Derivation of Entropy and Exergy Transport Equations, and Application to Second Law Analysis of Sugarcane Bagasse Gasification in Bubbling Fluidized Beds

Abstract

In the present work, the transport equations for mass, momentum, energy, and chemical species as given by the Euler–Euler formulation for multiphase flows are used together with the second law of thermodynamics to derive the entropy and exergy transport equations, suitable to the study of gas-particle reactive flows, such as those observed during pyrolysis, gasification, and combustion of biomass particles. The terms of the derived equations are discussed, and the exergy destruction contributions are identified. Subsequently, a kinetic model is implemented in a computational fluid dynamics (CFD) open source code for the sugarcane bagasse gasification. Then, the derived exergy destruction terms are implemented numerically through user-defined Fortran routines. Next, the second law analysis of the gasification process of sugarcane bagasse in bubbling fluidized beds is carried out. Detailed results are obtained for the local destructions of exergy along the reactor. This information is important to help improve environmental and sustainable practices and should be of interest to both designers and operators of fluidized bed equipment.