Application Note All Rights Reserved, Copyright © May 2016, NEO Monitors AS Continuous HF stack monitoring in Aluminium Plants Emissions from the Aluminium smelting process contains harmful gases for the environment, one of these gases is Hydrogen Fluoride (HF). The aluminium smelting process generates large amounts of HF gas, the majority of this gas is captured and treated in wet or dry scrubbers. NEO Monitors LaserGas TM II SP HF monitor is an excellent instrument for process and emission control, because of its low detection limit of HF gas, short response time and low maintenance requirements. HF emission is subject to increasingly stringent national and regional regulations, due to the demand for toxic gas measurement in the environment along with the emphasis on safety. PROCESS: Primary Aluminium is produced by reduction of Alumina by electrolysis in a molten bath of Cryolite. Aluminium Fluoride (AlF3) is one of the additives used to reduce the melting point, and the addition of AlF3 results in gaseous Hydrogen Fluoride (HF). A dry scrubber is typically used to remove HF from the off gas by mixing it with fresh (primary) Alumina. The gaseous HF bonds to the primary Alumina and the HF enriched Alumina is gathered in a bag filter system and transported to the process to be used in the electrolysis process. TYPICAL PROCESS DATA HF concentration: 200-400 mg/m3 (scrubber inlet), 0-1 mg/m3 (dry scrubber outlet/ stack), <0.1 mg/m3 (wet scrubber outlet/ stack) Temperature: 100-150 °C Pressure: atmospheric Optical Path Length: 1-6 meter Fig 1: HF measuring points in a typical aluminium plant. HF is commonly measured at the inlet (2) and outlet(1) of the scrubber system. NEO Monitors as • A subsidiary of Norsk Elektro Optikk • Prost Stabels vei 22 • N-2019 Skedsmokorset, Norway Phone +47 67 97 47 00 • www.neomonit

The accurate measurement of HF gas is of great importance for all aluminium plant operators due to the following reasons: The solution is LaserGasTM II SP HF monitor. With the high reliability and low maintenance requirements, it is the preferred solution to monitor HF emissions. The monitor is tailor made for the relevant process and it is HF specific, i.e. no interference from other gases With its high sensitivity LaserGasTM II is the best in-situ monitor for measuring low concentration of HF. LaserGasTM II SP HF is factory calibrated. No field calibration necessary and internal span check...