Versatile Cryogenic Nitrogen Rejection

Nitrogen is considered as ballast in natural gas and other fuel gas streams. Thus, most of the pipeline gas specifications limit the nitrogen content to 3 mol%. Fuel gas quality for gas turbines imposes other nitrogen constraints with respect to stability of Wobbe index. Further, the nitrogen concentration in LNG shall not exceed 1 mol% as otherwise stratification of LNG with varying density over the height of the tank might cause the dangerous roll-over effect, which can cause large methane vapor releases or even damage the integrity of flat bottom tanks.

Sophisticated nitrogen rejection unit (NRU) concepts will be discussed, which have been successfully applied to extract nitrogen from gaseous or liquid hydrocarbon fluids and to clean nitrogen for further use or for safe immission into the atmosphere. These case studies include

• N₂ rejection from end-flash gas of a LNG plant
• Processing of N₂ rich boil-off gas into LNG and fuel
• Clean-up of pipeline gas
• Handling of natural gas or associated gas with increasing N₂ content
• CO₂ tolerant operation of a NRU

Linde Engineering, which is active in the field of cryogenic methane/nitrogen separation since 40 years provides detailed insights into process technology and corresponding equipment as well as operational experience.