One of the key process technologies required for intensive fish farming is dissolving oxygen gas into the farm water. There are many technologies available to accomplish this, ranging from simple low head oxygenators (LHO) to very elaborate, multi‐stage processes operating at elevated pressures and controlled by computers. What the commercial fish farmer really wants and needs is a simple, reliable process for dissolving oxygen gas into the water that does not cost more than necessary and can be maintained by farm personnel without a huge time requirement. Above all it needs to be reliable, even during disruptive events like power failures.

In 2010, JLH Consulting and Aquacare began an initiative to lower the cost of land-based intensive fish farming operations. This initiative focused on two of the largest cost factors: pumping head and oxygenation. The pumping head has now been reduced by several meters by lowering the biofilter and CO2 strippers to a level where gravity can supply them, and only pumping clean filtered water back to the fish tanks with high flow, low head pumps. This reduction in pumping head led to another challenge: oxygenation with lower head.

In 2012, we had the good fortune to meet the people at France Oxygenation (FOX) who have developed and market a simple, reliable and efficient oxygen saturator under the name of OxyFlow®. Upon closer examination, this unit process technology was exactly what we were seeking to lower the cost of dissolving large amounts of oxygen into the fish farm water, reliably and efficiently.

Essentially, the OxyFlow® is an LHO that operates in a sealed vessel thus not breaking head pressure. Process water enters the top of the unit under mild pressure of about 0.3 bar. The water next passes through a horizontal drilled plate with specially shaped orifice holes (number and size determined by flow rate required) which jets the water downward though an oxygen atmosphere approx. 20 cm deep. When the jets strike the water surface below, they cause a high turbulence and create a bubble cloud of pure oxygen that extends downwards to 40 cm below the surface of the water. These buoyant bubbles flow upwards, counter to the downward water flow in such a way that the downward velocity is not strong enough to carry the bubbles out of the chamber, hence the only way the oxygen gas can escape the OxyFlow® unit is to become dissolved in the water. Bubbles that break the water surface inside the unit are again subjected to the turbulence of the downward jets until they become dissolved. A small amount of Nitrogen gas that remains in the oxygen rich atmosphere is vented off to prevent it from becoming dissolved in the water. Thus the goal of reliable, cost effective transfer of gaseous oxygen into dissolved oxygen is accomplished. While the oxygen use efficiency of the Speece Cone may be marginally higher than the OxyFlow®, the 3 x energy cost of the Speece Cone more than outweighs such benefits.

 

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Summary of features and benefits

1. Most cost efficient oxygen dissolving unit process device; operating at 0.3 bar vs. Speece Cone at 3 bar. This differential in pressure represents a significant cost savings on power bills.

2. Very reliable design, with no moving parts or restrictive passages. OxyFlow® is a very simple, low head device. The Speece Cone is somewhat similar but only with one large jet at high pressure instead of  multiple low pressure jets that create more oxygen/water contact area at much lower pressure. The LHO is also similar, but looses head as water flows through it and is less efficient at dissolving oxygen.

3. Facilitates the oxygenation of all the water supplied to the fish tank, not just a side‐stream loop, for more constant oxygen levels throughout the tank. This has important benefits for the fish in the tank, with better mixing and more even oxygen distribution inside the tank. The OxyFlow® can be combined with a constant pressure pump to maintain proper flow through the process unit under varying conditions.

4. The OxyFlow and its related devices have been in use on fish farms in Europe since 1994. There is currently an installed base of over 183 units in Europe, plus 47 units installed at a fish farm in the US and 16 units on order for a fish farm expansion in Australia. Many units are for repeat customers. A floating version is available for open water sea cage farm oxygenatio.

Fox France was established as a specialist oxygenation technology company in 2005, after founder Bohumil Sevic developed the technology in 1977 as a research engineer for Air Liquide in France. He was able to retain the I.P. after leaving Air Liquide. Since then Mr. Sevic has continued to refine and evolve the technology to where it is today. Aquacare is an OEM distributor for FOX, which allows us to cost effectively deploy this ideal oxygenation technology into our clients intensive fish farms world‐wide.