Slide Background
Slide Background

VARIABILITY AND UNCERTAINTIES IN THE AIR EMISSIONS INVENTORY FROM THE WORSLEY ALUMINA REFINERY

Forster P, Johnston P, Williamson S

An inventory of air emissions has been constructed for the Worsley Alumina Refinery from measurements made from major refinery sources since 2003. Over 700 chemical substances were assessed in the construction of the inventory, with 306 substances identified at concentrations above the analytical detection limit. Major emissions in terms of emission rates include CO2, SO2, NO, particulates, CO and NO2. Other substances with significant emission rates include acetone, acetaldehyde, hydrocarbons, ammonia, fluoride, chloride, methanol and some aliphatic amines. Total refinery VOC emissions are in the order of 148 tpa, with approximately 80% of those emissions due to the contributions for the above mentioned organics.

Of importance for use of the emissions inventory for purposes such as dispersion modelling and ground level impact assessments, is an understanding of the variability in the emission rates from the respective sources. This paper describes the variations observed for some key emissions over a range of time averaging from hourly to yearly. An assessment has been conducted of the uncertainty in the measurements for these substances that allows the contributions from process variability and measurement uncertainty to be considered when assessing the variability in the emissions data. Relatively low uncertainties have been determined for parameters such as combustion gases and total particulates from the more “stable” sources such as calciners and boilers, which suggests the majority of the observed variability is due to process changes. Higher variability in emissions is observed for digestion related sources, which is predominately due to process variability but also has a large component from the uncertainty in individual measurements.

This paper will present some findings from the evaluation of measurement of uncertainty for key parameters and an assessment of the variability in the emissions. The implications for use of the Emissions Inventory will also be discussed. Some discussion on the assessment of variability in odour emissions will also be included.