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(738g) Thermal Conversion of Biomass into Clean Energy and Resource Using Gasification Integrated with Power Generation and Bottom Ash Reutilization

Authors: 
Wang, C. H., National University of Singapore
Maneerung, T., National University of Singapore
Li, X., National University of Singapore
Dai, Y., Shanghai Jiaotong University
Gasification is a thermal-based process that slowly converts biomass waste into syngas (a mixture of CO and H2) by chemical reaction at high temperatures (> 700 °C) with very tiny amount of oxygen to avoid complete combustion. Therefore, gasification not only provides environmental friendly way of discharging biomass wastes, but also produces syngas as a clean energy fuel, offering an alternative clean process for recovering energy from biomass waste. In this work, a small-scale waste-to-energy system combined gasification and a set of internal combustion engine power generation was investigated by using redwood waste pellets was used as feedstock. It was found that the redwood waste pellets have a higher heating value of 21 MJ/kg and it can produce the maximum syngas yield of 47.9 Nm3/h by gasification at a power load of 10 kW. Subsequently, total energy and exergy efficiencies of the integrated system can harvest 10.7% and 10.1%, respectively. In addition to the syngas, gasification also produces two main solid residues as unavoidable by-products, i.e. bottom ash – primarily minerals and metals with minimal carbon, and char – unreformed carbon. Although bottom ash is not classified as hazardous wastes, it may create potential risks to human health and environment. Therefore, the conversion of those by-products into beneficial materials could provide an environmental friendly and economical way to re-utilize the solid residues from gasification process, and hence creating a clean waste-to-energy system. In this work, bottom ash produced from gasification of redwood pellets was found to have significant amount of silica (>30 wt. %) and it can be successfully converted into zeolite materials (aluminosilicate) by using alkali hydrothermal method. The batch adsorption experiments showed that the original bottom ash itself has low adsorption capability, while the adsorption capability is significantly increased after the alkali hydrothermal reaction of bottom ash, which is mainly due to the formation of zeolite (which is a mixture of Na-A and hydroxylsodalite phases).