Purification of water from dissolved gases in a film unit with discrete-rough walls

Abstract

This paper analyzes the use of a highly effective film unit for water purification from dissolved corrosive gases, in order to increase the resource efficiency and reliability of various equipment using water circulation systems at industrial plants and thermal power plants. The unit consists of a vertical bundle of tubes contained in tube grids and operates in the upward co-current gas and liquid in a pipe. The gas moves at a speed of 10 – 30 m/s (strong interaction of phases) and carries a liquid film from the bottom up. In this mode, there is a significant intensification of heat and mass transfer (5 – 15 times) in comparison with counter current. In addition, the inner surface of the tubes may have artificial discrete roughness (rectangular projections), which further increases the effectiveness of the processes. The paper presents the mathematical model and the efficiency calculation results for a film contact device with rough walls at strong phase interaction. The mathematical description is based on the models of the flow structure and the diffusion boundary layer. Expressions are given for calculating the mass transfer coefficient in a turbulent film with co-current gas, as well as parameters of the flow structure model in a contact tube. The main parameters of the equation for calculation of the mass transfer coefficient are the dynamic friction velocity on the interfacial film surface and the dimensionless thickness of the viscous sublayer. The dynamic speed is calculated using the equation of balance of forces in the contact tube, and the dimensionless thickness of the viscous sublayer-based on the known values on the plate adjusted for the phase interaction conditions. The cell model of the flow structure is used, and an expression is obtained for calculating the concentration profile of gas dissolved in water at the height of the pipes. The paper also presents an expression to calculate the number of cells in a complete mixing. The paper presents the calculated and experimental dependences of decarbonization efficiency for tubes with smooth and rough walls. The influence of spacing between roughness elements (projections) on water purification efficiency is shown. Conclusions are made about the design of a unit with a rising film at higher concentrations of dissolved gases in the water.