Hydrogen drying and purification

Understand

What this part does and what decides it

Why it matters

The main impurity in hydrogen leaving the electrolyser is water. On HXB-V1, purity is 98 to 99 percent without a dryer and above 99.999 percent with one. Most of that gap is water vapour. That remaining moisture is quoted as a dew point: the temperature at which dew starts to form as the gas is cooled. Less water means the gas has to go colder before dew appears, so a lower dew point means drier. Our stacks circulate KOH on the anode side only, so the hydrogen line carries moisture and trace oxygen and nothing else. The outlet gas is saturated, so it condenses as it cools in the piping, and removing oxygen as well adds heat from the catalyst. That is why two applications with the same purity target can need different trains.

RemovalDew point (atmospheric)Total impurityNotes

0 °C

—

Bounded by the freezing point

-40 °C

About 128 ppmv

-60 °C

About 10.7 ppmv

Water alone is already past it

10 ppmv — the 99.999% allowance

-70 °C

About 2.6 ppmv

Compatible with 99.999%

Below this point the axis is total impurity, not dew point

—

ppb level

Hydrogen duty does not go this far

Cooling and condensing

Adsorption (PSA, TSA)

Purification (getter, palladium membrane)

Spacing shows order only; it is not to scale.

Background

What is actually in the hydrogen

What leaves the stack during operation is moisture and trace oxygen. Nitrogen is not made by the stack; it enters from purge gas and air left in the pipework.

Moisture: The outlet gas is saturated. This is most of what the purity figure measures
Oxygen: Trace crossover from the anode. Fuel cell and refuelling specifications set a limit on it
Nitrogen: Enters from purge and residual air. It shows up at start-up and after maintenance, and does not grow during operation

Dew point and purity are different quantities

99.999 percent means total impurities, water and oxygen and nitrogen together, at or below 10 ppmv. Dew point describes water alone. Using one figure in place of the other produces the wrong specification. The conversions below are on an atmospheric basis. At -70 °C water uses only a quarter of the total allowance, so it is compatible with 99.999 percent and oxygen removal covers the rest. At -60 °C water alone is already past 10 ppmv: removing every trace of oxygen still would not reach 99.999 percent, so an application with that requirement has to dry further.

Dew point -40 °C: About 128 ppmv — enough to stop condensation, short of 99.999 percent
Dew point -60 °C: About 10.7 ppmv — water alone is already past the 10 ppmv allowance, short of 99.999 percent
Dew point -70 °C: About 2.6 ppmv — compatible with 99.999 percent

A dew point is stated with its pressure

-40 °C at atmospheric pressure and -40 °C at 10 barg are entirely different conditions. If you need a figure at line pressure we will convert it. One more reference point has to be agreed. The dryer outlet dew point is not the dew point at your point of use: moisture held on the pipe walls desorbs downstream and the reading there is higher. The longer the run, and the longer the system has stood idle, the wider that gap.

The methods available

The downstream train is not a choice between methods so much as a stack built to the requirement. The layers are below. An application that only needs a lower dew point stops after the first one or two; an application with a purity figure adds the later ones. The stack goes up to 99.999 percent, five nines, and stops. That is the figure fuel cells, refuelling and process supply ask for; the ppb level above it belongs to semiconductor and analytical duty. So the two purification layers below are here as explanation only and are not on the list of models we source. The rest either go into the HXD-V1 design or have no market product this small. That is why the table below is short.

Cooling and condensation: Chills the gas so water drops out as liquid. The simplest and cheapest arrangement, limited to a dew point near 0 °C by the freezing point of water. It earns its place by reducing the load on whatever follows
Adsorption, pressure swing (PSA): Water is held on an adsorbent, then driven off by dropping the pressure, with two vessels alternating. Regeneration needs no heat and is quick, but some product gas leaves with the purge, so hydrogen is lost
Adsorption, temperature swing (TSA): The same adsorption regenerated with heat instead of pressure. Regeneration takes longer and the heater draws power, but almost no product gas is discarded. This is the side to look at when hydrogen loss matters at small scale
Catalytic deoxo: Reacts the remaining oxygen with hydrogen to form water. The oxygen becomes moisture, so drying always follows. The reaction gives off heat, so cooling comes into the picture when the inlet oxygen is high
Getter (chemical absorption): A heated metal chemically binds oxygen, moisture and nitrogen. It reaches ppb level and discards no hydrogen. What it binds it does not release, so the unit is replaced outright at end of life
Palladium membrane purification: Only hydrogen atoms cross a heated palladium membrane, leaving everything else behind and taking total impurities to ppb level. The membrane has to be held at around 400 °C, and gas that does not cross is vented, so recovery is lower. It cannot be the first stage: manufacturers already require 99.95 to 99.99 percent at the inlet, so gas-liquid separation and drying have to stand in front of it
Polymer membrane separation: Separates on the difference in how fast species cross a membrane. Easy to run continuously and free of consumables, but the separation is incomplete so the achievable purity is limited. It belongs where continuity matters more than purity

Choose

The options and the models we handle

What you can choose

The two are not alternatives; they stack — the second puts one more layer on top of the first. A pre-order for HXD-V1 is the usual route; if you need one sooner, we find and source a dryer that matches your conditions.

DryingDownstream condensation · Process supply · Analysis

Moisture only. How far down you go is what the application decides — stopping condensation ends around -40 °C (about 128 ppmv), and a purity target takes it lower.

Quote this option

Drying with oxygen removalFuel cells and refuelling

One more layer on top of that: deoxo. For 99.999 percent the dew point goes to about -70 °C and oxygen removal takes the remaining allowance. Catalytic heat comes with it.

Quote this option

The dew points we quote are at atmospheric pressure, measured at the dryer outlet. We convert to another basis if you need one.

Models we can source

The three rows below are here to show what you move to at larger scale. There is no dryer in this table you could buy and fit at our scale today: either the throughput sits above ours, or the required inlet pressure sits above our outlet (10 barg at most). We are building one because there isn't one.

So this desk runs on two tracks. The usual route is a pre-order for HXD-V1, which launches in Q4 2026. If you need one sooner, give us the dew point, flow and pressure you need and we find and source a match at that point.

Our own, in development — if you can wait

Model	Method	Origin	Quote this
HydroXpandHXD-V1	Multi-layer train	Korea (made by us)	Get a quote

At larger scale — industrial drying and deoxo

Model	Method	Throughput	Outlet dew point and purity	Origin	Quote this
ON2QuestDe-Oxo Dryer	Catalytic deoxo · Adsorption, temperature swing (TSA)	20 – 2,000 Nm³/h	Dew point -65 °C · oxygen and water each below 5 ppm	–^†	Get a quote
Omega AirH2-PURE	Catalytic deoxo · Adsorption, temperature swing (TSA)	52.5 – 21,000 m³/h	Dew point -40 °C · oxygen below 5 ppm	Slovenia	Get a quote
DonaldsonHRC-T	Catalytic deoxo · Adsorption, temperature swing (TSA)	220 – 22,000 Nm³/h	Water and oxygen each below 5 ppm	–^†	Get a quote

^†ON2Quest and Donaldson do not publish where these units are made. We have not written an office location in place of a manufacturing one.

Reading this table

Our own product: HXD-V1 in development, targeting Q4 2026 · pre-orders taken
If you need one sooner: We find and source a dryer matched to your conditions (no standing model; manufacturer warranty passes through)
Specification basis: Figures in the table follow published manufacturer data. We re-confirm the current specification before ordering

Order

What to settle before a quotation

Questions we get

Only what has come up more than once in real enquiries.

How clean does it need to be

What dew point comes out of the dryer?

The target dew point has to be set first, because it decides the train. When you set it, tell us two things alongside it: whether the figure is on an atmospheric or a line-pressure basis, and whether it applies at the dryer outlet or at your point of use. Unless we say otherwise, our own figures are atmospheric and at the dryer outlet; we convert to line pressure or to your point of use on request. Without those two, the same number describes different conditions to each of us.

Does our application need oxygen removal as well?

It comes down to whether your application sets an oxygen limit. Fuel cells and refuelling usually do; process supply and analytical use often need only the moisture figure met. Send us the specification if one applies, and if none does, just telling us the application is enough for us to work out which side it lands on.

What should we buy

Is a dryer included with HXB-V1?

Not in the standard configuration. Purity of at least 99.999 percent was confirmed under our validated conditions with a dryer fitted. There are two routes to fitting one. Pre-order HXD-V1, which launches in Q4 2026; or, if you need one before then, we find and source a dryer matched to your conditions and pass the manufacturer warranty through to you. That second route has no standing model — we select against the dew point, flow and pressure you give us.

Do we need to go past 99.999 percent?

Hydrogen duty stops at 99.999 percent, five nines. That is what fuel cells, refuelling and process supply ask for; the ppb level above it belongs to semiconductor and analytical work. So the equipment that takes you above it, the palladium membrane purifier, is not on our list of models. A purifier is also no substitute for a dryer, because manufacturers already set an inlet purity of 99.95 to 99.99 percent. Our stack outlet is 98 to 99 percent without a dryer and saturated with water, so gas-liquid separation and drying have to come first before a purifier can be fitted. A purifier is the finishing stage, not the first one. The purifier itself also takes a nitrogen purge and instrument air, so those utilities grow with it. If you do have a duty that needs the ppb level, send us the conditions and we will put that train together separately.

Should we wait for HXD-V1?

It depends on when you need the hydrogen. HXD-V1 is targeting Q4 2026 and its specification is not yet fixed, so we cannot quote it today. If you can wait, we will take a pre-order to hold your place and send you the specification as soon as it is settled. If you need one sooner, send us your conditions: there is no dryer at our scale worth keeping on a standing list, so we go and source one against the dew point, flow and pressure you give us.

If several units run in parallel, do we need one dryer per unit?

No. The outlets join one shared hydrogen pipe and the dryer and storage are shared. Tell us the combined flow and the maximum number of units running at once and we will size against that.

Send us the checklist

Fill in only what you know. We ask about the rest.

Dew point and puritye.g. -40 °C dew point, 99.999%
Flow and operating pressuree.g. 0.5 Nm³/h, 10 barg
Applicatione.g. a fuel cell
Country of installatione.g. Korea
When you need ite.g. sourced now

Request a quote for this item

Warranty — Sourced items carry the manufacturer warranty through to you