Contents lists available at ScienceDirect Fuel journal homepage: www.elsevier.com/locate/fuel Insights on the role of primary and secondary tar reactions in soot inception during fast pyrolysis of coal B. Apicella a, ⁎ , C. Russo a , F. Cerciello a , F. Stanzione a , A. Ciajolo a , V. Scherer b , O. Senneca a a Istituto di Ricerche sulla Combustione, IRC-CNR, P. le Tecchio 80, 80125 Napoli, Italy b Department of Energy Plant Technology, Ruhr-Universität Bochum, Universitätsstr. 150, 44780 Bochum, Germany GRAPHICALABSTRACT ARTICLEINFO Keywords: Coal pyrolysis Fast pyrolysis Drop tube Tar analysis PAH Soot ABSTRACT In the present work fast pyrolysis of coal in N 2 and CO 2 atmospheres was studied in a drop tube reactor (DTR) and in a heated strip reactor (HSR). In the DTR the volatiles generated by coal pyrolysis were entrained in a hot gas stream and were collected at the reactor outlet by tar traps. In the HSR, the volatiles were ejected from the hot coal particles into a cool environment and the condensable species, including primary tar, deposited and/or condensed on a glass bridge located above the heated strip. The composition of tars produced in the two reactors was compared to study the role of gas tar reactions in soot inception, and reference compounds for each class of tar species produced were identifed. In the DTR the formation and growth of polycyclic aromatic hydrocarbons (PAH) were found higher than in the HSR. Soot formation occurred only in the DTR, being negligible in the HSR. It was concluded that the hot gas environment of the DTR favours secondary tar reactions, formation of PAH and eventually soot, while in the HSR this path was prevented due to prompt cooling down of volatiles. The presence of large concentration of CO 2 in the pyrolysis atmospheres further promoted formation of heavy PAH and soot in the DTR, but not in the HSR, where the cooler environment limits soot-CO 2 reactions in the gas phase. 1. Introduction Coal, petroleum and natural gas combustion is still widely used to produce energy and is expected to play a signifcant role in the next 20–30 years [1], in spite of the strong environmental and climate im- pact. Considering the higher tendency of coal to produce greenhouse https://doi.org/10.1016/j.fuel.2020.117957 Received 21 June 2019; Received in revised form 3 April 2020; Accepted 27 April 2020 ⁎ Corresponding author. E-mail address: apicella@irc.cnr.it (B. Apicella). Fuel 275 (2020) 117957 0016-2361/ © 2020 Elsevier Ltd. All rights reserved. T