| Liquefied natural gas (LNG) is becoming one of the prominent clean energy sources with its abundance, high calorific value, low emission, and price. Vapors generated from LNG due to heat leak are called boil-off gas (BOG). As world-wide LNG productions are increasing fast, BOG generation and handling problems are becoming more critical. Also, due to stringent environmental regulations, flaring of BOG is not a viable option. In this study, typical Propane-and-Mixed-Refrigerant (C3-MR) process, storage facilities, and loading facilities are modeled and simulated to study BOG generation at LNG exporting terminals, including LNG processing, storage, and berth loading areas. Factors causing BOG are presented, and quantities of BOG generated due to each factor at each location are calculated under different LNG temperatures. Various strategies to minimize, recover, and reuse BOG are also studied for their feasibility and energy requirements. Rate of BOG generation during LNG loading---Jetty BOG (JBOG)---changes significantly with loading time. In this study, LNG vessel loading is simulated using dynamic process simulation software to obtain JBOG generation profile and to study JBOG recovery strategies. Also, fuel requirements for LNG plant to run steam-turbine driven compressors and gas-turbine driven compressors are calculated. Handling of JBOG generated from multiple loadings is also considered. 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. |
