دانلود رایگان مقاله شبیه سازی دینامیکی بارگذاری LNG، تولید BOG در پایانه صادرات LNG

Abstract

Liquefied natural gas (LNG) is a prominent clean energy source available in abundance. LNG has high calorific value, while lower price and emissions. Vapors generated from LNG due to heat leak and operating-condition-changes are called boil-off gas (BOG). Because of the very dynamic in nature, the rate of BOG generation during LNG loading (jetty BOG, or JBOG) changes significantly with the loading time, which has not been well studied yet. In this work, the LNG vessel loading process is dynamically simulated to obtain JBOG generation profiles. The effect of various parameters including holding-mode heat leak, initial-temperature of LNG ship-tank, JBOG compressor capacity, and maximum cooling-rate for ship-tank, on JBOG profile is studied. Understanding JBOG generation would help in designing and retrofitting BOG recovery facilities in an efficient way. Also, several JBOG utilization strategies are discussed in this work. The study would help proper handling of BOG problems in terms of minimizing flaring at LNG exporting terminals, and thus reducing waste, saving energy, and protecting surrounding environments.

6. Concluding remarks

LNG loading is a dynamic process, and it was studied using dynamic simulation software. BOG generation during LNG loading varies with loading time due to ship tanks being relatively hotter initially, and change in loading rate. The factors affecting LNG loading are − LNG pipeline capacity, JBOG-compressor capacity, maximum allowed tank cooling-rate, JBOG pipeline capacity, initial ship-tank temperature, and condition of loading facility before the loading. For the studied case, JBOG generation rages from 1.2 to 2.5% of LNG transferred. LNG loading times range from 17 to 30 h depending on individual case. LNG loading time increased by about 8 h due to the ship-tank being hotter by 30 ◦C. Increasing compressor capacity from 80,000 kg to 100,000 kg, decreased the loading time by 2.5 h. If the maximum-allowed tank cooling-rate is below 2 ◦C per 20 min, it affects loading time significantly. The fuel requirement for the studied case (4 MTPA LNG productions) was about 33,000 kg/h. The additional BOG generated needs to be reused/recovered using other strategies such as use-BOG-asfeed-gas, BOG liquefaction. Storing and reusing BOG was studied as one ofthe BOG recovery strategies. This strategy can nullify the controllability issues that can occur in other BOG recovery strategies due to intermittent and varying JBOG generation. It also makes BOG handling easier for simultaneous loading of multiple LNG vessels. In our future studies, detailed cost analysis of BOG (particularly jetty BOG) handling will be conducted to understand its applicability in LNG industry.