Process Simulation And Optimization Of Low Temperature Seawater Multi-Effect Distillation System

As the sharp increase of the world population and the rapid development of economy, water resources problem is increasingly highlighted. Due to its vast raw material resources, desalination technology has a huge development prospects, and can continuously improve freshwater resources for mankind. As a kind of desalination technology, low temperature multi-effect evaporation desalination has been widely used in engineering practice with a lot of advantages, such as low risk of scale, low power consumption, high thermal efficiency, and can take advantage of the low grade heat source of thermal power plant.Based on the low-temperature multi-effect evaporation desalination system as the research object, the thesis outlines the commonly used three feed water arrangements in multi-effect desalting systems, e.g. forward, backward, and parallel. First, apply the Aspen Properties analysis the special physical properties of seawater. The operation process line of low temperature multi-effect evaporation desalination system can avoid the calcium sulfate scale formation area, reducing the risk of equipment fouling. Using Aspen Plus, corresponding of the four-effect parallel feed LT-MED desalination system of SIDEM French Corporation process flow diagram is established. Simulate on the same operating conditions, and compared the results with the literature for demonstrating the reliability of the process and the accuracy of the simulation. Keeping the content of heating steam and gained output ratio of TVC in agreement, temperature distribution method is applied to simulate desalination system of the three feed water types. It achieves the relationship between the systems of thermodynamic performance with the number of effects, concentration ratio, temperature difference and feed seawater temperature in the three feed water types. The results show that better performance is obtained for the increasing effects, and the parallel feed mode is suitably selected for LT-MED with only several effects. The enhancement seawater concentration ratio results in corresponding increase of gained output ratio (GOR), and the specific heat transfer area has a little change. While the concentration is large, forward feed can be used for reducing the risk of scaling. As the temperature difference across the effects increases, the GOR of backward feed is decreased, parallel and forward are increased. For all feed types, increasing the feed seawater temperature can improve thermodynamics performance, but the feed seawater temperature is limited by evaporation temperature of the end effect.For the characteristics of forward feed process, preheating measure is put forward. Extracting the secondary steam of end effect to preheat the feed seawater, can significantly improve the system performance. Appling the Aspen Process Economic Analyzer to analyze its investment economic, it can shorten payback period and increase the investment returns.AspenTech modular software is applied in this thesis to study the low-temperature multi-effect evaporation desalination system technological process. It has a certain theoretical guidance and practical value for the development and application of desalination technology.