Pseudo-adiabatic operation and runaway in tubular reactors

Critical conditions for thermal runaway in homogeneous tubular reactors with either constant or cocurrent external cooling were investigated through the applications of the generalized sensitivity criterion using reactor axial coordinate as the independent variable, and compared with those predicted by geometry-based criteria. All criteria are found to provide rather similar results when a hot spot is present inside the reactor. When the hot spot shifts to the reactor outlet, leading to the so-called pseudo-adiabatic operation (PAO), the geometry-based criteria become either invalid or conservative with respect to the generalized one. In addition, when the generalized criterion is applied to the cases where the PAO is present, it is required to use the axial coordinate rather than reactant conversion as the independent variable to predict the critical conditions, and the obtained runaway boundaries in the reactor parameter plane coincide with the PAO boundaries