HyDUS: The Pathway for Carbon-free Shipping

In the pursuit of realising a net-zero carbon economy by 2050, there is a current substantial global expansion of the hydrogen ecosystem across multiple energy sectors, extending beyond the borders of the United Kingdom. Concurrently, as continued efforts persist in positioning hydrogen as a primary substitute for the natural gas that the UK is relying on, the key role of hydrogen storage becomes even more apparent. HyDUS is a valuable technology that can be used for long-duration and large-scale energy storage finding applications in two major energy vectors: hydrogen and electricity. These vectors will be critical to delivering on global net zero ambitions. Institutions aimed to develop economically attractive and efficient energy storage solutions such as HyDUS can increase overall market potential and derive significant commercial benefits by aiding low-carbon energy transition.

As a result of facing increasingly stringent recent and future regulations on pollutant emissions, the marine industry is undergoing a swift and progressive transition. The technology advancements in the past decades helped ship owners reduce fuel consumption and environmental impacts of shipping operations. However, marine transport still accounts for significant amounts of global emissions of greenhouse gases (GHGs), particulate matter (PM), volatile organic compounds (VOCs), and Nitrogen/Sulphur-based toxic gases (NO_x, SO_x). The statistics also show that 3-5 % of global CO₂ emissions are coming from shipping activities. Given these insights, the International Maritime Organization (IMO) is actively striving towards a 40% reduction in CO₂ (compared to 2008 levels) by 2030 with an even more ambitious target of 70% by 2050. Moreover, the IMO also introduced emission control areas to enforce rigorous limits on NO_x, SO_x, and PM emissions. 

Numerous strategies can be employed to mitigate the emissions from marine vessels,  encompassing enhancements to shipping engines through techniques such as:

1. Exhaust gas recirculation
2. Smart combustion chamber design
3. Use of advanced fuel injection systems
4. Use of two-stage turbocharging systems, etc. 

Additionally, employing exhaust gas after-treatment and use of different gas bunker fuels (e.g. low Sulphur diesel/liquified natural gas) can also be considered. However, these approaches may augment the size, complexity, fuel consumption, and maintenance requirements of ship generators. Therefore, clean and efficient alternatives for maritime power plants are desired, positioning fuel cells as one of the most promising solutions for decarbonising onboard power generation in the marine industry. 

Fuel cells convert chemical energy into electrical energy directly, bypassing the indirect route through thermal energy, unlike conventional combustion engines. This direct conversion significantly diminishes the formation of hazardous gases like NO_x, minimizes the noise and vibrations – all achieved without compromising the overall efficiencies. However, the type of fuel cell and the logistic fuel used will have a large impact on its suitability in shipping applications. The notably swift electrochemical oxidation kinetics of hydrogen take precedence at practical power densities rendering most fuel cells highly effective when running on hydrogen. Furthermore, hydrogen proves suitable for fuel cells even at low temperatures and the conversion efficiency from hydrogen to electricity in fuel cells surpasses that achieved with the internal combustion engines. As a logistic fuel for maritime power generation, the primary limiting factor of hydrogen is the low storage density. Commonly, for automotive purposes, hydrogen is stored in pressurized vessels at extremely high pressures of 350 or 700 bar. However, this method proves volumetrically inefficient and raises safety concerns. An alternative approach involves cryo-compressed hydrogen storage where hydrogen is kept at an extremely low temperature of -253⁰ at ambient pressure, albeit at a considerable cost. The conversion of diesel to hydrogen emerges as a relatively cost-effective option, given the existing diesel infrastructure readily available on ships. This stands in contrast to the relatively higher costs and additional infrastructure requirements associated with the previously mentioned hydrogen storage methods. It’s essential to note, however, that the introduction of a diesel fuel processor may increase complexity and size, and eventually lead to GHG emissions. 

In such scenarios, the HyDUS technology has the potential to be transformative, offering a significant opportunity to assist the marine transport sector in overcoming a key barrier to the deployment of hydrogen-based fuel cells. HyDUS stands out as an innovative technology that facilitates efficient physical storage of large quantities of hydrogen ensuring safety and enabling prolonged storage periods. Depleted uranium (DU) stemming from the uranium enrichment process integral to the UK’s front-end nuclear fuel cycle has exceptional hydrogen storage properties. The UK currently holds approximately 4% of global DU inventory, positioning the country as a world leader in this domain.  Leveraging this capability, DU becomes a commercially viable bulk storage medium to provide cost-effective hydrogen storage options per kilowatt-hour (kWh) for the UK marine industry. The integration of HyDUS as a promising potential candidate for onboard hydrogen storage in the ships or incorporating hydrogen infrastructure into existing port facilities could pave the way for achieving carbon-neutral and environmentally responsible shipping activities. 

In summary, the imperative to decarbonise the marine sector underscores the need for a versatile energy solution that can be efficiently stored and transported in large quantities over extended periods. HyDUS emerges as a unique opportunity to develop the capability and capacity to deliver energy networks and storage infrastructure central to realising the net-zero vision. The inherent complexity of the marine sector encompassing a diverse spectrum of ship types and sizes, substantial energy demands, and the globally interconnected nature of transport that necessitates working across geographies makes shipping a harder sector to decarbonise. However, with the potential that HyDUS offers, a more sustainable and environmentally friendly maritime sector is within reach, turning this aspiration into a tangible reality.