1,720,982 research outputs found
Evaluation methodology for energy efficiency measures in industry and service sector
Full text linkDirective 2012/27/EU, transposed in Italy with Decree of 4 July 2014 No102, a common framework of measures for the promotion of energy efficiency in European Union, is an innovative tool for improvement of energy efficiency and also necessary to undertake main objective of European Union (save 20% of primary energy consumption by 2020). Large enterprises and energy-intensive firms, except those having an energy management system (EnMS) according to ISO 50001 or compliant with EMAS Eco-Management and Audit Scheme or ISO 14001 fall under obligations and must be carry out energy audits every 4 years starting by December 2015 having "SMART" requirements: be Specific, Measurable, Accessible, Realistic, Time related. The analysis on a sample of Italian companies, mainly of small and medium enterprises (SME) in industry and the service sector, was conducted. Energy audit was carried out to identify Energy Company Profile, rationalize energy consumption to increase energy efficiency, assessing potential for energy savings and reducing of environmental impact. For any business context a series of energy efficiency measures has been proposed, selecting high profitability energy saving options by applying a priority criterion. Technical and economic indicators were reported on best practices focusing on tertiary sector and also industry. The study, starting from the feasibility assessments, aims to establish a possible correlation between energy performance indicators (EnPIs) and a limited number of parameters of the energy systems, in terms of production, operation and power consumption. Comparative assessment of energy-saving measures provides an useful method for assessing applicability of standard energy-saving measures in similar contexts and cost-effectiveness of solutions, as a function of a limited number of parameters
A review of the properties of recycled and waste materials for energy refurbishment of existing buildings towards the requirements of NZEB
Full text linkIn Europe buildings account for 40% to 50% of total energy consumption and the largest greenhouse gases emitters and urgent measures and valid instruments are therefore required to improve energy saving, use of renewable sources in moving towards a sustainable materials management where waste becomes a "resource". In this context, there is an increase in research into development and manufacturing of new eco-friendly building envelope components from recycled and waste materials as high value-added good circular economy practice. Waste management may have significant effects in the sector of sustainable building the ultimate objective being the alternative construction materials replacing traditional materials: the development of innovative techniques aims to incorporate wastes into the production of building materials - for examples rubber, fly ash and sludge, etc. - to enhance thermal insulation properties. An effort in the sustainability in building design process is to develop researches aimed at enhancing thermal performance of components using materials capable of reusing a high waste content. The goal of this paper is to examine the technical feasibility of using inert waste materials from the combustion of municipal solid waste or solid recovered fuel and highlight changes in thermal characteristics (thermal conductivity, specific heat and density) by adding recycled and waste materials to the construction materials. The paper explores the potential of the use of thus obtained materials for the energy-refurbishment of existing buildings or with the challenge of meeting stringent energy consumption limits which are typical of a NZEB (net-zero energy building)
Gen-set control in stand-alone/RES integrated power systems
Full text linkPower supply in stand-alone power systems, such those in non-grid connected islands, represents an important area of study in investigating smart energy concepts. In particular, the discontinuity in renewable energy availability and the mismatch with power demand are likely to hinder grid stability and overall system efficiency. Typically, the load-levelling relies on diesel engine gen-sets which suffer the modulation of power output resulting in increased operation costs and life time reduction. Although energy storage can complement power fluxes balance, a proper dispatch strategy is needed in order to improve diesel engine operations in Renewable Energy Source (RES) integrated systems. The present study investigates the merit of a dispatch strategy aiming at improving gen-set performance in a hybrid RES/storage/Diesel Engine Generator set (DEGS) power configuration. The proposed dispatch strategy is modelled in a transient simulation software, with hourly based analysis over a year period and is applied to a small island case study
Variational control approach to energy extraction from a fluid flow
Full text linkEnergy harvesting from the environment is an important aspect of many technologies. The scale of energy capturing and storage can involve the power range from mWatt up to MWatt, depending on the used devices and the considered environments (from ambient acoustic and vibration to ocean wave motion, or wind). In this paper, the wind turbine energy harvesting problem is approached as an optimal control problem, where the objective function is the absorption of an amount of energy in a given time interval by a fluid-flow environment, that should be maximized. The interest relies on outlining general control models of fluid-flow-based extraction plants and identifying an optimum strategy for the regulation of an electrical machine to obtain a maximum-efficiency process for the related energy storage. The mathematical tools are found in the light of optimal control theory, where solutions to the fundamental equations are in the frame of Variational Control (the basis of the Pontryagin optimal control theory). A special problem, named Optimally Controlled Betz’s Machine OCBM-optimal control steady wind turbine, is solved in closed form, and it is shown that, in the simpler steady case, it reproduces the maximum efficiency machine developed in Betz’s theory
Performance and economic assessment of a grid-connected photovoltaic power plant with a storage system. A comparison between the north and the south of Italy
Full text linkGrid-connected low voltage photovoltaic power plants cover most of the power capacity installed in Italy. They offer an important contribution to the power demand of the utilities connected but, due to the nature of the solar resource, the night-time consumption can be satisfied only withdrawing the energy by the national grid, at the price of the energy distributor. Thanks to the improvement of storage technologies, the installation of a system of battery looks like a promising solution by giving the possibility to increase auto-consumption dramatically. In this paper, a model-based approach to analyze and discuss the performance and the economic feasibility of grid-connected domestic photovoltaic power plants with a storage system is presented. Using as input to the model the historical series (2008-2017) of the main ambient variables, the proposed model, based on Stochastic Hybrid Fault Tree Automaton, allowed us to simulate and compare two alternative technical solutions characterized by different environmental conditions, in the north and in the south of Italy. The performances of these systems were compared and an economic analysis, addressing the convenience of the storage systems was carried out, considering the characteristic useful-life time, 20 years, of a photovoltaic power plant. To this end the Net Present Value and the payback time were evaluated, considering the main characteristics of the Italian market scenario
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
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
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