| The supersonic cyclone separation technology has been successfully applied in dehydration of natural gas and heavy hydrocarbon removal of natural gas.However,there are still few studies on natural gas deacidification,especially hydrogen sulfide.Based on this,this paper proposes to apply supersonic cyclone separation technology to the field of hydrogen sulfide removal of natural gas.Based on the nucleation and field of liquid droplets in supersonic condensation process of gas,the supersonic condensation characteristics of hydrogen sulfide-containing natural gas were studied by combining theoretical research,numerical simulation and experimental test,taking methane gas with high hydrogen sulfide content(methane-hydrogen sulfide two-component mixture)as the research object.The phase characteristics and condensation flow law of methane-hydrogen sulfide gas in Laval nozzle were calculated by numerical simulation.The effects of different design parameters(inlet temperature,inlet pressure,hydrogen sulfide composition)and Laval nozzle structure on the supersonic condensation process of hydrogen sulfide were analyzed through the design under different working conditions.On this basis,the experimental platform of supersonic condensation flow measurement is built,and the experimental study of gas condensation flow is carried out in dry air-steam medium.The reliability of the mathematical model and calculation method used in numerical simulation is verified through the comparison and analysis of the experimental results and numerical simulation results.Finally,the effects of different inlet parameters and nozzle structures on gas condensation flow are analyzed.(1)The structure of Laval nozzle was designed.The flow process of methane-hydrogen sulfide gas in the nozzle was simulated by FLUENT software.The distribution of flow parameters under supersonic flow conditions was analyzed.The phase characteristics of methane-hydrogen sulfide mixed gas in Laval nozzle were simulated by exploring the influencing factors such as inlet operating conditions,component content and outlet back pressure.The phase distribution characteristics of methane-hydrogen sulfide mixture in laval nozzle were summarized.The results show that the gas mixture of methane and hydrogen sulfide changes from subsonic flow to supersonic flow at the throat of Laval nozzle.In the whole Laval nozzle,the temperature and pressure of mixed gas decrease.When the temperature drops to the critical condensation temperature of hydrogen sulfide gas,the condensation condition will occur.Reducing the inlet pressure and temperature is beneficial to the condensation of hydrogen sulfide gas.However,when the inlet temperature is lower than a certain value,hydrogen sulfide at the entrance of Laval nozzle has become liquid,and further lowering the temperature will result in a waste of cold energy;with the increase of the inlet pressure,hydrogen sulfide gas in Laval nozzle is more likely to condense;the higher the content of hydrogen sulfide,the higher the temperature required for condensation(that is,the easier the conditions for liquefaction to be achieved),and the larger the condensation area.The more easily hydrogen sulfide gas can be condensed and liquefied;with the increasing back pressure(pressure ratio)at the outlet,the shock position moves forward in the Laval nozzle,and the pressure and temperature fluctuations in the Laval nozzle become more intense,which destroys the refrigeration environment needed for condensation and is not conducive to the condensation of hydrogen sulfide gas..(2)Establish a numerical model and calculation method for describing and calculating spontaneous condensation of hydrogen sulfide gas with methane as carrier gas.Construct the governing equations of gas-phase flow and liquid-phase flow based on Euler-Euler fluid model.Combine the basic theory and empirical formula of nucleation and droplet growth during condensation of hydrogen sulfide,the mathematical model of supersonic condensation and flow of methane-hydrogen sulfide gas was established.For the problems that can not be solved in FLUENT software,user-defined scalar and user-defined function programs are written in C language,and the numerical simulation software is redeveloped.(3)Based on the established mathematical model and calculation method,the spontaneous condensation process of hydrogen sulfide gas in Laval nozzle was studied,and the distribution law of flow and condensation parameters of hydrogen sulfide gas under supersonic flow conditions was obtained.On this basis,different design parameters(inlet temperature,inlet pressure,inlet hydrogen sulfide composition)and the influence of nozzle structure on supersonic condensation of hydrogen sulfide.The results show that as the inlet temperature decreases and the inlet pressure increases,the nucleation rate moves forward,the nucleation area narrows,the number density of droplets decreases,the radius and mass fraction of droplets increase,and the molar fraction of hydrogen sulfide in the gas phase at the outlet of Laval nozzle decreases.When the molar fraction of hydrogen sulfide at the inlet is less than 0.05,the nucleation rate is low and the nucleation position is close to the outlet of nozzle,and the droplets grow.The long process is short,and very few hydrogen sulfide molecules condense out of the gas components.The outlet droplet radius of Laval nozzle is small and the liquid mass fraction is almost zero.Increasing the expansion ratio of Laval nozzle will prolong the droplet growth stage of hydrogen sulfide gas and promote the condensation of hydrogen sulfide gas in Laval nozzle.Under the given process conditions,the designed Laval nozzle still can not meet the requirements of pipeline transportation.The supersonic cyclone separator can be used to remove a large amount of hydrogen sulfide from highly acidic gases,and amine absorption process is needed to achieve the requirements of gas treatment.(4)In the experiment,air-gaseous water was used as medium,and the nozzles with different expansion angles were designed and manufactured by using the existing supersonic condensation flow experimental system in the laboratory.The experimental study and measurement of gas condensation flow in nozzles under different conditions were carried out.The reliability of the numerical simulation was verified by comparing the experimental data with the simulation data.On this basis,the effects of the expansion angle of Laval nozzle and the experimental conditions at the entrance of Laval nozzle on the supersonic condensation and flow characteristics of gas were studied by means of experiments.The results show that,generally speaking,the errors caused by the experimental methods and measurements,as well as some assumptions adopted in the simulation process,lead to some deviations between the experimental results and the simulation results of droplet number prediction and droplet radius,and the deviation range is at the same level as the current domestic and foreign research results.By comparing the measured and simulated results of the initial condensation point,the measured initial condensation point moves backward compared with the predicted results.The radius of droplets in Laval nozzle increases with the decrease of the inlet pressure,and the number of droplets at the outlet increases with the decrease of the inlet pressure.This is because the pressure drop of the gas flow through the nozzle increases with the increase of the inlet pressure,and the supercooling degree of the gas increases with the increase of the inlet pressure,so the faster the droplet growth rate is,the larger the final droplet radius is due to the faster the droplet growth rate is;Laval nozzle structure also has obvious influence on gas condensation.With the increase of nozzle expansion angle,the number of droplets increases gradually,but the radius of droplets decreases. |
PDF Full Text Request