|Alternative Title||Research on influencing factors of oil droplets motion in axial swirling hydrocyclone|
|Place of Conferral||北京|
With the development of oil field exploration in China, the water holdup of produced fluid in oil field keeps increasing, some may even exceed 95%. The oil exists in the produced fluid in the form of droplets, which increases the treatment cost and difficulty of production. At present, the treatment of produced liquid in crude oil exploitation is mainly divided into pre-process and oily sewage treatment. If the process can be optimized in procedures above, the production cost can be reduced and the economic benefit can be improved.
The centrifugal separation is widely used in industry due to its advantages of high specific treatment efficiency and wide application range, including a variety of liquid-liquid hydrocyclones. According to flow direction of the feeding fluid, the hydrocyclone can be divided into two types: tangential inlet type and axial inlet type. The axial inlet type hydrocyclone has the advantages of large capacity, light weight and small volume, which are suitable for application in some special environments such as offshore platforms. In order to improve the separation performance and scope of application of axial induced hydrocyclone, in view of the key scientific problems in the separation process of hydrocyclone, such as the crushing, coalescence and particle migration of dispersed phase particles, systematic analysis coupling experiment and CFD were conducted .
In the experimental study, a circulating system was built to simulate the oil-water two-phase separation of the axial induced hydrocyclone. The pressure and the droplet size distribution at each key position of the hydrocyclone were measured by the pressure sensor and the Marvin on-line particle size measuring instrument. Then, according to the experimental conditions and test results, different mathematic models of CFD were compared with tested data. Finally, in the numerical simulation study, method coupling Eulerian model, RNG –k-ε model and Luo model was used for simulation of the oil droplet coalescence and fragmentation.
The results showed that the pressure drop of the axial inlet hydrocyclone upstream and downstream the start-up device is large, and the pressure drop is positively related to the liquid flow. In downstream of the swirl generation device, the tangential velocity in the hydrocyclone reached the maximum at a distance of 40 mm from the center of the pipeline, and the maximum tangential velocity is about 2.2 times of the mixed flow velocity. With the increase of flow rate, the coalescence efficiency of dispersed phase oil drops increases first and then decreases. According to the structural parameter applied in this work, the coalescence efficiency is the highest when the flow rate is 14~16m3/h, which is mainly because the increase of flow rate not only improves the centrifugal force, but also increases the shear force, which will cause the large oil drops to break toreduce the coalescence efficiency. Increasing the oil concentration in the incoming liquid can increase the probability of oil drop collision and make it easier to form large oil droplets. However, increasing the oil content will also make some oil droplets emulsified in the flow process and thus make it difficult for separation. Adding the demulsifier is beneficial to reduce the emulsification of oil droplets. The effect of the demulsification is affected by the flow rate. In the specific application, the demulsifier should be selected according to the flow rate and oil content. The increase of oil-water interfacial tension and oil-water phase density difference are beneficial to the improvement of oil drop collision efficiency and collision probability, and has a positive effect on the oil-water separation. Increasing the viscosity of the oil phase will reduce the collision efficiencysince the viscosity will weaken the centrifugal force. At the same time, increasing the particle size of the oil phase in the liquid can significantly increase the volume fraction of large oil droplets in the hydrocyclone, and improve the oil-water separation efficiency.
Furthermore, by changing the number of guide vanes and the diameter of cone section, the influence of the structural paramters of hydrocyclone start-up device on oil droplet coalescence was carried out. The study showed that when the number of guide vanes was 6, the oil droplet coalescence rate is the largest; when the diameter of the cone section of the hydrocyclone is 60 mm, the pressure drop, tangential velocity amplitude and the degree of oil drop coalescence are the optimal.
The above research results of the oil droplet behavior in the hydrocyclone can provide theoretical support for the industrial application and development of the axial swing hydrocyclone. At the same time, above investigations can effectively improve the efficiency of oil-water separation and sewage treatment in crude oil production, and realize economic production.
|顾成曦. 轴向启旋式旋流器内油滴运动影响因素研究[D]. 北京. 中国科学院大学,2020.|
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