Full Papers Heat Dispersion Effects on the Functional Characteristics of Industrial-scale Adiabatic Membrane Reactors By E. Vogiatzis, M.K. Koukou, N. Papayannakos, and N.C. Markatos* The influence of heat dispersion on the performance of adiabatic industrial-scale membrane reactors is studied in this work. The results presented are from the application of the model to a membrane reactor that is introduced in an IGCC plant, to control carbon dioxide emissions. The performance of this reactor equipped with highly selective membranes is studied in detail. The thermal phenomena that take place in the interior of the membrane reactor have a considerable influence on the operation of the reactor thus the assumption of isothermal operation is not valid. The omission of thermal dispersion results on the underestimation of the system operation and the total gaseous fluxes that permeate through the membrane. The tem- perature distribution in the membrane reactor differs significantly from the calculated distribution predicted from the model that ignores thermal dispersion effects. 1 Introduction The membrane reactor concept has been widely studied during the last decades [1±12]. These devices have been proposed for various applications while the most promising application opportunity of them is the circumvention of a chemical equilibrium so as to achieve higher conversions by selective permeation, through the membrane, of at least one of the reaction products. The main advantages of the mem- brane reactors are [6]: shift of the thermodynamic equilibri- um, enhancement of yield and selectivity, control of reac- tants distribution and low costs, simultaneous reaction and separation of products. Despite the various advantages of the membrane catalytic reactors, the membrane reactor technology is still limited to specific kind of reactions and is not yet commercially utilized. It is widely accepted by the membrane community that future commercial membrane reactors would most likely be based on straight tubular membranes and that large indus- trial membrane reactors will be composed in many cases of banks of tubular ceramic membranes [5, 8]. The use of ce- ramic membranes in these reactors is recommended primar- ily due to their thermal and mechanical stability [8]. Until now, most of the modeling works have focused on a rather simple reactor setup studying issues like type of flow pat- terns or role of sweep gas flow rate. The simple membrane reactors considered are used for testing at a laboratory scale rather than for large scale industrial applications. However, when membrane reactors will gain penetration in the indus- try process, new models, much more complicated than those assembled until now will have to be solved. The assumption of isothermal operation, valid for several laboratory scale membrane reactors, will not hold anymore at a large scale, and more complex modeling will have to be developed. The need of describing properly heat balances in membrane re- actors will certainly become a major task if large scale indus- trial units will be ever put into operation. The effect of the non-isothermal conditions prevailing in experimental mem- brane reactors on their performance has been discussed in a recent work [9]. A first attempt on developing simulation tools for the design of industrial-scale membrane reactors has been published [8, 10, 11], where plug-flow conditions were assumed at both sides of the membrane reactor, ne- glecting heat dispersion effects. In this work, results from the simulation of a membrane reactor that is introduced in an Integrated Gasification Combined Cycle (IGCC) plant to control carbon dioxide emissions are presented taking heat dispersion effects into account [9]. The Water Gas Shift reaction (WGS) is consid- ered to take place on the feed side of the membrane reactor that is filled with catalyst particles. Two versions of the mod- el are used. The first one accounts for heat dispersion effects inside the reactor (Heat Dispersion Model, HDM) while the second one, neglects heat dispersion effects inside the reac- tor (Simplified Model, SM). The results obtained from those two versions of the model are compared for the purpose of investigating the possible influence of heat dispersion effects on the membrane reactor performance. Chem. Eng. Technol. 2004, 27, No. 8 DOI: 10.1002/ceat.200402027  2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 857 ± [*] E. Vogiatzis, N. Papayannakos, N. C. Markatos (corresponding author, N.Markatos@ntua.gr), National Technical University of Athens, Depart- ment of Chemical Engineering, 9, Heroon Polytechniou Str., GR- 157 80, Athens, Greece; M. K. Koukou, Technological Educational Institution of Chalkida, Faculty of Applied Sciences, 344 00, Psachna, Euboea, Greece.