Publications

Other Publications | 2023

Advanced Control ot the Generated Steam in a Municipal Waste Incineration Plant

Niederwieser H, Jäger F, Kirnbauer F, Gölles M. Advanced Control ot the Generated Steam in a Municipal Waste Incineration Plant. BEST Center Day. 28 June 2023

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

Peer reviewed papers | 2023

Automatic thermal model identification and distributed optimisation for load shifting in city quarters

Moser A, Kaisermayer V, Muschick D, Zemann C, Gölles M, Hofer A, Brandl D, Heimrath R, Mach T, Ribas Tugores C, Ramschak T. Automatic thermal model identification and distributed optimisation for load shifting in city quarters, International Journal of Sustainable Energy, 2023;42:1, 1063-1078, DOI: 10.1080/14786451.2023.2246079

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

Other Publications | 2023

Automation and Control of Renewable Energy Systems

Gölles M. Automation and Control of Renewable Energy Systems. BEST Center Day. 28 June 2023

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

Other Publications | 2023

BIOPOLYCOMP - Biochar for Polymer Composites

Martinie S, Kienzl N, Sarsteiner J. BIOPOLYCOMP - Biochar for Polymer Composites. BEST Center Day. 28 June 2023

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

Other Publications | 2023

Chemical Looping for efficient biomass utilization

Schulze K, Kienzl N, Steiner T, Martini S, Priscak J. Chemical Looping for efficient biomass utilization. BEST Center Day. June 2023

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

Peer reviewed papers | 2023

Control-oriented modeling of a LiBr/H2O absorption heat pumping device and experimental validation

Staudt S, Unterberger V, Gölles M, Wernhart M, Rieberer R, Horn M. Control-oriented modeling of a LiBr/H2O absorption heat pumping device and experimental validation. Journal of Process Control. 2023 Aug;128:103024. doi: 10.1016/j.jprocont.2023.103024

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

Other publication | 2023

Distributed Optimization Methods for Energy Management Systems

Kaisermayer V. Distributed Optimization Methods for Energy Management Systems. 2023.

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

Reports | 2023

District Heating and Cooling Networks in an Integrated Energy System Context (Guidebook)

Final Report of the IEA DHC Annex TS3

Böhm H, Cronbach D, Muschick D, Ianakiev A, Jentsch A, Cadenbach A, Kranzl L, Reuter S, Rossi J, Schmidt RR, Sorknaes P, Svensson IL, Trier D, Tunzi M, Widl E. IEA DHC Annex TS3 Guidebook, District Heating and Cooling in an Integrated Energy System Context, 2023.

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Annex TS3: Hybrid Energy Networks

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

 

Other Publications | 2023

Efficiency increase of biomass combustion systems by a modular CO-lambda optimization: method and results from long-term verification

Zemann C, Max A, Gölles M, Horn M. Efficiency increase of biomass combustion systems by a modular CO-lambda optimization: method and results from long-term verification. 7. Mitteleuropäische Biomassekonferenz: CEBC 2023. 19. Jan 2023. Oral presentation.

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Introduction and motivation
A key objective for the operation of biomass boilers is to achieve the highest possible efficiency while emitting the lowest possible pollutant emissions. In order to automate this task, CO-lambda optimization methods have been proposed in literature that ensure that the biomass boiler is operated at the lowest excess air ratio at which no relevant pollutant emissions occur, maximizing efficiency as a result. Since this optimal excess air ratio depends on various external factors, such as fuel properties, CO-lambda optimization methods continuously incorporate new measurements of the excess air ratio and the carbon monoxide content of the flue gas and estimate a new optimal excess air ratio during operation.
While achieving promising results in lab-scale tests, none of the CO-lambda optimization methods presented in literature has yet been able to gain practical acceptance. Either they are not robust enough and provide inaccurate estimates of the optimal excess air ratio or they are too slow and do not allow the optimal excess air ratio to be tracked sufficiently quickly. With the goal of providing a method that is fit for practical application, this publication presents a new modular approach for CO-lambda optimization that determines the optimal excess air ratio robustly and quickly, i.e. in real time.


Method
The new approach for CO-lambda optimization approximates the correlation between the excess air ratio and the carbon monoxide content of the flue gas, the CO-lambda characteristic, with a continuous, algebraic, non-linear model function. For this purpose, it uses a recursive-least-squares algorithm to continuously identify the model function’s parameters that lead to the optimal fit with the measured data, which are the excess air ratio and carbon monoxide content of the flue gas. From these model parameters, the optimal excess air ratio is calculated and defined as a desired value for the biomass boiler’s existing controller. This existing controller then ensures, that the biomass boiler is operated with this desired optimal excess air ratio, thus, maximizing efficiency and decreasing pollutant emissions. As a result, this new approach for CO-lambda optimization is entirely modular and can be applied to any biomass boiler with an existing control strategy capable of accurately adjusting the excess air ratio. For the measurement of the carbon monoxide content of the flue gas, a separate sensor has to be used. For this study the commercially available and proven in-situ exhaust gas sensor “KS1D” provided by the company LAMTEC has been used.


Long-term verification
The new approach for CO-lambda optimization was tested and validated at a biomass boiler with a nominal capacity of 2.5 MW that supplies a local heating network and combusts wood chips with a water content ranging from 30 w.t.% to 50 w.t.%. The long-term validation took place over an entire heating period, i.e. 5 months from November to March, during which the biomass boiler was operated alternately with the new approach for CO-lambda optimization and the standard control strategy, which means a constant desired residual oxygen content. In total the new approach for CO-lambda optimization was active for 1155 operating hours while the standard control strategy was active for 1310 operating hours. Compared to the standard control strategy, the new approach for CO-lambda optimization increased the biomass boiler’s efficiency by 3.8%, decreased total dust emissions by 19.5% and reduced carbon monoxide emissions on average (median) by 200 mg/m³. This demonstrates that the new approach for CO-lambda optimization is not only robust enough to run over a long period of time, it also leads to significant improvements in the biomass boiler’s operation. In addition, following these results, this new approach for CO-lambda optimization has also successfully been implemented and demonstrated at another biomass boiler with a nominal capacity of 1 MW where it has already been active for several months. This contribution presents the new approach to CO-lambda optimization in detail and discusses its technological and economic impact.

Peer reviewed papers | 2023

Extension of the layer particle model for volumetric conversion reactions during char gasification

Steiner T, Schulze R, Scharler R, Anca-Couce A. Extension of the layer particle model for volumetric conversion reactions during char gasification. Combustion and Flame. 2023:256,112940.

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

Peer reviewed papers | 2023

Fault detective: Automatic fault-detection for solar thermal systems based on artificial intelligence

Feierl L, Unterberger V, Rossi C, Gerardts B, Gaetani M. Fault detective: Automatic fault-detection for solar thermal systems based on artificial intelligence. Solar Energy Advances 2023;3:100033. https://doi.org/10.1016/j.seja.2023.100033.

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

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

Other Publications | 2023

FlowBattMonitor - Modellgestützte Überwachung von erneuerbaren Flow Batterien (Poster)

Nigitz T, Spirk S, Poms U, Wickenhauser D. FlowBattMonitor - Modellgestützte Überwachung von erneuerbaren Flow Batterien. Poster. 2023.

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Other Publications | 2023

Further development of gas-fermentation towards syngas utilization and electro-fermentation

Ludwig K, Hiebl C, Marzynski M, Deutsch M, Poms U, Schulze K, Neubauer M, Knoll L, Rachbauer L, Gölles M, Fuchs W, Drosg B. Further development of gas-fermentation towards syngas utilization and electro-fermentation. BEST center day. 28 June 2023.

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

Other Publications | 2023

Green Carbon as reducing agent in iron and steel production via the blast furnaces

Deutsch R, Krammer G, Kienzl N, Strasser C. Green Carbon as reducing agent in iron and steel production via the blast furnaces. BEST Center Day. 28 June 2023

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

Reports | 2023

Guidebook for the Digitalisation of District Heating: Transforming Heat Networks for a Sustainable Future

Final Report of DHC Annex TS4

Schmidt, Dietrich (ed.) et al. (2023). Guidebook for the Digitalisation of District Heating: Transforming Heat Networks for a Sustainable Future, Final Report of DHC Annex TS4. AGFW Project Company, Frankfurt am Main, Germany.

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Conference presentations and posters | 2023

IEA Cross TCP Workshop: Towards a flexible, cross sectoral energy supply

Gölles M, Schubert T, Lechner M, Mäki E, Kuba K, Leusbrock I, Unterberger V, Schmidt D. IEA Cross TCP Workshop: Towards a flexible, cross sectoral energy supply.7th Central European Biomass Conference CEBC 2023. 18. January 2023. Graz. Oral Presentation.

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A sustainable energy supply can only be achieved by a flexible, cross-sectoral energy system utilizing the specific advantages of the various renewable technologies. In this workshop possible roles of different technologies will be discussed based on a previous discussion of the users’ needs among the different sectors. In this a special focus should be given on the flexibility provision via the heating sector. By bringing together different users, representing municipal and industrial energy supply, and technological experts from different IEA Technology Collaboration Programmes (TCP) the workshop should support a holistic discussion.

List of presentations: 

  • Wien Energie‘s vision of a sustainable energy and ressource supply of Vienna, Teresa Schubert, Wien Energie, Austria
  • Digitalization of energy management systems – optimization of internal energy use as an industrial company, Maria Lechner, INNIO Jenbacher, Austria
  • Flexible Bioenergy and System Integration, Elina Mäki, VTT Technical Research Centre of Finland, Finland Task Leader – IEA Bioenergy Task 44 Flexible Bioenergy and System Integration
  • Use Case: Syngas platform Vienna for utilization of biogenic residues, Matthias Kuba, BEST – Bioenergy and Sustainable Technologies, Austria
  • Transformation of District Heating and Cooling Systems towards high share of renewables, Ingo Leusbrock, AEE INTEC, Austria – Lead of Austrian delegation – IEA DHC Annex TS5 Integration of Renewable Energy Sources into existing District Heating and Cooling Systems
  • Opportunities offered by long-term heat storages and large-scale solar thermal systems, Viktor Unterberger, BEST – Bioenergy and Sustainable Technologies, Austria Task Manager – IEA SHC Task 68 Efficient Solar District Heating Systems
  • Possibilities through digitalization on the example of District Heating and Cooling, Dietrich Schmidt, Fraunhofer Institute for Energy Economics and Energy System Technology IEE, Germany – Operating Agent – IEA DHC Annex TS4 Digitalisation of District Heating and Cooling

List of contributing IEA Tasks:

Other Publications | 2023

Increased flexibility of a fixed-bed biomass gasifier through advanced control

Hollenstein C, Martini S, Gölles M, Felsberger W, Horn M. Increased flexibility of a fixed-bed biomass gasifier through advanced control. BEST Center Day. 28 June 2023

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Conference presentations and posters | 2023

Increasing the flexibility of a fixed-bed biomass gasifier through model-based control strategies: method and practical verification

Hollenstein C, Zemann C, Martini S, Gölles M, Felsberger W, Horn M. Increasing the flexibility of a fixed-bed biomass gasifier through model-based control strategies: method and practical verification. 7. Mitteleuropäische Biomassekonferenz: CEBC 2023. 20. Jan 2023. Oral presentation.

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Future hybrid energy systems require flexible technologies for compensating the volatile nature of most renewable energies. As such, fixed-bed biomass gasifiers are especially relevant as they allow a flexible production of heat, electricity and in a broader sense bio-based products (e.g. biochar). Thus, flexible fixed-bed biomass gasifiers will continuously become more relevant for a sustainable and highly flexible energy and resource system (bioeconomy).

 

However, due to their current economic dependency on specific feed in tariffs for the produced electricity, they are almost always operated at nominal load, to maximize the electricity production. Thus, their potential for flexibility has not been revealed up to now. Consequently, the currently applied control strategies are typically designed with the focus on steady-state operation. Any operation differing from nominal load typically requires manual interventions of the plant operators to avoid lower efficiencies or operational difficulties. Thus, currently applied control strategies do not allow a fully-automatic and flexible operation of the gasifiers.

 

To unleash the full potential of the gasifiers’ flexibility, new and more advanced control strategies able to handle varying operating conditions automatically are required. For this reason, this contribution aims for the development of a model-based control strategy, since it allows to explicitly consider all the correlations between the different process variables, and an efficient adaptation of the control strategy to different plants. The development was carried out on the basis of a representative industrial small-scale fixed-bed biomass gasifier operated as combined heat and power plant (CHP) with a nominal capacity of 300 kWth and 150 kWel. In this contribution we present the developed method as well as the practical verification of the model-based controller for the industrial small-scale fixed-bed biomass gasification plant.

 

The practical verification revealed a significant potential for flexibility increase by the new model-based control strategy in comparison to state-of-the-art control strategies. For example, the new controller performs a step-wise load change from 150 kWel to 100 kWel (-33%) within less than 2 min without affecting the gasification performance. The new control leads to a much more homogeneous gasification, in particular during partial load operation, and reduces the fluctuation margin of relevant process parameters to less than 1%. This controlled stabilization and homogenization of the gasification at different operating conditions is also a prerequisite for further future flexibilization measures, e.g. the extension of the feedstock variety (fuel flexibility) or increasing product flexibility.

 

Due to the modular and model-based design, the new control strategy can also be implemented on other fixed-bed gasifiers of the same type without requiring any structural modifications, by solely adjusting the model parameters appropriately. Furthermore, the new control strategy makes only use of sensors and actuators typically already available in state-of-the-art fixed-bed gasification systems. In conclusion, the model-based control strategy to be presented states a very important contribution towards flexible fixed-bed biomass gasification systems.

 

Conference presentations and posters | 2023

Intelligent Building Control with User Feedback in the Loop

Kaisermayer V, Muschick D, Gölles M, Schweiger G, Schwengler T, Mörth M, Heimrath R, Mach T, Herzlieb M, Horn M. Intelligent Building Control with User Feedback in the Loop. 9th International Conference on Smart Energy Systems. Kopenhagen, Denmark, 12. September 2023. Oral Presentation.

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Buildings account for 30% of the globally consumed final energy and 19% of the indirect emissions, i.e., from the production of electricity and heat. Air-conditioned office buildings have an especially high energy footprint. Retrofitting buildings with predictive control strategies can reduce their energy demand and increase thermal comfort by considering future weather conditions. One challenge lies in the required infrastructure, i.e., sensors and actuators. Another challenge is about satisfying the comfort requirements of the users, getting their feedback and reacting to it. We propose a predictive control strategy, where an optimization-based energy management system (EMS) controls the thermal zones of such office buildings. The approach uses a mathematical model of the building within an optimization problem to predict and shift thermal demand. The individual thermal zones are modelled using a grey-box approach, where the simultaneous state and parameter estimation is handled by an unscented Kalman filter (UKF). This minimizes the needed effort for deployment of the system, as the parameters are learned automatically from historical measurement data. The objective function ensures the users’ comfort based on a comfort model, penalizes unwanted behaviour such as frequent valve position changes, and minimizes the costs for heating and cooling supply. Since the offices are typically shared by multiple users, the internal comfort model is calibrated based on their feedback. Each feedback is viewed as a measurement from the internal comfort model, and an UKF updates the parameters of the model, thus lowering or increasing the temperature setpoint of the zone controller in a robust manner. As a case study, an office building at the “Innovation District Inffeld” is considered. The proposed predictive control strategy, together with the user feedback, is implemented. A central information and communication technology (ICT) handles all communication with the building automation system. We developed a simple web-based feedback system with a five-point Likert scale for user feedback integration. The presented ideas are evaluated based on both a preliminary simulation study and potential evaluation using the building modelling software IDA ICE, and a real-world implementation. A key requirement was to limit the number of new sensors and actuators, thus focusing on how much can be achieved with a retrofit measure with minimal hardware, but intelligent software. The presentation will give, an overview of the developed methods and first results of the real implementation will be given.

Other Publications | 2023

Long-term validation of a new modular approach for CO-Lambda-optimization

Nigitz T, Hammer F, Gölles M, Horn M.

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Other Publications | 2023

Microgrids and Smart Energy Communities - Reference Projects and Use Cases

Aigenbauer S, Stadler M, Liedtke P, Sturmlechner R; Maier C, Mansoor M, Oberbauer C, Alavi F, Houben N, Haas R. Microgrids and Smart Energy Communities - Reference Projects and Use Cases. BEST Center Day. 28 June 2023

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Peer reviewed papers | 2023

MIMO state feedback control for redundantly-actuated LiBr/H O absorption heat pumping devices and experimental validation

Staudt S, Unterberger V, Muschick D, Gölles M, Horn M, Wernhart M, Rieberer R. MIMO state feedback control for redundantly-actuated LiBr/H2O absorption heat pumping devices and experimental validation. Control Engineering Practice.2023:140.105661. https://doi.org/10.1016/j.conengprac.2023.105661

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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.

Other Publications | 2023

Model-based Building Energy Management System with User Feedback in the Loop

Kaisermayer V, Muschick D, Gölles M, Horn M. Model-based Building Energy Management System with User Feedback in the Loop. BEST Center Day. 28 June 2023

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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.

Other Publications | 2023

Modelling and control of a small-scale fixed-bed biomass gasification system

Hollenstein C. Modelling and control of a small-scale fixed-bed biomass gasification system. 2023.

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Peer reviewed papers | 2023

Multi-scale modelling of a fluidized bed biomass gasifier of industrial size (1 MW) using a detailed particle model coupled to CFD: Proof of feasibility and advantages over simplified approaches

von Berg L, Anca-Couce A, Hochenauer C, Scharler R. Multi-scale modelling of a fluidized bed biomass gasifier of industrial size (1 MW) using a detailed particle model coupled to CFD: Proof of feasibility and advantages over simplified approaches. Energy Conversion and Management. 15 June 2023.286:117070

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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.

Other Publications | 2023

Numerical investigation of reaction mechanisms on NOx emissions from biomass combustion with enhanced reduction

Eßl M, Schulze K. Numerical investigation of reaction mechanisms on NOx emissions from biomass combustion with enhanced reduction. BEST Center Day. 28 June 2023

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With the increasing demand for lower emissions and innovative combustion technologies, it is necessary to have a reaction mechanisms that is accurate as well as computationally affordable for geometry and process optimization using computational fluid dynamics (CFD). The objective of this work is to explore the applicability of several reaction mechanisms in predicting NOx emissions from various combustion systems. This work focuses on the selection of suitable mechanisms from literature (see Table 1) in a full scale 3D model for the prediction of NOX especially for furnaces with low oxygen concentration in the fuel bed and enhanced reduction zones.

Other Publications | 2023

Operational optimization and error detection in biomass boilers by model based monitoring: methods and practice

Zemann C, Niederwieser H, Gölles M. Operational optimization and error detection in biomass boilers by model based monitoring: methods and practice. 7. Mitteleuropäische Biomassekonferenz: CEBC 2023. 20. Jan 2023. Oral presentation.

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One of the main tasks for operators of medium- and large-scale biomass boilers is the continuous operational monitoring of these plants in order to assess their performance, detect errors and identify possibilities for operational optimization. However, due to the high complexity of this task, errors are frequently detected too late or not at all, which can lead to even more costly secondary errors. In addition, possibilities for optimization remain unused in many existing plants, resulting in unnecessary pollutant emissions and low efficiencies.
To assist operators in performing this task and to achieve a high level of automation, methods for the automated, model-based monitoring of such plants have been focus of recent research activities. In this contribution, we will discuss the numerous possibilities provided by the application of such methods in a practical context. For this purpose, we present selected results from previous activities, demonstrating how methods for model-based monitoring were applied at combustion plants and used to enable automated error detection and support operational optimization.


Exemplary result 1: We developed a soft-sensor which accurately estimates the non-measurable internal state of heat exchangers and implemented it at a large-scale combustion plant with a nominal capacity of 38.2 MW. This soft-sensor uses a dynamic mathematical model of the heat exchanger in combination with measured data to determine a new estimate for the heat exchanger’s internal state every second. Based on this estimate, the soft-sensor accurately detects fouling and determines the non-measurable flue gas mass flow in real time. The estimated flue gas mass flow was used in a model-based control strategy which resulted in significant improvements of the combustion plant’s operational behaviour and load modulation capabilities. These results are discussed in this contribution.


Exemplary result 2: We developed a method for the real-time estimation of non-measurable fuel properties, i.e. chemical composition, bulk density, lower heating value, in biomass boilers. These estimates were subsequently used in a model-based control strategy and enabled the improvement of the biomass boiler’s fuel flexibility. Results of this estimator achieved for different biomass fuels, e.g. poplar wood chips, corncob grits and standard wood pellets, are discussed in this contribution.
On the basis of these selected results, it will be examined which possibilities arise from the use of methods for model-based monitoring in biomass boilers and also how these results can be extended to other technologies such as biomass gasifiers.

Peer reviewed papers | 2023

Optimal dispatch of a multi-energy system microgrid under uncertainty: a renewable energy community in Austria

Houben N, Cosic A, Stadler M, Mansoor M, Zellinger M, Auer H, Ajanovic A, Haas R. Optimal dispatch of a multi-energy system microgrid under uncertainty: a renewable energy community in Austria. Applied Energy. 1 May 2023.337:120913

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Microgrids can integrate variable renewable energy sources into the energy system by controlling flexible assets locally. However, as the energy system is dynamic, an effective microgrid controller must be able to receive feedback from the system in real-time, plan ahead and take into account the active electricity tariff, to maximize the benefits to the operator. These requirements motivate the use of optimization-based control methods, such as Model Predictive Control to optimally dispatch flexible assets in microgrids. However, the major bottleneck to achieve maximum benefits with these methods is their predictive accuracy. This paper addresses this bottleneck by developing a novel multi-step forecasting method for a Model Predictive Control framework. The presented methods are applied to a real test-bed of a renewable energy community in Austria, where its operational costs and CO2 emissions are benchmarked with those of a rule-based control strategy for Flat, Time-of-Use, Demand Charge and variable energy price tariffs. In addition, the impact of forecast errors and electric battery capacity on energy community operational savings are examined. The key results indicate that the proposed controller can outperform a rule-based dispatch strategy by 24.7% in operational costs and by 8.4% in CO2 emissions through optimal operation of flexibilities if it has perfect foresight. However, if the controller is deployed in a realistic environment, where forecasts for electrical load and PV generation are required, the same savings are reduced to 3.3% for cost and 7.3% for CO2, respectively. In such environments, the proposed controller performs best in highly dynamic tariffs such as Time-of-Use and Real-time pricing rates, achieving real cost savings of up to 6.3%. These results show that the profitability of optimization-based control of microgrids is threatened by forecast errors. This motivates future research on control strategies that compensate for forecast errors in real-world operation and more accurate forecasting methods.

Other Publications | 2023

Optimized Planning of Microgrids and Smart Energy Communities

Aigenbauer S, Stadler M, Liedtke P, Sturmlechner R, Maier C, Mansoor M, Oberbauer C, Alavi F, Houben N, Haas R. Optimized Planning of Microgrids and Smart Energy Communities. BEST Center Day. 28 June 2023

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Microgrids generate and store energy for self consumption (electricity, heating, cooling, etc.). Decentralized and renewable generation and storage technologies, as well as energy strategies increase efficiency, resilience, grid stability, independency of imports, sustainability, and climate neutrality.

Conference presentations and posters | 2023

Overview on flexible bioenergy options and implementation

Thrän D, Mäki E, Lange N, Hennig C, Schmieder U, Schildhauer T, Kiel J, Kroon P, Schipfer F, Philbrook A, Andersson K, Higa C, Gölles M. Overview on flexible bioenergy options and implementation. 7. Mitteleuropäische Biomassekonferenz: CEBC 2023. 20. Jan 2023. Oral presentation.

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Conference presentations and posters | 2023

Predictive control of biomass and biogas-based CHPs at the intersection between the electricity grid and heating networks – Improving electricity market participation through optimization and demand side management

Muschick D, Kaisermayer V, Moser A, Gölles M. Predictive control of biomass and biogas-based CHPs at the intersection between the electricity grid and heating networks – Improving electricity market participation through optimization and demand side management. 7. Mitteleuropäische Biomassekonferenz: CEBC 2023. 20. Jan 2023. Oral presentation.

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Other Publications | 2023

Smart Control of Coupled District Heating Networks

Kaisermayer V, Muschick D, Gölles M, Horn M. Smart Control for Couled District Heating Networks. BEST Center Day. 28 June 2023

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District heating (DH) networks have the potential for intelligent integration and combination of renewable energy sources, waste heat, thermal energy storage, heat consumers, and coupling with
other sectors. For growing networks in close geographical proximity, often the possibility arises to couple them using bidirectional heat exchangers, possibly unlocking synergies and reducing costs for the consumers. Each DH network may consist of producers, consumers and thermal energy storage (TES) devices. Often, each of the coupled DH networks will be already controlled via low-level controllers. Hence, a high-level control approach is needed, that coordinates the heat exchange between the
networks and takes renewable energy sources and the TES capacities in each network into account. These supervisory controllers are generally referred to as energy management systems (EMS).

Other Publications | 2023

Smart Microgrid Controller and Microgrid Research Laboratory

Stadler M, Aigenbauer S, Mansoor M, Oberbauer C, Houben N, Liedtke P, Sturmlechner R, Maier C, Alavi F, Haas R. Smart Microgrid Controller and Microgrid Research Laboratory. BEST Center Day. 28 June 2023

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To ensure that energy is optimally used on site in local energy grids/microgrids and to achieve cost and/or emission reduction targets, the technologies are controlled by predictive and adaptive microgrid controllers. Based on realtime measurement data as well as load, generation, market and weather forecasts, the optimal deployment plan for the local energy grid is thus calculated using mathematical
optimization algorithms. Synergies of different technologies and sectors (electricity, heating, cooling, mobility, etc.) are taken into account, resulting in high energy efficiency in the system.

Other papers | 2022

A control strategy for optimising the operational behaviour of biomass boilers

Zemann C. A control strategy for optimising the operational behaviour of biomass boilers. 2022. 225 S.

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Biomassefeuerungen spielen eine Schlüsselrolle in der Energiewende hin zu einem vollständig erneuerbaren Energiesystem. Allerdings müssen sie sich zukünftigen Herausforderungen stellen, um weiterhin relevant zu bleiben. Einerseits müssen Biomassefeuerungen mit dem höchstmöglichen Wirkungsgrad arbeiten, um wirtschaftlich rentabel zu bleiben während sie gleichzeitig eine hohe Lastmodulationsfähigkeit aufweisen müssen, um für eine breitere Palette von Anwendungen eingesetzt werden zu können. Andererseits müssen Biomassefeuerungen immer strengere Grenzwerte für Schadstoffemissionen einhalten und gleichzeitig in der Lage sein, neue und alternative Biomassebrennstoffe mit geringerer Qualität zu verbrennen.

In dieser Arbeit wird eine modellbasierte Regelungsstrategie entwickelt, die es Biomassefeuerungen ermöglicht, all diese Herausforderungen zu meistern. Diese Regelungsstrategie besteht aus drei Teilen, einer Verbrennungsregelung, einem Zustands- und Parameterschätzer und einer Methode zur CO-lambda-Optimierung. Alle drei Teile werden in dieser Arbeit hergeleitet und im Detail diskutiert, insbesondere im Hinblick auf ihre Implementierung an realen Biomassefeuerungen. Darüber hinaus werden alle drei Teile der modellbasierten Regelungsstrategie durch Simulationsstudien sowie durch eine Implementierung in realen Biomassefeuerungen verifiziert.

Als Grundlage für die modellbasierte Regelungsstrategie wird ein mathematisches Modell abgeleitet, welches das dynamische Verhalten der Prozesse in der Biomassefeuerungen einschließlich des Einflusses der Brennstoffeigenschaften beschreibt. Die berücksichtigten Brennstoffeigenschaften sind die Schüttdichte und die chemische Zusammensetzung einschließlich des Wasser- und Aschegehalts sowie der untere Heizwert.

Die Verbrennungsregelung nutz die Stellglieder der Biomassefeuerung um dessen stabilen Betrieb zu gewährleisten und schnelle Laständerungen zu ermöglichen. Diese modellbasierte Regelstrategie berücksichtigt durch ihre Formulierung, die auf dem oben genannten mathematischen Modell basiert, explizit alle relevanten Brennstoffeigenschaften. Dadurch reagiert sie gezielt auf Änderungen dieser Brennstoffeigenschaften und kompensiert direkt deren Einfluss auf den Betrieb der Biomassefeuerung. Gleichzeitig weist sie eine einfache Struktur auf und ist daher leicht zu implementieren und zu warten. Diese modellbasierte Verbrennungsregelung wird sowohl in Simulationsstudien als auch durch Experimente nach einer Implementierung an einer realen Biomassefeuerung verifiziert.

Es wird ein kombinierter Zustands- und Parameterschätzer entwickelt, der gleichzeitig die Brennstoffeigenschaften, die anschließend von der Verbrennungsregelung verwendet werden, und die Zustandsgrößen der Biomassefeuerungen in Echtzeit schätzt. Er basiert auf einem erweiterten Kalman-Filter, der das in dieser Arbeit vorgestellte mathematische Modell verwendet. Diese Methode wird für verschiedene Brennstoffeigenschaften sowohl in Simulationsstudien als auch durch Messdaten aus realen Biomassefeuerungen verifiziert. Die Ergebnisse dieser Verifikation zeigen, dass diese Methode in der Lage ist, die Brennstoffeigenschaften und Zustandsgrößen auch bei Last- oder Brennstoffwechseln genau zu bestimmen.

Um einen Betrieb der Biomassefeuerung mit möglichst hohem Wirkungsgrad und möglichst geringen Schadstoffemissionen zu gewährleisten, wird eine Methode zur CO-lambda-Optimierung entwickelt. Diese Methode verwendet einen erweiterten Kalman-Filter in Kombination mit Messdaten des Sauerstoffgehalts und des CO-Gehalts des Rauchgases zur Bestimmung eines optimalen Luftüberschussverhältnisses für den aktuellen Zustand der Biomassefeuerung. Diese Methode wird an einer realen Biomassefeuerung in einer Langzeitvalidierung über mehrere Monate verifiziert und validiert. Während dieser Langzeitvalidierung führte die Anwendung dieser Methode zur CO-lambda-Optimierung zu einer Wirkungsgradsteigerung von 3,8 %, einer Reduktion der CO-Emissionen um durchschnittlich 200 mg/m³ sowie einer Verringerung der Gesamtstaubemissionen um durchschnittlich 19 %.

Zusammenfassend ermöglicht die in dieser Arbeit vorgestellte modellbasierte Regelungsstrategie es, Biomassefeuerungen mit den geringstmöglichen Schadstoffemissionen und dem höchstmöglichen Wirkungsgrad zu betreiben und dabei ein hohes Maß an Brennstoffflexibilität und Lastmodulationsfähigkeit zu erreichen. Darüber hinaus weist die Regelungsstrategie eine geringe Komplexität auf und ist leicht in realen Biomassefeuerungen zu implementieren und zu warten. Dies ermöglicht den breiten Einsatz dieser Regelungsstrategie an bestehenden und zukünftigen Biomassefeuerungen. Dies unterstützt die weitere Verbreitung von Biomassefeuerungen im Energiesystem, was zur Reduzierung der CO2e-Emissionen beiträgt und auch die verstärkte Nutzung anderer, volatiler erneuerbarer Technologien, wie z.B. solarthermischer Anlagen, ermöglicht.

Peer reviewed papers | 2022

A multi-layer model of stratified thermal storage for MILP-based energy management systems

Muschick D, Zlabinger S, Moser A, Lichtenegger K, Gölles M. A multi-layer model of stratified thermal storage for MILP-based energy management systems. Applied Energy. 2022 May 15;315.118890. https://doi.org/10.1016/j.apenergy.2022.118890

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Both the planning and operation of complex, multi-energy systems increasingly rely on optimization. This optimization requires the use of mathematical models of the system components. The model most often used to describe thermal storage, and especially in the common mixed-integer linear program (MILP) formulation, is a simple integrator model with a linear loss term. This simple model has multiple inherent drawbacks since it cannot be applied to represent the temperature distribution inside of the storage unit. In this article, we present a novel approach based on multiple layers of variable size but fixed temperature. The model is still linear, but can be used to describe the most relevant physical phenomena: heat losses, axial heat transport, and, at least qualitatively, axial heat conduction. As an additional benefit, this model makes it possible to clearly distinguish between heat available at different temperatures and thus suitable for different applications, e.g., space heating or domestic hot water. This comes at the cost of additional binary decision variables used to model the resulting hybrid linear dynamics, requiring the use of state-of-the-art MILP solvers to solve the resulting optimization problems. The advantages of the more detailed model are demonstrated by validating it against a standard model based on partial differential equations and by showing more realistic results for a simple energy optimization problem.

Other papers | 2022

Application of Optimization-based Energy Management Systems for Interconnected District Heating Networks

Kaisermayer V, Muschick D, Gölles M, Rosegger W, Binder J, Kelz J. Application of Optimization-based Energy Management Systems for Interconnected District Heating Networks. 22. Styrian Workshop on Automatic Control. 6 Sep. 2022. Leitring/Wagna, Österreich.

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Peer reviewed papers | 2022

Assessment of measurement methods to characterize the producer gas from biomass gasification with steam in a fluidized bed

Anca-Couce A, von Berg L, Pongratz G, Scharler R, Hochenauer C, Geusebroek M, Kuipers J, Vilela CM, Kraia T, Panopoulos K, Funcia I, Dieguez-Alonso A, Almuina-Villar H, Tsiotsias T, Kienzl N, Martini S. Assessment of measurement methods to characterize the producer gas from biomass gasification with steam in a fluidized bed. Biomass and Bioenergy 2022.163:106527

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Measuring the producer gas from biomass gasification is very challenging and the use of several methods is required to achieve a complete characterization. Various techniques are available for these measurements, offering very different affordability or time demand requirements and the reliability of these techniques is often unknown. In this work an assessment of commonly employed measuring methods is conducted with a round robin. The main permanent gases, light hydrocarbons, tars, sulfur and nitrogen compounds were measured by several partners employing a producer gas obtained from fluidized bed gasification of wood and miscanthus with steam. Online and offline methods were used for this purpose and their accuracy, repeatability and reproducibility are here discussed. The results demonstrate the reliability of gas chromatography for measuring the main permanent gases, light hydrocarbons, benzene and H2S, validating the obtained results with other methods. An online method could also measure NH3 with a reasonable accuracy, but deviations were present for compounds at even lower concentrations. Regarding tar sampling and analysis, the main source of variability in the results was the analysis of the liquid samples, especially for heavier compounds. The presented work pointed out the need for a complementary use of several techniques to achieve a complete characterization of the producer gas from biomass gasification, and the suitability of certain online techniques as well as their limitations.

Conference presentations and posters | 2022

Automatic Thermal Model Identification and Distributed Optimisation for Load Shifting in City Quarters

Moser A, Kaisermayer V, Muschick D, Zemann C, Gölles M, Hofer A, Brandl D, Heimrath R, Mach T, Tugores C R, Ramschak, T. Automatic Thermal Model Identification and Distributed Optimisation for Load Shifting in City Quarters. 2nd International Sustainable Energy Conference: ISEC 2022. Graz, 07/04/2022. Oral presentation.

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Modern buildings with floor heating or thermally activated building structures (TABS) offer a significant potential for shifting the thermal load and thus reduce peak demand for heating or cooling. This potential can be realized with the help of model predictive control (MPC) methods, provided that sufficiently descriptive mathematical models describing the thermal characteristics of the individual thermal zones exist. Creating these by hand or from more detailed simulation models is infeasible for large numbers of zones; instead, they must be identified automatically based on measurement data. We present an approach using only open source tools based on the programming language Julia that allows to robustly identify simple thermal models for heating and cooling usable in MPC optimization. The resulting models are used in a distributed optimization scheme that co-ordinates the individual zones and buildings of a city quarter in order to best support an energy hub.

Other papers | 2022

Automatic thermal model identification and distributed optimization for load shifting in city quarters

Moser AGC, Kaisermayer V, Muschick D, Gölles M, Hofer A, Brandl D, Heimrath R, Mach T, Ribas Tugores C, Ramschak T. Automatic thermal model identification and distributed optimization for load shifting in city quarters. in Conference Proceedings - 2nd International Sustainable Energy Conference. 2022. S. 302-303 https://doi.org/10.32638/isec2022

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Modern buildings with floor heating or thermally activated building structures (TABS) offer a significant
potential for shifting the thermal load and thus reduce peak demand for heating or cooling. This potential can be realized with the help of model predictive control (MPC) methods, provided that sufficiently descriptive mathematical models describing the thermal characteristics of the individual thermal zones exist. Creating these by hand or from more detailed simulation models is infeasible for large numbers of zones; instead, they must be identified automatically based on measurement data. We present an approach using only open source tools based on the programming language Julia that allows to robustly identify simple thermal models for heating and cooling usable in MPC optimization. The resulting models are used in a distributed optimization scheme that co-ordinates the individual zones and buildings of a city quarter in order to best support an energy hub.

Other Publications | 2022

ÖKO-OPT-AKTIV: Optimiertes Regelungs- und Betriebsverhalten thermisch aktivierter Gebäude zukünftiger Stadtquartiere

Abschlussworkshop

Muschick D, Kaisermayer V. ÖKO-OPT-AKTIV - Optimiertes Regelungs- und Betriebsverhalten thermisch aktivierter Gebäude zukünftiger Stadtquartiere. Präsentation beim Abschlussworkshop in Graz, 16.09.2022.

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Conference presentations and posters | 2022

BEST-Day

Sustainable biorefineries and digitalization

Schwabl M, Wopienka E, Drosg B, Kuba M, Weber G, Eßl M, Gölles M, Kaiermayer V, Liedte P, Fuhrmann M. BEST-Day: Sustainable biorefineries and digitalization. 7th Central European Biomass Conference CEBC 2023. 18. January 2023. Graz. Oral Presentation.

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List of presentations:

Biorefineries

  • Learnings from biomass combustion towards future bioenergy applications (M. Schwabl)
  • Green Carbon perspectives for regional sourcing and decarbonization (E. Wopienka)
  • Bioconversion processes for renewable energy and/or biological carbon capture and utilisation (B. Drosg)
  • Second generation biomass gasification: The Syngas Platform Vienna – current status and outlook (M. Kuba)
  • Utilization of syngas for the production of fuel and chemicals – recent developments and outlook (G. Weber)

Digital methods, tools and sustainability

  • Evaluation of different numerical models for the prediction of NOx emissions of small-scale biomass boilers (M. Eßl)
  • Digitalization as the basis for the efficient and flexible operation of renewable energy technologies (M. Gölles)
  • Smart Control for Coupled District Heating Networks (V. Kaisermayer)
  • Integrated energy solutions for a decentral energy future - challenges and solutions (P. Liedtke)
  • Wood-Value-Tool: Techno-economic assessment of the forest-based sector in Austria (M. Fuhrmann)
Other Publications | 2022

Energiegemeinschaften im Tourismussektor

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Der Leitfaden „Energiegemeinschaften im Tourismus“ zeigt, welche Möglichkeiten Energiegemeinschaften für Tourismusbetriebe, ihre Beschäftigten und Menschen, die in Tourismusregionen leben, bieten können und wie eine Energiegemeinschaft ins Leben gerufen werden
kann.

Peer reviewed papers | 2022

Expert survey and classification of tools for modeling and simulating hybrid energy networks

Widl E, Cronbach D, Sorknæs P, Fitó J, Muschick D, Repetto M, Ramousse J, Ianakiev A. Expert survey and classification of tools for modeling and simulating hybrid energy networks. Sustainable Energy, Grids and Networks. December 2022.32:100913.

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Sector coupling is expected to play a key role in the decarbonization of the energy system by enabling the integration of decentralized renewable energy sources and unlocking hitherto unused synergies between generation, storage and consumption. Within this context, a transition towards hybrid energy networks (HENs), which couple power, heating/cooling and gas grids, is a necessary requirement to implement sector coupling on a large scale. However, this transition poses practical challenges, because the traditional domain-specific approaches struggle to cover all aspects of HENs. Methods and tools for conceptualization, system planning and design as well as system operation support exist for all involved domains, but their adaption or extension beyond the domain they were originally intended for is still a matter of research and development. Therefore, this work presents innovative tools for modeling and simulating HENs. A categorization of these tools is performed based on a clustering of their most relevant features. It is shown that this categorization has a strong correlation with the results of an independently carried out expert review of potential application areas. This good agreement is a strong indicator that the proposed classification categories can successfully capture and characterize the most important features of tools for HENs. Furthermore, it allows to provide a guideline for early adopters to understand which tools and methods best fit the requirements of their specific applications.

Conference presentations and posters | 2022

FAULT DETECTIVE: FAULT DETECTION FOR SOLAR THERMAL SYSTEMS

Feierl L, Bolognesi T, Unterberger V, Geatani M, Gerardts B. FAULT DETECTIVE: FAULT DETECTION FOR SOLAR THERMAL SYSTEMS. ISEC 2022. 05 - 07. April 2022, Graz. Poster presentation.

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Other Publications | 2022

Grundlagenforschung Smart- und Microgrids / Endbericht

Innovative, selbstlernende Systemregler für dezentrale Energieressourcen & Microgrids

Michael Zellinger, Michael Stadler

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Mikro-Netze (Microgrids), ein Unterbereich der Intelligenten Strom/Energie-Netze (Smartgrids),
die sich durch eine enge räumliche Bindung von Energieerzeugungseinheiten und Verbraucher
auszeichnen wird international ein sehr starkes Wachstum zugeschrieben. Microgrids sind kleine,
lokale Energienetze für Strom, Wärme und Kälte, die Haushalte, Betriebe und Gemeinden mit
Energie versorgen. Diese lokalen und regionalen Konzepte der Energieversorgung können in
Zukunft einen wesentlichen Beitrag in Richtung Energieunabhängigkeit und effizientere
Integration von Erneuerbaren in das Energiesystem leisten. Sie können ihren Energiebedarf
selbstständig aus erneuerbaren Energien oder anderen Energieformen decken, etwa Biomasse,
Wärmepumpen, PV, Windräder oder Kraftwärmekopplungen. Diese können nach den
individuellen Zielen der Gemeinden, Haushalte oder der Betriebe gesteuert werden, um
Kostenreduktionen, CO2 Einsparungen oder eine Erhöhung des Unabhängigkeitsgrades zu
realisieren. Sie berechnen den aktuellen und zukünftigen Verbrauch und können Energie im
Bedarfsfall dorthin verlagern, wo sie gerade benötigt wird, oder sie reduzieren den
Energieverbrauch direkt.

Reports | 2022

IEA Bioenergy Task 44: Flexible Bioenergie und Systemintegration (Arbeitsperiode 2019 - 2021)

Gölles M, Schipfer F. IEA Bioenergy Task 44: Flexible Bioenergie und Systemintegration (Arbeitsperiode 2019 - 2021). IEA Task Bioenergy 44. BMK. Schriftenreihe 49/2023. Deutsch, 40 Seiten.

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Ziel des Tasks ist es, Bioenergielösungen als flexible Ressource in einem dekarbonisierten Energiesystem herauszuarbeiten. Dabei sollen Typen, Qualität und Status von flexibler Bioenergie erhoben sowie Barrieren und Entwicklungsbedarf im Gesamtsystemkontext (Strom-, Wärme- und Transportsektor) identifiziert werden.

Conference presentations and posters | 2022

IEA SHC Task 68: Efficient Solar District Heating Systems

Unterberger V, Berberich M, Putz S, Byström J, Gölles M. IEA SHC Task 68: Efficient Solar District Heating Systems. ISEC 2022. 5 - 07. April 2022, Graz. Poster presentation.

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Peer reviewed papers | 2022

Increased Flexibility of A Fixed-Bed Biomass Gasifier through Advanced Control

Hollenstein C, Zemann C, Martini S, Gölles M, Felsberger W, Horn M. Increased Flexibility of A Fixed-Bed Biomass Gasifier through Advanced Control. Proceedings of the 30th European Biomass Conference and Exhibition. 2022. 704-711.

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Most industrial fixed-bed biomass gasification systems usually operate at steady-state to produce the maximum amount of energy possible although they can principally modulate their loads to compensate for the fluctuations of other volatile renewable energy systems. To unleash their full load modulation capability, their typically traditional control strategies should be improved, their gas residence times affected by typically basic char removal strategies adjusted and any required manual interaction of an operator avoided. In this respect, a new controller for the char handling (accumulation and removal) of the reduction zone in a fixed-bed biomass gasifier of a representative industrial small-scale gasification system is developed and experimentally verified. This new controller consists of a recursive least-squares estimator for the flow resistance of the gasifier representing the amount of char inside and a switching controller for rotating a grate located at its bottom. The experimental verification reveals that only the traditional (pressure-based) controller requires manual adjustment of the thresholds. Moreover, the new controller (flow resistance based) significantly reduces the fluctuation range during partial load and stabilizes the temperature and pressure downstream the gasifier. This provides the basis for enhancing its fuel flexibility too and is an important feature for flexible operation in future.

Conference presentations and posters | 2022

MATHEMATICAL MODEL FOR MODEL-BASED CONTROL OF ABSORPTION HEAT PUMPING SYSTEMS

Zlabinger S, Unterberger V, Gölles M, Horn M, Wernhart M, Rieberer R. MATHEMATICAL MODEL FOR MODEL-BASED CONTROL OF ABSORPTION HEAT PUMPING SYSTEMS. 2nd International Sustainable Energy Conference – ISEC 2022. October 2022.

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Conference presentations and posters | 2022

Model-based control of absorption heat pumping systems

Staudt S, Unterberger V, Muschick D, Wernhart M, Rieberer R. Model-based control of absorption heat pumping systems. 2022. Abstract from 22. Styrian Workshop on Automatic Control, Leitring/Wagna, Austria.

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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.

Peer reviewed papers | 2022

Multi-scale modelling of fluidized bed biomass gasification using a 1D particle model coupled to CFD

von Berg L, Anca-Couce A, Hochenauer C, Scharler R. Multi-scale modelling of fluidized bed biomass gasification using a 1D particle model coupled to CFD. Fuel. 15 September 2022.324:124677

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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.

Other papers | 2022

Netzdienliche Nutzung von Bauteilaktivierung in Gebäuden durch vorausschauende Regelungen – Ergebnisse aus dem Projekt ÖKO-OPT-AKTIV

Kaisermayer V, Muschick D, Gölles M. Netzdienliche Nutzung von Bauteilaktivierung in Gebäuden durch vorausschauende Regelungen – Ergebnisse aus dem Projekt ÖKO-OPT-AKTIV. Abschlussworkshop - IEA DHC Annex TS3: Hybride Energie-Netze. 20. Oktober 2022, online.

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Reports | 2022

Optimiertes Regelungs- und Betriebsverhalten thermisch aktivierter Gebäude zukünftiger Stadtquartiere (ÖKO-OPT-AKTIV)

Muschick D, Kaisermayer V, Moser A, Gölles M, Heimrath R, Brandl D, Mach T, Ribas-Tugores C, Ramschak T, Oswald S, Polster M, Lackner F, Eibisberger K, Nebel M. Optimiertes Regelungs- und Betriebsverhalten thermisch aktivierter Gebäude zukünftiger Stadtquartiere (ÖKO-OPT-AKTIV). Stadt der Zukunft 6. Ausschreibung. BMK. Schriftenreihe 60/2023. Jänner, 2022. Deutsch, 76 Seiten.

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Peer reviewed papers | 2022

Smart control of interconnected district heating networks on the example of “100% Renewable District Heating Leibnitz”

Kaisermayer V, Binder J, Muschick D, Beck G, Rosegger W, Horn M, Gölles M, Kelz J, Leusbrock I. Smart control of interconnected district heating networks on the example of “100% Renewable District Heating Leibnitz”. Smart Energy. 2022 Apr 7. 100069. https://doi.org/10.1016/j.segy.2022.100069

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District heating (DH) networks have the potential for intelligent integration and combination of renewable energy sources, waste heat, thermal energy storage, heat consumers, and coupling with other sectors. As cities and municipalities grow, so do the corresponding networks. This growth of district heating networks introduces the possibility of interconnecting them with neighbouring networks. Interconnecting formerly separated DH networks can result in many advantages concerning flexibility, overall efficiency, the share of renewable sources, and security of supply. Apart from the problem of hydraulically connecting the networks, the main challenge of interconnected DH systems is the coordination of multiple feed-in points. It can be faced with control concepts for the overall DH system which define optimal operation strategies. This paper presents two control approaches for interconnected DH networks that optimize the supply as well as the demand side to reduce CO2 emissions. On the supply side, an optimization-based energy management system defines operation strategies based on demand forecasts. On the demand side, the operation of consumer substations is influenced in favour of the supply using demand side management. The proposed approaches were tested both in simulation and in a real implementation on the DH network of Leibnitz, Austria. First results show a promising reduction of CO2 emissions by 35% and a fuel cost reduction of 7% due to better utilization of the production capacities of the overall DH system.

Other Publications | 2022

Solar goes Digital: Wie Solarwärme selbstlernende Algorithmen nutzt (Austria Solar Webinar 26)

Unterberger V. Solar goes Digital: Wie Solarwärme selbstlernende Algorithmen nutzt (Austria Solar Webinar 26). Online am 11.05.2022.

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Peer reviewed papers | 2022

Solid oxide fuel cell operation with biomass gasification product gases: Performance- and carbon deposition risk evaluation via a CFD modelling approach

Pongratz G, Subotić V, Hochenauer C, Scharler R, Anca-Couce A. Solid oxide fuel cell operation with biomass gasification product gases: Performance- and carbon deposition risk evaluation via a CFD modelling approach. 1 April 2022. 244.

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Solid oxide fuel cell (SOFC) models used in the past for biomass-to-power plant simulations are limited in their predictability of the carbon deposition risk. In this work, industrial-relevant cell designs were modeled in 2D-CFD considering detailed reaction kinetics which allowed more accurate performance simulations and carbon deposition risk assessments. Via a parametric study, the influence of varying cell operating conditions on the cell performance and carbon deposition risk was quantified when utilizing product gases from steam- and air gasification with varying steam addition. Considering the results from this parameter study and carbon deposition risk assessment, recommendations for promising gasifier-SOFC configurations and cell operating points for stable long-term operation are presented. For smaller-scale biomass-to-power systems, the utilization of product gas from air gasification in anode supported cells with Ni/zirconia-based anode can be recommended, with only moderate steam dilution of the product gas at 750°C cell operating temperature. For larger scales, steam gasification might be meaningful, offering a generally higher electrical efficiency and power output in fuel cells than air gasification. However, a higher risk for carbon deposition could be determined in comparison to air gasification. Hence, a cell temperature of 850°C besides the use of cells with Ni/ceria-based anodes is recommended.

Conference presentations and posters | 2022

Success Factors and Barriers for Integrated District Heating Networks

Muschick D, Cronbach D, Ianakiev A, Kallert A, Schmidt R-R, Sorknaes P et al. Success Factors and Barriers for Integrated District Heating Networks. 2022. Postersitzung präsentiert bei 2nd International Sustainable Energy Conference , Graz, Österreich.

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Other papers | 2022

Technology and Process Improvement of a Demonstration Unit for a Novel Aqueous Phase Reforming Process Via Virtual Commissioning

Nigitz T, Arlt S, Poms U, Weber G, Luisser M, Gölles M. Technology and Process Improvement of a Demonstration Unit for a Novel Aqueous Phase Reforming Process Via Virtual Commissioning. Proceedings of the 30th European Biomass Conference and Exhibition. 2022. 948 - 950.

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A process demonstration unit for a novel aqueous phase reforming (APR) process was built and scaled up by factor 666. The set-up of this demonstration unit was supported by virtual commissioning using a virtual test bed. By using virtual commissioning, it was possible to speed-up the commissioning and to support stable, reliable and continuous plant operation for 100h.

Peer reviewed papers | 2022

Unknown input observer design for linear time-invariant multivariable systems based on a new observer normal form

Niederwieser H, Tranninger M, Seeber R, Reichhartinger M. Unknown input observer design for linear time-invariant multivariable systems based on a new observer normal form. International Journal of Systems Science. 2022 Apr 6. https://doi.org/10.1080/00207721.2022.2046201

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In various applications in the field of control engineering, the estimation of the state variables of dynamic systems in the presence of unknown inputs plays an important role. Existing methods require the so-called observer matching condition to be satisfied, rely on the boundedness e variables or exhibit an increased observer order of at least twice the plant order. In this article, a novel observer normal form for strongly observable linear time-invariant multivariable systems is proposed. In contrast to classical normal forms, the proposed approach also takes the unknown inputs into account. The proposed observer normal form allows for the straightforward construction of a higher-order sliding mode observer, which ensures global convergence of the estimation error within finite time even in the presence of unknown bounded inputs. Its application is not restricted to systems which satisfy the aforementioned limitations of already existing unknown input observers. The proposed approach can be exploited for the reconstruction of unknown inputs with bounded derivative and robust state-feedback control, which is shown by means of a tutorial example. Numerical simulations confirm the effectiveness of the presented work.

Peer reviewed papers | 2022

Unknown Input Observer Design for Linear Time-Invariant Systems - A Unifying Framework

Tranninger M, Niederwieser H, Seeber R, Horn M. Unknown Input Observer Design for Linear Time-Invariant Systems - A Unifying Framework. International Journal of Robust and Nonlinear Control. 2022 Nov 18. https://doi.org/10.1002/rnc.6399

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This article presents a new observer design approach for linear time invariant multivariable systems subject to unknown inputs. The design is based on a transformation to the so-called special coordinate basis (SCB). This form reveals important system properties like invertability or the finite and infinite zero structure. Depending on the system's strong observability properties, the SCB allows for a straightforward unknown input observer design utilizing linear or nonlinear observers design techniques. The chosen observer design technique does not only depend on the system properties, but also on the desired convergence behavior of the observer. Hence, the proposed design procedure can be seen as a unifying framework for unknown input observer design.

Conference presentations and posters | 2022

Vereinfachung von Absorptionskälteanlagen-Modellen

Wernhart MW, Rieberer R, Staudt S, Unterberger V, Gölles M. Vereinfachung von Absorptionskälteanlagen-Modellen. Deutsche Kälte- und Klimatagung 2022: DKV-Tagung 2022. 18. November 2022. Magdeburg, Germany.

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Conference presentations and posters | 2021

A platform for energy management in communities

Derflinger N, Zellinger M. A platform for energy management in communities. ComForEn 2021 11. Symposium Communications for Energy Systems. 23 November 2021.

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Peer reviewed papers | 2021

Advanced Optimal Planning for Microgrid Technologies including Hydrogen and Mobility at a real Microgrid Testbed

Mansoor M, Stadler M, Auer H, Zellinger M. Advanced Optimal Planning for Microgrid Technologies including Hydrogen and Mobility at a real Microgrid Testbed. International Journal of Hydrogen Energy.2021.

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This paper investigates the optimal planning of microgrids including the hydrogen energy system through mixed-integer linear programming model. A real case study is analyzed by extending the only microgrid lab facility in Austria. The case study considers the hydrogen production via electrolysis, seasonal storage and fueling station for meeting the hydrogen fuel demand of fuel cell vehicles, busses and trucks. The optimization is performed relative to two different reference cases which satisfy the mobility demand by diesel fuel and utility electricity based hydrogen fuel production respectively. The key results indicate that the low emission hydrogen mobility framework is achieved by high share of renewable energy sources and seasonal hydrogen storage in the microgrid. The investment optimization scenarios provide at least 66% and at most 99% carbon emission savings at increased costs of 30% and 100% respectively relative to the costs of the diesel reference case (current situation).

Conference presentations and posters | 2021

Advances in biomass gasification for the production of Bioheat, bioelectricity and biofuels

Anca-Couce A, Archan G, Von Berg L, Pongratz G, Martini S, Buchmayr M, Rakos C, Hochenauer C, Scharler R. Advances in biomass gasification for the production of Bioheat, bioelectricity and biofuels. 29th European Biomass Conference and Exhibition, EUBCE 2021, 26-29 April 2021. 2021.

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Current barriers to increase the use of bioenergy for different applications are first discussed. Then, recent advances are presented on gasification-based technologies to overcome these barriers that have been reached at TU Graz together with several partners. Gasification-based fuel bed concepts integrated in biomass combustion can significantly reduce emissions for bioheat production. Advances are presented for modern biomass boilers, significantly reducing nitrogen oxides and particle matter emissions as well as increasing the feedstock flexibility; and micro-gasifiers for traditional biomass utilization, significantly reducing the emissions of unburnt products. Gasification-based processes have as well the possibility to score high electrical efficiencies and to synthetize several products as second-generation biofuels. Advances are presented on measures for reducing the presence of contaminants as tars, including the catalytic use of char for tar cracking; and in applications of the producer gas, including gas cleaning and direct coupling with a solid oxide fuel cell to maximize electricity production. © 2021, ETA-Florence Renewable Energies.

Peer reviewed papers | 2021

An adaptive short-term forecasting method for the energy yield of flat-plate solar collector systems

Unterberger V, Lichtenegger K, Kaisermayer V, Gölles M, Horn M. An adaptive short-term forecasting method for the energy yield of flat-plate solar collector systems. Applied Energy. 2021 Apr 16;2021(293). https://doi.org/10.1016/j.apenergy.2021.116891

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The number of large-scale solar thermal installations has increased rapidly in Europe in recent years, with 70 % of these systems operating with flat-plate solar collectors. Since these systems cannot be easily switched on and off but directly depend on the solar radiation, they have to be combined with other technologies or integrated in large energy systems. In order to most efficiently integrate and operate solar systems, it is of great importance to consider their expected energy yield to better schedule heat production, storage and distribution. To do so the availability of accurate forecasting methods for the future solar energy yield are essential. Currently available forecasting methods do not meet three important practical requirements: simple implementation, automatic adaption to seasonal changes and wide applicability. For these reasons, a simple and adaptive forecasting method is presented in this paper, which allows to accurately forecast the solar heat production of flat-plate collector systems considering weather forecasts. The method is based on a modified collector efficiency model where the parameters are continuously redetermined to specifically consider the influence of the time of the day. In order to show the wide applicability the method is extensively tested with measurement data of various flat-plate collector systems covering different applications (below 200 Celsius), sizes and orientations. The results show that the method can forecast the solar yield very accurately with a Mean Absolute Range Normalized Error (MARNE) of about 5 % using real weather forecasts as inputs and outperforms common forecasting methods by being nearly twice as accurate.

Peer reviewed papers | 2021

Analysis of H2S-related short-term degradation and regeneration of anode- and electrolyte supported solid oxide fuel cells fueled with biomass steam gasifier product gas

Pongratz G, Subotić V, Schroettner H, Hochenauer C, Skrzypkiewicz M, Kupecki J, Anca-Couce A, Scharler R. Analysis of H2S-related short-term degradation and regeneration of anode- and electrolyte supported solid oxide fuel cells fueled with biomass steam gasifier product gas. Energy.2021.218:119556.

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Using solid oxide fuel cells in biomass gasification based combined heat and power production is a promising option to increase electrical efficiency of the system. For an economically viable design of gas cleaning units, fuel cell modules and further development of suitable degradation detection methods, information about the behavior of commercially available cell designs during short-term poisoning with H2S can be crucial. This work presents short-term degradation and regeneration analyses of industrial-relevant cell designs with different anode structure and sulfur tolerance fueled with synthetic product gas from wood steam gasification containing 1 to 10 ppmv of H2S at 750°C and 800°C. Full performance regeneration of both cell types was achieved in all operating points. The high H2O content and avoided fuel depletion may have contributed to a lower performance degradation and better regeneration of the cells. A strong influence of the catalytically active anode volume on poisoning and regeneration behavior was quantified, thereby outlining the importance of considering the anode structure besides the sulfur tolerance of the anode material. Hence, cells with less sulfur tolerant anode material but larger anode volume might outperform cells less sensitive to sulfur in the case of an early detection of a gas cleaning malfunction.

Other Publications | 2021

Betrieb verbundener Nahwärmenetze mit getrennten Eigentümern

Zemann C, Muschick D, Kaisermayer V, Gölles M. Betrieb verbundener Nahwärmenetze mit getrennten Eigentümern. QM Heizwerke Fachtagung, Bad Vöslau, 14. Oktober, 2021. (oral presentation)

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Warum ist es sinnvoll, Wärmenetze zu verbinden?

  • Erläuterung am Beispiel des Projekts Thermaflex
  • Drei Wärmenetze bei Leibnitz in der Steiermark.
  • Sind gewachsen und haben die Grenzen ihrer Nachbar-Wärmenetze erreicht.
  • Die Wärmenetze werden durch zwei getrennte Eigentümer betrieben.
Peer reviewed papers | 2021

Bioenergy technologies, uses, market and future trends with Austria as a case study

Anca-Couce A, Hochenauer C, Scharler R. Bioenergy technologies, uses, market and future trends with Austria as a case study. Renewable and Sustainable Energy Reviews.2021;135:110237.

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The current bioenergy uses and conversion technologies as well as future trends for the production of heat, power, fuels and chemicals from biomass are reviewed. The focus is placed in Austria, which is selected due to its high bioenergy utilization, providing 18.4% of the gross energy final consumption in 2017, and its strong industrial and scientific position in the field. The most common bioenergy application in Austria is bioheat with 170 PJ in 2017 mainly obtained from woody biomass combustion, followed by biofuels with 21 PJ and bioelectricity with 17 PJ. Bioheat has a stable market, where Austrian manufacturers of boilers and stoves have a strong position exporting most of their production. Future developments in bioheat production should go in the line of further reducing emissions, increasing feedstock flexibility and coupling with other renewables. For bioelectricity and biofuels, the current framework does not promote the growth of the current main technologies, i.e. combined heat and power (CHP) based on biomass combustion or biogas and first generation biofuels. However, an increase in all bioenergy uses is required to achieve the Austrian plan to be climate neutral in 2040. The current initiatives and future possibilities to achieve this increase are presented and discussed, e.g. mandatory substitution of old oil boilers, production of biomethane and early commercialization of CHP with a high efficiency or demonstration of advanced biofuels production based on gasification.

Other Publications | 2021

CO-lambda Optimierung - Betrieb von Biomassefeuerungen mit maximaler Effizienz und minimalen Emissionen

Zemann C. CO-lambda Optimierung - Betrieb von Biomassefeuerungen mit maximaler Effizienz und minimalen Emissionen. CO-lambda Optimierung - Betrieb von Biomassefeuerungen mit maximaler Effizienz und minimalen Emissionen. March 2021.

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Reports | 2021

Control of DHC networks and Reduction of the operating temperatures in DH systems

Task 55 Towards the Integration of Large SHC Systems into DHC Networks

Gölles M, Muschick D, Unterberger V, Leoni P, Schmidt R, Lennermo G. "Control of DHC networks and Reduction of the operating temperatures in DH systems". EA SHC FACTSHEET 55.A-D4.2. Date of Publication: 28.01.2021. https://task55.iea-shc.org/fact-sheets

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Overview on different approaches for the control of the heat distribution networks in case of the integration of large-scale solar thermal systems, and different possibilities for the reduction of the operating temperatures in DH systems.

Reports | 2021

Control of large-scale solar thermal plants

Task 55 Towards the Integration of Large SHC Systems into DHC Networks

Gölles M, Unterberger V. "Control of large-scale solar thermal plants". IEA SHC FACTSHEET 55.B-D3.1. Date of Publication: 28.01.2021. https://task55.iea-shc.org/fact-sheets

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Overview on the control of large-scale thermal plants, limited to plants feeding into DH networks as well as theirkey components, i.e. the actual collector circuit and the heat exchanger between primary and secondary circuit.

Peer reviewed papers | 2021

Correlations between tar content and permanent gases as well as reactor temperature in a lab-scale fluidized bed biomass gasifier applying different feedstock and operating conditions

von Berg L, Pongratz G, Pilatov A, Almuina-Villar H, Scharler R, Anca-Couce A. Correlations between tar content and permanent gases as well as reactor temperature in a lab-scale fluidized bed biomass gasifier applying different feedstock and operating conditions.Fuel.2021.305:121531

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The major problem of fluidized bed biomass gasification is the high tar contamination of the producer gas which is associated with the complex and time-consuming sampling and analysis of these tars. Therefore, correlations to predict the tar content are a helpful tool for the development and operation of biomass gasifiers. Correlations between tars and gas composition as well as reactor temperature derived for a steam-blown lab-scale bubbling fluidized bed gasifier are investigated in this study to assess their applicability. A comprehensive data set containing over 80 experimental points was obtained for various operation conditions, including variations in temperature from 700 to 800 °C, feedstock, amount of steam for fluidization, as well as the addition of oxygen. Linear correlations between tar and permanent gases show good accuracy for H2 and CH4 when using pure steam. However, experiments conducted with steam-oxygen mixtures show high deviations for the CH4-based correlation and smaller but still significant deviations for the H2-based correlation. No relation between tar and CO or CO2 was found. The correlation between tar and temperature shows highest accuracy, including good agreement with the steam-oxygen experiments. All tar correlations showed useful results over a broad operating range. However, significant deviations can be obtained when considering just one gas compound. Therefore, a combination of different correlations considering gas components and temperature seems to be the best method of tar prediction. This leads to a powerful tool for fast online tar monitoring for a broad range of operating conditions, once a calibration measurement was conducted.

Peer reviewed papers | 2021

Dekarbonisierung in Salzburgs Skigebieten – Entwicklung von Optimierungsalgorithmen und Energiemanagementsystemen zur Steigerung der Energieeffizienz, Minimierung von Emissionen und Optimierung von Flexibilitäten [Decarbonization of the skiing areas in

Kritzer S, Passegger H, Ayoub T, Liedtke P, Zellinger M, Stadler M, Iglar B, Korner C, Aghaie H. Dekarbonisierung in Salzburgs Skigebieten – Entwicklung von Optimierungsalgorithmen und Energiemanagementsystemen zur Steigerung der Energieeffizienz, Minimierung von Emissionen und Optimierung von Flexibilitäten [Decarbonization of the skiing areas in Salzburg – development of optimization algorithms and energy management systems to increase energy efficiency, minimize emissions and optimize flexibility]. Elektrotechnik und Informationstechnik. 31 May 2021.

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Winter tourism is an energy-intensive branch of industry. The aim of the FFG funding project Clean Energy for Tourism is to support Salzburg’s skiing areas on the way to decarbonization by developing technologies and business models. In this article, the developed ICT infrastructure, the optimization algorithms and the business models are presented.

Peer reviewed papers | 2021

Emission minimization of a top-lit updraft gasifier cookstove based on experiments and detailed CFD analyses

Scharler R, Archan G, Rakos C, von Berg L, Lello D, Hochenauer C, Anca-Couce A. Emission minimization of a top-lit updraft gasifier cookstove based on experiments and detailed CFD analyses. Energy Conversion and Management. 2021.247:114755.

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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.

Reports | 2021

Endbericht: Heat Pumping system Control (HPC)

Modellbasierte Regelung von Absorptionswärmepump-Anlagen.

Zlabinger S, Wernhart M, Unterberger V, Rieberer R, Gölles M, Rohringer C, Poier H, Halmdienst C, Kemmerzehl C, Otto M. Heat Pumping system Control (HPC). Modellbasierte Regelung von Absorptionswärmepump-Anlagen. FFG, 4. Ausschreibung Energieforschungsprogramm, Projektnummer: 865095. Endbericht. 2021.

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Reports | 2021

Energiespeicher in Österreich

Marktentwicklung 2020

Biermayr P, Aigenbauer St, Enigl M, Fink C, Knabl S, Leonhartsberger K, Matschegg D, Prem E, Strasser C, Wittmann M. Energiespeicher in Österreich Marktentwicklung 2020. 2021

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Other Publications | 2021

HPC - Workshop

Experimentelle Analyse, Simulation und Regelung von Absorptionswärmepumpen/-kältemaschinen

Zlabinger S, Unterberger V, Gölles M, Wernhart M, Rieberer R, Poier H, Rohinger C, Kemmerzehl C, Halmdienst C. Experimentelle Analyse, Simulation und Regelung von Absorptionswärmepumpen/-kältemaschinen. Online-Workshop im Rahmen des FFG-Projekts HPC ("4. Ausschreibung Energieforschung 2017") am 09.04.2021.

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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.

Other Publications | 2021

Leitfaden: Energiegemeinschaften im Tourismussektor

Iglar B, Fina B, Jung M, Markotsky-Kolm E, Tölzer T, Zellinger M, Liedtke P, Oberbauer C. Leitfaden: Energiegemeinschaften im Tourismussektor. Klima- und Energiefonds. December 2021.

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Peer reviewed papers | 2021

Mixed-integer linear programming based optimization strategies for renewable energy communities

Cosic A, Stadler M, Mansoor M, Zellinger M. Mixed-integer linear programming based optimization strategies for renewable energy communities. Energy. 237.2021

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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.

Peer reviewed papers | 2021

Model-Based Estimation of the Flue Gas Mass Flow in Biomass Boilers.

Niederwieser H, Zemann C, Goelles M, Reichhartinger M. Model-Based Estimation of the Flue Gas Mass Flow in Biomass Boilers. IEEE Transactions on Control Systems Technology. 2021 Jul;19(4):1609 - 1622. https://doi.org/10.1109/TCST.2020.3016404

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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.

Other Publications | 2021

Modelling and control of large-scale solar thermal systems

Unterberger V. Modelling and control of large-scale solar thermal systems. 2021. 212 p.

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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.

Peer reviewed papers | 2021

Modelling fuel flexibility in fixed-bed biomass conversion with a low primary air ratio in an updraft configuration

Anca-Couce A, Archan G, Buchmayr M, Essl M, Hochenauer C, Scharler R. Modelling fuel flexibility in fixed-bed biomass conversion with a low primary air ratio in an updraft configuration. Fuel. 2021.296:120687.

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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.

Peer reviewed papers | 2021

Operation of coupled multi-owner district heating networks via distributed optimization

Kaisermayer V, Muschick D, Horn M, Gölles M. Operation of coupled multi-owner district heating networks via distributed optimization. Energy Reports. 2021 Okt;7(Suppl. 4):273-281. https://doi.org/10.1016/j.egyr.2021.08.145

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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.

Other Publications | 2021

Operation of Coupled Multi-Owner District Heating Networks via Distributed Optimization

Muschick D, Gölles M, Kaisermayer V, Horn M. Operation of Coupled Multi-Owner District Heating Networks via Distributed Optimization.17th International Symposium on District Heating and Cooling. Nottingham Trent University, Nottingham, United Kingdom. 7. Sep 2021. Oral Presentation. [online]

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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.

Reports | 2021

OptEnGrid Optimal integration of heat, electricity and gas systems to increase efficiency and reliability

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OptEnGrid is a cross-sectoral multi-energy system optimization tool for the optimal planning and dispatch of the Distributed Energy Resource (DER) technologies in smart- and microgrids. The methodology of OptEnGrid considers an optimization model which is based on Mixed-Integer Linear Programming (MILP) framework. The following sub-sections provide more details about the energy flow and system optimization inside OptEnGrid and the choice of the optimization over simulation

Other Publications | 2021

Optimal operation of cross-ownership district heating and cooling networks

Muschick D, Kaisermayer V, Gölles M, Horn M.Optimal operation of cross-ownership district heating and cooling networks. 20th European Roundtable on Sustainable Consumption and Production. 9. Sep 2021. Graz. Oral Presentation.

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Peer reviewed papers | 2021

Optimal planning of thermal energy systems in a microgrid with seasonal storage and piecewise affine cost functions

Mansoor M, Stadler M, Zellinger M, Lichtenegger K, Auer H, Cosic A. Optimal planning of thermal energy systems in a microgrid with seasonal storage and piecewise affine cost functions. Energy. 2021:215;119095.

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The optimal design of microgrids with thermal energy system requires optimization techniques that can provide investment and scheduling of the technology portfolio involved. In the modeling of such systems with seasonal storage capability, the two main challenges include the low temporal resolution of available data and the non-linear cost versus capacity relationship of solar thermal and heat storage technologies. This work overcomes these challenges by developing two different optimization models based on mixed-integer linear programming with objectives to minimize the total energy costs and carbon dioxide emissions. Piecewise affine functions are used to approximate the non-linear cost versus capacity behavior. The developed methods are applied to the optimal planning of a case study in Austria. The results of the models are compared based on the accuracy and real-time performance together with the impact of piecewise affine cost functions versus non-piecewise affine fixed cost functions. The results show that the investment decisions of both models are in good agreement with each other while the computational time for the 8760-h based model is significantly greater than the model having three representative periods. The models with piecewise affine cost functions show larger capacities of technologies than non-piecewise affine fixed cost function based models.

Reports | 2021

Planung zellularer Energiesysteme

Teil 1: Effektive integrierte Investitions- und Betriebsplanung von Energiezellen

VDE Verband der Elektrotechnik e.V. Energietechnische Gesellschaft (ETG)

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In einem zellularen Energiesystem wird die physikalische Balance zwischen Energieangebot und -nachfrage so weit als möglich bereits auf regionaler, lokaler Ebene hergestellt. Der zentrale Baustein dabei ist die Energiezelle. Sie kann Energie in Form von Wärme, Elektrizität oder Gas aufnehmen und/oder Elektrizität und Wärme (z. B. aus erneuerbaren Energien) selbst erzeugen, um so den eigenen Wärme- und Elektrizitätsbedarf zu decken. Energieüberschüsse können (elektrisch und/oder thermisch) gespeichert oder anderen Zellen im Nahbereich oder einem Energieversorger zur Verfügung gestellt werden. Ein Energiezellenmanagement kann in Koordination mit Nachbarzellen den Ausgleich von Erzeugung und Verbrauch über alle vorhandenen Energieformen organisieren.
Die Planung und der Betrieb zellularer Energiesysteme ist eine komplexe Aufgabe, da eine Vielzahl von dezentralen Energietechnologien, verschiedenste Ziele und auch Entscheidungsträger berück-sichtigt werden müssen.
Der vorliegende VDE Impuls beschreibt als ersten Schritt die Planung einer Energiezelle, welche mit Energieversorgern interagieren kann. Er ist der Auftakt einer Reihe weiterer Veröffentlichungen zur detaillierten Planung von Energiezellen und zellularen Energiesystemen.

Reports | 2021

Supervisory control of large-scale solar thermal systems

Task 55 Towards the Integration of Large SHC Systems into DHC Networks

Gölles M, Unterberger V, Kaisermayer V, Nigitz T, Muschick D. "Supervisory control of large-scale solar thermal systems". IEA SHC FACTSHEET 55.A-D4.1. Date of Publication: 28.01.2021. https://task55.iea-shc.org/fact-sheets

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Overview on different approaches for supervisory control strategies,deciding on operating modes and set points for the controls of the different plants and componentsintegrated in solar thermal systems.

Peer reviewed papers | 2021

Techno-economic optimization of islanded microgrids considering intra-hour variability

Mathiesen P, Stadler M, Kleissl J, Pecenak Z. Techno-economic optimization of islanded microgrids considering intra-hour variability. Applied Energy. 2021.304:117777.

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The intra-hour intermittency of solar energy and demand introduce significant design challenges for microgrids. To avoid costly energy shortfalls and mitigate outage probability, islanded microgrids must be designed with sufficient distributed energy resources (DER) to meet demand and fulfill the energy and power balance. To avoid excessive runtime, current design tools typically only utilize hourly data. As such, the variable nature of solar and demand is often overlooked. Thus, DER designed based on hourly data may result in significant energy shortfalls when deployed in real-world conditions. This research introduces a new, fast method for optimizing DER investments and performing dispatch planning to consider intra-hour variability. A novel set of constraints which operate on intra-hour data are implemented in a mixed-integer-linear-program microgrid investment optimization. Variability is represented by the single worst-case intra-hour fluctuation. This allows for fast optimization times compared to other approaches tested. Applied to a residential microgrid case study with 5-minute intra-hour resolution, this new method is shown to maintain optimality within 2% and reduce runtime by 98.2% compared to full-scale-optimizations which consider every time-step explicitly. Applicable to a variety of technologies and demand types, this method provides a general framework for incorporating intra-hour variability into microgrid design.

Other papers | 2021

The robust exact differentiator toolbox revisited: Filtering and discretization features.

Andritsch B, Horn M, Koch S, Niederwieser H, Wetzlinger M, Reichhartinger M. The robust exact differentiator toolbox revisited: Filtering and discretization features. in 2021 IEEE International Conference on Mechatronics, ICM 2021. Institute of Electrical and Electronics Engineers. 2021. 9385675 https://doi.org/10.1109/ICM46511.2021.9385675

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An extended version of a Simulink ® -block providing on-line differentiation algorithms based on discretized sliding-mode concepts is presented. Based on user-specified settings it computes estimates of the time-derivatives of the input signal up to order ten. Different discrete-time estimation algorithms as well as optional filtering properties can be selected. The paper includes an overview of the implemented algorithms, a detailed explanation of the developed Simulink ® -block and two examples. The first example illustrates the application of the toolbox in a numerical simulation environment whereas the second one shows results obtained via an electrical laboratory setup.

Conference presentations and posters | 2020

"Long-term verification of a new modular method for CO-lambda-optimisation"

Zemann C, Hammer F, Gölles M. Long-term verification of a new modular method for CO-lambda-optimisation. 6th Central European Biomass Conference CEBC 2020 (Oral Presentation). 2020.

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Peer reviewed papers | 2020

A MILP-based modular energy management system for urban multi-energy systems: Performance and sensitivity analysis

Moser AGC, Muschick D, Gölles M, Nageler PJ, Schranzhofer H, Mach T et al. A MILP-based modular energy management system for urban multi-energy systems: Performance and sensitivity analysis. Applied Energy. 2020;2020(261). 114342.

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The continuous increase of (volatile) renewable energy production and the coupling of different energy sectors such as heating, cooling and electricity have significantly increased the complexity of urban energy systems. Such multi-energy systems (MES) can be operated more efficiently with the aid of optimization-based energy management systems (EMS). However, most existing EMS are tailor-made for one specific system or class of systems, i.e. are not generally applicable. Furthermore, only limited information on the actual savings potential of the usage of an EMS under realistic conditions is available. Therefore, this paper presents a novel modular modeling approach for an EMS for urban MES, which also enables the modeling of complex system configurations. To assess the actual savings potential of the proposed EMS, a comprehensive case study was carried out. In the course of this the influence of different user behavior, changing climatic conditions and forecast errors on the savings potential was analyzed by comparing it with a conventional control strategy. The results showed that using the proposed EMS in conjunction with supplementary system components (thermal energy storage and battery) an annual cost savings potential of between 3 and 6% could be achieved.

Other papers | 2020

Advanced modular process analysis tool for biomass-based Chemical Looping systems

Steiner T, Schulze K, Scharler R. Advanced modular process analysis tool for biomass-based Chemical Looping systems. 3RD DOCTORAL COLLOQUIUM BIOENERGY. 2020.

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In order to limit global warming to 1.5 °C compared to the pre-industrial temperature level, zero net CO2 emissions are needed on a global scale until 2050. A Chemical Looping (CL) process represents a technological system which is CO2-negative when using biomass as fuel and thus can substantially contribute to this target. In principle, the process uses a metal oxide as oxygen carrier material (OC) which is cyclically oxidized by air or steam and reduced by the fuel. Without air as the direct oxygen source for fuel conversion, high calorific product gases or pure carbon dioxide in case of combustion are obtained after the condensation of water vapor, which can then be stored or further utilized.
Within the funded project ”BIO-LOOP”, different Chemical Looping processes (for example combustion, gasification, hydrogen production) and reactors (fixed bed, fluidized bed) are investigated numerically and experimentally. An advanced process analysis tool based on mass and energy balances of the system considered will be presented. It provides data about the specific internal and external streams, process conditions and efficiencies. Within the analysis tool, various independent modular units describe individual process steps, e.g. mixing, chemical reaction or splitting. These components can be adjusted, combined and interconnected according to the flow chart of the system. The process model represents the first step towards a flexible Chemical Looping reactor simulation toolbox to analyze various process scenarios. Emphasis is put on the flexibility regarding the fuels and oxygen carriers, their conversion and possible process variations. The tool developed will support upcoming CFD modeling and further economic considerations.

Other Publications | 2020

Betrieb bei maximaler Effizienz und minimalen Emissionen durch CO-lambda-Optimierung

Zemann C, Hammer F, Gölles M. Betrieb bei maximaler Effizienz und minimalen Emissionen durch CO-lambda-Optimierung. Informationstag für Biomassegenossen-schaften Bildungshaus Sankt Magdalena. February 2020.

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Peer reviewed papers | 2020

Biomass pyrolysis TGA assessment with an international round robin

Anca-Couce A, Tsekos C, Retschitzegger S, Zimbardi F, Funke A, Banks S, Kraia T, Marques P, Scharler R, de Jong W, Kienzl N. Biomass pyrolysis TGA assessment with an international round robin.Fuel.2020;276:118002.https://doi.org/10.1016/j.fuel.2020.118002

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The large variations found in literature for the activation energy values of main biomass compounds (cellulose, hemicellulose and lignin) in pyrolysis TGA raise concerns regarding the reliability of both the experimental and the modelling side of the performed works. In this work, an international round robin has been conducted by 7 partners who performed TGA pyrolysis experiments of pure cellulose and beech wood at several heating rates. Deviations of around 20 – 30 kJ/mol were obtained in the activation energies of cellulose, hemicellulose and conversions up to 0.9 with beech wood when considering all experiments. The following method was employed to derive reliable kinetics: to first ensure that pure cellulose pyrolysis experiments from literature can be accurately reproduced, and then to conduct experiments at different heating rates and evaluate them with isoconversional methods to detect experiments that are outliers and to validate the reliability of the derived kinetics and employed reaction models with a fitting routine. The deviations in the activation energy values for the cases that followed this method, after disregarding other cases, were of 10 kJ/mol or lower, except for lignin and very high conversions. This method is therefore proposed in order to improve the consistency of data acquisition and kinetic analysis of TGA for biomass pyrolysis in literature, reducing the reported variability.

Peer reviewed papers | 2020

Control of biomass grate boilers using internal model control

Schörghuber C, Gölles M, Reichhartinger M, Horn M. Control of Biomass Grate Boilers using Internal Model Control. Control engineering practice. 2020.

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A new model-based control strategy for biomass grate boilers is presented in this paper. Internal model control is used to control four outputs of the plant and to achieve a control structure with fewer control parameters needing to be experimentally tuned. A nonlinear state–space model describing the essential behaviour of the biomass grate boiler is used for controller design. The inverse system dynamics representing the main part of internal model control are designed with the help of this model. In doing so the properties of differentially flat systems are used. Due to a time delayed input, the inverse system is determined only for three input output channels. The stabilization of the inverse system dynamics, however, is a challenging task. A stabilization method with the help of the time delayed input is suggested and a stability analysis is given. The new control strategy has only three parameters to be tuned, representing a major reduction of complexity in comparison to existing model-based approaches. Finally, experimental results of the implemented control strategy on representative biomass grate boiler with a nominal capacity of 180 kW are presented and compared to an existing model-based control strategy based on input output linearization. The experimental evaluation proves that it is possible to operate the biomass boiler in all load ranges with high efficiency and low pollutant emissions.

Peer reviewed papers | 2020

Correction to: Investigation of solid oxide fuel cell operation with synthetic biomass gasification product gases as a basis for enhancing its performance

Pongratz G, Subotić V, Schroettner H, Stoeckl B, Hochenauer C, Anca-Couce A, Scharler R. Correction to: Investigation of solid oxide fuel cell operation with synthetic biomass gasification product gases as a basis for enhancing its performance. Biomass Conversion and Biorefinery. 2020

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The authors want to acknowledge, that during the production of the final version of the publication the image for Figure 9 has been replaced with the image for Figure 12, however without changing the content of the paper. This issue is resolved in the current version of the publication.

Peer reviewed papers | 2020

Decentralized heating grid operation: A comparison of centralized and agent-based optimization

Lichtenegger K, Leitner A, Märzinger T, Mair C, Moser A, Wöss D, Schmidl C, Pröll T. Decentralized heating grid operation: A comparison of centralized and agent-based optimization. Sustainable Energy, Grids and Networks. 2020;2020(21).

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Moving towards a sustainable heat supply calls for decentralized and smart heating grid solutions. One promising concept is the decentralized feed-in by consumers equipped with their own small production units (prosumers). Prosumers can provide an added value regarding security of supply, emission reduction and economic welfare, but in order to achieve this, in addition to advanced hydraulic control strategies also superordinate control strategies and appropriate market models become crucial.

In this article we study methods to find a global optimum for the local energy community or at least an acceptable approximation to it. In contrast to standard centralized control approaches, based either on expert rules or mixed integer linear optimization, we adopt an agent-based, decentralized approach that allows for incorporation of nonlinear phenomena. While studied here in small-scale systems, this approach is particularly attractive for larger systems, since with an increasing number of interacting units, the optimization problem becomes more complex and the computational effort for centralized approaches increases dramatically.

The agent-based optimization approach is compared to centralized optimization of the same prosumer-based setting as well as to a purely central setup. The comparison is based on the quality of the optimization solution, the computational effort and the scalability. For the comparison of these three approaches, three different scenarios have been set up and analysed for four seasons. In this analysis, no approach has emerged as clearly superior to the others; thus each of them is justified in certain situations.

Peer reviewed papers | 2020

Detailed experimental investigation of the spatially distributed gas release and bed temperatures in fixed-bed biomass combustion with low oxygen concentration

Archan G, Anca-Couce A, Gregorc J, Buchmayr M, Hochenauer C, Gruber J, Scharler R. Detailed experimental investigation of the spatially distributed gas release and bed temperatures in fixed-bed biomass combustion with low oxygen concentration. Biomass and Bioenergy. 2020;141:105725

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This publication focuses on the experimental investigation of a novel small-scale fuel flexible biomass combustion technology with a fixed-bed employing a low oxygen concentration. It was obtained through a low primary air ratio and the additional supply of recirculated flue gas. The plant was operated with spruce wood chips, which contained three different mass fractions of water, and miscanthus pellets. All relevant components of the released gas above the fixed-bed were measured, as well as the 3D bed temperature distribution. The balances confirmed a high experimental data consistency. Therefore, it was possible to determine the location of the four different conversion zones inside the fixed-bed: drying, pyrolysis, char gasification and char oxidation. The reduction of CO2 to CO in the char reduction zone worked efficiently across the entire grate area. Furthermore, the results showed that the water mass fraction of the fuel did not influence the dry product gas composition, but significantly affected the location for the release of pyrolysis products such as tars. It was found that the low oxygen concentration in the fixed-bed combined with flue gas recirculation was an effective method to reduce bed temperatures and therefore its inorganic emissions while significantly increasing feedstock flexibility. The investigations provided fundamental findings on the conversion and release behavior of the new technology under real operating conditions and are very useful for further experimental work and CFD simulations targeting the reduction of PM and NOX emissions.

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