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

The work proposed a novel micro-bubble system using swirling jet flow method for improving the physical absorption of CO2 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 CO2 concentration (from 5 to 60 % v/v in CO2 /N-2 gas mixture) on the physical absorption of CO2 were studied. It was found that the CO2 absorption system reached to steady state after 30 min with the outlet CO2 concentrations of 2.9 % and 8.8 % at 40 % and 60 % of inlet CO2 concentrations, respectively. These outlet CO2 concentrations demonstrated the standard of bio-methane for replacing natural gas in vehicle use, from which <10 % CO2 is required. Moreover, the increase of gas flow rate resulted in increase of outlet CO2 concentration. The rising of inlet pressure from 2 to 3.5 bars let to reduction of the outlet CO2 concentration together with enhancing the dissolved CO2 concentration in water from 49.1 to 51.7 mg/L at gas flow rate of 2000 mL/min and 60 % of inlet CO2 concentration. The highest efficiency of CO2 removal was 98.41 % under gas flow rate at 500 mL/min with 60 % of inlet CO2 concentration. Under the optimized conditions, this system was tested with real biogas as raw material containing mainly 57.7 % of CH4 and 40.3 % of CO2 which achieved to remove the 95.1 % of CO2 removal and no significant loss of CH4 . This highlight demonstrated the potential application of this technology for biogas upgrading or purification further.