Numerical Simulation Of High-salinity Oilfield Wastewater Treatment Adopting Spray Dryer

Most of our oilfields have entered the middle-later period of oilfield development,and the water content of the produced liquid is as high as 80%,which makes the throughput of oilfield wastewater become more arduous.The salinity of oilfield wastewater has been up to thousands or hundreds of thousands milligrams per liter.It will damage the surrounding environment seriously if it is discharged and re-injected directly,so the research and development of processing technology has become one of the urgent tasks to be solved.Compared with the traditional oilfield wastewater treatment technology,the spray drying technology has the advantages of simple equipment,rapid evaporation of water,large-scale production and so on.Occupying a very important position in the field of industrial and agricultural production,it has been widely used in the chemical,food and pharmaceutical industries.This paper proposed a spry drying technology to treat the high-salinity oilfield wastewater based on the spry drying technology.The FLUENT software was used to study the spray drying process.Meanwhile,the feasibility of adopting spray drying technology to treat the high-salinity oilfield wastewater was explored.The results can provide a reference for the relative theoretical research and engineering practice.(1)As for the high-salinity oilfield wastewater with the salt content of 7×104mg/L,a counter-current spray dryer whose capacity is 28.8kg/h was designed.Under the framework of standard k-s two-equation model and DPM model,the relative motion and heat transfer process between the air and droplets are described based on the Euler-Lagrange method.In order to obtaining the flow field and evaporation characteristics,the droplet evaporation process in the dryer was simulated.The droplet particle trajectory and NaCl concentration was tracked by adopting stochastic trajectory model.The results indicate that the injections of wastewater droplets play an obviously disturbed effect on the air,the area nearby axes line has the largest disturbance.The farther away from the nozzle,the more uniform the velocity distribution is.Because of the interaction between droplets and counter-current air,vortex circumfluence areas are formed on both sides of droplets.In the area nearby axes line where the droplets gather has a large gas phase temperature gradient.From top-down along the axial line,the temperature becomes low,the moisture content increases gradually and the evaporation rates show an increasing trend.Droplets can evaporate in 3 to 7seconds.In the working condition,the tower evaporation efficiency peaks at 58.9%.(2)The flow field and evaporation characteristics were investigated and the influences of the inlet air velocity,inlet air temperature,spray angle,and droplet diameter on the evaporation rate were considered.The results indicate that the inlet air velocity and temperature are two key parameters influencing the evaporation of wastewater particles.An increase in inlet air velocity and in temperature can enhance the evaporation rate.But because of the sedimentation velocity of droplets and particles,the effect on the evaporation rate is weakened when the inlet air velocity reaches 0.4m/s in the case of droplet diameter and the flow of wastewater.The inlet air temperature has no significant influence on the enhancement of the evaporation rate when it is up to 313K.With the increase of spray angle,the evaporation rate is slightly increased.The smaller the droplet,the faster the evaporation rate.(3)Due to the practical engineering application in the oil field enterprises,it is necessary to consider the site limitation and the convenience of the installation.Therefore,based on the numerical simulation method of the counter-current spray dryer,the evaporation characteristics of the co-current flow horizontal box structure were also studied,and the evaporation effects of different nozzle arrangement schemes are analyzed and compared.Further,in order to provide a reference for the setting of practical project,according to the box structure used by Sinopec Petroleum Exploration and Production Research Institute in Deyang,Sichuan,the optimal setting of operation parameters is studied.In order to get the effect of evaporation under the condition of Deyang,Sichuan,the orthogonal experimental design principle was used to simulate the box structure under different environmental conditions.The conclusions are shown that,the droplets exist a certain offset in the box structure to the right.At the same time,the velocity field is uneven distribution.There is unreasonable a vortex recirculation zone in the corner of the right of box.Because of droplet in the left entrance of box and the cross flow of air,the mixing of droplets and air mainly exists in the middle and back of the box.In the working condition,the layout of single nozzle is the best.If the air velocity is 0.4 m/s which is small,there is no much differences between the right draft and the top draft.If the air velocity is added to 0.6 m/s or 0.8 m/s,the right draft is better than the top draft.When the droplet diameter is in the range of 20?m to 150?m,the optimum inlet air flow rate is 0.4m/s and 0.6m/s.The flow rate of 0.4m/s is suitable for droplets having a diameter of 25?m,50?m,100?m and 150?m,and the flow rate of 0.6m/s is applied to droplets having a diameter of 100?m and 150?m.The best environmental conditions were obtained by orthogonal test,where the air temperature is 30?,the relative humidity is 60%,the air flow rate is 0.6m/s and the droplet diameter is 25?m;or the air temperature is 20?,the relative humidity is 40%,the air flow rate is 0.6m/s and the droplet diameter is 25?m.In conclusion,this paper combines the practical needs of oil companies,which has practical guidance and provides some engineering design basis for spray drying technology in high salinity wastewater treatment field.