Modeling and Calculation of Heat and Mass Transfer Process in Multistage Multiflow Flash Evaporators

Abstract

Thermal methods that have several environmental and economic advantages are widely applied for water treatment at thermal (TTP) and nuclear power plants (NPP) along with chemical methods. Multistage flash evaporation plants are important in case of use of thermal methods for desalinated water treatment as they can use low-temperature steam of thermal power plants. Despite the considerable number of scientific papers on this issue, the effective performance and improvement of the heat and mass transfer process in evaporator plants remains an urgent task, especially with variable operating modes of the technological equipment of TPPs and NPPs. On the one hand, it is due to the need to match the variable parameters of steam and the variable flow rates of make-up water for the process needs of the station. On the other hand, it is due to the lack of universal methods to calculate and design the equipment. Thus, the development of new methods to model and improve heat and mass transfer processes in thermal water treatment plants of thermal power plants and nuclear power plants is an urgent task for the power energy industry and related ones. To solve the problems of modeling heat and mass transfer processes in flash evaporation plants, models based on the mass and energy balance equations have been used. The obtained differential and linear equations are solved by analytical methods and methods of mathematical programming. A matrix model of the process of heat and mass transfer in a multi-stage multi-flow evaporative flash installation has been developed, considering evaporation of part of the water when it enters the low-pressure region. The steady-state pressure distribution over the stages and the performance of each stage of the evaporative installation have been found. Comparison of the calculated and known results have shown an adequate description by means of the model of the real process of heat and mass transfer in flash evaporation plants. It makes possible to set and solve problems to choose the optimal design and operating parameters of equipment for multi-flow evaporation plants. The proposed method to solve the problem of modeling heat and mass transfer provides the possibility of simultaneously search for acceptable values of design and operating parameters of multistage evaporative plants for various purposes.