Is Green Hydrogen A Silver Bullet?

Online Editor

Dr Maria Anez-Lingerfelt assesses the role of green hydrogen in achieving net zero

The pressure to use clean energy to power industrial operations and consumer services is building. However, the industry is still struggling with the challenge of how to do this at scale and in a cost-effective way. Renewables have been a key focus for many years now, but each source has its limitations. If we are to reach net zero carbon emissions by 2050, we need to harness clean power that is practical across production, storage, delivery and usage.

Hydrogen is seen as a guiding light for the future as it produces no toxic emissions, but different production processes have different environmental impacts. The majority of hydrogen produced is derived from fossil fuels, yet with the gasification of coal for ‘brown’ hydrogen and steam methane reforming from natural gas for ‘grey’ hydrogen, the downside is the production of carbon dioxide. ‘Blue’ hydrogen is also processed from fossil fuels, but it encompasses the capture of CO2. The CO2 then is turned into liquid and stored underground – which is a complex and expensive process.

By contrast, ‘green’ hydrogen does not produce CO2 and so is the ‘cleanest’ option. It is made by the electrolysis of water powered by renewable energy sources, such as wind or solar. Green hydrogen production has been proven to work at a small-scale, but the challenge remains as to how to make it commercially viable, with hurdles including technological constraints, regulation, and cost. All three need to be tackled to realise green hydrogen’s potential to become a truly transformational energy source.

What Are The Processing Options?

The methods for producing green hydrogen are complicated. The electrolysis process involves the dissociation of the water molecule in an electric field. Hydrogen is then produced at the cathode and oxygen at the anode with an electrolyte present in between the electrodes.

There are three types of electrolysers used to achieve this. The alkaline electrolyser (AEL) uses liquid potassium hydroxide as the electrolyte and is the most widely used in industrial applications, but comes with some drawbacks, including lower purity levels and lower energy efficiency. Polymer electrolyte membrane electrolyser (PEM) uses a solid polymer electrolyte and is increasingly being favoured because it has fewer of these drawbacks but is still expensive compared to AEL. Finally, solid oxide electrolysers (SOEC) use a solid ion-conducting ceramic electrolyte – a technology that holds great potential but is still in the early stages of commercialisation.

Regardless of the electrolysis technology used, the hydrogen stream produced needs to be further processed to remove solid, liquid, and gaseous contaminants. It is in this process that the real technical challenge lies because the regulations around gas purity specifications are extremely stringent. Typically, concentrations between 2,000-6,000ppm (parts per million) of oxygen and more than 2,000ppm of water are seen contaminating the hydrogen produced using commercial alkaline electrolysis. The maximum concentration allowed for fuel cell vehicles is 5ppm of each under the ISO standard for hydrogen fuel quality.

Tackling The Purity Challenge

This gap between outputs and purity standards is why AEL systems – the most widely used in industrial applications – require further optimisation to produce green hydrogen at a large scale. Several unit operations using filtration, separation and purification technology are needed to achieve the required purity levels.

Once the hydrolysis has taken place, the liquid/gas mixture needs to be cooled, separated and compressed. However, cooling the gas has major cost implications and can be as high as 5% of the total system outlay. Gravity separators, mist eliminators pads, filter vane separators and more recently liquid/gas coalescers are used to separate the liquid contaminants. These typically require large housings and must be operated at low velocities to prevent liquid re-entrainment.

To add to the purification costs, solid contaminants, originating from oxidation in process piping and equipment such as pumps and compressors, must be eliminated. Adsorbent fines – if being used – are situated in the final drying equipment and may also get released, contaminating the gas. To remove the solid contaminants, disposable gas filters in different micron ratings can be deployed throughout the process.

The final step is the efficient storage of the hydrogen once it is produced. It can be compressed and stored in tanks, pumped into salt caverns or converted into liquid ammonia using the Haber-Bosch process.

Using Innovation For Strategic Investment

There are now many organisations considering their impact on the environment and how they can create or use green energy. Since hydrogen is the most abundant substance in the universe, we must use its capabilities for sustainable advantage. Pall Corporation partners with companies to provide R&D, strategic support and products – collaborating to implement innovative solutions to complex challenges.

Governmental regulations also play an important role in energy developments, such as the EU’s Green Deal and a range of tax incentives in the USA for environmentally friendly measures. But can more be done?

If we look at the global picture, the need to decarbonise and minimise the damage from climate change is becoming ever more apparent. In 2021 there were numerous episodes of catastrophic and unprecedented weather events across the world: fatal floods in Germany, Belgium, China and the US; a typhoon in the Philippines that killed at least 375 people; rain falling on the summit of Greenland instead of snow for the first time on record – to name a few.

With COP27 due to take place in Egypt in November, all eyes will be on the world’s leaders to see what progress has been made since COP26 and what international legislation may be formed to reduce global warming to 1.5°C – the threshold set by the Paris Agreement to minimise the worst effects of the climate crisis.

Green hydrogen alone will never be the whole solution, but it can provide a major route on the road to decarbonisation. If environmental sustainability is to be achieved, there needs to be more investment and a cohesive global strategy to enable innovative processes to become fully viable solutions.

Dr Maria Anez-Lingerfelt is a senior scientist in Pall's application developemtn team