Analysis of liquefaction processes for liquid air energy storage systems: Conceptualization and evaluation of two-phase expansion concepts

The growing share of variable renewable electricity increases the need for large-scale storage. Liquid Air Energy Storage (LAES) offers high energy density and flexible siting; however, its overall performance fundamentally depends on the thermodynamic coupling between the cooling cycle and the two-phase expansion method. While previous studies have often treated these stages in isolation, this work comprehensively evaluates the integrated effects of four liquefaction cycles—Linde (non-bypass), Claude, Kapitza, and Heylandt (bypassed)—and four expansion schemes, including the two-phase turbine (TPT), Joule–Thomson valve (JTV), and a novel “combined expansion” concept utilizing a single-phase expander (SPE) with either a JTV or a nozzle. A steady-state thermodynamic model, supplemented by an in-depth exergy destruction analysis, is utilized to investigate operational trends and fundamental physical limits within feasible ranges. The results suggest that non-bypass cooling combined with near-isentropic expansion performs best; specifically, the Linde cycle integrated with an SPE and a nozzle attains a maximum liquid yield of 87.1% and a round-trip efficiency (RTE) of 54.0%. Exergy analysis confirms that placing the expander in the single-phase region and using a nozzle in the two-phase region significantly mitigates thermodynamic irreversibilities, such as isenthalpic throttling losses. Furthermore, component-level evaluations demonstrate that higher nozzle efficiency raises both liquid yield and RTE, making it a critical target for component development. Ultimately, these comprehensive insights establish a robust comparative baseline and provide clear guidance for the optimal, liquid yield-driven design of LAES systems.