Thermochemical analysis and experimental investigation of a recuperative waste heat recovery system for the tri-reforming of light oil

Abstract

This paper presents a thermochemical and experimental investigation into the use of oxy-fuel exhaust gases for the tri-reforming of light oil. The thermochemical recuperation of light oil makes it possible for the furnace to burn hydrogen-rich syngas, and thereby significantly improve furnace efficiency. This study investigates three process parameters: the exhaust gas recirculation rate, the syngas temperature, and the exhaust gas temperature. (1) The more exhaust gas that is recirculated, the less oxygen is required for complete conversion into syngas, and the higher the heating value of the produced syngas. A maximum increase in the heating value of 31.6% (compared to the primary fuel) is possible if pure bi-reforming is performed. (2) The chemical equilibrium calculations showed that the syngas temperature has a strong effect on the composition of the syngas; a syngas temperature of 1265 °C is necessary to achieve a conversion rate of 99.9%. The thermodynamic analysis was performed using the Gibbs free energy minimization method. In order to prevent carbon formation, a slight oxygen excess of 1% must be present. In this case, a syngas temperature of 970 °C is sufficient for the stationary tri-reforming of light oil. (3) The energy required for reforming the primary fuel increases with increased syngas temperature, while the energy contained in the hot exhaust gas stream increases with increased exhaust gas temperature. In order to achieve a syngas temperature of at least 970 °C, both the required exhaust gas recirculation rate and the amount of oxygen for reforming and combustion are directly dependent on the temperature of the exhaust gas. An exhaust gas temperature of 1000 °C requires an exhaust gas recirculation rate of 16.2%, while a recirculation rate of 26.9% is necessary at an exhaust gas temperature of 1600 °C. In the latter case, it is possible to increase the efficiency of the oxy-fuel furnace by 22.8%.