A Study of a Liquid Piston System and its Integration with Liquid Air Energy Storage, NH3 and CO2 Cycles: Modelling, Simulation, and Experimental Design

This study studies the performance of a Liquid Air Energy Storage (LAES) system integrated with a Liquid Piston (LP) system for electricity generation. The novel LAES-LP system incorporates an LP device to recover energy during the discharge phase of the LAES plant. It replaces the conventional air turbine with an LP system, which expands vaporised air to generate power. LP expansion systems generate mechanical work by utilising gas pressure within a liquid reservoir. The potential energy of the gas performs boundary work on the liquid gas interface, enabling the liquid to gain momentum as it flows outside the container. The liquid goes towards a hydraulic turbine to generate power. The benefits of integrating LP technology into a LAES system, are high conversion efficiency (70-96%), high specific power (100-220 kJ/kg), design flexibility, scalability, cost reduction, and increased life span. The research aims to enhance the round-trip efficiency (RTE) of the LAES-LP system. Additionally, there is an objective to experimentally investigate the novel LP system in collaboration with the Technical University Federico Santa Maria in Chile. The methodology of the study is by performing modelling, simulation, and optimisation of the LAES and LP using gPROMS Model Builder®. This content is presented in Chapter 3, where the equations and assumptions for the LAES and LP models are detailed. The validation of the models is shown in Chapter 4, where the simulation results of the LP system are contrasted with similar LP systems of power ratings of 300 W and 4 kW. The predicted relative errors were less than 6.4%. Moreover, the results of the LAES model validation for predictions of parameters such as temperature, liquid yield, and round-trip efficiency (RTE) were less than 2.8% with experimental data, thus validating the research methodology.