Design of a tar catalytic cracker based on hot syngas clean-up tests

Catalytic tar cracking is a promising technique for hot syngas cleaning section in gasification plants since it can remove tars without losing their chemical energy, thereby increasing syngas heating value. Anyway, concerns associated with catalyst selection and preparation and those related to the deactivation phenomenon induced by coke deposition on the active sites still hinder the technical feasibility and economic viability of the process. This study investigates the role of the main operating conditions in the cracking of naphthalene (used as a tar model compound) by means of tests carried out with an iron-supported catalyst (Fe/γ-Al2O3), under different values of gas residence times (0.055 s, 0.11 s, 0.165 s and 0.22 s), steam concentrations (0 % and 7.5 %), and reactor temperature (750 °C and 800 °C). The results were used to implement a diffusivity analysis and a kinetic study that drove the design of a tar cracking fixed bed reactor to be used in the clean-up section of a large pilot-scale bubbling fluidized bed gasifier.