Heap leaching and SX/EW are under the spotlight in the upcoming November issue. It was not possible to publish all the news of advances, and one of those came from TechnipFMC. Over the past four years, TechnipFMC has improved its proprietary TechnipFMC-Krebs Mixer-Settler equipment, operated worldwide, as reported by Guillaume Fenol and Francois Daroux, TechnipFMC, in Technological Innovations in TechnipFMC-Krebs Mixer-Settlers Guarantee 100 ppm Solvent Entrainment in Solvent Extraction Plants in a paper presented at ALTA 2017. These are pioneering modules that use conical pumps and pre-settling launders, allowing a settling surface reduction by two to three, compared to conventional equipment.
“The main objective of the recent development program is to reduce solvent entrainment in the aqueous phase leaving the settler, responsible for important OPEX loss for clients. The R&D program was structured around three axes.”
The first is conical pump performance: “Computational Fluids Dynamics (CFD) showed that a novel mixing impeller and conical pump design could generate less shear and less solvent entrainment. This was proven with the construction of a new 15 m2 equivalent settling surface pilot plant, operating with high performance Total Fluids’ Elixore® diluent.
“Significant progress was made on the conical pump technology, above and beyond impeller improvements. Initially, Krebs technology was made of straight blades rotating in a fixed cone. Now, the bottom of the blades has been curved and trials have shown that, combined with a new in-house impeller design, entrainments were reduced by 40% compared to Krebs standard design.
“Our efforts are now focused on a new third generation patented concept: a rotating cone located at the bottom of the fixed cone, further reducing solvent entrainment at settler outlet, compared to the previous conical pump models.”
“Secondly, flow pattern optimisation in the launder: “Phase separation is improved when flow patterns in the launder and settler are perfectly straight. From 2017, each time a new mixer-settler will be manufactured, a complete flow mapping will be modelled with CFD. Picket fences and baffles position will be optimised with pilot plant trials to equalise flow velocities of the settling fluids.”
The third consideration was a new settler feed box design: “Both aqueous and organic phases are preliminary separated when arriving in the launder end, before entering the settler tank. This launder end has been greatly simplified compared to initial Krebs standard. No more crud accumulation, air bubble entrainment and phases re-mixing are now observed.
“The combination of these new designs contributed to a drastic reduction of solvent entrainment by 50% in a revamped SX plant in 2015 and 2016.
“This innovative R&D program:
- Guarantees organic entrainments reduction down to 100 ppm under certain conditions, and ensures tens of thousands dollars OPEX reduction per year for new SX plants compared to traditional Krebs standards, or
- Allows removal of after-settler tanks for future designs, or
- Allows further reduction of the size of the TechnipFMC-Krebs mixer-settlers.”
Unique features of the TechnipFMC-Krebs mixer-settler are shown in the picture