Experimental study on operation of heating type pressurization of cryogenic liquid applicable to LNG fueled shipping

Abstract

This study proposes a new boosting system that is capable of increasing the pressure of a low-temperature liquid such as liquefied natural gas (LNG) and supplying it continuously to a ship engine without using cryogenic pumps. The process development, device design, dynamic process simulation with control logics, and experimental study for evaluating the pressurizing performance of the proposed system were carried out in this study. The system consists of two boosters, each of which is equipped with a mini-vaporizer and regulating valves. The two boosters operate alternately to ensure a continuous supply of the low-temperature pressurized liquid. The operating philosophy is that the mini-vaporizer of the first booster increases the internal pressure and supplies the pressurized liquid to the engine while the other booster is filled with the low-pressure fresh liquid, waiting for its turn to supply the liquid to the engine. A parallel-type control option and a cascade-type control option are proposed as methods for controlling the two pressurizing devices. A basic performance test analyzes the pressurization effect in a fluid storage tank injected with superheated vapor. It was found that the pressurizing time reduces as the initial liquid filling ratio and heat input rate increase. Furthermore, a mathematical formulation, which can effectively predict a pressure increase by considering the influence of material and energy transfer at the interface, was suggested and analyzed. The condensable model predicted the experimental value within the error range of approximately 3%. A dynamic process simulation and small-scale experiment were conducted to demonstrate the operational feasibility. The result of the small-scale experiment indicated that the two pressurizing devices alternately operated to continuously deliver the pressurized liquid within the control range. The results of this study provide meaningful information for a decision maker during the early design stages of an LNG fuel gas supply system.