How to purge dual purpose liquefied natural gas / liquefied nitrogen storage tanks

摘要

A method of loading liquefied nitrogen (LIN) into a cryogenic storage tank that initially receives liquid natural gas (LNG) and vapor space above the LNG. A first nitrogen gas stream and a second nitrogen gas stream are provided. The first nitrogen stream has a temperature lower than the temperature of the second nitrogen gas stream. During the discharge of the LNG from the storage tank, the first nitrogen gas stream is injected into the vapor space. The storage tank is purged by injecting the second nitrogen gas stream into the storage tank to reduce the natural gas content of the vapor space to less than 5 mol%. After purging the storage tank, the storage tank is loaded with LIN.