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. 2018 Oct 11;8(61):34926-34936.
doi: 10.1039/c8ra06821f. eCollection 2018 Oct 10.

Operating envelope of Haber-Bosch process design for power-to-ammonia

Izzat Iqbal Cheema  1   2   3 , Ulrike Krewer  1
Affiliations

Operating envelope of Haber-Bosch process design for power-to-ammonia

Izzat Iqbal Cheema et al. RSC Adv. .

Abstract

The power-to-ammonia concept allows for the production of ammonia, one of the most produced inorganic chemicals, from air, water and (renewable) electricity. However, power-to-ammonia requires flexible operation for use with a directly intermittent renewable energy supply. In this paper, we systematically analyse the operating envelope for steady-state operation of the three bed autothermic Haber-Bosch reactor system for power-to-ammonia by pseudo-homogeneous model. Operational flexibilities of process variables, hydrogen intake and ammonia production flexibilities are analysed, along with maximum and minimum possible changes in recycle load and recycle to feed ratio for the following process variables: reactor pressure, inert gas percentage in synthesis loop, NH3 concentration, H2-to-N2 ratio, total flow rate and feed temperature. Among the six process variables, inert gas fraction and H2-to-N2 ratio provided very high flexibilities, ca. 255% operational flexibility for Ar, up to 51 to 67% flexibility in hydrogen intake, and up to 73% reduction and 24% enhancement in ammonia production. However, a decrease in ammonia production by H2-to-N2 ratio significantly increases recycle load. Besides inert gas fraction and H2-to-N2 ratio, the total mass feed flow rate is also significant for minimum hydrogen intake and ammonia production.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. Ammonia synthesis loop with small quantity ammonia storage for power-to-ammonia.
Fig. 2
Fig. 2. Reactants conversion (a), temperature profiles (b) and temperature-reactants conversion trajectories (c) for the reactor system along the catalyst beds.
Fig. 3
Fig. 3. Steady-state characteristics of the reactor system for highest (X), high (H), normal (N) and low (L) operational pressures of the reactor system.
Fig. 4
Fig. 4. Steady state characteristics of the reactor system for outlet temperature versus operational pressure of the reactor system.
Fig. 5
Fig. 5. Steady-state characteristics of the reactor system for low (L), normal (N) and high (H) argon (inert gas) concentrations in feed ③ of the reactor system.
Fig. 6
Fig. 6. Steady state characteristics of the reactor system for outlet temperature versus ammonia concentration in feed ③ of the reactor system.
Fig. 7
Fig. 7. Steady-state characteristics of the reactor system for low (L), normal (N) and high (H) H2-to-N2 ratios in feed ③ of the reactor system.
Fig. 8
Fig. 8. Steady-state characteristics of the reactor system for lowest (X), low (L), normal (N) and high (H) total feed ③ flow rates of the reactor system.
Fig. 9
Fig. 9. Steady-state characteristics of the reactor system for high (one (H) and two intersections (H*)), normal (N) and low (L) feed ③ temperatures of the reactor system.
See this image and copyright information in PMC

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