Fuelling the future: Linde’s ionic compressor

At the heart of many of the world’s hydrogen refuelling stations lies a result of Linde innovation that totally transformed the traditional.

Every once in a while, innovation gives rise to a new technology that sets a new standard. Take light-emitting diodes for example. LEDs transformed traditional lighting by offering a lifespan and electrical efficiency several times greater than their incandescent predecessors – and in doing so, opened up many new avenues of application.

In the context of the hydrogen economy, the equivalent is arguably one of Linde’s patented inventions: the ionic compressor. It is at the very core of refuelling technology in a growing number of stations the world over, changing the game through its design while facilitating the expansion of hydrogen infrastructure.

Linde is a one stop shop when it comes to hydrogen fuelling. It leads the way in technology at every point of the value chain: from production and distribution to storage, to processing and finally dispensing. The thing is, the hydrogen does not simply stay in exactly the same state throughout this journey.

In the case of hydrogen refuelling stations, the supplied hydrogen may be either produced on site or delivered as a liquid or gas, each calling on different processing technologies before dispensing. The ionic compressor is used to compress gaseous hydrogen (or indeed, vaporised liquid hydrogen) to just the right pressure for fuelling passenger vehicles: typically, around 35 MPa (350bar) for buses and 70 MPa (700bar) for cars. But how does it work and what exactly makes it so revolutionary?

A Linde employee assembling components of a compressor station.

A lesson in compression

Compressors work by taking advantage of the fact that gases are compressible. Since most of the volume of a gas is composed of empty space between the particles, you can basically pack them tighter so you squeeze more into a given volume. It’s all explained by the kinetic-molecular theory.

Ordinary compressors use mechanically driven pistons in reciprocating motion to compress the gas in cylinders before being discharged. The pistons cannot be lubricated by oil, since the oil would evaporate and impurify the hydrogen; hence they need to run dry, which is a big challenge to materials and mechanics.

One difference of Linde’s ionic compressor lies in the fact that the pistons are lubricated by an ionic liquid which moves up and down in a similar fashion. The main advantage of the liquid however, is that it allows nearly 100% of the compression space to be used. The specially designed ionic liquids are nearly incompressible and because they do not have a vapour pressure, they do not evaporate or mix with the hydrogen. What is even more, they cool the hydrogen during the compression and make sure there is no dead volume at the end of the cylinder, which increases the energetic efficiency of the compressor.

The ionic compression technology is a well-proven system that is already in operation at more than 100 hydrogen fuelling stations around the world: in Japan, Korea, California, Germany, Italy and the UK to name just a few countries. Each one uses the workhorse of Linde’s compressor range: the IC90. Despite its compact design, this model offers several benefits. Its five-stage compression concept means continuous and fast high-performance fuelling at lower operating costs. Efficiency is also a big plus with energy savings of around 30% compared to traditional compressors.

Linde’s hydrogen hub

Linde’s invention was conceived at the company’s ATZ – or Advanced Technology Centre – in Vienna in 2006. What started out as an R&D centre for high pressure gas applications has become not only a hub of hydrogen innovation but also the site for Linde’s current small series production of the H2 refuelling station. This station, Linde believes, will be the backbone of the future hydrogen infrastructure due to their ease of setup and performance efficiency.

The typical turnkey solution includes the hydrogen supply (a cryogenic liquid or compressed gaseous hydrogen tank or an on-site production unit); the compression station (the IC90 with accompanying cooling and storage, all in a transportable 14 ft steel container) and finally, Linde’s dispenser.

With close to 100 percent energy conversion efficiency as well as low energy consumption, low maintenance and low noise emission, the ionic compressor could well become an iconic component of hydrogen mobility in years to come.