Minimizing the impacts of the ammonia economy on the nitrogen cycle and climate

Abstract

Ammonia (NH 3 ) is an attractive low-carbon fuel and hydrogen carrier. However, losses and inefficiencies across the value chain could result in reactive nitrogen emissions (NH 3 , NO x , and N 2 O), negatively impacting air quality, the environment, human health, and climate. A relatively robust ammonia economy (30 EJ/y) could perturb the global nitrogen cycle by up to 65 Mt/y with a 5% nitrogen loss rate, equivalent to 50% of the current global perturbation caused by fertilizers. Moreover, the emission rate of nitrous oxide (N 2 O), a potent greenhouse gas and ozone-depleting molecule, determines whether ammonia combustion has a greenhouse footprint comparable to renewable energy sources or higher than coal (100 to 1,400 gCO 2 e/kWh). The success of the ammonia economy hence hinges on adopting optimal practices and technologies that minimize reactive nitrogen emissions. We discuss how this constraint should be included in the ongoing broad engineering research to reduce environmental concerns and prevent the lock-in of high-leakage practices.

Climate Impacts of Hydrogen and Methane Emissions Can Considerably Reduce the Climate Benefits across Key Hydrogen Use Cases and Time Scales

“…Note that we have not accounted for the various levels of N 2 O that can be directly emitted and indirectly formed from the release of reactive nitrogen compounds across the blue ammonia pathway, which can further increase its overall climate impact. 50,51 3.1.3. Effect of Carbon Capture Rates.…”

“…For the blue ammonia power generation pathway, high methane emissions can lead to more warming in the near term than using natural gas for power generation (Figure d). Note that we have not accounted for the various levels of N 2 O that can be directly emitted and indirectly formed from the release of reactive nitrogen compounds across the blue ammonia pathway, which can further increase its overall climate impact. , …”

Boosting the cost competitiveness of low-carbon ammonia by expanding emission trading system coverage in China

“…Promoting material recycling through actions like creating a comprehensive material input inventory and pinpointing material-intensive processes proves to be a proactive measure in mitigating the potential impacts of critical material price surges 34 . Furthermore, as a potential threat to the nitrogen cycle, it is imperative to address reactive nitrogen emissions resulting from ammonia used in energy 37,38 .…”

Helping the climate by replacing liquefied natural gas with liquefied hydrogen or ammonia?

“…(For the sake of completeness we illustrate the overall efficiency of 'green' ammonia and hydrogen fuel cell pathways, see SI tab 'charts'). N 2 O emissions rates from ammonia combustion are estimated as 0.5 g per kWh for the central case [24], 1 g per kWh for the high estimate [25], and 0.1 g per kWh for the low estimate [26]. CO 2 and CH 4 emissions rates from natural gas combustion turbines are based on Spath and Mann [27, see table 5 on page 12 therein].…”