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[en] Based on the discrete ordinates scheme with (an) infinitely small weight(s) (DOS+ISW) which was recently proposed by the present authors, a new discrete ordinate algorithm is developed for computing the radiative transfer in 1-D atmospheres. The biggest feature of the new algorithm is that it is simple and universally applicable. It is also suited to parallel computation
[en] This paper aims at the optimum design of a solar reactor for carbon product processing by vaporization. The chosen reference case is the CNRS 1 MW solar furnace and graphite vaporization for fullerene synthesis. The method, which accounts for heat transfer and chemical reaction kinetics, is based on the combination of both experimental data obtained at laboratory scale and numerical simulation. For this very high temperature process (carbon vaporization is only significant at temperatures higher than 3200 K), the optimum diameter of the target is 22 cm and the soot production ranges between 80 and 150 g/h for an effective power of 325 kW (P=240 h Pa). The model is validated by experiments using a 6 cm o.d. graphite target
[en] Highlights: • Combined effect of solar pyrolysis parameters was investigated by RSM. • Temperature and heating rate were the first and second influential factors. • Gas products LHV generally increased with temperature and heating rate. • Interaction effects between temperature and heating rate increased in high ranges. • Maximum gas LHV of 14,589 kJ/kg of wood higher than initial wood LHV was obtained. - Abstract: Solar pyrolysis process offers solution to utilize solar energy for converting biomass energy into solar fuel. A Box–Behnken design of experiments was performed to optimize a solar pyrolysis process for the production of combustible gases from beech wood. Response surface methodology (RSM) was used to study the effects of temperature, heating rate and argon flow rate on products distribution, gas LHV (lower heating value) and gas composition. The operating variables were as follows: temperature (800–2000 °C), heating rate (50–450 °C/s) and argon flow rate (4–8 NL/min). A second-order regression model was used to predict the responses. The proposed model described well the experimental values. The analysis of variance (ANOVA) was performed with Minitab 17 software and the significant effect of the factors and their interaction effects were tested at 95% confidence interval. The gas LHV was significantly influenced by temperature and heating rate. The maximum gas LHV higher than that of initial beech wood was found as 14,589 kJ/kg under process conditions as: 2000 °C temperature, 450 °C/s heating rate. The beech wood calorific value is upgraded through solar pyrolysis.
[en] This study deals with solar hydrogen production from the two-step iron oxide thermochemical cycle (Fe3O4/FeO). This cycle involves the endothermic solar-driven reduction of the metal oxide (magnetite) at high temperature followed by the exothermic steam hydrolysis of the reduced metal oxide (wustite) for hydrogen generation. Thermodynamic and experimental investigations have been performed to quantify the performances of this cycle for hydrogen production. High-temperature decomposition reaction (metal oxide reduction) was performed in a solar reactor set at the focus of a laboratory-scale solar furnace. The operating conditions for obtaining the complete reduction of magnetite into wustite were defined. An inert atmosphere is required to prevent re-oxidation of Fe(II) oxide during quenching. The water-splitting reaction with iron(II) oxide producing hydrogen was studied to determine the chemical kinetics, and the influence of temperature and particles size on the chemical conversion. A conversion of 83% was obtained for the hydrolysis reaction of non-stoichiometric solar wustite Fe(1-y)O at 575 deg. C
[en] Highlights: • A hybrid system of increasing boiler inlet feedwater temperature by solar energy is proposed. • An all-condition mechanism model of hybrid system is simulated by MATLAB/Simulink. • The maximum solar energy input exists for hybrid system. • The solar-to-electricity efficiency of hybrid system negatively correlates to solar energy input. • Hybrid system has a high coal saving rate in a lower load condition. - Abstract: Hybridizing solar energy with a coal-fired power plant has proven to be an efficient way of reducing coal consumption and discharged pollutants. In this study, solar energy was employed to heat boiler inlet feedwater through a solar high-pressure feedwater heater H0 to increase its temperature. Solar-aided feedwater heating of a N600-24.2/566/566 supercritical coal-fired power plant is discussed as a case study. An all-condition mechanism model (ACMM) of SACFPP was proposed and simulated by MATLAB/Simulink. The maximum solar energy input for the safe operation of a boiler was determined as 66,544 kW based on ACMM simulation results. Moreover, the boiler efficiency and solar-to-electricity efficiency plummeted as solar energy input increased. The solar-to-electricity efficiency decreased from 23.33% to 20.33% when the solar energy input increased from 16,636 kW to 66,544 kW (in 100%THA). The solar-to-electricity efficiency decreased from 16.76% to 13.29% when the solar energy input increased from 16,636 kW to 66,544 kW (in 35%BMCR). A high unit load corresponds to high solar-to-electricity efficiency. SACFPP had a high coal saving rate when it operated in a lower load condition.
[en] The combined effects of feedstock water content and heating parameters (final temperature and heating rate) on solar pyrolysis product distribution, and on the composition and LHV (lower heating value) of the gas products, were investigated. Beech wood sawdust with 0%, 6%, 11% and 41% initial water content were pyrolyzed in a solar reactor at 900, 1200 and 1600 °C with heating rate ranging from 10 to 150 °C/s. Due to the advantage of solar pyrolysis (high temperatures and heating rates), high water content beech wood can be upgraded into CO- and H_2- rich gas products. Under the used operating conditions, the beech wood drying and pyrolysis proceed simultaneously, which gives rise to a process combining pyrolysis, gasification and reforming. As a result, the combined effects of water content and temperature or heating rate are reinforced, which favors tar steam reforming into more gas product. - Highlights: • Combined effects of water content and heating parameters on products were determined. • Pyrolysis of 41 %w H_2O beech wood at high temperature and heating rate produces 65% gas. • H_2/CO ratio is about 1 at 1200 °C and 50 °C/s heating rate with 0% and 41% water content. • Low temperatures and heating rates favor the production of liquid (about 50%). • Pyrogasification mechanisms are analyzed as a function of operation conditions.
[en] High temperature solar receiver is a core component of solar thermal power plants. However, non-uniform solar irradiation on the receiver walls and flow maldistribution of heat transfer fluid inside the tubes may cause the excessive peak temperature, consequently leading to the reduced lifetime. This paper presents an original CFD (computational fluid dynamics)-based evolutionary algorithm to determine the optimal fluid distribution in a tubular solar receiver for the minimization of its peak temperature. A pressurized-air solar receiver comprising of 45 parallel tubes subjected to a Gaussian-shape net heat flux absorbed by the receiver is used for study. Two optimality criteria are used for the algorithm: identical outlet fluid temperatures and identical temperatures on the centerline of the heated surface. The influences of different filling materials and thermal contact resistances on the optimal fluid distribution and on the peak temperature reduction are also evaluated and discussed. Results show that the fluid distribution optimization using the algorithm could minimize the peak temperature of the receiver under the optimality criterion of identical temperatures on the centerline. Different shapes of optimal fluid distribution are determined for various filling materials. Cheap material with low thermal conductivity can also meet the peak temperature threshold through optimizing the fluid distribution. - Highlights: • A 3D pressurized-air solar receiver based on the tube-in-matrix concept is studied. • An original evolutionary algorithm is developed for fluid distribution optimization. • A new optimality criterion is proposed for minimizing the receiver peak temperature. • Different optimal fluid distributions are determined for various filling materials. • Filling material with high thermal conductivity is more favorable in practical use.
[en] Highlights: • A CFD two-scale model is formulated to simulate heavy metal vaporization from waste incineration in fluidized beds. • MSW particle is modelled with the macroscopic particle model. • Influence of bed dynamics on HM vaporization is included. • CFD predicted results agree well with experimental data reported in literature. • This approach may be helpful for fluidized bed reactor modelling purposes. - Abstract: Municipal Solid Waste Incineration (MSWI) in fluidized bed is a very interesting technology mainly due to high combustion efficiency, great flexibility for treating several types of waste fuels and reduction in pollutants emitted with the flue gas. However, there is a great concern with respect to the fate of heavy metals (HM) contained in MSW and their environmental impact. In this study, a coupled two-scale CFD model was developed for MSWI in a bubbling fluidized bed. It presents an original scheme that combines a single particle model and a global fluidized bed model in order to represent the HM vaporization during MSW combustion. Two of the most representative HM (Cd and Pb) with bed temperatures ranging between 923 and 1073 K have been considered. This new approach uses ANSYS FLUENT 14.0 as the modelling platform for the simulations along with a complete set of self-developed user-defined functions (UDFs). The simulation results are compared to the experimental data obtained previously by the research group in a lab-scale fluid bed incinerator. The comparison indicates that the proposed CFD model predicts well the evolution of the HM release for the bed temperatures analyzed. It shows that both bed temperature and bed dynamics have influence on the HM vaporization rate. It can be concluded that CFD is a rigorous tool that provides valuable information about HM vaporization and that the original two-scale simulation scheme adopted allows to better represent the actual particle behavior in a fluid bed incinerator
[en] Hydrogen, a promising and clean energy carrier, could potentially replace the use of fossil fuels in the transportation sector. Currently, no environmentally attractive, large-scale, low-cost and high-efficiency hydrogen production process is available for commercialization. Solar-driven water-splitting thermochemical cycles may constitute one of the ultimate options for CO2-free production of hydrogen. The method is environmentally friendly since it uses only water and solar energy. First, the potentially attractive thermochemical cycles must be identified based on a set of criteria. To reach this goal, a database that contains 280 referenced cycles was established. Then, the selection and evaluation of the promising cycles was performed in the temperature range of 900-2000 oC, suitable to the use of concentrated solar energy. About 30 cycles selected for further investigations are presented in this paper. The principles and basis for a thermodynamic evaluation of the cycles are also given
[en] Created on 17 July 2009, ANCRE (French National Alliance for Energy Research Coordination) brings together 19 research and innovation bodies and higher education institution consortia in the field of energy. Its missions, carried out in liaison with competitiveness clusters and funding agencies, are to: - reinforce synergies and partnerships between research bodies, universities and companies, - identify scientific and technical challenges hampering industrial development, - propose research and innovation programs and approaches to their implementation, - contribute to the development of national research strategy in the field of energy, as well as funding agency program development. Its 2 main societal challenges are: Clean, secure and efficient energy, and Sustainable mobility and urban systems. ANCRE mobilizes 200 scientists involved in 10 programmatic groups (1 - Energy from biomass, 2 - Fossil energy, geothermal energy, critical metals, 3 - Nuclear energy, 4 - Solar energy, 5 - Ocean, hydraulic and wind energy, 6 - Transport, 7 - Buildings, 8 - Industries and agriculture, 9 - Energy forecasting and economics, 10 - Energy networks and associated storage) and 2 cross-disciplinary groups (Strategy, Europe and international). This activity report presents the ANCRE's 2015-2016 Highlights, its future challenges, its contribution to public policy-making, its close cooperation with the French national research agency and active participation in European programs, its mobilizing, structuring and uniting communities, and its knowledge production and dissemination