Measurements of fluoride emissions in aluminum smelters by tunable diode laser spectroscopy

Tunable Diode Laser Absorption Spectrometry (TDLAS) is an effective method for measuring the emissions of fluoride compounds from primary aluminum production. Hydrogen fluoride is a highly toxic substance, harmful to both human health and the environment. The perfluorocarbons, CF{sub 4} and C{sub 2}F{sub 6}, are strong greenhouse gases with atmospheric lifetimes of more than 5,000 years. The LasIR systems based on near infrared tunable diode lasers have been used to measure HF in stacks, on both sides of scrubbers and in the pot-rooms of the smelter. Examples of these measurements are presented. The perfluorocarbons have been measured with a mid infrared TDLAS system by continuous extraction into a multipath White cell. Earlier measurements by this method clearly revealed the factors, which govern perfluorocarbon emissions and have led to improvement in aluminum production technology. Recent measurements have shown that the use of these technologies does, in fact, result in appreciable reduction in the emissions of the perfluorocarbons. The examples given in this paper demonstrate the ability and versatility of TDLAS systems for providing reliable, interference-free measurements of important gases in a complex mixture and in hostile environments.