Optimization of an Ammonia Synthesis Converter

Abstract

A scheme that optimizes the converter of an ammonia synthesis plant to determine optimal inlet temperatures of the catalyst beds has been developed. The optimizer maximizes an objective function-The fractional conversion of nitrogen on the four catalyst beds of the converter subject to variation of the inlet temperature to each catalyst bed. An iterative procedure was used to update the initial values of inlet temperature thus ensuring accurate results and quick convergence. Converter model results obtained with optimized operating conditions showed significant increase in fractional conversion of 42.38% (from 0.1949 to 0.2586), increased rate of reaction evident in a 13.18% (0.5317 to 0.4616) and 23.84% (0.1946 to 0.1482) reduction in reactants (hydrogen and nitrogen) concentration respectively and a 56.48% increase (from 0.1181 to 0.1838) in ammonia concentration at the end of the fourth catalyst bed compared to results obtained with industrial operating conditions.

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

“…Therefore, a pseudohomogeneous reactor model is adapted and heat losses are ignored, though with this assumption, behaviour of the reactor system remains quite similar to real plant. 36,37,39,41 Future studies may tailor the separation section to the required exibility envelope of the Haber-Bosch process.…”

Optimisation of the Autothermal NH3 Production Process for Power-to-Ammonia

“…A large amount of optimisation work on multi-bed reactor systems can also be found [14][15][16][17][18]. A four-bed direct cooling reactor system for optimal operational temperature was presented by Gaines [14], whereas an indirect cooling reactor system for maximum N 2 conversion by a one-dimensional homogeneous model was analysed by Aka and Rapheel [15]. Gaines optimisation results show that, with good temperature control, NH 3 production can be increased by 1% forthe constant feed rate.…”

“…In addition, the impact of quench fractions alone or with one process variable at a time on reactor efficiency was studied [14]. Aka and Rapheel considered each bed inlet temperature as a decision variable for maximising N 2 conversion from 0.19 to 0.26 [15]. Elnashaie et al [16], Elnashaie and Alhabdan [17], and Azarhoosh et al [18] optimised three-bed indirect cooling reactor systems for maximum NH 3 production by using a one-dimensional heterogeneous model.…”

“…Therefore, a pseudo-homogeneous model is adapted and heat losses are neglected. With these assumptions, behaviour of the reactor system remains comparable to an actual ammonia synthesis plant [15,18,22,23]. The assumptions and mathematical models applied within the system boundaries I and II are given as follows.…”

“…T b1 in + ∆T MIN ≤ T b3 out (15) whereμ NH 3 is the gross NH 3 production for reactor systems RS ∈ {2Q, HQ, QH, 2H}. All reactor systems have the following process variables: inert gas concentration in process feed, process feed mass flow rate, and reactants ratio in process feed z 3 ,RS ∈ {y Ar |ṁ | y H 2 : y N 2 } 3 ,RS .…”