Plug-flow reactors runaway

Runaway criteria developed for plug-flow tubular reactors, which are mathematically isomorphic with batch reactors with a constant coolant temperature, are also included in the tables. They can be considered conservative criteria for batch reactors, which can be operated safer due to manipulation of the coolant temperature. Balakotaiah et al. (1995) showed that in practice safe and runaway regions overlap for the three types of reactors for homogeneous reactions (1) batch reactor (BR), and, equivalently, plug-flow reactor (PFR), (2) CSTR, and (3) continuously operated bubble column reactor (BCR). 

It is not practical to stir all reaction systems, for example, bulk polymerizations, postpolymerization reactions, fixed-bed catalytic reactors, and plug-flow reactors. Although multipoint temperature sensing is often used as a key solution to determine a runaway in nonagitated vessels, the occurrence of hot spots may not always be detected. 

TABLE 4-5 Reactor Design Strategies to Prevent the Phenomenon of Thermal Runaway in Plug-Flow Tabular Reactors... 

TABLE 4-7 System of Equations That Must Be Analyzed to Prevent Thermal Runaway in a Plug-Flow Tiibular Reactor with Countercurrent Cooling in a Concentric Double-Pipe Configuration That Is Not Insulated from the Surroundings"... 

This reasoning also indicates the importance of gas flow rates. If, for example, in a tube of a multitubular reactor, a deposit is formed that decreases the gas velocity because of plugging, at some point pellet runaway will occur irreparably and, consequently, full runaway of that tube [12]. 

---