Feasibility assessment of a spray tower for gas-liquid reactive precipitation in CO2 capture

The industrial deployment of ${CO}_2$ capture technologies for purifying gases with low ${CO}_2$ partial pressure (e.g., flue gas) has been limited due to substantial economic hurdles. Process intensification offers a pathway to enhance the cost efficiency of ${CO}_2$ sequestration. One approach that has garnered significant attention is the process integration of phase-change absorbents. Among these, bis(iminoguanidines) have shown considerable promise in recent literature. Particularly, glyoxal-bis(iminoguanidine) (GBIG) has demonstrated the ability to precipitate ${\mathrm{HCO}}_3^{-}$ with low regeneration energy demand. However, GBIG and comparable phase-change absorbents require the integration of alkaline scrubbing with reactive precipitation in a single unit operation (gas-liquid reactive precipitation), introducing operational challenges such as scaling and clogging in conventionally applied packed-bed columns. To mitigate these issues, this study investigates the use of a spray tower as a gas-liquid reactive precipitator for ${CO}_2$ capture from a flue gas surrogate. A pilot-scale spray tower is designed, constructed, and operated. Contrary to expectations, Rayleigh breakup of liquid jets induces a bimodal droplet size distribution in the lower sections of the tower, indicating limited scalability and highlighting the need for liquid recycling. For comparative purposes, the investigation includes a ${CO}_3^{2-}$-precipitating system (${\mathrm{Ba}\left(\text{OH}\right)}_2$) and a non-precipitating system ($\mathrm{NaOH}$), alongside GBIG. All systems demonstrate stable operability in single-pass and batch modes. During liquid recycling, small amounts of solids are entrained to the tower top. Nevertheless, no evidence of scaling or clogging is detected at the orifice plate, suggesting that the precipitated solids are significantly smaller than the orifice diameter. In the final performance comparison, the $\mathrm{GBIG}$ system demonstrates superior ${CO}_2$ capture efficiency relative to the ${\mathrm{Ba}\left(\text{OH}\right)}_2$ system. However, achieving this efficiency comes at the expense of process kinetics.