Methods of Mathematical Modeling of Desorption of Poorly Soluble Gases in Packed Devices

Abstract

To solve problems of removing poorly soluble corrosive gases from water in chemical shops of thermal power plants and industrial enterprises, the article examines mathematical models and methods for calculating the efficiency of heat and mass transfer in packed desorbers. A system of two-dimensional differential equations of mass transfer with partial derivatives and an interphase source of mass transfer is presented. An expression is given for the interphase source and the coefficient of turbulent diffusion in the gas phase, as well as the boundary conditions for the system of equations taking into account the turbulent mixing of the gas phase at the entrance to the packed bed. It is noted that the presented system of mass-transfer equations is solved numerically and makes it possible to calculate the concentration profiles of the component in the gas and liquid phases from the input to the output of the apparatus and to determine the efficiency of extracting dissolved gases from water. To reduce the complexity and time of the numerical solution of the presented problem, the use of a system of differential equations of diffusion models of the hydrodynamic structure of gas and liquid flows is shown. The main parameters of the models are the Peclet numbers (Bodenstein criterion), which take into account the back mixing of gas and liquid, as well as the total and partial numbers of transfer units. For simplified engineering calculations, a modified method of transfer units is considered with the expression for the packing height written with additional terms that take into account deviations from the ideal phase displacement model, i.e., taking into account the reverse mixing of flows, which increases the required packing height for a given mass-transfer mode. Expressions for mass transfer and thermal efficiency of processes are obtained. Examples of calculations of a packed decarbonizer with Raschig rings, as well as with modern chaotic packings are presented. As a result, a universal expression was obtained for calculating the packing height for a given hydraulic load and liquid-cleaning requirements.