A Mathematical Model and Design Calculation of a Thermal Deaerator with a Bubbling Storage Tank

Аннотация

A mathematical model of mass transfer in an atmospheric bubbling deaerator storage tank at thermal power stations (TPS) to calculate the removal efficiency of dissolved gases from water is considered. For mathematical simulation and calculation of the deaerator efficiency, a system of differential equations of mass and heat transfer is written in a local form for the liquid phase of the layer with volume interphase sources of mass and heat. Mass transfer of the dissolved gases from water to the vapor phase is taken into account using volume interphase sources and the balance equations. Parameters of the interphase sources and correlations for calculating the eddy viscosity of the liquid phase depending on bubbling conditions are given. Results from the system of equations' numerical solution are presented and compared with the available experimental data on the final concentration of dissolved oxygen at the deaerator outlet. Curves of the efficiency of dissolved oxygen removal depending on the operating conditions and design characteristics of the bubbling process are presented, and scientific-and-engineering solutions have been developed to upgrade the bubbling storage tank. It has been found that an increase in gas velocity sharply raises the deaeration efficiency to a certain value (depending on the specified initial parameters), and the efficiency growth is then retarded. Similarly, increasing the length of a bubbling device improves the efficiency in removal of dissolved oxygen from water. One of the causes of a decrease in the water deaeration efficiency is likely to be back mixing of the flow. Upgrading of the deaerator tank is in the installation of perforated baffles across the flow to considerably reduce back mixing of the liquid phase. This increases the driving force of mass transfer, and its efficiency improves by five to 20% depending on the steam velocity. The presented mathematical model can be generalized to a wide range of bubbling apparatuses with a high two-phase layer.