| Natural gas is a high-efficient,high-quality,clean low-carbon and green energy,which can form a benign complementarity with the development of renewable energy.However,the existence of water has a serious impact on the process of natural gas exploitation and the gathering and transportation.The conventional methods for natural gas dehydration,such as solid adsorption,solvent absorption and membrane separation,are not only the relatively high investment,but also the complex process and equipment.At this point,supersonic separation technology is a new type of gas-liquid separation technology with high efficiency,energy saving,environmental protection and low cost,which has attracted scholarly attention home and abroad.The concept of the supersonic separator was developed half a century ago and has been refined over the following decades.The supersonic separator uses Laval nozzle to convert the pressure energy into kinetic energy when the fluid flows through the flow passage with variable section and is accelerated to supersonic speed.At the same time,heat exchange takes place and the temperature of fluid drops rapidly.Then the purpose of low-temperature separation for gas-liquid is achieved Through the mechanical cyclone.Supersonic separator equipment has the advantages of compact structure,small size,easy processing,low cost,no rotating parts,free of maintenance,and can be opened and shut down quickly.The technology has been successfully used in natural gas dehydration and condensate recovery.Although the technology has been applied in China,it has been stopped due to the problems of gas source fluctuation.In addition,the current researches on supersonic separator also face the following problems:?The influence of swirling generator and drainage structure on flow field and separation efficiency has been rarely studied.?The influence of swirler and cone on the flow field was not considered in the study of nozzle profile.?The existing supersonic separators have low separation efficiency,the generation and position of positive shock wave is not easy to control,and the flow field is easy to produce back-mixing,so the devices cannot be started automatically.?Two-dimensional numerical simulation can not accurately reflect the state of actual flow field in the nozzle.?The drain chamber of supersonic separator can carry part of gas,which need be recovered and treated,as it discharges the liquid.The process increases the load and complexity of the device.?The research on the motion law of strong swirling flow and the interaction between shock wave and boundary layer in supersonic separator is insufficient.In this paper,on the basis of researches on the structure and flow field characteristics of the supersonic separator,the structure of the supersonic device and the method to improve the separation performance are explored.The structure system of the supersonic separator with guide cone and front swirler is established.A new type of drainage structure,a new supersonic separator and method for self-ejecting reflux are proposed.The mathematical model of supersonic and rotational flow in a supersonic separator,three dimensional numerical model and discrete phase model are established to describe the internal flow of rotating supersonic gas.An effective strategy to improve the performance of device by using supersonic separator with reflux cascade drainage is explored.The experimental platform is established to study the separation performance of device and verify the effectiveness of the strategy.The main research work,results and conclusions are as follows:(1)A profile structure system for the supersonic separator with guide cone is established,which gives a variety of profile structures in detail and solves the problem that the guide cone and other components do not match the traditional structure.The flow field in the device was analyzed by three-dimensional numerical model and the optimum configuration was determined as following:stable length of 0.5Din,linear surface for convergent section,throat transition with arc and straight,equal slope method for divergent section and diffuser with two stage method.(2)The structure system of axial flow swirler is established.Four different types of guide vane for axial-flow swirler are presented by different design methods of profile.The results show that the flow through each swirler can produce strong cyclone strength,which solves the problem of the lack of design method.The flow fields in the nozzles with circular guide vane and power guide vane are more uniform.In addition,the attenuation of centrifugal acceleration for the circular curved guide blade is the slowest,and the centrifugal acceleration of circular curved guide blade at the nozzle outlet is the largest,which is more conducive to the separation of the condensate.And the circular curved guide blade is more smooth and convenient for design and processing.(3)A mathematical model of supersonic flow and rotational flow in a supersonic separator is established.The analysis of flow field in supersonic separator shows that the temperature,pressure and density of supersonic fluid increase after shock wave,the total temperature of the fluid remains constant and the total pressure drops.The error between the mathematical model and the 3d numerical model is within 9%.Because of the viscous loss of the fluid in the supersonic nozzle,the existence of the diversion cone and the influence of the structure surface with violent shrinkage,the motion of the rotating fluid in the convergent section of the nozzle and throat does not have the characteristics of combined eddies.Furthermore,on the basis of mathematical model,the program for calculation and profile design of supersonic separator suitable for this research was developed,which improved the efficiency of design,calculation and model selection of supersonic separator.(4)A new type of supersonic separator with self-injection and circulating reflux is presented.As studies show that the design utilizes the low pressure near the throat of Laval nozzle by the swirl and supersonic velocity,which introduces fluid from the discharge chamber to the throat and diverging part.The guide cone can be moved back and forth along the axis,which can change the cross-sectional area of throat.Moreover,the device has different opening forms,adjustable diameter and insertion depth of the reflux pipe,which can change the flow field of the fluid in the nozzle,such as swirl strength,strength and position of shock wave,refrigeration temperature etc,so as to improve the adaptability and application range of the device.In addition,based on the one-dimensional isentropic flow theory with variable cross-section in the nozzle and the law of fluid flow,the interaction between shock waves and the boundary layer was explored,and the improvement strategy of the cyclic supersonic separator was proposed.(5)The influence of structure and operating parameters on the performance of the circulating supersonic separator was studied by three dimensional numerical simulation.The researches show that the device with axial reflux outlet has stronger anti-backmixing ability and refrigeration performance.Although the swirling strength in device with tangential reflux outlet is the largest and the distribution is more uniform,the equipment has the disadvantages of the rapid attenuation of centrifugal acceleration and the the shortcoming of processing difficulties,which is not conducive to application.With the increase of the pressure ratio,the shock wave moves towards the nozzle outlet,the characteristic of fluid expansion is improved and the pressure loss increases gradually.At the same time,the reflux propulsion of device with the axial reflux outlet decreases first and then increases,and the reflux propulsion of device with tangential reflux outlet increases first and then decreases.The cooling temperature in the nozzle increases as the temperature increases.The optimal reflux structure determined in this study is Dreflow=20mm,Dinsert=7mm,LDepth=30mm and ?=55°.(6)A three dimensional numerical model with droplet discrete phase coupling for predicting the separation efficiency of device was established.Experimental data were used to verify the model.The prediction and analysis of particle separation efficiency and trajectory in the nozzle show that the established prediction model is in good agreement with the experimental data.The separation efficiency of liquid particles increases with the increase of droplet diameter.Particle diameter of 2?m?4?m is a sensitive area for particle separation.There are three kinds of moving trajectories of particles in the device:droplets attached to the wall,droplets directly entering the drainage cavity and droplets carried out by the flow.Meanwhile the reflux pipe eliminates the eddy current in the traditional supersonic separator to a great extent,which is beneficial to the separation and reduction of pressure drop.(7)An effective method is put forward,which can improve the separation efficiency and prevent shock wave interaction with boundary layer.This study indicates that the advantage of the cylindrical drainage structure is that it has multiple openings and relatively large drainage area.When the shock wave is located in the gradually expanding section of the nozzle,the high pressure generated at this time will make more fluid enter the opening of the ring,which is equivalent to increasing the flow capacity at the "second throat".At this time,the shock wave is weakened and the total pressure loss is reduced.This method can make all fluid in the nozzle supersonic and enhance the stability of flow field and separation performance in the nozzle.(8)The influence of operational and structural parameters on the separation performance of the supersonic separator were studied experimentally.It can be seen that the reflow channel can effectively improve the flow field and the separation performance of the device.The inlet temperature has little effect on the performance of the device.With the increase of pressure,the separation performance of the device first increases and then decreases,with a maximum value at Rnp=1.4.As the exit angle of the swirler increases,the separation performance of the device increases first and then decreases,reaching the highest at ?=55°.The removal rate and dew point drop of the device reach the maximum at LDepth=30mm and the minimum at LDepth=20mm.The removal rate and dew point drop of the device have maximum and minimum values as the diameter of the reflux pipe increases.When Dinsert=7mm,the separation performance of the device increased significantly,and the device has the best separation performance.When Dreflow=28mm,the removal rate and dew point drop of the device are relatively significantly reduced.The separation efficiency of the device is the best when Dreflow=24mm.(9)Experimental studies on the separation performance of the device with conical and cylindrical drainage structures were carried out.The researches show that the removal rate and dew point drop of the flush drainage device with reflow channel can be up to 47.72%and 17.41k when LDepth=0mm,which is 12.02%and 5.42k higher than those of flush drainage device without reflow channel,and is 2.04 times and 2.23 times of the flush drainage device with reflow channel when LDepth=30mm,respectively.The relation of separation performance of devices with different cylindrical drainage is circular drainage without reflow channel>circular drainage with reflow channel>oblique drainage with reflow channel>oblique drainage without reflow channel. |
PDF Full Text Request