One solution is Tedur® from MOCOM: together with the Austrian compressor manufacturer Leobersdorfer Maschinenfabrik GmbH (LMF) as well as Austrian universities and research institutes, four commercially available Tedur® grades have been tested for their suitability as possible piston and packing ring materials for use in hydrogen compressors – with promising first results.

Hydrogen: necessary purity only in oil-free operation

To replace carbon-emitting energy sources in the long term, existing supply infrastructure needs to be used to store and transport hydrogen. In the process, power-to-gas concepts and electrolysis technology from renewably sourced energy are also utilized. However, energy densities and flow rates that can compete with those of batteries or natural gas require high pressures of more than 500 bar for hydrogen as an energy carrier. This poses extreme challenges for compressors, which current applications only overcome with oil-lubricated cylinders and several compression stages. However, only unlubricated, dry-running operation allows the hydrogen gas to meet the high purity requirements for the fuel cell.

Oil-free operation, in turn, means that the piston and packing rings of the compressor are subjected to high pressure loads and extreme challenges in terms of friction and abrasion. Critical for the service intervals, long-term durability is therefore significantly linked to the operation and associated costs of the high-pressure compressors.

Tedur®: inherently wear-resistant

LMF is a leading original equipment manufacturer for reciprocating compressors from Austria that is facing up to these challenges of hydrogen compression. Together with MOCOM and the University of Applied Sciences Upper Austria in Wels, the company is developing advanced polymer piston ring solutions to deliver high-pressure hydrogen in dry-running operation.

The design of oil-free running cylinders places the highest demands on the strength, wear resistance, and thermal stability of plastics used in packing and piston rings. PPS compounds such as Tedur® inherently have many of these properties, making them promising material candidates for these applications.

Promising first results

The researchers from LMF and the University of Applied Sciences Upper Austria therefore investigated the thermomechanical properties and microstructural effects on deformation mechanisms in PPS matrix composites on Tedur® and Tedur®-like grades. The measurements were performed at the synchrotron beamline P05 at the Petra 3 ring, operated by the Helmholtz Center Hereon at the Deutsches Elektronen-Synchrotron (DESY) in Hamburg.

Synchrotron-based in-situ microtomography allowed the researchers to observe the fiber-reinforced PPS polymers under load and thus evaluate their microstructure and failure mechanisms under simulated operating conditions. They found that, in addition to variations in the polymer composition, their fiber orientation, length, and quantity also influence the deformation and damage of the structures. This enabled the researchers to identify the optimum compositions of fiber-reinforced polymers for piston and packing ring solutions for high-pressure hydrogen compressors.

New Tedur® formulations already under development

To achieve these ideal structures, new Tedur® formulations are currently being developed to adapt the product properties of the plastic even better to its intended use as a piston and packing ring material in hydrogen compressors. These new grades are currently evaluated at the University of Applied Sciences Upper Austria in Wels, where the microtomography data is analyzed with high-performance computers and special analysis software.