The Reuse Technology Of Silica-rich Heavy Oil Wastewater And Its Applying Basic Research

Heavy oil wastewater is the associated pollutants in the process of heavy oil exploitation and has the characteristics of high temperature and great quantity. For heavy oil wastewater reused to boilers is the best way. The technology of heavy oil wastewater reused to thermal recovery boiler mainly includes four aspects:the removal of oil and suspended solids, the removal of hardness, TDS and silica. In Xinjiang oilfield the produced water of heavy oil is silica-rich waters. In the process of recycling boiler, furnace tubes face fouling problem. To solve this problem, this paper carried out the related research works.This article studied the influences of the formation of silica by measuring the change between the reaction silica and non-reaction silica. The results showed that, in the supersaturated silica solution reaction silica has the tendency to polymerize to form non-reaction silica, but the process is very slow; temperature influences the formation of silica by affecting the solubility and polymerization rate of silica. The pH of the simulated water affects the forms of silica. In acidic and alkaline conditions silica is more stable, while under the neutral conditions, the polymerization rate of silica is accelerated, so the trend of scale is obvious. The effect of ionic strength to silica is complex, and different ions have the different effect. Cl^- and Br^- can t be in favor of the form of silica through salting out, while ?CO₃?^2- and ?SO₄?^2- can inhibit the formation of silica in the water. Metal ions can react with silicon and precipitate in solution, and promote the polymerization of silica.Compared with several common adsorption materials, the property of Al₂O₃ is the best. The results showed that MnCl₂.4H₂O is the optimal metal salts for neutral silica removal, and found that the effect of bivalent manganese in the remove of silica includes two aspects: the precipitation reaction with the reaction silica and the catalysis in the polymerization of reaction silica. For the simulated water which the content of silica is 200mg/L, the optimal removal conditions in the alkaline precipitation method:the dose of magnesium is 400 mg/L, water bath temperature is 75 ?, the pH of wastewater 9.5?10, the pH of treated water 8.5-9.0.The pH of the wastewater is the most important to the efficiency of silica removal, and the condition of temperature and reaction time is relatively small, so in practice the impact of them can ignore. Studies have show that the greater the dosage of magnesium chloride, the better the efficiency of silica removal. In order to meet the requirement of the content of silica in the boiler' feed water, less than 50mg/L, the optimal conditions for silica removal in Fengcheng NO.2 station is that the dosage of magnesium 500mg/L, the pH of wastewater 9.5 ?10, the pH of treated water 8.5?9.0.