Publication

Abstract : The Fischer – Tropsch synthesis (FTS) involves a catalytic reaction where synthesis gas (A mixture of carbon monoxide and hydrogen) is converted to liquid hydrocarbons of different molecular weights. FTS is a highly exothermic reaction. Among many other types of reactors, the slurry bed reactor is used in common. The heat of the reaction is removed using a heat transfer fluid flowing through the tube bundle within the reactor. The catalyst slurry and the syngas are fed to the reactor. During the course of the reaction in the slurry reactor, the catalyst particles in the slurry undergo several collisions with the other catalyst particles, tubes, and reactor walls. These collisions result in breakage/agglomeration of catalyst particles, which result in the change in shape and size of the particles. This phenomenon will alter the interfacial surface area of the catalyst for the reaction and thus the rate of the reaction will greatly be affected. Further, the change in the size of the particles will affect the settling behavior of the particles and their dispersion in the slurry. Because of this, the designed catalyst residence time in the slurry reactor may vary. This work addresses the change in residence time of the cobalt supported on alumina Fischer-Tropsch catalyst due to breakage/agglomeration. The particle breakage mechanism was coupled with multi-size particle dispersion model for analyzing the changes in the residence time. Weibull distribution was used for calculating the particle breakage probability and the size of the daughter particles was calculated using dynamic fragmentation model developed by Grady (1995). The individual particle velocities were calculated using Richardson-Zaki model. The coupled models of particle breakage with dispersion were coded in MATLAB. The concentration of the different sized catalyst particles as a function of bed height and its influence on the reaction residence time was analyzed.