Enhanced Separation Of Bubbles And Dissolved Gas By Swirling Turbulence

Bubble and dissolved gas exist in the liquid which is a common phenomenon in nature and industrial process.The removal of bubble and dissolved gas from liquid plays an important role in environmental engineering,metallurgical process and petrochemical industry.For example,the unorganized discharge of dissolved gas from wastewater leads to more serious air pollution.Degassing of molten metal is necessary for preventing the blowhole defects.Separation hydrogen gas from hydrogenated product in petrochemical production is important for green production.These processes challenge the performance of liquid degassing.Degassing hydrocyclones offer a high separation precision,a small size and little heat energy loss.The separation of small bubbles and dissolved gas by swirling turbulent flow shows a more safe and efficient performance.Due to the soft property of bubble and the velocity fluctuation in turbulence,mechanism of dissolved gas and bubbles escaping from liquid in the swirling turbulence is not clear.The relationship between bubble dynamics and mass transfer of dissolved gas in swirling turbulence is not well developed.Based on the microfluid,high-speed photography,and multi-scale component simulation,enhanced separation method for bubbles and dissolved gas by swirling turbulence was built.The swirling turbulence promoting bubbles coalescence and dissolved gas desorption was discovered.The movement of gas molecular clusters with each size scale in swirling turbulence was revealed.Separation mechanism of dissolved gas by bubbles adsorption and stripping was discussed.Equipment for removal of fine bubbles and dissolved gas from liquid by swirling method was invented.The degassing hydrocyclone is applied to the degassing of transporting crude oil on offshore oil platform.The main innovation points include:(1)Euler-Euler two fluid simulations combined with Multi Size Group Model are used to predict the coalescence of small bubbles in swirling turbulence.The effect of bubble coalescence on the degassing efficiency is discussed.The fluid domain initially is filled with gas and is gradually filled with liquid-gas fluid.Eventually gas is enriched at the center.It is found that the efficiency increases from 30%to 99.53%with increasing the maximum size of bubble.The change of gas volume fraction from the inlet to the outlet in the three seconds is studied.Liquid exhibits swirling flow near the wall,and gas was riched in the center region.Larger value of Ad leads to faster buble slip velocity and less time to reach a stable state.(2)A new designed degassing hydrocyclone is applied to study desorption of dissolved CO2 from water.The removal of dissolved gas under the coupling of pressure gradient field and centrifugal field is studied.Reynolds Stress model and two-equation turbulent model are used to indicate the pressure distribution.The concentration of carbon dioxide at water outlet is lower than the saturated solubility under the same pressure.Swirling turbulence breaks the gas-liquid equilibrium in which contributes to escape rate of dissolved gas from the water.Separation efficiency of dissolved carbon dioxide exhibits a maximum value of 40.2%.(3)A planar cyclone is designed for visualizing bubbles in the cross-section of a degassing hydrocyclone.The velocity distribution of the planar cyclone mostly exhibits the quasi-forced vortex zone and boundary layer zone.The bubble dynamics are simulated using both Euler-Euler and Euler-Lagrange approaches,and the output is compared with the imaging results.The Euler-Euler simulation provides more accurate predictions of the bubble trajectory.The histograms of residence time and traveling distance given by the Euler-Lagrange approach exhibit a reasonably regular pattern.With higher feed flow,stronger forces acting on the bubbles lead to a decreased but more uniform residence time.(4)This paper discusses the use of a multi-cyclone separator,which is a simplified form of a degassing hydrocyclone,in the separation of sweeping nitrogen bubbles and dissolved oxygen from water.The multi-cyclone shows well mass transfer performance.The bubble Sauter diameter in multi-stage swirling experiments is modified by that in the single swirling experiment.With the increase of gas volume ratio from 0.015 to 0.090,the bubble Sauter diameter ranges from 0.11mm to 0.21mm,and the volume fraction of bubbles increased from 0.02 to 0.11.The mass transfer coefficient increased from 0.16 to 0.55,and the desorption efficiency of dissolved oxygen ranged from 0.08 to 0.25.(5)The degassing hydrocyclones are applied for degassing of transporting crude oil on offshore oil platform.The transporting crude oil shows a high viscosity which has been settled more than 3 min before flowing into the degassing hydrocyclones.The degassing efficiency is about 83%resulting from PVT analysis.The degassing process relieves the vibration of the transporting equipment.This application satisfies the efficient and rapid degassing for the high-viscosity crude oil.In next work,the adsorption and desorption of gas molecular clusters in swirling flow at gas-liquid surface need be further discussed.Diffusion rate of molecular clusters in bubble internal flow after moving through the gas-liquid interface requires a detailed analysis.We will verify that bubble tailing in swilring turbulence affects the surrounding bubble movement.