Reaction-front and char characterization from a palm kernel shell – Oil sludge mixture under oxygen lean regimes in a fixed-bed gasifier

Abstract

A reaction-front assessment and char characterization of a mixture of oil sludge and palm kernel shell in a fixed-bed reverse-downdraft gasifier using air as the oxidizing agent has been performed. The investigation was focused on assessing the effect of airflow (from 30 up to 60 L/min) on the reaction front as well as on the characterization of char derived from the thermochemical treatment. The thermochemical conversion process was described by output parameters such as fuel consumption rate, flame front velocity (Vff), maximum process temperature (Tmax), air–fuel equivalence ratio, and char yield. The char was characterized regarding its surface structure by determining Brunauer, Emmett, and Teller (BET) surface area, pore volume, and pore size distribution. The results demonstrated that as the airflow rate increased from 30 to 60 L/min, Vff and Tmax augmented from 4.36 to 6.49 mm/min, and from 967 to 1090 °C, respectively, as the process approached a combustion regime. In parallel, the char yield decreased from 13.4 to 4.5 % for the same airflow range due to the higher temperatures, which favors oxidation reactions. The char characterization showed that the BET surface area reached a maximum value of 269.8 m2/g at 50 L/min and subsequently decreased, which was attributed to the thermal deformation of the pore structure as the process temperature increased. Furthermore, pore size distribution showed that the char was mainly composed of micropores. Besides providing useful information related to the operation of gasifiers and char production, this analysis is particularly relevant for solutions aimed at mitigating environmental impacts, as it involves renewable sources and energy recovery.