Structure And Hydraulic System Design Of Emergency Release System For LNG Unloading Arm

Liquefied natural gas(LNG)is widely concerned because of its safety,cleanliness,high efficiency and high storage efficiency.The domestic natural gas is in a state of short supply and needs to be imported from abroad.The imported LNG is transported from the transport ship to the coastal receiving station,and the LNG is transported to the large storage tank of the receiving station by the LNG unloading arm of the receiving station and the shipping manifold.In the process of loading and unloading LNG,when the sudden situation of typhoon and wave,such as typhoon,sea wave,and so on,the transport ship is drifting away from the working area,the unloading arm and the transport ship need to be detached urgently.Otherwise,the pulling and unloading arm of the transport ship will lead to the leakage of the LNG and even cause serious accidents such as the explosion.For this reason,an emergency release system is installed on the unloading arm,so that the unloading arm and the transport ship are separated rapidly.Due to the lack of corresponding theoretical basis in China,the large diameter cryogenic emergency detachment device has not been studied and designed,and the equipment has long relied on imports.Foreign products have problems such as low pressure in hydraulic system,no pressure on accumulator and frequent starting of pumps.With the construction of LNG receiving station in China,it is urgent to study the emergency release device of LNG unloading arm.In this paper,a 16 inch LNG unloading arm emergency release system is taken as the research object.The structure and hydraulic system are designed.The design of the sealing structure of the emergency detachable device under the ultra low temperature condition is focused on.The finite element method is used to analyze the temperature field and stress field to verify the rationality of the structural design.The research results solve the problem of long term dependence on imports and localization of products,and provide reference for their design and theoretical research.According to the function requirements of the emergency release system,the general scheme of the device is the form of double ball valve plus emergency disengagement joint,and the driving mode is hydraulic drive mode.According to the plan of emergency detaching device,the design requirement is designed and formulated,which provides basis for structure and hydraulic design.According to the functional characteristics,the emergency release device is divided into double ball valve parts,transmission mechanism and emergency release parts.Through thedetailed design and analysis of each component,the device structure is designed,and the three dimensional modeling of each component is drawn up,and the general modeling of emergency release system is completed.The double ball valve belongs to the non-standard design,and focuses on the sealing design of the ball valve under ultra-low temperature.The ball valve body adopts an integrated structure design,and the valve seat and spool adopt a new structural design,which makes the structure more compact.The transmission mechanism adopts four connecting rod structure to ensure the synchronization of two ball valves opening and closing.The emergency release joint is designed by four splint structure,which realizes the safe and reliable separation between the unloading arm and the transport ship.Considering the effect of medium pressure and temperature load on the structure of the ball valve in an emergency release system,the temperature field analysis and stress coupling analysis of the ball valve under the condition of ultra low temperature are analyzed by the finite element analysis software.The relationship between maximum stress and material allowable stress is judged,and the reliability of design strength of ball valve is verified.According to the design requirements of hydraulic system,the schematic diagram of hydraulic system is designed,and the principle of each unit loop is analyzed.In view of the leakage in the hydraulic system of the existing unloading arm and emergency release system,a new type of leakproof valve group is designed.Through the test,it is proved that the valve group is well sealed and applied to the hydraulic system of the dump arm of the Dapeng LNG receiving station in Guangdong to verify the correctness of the design.This study will provide a reference for the research and development of the emergency release system of LNG unloading arm.