Queensland Alumina Limited (QAL)
Digestion heaters save energy and production costs
David Gallagher and Janis Barker are part of the team responsible for improving Digestion heat recovery.
Huge progress was made in improving Digestion heat recovery in 2014. For the first time in many years, the Digestion heaters reached their most efficient level and, as a result, QAL’s energy consumption and production costs were reduced.
In the second half of 2013, the average T9 temperature across the three Digestion units was 200 degrees Celsius, 9 degrees below the target of 209 degrees Celsius. This inefficiency meant the site had to burn additional coal and gas to maintain energy demands.
For the full year of 2014, the average T9 temperature across the three Digestion units increased to 206 degrees and, since July 2014, the three Digestion units have consistently achieved or exceeded the average T9 target of 209 degrees.
Redside manager Greg Doyle said maintaining this trend would save significant dollars each year and significantly reduce QAL’s consumption of coal and gas.
There are a number of factors responsible for these positive results, but in particular there has been strong teamwork between the Digestion Technical and Operations teams to ensure that the spent liquor heater acid washes are performed on schedule and to the right quality, specification and standard while underperforming heaters are rapidly identified and actioned.
Rio Tinto Alcan Yarwun
Mud farming improvements at the RMA
Rio Tinto Alcan’s Residue Management Area.
A team led by Mike Colledge, manager of the Gladstone Project Hub, developed a plan to increase mud farming capability at the Residue Management Area (RMA). The plan consisted of a twofold strategy that aimed to:
- immediately minimise, and eventually cease, decant storage on the mud stack; and
- source the necessary resources required to farm the entire dam footprint.
The target density for the RMA is one tonne per cubic meter and achieving this will require use of the whole dam footprint. Over the course of 2014, we made strong improvements to our mud farming activities and by October we were farming 190 hectares. Compare this to one year earlier which, due to a number of unforeseen circumstances, saw us farming less than five hectares.
To remove decant from the mud, a channel was dug, using specialist mud crawling excavators, through existing unfarmed mud, from the northern end of the dam to the southern end. Once the drainage path was established, decant was able to collect in the southern area of the dam where it can be pumped to the thickener, before it is returned to the ocean.
Execution of the plan required high levels of cooperation and collaboration between the project team, mud farming team, and thickeners and pigging teams.
The mud is now being dozer farmed in the south and eastern area of the RMA and the team has recovered 25 per cent of the dam. This achievement vastly reduces business risk and capital expenditure as it increases the forecast lifetime of the dam and ensures the foundations are suitable for our wall raise projects.
The refinery has more than two kilometres of Jacketed Pipe Units (JPUs), which facilitate heat exchange in Digestion.
Energy efficiencies in Redside
Changes to the cleaning process for Jacketed Pipe Units (JPUs) in Digestion have delivered significant improvements for the refinery. Previously all live steam JPUs were cleaned via hydroblasting, which took four days and was completed every 14 weeks. In 2014, we began cleaning via a pigging process, which takes just 57 hours and is completed every nine weeks.
With some industry leading processes, capital improvements and teamwork, this timeframe is targeted to be reduced to just 36 hours, bringing about huge cost savings and production opportunities for the business.
The new cleaning process has improved the efficiency of heat transfer to the bauxite, increasing flow and yield rates. Further environmental benefits were delivered through reduced water usage and diesel usage. Operational costs and safety benefits were realised as the new process does not require scaffolding to be erected and dismantled. And lastly, the acid washing is now controlled by the condition of the equipment as opposed to being time based, which results in reduced acid consumption and more effective cleaning.
Although work continues to reduce cleaning turnaround times even further, the project has contributed significantly to the recovery of residual life in Digestion. Improvement projects have been undertaken across the refinery to recover residual life (a measure of completing critical work on time) and with Digestion and Clarification recovered, efforts will be ongoing in 2015 to recover residual life in Calcination.