Tratamento térmico de resíduos sólidos urbanos para produção de combustível derivado de resíduo

Abstract

Municipal solid waste (MSW) management in Brazil poses a substantial challenge to society. Energy recovery by means of thermal treatment can be a viable route to properly manage these wastes. However, challenges related to the poor lower heating value (LHV), composition, heterogeinity and high moisture of these wastes pose difficulties to the use of traditional treatment processes. This thesis aimed to assess a new thermal treatment technology for MSW, with temperatures ranging from 150°C to 250°C, without prior screening, for refuse derived fuel (RDF) production. A pilot plant with the capacity to treat up to 1.0 t/day of MSW was developed in order to manufacture 3.2 tonnes of RDF. During the operation of the plant, atmospheric emission levels for PM, CO, SOx, NOx, HCl and chlorine, fluorides and PCDD/Fs were evaluated. RDF samples were characterized and compared with national and international normative. Part of the RDF was pelletized and used as source material for a gasification process. The resulting syngas was characterized by chromatographic analyses to determine its compostion and estimate its LHV, and the results were compared to syngas produced from wood chips in the same operational conditions. An exploratory investigation of VOCs and organochlorine substances in the syngas was also conducted using gas chromatography coupled to mass spectrometry. The remaining RDF was destined to a cement factory for an industrial scale coprocessing test. The MSW treatment process was shown to be adequate to most current brazilian normative emission standards, with PCDD/Fs emissions of 0.021 ngTEQ/Nm³. The average LHV of the RDF samples was of 4450 kcal/kg, with average moisture content of 11%, 0.22% chlorine and less than 0.01 mg/kg mercury, indicando good potential for usage as an industrial solid fuel and compatibility with both national and international standards. The pelletizing process showed technical feasibility, with ideal moisture content of 18% and an average compression strength of 15.3 MPa. The LHV of the RDF syngas was of 6.61 MJ/Nm³, which indicates potential for thermal use in industrial processes. The method used in the cromatography investigation did not identify any organochlorine in the syngas, with the detection of BTEX and acetonitrile in relevant concentration. Comparison between the RDF and wood chip syngases using the Mann-Whitney method for a 5% significance level did not show significant differences in gas composition between the two feeds. In the coprocessing test, no expressive variations of operational conditions, environmental performance or clinker quality were observed, for a thermal substituion ratio of up to 45%. SOx emissions showed an average reduction of 81.2% when compared to standard operation. From a general standpoint, the proposed treatment was shown to be environmentally and technically viable, and the RDF was shown to be an adequate feed for gasification, pelleting or for coprocessing, with no observed drawbacks when compared to standard operation.