Danfoss VLT® AQUA Drive Produces Huge Water Savings from Food Processor’s Deep Well
Food processing plants require a dependable source of water in large quantities for the washing and rinsing, steaming, cooking, and cooling of food, and during plant sanitation operations. That’s why a large Midwest food processor wanted full control over its water supply by constructing a private water well on its own property. However, what looked like a simple solution was quite complex below the surface — as the well driller discovered when he embarked on the project.
"The food processor's water production requirements and the utilization of local wells meant our first and second drilling choices wouldn’t work," says Roger Renner, owner of E.H. Renner and Sons, a leading well-drilling firm located in Elk River, Minn., near the Twin Cities metro area. "In fact, I'm the fourth generation in our family firm, and I can truly say this was the most challenging job I've ever had."Difficulties with a deep aquifer
From the start, Renner realized the project would be difficult when there were objections to using a desirable shallow aquifer. An aquifer is a water-bearing layer of permeable sand, gravel or rock that channels water to a well. In this case, the first choice aquifer — a shallow sand and gravel formation located from 112 feet to 442 feet deep —could not be used, because local residents were concerned that their wells would dry up.
"That meant we had to look at deeper aquifers in two geological formations known as the Jordan formation and the Franconia-Ironton-Galesville (FIG) formation," says Renner. "A nearby city was drawing water out of the Jordan formation. That forced the processing plant to go deeper — down 705 feet, over a tenth of a mile. At that depth, the bedrock is the FIG formation, which dates to the Cambrian Era. This water was deposited millions of years ago before the dinosaur age. Yet, the water quality is generally acceptable for all types of use today."
Although drilling a deep well is difficult, Renner's main challenge was that the FIG formation has extremely low well productivity, which was measured at a specific capacity of one to two gallons per foot of drawdown — compared to a specific capacity of 20 gallons per foot drawdown in the sand and gravel formation. Also, the FIG formation would max out at a relatively low 350 gallons-per-minute (GPM). The food processing plant’s operation, however, needs a dependable 350 GPM flow rate running 24 hours a day, 7 days a week. That adds up to 10 to 12 million gallons per month, 150 million gallons per year —a larger volume of water than used by small cities.
"The plant depends on that rate of flow to process food around the clock all year long," Renner emphasizes. "At the same time, we had to respect the low specific capacity to avoid over pumping the well and prevent excessive drawdown. Plus, the state Department of Natural Resources requires the pumping water level to be monitored and controlled to keep the pumping water level above the existing horizon of the formation. That meant we needed an intelligent pump control system that could monitor and adjust a lot of different factors to ensure reliable water production."Controlling all the variables with VFD intelligence
Considering the challenges, Renner contacted Brian Peterson of Schwab, Vollhaber and Lubratt, Inc., (SVL) of Shoreview, Minn., near St. Paul. As a provider of technical and engineering services for HVAC and pump applications, Peterson recommended a Danfoss VLT®
AQUA Drive to operate the pump motor.
“This facility is extremely dependent on maintaining a variable water flow between 150 GPM to 350 GPM at a constant pressure of 65 pounds per square inch (psi),” says Peterson. “The Danfoss VLT®
AQUA Drive is a variable frequency drive (VFD) that is built in Loves Park, Ill., and is specifically dedicated to water and wastewater applications. They come off the shelf with the onboard intelligence to handle all the monitoring and control parameters this job required."