Modeling And Simulation Of The MSF System

With increasing of population and development of society, the shortage of fresh water resource of the coastland in China will become more severe. It is necessary to select desalination of seawater to solve the supply of fresh water in 21 century. The technique of multi-stage flash (MSF) distillation is dominant and widely used in the market of desalination at present in the world. Therefore, it is necessary to develop more advanced MSF desalination equipment made in China. Based on research experience published in literatures, dynamic behavior of MSF system was focused on in this paper.The brine heater, a tube heater with single import and export, is one of the main devices for the MSF system. Although it is not difficult to model and simulate its dynamic process for such a heater, some mistakes in literature are found. On the basis of the consideration of distributing parameter model and its simplification a linear ramp method with subsection is presented and a simulation is accomplished. For the various disturbance factors, the manners of connections between the subsections are not the same and can be not simply treated as a series structure; otherwise a mistake will take place. For the step temperature disturbance of seawater, the manner of connection between the subsections is in series. But for step flow disturbance of seawater or heat disturbance, due to simultaneity of effects of these step disturbances on the whole system space, the manner of connection is either in series or in parallels.The dissertation presents the total transfer functions with three step disturbances of subsection linearization, and proves that the limits of the total transfer functions are the same as the analytical solution, if the number of subsection goes to infinity. Therefore, the precision of simulation can be improved by increasing the number of subsection.According to thermodynamic theory, the dissertation establishes the mathematical models of dynamic process of the MSF system and the Matlab simulation models on the basis of each flash evaporator unit. The models are better than the ones presented by other references. The connection between one stage and another stage is expressed as a vector of coupling disturbance, which makes it easy to understand the coupling effects of disturbance and avoids of establishing large state matrix of the whole system, and makes it easy to simulate. The linearization methods of the mathematics models for dynamic process of the MSF system are studied and case studies are given. The aforementioned researches and analyses can provide the help on making operation regulation and control strategy of the MSF system.