| In a system of mechanical vapor compression desalination(MVCD), the low-temperature saturated steam is compressed into a high-temperature superheated state by a compressor, the high-temperature superheated steam is then condensed in a condenser. While the saturated salt water is heated by the latent release so that the salt water can be partially evaporated to saturated steam in an evaporator. This thermophysical process can effectively alleviate brine fouling and corrosion problems of salt water, and fully recover latent heat of condensation, therefore it can result in a higher thermal efficiency of the system.The designed and established experimental system of mechanical vapor compression desalination(MVCD) uses a centrifugal compressor. Its production capacity is2m3/d. The effects of the parameters of compression ratio, evaporation temperature and salt concentration on the production and energy consumption of freshwater were investigated. It was found that the MVCD system can operate well when the evaporating temperature is the range from89.1℃to97.6℃, the compression ratio in the range from1.1to1.25, and brine concentration in mass ratio varies from2.0%to4.0%. The energy consumption of fresh water of the MVCD system is59.4-86.4k.Jkg-1.The second law of thermodynamics was used to analyze the exergy efficiency of the MVCD system. A mathematical model was developed to analyze the effects of the compression ratio, evaporation temperature and salt concentration on the exergy efficiency of the system, when the initial state of seawater is assumed to be the reference state. The results of analysis indicate that the exergy efficiency of the system is10.7%, and the exergy losses of the evaporator-condenser, the centrifugal compressor, the water pump and the preheater respectively are respectively23.2%,37.5%, and28.6%.The feasibility and economy of the MVCD system for distilling acesulfame dilute solution to recover industrial raw materials was investigated. The solution was gradually concentrated to the concentration of the design by the cycle distillation process. The thermodynamic process of the compression of the vapor was analysed. The parameters of the compressor were designed. Based on the thermodynamic equation of the evaporator-condenser, the distillation experimental system was set up. The ability of the experimental system was tested when the evaporating temperature was the range from73℃to100℃. The economic cost of the MVCD technology is about28RMB/D, while the traditional process cost about110RMB/D, here RMB=Yuan,D=1000kg.The commercial software platform TRNSYS was used to establish a thermodynamical model to describe the operation of test MVCD system with the production capacity2m3d-1. The fresh water production and the temperature distributions at various location points were obtained under different experimental conditions. The energy consumption of fresh water production was also predicted. It was found that the simulation model can describe the operation performance of experimental MVCD system approximately.The effect solar energy as an auxiliary heat source on the MVCD system was studied with respect to the meteorological parameters in Hefei in the software TRNSYS. The heating system consists of a electric heating and a solar heating system. The solar heating system was a4m2vacuum tube solar collector,and the outlet temperature was controlled to75℃. Through adjusting the flow speed in water pump, the temperature of the outlet water of vacuum tube solar collector can be properly controlled, and the water tank can buffer the impact of solar radiation on the performance of the compressor of the MVCD system. When solar radiation intensity is over600Wm-2, the evaporation temperature is about70℃, using the auxiliary solar energy, the system can save about25%of the auxiliary energy consumption. |
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