CO2 capture using gas-lift pumps operating under two-phase flow conditions

Abstract

• Gas-lift pumps is evaluated for degasification (CO 2 stripping). • Simulated flue gas containing different volumetric CO2 concentrations is investigated. • Two-phase flow hydrodynamics is evaluated using high-speed imaging and capacitance sensor . • Churn flow is found to demonstrate superior mass transfer performance. • The CO 2 mass transfer performance exhibits a linear growth trajectory within the slug flow regime. CO 2 capture through dissolution in water offers environmental benefits and industry applications. However, current studies mostly focus on CO 2 extraction into solvents, overlooking its direct solubility in water. Alternatively, gas-lift pumps may hold significant potential for capturing and storing CO 2 in water; but this ability remains unexplored. Therefore, this study experimentally delves into the CO 2 capture capacity and hydraulic performance of a dual injection gas-lift pump with a 25.4 m m riser diameter. Operating at a constant submergence ratio of 70 %, the pump is fed with simulated flue gas with flow rates within 5–30 L P M at volumetric CO 2 concentrations of 10 %, 15 %, and 25 %, and temperatures of 22 °C (isothermal operation) and 110 °C (non-isothermal operation). Two-phase flow hydrodynamics is also evaluated using high-speed imaging in conjunction with time-series void fraction measurements. Within the riser pipe, three distinct two-phase flow patterns — slug, intermittent, and churn flows — are identified. The results reveal that under both isothermal and non-isothermal operations and across all volumetric CO 2 concentration levels, churn flow demonstrates superior mass transfer coefficient and lifted liquid flow rate, while slug flow achieves minimum energy consumption per ton of captured CO 2 , highest CO 2 capture degree, and maximum lifting efficiency. Also, the highest degrees of sensitivity to inlet gas flow rate for volumetric mass transfer coefficient, delivered liquid flow rate, and void fraction were observed in slug flow regime. Both gas temperature and volumetric CO 2 concentration positively impacted the mass transfer performance. However, the pump showed remarkably higher lifting efficiencies under isothermal operation conditions. Moreover, compared to four established CO 2 capture methods (absorption, adsorption, cryogenic distillation, and membrane diffusion), the gas-lift pump exhibits moderately lower energy consumption, at 38-266 k W h / t o n C O 2 , but with lower CO 2 capture degree of 2.3 % to 6.7 %.

Topics & Concepts