Numerical Simulation And Experimental Investigation Of Dynamic Transportation Of Cryogenic Liquid On FPOS

It has been estimated that about one third of the total gas production inworld are contained in the deep oceans, in the forms of marginal gas fieldand oil-associated gas field. They are called stranded gas resources fortechnical and economical reasons. LNG-FPSO and similar units have beenproposed, and supposed to be the solution to the stranded gas resources. TheLNG-FPSO is a floating platform supporting gas-to-liquids process facilitiesand also storing and offloading LNG production in offshore areas. Due tothe remarkable advantages of lower capital, movability and reusability, thenovel unit LNG-FPSO is predicted to be the highlight in the field of offshoreenergy.There are several key technologies unsolved before to build a realLNG-FPSO. The transportation and storage systems of cryogenic liquidbetween floating platforms are limited by the cryogenic features and theplatform movement. The traditional systems on offshore oil platform can notbe directly used on LNG-FPSO. Therefore it is necessary to carry out theresearch on the processes of the transportation and storage of offshorecryogenic liquid. The thesis is based on this background and to carry out thedetailed numerical simulation and the experimental study.Based on the conceptual designs of the transporation process in literatures,and the associated gas conditions of Wenchang oil field in South China Sea,the LNG transportation process between the LNG-FPSO and LNG carrier isdesigned and simulated. Combining with theoretical analyses, the criticalparameters and their influences on the performance of the transportationsystem are investigated, including the flow rate, the pipeline diameter,etc. From the view of the pump power and BOG generation, it is found that there was an economic mass flow rate for practical design. The heightdifference of the pipeline must be considered for the increase of requiredpump head and harms from pressure changes. After meeting therequirements of the cost, ship distance and the bending radius of pipeline,the large diameter tube of small number is suggested when designing thepipeline program. By these findings, the values of key parameters of theLNG transportation system are proposed for associated gas in South ChinaSea, such as the flow velocity, the diameter, etc.Since the pipeline plays the most important role in the transportationsystem, the theoretical analysis and numerical simulations have beenconducted. Combining the inertial coordinate and the non-inertial coordinate,the momentum equation of the rolling pipeline is simplified and analyzedwithout considering the viscosity. The analyses help to discover theinfluencing factors on the flow parameters. The relationships of the pressureloss, the amplitude of the pressure fluctuation and the average pressure aretheoretically derived. In order to predict the influences of the factors on thefliud pressure, a pipeline physical model is established in CFD software.Using user-defined functions (UDF) and dynamic mesh model, the fluidflowing in the rolling pipeline is simulated, at the rolling frequencies of3-15rpm and the rolling angles of6-15°, respectively. It is found from thesimulation results that the pressure fluctuates in the period of2/0. Theamplitude of pressure fluctuation increases with the increase of the rollingfrequency, the rolling angle and the flow velocity. Compared with thesimulation results of ideal fluid, the friction loss of fluid in the rolling pipecan be gained. The friction loss fluctuates in the period of2/0as well.The fluctuation amplitude and the mean value of the friction loss grow withthe increase of the rolling frequency, angle and the flow velocity. Moreover,the modified coefficient of the mean frition loss in the rolling pipe is fitted.According to the similarity principle, a40:1experimental setup isdesigned and constructed, which could roll in different angles andfrequencies, to simulate the freedom of the platform movement in the ocean. The dynamic measurements of the temperature and pressure in thecryogenic tanks and pipeline are well designed, with adiabatic environment,accurate testing method, and good repeatability.In the experiments the cryogenic liquid will be transported between therolling platforms. First, through the heat leak calculation of the system andthe test data, it shows that the rolling motion has little effect on thetemperature of the high-velocity flow in the insulating pipe. Then theinfluences of the flow velocity and the rolling motion including the rollingfrequency and angle on the pressure characteristics of cryogenic liquid areinvestigated. It is found that the rolling motion of the platform causes theperiodically fluctuation of the pressure. The period of the pressurefluctuation is determined by the platform rolling frequency. The amplitudeof the pressure fluctuations increases with the increase of the rollingfrequency, angle and the flow velocity. In the cases in this paper, theamplitude of the pressure fluctuation is in the range of2~6kPa. Comparedwith the simulation results, it can be found that the pressure fluctuationcharacteristics in the experiments and that in the simulations are veryconsistent. The comparison illustrates that the numerical model is reasonableand reliable.The dynamic storage of cryogenic liquids is experimentally studied. Avariety of rolling motion conditions is designed when the cryogenic liquid isstored in the tank. The gas evaporation rate of the cryogenic tanks in24hours is tested. It is found that the evaporation rate increases caused by thetank rolling motion.