Potential for Decarbonizing Ammonia Production Using Cargen® Technology

Ammonia (NH3) stands as a pivotal industrial chemical, primarily synthesized through the renowned Haber-Bosch process. Beyond its significance in agriculture, ammonia has garnered attention as a promising energy carrier due to its substantial hydrogen (H2) content. However, ammonia production demands considerable energy, resulting in approximately 2% of the world's total energy consumption. Consequently, ammonia synthesis contributes up to 1.6% of global CO2 emissions and 5% of CO2 emissions from chemical industries. In particular, 1.25-2.16 kg of CO2 is emitted per kg of ammonia produced in conventional ammonia production. Therefore, extensive efforts are underway to decarbonize the process for ammonia production to become environmentally sustainable. These efforts include transforming existing coal and natural gas-based ammonia plants (often termed black or grey ammonia) into blue ammonia facilities by integrating carbon capture and sequestration (CCS) technology or transitioning to green ammonia plants powered by renewable energy sources. However, green ammonia production, in particular, faces challenges in scalability due to the decentralized and sporadic availability of renewable energy and the elevated costs associated with it, which diminishes the economic viability of green ammonia.

One approach to significantly reducing CO2 emissions in ammonia synthesis involves the application of innovative CARGEN® (CARbon GENerator) technology, which converts CO2 and methane into multi-walled carbon nanotubes (MWCNTs) and hydrogen-rich syngas. The Texas A&M University technology has successfully reduced the energy consumption of the conventional methane dry reforming (DRM) process by 50% and demonstrated a remarkable reduction in CO2 emissions by up to 73% upon integration in conventional gas-to-liquid (GTL) process plants. Therefore, the work aims to retrofit ammonia reformers with Carbon Capture and Utilization (CCU) systems such as CARGEN® technology to decarbonize conventional ammonia production sustainably and economically.

In the present study, a conventional ammonia synthesis process flowsheet with a capacity of 1,265 tons per day has been developed to identify various sources of direct CO2 emissions and assess energy and power utilization. The simulation has been developed using the ASPEN® Plus process simulator and serves as a reference point for comparison with a similarly sized ammonia plant employing CARGEN® technology reformer. The retrofitting approach replaced the combination of steam methane reformer (SMR) and autothermal reformer (ATR) processes with an equivalent-capacity CARGEN® process that yields a product stream composition similar to that of the base case reformer unit. Next, a comprehensive mass and energy balance analysis was conducted to evaluate the CO2 utilization and abatement potential of the CARGEN®-based ammonia plant compared to the base case ammonia process. Our preliminary results demonstrate that besides full CO2 recycling from

the amine separation unit, the CARGEN® process consumes a surplus of 3,000 tons/day of CO2 to fulfill its CO2 feedstock requirements.

Moreover, the CARGEN® based ammonia process requires up to 67% less steam than the base case process; however, the process requires about 2.5 times more natural gas compared to the base case process. In addition, the results show that ammonia plants based on the CARGEN® process have 19% higher energy requirements and 11% higher power requirements due to additional supply of natural gas and CO2. However, plant-wide consideration of direct and in-direct CO2 emissions reveals that the CARGEN® Technology integration reduces the net CO2 emission from 3,013 to 1,321 tons/day. Consequently, an ammonia plant based on CARGEN® Technology reduces the overall carbon footprint of the process to 2.16 kg CO2-eq/kg NH3 compared to 4.76 kg CO2-eq/kg NH3 in the conventional process.

This paper will provide more details on the potential impact of the CARGEN® technology for decarbonizing ammonia plants to provide a better carbon footprint product than blue ammonia. This innovative approach offers a promising pathway for generating carbon-negative ammonia, presenting a significant and alternative technology to address the challenges posed by climate change.

References:

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