Experimental study and characterization of a two-compartment cylindrical internally circulating fluidized bed gasifier

• ICAFB was designed and constructed for sawdust gasification investigation.
• Indirect heating principle was applied to the gasification zone.
• Solid circulation acts as the heat carrier from the draft tube to annulus.
• Solid circulation rate depend on the fluidization ratio.
• Optimum parameter used resulted producer gas with heating value of 6.96 MJ m3.

This study aims to improve the heating value (HV) of gas produced during the gasification of sawdust using a new type of air-blown gasifier based on a two-compartment cylindrical fluidized bed. The gasification process is based on an internally circulating aerated fluidized bed (ICAFB) and consists of two individual zones; a gasification zone in the annulus and combustion zone in the draft tube. The annulus and draft tube are connected via orifices at the lower section of the draft tube wall to enable the solids to move from the annulus to the draft tube. Char, gasified residue, together with hot bed material move to the draft tube and combust to produce heat. Fluidization ratio (RQ) which is the ratio of air flow rate in the annulus (Qan) to the air flow rate in the draft tube (Qdt) together with equivalence ratio (ER) were used to control the temperature of the gasifier. The effects of ER on the temperature system stabilization, composition, HV of producer gas (PG) and gasifier performance were presented. ER ranges from 0.148 to 0.203 were used in this study. PG compositions of 3.13%, 2.28%, 25.8%, 8.2% and 22.48% for H2, O2, CO, CH4 and CO2 respectively with a HV of about 6.96 MJ m−3 were obtained at an ER of 0.185 and temperature of about 866 °C. Compared with previous air-blown fluidized bed biomass gasification results, the ICAFB gasifier is capable of producing producer gas with higher CO and CH4 fractions.