Abstract

Liquid piston systems (LP) are an efficient, simple, and environmentally friendly way to harvest energy from relief pressurised gas flows. In this paper, we study an LP system that operates by constantly introducing gas into a piston chamber containing water. The expansion of the gas propels the water, resulting in an isothermal expansion process due to their interaction. The discharged water is used to generate electricity. A dynamic model was developed using gPROMS and the numerical results were validated against previously published experimental data. The power output predictions show a maximum relative error of 6.4% from the experimental results. The performance of the LP system was evaluated employing waste gas data obtained from a liquefaction plant utilised to supply oxygen to a metallurgical furnace located in Chile. The predicted thermal efficiencies for the case study were as high as 80%, and the produced power output was 90 kW. The cost analysis demonstrated a decrease of 5.9% in electricity consumption attributed to the LP recovery system. Furthermore, the economic analysis illustrated a payback period for the investment ranging from 1.7 to 3.8 years, followed by an annual savings generation spanning from 24 to 47 kUSD depending on the electricity cost.