This invention is a method for liquefying permanent gasflow. It contains several steps: The temp. of the gasflow which is a permanent gasflow at a high pressure is reduced to what is lower than the critical temp. The reduction of temp. is excuted at least partly through the inverse thermal exchange of working expansion of permanent gasflow. At least, a part of this working fluid is at the temp. Lower than the critical temp. as above permanent gas when it is in exchange with the permanent gas. The permanent gasflow of the temp. lower than the critical temp. is isenthalpically expanded at least three times sequentially. After every isenthalpic expansion, the flash vapor is separated from the resulting liquid. The liquid from every isenthalpic expansion is exactly the fluid for next expansion (except the last time) and will excute thermal exchange with at least part of the said flash vapor and the above said permanent gasflow at high pressure. |