Improving solids capture

A recent development in trihydrate flocculant technology for alumina processing plants has been released internationally following successful site trials in plants on three continents.

Based on laboratory testing and results from the trials, this new technology will deliver underflow density increases in the area of 20 percent along with tangible cost savings and environmental benefits.

Developed by chemical solutions provider Nalco, the new HyClass technology was first presented to the industry at the 9th International Alumina Quality Workshop in Perth earlier this year. 

It represents the first major breakthrough in trihydrate flocculant technology since such programs were introduced into Bayer Process alumina processing.

Hydrate flocculants have been used in alumina trihydrate classification circuits since introduced by Nalco some 20 years ago. Typically dosed into the secondary overflow launder or tray feed line, they improve overflow clarity, increase settling rates and improve underflow composition and flow.

The test of time has proven the success of hydrate flocculants in alumina processing but as production input costs have risen, the need for improved productivity and cost minimisation methods has created a demand for better technologies. HyClass technology is the result.

The trial results, achieved under operational conditions, mirrored the results and benefits first seen in the extensive laboratory test program.

Reports from the site trials indicate a consistent improvement in fines capture, faster settling rates and tangible improvements in underflow rheology – all of which, along with a range of direct and indirect savings, will contribute to improved productivity.

During the trials the new polymer yielded the same overflow solids ratio as achieved with the former product – but with the dose rate reduced by up to 40 percent.

Conversely, maintaining the dose at the old rate would see a direct increase in production. At the other end of the equation, overflow solids reductions in the range of 30 to 50 percent were achieved, depending on the quality of the base product.

To extrapolate these figures into a full year analysis, for a generic refinery producing one million tonnes of alumina (Al2O3) per year, with a circulation flow of 1700 kL/hr, the return on investment results are impressive. Based on full year figures the plant can expect significant savings.

Improvements in yield

For such a generic plant, the captured overflow solids would give a direct production increase of more than 3000 tonnes per year. In addition, improvements in yield due to the increased seed tonnage and surface area translate to increased production of approximately 1500 tonnes a year.

At a net treatment cost of about $60,000/year (replacing old treatment at equivalent dose) this is a 500 percent return on investment.

Further indirect benefits of this new technology derive from improved efficiency – lower unit cost of production resulting from more efficient use of raw materials.

Along with savings and productivity increases, this new technology has been shown to extend processing equipment life including rakes and vessels.

With the new technology capturing all the fines, scale build-up is virtually eliminated from processing equipment. This in turn, has reduced maintenance costs and extended time between major overhauls/rebuilds.

According to a company spokesman, the value of capturing more hydrate provides a substantial ROI over the entire HyClass technology program cost.

Other benefits – including a reduction in water, energy consumption and CO2 emissions – provide additional significant and measurable savings.

[This report was provided by Nalco Australia.]

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