Modeling And Simulation Of Multistage Flash Desalination System

With the rapid development of the social economy,the problem of the shortage of fresh water resources is becoming more and more apparent.Desalination is one of the important ways to solve the problem of lack of fresh water resources.At present,among many seawater desalination methods,multi-stage flash(MSF)seawater desalination is considered to be effective and widely used in practice.However,its operating cost is high,and affected by operating parameters greatly.Improving operating parameters plays an important role in reducing system operating costs.Based on the basic principle and technological process of MSF desalination,this paper studies the simulation and operation optimization of the system,which lays the foundation for reducing the operating cost of the system.On the basis of reading and analyzing a large number of domestic and foreign literatures,this paper has carried out the following work:(1)A rigorous steady-state mechanism model was established for the typical MSF seawater desalination process.Firstly,the model is divided into three main parts: flash chamber module,brine heater module and physical parameter equation.Then,based on the basic laws of energy conservation,the strict mechanism model of each part is established.Finally,the overall model is obtained by combining each module.On this basis,the simulation is carried out for the typical process flow,and compared with the literature results,the model is proved to have good accuracy.(2)Based on the steady-state model of the MSF seawater desalination system,the sensitivity analysis of important parameters affecting system performance was carried out.Considering that the system performance is greatly affected by the operating parameters,this paper simulates and analyzes the five parameters of flash chamber level,feed seawater temperature,heating steam temperature,circulating seawater flow rate and brine heater fouling coefficient.Under the simulation and analysis,the influence law of each operating parameter on the system performance is obtained.(3)For the fixed fresh water demand,the operation optimization of MSF seawater desalination system is studied aiming at the lowest operating cost.Firstly,considering the different sea temperatures at different times of the day,the optimal operation parameters are obtained aiming at the minimum daily operation cost,and the optimal operating parameters are obtained for each time phase.Subsequently,considering the long-term operation of the system will result in the increase of scaling coefficient,the optimal operation parameters of each month are obtained by taking the lowest annual operation cost as the optimization objective.The results show that the optimized operation can reduce the operating cost of the system significantly and improve the water production ratio.(4)Based on the steady-state simulation of the MSF seawater desalination system,a general dynamic mechanism model was established.Firstly,the flash chamber is divided into four parts: flash salt pool,steam space,fresh water tray and condensing tube bundle,and then modeled separately.Then a complete system model is formed by combining salt water heater model and physical parameter equation.The model considers the changes of physical properties with concentration and temperature,non-ideal differences and heat loss of demister,which can reflect the dynamic characteristics of the system more comprehensively.Based on this model,the influence of feed seawater temperature and heating steam temperature on system performance was analyzed.At the same time,the system transfer function is fitted by least squares method,which lays a foundation for further control research.