Thermogravimetric analysis of thermal degradation of municipal solid waste (MSW) in N2, CO2 and O2/CO2 atmospheres

According to the Green Deal document, the ambition of the European Union is to achieve net-zero greenhouse gas emissions by 2050. To accomplish this goal all sectors of the economy will be obligated to reduce or eliminate the CO2 emissions. In the case of a waste-to-energy plant that is an important part of the waste management sector, the only possible method to avoid the emission of carbon dioxide is the implementation of carbon capture and storage (CCS) technology. One of the techniques of CCS is oxy-fuel combustion that uses the oxygen and recirculated exhaust gas as an oxidizer instead of air. As a result, the produced flue gas is composed mainly of carbon dioxide and water vapour, which makes its sequestration relatively easy and cost-effective. Nevertheless, oxy-waste incineration is rarely investigated, although changing the atmosphere from N2 to CO2 will strongly affect combustion behaviour. To study the influence of the combustion atmosphere on the particular stages of the process, such as pyrolysis and char burnout, the thermal decomposition of representative types of municipal solid waste (MSW) under N2, CO2 and O2/CO2 atmospheres was analysed using a thermogravimetric instrument. A non-isothermal program with the temperature range from 100 to 1000 °C was applied and three different heating rates (5, 10 and 15 K/min) were examined. The TGA (thermogravimetric) and DTG (derivative thermogravimetric) curves were analysed, while isoconversional method was employed to determine kinetic parameters of devolatilization and char burnout. Comparing N2 and CO2 atmospheres, it was found that below 600 °C, the shape of mass loss curves is not affected significantly. However, at high temperature (above 600 °C) under CO2 atmosphere the second peak appears, which indicates gasification reactions of the char with CO2, such as Boudouard reaction. In the presence of oxygen, the second peak is shifted to lower temperatures, indicating that thermal decomposition with O2 is faster and more rapid. The calculated and reported kinetic parameters provide fundamental information on the conversion of solid waste; thus, they are essential for designing chambers dedicated to the oxy-combustion of this feedstock.