Study On Desalination By Hybrid Process Of Reverse Osmosis And Multi-effect Distillation

Water resources crisis,affecting human survival,has become increasingly serious.Borrowing water from the sea through developing seawater desalination technology is the most promising way to solve this crisis.Compared with the current municipal water prices,desalination costs is still high.To make full use of the advantages of the thermal and membrane desalination technologies and reduce comprehensive cost by hybrid process of reverse osmosis and multi-effect distillation is the research direction deslination at presentIn this paper,the pretreatment of seawater and brine from low-temperature multieffect desalination was studied firstly.Seawater and brine were able to reach the indicators that SDI is less than 3,the turbidity is less than 1NTU,when treated by the process of coagulation sedimentation / filtration / ultrafiltration,which meet the processing requirements of RO.Further,based on the theory of dissolution diffusion,a mathematical model of reverse osmosis system was established to optimize the cost of water production.The results showed that the demand of membrane element increases with the increase of feed salinity under the situation of same water yield and quality.The cost of water making was lowest at 4.76 yuan/ton(fresh water)by reverse osmosis technologyA horizontal tube falling film evaporator was used to simulate low temperature multi-effect evaporation(MED),which explored the effect of hybrid measures of seawater acidification and scale inhibitor on the loss of calcium and magnesium ions in 2.5 times of seawater concentration process.The results showed that in a fixed degree of acidification,loss of calcium ions decreased with the increase in the amount of the scale inhibitor;and when the dosage of scale inhibitor is fixed,the loss of calcium ions decreased with the increase of the degree of acidification.But the whole process had little effect on magnesium ions.On the basis of experient,a model of low temperature multi-effect system was established and the minimum cost of water production was optimized by GA.The results showed that the lowest cost of water production is 6.14 yuan/ton(fresh water).Finally,according to the characteristics of RO and MED technology,three RO/MED coupling processes were designed.The mathematical models of these systems were established respectively,and the minimum cost of water production was taken as the goal by GA genetic algorithm.The results showed that the capacity of MED increases gradually with the improvement of water quality.When the quality requirement is 300mg/L,the capacities of RO and MED accounted for 64.5% and 35.5%,respectively.