A Comparative Environmental Life Cycle Assessment of the Combustion of Ammonia/Methane Fuels in a Tangential Swirl Burner

Abstract

Ammonia has been proposed as a replacement for fossil fuels. Like hydrogen, emissions from the combustion of ammonia are carbon-free. Unlike hydrogen, ammonia is more energy dense, less explosive, and there exists extensive experience in its distribution. However, ammonia has a low flame speed and combustion emits nitrogen oxides. Ammonia is produced via the Haber-Bosch process which consumes large amounts of fossil fuels and requires high temperatures and pressures. A life cycle assessment to determine potential environmental advantages and disadvantages of using ammonia is necessary. In this work, emissions data from experiments with generating heat from tangential swirl burners using ammonia cofired with methane employing currently available technologies were utilized to estimate the environmental impacts that may be expected. Seven ammonia sources were combined with two methane sources to create 14 scenarios. The impacts from these 14 scenarios were compared to those expected from using pure methane. The results show that using ammonia from present-day commercial production methods will result in worse global warming potentials than using methane to generate the same amount of heat. Only two scenarios, methane from biogas combined with ammonia from hydrogen from electricity and nuclear power via electrolysis and subsequent ammonia synthesis using nitrogen from the air, showed reductions in global warming potential. Subsequent analysis of other environmental impacts for these two scenarios showed potentially lower impacts for respiratory organics, terrestrial acidification-nutrification and aquatic acidification depending on how the burner is operated. The other eight environmental impacts were worse than the methane scenario because of activities intrinsic to the generation of electricity via wind power and nuclear fission. The results show that generating heat from a tangential swirl burner using ammonia currently available technologies will not necessarily result in improved environmental benefits in all categories. Improvements in renewable energy technologies could change these results positively. Other means of producing ammonia and improved means of converting ammonia to energy must continue to be explored.

Environmental Life Cycle Assessment of Ammonia-Based Electricity

“…Valera-Medina [16] Ammonia blends with methane for heat generation. Most studies conclude that current technologies used to produce green ammonia need to be improved.…”

“…Their study focused on alkaline units, denoting that there is still work to do to improve cell lifetime, power densities, and fuel consumption for less impactful devices. Further work was presented by Razon and Valera-Medina [16], who studied ammonia in gas turbines. Blends of ammonia-methane were evaluated, with results showing that ammonia produced from nuclear or wind energy could potentially support global decarbonisation with a −27% to −32% reduction in global warming potential.…”

“…LCA studies on ammonia as a fuel for transport [11,[61][62][63] and power generation [12,15,16,64] are less numerous than studies on ammonia production solely. Even though a straightforward comparison cannot be made due to differences in functional units, impact assessment methods, and in some cases, blends with other fuels, our results show a good agreement with those found in the literature.…”

“…In this study, without co-generation, the average impact of 1 kWh of ammonia-based on wind electrolysis is −41%, −36%, and 2629% relative to a natural gas conventional power plant, for GWP, ODP, and TAP, respectively. Razon and Valera-Medina [16] used pure methane as the benchmark for their LCA results of ammonia/methane blends in a gas turbine. A summary of the average percentage difference relative to benchmark they reported for GWP and those found in this study (without co-generation) are shown in Figure 7.…”

Methane/Ammonia Radical Formation during High Temperature Reactions in Swirl Burners

“…Currently, comparisons with other fuels have shown that ammonia's versatility can enable its use for combustion or in fuel cell devices [4], potentially delivering greater hydrogen quantities than other options (i.e., liquid organic hydrogen carriers, LOHC) at lower costs. Similarly, life cycle analyses denote how ammonia-fuelled systems present great potential to deliver green, sustainable stranded hydrogen [5][6][7] whilst reducing greenhouse emissions in support of the reduction in large carbon footprint scenarios.…”