Silvia Nebra
UFABC - Federal University of ABC, CECS, Department Member
ABSTRACT A system of latent heat of fusion storage has been designed with paraffin as the working substance. A prototype apparatus has provided data on local temperatures and fluid flow in the system. The heat charging and discharging... more
ABSTRACT A system of latent heat of fusion storage has been designed with paraffin as the working substance. A prototype apparatus has provided data on local temperatures and fluid flow in the system. The heat charging and discharging phases of operation involve different heat transfer problems which require separate analyses.
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A model of simultaneous transport of heat and mass in a hygroscopic capillary porous medium was developed and applied to the drying of wood. Water is considered to be present in three forms-free water, bound water, and vapor—which remain... more
A model of simultaneous transport of heat and mass in a hygroscopic capillary porous medium was developed and applied to the drying of wood. Water is considered to be present in three forms-free water, bound water, and vapor—which remain in local equilibrium. It is assumed that the heat and mass transport mechanisms are: capillarity of free water, diffusion of vapor due to the concentration gradient, and diffusion of bound water due to the gradient of chemical potential between the water molecules. The constants of the phenomenological coefficients were adjusted. Finally, the drying process in wood chips was simulated in a unidimensional mesh. The results were compared with experimental data on drying kinetics obtained from the literature. Concentration profiles are shown, and the weight of each of the mechanisms present in the drying phenomenon is shown in graphic form and discussed.
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A gestão de resíduos sólidos urbanos (RSU) foi impulsionada com a implantação da Política Nacional de Resíduos Sólidos, através da Lei 12.305/2010, que também prevê a recuperação energética dos resíduos. Apesar deste marco legal, a... more
A gestão de resíduos sólidos urbanos (RSU) foi impulsionada com a implantação da Política Nacional de Resíduos Sólidos, através da Lei 12.305/2010, que também prevê a recuperação energética dos resíduos. Apesar deste marco legal, a geração de energia a partir de RSU no Brasil ainda é incipiente se consideramos a quantidade de resíduos gerados diariamente. Assim, a presente pesquisa objetivou levantar a situação da gestão de RSU no Brasil, o potencial das usinas elétricas em operação, e as políticas públicas para o desenvolvimento da geração de energia a partir de RSU. Para fins de comparação foram investigadas também as experiências de políticas públicas dos Estados Unidos da América (Califórnia), Reino Unido e Alemanha. Como resultado, verificou-se que apesar de existirem políticas em diversos setores no Brasil voltadas à geração de energia, estas não foram capazes de ampliar a participação dessa fonte na matriz elétrica como em outros países.Palavras-chave: Resíduos Sólidos Urbano...
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Com a publicação da Política Nacional de Resíduos Sólidos (PNRS) em 2010, o artigo identifica a necessidade de coordenação técnica, política, econômica e socioambiental para a gestão de Resíduos Sólidos Urbanos (RSU) no Brasil. Considera... more
Com a publicação da Política Nacional de Resíduos Sólidos (PNRS) em 2010, o artigo identifica a necessidade de coordenação técnica, política, econômica e socioambiental para a gestão de Resíduos Sólidos Urbanos (RSU) no Brasil. Considera que essa gestão é de incumbência municipal, e que a maior parte dos municípios brasileiros é de pequeno porte, logo, não possui capacidade técnica e financeira para realizar o manejo adequado dos RSU. Dessa forma, este artigo apresenta os resultados da pesquisa referente ao mapeamento dosconsórcios públicos intermunicipais da área ambiental no Estado de São Paulo, no intuito de que esta caracterização estimule estudos futuros acerca de novasabordagens de arranjos municipais, e que sejam adotadas outras soluções de tratamento e destinação final dos resíduos, além da simples disposição final nos aterros sanitários.Palavras-chave: Resíduos sólidos urbanos, arranjos intermunicipais, consórciospúblicos.
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Brazil has a large population with a high waste generation. The municipal solid waste (MSW) generated is deposited mainly in landfills. However, a considerable fraction of the waste is still improperly disposed of in dumpsters. In order... more
Brazil has a large population with a high waste generation. The municipal solid waste (MSW) generated is deposited mainly in landfills. However, a considerable fraction of the waste is still improperly disposed of in dumpsters. In order to overcome this inadequate deposition, it is necessary to seek alternative routes. Between these alternatives, it is possible to quote gasification and incineration. The objective of this study is to compare, from an energetic and economic point of view, these technologies, aiming at their possible implementation in Brazilian cities. A total of two configurations were evaluated: (i) waste incineration with energy recovery and electricity production in a steam cycle; and (ii) waste gasification, where the syngas produced is used as fuel in a boiler of a steam cycle for electricity production. Simulations were performed assuming the same amount of available waste for both configurations, with a composition corresponding to the MSW from Santo André, Brazil. The thermal efficiencies of the gasification and incineration configurations were 19.3% and 25.1%, respectively. The difference in the efficiencies was caused by the irreversibilities associated with the gasification process, and the additional electricity consumption in the waste treatment step. The economic analysis presented a cost of electrical energy produced of 0.113 (US$ kWh(-1)) and 0.139 (US$ kWh(-1)) for the incineration and gasification plants respectively.
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Brazil has an increasing production of municipal solid waste that, allied to the current waste management system, makes the search for alternatives of energy recovery essential. Thus, this work aims to study the incineration of municipal... more
Brazil has an increasing production of municipal solid waste that, allied to the current waste management system, makes the search for alternatives of energy recovery essential. Thus, this work aims to study the incineration of municipal solid waste and the electricity production through steam cycles evaluating the influence of municipal solid waste composition. Several scenarios were studied, in which it was assumed that some fractions of municipal solid waste were removed previously. The municipal solid waste generated in Santo André city, São Paulo State, Brazil, was adopted for this study. Simulation results showed that the removal of organic matter and inert components impacts advantageously on the cycle performance, improving their parameters in some cases; in addition, there is the possibility of reusing the separated fractions. The separation of some recyclables, as plastic material, showed disadvantages by the reduction in the electricity generation potential owing to the h...
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ABSTRACT This paper presents an overview of the flow, heat and mass transfer characteristics of vortex (or cyclone) dryers. The focus is on the potential of the cyclone configuration for drying of particulates. A selective review is made... more
ABSTRACT This paper presents an overview of the flow, heat and mass transfer characteristics of vortex (or cyclone) dryers. The focus is on the potential of the cyclone configuration for drying of particulates. A selective review is made of the literature pertains to single phase and gas-particle flow in cyclone geometries. Recent data on drying of particulates in cyclone dryers are summarized.
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ABSTRACT A system of latent heat of fusion storage has been designed with paraffin as the working substance. A prototype apparatus has provided data on local temperatures and fluid flow in the system. The heat charging and discharging... more
ABSTRACT A system of latent heat of fusion storage has been designed with paraffin as the working substance. A prototype apparatus has provided data on local temperatures and fluid flow in the system. The heat charging and discharging phases of operation involve different heat transfer problems which require separate analyses.
Research Interests:
Research Interests: Engineering, Environmental Engineering, Chemical Engineering, Thermodynamics, Biochemical Engineering, and 14 moreWater quality, Bioenergy, Water Treatment, Wastewater Treatment, Heat Exchanger, Sugar cane, Biofuels, Process Integration, Bioprocessing, Water Quality, Optimal Design, Bioproducts, Biomass Processing, and Process Parameters
Currently, transport is highly dependent on fossil fuels and responsible for about 23% of world energy-related GHG (greenhouse gas) emissions. Ethanol from sugar cane and corn emerges as an alternative for gasoline in order to mitigate... more
Currently, transport is highly dependent on fossil fuels and responsible for about 23% of world energy-related GHG (greenhouse gas) emissions. Ethanol from sugar cane and corn emerges as an alternative for gasoline in order to mitigate GHG emissions. Additionally, deeper offshore drilling projects such as in the Brazilian Pre-Salt reservoirs and mining projects of nonconventional sources like Tar Sands in Canada could be a solution for supplying demand of fossil fuels in the short and midterm. Based on updated literature, this paper presents an assessment of GHG emissions for four different fuels: ethanol from sugar cane and from corn and gasoline from conventional crude oil and from tar sands. An Ecological Footprint analysis is also presented, which shows that ethanol from sugar cane has the lowest GHG emissions and requires the lowest biocapacity per unit of energy produced among these fuels. Finally, an analysis using the Embodied Water concept is made with the introduction of a new concept, the "CO(2)-Water", to illustrate the impacts of releasing carbon from underground to atmosphere and of the water needed to sequestrate it over the life cycle of the assessed fuels. Using this method resulted that gasoline from fossil fuels would indirectly "require" on average as much water as ethanol from sugar cane per unit of fuel energy produced.
Research Interests: Environmental Science, Water, Carbon Dioxide, Air pollution, Multidisciplinary, and 15 moreEnvironmental science and technology, Carbon Footprint, Biofuels, Mining Industry, Alcohol, Fossil Fuels, Biofuel, Ecological Footprint, Ethanol, Greenhouse Gas, Greenhouse Effect, Conservation of Natural Resources, Gasoline, Environment, and Fossil Fuel
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ABSTRACT This work presents a complete improved mathematical model of drying in cyclone. The slip condition of the particles on the wall, the heat transfer wall-panicle and the shrinkage of the panicles during the drying process were... more
ABSTRACT This work presents a complete improved mathematical model of drying in cyclone. The slip condition of the particles on the wall, the heat transfer wall-panicle and the shrinkage of the panicles during the drying process were considered. The mathematical model considers a two-dimensional turbulent gas-particle flow where the panicle phase is treated as a continuum. The momentum equations of both particle and gas phases were written in cylindrical coordinates. The discretized equations were solved by the SIMPLE algorithm. Considering the slip condition to the panicle phase and the shrinkage of the material during the drying process it was revealed a better fitness between numerical and experimental results than the previous model.
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Page 1. THEORETICAL STUDY OF INTERMITTENT DRYING (TEMPERING) IN PROLATE SPHEROIDAL BODIES AGB de Lima1 and SA Nebra2 1Department of Mechanical Engineering, CCT, Federal University of Paraıība ...
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The aim of this work is to carry out a thermoeconomic analysis of a single and double-effect LiBr/H 2O absorption refrigeration system. The methodology of functional analysis with negentropy is used. The exergetic cost of the main... more
The aim of this work is to carry out a thermoeconomic analysis of a single and double-effect LiBr/H 2O absorption refrigeration system. The methodology of functional analysis with negentropy is used. The exergetic cost of the main product, the cooling cost, was calculated as a function of the exergy of the heat source. Two cases were analyzed for each system:
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... Address correspondence to Professor Sılvia A. Nebra, Interdisciplinary Cen-tre of Energy Planning, State University of Campinas (NIPE/UNICAMP), PO Box 1170, Campinas, SP, Brazil, 13084-971. E-mail: silvia.nebra@ pq.cnpq.br ...
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The sugarcane industry represents one of the most important economic activities in Brazil producing sugar and ethanol for the internal and external markets. Most of the sugarcane plants in Brazil have been projected to produce both sugar... more
The sugarcane industry represents one of the most important economic activities in Brazil producing sugar and ethanol for the internal and external markets. Most of the sugarcane plants in Brazil have been projected to produce both sugar and ethanol, prioritizing one over the other according to market prices. There are also plants dedicated only to ethanol production. Nevertheless, this change in the production pattern affects parameters in their production such as water consumption, steam demands, bagasse surplus and electricity production. Thus, the aim of this study is to evaluate the production parameters for different configurations of sugarcane plant: (a) all sugarcane juice is destined to produce ethanol without sugar production and (b) distribution of 50 %/50 % of total recoverable sugars in sugar and ethanol production. Simulations in ASPEN PLUS® software were performed in order to evaluate the mass and energy balances and thermal integration using the Pinch Method was applied in order to minimize the utilities consumption.
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The objective of the extraction process in the ethanol production from sugarcane is to separate the sucrose-containing juice from the remainder of the cane, mainly fibre. The two currents, products of this process, are the juice and the... more
The objective of the extraction process in the ethanol production from sugarcane is to separate the sucrose-containing juice from the remainder of the cane, mainly fibre. The two currents, products of this process, are the juice and the bagasse. The juice is used to produce ethanol and the bagasse is the fuel for the boilers. Two types of devices are employed to perform this operation: mills and diffusers. Each one of them consumes different types of energy: mills consume mechanical energy, diffusers consume basically thermal energy. As both devices utilize an important quantity of energy, their effect in the energy balance of the factory needs to be taken into account. Aiming to discuss and characterize these effects, simulations of the complete ethanol production process, including the cogeneration system, were carried out using the Aspen Plus software, considering both devices. Process integration was also performed targeting to reduce the energy consumption. These results are presented and compared. Considering the integrated ethanol production process, with extraction -condensing steam turbines in cogeneration system, working with mills, it can produce an electricity surplus of 83.4 kWh/t of sugarcane, however, for the same conditions, working with the diffusion extraction process a production of 91.3 kwh/t of cane can be obtained, including also a small increase of 2 % in the ethanol production. Keywords: ethanol, sugarcane, energy, process integration, extraction.
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Abstract. The aim of this study is to evaluate the potential of ethanol production increase, and the impacts in electricity surplus of the cogeneration plant due to the introduction of enzymatic hydrolysis of bagasse in a conventional... more
Abstract. The aim of this study is to evaluate the potential of ethanol production increase, and the impacts in electricity surplus of the cogeneration plant due to the introduction of enzymatic hydrolysis of bagasse in a conventional distillery. Moreover a comparison of these results is performed with another scenario, where all available bagasse and trash are used in the distillery cogeneration system, in order to maximize electricity surplus, considering a steam cycle provided with extraction-condensing turbines. Simulations in ASPEN PLUS® software were performed, in order to evaluate the mass and energy balances, for the studied processes. For the case of enzymatic hydrolysis, it was assumed that sugarcane trash and lignin cake, which is a residue of the hydrolysis process, are available as fuel in the cogeneration system in order to achieve a significant ethanol production increase. In the electricity surplus study, an adequate higher pressure in the boiler and turbine has been considered. Ethanol production increase resulted 12.3% and 15.1% for the hydrolysis cases evaluated, while surplus electricity increase was 236.5% and 267.5% for the cases where condensing-extraction steam turbines were adopted without enzymatic hydrolysis.
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Abstract: The aim of this study is to make an evaluation of the possibilities of ethanol production increase through the introduction of bagasse hydrolysis process in conventional distilleries, considering the limiting situation of... more
Abstract: The aim of this study is to make an evaluation of the possibilities of ethanol production increase through the introduction of bagasse hydrolysis process in conventional distilleries, considering the limiting situation of bagasse use: it is the major by-product in sugar and ethanol production and is burnt in boilers to satisfy the steam and power requirements of the process. Simulations in ASPEN PLUS® software were performed, in order to evaluate the mass and energy balances, for the integrated process, considering ...
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The sugar and alcohol production is one of the most important economical activities in Brazil, mainly due its high efficiency, and competitiveness. The sugar production is done by several steps: juice extraction, treatment, preheating and... more
The sugar and alcohol production is one of the most important economical activities in Brazil, mainly due its high efficiency, and competitiveness. The sugar production is done by several steps: juice extraction, treatment, preheating and evaporation, syrup treatment, crystallization, centrifugalization and drying. In the alcohol production the steps-productions are: juice extraction, fermentation and distillation. The process begins with the sugar cane juice extraction, usually done by devices namely mills, where the cane is compressed ...
Page 1. AVALIAÇÃO DA INTRODUÇÃO DA COGERAÇÃO PARA REFRIGERAÇÃO NO SETOR PESQUEIRO DO AMAZONAS RICARDO WILSON AGUIAR DA CRUZ Universidade Estadual do Amazonas - UEA (rcruz@uea.edu.br) ...
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Page 1. OPTIMIZATION OF THERMAL ENERGY CONSUMPTION IN SUGAR CANE FACTORIES Adriano V. Ensinas; Silvia A. Nebra Energy Department State University of Campinas Miguel A. Lozano; Luis Serra* Mechanical Engineering Department University... more
Page 1. OPTIMIZATION OF THERMAL ENERGY CONSUMPTION IN SUGAR CANE FACTORIES Adriano V. Ensinas; Silvia A. Nebra Energy Department State University of Campinas Miguel A. Lozano; Luis Serra* Mechanical Engineering Department University of Zaragoza ...
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Energy market consumption is expected to increase by 44% from 2006 to 2030, mostly because of the lifestyle standards evolution, and development of industries and economics. In addition, the variations of the fossil fuel prices and the... more
Energy market consumption is expected to increase by 44% from 2006 to 2030, mostly because of the lifestyle standards evolution, and development of industries and economics. In addition, the variations of the fossil fuel prices and the increase in pollutant gas emissions have instigated the research on other types of power generation systems. From the available technologies, Stirling systems have demonstrated simplicity and reliability, which are the key parameters to develop a cost-effective energy system. The study aims the development of a methodology for the thermal-economic optimization, at the design stage, of micro-CHP systems based on Stirling engine technology, and combined with a renewable energy source, the solar energy. To properly size the system, a methodology is proposed to define the total annual thermal power duration curve of a reference residential building in the North of Portugal. The methodology accounts for both heating and the domestic hot water needs. The thermal-economic model was formulated as an non-linear optimization problem with non-linear constrains. Each component of the cycle is modelled using the energy balances of the first law of thermodynamics. It is also proposed an economic model that defines the purchase cost of each system component. The cost equations include thermodynamic variables that directly affect the component cost and performance. The model yields two non-linear objective functions: the minimization of the total investment cost and the maximization of the efficiency of the system. Numerical simulations were developed in MatLab Ò programming language using evolutionary algorithms. The multi-objective optimization results were expressed by Pareto curves. The obtained curve disclosed several design possibilities for which the thermal efficiencies vary between 66.3% and 76.1% for an annualized investment costs fluctuating between 1250 €/year and 2675 €/year.
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The sugarcane industry represents one of the most important economic activities in Brazil producing sugar and ethanol for the internal and external markets. There are also plants dedicated only to ethanol production. The aim of this study... more
The sugarcane industry represents one of the most important economic activities in Brazil producing sugar and ethanol for the internal and external markets. There are also plants dedicated only to ethanol production. The aim of this study is to accomplish a joint assessment to evaluate the reduction of process steam demand and water usage obtained through heat integration and an exergy analysis to quantify the reduction in irreversibility generation owing to heat integration procedure. Two configurations of plant were analysed Case I e all sugarcane juice is destined to produce ethanol without sugar production and Case II e distribution of 50%/50% of total recoverable sugars in sugar and ethanol production. Simulations in ASPEN PLUS ® software were performed in order to evaluate the mass and energy balances and heat integration using the Pinch Method was applied in order to minimize the utilities consumption. The results showed that heat integration promoted a reduction in steam consumption of 35% approximately, while the reduction in water consumption (water collecting requirement) was 24 and 13% in comparison to the conventional cases without heat integration.
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This work presents an experimental efficiency analysis of sugar cane bagasse boilers performed according to the first law of thermodynamics. The methodology employed to determine efficiency regarding the first law is the indirect or... more
This work presents an experimental efficiency
analysis of sugar cane bagasse boilers performed according
to the first law of thermodynamics. The methodology
employed to determine efficiency regarding the first law is
the indirect or energy losses method, based on the energy
balance method established in the most recent standards,
ASME PTC 4-2008 and EN 12952-15:2003. Experimental
data were obtained from boilers installed in sugar and
ethanol mills in the state of São Paulo, Brazil. Calculation
of heat losses through the boiler walls is presented in
detail and compared with a previous calculation method
recommended in an older standard (ASME PTC 4.1 1964).
Moreover, calculation of the uncertainty of the efficiency
determination is presented and discussed. On the basis of
the obtained results, the main causes of energy losses are
identified, and suggestions aimed at improving boiler efficiency
are made.
analysis of sugar cane bagasse boilers performed according
to the first law of thermodynamics. The methodology
employed to determine efficiency regarding the first law is
the indirect or energy losses method, based on the energy
balance method established in the most recent standards,
ASME PTC 4-2008 and EN 12952-15:2003. Experimental
data were obtained from boilers installed in sugar and
ethanol mills in the state of São Paulo, Brazil. Calculation
of heat losses through the boiler walls is presented in
detail and compared with a previous calculation method
recommended in an older standard (ASME PTC 4.1 1964).
Moreover, calculation of the uncertainty of the efficiency
determination is presented and discussed. On the basis of
the obtained results, the main causes of energy losses are
identified, and suggestions aimed at improving boiler efficiency
are made.
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ABSTRACT A numerical solution of the diffusion equation to describe solute transport inside ellipsoids, assuming a constant difiusion coefficient and a corrective boundary condition, is presented. The difiusion equation in a prolate... more
ABSTRACT A numerical solution of the diffusion equation to describe solute transport inside ellipsoids, assuming a constant difiusion coefficient and a corrective boundary condition, is presented. The difiusion equation in a prolate spheroidal coordinate system was used for a hidimensional case. The finite volume method was employed to discretize the basic equation, utilizing a uniform grid size. The equation was solved irteratively using the Gauss-Seidel method. The effect of Biot number and the aspect ratio of the body on diffusion rate ...
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An alternative thermoeconomic approach is applied to a two-stage vapour compression refrigeration cascade cycle. This approach, called the UFS Model, is based on the splitting of the physical exergy into three terms, namely, internal... more
An alternative thermoeconomic approach is applied to a two-stage vapour compression refrigeration cascade cycle. This approach, called the UFS Model, is based on the splitting of the physical exergy into three terms, namely, internal energy term, flow work term and entropic term. Application of the UFS Model allows the isolation of both valves and condensers in the productive structure. The goal is to obtain the exergetic unit cost of each internal flow and plant product. This alternative approach yields consistent results, because exergetic unit costs are greater than or equal to 1 and the product-fuel ratio of each productive unit is less than or equal to 1. Besides the allocation of the external power cost of the plant, analyses on the irreversibilities of each cycle unit are carried out. Thus, it is shown that the UFS Model can also be used to quantify irreversibilities as well as the conventional exergy analysis. Keywords Refrigeration cycle Thermoeconomics
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Brazil has an increasing production of municipal solid waste that, allied to the current waste management system, makes that the search for alternatives becomes needed. In this aspect, the waste incineration aiming the electricity... more
Brazil has an increasing production of municipal solid waste that, allied to the current waste management system, makes that the search for alternatives becomes needed. In this aspect, the waste incineration aiming the electricity production in steam cycles presents several advantages so it is presented as a good alternative that can be adopted. However, its application needs studies in order to apply it in the most appropriate way. Thus, this work aims to study the incineration of MSW and the electricity production through steam cycle evaluating the influence of MSW composition. Several scenarios were studied in which some fractions of MSW are removed previously. The MSW generated in Santo André city was adopted for this study. Simulations results showed that the removal of metals, organic matter and inert components impacts in a good way on the cycle performance improving or remaining these parameters; moreover there is the re-use possibility of the separated fractions. The separa...