Effect of Parameters on Vapor Generation in Ship-to-Ship Liquefied Natural Gas Bunkering

Abstract

Liquefied natural gas (LNG) is attracting increasing attention as an alternative fuel in the maritime sector, as it can reduce harmful emissions for compliance with stricter environmental regulations. Owing to this environmental advantage, the number of ships using LNG as a fuel is increasing; thus, the demand for ship-to-ship LNG bunkering is increasing. One of the challenges of ship-to-ship LNG bunkering is boil-off gas (BOG) management, as it is more difficult than normal BOG management. This study analyzed the influences of the parameters on vapor generation, including the temperature difference between the bunker tank and receiving tank, bunkering flow rate, insulation performance, and compositions. A model based on a typical bunkering system was established, and a dynamic simulation was conducted using a commercial process simulator, Aspen HYSYS. The results indicated that as the initial temperature of the receiving tank increased, the amount of vapor return increased proportionally. In addition, increasing the bunkering flow rate decreased the amount of heat entering through the pipes and tanks; however, the heat dissipated by the pump shaft power increased. Different LNG compositions in the bunker tank led to changes in the initial pressure of the bunker tank, influencing the vapor return and vapor generation in the receiving tank. Through a parametric study, it was found that the pressure of the tank is the most important factor in terms of vapor return and vapor generation. As such, a pressure control method was proposed for the tank, so as to reduce vapor generation and vapor return. With pressure control, the total amount of vapor return to the bunker tanks is reduced from 7392 to 3317 kg. The net vapor generation in the receiving tank is reduced by up to 4047 kg and the net vapor generation in the overall system is reduced by 16.2%.

Determination of the LNG Bunkering Optimization Method for Ports Based on Geometric Aggregation Score Calculation

“…The geometric aggregation score calculation method must be selected carefully considering the object of evaluation for each factor because there can be differences in the selection of the method and the quality level of the evaluated organization in aggregate score calculation. A representative algorithm for selecting the optimal aggregate score calculation method was proposed by [22]. The geometric aggregation score calculation based on this algorithm requires quantification considering individual factors for the selection of a theoretical framework, selection of more representative indicators, treatment for comparison, and cumulative aggregation.…”

“…Thus, we review studies conducted on the risks through various methods. Lee et al [22] focused on LNG fuel boil-off gas (BOG) management because it is more difficult than normal BOG management; dynamic simulations were conducted using Aspen HYSYS (Aspen Technology, Inc., Bedford, MA, USA), a chemical process simulator used to mathematically model chemical processes. Vidmar et al [23] provided a risk assessment framework for incorporating collisions between sailing and moored ships.…”

Sustainability Analysis of an LNG Bunkering Protocol

“…They focused exclusively on BOG generation during the filling step and presented an optimum filling rate to minimize BOG. Later, for the same system, H. Lee, J. Choi, I. Jung, S. Lee, S. Yoon, B. Ryu, and H. Kang 17 conducted a parametric study on the effects of temperatures/compositions of the two tanks, LNG filling rate, and heat leak through BL/VRL on tank pressures and BOG generation. Apart from these, we are unaware of any study in the open literature that assesses LNG bunkering from the standpoints of process, operations, emissions, efficiency, or environment.…”

Numerical Study on the Tank Heel Determination Using Smoothed Particle Hydrodynamics

“…Some references considered the sloshing impact on the structure to strengthen the tank. Studies on the effects of parameters on LNG bunkering addressed many factors, such as the temperature difference between tanks, pressure control, transfer rate, pipe thermal insulation, pipe diameter, and LNG composition [14][15][16][17]. The optimization work for the LNG fuel tank was towards the unloading operations and regasification [18][19][20][21].…”