Coal pyrolysis to acetylene in hydrogen plasma is carried out under ultrahigh temperature and milliseconds residence time. To better understand the complex gas-particle reaction behavior, a comprehensive computational fluid dynamics with discrete phase model has been established, with special consideration of the particle-scale physics such as the heat conduction inside particle. The improved chemical percolation devolatilization model that incorporates the tar cracking reactions is adopted. The model predictions are in good agreement with the performances of two pilot-plant reactors. The simulations reveal the detailed unmeasurable information of gas phase and particle-scale behaviors, then point out the facts that coal devolatilization almost finishes in the first 100 mm of the reaction chamber and the optimal particle diameter is suggested to be 2050 m. The different reactor performances during the scale-up from 2- to 5-MW unit are analyzed based on the detailed simulation results in combination with the operational experience. (c) 2012 American Institute of Chemical Engineers AIChE J, 59: 21192133, 2013