1. Present Situation of Oil Field Crude Oil Dehydration
According to the statistics, almost 80% crude oil in the world exists in the form of crude oil emulsion. The existence of oil-water emulsion will increase the burden of storage and transportation, reduce the service life of pipeline, and easily cause catalyst poisoning and serious corrosion of high-temperature distillation equipment. With the development of crude oil development, many mature methods have already been formed for the crude oil demulsification technology, mainly including physical method, chemical method and biological method. The demulsification method mainly includes gravity, centrifuge, heating, electric, ultrasonic and microwave demulsification.
In the present crude oil dehydration works, the physical method is mainly used in combination with the chemical method. It is realized through the efficient three-phase separator. Therefore, the efficient three-phase separator plays a more and more important role in crude oil dehydration. Its dehydration effect directly influences the crude oil temperature rise costs of the Combination Station and the stable and normal operation of crude oil as well as the crude oil transportation indexes.
2. Advantages of Efficient Three-phase Separator
Advantage of the efficient three-phase separator will be described through its workflow:
2.1 The efficient gas-liquid cyclone separator improves the effective volume of the equipment, and can balance the equipment pressure and stabilize the flow state. Besides, the defoaming and energy absorption unit also plays a certain role.
The inlet cyclone pre-degassing technology is adopted. In other words, centrifugal force is used for quick separation of gas and liquid at the entrance after the oil, gas and water mixture enters the three-phase separator, firstly removing more than 99% crude oil associated gas. After being treated, the gas will directly enter the two-stage mist catcher instead of the internal space of the equipment. Thus, the phase volume of the oil-water separation liquid is improved from the original 50 to above 95. This technology is quite effective for oil-gas separation of crude oil with high gas-oil ratio and easy bubbles.
2.2 The efficient coalescent packing and oblique plate settlement technology changes “crude oil dehydration” into “oil removal in the water”, making the two items to be quite different in speed, quality and effect, giving a radical solution to the problem of slow speed in crude oil dehydration.
Through a specific inlet and liquid arrangement unit, the efficient separator changes “crude oil dehydration” into “oil removal in the water”. As a continuous phase, water makes oil drops as the dispersion phase to be separated from the continuous phase. Under the specific temperature, the viscosity of water is less than the viscosity of crude oil. Therefore, the floating speed of oil drops in the water is much larger than the settling velocity of water drops in the oil. The efficiency of “oil removal in the water” is much higher than the efficiency of “crude oil dehydration”.
2.3The efficient three-phase separator achieves the purpose of intensified washing demulsification with active water by designing specific washing and liquid arrangement members. At the same time, the equal-proportion intelligent chemical adding scheme is used for chemical adding to the separator, thus improving the service effect of the demulsifier.
The oil-water mixture is subject to collision, friction, rolling, mixing and others in the washing chamber. On the one hand, it is subject to washing intensified demulsification, making most free water to be quickly separated from crude oil. On the other hand, the flow velocity of crude oil slows down on the oil-water interface along the separator section, creating favorable conditions for settlement of water drops with small grain size in crude oil.
2.4 Accurate gas, oil and water interface detection analysis and its control system: RF admittance interface detector and PLC automatic control system are adopted for the efficient three-phase separator. The gas, oil and water outlet indexes are detected by adjusting the “interface” value of gas, oil and water, so as to finally selecting the optimal gas, oil and water “interface” value under certain operating conditions as our experimental parameter. We set this “interface” parameter as the control value of the gas, oil and water interface. The gas, oil and water interface is stably operated through the adjustment to the control system.
2.5 With respect to the operation safety of efficient three-phase separator, the graded pressure safety management scheme is used for automatic processing of different pressure fluctuations in different sections. In other words, the small pressure-fluctuation sections will be eliminated and alarmed by the PLC control system through drain valve. The medium fluctuation sections will be processed by drainage via the safety valve, and alarmed by the PLC control system. The high fluctuation sections will be processed by the safety valve through oil ingress, and alarmed by the PLC control system. Such sectional processing can not only guarantee safe and stable operation of the separator under special circumstances but also achieve the cleaning and environmental protection objective of the efficient three-phase separator to the maximum extent. 3. Application Occasion and Benefit of Efficient Three-phase Separator
Application occasion: Three-phase (namely oil, gas and water) separation of land oil & gas field; three-phase separation of offshore platform; refining, chemical and coal chemical oil, gas and water separation.
Benefit analysis: The efficient three-phase separator is applied in the Combination Station. Its function can replace free water removal unit and electric water removal unit, which is the first pass for liquid treatment in the Station. Its safety is much higher than that of electric water removal unit. Besides, it also enjoys considerable economic benefits. According to the operation comparison of one combination station, RMB 670,000 can be saved a year (including main equipment investment matching technology investment annual gas cost annual power cost annual maintenance cost), including RMB 480,000 operating cost (including annual gas cost annual power cost annual maintenance cost). 4.Technical Parameters of Efficient Three-phase Separator
The efficient three-phase separator is a horizontal one.
Applicable crude oil density: ≤930kg/m3.
Spec.: diameter 4m, length: 22m, weight: 54t.
Treatment capacity: liquid 3,000m3/d.
Wastewater index: oil content of outlet wastewater: ≤300mg/l.
Outlet gas index: liquid content of gas: ≤0.05g/Nm³.
Water content index: water content of crude oil: ≤1%.
5. Selection of Efficient Three-phase Separator
Application of the above technologies highlights the adaption of the efficient three-phase separator. It is of high dehydration quality. After being treated by this device, water-containing crude oil can reach the design indexes. As judged based on the present field application of the separator, it has the following advantages in terms of treatment of oil, gas and water mixture: good treatment effect, stable operating index, low energy consumption, simple operation and convenient management.
Note: For the selection of efficient three-phase separator, it needs to formulate specific parameters according to the production data (e.g. quantity of crude oil, crude oil properties, water content, gas-oil ratio and dehydration temperature) and the customer’s index requirements. It is of great importance for initial basic data collection. Therefore, it needs to make a survey on the customer´s actual condition and demands while manufacturing the efficient three-phase separator, so as to manufacture the separator in compliance with the customer requirements.
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