A comparative study of air and nitrogen thermal plasmas for PFCs decomposition

Air and nitrogen thermal plasmas were generated from a plasma torch with hollow electrodes to abate CF4 which is a serious non-degradable greenhouse gas exhausted from the semiconductor manufacturing process. Numerical analysis and experimental demonstration have been carried out to compare effects of plasma forming gas on the decomposition process at the same electric input power of 60 kW and waste gas flow rate of 200 L/min. Higher temperature and longer residence time were expected in nitrogen thermal plasma than air thermal plasma, because relatively low flow rate of nitrogen plasma gas is required at fixed input power compared with air plasma gas. Although small quantity of NF3 was produced in nitrogen thermal plasma process with hydrogen reactant gas, high destruction and removal efficiency of 99.6% was achievable along with suppression of unwanted NOx generation.

► CF4 included waste gas of 200 L/min was decomposed by air and nitrogen thermal plasmas.
► N2 plasma has higher temperature and residence time than air plasma.
► Unwanted byproduct of NOx is strongly suppressed in nitrogen thermal plasma.
► High DRE of 99.6% was achieved in N2 plasma process with H2 though NF3 and soot were generated.