Research On Reusing Of Heavy Oil Sewage In Thermal Steam Generators

A lot of research work has been done about reusing the heavy oil sewage in thermal steam generators in china. Part of sewage treatment equipment has been in use. No substantive progress has beeen made in research of reusing heavy oil sewage, because of the serious emulsification of heavy oil effluent and great changes happened usually to water quality and little density difference between water and oil.In the light of the problems above mentioned, the main purpose of this paper is to design a set of sewage treatment techniques which offer theoretical basis and technical support for realizing industrialization of reusing of heavy oil sewage in thermal steam generator.The innovative research results and conclusions of laboratory simulation test and field pilot scale test are summarized as follows:1. Laboratory simulation test1) A bacteria community SL-16 with capacity of heavy oil degradation was constructed by the techniques of limited cultivation. Through shaking experiments, the best degradation conditions of bacteria community presented as follows: the temperature was 35～45°C, the pH was 7.0～9.0, the mineralized rate was 4 000～14 000 mg/L, the inoculation was 2 %,the initial crude oil concentration was lower than 1000mg/L,and the rotating speed was 140 r/min. In the best degradation conditions, the oil removal rate of the heavy oil reached 68 %.2) In the laboratory simulation, oil was removed by gas floatation and biological contact oxygen method; suspend solid was removed by sand filter; salinity was removed by double membrane of ultra-filtration and reverse osmosis. Oil content of gas floatation effluent was lower than 20 mg/L averagely. The best operating condition of biological oxygen method presented as follows: the temperature was 35～45°C, HRT was 16 h; The optimum fertilization proportions (COD_Cr:N:P) was 100:5:1 when nitrogen was ammonium nitrate and phosphorus source was dipotassium hydrogen phosphate. In this conditions oil content of effluent of biological reactor was lower than 1mg/L.The residual suspend solids was less than 5 mg/L after filtrated by sand filtration under the filtration pressure of 0.6 MPa. SDI of producing water of ultra-filtration was 2.6, turbidity of producing water of ultra-filtration was 0.19 NTU under the operating pressure of 0.3 MPa, which can meet the request of reverse osmosis. Reverse osmosis can removed scaling ions and most of salinity, the removal rate of Ca2+ reached 94 % and the removal rate of Mg2+ reached 100 %, desalination rate was 90 %.the quality of producing water of reverse osmosis was better than fresh water. The experiment showed that the process was feasible to realize the reusing treatment of heavy oil waste water, which including gas floatation, biological contact oxygen method, sand filtration, ultrafiltration and reverse osmosis.2. Field pilot scale test1)The design of reusing treatment adopts heat exchanger, cooling tower, gas floatation, biological contact oxygen method, sterilization, flocculation sedimentation, two media filter, ultrafiltration and reverse osmosis. Heavy oil waste water heated the producing water of RO by heat exchanger, and the temperature of producing water increased 10°C.The cooling extent of cooling tower was from 10°C to 15°C, which could ensure the temperature of influent of biological contact oxygen method was not higher than 45°C.The oil concentration of gas floatation effluent was less than 30mg/L, which meet the request of biological contact oxygen method. Under the conditions of influent flow was 8.3 m3/h, the quality of effluent of biological contact oxygen method reached secondary discharge standard of national standard GB8978-1996, and oil concentration was less than 1mg/L. Sodium hypochlorite containing available chlorine 10 % was used to kill bacteria and it's amount was 100 mL/L. the residual pollutants was removed by flocculation sedimentation and two medias filter, inputting amount of poly aluminium chloride was 80 mg/L and Polyacrylamide was 1.25 mg/L .Fine filter as security filter could avoid the damage of suspend solid to ultrafiltration membrane. SDI of producing water of ultrafiltration was no more than 3, turbidity of producing water of ultra-filtration was no more than 0.23 NTU under the operating pressure of 0.24 MPa, which could offer influent with stable quality for reverse osmosis. Reverse osmosis could remove scaling ions and most of salinity, the average removal rate of Ca²⁺ reached 93 % and the removal rate of Mg²⁺ reached 100 %, the average desalination rate was 92.5 %.The quality of producing water of reverse osmosis is better than fresh water, producing water can be used to replace fresh water.2) Degreasing mechanism of multilevel biological contact oxygen reactor includs the Aeration Flotation, biological oxygen, interception and adsorption, and food chain grade predator prey. Bacterial community structure was determined by component of oil in biofilm, which changed along the flow direction. The molecular biological analysis results showed that the effluent of biological contact oxygen reactor was of good quality when dominant bacteria community was SL-16 community.Research results of this paper offer theoretical basis and technical supports for realizing industrialization of reusing of heavy oil sewage in thermal steam generators, and the reseach established effective pretreatment technology for ultrafiltration and reverse osmosis. In summary, the results of this reseach have positive guiding significance for resourceful disposal of oil field waste water.