See this summary for a PFD type working description for the APCI N process which uses gas nitrogen for all 3stages of cooling natural gas.

http://www.airproducts.com/~/media/downloads/white...

Scheme looks simple enough. Reduced thermodynamic eff of an all gas low mol wt refrigerant cycle is accepted here to gain operational safety in a cramped, less than optimally ventilated offshore environment. Would agree that operational safety and cycle simplicity / ruggedness would be a key driver in an offshore environment where the plant can be towed from one evacuation location to another.

APCI are not the first to use nitrogen as a refrigerant for LNG liquifaction. Years before, Linde used nitrogen also for LNG liquifaction in an NRU plant. If Petronas are ambitious, their process and mechanical engineers should be able to come up with their own version of refrigeration cycle for NG liquifaction, given they have been in the LNG plant operations business since the 1970s'.