Aproveitamento Energético de Combustíveis Derivados de Resíduos via Co-Gaseificação Térmica

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Characterization of Municipal, Construction and Demolition Wastes for Energy Production Through Gasification - A Case Study for a Portuguese Waste Management Company

Publication . Alves, Octávio; Passos, Jeysa; Brito, Paulo; Gonçalves, Margarida; Monteiro, Eliseu

Gasification 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.

2019Journal article

Open access

Modelling higher heating value of different separated fractions from municipal and construction and demolition wastes

Publication . Alves, Octávio; Gonçalves, Margarida; Brito, Paulo; Monteiro, Eliseu

Higher 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 0.0O/C1.2 and 0.1H/C0.2), 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.

2018Conference object

Open access