Study On Technology Of Ozone Enhanced Coagulation Of Oil-field Produced Water

The exploitation of Shengli oil-field has already gone through nearly 40 years, majority of oil-fields are in the oil development of the middle and the later period, the water content of produced oil is 70%～80%, even reached as high as 90%, which bring a great deal of oil-field produced waste water. At the same time, injecting the treated oil-field produced water into stratum not only can recover crude oil from the water, realize the reuse of water, reduce environmental pollution, but also can provide sufficient affusion source, economize a huge amount of fresh water resources. However, with the development of continuous exploitation, Shengli oil-field has already entered the specially high water containing period, oil-field produced water has experienced a cycle, which is to be exploited, to be disposed and to be injected into stratum time, plus, plenty of chemistry medicine has be injected, the property of oil-field produced water has also taken place. The pollutants composition of the oil-field produced water was complex, so the effect of traditional flocculation and deposition was bad, the produced water treatment process has been unable to meet demand, therefore it has brought new issues to the treatment of oil-field produced wastewater.This research aimed at the problems consisted in traditional coagulation process of Shengli oil-field produced water, and the actuality that unstable substances in oil-field produced water are difficult to remove, add O₃ before coagulation process, enhance coagulation effect by ozone, and utilize ozone-oxidation to remove unstable substances, improve the treatment effect of oil-field produced water. Therefore, the emphasis of the research investigated the effect of ozone on coagulation enhancement and removal efficiency of unstable substances, determine the best parameter of ozone enhanced coagulation, analyse the economic feasibility of ozone enhanced coagulation from a practical point of view of production, put forward a practical application of the conditions and measures.The results showed: (1) Aims at Shengli oil-field produced water, the optimum parameters of ozone enhanced coagulation was that pH was 7.0～8.0, the appropriate temperature was 50℃, the best dosage of O₃ was 5mg/L, PAC was 20mg/L, PAM was 5mg/L. Oil of untreated water was 27.6mg/L, SS was 21.37mg/L, after treatment, oil content droped below 5mg/L, SS droped below 3mg/L, the treated water consisted with the standards, therefore, the traditional processing of the filter unit can be omitted. At the same time ozone can play to address the effectiveness of enhanced coagulation, improve the effect of flocculation, compared with traditional coagulation, achieved the same standards of treatment, ozone enhanced coagulation can reduce PAC 10g/m³, PAM 5g/m3, achieved the purpose of lower pharmacy costs and economic operation. (2) Aims at Shengli oil-field produced water, ozone also had a good effect on the unstable substances removal, the best dosage ozone pre-oxidation was 5mg/L, with the same results identified by ozone enhanced coagulation effects. In this dosage, when the contact time was 10min: Fe²⁺ in oil-field produced water droped from 7mg/L to 0mg/L, S^2- droped from 5mg/L to 0mg/L,SRB droped from 250 units/L to 0 units/L. (3) Utilization efficiency of ozone reaction tended to be affected by ozone dissolved capacity in the water, adding fills to the ozone reactor had a certain improvement of the ozone utilization rate, however, the improvement was limited, suggested that use the methods of releasing dissolved air to improve utilization efficiency of ozone reaction. (4) Aims at Shengli oil-field produced water, ozone had a certain effect on the oil-field water quality, when dosage of O₃ was 5mg/L, pH dropeds from 8.01 to 7.96, adding ozone had little effect on the pH of oil-field produced water; at the same time, the salinity droped from 7125mg/L to 6893mg/L, the conductivity droped from 11.1mS/cm to 10.7mS/cm, ozone oxidation can reduce the salinity of oil-field produced water in a certain extent, thereby, reduced the risk of electrochemical corrosion caused by high salinity. (5) Using Na₂SO₃ as deoxidizer, when the dosing was 40mg/L, the oxygen content in water droped to less than 0.3mg/L.