Pressure Drop in a Packed Bed Reactor (PBR) Using the Ergun Equation
A first-order, irreversible reaction takes place in two isothermal packed bed catalytic reactors; their lengths are 14 m and 21 m. This Demonstration compares the conversion, pressure, molar flow rate, and volumetric flow rate for the two reactors as a function of distance down the reactor. The inlet pressure is the same for each reactor and, for a given particle diameter, the outlet pressure is also the same. As a result, the flow rate into the longer reactor is lower. The Ergun equation is used to model the pressure drop; you can vary the diameter of the catalyst particles in the packed bed.
The pressure decreases down the length of the reactor, and thus the volumetric flow rate increases. As a result, the concentration of the reactant decreases (in addition to the decrease because A reacts to B), which decreases the rate of reaction.
Following is the Ergun equation for the pressure drop in a packed bed:
= laminar flow term
= turbulent flow term
= void fraction
= volumetric flow rate
= diameter of catalyst particles
= mass flow rate
= cross section area of PBR
= length of PBR
Material balance on reactant A for a first-order reaction: