Numerical Simulation Study On The Sloshing Effect On Gas-liquid Countercurrent Packed Column

FLNG is a floating production unit which combines the exploration,pretreatment,liquefaction,storage,load and unload.Acid gas removal is a critical step in the chain of processing stages for natural gas liquefaction.The effect of offshore sloshing conditions on the operating performance of acid aborption columns attracts much attention.The countercurrent gas-liquid packed column is taken as the research object.The porous media model is used to simplify the complex structured packing geometry.The two-dimensional and three-dimensional CFD models for packed column under sea conditions are developed considering porous resistance force,inter-phase drag force and mechanical dispersion force and etc.In order to provide guidance for the optimization design of the floating Acid Gas Removal Unit on FLNG vessels,the effect of offshore sloshing conditions on gas-liquid flow field and mass transfer performance in packed column is analyzed.Firstly,in order to predict liquid spreading in countercurrent gas-liquid packed column accurately,the liquid dispersion mechanism is introduced.The numerical simulations are in good agreement with the experimental results.The spreading factor S is optimized and the sensitivity analysis of influence factors on liquid spreading is made.Secondly,the comparison of the gravitational and inertial acceleration of hexapod and usual set-ups is provided.The moving mesh method is used to perform the martime boundary conditions.The effect of sloshing with different angles,periods and displacements is quantitatively analyzed on hydrodynamic parameters in two-dimensional packed column.Thirdly,the amine absorber numerical model is coupled with moving mesh method.The effect of tilt angles,sloshing angles and sloshing periods on gas-liquid flow field and mass transfer performance in amine absorber is analyzed using liquid maldisribution index.Then,the sensitivity analysis of column installation positions in the FLNG vessel is performed.The study shows that the pressure drop is relatively uniform in two-dimensional packed columns under different sloshing conditions.The hydrodynamic parameters such as liquid volume fraction,liquid axial velocity,liquid radial velocity present periodic wave.The wave period is the same as the sloshing period and the wave amplitude is related to sloshing angle and sloshing displacement.The liquid distribution tends to be uniform in the central area under sloshing conditions.The amplification of uniformity index becomes larger as sloshing displacement becomes larger at 1/2T.However,The amplification of uniformity index becomes lower as sloshing displacement becomes larger at 3/4T.The liquid maldistribution in three-dimensional packed columns becomes more severe in the first sloshing period.After the given time,the uniform index of hydrodynamic parameters tends to increase to the static state.The CO₂ molar fraction in purified gas fluctuates around the value in the static state.The wave period is approximately the same as the sloshing period of the packed column.The wave amplitude is related to the sloshing period and sloshing angle.The inertial acceleration of the packed column is different due to the installation position on the vessel.Therefore,the packed column is recommended to install in the middle of the FLNG vessel.The variation of gas-liquid flow field and mass transfer performance under offshore sloshing conditions is obtained.The study provides the reference value for the operation of acid gas removal unit in the FLNG vessel.