Assessment of the inherent CaO in char on tar catalytic conversion by a micro fluidized bed reaction analyzer for biomass gasification

In this study, a newly-developed micro fluidized bed reaction analyser (MFBRA) was adopted to examine the effects of char's inherent CaO on tar catalytic cracking from 1023 K to 1173 K. A simulated CaO-based char catalyst was prepared by impregnation method. For comparison, the blank experiments were also conducted by employing the demineralized char free of CaO. The tar cracking behaviour and reaction kinetics based on the gas products generation were systematically compared. The structure and reaction activity of char sample before and after experiment were also analyzed. The results shows that tar conversion processes can be divided into a fast cracking stage and a stable conversion stage. By increasing the reaction temperature, the tar conversion by char without CaO to the total gas products and its reaction rate changed from 41.15 % to 71.50 % and from 0.055 s-1 to 0.081 s- 1, respectively; but for char with CaO, they improved from 57.54 % to 88.25 % and from 0.062 s-1 to 0.096 s-1, respectively. The presence of CaO dramatically enhanced tar conversion even at a low temperature of 1023 K, producing more effective gas components, such as H2, CO, CO2, and C2H6. For CH4 and C3H6, the promotion became obvious at high temperatures above 1123 K. During tar catalytic cracking, CaO suppressed carbon deposition on char surface to some extent. Meanwhile, the generation activation energy (Ea) of CH4, the total gas products, H2, CO2, CO, C2H6, and C3H6 decreased to a great extent, indicating the good catalytic activity of the inherent CaO in char.