(185d) Optimal Operation for LNG Multiple Ship Tanks Commissioning and Uploading Via Rigorous Dynamic Simulations
AIChE Spring Meeting and Global Congress on Process Safety
Wednesday, April 3, 2019 - 2:45pm to 3:10pm
In this work, rigorous dynamic process simulation for commissioning and LNG loading of multiple LNG ship-tanks has been performed to study the optimal procedures when new LNG ship-tanks are put to service or old LNG ship-tanks come back to service after maintenance. At the beginning, the tanks contain humid air at ambient temperature. Before LNG can be loaded, the tanks require drying, inerting, gassing up, and cooling. Drying is necessary to avoid moisture from air to condense and solidify during cooling of the tank. Air is purged using inert gases to remove oxygen from the tanks. Then methane vapors are used to remove inert gases because some inert gases like CO2 can solidify after adding LNG and can chock valves. Cold methane is used for initial cooling of the tank. LNG liquid is sprayed for further cooling to desired temperature. Finally, LNG is loaded into the ship tanks. The LNG ship-loading is constrained by maximum allowable cooling-rate of ship-tanks, jetty boil-off gas (BOG) compressor capacity, LNG loading line capacity, and LNG level in ship-tank. Overall, LNG loading is complicated process. Dynamic simulation is helpful to study the commissioning and loading operations. The changes in the composition of material inside the tank are reported for each step in the commissioning and loading procedures. Optimization of the process to minimize time of commissioning and loading operations, emissions, and energy requirements is carried out using the Aspen Plus Dynamics simulation tool. This study would help LNG industry to operate LNG exporting terminal smoothly and in an optimal way.