The Theory And Practice Of Multi-stage Flash Desalin Ation Of Combined Heat And Power

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, design theory, manufacture techniques, static performance, especially dynamic behavior of MSF system is studied in this dissertation. Meanwhile, an industrial trial has been carried out. In the light of the different criteria to evaluate the thermal performance about various techniques with the same objective, it is very difficult to evaluate their thermal performance of these energy utilization systems. In this dissertation a unified criterion to assess various energy utilization processes is discussed and presented. I. Flash evaporation process is analyzed by means of non-equilibrium thermo- dynamic theory, which it is easier for the flash process to be understood. By the way, a static performance model of MSF system is provided and used to analyze MSF system. A good coincidence between the practical data and analytical results can be observed. 2. Main factors to influence the design of the MSF system are discussed and the standardized design method is presented. It must be pointed out especially to pay attention to avoid scaling in service. 3. 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. 4. For the system with single import and export, a new method of simplification of distributing parameter model is presented. Comparing with other methods, this new method is much more simple and precise. 5. 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 vectorof coupling disturbance, which makes it easy to understand the...