Combined Partial Oxidation and Carbon Dioxide Reforming Process: A Thermodynamic Study

Abstract

Problem statement: CO₂ reforming is one of the methods to utilize a greenhouse gas to produce syngas, an important feed for methanol and Fischer-Tropsch synthesis. However, CO₂ reforming is strong endothermic reaction requiring large amount of supplied energy. Partial oxidation, an exothermic reaction, is combined with CO₂ reforming to serve the energy requirement. Thus, the optimum ranges of O₂ and CO₂ fed to the process corresponding to feedstock are needed to find. Moreover, one of the most important problems found in this process is solid carbon formation. Therefore, the operating range in which the carbon formation can be avoided is also required to study. Approach: In this study CH₄ was used as feedstock. The optimum rage of O₂ and CO₂ fed to the process was found by using thermodynamic equilibrium method based on minimization of Gibbs free energy. The Lagrange multiplier method was conducted to form the equations and they were solved by the Newton-Raphson method. The solid carbon formation zone was also simulated. Results: The simulation showed that higher reaction temperature caused higher CH₄ and CO₂ conversions. Syngas production increased with increasing temperature. Operating the process with high temperature or high O₂/CH₄ and CO₂/CH₄ rations could eliminate solid carbon formation. Increase of O₂/CH₄ ration higher than 0.1 led decreasing syngas while increase of CO₂/CH₄ ration caused increasing H₂ and CO. However, when CO₂/CH₄ ration was higher than 0.85, increasing CO₂/CH₄ ration showed insignificant change of syngas concentration. Conclusion: The combined partial oxidation and CO₂ reforming of method should be operated with reaction temperature of 1050 K. The optimum range of CH₄:CO₂:O₂ for this process is 1: 0.85-1.0:0.1-0.2.