Modeling, simulation and model validation for an axial-radial ammonia synthesis reactor

Abstract

This study is aimed at modeling axial-radial reactors and validating the model by comparing its prediction to experimental data. The axial-radial reactor is characterized by a gas-flow configuration which is an hybrid between the classical axial-flow and radial-flow configurations. The steady-state behavior of the reactor is found as solution to the Navier-Stokes equations describing the velocity field and pressure profile and to the mass and heat balance equations. A new solution approach is developed which decomposes the partial differential equation system into two subsystems, for each of which the most suited solution method can be applied.The Navier-Stokes equations are solved using two-dimensional collocation on finite elements while the mass and energy balance equations are solved using alternatively the collocation and the finite-difference methods together with an integration method.The solution to the Navier-Stokes equations is found to be very sensitive to the choice of boundary conditions. The mass and energy balance subsystem, on the other hand, is highly sensitive to the choice of the spatial coordinate that is integrated, the other being discretized. Since the two subsystems are coupled an appropriately devised iteration scheme is proposed to solve the complete system.Although rigorous parameter fitting was purposefully not attempted, satisfactory model prediction was obtained.