Sealless Nonmetallic Pumps in Ultra-Acidic & Ultra-Caustic Applications

ChemTreat Inc. is one of the world’s largest suppliers of acid- and caustic-based industrial water treatment products. ChemTreat custom blends raw materials for customers across a wide array of industries, making more than 55 specific blends. ChemTreat’s manufacturing processes are designed to address the specific requirements of one order at a time. No single manufacturing approach or blend of chemicals applies across the board. One consequence is the pumps that facilitate these processes must be quickly removed, reset and reinstalled each time a blend order is completed and a new order is queued up. But recent growth, which led to an unprecedented number of new orders, also meant that pump failures increased along with production volume and variety. Management at ChemTreat began the search for a pump that would meet the needs created by the company’s success while delivering finished products at its established service levels. The options were tested against such criteria as chemical compatibilities, flow rate, reliability and manufacturers’ turnaround times.

Needed: A Tough Pump for Caustic Corrosive Fluids

Most of ChemTreat’s blends are at the extreme ends of the pH range—ultra-acidic or ultra-caustic. Chemicals at both ends are highly corrosive, so containment is always an issue. In conventional centrifugal pumps, the shaft from the external motor must enter the pump, passing through the pressure-retaining casing, to drive the impeller. This aperture must be properly sealed to prevent any of the fluid escaping. In the case of highly corrosive blends, any leakage not only lowers gallons-per-minute throughput but also may corrode the outside of the casing and, if in any significant quantity, possibly endanger plant personnel. In practice, even the best seals corrode under ultra-caustic or ultra-acidic conditions, triggering pump shutdowns and requiring the installation of replacement seals. The pump chamber must also be corrosion- resistant. Today, this is typically accomplished by using polytetrafluoroethylene (PTFE) to line the metal casing or to sheathe the impeller. PTFE is not robust enough to form a chamber or an impeller on its own.

Magnetic Pumps—No Seal Required

Magnetic pumps are an effective solution to this problem. The external motor spins a ring of powerful electromagnets around the impeller, which contains a corresponding set of permanent magnets. The motor shaft does not need to enter the pump chamber, which means that no seal is required and the leakage problem is eliminated. Because magnetic force diminishes according to the inverse square law, the motor magnets and the corresponding impeller magnets must be extremely close to one another for the pump to operate effectively. Most magnetic pump impellers are PTFE-coated metal, like the chamber itself. The thicker the PTFE coating, the more wattage must be used to power the motor. Moreover, the rotation of the impeller generates electric force, which can cause thermal eddy currents to flow through the metal and lead to corrosion within the system. With all of these concerns in mind, ChemTreat chose a close-coupled sealless magnetic-drive pump. The pump is a solid, one-piece molded thermoset unit, which features no welded, sealed or lined parts. The pump leverages a proprietary process to match metal’s strength and capabilities due to the controlled placement of long-strand fiberglass reinforcement in high-stress areas. The result is solid, homogeneous components with excellent physical properties and strength-to-weight relationships equivalent to those of metal parts. Crucially, the pump delivers optimum corrosion resistance and chemical compatibility. This allows it to handle the highly caustic and highly acidic raw materials ChemTreat processes. Together with temperature thresholds and robust solids-handling capabilities, these properties make the new pump highly reliable, eliminating much of the unplanned maintenance required by ChemTreat’s previous pumps. Moreover, the new pump has helped increase plant safety and address compliance mandates by ensuring negligible or zero fugitive emissions from the pumping equipment.

New Pumps in Action

Because the majority of the company’s orders are processed batch by batch, it is very easy to predict when a particular pump will need to be replaced. Because the pumps are available on demand, plant managers may order a new pump, install it and move forward with the next order, all without storing thousands of dollars worth of spare pumps. In the 10 years since the company installed its first unit of this pump model, management has been consistently impressed by how well the pumps can stand up to the rigors of the company’s manufacturing processes. They rarely require service. Together, these factors have helped ChemTreat reduce its manufacturing downtime by more than 80 percent. And as the frequency of both planned and unplanned interruptions has dropped, the company has seen a significant rise in productivity, which has translated to more orders completed at a faster rate. This has all allowed ChemTreat to recoup its investment in the pumps eight months after they were first installed.