Models for nonisothermal trickle-bed reactors

Here A0 and E are the frequency factor and the activation energy for the reaction, respectively, Rg is the universal gas constant, 7] is the reactor inlet temperature pG and pi are the gas and liquid densities, respectively, Cpr. and CpL are the gas and liquid heat capacities respectively, V0G and U0L are the superficial gas and liquid velocities respectively, e. is the void fraction of the undiluted catalyst, r is the space time, C-, is the reactor inlet concentration of the reactant, m is the order of the reaction, and A7/r is the heat of reaction. The results shown in Figs. 4-5 

Shah and Paraskos47 applied their analysis to evaluate the importance of axial dispersion on pilot scale (a) residue hydrodesulfurization, (b) gas-oil hydrocracking, and (c) shale-oil denitrogenation reactor performances. The calculations indicated that the axial dispersion effect is less important in case (c) than in cases (a) and (b). Under certain pilot-scale operations, axial dispersion effects could be significant in cases (a) and (b). 

4-4-2 Dynamics of Commercial Adiabatic Reactors with an Aging Catalyst (Commercial Hydrodesulfurization Reactor with Quench Fluids ) 

The commercial trickle-bed reactors, such as hydrodesulfurization and hydrocracking reactors, are often operated adiabatically. The temperature rise in such reactors is often controlled by the additions of a quench fluid (normally hydrogen) at one or more positions along the length of the reactor. A schematic of an adiabatic trickle-bed HDS reactor with a single quench is shown in Fig. 4-7. 

As time progresses, the catalyst in the HDS reactor decays because of metal (vanadium and nickel) and coke depositions. The deposition of these metals occurs nonuniformly along the length of the reactor (more deposits occur near the reactor inlet than at the reactor outlet). In normal plant operations, the catalyst activity decline is counterbalanced by a rise in feed temperature, a reduction in the amount of quench fluids fed to the reactor or both, so as to achieve the same quality product. The process is terminated upon the attainment of a maximum allowable temperature (MAT) anywhere in the reactor. The catalyst bed is then regenerated. The time required to achieve the MAT is often called the reactor cycle life. 

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