Open Cut » Environment
The objectives of the research project were to validate existing particulate emission estimation techniques for open area sources at coal mines and to provide local data for related field conditions that affect particulate emission rates.
The impetus for the project was industry concerns about the accuracy of existing emission estimation equations, particularly when used to calculate mass emission rates for annual returns as required for the National Pollutant Inventory (NPI).
A wind tunnel approach for generation and measurement of emissions was adopted for the validation studies. This approach is based on existing methodologies, however, a number of modifications were incorporated to improve data quality and usability of the technique.
Measurements of particulate emissions were made at a total of three mines, two in Queensland and a third in New South Wales. Within each mine a range of surfaces was tested.
Results of the emissions testing confirm that emission rates generally increase as surface wind speeds increase.
Analysis of watering as a mechanism for controlling dust confirmed an average control efficiency of 70 % for watering regimes currently being used (application rate of < 1 litre water applied per m2). This is a better control efficiency for the water application rate used than would be adopted using the NPI methodology (50%).
The particulate emission data from the wind tunnel testing suggests that PM10 may comprise a significantly higher proportion of total suspended particulate matter than the 50 percent assumed in the NPI. This may be attributed to the fact that wind erosion of surfaces is determined by threshold pickup velocities, and TSP size particles are less likely to be generated by such a mechanism. Therefore, for the purposes of the data presented in this report, a conservative assumption that PM10 emission rates are equivalent to TSP has been adopted.
The emission test data were used to validate the open area emission estimation equations currently adopted for the NPI. They indicate that the open area emission factor of 0.4 kg ha-1 hr-1 may overestimate by a significant margin actual particulate emissions from tested open area surfaces for some open cut coal mines. Validation of the NPI emission factor for active stockpiles has also been completed. Less data are available for this analysis, hence there is some uncertainty attached to the result. The available data suggest that the National Pollutant Inventory emission equation may overestimate by a factor of 3 the actual emissions from active coal stockpiles.
Ancillary testing was completed for surface silt content and moisture content. The results of these tests indicate that the percentage silt contents of surfaces at Australian mines covers a broad range, both significantly lower and higher values than the 7 – 10 percent default values adopted in the NPI. The moisture contents naturally occurring in the mine surfaces tested were consistent with the NPI default values.