Biofuels from Lignocellulosic Biomass - Sustainable Biotechnology: Sources of Renewable Energy - page 32

Ta b l e 2 Characteristics and types of gasifiers [21, 22]

Flow Direction

Gasifier Type Biomass Oxidant Heating source and major features

Updraft fixed-bed Down Up Combustion of char; simple process but

high tar in syngas, minimal feed size

Downdraft fixed-bed Down Down Partial combustion of volatiles; simple

process, low tar in syngas, minimal
feed size and limit ash content

Bubbling fluidized-bed
(BFB)

Up Up Partial combustion of volatiles and char;

high CH 4 , excellent mixing, heat
transfer, and C conversion, extensively
tested with biomass

Circulating fluidized-bed
(CFB)

Up Up Partial combustion of volatiles and char;

high CH 4 , possible corrosion and
attrition problem, not extensively
tested with biomass

Entrained flow-bed Up Up Partial combustion of volatiles and tar;

very low in tar, CO 2 ,lowinCH 4 ,
biomass has to be pulverized, fluid ash

Fig. 3 Illustrative structures of different types of gasifiers (modified from Dr. R. L. Bain's 2004
presentation at DOE/NASCUGC Biomass and Solar Energy Workshop)