DOI RECORD
Determination of the effective plasma-tail temperature from NOx measurements in thermal plasma torch for application to operational radioactive waste treatment
Abstract
Accurate characterization of the thermal conditions in the plasma tail of non-transferred arc torches is important for optimizing and controlling plasma-based thermal treatment processes, including the gasification of operational radioactive waste. In this work, an indirect method for estimating the effective temperature of the plasma tail from the concentration of nitrogen oxides (NO + NO2) generated by an air-fed non-transferred arc plasma torch is presented. The method is based on the Zeldovich mechanism for thermal NO formation and incorporates equilibrium calculations performed using HSC Chemistry software over the temperature range of 1293-3793 K. Experiments were performed at plasma torch electrical powers levels of (32 ± 1), (34 ± 1), (39 ± 1), and (42 ± 1) kW, with an air flow rate of 30 kg/h. The NO + NO2 concentrations measured at these electrical power levels were (3192 ± 50), (4609 ± 118), (5447 ± 138), and (5814 ± 134) ppm, respectively, corresponding to estimated effective plasma-tail temperatures of (1716 ± 4), (1825 ± 8), (1879 ± 8), and (1901 ± 8) K. A Damköhler number of approximately 2.5 at 1850 K supported the appliacability of the equilibrium approximation under the investigated conditions. Additionally, an energy balance for the plasma torch was used to estimate the plasma enthalpy and the corresponding plasma tail temperatures. The resulting temperature estimates were (1739 ± 160), (1604 ± 149), (1882 ± 241), and (2171 ± 261) K, respectively, and were in good agreement with those obtained from NO + NO2 experimental measurements.