© TU Wien

The decentralized production of hydrogen from eco-power – whether used to stabilize the grid or utilize excess capacities – will play an increasingly larger role in future energy systems. The created hydrogen can either be stored locally, converted to methane by adding carbon monoxide or fed directly into the natural gas network. The HylyPure project supported by the Austrian Climate and Energy Fund was the first opportunity for a successful test of a technology that recovers hydrogen fed into the natural gas grid at fuel cell quality.

A key challenge of the energy transformation is the storage of excess electrical energy from regenerative sources (wind, solar) and a promising approach in this field is power-to-gas. Like methane, hydrogen is an ideal energy carrier for storage solutions, as it is highly efficient in end-use scenarios and carbon-neutral.

The objective of HylyPure was to feed hydrogen into the natural gas network (existing infrastructure), transport it cost-effectively and extract it at any given location and at fuel cell quality. The three-year project by Austrian-based TU Wien and OMV aimed at finding a technological solution and carrying out experimental tests at laboratory scale. One important technological benchmark for the application is an energy demand of no more than ten per cent difference to electrolysis.

Three-stage implementation

The HylyPure concept consists of three stages to ensure the most environmentally friendly and economical outcome (see figure): In stage 1, membrane gas separation provides for an energy-efficient increase in hydrogen concentration and a reduction in volume flow, as the gas is transported around 80 to 100 times faster through a selective polymer membrane than methane. In stage 2, a hydrogen-methane mixture is being enriched further inside a pressure swing adsorption system. Stage 3 is optional and can be used to add another adsorption-based precision cleaning to guarantee the desired product quality.

The TU Wien developments have led to the creation of compact plant technology that makes it possible to extract hydrogen of any quality required. The remaining mixture will be raised to outlet pressure and returned to the natural gas line. If the required electrical energy comes from renewable sources, the process is carbon-neutral. Experimental testing was done in a laboratory environment, where characteristic curves on performance were plotted for each enrichment stage – based on a natural gas-hydrogen mixture at 50 bar (5,000 kPa) – to lay the foundation for process design, optimized controls and reduced energy demand during gas purification. Proof of concept was successful as well: The purity grade of the hydrogen after adsorption was, in fact, 99.97 volume per cent …