# Effect of Parameters on Vapor Generation in Ship-to-Ship Liquefied Natural Gas Bunkering
## 1 Introduction
During bunkering, additional BOG is generated owing to the heat ingress through the bunkering pipes, heat transferred by the cargo pumps, and cooling effect of the LNG on the storage tank [11; 12]. In the case of LNG carriers, the BOG generated through a transfer operation is typically 8-10 times more than that generated during storage [13]. Therefore, adequate BOG handling during bunkering is an important concern. It must be managed effectively, e.g., by considering pressure accumulation in the tanks, burning in the gas combustion unit (GCU), and using the LNG as fuel or in re-liquefaction to maintain the pressure in the cargo tank below the tank design pressure [14]. Another study proposed managing excessive BOG by using an energy storage system in bunkering ships [1]. As evaluating the amount of BOG generated during bunkering under realistic conditions is important for applying the appropriate BOG handling methods, a literature review on BOG assessment was conducted, as discussed in the following section. [PERSON] et al. [15] conducted a performance evaluation of LNG storage tanks in refueling stations with varying initial LNG temperatures, tank storage sizes, and tank thermal performances. The results showed that the amount of BOG generated in a tank filled with unsaturated (cold) LNG was larger than that in a tank with saturated (warm) LNG, and as the tank size increased, the BOR (%/day) decreased. In addition, a tank with overall heat transfer coefficient (U\({}_{\text{Insulation}}\)) of 0.01 W/m\({}^{2}\cdot\)K could hold the BOG eight times longer than a tank with U\({}_{\text{Insulation}}\) of 0.10 W/m\({}^{2}\cdot\)K under the studied conditions. [PERSON] et al. carried out dynamic simulations of ship-to-ship LNG bunkering with varying parameters by using Aspen HYSYS. Results show that the BOG and resulting pressure increase in the receiving tank were mainly determined by the temperature difference between bunkering and the receiving tank, pressure of the receiving tank, and amount of heel which is remained in the tank [16]. [PERSON] et al. investigated the optimal time limit for ship-to-ship LNG bunkering using Aspen HYSYS. The capacities of the cargo tank and fuel tank for the bunkering and receiving ships were set as 4538 and 700 m\({}^{3}\), respectively. The results revealed that the pressure difference between the bunkering and receiving tanks decreased with increasing bunkering time. In addition, to avoid additional BOG generation, an optimized bunkering time was recommended [17]. [PERSON] et al. estimated the BOG generation in LNG terminals, and proposed a BOG cogeneration plant. The results indicated that the amount of generated BOG increased as the LNG became heavier, due to differences in the heat of vaporization with the varying compositions. Therefore, a composition close to the actual composition was suggested for the BOG assessment [18]. [PERSON] et al. developed six models for LNG offloading from a tanker to an LNG refueling station, and implemented a parametric study using Aspen Plus. The results indicated that an LNG offloading model with a pressure buildup unit (PBU) causes more methane emissions than models using a pump or controlled PBU. In the parametric study, the insulation, pipe diameter, length of delivery pipeline, and PBU design influenced the LNG transfer process [19]. [PERSON] and [PERSON] investigated the performances of offloading LNG from floating production and storage to LNG carriers. The results indicated that the mass flow rate of the BOG increased with an increasing height difference between the pipes, although the difference was minor. The results also showed that as the mass flow rate of the LNG transfer increased, the mass flow rate of the generated BOG initially started to decrease and then increased, implying that an optimal mass flow rate existed for the LNG transfers. In addition, the mass flow rate of the BOG increased with the addition of heavy hydrocarbons [12].