This work aims to improve the understanding on the principles of coal/hydrocarbons pyrolysis to acetylene (C2H2) in thermal plasma reactors by thermodynamic analysis in association with the practical operation experience at lab- and pilot-plant scale reactors. The thermodynamic predictions agree well with the experimental data in the literature and the representative data in megawatts plasma reactors. Accordingly, it is summarized that the effective mass ratio of C/H (R-C/H) in the gas phase and the quench temperature are the two key factors influencing the reactor performance. The C2H2 concentration is very sensitive to the quench temperature varying around 1500-1800 K, which is therefore suggested to maintain above 1800 K for a better yield of C2H2. Higher effective mass ratio of C/H would have a more positive effect on the reactor performance in terms of C2H2 concentration. The additional input of hydrocarbons to the reaction system provides an effective means to flexibly adjust the performance of the plasma reactor for the raised R. The additional water/steam helps to inhibit coking on the wall but reduce the R, leading to the trend from thermal pyrolysis to gasification process. (C) 2012 Elsevier Ltd. All rights reserved.