First evaluation of a multicomponent flue gas cleaning concept using chlorine dioxide gas - Experiments on chemistry and process performance

This work has investigated a multi-pollutant flue gas cleaning concept based on oxidation using chlorine dioxide (ClO2) gas with subsequent absorption. The chlorine dioxide gas converts the relatively insoluble nitric oxide (NO) to the more soluble nitrogen dioxide (NO2). This makes a downstream wet scrubbing process feasible for simultaneous removal of sulphur oxides (SOx) and nitrogen dioxide (NO2). An experimental evaluation of the proposed process using chlorine dioxide gas has been performed on a laboratory scale. The experimental setup, designed and built by Akzo Nobel, consists of a reactor for oxidation, a flue gas condenser and a wet scrubber. The results show that ClO2 gas oxidises NO with high efficiencies under a wide range of process conditions, also in the presence of sulphur dioxide (SO2). The more ClO2 gas is added, the higher the degree of NO oxidation and the total nitrogen oxides (NOx) removal efficiency becomes. The results also show that the presence of water strongly increases the removal of SO2, which is believed to be an effect of liquid phase nitrogen-sulphur interactions. The absorption solution, sodium carbonate and sodium sulphite, is efficient in removing NOx (especially NO2) from the oxidised flue gas. The total NOx reduction at 0.6 ClO2:NO mole ratio and subsequent wet scrubbing is between 79% and 94%, depending on the process conditions used. The total SO2 reduction in the scrubber is between 97% and 100% independent of ClO2 gas addition. Furthermore, the total NOx balance shows that the major part of the NOx is converted to nitrate in the condensate liquor and as nitrite in the absorption solution. A higher ClO2 gas addition and a higher reactor temperature convert more of the NOx to nitrite in the absorption solution.