Reducing Power Use in the Cold Section of LNG Plants

Abstract

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 selfsustaining 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.

Roadmap toward energy‐positive upfront nitrogen removal process in baseload LNG plant

“…16 The work implementing integrated alternatives systems for LNG/NGL production reported an SPC of 0.4 kWh/kg LNG. 17 Whereas the energy optimization of the cold section in another study deploying double-column NRU and heat integration reported specific energy consumption of 0.27 kWh/kg LNG, 5 our work methodology results in the lowest specific energy consumption (0.24 kWh/kg LNG) among these studies, highlighting the importance of UN rem technique. Abbreviations: LNG, liquefied natural gas; SPC, specific power consumption.…”

“…Within the LNG plant, the cold section is the pillar of the liquefaction process and consumes roughly 60% of the total energy demand. 5 This section is composed of the refrigeration cycles (C3MR or SMR, etc. ), fractionation unit, nitrogen removal unit (NRU), and helium extraction unit.…”

“…They concluded that a suitable configuration is based on fuel requirements and nitrogen concentration in the feed. Pal et al and Almomani et al 5,9 studied process integration in the cold section with different configurations for the NRU (single vs. multi-column) while ensuring parity between the fuel generation and requirement. The results showed a two-column NRU integrated process lowered total power usage by 4.83% while increasing LNG output by 16kt/a (0.48%) as compared with the base case.…”

“…The NG processing and liquefaction include complicated unit operations such as impurities removal (eg, CO 2 , H 2 S, He, N 2 , H 2 O, and Hg), separation of heavy hydrocarbons (C 3+ ), and then liquefaction. Within the LNG plant, the cold section is the pillar of the liquefaction process and consumes roughly 60% of the total energy demand 5 . This section is composed of the refrigeration cycles (C3MR or SMR, etc.…”

A critical review on the practical use of lithium cycle as an upfront nitrogen removal technology from natural gas

“…The gas stream is cooled by a complex web of heat exchangers, pumps and compressors, fractionation units, and phase separation units, which use the propane and refrigerant cycles. According to Pal et al, 84 the energy cost of the cold section is reported to be approximately 60%. However, the cost can be optimized with improved resource management, structural design changes, and mathematical optimization techniques.…”