Holzpellets werden in zunehmendem Maße aus Hackschnitzel hergestellt. Es ist davon auszugehen, dass diese Veränderung der Rohstoffbasis zu erhöhten Aschegehalten im Brennstoff führt und zu Schwierigkeiten bei der Nutzung führen kann. Die vorliegende Arbeit kommt zum Schluss, dass moderate Anteile (< 5%) sauberer Rinde zu keinen wesentlichen Verschlackungen führen. Bei Verunreinigung oder / und sehr hohen Rindenanteilen ist mit
Verschlackungsproblemen jedenfalls zu rechnen.

The release of potassium during biomass combustion leads to several problems as the emissions of particle matter or formation of deposits. K release is mainly described in literature in a qualitative way and this work aims to develop a simplified model to quantitatively describe it at different stages. The proposed model has 4 reactions and 5 solid species, describing K release in 3 steps; during pyrolysis, KCl evaporation and carbonate dissociation. This release model is coupled into a single particle model and successfully validated with experiments conducted in a single particle reactor with spruce, straw and Miscanthus pellets at different temperatures. The model employs same kinetic parameters for the reactions in all cases, while different product compositions of the reactions are employed for each fuel, which is attributed to differences in composition. The proposed model correctly predicts the online release at different stages during conversion as well as the final release for each case.

For many fluidized bed applications, the particle movement inside the reactor is accompanied by reactions at the particle scale. The current study presents for the first time in literature a multi-scale modelling approach coupling a one-dimensional volumetric particle model with the dense discrete phase model (DDPM) of ANSYS Fluent via user defined functions. To validate the developed modelling approach, the current study uses experimental data of pressure drop, temperature and gas composition obtained with a lab-scale bubbling fluidized bed biomass gasifier. Therefore, a particle model developed previously for pyrolysis was modified implementing a heat transfer model valid for fluidized bed conditions as well as kinetics for char gasification taken from literature. The kinetic theory of granular flow is used to describe particle–particle interactions allowing for feasible calculation times at the reactor level whereas an optimized solver is employed to guarantee a fast solution at the particle level. A newly developed initialization routine uses an initial bed of reacting particles at different states of conversion calculated previously with a standalone version of the particle model. This allows to start the simulation at conditions very close to stable operation of the reactor. A coupled multi-scale simulation of over 30 s of process time employing 300.000 inert bed parcels and about 25.000 reacting fuel parcels showed good agreement with experimental data at a feasible calculation time. Furthermore, the developed approach allows for an in-depth analysis of the processes inside the reactor allowing to track individual reacting particles while resolving gradients inside the particle.

Fluidized bed biomass gasification is a complex process whereby gas source terms are released by reactions at the particle level during the movement of fuel particles throughout the reactor. The current study presents for the first time the application of a multi-scale modelling approach for a fluidized bed biomass gasifier of industrial size, coupling a detailed one-dimensional particle model based on the progressive conversion model (PCM) with a commercial CFD software. Results of particle movement and gas source terms are compared with results of an additional simulation employing the simplified uniform conversion model (UCM) which is commonly used in literature. Validation at the particle level showed that the UCM leads to a massive underprediction of the time needed for pyrolysis whereas the PCM is in good agreement with experimental data. This heavily influences the gas sources released during pyrolysis of the biomass particles in the coupled reactor simulations. Volatiles are much more concentrated to the close proximity of the fuel feed when using the UCM whereas the PCM leads to a more homogeneous distribution over the reactor cross-section. The calculation time analysis of the coupled simulations showed that despite the increased complexity, the PCM shows only an increase of 20% in calculation time when compared to the UCM, whereas it is much better suited for these conditions. The coupled multi-scale simulations using the PCM showed the numerical feasibility of the modelling approach for 1,200,000 bed parcels and about 80,000 reacting fuel parcels and furthermore highlighted the importance of a comprehensive description of the particle level.

A transient 3D model for two main zones, namely the fuel bed and the freeboard, of biomass packed bed combustion systems was developed. It integrates the models for the biomass conversion sub-processes and solves the governing equations for the gas and solid phase and their interactions. The intra-particle gradients are included by considering the biomass particles as thermally thick particles. The shrinkage of the packed bed and the variations of the bed porosity due to the uneven consumption of the fuel are taken into account. Detailed kinetic mechanisms are used for the simulation of homogeneous gas phase reactions. To verify the model and to increase the understanding of packed bed combustion, laboratory-scale fixed-bed batch experiments have been performed in a reactor with 9.5 cm diameter and 10 cm length. The model performance was extensively validated with gas phase measurements (CO, CO₂, CH₄, H₂, H₂O and O₂) above the fuel bed, temperatures at different heights in the bed and in the freeboard, and the propagation rate of reaction front. The simulation results are in a good agreement with the measured values. © 2014 Elsevier Ltd. All rights reserved.

The use of renewable-energy-based heat producers within district heating grids is getting more and more popular. In order to benefit from the advantages and compensate for the different disadvantages of the various types of heat producers powered by renewable energy sources like biomass, solar energy or waste heat, a combination of these systems could be favoured over using, for example, only one main biomass-based boiler. Furthermore , in many cases, the additional use of buffer storages is necessary to fully benefit from the use of these kinds of heat producers. A major challenge with such multi-producer heating grids is the cost optimal management of all heat producers and buffer storages. Therefore , a high-level control strategy is necessary, which is able to plan ahead the use of slowly reacting and/or weather dependent heat producers while minimizing operational costs and pollutant emissions. This article shows the development of a linear model predictive controller (MPC) for a district heating grid with several (renewable) decentralized heat producers and heat storages. In order to provide the MPC with the required forecast of the future heat demand, an adaptive load forecasting method has been designed. Additionally, in order to be able to incorporate solar panels, the MPC needs to have a forecast of their possible future heat output. Therefore, a physically motivated solar yield forecasting method has been designed. The required prediction models for the MPC were represented by so-called mixed logical dynamical (MLD) system models. MLD system models combine the modelling power of discrete state system models (finite state machines) and discrete time system models by the extension of the regular linear state-space system model approach with integer and continuous auxiliary variables and linear inequality constraints. The occurrence of both integer and continuous variables within the resulting optimization problem of the MPC leads to a mixed-integer linear program (MILP), which can be solved efficiently using modern MILP solvers. The resulting control strategy is tested in a thermo-hydraulic simulation environment of an actual small-scale multi-producer district heating grid consisting of a medium-scale wood chip boiler with buffer storage, a solar collector with buffer storage and a high temperature heat pump, an oil boiler and 25 heat consumers. Additionally, a state observer was designed and connected with the MPC in order to detect control errors and to incorporate feedback from the heat producers and the buffer storages. The simulations have indicated that the designed MPC and the state observer work properly. Therefore, these elements have been implemented on-site on the actual heating grid, with the first test run scheduled for October 2017.
Modellprädiktive Regelung eines solar-und biomassebasierten Fernwärmenetzes | Request PDF. Available from: https://www.researchgate.net/publication/321314304_Modellpradiktive_Regelung_eines_solar-und_biomassebasierten_Fernwarmenetzes [accessed Feb 21 2018].

A new mathematical model for the grate combustion of biomass has been derived from physical considerations. Various models for grate combustion can already be found in the literature. Usually their intention is to simulate the real situation in a furnace as precisely as possible. Hence they are very detailed, typically consisting of many partial differential equations. However, because of their complexity they are useless for control purposes. The new model is very simple, consisting of only two ordinary differential equations, which makes it particularly suitable as a basis for model based control strategies. To verify the model, experiments were performed at a pilot scale furnace with horizontally moving grate. The pilot plant is a downscaled version (180 kW_th) of a typical medium scale furnace in terms of geometry and instrumentation. Comparison of the measured and calculated values shows good agreement. © 2009 Elsevier Ltd. All rights reserved.

 Im Bereich der thermischen Biomassenutzung (speziell Rostfeuerungen) werden CFD-Simulationen eingesetzt, um Hilfestellung bei der Diagnose und Lösung von Betriebsproblemen zu leisten sowie bei der Entwicklung von neuen Feuerungen und Kesseln zu unterstützen. Zurzeit sind keine Modelle verfügbar, mit denen sowohl die Vorgänge im Brennstoffbett als auch in der Gasphase einer Biomasse-Rostfeuerung mit Hilfe von detaillierten numerischen Modellen bei akzeptabler Berechungszeit simuliert werden können. Um die direkte Kopplung des Bett-Modells mit der Gasphase zu bewerkstelligen, ist es nötig, ein geeignetes Partikel-Modell zu entwickeln, welches die thermische Konversion (Trocknung, Pyrolyse und Holzkohle-Ausbrand) von thermisch dicken Biomassepartikeln beschreibt und mit bereits vorhandenen CFD-Modellen für die Gasphasensimulation gekoppelt werden kann. In diesem Schalenmodell werden die einzelnen Biomassepartikel als thermisch dick behandelt, d.h. die Temperaturgradienten in den einzelnen Partikeln sowie der gleichzeitige Ablauf mehrerer Umwandlungsprozesse berücksichtigt. Das Schalenmodell wurde mit Hilfe von gemessenen Partikeloberflächen- und -zentrumstemperaturen sowie mit Messwerten des Gesamtmasseverlustes während der Verbrennung in einem Einzel-Partikelreaktor validiert. Ein weiteres Problem, das bei der Simulation von Biomasse-Rostfeuerungen auftritt, ist die Modellierung der Gas-Festkörper-Mehrphasenströmung. Das Modell muss dabei in der Lage sein, den Einfluss der Partikel-Partikel-Wechselwirkung währenden der Partikelbewegung am Rost korrekt zu beschreiben. Aus diesem Grund wurde durch Kopplung von Euler- und Lagrange Mehrphasenströmungs- Ansätzen ein neues, dreidimensionales Schüttungsmodell entwickelt. Dabei wird die Partikelbewegung am Rost mit Hilfe eines Euler-Ansatzes (Euler-Granular-Modell) beschrieben, während die thermische Umwandlung der Biomassepartikel mit Hilfe eines Lagrange-Ansatzes und dem entwickelten Einzelpartikelmodell beschrieben wird. Das 3D-Festbettmodell für Biomasserostfeuerungen wurde eingesetzt, um eine 20 kW Biomasse-Unterschubfeuerung zu simulieren. Da es keine experimentelle Daten hinsichtlich der Bedingungen im Brennstoffbett gab, wurden qualitative Informationen hinsichtlich der Positionen der Trocknungs-, Pyrolyse- und Holzkohle-Ausbrandzonen, sowie mit Thermoelementen gemessenen Rauchgastemperaturen an verschiedenen Positionen in der Brennkammer zum Vergleich mit den Simulationsergebnissen herangezogen. Des Weiteren erfolgte im Zuge dieser Arbeit eine Weiterentwicklung des Festbett-Modells, indem der Strahlungsaustausch zwischen den Partikeln sowie detaillierte kinetische Modelle für die Gasphasenverbrennung im Modell implementiert wurden. Das weiterentwickelte Modell wurde mit Hilfe von experimentellen Daten aus Testläufen in einem Festbett-Laborreaktor validiert. Diese Messdaten beinhalten gemessene Konzentrationen von CO, CO2, CH4, H2, H2O und O2 im Rauchgas über dem Brennstoffbett sowie Temperaturen in unterschiedlichen Positionen im Bett und über dem Bett. Die vorhergesagten Werte zeigten eine gute Übereinstimmung mit den gemessenen Werten.

Primary devolatilization and the exothermic heterogeneous secondary charring of the primary volatiles need to be described in a consistent manner in order to correctly predict the heat of reaction of biomass pyrolysis. Detailed reaction schemes can currently predict mass loss and product composition of biomass pyrolysis with good accuracy, but have a weakness in the description of the heat of reaction. In this work it is shown for the first time that including secondary charring reactions a detailed reaction scheme can predict the evolution of the heat of pyrolysis for different conditions. The enthalpy of reaction is calculated for each reaction as the difference between the net calorific value of reactants and products. The presented model is able to describe the heat evolution in micro-TGA-DSC experiments conducted without a lid, where pyrolysis is endothermic, and with a lid, where secondary reactions are enhanced and the global heat of reaction shifts to exothermic. Furthermore, when it is coupled to a particle model, it correctly describes single particle pyrolysis experiments conducted with beech spheres where there is a remarkably exothermic peak in the centre temperature.

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.

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.

Die Verbrennung fester Biomasse gewinnt als nachhaltige Form der Energieerzeugung stetig an Bedeutung. Eine mögliche Technologie stellen dabei Biomasse-Thermoölkesselanlagen dar, deren Regelungen bis jetzt noch nicht auf einem mathematischen Modell basieren und dementsprechend deren verkoppeltes und zum Teil nichtlineares Verhalten nur ungenügend berücksichtigen. Ziel dieser Arbeit ist es, ein für Biomassefeuerungsanlagen mit Wasserkesseln existierendes Modell sowie die darauf aufbauende Regelungsstrategie an die speziellen Gegebenheiten von Thermoölkesselanlagen anzupassen. Dazu wird zunächst ein einfaches Modell für Thermoölwärmeübertrager auf Basis einer Energiebilanz hergeleitet und anhand von verfügbaren Betriebsdaten qualitativ verifiziert. Anschließend wird die bei der Regelung von Wasserkesselanlagen eingesetzte Eingangs-Ausgangslinearisierung verallgemeinert. Darauf aufbauend wird eine Regelungsstrategie zur Regelung des Thermoölwärmeübertragers hergeleitet. Die Leistungsfähigkeit des Regelungskonzeptes wird schließlich in Simulationsstudien gezeigt. 

Die vorliegende Arbeit widmet sich der Herleitung mathematischer Simulationsmodelle eines Pufferspeichers, eines Solarkollektors sowie eines Plattenwärmeübertragers. Dabei wird das Simulationsmodell des Pufferspeichers anhand eines am Markt verfügbaren Pufferspeichers entwickelt. Die mathematischen Beschreibungen der Simulationsmodelle basieren auf einer partiellen Differentialgleichung zur Beschreibung der Wärmeübertragung in einem durchströmten zylindrischen Rohr. Nach dem Erhalt der mathematischen Modelle werden diese mit einem impliziten Lösungsverfahren numerisch gelöst. Anschließend werden die experimentell zu ermittelnden Parameter des Pufferspeichermodells anhand gezielt durchgeführter Versuche bestimmt. Nach dem Ermitteln der Parameter wird das Simulationsmodell des Pufferspeichers mit einem weiteren Versuch experimentell verifiziert. Schlussendlich bildet das mathematische Modell des Pufferspeichers den untersuchten Pufferspeicher sehr zufriedenstellend ab, womit ein Simulationsmodell vorliegt, das gezielte Untersuchungen ohne aufwändige Versuche ermöglicht. Abschließend wird eine Regelung für die Wärmeübertragung aus dem Solarkollektor in den Pufferspeicher entwickelt. Dabei werden zwei in der Praxis übliche Verfahren untersucht. Bei der ersten Variante erfolgt die Übertragung der Wärme in den Pufferspeicher über ein im Pufferspeicher integriertes Solarregister. Bei der zweiten Variante erfolgt die Übertragung der Wärme über einen Plattenwärmeübertrager vom Wasser-Frostschutzgemisch auf Wasser, welches dann direkt in den Pufferspeicher eingespeist wird. Als Reglerstruktur wird in beiden Fällen ein Standard-Regelkreis mit einer statischen Vorsteuerung verwendet. Anhand von Simulationsstudien werden zunächst die Parameter des PI-Reglers festgelegt und in weiterer Folge die mit der jeweiligen Variante resultierenden Temperaturverläufe des Wassers im Pufferspeicher untersucht und gegenübergestellt. Dabei stellt sich heraus, dass die Temperatur des Wassers im Pufferspeicher, bei gleich bleibender Strahlungsstromdichte der Solarstrahlung Igauf den Solarkollektor, die gewünschte Solltemperatur bei Wärmeübertragung mittels Plattenwärmeübertrager schneller erreicht, als bei Wärmeübertragung durch das Solarregister. Darüber hinaus ermöglicht die Verwendung des Plattenwärmeübertragers eine Schichtung der Temperatur des Wassers im Pufferspeicher und somit eine Speicherung der Wärme auf einen höheren Temperaturniveau.

For an appropriate operation of a heat exchanger it is very helpful to know its dynamic behaviour. To this a simple sufficient accurate nonlinear model for the description of the dynamic behaviour is derived on the basis of a gas tube heat exchanger. Due to the general approach used for the derivation the model could be adaptet easily for other types of heat exchangers. The presented model can be used to estimate not measured physical values, to monitor the deposit formation in the heat exchanger and as a basis for the design of a model based control strategy. © Oldenbourg Wissenschaftsverlag.

Scheitholzkessel sind die in Europa immer noch am stärksten verbreitete Form von Holz-basierten Zentralheizungssystemen. Der Bestand ist überaltert und weist die größten Anteile an den verursachten Schadstoffemissionen aus Festbrennstoffzentralheizungssystemen auf. Das Ziel des Projektes, die komplette Neuentwicklung einer modellbasierten Regelung für Scheitholzkessel mit Pufferspeichern und einer Solaranlage, stellte einen Technologie-sprung in Richtung einer drastischen Reduktion der Schadstoffemissionen (CO, org. C, Fein-staub) bei gleichzeitiger Erhöhung des Nutzungsgrades und Benutzerkomforts dar. Dabei erfolgte sowohl die übergeordnete Regelung des Zusammenspiels der Komponenten (Systemregelung) als auch die Regelung der einzelnen Komponenten (Feuerungsregelung, Hydraulikregelung) modellbasiert. Die neue Regelung basiert auf einer gezielten Interaktion mit dem Benutzer, in welcher der Benutzer zielgerichtet zum Nachlegen einer bestimmten Brennstoffmenge in einem bestimmten Zeitraum aufgefordert wird. Zusätzlich dazu werden alle Teilprozesse (Verbrennung des Scheitholzes, Übertragung der Wärme in den Pufferspeicher, usw.) modellbasiert und damit deutlich effizienter und genauer geregelt. Im Fall der Feuerungsregelung wurde zusätzlich zur modellbasierten Regelung von Vorlauf-temperatur und Sauerstoffgehalt auch eine innovative CO-l-Regelung eingesetzt, die basierend auf einer kontinuierlichen Schätzung der CO- l-Charakteristik unter Verwendung eines kombinierten Sensors zur Sauerstoffmessung und Detektion unverbrannter Kompo-nenten stets einen für den aktuellen Betriebszustand optimalen Sollwert für den Sauer-stoffgehalt vorgibt. Die laufende Anpassung des Sauerstoffgehaltes führt zu einer deutlichen Reduktion der Schadstoffemissionen (CO, org. C, Feinstaub). Zum Erreichen dieser Ziele wurden im Wesentlichen folgende Schritte durchgeführt:

• Experimentelle Untersuchung und Modellierung des Abbrandverhaltens von Scheitholz (inklusive der CO-l-Charakteristik)
• Entwicklung einer übergeordneten modellbasierten Systemregelung
• Entwicklung einer modellbasierten Feuerungsregelung (inkl. CO-l-Regelung) für einen effizienten und schadstoffarmen Betrieb des Scheitholkessels
• Experimentelle Bewertung des Potentials der modellbasierten Regelung
• Analyse der Anforderungen zur Anpassung der Regelung an andere Konfigurationen

Das beantragte Projekt leistete somit einen entscheidenden Beitrag zum Ausschreibungs-schwerpunkt „Effiziente und emissionsarme Klein- und Kleinstfeuerungen durch Integration einer intelligenten Verbrennungs- und Leistungsregelung“ und ging zusätzlich explizit auf die im Ausschreibungsleitfaden adressierte Verwendung von kombinierten Sensorsystemen wie CO- l-Sensorsysteme zur Verbrennungsregelung ein. Dabei ist insbesondere hervorzuheben, dass der durchdachte Ansatz das Sensorsignal zu Schätzung der CO- l-Charakteristik zu verwenden den wesentlichen Vorteil mit sich bringt, dass die exakte Messung der CO-Emissionen durch den Sensor nicht erforderlich ist, sondern es ausreicht, wenn dieser die Tendenzen richtig wiedergibt.

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.

The integration of solar thermal plants into district heating grids requires advanced control strategies in order to utilize the full potential in terms of efficiency and least operating effort. State-of-the-art control strategies cannot completely fulfil this since they are not able to consider the physical characteristics of the different components, nor do they take information on future conditions and requirements into account properly. A promising attempt for improvement is the application of model-based control strategies together with practicable forecasting methods for both the solar yield as well as the heat demand. This contribution will present the results of several projects performed on the development of suitable mathematical models, forecasting methods and control strategies relevant for the integration of solar thermal plants into district heating grids.

With the share of renewable energy sources increasing in heating and hot water applications, the role of hydraulic heat distribution systems is becoming more and more important. This is due to the fact that in order to compensate for the often fluctuating behaviour of the renewables a flexible heat transfer must be ensured by these distribution systems while also taking the optimal operating conditions (mass flow, temperature) of the individual components into consideration. This demanding task can be accomplished by independently controlling the two physical quantities mass flow and temperature. However, since there exists an intrinsic nonlinear coupling between these quantities this challenge cannot be handled sufficiently by decoupled linear PI controllers which are currently state-of-the-art in the heating sector. For this reason this paper presents a model-based control strategy which allows a decoupled control of mass flow and temperature. The strategy is based on a systematic design approach from models described in this contribution, which are validated by commercially available components from which most of them can be parametrized by the data sheet. The control strategy is designed for a typical hydraulic configuration used in heating systems, which will allow the accurate tracking of the desired trajectories for mass flows, temperatures and consequently heat flows. The controllers are validated experimentally and compared to well-tuned state-of-the-art (PI) controllers in order to illustrate their superiority and prove their decoupling of the control of mass flow and temperature in real world applications.

Absorption heat pumping systems (AHPSs, comprising absorption heat pumps and chillers) are devices that mainly use thermal energy instead of electricity to generate heating and cooling. This thermal energy can be provided by, e.g., waste heat or renewable energy sources such as solar energy, which allow AHPSs to contribute to ressource-efficient heating and cooling systems. Despite this benefit, AHPSs are still not a widespread technology. One reason for this is unsatisfactory controllability under varying operating conditions, which results in poor modulation and partial load capability. Emloying model-based control is a promising approach to address this issue, which will be the focus of this  contribution.
First, a viable control-oriented model for AHPSs is developed. It is based on physical correlations to facilitate systematic adaptions to different scales and operating conditions and considers only the most relevant mass and energy stores to keep the model order at a minimum. The resulting model is mathematically simple but still has the structure of a nonlinear differential-algebraic system of equations. This is typical for models of thermo-chemical
processes, but is unfortunately not suitable for many control design methods. Therefore, linearization at an operating point is discussed to derive a model in linear state space representation. Experimental validation results show that the linearized model does have slightly worse steady-state accuracy than the nonlinear model, but that the dynamic accuracy seems to be almost unaffected by the linearization and is considered sufficiently good to be used in control design.
As a next step, the linearized model is used to design model-based control strategies for AHPSs. A special focus is put on redundantly-actuated configurations, i.e. configurations with more manipulated variables than controlled variables, which allows using additional degrees of freedom to extend the operating range of AHPS and hence improve their partial load capability. Two model-based control approaches are discussed: First, a linear model predictive control (MPC) approach is presented - a well-established and generally easy-to-parameterize approach, which, however, often results in high computational effort prohibitive to its implementation on a conventional PLC. Therefore, a second control approach based on state feedback is presented which is mathematically simple enough for implementation on a conventional PLC. It consists of an observer for state variables and unknown disturbances, a state feedback controller and, in case of redundantly-actuated configurations, a dynamic control allocation algorithm. Both approaches are experimentally validated and compared to a state-of-the art control approach based on SISO PI control, showing that the model-based MIMO control approaches allow for a wider operating range and hence better modulation and partial load capability compared to the SISO PI approach. This, in turn, reduces ON/OFF operation of AHPSs and also facilitates their integration into complex energy systems to generate heating and cooling in a ressource-efficient manner.

Absorptionswärmepumpenanlagen (AWPA, beinhaltet Absorptionswärmepumpen und –kältemaschinen), sind Anlagen, die hauptsächlich thermische statt elektrischer Energie nutzen, um Wärme und Kälte zu generieren. Dadurch wird die Nutzung von Abwärme und erneuerbaren Energiequellen wie Solarenergie in Heiz- und Kühlsystemen erleichtert. Trotz dieses Vorteils ist der Einsatz von AWPA nach wie vor stark eingeschränkt. Ein Grund dafür ist das Fehlen von Regelungsstrategien, die eine zufriedenstellende Regelgüte über einen weiten Betriebsbereich, insbesondere unter Teillast, bieten. Deshalb befasst sich diese Arbeit mit der Entwicklung eines neuen, modellbasierten Regelungsansatzes für AWPA, die den Betriebsbereich durch den Einsatz von Mehrgrößen-Regelungsmethoden (multi-input-multi-output (MIMO) Regelungsmethoden) erweitern kann.



Zunächst wird ein geeignetes dynamisches Modell abgeleitet, das im modellbasierten Regelungsansatz verwendet werden soll. Es handelt sich um ein physikalisch basiertes Modell mit modularer Struktur, was eine systematische Anpassung an verschiedene AWPA erleichtert. Um die Anzahl der Zustandsvariablen niedrig zu halten, werden nur diejenigen Masse- und Energiespeicher berücksichtigt, die zu Zeitkonstanten und Totzeiten führen, die für die spätere Regelungsaufgabe relevant sind. Das entwickelte Modell ist mathematisch einfach, hat jedoch die Struktur eines nichtlinearen differential-algebraischen Gleichungssystems. Als solches ist es sehr gut als Simulationsmodell geeignet um verschiedene Regelungsstrategien in der Simulation zu testen, aber es ist zu komplex für viele modellbasierte Regelungsmethoden. Um eine noch einfachere Modellstruktur zu erhalten, wird das Modell an einem Betriebspunkt linearisiert, was auf ein Modell in linearer Zustandsraumdarstellung führt. Die entwickelten nichtlinearen und linearen Modelle werden experimentell validiert und mit zwei alternativen Modellierungsansätzen als Benchmark verglichen. Ein Vergleich zwischen dem abgeleiteten nichtlinearen Modell und den Benchmark-Modellen zeigt eine höhere Genauigkeit für das neue Modell, sowohl stationär als auch dynamisch. Ein Vergleich zwischen dem abgeleiteten nichtlinearen und dem linearisierten Modell zeigt, dass das linearisierte Modell zwar eine etwas schlechtere stationäre Genauigkeit aufweist, die dynamische Genauigkeit jedoch durch die Linearisierung nahezu unbeeinflusst zu sein scheint. Das vorgestellte neue linearisierte AWPA -Modell gilt daher als geeignet, als Grundlage für den Entwurf des modellbasierten Regelansatzes verwendet zu werden.



Als nächstes wird dieses Modell verwendet, um einen neuen modellbasierten Regelungsansatz für AWPA zu entwerfen. Der neue Regelungsansatz kann für verschiedene AWPA-Anwendungen und damit für verschiedene Regelungskonfigurationen verwendet werden, d.h., verschiedene Kombinationen von Stell- und Regelgrößen. Er kann auch für redundante aktuierte Konfigurationen mit mehr Stell- als Regelgrößen verwendet werden, was die Erweiterung des Betriebsbereichs einer AWPA ermöglicht. Der Ansatz besteht aus einem Beobachter für die Zustandsvariablen und unbekannte Störgrößen, einem Zustandsregler und, im Falle von redundant aktuierten Konfigurationen, einem Algorithmus zur dynamischen Stellgrößenverteilung. Der vorgeschlagene Regelungsansatz wird experimentell für zwei verschiedene Regelungskonfigurationen validiert und mit zwei Benchmark-Ansätzen verglichen – einem Eingrößen-PI-Regler (Single-input-single-output (SISO) PI-Regler), der den Stand der Technik repräsentiert, und einem modellprädiktiven Regelungsansatz (model predictive control, MPC) als alternative fortschrittliche Regelungsmethode. Die experimentelle Validierung zeigt, dass die beiden MIMO-Regelungsansätze (der vorgeschlagene Zustandsregler und der MPC-Ansatz) einen erweiterten Betriebsbereich und somit eine bessere Teillastfähigkeit im Vergleich zum SISO-PI-Regler ermöglichen. Während MPC durch die Notwendigkeit zur kontinuierlichen Lösung eines Optimierungsproblems im Allgemeinen eine vergleichsweise hohe Rechenleistung benötigt, ist der vorgeschlagene Zustandsregler-Ansatz mathematisch einfach genug, um auf herkömmlichen speicherprogrammierbaren Steuerungen für AWPA implementiert werden zu können. Er wird daher als vielversprechender neuer Regelungsansatz für AWPA betrachtet, der die Möglichkeit bietet, ihren Betriebsbereich zu erweitern und ihre Teillastfähigkeit zu verbessern, was wiederum eine einfachere Einbindung in moderne Energiesysteme ermöglicht und somit die Nutzung nachhaltiger Wärmequellen für Heizen und Kühlen erleichtert.

Optimization-based energy management systems (EMS) are a high-level control approach for energy systems like district heating networks. A descriptive model and objective function are required to solve an optimization problem and apply the resulting schedule in a receding horizon fashion. EMS for buildings require a simplified model of each thermal zone, and the objective function includes costs for heating and cooling, virtual costs, and a comfort model. Feedback from users is necessary since thermal comfort varies among individuals.

To influence the combustion process of modern biomass furnaces specifically the combustion-controller determines the necessary mass flows. The gaseous mass flows can be adjusted by fans and flaps. To ensure the desired overall performance of the furnace the mass flows need to be set by inner control loops respectively. Within the work described in this paper a model based approach for the control design of the inner control loop is presented exemplarily for the secondary air supply. Thereby a flatness-based feedforward control will be designed by means of an appropriate model. © 2014 Oldenbourg Wissenschaftsverlag GmbH.

Because of increased efforts to reduce CO₂ emissions a significant step in the development of small-scale (residential) biomass boilers for space heating has been achieved in recent years. Currently, the full potential for low-emission operation at high efficiencies, which is in principle possible due to optimized furnace geometries as well as combustion air staging strategies, cannot be exploited since there is still the need to enhance the controllers applied. For this reason, a model based control strategy for small-scale biomass boilers was developed and successfully implemented in a commercially available system. Thereby, appropriate mathematical models were developed for all relevant parts of the furnace and connected to an overall model subsequently used for the control unit design. The resulting controller is based on the input–output linearization and the state variables are estimated by an extended Kalman filter. Finally, the new control was implemented at a commercially available small-scale biomass boiler and the experimental verification showed a significant improvement of the operating behaviour in comparison to the conventional control.

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.

A novel biomass combustion technology was investigated that operates at a low oxygen content under fixed-bed and double air staging conditions. This technology was used to achieve extremely low NO_X and particle matter emissions in a 30 kW lab-scale reactor, displaying high fuel flexibility and no slagging. In this experimental work, the aim was to minimize inorganic particulate matter emissions, this aim was achieved by enabling the very low release of inorganics such as K from the fixed bed, which operates like a compact updraft gasifier. The elemental composition of the employed fuels, emitted dust particles, and fuel particle samples taken at three different heights within the fixed bed, and the bed temperatures were measured. The main objective in this study was to determine and understand the different processes of inorganic matter release that take place within the compact fixed bed. The results show that 98% and 99.7% of the K could be retained in the fixed bed for wood chips and miscanthus pellets, respectively, thus minimizing the particulate matter emissions. Different processes in the context of K release within the fixed bed could be identified for silica rich/agricultural and calcium rich / woody fuels, respectively and inconsistencies in the literature on these mechanisms could be resolved. In the case of miscanthus pellets, K is retained in silicates, and no accumulation of K, Cl and S occurs in the fixed bed above. In the case of wood chips, on the other hand, there is an unexpected K accumulation in the fixed bed, which is due to the release of K in the hot oxidation zone and the subsequent formation of large amounts of K chlorides and sulfates by condensation in the cooler upper region. Furthermore, for woody fuels, bounding or intercalation of K into the char matrix plays a more important role than the formation of carbonates in avoiding K release from the bed.

Absorption heat pumping devices (AHPDs, comprising absorption heat pumps and chillers) use mainly thermal energy instead of electricity as the driving energy to provide resource-efficient heating and cooling when using waste heat or renewable heat sources. Despite this benefit, AHPDs are still not a very common technology due to their complexity. However, better modulation and part-load capability, which can be achieved through advanced control strategies, can simplify the use of AHPDs and help to better integrate them into complex energy systems. Therefore, this paper presents a new, dynamic model-based control approach for single-stage AHPDs that can extend an AHPD’s operating range by employing multi-input-multi-output (MIMO) control methods. The control approach can be used for different AHPD applications and thus control configurations, i.e., different combinations of manipulated and controlled variables, and can also be used for redundantly-actuated configurations with more manipulated than controlled variables. It consists of an observer for the state variables and unknown disturbances, a state feedback controller and, in case of redundantly-actuated configurations, a dynamic control allocation algorithm. The proposed control approach is experimentally validated with a representative AHPD for two different control configurations and compared to two benchmark control approaches – single-input-single-output (SISO) PI control representing the state-of-the-art, and model-predictive control (MPC) as an alternative advanced control concept. The experimental validation shows that the two MIMO control approaches (the proposed state feedback and the MPC approach) allow for a wider operating range and hence better part load capability compared to the SISO PI control approach. While MPC generally results in a comparably high computational effort due to the necessity of continuously solving an optimization problem, the proposed state feedback control approach is mathematically simple enough to be implemented on a conventional programmable logic controller. It is therefore considered a promising new control approach for AHPDs with the ability to extend their operating range and improve their part load capability, which in turn facilitates their implementation and thus the use of sustainable heat sources in heating and cooling systems.

Microgrids, a research topic within the smart grids area, build on close relationships between demand and supply and will create a 170 Mrd. € market potential in 2020[1]. These individual markets are characterized by different technologies in use. For example, biogas will play a key role in microgrids in Asia compared to Photovoltaics, Combined heat and Power (CHP), as well as storage technologies in North America. All these different technologies need to be coordinated and controlled. BIOENERGY2020+ GmbH is the industry leader when it comes to biomass control systems in Austria. Thus, BIOENERGY2020+ GmbH is already combining this knowledge within the OptEnGrid and “Grundlagenforschung Smart- und Microgrid“ (K3-F-755/001-2017) research projects, which are based on the leading microgrid optimization tool DER-CAM from Lawrence Berkeley National Laboratory at the University of California in Berkeley. These two BIOENERGY2020+ GmbH basic research projects constitute the basis for new innovative microgrid controller concepts and these new microgrid controller will be implemented and tested in the suggested Microgrid Research Lab in Wieselburg. The Microgrid Research Lab will include the Technology- und Reseach Centre (tfz) Wieselburg-Land and the new firefighting department next to the tfz.

Microgrids are local energy grids that (partly) cover their own energy demand. Decentralized renewable energy sources reduce energy costs and CO2 emissions in a microgrid. Various storage systems and strategies like load shift are employed to balance the volatile energy flows. Intelligent controllers improve the energy management of the micro and smart grids. BEST GmbH is the industry leader when it comes to biomass control systems in Austria. Thus, BEST GmbH is already combining this knowledge within the “OptEnGrid” (FFG 858815) and “Grundlagenforschung Smart- und Microgrid“ (K3-F-755/001-2017) research projects, which are based on the leading microgrid optimization tool DER-CAM from Lawrence Berkeley National Laboratory at the University of California. These two BEST GmbH basic research projects form the basis for new innovative microgrid controller concepts which will be implemented and tested in the presented Microgrid Research Lab in Wieselburg (project Microgrid Lab 100%). The Microgrid Research Lab will include the Technology- und Reseach Centre (tfz) Wieselburg-Land and the new firefighting department next to the tfz.

Wood pellet combustion units are a comfortable, full automatic and low emission solution for the provision of space heating in small scale applications. The requirement of an auxiliary energy source for the heat supply and distribution however results in a dependence on the electrical grid. The goal of this work is thereby to eliminate this dependence and to meet the auxiliary energy demand through the independent production of electrical energy. The thermoelectric power production method was chosen from a number of technology variations so as to guarantee the silent and maintenance free production of direct current that can be implemented in cellars and space heaters. The first development step was the implementation of a Prototype with a fuel heat input of 10 kW and a nominal electrical power of 200 W. The central point of the implementation was the integration of a thermo-generator in a pellet combustion unit and the subsequent evaluation of the system concept. The integrated system implemented in the prototype confirms the feasibility of the combination of these technologies. The electrical efficiency of the thermo-generator was found to be in accordance with the target value of 4%, corresponding to a produced nominal electric power of 200 W.

La combustione di biomassa legnosa con piccoli apparecchi e caldaie è oggi vista con rinnovato interesse per il raggiungimento degli obiettivi comunitari di produzione di energia rinnovabile al 2020. L’aumento dell’utilizzo della biomassa combustibile è di stretto interesse del settore agroforestale, per via del notevole indotto economico che peraltro interessa tutto il territorio nazionale. Tuttavia, la combustione della biomassa è legata ad una serie di problematiche ambientali quali le emissioni in atmosfera di polveri sottili che influenzano direttamente la qualità dell’aria. Si ritiene, quindi, che l’auspicato aumento dell’utilizzo delle biomasse, soprattutto ai fini della produzione di calore (riscaldamento ambienti), sia legata al contenimento delle emissioni al camino. In questo contesto, è quindi importante la corretta misura delle polveri emesse dagli apparecchi di riscaldamento domestico alimentati a biomassa solida, tenendo conto anche della frazione condensabile, come richiesto dalla normativa. Il lavoro mette a confronto due tecniche di misura delle polveri, la tecnica di prelievo a caldo con raffreddamento dei fumi in impinger e la tecnica di diluizione con tunnel. Sono stati selezionati per il confronto due apparecchi di ridotta potenza (< 15 kWt) ed elevata efficienza: una caldaia a pellet ed una stufa a pellet. In condizioni di combustione completa le due tecniche restituiscono fattori di emissione simili. Nella stufa a pellet la misura a freddo è maggiore del 20 – 30 % rispetto alla misura a caldo. La ridotta presenza della frazione condensabile è stata confermata dall’analisi NPOC degli impinger. Sono state misurate le emissioni totali prodotte da un utilizzo reale del dispositivo, comprendendo anche le fasi transitorie di combustione (accensione, riscaldamento a regime e spegnimento), solitamente non considerate nelle misure standard di laboratorio. La fase di accensione produce fino a tre volte le polveri emesse in condizioni stazionarie. L’emissione totale si riduce all’aumentare del tempo di utilizzo del dispositivo, rientrando nell’intervallo delle emissioni delle condizioni stazionarie dopo circa 6 h. Gli IPA, emessi in quantità elevate, sono costituiti maggiormente da congeneri a peso molecolare medio – basso, associati a minore tossicità. Il TEQ è funzione della potenza e delle condizioni di
combustione del dispositivo.

Utilization of biomass as feedstock in dual fluidized bed steam gasification is a promising technology for the substitution of fossil energy carriers. Experience from industrial scale power plants showed an alteration of the olivine bed material due to interaction with biomass ash components. This change results mainly in the formation of Ca-rich layers on the bed particles. In this paper, a mechanism for layer formation is proposed and compared to the better understood mechanism for layer formation on quartz bed particles. Olivine bed material was sampled at an industrial scale power plant before the start of operation and at pre-defined times after the operation had commenced. Therefore, time dependent layer formation in industrial-scale conditions could be investigated. The proposed mechanism suggests that the interaction between wood biomass ash and olivine bed particles is based on a solid-solid substitution reaction, where Ca2+ is incorporated into the crystal structure. As a consequence Fe2+/3+ and Mg2+ ions are expelled as oxides. This substitution results in the formation of cracks in the particle layer due to a volume expansion in the crystal structure once Ca2+ is incorporated. The results of this work are compared to relevant published results including those related to quartz bed particles.
 

Product gas produced by biomass gasification contains small amounts of sulfur compounds (hydrogen sulfide) which can reduce catalyst activity during steam reforming process. Sulfur removal has a negative effect on process efficiency and steam reforming has to be run without cleaning the gas prior to the reactor. It is therefore of interest to investigate the effect of sulfur on the performance of steam reforming reactions. In this work a packed bed reactor filled with nickel based catalysts is mathematically modeled to simulate the steady state pseudo-heterogeneous equations representing heat and mass transfer in the reactor tube. Catalytic bed is subjected to hydrogen sulfide and an isotherm model for the sulfur coverage on the Ni surface is considered to exactly investigate sulfur poisoning effects on methane conversion, hydrogen yield, carbon dioxide and carbon monoxide concentration. It is shown that even when present in the hydrocarbon feedstock in small quantities, (ppm) levels, sulfur can have a significant effect in methane conversion and temperature distribution within the reactor. © 2013 Elsevier B.V.

Im Rahmen dieser zusammenfassenden Machbarkeitsstudie werden Untersuchungen zum Biomassepotential in Österreich im Jahr 2050 sowie der Synthese von BioSNG auf Basis der Biomassewirbelschichtvergasung durchgeführt. Dabei werden verschiedene Vergasungsverfahren, welche durch den Reaktortyp charakterisiert sind, dargestellt. Bedingt durch das homogene Temperaturprofil, welches in einem Wirbelschichtvergaser gegeben ist und die dadurch gegebene einfache Regelbarkeit des Prozesses, stellt sich die Wirbelschicht als vorteilhaft im Vergleich zu Flugstromvergasern dar, welche durch das hohe Temperaturniveau einen höheren technischen Aufwand mit sich bringen und daher für Anlagen mit großen Brennstoffwärmeleistungen zu bevorzugen sind. In weiterer Folge wird auf den DFB Prozess und dessen Weiterentwicklung, den G-Volution Vergaser eingegangen, welcher den Vorteil eines größeren einzusetzenden Brennstoffspektrums aufweist.

Long Term Validation of a New Modular Approach for CO-Lambda-Optimization

The optimization of existing biomass boilers in terms of efficiency and pollutant emissions is essential for their continued economic and ecological viability in future energy systems. These improvements are typically achieved by constructive changes which are expensive and can require prolonged downtimes. A well-known method for optimizing biomass boilers in terms of efficiency and pollutant emissions without constructive changes is the so-called CO-lambda-optimization. While multiple approaches for CO-lambda-optimization have been presented in literature, they are still rarely used in real biomass boilers. This is partly due to the fact that these approaches do not meet the requirements associated with their long-term operation in real biomass boilers. This contribution presents a new and modular approach for the CO-lambda-optimization which is specifically designed to meet these requirements. Particular emphasis in this contribution is laid on the long-term validation of the presented approach for CO-lambda-optimization at a medium-scale fixed-bed biomass boiler.

The present paper introduces a life cycle modeling approach for representing actual demand of energy or energy intensive products delivered within a system (electricity, heat, etc.) for optimization of the energy mix, according to some of the available life cycle impact assessments (LCIAs). Unlike classical LCA modeling approach, the real amount of several energy products leaving the system and the interactions due to the presence of multi-output processes are considered within the present approach. As a case study, future scenarios are obtained for the Belgian electricity mix production and the heat mix potentially substituted by CHP or biomass, switching between abandoning or not power from nuclear energy. The possibility of using natural gas, biomass for cogeneration, wind power and solar photovoltaic energy are considered within the availability ranges of these resources. Finally, results are presented from successive optimizations according to the sustainability potential defined in a previous paper. A pathway to a more sustainable Belgian energy system is obtained. Finally it is concluded that under the modeling conditions and without nuclear energy it is not possible to obtain a reduction of GHGs and despite diminishing of non-renewable resource consumption, a rising of toxicity is obtained. © 2013 Elsevier Ltd.

Decarbonising the transport sector is one of the key goals of national and international climate change mitigation policies. Rapid and effective market introduction of alternative fuels and vehicles is needed to reduce greenhouse gas emissions from the existing vehicle fleet as soon as possible and as extensively as possible.

However, experience with various attempts to introduce alternative fuels and vehicles to the market has shown that this is not always successful. Several participants in the Advanced Motor Fuels Technology Collaboration Program (AMF TCP) have therefore proposed an annex on lessons learned from market launch attempts.

The circumstances of the introduction of advanced motor fuels and the factors influencing their commercialization (resource, transport infrastructure, economic situation, etc.) in each country are different, and it is difficult to universally evaluate an advanced motor fuels policy.

For this reason, this annex clarifies the background and objective of the central government and local governments’ introduction policy and specific measures on advanced motor fuels in the past, and summarizes the effectiveness, successes, and lessons learned regarding the promotion of advanced motor fuels in each individual case of introduction and commercialization.

The participating countries Austria, China, Finland, Japan, Sweden and the USA conduct analyses of their own case studies on past market introductions taking into account specific framework conditions for each country:

Austria: low blend biofuels, CNG-driven cars, prevented introduction of E10

China: Ethanol

Finland: E10, E85, drop-in components for diesel, biogas

Japan: FAME, natural gas

Sweden: reduction obligation, high blend biofuels and biogas, E85

USA: low and high level blends of ethanol, methanol and FFVs, natural gas

The sum of the case studies is analysed and key drivers of successes and key barriers of failures are identified. Preliminary results from this work will be discussed in an expert workshop in 2020, and then the final lessons learned and recommendations will be derived. Policy briefs including key messages, best practices, lessons learned and avoided mistakes related to advanced motor fuels covering both fuels and related vehicle technologies will be developed and provided as recommendations for political decision makers.

Operating biomass stoves in modern buildings with tight shells often requires a room-independent air supply. One possibility to arrange this supply is to use a double-wall chimney with fresh air entering through the annular gap. For this setup, a mathematical model has been developed and checked with experimental data. It turned out that for commercially available chimneys, leakage is not negligible and inclusion of leak air in the calculation is crucial for reproduction of the experimental data. Even with inclusion of this effect, discrepancies remain which call for further investigations and a refinement of the model.

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

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

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

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

The use of phosphorus-rich fuels in fluidized bed combustion is one probable way to support both heat and power production and phosphorus recovery. Ash is accumulated in the bed during combustion and interacts with the bed material to form layers and/or agglomerates, possibly removing phosphorus from the bed ash fraction. To further deepen the knowledge about the difference in the mechanisms behind the ash chemistry of phosphorus-lean and phosphorus-rich fuels, experiments in a 5 kW bench-scale-fluidized bed test-rig with K-feldspar as the bed material were conducted with bark, wheat straw, chicken manure, and chicken manure admixtures to bark and straw. Bed material samples were collected and studied for layer formation and agglomeration phenomena by scanning electron microscopy combined with energy dispersive X-ray spectrometry. The admixture of phosphorus-rich chicken manure to bark changed the layer formation mechanism, shifting the chemistry to the formation of phosphates rather than silicates. The admixture of chicken manure to straw reduced the ash melting and agglomeration risk, making it possible to increase the time until defluidization of the fluidized bed occurred. The results also highlight that an increased ash content does not necessarily lead to more ash melting related problems if the ash melting temperature is high enough.

A kinetic scheme for the prediction of product composition of torrefaction is presented in this work. The scheme is based on a pyrolysis scheme for fast pyrolysis of small ash free biomass particles and was adapted to consider the presence of secondary char formation reactions, the inhibition of sugar formation due to the catalytic effect of alkali metals in biomass, as well as the typical hemicellulose structure of hardwoods. The torrgas composition predicted by the model is compared to experimental data of torrefaction in a lab-scale packed bed reactor. It is shown that the adapted model is able to predict the yields of the main volatile groups, i.e., permanent gases, light and heavy condensable species and the yields of the several groups in which condensable species were classified based on their structure, i.e., carbonyls and alcohols, furans, phenolics as well as water vapour. Copyright © 2014,AIDIC Servizi S.r.l.

A widely applicable kinetic scheme for pyrolysis is still missing. In this work an adaptation of the mechanistic scheme developed by Ranzi et al. (2008) for pyrolysis of small ash free biomass particles is proposed. The scheme is modified to include secondary char formation reactions, which are relevant for particles of a certain thickness, and sugar formation is avoided due to the catalytic effect of alkali metals in biomass. The predictions of the adapted scheme are compared to experimental data from the literature of pyrolysis in fixed beds of particles with a size of around 1 cm. It is shown that the adaptation improves the prediction of the final char yield and its CHO composition and also the yields of the main groups of volatiles, as carbonyls + alcohols, sugars and water vapor. © 2014 Elsevier Ltd. All rights reserved.

„Welche Heizung passt zu mir/uns? Vielleicht auch Kühlen oder selber Strom erzeugen?“ – Diese
Fragen stellen sich oft, wenn der Traum von den eigenen vier Wänden näher rückt. Egal ob bei Neubau
oder Sanierung, die Wahl eines passenden Energiebereitstellungssystems (EBS) sollte wohl überlegt
sein. Neben den technologischen Fragen sind es auch persönliche Motive, welche die Entscheidung
der Nutzer*innen beeinflussen.