SECONDARY TAR REACTIONS AND SOOT FORMATION IN PYROLYSIS OF COAL

In the present work fast pyrolysis of coal in N2 and CO2 atmospheres was studied using two different systems: a drop tube reactor (DTR) and a heated strip reactor (HSR). The two systems allow comparable particles heating rates with different temperature of the gas phase. The tars produced in the two systems have been analyzed with the aim to study the role of gas tar reactions in soot inception. It was found that in DTR, where volatiles react in a hot atmosphere, polycyclic aromatic hydrocarbons (PAH) formation and growth is larger than in the HSR, where the volatile species are quickly quenched. The results provide evidence that secondary reactions of the tar are a source of PAH, which in turn, can be soot precursors, even in pyrolytic conditions. Also soot formation is highly limited in the HSR system, confirming the role of tar in soot formation mechanism. The effect of CO2 is not straightforward and varies according to pyrolysis time and temperature.