Method of type-C liquefied natural gas tank modeling based on volume optimization for future “milk-run” exploitation

Common practice methods of tank design for transportation of liquefied natural gas don't take into account the specifics of the gas carriers operation under the condition of partial filling of cryogenic tanks. A new method for designing of type-C tank is proposed. Method is based on solving the problem of increasing the volume of transported liquefied natural gas by small-scale inland carriers. The method is based on usage of a number of limiting parameters: minimal allowable ventless operation time, allowable values of the ship's draft, and the actual duration of voyages between neighboring consumers. The method allows optimizing type, shape, wall thickness, and heat insulation thickness of cryogenic tank. The proposed method is aimed at enlargement of usage of the ship's hull dimensions. This is achieved by changing the diameter, the distance between centers of the bi-lobe tank, the thickness of the insulation, and the maximum allowable working pressure. An increase in the volume of the tank is achieved by coordination such parameters as the maximum allowable draft of the vessel, the minimum time of ventless storage, and the time of ventless operation under partial filling conditions. The calculation of the ventless operation time is determined by the operating conditions of type-C tanks. The calculation of the heat ingress into the tank takes into account the contact area of liquefied gas and its vapors with the metal wall of the tank. The calculations do not take into account the assumption of thermal equilibrium between the liquid and vapor fractions, which leads to the need to take into account heat transfer from vapor to liquid. The implementation of the method is shown on the example of the modeling of the two-way river-sea type vessel. It is shown that optimization of tank parameters in accordance with proposed criteria can lead to an increase in the volume of transported natural gas by more than 4 %. The method can be used in the development of new and modernization of existing vessel projects to transportation of liquefied natural gas operating in water basins of Lena and Yenisei rivers in the East Siberian region. The described method can also be used in the design of road and rail tanks as well as smallscale bullet tanks for liquefied natural gas.