Scaling can sap energy, maintenance time
Solving the problem
If some means can be found to control scaling, there is potential to save energy, prevent equipment failure, reduce maintenance, and save money.
A range of physical methods can be used to remove fouling deposits. Water jetting, or sand or plastic-bead blasting can be used in accessible locations. However, such methods can be expensive and abrade surfaces.
Magnetic and electronic descaling does not stop precipitation but alters the shape of the crystals to reduce the adherence and buildup of deposits on the pipewall. Perhaps the most remarkable observation is that devices can affect descaling downstream of the point of installation; a softening and loosening of existing scale several weeks after installation is commonly reported.
To understand the mechanism, some knowledge of mineral scale precipitation is necessary. We know that in order to form a scale deposit, three conditions must be met:
- The solution must be supersaturated.
- Nucleation sites must be available at the pipe surface.
- Contact/residence time must be adequate.
To prevent scale it is necessary to remove at least one of these preconditions. Clearly, contact time is not an alterable factor. To be effective, any device must therefore affect either the supersaturation value or the nucleation process.
The direct effect on electronic devices is on the nucleation process and in particular to enhance initial nucleation through the creation of new nucleation sites within the bulk fluid flow. Crystal growth then occurs at these points of nucleation and not at the pipe wall. Suspended solids increase with a corresponding drop in the level of supersaturation, and these effects have been observed in the field. The localized pH increase near the pipewall caused by hydroxyl radicals formed by electromechanical interactions is one mechanism that drives the changed nucleation characteristics.
Electronic devices are not flow-rate dependent and can be built to fit pipe diameter up to at least 60 in. The units are lightweight and easy to install, can be retrofitted, and produce no significant magnetic field. They are usually effective on calcium carbonate, are claimed to reduce iron fouling, and appear to prevent fouling by various other substances.
Jan de Baat Doelman is president of Scalewather North America Inc.