The First Westfall Model 2900 Variable Static Mixer
Solving a customer’s unique problem
Multiple wells, inconsistent flow rates
Archie MacDonald, an engineer with Pureflow Filtration Division, was designing a filtration system for the Sundance Water Reclamation Facility, with a capacity of 1.2 MGD serving 5,722 customers in a population of 15,000. Sundance is one of four facilities serving Buckeye, Arizona.
The problem was that there were multiple wells feeding into a water filtration plant, each with a different flow rate ranging from 700 to 7,000 gallons a minute. Any combination of four wells could be used at a time. Excellent mixing was needed for the arsenic removal process. The mixer would facilitate bonding of ferric sulfate with the arsenic that was present, creating bigger particles so the system’s filtration media could filter them out.
Each well had its own pump designed to lift as high as local reservoirs around its well fields. Putting a mixer there would rob energy that was needed to lift the water.
Working together to find a solution
MacDonald was familiar with Westfall because his company has been using Westfall’s Model 2800 Static Wafer Type Mixers routinely in its installations for some time. He called Bob Glanville at Westfall and presented his problem.
Bob had some ideas for a solution, which they explored together and developed with the project budget in mind. Westfall built a prototype and had it tested at Alden Labs. The data was convincing, and the mixer was manufactured and installed.
Solving variable flow mixing with minimal headloss
This innovative design (patented) features two in-line wafer type mixers: one stationary and one mounted on a pivot that adjusts incrementally to changing flow conditions. Each mixing plate’s computer designed, geometric shape creates vortex shedding and shear-induced turbulence inside the pipeline, which effectively mixes the injected fluid(s) with the main process stream. As a bonus, the unit requires very little laying length, saving much needed space.
Providing precise control
Westfall also developed a control panel for the system to work with Pure Flow’s software. Flow meters monitor flow and logic boards to signal the mixer to modulate its opening according to flow. When flow is low, the movable mixing plate closes to enhance mixing turbulence, and when flow is high, the plate is wide open to reduce headloss. This maintains optimal mixing for the arsenic removal process, and keeps headloss to a minimum through a 20 to 1 turndown ratio.
“It works perfectly and has been running like a champ ever since, for at least three years now,” says MacDonald.
