Techno-economic comparison of ammonia production processes under various carbon tax scenarios for the economic transition from grey to blue ammonia

Ammonia synthesis is a carbon-intensive process, with significant volumes of carbon dioxide produced during the preliminary production of hydrogen from a fossil fuel feedstock. Since carbon emissions vary significantly depending on the hydrogen production method, the impact of carbon capture and storage (CCS) implementation on the overall economic performance of the ammonia synthesis process differs. Therefore, it is crucial to (1) integrate cost-effective CCS into various ammonia synthesis processes and (2) conduct a comprehensive comparison of grey and blue ammonia systems together, considering the economic costs of the carbon emissions. This study aims to investigate the economic feasibility of large-scale ammonia processes under various carbon tax scenarios and suggest carbon-efficient options for the ammonia industry. Three ammonia synthesis processes are designed that differ in their hydrogen production method - steam methane reforming (SMR), autothermal reforming (ATR), and hybrid SMR-ATR - and these three options also have grey ammonia and blue ammonia production versions. The grey ammonia production systems do not include a carbon capture procedure, while the blue ammonia systems ensure that the CO2 emissions are below 0.065 t CO2/t NH3. In the present study, both the grey and blue versions of the three ammonia production processes are subjected to techno-economic evaluation under various carbon tax scenarios. For the grey ammonia systems, economic feasibility varies depending on the carbon tax scenario under consideration. Grey ATR becomes the most cost-effective option within a carbon tax of 95 $/ton to 115 $/ton. In contrast, the economic viability of the blue ammonia systems is unaffected by the carbon tax policy environment. In particular, blue ATR exhibits 6% and 14% lower levelized cost of ammonia (LCOA) compared to the blue SMR and blue Hybrid SMR-ATR, respectively. Overall, the results indicate that, below a carbon tax threshold of 62 $/ton, the SMR process without carbon capture is economically favorable. However, for carbon tax above 62 $/ton, the ATR process with carbon capture has greater economic feasibility than other options. A minimum carbon tax of 62 $/ton is required to promote the transition to blue ammonia. These findings thus provide valuable insight into the establishment of effective carbon regulations in response to the global demand to tackle the climate crisis.