An equation-oriented novel approach for modeling the falling film absorber using rigorous thermodynamic and transport description

摘要

Falling liquid films are largely employed in heat and mass transfer processes in a variety of industrial systems, including absorption processes using NH3 and H2O as working fluid. This study develops a new approach based on differential algebraic model for the absorption of NH3 from a gaseous stream by a solution of NH3 and H2O in a falling film absorber at steady-state. Unlike the usual approach in literature, wherein sequential algorithms are specifically tailored to solve the model, the full set of differential algebraic equations (DAE) has been formulated and solved in an equation-oriented fashion. A rigorous modeling of the vapor-liquid equilibrium at the interface is proposed and compared with the usually employed empirical correlations. Thermal and transport properties (TTP) are computed by CAPE-OPEN interfaces, providing robustness and flexibility to the model. The TTP and the falling film model are validated with experimental data from literature. The results indicate that the liquid falling film imposes the dominant mass transfer resistance compared to the gas phase, whereas the coolant-side imposes the dominant heat transfer resistance. The simultaneous solution of the DAE system is very efficient, robust and flexible, as it can be applied for absorbers with different geometries and working fluids. (C) 2020 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.