Steady-state multiplicity in cocurrently cooled autothermal reactors

The steady‐state simulation of a cocurrently cooled autothermal fixed‐bed reactor was carried out using a 2‐D heterogeneous mathematical model. The ammonia synthesis was chosen as a case study. Unlike the not‐autothermal cocurrent reactor, which is unconditionally stable, the autothermal cocurrent reactor shows multiple steady states within a broad range of operating conditions. This finding, not reported in the literature, is explained through the mass transport from the bottom to the top of the reactor, associated with a feedback of energy. The feedback of heat, which is inherent to autothermal reactors, leads to an ignition‐extinction phenomenon similar to that found in the countercurrent configuration. The influence of different parameters on the stability of the autothermal cocurrent reactor was analyzed. The regions where steady‐state multiplicity occurs were compared with those presented by the autothermal countercurrent reactor. The influence of an additional heat exchanger on the reactor stability was considered.