Air-gasification of pine sawdust using dolomite as in-bed material: Effects of gasification conditions on product characteristics

Abstract

Air-gasification has emerged as preferred means of converting biomass to valuable synthesis gas (syngas). In present work, the gasification characteristics of pine sawdust were studied in a small-scale fluidized bed using calcined dolomite as in-bed material. Dolomite is characterized by higher tar conversion and H2 production during biomass gasification. Different operation conditions, equivalence ratios, reaction temperatures and dolomite contents, are studied for their influence on the gas compositions, gas yields, tar yields and higher heating values of producer gas. The results show that increasing either temperature or dolomite content enhances the tar conversion, where the latter accounts for the syngas with the lowest tar content. At 850 °C, the addition of 50 wt% dolomite can increase the gas yield from 1.48 to 1.85 Nm3/kg, and lowering the tar yield from 11.5 to 4.6 g/Nm3. Furthermore, the addition of more dolomite enhances the quality of the product gas, as indicated by increased values of the higher heating values of producer gas. Increasing the dolomite content within the 0–50% range resulted in higher H2 and CO contents, whereas the CH4 content declined. A slight change in CO2 content was observed with increasing dolomite content, which might cause by the limited carbonation. In contrast, the H2 content enhances non-linearly with the increase of dolomite content, which indicates that the catalytic activity of dolomite improves with the increase of dolomite share in the feedstock, due to the reforming of tar over dolomite. Increasing the ER from 0.14 to 0.3 elevates the gas yield, but decreases the tar yield and increases the H2 content in the product gas.