Theoretical & Experimental Study Onto The Voraxial-Separator

In order to solve the conflicts between ever-growing produced water and limited space on platform for offshore oilfields, there is a great deal of interest in the study of inline and compact separation technology with high efficiency. The Voraxial Separator (VAS), which integrates centrifugal force and axial lift force within a tubular apparatus, can separate large volumes of oily water efficiently within a tubular compact structure. Therefore, the inline separation is truly achieved. The successful application of VAS must prove an important means for solving the problem of water treatment in offshore oilfields. However, there is a lack of systematic research into the working mechanism and validation of the design theory of the separation technology.In this thesis, the key factors influencing the separation efficiency of the VAS were analyzed by theory of vortex dynamics and a design theory model for this new separation technology was established. The structure parameters of gradient helical blade and static cone shaped barrel, which are the key parts of the VAS, were analyzed with the established theoretical model, and the BIPTVAS-I pilot was designed. Then the geometer model was built based on the pilot. Different geometer models of VAS were quantitative analyzed by CFD soft package Ansys Fluent 14.0, when the structure parameters of the gradient helical blade and static cone shaped barrel varied in certain range which were primarily confirmed by the design theory model.Taking the results of CFD numerical simulation as samples, the parameters of the gradient helical blade were analyzed by BP neural network, because there were many structure parameters with no obvious relationship between them. The results show that the optimum combination parameters of the gradient helical blade are that the length is 170mm, the height is 21.5mm and the outlet lead angle is 72°when the swirler rotary velocity is 2300rpm and the diameter of drum is 60mm. However, the results of CFD numerical simulation were analyzed directly by single factor analysis method to the structure parameters of the static cone shaped barrel as there were 2 parameters only. The results show that the outlet diameter of continuous phase is 40mm, the length of cone shaped barrel is 800mm. When the parameters of the gradient helical blade and static cone shaped barrel are given the optimum values, the separation efficiency of VAS can achieve up to 90% and the separation efficiency value gotten by CFD number simulation and BP predicted values are in good agreement, the maximum error is 8.67% only.The separation efficiency values at different operation parameters of VAS were analyzed by CFD number simulation. The results show that the flow ratio in central hollow region is the basis for adjusting the VAS operation parameters. When it is in the vicinity of zero, there good separation performance can be achieved. The distribution of pressure, axial velocity and tangential velocity in the cone shaped barrel were also analyzed by CFD numerical simulation. The results show that the pressure is distributed uniformly in radial direction, with lower pressure in barrel center and higher nears the wall. And yet the pressure does not change with the length of the barrel. The pressure in barrel center is also less than zero when the flow ratio in the central hollow region is less than zero. The tangential velocity distribution at the swirler end is in accordance with the pattern of Solid Body vortex. The tangential velocity remains the same in barrel center while there has a significant reduction near the barrel wall with eddy dissipation, and the tangential velocity distribution acts as a parabola near the wall when the cone angel is bigger than 08°. The initial axial velocity distribution in radial direction is similar to the distribution of pressure in the static cone shaped barrel, and the maximum value appears near the barrel wall. But the position of maximum axial velocity value approaches gradually in the barrel by the edge to the center with the distance from the swirler outlet.Comparing between the results of CFD simulation model and theoretical model, it can be seen that, they are in well agreement for tangential velocity at more than 73.56% region. The tangential velocity errors between two models occur in the region near the wall and the axial velocity errors between two models grow significantly with the increase of distance from the swirler outlet. In order to improve the theoretical model calculation precision, the estimating formulas of tangential velocity were got and the traditional axial velocity formulas were improved according to the results of CFD numerical simulation.The pilot BIPTVAS-I and prototype pilot BIPTVAS-II were designed based on theoretical and CFD numerical simulation analysis. And the visible experiment, separation performance experiment and three situ experiments were done used the two pilots. An asymmetric spiral flow in the static cone shaped barrel was observed in the visible experiments. It can be found though the experiments that the flow ratio in the central hollow region is the critical parameter. The result between the separation performance experiment and the CFD numerical simulation was agreement well, and the average error is only 15%. The result of the situ experiment in Zhongyuan oilfield and CFD number simulation is in good agreement too which average error is only 2.46%. Besides, the comprehensive analysis of the CFD number simulation, the BP neural network prediction, the laboratory experiments and the suit experiments, the results show that the physical parameters of oily water have a big impact on the separation efficiency of VAS. The main influence factors are density difference between the light phase and heavy phase, the diameter of the dispersed phase oil droplet. Summarizing the results in this paper, the VAS can be designed personalized according to the physical parameters of oily water. These research result lay a solid theoretical foundation for promoting the inline and compact separation technology for industrial application and provide a new solution to the bottlenecks hindering the further development of offshore oilfield in our country.