1,721,041 research outputs found
Process simulation of a hybrid SOFC/mGT and enriched air/steam fluidized bed gasifier power plant
No full textThe aim of this work is to experimentally and numerically analyze the performance of a integrated power plant composed by a steam oxygen fluidized bed biomass gasifier fed by woods, a Solid Oxide Fuel Cell (SOFC) and a micro Gas Turbine (mGT). The numerical analysis is carried out by using ChemCAD software. In particular, SOFC and gasifier were modeled using proper developed Fortran subroutines interfaced to the basic software. The adopted SOFC model was already validated by the authors in previous works, while the gasifier model was here developed and validated by means of experimental activities carried out by using a bench scale gasifier. Different compounds (Benzene, Toluene, Naphthalene, Phenols) were chosen to analyze the tar evolution in the gaseous stream during the gasification process. Hot gas cleaning (based on catalytic ceramic filter candles inserted in the freeboard of the gasifier-UNIQUE concept) was adopted to remove tar and particulates from the fuel hot gas stream. Different moisture contents in the range between 10 and 30% (i.e. in a deviation of 10% around the usual wood moisture content of 20%) were numerically simulated as well as the degree of purity of the oxygen utilized in the power plant (between 25% and 95%, the rest being N2). The power requirement for pure oxygen production leads to a reduction of the electrical efficiency of the whole power plant. For this reason, a sensitivity analysis was conducted to find the optimal operation conditions in order to maximise the syngas (H2, CO) content in the produced gas, while maintaining a high overall electrical efficiency. Copyright © 2013, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved
Il product placement cinematografico fra teoria e prassi aziendale. Organizzazione, management e casi di successo
No full text
Non-Linear k-ε-ζ-f model sensitized to rotation for blade turbine internal cooling
No full textThe need to study flow and heat transfer in turbine blade cooling design calls to develop appropriate modelling approaches able to return accurate predictions at a reduced computational costs. Here we propose and scrutinize a quadratic version of the well-known k-ε-ζ-f RANS turbulence models, aiming at sensitizing the model to the effect of rotation in configurations mimicking the flow in turbine internal cooling. Starting from the evidence that rotation modified turbulent flow through a turbulence suppression (enhancement) on the stabilized (destabilized) surface, we modified the C coefficient present in the formulation of turbulent viscosity introducing a dependence on the strain and vorticity tensors, the latter explicitly including solid body rotation. The proposed model was tested on plane channel and square-sectioned duct flows, and then used for simulating a rib-duct rotating channel. Results are assessed against DNS literature data and properly developed LES computations, by examining flow variables, heat transfer and turbulence budgets. We demonstrate that, as for the channel flows, the proposed quadratic model is able to accurately reproduce velocity, temperature and turbulent variables at various angular velocity regimes. In the duct flow the flow is subjected to the mutual influence vorticity induced by rotation and turbulence anisotropy developing close the walls. In particular, the non-linear rotation-sensitized model is able to reproduce the near-wall turbulent kinetic energy distribution close to the suction side, returning a zero value in the mid-span and a small peak close to the wall on the suction side. Turbulent kinetic energy and temperature budgets analysis demonstrates the capabilities of the model in describing all the terms in the equations. Also if some tuning of the model is required, these analysis showed very encouraging results. In fact if the basic mechanisms of turbulence and heat transfer are properly predicted, then it can be expected that the model can be successfully applied to a set of different cases. For such reason, the model was applied to the analysis of flow and heat transfer in a rotating ribduct with reasonably results
Municipal solid waste thermochemical conversion to substitute natural gas: comparative techno-economic analysis between updraft gasification and chemical looping
No full textA comparative techno-economic analysis has been performed on two innovative pathways for municipal solid waste (100 t/h) thermochemical processing to substitute natural gas. The first pathway is based on updraft gasification with bottom hydrogen oxy-combustion and ashes melting, the second on autothermal chemical looping hydrogen production with Fe2O3/SiC oxygen carrier. Catalytic methanation in a series of adiabatic fixed bed reactors has been implemented and substitute natural gas quality has been evaluated based on the Italian legislation. Although the updraft gasification process shows higher substitute natural gas productivity (16.3 t/h vs 13.7 t/h), better system energy efficiency (42 % vs 35 %) and energy intensity (125 vs 141 GJ/t), the levelized cost of substitute natural gas is more competitive in the chemical looping configuration due to the lower capital expenditure. Product prices of 2.26 /kg and 1.76 /kg have been calculated for updraft gasification and chemical looping, respectively, assuming 8 % discount rate, 80 % capacity factor, and 90 /MWh electricity cost. Sensitivity analyses indicate that, among other parameters, the plant capacity factor and the electric power cost have a relevant impact on the final product cost. Additionally, both pathways are shown to be economically competitive with substitute natural gas production from H2O electrolysis and CO2 capture/purchase. Finally, actions to reach competitivity with fossil natural gas for industrial uses are qualitatively discussed
Decarbonizing cement plants via a fully integrated calcium looping-molten carbonate fuel cell process: assessment of a model for fuel cell performance predictions under different operating conditions
No full textThis study is part of a comprehensive research devoted to the integration of a Calcium Looping (CaL) process with a Molten Carbonate Fuel Cell (MCFC) for the decarbonisation of a full-scale cement plant. In the proposed process, where the energy intensive oxy-combustion occurring in the CaL calciner is replaced with a conventional combustion in air. The CO2-rich gas leaving the calciner is injected into the MCFC cathode while the anode side is fuelled by H2-rich gases produced by a sorption-enhanced reforming (SER) process. The high CO2-concentrated gas leaving the anode will be sent to valorisation processes and/or the CO2 final disposal. Here we focus on modelling, simulation and characterization of the MCFC used as a device for CO2 separation as well as electricity production, here considered as a process by-product. Polarization curves (I–V curves) and Electrochemical Impedance Spectroscopy (EIS) were measured to support the development and the calibration of a semi-empirical model obtained by theoretical consideration. The experimental campaign demonstrated that the fitted model is able to reproduce the real cell performance when varying the temperature, H2 concentration, CO2 concentration at anode and cathode respectively as well as CO2 CaL capture rate. Indeed, the average difference between numerical and experimental results is always below 2%. Results also demonstrated that the MCFC can be usefully considered as an efficient CO2 concentrator, with a CO2 fraction at the anode outlet that is greater than 51% on a dry basis
Decarbonizing power and fuels production by chemical looping processes: Systematic review and future perspectives
No full textThe decarbonization of power and fuels production is a crucial element of the energy transition. Among several available technologies, chemical looping processes promise to be a feasible solution to support the decarbonization of large-scale industrial sectors. They involve a solid material, commonly called an oxygen carrier, that circulates between two or more reactors according to a redox process. In the reduction step, the oxygen carrier loses some its oxygen atoms by reaction with a fuel. In the oxidation step, it is oxidized back to the initial phase by an oxidizing agent such as air, steam and/or CO2. The flexibility of this process enables it to be used in diverse applications, such as: (1) fuel combustion; (2) hydrocarbon reforming; (3) solid fuels gasification, with limited energy penalties for CO2 separation and possibility of autothermal operation within the cycle. Therefore, this technology has a significant potential to contribute to the sustainable transition. This review paper aims at shedding light on a range of chemical looping progresses and to explore open questions in this field. The discussion is divided into three main chemical looping variants: combustion, reforming, and gasification. For each of these, recent progresses and challenges are highlighted by considering two scales of analysis: lab-scale and system scale. At the lab-scale, advances in materials development and process performance are discussed, while at the system scale, technical, environmental and economic analyses are presented in comparison with benchmark alternative technologies. Materials development and testing represents a crucial element hampering chemical looping development. Combination of costly and often toxic synthetic materials with natural ores is considered a promising solution that can reduce cost, increase stability and environmental compatibility. Iron oxides have several decontaminating properties and due to their low cost, large availability and high stability and appear as promising oxygen carriers. The synergistic mixing of metal oxides is also a solution to optimizing oxygen carrier properties. Different reactor configurations have been proposed with circulating fluidized beds being the most mature in terms of operational hours. Nevertheless, pressurized operation has been mainly conducted with fixed bed reactors. Techno-economic analyses indicate that chemical looping reforming can approach competitiveness with the unabated benchmark, while in power production the limit in the maximum reactor temperature is a significant drawback. An interesting application with still limited experimental and modelling research is the application of chemical looping for energy storage applications
Development of a novel carbon capture and utilization approach for syngas production based on a chemical looping cycle
No full textThe present work assesses the potential of reducing CO2 emissions associated with steel production through the introduction of a decarbonization process downstream of a steel mill eventually producing an alternative fuel/syngas. The analysed system is composed of a calcium looping process for CO2 separation followed by a chemical looping section for syngas production from CO2 and H2Os. The main units in the chemical looping cycle are: the oxidizer, where a flux of CO2 and H2Os reacts with an oxygen carrier to produce CO and H2; the air reactor, where the oxidation of the oxygen carrier is completed by the interaction with air; the reducer, where the reduced oxygen carrier is regenerated to the initial state (Fe2O3 or NiFe2O4 in the present case) through an endothermic reaction occurring at high temperatures. A MATLAB model was created to determine the molar flow rate of the components flowing through the thermochemical cycle and the thermal power associated with each unit at the operating conditions. The analysis is carried out focusing on the treatment of 1 t/h of CO2, resulting in 7.1 t/h of NiFe2O4 or 12.1 t/h of Fe2O3. The syngas at the outlet from the oxidizer reactor is composed of equimolar H2 and CO with a mass flow rate of 0.05 t/h and 0.64 t/h, respectively. A separate MATLAB model was developed to identify the experimental conditions necessary to reach fluidization of FeO particles in a lab-scale oxidizer reactor (u_mf = 0.162 m/s). Companion CFD simulations were carried out to evaluate the hydrodynamics of the lab-scale oxidizer reactor and the associated reaction kinetics (Langmuir-Hishelwood) above minimum fluidization conditions with the aim of assessing the assumptions performed in the MATLAB in terms of conversion rates. For the imposed inlet velocity conditions of the gas mixture (2.6 times above the minimum fluidization velocity) large bubbles with low frequency are observed, while full consumption of the reactant gases is achieved during the first 15 s of simulation, due to the significant reaction rate (2.6 kmol/sm^3). The results of the CFD simulation and the comparison with existing literature allow to validate the assumptions on the oxidizer conversion and the overall accuracy of the model
Effects of wall curvature on the dynamics of an impinging jet and resulting heat transfer
Full text linkThe effects of wall curvature on the dynamics of a round subsonic jet impinging on a concave surface are investigated for the first time by direct numerical solution of the compressible Navier-Stokes equations. Impinging jets on curved surfaces are of interest in several applications, such as the impingement cooling of gas turbine blades. The simulation is performed at Reynolds and Mach numbers respectively equal to 3, 300 and 0.8. The impingement wall is kept at a constant temperature, 80 K higher than that of the jet at the inlet. The nozzle-to-plate distance (measured along the jet axis) is set to 5D, with D the nozzle diameter. In order to highlight the curvature effects, the present results are compared to a previous study of jet impinging on a flat plate. The specific influence of wall curvature is investigated through a frequency analysis based on discrete Fourier transform and dynamic mode decomposition. We found that the peak frequencies of the heat transfer also dominate the dynamics of primary vortices in the free jet region and secondary vortices produced by the interaction of primary vortices and the target plate. These frequencies are approximately 30% lower than those found in the reference study of impinging jet on a flat plate. Imperceptible differences were instead found in the time-averaged integral heat transfer
Energy Management of a Residential Heating System Through Deep Reinforcement Learning
Full text linkIn this study, a controller based on deep reinforcement learning was tested for a residential building equipped with a radiant heating system. In detail, a Soft Actor-Critic (SAC) algorithm was implemented to optimize the operation of the heating system while ensuring adequate levels of indoor temperature. A probabilistic window opening behavior model was implemented within the simulation framework in order to emulate the interaction of the occupants with the building. A sensitivity analysis on SAC hyperparameters was carried out to determine the best configuration that was then deployed in four different scenarios in order to analyze the adaptability of the controller to different boundary conditions. The performance of the reinforcement learning agent was evaluated against a baseline strategy which combines rule-based and climatic control. The developed agent was able to achieve a saving of heating energy provided to the building in the range between 2 and 6% while increasing temperature control performance up to 65% in the four scenarios investigated
- …
