Fluidized Bed Gasification of Torrefied and Raw Grassy Biomass (Miscanthus x gigantenus). The Effect of Operating Conditions on Process Performance

Torrefaction is suggested to be an effective method to reduce the cost of biomass provision and improve the fuel-properties. In this :study, both raw and torrefied Miscanthus X giganteus (MXG) were gasified in an externally heated air-blown bubbling fluidized bed (BFB) gasifier using, olivine as the bed material. The effects of-equivalence ratio, (ER) (0.18-0.32) and bed temperature (660-850 degrees C) on the gasification performance were investigated. Torrefied MXG has higher energy density primarily due to a higher ratio of lignin to cellulose and hemicellulose; it has lower bulk density, smaller particle diameter and lower reactivity than the-original biomass. These properties affect its performance during gasification. The cold gas efficiency was On average 12% lower for torrefied than for raw MxG for the range of operating conditions studied., Within the same temperature range the carbon conversion was about 10% higher for raw than for torrefied biomass. The hydrogen conversion was higher for torrefied MXG since gasification of this feedstock results in higher yields of methane and ethane and lower yields of unreacted process water The carbon loss with char elutriated from the gasifier for torrefied MxG was significantly higher than that of raw (5% vs 3%) and was driven by physical properties of torrefied MxG. The results obtained suggest that chemical composition expressed as lignin to cellulose and hemicellulose ratio has a pronounced effect on carbon conversion efficiency and tar production.