Experimental study and modeling of a droplet CO2 absorber for the carbon-negative soda ash production

• Experimental evaluation of droplet absorber in DAC applications to produce Na 2 CO 3 . • New type of co-current droplet absorber: vertical injection without spray and fan. • Model with and without using CFD simulations to consider droplet coalescence. • CO 2 capture rate as engineering parameter to estimate the size the absorber. • Comparison to packed absorbers in terms of capture rate and energy consumption. As part of a new environmental-friendly and carbon-negative process for soda ash production, the use of a novel droplet absorber for the Direct Air Capture (DAC) of CO 2 with NaOH solutions is studied experimentally and by concomitant process modeling. Two different nozzle plates with different number of holes are tested, and the counter-current and co-current arrangements are evaluated in terms of change of CO 2 concentration, capture rate and energy consumption. In the co-current operation, the fall of small droplets drives the flow of air inside the absorber and no fan is required. The effect of the liquid flow rate, the CO 2 inlet concentration, the gas velocity, the temperature and the liquid concentration is quantified. Two models are compared: one neglecting and the other considering droplet coalescence using CFD simulations. The inclusion of the force balances in the model allowed proper description of the fluid velocities and specific surface area inside the droplet absorber. Due to the high specific surface areas obtained (100–400 m 2 /m 3 ), the studied droplet absorber outperforms reported spray absorbers for CO 2 capture. The capture rate is in the range between 0.7 and 2.4 kg CO 2 /(h-m 3 absorber) and the energy consumption between 248 and 1008 kWh/(t CO 2 ), depending on the operational conditions. The performance and practical implementation of the droplet absorber in comparison with standard absorbers for DAC applications are discussed.