Decarbonisation Technology - August 2023 Issue

technical feasibility, process safety, mechanical integrity, financial, and regulatory criteria that must be met for the supply chain to function and remain viable. The key challenge with the hydrogen economy in its present state is that each of these criteria need to be assessed, built out, and made more efficient in order to be sustainable. Consumers As with most products within an economic system, the value flow starts with the demand side and how the product will be used. Historically, most hydrogen has been used within the fossil fuels industry to produce transportation fuels, to meet low sulphur and emission quality mandates, and to convert low- value crude oil cuts into highly valued products. Future growth in hydrogen consumption will be driven by the need to reduce CO₂ emissions. Hydrogen is essential for the production of ‘zero-carbon emission’ combustion sources, converting seed oils, animal fats, and used cooking oils into renewable diesel and sustainable aviation fuel, and transforming renewable electricity into e-fuels. Hydrogen can also be considered a medium for longer term storage of renewable power. Within the refining sector, replacing existing hydrogen sources with decarbonised (such as low carbon intensity) hydrogen is relatively straightforward as long as the production volumes are available and sustainable and the logistics are in place. Fundamentally, as long as it meets the quality and supply condition targets, the refining process unit does not differentiate the source of the hydrogen. However, for some of the newer uses of hydrogen, limitations can exist on how far its usage can be expanded. As an example, in order to decarbonise combustion sources for heat, whether it be within a process heater, home or office heating, or even cooking, hydrogen as a combustion fuel becomes a viable mechanism to reduce CO₂ emissions, as the product of hydrogen combustion is primarily water. While post- combustion CO₂ removal, which involves extraction of CO₂ from the combustion flue gas and sequestering, can be retrofitted to existing industrial plant, it is not practical in household

heating applications. One novel alternative is to remove the CO₂ pre-combustion. The basic flow scheme for pre-combustion CO₂ capture is to reform streams such as natural gas, produced gas and lighter liquid fuels or to gasify heavier hydrocarbon streams to create syngas (CO and H₂) and then process the syngas in a water gas shift reactor to convert the CO to CO₂ and separate out the hydrogen for use as the downstream combustion fuel source. The primary advantages of this approach are  A higher concentration of CO₂ for more effective extraction  A reduced number of processing points and facilities to capture CO₂  The ability to provide a consistent fuel source to downstream consumers. However, this option does come with challenges. Firstly, hydrogen has a lower heating value on a standard volume basis compared to other typical fuel sources (such as natural gas), which means that up to three times as much standard volume of fuel will be required to meet the caloric requirements for combustion. Therefore, fuel supply lines, system pressures, pressure control valves, and even burners may have to be modified to use high percentages of hydrogen. Secondly, hydrogen has a higher flame temperature compared to other fuel sources, which impacts firebox performance and NOx emissions. One benefit of firing hydrogen is that the oxygen and, therefore, air requirements are lower for the same heat release, potentially reducing induced and forced air blower power requirements and debottlenecking draft- limited furnaces. While the firing of high hydrogen content streams in industrial heaters is highly plausible, the use of hydrogen to replace natural gas within commercial and home heating systems can be more challenging. Based on most evaluations, typical natural gas pipelines and home/commercial users can utilise between 5 and 10% hydrogen within the fuel system. The use of higher concentrations would require modification of the pipeline and compression supply systems as well as the point source combustion equipment and fugitive emissions. As an example, Becht supported a client to evaluate pre-combustion CO₂ removal as