Chemical Looping Gasification of a Biomass Pellet with a Manganese Ore as an Oxygen Carrier in the Fluidized Bed

摘要

As a result of the increasing transport cost of biomass and benefiting from the more efficient treatment of a compacted, dustless product, the use of pelletized biomass has gained interest over recent years in China. Chemical looping gasification (CLG) with circulating oxygen carriers provides a novel process, which integrates biomass gasification with the hot gas conditioning with the aim to obtain pure syngas with a low tar amount. The study focuses on the CLG application using a single typical rice husk pellet as fuel, which is characterized by high silicon dioxide in ash. Some experiments in a fluidized bed unit with the mixture of quartz sand and an active manganese ore as bed materials were performed using a single rice husk pellet as fuel and steam as the gasifying agent. The objectives of the work are to investigate its CLG performance and bottom ash characterization. Effects of the gasification temperature (750-950 degrees C) and oxygen carrier/fuel ratio on syngas distributions, effective gas content, and syngas yield were investigated. The conversion of the rice husk pellet is very dependent upon the reaction temperature. A high temperature promoted tar cracking and gasification reactions, leading to a fast carbon conversion. The effective gas content (CO + H-2 CH4) during the gasification process was in the range of 74.2-79.9% under the temperature of 750-950 degrees C. With regard to the CLG application of a rice husk pellet as fuel, much attention should focus on bottom ash, which was not separate during the process but still kept the original pellet shape, with some irregular pores inside the ash as a result of the formation of molten grains. The ash demonstrates a rigid skeleton-like structure. The trapped carbon particles inside the molten ash cannot be gasified, thus limiting the fuel conversion.