Thermal Efficiency – Design, Lifecycle, and Environmental Considerations in LNG Plant Design

Thermal efficiency is a common benchmark used to compare competing processes when a new LNG project is being developed. Often this type of comparison can be misleading when used in isolation because plant design premises are not consistent from project to project. Thermal efficiency depends on numerous issues such as gas composition, inlet pressure and temperature, and even more obscure issues such as the location of the loading dock relative to the liquefaction process. Higher thermal efficiency is also typically a trade-off between capital and lifecycle costs. Gas turbine selection, the use of waste heat recovery, ship vapor recovery, and self-generation versus purchased power all have a significant effect on the overall thermal efficiency of the process. Process flexibility and stability of operation also need to be considered. The value of a highly efficient process is quickly lost if plant reliability and availability are sacrificed. Design issues that extend from the inlet pipeline to the delivery of LNG onto the ship will be discussed relative to their impact on thermal efficiency. How these issues have been addressed in various designs using the Phillips Optimized Cascade LNG Process will also be reviewed to demonstrate the flexibility this LNG process can provide to balance economic merits and environmental impacts.