At present, most oil fields in China have entered the high water cut stage, and water injection is still the main means to increase crude oil production. With the increase of water output, a large amount of oily sewage will flow back to the oilfield surface in the production water. In order to achieve the goal of ecological environment protection and resource recycling, how to treat oily sewage in oil fields efficiently with less investment is a difficult problem faced by the majority of oil workers.
In recent years, with the maturity of separation membrane technology, some experts and scholars have studied the treatment of oilfield sewage with this technology. Compared with the previous methods of sewage oil separation, the supporting treatment facilities are simpler, easier to operate effectively, with good separation effect and less energy consumption, which is an important research and development direction of oilfield sewage treatment technology.
Problems in the application of 1 membrane separation technology in oily wastewater treatment in oil fields
During oilfield exploitation, the proportion of dirty oil in oily sewage returning to the surface is 1.2- 100mg/l, while the proportion of total dissolved solids in sewage is 1000- 1500mg/l, and the content of organic pollutants is 20-1L. Faced with the above pollutants, membrane separation technology is difficult to deal with, especially for organic pollution. For example, when the content of dirty oil is 200mg/L, the content of organic pollutants will exceed 5000mg/L, and the total suspended solid content will exceed 4000 mg/L. Under this condition, the removal of impurities by membrane separation technology is likely to block the pore size of the filtration membrane and reduce its service life. Filtration membrane oilfield sewage treatment technology should be combined with other sewage treatment processes in order to achieve greater results in practical application.
2 factors affecting the treatment of oily wastewater by membrane separation technology
2. 1 Material and pore size of separation membrane.
In order to make the separation membrane technology play a role in the treatment of oily wastewater in oil fields, the material of separation membrane should be determined with reference to the chemical characteristics of oily wastewater. If the crude oil of oily sewage is mainly composed of dispersed oil droplets and floating oil, the pore size of the filtration membrane should be determined as a microfiltration membrane within the range of 10- 100 micron. When the oil in sewage is composed of emulsified oil in a stable state and soluble oil, the lipophilic ultrafiltration membrane should be selected.
2.2 operating temperature and pressure difference
The effect of sewage treatment by separation membrane will be affected by temperature conditions. In most cases, 30-50 degrees Celsius is the best temperature for sewage treatment. When oily sewage is treated by filtration membrane, the critical operating pressure difference should be applied on both sides of the membrane. If the pressure difference is not greater than the critical value, the permeability will increase with the gradual increase of the pressure difference. If the applied pressure difference is less than the critical value, the permeability will decrease due to the increase of pressure difference.
2.3 feed liquid concentration and flow rate
When treating oily wastewater with separation membrane, if the feed concentration is not high, the flux of filtration membrane is proportional to the applied pressure difference. However, when the feed concentration is greater than a specific value, the amount that can permeate is not directly related to the pressure conditions, but only related to the flow rate on the surface of the filter membrane. Because changing the flow rate of feed liquid is helpful to improve the working efficiency of membrane separation of sewage, we should refer to the actual situation of feed liquid in the filtration membrane separation system and choose a scientific and reasonable feed flow state, so as to further improve the treatment efficiency of oily sewage by filtration membrane.
2.4 membrane pollution
The so-called pollution to the filtration membrane refers to the deposition of various substances in oily sewage on the membrane surface in physical, chemical or mechanical forms. Filtration membrane pollution is a restrictive factor that membrane separation technology can not be widely used. Therefore, when using filtration membrane separation technology to treat oily sewage, we must choose reasonable filtration membrane and suitable operation method.
Process design of membrane separation technology in oily wastewater treatment
In the process of oilfield water injection, the oily sewage discharged from the ground is separated by filtration membrane technology, the organic matter and dirty oil components in the sewage are pretreated by primary buffer disinfection and catalytic oxidation, and the substances with larger particle size in the sewage are separated by filtration membranes with different pore sizes, so that the treated oily sewage can be injected into the stratum again.
3. 1 Property Analysis of Oily Sewage
Oily sewage formed by oil field water injection is a special type of industrial wastewater, with complex specific components, good salinity and many kinds of organic matter. These characteristics provide a hotbed for the existence and mass reproduction of microorganisms. The performance index of chemical oxygen consumption required for treating organic matter is in an unstable state. Chemical oxygen consumption is a key parameter in oily wastewater treatment, and its value has become the focus of membrane filtration separation technology in oily wastewater treatment.
3.2 Selection of membrane materials and pore size parameters
The composition of filtration membrane is the main factor affecting the treatment effect of oily sewage. It is necessary to carefully study and analyze the components in oily sewage to determine their chemical characteristics. For example, the microfiltration membrane should be made of hollow fiber for sewage treatment, and the main material component is inorganic ceramics. If ultrafiltration membrane and nanofiltration membrane technology are used, the filtration membrane of polymer material should be selected. In the process of oily sewage filtration, the detection indexes of discharged water include solid suspended solids, pH value, organic matter content, sulfide and petroleum substances content. The pore size of the filter membrane should be determined according to the size of the material particles during treatment, so that the treated water can meet the requirements of discharge or injection into the formation.
3.3 Treatment procedures of various harmful substances in oily sewage
There are mainly the following procedures for filtering and eliminating various substances existing in oily sewage:
1) The oily sewage is treated for the first time by using the buffer disinfection program, and the ozone gas which is not polluted again is generated by the ozone generator, and then is input into the oily sewage, and the organic matter is treated by using the function of ozone to kill microorganisms, and at the same time, it has the function of isolating the combustible gas from the subsequent treatment equipment.
Suspended oil droplets rise together with the generated ozone gas to produce oil film or oil layer, and the diameter of oil droplets is not less than 100 nm. When the sewage liquid treatment is in a static state, the dispersed oil droplets will be distributed in the sewage in a suspended state, and after a certain period of static treatment, they will converge and integrate oil blocks with larger particles and float on the sewage. At this time, the oil droplets can reach 10- 100 micron.
2) Primary separation of sewage is realized by microfiltration membrane. This type of filter membrane has the characteristics of high treatment efficiency, less adsorbed substances on the membrane surface, and the medium is not easy to fall off, so it has good popularization and application value. Microfiltration membrane can filter out 0.02- 10 micron of organic matter and smaller ions in sewage, and emulsified oil droplets can be separated in this treatment process, which can be used in the treatment process before ultrafiltration membrane and nanofiltration membrane because of its large flux. Ultrafiltration membrane can permeate substances with a diameter of about 2-20 nanometers, and can effectively separate high molecular weight substances such as colloid, protein and virus.
3) Nano-filtration membrane is used for the secondary treatment of oily sewage, and the salt in the sewage is removed after concentration. Only when the sewage discharged before this procedure can not meet the corresponding water quality standards can it be used. This treatment program is an auxiliary program of the previous treatment process, which is even worse for oily sewage with more impurities. The pore size of nanofiltration membrane is 1-2 nm, and its filtration and separation function is between ultrafiltration and reverse osmosis, which realizes the treatment of small molecular weight organic matter, antibiotics and inorganic salts.
4 conclusion
Using membrane separation technology to treat oily sewage produced in the process of oil field water injection can achieve the purpose of green ecology, environmental protection and energy saving, and can also re-inject the treated sewage into the formation, which has a good application prospect. However, when using membrane separation technology to treat sewage, it should be combined with various water treatment technologies efficiently to achieve ideal results.
I believe that after the above introduction, everyone has a certain understanding of the application of membrane separation technology in the treatment of oily sewage in oil fields. Welcome to Zhong Da for more information.
For more information about project/service/procurement bidding, and to improve the winning rate, please click on the bottom of official website Customer Service for free consultation:/#/? source=bdzd