Comparison, operation and cooling design of three general reactor types for Power-to-Ammonia processes

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Abstract

This work investigates the heat transfer design and performance of three general types of ammonia reactors for Power-to-Ammonia (P2A). Specifically, the reactors are an adiabatic quench cooled reactor (AQCR), an adiabatic indirect cooled reactor (AICR), and an internal direct cooled reactor (IDCR).
We present rigorous steady-state and dynamic models for the three reactor types. Steady-state optimisation at nominal load shows that the AICR and IDCR achieve the highest reactant conversion at 30.0% and 29.4%
respectively, whereas the AQCR reaction conversion is significantly lower at 26.9%. Through open-loop simulations around the optimal operating point, we illustrate the unstable oscillatory dynamics of the AQCR. In contrast, the AICR and IDCR showcase stable and fast decaying oscillations. Nonetheless, our stability analysis reveals that the optimal operating points for all reactors are situated precariously close to the reactor extinction threshold. As a result, even minor disturbances pose a substantial risk of extinguishing the reactors at optimal operating conditions.
We optimise the reactors across an operating window from 30% to 130% of its nominal load, reflecting varying load in a P2A plant. Over this operational range, the AICR and IDCR yield similar reactant conversions and demonstrate adaptability to varying loads by achieving significantly higher conversions at lower loads. In contrast, the AQCR shows a less pronounced increase in reactant conversion at reduced loads.
Considering the location of the optimal operating points close to reactor extinction, we evaluate operating the reactors at a 15 K higher feed temperature than optimal value (stability margin). Our analysis demonstrates that a 15 K safety margin only slightly reduces ammonia conversion across the operating window, while ensuring stable operation even in the event of a 15% decrease in the catalyst activity.
Original languageEnglish
Article number153660
JournalChemical Engineering Journal
Volume496
Number of pages20
ISSN1369-703X
DOIs
Publication statusPublished - 2024

Keywords

  • Dynamic simulation
  • Flexible operation
  • Power to Ammonia
  • Reactor design
  • Stability analysis
  • Steady-state optimisation

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