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•Case Study: Mixing Eliminates Ice And Prevents Damage In New England Standpipe

By PAX Water Technologies

Ice formation inside steel potable water storage tanks is a common occurrence in the northern US and throughout most of Canada during the winter. Depending on the average air temperature, the inlet water temperature and the amount of turn-over, ice formation can range from a thin skin on the top and northern walls of a water tank to a massive ice cap that weighs many tons.

While most people enjoy a little ice in their glass of water, thick ice in a water tank can spell disaster. Operations are compromised when ice build-up inside tanks can lock-up millions of gallons of storage, leaving utilities exposed and unable to respond in emergency situations. Infrastructure is damaged when a jagged plug of ice scrapes the sides of a water tank as the water level fluctuates. If internal hardware (such as ladders and cathodic protection) inside a tank becomes locked in the ice, the rise and fall of the ice cap can literally tear this hardware apart. Each spring, even modest damage to tank coatings may require partial or complete overhaul, costing tens of thousands of dollars. This damage is preventable.

Moving water is more difficult to freeze than still water. If the warm water (~35-42°F) which enters the bottom of tanks during fill cycles is circulated to the top layers in a consistent flow pattern, then freezing should be reduced or prevented.

Operators observed changes in the mixed tank within the first few days of operation. A thick cap of ice had formed in the few days between when the mixer had been installed and when it was turned on, and upon activation this cap immediately began to melt, creating open water at the tank top. After a few more weeks of operation, and despite continued sub-freezing conditions, the ice in the mixed tank continued to melt away. In contrast, the ice in the unmixed tank was thick, jagged, and unchanged. After several weeks of operation, the mixed tank contained only liquid water, while the unmixed tank had a persistent, frozen ice cap.

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•Case Study: Mixing Eliminates Ice And Prevents Damage In New England Standpipe