Compressed Air & Gas Dryers

Hydrogen Dryer and De-Oxo Unit

Fuel-cell-grade hydrogen straight from your electrolyser, with oxygen and water each below 5 ppmv and no hydrogen vented in normal running.

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A skid-mounted hydrogen purification unit with its vessel, flanged pipework and automated valves

Product overview

Pure, dry hydrogen from your electrolyser

Our hydrogen dryer and de-oxo unit purifies the hydrogen your electrolyser makes. It removes the two impurities every electrolyser releases with its product gas, oxygen and water vapour, and delivers hydrogen with each below 5 µmol/mol (ppmv), the limits ISO 14687:2019 Grade D sets for fuel cell vehicles.

First, a palladium or platinum catalyst recombines the oxygen with hydrogen to form water. Then twin towers of molecular sieve adsorb the water vapour, including the water the reactor has just made. One tower dries while the other is regenerated by heat, so purified hydrogen flows continuously.

The regeneration gas is heated, passed through the saturated tower, cooled and returned to the process, so the water leaves as liquid condensate and no hydrogen is vented during normal operation. With hydrogen added, the same catalytic process removes oxygen from nitrogen and argon.

A skid-mounted hydrogen purification unit with its vessel, flanged pipework and automated valves
  • Below 5 ppmvOxygen and water, each
  • Below 1 ppmvOutlet oxygen, commonly achieved
  • 0.2 %Of product flow used to remove 1,000 ppmv oxygen
  • ZeroHydrogen vented in normal operation

Benefits

The problems it solves

Every electrolyser keeps its hydrogen and oxygen apart with only a thin membrane or diaphragm, so raw electrolytic hydrogen is always wet and carries oxygen. Here is what that does, and how the unit stops it.

  • Off-specification fuel

    The problem

    ISO 14687:2019 Grade D limits water and oxygen each to 5 µmol/mol, and oxygen at 1,000 ppmv alone exceeds the 300 µmol/mol total impurity allowance more than threefold.

    How it solves it

    Oxygen and water below 5 ppmv meet Grade D, and outlet oxygen below 1 ppmv is commonly achieved.

  • Ice at the dispenser

    The problem

    Stations pre-cool hydrogen to about −40 °C before filling at 70 MPa, and water in the gas freezes in valves, filters and the nozzle.

    How it solves it

    Water at 5 ppmv corresponds to a frost point of about −65 °C at atmospheric pressure, so your dispensers and pre-cooled lines stay free of ice.

  • Oxygen gathering in storage

    The problem

    Hydrogen containing oxygen becomes flammable above roughly 6 % oxygen, and oxygen concentrates during part-load operation of the electrolyser.

    How it solves it

    Removing oxygen at the source keeps your storage vessels, compressors and pipelines free of accumulating oxygen.

  • Swings in electrolyser load

    The problem

    At part load, crossover through the membrane continues while hydrogen production falls, so the oxygen in the gas rises.

    How it solves it

    The catalyst converts the higher oxygen concentrations produced at low load, which suits electrolysers following wind and solar power.

  • Hydrogen lost to purging

    The problem

    Electrolytic hydrogen costs the electricity used to make it, typically 50–55 kWh per kilogram at the system level.

    How it solves it

    Regeneration gas returns to the process, and removing oxygen consumes only twice its own volume of hydrogen, 0.2 % of the product flow at 1,000 ppmv oxygen.

  • Damaged downstream equipment

    The problem

    Water carries ions into fuel cells that reduce membrane conductivity, and oxygen compounds poison ammonia synthesis catalysts.

    How it solves it

    Your compressors, dispensers, fuel cells and synthesis catalysts receive dry, oxygen-free gas.

Where it’s used

Wherever electrolytic hydrogen is made or used

From green hydrogen plants to the industries that run on hydrogen, clean, dry, oxygen-free gas keeps your process and your equipment on specification.

  • Stainless steel gas storage vessels with access ladders

    Green hydrogen production

    Alkaline, PEM and AEM electrolysers reaching 99.97 % purity for fuel cells, or 99.999 % (grade 5.0) for industrial customers.

  • A hand holding a refuelling nozzle at a vehicle

    Hydrogen refuelling stations

    On-site electrolytic hydrogen purified before compression to 45–90 MPa storage, with fuel quality controlled to ISO 19880-8.

  • Rows of servers lit blue in a data centre rack

    Fuel cell power

    Stationary PEM fuel cells supplying telecom sites, data centres and off-grid power.

  • Test tubes of coloured chemicals in a laboratory rack

    Ammonia and methanol

    Power-to-X plants purify electrolytic hydrogen before synthesis, because oxygen compounds poison the iron-based ammonia catalyst.

  • Glowing glass bottles being formed on a production machine

    Float glass

    A tin bath atmosphere of nitrogen with a few percent hydrogen, kept free of the oxygen and moisture that leave tin oxide defects on the glass.

  • Molten metal pouring from a ladle in a foundry

    Metal heat treatment

    Bright annealing of stainless steel and powder metallurgy sintering, where very low dew points prevent chromium oxide forming.

Also electronics and semiconductors, hydrogen-cooled turbogenerators, edible oil and chemical hydrogenation, chlor-alkali by-product hydrogen, nitrogen and argon purification, and hydrogen for laboratory gas chromatographs.

How it works

React, cool, adsorb, regenerate

The oxygen is turned into water first, then all the water is taken out. The dryer’s regeneration loop runs on a slip stream of your own hydrogen, and gives it back.

How a hydrogen dryer and de-oxo unit works: wet hydrogen from the electrolyser is pre-heated, its oxygen is recombined with hydrogen into water on a precious-metal catalyst, the after-cooler and separator drain most of that water, and a tower of molecular sieve adsorbs the rest. A slip stream is heated, regenerates the second tower from the top down, is cooled so its water drains, and rejoins the main flow, so no hydrogen is vented. Wet H₂ + O₂ inPre-heater De-oxoreactor≈ 17 K per 1,000 ppmv O₂ After-coolerSeparator Tower AadsorbingΔP valve Purified H₂ outO₂, H₂O < 5 ppmv Tower BregeneratingHeater200–300 °C 12345Wet hydrogenPurified hydrogenHot regeneration gasOxygenCondensate

  1. 1. Pre-heatHydrogen leaves the electrolyser’s separator saturated with water. The pre-heater warms it a few kelvin above its dew point, so no liquid water forms on the catalyst.

  2. 2. De-oxoOn a palladium or platinum catalyst, the oxygen recombines with hydrogen to form water vapour. The reaction heats the gas by about 17 K for every 1,000 ppmv of oxygen converted, so the temperature rise across the reactor shows the conversion.

  3. 3. Cool and separateThe after-cooler condenses most of the reaction water, which drains from the separator, and brings the gas down to a temperature at which molecular sieve holds much more water.

  4. 4. AdsorbThe hydrogen rises through Tower A, where the molecular sieve holds its water, and leaves with oxygen and water each below 5 ppmv. Adsorption steps commonly last from several hours to a day.

  5. 5. RegenerateA slip stream taken upstream of the differential pressure valve is heated, typically to 200–300 °C, and flows down through Tower B. The regeneration cooler condenses the released water, which drains away, and the gas rejoins the main flow downstream of the valve, so no hydrogen is vented.

Get the full details

Our brochure covers it in detail, and our questionnaire tells us what we need to recommend the right one for your plant.

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