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Item type:Publication, Access status: with files , Comparative Analysis of Primary and Secondary Emission Mitigation Measures for Small-Scale Wood Chip Combustion(Multidisciplinary Digital Publishing Institute (MDPI), 2024-09-03); ; ; The objective of this study is to systematically investigate not only the influence of different additive types—beyond the much-considered case of aluminum-silicate-based additives—but also to carry out an additional comparison between primary and secondary emission mitigation measures during small-scale wood-chip combustion. Hence, combustion trials are realized within a 33-kW combustion plant. Pine wood chips additivated with 1.0 wt%<sub>a.r.</sub> of four additives have shown promising emission reduction effects in the past; namely kaolin (i.e., aluminum-silicate-based), anorthite (i.e., aluminum-silicate- and calcium-based), aluminum hydroxide (i.e., aluminum-based), and titanium dioxide (i.e., titanium-based). In addition to the primary mitigation measure (i.e., (fuel) additivation), an electrostatic precipitator (ESP) as a common secondary mitigation measure for total particulate matter (TPM) reduction is used for comparison. In addition to standard analyses (e.g., gravimetric determination of TPM emissions), an extended methodology (e.g., characterization of the elemental composition and ultrafine particle fraction of TPM emissions) is applied. The results show that the additivation of wood chips with kaolin and anorthite can lead to an operation of the combustion plant in compliance with the German legal TPM limit values by undercutting the absolute emission level achievable by the ESP. Additionally, kaolin and anorthite achieve significant reductions in carbon monoxide (CO) emissions, while kaolin simultaneously, and similarly to ESP, also leads to a shift in the particle size number distribution of PM emissions towards coarser particles. All additives show a significant reduction of potassium (K) emissions by the formation of high-temperature stable K compounds in the resulting ashes.Publicationtype: Journal Article38 35 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Sustainable Carbon Utilization for a Climate-Neutral Economy - Framework Necessities and Assessment Criteria(Multidisciplinary Digital Publishing Institute (MDPI), 2024-08-19); The need to limit anthropogenic climate change to 1.5–2 °C, as agreed in the Paris Agreement, requires a significant reduction of CO2 emissions resulting from the use of fossil carbon. However, based on current knowledge, carbon is expected to remain crucial in certain industrial sectors, e.g., the chemical industry. Consequently, it is essential to identify and utilize sustainable carbon sources in the future. In this context, various carbon sources were examined and classified in terms of their disruption of the Earth’s (fast) carbon cycle. Furthermore, the examined carbon sources were qualitatively analyzed with regard to their technical readiness level, their energy expenditure, and their current and future availability, as well as legal regulation within the European Union. As a result, only biogenic and mixed carbon from the ambient air can be considered genuinely sustainable within the Earth’s (fast) carbon cycle. Mixed carbon streams, e.g., from waste recycling, fall into a gray area. The same applies to certain process-related emissions that originally descend from fossil fuel energy. In terms of energy considerations, technical maturity, and exploitable potentials, prioritizing the utilization of biogenic carbon sources is advisable for the time being, especially for CO2 produced as a by-product originating from biogenic carbon carriers.Publicationtype: Journal Article28 29 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Co-Simulation of a cellular energy system(Multidisciplinary Digital Publishing Institute (MDPI), 2023-08-24); ; ; ; The concept of cellular energy systems of the German Association for Electrical, Electronic & Information Technologies (VDE) proposes sector coupled energy networks for energy transition based on cellular structures. Its decentralized control approach radically differs from that of existing networks. Deeply integrated information and communications technologies (ICT) open opportunities for increased resilience and optimizations. The exploration of this concept requires a comprehensive simulation tool. In this paper, we investigate simulation techniques for cellular energy systems and present a concept based on co-simulation. We combine simulation tools developed for different domains. A classical tool for studying physical aspects of energy systems (Modelica, TransiEnt library) is fused with a state-of-the-art communication networks simulator (OMNeT++) via the standardized functional mock-up interface (FMI). New components, such as cell managers, aggregators, and markets, are integrated via remote procedure calls. A special feature of our concept is that the communication simulator coordinates the co-simulation as a master and integrates other components via a proxy concept. Model consistency across different domains is achieved by a common description of the energy system. Evaluation proves the feasibility of the concept and shows simulation speeds about 20 times faster than real time for a cell with 111 households.Publicationtype: Journal Article121 134 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Emission mitigation by aluminum-silicate-based fuel additivation of wood chips with kaolin and kaolinite(Multidisciplinary Digital Publishing Institute (MDPI), 2023-03-28); ; This study investigates the transferability of aluminum-silicate-based fuel additivation as a primary, fuel-based mitigation measure for inorganic alkali-based particulate matter (PM) emissions during the complete combustion of wood chips. Therefore, wood chips are additivated with 0.5 wt% of three different types of the aluminum-silicate-based additive kaolin, which differ mainly in their particle size distribution, and with one type of kaolinite. The subsequent combustion trials with non-additivated and additivated wood chips are carried out in a small-scale combustion plant. To evaluate the effect of the additivation of the wood chips, the total particulate matter (TPM) emissions, the potassium (K) emissions, the ultra-fine PM emissions and the carbon monoxide (CO) emissions, as well as the chemical composition of the resulting ashes, are analyzed. In order to compare the primary, fuel-side mitigation measure of fuel additivation with the established secondary mitigation measures, an electrostatic precipitator (ESP) is additionally utilized. The respective result shows that the aluminum-silicate-based fuel additivation of the wood chips with kaolin and the use of the ESP lead to comparable reductions in the TPM emissions, as well as the share of the ultra-fine particle fraction in the PM emissions. The addition of the additive kaolin additionally causes the significant mitigation of the K and CO emissions. Overall, the obtained results suggest that the combined utilization of fuel-side aluminum-silicate-based fuel additivation, together with the secondary mitigation measure of the ESP, might be very promising to further reduce PM emissions from combustion devices that operate with wood chips.Publicationtype: Journal ArticleScopus© Citations 1 71 87 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Techno-economic analysis of carbon dioxide separation for an innovative energy concept towards low-emission glass melting(Multidisciplinary Digital Publishing Institute (MDPI), 2023-02-22); ; ; ; The currently still high fossil energy demand is forcing the glass industry to search for innovative approaches for the reduction in CO₂ emissions and the integration of renewable energy sources. In this paper, a novel power-to-methane concept is presented and discussed for this purpose. A special focus is on methods for the required CO₂ capture from typical flue gases in the glass industry, which have hardly been explored to date. To close this research gap, process simulation models are developed to investigate post-combustion CO₂ capture by absorption processes, followed by a techno-economic evaluation. Due to reduced flue gas volume, the designed CO₂ capture plant is found to be much smaller (40 m³ absorber column volume) than absorption-based CO₂ separation processes for power plants (12,560 m³ absorber column volume). As there are many options for waste heat utilization in the glass industry, the waste heat required for CO₂ desorption can be generated in a particularly efficient and cost-effective way. The resulting CO² separation costs range between 41 and 42 EUR/t CO₂, depending on waste heat utilization for desorption. These costs are below the values of 50–65 EUR/t CO₂ for comparable industrial applications. Despite these promising economic results, there are still some technical restrictions in terms of solvent degradation due to the high oxygen content in flue gas compositions. The results of this study point towards parametric studies for approaching these issues, such as the use of secondary and tertiary amines as solvents, or the optimization of operating conditions such as stripper pressure for further cost reductions potential.Publicationtype: Journal ArticleScopus© Citations 4 118 323 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Anaerobic digestion of lignocellulose components : challenges and novel aproaches(Multidisciplinary Digital Publishing Institute (MDPI), 2022-11-10); ; ; ; The reuse of lignocellulosic biomaterials as a source of clean energy has been explored in recent years due to the large amount of waste that involves human activities, such as those related to agriculture and food. The anaerobic digestion (AD) of plant-based biomass for bioenergy production poses a series of challenges that new technologies are attempting to solve. An improved decomposition of recalcitrant lignocellulose together with an increase in biogas production yield are the main objectives of these new approaches, which also seek the added value of being environmentally friendly. Recent research has reported significant progress in this regard, offering promising outcomes on the degradation of lignocellulose and its subsequent transformation into biomethane by specialized anaerobic microorganisms, overcoming the drawbacks inherent to the process and improving the yield of methane production. The future of the agri–food industry seems to be heading towards the implementation of a circular economy through the introduction of strategies based on the optimized use of lignocellulosic residues as a source of clean and sustainable energy.Publicationtype: Journal ArticleScopus© Citations 8 103 119 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Fractionation of lignocellulosic fibrous straw digestate by combined hydrothermal and enzymatic treatment(Multidisciplinary Digital Publishing Institute (MDPI), 2022-08-23); ; ; ; In industrial-scale biogas production from cereal straw, large quantities of solid fiber-rich digestate are produced as residual material. These residues usually contain high amounts of cellulose, hemicellulose and lignin and thus have potential for further utilization. However, they also contain impurities such as ammonia and minerals, which could negatively affect further utilization. Against this background, the present study investigates how this fibrous straw digestate can be fractionated by a combined hydrothermal and enzymatic treatment and what influence the impurities have in this process. Therefore, it is analyzed how the fractions cellulose, hemicellulose and lignin are modified by this two-stage treatment, using either raw digestate (including all impurities) or washed digestate (containing only purified fibers) as the substrate. For both substrates, around 50% of the hemicellulose is solubilized to xylans after 50 min of hydrothermal treatment using steam at 180 °C. Furthermore, by subsequent enzymatic treatment, around 90% and 92% of the cellulose and hemicellulose still contained in the solids are hydrolyzed to glucose and xylose, respectively. Lignin accumulates in the remaining solid but structurally degrades during the hydrothermal treatment, which is indicated by decreasing ether and ester bond contents with increasing treatment times. Impurities contained within the raw digestate do not hinder this fractionation; they even seem to positively affect hemicellulose and cellulose valorization, but apparently lead to a slightly higher lignin degradation.Publicationtype: Journal ArticleScopus© Citations 4 115 149 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Control of a PVT-heat-pump-system based on reinforcement learning : operating cost reduction through flow rate variation(Multidisciplinary Digital Publishing Institute (MDPI), 2022-04-02); This study aims to develop a controller to operate an energy system-consisting of a photovoltaic thermal (PVT) system combined with a heat pump, using the reinforcement learning approach to minimize the operating costs of the system. For this, the flow rate of the cooling fluid pumped through the PVT system is controlled. This flow rate determines the temperature increase of the cooling fluid while reducing the temperature of the PVT system. The heated-up cooling fluid is used to improve the heat pump’s coefficient of performance (COP). For optimizing the operation costs of such a system, first an extensive simulation model has been developed. Based on this technical model, a controller has been developed using the reinforcement learning approach to allow for a cost-efficient control of the flow rate. The results show that a successfully trained control unit based on the reinforcement learning approach can reduce the operating costs with an independent validation dataset. For the case study presented here, based on the implemented methodological approach, including hyperparameter optimization, the operating costs of the investigated energy system can be reduced by more than 4% in the training dataset and by close to 3% in the validation dataset.Publicationtype: Journal Article94 219 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Aggregation of demand-side flexibilities: A comparative study of approximation algorithms(Multidisciplinary Digital Publishing Institute (MDPI), 2022-04-01); ; ; ; Traditional power grids are mainly based on centralized power generation and subsequent distribution. The increasing penetration of distributed renewable energy sources and the growing number of electrical loads is creating difficulties in balancing supply and demand and threatens the secure and efficient operation of power grids. At the same time, households hold an increasing amount of flexibility, which can be exploited by demand-side management to decrease customer cost and support grid operation. Compared to the collection of individual flexibilities, aggregation reduces optimization complexity, protects households’ privacy, and lowers the communication effort. In mathematical terms, each flexibility is modeled by a set of power profiles, and the aggregated flexibility is modeled by the Minkowski sum of individual flexibilities. As the exact Minkowski sum calculation is generally computationally prohibitive, various approximations can be found in the literature. The main contribution of this paper is a comparative evaluation of several approximation algorithms in terms of novel quality criteria, computational complexity, and communication effort using realistic data. Furthermore, we investigate the dependence of selected comparison criteria on the time horizon length and on the number of households. Our results indicate that none of the algorithms perform satisfactorily in all categories. Hence, we provide guidelines on the application-dependent algorithm choice. Moreover, we demonstrate a major drawback of some inner approximations, namely that they may lead to situations in which not using the flexibility is impossible, which may be suboptimal in certain situations.Publicationtype: Journal ArticleScopus© Citations 7 21 59 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Electrical launch catapult and landing decelerator for fixed-wing airborne wind energy systems(Multidisciplinary Digital Publishing Institute (MDPI), 2022-03-29); ; ; ; This paper presents a (pre)feasibility study of the rail-based ultra-short launch and landing system ElektRail for fixed-wing airborne wind energy systems, such as Ampyx Power. The ElektRail concept promises airborne mass reductions through the elimination of landing gear as well as decreased landing stresses and ground stability requirements, opening possibilities for improved aerodynamics through a single fuselage configuration. Initially designed for operating fixed-wing drones from open fields, the ElektRail concept had to be significantly shortened for application in an airborne wind energy (AWE) context. This shorter size is required due to the much more limited space available at AWE sites, especially on offshore platforms. Hence, a performance enhancement using the integration of a bungee launching and landing system (BLLS) was designed and a system dynamics model for the launch and landing was derived. The results demonstrated the possibility for the ElektRail to be shortened from 140 m to just 19.3 m for use with an optimised tethered aircraft with a mass of 317 kg. A system length below 20 m indicates that an enhanced ElektRail launch and landing concept could be viable for airborne wind energy operations, even with relatively low-tech bungee cord boosters. Linear motor drives with a long stator linear motor actuator could potentially shorten the system length further to just 15 m, as well as provide better control dynamics. An investigation into improved AWE net power outputs due to reduced airborne mass and aerodynamic improvements remains to be conducted.Publicationtype: Journal ArticleScopus© Citations 4 119 237