New BOG Recondensing System Utilizing Gas-Liquid Direct Mixing Technology

Abstract

LNG stored in a tank is always subject to heat input because the temperature of LNG, at approximately –160°C, is far below the ambient temperature. The LNG is partly evaporated by the heat, and this evaporated gas is the BOG (boil off gas). Processing BOG is a challenge for the industries importing LNG such as city gas industry or electric power industry. The industries have been addressing the issue by installing BOG recondensing systems, which reduce power consumption by the BOG compressor. To further minimize the lifecycle cost of BOG processing, the authors developed a new BOG recondensing system utilizing gas-liquid direct mixing technology, which enables to substantially reduce the size of the BOG recondenser. In a course of developing the gas-liquid mixer, as a key device of the recondensing system, several technical features have to be taken into account and confirmed, such as, high recondensing performance, low pressure loss, prevention of internal cavitation-erosion, and, reduction of thermal stress due to large temperature difference of BOG and LNG. The paper describes the confirmed recondensing performance and features of the system. This paper also introduces the first commercial system utilizing developed mixer with a volume of only 2% of conventional system.