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Gasification is considered to be a promising way to use biomass with high efficiency in combined heatand power production, for the production of second generation biofuels and in the chemical industry.Especially allothermal fluidized bed steam gasification produces a medium calorific, nitrogen free gassuitable for a variety of downstream processes. In general the raw product gas has to be cleaned fromcondensable hydrocarbons (tar) and conditioned (e.g. adjustment of the H2/CO-ratio) before downstreamuse. The operating conditions of the gasification reactor have a large impact on the quality of the productgas. Hence first steps to a product gas low in tar content can be undertaken directly in the reactor. In thisstudy the capability of influencing the tar content and gas composition by changing temperature (750?840 C), steam to biomass (S/B) ratio (0.8?1.2) and pressure (0.1?0.25 MPa) in an allothermal bubblingfluidized bed steam gasifier is investigated. It is found that rising temperature reduces the total tar contentand affects especially heterocyclic and light aromatic compounds. At atmospheric pressure the naphthalenecontent increases slightly with increasing temperature in contrary to pressurized gasificationwhere naphthalene decreases significantly with increasing temperature. An increase in the S/B ratio leadsto a decreasing total tar content, this tar reduction according to a higher steam content is higher at highertemperatures. Increasing pressure leads to increasing total tar content mainly due to naphthalene, theeffect is most distinct for low S/B ratios.

Abstract The storage of heat in aquifers, also referred to as Aquifer Thermal Energy Storage (ATES), bears a high potential to bridge the seasonal gap between periods of highest thermal energy demand and supply. With storage temperatures higher than 50 °C, High-Temperature (HT) ATES is capable to facilitate the integration of (non-)renewable heat sources into complex energy systems. While the complexity of ATES technology is positively correlated to the required storage temperature, HT-ATES faces multidisciplinary challenges and risks impeding a rapid market uptake worldwide. Therefore, the aim of this study is to provide an overview and analysis of these risks of HT-ATES to facilitate global technology adoption. Risk are identified considering experiences of past HT-ATES projects and analyzed by ATES and geothermal energy experts. An online survey among 38 international experts revealed that technical risks are expected to be less critical than legal, social and organizational risks. This is confirmed by the lessons learned from past HT-ATES projects, where high heat recovery values were achieved, and technical feasibility was demonstrated. Although HT-ATES is less flexible than competing technologies such as pits or buffer tanks, the main problems encountered are attributed to a loss of the heat source and fluctuating or decreasing heating demands. Considering that a HT-ATES system has a lifetime of more than 30 years, it is crucial to develop energy concepts which take into account the conditions both for heat sources and heat sinks. Finally, a site-specific risk analysis for HT-ATES in the city of Hamburg revealed that some risks strongly depend on local boundary conditions. A project-specific risk management is therefore indispensable and should be addressed in future research and project developments.

In this article, we investigate the passivation quality and electrical contact properties for samples with a 150 nm thick n+ polysilicon layer in comparison to samples with a phosphorus diffused layer. High level of passivation is achieved for the samples with n+ polysilicon layer and an interfacial oxide underneath it. The contact properties with screen-printed fire-through silver paste are excellent (no additional recombination from metallization and specific contact resistivity (ρc) ≤ 2 mΩ·cm2) for the samples with the polysilicon layers. Fast-firing peak temperature was varied during the contact formation process; this was done to see the trend in the contact properties with the change in the thermal budget. The differences in the J0met and ρc for the two different kinds of samples are explained with the help of high-resolution scanning electron microscope imaging. Finally, we prepare M2-sized n-passivated emitter rear totally (PERT) diffused solar cells with a 150 nm thick n+ polysilicon based passivated rear contact. The best cell achieved an efficiency of 21.64%, with a Voc of 686 mV and fill factor of 80.2%. ; Photovoltaic Materials and Devices ; Electrical Sustainable Energy

Deposits formation on heat transfer surfaces is one of the main problems associated to biomass co-combustion. It reduces plant efficiency and availability and increases maintenance costs. It is obvious that an increasing amount of low-temperature melting components in fuel ash accelerates and aggravates this process. Research is done to evaluate the validity of thermal analysis methods to characterise fusion of biomass and waste ashes. Laboratory ashes from a set of biomass and waste fuels are leached in successive steps. The original and the leached ashes are analysed by Thermo-Mechanical Analysis (TMA). Traces obtained from TMA show to be promising ash fingerprints to classify deposition tendencies. Additionally Simultaneous Thermal Analysis (STA) is performed on selected samples. Furthermore, improved chemical equilibrium calculations are proposed to predict the proportion of melted species resulting from combustion of biomass fuels. The model takes into account the reactivity of the inorganic matter in the fuel as issued from ash leaching.

Abstract In a real turbulent spray flame, dispersion, continuous phase turbulence modification, dispersed phase inter-particle collisions, evaporation, mixing and combustion occur simultaneously. Dealing with all these complexities and their interactions poses a tremendous modeling task. Therefore, in order to advance current modeling capabilities, it seems reasonable to aim for progress in individual sub-areas like breakup, dispersion, mixing and combustion, which however cannot be viewed in complete isolation. Further, one has to consider advantages and disadvantages of the general modeling approaches, which are direct numerical simulation (DNS), large eddy simulation (LES), simulations based on Reynolds averaged equations and probability density function (PDF) methods. Not least one also has to distinguish between Eulerian and Lagrangian dispersed phase descriptions. The goal of this paper is to provide a review of computational model developments relevant for turbulent dilute spray combustion, i.e. the dense regime, including collisions as well as primary and secondary atomization, is not covered. Also not considered is breakup in dilute sprays, which can occur in the presence of sufficiently high local turbulence. It is intended to guide readers interested in theory, in the development and validation of predictive models, and in planning new experiments. In terms of physical phenomena, the current understanding regarding turbulence modification due to droplets, preferential droplet concentration, impact on evaporation and micro-mixing, and different spray combustion regimes is summarized. In terms of modeling, different sets of equations are discussed, i.e. the governing conservation laws without and with point droplet approximation as employed by DNS, the filtered equations considered in LES, the Reynolds averaged equations, and Lagrangian evolution equations. Further, small scale models required in the context of point droplet approximations are covered. In terms of computational studies and method developments, progress is categorized by the employed approaches, i.e. DNS, LES, simulations based on Reynolds averaged equations, and PDF methods. In terms of experiments, various canonical spray flame configurations are discussed. Moreover, some of the most important experiments in this field are presented in a structured way with the intention to provide a database for model validation and a guideline for future investigations.

Deep sea mining was identified in the middle of last century. However, its industrialization and commercialization today are limited in the costal mining industry due to the high mining cost and technical issues. The purpose of this paper is to analyze a green transport plan of deep sea mining systems in terms of the optimal efficiency of the rigid pipe lifting system and the total energy consumption. The deep sea mining facilities considered in this paper consist of a mineral collecting machine, a flexible hose, a rigid pipe, a grinding machine, a concentrating machine and a horizontal pipe conveyor. Centrifugal pump modelling and its working principle are researched, because it is the major transport facility. The relationship between the optimal efficiency, total energy consumption, transport loss factor, and the relating mining parameters is determined by numerical simulations and fittings under Fortran and Matlab environment, and the optimization under 1st Opt environment. The research conducted in this paper is valuable for the pre-evaluation of deep sea mining transport systems and the further realization of its industrialization and commercialization process.

The paper proposes a new concept of protection philosophy for Dutch distribution grids with high penetration of renewable energy. Conventional protection concepts are normally based on protection schemes that consist of definite or inverse time overcurrent relays. In future power systems, these schemes can lead to high fault clearing times, unselective tripping and massive DG disconnections, which are not acceptable in a deregulated multi-owner energy market. This research work proposes an efficient intelligent communication-based protection algorithm that implements different multi-functional protection principles supported by blocking schemes. The real-time organization of both the hardware architecture and communication infrastructure of the protection algorithm is illustrated in detail. Special emphasis is given to the network reconfiguration scenario cases and detailed simulation results of such illustrative studied cases are provided. The new protection strategy guarantees protection selectivity and provides DG-unit availability during and after the fault. The intelligent algorithm is applied on existing Dutch distribution network and meaningful conclusions are derived.

Abstract Based on the increasing concern about human-induced global warming, it is expected that constraints on carbon emissions will be much stricter in the future. Integrated gasification combined cycle (IGCC) power plants are an option in the attempt to mitigate the effect of CO 2 emissions, because they can be fuelled or co-fuelled with biomass, but also, very importantly, because they can be equipped with pre-combustion CO 2 capture units. Moreover, the rapidly growing share of electricity produced by converting renewable energy sources demands for more flexible operation of future IGCC plants in order to compensate for inherently intermittent operation of wind and solar power plants. The CO 2 capture unit should therefore be able to follow the dynamic operation of the power plant, and, at the same time, meet environmental targets in terms of CO 2 removal. In order to investigate and improve the transient performance of such complex systems, dynamic process simulations performed with accurate physically based models are essential. This paper presents the development and validation of the dynamic model of the absorption and solvent regeneration unit as part of a pre-combustion CO 2 capture system, with focus on the absorber column model. The models are implemented into an open source software library following an object-oriented, equation-based modelling approach using the Modelica language. The models are validated by comparison against two sets of transient experimental data generated at the CO 2 capture pilot plant realized and operated at the Buggenum IGCC power station in the Netherlands. The model predictions satisfactorily reproduce the dynamic performance of the pilot plant considering the main process variables, such as pressures, flow rates and compositions. One of the results of this work is that, in case of physical absorption of CO 2 a well-tuned, equilibrium-based absorber model is able to accurately predict transient operation. The validated process models enable process and control system design aiming at improvement of transient performance of the pre-combustion capture unit.

This paper reports on a characterization of structures fabricated by electrochemical etching in hydrofluoric acid (HF) using different types of initial pits. An initial pit has been thought to require a sharp tip in order to collect electronic holes generated by illumination. Therefore, the initial pits have been formed by etching in a KOH solution, which suffers from crystal orientation dependence. We successfully demonstrate the structures fabricated by the electrochemical etching with the initial pits, which have flat or round base. These pits are formed by isotropic wet etching or reactive ion etching (RIE), which are free from crystal orientation of silicon substrate. Furthermore, regular hole patterns can be achieved without initial pits. This makes the electrochemical etching process more simple. The electric field in the silicon is calculated and the calculated results support the experimental results.