Effect of auto thermal biomass gasification on the sintering of simulated ashes

Abstract

Ash sintering is an essential factor for the competitiveness of biomass gasification. Compared to conventional air biomass gasification, the gasification temperature is reduced in the auto thermal biomass gasification, as the utilisation of thermal compensation for the CaO carbonation reaction, which ultimately could suppress the extent of ash sintering. This work firstly investigated the inhibition effect of this process on the sintering of simulated ashes (silica, potassium oxide and alumina) in a lab-scale fixed bed reactor. The results indicate that the alumina particles are present under different CO2 concentrations, gasification temperature and CaO/ biomass ratios. However, silica and potassium oxides react with CaO and disappear at high temperatures. Among the three simulated ashes, alumina particles are relatively stable in the auto thermal biomass gasification. The average particle size decreases from 116.9 µm to 64.9 µm and 93.8 µm when CaO/alumina ratio is 2 and 5, respectively, indicating the increase of CaO addition under the flue gas atmosphere could inhibit the sintering degree of simulated ash. Meanwhile, the reaction between CaO and CO2 in the carrier gas can reduce the formation of calcium silicate. Therefore, compared with conventional biomass gasification, auto thermal biomass gasification is favourable to restrain the degree of ash sintering because of the relatively low gasification temperature.