| Due to the increase in population,economic development,the demand for fresh water is increasing,the shortage of fresh water is not optimistic,and excessive development and pollution have caused global water resources to be threatened.Water shortage is one of the urgent challenges facing the world and has become a worldwide problem.Although there is a lot of water on the earth,especially sea water is very rich,only 3% of the total water is fresh water,most of which is salt water.Therefore,desalination can be an effective method to solve the problem of scarcity of fresh water.The multi-effect evaporation system has a relatively large structure.It is not only necessary to set up a condensing system but also to provide an additional source of raw steam for the system.If combined with MVR technology,the final secondary steam is heated and boosted by the compressor and reused.The heat source of the first effect evaporator,so that there is no need to set up a condensing system.In view of the advantages of multi-effect evaporation and MVR technology,this paper combines two processes,proposes a new idea of multi-effect MVR energy-saving technology,and introduces the working principle of three-effect MVR evaporation system.Using Aspen Plus to simulate its process flow,a flow chart of three feed modes of downstream,advection and countercurrent for multi-effect MVR system was constructed.The effects of different feed modes and effect changes on system COP were analyzed.Efficient flow MVR evaporation system,using Aspen Plus software to change the parameters in the process,the performance of the three-effect MVR system was studied by the evaporator evaporation,seawater feed temperature,fresh steam,evaporation pressure,secondary steam pressure through the compressor,feed concentration,condenser heat load,compressor power,evaporator heat exchange and the heating efficiency ratio of the whole system.Finally,an economic analysis was carried out by comparing the energy consumption of the three-effect MVR with the three-effect evaporation.The results show that the three-effect MVR heating energy efficiency ratio is higher than the first effect and the second effect,and the COP is better than the advection and countercurrent when the system adopts the downstream feed mode.For the three-effect downstream MVR seawater desalination system,in order to reduce the heat transferstrength,the evaporation pressure should be reduced as much as possible,and the vapor compression ratio of the compressor is maintained at 1.6 to 2.0.The feed concentration should not be too large,and the high concentration feed liquid should be properly diluted before evaporation.In order to improve the heating of the evaporation system,the energy efficiency ratio needs to reduce the compression ratio appropriately.Considering the energy saving effect of the whole system,the system is more suitable when operating at low temperature and low pressure.Taking the 1 t/h sodium chloride solution as an example,the energy consumption of the three-effect MVR and the three-effect evaporation were compared.The results show that the three-effect MVR evaporation system can save30,8697.6 yuan of heating steam per year,and also saves the last-effect steam condensation device,so it can save 85564.8 yuan of condensed water per year,which is equivalent to saving 63.6% of the standard coal. |
