טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
M.Sc Thesis
M.Sc StudentOldek Rina
SubjectModeling of a Catalytic Reactor with Flow Reversal
DepartmentDepartment of Chemical Engineering
Supervisors Professor Emeritus Moshe Sheintuch
Dr. Olga Nekhamkin


Abstract

Catalytic combustion of volatile organic compounds is widely applicable for the decontamination of waste gases. However, it requires the attainment of high temperatures, which typically cannot be sustained in a simple reactor with diluted streams. One possible technology is the flow-reversal reactor, which combines a reactor and direct heat transfer, and in which the temperature can exceed significantly that of the once-through operation. Another operation is internal-recirculation, which combines a reactor and indirect heat transfer, in which the feed enters through one reactor and then turns around through another.

The three modes of operation discussed are modeled, analyzed and compared with experimental results (conducted in previous works). The reactor was built from two concentric tubes packed with a catalytic section and two inert sections on each side allowing different modes of operation. The oxidation of ethylene and propane on Pt/Al2O3 are used as model reactions.


Design and operation of a reactor with flow reversal requires accurate prediction of the domain of operating conditions. Thus, simulations, based on homogeneous and heterogeneous models, are compared with experimental observations and approximate solutions based on instantaneous or very fast reactions.

Adequate agreement between the experimental results and simulations is demonstrated. The difference between the homogeneous and heterogeneous model predictions is usually small. The approximations show that the conductivity and bed length are the most important parameters for predicting the highest temperature.


The behaviour of a packed-bed reactor operating in the three modes mentioned previously is analysed. The simple internal-recycle reactor operated better, at low flow rates and low feed concentrations, however, at high flow rates the flow reversal operation exhibits higher temperatures than the other modes.


Analysis of various parameters that affect the design of a reverse flow reactor was conducted. Propane oxidation is used as the model reaction for which several approximations for the extinction points can be derived. The simulations show that the performance of the reactor is insensitive to the preexponential factor, but highly dependent on the heat transfer coefficient and the bed conductivity. The extinction point, however, is very sensitive to the kinetic properties.