Minnesota Power’s Arrowhead High Voltage Direct Current Terminal was experiencing scale and white rust build-up inside their cooling tower condenser tubes, creating obstacles cooling the inverter. If left untreated, the built-up could result in a costly asset replacement and unscheduled down-time. At the same time, the Minnesota Pollution Control Agency (MPCA) was instituting new phosphate discharge limits and encouraging plant management to meet the new state limits before implementation.
Minnesota Power’s Environmental Compliance Specialist Crystal Tokarczyk, reached out to ALLETE sister company U.S. Water for assistance in achieving system efficiency and meeting new state discharge limits.
The existing water treater’s ineffective program had resulted in years of built-up galvanized corrosion on the condensor tubes which impacted the inverter cooling and eventually, could result in permanent damage to the asset. The phosphorus discharge was also outside of the new state regulated limits, leaving the Arrowhead terminal in need of an environmentally friendly solution that provided scale and corrosion control without the discharge or aquatic toxicity concerns of traditional phosphorus chemistries.
U.S. Water worked with Minnesota Power’s Amanda Middleton, Peter Schommer and Dan Fahland to implement PhosZeroTM into the system. The PhosZero chemistry provided low enough toxicity to gain approval by the MCPA, yet strong enough scale inhibition properties and corrosion protection to keep their system running efficiency.
The PhosZero program was paired with a TowerAssureTM automation system. TowerAssure’s wireless communications program monitors Arrowhead’s chemical program for consistency and instantly alerts the plant’s maintenance team if the system is experiencing any irregularities. The alerts allow the team to respond immediately and make adjustments from the site or home via U.S. Water ReportsTM.
A few months after introducing the PhosZero chemistry into the system, hardness balance testing showed that the scale was being removed. Minnesota Power and U.S. Water employees inspected the system in the following months. Due to its success, Minnesota Power installed the same U.S. Water chemistry system on another cooling tower and works closely with U.S. Water in monitoring the system’s efficiency.
By implementing U.S. Water’s solution, Minnesota Power was also able to forgo the need to rent an anion exchange resin to remove phosphate from their system, saving approximately $35,000/yr.