EvenFlo^® Feedwell

Advanced Feedwell Design Improves Thickener and Clarifier Performance

WesTech’s patented EvenFlo® Feedwell achieves peak performance with its simple two-stage design. It significantly improves the overflow clarity while using a lower polymer dosage.

Optimize Your Feedwell, Optimize Your Thickener

The thickener or clarifier is the major piece of equipment used to recover water in mineral and industrial processes. The one thing all thickeners have in common, the feedwell, is the core of every thickener’s performance.

A thickener relies on a feedwell for even distribution of solids and flocculation of suspended particles. The feedwell receives the feedpipe flow and transitions it to a slow vertical downward flow, while flocculating the suspended solids into floccules that settle quickly.

Conventional thickener feedwell designs have two main shortcomings: short circuiting, where the feed stream momentum carries the flow prematurely down and around the feedwell, past the shelf and deflector, and out of the feedwell; and inefficient flocculation, where only a small area around the inlet of the feed provides good mixing.

Due to these issues, most sites experience the following problems:

Solids leave the feedwell under-flocculated
Fine particles can be carried directly to the overflow
Premature flow release forms a “sand bar” to one side in the thickener
Poor clarity results from a mixing intensity and duration that is insufficient to capture the fines
Over dosing of polymer to compensate for poor feedwell performance

The only real option to overcome these inherent flaws is to increase the polymer dosage and increase the rake torque; both add expense or capacity limitations. A thickener that operates efficiently can actually be an untapped source of lowering plant costs.

Short-circuiting Thickener — Short-Circuiting Flow

EvenFlo’s Two-Stage Design Corrects Thickener Issues

WesTech introduced the innovative EvenFlo feedwell technology to efficiently address feedwell problems, without using shelves, vanes, or deflectors.

The two-stage design first uses an inner channel to convert the tangential feed energy into a concentric radial flow that empties into the main feedwell.

In the second stage, the flow exits the inner channel through bottom ports, directing the flow radially outward into the feedwell for optimal mixing of flocculant and solids, uniquely utilizing all area of the feedwell volume, which provides even distribution into the thickener.

This method extends the optimum mixing zone around the full periphery of the outer feedwell, providing the largest consistent mix zone in the industry, and creating an environment to sweep the solids, including hard-to-collect ultra-fines, producing clean overflow and fast-settling floccules.

In addition, the EvenFlo’s outer feedwell provides a very robust, effective self-dilution system, with accelerated dilution using airlift pumping or density differential dilution ports, to return clean water to the feedwell from the clarification zone.

WesTech self-diluting feedwell — WesTech Self-Diluting Feedwell

Optimizing your thickener’s feedwell with EvenFlo produces consistent cost savings in two ways:

Mixing and polymer dosage are interdependent, so providing the optimum condition for flocculation allows the reduction of polymer by up to 40%.
Optimized flocculation increases the underflow density, recovering more water at the thickener and reducing the water sent to downstream operations by 10% or more. This provides tremendous added benefit when the process value is in the water.

For Highly Variable or Extreme Dilution Rates

For slurries that require excessive dilution or may have wide swings in dilution requirements, WesTech provides the AirLift™.

The AirLift dilution system employs the use of air lift pumps. These pumps are located next to the feedwell, spaced around the periphery and their discharge communicates with the feedwell through launders (see the image below). The air lift pump draws up clear water from low in the clarification zone, that does not disturb the surface of the thickener, to dilute and mix with the feed slurry in the feedwell.

WesTech has the full range of feed dilution capability with the self-dilution ports or with the AirLift system to optimize the feedwell operation for any of your thickener needs.

Retrofits

Not only a great solution for new thickeners, the EvenFlo is also an excellent choice for retrofits. Replacing a poorly functioning feedwell with an EvenFlo in an existing thickener or clarifier will eliminate many of your problems and save you money in polymer consumption and other operation costs. You will see a quick return on your investment.

Example: Traction Thickener Retrofit

The benefits of retrofitting three 135-meter traction thickeners is shown below; the short-circuiting flow seen in the Before photo is corrected by retrofitting an EvenFlo Feedwell in the thickener in the After photo.

Example: Primary Clarifier Retrofit

Effective flocculation of the full feed flow provides improved overflow clarity and increased underflow density, all while reducing the flocculant dosage. Three-month averages from before and after retrofitting a primary clarifier show:

Overflow clarity improved by 50 percent or more
Underflow wt percent increased by 3 percentage points
Polymer consumption reduced by 40 percent

exceptional clarity of overflow — Exceptional clarity of the overflow

Proven Advantages: CFD Analysis and Third-Party Study

EvenFlo’s dramatic improvement in optimal mixing intensity, extended duration, and preventing of short circuiting is confirmed with computational fluid dynamics (CFD) analysis and validated by a third-party study by CISRO.

The inner EvenFlo raceway separates the two steps of receiving the feed stream and distributing it into the feedwell. This buffers the feedwell performance from feed stream momentum, providing steady mixing in the outer feedwell regardless of the feed stream velocity. Conversely, other tangentially-fed feedwells cannot effectively manage the feed momentum, and they greatly lose efficiency at low or high velocities.
Short circuiting is eliminated with the two-stage feedwell design, which keeps the feed flow in the feedwell for the designed time and produces even distribution into the thickener or clarifier (see CFD comparison below).
Optimal mixing, driven by the radially distributed flow into the outer feedwell, gives the largest optimal mix zone of any feedwell design. Optimal mixing intensity rapidly builds floccules, while the increased duration is able to sweep hard-to-collect, ultra-fine particles.
Improvement in mixing reduces flocculant dosage requirements

CFD Analysis Before — The short-circuiting flow prematurely exits to one side from a typical tangential-feed feedwell.

CFD Analysis After — WesTech’s EvenFlo feedwell prevents short circuiting and produces even distribution of solids into the thickener.

CISRO studied floccule generation as a function of feedwell design and mixing intensity (feed velocity). The floccule growth results were displayed, with optimum flocculation depicted as large red spheres and poor flocculation as small blue spheres. Compare the small, effective flocculation area in the shelfed and deflector feedwells to the large, efficient area of the EvenFlo design.