(186e) Biomass and Solid Waste Gasification for Clean Energy Production: Experimental and Simulation Studies

As urbanization increases dramatically worldwide over the past two centuries, nowhere is the impact more obvious than in society’s “detritus” or solid waste. Improper solid waste management can cause all types of pollution: air, soil, and water. Therefore, it has become a matter of urgency to unearth alternative options to solve this problem. One promising method is to actively treat the solid waste and process it into energy. Incineration is known as a commercialized technology which converts waste into electricity. However, burning of waste in incinerators causes well-known negative environmental and public health effects.

GASIFICATION can be considered as an alternative clean process which converts biomass and/or solid wastes into synthesis gas (a mixture of H₂ and CO). In this work, we have experimentally investigated gasification of several solid wastes including woody biomass, sewage sludge (from wastewater treatment plant) and food wastes by using a downdraft fixed-bed gasifier. These solid wastes were successfully converted into the producer gas containing 30 to 50 vol. % of synthesis gas (with an average lower heating value up to 4.9 MJ/Nm³) which can be directly used for electricity production. For co-gasification of woody biomass and sewage sludge, the maximum of 20 wt. % dried sewage sludge in the feedstock can be effectively gasified to generate producer gas comprising over 30 vol. % of synthesis gas; further increasing sewage sludge content to 33 wt. % leads to the failure of the gasifier. This is because sewage sludge contains large amount of ashes which is readily agglomerated at high temperature and, consequently, formed the large agglomerated ash, causing the blockage of gasifier.

Moreover, carbon soot, by-product powder from oil refinery industries, will also be used as a feedstock for gasification due to its high carbon content (>90 wt. %). However, the small power form of carbon soot can cause the blockage of the whole system. Torrefaction, a mild pyrolysis at temperatures ranging from 200 to 320 °C, has been used to from the suitable shape with high energy-density of carbon soot.

Last but not least, we also attempted to simulate the gasification process occurring inside the downdraft fixed-bed gasifier which typically involves four different processes i.e. drying, pyrolysis, combustion, and gasification. A time derivative based model was used to numerically simulate the drying, pyrolysis and combustion zones; whereas a spatial derivative approach was applied to the gasification zone as this zone plays a key role in determining the composition of the producer gas. The simulation results produced are then validated and are in good agreement with the experimental data obtained from literature and our experiments. The model is then further used to conduct parametric studies on the effects of equivalence ratio, feedstock composition and moisture content on Cold Gas Efficiency (CGE) during biomass and/or solid waste gasification.