Feedwells are essential in generating optimal thickener performance. Outotec’s Vane Feedwell incorporates seven patents and is now the standard on all its thickeners globally. One of the key design features is the interconnected upper and lower zones.
The upper zone, with ‘vanes’, is where feed, dilution water, and flocculent are added, and incoming slurry is mixed and deaerated, maximizing flocculant dispersion, and therefore minimizing coarse/fine segregation. The lower zone is concentrated around promoting gentle mixing through aggregate growth, with the option of secondary flocculant addition.
This patented design delivers benefits including higher solids throughput, increased solids density, optimized operability, lower flocculant costs and minimized downtime, amongst others.
The Deaeration tank was developed by Outotec to remove aeration and excessive froth from the feed before it reaches the thickener feedwell. The Deaeration tank is mounted on the thickener bridge. Part of this patented design incorporates tangential feed inlet and outlet pipes. The internals of the tank are designed so that the feed is received tangentially in the upper section of the tank and passes through an orifice plate to the lower section before exiting to the feedwell.
Working closely with the customer and meticulously planning the installation, the focus on site was remaining operational during the upgrade. All disruptive work was therefore completed during shutdowns, ensuring minimal interruption to production. This type of upgrade typically occurs over one shutdown but shutdown schedules at site were such that the best option was to implement the upgrade in two phases.
Some modifications occurred during one shutdown, in February 2015, with the actual installation of the feedwell and Deaeration tank during a subsequent shutdown in May 2015. The final installation was a smooth process, with all equipment bolting together without modification first time round.
With this EPC partnership approach, procurement was also carried out on a collaborative basis to deliver the most cost-effective and timely result for site. Outotec utilized, where possible, the customer’s local labour and contractors for the turnkey upgrade. The customer carried out the commissioning of the upgrade, partnered and supported by Outotec. The upgrade was on time and on budget and, most importantly, was incident-free.
The thickener upgrade has delivered multiple benefits. Following commissioning, visible froth was significantly reduced from the surface of the thickener. Lost product in the overflow was decreased by 91% post installation. This performance improvement had a payback period of approximately nine months. Flocculant consumption was also halved, with the additional benefit of less overload in the flotation circuit from recirculating load.