Learning centre
The numbers behind Minox
Utilities, chemical cost, reservoir impact and four decades of published research. The detail engineers ask for, in one place.
Minox™ - Utilities & chemicals
Low on utilities
Free of scavenger
Minox strips oxygen with nitrogen in a closed loop. Its only consumable is a small, steady methanol feed that regenerates the stripping gas, so nothing is dosed into the injection water.
[01]
Methanol
A small, continuous feed of about 7.5 L/h at maximum capacity for a 150 – 200 kBWPD system. It is drawn from the bulk storage most FPSOs already have and metered automatically by the Minox control panel.
[02]
Nitrogen
The stripping gas circulates in a closed loop and is regenerated over a catalyst. Make-up only replaces the nitrogen that dissolves into the treated water.
[03]
Oxygen scavenger
Not needed in normal operation. Minox meets the dissolved-oxygen spec on its own, so no sulphur chemicals go downhole with the injection water.
methanol at maximum capacity
of a typical FPSO’s methanol design demand
nitrogen make-up, maximum
Chemical saving per year vs. scavenger
23×
less chemical sent downhole
Methanol supply
A minor share of
methanol demand
Methanol is already critical on most FPSOs, for hydrate inhibition, gas export and gas lift. Minox adds a small, continuous load that fits within existing storage and logistics.
Hydrate inhibition
Gas export
Subsea production wells
Gas lift
Minox
Methanol supply
Spared at every step
Methanol is drawn from the bulk tanks that already serve other consumers. The Minox control panel meters the flow automatically, and an optional buffer tank adds autonomy.
[01]
Comparison
Direct supply
Fed straight from bulk storage through redundant pumps.
Bulk methanol storage
Existing tanks, 3 × 3,000 bbl
Methanol pumps
2 × 100%, ≈ 7.5 L/h
Minox deoxygenation
[02]
Extra redundancy
Buffer tank
A small local tank, topped up in batches, decouples Minox from the bulk system.
Bulk methanol storage
Existing tanks, 3 × 3,000 bbl
Buffer tank
2 m³, ≈ 10 days autonomy
Methanol pumps
2 × 100%
Minox deoxygenation
Continuous
Existing methanol consumers continue to draw from the same bulk storage. Tank sizes are an example.
Chemical consumption
≈ USD 0.7 million a
year less in chemicals
Minox reaches the dissolved-oxygen spec without scavenger polishing. Its only chemical is methanol, so the fair comparison is methanol against oxygen scavenger.
[01]
176 000 BWPD seawater
Full flow
CHEMICAL, L/H
Minox (methanol)
7.5
Vacuum (O₂ scavenger)
29
CHEMICAL COST, USD PER YEAR
Minox (methanol)
33–66 k
Vacuum (O₂ scavenger)
762 k
[02]
88 000 BWPD seawater
Half flow
CHEMICAL, L/H
Minox (methanol)
3.75
Vacuum (O₂ scavenger)
14.5
CHEMICAL COST, USD PER YEAR
Minox (methanol)
16–33 k
Vacuum (O₂ scavenger)
381 k
Assumptions
4 ppm
chlorine in seawater
< 50 ppb
O₂ from vacuum tower
0.5–1 USD/L
methanol, incl. worst case
3 USD/L
oxygen scavenger
8,760 h/yr
continuous operation
Reservoir impact
Nothing dosed
into the water
Scavenger is dosed straight into the injection water and goes downhole with it. Minox consumes its methanol in the gas loop, leaving the water and its chlorination untouched.
Worst case: if 0.8 L/h of methanol reached the water
0.54 mg/L
methanol in 1,166 m³/h seawater
≈ 23× less
than the bisulphite dose it replaces
0.64 vs 14.7
kg/h of chemical sent downhole
1 teaspoon
in a 7,500 L tank, the same dilution
Redundancy & back-up
Redundant by design
Losing nitrogen or methanol supply takes at least a double failure. For short upsets, such as off-spec inlet water, one IBC of scavenger on standby is enough.
Spared, with air back-up
Nitrogen
A small add-on to the N₂ package
Closed loop, regenerated catalytically
Make-up ≈ 41 Sm³/h at maximum
≈ 10–16 kW extra at N₂ generator
Instrument air as back-up make-up
Spared at every step
Methanol
No single point of failure
Any of the existing bulk tanks
Optional 2 m³ buffer, ≈ 10 days
2 × 100% metering pumps
Automatic flow control
For short upsets only
Scavenger
No bulk inventory on board
1 × 1,000 L IBC on standby
≈ 34 h at full flow, 50 → 10 ppb
Vacuum case uses this every 34 h
≈ 254 m³ per year avoided
N₂ generation is normally outside Minox scope. Power is an indicative range for membrane or PSA at > 98% N₂. IBC endurance depends on seawater chlorine content.
CO₂ in seawater.
CO₂ in seawater
Why seawater holds far more CO₂ than oxygen, and how carbonate chemistry keeps most of it as bicarbonate.
~330 ppm
CO₂ in air
~90 ppm
dissolved CO₂ in seawater
~7 ppm
dissolved O₂, for comparison
Over 10× more soluble than O₂, because CO₂ reacts with water.
Why seawater holds far more CO₂ than oxygen, and how carbonate chemistry keeps most of it as bicarbonate.
CO₂(aq) + H₂O ⇌ H₂CO₃
H₂CO₃ ⇌ HCO₃⁻ + H⁺
HCO₃⁻ ⇌ CO₃²⁻ + H⁺
Species distribution in seawater
CO₂(aq) + H₂CO₃
~1%
Bicarbonate, HCO₃⁻
~93%
Carbonate, CO₃²⁻
~6%
Technical papers
Published research
Minox was developed with Norsk Hydro’s research centre in Porsgrunn from 1985 and first installed on Snorre A in 1991. Since then our engineers have published on nitrogen stripping, catalytic regeneration, hydrogen deoxidisers and compact CO₂ capture.
Paper titles link to OnePetro or the publisher. Full texts available on request.