Design exploration of a two-phase methanol expander with high gas fraction and thermodynamic, economic, and sensitivity analyses of it in the Rectisol system

In recent years, liquid expanders have increasingly replaced traditional Joule-Thompson (JT) valves in high-energy Rectisol processes for energy savings. Besides liquid throttling, gas-liquid two-phase throttling is also common, with gas fractions of 0.1-0.2. However, the existing studies have not addressed two-phase expanders with such high gas content, and the application and research on them in the Rectisol system have not been reported. This paper develops two-phase methanol expanders for various Rectisol locations, conducts flow simulations to assess feasibility. The obtained performance parameters are then used in process simulation to analyze how two-phase expanders affect energy efficiency in a validated Rectisol system. Introducing a two-phase expander at three locations in the Rectisol system reduces energy use by 0.33, 1.54, and 2.03, boosts CO2 capture by 0.28, 4.40, and 6.07, and decreasing in energy consumption per unit of CO2 by 0.60, 5.69, and 7.63, respectively. The CO2 footprint analysis and Exergy analysis are conducted to demonstrate how replacing the JT valve with a two-phase expander affects the system and also explain their differences at different locations. Economically, replacing the JT valve with a two-phase expander is cost-effective and low-risk.