A numerical study was carried out to investigate steady-state and transient phase distribution, evaporation, and thermal runaway in a large-scale high-pressure trickle bed reactor. A cooling recycle stream, containing reaction products and a fresh feed, was included via a closed loop calculation. It was found that, as expected, phase distribution in the catalyst bed had a substantial impact on production rate; a faulty feed distribution system can cost approximately 20% in overall steady-state product conversion. In the event that the cooling recycle stream is lost, the external reactor shell temperature can exceed its design intent. It was found that reducing the quantity of fresh reactant feed in this situation can dramatically reduce the potential for vessel damage. Thermal inertia of the catalyst particles proved to be a significant contribution to the transient energy balance. Model results are supported with a posteriori thermal excursion plant data. (C) 2010 Elsevier B.V. All rights reserved.