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Agitator advantages spell end for water industry love affair with submersible mixers

Posted: Wednesday 4th June 2008

Typically using less than one quarter of the energy of submersible mixers, Chemineer claim that for anoxic applications, vertical shafted top-entry agitators are becoming a far more economic and reliable option for water companies and their contractors.

Based on conclusive new results from independent modelling of a full scale WWTW, agitators were found to require a massive 85% less kW to achieve better mixing than an optimally positioned submersible mixer. Furthermore, say Chemineer, agitators are now similar capital cost, but require much less maintenance.

The modelling looked at surface and base fluid velocities in all areas of the basin, as well as RTD (plug flow characteristics) in water-like fluids. In all cases the slower speed agitator system was found to better distribute the energy and mixing into all corners of the basin, as well as reduce surface velocities compared to the submersible design, which is particularly important on anoxic applications. The benefits of agitators are even greater when handling high solids containing non-Newtonian sludges.

Neil Cathie, Sales Manager at Chemineer, commented: “As the water companies increasingly look at whole life rather than first-installed costs for the best possible long-term solutions, they demand reliable, energy efficient equipment with low maintenance needs. Submerged seals, typical of submersible mixers wear out all too quickly in dirty fluids. Additionally, the first cost of top-entry agitators has declined relative to submerged mixers in recent years as more compact, more efficient gearbox designs and lower cost parts sources have been adopted”.

He added: “Submersible mixers are readily available and are perceived as a cheap and simple fix to tank mixing problems. However, an agitator will dramatically reduce energy costs, be far easier and cheaper to maintain – and with no submerged guide-rails or electrical cables to contend with, is much easier to install, especially in wet conditions. The energy savings alone can justify the replacement of submersibles with of top-entry agitators with 1-2 year paybacks, depending on the plant size and site specific installation costs”.

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