Experimental and Aspen Plus modeling research on bio-char and syngas co-production by gasification of biomass waste: the products and reaction energy balance evaluation

Co-production of bio-char and syngas by gasification is a promising way for biomass comprehensive utilization. In this work, mainly two co-products from pinewood pellet gasification, namely bio-char and syngas were studied on a downdraft reactor. Based on the experiment, a detailed kinetic gasification model was built by Aspen Plus. The influence of temperature, ER, and steam amount was studied. Results of the pyrolysis stage show that bio-char yield during pyrolysis was about 22.8%wt and the initial pore structure was formed with a BET surface area of 36.8 m(2)/g. The main pyrolysis tar compounds detected by GC/MS were furfural and phenols. The gasification stage results show that H-2 concentration reached the maximum of 18.62%vol at ER = 0.3. The maximum concentration of CO was 16.2%vol at ER = 0.25. The syngas yield increased with ER value. At low ER of 0.15, the syngas yield was 1.22 Nm(3)/kg and increased to 2.26 Nm(3)/kg at ER of 0.4. The carbon conversion ratio also increased with ER value. When ER = 0.4, the highest carbon conversion ratio reached 91.7%. The bio-char at gasifier outlet was a kind of highly carbonized material and the carbon content was 82.5%wt. During gasification, pore structure of bio-char was enlarged and the BET-specific surface area was about 215 m(2)/g. Modeling results show that by adjusting the gasification parameters, such as temperature, air equivalent ratio, and steam amount, the product distribution in the gasifier outlet could be effectively controlled. Mass and energy balance evaluation for the downdraft gasification system indicates that the pyrolysis stage and reduction stage are endothermic processes, which adsorb heat of 2.47 kW (Q1) and 2.44 kW (Q2) respectively from the partial oxidation stage. Partial oxidation stage acts as the heat source of the gasifier.