A comprehensive analysis of the nitrogen expansion process for liquefied natural gas industry from the operational point of view

One of the significant challenges faced by operators of Liquefied natural gas (LNG) units is maintaining production capacity under various and often challenging conditions. Liquefied natural gas (LNG) units, characterized as energy intensive units, are significantly affected by seasonal variations and the quality of feed gas, which are crucial for their strategic product output. This study employs thermodynamic principles, exergy analysis, and sensitivity analysis of a nitrogen expansion process, optimizing production capacity through a detailed operational assessment. A novel approach is introduced, categorizing cooling capacity into internal and ambient components to establish an optimal balance. Plant optimization, constrained by equipment limitations, effectively mitigates issues associated with conventional methods. Exergy analysis reveals that the cooling section of the gas post-compressor is a major contributor to exergy destruction, accounting for approximately 60 % of the total irreversibility in the system. The analysis also highlights that air-coolers have an irreversibility rate about 30 % higher than water-cooling systems. Sensitivity analysis demonstrates the impact of ambient temperature and feed gas pressure on production capacity. LNG production shows stability within a temperature range of 5–15 °C, but significant declines occur at temperatures exceeding 15 °C. Additionally, a severe reduction in output is observed when feed gas pressure drops below 30 bar.