Thermoflow multiplicity in a packed-bed reactor
Steady states with different flow rates and temperature profiles may exist in a packed-bed reactor operating under a prescribed pressure drop, due to the coupling among the species, energy, and momentum balances, and the change of the physical properties with temperature and pressure. This thermoflow multiplicity may lead to highly undesired operation in multitube packed-bed reactors. A pseudohomogeneous one-dimensional plug-flow model with no axial dispersion is used to describe the system. The parameter space is divided into regions with different flow rate vs. exit pressure diagrams by the construction of the generalized hysteresis variety, the boundary limit sets, and the double limit variety. As many as five solutions are found for some parameters. However, no more than three steady states are expected to be observed for the same pressure drop under practical operating conditions. A hierarchy of limiting cases based on different assumptions on momentum transport is used to derive criteria for predicting the conditions under which this thermoflow multiplicity may occur for a gaseous reaction. For reactions with no volume change, thermoflow multiplicity is observed in an adiabatic reactor only for highly exothermic reactions. A reaction induced volume increase enables thermoflow multiplicity to occur for reactions with a lower adiabatic temperature rise. A surprising finding is that thermoflow multiplicity may be found for an isothermal reaction involving a volume decrease. This point emphasizes the difference in the feedback mechanism leading to the thermoflow and thermokinetic multiplicity.
- Research Organization:
- Houston Univ., TX (USA)
- OSTI ID:
- 6719590
- Country of Publication:
- United States
- Language:
- English
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