Evaluation of air-lift pump capabilities for water delivery, aeration, and degasification for application to recirculating aquaculture systems
1998
Loyless, J.C. | Malone, R.F.
A methodology is demonstrated for evaluating the feasibility of using air-lift pumps for water movement, aeration, and degasification in a recirculating aquaculture system. A set of empirical equations are presented modeling the performance of a 5.08-cm (2") diameter air-lift submerged 91.44 cm (36") with a 15.24-cm (6") lift operated at 28-142 1 min(-1) (1-5 scfm) of air injection. A steady state mass balance on oxygen and carbon dioxide, equating the system requirements to the air-lift capabilities is illustrated. Using the empirical relationships developed and standard methods to estimate system O2 demand and CO2 production, equations are derived to calculate steady state DO and DC concentrations for any number of air-lifts used in a given recirculating system. The predicted air-lift performance in a typical system indicates the water delivery capacity for low head applications is significantly above the gas exchange capabilities. It is recommended that air-lifts be designed for water delivery and that the demonstrated methodology be used to estimate their supplemental aeration and degasification performance. Open-water aeration is shown to be more energy efficient than aeration using air-lifts. The data suggests that, for blown air systems, when the aeration requirements are met, the carbon dioxide stripping requirements are also. Suggestions for designing recirculating systems utilizing air-lifts are also presented.
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