The Problem of Utilization of Liquefied Natural Gas Vapor at Large-scale LNG Plants

The liquefied natural gas (LNG) is stored under low overpressure in a saturated state in large-capacity tanks with multilayer thermal insulation. Owing to the input of heat from the environment through thermal insulation, LNG is continuously evaporated. Since natural gas is a multicomponent mixture, LNG vapors are enriched with its low-boiling components, then the supply of heat from the environment reduces the amount of liquid in the reservoir and changes its chemical composition. Similar phenomena occur during LNG transportation. The present paper deals with the problem of LNG vapor utilization during its storage and transportation. Information is presented on the causes of the LNG vapor formation (boil-off gas) and methods for its disposal during storage and transportation to consumers. A numerical experiment was performed based on the data of LNG storage in large-capacity storage facilities at the Yamal LNG plant. The technique consists of the estimation of material flows toward the system of accumulation and extradition of LNG. The results show that the vapor flow generated from the inflow of new LNG portions into the storage significantly exceeds that generated from the heat supply from the environment.