Analysis of particle heating and devolatilization during rapid coal pyrolysis in a thermal plasma reactor

Using thermal plasma for coal pyrolysis to acetylene provides a direct route to make chemicals from coal resources, where the temperature field in the reactor plays a dominant role in the performance of coal devolatilization. A comprehensive computational fluid dynamics with discrete phase model (CFD-DPM) has been established to describe the rapid coal pyrolysis process in a reactor under ultra-high temperatures. The simulations based on this model helped to understand the complex gas–particle reaction behavior in the millisecond process of coal pyrolysis. The particle-scale physics such as the heat conduction inside solid materials, diffusion of released volatile gases, coal devolatilization, and tar cracking reactions were incorporated. The improved chemical percolation devolatilization (CPD) model was applied to describe the devolatilization behavior of rapidly heated coal based on the physical and chemical transformations of the coal structure. This model was proved to be qualified for describing the complex gas–particle reaction behavior with milliseconds residence time by the operation experience of a 5-MW plasma reactor. Then the simulations revealed the fact that the particle heating and devolatilization are strongly affected by the grade of the temperature and the residence time of coal particles in the high temperature zone(s). Highly concentrated energy input in the reactor may not intensify the reactor performance. As a potential solution, multi-stage heating design would provide more flexibilities to effectively adjust the devolatilization performances under the same energy input.

► A cross-scale CFD model incorporating particle-scale physics and improved CPD model.
► Theoretical analysis of coal devolatilization with experimental validation.
► Particle heating: strongly affected by temperature field and residence time.
► Multi-stage heating design: more flexible to adjust the pyrolysis performance.