Study On Treatment Of Simulated Oil Field Produced Water By Electro-coagulation Technology

Oilfield produced water is the oily wastewater separated especially from the water content of crude oilin the process of the oilfield exploitation. Its composition is relatively complex, not only is contaminatedby crude oil, but also dissolves a large amount of salts and various gases in the formation of hightemperature and high pressure, carrys a lot of suspended solids, and includes various types of chemicalagents, such as demulsifiers, viscosity reducer, wax etc in the process of oil extraction, oil-gas gatheringtransportation and crude oil dehydration. Therefore oilfield produced water is industrial wastewatercontaining many impurities. Oilfield produced water has a higher reservoir damage resistance, corrosionresistance and a certain scale, its serious pollution increasingly poses a great potential threat to ecologicalenvironment and human health, which must be subjected to rigorous treatment to back to re-injection.Although these methods, including physical, chemical, physics-chemical, biological and other methods,may be on a certain treatment effect for oilfield produced water, they are either inefficient or sometechnical defects.Due to oil field produced water containing large amount of sodium chloride, the developingelectro-coagulation method may overcome these deficiencies, it has the function of agglomeration,adsorption, flotation, oxidation and reduction, so it is a highly efficient wastewater treatment technology.This paper use electrocoagulation method to deal with simulated oil field produced water. First, adoptingthe single factor method determined the best operating conditions, improved electrocoagulation technologyand discussed the dynamics of oil removal, which the static reaction device was homemade and electrodematerials and connection mode were ascertained in advance; Second, study the electrochemical behavior ofelectrode, the electrode morphology structure and on this basis to explore the measures for decreasing theelectrode passivation; Finally, under dynamic experiment condition, using single factor method andorthogonal experiment method determined the optimal parameter combination, and using electric floatingtechnology to strengthen the treatment effect and researched effluent chemical forms for aluminum ion andiron ion. A serious of study is carried out and to establish the foundation for application and popularizationof the technology. This paper made studies mainly on the following three aspects:1. The static test(1) Taking rate of turbidity, oil removal rate and energy consumption as the comprehensive evaluationindex, aluminum alloy and iron composite electrode was the best electrolytic electrode and connectingmethod was modular. On this basis, the optimum process parameters for electro-coagulation treatsimulated oilfield produced water were: NaCl dosage of5000mg/L, pH value of6, electrode plate spacingof2cm, the current density1.33mA/m2, electrolytic time of40min. In this experimental condition,turbidity removal rate was more than94%and oil removal rate exceeded95%. (2) The optimal combation conditions, microwave heating demulsification method to treat simulated oilfield produced water, were as follows: microwave power was616W, radiation time was4min, wastewaterpH value was6and standing time was1h; the reinforcement method, microwave and aeration technology,might enhance wastewater treatment effct on electrocoagulation, turbidity and CODCrseverally reached97.3%,98.0%and95.2%.(3) In the process of treatment of simulated oil field produced water by electrocoagulation, there were lessoil droplets in the effluent supernatant and produced floc features were composed of large and close(containing larger oil-droplet, which size was10times than of raw wastewater) fast settling velocity, lesssuspended solids and less sludge generation. Oil removal by electrocoagulation fitted first-degreedynamics equation and fitting dynamic equation was ln (C0/Ct)=0.08755t and correlation coefficient R2=0.9929.2. The electrochemical behavior research(1) The cyclic voltammetric curve and polarization curve were studied on these electrodes includingaluminum electrode, iron electrode, aluminum alloy electrode and aluminum-iron composite electrode, andit could be seen that electrochemical behavior of aluminum alloy-iron composite electrode was similar toelectrochemical behavior of iron. In the treatment process of simulated oil field produced water, aluminumalloy-iron composite electrode had certain electric catalytic oxidation ability and showed electrodepassivation phenomenon.(2) Through the study of scanning electron microscopy (SEM) on aluminum alloy and iron electrodematerials, it could be concluded, from rough electrode structure before the reaction and porous structureafter the reaction, that main components of electrode (aluminum and iron) had been dissolved. Fromenergy spectrum analysis, it could be seen that the surface of electrode produced oxide film and wasattached with the other ions in wastewater, which further proved electrode passivation phenomenon.(3) Effective measures, in the process of simulated oil field produced water was dealt with byelectrocoagulation, of decreasing the anode passivation were: wastewater temperature of50℃,stirring rateof200r/min, sodium chloride dosage of2000mg/L and time intervals of changing electrodes10min.3. The dynamic test(1) Using the self-made electrolytic tank for dynamic reaction device, the electrocoagulation processviewing aluminum alloy-iron composite electrodes as electrolytic electrode (connection way of modulartype) was used for the treatmentof simulated oilfield produced wastewater with orthogonal test and singlefactor tests. And the optimum technology conditions was that NaCl sodium chloride dosage was1g/L, pHof wastewater was7, electrolytic current was0.2A and residence time was20min. Taking graphiteelectrodes as electrolytic electrode, simulated oil field produced water was dealt with orthogonal test andthe optimum experimental conditions (hydraulic retention time for30min, nacl dosing quantity of1g/L, wasterwater pH of7, current intensity of0.5A) were obtained.(2) Based on wastewater treatment technology study of simulated oilfield produced wastewater withsedimentation method, electrocoagulation, electroflotation and electrocoagulation-electroflotation, thetreatment effect of electrocoagulation-electroflotation was the best, turbidity removal rate and oil removalrate, respectively, were more than96%and99%, which reached A level criteria specified inRecommended Indexes on Injection Water Quality for Detrital Rock Oil Reservoirs and AnalyticalMethods(SY/T5329-94). At the same time, adopting the experimental method proved that the mainoperation unit of affecting degreasing rate was electrocoagulation and higher turbidity removal rate was aresult that electrocoagulation, electroflotation and sedimentation method acted together.(3) A series of reatment effect on different oil concentration of simulated oilfield produced wastewatercould be seen that self-made dynamic test integrated device had a good feasibility and appropriatelyreducing the settling time did not influence the treatment effect of wastewater.