Process development and reactor analysis of coal pyrolysis to acetylene in hydrogen plasma reactor

Abstract

Coal pyrolysis in hydrogen plasma opens up a direct means for producing acetylene. This process is operated under high temperature conditions (e.g., ∼3000 K) with the residence time in milliseconds. To better understand the complex reaction behavior in a 2 MW pilot-scale reactor, a comprehensive CFD model was established to describe the gas-particle reacting flows for the process of coal pyrolysis in hydrogen plasma. Equilibrium chemistry in the gas phase was introduced and the mixture fraction approach with β-shape probability density function was used. The coal particles were modeled by discrete phase model approach so that the heating and devolitilization processes of coal particles can be well quantified in the reactor. The 3-dimensional simulations revealed the detailed flow field, temperature field, devolitilization process of coal and the spatial distribution of product gases. The unique structure of the V-shape plasma torch leads to the non-uniformity of temperature distribution in the reactor as well as the dissimilar courses of devolatilization of coal particles injected from different inlet s. The results indicated that coal released its volatile matter in the first third of the reactor. Increasing the coal feeding rate results in the temperature drop of the reactor and an increase of the concentration of methane. The concentration of acetylene may reach its maximum in a good match between the plasma power input and the feeding rate of coal. All the results showed good accordance with the operation experience on the 2 MW pilot-plant reactor. © 2009 The Society of Chemical Engineers, Japan.