Introduction of chilled ammonia process

https://doi.org/10.1016/j.seppur.2021.118959

“In NH₃-based CO₂ capture processes, NH₃ can reach concentrations between 4,500 and 31,000 ppm in the FG exiting the CO₂ absorber [7]. Nevertheless, the maximum NH₃ concentration recommended by the US National Institute of Occupational Safety and Health is 25 ppmv [8], and emission limits at the stack of existing ammonia production facilities in the European Union (EU) do not exceed concentrations higher than 10 to 40 ppmv, depending on the specific national legislation [9]. NH₃ concentration in the FG leaving the CO₂ absorber can be limited by lowering the temperature, by decreasing the NH₃ concentration and by increasing the CO₂ content of the solvent [3]. To this aim, the Chilled Ammonia Process (CAP) patented by Alstom [10] uses aqueous NH₃ solutions at temperatures between 0 and 20 °C to limit the NH₃ slip to the FG, which requires additional energy for solvent refrigeration. The original CAP concept suggests the formation of solids in the absorber tower as a way to limit the energy consumption in the CO₂ desorber. Nevertheless, clogging of the tower packing and difficulties in operating the system have prompted the CAP towards a solid-free operating mode [11], [12]. Accordingly, the current CAP implementations avoid solid formation by limiting the solvent NH₃ and CO₂ concentration in the absorber [13], [14]. Although the energy consumption of the CAP, including the solvent chilling demand, can be minimized by proper selection of the operating conditions throughout process optimization [3], [14], the FG exiting the CO₂ absorber still requires further treatment to limit the NH₃ concentration at the stack to values below 10 ppmv. “