Research For Supersonic Experiment Device Of Separating Hydrate And Heavy Hydrocarbons At Low Temperature

In recent years,China's air pollution has seriously affected people's daily life,so the natural gas,as a clean energy,which demand is increasing.At present a large area of oil field has been investigated in the sea,however natural gas found contain a large amount of water vapor and heavy hydrocarbons.These substances in the natural gas transport process will form gas hydrate plugging pipe to increase maintenance cost of transportation.At the same time,the acid in natural gas is dissolved in water vapor to corrode pipeline,and to some extent,it will increase the cost of natural gas transportation.A large number of heavy hydrocarbons affect the combustion heat of natural gas,which will have a large part of the impact of natural gas utilization ratio,so it should be separated from natural gas.At present,the commonly used methods in engineering applications include J-T valve,solvent absorption method,solid adsorption method,membrane separation technology.Some of these methods will cause pollution to natural gas,and some will increase the cost of exploitation of natural gas.Supersonic separation technology is a kind of advanced technology which uses gas dynamics and thermodynamics.The gas will form a supersonic flow field with low temperature and low pressure through the tube of contraction and expansion(Laval nozzle).When the gas temperature is lower than the dew point temperature of water and the components of heavy hydrocarbon,it will condense into liquid water droplets.The centrifugal acceleration is used to separate the droplets after the cyclone generating device.This method makes use of the thermodynamic properties of natural gas,which can save energy and protect environment.At the same time,the operation cost is lower.The experimental study and numerical simulation of the supersonic cryogenic separation device are carried out in this paper.Because the small scale experiment is small in the laboratory,considering the safety and economic factors,the group used wet N2 gas instead of natural gas in the actual project.Supersonic cryogenic separation devices was designed under the condition of nitrogen flow 2000 Nm3/h,which mainly includes inlet cyclone and Laval nozzle.The accuracy of numerical simulation is verified by the pressure value of each pressure point in the experimental device.The experiment mainly includes the analysis of the efficiency to the supersonic cryogenic separation device under different operation parameters and the size and structure of different nozzle.Its efficiency is mainly quantified through dew point temperature difference between the import and export.The results show that:(1)The experimental results are compared with the numerical simulation results,the error is small.The numerical simulation results can be used to predict the flow field inside the device.(2)Under the design condition of entrance pressure 13.2MPa,outlet pressure 9.25MPa(pressure loss ratio is 30%)and entrance temperature28?,the temperature difference between the import and export of device is 6.3?,and the difference of dew point temperature is 7?.When the loss ratio of inlet pressure is 54%,the maximum difference of dew point temperature is 15? in experimental device.(3)The experimental results show that,with the increase of the pressure loss ratio,the difference of dew point temperature between the import and export of device increases continuously.The total temperature of the import has little influence on the flow field inside the device.(4)The results of simulation show that the position of the shock wave moves to the throat,which is not conducive to the condensation of water vapor under the condition of constanted inlet pressure and the increasd outlet pressure.With the temperature difference between inlet and outlet increased,the maximum Maher number decreases.When inlet diameter and throat diameter is fixed,exit diameter of the nozzle has a great influence on the flow field.With the outlet diameter increased,the position of the shock wave moves to the throat,but the temperature of gas can reach a lower temperature.However the radial size of the diffuser has a little influence on the flow field of nozzle coMPared with outlet diameter.