Study On The Effect Of Sloshing On Double Mixed Refrigerant Natural Gas Liquefaction Process

Offshore natural gas liquefaction system is the significant part of FLNG.The key performance such as safety,adaptability and production efficiency are different from those in onshore LNG plant.Offshore liquefaction plant is placed on the FPSO,and the wave shaking will affect the performance of the production equipment and the overall liquefaction performance.The mixed refrigerant process has the advantages such as high efficiency,large processing capacity and small footprint after the skid,which can deal with complex environmental conditions at sea.In this paper,we simulate and optimize the process of the double refrigerant mixture,and build the relevant experimental device to verify the accuracy of the process.The sloshing theory is studied to obtain the effect of sloshing on liquefaction system.This paper investigates the application of DMR process to understand the conditions and scope of their adaptation.The static simulation of DMR process is carried out and sensitivity analysis is performed to obtain the key parameters which affecting the process.We optimize the process so that the overall performance of the process to achieve optimal state.The optimized specific consumption of DMR process is 0.373kWh/m~3.The liquefaction experiments were built out to carry out static experiments.Compared with the simulation results,the experimental results error of the key nodes in the process is less than 10%,which verifies the accuracy of the process.At the same time,it shows that the experimental device can complete the liquefaction process well.And sensitivity experiments of feed gas and refrigerant were carried out,including:testing the adaptability to different gas fields,sensitivity to fluctuations in gas production,sensitivity to changes in environmental conditions and the influence of variable frequency control on system power consumption.Then we can come to a conclusion that DMR process can adapt to sea conditions and the use of variable frequency compressor can reduce power consumption effectively.In this paper,through the study of the form of the wave movement,we can confirm sloshing mode and working condition of sloshing platform.The motion equation of fluid in sloshing platform and equipment is studied and the related factors are analyzed.The thermodynamic properties of the device under different working conditions and motion cycles were studied by sloshing test.The effect on key equipment and the critical parameters of double mixed refrigerant process in sloshing experiment are obtained by the analysis of the motion parameters of key nodes.It is concluded that the affected degree of the fluid in the device is related to the direction of the fluid movement and the direction of equipment installation.The liquefied natural gas pipelines and equipment on board shall be as far as possible along the long axis of the ship.When the sloshing period is longer than 18s,the effect of sloshing on the fluid can be neglected,and there is a sharper influence on the system when the sloshing period is shorter than 5.5s.The system will be affected significantly when the swing angle more than 7°.The liquid is stable when the device swings,yaws and surges,which has less effect on the liquefaction system than the rolling and pitching.The translation has little effect on the compression and the liquefaction of raw gas.The effect of pitching on liquefaction performance of the system is the largest.In the process of sloshing,the single tube heat exchanger is affected heaver than the separator and the separator is affected heaver than plate fin heat exchanger.