The present invention discloses a hydrogen or helium throttling liquefaction system using direct current (DC) flow from the cold and hot ends of the regenerative cryocoolers, which belongs to the technical field of refrigeration and cryogenics. It includes a regenerative cryocooler module, a hot-end DC flow module, a cold-end DC flow module, a throttling liquefaction module, and a gas-phase circulation module. The modules are interconnected to form a closed loop for the flow of hydrogen or helium working fluid. DC flow is introduced from the cold and hot ends of the regenerative cryocooler through the DC flow pipelines and DC flow valves. The hot-end DC flow exchanges heat with the reflowing low-temperature working fluid and is cooled down. After that, it mixes with the cold-end DC flow and enters the throttling liquefaction module to generate liquid phase through throttling and liquefaction. After the liquid phase has output cooling capacity, it flows through the gas-phase circulation module and then enters the back-pressure chamber of the compressor to complete the cycle. Compared with the existing small-scale hydrogen and helium liquefaction technology using regenerative cryocoolers, the present invention has the advantages of simple structure, easy installation, high heat transfer efficiency and liquefaction efficiency of the system.

An apparatus and process for recycling hydrogen can be provided so that hydrogen is recycled during hydrogen liquefaction processing to account for an unexpected loss of feed of hydrogen so the recycled hydrogen can be provided to avoid liquefier operations having to be shut down. Embodiments can utilize a parahydrogen to ortho-hydrogen conversion unit to facilitate such recycling of hydrogen to avoid liquefaction processing problems in liquefaction of the recycled hydrogen included into the feed to account for the loss of fee hydrogen.

Methods and systems for liquefying natural gas by: cooling and liquefying a natural gas feed stream via indirect heat exchange with at least a first cold refrigerant stream to form a first liquefied natural gas stream and a warmed gaseous refrigerant stream; flashing and separating the first liquefied natural gas stream to form a liquefied natural gas product stream and at least a first flash gas stream; combining and compressing the first flash gas stream and the warmed gaseous refrigerant stream to form a compressed refrigerant stream; and expanding at least a first portion of the compressed refrigerant stream to form the first cold refrigerant stream; wherein the natural gas feed stream is kept separate from and is not combined with either the first flash gas stream or the compressed refrigerant stream.

The invention relates to a facility and a method for the liquefaction of hydrogen, comprising a hydrogen circuit having an upstream end configured to be connected to a source of gaseous hydrogen and a downstream end connected to at least one store, the facility comprising a cold box housing a set of heat exchangers in a heat exchange relationship with the hydrogen circuit, the facility comprising a cooling device in a heat exchange relationship with at least part of the set of heat exchangers, the facility comprising a collecting pipe configured to collect boil-off gas and equipped with at least one upstream end connected to the store and/or a tank to be filled, and a downstream end connected to the hydrogen circuit, inside the cold box, said downstream end of the collecting pipe comprising, ahead of its connection to the hydrogen circuit, a portion in a heat exchange relationship with at least one heat exchanger of the set of heat exchangers.

In a method for liquefying a gas rich in carbon dioxide, the gas is compressed to a first pressure greater than its critical pressure in a compressor to form a compressed gas, the compressed gas is cooled through heat exchange with a refrigerant to a variable temperature to form a cooled compressed gas with a density between 370 and 900 kg/m.sup.3, the cooled compressed gas is cooled at supercritical pressure in a first heat exchanger to a temperature below the critical temperature, the gas cooled below the critical temperature is expanded to a second pressure between 45 and 60 bara to form a diphasic fluid which is separated in a phase separator to form a liquid and a gas, and a liquid portion originating from the phase separator provides cold to the first heat exchanger.