Design of co-current moving-bed gasifiers fueled by biomass

The physical and chemical phenomena occurring in a co-current moving bed gasifier have been analyzed from experimental results along with model calculations for different zones of the gasifier. A number of previously known empirical design rules can be understood and possible process limitations are predicted. With the reaction engineering model for the reduction zone, the gas composition can be related to the fuel characteristics, reduction zone dimensions, heat losses and recovery. From the analysis of the pyrolysis/oxydation zone it can be concluded that its dimensions are limited by the time to complete the devolatilization and the penetration length of the air jet. For larger capacities, an annular throat is thus preferred over the classical throat design. An example is given for a 100 t/d gasifier.