The Analysis Of Low Temperature Multi-effect Evaporation Desalination Feed Water Configuration

With the development of economy and the increase of population, the fresh water shortage is becoming a more and more severe social problem for the sustainable development, Sea water desalination is a way to mitigate the problem. In the numerous methods of desalination, As low-temperature multi-effect evaporation desalination has some technical advantages through the possibility of utilizing low temperature waste heat sources, reducing water cost and relieving scaling and corrosion problems, the simpler pretreatment process, low-temperature multi-effect evaporation in a dual-purpose power plant configuration may become the main technology for future desalination plant.In the thesis, a physical model and a mathematical simulation model is developed to describe the low-temperature multi-effect evaporation desalination system, including the low temperature multi-effect distiller, the preheater, the condenser, the flashing box and the thermal vapor compress (TVC), which considers the boiling point elevation and the temperature losses in the demister, vapor transmission lines and the lines connecting the vapor space in effect i and the evaporator tubes of the next effect. And on the basis of balance of mass and energy, the thermal analysis is illustrated. All the solving of the models and the thermal calculation are accomplished using the tool of VB6.0.Based on the different of feed seawater flow in every effect, there are three configurations:the forward feed water configuration, the parallel feed water configuration, the forward and parallel feed water configuration. The thermodynamic calculation of three configurations is compared, analyzes the variation of thermodynamic performance with brine concentration, feed seawater flow in every effect, secondary steam flow, GOR, heat transfer areas. In conclusion, the forward and parallel feed water configuration has the highest GOR and the less heat transfer areas, fulfills the requirement of flow density, and it presents a higher utilization ratio of thermal energy. In allusion to this configuration, the analysis of the variation of thermodynamic performance with heating steam temperature in the first effect and evaporation temperature in the last effect is discussed for the same working condition.The procedure of low-temperature multi-effect evaporation desalination with thermal vapor compress (TVC-MED), the introduction of working principle and thermodynamic calculation of which is showed in the paper, including the variation of TVC extracting position and the parameter of TVC. Based on the calculation data, analyzes the variation of GOR, heat transfer areas, TVC outlet steam temperature and entrainment ratio with temperature of suction steam and motive steam, pressure of motive steam, the number of evaporation effects. The installation position of TVC in the MED plant can be calculated. If it is used suitably, the energy efficiency of a desalination plant could be enhanced more.