Turn sustainability challenges into corporate advantages.

BHP Metalloys Casting Area

In the spirit of an objectives-based approach to improving the air quality within the Vaal Triangle Airshed Priority Area (VTAPA), BHP Metalloys committed to various Emission Reduction Strategy (ERS) Projects in order to reduce its particulate emission footprint within the Vaal Triangle.

This commitment subscribed to their values of sustainability, prioritizing health and safety and being environmentally responsible, whilst supporting their communities.

BHP Metalloys thus identified an ERS Project - namely the capturing of fugitive emissions generated from the metal casting at the Oxygen Blown Convertor (OBC) located at West Plant in Meyerton.

After considering various options it was decided to install a high pressure misting system with a specifically formulated, environmentally friendly, adhesive dust control agent (a derivative of our Micromass Particle product) that would not adversely affect employees' health whilst facilitating suppression of both fugitive dust as well as ambient dust.

From a scientific perspective, “high pressure misting” requires an operating pressure of 70 bar:

In order to ensure adequate gravitational settling of dust, atomised water mist is required in conjunction with a binding agent.  At 70 bar (i.e. high pressure), a homogeneous (uniform) particle distribution of atomised water particles of approximately 10 microns in diameter are created.  This is of high significance, owing to the fact that this coincides with the median particle distribution diameter for airborne dust (ambient, i.e., environmental dust) as well as fugitive dust.  In accordance with the principles of colloid and interface science, in order to bind to and consequently gravitationally settle the dust, the atomised water particles should coincide with approximate diameter of the dust particles, which is thus only achieved at high pressures.

Furthermore it is generally accepted that dust (which represents an aerosol suspension in air) is positively electrostatically charged. In order for the water droplets to efficiently bind to the dust a requirement therefore exists that the water droplets be coated with a negatively charged adhesive agent that is both oleophilic and hydrophilic, thus forming a “layer/shell” around the atomized water droplets.  This would electrostatically neutralise the positively charged dust particles in order to facilitate the cohesion of the atomized droplets with the dust particles; thereafter, the newly formed larger particles containing the dust would collide with similar larger particles and merge to facilitate gravitational settling.

Lastly, the adhesive agent is essential to prevent redispersal of the dust – this is owed to cohesion of the settled dust to form a matrix.

In conclusion the scientific principles involved in this approach represented a sound basis for dust suppression - both fugitive and ambient.

This system consisted of eight (8) fans with spray manifolds to direct the fugitive emissions towards the south-eastern side vapour curtains. The dust was then entrapped within the fine mist, preventing the escape of fugitive emissions from the casting bay area.

The reason this project was expedited was owed to the high impact emission reduction on the neighbouring communities of Meyerton Park and Sicelo.

The expected emission reduction in fugitive emissions through the implementation of this project is expected to be approximately 10 tonnes per annum, and as such the project was well received as a great success within BHP Billiton as a world-first in treating emissions from casting areas.