Decarbonisation Technology - May 2023 Issue

combustion temperatures present within hydrogen engines, the production of NOx can be higher than for hydrocarbon fuels (Ammar & Alshammari, 2018). To mitigate NOx emissions, current technologies such as exhaust gas recirculation and catalytic converters will be required (Ammar & Alshammari, 2018). One key issue is that hydrogen production relies heavily on hydrocarbon feedstocks, as 96% of all hydrogen is currently produced by reforming fossil fuels (van Hoecke, et al. , 2021). In the near term, low carbon intensity hydrogen produced from steam methane reformers (SMR) fitted with carbon capture represents the lowest cost route. In the longer term, the production of hydrogen without the use of fossil fuels via the electrolysis of water is being developed at a commercial scale. The electrolysis process uses a large amount of electricity, which depending on the energy mix of the grid, can produce a substantial amount of carbon emissions. Electricity grid carbon emissions can be mitigated by using electricity from renewable sources. Unfortunately, producing hydrogen from electrolysis currently remains economically unviable compared to reforming fossil fuels (van Hoecke, et al., 2021). For inland waterways and short-sea shipping, hydrogen has the potential to serve as a promising low-emission fuel option. However, transitioning to alternative fuels will require proactive planning by governments and regulators, particularly over the medium term (2030-2040). Ammonia has also gained much attention in recent years as a possible future fuel. It is a simple molecule consisting of one nitrogen

atom and three hydrogen atoms. Ammonia is synthesised using the Haber-Bosch process by the catalytic reaction of nitrogen and hydrogen under high pressure and temperature (Ricardo, 2019). The Haber-Bosch process is highly energy intensive, leading to a large carbon footprint. Currently, most ammonia produced is done so via steam reforming of methane into hydrogen (The Royal Society, 2020). However, there are proposals to make hydrogen through electrolysis, powered by renewable energy, in countries such as Morocco (Ricardo, 2019). Like hydrogen, ammonia has the advantage of producing no CO 2 , SOx, or PM when combusted. However, NOx emissions can be substantial, depending on the combustion conditions (Li, et al ., 2021). NOx emissions can be mitigated by controlling the air-to-fuel ratios and the implementation of technologies such as exhaust gas recirculation and catalytic converters (Li, et al. , 2021). Methanol has also been successfully trialled as a marine fuel (Liu, Li, Koh, Ang, & Lee Lam, 2021). It is the simplest form of primary alcohol, and when combusted only produces water and CO 2 . Methanol produces no SOx and much lower PM/NOx than HFO (Liu, Li, Koh, Ang, & Lee Lam, 2021). A key advantage of methanol is its comparable energy density (15.8 MJ/L) to LNG (20.8 MJ/L). Nevertheless, most of the current world supply of methanol relies on the production of syngas from fossil fuel feedstocks, often coal or natural gas. The syngas is passed over a catalyst at high temperatures and pressures. This energy-intensive process can have a large carbon footprint, depending on the energy mix of the electricity grid. One advantage of methanol is that it can be