ALUMINA REFINING AND AIR QUALITY: VOCS AND ODOUR

Galbally, I., Lawson, S., Brodie, G., Loh, J., Cheng, M., Hibberd, M. and Power G

The importance of understanding the nature and origins of volatile organic compounds and the associated odour emitted from alumina refineries has become increasingly evident in recent years, driven by the need to respond to community and workforce concerns, and regulatory requirements. This paper outlines the current state of knowledge of volatile emissions based on measurements at a refinery in Western Australia, describes laboratory experiments which model key refinery sub-processes, and provides explanations of the presence of the main VOCs based on chemical reaction mechanisms. Real time measurements of VOCs in air approximately 2 km away from an alumina refinery showed that acetone, acetaldehyde, methanol and NOx have sources in the direction of the refinery. Measurements of VOCs and odour from the digestor vents, calciner, and liquor burner in the refinery revealed many compounds of which methanol, acetaldehyde and acetone occurred at the highest concentrations. Odours were observed but the compound/s responsible could not be determined, nor was odour directly related to total VOC concentrations in the samples. A laboratory study which measured VOC emissions from slurry mixtures simulating bauxite milling and predesilication sub-processes generated VOCs consistent with those found in emissions from those parts of the refinery. This knowledge will be a key to the design of equipment and strategies for improving refinery ambient air quality into the future.