Numerical simulation on the influence of water spray in thermal plasma treatment of CF4 gas

Nitrogen thermal plasma generated by a non-transferred DC arc plasma torch was used to decompose tetrafluoromethane (CF₄). In the thermal decomposition process, water was used as a chemical reactant source. Two kinds of water spray methods were compared: water spray directly to the arc plasma flame and indirectly to the reactor tube wall. Although the same operating conditions of input power, waste gas, and sprayed water flow rate were employed for each water spray methods, a relatively higher decomposition rate was achieved in the case of water spray to the reactor wall. In order to investigate the effects of water spraying direction on the thermal decomposition process, a numerical simulation on the thermal plasma flow characteristics was carried out considering water injection in the reactor. The simulation was performed using commercial fluid dynamics software of the FLUENT, which is suitable for calculating a complex flow. From the results, it was revealed that water spray to the reactor wall and use of a relatively small quantity of water are more effective methods for decomposition of CF₄, because a sufficiently high temperature area and long reaction time can be maintained over large area.