Numerical Simulation of Multi-Phase Flow Distribution in Parallel Pipelines System of Oil Transfer Station

The mal-distribution of gas-oil-water multi-phase flow in parallel petroleum processing pipelines can directly affect the working condition of the separators. In this paper, the influence of different factors on the flow distribution and the characteristics of gas-oil-water distribution in parallel pipelines was investigated by three-dimensional CFD numerical simulation. Firstly, four different simulation models are established based on different arrangement types of parallel pipelines. The simulation results show that the distribution of gas-oil-water flow in the radial entry symmetrical two-stage pipe-laying simulation model was the most uniform among the four simulation models. Then, four radial entry symmetrical two-stage pipe-laying simulation models with different distance between branch pipes were establish. From the simulated results, it can be found that the distance has no effect on the distribution of gas-oil-water flow in each branch pipe, but great influence on distribution of flow rate in each branch pipe. Finally, the influence of the inlet flow characters on the flow distribution is investigated. It can be found that the “bias flow” phenomenon of the parallel pipelines decreasing with the increase of the inlet flow velocity, the gas content of inlet flow and the water content of inlet liquid.

Measurement of Environmental Stress Cracking Resistance of Polyethylene Pipe: A Review

Use of polyethylene (PE) for water and natural gas transportation has increased rapidly due to its good physical and mechanical properties, especially its excellent corrosion resistance property. However, when immersed in adverse environment and subjected to applied stress, PE will suffer from accelerated crack growth in a phenomenon known as environmental stress cracking (ESC). ESC occurs in a brittle manner without little pre-fracture deformation, thus can cause catastrophic, unexpected failure for PE pipe. A number of different test methods have been developed for characterizing ESC resistance (ESCR) of PE materials. Within this paper, a state-of-the-art review is given on the current ESCR characterization methods, including the working principle and limitations of each method.

A Three-Dimensional Coupled Finite Element Model for the Simulation of Stress Corrosion on Pipeline Steel

In this study, a three-dimensional finite element model was constructed to study the stress corrosion behavior of pipeline steel. Stress analysis and electrochemical calculation were incorporated into the model through multiphysics field coupling technique. Tensile property and electrochemical corrosion behavior of X70 pipeline steel were measured by experiments to formulate the model. The modeling results show that the corrosion is accelerated on the surface of corrosion defect where the stress tends to concentrate because of mechanoelectrochemical effect. The effect of elastic strain on corrosion enhancement is not obvious. The plastic deformation on defect bottom increases the corrosion rate significantly, especially for the conditions with high operating pressure or large defect depth. The corrosion current distribution indicated that the “self-acceleration effect” exists on corrosion defect. This effect makes the corrosion develop to depth and the shape of corrosion defects is more likely to cause stress concentration, and finally induces corrosion perforation or cracking. The two directions, i.e. axial and circumferential direction, have the different stress corrosion behaviors. The “self-acceleration effect” is more obvious on circumferential direction than that on axial direction, which can explain the phenomenon that there are mostly axial stress corrosion cracks on the pipeline in field.

Investigation on Corrosion Base Characteristics and Deep Dehydration Technology of Micro-Droplets in Oil Pipelines

Corrosion is an important cause of steel pipeline failure and oil leakage, especially local pitting corrosion in long distance crude oil pipelines. Deep dehydration is of great significance to pipeline anticorrosion, however, further experimental results show that it is very difficult to achieve deep dehydration by a single electric field. Recent studies have shown that the particle size change of dispersed phase for the emulsion with large droplets after electromagnetic synergistic treatment is more obvious than that of a single electric field. In this study, the effect of micro-droplets on corrosion of oil pipelines are revealed. The role of micro-droplets in the process of microbial corrosion and electrochemical corrosion in a strong or weak acid solution for oil pipelines was summarized. A structural model of on-line tubular electromagnetic synergistic intensification coalescing device was established. The size change of particle of the dispersed phase in emulsions was studied. Crude oil and water were used as experimental materials, and the particle size distribution of dispersed phase in emulsions was tested by the evaluation system. The results showed that mean radius, d10 and d50 of water droplets in emulsion treated by electromagnetic synergism are larger than those treated by a single electric field. Strengthening droplets coalescence by electromagnetic synergism is also effective on emulsions whose particle size of the dispersed phase is less than 100μm. The role of micro-droplets in pitting corrosion is summarized based on corrosion channels. In the process of microbial corrosion and electrochemical corrosion in strong or weak acid solution, the role of water is presented in two aspects like participating in the reaction and providing ion electron transmission media. Analogous to culture medium, micro water droplets can be called corrosion medium for pitting corrosion in long-distance crude oil pipelines. A structural model of on-line tubular electromagnetic synergistic intensification coalescing device was established, including an electric field generation device and a magnetic field excitation component with orthogonal distribution and synchronous synergy. And emulsions are treated by electric and magnetic fields while flowing through the medium channel. The particle size change of dispersed phase in emulsions with average particle size of dispersed phase less than 100μm was experimental studied. It is found that mean radius, d10 and d50 of water droplets in emulsion treated by electromagnetic synergism are larger than that by a single electric field. Therefore, electromagnetic synergism can further enhance the dehydration depth compared with a single electric field.

Numerical and Experimental Research of Oil Replacement Rule in Station Processing Facilities of Product Pipeline

In order to study the impact of blind pipes in the oil contamination of product oil stations, the paper first gave the summary, definition and classification for typical blind pipe, then use the commercial CFD software CFX to make numerical simulation and conduct related experiment. The oil replacement process achieved from numerical simulation was compared with the experiment. The results showed a high degree of agreement. Then the oil replacement rules of straight blind pipe, bend blind pipe and L-shaped blind pipe were carried on by CFX numerical simulation. The results showed that L-shaped blind pipe had the greatest influence on the oil quality and longest replaced time, followed by bend blind pipe, and straight blind pipe was the least. We do the numerical simulation to obtain oil replacement rate, contaminated oil concentration and rules of oil replacement under different blind pipe length, oil velocity, and the structure of blind pipes. The research can provide a basis for construction, process modification and equipment layout of product oil stations, and improve the operation efficiency and economic benefit of product pipeline.

The Comparison and Parameters Optimization for the Mixed Intermediate Fluid of Intermediate Fluid Vaporizer

In this paper, an establishment of heat transfer model is performed to study the effects of different types of mixed intermediate fluid on the vaporizer performance. It is found that compared with pure propane, mixed ethane-propane working fluid can bring about a reduction of 10% ∼ 25% for the heat exchange area of intermediate fluid vaporizer IFV. In addition, using mixed butane-propane working medium could stabilize the saturated pressure of intermediate fluid at a relatively low level of 0.2 MPa, while the saturated pressure of pure propane ranges from 0.33 MPa to 0.65 MPa. Thereby, the former one is more reliable than the latter one in an aspect of safe operation. Moreover, after an investigation and selection, the results show that the saturated pressure of intermediate fluid varying from 0.3 MPa to 0.6 MPa and the amount of LNG overloaded over than 130% is beneficial for the improvement of comprehensive heat transfer performance of IFV.

Research on Closed-Loop Safety Production System of Hot Oil Pipeline Based on Big Data Mining

The process of long-distance hot oil pipeline is complicated, and its safety and optimization are contradictory. In actual production and operation, the theoretical calculation model of oil temperature along the pipeline has some problems, such as large error and complex application. This research relies on actual production data and uses big data mining algorithms such as BP neural network, ARMA, seq2seq to establish oil temperature prediction model. The prediction result is less than 0.5 C, which solves the problem of accurate prediction of dynamic oil temperature during pipeline operation. Combined with pigging, the friction prediction model of standard pipeline section is established by BP neural network, and then the economic pigging period of 80 days is given; and after the friction database is established, the historical friction data are analyzed by using the Gauss formula, and 95% of the friction is set as the threshold data to effectively monitor the variation of the friction due to the long period of waxing in pipelines. The closed loop operation system of hot oil pipeline safety and optimization was formed to guide the daily process adjustment and production arrangement of pipeline with energy saving up to 92.4%. The prediction model and research results based on production big data have good adaptability and generalization, which lays a foundation for future intelligent control of pipelines.

Characterization of a Water-in-Waxy Crude Oil Emulsion by its Steady Apparent Viscosity

The rheological properties of water-in-waxy crude oil emulsion depend highly on its forming conditions. Among these, the steady apparent viscosity is capable of characterizing its degree of emulsification. Adopting waxy crude oil in the field, we examine the influence of the water cut, the stirring speed, and the stirring time on the steady apparent viscosity of the emulsions formed under various conditions in this study. A model based on the viscous flow entropy generated in emulsion preparation is applied to correlate the steady apparent viscosity with the key parameters. A regression model is constructed for the dependence of the steady apparent viscosity on the viscous flow entropy, the shear rate, the rheological parameters of blank crude oil, and the wax deposition volume.

CFD Analysis of Melting Process in Pipelines for Wax Removal by Hot Water

This paper focuses on the numerical study of the melting process of the wax when using the “stuffy pipeline” operation to remove the wax. Transient two dimensional heat transfer analysis was performed by using the enthalpy-porosity and Volume of Fluid (VOF) methods in ANSYS FLUENT. This study aimed at revealing the phase change heat transfer characteristics of wax melting process. The effects of water temperature, the thickness of the wax layer and wax layer composition on the melting process were investigated. The results show that when the “stuffy pipeline” operation is adopted, the operation time should be controlled wisely, the effect of wax removal does not increase over time. Moreover, the thickness of the wax layer is smaller, and the effect of wax removal is greatly reduced. The composition of wax layer has a significant influence on the melting process. When the wax is distributed in a single or double layer, the liquid contours of wax varies greatly.

The Role of Emulsified Water in the Wax Deposition Path of a Waxy Crude Oil Multiphase Transportation Pipeline

Although the problem of wax deposition in multiphase transportation pipelines have been addressed and some related wax deposition models have been developed in recent years, the complex wax deposition paths derived from the potential variety of flow regimes in multiphase flow have not been well understood. This study presented a method for characterizing wax crystals aggregation behavior and developed a model for describing wax deposition path in oil/water two-phase flows. The impact of the emulsified water droplets on wax crystals aggregation in shearing flows was quantified using polarized light microscopy and image analysis method. The role of the emulsified water droplets in the wax deposition path reaching the upper side and lower side of pipeline wall was discussed by solving the developed model which involves the possible inclination angle of multiphase transportation pipeline. The availability of the mechanistic model was validated by the data and knowledge in the existing literature. The results indicated that wax crystals morphologies and structures tended to be regular with the enhancement of shearing effect, and their aggregation behavior were restrained. The circular degree and particle size of wax crystals showed a characteristic that it firstly increased and then decreased with the accumulation of emulsified water droplets in shearing flow, and this transition appeared to the phase inversion point of the oil/water two-phase. The velocity for wax crystals depositing to pipeline wall decreased and the time for wax crystals depositing to pipeline wall extended with the existence of emulsified water droplets. The wax deposition path became more complex in multiphase transportation, and such effect became remarkable when the dispersity of oil/water two-phase enhanced. Accordingly, the intractable wax deposition of waxy crude oil in cold environment transportation would be mitigated to some extent. This study contributes to comprehending the distinction of wax deposition mechanism in single-phase and multiphase transportation of waxy crude oil, and the proposed method and model are valuable for further predicting wax deposition in waxy crude oil emulsions pipelines. The findings in this study also point out an approach to conducting cost-effective flow assurance operations in crude oil production and transportation.