The problems of scale are well known to those living and working in 'hard' water areas. Scale is the undesirable consequence of water supplies becoming super-saturated with dissolved minerals. These problems are of greater significance if found in industrial water systems and commercial buildings. Scaling problems commonly occur, even in 'soft' water areas, when a fluid stream is circulated, liquid losses causing concentration of the dissolved mineral ions and eventually forcing the minerals to precipitate at their solubility limit.
In process industries, it is common for chemicals to be added either because the water is being used for 'scrubbing' or cleaning, or to achieve a chemical/mineral effect as part of the production process, so increasing the scaling tendency. Scaling deposits are very common in flow lines subject to changes in pressure or temperature. Regardless of how hard water effects are achieved, the outcome is the same for all. Scale fouling results in reduced diameter or blocked pipes, reduced heat transfer efficiency, seized pumps, inoperable valves, misleading meter readings, defective-heating elements etc.
Aqueous solutions can become supersaturated, which means that they contain higher concentrations of dissolved solute than their equilibrium concentration. Such solutions are not stable and are easily triggered into dropping back to saturation level, forcing the dissolved compound to precipitate. Even when a bulk solution is less than fully saturated, scale formation can occur spontaneously due to localized super saturation, at a surface for example.
pH Effect on Scale Formation
The pH of the solution is directly related to its acid content (typically carbonic acid). The higher the acid content, the lower the pH number. The solubility of calcium carbonate is directly affected by the pH of the water. If the pH of the water is decreased, more calcium carbonate solid can be dissolved. Conversely, if the pH of the water rises, it will force calcium carbonate out of solution and hence scale deposits will form.
Temperature Effect on Scale Formation
Gases in general, and specifically carbon dioxide, are less soluble in water at high temperatures. Therefore, as the temperature rises, the dissolved carbon dioxide decreases. This increases the pH of the fluid, reducing the solubility of the calcium carbonate and forcing the mineral to deposit.
Pressure Effects on Scale Formation
Carbon dioxide and gases in general are more soluble under higher pressure. Therefore, as the pressure drops, carbon dioxide gas will be forced out of solution, lowering the carbonic acid concentration. The rise in pH is associated with a drop in calcium carbonate solubility, leading to the formation of mineral scale deposits.
Scalewatcher Electronic Water Conditioning
Scalewatcher is a non-invasive system utilizing a solenoid coil or coils wrapped around the pipework to be treated. A signal generator of which the frequency is continuously changed supplies current to the coils. The pulse shaped current creates an induced electric field, concentric around the axis inside the pipe. As a consequence to this arrangement, any charged particle or ion moving within the field experiences a so called Lorenz force generated by the interaction between charged particles and magnetic and electric fields. Research at a major University in Philadelphia confirmed that the Lorenz Force is unchanged, irrespective of flow rate. Generated magnetic fields have been measured and have been found to be below 1 Gauss, lower than the earth magnetic field strength. This technology overcomes one major disadvantage of permanent magnet devices, viz, that they work well only within a certain flow rate ‘window’ and that at higher and lower flows the performance drops to zero.
Scalewatcher EWT affects the formation of scale by increasing the homogeneous precipitation rate of calcium carbonate and certain other minerals. The ability to adjust power, frequency and coil configurations on site enables performance to be optimized with no downtime and no pipe replacement.
Operating Mechanisms of Electronic Devices
Current scientific literature describes the macro effects, which are the consequence of fundamental interactions between applied fields and precipitating substances. The amount of energy that is introduced by a solenoid coil is very small (the consumption of a household Scalewatcher unit is one order of magnitude less than a cordless telephone). To study the induced fields, scientific tools of high precision are needed which do not interfere with the interactions that we want to measure. The atomic force microscope (AFM), capable of examining growth patterns on surfaces at the highest resolution, is a tool that can demonstrate some of the key interactions.
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;
1. The solution must be supersaturated with mineral ions.
2. Nucleation sites must be available at the pipe surface.
3. Contact / residence time must be adequate.
To prevent scale it is necessary to remove at least one of these pre-conditions. Clearly contact time is not an alterable factor. To be effective any device must therefore affect either the super saturation value or the nucleation process.
The direct effect of the electronic device described above is on the nucleation process and in particular to enhance initial nucleation through the creation of new nucleation sites within the bulk fluid flow. This is controlled precipitation. 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 super saturation, and these effects have been observed in the field. The localized pH increase near the pipe wall caused by hydroxyl radicals formed by electromechanical interactions is one mechanism that drives the changed nucleation characteristics.
A Lorenz force F is experienced by charged particles that flow through a field:
F = qE + q (V x B) where q is the charge on the particle, E is the electric field vector; V is the particle velocity vector, and B the magnetic field vector. Electronic devices operate at very weak magnetic fields whereas magnets need high field strength (>1000gauss) for optimum performance. The flow dependency of magnetic devices is explained by the velocity parameter, V, and E=0. The flow non-dependency of electronic devices is explained by the fact that the force of the electric field component is independent of the flow rate. This suggests that the key performance parameter is the total value of the ‘Lorenz’ force acting on the charged particles, rather than the individual magnetic and electric field vectors.
By nature all particles in water have a negative charge and are surrounded by the so-called “electric double layer”, layers of positive and negative ions around the particle. These layers may be seen as “protective” layers preventing more ions to stick to the surface of the particle. The Lorenz Force, if strong enough, will distort these layers and ions in the bulk of the liquid may now stick to the surface forming crystals. These crystals will not adhere to pipe walls and will go down the drain or remain suspended in a circulating system. As a result less mineral ions will be present in the liquid. An important side effect is the fact that pipe walls corrode less as a lower amount of positive ions are present.