Modeling and Simulation of a Single Catalytic Fixed Bed in an Ammonia Reactor

Abstract

We present a dynamical model of a single catalytic fixed bed in a quench-type ammonia reactor. This model consists of thermodynamics, kinetics, pressure loss, and mass and energy balances, which upon spatial discretisation results in a set of differential-algebraic equations. Compared to similar models in the literature, the main novelties in the model are: 1) a rigorous thermodynamic model using a thermodynamic software library; and 2) a correlation between the gas velocity and the pressure gradient throughout the bed, i.e. the pressure loss is included in the model and used to compute the gas velocity. We investigate steady state solutions and dynamical simulations to understand the behaviour of the single catalytic fixed bed. We determine the optimal steady state operational area and inverse response dynamics are observed. The model can be used to develop model-based control, which is relevant for dynamic and flexible operation of ammonia reactors in a Power-to-Ammonia plant.