Design Technology Research On Separated C-type Liquefied Tank Of The Small And Medium LNG Carriers

LNG (Liquefied Natural Gas), as green energy, has got great attention. There are two ways of transportation including pipeline and marine transport. Now researching on LNG carriers has become a hot issue as increasing demand.A new concept- small and medium LNG ship loading less than 10000m~3 has emerged in LNG carriers development history, and it must be prized for short distance, frequency transit, low cost and inland transportation meeting the demands of the markets. At the present, the research data is not so much, and design technology is not yet mature. At the same time, Cargo tank is the core of the hull, and it needs special cargo surroundings due to the property of LNG. Therefore, to study cargo tank system design method and key technology will have important theoretical significance and application value.The traditional membrane tank and Spherical tank are more complex and expensive. As for small loading and low return, it is not worth adopting it, so a new approach is really needed. Design technology of ethylene ships and LPG ships has been mature, and the manufacturing process of liquefaction tank is simple and low cost. So it is feasible to find the tank design methods through imitating ethylene ships and LPG ships tank system as for small and medium LNG carriers are similar to the above two kinds of ships in hull type, cargo and transporting environment.To summarize the whole work, the design approach and research steps of my paper are the followings:1. Collect a large number of domestic and international related LNG ship information on hull form, main scale and cargo tanks data, study the characteristics and design methods of LPG and ethylene carriers and their tanks, elaborate the features of the new type ship - the small and medium LNG carrier;2. Demonstrate the storage and transport means of liquefied gas carrier and cylindrical shell and head form of the separated C-type liquefied tank, describe the design methods and processes of tank in detail from design pressure and design temperature, design load, shell and head thickness, selection materials, insulation layer, connected components and the wash bulkheads and so on. Finally, discuss two kinds of checking methods;3. Summarize the key technologies of designing separated C-type liquefied tank, including the acceleration ellipse method, which composes the acceleration of tank from the non-synthetic three direction acceleration of ship movement in the calculation process of thickness, structural design techniques and material selection principles in order to achieve extremely low temperature transportation environment, control method of balancing the temperature and pressure, as well as reducing the liquid sloshing loads;4. Design a 6000m~3 LNG tank to verify the feasibility of the design method in this paper and check it by finite element calculation method. The results show that high stress region may be risen if only checking the axial stress, circumferential stress and shear stress in determining the size of tank structure and supporting components, so dynamic load due to ship motion must be think about. At the same time there are three measures to enhance the structure including increasing the cargo tank thickness, changing the location of the support saddle, adding reinforcement ring. But sharply increase the weight of the cargo tank while increasing the thickness. Therefore, it is recommended to change the location of the support saddle and adding reinforcement ring to strengthen the structure.