Gasification is a thermochemical process that transforms carbonaceous matter into a gaseous secondary energy carrier, referred to as product gas. This product gas can be used for heat and power generation but also for syntheses. One possible gasification technology suitable for further synthesis is dual fluidised bed (DFB) steam gasification. The H2:CO ratio, which determines the suitability of the product gas for further synthesis, is influenced by the catalytic activity inside the gasification reactor. Eleven DFB steam gasification experiments were performed comparing the catalytic activity for various bed material and fuel combinations. The bed materials used were K-feldspar, fresh and layered olivine, and limestone, and the fuels gasified were softwood, chicken manure, a bark–chicken manure mixture and a bark-straw-chicken manure mixture. The water-gas-shift (WGS) equilibrium deviation was used to evaluate the catalytic activity inside the gasification reactor. It was shown that both the fuel ash and bed material have an effect on the catalytic activity during gasification. Scanning electron microscopy and energy dispersive X-ray spectrometry showed the initial layer formation for experiments with ash-rich fuels. Isolated WGS experiments were performed to further highlight the influence of bed material, fuel ash and fuel ash layers on the WGS equilibrium.

Iron production via blast furnace utilizes coal and coke to reduce iron oxides which results in high greenhouse gas emissions. Biomass-based reducing agents may reduce its fossil carbon footprint. Charcoal as bioreducer has been since the beginning of steelmaking. In order to obtain a reducing agent which is appropriately fluidizable for pulverized coal injection (PCI), the most influential powder characteristics must be named and the influence of thermal pre-treatment and comminution technique on particle properties have to be examined. The aim is to show that particle shape design of a grinding product is feasible to a certain extent by varying mill types and how pyrolyzed wood powder properties technically relevant for powder conveying processes can be influenced .

Around 2.7 billion people worldwide have no access to clean cooking equipment, which leads to major health problems due to high emissions of unburned products (VOC, CO and soot). A top-lit updraft gasifier cookstove with forced draft was identified as the technology with the highest potential for reducing harmful emissions from incomplete combustion in simple cookstoves. The basic variant of the stove was equipped with a fan for efficient mixing of product gas with air and fired with pellets to increase the energy density of low-grade residues. The development was conducted based on water boiling test experiments for wood and rice hull pellets and targeted CFD simulations of flow, heat transfer and gas phase combustion with a comprehensive description of the reaction kinetics, which were validated by the experiments. Emphasis was put on the reduction of CO emissions as an indicator for the burnout quality of the flue gas. The optimisation was carried out in several steps, the main improvements being the design of a sufficiently large post-combustion chamber and a supply of an appropriate amount of primary air for a more stable fuel gasification. The experiments showed CO emissions <0.2 g/MJdel for wood and rice hull pellets, which corresponds to a reduction by a factor of about 15 to 20 compared to the basic forced draft stove concept. Furthermore, these values are between 5 and 10 times lower than published water boiling test results of the best available cookstove technologies and are already close to the range of automatic pellet furnaces for domestic heating, which are considered to be the benchmark for the best possible reduction of CO emissions.

The aim of this work is to utilize various biogenic fuels without ash slagging and to significantly reduce NOX and particulate matter emissions in comparison to modern combustion technologies. For this purpose, a novel small-scale multi-fuel biomass grate furnace technology was developed and experimentally investigated. It employs a low oxygen concentration in the fixed-bed and a double air staging, including the supply of flue gas recirculation. In this way slagging is prevented on the grate, reducing the release of ash-forming volatiles, NOX emissions are minimized in the reduction zone and an efficient flue gas burnout is achieved in the tertiary zone. Wood pellets and chips as well as miscanthus briquettes were investigated.

The measured total particle emissions showed a reduction of 68% for pellets and 70% for wood chips compared to typical small-scale furnaces. Furthermore, a reduction of NOX emissions of 39% for wood chips, 40% for wood pellets and 45% for miscanthus briquettes was achieved compared to typical small-scale furnaces. The experimental parameter study provided fundamental insights into the various mechanisms involved in this novel technology, which is close to market introduction, and proved its high fuel flexibility and great potential for particulate matter and NOX emission reduction.

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

This study focuses on the combustion behaviour of poultry litter which was experimentally studied in a fixed bed lab-scale reactor. The combustion experiments not only provided useful insights pertaining to the thermal decomposition of poultry litter over time, release of main gaseous compounds and nitrogen (N) species, but also the release of elements found initially in the ash composition. The main gaseous species were released during the devolatilisation phase, whereas Ammonia (NH3) was found to be the most abundant compound of N-gaseous species (45%) followed by nitrogen oxide (NO) with a fraction of ~10%. Alkali metals showed moderate release rates, whilst Chlorine (Cl) was observed to have the highest one (90%) of the ash forming elements, depicting the high volatility of the specific compound.

Durch die vermehrte Einbindung von Absorptionswärmepumpen und -kältemaschinen in bestehende und zukünftige Energiesysteme des Kälte- und Wärmesektors kann der Anteil erneuerbarer Energien deutlich gesteigert werden. Um dies erfolgreich umsetzen zu können, müssen die Betriebsstrategien und Regelungen dieser Systeme jedoch in der Lage sein, auch mit dynamischen und stark variierenden Betriebsbedingungen umgehen zu können. Dieser Herausforderung hat sich das von der FFG geförderte Projekt HPC – heat pumping system control gewidmet. Im Rahmen dieses Workshops sollen die Ergebnisse und deren Nutzen für die Praxis präsentiert und diskutiert werden.

This abstract gives a glimpse of the output revealed in a project focusing on recycling used medium from algae cultivation. In close cooperation with the University of Natural Resources and Life Sciences Vienna, the Institute of Microbiology - The Czech Academy of Sciences as well as the algae biomass production company Ecoduna GmbH, it was possible to target industrial needs with scientific research approaches.

Tar condensation is a cause of blockage in downstream application of the gasification process. An oil scrubber is considered as an effective method for tar removal. In this research, the naphthalene solubility in different local Thai oils and water was investigated in a laboratory-scale test-rig. The solubility value was conducted at 30, 50, 70, and 80°C. Biodiesels investigated were rapeseed methyl ester (RME) and two different palm methyl esters (PME 1 and PME 2). Furthermore, vegetable oils including sunflower oil, rice bran oil, crude palm oil, and refined palm oil were examined. The results showed that higher temperature enhanced naphthalene solubility in all types of investigated oils. Biodiesel has the highest value of naphthalene solubility. All scrubbing oils have similar naphthalene solubility trends at the temperature range of 50-80°C in the order of RME > PME 1 > PME 2 > diesel > sunflower oil > refined palm oil > rice bran oil > crude palm oil. Based on these experimental investigations, PME 1 has a naphthalene solubility value similar to RME. Therefore, PME 1 has been selected to be tested as scrubbing solvent in the 1 MWel prototype dual fluidized gasifier located in Nong Bua district, Nakhon Sawan province, Thailand.

Chemical-looping combustion (CLC) is a highly efficient CO2 separation technology with no direct contact between combustion air and fuel. A metal oxide is used as an oxygen carrier (OC) and acts in a dual fluidized bed as a separation tool and supplies the fuel with oxygen, which as an oxidation medium causes combustion to CO2 and H2O. The use of solid fuels, especially biomass, is the focus of current investigations. The OC plays a key role, because it must meet special requirements for solid fuels, which are different to gaseous fuels. The ash content, special reaction mechanisms, and increased abrasion make research into new types of OC essential. Preliminary testing of OC before their use in larger plants regarding their suitability is recommended. For this reason, this work shows the design and the results of a laboratory reactor, which was planned and built for fundamental investigation of OC. Designed as a transient fluidized bed, the reactor, equipped with its own fuel conveying system and an in situ solid sampling, is intended to be particularly suitable for cheap and rapid pre-testing of OC materials. During the tests, it was shown that the sampling device enables non-selective sampling. Different OC were tested under various operating conditions, and their ability to convert different fuels could be quantified. The results indicate that OC can be sufficiently investigated to recommend operation in larger plants.

Due to a variety of applications and complex requirements in specific fields of use, the number of different materials is increasing. Thereof, the majority fails at the stage of market introduction, because the focus of material development is mostly on technical aspects, while market aspects are often neglected. One possible way of market introduction is material substitution. Thereby, requirements a material needs to meet are well known. However, a certain market focus on material development would be helpful regarding the final goal of the customer satisfaction. Therefore, this study presents an approach, which aims at guiding the technical material development and thus starts one stage earlier than most other studies, which focus on market introduction. A multi-stage approach helps integrating market aspects into material development, using the following methods: (1) method of Ashby to compare materials from a technical point of view and identify theoretically substitutable material groups and potential applications, (2) market data research and comparison for the identification of attractive markets, (3) method of Kano to classify material requirements and prioritize the optimization of material properties to satisfy the customers in selected markets. This approach is showcased and discussed using the example of an innovative wood composite under development, where it represented an aiding tool for guiding the further material development. An adaptation to any other material is possible at each of the three stages, although there are some limitations, which have to be considered, for example the selection of technical properties for the material comparison.

Interactions between olivine or silica sand and potassium (K)-rich grape marc or silicon (Si)-rich wheat straw were studied in a fixed-bed reactor under combustion, steam, or a CO₂ gasification atmosphere. This study focused on the effects of atmosphere composition, feedstock, and bed material type on the thermochemical aspects of agglomeration. The agglomeration extent of grape marc with olivine as the bed material under air and steam atmospheres is significantly less than with silica sand. The presence of CO₂, compared to that of O₂ or steam, was found to promote the reaction between K and olivine by facilitating the production of reactive silica from olivine carbonization. The use of olivine promotes the release of K by more than 10% compared with silica. No significant differences were observed in the agglomeration extent of wheat straw in its interaction with either olivine or silica sand. Nevertheless, olivine alters the agglomeration mechanism of wheat straw to become “melting-induced” from “coating-induced” in a silica bed.

Interactions between olivine or silica sand and potassium (K)-rich grape marc or silicon (Si)-rich wheat straw were studied in a fixed-bed reactor under combustion, steam, or a CO2 gasification atmosphere. This study focused on the effects of atmosphere composition, feedstock, and bed material type on the thermochemical aspects of agglomeration. The agglomeration extent of grape marc with olivine as the bed material under air and steam atmospheres is significantly less than with silica sand. The presence of CO2, compared to that of O2 or steam, was found to promote the reaction between K and olivine by facilitating the production of reactive silica from olivine carbonization. The use of olivine promotes the release of K by more than 10% compared with silica. No significant differences were observed in the agglomeration extent of wheat straw in its interaction with either olivine or silica sand. Nevertheless, olivine alters the agglomeration mechanism of wheat straw to become “melting-induced” from “coating-induced” in a silica bed.

Local and renewable energy communities show a high potential for the efficient use of distributed energy technologies at regional levels according to the Clean Energy Package of the European Union. However, until now there are only limited possibilities to bring such energy communities into reality because of several limitation factors. Challenges are already encountered during the planning phase since a large number of decision variables have to be considered depending on the number and type of community participants and distributed technologies. This paper overcomes these challenges by establishing a mixed-integer linear programming based optimal planning approach for renewable energy communities. A real case study is analyzed by creating an energy community testbed with a leading energy service provider in Austria. The case study considers nine energy community members of a municipality in Austria, distributed photovoltaic systems, energy storage systems, different electricity tariff scenarios and market signals including feed-in tariffs. The key results indicate that renewable energy communities can significantly reduce the total energy costs by 15% and total carbon dioxide emissions by 34% through an optimal selection and operation of the energy technologies. In all the optimization scenarios considered, each community participant can benefit both economically and ecologically.

Three estimators for the estimation of the flue gas mass flow in biomass boilers are presented and compared, namely a sliding-mode observer, a Kalman filter, and a so-called steady-state estimator. The flue gas mass flow is an important process variable in biomass boilers as it contains information about the supplied mass flows of air and decomposed fuel. It is also related to the generated heat flow. Furthermore, its knowledge may be exploited in model-based control strategies which allow one to keep pollutant emissions low, on the one hand, and to achieve high efficiency, on the other hand. However, due to fouling of the equipment over time, measurements and existing estimation methods are not suitable for long-term applications. The estimators proposed in this article are based on a dynamic model for gas tube heat exchangers. They are capable of handling the fouling of the heat exchanger and, additionally, they offer the possibility of monitoring the degree of fouling. By incorporating an additional differential pressure measurement and extending the aforementioned estimators, an improvement regarding the dynamic response and the estimation accuracy is achieved. The application of the estimators to real measurement data from both, a medium-scale and a small-scale biomass boiler, demonstrates their wide applicability.

Heat makes up the largest share of energy end-use, accounting for 50% of global final energy consumption in 2018 and contributing to about 40% of global carbon dioxide (CO2) emissions. Of the total heat produced, about 46% was consumed in buildings for space and water heating. Large-scale solar thermal systems provide a highly valuable possibility to increase the share of renewables in heating systems and to reduce carbon dioxide emissions. In this context, the worldwide number of large-scale solar heating systems has increased rapidly in the last couple of years, especially in China and European countries, e.g. in Denmark. This has led to the installation of about 400 large-scale solar thermal systems ( ≥ 350kWth, 500m²) by the end of 2019.
Unlike other heating systems, their main source of power (solar radiation) cannot be manipulated and is subject to changes on a seasonal as well as on a daily basis. That is why control systems play a very important role for the efficient operation of these systems. This thesis therefore focuses on the application of model-based control strategies, and the necessary preliminary work regarding modelling, in order to achieve an efficient control of large-scale solar thermal systems. Consequently, the thesis addresses three important aspects:
In the first main section, models of components of large-scale solar thermal systems are developed and validated. For the most important components (heat exchanger, solar collector and sensible heat storage), two models of different complexity, one simulation-oriented, one control-oriented, are developed. While the simulation-oriented models aim to model the physical behaviour very accurately in order to be used in simulation studies, control-oriented models aim to model the physical behaviour only as accurately as necessary in order to serve as a basis for model-based control strategies. All models are validated with measurement data from a typical solar system, and it is shown that they are sufficiently accurate for their intended purpose. The sum of the models provides a holistic view on all modelling aspects that have to be considered in large-scale solar thermal plants, and serves as a reasonable basis for model-based control strategies and accurate simulation studies of solar systems.
In the second main section, adaptive forecasting methods for the future solar heat production as well as the heat demand are developed and validated with measurement data and using real weather forecasts. These methods are important to most efficiently integrate and operate solar systems by better scheduling heat production, storage and distribution for the near future. In order to be used in real-world applications, the methods are developed with the goal to meet three important practical requirements: simple implementation, automatic adaption to seasonal changes, and wide applicability. The final long-term evaluation for half a year proves that the developed methods can forecast the solar heat production as well as the heat demand very accurately and outperform common forecasting methods, yielding results that are nearly twice as accurate.
In the third main section, model-based control strategies for the high-level as well as for the low-level control of solar thermal systems are developed and validated. For the high-level control an approach is presented which considers future information by using the developed forecasting methods. It achieves higher profits (plus 3 %) and leads to a more stable operation, compared to the existing commercial solution. For the low-level control, model-based control strategies based on the developed models for the heat generation and distribution are presented. The model-based control strategy for the heat generation considers the dynamic behaviour of the collector and especially considers the variable time-delay. This, compared to conventional control strategies, leads to a significantly better control performance in case of fluctuating solar radiation and changing inlet temperatures. The model-based control strategy for the heat distribution follows a modular approach which can be applied for several hydraulic settings, leading to an accurate and independent control of mass flow and temperature, and outperforms state-of-the-art control strategies. For both control levels, care was taken that the applied strategies can be used in real-world applications regarding their mathematical complexity and computational resources required.
In summary, this thesis presents a holistic approach regarding modelling (simulation-oriented models, control-oriented models and adaptive forecasting methods) and control aspects (high-level as well as low-level control) which can help to improve the efficiency of large-scale solar thermal plants on various levels, making them more competitive, and is furthermore essential for a successful integration of these plants in larger energy systems.

Fixed-bed biomass conversion with a low primary air ratio and a counter-current configuration has a high feedstock flexibility, as it resembles updraft gasification, and the potential to reduce emissions when integrated in biomass combustion systems. A 1D bed model was validated with experimental results from a biomass combustion boiler with such a bed conversion system, predicting with a good accuracy the temperatures in the reactor and producer gas composition. The model was applied for different cases to investigate the fuel flexibility of this combustion system, including the influence of moisture content and the maximum temperatures achieved in the bed. It was shown that with variations in fuel moisture content from 8 to 30% mass w.b. the producer gas composition, char reduction to CO or maximum temperatures at the grate were not affected due to the separation of the char conversion and pyrolysis/drying zones. Flue gas recirculation was the only possible measure with the tested configuration to reduce the maximum temperatures close to the grate, which is beneficial e.g. to avoid slagging with complicated fuels. A higher tar content was obtained than in conventional updraft gasifiers, which is attributed to the absence of tar condensation in the bed due to the limited height of the reactor and the integration in the combustion chamber. The presented model can support the development of such combustion technologies and is a relevant basis for detailed CFD simulations of the bed or gas phase conversion.

The growth of district heating and cooling (DHC) networks introduces the possibility of connecting them with neighbouring networks. Coupling networks can save costs by reducing operating hours of peak load or backup boilers, or free up production capacity for network expansion. Optimization-based energy management systems (EMS) already provide operators of individual DHC networks with solutions to the unit commitment and economic dispatch problem. They are especially useful for complex networks with multiple producers and integrated renewable energy sources, where incorporating forecasts is important. Time-dependent constraints and network capacity limitations can easily be considered. For coupled networks, a centralized optimization would provide a minimum with respect to an objective function which can incorporate fuel costs, operational costs and costs for emissions. However, the individual coupled networks are generally owned by different organizations with competing objectives. The centralized solution might not be accepted, as each company aims to optimize its own objective. Additionally, all data has to be shared with a centralized EMS, and it represents a single point of failure. A decentralized EMS may therefore be a better choice in a multi-owner setting. In this article, a novel decentralized EMS is presented that can handle multi-owner structures with cooperative and non-cooperative coupling. Each local EMS solves its own optimization problem, and an iterative Jacobi-style algorithm ensures consensus among the networks. The distributed EMS is compared to a centralized EMS based on a representative real-world example consisting of three coupled district heating networks operated by two companies.

The simultaneous operation of multiple connected heating networks can be handled by optimization techniques. However, a global optimum might not represent a good operating strategy if the networks belong to different owners and thus might habe competing interests. An approach from game theory then needs to be applied, which finds a generalized Nash equilibrium instead.