Problem No. 45: Effect on reactor liner in case of reactor hold up

In the case of a failure in a urea plant, when the problem is expected to be solved within a short period, the high pressure synthesis section is typically blocked in (referred to in this article as reactor hold up). All input and output streams are closed and the synthesis section remains partly filled with a solution consisting of ammonia, CO₂, water, ammonium carbamate and of course urea. Several risks can occur during this blocked in situation: 1) as the temperature slowly reduces crystallisation could occur; 2) active corrosion could start as no fresh oxygen is supplied to the synthesis during blocking in and; 3) an explosive gas mixture could occur as hydrogen and oxygen are present.