| With the uneven distribution of freshwater resources globally and water shortage in some regions,desalination of seawater is a potentially important source of freshwater.Hydrate method desalination is considered as a low energy consumption method to obtain freshwater,meanwhile,with the in-depth research and innovation of gas hydrate generation and decomposition technology,the feasibility of this technology is further improved by using suitable hydrate forming agent as hydrate method desalination guest molecule.Based on the above background,this paper firstly designs an integrated system for gas hydrate desalination based on hydrate desalination principle and process independently.Secondly,a visualization cold storage study was conducted for the influence of hydrate forming agent cyclopentane hydrate growth characteristics of hydrate method desalination.Finally,the phase equilibrium conditions of the hydrate forming agent propane hydrate were measured and the growth characteristics of propane hydrate in porous media were studied using a visualized pressure reactor.The salt removal effect of hydrate formation process is the basic principle of hydrate method desalination.Hydrate method desalination is achieved by hydrate generation,separation and decomposition.When hydrate is generated from water inside a porous medium placed in the gas at the same time,the hydrate grows outside the porous medium due to the capillary action of water.Based on this paper,we independently design three desalination systems for hydrate crystal generation,mechanical separation of hydrate and heating decomposition of hydrate.The desalination systems can be operated in series/parallel to obtain fresh water of certain quality and introduce the specific implementation methods of water-legal desalination systems in detail.In order to comprehensively evaluate the effect of cyclopentane as hydrate forming agent for seawater desalination,this paper carried out experiments on the influence of cyclopentane hydrate growth characteristics,and found that the increase of cyclopentane concentration prompted the increase of cyclopentane hydrate generation and the gradual increase of desalination efficiency;it was found that the addition of porous media could effectively promote hydrate generation,and when the liquid level of the mixed liquid solution of cyclopentane and artificial seawater was about 1 cm above the porous media,the The most amount of cyclopentane hydrate was grown when the liquid level of cyclopentane and artificial seawater mixture was about 1 cm above the porous medium;comparing the effect of different particle sizes of glass sand on the growth of cyclopentane hydrate,it was found that the most amount of cyclopentane hydrate was grown in the glass sand with an average particle size of about 0.4 mm,which means that the glass sand with an average particle size of about 0.4 mm is more suitable for the hydrate method desalination process.The hydrate phase equilibrium is the key physical parameter to determine whether propane hydrate can exist stably in the porous media-water system.Based on the constant volume pressure search method,the phase equilibrium data of propane hydrate in porous media-water system were measured in this paper,and the enthalpy of decomposition was also calculated by the phase equilibrium data to determine the propane hydrate generated in the system as structure type II.Based on the phase equilibrium data of propane hydrate,experiments on the growth characteristics of propane hydrate were carried out using a visualization reactor.It was found that the growth rate of hydrate slowed down as the particle size of porous media increased;the amount of hydrate grown on the surface of glass sand with an average particle size of 0.4 mm was found to be the highest;it was found that the addition of small particle size glass sand to large particle size glass sand could increase the growth rate and the amount of hydrate in large particle size glass sand,and it can be concluded that the average particle size of porous media is the main control factor affecting the growth of hydrate.The average particle size of porous media can be considered as the main controlling factor for hydrate growth.The experimental results can also provide direct guidance for the selection of the particle size of porous media when propane is used as a hydrate forming agent in hydrate desalination,and it is suggested that porous media with an average particle size of 0.2～0.4 mm are the most effective media for propane hydrate desalination. |
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