Application Of Electrochemical Technology As Pretreamnted For Production Of Ultra-pure Watera By Membrane Technology

With the rapid development of science and technology, an increasing strict requirement on water quality is needed in the field of electronic industry, power industry, pharmacy, chemical engineering, light industry, aeronautic and astronautic industry and metallurgy. At present, more and more departments are using ultra-pure water as raw material and process water directly. As a kind of by-product, oilfield associated gas is produced during oil extraction process, because of its complex components, ultra-pure water is always used for washing by spray in recovery process.In this thesis, how to prepare ultra-pure water is studied. The raw water is micro-polluted underground water, and preparation process is pretreatment + two stage reverse osmosis + EDI + mixed bed.Appropriate pretreatment is essential to the preparation of ultra-pure water. In this thesis, quartz sand filter + security filter is adopted as the pretreatment process. As the high levels of organic impurities and S^2- in raw water, the membrane fouling is serious, the reverse osmosis membrane flux decreases obviously after continuous running of 120 hours. This indicates that this pretreatment is not suitable. As a pretreatment technology, electrochemical technology is good for degradation of organic substances and oxidation of S^2- into S, so we can reduce the fouling of follow-up reverse osmosis membrane.Electrode is the key to electrochemical method as pretreatment technology. With the comparison of oxygen evolution potential, chlorine evolution potential and the service 1ife between Ti-coated Ru-Ir-Ta electrode and Ti-coated Ru-Ir electrode, the test result is that the former has stronger corrosion resistance, more excellent catalytic performance and better electrochemical performance than the latter. The electrochemical oxidation process produces residual chlorine and solvated electron,·OH, O2·, HO2·, OH and another active substances, S^2- can be oxidized into S by residual chlorine, and organic compounds will be degraded by active substances. The concentrations of residual chlorine and active substance produced in oxidation are related with current density, electrode distance and oxidation time. According to the experimental results, when the current density is 0.10A/cm2 and the electrode distance is 30mm, the maximum oxidation efficiency of residual chlorine concentration is reached. When the oxidation time is 6.5min, produced residual chlorine can meet the need for oxidation of S^2- (4mg/L). As the oxidation time is 7min, free radical concentration is optimal, and the removal ratio of organic compounds can be up to 66.9%. The S and another impurities will cause the pollution to the follow-up membrane process. When PAC dosing is 0.10g/L and PAM(1%) is 6mL/500mL, the coagulation effect is optimal, and the removal ratio of turbidity is about 89.1%.After one month of operating the system, the experimental results for ultrapure water show that Ca²⁺ concentration is less than 2μg/L, Na⁺ concentration is less than 5μg/L, SiO2 concentration is less than 5μg/L and its electric resistivity >17M??cm stably, TOC content can not be detected basically. Stable and reliable water quality can meet the requirements for oil associated gas washing water quality.The total investment for the ultrapure water system is about $268,000, and the running cost is about $3.60 /t ultra-pure water.