, which can result in poor modulation and part load capability. A promising approach to tackle this issue is using dynamic, model-based control strategies, whose effectiveness, however, strongly depend on the model being used. This paper therefore focuses on the derivation of a viable dynamic model to be used for such model-based control strategies for AHPDs such as state feedback or model-predictive control. The derived model is experimentally validated, showing good modeling accuracy. Its modeling accuracy is also compared to alternative model versions, that contain other heat transfer correlations, as a benchmark. Although the derived model is mathematically simple, it does have the structure of a nonlinear differential–algebraic system of equations. To obtain an even simpler model structure, linearization at an operating point is discussed to derive a model in linear state space representation. The experimental validation shows that the linear model does have slightly worse steady-state accuracy, but that the dynamic accuracy seems to be almost unaffected by the linearization. The presented new modeling approach is considered suitable to be used as a basis for the design of advanced, model-based control strategies, ultimately aiming to improve the modulation and part load capability of AHPDs.

Aqueous phase reforming (APR) describes the conversion of oxygenated hydrocarbons dissolved in
an aqueous phase to hydrogen and carbon dioxide.

Efficient control of energy systems is an important factor in achieving the CO2-emission goals. District heating (DH) networks are an especially relevant example of such energy systems. State-of-the-art control of small and medium-sized DH networks, however, still mainly relies on simple rule-based control concepts. Handling future challenges such as varying prices and intermittent renewable production is difficult to achieve with such control concepts. Optimization-based energy management systems (EMS) are a promising high-level control approach for the efficient operation of DH networks and complex energy systems in general. An especially interesting challenge arises when DH networks grow, as often the opportunity arises to interconnect them. However, if they operated by different owners, the control task becomes challenging, especially for optimization-based EMS. This is because, in the overall objective function, the cost and revenue for any exchange of energy would cancel out. This thesis presents a solution to this challenge. The main focus of this thesis is on the application of distributed optimization methods for EMS in the context of coupled energy systems, operated by multiple owners, especially interconnected DH networks. The presented methods and ideas are evaluated on a practical application of three DH networks in Austria.  

Annex TS3: Hybrid Energy Networks

The aim of the IEA DHC Annex TS3 „hybrid energy networks" is to promote opportunities and to overcome challenges for district heating and cooling (DHC) networks in an integrated energy system context, focusing on the coupling to the electricity and the gas grid.

K-feldspar was utilized as bed material for fluidized bed combustion of bark, chicken manure, and their mixture. Bed samples were extracted after 4 and 8 h and the samples were analyzed with scanning electron microscopy to study the impact of P-rich chicken manure on the bed material. The results were compared to fixed bed exposures with different orthophosphates to investigate their influence in detail.

The fresh bed material used for this study exhibited an uneven surface with many cavities which facilitated the deposition and retention of the fuel ash. Utilizing pure chicken manure as fuel led to the formation of Ca- and P-rich particles which accumulated in these cavities. At the same time, larger ash particles were formed which consisted of the elements found in chicken manure ash. The co-combustion of bark and chicken manure led to the interaction of the two ash fractions and the formation of a thicker ash layer, which consisted of elements from both fuel ashes, namely Ca, P, Si, K and S. The layer appeared to be partially molten which could be favorable for the deposition of ash particles and thereby the formation of a mixed Ca/K-phosphate. Fixed bed exposures of the K-feldspar particles with Na3PO4 or K3PO4 caused particle agglomeration which means presence of alkali-phosphates should be limited.

The co-combustion of bark with chicken manure showed promising results both regarding a shift from Ca-phosphates to more bioavailable Ca/K-phosphates and an acceleration in ash layer formation. The formation of an ash layer after only 4 h of exposure with the mixture of bark and chicken manure could be advantageous for catalytic activation of the bed material.

Oxygen carrier aided combustion (OCAC) is a novel technology that aims to enhance combustion of heterogenous fuels by replacing the inert bed material with an active oxygen carrier. One of the promising oxygen carriers is natural ilmenite which shows decent oxygen transport capacity and mechanical stability under OCAC operating conditions. However, interactions between ilmenite and woody biomass ash lead to the formation of a calcium-rich ash layer, which affects the ability of the oxygen carrier (OC) to transfer oxygen throughout the boiler and subsequently decreases the combustion efficiency. This paper focuses on the time-dependent morphological and compositional changes in ilmenite bed particles and the consequence effects on the oxygen transport capacity and reactivity of ilmenite. Ilmenite utilized in this study was investigated in a 5 kW bubbling fluidized bed combustion unit, utilizing ash-rich bark pellets as fuel. A negative effect of iron migration on the oxygen transport capacity was observed in ilmenite bed particles after 6 h of operation in the bubbling fluidized bed reactor. The decrease in the oxygen transport capacity of ilmenite was found to correlate with the increased exposure time in the fluidized bed reactor and was caused by the migration and subsequent erosion of Fe from the ilmenite particles. On the other hand, the older bed particles show an increase in reaction rate, presumably due to the catalytic activity of the calcium-enriched outer layer on the bed particle surface.

Many processes in environmental biotechnology are working due to the presence of a mix of microbes, with each group playing a specific role, like being responsible for one step of a multistage conversion process. Even in industrial fermentations which have the purpose of producing biomass of one specific microorganism, an accompanying flora of other microbes is almost always present.

The so-called “layer model” or “interface-based model” is a simplified single particle model, originally developed for shorter computation time during computational fluid dynamics (CFD) simulations. A reactive biomass particle is assumed to consist of successive layers, in which drying, pyrolysis and char conversion occur sequentially. The interfaces between these layers are the reaction fronts. The model has already been validated for drying, pyrolysis and char oxidation. Layer models in the literature have commonly employed surface reactions at the reaction front to describe char conversion. In this work, the suitability of this surface reaction concept is assessed when gasifying biochar. It is shown that a particular layer model, already available, which originally employed surface reactions, was unable to adequately describe the mass loss during gasification of a biochar. In order to overcome this incapability, the model was extended to consider volumetric reactions in the char layer. The influence of intraparticle diffusion was considered through an effectiveness factor. The model is easily adaptable for different gas-solid kinetic rate laws, while still allowing for comparably fast solutions of the model equations. The extended model was validated using theoretical calculations and experimental measurements from literature. It was demonstrated that intraparticle diffusion can significantly slow down the biochar gasification process. A general guideline for when to employ volumetric reactions, rather than surface reactions, and when to consider intraparticle diffusion is provided based on the Thiele modulus as the criterion.

Fault-Detection (FD) is essential to ensure the performance of solar thermal systems. However, manually analyzing the system can be time-consuming, error-prone, and requires extensive domain knowledge. On the other hand, existing FD algorithms are often too complicated to set up, limited to specific system layouts, or have only limited fault coverage. Hence, a new FD algorithm called Fault-Detective is presented in this paper, which is purely data-driven and can be applied to a wide range of system layouts with minimal configuration effort. It automatically identifies correlated sensors and models their behavior using Random-Forest-Regression. Faults are then detected by comparing predicted and measured values.

The algorithm is tested using data from three large-scale solar thermal systems to evaluate its applicability and performance. The results are compared to manual fault detection performed by a domain expert. The evaluation shows that Fault-Detective can successfully identify correlated sensors and model their behavior well, resulting in coefficient-of-determination scores between R²=0.91 and R²=1.00. In addition, all faults detected by the domain experts were correctly spotted by Fault-Detective. The algorithm even identified some faults that the experts missed. However, the use of Fault-Detective is limited by the low precision score of 30% when monitoring temperature sensors. The reason for this is a high number of false alarms raised due to anomalies (e.g., consecutive days with bad weather) instead of faults. Nevertheless, the algorithm shows promising results for monitoring the thermal power of the systems, with an average precision score of 91%.

This work presents the first results of a newly commissioned biomass-to-liquid Fischer-Tropsch (FT) pilot plant. A 1 MWth dualfluidized bed (DFB) steam gasifier, a 55 Nm3/h 4-step gas cleaning plant and a 250 kW slurry bubble column FT synthesis reactor (SBCR) form the full process chain.

Gas-fermentation is the conversion of gaseous feedstocks (e.g. CO2-rich off gases, CO, H2) into
valuable products such as organic acids and alcohols by microorganisms such as clostridia.
By supplying electrical energy (an alternative source of reducing/oxidizing energy), the fermentation
environment can be further optimized, resulting in products with higher purity, a broader product
spectrum and higher cell densities.

Iron production via blast furnace utilizes coal and coke to reduce iron oxides resulting in high greenhouse gas emissions. This important issue for the iron and steel industry may be mitigated by application of biomass-based reducing agents (bioreducer).