Experimental study on coal pyrolysis to acetylene in thermal plasma reactors

Abstract

Coal pyrolysis in thermal plasma provides a direct and cleaner route for producing acetylene from coal resources. Owing to the complex physical–chemical properties of coal and integrated multiple processes in milliseconds, the selection of coal feedstock becomes of great importance to the reactor performance. Experiments were carried out in a lab-scale plasma reactor to investigate the effects of coal properties and key operating conditions including the coal specific enthalpy, gas specific enthalpy, plasma atmosphere, and residence time. The results demonstrate that higher coal–gas mixture enthalpy leads to higher coal conversion and yield of light gases. The fixed carbon in coal can be partly converted to gaseous products in Ar/H2 plasma, where the increased H2 concentration enhances the carbon conversion, and correspondingly raises the yields of CO and C2H2. Since oxygen in coal is more easily released than carbon, the oxygen compounds in coal are disadvantageous to the acetylene yield. A non-coking coal with volatile matter content on dry ash-free basis higher than 37%, oxygen content lower than 13% and low ash content would lead to a better reactor performance. The relationship between rapid plasma pyrolysis and slow thermal pyrolysis processes is discussed by comprehensively comparing the gas products and solid residues in order to pursue an alternative, simple method of preliminary selection of coal rank for the plasma pyrolysis technology.