The Shortening of the Reaction Time in the Solid Particles/Gas System

Abstract

In some solid particles/gas systems, reaction occurs first on the outer skin of each particle. The reaction zone then goes into each solid, leaving behind both converted and inert materials. This paper deals theoretically with the reaction time in such systems, where, the concentration of reactants is again made uniform throughout the particles in an arbitrary instant in the reaction process. The log-normal size distribution was assumed for these particles. The mathematical expressions for the reaction time were derived from the unreacted-core model. Digital computations were performed for the value of (ti-Ft2)jr, which was the total time needed to reach a given conversion F by the two reaction operations before and after the homogenization of all the particles. The value of (ti-Ft2)1I- was illustrated as a function of FIT in the Figures shown in the paper.The value of (tr-F t2)ir when FfT*FiT was found less than or equal to that of (ti-Ft2)1s- when FfT=F1T. This fact suggests that the shortening of the reaction time is expected by homogenization.The minimal value of (ti+ t2)/s- for an arbitrary, large F f7: decreased with increasing a in the range of a0.2. The double operation with the homogenization process in mid course was, therefore, more effective for shortening of the reaction time, as the extent of the size distribution of the particles increased within this range. This operation was, however, of little or no use in the system where the gas-film-diffusion controlled the rate of reaction in each particle (Case I) and whose a was near or equal to zero. It did not be applied in the system where no large FIT was required.In order to complete the reaction quickly or to allow it to arrive at FIT (F1T<ca.1) in the shortest time, it is generally recommended to consume a half of the total reaction time in the first process.