LNG 추진선 연료 공급 시스템용 극저온 고압 기화기의 피로 수명 개선

Abstract

The International Maritime Organization has tightened emission regulations on ships due to the problem of air environmental pollution. Accordingly, since the demand for eco-friendly LNG propulsion ships is increasing, the development and stabilization of various equipment technologies are required. LNG can be cooled to -165°C for transportation and storage, and then stored to a tank by high pressure liquid state. And it is vaporized into a high-pressure gaseous state of -30℃ and supplied to the engine through a high-pressure vaporizer. At this time, the high-pressure vaporizer has a large temperature difference between the inside and outside, as well as the inlet and outlet, so thermal characteristic analysis and structural design must be performed in consideration of thermal deformation. In this paper, the structural integrity of the high-pressure vaporizer was evaluated under the design and operating conditions through finite element analysis. The integrity evaluation results based on ASME B&PV Section Ⅷ Div. 2 was confirmed to be within the allowable limit in the design conditions of the high-pressure vaporizer and it was confirmed that the cycle required by the manufacturer was satisfied by calculating the usable fatigue life cycle under the operating conditions. Additionally, the optimal design improvement was presented by comparing and analyzing the effects of the thickness of the partition plate, the change of head shape, and the rearrangement of the central hole of the tube sheet. The tube sheet of the high-pressure vaporizer is in the form of a perforated plate because it combines with about 2,500 tubes to vaporize by increasing the temperature of LNG. However, since the number of elements and nodes increase to implement as a finite element model, there was a problem of efficiency in analysis. Therefore, equivalent material properties were calculated and applied to the tube sheet according to the ligament efficiency of ASME B&PV Section Ⅷ Div. 2, while the analysis result of the entire equivalent model and the perforated & equivalent mixed model were compared to ensure the reliability of the equivalent material properties.