"Salt-Cavern Hydrogen Storage: Why the Store Sets the Compressor's Duty"

China's first million-cubic-metre-class salt-cavern hydrogen store is injecting with two compressors at 15 MPa and 2,000 Nm³/h, through a borehole 1,418 m deep into a leached cavity of more than 30,000 cubic metres, for a stated storage capacity of 1.5 million standard cubic metres of hydrogen. The project, in Pingdingshan, Henan, was commissioned on 25 April 2026 and was reported in routine operation by September 2026 (1)(2)(3).

This article sets out why the storage medium is a leached cavity rather than a tank, why the injection pressure is a geological number, what the project's own development list turned out to contain, what is published about the compression side, and where the evidence stops.

Why is a salt cavern used as a hydrogen store at all?

Because a cavity in rock salt is a pressure vessel that self-seals, and it is made with water rather than with machines.

The cavity is not excavated. A borehole is drilled into the salt bed, water is injected, the salt dissolves, and the brine is brought to surface; repeated over years this leaves a large void underground. The reason the void is usable is a property of the rock: salt is plastic, so micro-cracks close slowly under confining pressure, which is what makes it a natural barrier for storage (2).

The Chinese difficulty is the geology. Mature salt-cavern stores elsewhere in the world generally sit in salt domes, where the deposit is homogeneous. Chinese salt beds are layered — salt interbedded with mudstone — and the interlayers have higher permeability, so the sealing problem is harder. The Pingdingshan project is reported as the first time a hydrogen store has been built in layered salt rock (2)(3).

That is not a new problem for the industry, only a new gas. China National Salt Industry Group (中国盐业集团) states a salt-cavern gas-storage technology system built over more than twenty years, comprising two-pipe cavity leaching, cluster directional drilling, injection-and-production tubing welding, and staged milling-and-plugging abandonment of old wells, assessed by the China National Light Industry Council as internationally advanced and already used in salt-cavern gas storage and compressed-air energy storage (5).

Why is the injection pressure a geological number?

Because the store is a cavity in a rock mass and its working pressure is bounded by the formation and by the pressure boundary at the wellhead — which is why this project's development list contains casing, cement and wellhead items far ahead of any compression item.

Start with the published pair of numbers. The injection pressure is 15 MPa and the borehole depth is 1,418 m. The pressure that has to be contained is therefore a property of the site: the project's selection work is described as a fine site-and-layer selection method that fixed the drilling depth, and its stated technical achievement includes verifying the long-term sealing performance and engineering feasibility of hydrogen storage in layered salt rock (1)(3).

Then look at the pressure boundary, which is where the project put its engineering. The named development items are a low-permeability toughened well-cement system, hydrogen-embrittlement-resistant casing, and a high-sealing wellhead assembly. Alongside them the project reports overcoming hydrogen-facing material corrosion and equipment sealing (1)(3).

Read as a list, that is a pressure-containment list. The machine that puts gas into a cavity has to deliver a discharge pressure; the cavity, the casing string, the cement sheath and the wellhead have to hold it, and those four items are where a hydrogen store is hard.

One arithmetic note. The project publishes a cavern volume above 30,000 m³ and a storage capacity of 1.5 million standard cubic metres of hydrogen. The ratio of the two is about 50. That is an arithmetic relationship between two published figures and not a stated working pressure — neither source gives the cavern's operating pressure range — but it is the reason the injection pressure matters as much as the volume.

What did the project's own problem list turn out to contain?

Hydrogen containment and hydrogen-facing materials, in three specific items, plus a monitoring system that watches the whole assembly.

Materials and equipment. The project reports overcoming hydrogen-facing material corrosion and equipment sealing, and developing a low-permeability toughened well-cement system, hydrogen-embrittlement-resistant casing and a high-sealing wellhead assembly. It states that key core equipment reached 100% domestic supply (1)(3).

Site selection. The team states it clarified the multi-scale migration behaviour of hydrogen in ultra-low-permeability rock salt and formed a technique for fine site-and-layer selection of a salt-cavern hydrogen store, verifying the long-term sealing performance and engineering feasibility of layered salt rock for the duty (1)(3).

Monitoring. The project reports a first integrated "surface–wellbore–cavern" monitoring technique giving real-time warning across ground hydrogen concentration, cavern seismic signals, wellbore vibration, the gas-water interface, hydrogen pressure, temperature and leakage (1)(3).

The compression side, by contrast, is reported as a number rather than as a development item.

What is published on the compression side?

Unusually little, for a project whose core equipment is otherwise described in detail.

The stage count, the machine class, the drive, the suction pressure, the discharge temperature and the motor rating are not published. The same is true of the withdrawal side: the sources describe injection and brine displacement, and give no withdrawal compression arrangement at all.

What does the companion programme add?

The programme run by China National Salt Industry Group (中国盐业集团) is at an earlier stage, and it is the one that will produce the design rules.

Its main construction works for large-scale salt-cavern hydrogen storage started on 25 July 2025 at Jintan, Changzhou, Jiangsu, under a National Key R&D Programme hydrogen-technology project — key technologies and test verification for large-scale geological hydrogen storage — carried out with Tsinghua University and eight other institutes and companies. The works plan two groups of caverns forming two hydrogen injection-and-production wells and two brine injection-and-extraction wells, to run cyclic storage-and-release performance tests. Five sub-topics are named: geological evaluation, new material development, cavern structure design, cyclic safety control, and engineering demonstration and verification (4).

The same group's operating record on the neighbouring duty is the useful reference for what a cavern can take. The Jintan 60 MW salt-cavern compressed-air energy storage national demonstration project entered production in May 2022; by the end of June 2025 it had completed more than 650 storage-and-generation cycles and delivered more than 460 GWh of peak-shaving energy, equivalent to about 138,000 tonnes of standard coal saved and about 403,600 tonnes of CO₂ avoided. The assessment by the China Electricity Council in May 2023 placed the project's results at internationally leading level, and phase two at 2×350 MW has started construction (5).

Those cycles are air cycles rather than hydrogen cycles, and the two duties are not interchangeable. What they establish is the number of pressurisation cycles a lined cavern at this site has been through — which is the number that matters when the same geology is asked to hold hydrogen instead.

Where does this route stop?

At five places, all of them visible in the published record.

The 1.5 million cubic metres is described in two different ways. At commissioning it is stated as the storage capacity the project is designed to achieve. In the September report it is stated as the volume held in the cavern. Neither report gives a measured working-gas volume, a cushion-gas volume or the amount actually cycled, so the two statements should not be read as a target and a measurement of the same quantity.

No cycle data is published for the hydrogen store. There is no cycle count, no cycle duration, no injection-withdrawal cadence and no round-trip efficiency for the Pingdingshan store. The 650-cycle figure from the Jintan air store is a different gas, a different machine and a different duty.

The compressors are reported as a count and a duty point, nothing more. Two machines, 15 MPa, 2,000 Nm³/h is enough to know the duty exists and not enough to describe the machine. No source in this article identifies the compressor supplier, so the "100% domestic key equipment" statement cannot be checked item by item.

The second programme has not reached the storage stage. The Jintan hydrogen programme's construction started in July 2025 and is at the cavern-leaching stage; it has not published injection results. The design rules for salt-cavern hydrogen storage are therefore still being written, and every figure in this article about hydrogen in a cavern comes from one site.

And the geology is not settled as a national answer. The layered-salt problem that the Pingdingshan project reports solving is the same problem the second programme is chartered to attack through geological evaluation and cavern structure design. Where two programmes are still working on the same problem, one project's method is a method and not yet a standard.

What does the trend add up to?

Three movements are visible, and they point the same way.

The bottleneck moved from the electrolyser to the store. Both projects in this article exist because the hydrogen problem on the supply side has become a storage-duration problem, and the store is the part without a mature domestic precedent.

The engineering moved to the wellhead. The named developments are casing, cement and wellhead sealing — the pressure boundary between a rock cavity and the surface — rather than the rotating equipment. A hydrogen store's difficulty sits where the gas leaves the rock.

And the machine's specification moved onto the site plan. The compressor at Pingdingshan is specified at 15 MPa because the cavity is 1,418 m down, not because a customer asked for 15 MPa. On this route the store and the compressor are selected together.

What has not moved is the evidence base. There is one hydrogen cavern in the record with a stated injection duty, it has been in routine operation for months rather than years, and the compression equipment behind it has not been described in public.

What this article does not cover

Note that this article does not select a compressor or a machine class, size a train or a stage count, calculate a discharge temperature or a ratio, specify a casing, a cement, a wellhead or a material, or give prices and delivery times. It describes the storage medium, the published injection duty, the project's named development items and the boundary of that evidence. It is not a purchase specification and it carries no compliance determination.

Where the next constraint sits

The store in this article exists to serve a plant that has to keep running when the wind drops, and the machine duty on that side is a different one: Green Ammonia Synthesis Gas: What the Hydrogen in the Feed Changes sets out why a synthesis-gas compressor in a weather-fed ammonia plant is specified for load following as much as for pressure.

The same question — a compressor whose duty is set by the installation rather than by the process — appears in the offshore case, where the environment rather than the geology fixes the machine: Offshore CO₂ Injection: Why the Compression Route Went from Three Stages to Four.

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