Analytical Study of the Effect of Gas Composition Variability on the Performance of Nigerian LNG Export Operations

The composition of feed gas supplied to liquefied natural gas export facilities is a critical operational parameter affecting liquefaction process efficiency, LNG product specification compliance, and export contractual performance. This study analytically investigates the effects of gas composition variability on the operational performance of Nigeria's LNG export operations, drawing on process data from the NLNG Bonny facility and feed gas composition records from the eastern Niger Delta gas gathering network. The research employs a process engineering simulation methodology, developing a HYSYS-based liquefaction process model that captures the response of the propane pre-cooled mixed refrigerant (C3-MR) liquefaction cycle to feed gas composition variations. Simulation scenarios are designed to reflect the documented range of feed gas Wobbe Index, nitrogen content, CO2 concentration, and heavy hydrocarbon variability observed in historical supply records. The study investigates the operational adjustments required to maintain LNG product specification compliance under varying feed compositions, including refrigerant reblending, nitrogen rejection unit operation, and acid gas removal unit load management. A research gap addressed is the absence of published analytical studies quantifying the operational cost and efficiency implications of the specific feed gas variability profile experienced by NLNG, as opposed to more generic sensitivity studies in the international LNG literature. Findings demonstrate that feed gas nitrogen variability above two percent by volume triggers significant operational adjustments with a measurable liquefaction energy efficiency penalty, while heavy hydrocarbon variability primarily impacts refrigerant composition management and freeze protection controls. Recommendations include enhanced feed gas nitrogen specification tightening upstream and investment in online feed gas composition optimisation systems. Keywords: LNG operations, gas composition, liquefaction, NLNG, feed gas variability.