Power to X – pathways to decarbonisation
written by Mary Snowdon & Duncan McLachlan
Climate change requires that society rapidly transitions from a hydrocarbon-based energy system to one that is decarbonised. This challenge is compounded by the need to do so in a manner that provides an affordable and secure supply of energy. Collectively these three elements are known as the energy trilemma and there is no single solution to this trilemma; solving for these variables requires a mix of solutions.
One solution in this mix is Power to X (PtX). This refers to pathways for the conversion of electricity into a variety of versatile products, such as hydrogen, ammonia or methanol. PtX offers a range of benefits that ensure it is a key element in solving the energy trilemma. These include storing excess variable renewable energy (VRE); decoupling decarbonisation from the power sector to provide opportunities in hard to abate sectors, such as steel and cement production, decarbonisation of chemical production; and even presents opportunities for the utilisation of captured Carbon Dioxide (CO2).
Critics of PtX products highlight the thermodynamic inefficiencies of converting electricity into other products, which is exacerbated by many PtX products requiring multiple conversion steps. However, energy efficiency is not the only important assessment criteria. As highlighted in numerous energy scenarios, many hard to abate sectors cannot utilise electricity directly for decarbonisation and PtX may enable commercially viable power exports from renewable rich countries to demand centres in countries with limited access to renewable power or low-cost renewable power demonstrating the range of use cases that should be assessed. These assessments must also factor in the suitability of the different PtX options for each specific project as many PtX technologies are not commercially proven, and the costs may be prohibitive.
a project PtX decision approach
These competing positive and negative factors require a robust assessment of the techno-economic and strategic criteria, specific to project aims and objectives, to identify the optimal PtX option. This system level project architecture is core to io’s execution, and here we explore some of the variables at play in PtX projects.
As with most major capital projects, cost is a significant constraining variable in as much that project CAPEX often drives levelized cost of green products to be uncompetitive with their grey equivalents. There are a variety of mechanisms in development to enable more competitive costs, including certification, premium pricing and taxation of grey products. This is a developing area and the latest mechanisms must be included in techno-economic evaluations.
scale of the facility
One of the most significant factors in identifying the optimal product is the scale of the facility, with smaller scale projects lending themselves more easily to the export of Hydrogen and larger scale projects requiring alternative products with more established export infrastructure to be optimal.
Electrolytic production of Hydrogen will be required for most PtX products. The choice of electrolyser has impacts on plant design, maintenance strategies and vendor selection, amongst others, but availability of supply is currently one of the most significant constraining variables as the electrolyser supply chain attempts to scale to unprecedented levels while still grappling with uncertain demand. Several vendors have manufacturing capacity expansions plans & funding that they are ready to implement if and when the projects driving the demand obtain Final Investment Decision (FID).
Utilising molecular Hydrogen as the end product is advantageous as it has the least number of conversions from the power source to the end user and therefore has the least thermodynamic destruction relative to other PtX products. However, Hydrogen has the lowest volumetric energy density of the PtX products and requires compression or liquefaction to reduce the storage volume or number of shipments required for export.
85% of the Hydrogen produced today is local to the consumer, the remaining 15% is transported by road or pipeline , there is therefore limited experience of Hydrogen shipping. There is currently no bulk cargo compressed Hydrogen ship in commercial operation, however, different technologies are in development , including Gen2 Energy who signed a contract with Sirius Design & Integration AS in 2022 for the design of two ships that would transport containers with compressed Hydrogen .
Hydrogen can be liquefied to increase the volumetric energy density and reduce the storage volumes required. Hydrogen liquefaction is an established technology, however, the global demand for liquid Hydrogen today is approximately 300 t/d. Therefore, relative to other PtX products the production scale is low. The largest operating liquefaction plant in the World today produces 34 t/d of liquid Hydrogen . Air Products is currently developing a 90 t/d Hydrogen liquefaction facility for a project in Asia, but this is not yet in operation . There are no commercial-scale liquid Hydrogen carrier ships in operation. Kawasaki has developed a pilot scale liquid Hydrogen ship which completed the first export of liquid Hydrogen in February 2022, however this is still in the pilot phase .
Liquid Organic Hydrogen Carriers (LOHC) are used to store Hydrogen, within a molecule, through a hydrogenation process. Hydrogenated LOHCs are liquid at ambient conditions, which is advantageous as it enables a more manageable method of storage and transportation in comparison with molecular Hydrogen, which requires high levels of compression or refrigeration. Additionally, LOHCs have similar properties to hydrocarbon based fuels and can thus utilise the existing export infrastructure. LOHCs also have a higher volumetric energy density than compressed Hydrogen, which may reduce the number of ships required for export. However, once the Hydrogen has been unloaded from the LOHC in the dehydrogenation process, the LOHC is reused and must be returned to the Hydrogen facility, which may negate the shipping benefits associated with the higher volumetric energy density. The LOHC will also require regular replenishment as the dehydrogenation process does not unload all of the Hydrogen, reducing the overall storage capacity. The dehydrogenation process is also relatively energy intensive, requiring approximately 35 - 40% of the equivalent energy of the stored Hydrogen .
Hydrogen and Nitrogen can be converted into ammonia via the Haber-Bosch process, which is a mature widely deployed technology. Although additional energy is required to convert Hydrogen into ammonia, there are many advantages such as the increase in volumetric energy density relative to gaseous and liquid Hydrogen, and LOHCs. Ammonia is one of the largest chemical markets in the World and international shipping of ammonia is well established and supported by existing infrastructure and regulations. Ammonia could be used directly by an off taker. As existing ammonia supply is almost entirely produced from hydrocarbons, there is a significant opportunity to utilise green-ammonia directly to decarbonise the existing ammonia market. Additionally, there are also several pilots assessing the potential to use Ammonia in hard to abate sectors such as marine and aviation fuel. However, it should be noted that if the end product is not ammonia but Hydrogen, a cracking process will be required to decompose the ammonia back into Nitrogen and Hydrogen.
e-methane, e-methanol and e-fuels
e-methane, e-methanol and e-fuels can be produced from Hydrogen and CO2. CO2 can be sourced from a biogenic source, Direct Air Capture (DAC) or from carbon capture at an industrial facility. Importing CO2 from a third-party increases the amount of power available for production and increases the production of the PtX product from the project. However, as the CO2 from the third-party is only temporarily stored, the emissions from the PtX product must be calculated to ensure that it meets any regulatory or certification requirements. Fuels produced from recycled Carbon from non-sustainable Carbon sources will be subject to current and future certification requirements. This poses a future risk for any projects that utilise recycled Carbon from a non-sustainable source. There are also operational complexities and risks associated with utilising CO2 from a third-party as the supply must be available for the entire lifetime of the project and maintenance cycles should be coordinated to minimise production outages.
On the other hand the US Infrastructure Law allocated $3.5bn of funding to DAC, which will be used to establish four DAC hubs in the USA. This funding is intended to accelerate the commercialisation of CO2 captured from the atmosphere and the eligibility includes projects that convert CO2 to valuable products and demonstrate a reduction in the lifecycle greenhouse gas (GHG) emissions when compared to the equivalent incumbent product . This presents a PtX opportunity where DAC is coupled with a PtX process to develop sustainable fuels, this is exemplified by the Oxy Low Carbon Ventures (OLCV) project to develop sustainable aviation fuel from DAC, “Air to Fuel™” .
DAC is currently the most expensive form of carbon capture, therefore, significant cost reductions in the technology, or taxation or incentive schemes are required to ensure green products derived from DAC are competitive.
However, if we assume CO2 can be obtained through means that do not destroy a projects viability, each of the e-fuels have their own benefits and challenges.
e-methane could be produced to decarbonise existing methane users, this is advantageous as it could utilise existing export infrastructure. e-methane is produced through the conversion of Hydrogen and CO2 in a methanation unit. However, the cost of e-methane is high relative to grey sources.
e-methanol can also be produced using Hydrogen and CO2, and could be used to decarbonise existing methanol users. Like ammonia, methanol is also being assessed for direct use in hard to abate sectors such as marine fuel. The process for e-methanol is similar to methanol production from hydrocarbon sources, however e-methanol synthesis produces higher volumes of water and therefore minor modifications are required for the catalyst. Methanol is shipped globally therefore existing export infrastructure and regulations exist. As with e-methane, the cost of e-methanol is currently high relative to grey sources.
e-fuels, also known as synthetic fuels or synfuels are produced from carbon dioxide and hydrogen. The advantages of e-fuels are the higher volumetric energy density compared to hydrogen and the use of the existing infrastructure, including production and export processes, and end-uses, for example Internal Combustion Engines. E-fuels can be produced to decarbonise existing users of hydrocarbon equivalents, and to meet new demands, such as sustainable aviation fuel. The Reverse Water Gas Shift Process and Fischer-Tropsch process used to produce e-fuels are the same processes used for hydrocarbons. The process can be scaled down to smaller capacities, however, this will negatively impact project economics and make the e-fuels less competitive with the traditional hydrocarbon sourced alternatives. Existing infrastructure can be utilised for distribution, storage and delivery.
PtX technology has the potential to support the transition towards a more sustainable energy system. While there are challenges to overcome, such as the high cost, the benefits of PtX technology make it worth pursuing and investing in as one thread of the solution for the energy trilemma. Governments and industries can support the development of PtX technology through investment in research and development, as well as implementing policies that incentivise the adoption of PtX systems. For example, governments can provide financial incentives for the adoption of PtX technology, such as tax credits or grants.
Furthermore, PtX technology can be integrated into existing energy systems, allowing for a gradual transition towards a more sustainable and efficient energy future. By utilising excess renewable energy to produce PtX products, we can reduce our reliance on fossil fuels and lower greenhouse gas emissions. Finding the optimal product given specific project constraints and success criteria requires a holistic approach to establish the best project architecture, this is io’s expertise as is exemplified by our stellar track record on PtX projects across multiple geographies, power sources and product choices.
1 IEA (2019), The Future of Hydrogen
3 M. Aziz (2021) Liquid Hydrogen: A Review on Liquefaction, Storage, Transportation and Safety
6 IEA (2019), The Future of Hydrogen