Objective Supersonic separation is a new gas purification and fuel gas processing technology based on contraction-expansion nozzle.The cyclone in the post-swirl supersonic separator is usually set in front of the diffuser section,which is easy to induce the positive shock wave and destroy the low temperature environment inside the separator.Moreover,the shock wave is difficult to control.Therefore,this study intends to reduce the impact of shock waves by optimizing the structure.Methods Firstly,based on the principles of thermodynamics and aerodynamics,a shock wave control theory for a rear-swirl supersonic separator was proposed.Secondly,according to the theory,a trans-swirl structure which could control shock waves was designed,and a universal design formula for the structure was established.Thirdly,through numerical simulation,the effects of three important structural parameters on the shock waves control were analyzed,namely,the dip angle of the trans-swirl structure,the length of the gradually expansion section and the twist angle of the cyclone blade.Results The separator had the best performance when the dip angle of the trans-swirl structure was set to 3.3°,the length of the gradual expansion section was set to 107 mm,and the blade torsion angle of the cyclone was set to 120°.Conclusions Compared with the traditional cyclone post-separator,the addition of the trans-swirl structure can ensure that the fluid flow area continues to increase in the gradual expansion section,thereby achieving effective control of shock waves and improving the condensation and separation efficiency.
Objective The residual catalyst during the preparation of helical carbon nanofibers(HCNFs)can affect its intrinsic properties.Acid washing is often used to remove the catalyst in helical carbon nanofibers,but it can destroy the structure of the fiber and increase the cost of use.Helical carbon nanofibers were prepared by using water-soluble salt as catalyst,and the catalyst was removed by washing to obtain high-purity helical carbon nanofibers.Methods Helical carbon nanofibers were prepared by chemical vapor deposition using potassium carbonate as catalyst and acetylene as carbon source.The potassium carbonate catalyst was removed by simple water washing,and the effect of preparation temperature on the morphology of helical carbon nanofibers was investigated.The microstructure and elemental composition of the helical carbon nanofibers were characterized by field emission scanning electron microscopy,transmission electron microscopy and energy dispersive spectroscopy.The crystal structure and surface functional groups of the helical carbon nanofibers were characterized by X-ray diffraction,Raman spectroscopy and Fourier transform infrared spectroscopy.Results The helical carbon nanofibers prepared at 700℃have a diameter of about 60 nm,a helical structure and a uniform morphology.The carbon atoms of HCNFs are arranged in a short-range order,mainly composed of C-H and C=C functional groups.The potassium carbonate catalyst has a rhombic symmetrical structure in the fiber,resulting in a chiral symmetrical growth of the fiber on both sides of the catalyst.Conclusions Helical carbon nanofibers with uniform morphology were prepared by chemical vapor deposition.High purity helical carbon nanofibers can be obtained by washing off the surface catalyst.
Objective The effect of mechanical properties of hydrate decomposition on reservoir stability was studied by multi-stage depressurization of gas hydrate under the action of different types of decomposition promoters.Methods The effect evaluation and law analysis of rock mechanics stability of hydrate sediment reservoir are carried out by using multiple factors such as different effective confining pressures,different decomposition agents and their concentrations,soaking time,and through multi-level depressurization decomposition.Results With the pressure drops and decomposition,hydrate saturation,shear strength and elastic modulus decrease gradually,and methane hydrate sediments show brittle failure.Conclusions The higher the concentration of decomposition agent is,the greater the influence on hydrate mechanics is caused.The higher the injection concentration is,the longer the soak time is,the lower the hydrate strength is,and the more obvious the effect of the decomposition agent on reducing the hydrate strength is.Alcohol decomposition agent(ethylene glycol)is easier to weaken the strength of hydrate samples and to reduce reservoir stability than salt decomposition agent(CaCl2)during hydrate production.
Objective The aim is to solve the problem that the contamination type of the completion fluid can not be effectively identified after being contained by brine and residual acid during the drilling of the target layer.Methods The contamination of brine and residual acid with different mass fractions of the completion fluid was measured,and the labels of the data samples with different contamination degrees were revised by K-means clustering algorithm.Different BP neural network models were trained according to the difficulty of obtaining data sample features and the number of hidden layers,and the classification accuracy of the models was tested by leave-one-out cross validation method.Results It is found that the more features the data samples possess,the higher classification accuracy of the trained BP neural network could be achieved,while more hidden layers would lower the classification accuracy.The BP neural network model with one hidden layer was subsequently established with data samples that contain four kinds of features including"rheology+aging+filtration loss+well name".The average classification accuracy rate reached as high as 93.18%.Conclusions The BP neural network model trained by rheology and filtration loss features can be quickly deployed in the oil-testing sites to solve the problem of failing to identify the type of completion fluid contamination due to the lack of special equipment in the field.
Objective The aim is to prepare reformate oil dechlorination agent with high chlorine capacity and realize industry application.Methods The dechlorination agent for reformate oil was prepared by using pseudo-boehmite as the carrier,loading two-component activator,screening the pore-forming components,adjusting the pore structure and optimizing the reasonable molding and baking process.The physico-chemical properties of the dechlorination agent were characterized by using BET,XRF,SEM,and the dechlorination agent performance was evaluated by using a 20 mL small test device.Results At a reaction temperature of 50℃,a volumetric space velocityof 3 000 h-1,and a chlorine mass fraction of 60 000 mg/kg in the reaction gas,the chlorine capacity of self-made dechlorination agent was 18.4%.The dechlorination agent product was applied to the reforming unit of CNOOC Ningbo Daxie Petrochemical Ltd.,the differential pressure before and after dechlorination tank was less than 50 kPa,and the chlorine mass fraction at the outlet of the dechlorination tank dropped to below 0.5 mg/kg.Conclusions The influences of adding different types and contents of active compounds and pore-forming agents,as well as the baking process parameters on the properties of dechlorination agent was clarified,which could provide reference for the preparation and optimization of similar dechlorination agents.
