Large-scale gas liquefaction has become a key technology in the energy supply field with the developments of new energy sources and energy carriers. While liquefaction plants are rather complicated with numerous components interacting with each other and consume a large amount of process energy, it is vital to develop efficient liquefaction processes for improving the overall system performance and economic competitiveness.

Researchers with University of Leeds and Institute of Process Engineering (IPE) proposed an optimal design methodology for large scale gas liquefaction systems on the basis of the pinch technology and the genetic algorithm (GA).

The method enables configuration selection and parametric optimization to be implemented simultaneously. The methodology has been applied to the design of expander cycle based liquefaction processes. A parameter named Effective Heat Transfer Factor (EHTF) was found to be able to indicate the performance of heat exchanger networks.

In their work, liquefaction processes of hydrogen, methane and nitrogen were selected as case studies to illustrate the optimal design methodology. The simulation results showed that relatively high exergy efficiencies of liquefaction (52% for hydrogen and 58% for nitrogen and methane) can be achieved under some general assumptions, and the use of a cryoturbine could significantly enhance the exergy efficiency compared with the use of a throttle valve.

In addition, the results also indicated that an optimized system configuration may be too complicated and multi-objective optimization is needed to consider both the efficiency and the capital cost.

The paper was published in Applied Energy.