Liquid air energy storage for combined cooling, heating and power : techno-economic performance enhancement through waste heat & cold recovery

• Main Author: Tafone, Alessio
• Other Authors: Alessandro Romagnoli
• Format: Thesis-Doctor of Philosophy
• Language: English
• Published: Nanyang Technological University 2020
• Subjects: Engineering::Mechanical engineering::Alternative, renewable energy sources; Engineering::Mechanical engineering::Motors, engines and turbines
• Online Access: https://hdl.handle.net/10356/142963
• Institution: Nanyang Technological University

Large scale or grid scale Electrical Energy Storage systems (EESs) represent one of the most viable solutions to address some of the issues related with the integration of large portion of renewables into the future grid and to facilitate their further penetration guaranteeing the required flexibility and reliability of the electrical grid. Besides mitigating grid instability, large scale EESs also allow decoupling demand and supply, hence offering the opportunity to be operated as peak-shavers during peak demand hours. Concurrently, another global pressing issue is represented by the constant increase of cooling demand arising by the global warming and rapid development of emerging countries, usually located in the warmer areas of the world. Indeed, using conventional cooling technologies might be not sustainable putting at stake the reliability of existing electrical networks and dramatically increasing the greenhouse gas emissions. As a consequence, new thinking on how to efficiently integrate and recover cold into the wider energy system becomes necessary. Liquid Air Energy Storage (LAES) is one of the most promising large scale energy storage concept that stores electricity in the form of liquefied air/nitrogen discharging electric power back to the grid by means of liquid air regasification and expansion in power producing devices. LAES has recently attracted significant attention in research and industry due to several advantages among which viable capital costs, high energy density and no geographical/geological constrains. In particular, due to its intrinsic thermo-mechanical nature, it is capable to be integrated with other valuable high exergy energy carriers (e.g. waste heat/cold from industrial process/ Liquefied Natural Gas regasification) and to simultaneously produce both electricity and free cooling energy being configured an ideal technology bridge between enhancement of RES exploitation and the necessity to face the booming of cooling demand. Beside those benefits, the main LAES drawback has been identified in the low value of the round-trip efficiency, estimated around 50-60 % for large scale systems, mainly due to the low exergy efficiencies during the air liquefaction and power recovery processes. This thesis aims at contributing at the broader field of large scale energy storage by adopting a novel system perspective which puts a special focus on interactions within the system in order to seek the optimal operation conditions and the best route for performance enhancement of LAES system. In particular, the thesis proposes a novel and systematic methodology for LAES system (plant based) design in order to investigate LAES performance and identify potential areas of improvements. To this end, a steady state model has been developed and used then to simulate the performance of different system architectures. Based on a comprehensive sensitivity analysis carried out on different LAES operative parameters, a methodology for the LAES design is progressively developed and integrated in a well defined procedure. The novel methodology incorporates new parametric performance maps as a unique and user-friendly tool for LAES design under operative parameters variation for different configurations. The optimized LAES system have been environmentally analyzed by means of LCA methodology: among three large scale EESs assessed LAES has proved to deliver the lowest environmental impact. Once defined the main areas of opportunity based on the outcomes of the previous technical analysis, the thesis aims to develop and assess, from a techno-economic perspective, novel LAES architectures either operating in the conventional full electric configuration or providing both electricity and cooling energy in the novel polygeneration configuration. Indeed, the second part of the thesis proposes different and novel technology solutions to enhance both the thermodynamic and economic performances of LAES by a more efficient utilization of the thermal energy (heat and cold) streams during LAES operation. Firstly, waste heat recovery concept is proposed and efficiently integrated in LAES. Indeed, the most remarkable results are achieved by LAES in polygeneration configuration where the Organic Rankine Cycle technology allows to improve the LAES round trip efficiency by 20 % decreasing at the same time the Levelized Cost of Storage by 10 %. Finally, to effectively recover the waste cold discharged by liquid air regasification, a Phase Change Material-based (PCM) High Grade Cold Storage (HGCS) is proposed. Two different configurations (single and cascade PCM) have been modeled and compared with a baseline case configuration where Sensible Heat material is implemented. For this purpose, a numerical model of the HGCS has been developed and successfully validate against experimental data to increase the confidence on the results. The techno-economic analysis has shown that, due to its ability to act as thermal buffer, PCM implementation guarantees a decrease of LAES specific consumption up to 10 % with a remarkable payback period inferior to 5 years.