Coal Preparation » Fine Coal
The primary objective of this project was to develop practical process control procedures to automate and optimise the new flotation technologies using currently available equipment.
This was achieved by fulfilling a series of secondary objectives, which included a study of the operational performance of the Jameson Cells at full plant scale and investigation of their response to changes in the key operating parameters. Based on the results of the test work programme and reviews of current plant operating philosophies, optimisation and control procedures have been developed. These allow the Jameson Cells to be operated at their optimum with respect to the overall plant performance.
Control of flotation in conventional cells has been extensively studied for many years and trials integrating on-line analysers with full plant circuits have successfully demonstrated that good control is possible. However, such control loops have seldom been implemented on a permanent basis for a variety of reasons. The predominant form of conventional flotation control has been automatic level control with a manually determined setpoint and manual control of reagents.
In recent times, the installation of the newer, high intensity, column-style flotation cells, typified by the Jameson Cell and Microcel, has been favoured by the Australian coal industry for the combined treatment of the full fines fraction. To improve the viability of this equipment, a greater understanding of the operating parameters was needed. Earlier test work demonstrated that the column-style units, with their deep froths and higher frother consumption, respond to feed and operational variables in a different manner to conventional cells. Consequently, these units require a different control philosophy to ensure they are operated at their optimum.
The results of this programme established that the frother dosage was the most useful short-term operating parameter to control and adjust the flotation process up and down the yield-ash curve. Wash water addition was the second major parameter that should be addressed, but once optimal levels are established it should be maintained at the required flow rate with uniform distribution.
Optimum values for the remaining variables (diesel dosage, froth depth and air rate) should be determined via metallurgical test work post-commissioning. A 'set and forget' strategy can then be adopted if the response of the flotation process to minor changes in their settings has minimal effect on performance. This simply ensures operation at or near their optimum level. Periodic metallurgical checks in response to long-term feed changes or plant operational changes should still be performed.
This approach may not be applicable at all sites, and each will ultimately have to be evaluated according to its particular needs.
Experience at both Goonyella and Riverside, as well as other sites such as Peak Downs, indicates that the new flotation technologies are more robust in their operation compared to the conventional flotation cells they replaced. Once they have been optimised and the settings fine-tuned, they can potentially operate relatively efficiently and produce low ash concentrates with minimal operator intervention.