Calculation of BOG production in LNG receiving terminal under nonunloading condition

Accurate calculation of BOG production is an essential task for safe production during the operation of LNG receiving terminal. Based on the commonly used calculation methods for BOG production, the key factors that affect BOG production under non-unloading conditions were summarized, mainly including the tank heat absorption, the cold insulation pipeline heat absorption and the heat generation by pump running. The non-negligible factor that the BOG is condensed by recondenser and flows back to the tank together with cold insulation circulating LNG was additionally taken into account, and the influence of tank pressure change on BOG production was analyzed. The BOG production and handling capacity under the three conditions of constant tank pressure, gradually rising tank pressure and gradually dropping tank pressure were calculated respectively. The results show that, under the three different conditions, the BOG production calculated with the tank heat absorption, the cold insulation pipeline heat absorption, the pump heat reflux and the BOG which is condensed by recondenser and flows back to the tank performs well in accuracy and feasibility. The calculation results of both BOG production and handling capacity deviates within 5%, whereas if the influence of the condensed BOG flows back to the tank and the pressure change are ignored, the deviations of the two may be up to 50% and 23% respectively. During the production and operation of LNG receiving terminal, attention should be given to the influence of tank pressure change on BOG production, and the condensed BOG flow back to the tank should be appropriately controlled.