Investigation Of Affecting Factors And Desalination Process By Hydrate Desalination Using Cyclopentane Hydrates

The shortage of fresh water has been a critical issue in many regions of the world and will be more important in the future.Traditional desalination methods,such as the distillation method,consume large amounts of energy and the costs for producing water are high.The idea of desalination by hydrate formation is not newfangled.However,it still needs more investigation to understand the process and to decrease the cost.This thesis presents the fundamental components of a hydrate-based desalination process using cyclopentane(CP)hydrates,which can be formed at atmospheric pressure.The effects of generating condition(including temperature、initial salinity、water content)and strengthening condition(covering agitation speed、pressure、annealing time)on hydrate formation and desalination efficiency are investigated.For purposes of rapid hydrate formation,nucleation is studied for its hydrate formation rate.It is observed that little hydrate nucleate formed while 3.5 wt% saline combined with CP without agitation.Hydrates nucleated and formed very quickly once the mixed liquor was frozen to some extent and agitation done later on.Therefore,in this thesis report,agitation and refrigeration are the prime methods of hydrate formation that were investigated.Through studying the effect of temperature、initial salinity and water content on hydrate formation,it is found that lower operating temperature,higher sub-cooling,and lower initial salinity enable higher water conversion into hydrates.Lower operating temperature makes the sub-cooling and the driving force for hydrate formation lower,as well as water conversion.The relationship between the initial salinity and the waterconversion is observed to be almost linear.The increasing salinity causes the hydrates equilibrium temperature to decrease,restrains the hydrate formation and reduces water conversion.The salinity of hydrate-based desalination research system is determined to 3.5 wt%.The water conversion reaches a maximum as 23.3% and the desalination reaches 86.85% while the initial water content was at 60%.The agitation is suspected to help hydrate growth by breaking hydrate shells around CP droplets and releasing CP nucleation sites for further reaction and mixing with hydrate seeds thus creating more nucleation sites.Therefore,an increase in the agitation speed results in a higher water conversion.At the same time,higher pressure increase the desalination efficiency and water conversion.Longer Annealing time longer converts more salt water into hydrates.The best annealing time was found to be 8 hours thus hydrates desalination results got worse whenever the annealing was done for a period longer.Separation of hydrates and salt solution from concentrated hydrate slurries was the key to increasing desalination efficiency.Several steps involved in water removal were performed: gravitational separation,preliminary suction filtration,washing and vacuum filtration.The filtration operation is very important and can augment salt solution removal.Washing is of great help to hydrate-based desalination efficiency.The highest desalination efficiency and water conversion are achieved when the radio of washing water and filtrated hydrate mass is 1:2.3 measured by experiments.