Analysis and evaluation of periodic separations using COPS trays

Stripping of dilute aqueous ammonia solutions with air, using an in-house developed cyclically operated column, has been explored in the past by our group [Toftegård B. et al., 2016. Ind. Eng. Chem. Res., 55 (6): 1720]. The column uses novel so-called cyclically operated perforated sheet (COPS) trays with a Sulzer Mellapak™ layer on top to prevent oscillations and enhance point efficiency. The column operates by the principle of sequential liquid draining. This enables continuous vapor flow, thereby avoiding interrupting the vapor flow during the liquid flow period, and allows the feed streams for distillation systems to be two-phased. It also means that, when applied to distillation operations with reboilers, one can avoid the necessity of special precautions (such as large control valves) against pressure dynamics possibly resulting from having to interrupt the vapor flow rate, during liquid flow. In this paper, an extended range of operation is explored with the realization mentioned above. The proposed periodic trays are operated - without weeping problems - at higher holdups with column efficiencies approaching 200%. This exceeds greatly past results obtained with other internals, such as conventional sieve trays. Also point efficiencies were determined for a series of combinations of liquid hold up and gas flow with the objective of validating the Lewis case 2, which forms the basis of periodic separation process. The COPS tray efficiency was almost twice as large as those of conventional sieve trays.