Analysis Of Low Temperature Characteristics Of LNG Handling System

In liquefied natural gas(LNG)terminal building has been completed,the need for LNG receiving station on the LNG pipeline precooling operations,make the pipe cooled to the desired operating temperature,in this work,the precooling process of temperature drop pipeline caused by uneven distribution of temperature and thermal stress,and thus,and,with the gravity load of pipeline deformation,When the deformation is too large,it will cause damage to the LNG pipeline and affect the safety of the pipeline.Moreover,LNG pipelines work under the condition of deep cold for a long time.Due to the low temperature,water droplets in the air on the outer wall will condense into ice.With the growth of pipeline operation time,the thickness of frost layer on the outer wall increases,resulting in increased stress,which will cause harm to the pipeline.In this paper,the horizontal pipeline in front of LNG receiving station was studied.UDF was used to establish the characteristics of material physical parameters changing with temperature by using ANSYS software.A numerical model of LNG pipeline in the process of precooling was established by using heat fluid-solid coupling method,and the influence of temperature drop rate on stress and displacement was studied.A numerical model of frost layer thickness was established to study the influencing factors of frost layer thickness.The distribution law of temperature,displacement and stress of LNG pipeline under different pre-cooling time was explored.The thermal stress displacement of LNG pipeline under different pre-cooling time was studied for 10 m pipeline.The hot arch of the pipeline first increased and then decreased with the pre-cooling time,and the temperature difference between top and bottom of the pipeline reached the maximum when it passed through half of the pipeline length.At this time,the displacement caused by the hot arch of the pipeline is also the most serious.In order to prevent damage caused by excessive displacement,the temperature difference between top and bottom is controlled to be about75℃,and the optimal liquid level height is obtained according to the temperature difference between top and bottom caused by different inlet liquid level heights.Pipe ends under different temperature drop rate of stress analysis,respectively to four different temperature drop rate of research and analysis,it is concluded that stress under different temperature drop rate increases as the temperature drop rate,further consider the LNG pipeline outer insulation layer thickness on the influence of thermal stress,take different insulation thickness,It is concluded that thermal insulation thickness is positively correlated with thermal stress.Considering the thermal insulation thickness obtained by anti-condensation algorithm,it is best when the thickness of thermal insulation layer is about 30 mm.The formation of ice in the low temperature environment outside the LNG pipeline was studied,and the water vapor in the cold air around the pipeline was regarded as subcooled droplets.FENSAP was used to establish a numerical model,and the frost thickness was analyzed under different working conditions.The control variable method was adopted to study the air flow temperature,water content in the air and speed.It is concluded that the windward side of the pipeline begins to frost first,and with the increasing amount of frost,the frost layer gradually begins to form on the leeward side.It is found that flow separation occurs when the air flows through the frosted pipe,and the initial point of flow separation is located behind the side of the pipe.