Method for analysis of ClO₂ and Cl₂ air emissions from pulp mill

Abstract Chlorine dioxide is commonly used as a bleaching agent in kraft pulp mills. Scrubbers are required to remove any remaining ClO₂ from the plant tail gases. To control the air emissions of chlorine compounds, chlorine dioxide and chlorine contents must be monitored to ensure that the strict regulatory standards are met. However, the currently used analytical method is not suitable for detection of low concentrations of chlorine and chlorine dioxide. A new method for measuring chlorine dioxide and chlorine emissions was developed, which ensures compliance with the stringent requirements imposed by the authorities. The two species could be measured separately with a limit of quantification of 3 ppm. The method was robust and easy to use in the pulp mill environment and it was validated both in the laboratory and the field. The specificity of the method was demonstrated, Cl₂ analysis was not sensitive to the presence of ClO₂ and vice versa. The uncertainty (±2×RSD) of the analytical method in the field was estimated from duplicate measurements performed in the range of 3–500 ppm for ClO₂ and 3–300 ppm for Cl₂, and was found to be ±20 % and ±10 %, respectively. Possible interferences in the analytical method are also discussed.