Thermodynamic analysis of mixed and dry reforming of methane for solar thermal applications

Abstract

Thermodynamic analysis of the reforming of methane with carbon dioxide alone (“dry reforming”) and with carbon dioxide and steam together (“mixed reforming”) is performed as part of a project which investigates the suitability of these endothermic reactions for the storage of solar thermal energy. The Gibbs free energy minimization method was employed to identify thermodynamically optimal operating conditions for dry reforming as well as mixed reforming with a desired H 2/CO molar ratio of 2. The non-stoichiometric equilibrium model was developed using FactSage software to conduct the thermodynamic calculations for carbon formation, H 2/CO ratio, CH 4 conversion and H 2 yield as a function of reaction temperature, pressure and reactant molar ratios. Thermodynamic calculations demonstrate that in the mixed reforming process, optimal operating conditions in a carbon-free zone are under H 2O/CH 4/CO 2 = 1.0/1.0/0.5, p = 1 to 10 bar and T = 800 to 850 °C for the production of syngas with a H 2/CO molar ratio of 2. Under the optimal conditions, the maximum H 2 yield of 88.0% is achieved at 1 bar and 850 °C with a maximum CH 4 conversion of 99.3%. In the dry reforming process, a carbon formation regime is always present at a CO 2/CH 4 molar ratio of 1 for T = 700-1000 °C and p = 1-30 bar, whereas a carbon-free regime can be obtained at a CO 2/CH 4 molar ratio greater than 1.5 and T≥800°C.