Intensifying the recarbonation process of water

Abstract

Gas–liquid contacting operations emphasize the enhancement of inter-phase mass transfer which is usually achieved by dispersing the gases into fine bubbles. Several reactor-contactor types are used for this purpose; however, many of which remain improperly designed because of their complex hydrodynamics. Lately, the interest is growing in the use of tubular reactors equipped with static mixers as they present an attractive alternative whereby the hydrodynamics are better controlled in order to enhance the mixing efficiency and mass transfer performance of the operations. A new type of static mixing element was recently introduced in which screens or grids are used and were found to be very effective at processing multiphase operations. Therefore, this study aimed at employing these static mixers in an attempt to intensify the absorption of CO2 in RO water without chemical reactions. Its success would allow achieving smaller reactor volumes and introducing various economical and safety enhancements to the process. Faster and more efficient re-carbonation processes can thus be conducted at lower energy consumption and space requirements. In addition, the success of the work would also impact the design of photo-bioreactors and influence various applications of biogas upgrading. To assess the efficiency of the reactor, the amount of absorbed CO2 was tracked along the reactor using two methods, namely, pH measurements and direct CO2 measurements using a CO2 analyzer. The effect of varying the liquid and gas flow rates, screen geometry, and inter-screen spacing on the mass transfer performance were investigated and analyzed. It was found that the measured volumetric mass transfer coefficients, kLa, were several orders of magnitude larger than those reported using conventional reactors. kLa values increased with increasing both the liquid and gas flow rates and reached a maximum value of 1.01 s-1 at low specific energy consumption rates (0.013 kWh-tonne). In addition, as the screen open area decreased, the kLa