Theoretical And Experimental Study On The Critical Deposition Velocity Of Hydrate Particle In Gas Pipeline

Deep-sea oil and gas pipelines are prone to hydrate blockage due to long-term operation under the conditions of low temperature and high pressure in the deep sea,resulting in economic losses and safety hazards.At present,hydrate avoidance and hydrate management are the mainstream deep water oil and gas pipeline flow assurance technologies.The former requires a large amount of consumption of inhibitors which increase the operating cost of the pipeline,so the latter has an absolute advantage in economy and has gradually become a hot topic in the industry.The hydrate management method allows hydrates to form in the pipeline without deposition.Related studies have shown that there is a critical flow velocity in the fluid inside the pipeline-above which the hydrate does not plug in the pipeline-the critical flow velocity in the field of fluid-solid transport is defined as the critical deposition velocity,which is the critical flow rate at which the particles in the pipe do not deposition.Therefore,studying the limit precipitation rate of hydrates in pipelines can guide the safety of fluid flow in oil and gas pipelines.The theoretical model and experimental measurement were used to study the critical deposition velocity of hydrate.Based on the analysis of the balance of the static forces,a theoretical model of the critical deposition velocity is obtained.The model mainly considers the effects of drag force,lift force,turbulence force,net gravity,adhesion and friction on the hydrate particles.Based on the criteria corresponding to the three removal mechanisms(sliding,rolling and floating),the corresponding critical deposition velocity equation is obtained and then nondimensionalized.Analysis of the main parameters of the equation found that the particle size,the wall roughness of the pipe and the moisture in the pipe are important parameters affecting the critical deposition velocity.With the increase of particle size,the critical deposition velocity-particle size curve can be divided into two parts: the adhesion dominant zone and the gravity dominant zone.The critical deposition velocity in the dominant zone of adhesion decreases with the increase of particle size;in the gravity dominant zone,the critical deposition velocity increases as the particle size increases.The critical deposition velocity increases first and then keeps constant with the increase of the friction coefficient between the wall and the particles,and the removal mode of the particles also changes from sliding to rolling.The presence of a small amount of free water in the pipeline can greatly increase the critical deposition velocity,which is consistent with the view that the hydrate adhesion in the gas phase dominated system is mainly liquid bridge force.An experimental system for the critical deposition velocity of particles in a single-pass gas transport pipeline was established.The system was used to measure the critical deposition velocity of glass particles under the action of liquid-free bridge,glass particles under liquid bridge and ice particles under liquid bridge.It was found that the data points of glass particles appeared dispersed under the action of no liquid bridge,which was consistent with the literature results.Different from the statistical processing methods in the literature,this thesis improved the experiment by increasing the controllable factors and reducing the effects of the uncontrollable random factors,and improved the repeatability of the experiment.The initial model calculation shows that the critical deposition velocity of glass particles and ice particles under the action of liquid bridge is quite different from the experimental results.Therefore,the initial model is improved on the basis of experiments.Based on the analysis of the liquid bridge morphology,the lateral capillary force is introduced to replace the capillary force in the initial model.The improved model results are in good agreement with the experimental results,indicating the rationality of the model correction.