Tar and soot in product
gas have been a major technical challenge
toward the large-scale industrial installation of biomass gasification.
This study aims at demonstrating that the formation of tar and soot
can be reduced simultaneously using the catalytic activity of alkali
metal species. Pine sawdust was impregnated with aqueous K2CO3 solution by wet impregnation methods prior to the
gasification experiments. Raw and alkali-impregnated sawdust were
gasified in a laminar drop-tube furnace at 900–1400 °C
in a N2–CO2 mixture, because that creates
conditions representative for an entrained-flow gasification process.
At 900–1100 °C, char, soot and tar decreased with the
temperature rise for both raw and alkali-impregnated sawdust. The
change in tar and soot yields indicated that potassium inhibited the
growth of polycyclic aromatic hydrocarbons and promoted the decomposition
of light tar (with 1–2 aromatic rings). The results also indicated
that the catalytic activity of potassium on tar decomposition exists
in both solid and gas phases. Because alkali salts can be recovered
from product gas as an aqueous solution, alkali-catalyzed gasification
of woody biomass can be a promising process to produce clean product
gas from the entrained-flow gasification process at a relatively low
temperature.
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