A critical review on the practical use of lithium cycle as an upfront nitrogen removal technology from natural gas

The increase in energy demand as the world population grows, as well as the competition in the liquefied natural gas (LNG) market, force producers to work hard on developing cost-effective production technologies. Upfront nitrogen removal (UNR) before the LNG plant's cold section is considered a promising option to save energy that would otherwise be wasted to cool down a large volume of unused nitrogen in the gas stream. In this study, the use of the lithium cycle (Li-Cy) as a cost-effective method for UNR is investigated. The Li-Cy is compromised of three stages: lithium chemisorption of nitrogen (Chem_N₂), hydrolysis of lithium nitride (Hyd_Li₃N), and electrowinning (Elec.-w) of the final product to precipitate lithium metal for further reuse. The relevant chemistry, applicability, economic, and future challenges of Li-Cy as a UNR technology from natural gas (NG) were explored and discussed. The main challenges that required further investigation to apply Li-Cy to large-scale applications were highlighted for future works. The literature review revealed that Li-Cy can spontaneously remove nitrogen from NG even at low temperatures and produces ammonia as a valuable hydrogen storage material. The used lithium can be regenerated via Hyd_Li₃N and Elec.-w and reused again many times. The cost of the Li-Cy can be compensated by energy savings, the increase in production rate, and by selling the generated ammonia. Calculations showed that selling the produced ammonia from LNG plants with capacity in the range of 1–5 MTPA would not only offset the costs of Li-Cy but would generate a net profit of $21MM to $103MM, respectively. 

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Published in: Energy Science & Engineering
License: http://creativecommons.org/licenses/by/4.0/
See article on publisher's website: http://dx.doi.org/10.1002/ese3.1274