Transporte de calor em reator cilíndrico-elíptico de leito fixo via modelo de duas fases em regime permanente.

Abstract

The study of heat transfer in fixed bed tubular reactors of heated or cooled walls is of great interest to the industry promoting exothermic or endothermic gas-solid heterogeneous catalytic reactions. The adequate and safe design of such equipment requires the adoption of reliable, realistic mathematical models that are in harmony with the physical principles that govern the problem. The objective of this work was to study the heat transfer in packed-bed elliptical-cylindrical reactor. A heterogeneous mathematical model was proposed, written in elliptical cylindrical coordinates, consisting of two continuous phases, a solid phase and another fluid phase, in which the energy balances of each constituent are developed separately. The governing differential equations were solved mathematically using the finite volume method and the WUDS scheme as an interpolation function for convective and diffusive terms, in a totally implicit formulation. The system of linear algebraic equations resulting from the discretization of the energy equation at all points of the computational domain are solved iteratively by the Gauss-Seidel method. Heat transfer was simulated under different operating conditions, varying: (1) the geometric aspect ratio (L2 / L1); (2) the height of the reactor; (3) the material of the reactor wall; (4) the air velocity at the reactor inlet; (5) the temperature of the reactor's cooling fluid; (6) the temperature of the internal fluid of the reactor; (7) the dimensions of the reactor particles. The results of the temperature distribution of the gas and solid phases along the reactor were presented and analyzed. It was found that the axail and radial temperature gradients inside the reactor were higher for the fluid phase in all cases analyzed; that the temperature isolines are higher for positions closer to the center and inlet of the reactor; that the axial temperature gradients are more relevant in the region close to the reactor inlet for the fluid and solid phases and that the radial temperature gradients are larger near the reactor wall for both phases.