A study of nano-micro-bubble process for CO2 absorption in water for biogas upgrading application

• Novel micro-bubble system for physical absorption of CO 2 in water was developed. • Effects of inlet pressure, flow rate and CO 2 content on CO 2 removal were studied. • Under optimum conditions, 95.1% of CO 2 removal was achieved from biogas testing. The work proposed a novel micro-bubble system using swirling jet flow method for improving the physical absorption of CO 2 in water. The effects of operating conditions; e.g. gas flow rate (from 500 to 2000 mL/min), inlet pressure (2 and 3.5 bar) and inlet CO 2 concentration (from 5 to 60% v/v in CO 2 /N 2 gas mixture) on the physical absorption of CO 2 were studied. It was found that the CO 2 absorption system reached to steady state after 30 minutes with the outlet CO 2 concentrations of 2.9% and 8.8% at 40% and 60% of inlet CO 2 concentrations, respectively. These outlet CO 2 concentrations demonstrated the standard of bio-methane for replacing natural gas in vehicle use, from which less than 10% CO 2 is required. Moreover, the increase of gas flow rate resulted in increase of outlet CO 2 concentration. The rising of inlet pressure from 2 to 3.5 bars let to reduction of the outlet CO 2 concentration together with enhancing the dissolved CO 2 concentration in water from 49.1 to 51.7 mg/L at gas flow rate of 2000 mL/min and 60% of inlet CO 2 concentration. The highest efficiency of CO 2 removal was 98.41% under gas flow rate at 500 mL/min with 60% of inlet CO 2 concentration. Under the optimized conditions, this system was tested with real biogas as raw material containing mainly 57.7% of CH 4 and 40.3% of CO 2 which achieved to remove the 95.1% of CO 2 removal and no significant loss of CH 4 . This highlight demonstrated the potential application of this technology for biogas upgrading or purification further.