Optimising the Diesel Droplet Size in Coal Preparation Plants

Diesel collectors are widely used in Australian coal flotation circuits; however, inefficient dispersion under saline recycled water conditions can lead to excessive reagent consumption and variable flotation performance. Laboratory studies have shown that reducing diesel droplet size can improve flotation efficiency and reduce diesel usage, but the extent to which these benefits can be achieved under full scale plant conditions has not been clearly established.

This project addressed this gap by developing and deploying a full scale diesel emulsification system, quantifying achievable droplet sizes under plant conditions, evaluating flotation response, and establishing a site-dependent implementation framework for coal preparation plants.

An integrated emulsification system combining Venturi-static mixing with optional ultrasound-assisted dispersion was developed and installed at a Queensland coal preparation plant. The system incorporated in-situ droplet size measurement using Focused Beam Reflectance Measurement (FBRM) and replaced the existing Venturi-based diesel dosing arrangement, enabling controlled evaluation under continuous plant operation.

The report includes the following:

• Laboratory benchmark (reference condition)
• Queensland plant performance (full-scale conditions)

- Key plant-scale outcomes

- Queensland plant interpretation

- Economic interpretation (Queensland plant)

• Implementation implications

- Queensland-type (constrained) plants

- More favourable operating conditions

This project demonstrates a validated full scale diesel emulsification system and establishes a clear relationship between achievable diesel droplet size and flotation performance under industrial conditions; confirming that:

• Laboratory-derived optimal droplet sizes represent a performance benchmark rather than a directly transferable operating target.
• Plant-scale performance is governed by site-specific water chemistry and hydraulic constraints.
• Realised benefits depend on whether the system can achieve sufficiently fine droplet dispersion in the operating environment.

Overall, diesel emulsification is a site-dependent technology that delivers:

• Reliable reagent and product quality benefits under constrained conditions, and
• Additional flotation enhancement potential under more favourable operating environments.

  This provides a clear, evidence based framework for evaluating and implementing diesel emulsification systems in coal preparation plants, with explicit linkage between site conditions, achievable droplet size, and expected operational benefit.