A critical review on the practical use of lithium cycle as an upfront nitrogen removal technology from natural gas. Issue 10 (22nd August 2022) - Omar, Abdullah
Abstract: 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 N 2 ${\mathrm{Chem}}_{{{\rm{N}}}_{2}}$ ), hydrolysis of lithium nitride ( Hyd Li 3 N ${\mathrm{Hyd}}_{{\mathrm{Li}}_{3}{\rm{N}}}$ ), 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 Li 3 N ${\mathrm{Hyd}}_{{\mathrm{Li}}_{3}{\rm{N}}}$ 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. Abstract : The lithium cycle has been proposed as a technique for removing nitrogen from natural gas. Upfront N2 removal eliminates the need for a nitrogen rejection unit and saves energy. There is a synergy between liquefied natural gas production, energy demand, and nitrogen removal. Upfront N2 removal generated a net annual profit of $46 million USD.