Editor-in-Chief Elisabeth Lisican showcases a handful of features to read in the April 2017 issue of Water & Wastes Digest.
Pumping lime slurry is not an easy task, nor is it easy on your pump. The inability of lime slurry to dissolve and the frequent scaling issues that occur can lead to serious maintenance headaches for a facility. Fortunately, officials at municipal water treatment plants, like the one in Ste. Genevieve, Mo., are discovering that using a peristaltic pump helps alleviate these problems.
The Problem with Lime
Used in either a dry form or made into slurry, lime is most often used at water treatment facilities to maintain pH levels for domestic use. This highly viscous, abrasive fluid is often associated with plating out, a condition where surfaces become caked with lime. This caking, along with grit and pebbles, is known for its wear and tear on centrifugal and diaphragm pumps, which requires regular cleaning and frequent maintenance. For many treatment plants this can mean costly repairs and frequent downtime.
Rather than running into the same type of caking problems when using a centrifugal or diaphragm pump for the lime softening process, Ste. Genevieve’s treatment plant opted for a Vector 2004 peristaltic pump manufactured by Wanner Engineering. Used to pump roughly 250 lb of lime slurry per hour, this positive displacement pump provides efficient metering, output and flows for easier operations.
At the Ste. Genevieve plant, the pumps are strictly used for the lime softening process. “Since I’ve been here it’s worked like a champ,” said Jeffery Crannick, water department superintendent. “It’s extremely efficient for pumping lime slurry with virtually no service issues. In fact, the only real maintenance we do is to periodically replace the hose due to contact between pump rollers and the hose which cause natural wear.”
Crannick also noted that their pump is very user-friendly. “The positive displacement design of the pump provides a peristaltic pumping action. This action never allows the lime slurry to come into contact with any pump parts—only the hose and connectors. So caking is never a real concern.”
The peristaltic pumping action of the pump and its durable design allow it to adeptly handle abrasive materials and solids that are commonly associated with lime slurry. Its compact size also means that there is a small footprint, clearing the plant floor from potential hazards. “Less space, cleaner, more efficient, we just don’t have the problems that other plants have using progressive cavity pumps,” said Crannick. “Simplicity and reliability are what make it so effective for our operations.”
The plant has a large storage vat where the lime slurry is stored. The suction line of the pump is connected to the vat itself. “With the discharge line we pump up the lime slurry to the clarifier where it’s injected down into the mixing chamber,” said Crannick. “Basically, it is an inlet pipe and an outlet pipe that utilizes pumping power — it’s quite simple really.”
At the facility the slurry is mixed 24 hours a day. “We never really have to come in contact with the slurry,” said Crannick. “Which is much safer than having to handle it ourselves.”
Additional features of the peristaltic pump at the Ste. Genevieve plant include its self-priming ability, suction lifts up to 24 ft and the ability to run dry without any damage. The pumps can also discharge pressures to 200 psi, handle solids up to 2.5 in. and pump gases and fluids, making it a versatile pump for the plant.
The Ste. Genevieve facility is quickly discovering just how much more efficient the plant can be with a peristaltic pump. “This is actually the first place that I have used a pump like the Vector,” said Crannick. “At previous facilities I’ve used the powdered lime slurry and a volumetric pump. I was never really crazy about those types of systems because you run into all types of problems with the lime caking up … thankfully we don’t have to worry about that here.”