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Microwave-assisted torrefaction of biomass: Effect of biochar and recycled polymer plastic (HDPE) on the physical quality of fuel pellets

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  2018 ASABE Annual International Meeting  1801398.(doi:10.13031/aim.201801398)
Authors:   Obiora s Agu, Lope G Tabil, Bagher Emadi, Edmund Mupondwa
Keywords:   Wheat and barley straw, binder, densification, microwave torrefaction, solid fuel.

Abstract. Biomass fuel properties can have enhanced properties for heat and power applications through combined microwave-assisted torrefaction and pelleting. Fuel pellet characteristics such as durability, density, tensile strength and water absorption was used to evaluate the pellets produced from single pelleting technique. Recently, plastics wastes were considered as a replacement source binder in pellets to minimize their effect on the environment as pollutants. High density polyethylene (HDPE) an extractable plastic from recycle waste was investigated as a binder for torrefied biomass pellets. The results show that addition of HDPE as binder significantly increased the pellet quality in terms of density, tensile strength and reduced the ash content of the pellet from 10.34 to 4.59% for barley straw pellet and 10.66 to 3.88% for wheat straw pellets. The higher heating value (HHV) increased with increasing biochar mix and HDPE binder blend. For barley straw, the highest HHV value is 28.34 MJ/kg while wheat straw is 29.78 MJ/kg. The study further indicated that microwave torrefaction of biomass-biochar mix with HDPE binder reduced the moisture adsorption of wheat and barley straw pellet, which significantly improves their storage capability in humid locations. The moisture uptake ratio for MW torrefied barley straw pellets were found to be 0.10 – 0.25 and wheat straw pellets 0.11 – 0.25 against a moisture uptake ratio of 1.0 for untreated biomass. Microwave torrefaction of wheat and barley straw with biochar and HDPE binder addition during pelleting is a promising technique that can improve biomass fuel pellet properties.

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