Efficiency of Water Purification from Dissolved Gases under Weak and Strong Phase Interaction in Film Degassers

Abstract

Water purification processes in film decarbonizers and thermal deaerators with different contact arrangements in the modes of weak and strong interaction between phases are considered. Weak interaction is characterized by a separate movement of phases, wherein a gas or vapor flow hardly affects the hydrodynamics of a liquid film. Such a mode is most often implemented in the case of countercurrent phases. At a gas or vapor velocity greater than 8 m/s and an atmospheric pressure, the gas flow carries the liquid film in an ascending or descending flow. In this mode, mass and heat transfer processes are greatly intensified. The modes are considered by the example of removal of aggressive corrosive gases at TPPs and industrial enterprises. Expressions are given for the calculation of the mass exchange characteristics of degassers and for the efficiency of water purification from oxygen and carbon dioxide. It is shown that a strong interaction occurs in the tubes with discrete-rough walls and a ribbon swirler, whereas a weak one takes place in irregular (chaotic) packed beds and regular corrugated packed beds with a rough surface. To calculate the efficiency of mass transfer (the extraction of dissolved gases from water), we used such flow structure models as a diffusion model and a cell model with bulk mass sources. Expressions for the calculation of model parameters—dispersion coefficients, number of cells, mass transfer coefficients in the liquid phase—are presented. The results of calculations of the mass transfer efficiency in packed columns and channels with discrete-rough walls and swirling flows are given. An example for mounting a packed bed in a DSA-300 deaerator is presented. Conclusions are drawn concerning the most rational designs and operating modes of thermal deaerators and decarbonizers.