Basic Study On The Performance Of Packing Columns Under FLNG Motion Condition

The floating LNG production,storage and transportation（FLNG）equals to the offshore liquefied natural gas plant which integrates the natural gas exploitation,pretreatment,liquefaction,storage and transportation.Packing column is the core device in the natural gas pretreatment process on FLNG.Compare to the working conditions on land,the basics of packing columns on FLNG（FLNG packing column）is floating platform,hence the performance of the packing column will be affected by the motion of floating platforms.At present,it is generally believed that the motion of floating platform will worsen the performance of packing columns,leading to the disqualification for the pretreatment of natural gas,bringing safety risks to the downstream liquefaction process.The mass-transfer performance of FLNG packing columns is the key factor for natural gas pretreatment.In this paper,a six-degree-of-freedom motion platform is used to set up three FLNG packing columns.Based on the mass-transfer area which is the key index of the mass-transfer performance,the change rate of the mass-transfer area is proposed to investigate the effects of operating conditions and motions on the mass-transfer performance of packing columns.Further,the numerical method for liquid distribution in FLNG packing columns is studied.The main research works are summarized as follows:（1）Through the small-scale FLNG packing column,utilizing the "NaOH-CO₂" system,effects of tilt and roll on the mass-transfer performance of random and structured packing are studied.According to the overall absorption rate and overall mass transfer coefficient,it is found that increasing liquid parameters（liquid load and NaOH concentration）reduces the adverse effect of tilt by improving the liquid distribution in the column as well as increasing the NaOH concentration at the gas-liquid interface;increasing gas parameters（gas velocity and CO₂ volume fraction）further enhances the deterioration influence from tilt.In the study of roll,it is found that roll enhances the mass-transfer performance of the packing column,which is contrary to the general view.（2）Through the middle-scale FLNG packing column,utilizing the "NaOH-air" system,further investigate the effect of roll on the mass-transfer performance of three types of structured packing.It is found that the effect of roll on the mass-transfer performances of packing columns（enhance or deteriorate）depends on liquid load,gas velocity and rolling velocity.The mass-transfer performance of structured packings with higher special area is enhanced under roll.（3）Through the large-scale FLNG packing column,utilizing the "NaOH-air" system,effects of tilt,roll,sway and heave on the mass-transfer performance of packing columns are comprehensively studied.Tilt deteriorates mass-transfer performance,the effect of roll on the mass-transfer performance of packing columns（enhance or deteriorate）depends on gas velocity and rolling velocity.Therein,increasing the rolling velocity or decreasing the gas velocity deteriorates the mass-transfer performance.Sway and heave deteriorate the mass-transfer performance.（4）The large-scale FLNG packing column is modified by the divided structured packing.Utilizing "NaOH-air" system,effects of tilt,roll,sway and heave on the mass-transfer performance of the divided structured packing are studied.Tilt deteriorates the mass-transfer performance,roll,sway and heave basically enhance the mass-transfer performance.Therefore,utilizing the divided structured packing is a necessary and feasible way to resolve the engineering problem that the mass-transfer performance deteriorated by the motion of FLNG.（5）Numerical investigation on the liquid distribution in the structured packing column under roll is carried out.Through the strategy that modify the porous resistance and keep one radial dispersion force,an Euler-Euler anisotropic porous media numerical model for structured packing column is established.It is found that the liquid distribution changes periodically with the half of the rolling period.The non-uniform liquid distribution is more serious with larger rolling amplitude and shorter rolling period,particularly in the top domain of the column.