Experimental and Modelling Analysis of Char Decomposition: Experiences with Real Scale Gasification Systems

The main issue to be faced when dealing with gasification processes is the removal of tars in order to obtain a good quality producer gas for later use, either as energy vector or for production of chemicals. Char has been observed to have a high potential for catalytic tar reduction, but the properties that promote this activity are still being investigated. An understanding of the mechanisms involved in the process of tar removal is needed, including the deactivation of the char as a catalyst and its degradation. This work addresses the process of thermal decomposition of char with different operating conditions and under inert atmosphere (N2), in order to determine the mass loss occurring under high temperature treatment. For this purpose, chars collected from local gasification plants have been used. Firstly, a complete characterization of the chars has been carried out to determine their composition, heating value and BET surface area. Secondly, thermogravimetric analyses have been used to calibrate a one-step kinetic model for describing the kinetics involved in the process of char thermal decomposition. The coupling of the kinetics with a CFD model allowed then to consider mass, heat, and momentum transfer phenomena, and to quantitatively estimate the decomposition in a fixed-bed test reactor. The model, whose results have been compared to reference experimental tests, predicts satisfactorily the thermal behavior of the char inside the reactor and its mass loss.