Reducing Power Use in the Cold Section of LNG Plants

Liquefied natural gas (LNG) has garnered global attention as a relatively cleaner, environmentally more friendly, and more efficient energy source than other fossil fuels. Upgrading and liquefying natural gas to LNG is highly energy-intensive, and the most energy-consuming section of a typical LNG plant is its cold section. While much existing research has focused on heat integration and efficient refrigeration cycles to reduce power use in the cold section, energy sourcing for the cold section has received limited attention. Furthermore, several processes and product/fuel quality constraints such as high heating value are not addressed adequately. In this study, we first develop a realistic, energy self-sustaining model of the cold section of a conventional LNG plant. Boil-off gas and end flash gas are hydrocarbon-rich waste streams that are used to power gas turbines that meet the plant’s power needs. Then, we propose various structural changes to the conventional plant design, identifying opportunities to reduce energy requirements while increasing LNG production with the same feed flow rate. We develop the process models using a commercial simulator and deploy a simulation-based optimization paradigm to determine optimal design parameters and minimize specific power consumption (SPC) while ensuring that various process and product/fuel constraints are met. The findings reveal those structural improvements to a conventional LNG plant’s cold section lower total power usage by 4.83% while increasing LNG output by 16 kt/a (0.48%). The SPC is further reduced by 5.52% due to lower total power usage and increased LNG output.