The Heat Transfer And Thermal-Mechanical Coupled Analysis Of LNG Cryogenic Ball Valve

With the rapid development of natural gas liquefaction technology, Liquefied Natural Gas industry has formed a integrated chain which includes liquefaction 、transportation、gasification and terminal using.Becoming a widely-used clean energy,LNG consumption is growing at 10% per year.During each process of LNG industry chain,cryogenic ball valve plays a very important role for the safe and reliable operation of the system.LNG industry device has developed toward the mode of high parameter,large scale.As the key equipment of LNG industry,however,LNG cryogenic valves is lack of theoretical research and standards when designing relevant technical parameter,so it used to leak in practice due to cold shock and seat leakage problems.As a result,it is extremely necessary to do technical research and development on LNG cryogenic valves.In LNG industry chain, the working condition of cryogenic valve is much more complex than those ordinary industrial valves.The temperature distribution of the cryogenic valve,thermal stress in low temperature and the material property are the key factors to ensure the safe operation of the LNG valve,especially the stuffing box seal.Because of wide temperature ranges,sealing property is badly influenced by the ultra-low temperature.With the decreasing of valve temperature,the loss of stuffing box flexibility owing to the ultra-low temperature leads to sealing failure.The leak in stuffing box causes LNG freeze which affect valve working performance.Moreover,the movement of valve stem scratches stuffing box which bring about worse leakage.In order to ensure the temperature of the stuffing box is above 0℃,the long neck bonnet structure must be applied.Meanwhile with the LNG medium effect of both temperature and pressure,the junction of long neck bonnet and flange often occur deformation which could cause leakage.According to the problems above,this thesis analyze a specification of LNG cryogenic ball valve.Based on theory of heat transfer and combining theoretical analysis with numerical simulation,doing the research in the following aspects:(1)Taking LNG physical and chemical properties into consideration,studying on the special structure of the cryogenic ball valve and designing the key technical parameters by reviewing technical document and relevant standard.(2)Simplifying LNG ball valve bonnet physical model and setting up the heat conduction differential equation.By applying variable separation,establishingestablishing the mathematical relationship between LNG ball valve bonnet neck length and the temperature field,getting the minimum length of the long neck bonnet which ensure the temperature of long neck above 0℃.(3)Calculating LNG ball valve bonnet stress、strain and deformation under the condition of thermal-structure by theoretical inference.According to the knowledge of material mechanics,comparing maximum stress with allowable stress,verifying the design reliability and rationality of LNG ball valve.(4)Analyzing the effect of medium pressure and low temperature loading on deformation of the long neck bonnet.Using finite element numerical simulation software ANSYS thermal-structure coupled module to calculate the deformation of the bonnet and comparing it with theoretical analyzing results.