The Design Analysis And Heat Transfer Problems For Cryogenic Storage Tank Of A Large LNG Cryogenic Lorry

This paper designs and analyzes the cryogenic storage tank(CST) using in a certain type of native LNG cryogenic liquid tanker(CLT), which is based on the needs of the enterprise. Lots of practice is gathered so far for the CST employed the traditional design method that is simple and easy, however, this method is based on the overall design rules, moreover, the local stress distribution has not yet been considered. Local stress evaluation and design optimization are carried out to ensure the operation safety. Firstly, the paper introduces the design principles and standards, and selects the HDS9404 GDY type cryogenic liquid transportation semi-trailer CST, and briefly explains the structural design. Meanwhile, according to GB150-2011, sorting out the traditional design process, the order is: the CST volume calculation of tank, inner container intensity checking, shell, shell wall thickness reinforcing ring design, overpressure discharge device design, the supporting design, center of gravity position and axial load distribution, mass center height of tank car and train maximum angle of lateral stability, design calculation and checking, etc. Through analyzing the traditional design process, points out its advantages and disadvantages of design, and then optimize the insufficient, make it more meet the demand of practical engineering.Secondly, basing on the structure and bearing behavior of the CST, the global and local stress distribution are obtained by the finite element method for different working conditions in the practical use such as starting, braking and jolt, which draw the following conclusion:(1) Every strength index requirement basically adapts the needs of transportation conditions, and the structure is reasonable and reliable;(2) The maximum stress is found at the inner container bottom of the sliding side under different working conditions, and especially at the jolt that the linearized membrane stress is very close to the allowable value which leads to a risk. As a safety precaution, it is recommended to reduce the distance of two reinforcing rings at the location of maximum stress or increase the thickness of the rings if the distance remains unchanged;(3) The stress-strength distribution results show that different levels of stress mutation exist at the bearing and locale inforcement structure, which indicates that the membrane stress state of the internal and external tanks broken, which generates the acorresponding peak stress that is the principal cause for fatigue failure, so what call for special attention are the attachment weld quality and the smooth transition between the weld and the tank, and try to avoid the unfilled or sunken welding beads(e.g. the attachment weld between the tank and support), rough surface, and unpolished operation after welding;(4) From engineering design point of view, the ideal carrying state of shell-body is at the membrane-stress status, while the stress state caused by the required supporting and strengthen structure cannot obtain the complete guarantee, thus the edge connect should be as smooth as possible that can be achieved by using the tangential bearing and avoiding the normal bearing, etc. Furthermore, the connection between the various strengthen structures and tank should have a minimum break to the membrane-stress status, so the connection type of reinforcing ring, washboard with the tank commonly adopts the discontinuous welding or bolted connection method, meanwhile, the traditional structure design, the processing and welding technology should be further optimized for engineering requirements according to the stress evaluation results.At last the thermo-mechanical and static evaporation calculations are also given to meet the enterprise demands, which shows that the heat transfer quantity by the methods of high vacuum multi-layer insulation is one half of that by the vacuum powder insulation, that is to say, the former insulation performance is much better than the latter one. Daily evaporation rate of LNG and the transformational LN2 is lower than 0.139%/d and 0.217%/d(0.145%/d through test), respectively, which meets the engineering demands and shows that the thermal-isolate structure designs reasonable.In conclusion, the combined method of traditional design and stress evaluation would be more realistic for the enterprise design, processing, manufacturing and engineering requirements, and then this method can be expanded to the whole industry and be very benefit to the promotion of the industry development and design level.