Thermodynamic Analysis of Methanation of Pyrolysis Gas from Anthropogenic Residues

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