Thermodynamic Analysis of Methanation of Pyrolysis Gas from Anthropogenic Residues

The methanation of pyrolysis gas was investigated using the open access software DWSIM v9.0.5 to assess its potential for producing methane-rich gas. The pyrolysis gas composition was derived from known experimental tests of anthropogenic residues, namely sewage sludge and digestate. Four gas compositions were considered; they were obtained by the pyrolysis of residues with and without a sorbent for CO2 capture. The methanation process was simulated by a non-stoichiometric thermodynamic approach to calculate the chemical equilibrium composition of the gas. A parametric investigation was carried out under a temperature range of 300–500 °C and a pressure range of 10–40 bar. Carbon oxide conversion, methane selectivity and methane yield were calculated. CO almost underwent quantitative conversion, while CO2 showed significantly lower or negative conversion. Synthetic biogas was obtained from the pyrolysis gas of the residues, showing a methane content of about 50 mol%. Synthetic natural gas was obtained from the pyrolysis gas residues plus sorbent, showing a methane content of about 90 mol%.