The Study Of Scale Inhibition In High Salinity Wastewater At High Temperatures

Precipitation of calcium carbonate sclae is an inevitable problem in the process of yielding. As the process going on, the scaling problem will be more and more prominent in the mid- to late -stage, with the development cost surging. Because most of the surplus wastewater in Shengli Oil Field contains high salinity(1%～4%) and complicated organic matter (a lot of petroleum hydrocarbons and various of chemicla agents), it is necessary to screen out the best scale inhibitor with high efficiency at high temperature, control the scaling problem in the mechanical compression evaporative desalination processing effectively, prolong the service lif of the equipment and then provide the technical support for the resourcelization and recyclling of the high salinity oilfield wastewater.At the basis of the chemical and instrumental analysis on the chemical composition and the contents of Calcium and Magnesium, this paper chooses the Davis-Stiff saturation index method and the Ryznar stability index method to predict the scaling tendency of the oilfield wastewater with high salinity and provide the theoretical guidance for the screening of the efficient scale inhibitor. In addition, we compared the scale inhibition effect of six kinds of commercial scale inhibitors and screened out the best one (scale inhibitor SQ-1211) to investigate its scale inhibition performance in highly saline conditions at high temperature through static scale inhibition tests. The influences of temperature, heating time, pH and scale inhibitor dosage on the inhibition efficiency of the optimal scale inhibitor were investigated. The morphologies and crystal structures of the precipitates were characterized by Scanning Electron Microscopy and X-ray Diffraction analysis. In addition, this article preliminarily studied the scale-control method of seeding technique of gypsum.Results showed that the surplus wastewater in Shengli Oil Field has the scaling tendency at 80℃ and worse at 100℃. The scale inhibition SQ-1211 has the best scale inhibition among the six kinds of commercial scale inhibitors. The scale inhibition efficiency of the wastewater in Shengli Oil Field using optimal scale inhibitor could reach 91%at 80℃ when the dosage of scale inhibitor is 11mg/L. When treating simulated salinity wastewater with the concentration of Ca2+ as high as 1600 mg/L, the scale inhibition efficiency could reach 90.7% at 80℃ at pH 8. Besides, the optimal scale inhibitor could effectively retard scaling at high temperature. What’s more, because of the presence of the optimal scale inhibitor, it could occupy the active growth sites on the surface of the CaCO3 crystal, interfere with the normal crystal nucleation and growth, lead to the lattice distortion, and make the main crystal structure of CaCO3 change from calcite to aragonite. Compared to the calcite, the aragonite is more dispersed and more instable, which leads to the scale dissolved and washed away by water easily. Besides, in the study of seeding technique of gypsum, when the dosage of anhydrous calcium sulfate crystal was 10 g/L and the residence time was 10 h, the experiment had the biggest seed crystal and best scale inhibition effect.