Instituto Politécnico de Portalegre
Permanent URI for this community
Browse
Browsing Instituto Politécnico de Portalegre by Author "Alves, Octávio"
Now showing 1 - 3 of 3
Results Per Page
Sort Options
- 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.
- 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.
- 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.