The Study Of Effects Of Magnetic Water Treatment For Anti-fouling

Scale is a commonly incurred problem in industry field. The economic loss due to it exceeds ten billion dollars every year all over the world. The loss is usually produced by energy losses due to efficiency decay of heaters and heat exchangers and unscheduled maintenance due to a severely pipe and manifolds clogging. How to remove existing scales and prevent forming of scale is an essential research subject of water supply and sewage engineering. Currently, the prevalent method to prevent scaling is the usage of scale-inhibiting chemicals, however these chemicals are expensive and harmful to human health and environment. The technique of magnetic water treatment has been widely applied in industrial, agricultural, medical and biological fields since Belgian T.Vermerien got rid of boiler scale by the use of magnetic field in1945, and the Technology has got extensive development. Now to meet the stricter environmental requirements and to solve the problem of shortage of water resource, magnetic water treatment (MWT) attracts special attention due to their ecological purity, simple in design, inexpensive to manufacture, and reliable in operation once properly installed. They also do not require a special delicate maintenance program. Over the years, this technique was widely employed to prevent or mitigate fouling of water system.Though MWT was employed to prevent scale for several decades, there is unceasing controversy on its effects, the mechanism through which it exerts its influence on the processes of scale formation and the characteristics of scaling compounds is as yet not adequately explained. In our practical application in domestic and industrial water systems, the optimal anti-scale effects usually cannot be achieved by choosing the appropriate magnetic treatment parameters (such as How velocity, the geometric arrangement of the magnetic treatment devices, the magnetic flux density, etc.) when we treat different water systems. Thus there is lots of fundamental works to be done to obtain optimal effects and to find out the mechanism. The main contents of this paper are as follows:1. Effects of magnetic field (MF) intensity, temperature on precipitation process of CaCO3for CaCO3is the main scale component. The calcocarbonic pure water (water containing only Ca2+,CO32-,HCO3-ions) was tested to avoid the influence of foreign ions and high supersaturation. At10℃,30℃.60℃. the parameters of conductance, turbidity and concentration of Ca2+of water were tested when they flowed vertically throwing magnetic field(0,1850,2850,4100mT). The anti-scaling effeciencies have been compared of different water systems. The results showed that MF intensity and temperature accelerated the process of nucleation of CaCO3, more microcrystals were produced in water, the supersaturation of CaCO3were reduced, the growing of microcrystals were hindered, thus less CaCO3deposited on the vessel walls to mitigate fouling. At lower temperature, the anti-scaling effects were not obvious, when temperature was higher than30℃, the anti-scaling effects were obvious, The more intensive MF can strengthen the effects.2.Effects of MF intensity and temperature on CaCO3scale and morphology composition of CaCO3precipitated in water. The size distribution of CaCO3scales on the loading slice were observed by electron microscope, the morphology composition of the CaCO3precipitated in water were identified by XRD. The results showed that CaCO3scale particles is more bigger and its amount is less when water samples were treated with more intensive MF at higher temperature, MF had no effect on composition of CaCO3at10℃, MF favored the forming of aragonite at30℃, MF favored the forming of aragonite and vateriteat60℃.3.Mechanisms of effects of MF intensity and temperature on the precipitation process of CaCO3. The results suggested that MF influenced the precipitation process and polymorph composition of CaCO3by influencing the hydration and dehydration process of hydrated CaCO3as the precursor of crystal nuclei for MF changed the structure of water cluster. The free energy of CaCO3increased with the action of MF, the precursor of CaCO3crystal nuclei (ACC and HCC) can transformed to calcite and calcite can transformed to aragonite and vaterite directly for the CaCO3can overcome more large activation energy barrier.4.Effects of MF on precipitation process of CaCO3in presence of foreign ions such as Al3+, Fe2+, Mg2+. SO42-and Cl-. The parameters of conductance, turbidity and concentration of Ca2+of the calcocarbonic water in presence of different foreign ions were compared during water samples were treated by different MF. The anti-scaling effeciencies have been compared of diferent water systems. The results showed that foreign ions accelerated the process of nucleation of CaCO3, The order of effects of ions were Al3+>Fe2+>Mg2+>SO42->CI-when treated by less intensive MF. the order were Fe2+>Al3+>Mg2+>SO42->Cl-when water samples treated by more intensive MF.5. Effects of MF on CaCO3scale and morphology composition of CaCo3precipitated in water in presence of foreign ions of Al3+, Fe2+, Mg2+. SO42-and Cl-. The size distribution of CaCo3scales on the loading slice were observed by electron microscope, the morphology compositions of CaCO3precipitated in solution were identified by XRD. The results showed that CaCO3scale particles were more bigger and its amounts were less in presence of foreign ions. The presence of Mg2+. SO42-favored the forming of aragonite. the presence of Al3+. Fe2+favored the forming of aragonite and vaterite. and MF strengthened the effects.6. Mechanism of the effects of MF on the precipitation process of CaCO3in presence of foreign ions. The results suggested that MF and foreign ions influenced the precipitation process and polymorph composition of CaCO3by influencing the hydration and dehydration process of the ions and hydrated CaCO3as the precursor of crystal nuclei. The effects of ions were increased by MF for MF strengthened the polarity and deformation capacity of ions. Perhaps the presence of foreign ions inhibit transformation of metastable or unstable morphology to a stable morphology for the coprecipitation of (Mx. Ca1-x)CO3is more unstable. Perhaps foreign ions and MF changed the activation energy needed to overcome by the transformation of amorphous CaCO3and hydrated CaCO3to different CaCO3crystal forms, then polymorph compositions of CaCO3were changed.7. Effects of strong permanent magnetic field on circuit water. Magnetic water treatment device designed by ourselves was employed in circuit water. The results showed that MF intensity, temperature and flow rate had notable impact on effects of MF, and water quality influenced effects of MF obviously.