Analysis of Design Factors Influencing the Oxygen Transfer of a Pilot-Scale Speece Cone Hypolimnetic Aerator

Abstract

The objective of this research was to characterize the performance of a pilot scale downflow bubble contact (DBCA) hypolimnetic aerator, the Speece Cone. The effect of two key design factors, inlet water velocity and the ratio of gas flow rate to water flow rate on four standard units of oxygen transfer, was examined: (a) the oxygen transfer coefficient, KLa, corrected to 20°C, KLa20 (h−1); (b) the standard oxygen transfer rate, SOTR (g O2·h−1); (c) the standard aeration efficiency, SAE (g O2·kW h−1); and (d) the standard oxygen transfer efficiency, SOTE (%). Two sources of oxygen, pressure swing adsorption (PSA) oxygen (87% purity oxygen) and air (∼21% oxyzen) were compared. KLa20, SOTR, and SAE increased with an increase in the ratio of gas flow rate to water flow rate for both air and oxygen, over a range of 0.5% to 5.0%; while SOTE deceased. An increase in inlet water velocity resulted in a decrease in KLa, corrected to 20°C, SOTR, and SAE, but an increase in the SOTE. Experimental treatments with air showed similar, but much less dramatic effect of the gas flow rate to water flow rate ratio and water inlet velocity on KLa20, SOTE, SAE, and SOTE, when compared to treatments with PSA oxygen. The best oxygen transfer performance was achieved with an inlet water velocity of 6.9–7.6 m·s−1 and oxygen flow rate to water flow rate ratio of about 2.5%. At this combination, the SOTE was about 66–72%. Further experimentation with inlet water velocity is required to increase oxygen transfer performance to the >95% range which has been reported in the literature for Speece Cone oxygenation systems.