226 research outputs found
Thermochemical Conversion Processes for Solid Fuels and Renewable Energies: Volume II
No full textThe increasing share of renewable energy sources is drawing attention to a critical challenge. The availability of wind turbines and photovoltaic solar cells is limited and difficult to predict. They usually provide a fluctuating feed-in to the grid, so energy reserves, e.g., conventional thermal power plants or energy storage systems, are necessary to establish a balance between electricity supply and demand. Various solutions can be adopted to maintain the security of supply and improve the flexibility of the future power system, such as improving the efficiency of technical processes in areas such as thermal power plants, cement and metallurgy industries, the use of advanced thermochemical conversion technologies such as gasification, the expansion of high-voltage transmission infrastructure, the promoting of renewable energy sources, the employment of large-scale energy storage systems, and the use of highly flexible power generation units with carbon capture and utilisation, such as combined-cycle power plants. Given this background, this Special Issue contains fundamental scientific studies on the latest research progress in the development and optimisation of gasification processes, renewable energy source “solar energy”, synthesis of new hybrid nanocomposites and nanofluids, carbon capture, and energy storage systems. Special Issue Editors Falah Alobaid Jochen Ströhl
Wide band correlated-k approaches for non-grey radiation modelling in oxy-fuel combustion with dry recycling
No full textIncreased CO2 and H2O concentrations in oxy-fuel combustion promote radiation compared to conventional air based technologies. Spectral radiation models are necessary to calculate the radiative properties of CO2 and H2O. In the present study, the wide band correlated-k method (WBCK) is evaluated for non-grey radiative transfer calculations in oxy-fuel combustion. Several WBCK formulations are presented and applied to virtual gas turbine combustors for both air and oxy-fuel combustion with dry recycling involving strongly varying H2O/CO2 ratios. The spectral formulation of the WBCK is the most exact approach, but leads to excessive computational times. The multiple gases formulation using three optimised absorption coefficient is found to be the optimum choice regarding accuracy and computational efficiency. The results of a standard weighted-sum-of-grey-gases method strongly deviate from those of the WBCK
Assessment of the re-ordered wide band model for non-grey radiative transfer calculations in 3D enclosures
No full textThe objective of the present study is to evaluate variations of the re-ordered wide band model for non-grey radiative transfer calculations in 3D enclosures using the discrete ordinates method. First, the performance of various angular and spatial discretisation schemes of the discrete ordinates method is investigated. Then, several formulations, averaging procedures, and scaling methods of the re-ordered wide band model are tested, and the results are validated against those of a statistical narrow band model. The grey gases formulation using three optimised absorption coefficient is found to be the most efficient method
Online mechanism design for scheduling non-preemptive jobs under uncertain supply and demand
No full textWe design new algorithms for the problem of allocating uncertain flexible, and multi-unit demand online given uncertain supply, in order to maximise social welfare. The algorithms can be seen as extensions of the expectation and consensus algorithms from the domain of online scheduling. The problem is especially relevant to the future smart grid, where uncertain output from renewable generators and conventional supply need to be integrated and matched to flexible, non-preemptive demand. To deal with uncertain supply and demand, the algorithms generate multiple scenarios which can then be solved offline. Furthermore, we use a novel method of reweighting the scenarios based on their likelihood whenever new information about supply becomes available. An additional improvement allows the selection of multiple non-preemptive jobs at the same time. Finally, our main contribution is a novel online mechanism based on these extensions, where it is in the agents' best interest to truthfully reveal their preferences. The experimental evaluation of the extended algorithms and different variants of the mechanism show that both achieve more than 85% of the offline optimal economic efficiency. Importantly, the mechanism yields comparable efficiency, while, in contrast to the algorithms, it allows for strategic agents
Special Issue “Thermochemical Conversion Processes for Solid Fuels and Renewable Energies”
No full textThe world society ratifies international measures to reach a flexible and low-carbon energy economy, attenuating climate change and its devastating environmental consequences. The main contribution of this Special Issue is related to thermochemical conversion technologies of solid fuels (e.g., biomass, refuse-derived fuel, and sewage sludge), in particular via combustion and gasification. Here, the recent activities on operational flexibility of co-combustion of biomass and lignite, carbon capture methods, solar-driven air-conditioning systems, integrated solar combined cycle power plants, and advanced gasification systems, such as the sorption-enhanced gasification and the chemical looping gasification, are shown
CO2 Capture Based on Chemical and Carbonate Looping
No full textDie Chemical- und Carbonate-Looping-Verfahren sind zwei effiziente und umweltfreundliche Prozesse zur CO2-Abscheidung aus fossil befeuerten Kraftwerken. Beide Verfahren versprechen hohe Wirkungsgrade und geringe Kosten im Vergleich zu anderen CO2-Abscheidungstechnologien, stehen aber noch am Anfang ihrer Entwicklung. Hier wird ein Überblick über den momentanen Stand der Forschung gegeben. Das Chemical-Looping-Verfahren hat die potentiell niedrigsten Wirkungsgradeinbußen, da keine Energie zur Abtrennung von CO2 oder O2 aufgebracht werden muss. Es eignet sich nur bedingt für die Nachrüstung bestehender Anlagen und ist deshalb für neue Kraftwerke mit CO2-Abscheidung eine vielversprechende Option. Das Carbonate-Looping-Verfahren hat durch die Bereitstellung von O2 etwas höhere Wirkungsgradeinbußen, die jedoch deutlich geringer als bei der Oxyfuel-Verbrennung oder der MEA-Wäsche ausfallen. Das Verfahren ist besonders für die Nachrüstung bestehender Anlagen geeignet. Für weitergehende Untersuchungen hinsichtlich der technischen Umsetzung beider Verfahren wird an der TU Darmstadt ein Versuchsfeld im1 MWth-Maßstab errichtet
Special Issue "Thermochemical Conversion Processes for Solid Fuels and Renewable Energies"
No full textThe world society ratifies international measures to reach a flexible and low-carbon energy economy, attenuating climate change and its devastating environmental consequences. The main contribution of this Special Issue is related to thermochemical conversion technologies of solid fuels (e.g., biomass, refuse-derived fuel, and sewage sludge), in particular via combustion and gasification. Here, the recent activities on operational flexibility of co-combustion of biomass and lignite, carbon capture methods, solar-driven air-conditioning systems, integrated solar combined cycle power plants, and advanced gasification systems, such as the sorption-enhanced gasification and the chemical looping gasification, are shown
Solid flux measurement in dual fluidized bed processes based on solid samples
No full textChemical looping gasification is a novel dual fluidized bed technology for the conversion of solid feedstock to a nitrogen-free syngas without the need of pure oxygen. Recently, a pilot plant has been erected to advance chemical looping gasification towards autothermal operation. For autothermal operation, the solids flux between the two reactors becomes important, as it transports the required sensible heat in addition to the oxygen required for the process. As a reliable method to accurately measure the solids flux under process conditions currently does not exist, a method has been devised to measure the solid circulation for dual fluidized bed systems and tested utilizing the process specifics of chemical looping gasification to allow for calibration of online measurement equipment without opening the reactor system. This method utilizes solid samples from coupling elements to calculate the solids flux in chemical looping gasification with an overall uncertainty smaller than 20%
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