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• Catalytic role of char's CaO in tar conversion was examined in micro fluidized bed reaction analyser. • Reaction Characteristics and kinetics were analyzed based on gas products release and evolution. • CaO dramatically enhanced the generation of H 2 , CO, CO 2 even at 1023 K. • CaO greatly reduced the generation activation energy of H 2 , CO, and C 2 H 6. 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 H 2 , CO, CO 2 , and C 2 H 6. For CH 4 and C 3 H 6 , 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 CH 4 , the total gas products, H 2 , CO 2 , CO, C 2 H 6 , and C 3 H 6 decreased to a great extent, indicating the good catalytic activity of the inherent CaO in char. [ABSTRACT FROM AUTHOR]

• Catalytic role of char's Fe 2 O 3 and K 2 O in tar cracking were assessed on a micro fluidized bed reaction analyzer. • Reaction characteristics and kinetics were analyzed based on gas products release and evolution. • Fe 2 O 3 displayed better catalytic activity in tar conversion than K 2 O. In this research, a newly-designed micro fluidized bed reaction analyzer (MFBRA) was used to evaluate the catalytic activity of char's inherent Fe 2 O 3 and K 2 O on bio-tar in Ar at temperatures of 1023 K, 1073 K, 1123 K, and 1173 K. The adopted samples of char and tar were obtained by biomass pyrolysis in Ar at 1273 K. Fe 2 O 3 - and K 2 O-loaded char were prepared by doping metal oxides on the demineralized char samples to simulate the inherent metal oxides in char. The real-time cracking properties of tar were examined and compared on the basis of the analyzer's high heating rate, quick sample loading at the predetermined temperature, and online analysis of gas products. The results show that both Fe 2 O 3 and K 2 O displayed obviously catalytic activity by improving tar conversion and reaction rate, and lowering activation energy (Ea). Compared to K 2 O at 1173 K, Fe 2 O 3 -loaded char promoted the generation of H 2 , CO, CO 2 , CH 4 , C 3 H 6 , and the total gas products with the conversion ratio (X Fe2O3/K2O) of 2.04, 1.02, 1.24, 1.32, 1.56, and 1.12, respectively. However, it suppressed the formation of C 2 H 6 with the X Fe2O3/K2O of 0.43. Meanwhile, the maximum generation rates for CO, CO 2 , CH 4 , and the total gas products improved to different extent. During tar catalytic cracking, Fe 2 O 3 suppressed carbon deposition on the char surface because of the larger specific area after experiments. Finally, the generation Ea of CH 4 , H 2 , CO, CO 2 , C 3 H 6 and the total gas products by Fe 2 O 3 -loaded char further decreased drastically and that of C 2 H 6 increased obviously. All of these indicated the catalytic activity of the inherent Fe 2 O 3 in char was better than K 2 O. [ABSTRACT FROM AUTHOR]

• Oxidative pyrolysis was introduced into the two-stage gasification system. • Its low-tar gasification capability in producer gas from biomass is tested in a 6 kg/h pilot facility. • Oxidative pyrolysis positively impacted on cracking of heavy tar in two-stage gasification. • Using air as a reagent produced fuel gas containing tar below 1.3 g/Nm3 in the pilot testing facility. Oxidative pyrolysis of fuel was adopted to configure an advanced two-stage fluidized bed gasification system, aiming to produce low-tar producer gas efficiently. A series of tests were carried out to investigate the effect of oxygen allocation in supply on gasification of pine chips in terms of both efficiency and producer gas quality. Compared with the case without pre-oxidation, coupling oxidative pyrolysis increased gas volume fraction of CO, CH 4 , and C n H m while decreasing that of CO 2 and H 2 in the produced gas. Further analysis showed that adopting oxidative pyrolysis reduced fuel gas yield, but the tar in the produced gas was lighter. The generated tar is easily transformed into small-molecule combustible gas by the catalytic action of hot char, thus increasing the calorific value of product gas. The long-term operation of the pilot plant presents a great steady continuous running with a minimum tar content in the producer gas of 1.3 g/Nm3. The above-mentioned results thus well verified the technical advantage and feasibility of the two-stage fluidized bed gasification with oxidative pyrolysis. [ABSTRACT FROM AUTHOR]