Browsing by Author "Brito, Paulo"
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- Aproveitamento energético de biomassaPublication . Brito, Paulo; Rodrigues, Luíz; Oliveira, AnabelaNesta comunicação faz-se uma breve apresentação da central de gaseificação e estudo de biomassas da ESTG do IPP e da sua actividade no âmbito do laboratório de energias renováveis e ilustra-se a actividade da central e do laboratório de análises da escola que lhe dá apoio analisando as biomassas e os gases oriundos da central com os resultados do estudo preliminar da gaseificação térmica de pellets de mischantus.
- Are renewable energy stocks a possibility to diversify portfolios considering an environmentally friendly approach? The view of DCCA correlation coefficientPublication . Ferreira, Paulo; Loures, Luis; Nunes, José; Brito, Paulo
- Characterization of Municipal, Construction and Demolition Wastes for Energy Production Through Gasification - A Case Study for a Portuguese Waste Management CompanyPublication . Alves, Octávio; Passos, Jeysa; Brito, Paulo; Gonçalves, Margarida; Monteiro, EliseuGasification of wastes is considered a promising alternative for energy generation due to its lower environmental impacts when compared with conventional landfilling and incineration. Valorisation of such wastes improves sustainability of resource management and of energy production. However, an appropriate characterisation of wastes in terms of physical and chemical properties is essential for the prediction of their behaviour during gasification, allowing to identify possible problems for the environment and installed equipment and also to define which materials present a greater energy potential. This study aimed to characterise 10 different fractions from municipal, construction and demolition wastes received in different fluxes by a Portuguese waste management company. These fractions included wood (44.83 wt%), plastic (22.15 wt%), paper/card (0.04 wt%), mixtures of paper and plastic (14.67 wt%) and sewage sludge (18.31 wt%). For this purpose, determination of density, proximate and ultimate analysis, higher heating value (HHV), thermogravimetric profiles and inorganic composition of ashes were performed for each fraction. Analysis revealed that plastics and their mixtures with paper/card possess the highest HHV’s (25–45 MJ/kg db), thus exhibiting a greater capacity for energy production. High levels of ashes found in dried sewage sludge (50 wt % db) indicate that a lot of by-product will be generated after gasification, possibly increasing the treatment costs. A gasification unit operating at 50 kg/h and admitting a mixture of all these wastes would generate 109.7 kW of total power, having capacity to receive more waste fluxes along the year.
- Comparative scaling analysis of two different sized pilot-scale fluidized bed reactors operating with biomass substratesPublication . Cardoso, João; Silva, Valter; Eusébio, Daniela; Brito, Paulo; Hall, M.J.; Tarelho, LuísThis paper presents a comparative scaling analysis of two different sized pilot-scale fluidized bed reactors operating with biomass substrates. A multiphase Eulerian-Eulerian 2-D mathematical model was implemented, coupled with in-house user-defined functions (UDF) built to enhance hydrodynamics and heat transfer phenomena. The model validation was attained by comparison to experimental data gathered from both reactors. A grid refinement study was carried out for both geometries to achieve an appropriate computational domain. Hydrodynamics was deeply studied for both reactors concerning the scale-up effect. Mixing and segregation phenomena, solid particle distribution and biomass velocity were matters of great concern. Results showed that UDF implementation successfully minimized deviations and increased the model’s predictability. The largest deviations measured between experimental and numerical results for syngas composition were of about 20%. Solids mixing and segregation was found to be directly affected by the particles size, density, and superficial gas velocity, with the larger reactor revealing improved mixing ability. Improved mixing occurred for smaller particles size ratio (dbiomass ¼ 3 mm), smaller particles density ratio (rbiomass ¼ 950 kg/m3), and higher dimensionless superficial gas velocities (U0=Umf¼3.5). The larger unit showed an increase in near-wall velocity, lateral dispersion, and bubble size. As for the smaller reactor, higher velocities were obtained at the center region due to a more pronounced wall boundary layer. Similarities were found between the two reactors regarding the bubble distribution, dimensionless average bed pressure drop and biomass velocity vector profiles when dimensionless parameters were employed.
- A Heuristic Solution Based on Clarke & Wright's Savings Algorithm for the Optimization of Sludge Hauling: the case of a Portuguese companyPublication . Passos, Jeysa; Lourinho, Gonçalo; Alves, Octávio; Brito, PauloSewage sludge originating from wastewater treatment plants (WWTPs) can be a major cause of environmental pollution and their appropriate management should be viewed as a priority. A critical aspect in sludge management practices is route optimization since significant costs are associated with the transportation of waste. In this work, we propose a heuristic solution based on Clarke-Wright savings method for the sludge collection problem of a Portuguese company within a perspective of reducing collection costs (transportation) and negative impacts on the environment. Two case studies were considered in the methodology: the first one focused on the comparison between the general weekly collection plan presently used by the company and the solution generated by CW algorithm (Case Study A); the second one explored a new hypothetical scenario centered on the expansion of the company’s activities (Case Study B). In general, the application of CW method led to a decrease in traveled distances and transportation costs, as well as carbon dioxide emissions. Specifically, with the adoption of the optimized plan in Case Study A we found that a single vehicle (instead of three) would be capable of performing sludge hauling operations in a given week leading to total weekly savings of 346 km, representing a decrease of almost 40% for both cost and pollutant emissions. Regarding Case Study B, the model suggests that for about 76% of the initial cost, the company would be capable of attending twice the number of customers, i.e., via route optimization, it is possible to expand their client portfolio while still creating savings. Moreover, a sensitivity analysis (SA) was carried out in order to check the robustness of results when undergoing changes in the input parameters. We found that vehicle capacity and fuel price are two important factors in route optimization with model results greatly influenced by changes in both parameters.
- Hydrodynamic Modelling of Municipal Solid Waste Residues in a Pilot Scale Fluidized Bed ReactorPublication . Cardoso, João; Silva, Valter; Eusébio, Daniela; Brito, PauloThe present study investigates the hydrodynamics and heat transfer behavior of municipal solid waste (MSW) gasification in a pilot scale bubbling fluidized bed reactor. A multiphase 2-D numerical model following an Eulerian-Eulerian approach within the FLUENT framework was implemented. User defined functions (UDFs) were coupled to improve hydrodynamics and heat transfer phenomena, and to minimize deviations between the experimental and numerical results. A grid independence study was accomplished through comparison of the bed volume fraction profiles and by reasoning the grid accuracy and computational cost. The standard deviation concept was used to determine the mixing quality indexes. Simulated results showed that UDFs improvements increased the accuracy of the mathematical model. Smaller size ratio of the MSW-dolomite mixture revealed a more uniform mixing, and larger ratios enhanced segregation. Also, increased superficial gas velocity promoted the solid particles mixing. Heat transfer within the fluidized bed showed strong dependence on the MSW solid particles sizes, with smaller particles revealing a more effective process.
- Improved numerical approaches to predict hydrodynamics in a pilot-scale bubbling fluidized bed biomass reactor: A numerical study with experimental validationPublication . Cardoso, João; Silva, Valter; Eusébio, Daniela; Brito, Paulo; Tarelho, LuísA computational 2-D Eulerian-Eulerian approach was developed to simulate the hydrodynamics and heat transfer of a biomass gasification process in a pilot-scale bubbling fluidized bed reactor. The mathematical model was validated under experimental results collected from fluidization curves gathered at different temperatures in a pilot-scale reactor (75 kWth). Own user defined functions (UDFs) were developed in C programming and included to improve drag and heat transfer phenomena, as well to minimize deviations between experimental and numerical data found in previous works. Mesh selection was achieved by comparing solid fraction and pressure drop contours with grids comprised of different number of cells. A comparative study for particle diameter and inlet gas velocity was conducted for three different biomass feedstocks’ and their impact in the mixing and segregation index was studied. Mixing and segregation index were measured by implementing the standard deviation concept. Results indicated that UDFs significantly improved the mathematical model predictions on the reactor’s fluidization curves. Biomass and sand particles size and density showed direct influence on the solids distribution along the bed height. Smaller biomass particles revealed faster heat conduction and improved mixing properties.
- Modelling higher heating value of different separated fractions from municipal and construction and demolition wastesPublication . Alves, Octávio; Gonçalves, Margarida; Brito, Paulo; Monteiro, EliseuHigher heating value (HHV) is an important property of biomass and wastes used to evaluate their potential conversion to useful thermal or electric energy. Because the measurement of this property requires expensive resources and is somewhat time-consuming, many works focused their attention on the determination of mathematic models relating the HHV with the composition of lignocellulosic biomass or other fuel materials, such as their ultimate and proximate analysis. These models can supply appropriate estimates of HHV but only for analogous materials, so they should not be used to compare samples with marked differences in composition or physical and chemical properties. In this work, 9 different separated fractions of municipal and construction and demolition wastes (wood, paper/card, plastics, sewage sludge and mixtures among them) were used to deduce a mathematical expression relating HHV with their contents of carbon, hydrogen, oxygen, nitrogen, sulphur and ash. For this purpose, HHV's, proximate and ultimate analysis were experimentally obtained and the results used to create three different expressions applying linear regression methods. The best expression was selected and validated by comparing deviations among the calculated results and those retrieved from the literature and from experimental measurements regarding different wastes. It was concluded that the best expression was HHV (MJ/kg db) = 0.3845×C+0.8831×H- 29.1217×S-0.0630×O-1.0063×N+0.3888×ASH-0.2546 (with C, H, S, O, N and ASH in wt% db, considering atomic ratios O/C and H/C within 0.0O/C1.2 and 0.1H/C0.2), giving an average absolute error of 8.5 % and an average bias error of -1.6 %. However, appreciable deviations may be found when estimating the HHV of polyurethane, paper/card, mixtures of paper/plastic and sewage sludge and thus the application of the expression for these materials is questionable.