LNG processing can tolerate feed gas with low nitrogen content without issue. A “grey zone” exists at ~3–4% nitrogen, where an NRU (Nitrogen Rejection Unit) may or may not be required depending on fuel gas usage in turbines. Above ~4% nitrogen, an NRU is typically required or excess high nitrogen gas must be exported (e.g., to a power station via fuel gas). Prospective greenfield LNG plants are considering using a variable feed gas with 5–10% nitrogen that could change on daily timescales and potentially experience step-changes in nitrogen content. Existing processing techniques for handling nitrogen content in LNG plants are optimised for constant N2 content, requiring tight control of the feed gas to avoid instability with very limited ability to handle variable compositions.
There is a need to develop a more efficient, flexible nitrogen rejection approach that handles variable nitrogen feed (5–10%), removes only the nitrogen required (e.g. reduce 5% → 4%, not over-process) and minimises both energy consumption (refrigeration load) and capital intensity (equipment count). This project will review and assess literature on cryogenic NRU processes in the context of this need and analyse a possible new process relative to those in the literature and/or offered by existing vendors of LNG process technology.
Partners: The University of Western Australia, Woodside Energy Limited
Researchers: Prof. Eric F. May, Dr. Luke McElroy, Dr. Gongkui Xiao
Duration: 1 year