Int. J. Hydrogen Energy, Vol. 15, No. 3, pp. 171-178, 1990. Printed in Great Britain. 0360-3199/90 $3.00 + 0.00 Pergamon Press plc. © 1990 International Association for Hydrogen Energy. A SIMULATION STUDY OF THE UT-3 THERMOCHEMICAL HYDROGEN PRODUCTION PROCESS K. YOSHIDA,* H. KAMEYAMA,'~ T. AOCHI,~ M. NOBUE,§ M. AIHARA,* R. AMIR,'I" H. KONDO,t T. SATO,~" Y. TADOKORO,~ T. YAMAGUCHI§ and N. SAKAI§ *Department of Chemical Engineering, University of Tokyo, Bunkyo-ku, Tokyo 113, Japan, tDepartment of Chemical Engineering, Tokyo University of Agriculture and Technology, 2-24-16 Nakamachi Koganei-shi, Tokyo 184, Japan, :~Japan Atomic Energy Research Institute, 2-2-2 Uchisaiwaicho, Chiyoda-ku, Tokyo 105, Japan, and §Process Engineering Division, Tokyo Engineering Corporation, 3-2-5 Kasumigaseki, Chiyoda-ku, Tokyo 100, Japan (Received for publication 8 September 1989) A~tract--A series of kinetic and simulation studies of four reactions consisting of the UT-3 cycle was made aiming at industrialization of this process. This cycle is given by 700-750°C CaBr2(s ) + H20(g ) , CaO(s) + 2HBr(g) (1) CaO(s) + Br2(g) 50~600oc CaBr2(s) + 1/202(g ) (2) Ee304(s ) + 8HBr(g) 2°°-3°°°c, 3FeBr2(s ) + 4H20(g ) + Br2(g ) (3) 4004J00°C 3FeBr2(s ) + 4H20(g ) , Fe304(s ) + 6HBr(g) + H2(g ). (4) This paper deals with rate expressions of these gas-solid reactions experimentally measured. Then, a simulation model for four fixed-bed reactors, in which four reactions are performed, and the calculation results are described. Also, the concept of process simulator is explained. N O M E N C L A T U R E C, Concentration of ith substance, mol m -s Cpg Average heat capacity of gaseoussubstances, kcal mol- I °C Cps Average heat capacity of solid substances, kcal m-3°C D O Diameter of tubular reactor, m Dp Diameter of solid particle, m G Molar specific velocity of gas, mol s -l m -2 hp Film coefficient of heat transfer, kcal m- 2 s- ~ °C AH Heat of reaction, kcal mol -I k~ Rate constant of ith reaction based on a unit volume of pellet, m s s- i mol- 1 P Reaction pressure, atm r~ Reaction rate of ith reaction, mol s -1 m -3 T Reaction temperature, K tg Temperature of gas reactant, K t~ Temperature of solid reactant, K U Over-all heat transfer coefficient, kcal m -2 s-t°C - Z Distance from the inlet of reactor, m 0 Reaction times, s t Voidage pg Molar density of gas, mol m -3 I N T R O D U C T I O N A multistep thermochemical water-decomposition cycle named UT-3 was proposed in 1978 [1]. Since then, a series of kinetic measurements has been con- ducted to verify this cycle, and a bench-scale plant with a nickname " M A S C O T " was constructed in 1982 [2]. This plant is being successfully operated with the follow- ing objectives: (i) to ascertain whether the designed conversion could be maintained in cyclic operation for a long span of time, and (ii) to obtaindata necessary for designing an indus- trial-scale plant. The basic conceptof the UT-3 process is shown in Fig. 1. It is the specific feature of this scheme that only gaseous substances flow through four fixed bed reactors connected in series, in which each reaction of the UT-3 cycle takes place, and that hydrogen and oxygen are separated from a loop-flow of gaseous substances by two separators, respectively. 171