Experimental and modeling investigation of partial oxidation of gasification tars

Among the methods to reduce tar emission, the partial oxidation (POX) of biomass gasification tars has been studied both experimentally at a pilot-scale and numerically. The gasification producer gas was obtained at a temperature of 800 degrees C in an air-blown fluidized bed with an equivalent ratio (ER) of 0.25. For the POX unit, two secondary ER values were selected: 0.05 and 0.10, with the option of pre-heating air or not. Multiple advanced analytical methods were employed to provide a detailed composition of the producer gas, tars and acid gases. The POX unit demonstrated the ability to reduce tar levels by 60 to 90% depending on the secondary ER (from 6.5 to 2.4 and 0.72 gtars/Nm3, excluding benzene). The lighter tars were almost completely eliminated. The permanent gases were barely modified while the light hydrocarbons (except C2H2) and benzene were significantly reduced. Consequently, there was a slight decrease in the lower heating value. These results were compared to an isothermal plug flow reactor model, which utilized a detailed radical kinetic scheme constructed from various sources to account for all the species measured during the experiments as well as soot mass yield. The model provided relatively accurate predictions of the hydrocarbon species variations, even though it did not consider the mixing between air and syngas at the inlet of the POX unit.