Exploring Hydrogen Production: Key Insights from the Engineers Australia Lecture Series.
Hydrogen has emerged as a promising alternative energy source, potentially revolutionising the global energy landscape and contributing significantly to a sustainable and low-carbon future. As countries strive to meet ambitious climate goals and shift away from traditional fossil fuels, hydrogen offers a versatile and clean solution for various applications, ranging from transportation and power generation to industrial processes. To explore the cutting edge of hydrogen production and the challenges ahead, I attended the first in a series of lectures on this subject organised by Engineers Australia. Featuring insights from experts at Siemens Sustainable Energy and Skai Energies, this article will delve into the critical aspects of hydrogen production, including the current state of the art, opportunities for innovation, and potential pathways to a hydrogen-powered future.
Hydrogen's Unique Properties and Challenges
With an energy content of 120-142 MJ/kg (higher than most fossil fuels), hydrogen has the potential to store and deliver a considerable amount of energy. In addition, its low specific heat of 14.3 kJ/kg·K at room temperature implies that hydrogen can absorb or release energy with relatively small temperature changes, making it suitable for various energy applications. However, these properties also pose challenges when working with hydrogen. Its low density requires substantial compression or liquefaction for efficient storage and transportation, while its wide flammability range and high combustion energy necessitate stringent safety measures. While hydrogen's unique properties offer numerous advantages as an alternative energy source, they also present challenges that must be addressed for successful implementation in various applications.
Electrolysis Methods: PEM vs. Alkaline Electrolysers
Electrolysis of water is a process that separates water into hydrogen and oxygen gas using an electric current. Producing 1 kg of hydrogen requires 9 litres of water theoretically. Still, water usage is significantly higher, around 50L per kg, due to ancillary requirements, with a large portion attributed to the cooling process. Therefore, much of the additional water use can be attributed to cooling. The lecture covered various electrolysers that convert electrical energy into chemical energy by splitting water molecules into hydrogen and oxygen. The Proton Exchange Membrane (PEM) electrolyser, introduced in 1973 by J. H. Russell, and the alkaline electrolyser, developed in 1890 by Charles Renard, are two prevalent methods for hydrogen production. PEM electrolysers use electrodes attached to a proton exchange membrane, while alkaline electrolysers utilise a liquid alkaline electrolyte within a stack of plates, creating multiple cells.
Some key differences between the two methods include the operating temperature ranges and the hydrogen purity produced. PEM electrolysers operate at up to 80°C and yield high-purity hydrogen gas with higher efficiency than alkaline electrolysers, which require temperatures of around 70-90°C. Additionally, PEM electrolysers are more durable and less susceptible to corrosion and degradation. However, alkaline electrolysers do not rely on noble metals and offer high delivery pressure (approximately 30 bar) with low water purity requirements.
The choice of electrolyser technology depends on the intended use of the gas. Some applications, such as fuel cells, necessitate high purity levels, while others may benefit from the delivery pressure of an alkaline electrolyser. Additionally, PEM electrolysers are more durable and less prone to corrosion and degradation than their alkaline counterparts.
Scaling Up Hydrogen Production
Scaling up hydrogen production is vital for the widespread adoption of this renewable energy source. The speakers emphasised the need for cost-effective and sustainable scaling of hydrogen production. Scaling is achieved by increasing the number of electrolyser stacks or cells. The economy of scale is therefore achieved in scaling the ancillary equipment. Additionally, systems should be designed considering maintenance requirements, including equipping rooms with the necessary tools like cranes.
Addressing Harmonics and System Efficiency
Harmonics distort the waveform of the AC input voltage converted into DC by the rectifier and are a common issue in hydrogen production systems using electrolysers. Passive or active filters can mitigate harmonics and electromagnetic interference (EMI). In addition, pulse-width modulation (PWM) techniques can also be used to generate smoother waveforms with reduced harmonic content.
The efficiency of hydrogen production systems depends on the output requirements. More ancillary equipment is needed as the demand for higher purity or pressure increases. From the base electrolyser, heat losses occur from the electrolyser stack, transformer, rectifier & control cabinets. This was quoted as greater than >76% for the 17.5MW system shown. However, this drops to >72% with the addition of compression & auxiliaries.
Compression Technologies in Hydrogen Production
Compression of hydrogen is another challenging and energy-intensive aspect, with technology continuously under development. For example, existing turbocompressor impeller technology requires many impellers to achieve pipeline compression. At this stage, most hydrogen is compressed by reciprocating compressors, as they better handle the inlet volume flow and desired discharge pressure. The arrangements include Diaphragm, Ionic, Dry & Wet Screw, Reciprocating & single-shaft compressors. The lecture series has dedicated a separate lecture to compressors & compression.
Cooling Strategies for Hydrogen Production Systems
Hydrogen production requires efficient cooling strategies to maintain optimal operating temperatures and ensure system performance. Various cooling methods exist, each with advantages and drawbacks regarding water usage, quality requirements, costs, energy consumption, and applicability. The lecture explored various cooling strategies: once-through, evaporative, air cooling (adiabatic and non-adiabatic methods), chiller refrigeration, and waste heat utilisation. When selecting a cooling strategy for hydrogen production systems, it's essential to consider factors such as water consumption, water quality, costs, energy efficiency, and the specific use case. By selecting the most appropriate cooling method, hydrogen production facilities can optimise system performance, minimise environmental impacts, and reduce costs, ultimately contributing to hydrogen's sustainability and viability as a clean energy source.
Operational and Safety Considerations for Hydrogen Production
The operation of the systems was touched on. Another difference between the two electrolyser technologies was the ramp-up time of the systems. Several methods of starting are available, including cold & warm starts. In terms of operation, the intermittent availability of green energy and fluctuations in the grid price of electricity are of concern, necessitating systems that monitor the grid price and adjust operations accordingly to produce hydrogen economically.
Hydrogen's characteristics present various safety considerations that must be considered when handling and utilising it as an energy source. Hydrogen gas leaks are challenging to detect due to their odourless and colourless nature. Furthermore, its flame, when burning in the air, is nearly invisible and has low heat penetration, posing challenges in identifying and managing fires. Hydrogen's wide flammability range (4-75% by volume in air) and low minimum ignition energy make it susceptible to explosions, necessitating proper safety measures.
Conclusion & Future Prospects
As we continue exploring hydrogen production technologies and solutions, we can expect significant advancements in the field, ultimately contributing to a cleaner and more sustainable world where Australia plays a key role in driving progress. First, however, much work must be done in developing standards, knowledge & a competent workforce.
Overall it was an enjoyable evening and an informative lecture of the series. The second lecture covers compressor plant & safety. If you found this information interesting and would like to learn more, I have several more weeks of lectures, providing access to industry experts. Feel free to email me with any enquiries.