Investigation of LNG Underwater Release and Combustion Behavior on Water Surface

Abstract

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper OTC 30646, “Experimental Investigation of LNG Underwater Release and Combustion Behavior on the Water Surface,” by Yixiang Zhang, Jianlu Zhu, and Youmei Peng, China University of Petroleum, et al., prepared for the 2020 Offshore Technology Conference, originally scheduled to be held in Houston, 4-7 May. The paper has not been peer reviewed. Copyright 2020 Offshore Technology Conference. Reproduced by permission. Most liquefied natural gas (LNG) is transported by ship, creating opportunities for potential hazards to surrounding devices and the environment. Nevertheless, few studies have examined the characteristics of LNG underwater leakage and subsequent vapor flame. The paper considers transportation safety and risk evaluation for LNG, with emphasis on accidental release and vapor flame. Introduction The cryogenic nature of LNG, with a boiling point of -162°C, raises safety concerns with regard to vaporization gas hazards and the potential for pool fires. According to the literature devoted to LNG accidental release and spill, three puncture positions have been proposed: Category I, where the leakage point is above the water line; Category II, where the point is at or close to the water line; and Category III, where the point is below the water line. A need exists to investigate LNG underwater leakage and combustion behavior for risk assessment. This work focuses on experimental research of the dynamic behavior of LNG jet release under water and the immediate burning on the water surface using three orifices and different crosswinds. The main points of investigation include the following: - Liquid-rising process and microbehavior in the orifice - Flame geometry on the water surface under crosswinds - Flame-temperature distribution on the water surface Experimental Setup Experimental Facilities. Experiments were conducted in a rectangular tank measuring 1000 mm long, 500 mm wide, and 500 mm high, which was placed in a wind tunnel. The nozzles have diameters of 1, 3, and 5 mm in the middle of the discharge pipe. An inline cryogenic flow-meter with a measuring range of 0.06 - 0.6 m3/h was used to regulate the volume flow rate with an accuracy of 1.5 %. The pressure measurements were performed by a pressure gauge with a range from 0 to 4 MPa placed on the end of the discharged pipeline. The LNG jets were re-leased vertically into the bulk water at a depth of 0.6 m. Images were recorded using a high-speed video camera system. Experimental Conditions. The window was closed when LNG was released, and the discharged gas was quickly diffused from the wind tunnel. The temperature in the room was 17±1°C and 14±0.5°C in water. The relative humidity was approximately 50%. All tests were conducted three times.