Off-gas detection and treatment for green air-plasma process

Thermal plasma is a promising technology widely used in materials processing and waste treatment due to its unique properties including high temperature, high energy density, high chemical activity, and high quench rate. Air-plasma is preferentially used because air is of low price as plasma gas. The content of NOx in off-gas from air-plasma was determined using a gas analyzer, and a treatment unit was designed for the green air-plasma process. Results show that the concentration of NOx in off-gas from air-plasma was 2,489 and 9,112 ppm when the plasma input power was 50 and 150 kW, respectively. O2 in the off-gas would act as an oxidant to promote NOx absorption; thus, alkali absorption method was directly used for the treatment of the present off-gas from air-plasma. The absorption efficiency could be increased to 62.2% when additional O2 was provided into the off-gas to change its O2 content from 20% to 50%. The absorption rate was estimated based on the experimental data and a multistage absorption unit design, which could be reduced below 100 ppm and meet the emission standard. This article presents the feasibility of thermal plasma off-gas purification, so as to truly realize the green plasma process.