Primary aluminium smelting generates large amounts of hydrogen fluoride gas (HF). Concerns for worker safety and ambient air quality require that HF be monitored at several locations in smelters. Historically, a variety of methods have been used for HF monitoring. Cassette samplers and wet chemistry techniques, coupled with complex and expensive sampling manifolds have monitored roof-line and scrubber duct HF levels. In recent years, open path infrared detectors have been used in rooflines. Laser gas detectors are now displacing traditional methods by providing HF data that is more accurate, and with faster response times, in packages that are both simpler and less expensive. Boreal Laser’s portable GasFinder has proven very effective for HF emissions studies in pot room roofs, ducts, stacks and at smelter fencelines. Both GasFinder and the multichannel GasFinderMC are used in permanent installations.
Why laser gas detection?
Laser gas detection has many advantages over other techniques for HF monitoring in primary aluminium smelters:
It is an optical technique which works by absorption of infra-red light by HF. It therefore provides a direct measurement of HF, rather than relying on secondary measurements such as F ion concentration. A very important additional benefit is that HF can be measured in-situ. This overcomes the uncertainties and errors inherent in sampling systems (especially significant for a very reactive gas like HF). The laser method is interference-free - the linewidth of the laser light used is about 1/10th of the width of the single HF absorption line detected. This absorption line was selected to be well isolated from absorption lines of other atmospheric gases. The laser method therefore does not suffer from absorption interferences, especially from ever present gases like H2O and CO2, that cause problems with standard IR detectors. As a consequence, laser gas detectors can measure over long ambient paths, up to