Oxygen Cones for RAS — Specs, Sizing & Supplier Quotes
Oxygen cones — downflow bubble contactors — dissolve pure oxygen into a pressurised side-stream at 90%+ absorption efficiency. They are the standard oxygenation stage in RAS and high-density land-based farms. This guide covers sizing to your oxygen demand, the LOX versus on-site generation decision, and what drives price.
What oxygen cones do
- A cone-shaped pressure vessel: water enters at the top with injected pure oxygen and flows downward as the cone widens, slowing velocity until bubbles are held in suspension long enough to fully dissolve.
- Achieves 90–99% oxygen absorption at pressure, versus roughly 30–50% for coarse diffusers — the reason it dominates in RAS, where oxygen is a purchased consumable.
- Installed on a pressurised side-stream, typically 5–20% of loop flow, so only part of the flow needs pumping to cone pressure.
- Alternatives include low-head oxygenators (LHO), U-tubes and oxygenation in the pump sump; cones win where head is available and oxygen cost matters.
Typical specifications
| Parameter | Typical range | What it means for you |
|---|---|---|
| Absorption efficiency | 90–99% | The core selling point; verify at your operating pressure and flow, not at best case. |
| Operating pressure | 0.7–2.0 bar | Higher pressure means better absorption and higher pumping energy — the key trade-off. |
| Water flow per cone | 20–500 m³/h | Cone sized to side-stream flow, not total loop flow. |
| Oxygen transfer per cone | 5–120 kg O₂/day | Match to peak oxygen demand plus a safety factor. |
| Outlet DO | 15–35 mg/L in the side-stream | Blends back into the loop to reach the target tank DO. |
| Materials | GRP or 316L stainless | 316L for seawater and ozone service; confirm pressure-vessel certification. |
| Certification | PED / ASME pressure vessel | Often a permit and insurance requirement — confirm before ordering. |
| Instrumentation | DO probe, mass-flow control, pressure gauge | Automatic oxygen dosing to setpoint is what keeps consumption in check. |
Sizing guidance
Size oxygenation on peak oxygen demand at maximum biomass and temperature, then add capacity for the emergency case. Undersized oxygenation is the failure that kills fish fastest.
| Project scale | Indicative oxygenation duty | Design notes |
|---|---|---|
| Hatchery / nursery | 1 small cone or LHO, 5–20 kg O₂/day | Low absolute demand but zero tolerance — full backup oxygen supply required. |
| RAS grow-out, 200–500 t/yr | 2–4 cones, 100–350 kg O₂/day total | Cone per module plus a shared standby; automatic DO-setpoint dosing. |
| RAS grow-out, 1,000 t/yr+ | Multiple cones per module | Consider on-site PSA/VPSA generation with LOX backup at this consumption. |
| Post-smolt / high-density flow-through | Cones on the pumped side-stream | Confirm available head — cone pressure is only cheap when the pump already delivers it. |
Oxygen demand rule of thumb: 0.20–0.25 kg O₂ per kg of daily feed for fish respiration, plus biofilter nitrification demand of roughly 4.3 kg O₂ per kg of ammonia-N oxidised. Add 30–50% design margin for peak temperature, post-feeding spikes and future stocking increases.
How to choose
- Efficiency at your duty
Ask for absorption efficiency curves at your flow and pressure, not a headline 99% at a single ideal point.
- Head and pumping cost
The cone is cheap; the pressure it needs is not. Model the pumping energy over the project life before choosing cone over LHO.
- Oxygen supply route
LOX means lower CAPEX and higher OPEX with delivery dependency; PSA/VPSA means higher CAPEX, lower OPEX and a power dependency. Crossover typically sits around 300–500 kg O₂/day, site-dependent.
- Backup oxygen
An independent emergency oxygen supply with automatic low-DO release is non-negotiable and is checked by lenders and insurers.
- Certification
Pressure vessel certification (PED, ASME or local equivalent) plus documentation — retrofitting compliance after delivery is painful.
- Control and monitoring
DO probes with redundancy, mass-flow control to setpoint, alarm escalation and logging of oxygen consumed per tonne produced.
What drives the price
- Capacity and vessel size
Price tracks flow and transfer capacity; larger vessels step up materially.
- Material and certification
316L and certified pressure-vessel construction add substantially over GRP.
- Instrumentation package
Mass-flow control, redundant DO probes and PLC integration are a real cost line.
- Oxygen supply system
LOX tank, vaporiser and site works, or a PSA/VPSA plant, usually exceed the cones themselves.
- Redundancy
Standby cones and independent emergency supply are expected in a bankable design.
- Installation
Pipework, valves, supports and commissioning on a pressurised system are specialist scope.
Indicative pricing: €4k–€15k per small cone, €15k–€60k for large certified units with instrumentation. The complete oxygenation package — cones, LOX tank and vaporiser or a PSA plant, controls and emergency supply — typically runs €150k–€900k on a mid-scale RAS.
Common specification mistakes
- Sizing to average demand instead of peak biomass at peak temperature after feeding.
- Choosing cones without checking that the required head is already available in the loop.
- Comparing absorption efficiency figures quoted at different pressures and flows.
- No independent emergency oxygen supply with automatic low-DO release.
- Sizing the oxygen supply, LOX or PSA, before the cone duty is fixed, then buying twice.
Oxygen cones — buyer questions
Get quotes for oxygen cones
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