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Recirculating Aquaculture Systems Short Course GAS TRANSFER M. B. Timmons, Ph.D. Biological & Environmental Engineering Cornell University Brian J. Vinci.

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Presentation on theme: "Recirculating Aquaculture Systems Short Course GAS TRANSFER M. B. Timmons, Ph.D. Biological & Environmental Engineering Cornell University Brian J. Vinci."— Presentation transcript:

1 Recirculating Aquaculture Systems Short Course GAS TRANSFER M. B. Timmons, Ph.D. Biological & Environmental Engineering Cornell University Brian J. Vinci The Conservation Funds Freshwater Institute

2 Recirculating Aquaculture Systems Short Course Dissolved Gases - Fundamentals Species% volume% mass Molecular Wt. Nitrogen Oxygen CO Argon Air Dry Air Components

3 Recirculating Aquaculture Systems Short Course Dissolved Gases - Fundamentals Gas Species Solubility in Air* (mg/L) Solubility of pure gas* (mg/L) Oxygen Nitrogen Argon Carbon dioxide *At 15 Deg. C. The solubility of a gas (mg/L)

4 Recirculating Aquaculture Systems Short Course Gas Solubility Equations The solubility of a gas (mg/L) is determined using Henrys Law i = Bunsen Coefficient for gas species i, L/L-atm X i = Mole fraction of gas (dimensionless) P BP = Barometric pressure, mm Hg P WV = Water vapor pressure, mm Hg Solubility (gas) Coefficient = mls gas per mls liquid (water)

5 Recirculating Aquaculture Systems Short Course Gas Transfer Gas Transfer Occurs Due to Pressure Differences Q x (mass/time) = ( 1/ R) (P i,high – P i,low ) where Q = rate of gas flow of species x P = pressure X = gas species R = Resistance to flow (design related ) Design and Operation will influence RESISTANCE to gas transfer RESISTANCE to gas transfer

6 Recirculating Aquaculture Systems Short Course Values for Pressure Atmospheric Pressure –Sea Level 760 mm Hg (mercury) 34 feet of water column psi Correcting for Elevation h is feet (not meters) of elevation above sea level

7 Recirculating Aquaculture Systems Short Course Terms Used to Describe Pressure Total Gas Pressure = SUM of all Partial Pressures where: Partial Pressure = pressure contribution of an individual gas Gauge Pressure = Total Pressure – Atmospheric Pressure

8 Recirculating Aquaculture Systems Short Course Fundamentals of Gas Transfer Two factors that directly impact the rate of gas transfer: the area of gas-liquid interface the difference between the concentration (partial pressure) at saturation and the existing concentration of the gas in the water.

9 Recirculating Aquaculture Systems Short Course Gas Transfer Options Aeration Systems – Air Stones, Packed Towers Sources of Air

10 Recirculating Aquaculture Systems Short Course Gas Transfer Options Air stones: very inefficient O 2 transfer devices (3 – 7%)

11 Recirculating Aquaculture Systems Short Course Gas Transfer Options Oxygen Transfer Systems Sources of Oxygen

12 Recirculating Aquaculture Systems Short Course Gas Transfer Options U-tubes "Rule of Thumb" U-Tube Aerator Design U-Tubes for a down flow velocity between 2 m/s to 3 m/s Limit G/L ratio to <25%

13 Recirculating Aquaculture Systems Short Course Gas Transfer Options Packed Columns

14 Recirculating Aquaculture Systems Short Course Gas Transfer Options LHOs

15 Recirculating Aquaculture Systems Short Course Gas Transfer Options Aeration Cone Or Down-Flow Bubble Contactors

16 Recirculating Aquaculture Systems Short Course Gas Transfer Options Diffused Aeration (Air Stones)

17 Recirculating Aquaculture Systems Short Course Gas Transfer Options Oxygen Injection

18 Recirculating Aquaculture Systems Short Course Gas Transfer CO 2 Degassing: Carbon Dioxide (Nitrogen)

19 Recirculating Aquaculture Systems Short Course Gas Transfer CO 2 Carbon Dioxide Stripping: counter-current air-stripping columns

20 Recirculating Aquaculture Systems Short Course Gas Transfer CO 2 Carbon Dioxide Stripping: counter-current air-stripping columns

21 Recirculating Aquaculture Systems Short Course Gas Transfer HLR Gas Transfer DeviceGas Species Hydraulic Loading Rate kg/m 2 sgpm/ft 2 Packed Columns Sealed columnsoxygen <166 <244 High Pressure Columnsoxygen45–24666–361 Pure Oxygen, atmosphere pressureoxygen73107 Open to atmospherecarbon dioxide17–3425–50 Spray Toweroxygen35–9551–140 Low Head Oxygenator (LHO)oxygen34–6850–100 Down Flow Bubble Contactors (Speece cone) at inletoxygen1, at outlet (to keep bubbles in) U-Tubesoxygen2,000–3,0002,940–4,410

22 Recirculating Aquaculture Systems Short Course Gas Transfer Installation and Safety Concerns


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