Study On The Characteristcs Of Salt-out Flow Within Wet-gas Centrifugal Compressor

Wet-gas boosting technology is a conventional process for natural gas gathering a nd transportation under low-pressure and high-moisture enviroment.It is helpful to red uce the load of triethylene glycol dehydration having considerable economic benefit.H owever,the presence of mineralized water flowing with bulk gas makes the problem o f salt-deposition extremely serious within the centrifugal compressor,which has a badl y impact on the stability and safety of normal production.At present,researches on t he salt-depisition problem within centrifugal compressor during wet compression in the process of natural-gas gathering and transportation are still quite lacking.Therefore,it i s of cgreat practical significance to carry out relateded research.The phenomenon of salt-deposition within centrifugal impeller boosting wet-gas ca n be classified as the problem of multi-droplet gasification under complex turbulence e nvironment.it is very difficult to carry out the relevant experimental study by the rest riction of experimental cost and the existing measuring methods.In this paper,the Ec kardt centrifugal impeller designed by the German Aerospace Center(DLR)is used as the research object.Numerical simulation and theoretical analysis are adopted to analy ze the salt-deposition mechanism from the point of view of the behavior(motion,gasifi cation,shed and forming water-film or splashing while crushing on a wall)of droplets in the channel of the ratating eckardt impeller.Eckardt impeller is a radial centrifugal impeller and its structure data are public.Until now,many domestic and foreign schol ars have carried out a series of theoretical and experimental researches,thus accumulati ng affluent research data which can provide verification for numerical calculation.That is the reason why the eckardt impeller is chosed.Firstly,the flow characteristics of Eckardt impeller are studied by using the Multi-Reference Frame(MRF)and periodical boundary conditions,and the numerical results are compared with the authoritative experimental data.The results show that the num erical calculation can reflect the complex flow characteristics well such as secondary f low and fluid separation in the channel of the impeller.Especially,the numercial result s are able to accurately calculate the scale and range of the low-pressure zone,thus co nfirming the correctness of the numerical calculation.Hence,it is realiable to carry ou t salt-deposition research based on this model and using related conclutions about the fluid field.Secondly,based on the detailed analysis of the flow characteristics,the DPM mo del combined with the TAB model,the Euler wall liquid film model(EWF)and the customized droplet gasification model(UDF)were taken to respectivly study the effect s of droplets' movement,aerodynamic secondary crushing,evaporation,spashing or for ming water-film while impacting on a wall in the flow path,after the correctness of t he EWF model and UDF program have been validated by comparing to experimental results of the Spray gasification experiment and the plate water-film experiment.The d roplets' diameter and the impeller's ratation speed are considered as the main influenc e factors on these effects noted above to be studied deeply.The main conclusions areas follows: 1)Compared with droplet gasification salt-out,liquid membrane evaporation salt-out is the main form of salt-deposition in centrifugal impeller;2)Under the norm al condition of natural gas gathering and transportation system,the increase of total ar ea for heat transfer caused by splashing is the main reason accounting for the droplet gasification,rather than the change of temperature and pressure conditions.3)The dr oplets of different diameters are not evenly distributed in the impeller flow path,and the larger the diameter,the more the droplets tend to accumulate toward the pressure surface.4)The second half of the pressure surface is the main position where the wa ter film form,whilst the suction surface almost have no water film.Finally,according to the conclusion of the study,the following aspects of anti-salt measures are put forward for the problem of salt-deposition in the gas pressurization system of gas field: 1)The choice of axial flow compressor or centrifugal compressor that have a gentle circumferential and radial change at its blade;2)parallel pressurization,reducing the flow of a single compressor;3)the choice of centrifugal compress or equipted with blades having smaller front area;4)In the dehydration process befo re pressurization,droplet diameter should be avoided 5?m,controlled at about 7?m..