Objectives/Scope: Keppel has identified the market need for a simple and safe natural gas liquefaction process to meet challenging offshore environments where production supports are limited. Such need is also amplified in smaller scale FLNG production plants of up to 2-3 MTPA.

Methods, Procedures, Process: Leveraging on Keppel extensive experience in FPSO conversion, Keppel is trusted to convert the first of its kind FLNG from an existing LNG carrier. In the pursuit of FLNG applications, operators desire a safe and robust process with easy operation consisting of low equipment count and low complexity. To respond to this market need and to leverage in its vast knowledge and experience in the FPSO conversion business; Keppel has developed a proprietary liquefaction process named PreNEx (Precooled Nitrogen Expansion), which is based on a widely accepted nitrogen expansion technology. It employs a single Nitrogen Expansion cycle together with an independent biphasic non-flammable refrigeration cycle for precooling, which is widely used in the air separation industries to achieve comparable liquefaction efficiency to that of multiple expander system without compromising safety, process simplicity, reliability, robustness and flexibility. Such innovative process allows for the conversion of old LNG carriers into FLNG facilities, thus providing a safe and simple alternative solution for small and midscale FLNG solutions. This study covers the optimization of the liquefaction process through simple heat flow redistribution with a process knowhow based on proven process cycles that are already in use, industry wide.

Results, Observations, Conclusions: PreNEx provides a simple, safe and sustainable alternative natural gas liquefaction process for deployment of FLNG. Precooling, condensate recovery and handling become independent from liquefaction operation. It has simple configuration of liquefaction heat exchanger and compression expansion of refrigerant, yet giving comparable thermal efficiency as other refrigerant compression expansion process.

Novel/Additive Information: While LNG liquefaction technologies in the market go towards complexity and fine process conditions to achieve efficiency, PreNEx uses the fundamentals of thermodynamic and heat transfer to achieve efficiency through redistribution of heat load in the process.

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