Design And Test Of Alkali Salt Water-gas Separation Device In Farmland Under The Effect Of Solar Collector Tube

The farmland flooding and salting method is a widely used method in the control of farmland soil salinization in Xinjiang.However,the saline-alkali water produced by flooding and salting is discharged to rivers and other agricultural areas through various farmland alkali drainage channels,causing more salinization pollution.How to separate and desalinate farmland saline-alkali water to reduce salinization pollution has attracted more and more attention from the society.In response to this problem,this paper proposes a farmland saline-alkali water separation and desalination process and develops a farmland saline-alkali water separation and desalination device under the effect of solar recycling solar collectors.The test site was selected in the soil tank laboratory of Tarim University,Alar City,Xinjiang,to verify the rationality of the design of the farmland saline-alkali water separation and desalination device under the effect of solar collectors and sun tubes.The research shows that the device can provide new technical reference and beneficial engineering exploration for solving the problem of irrigation water in saline-alkali land-enriched areas in arid areas.The main research contents are as follows:(1)By investigating the causes of the formation of saline-alkali water in the farmland alkali drainage canal in Alar City,Xinjiang,as well as the impact of the farmland saline alkali water on the surrounding environment and the harm to crops,the saline-alkali water in the 10-group alkali drainage channel in Alar City,Xinjiang Water is the research object,and the composition of farmland saline-alkali water is obtained through experiments.The results show that:after conventional treatment,the average ionic composition of the original farmland saline-alkali water is 4411.58 mg/L for Na⁺,798.75 mg/L for Ca²⁺,and 798.75 mg/L for Mg²⁺.543.41 mg/L,Cl^-is 7468.89 mg/L,SO₄^2-is 2124.12 mg/L,HCO₃^-is 763.25 mg/L and total salt is16110 mg/L;ion concentration percentage is Na⁺is 27.38%,Ca²⁺is 4.96%,Mg²⁺is 3.37%,Cl^-is 46.36%,SO₄^2-is 13.19%,HCO₃^-is 4.47%.(2)Through the joint design of the nanofiltration-reverse osmosis membrane and the heating flash condensation method of the circulating heat collecting and drying tube,the separation and desalination process of the farmland saline-alkali water is determined and the farmland saline-alkali water separation and desalination process is proposed.The process of farmland saline-alkali water separation and desalination is mainly composed of saline-alkali water pretreatment,nanofiltration-reverse osmosis membrane separation and desalination treatment,solar circulating heat collection and drying tube heating treatment,flash distillation treatment and shell-and-tube circulating condensation treatment.The farmland saline-alkali water separation and desalination process provides a theoretical basis for the design of farmland saline-alkali water separation and desalination devices under the effect of solar collectors.(3)According to the separation and desalination process of farmland saline-alkali water,the key components of the farmland saline-alkali water separation and desalination device under the effect of solar circulation heat collecting and drying tubes were developed.The pretreatment equipment is composed of activated carbon filter,quartz sand filter and ultrafiltration filter in series to remove sediment,impurities and peculiar smell in saline-alkali water;The outer wall of the inner tube is coated with a blue film,which has high light absorption,and there is a vacuum between the inner tube and the outer tube,which can increase the heating and thermal insulation of the solar circulation heat collecting tube;Heat demand;shell-and-tube circulating condenser meets flash condensation demand.(4)The treatment effect of the pretreatment equipment by the farmland saline-alkali water separation and desalination device,the separation effect of the nanofiltration-reverse osmosis membrane filtration equipment,the heat collection effect of the solar circulation heat collection tube,the desalination effect of the flash tank and the tube.The condensing effect of the shell-type circulating condenser was tested.The results show that the average turbidity of the produced water is less than 1 and the average pollution index is less than 3 after the saline-alkali water is pretreated,which meets the working conditions of the nanofiltration membrane and the reverse osmosis membrane.The water desalination rate is 96.06%,the total hardness removal rate is 98.93%,and the Cl^-removal rate is 99.32%,which can meet the water standards for farmland irrigation,and some indicators meet the sanitary standards for drinking water,realizing the secondary utilization of water resources.The solar circulation heat collecting and drying tube of the device has a heat collecting area of 6 m²,which basically meets the heat demand of flash tank distillation.The fresh water production of the flash tank increases with the increase of the concentrated water temperature of the flash tank inlet,and increases with the increase of the vacuum degree in the flash tank.When the concentrated water temperature of the flash tank inlet is 80?,when the vacuum degree is 0.8 bar,the fresh water output of the flash tank can reach 48.32 kg/h.The temperature at the end of the heat pipe of the shell-and-tube circulating condenser reaches about 25°C,which can meet the requirements of water vapor condensation.Under the action of solar energy,the crystals were precipitated in the salt drying box.It was verified by XRD that the main compound of the crystals was Na Cl,and Na and Cl elements accounted for 97.87%of the relative element content,indicating that the precipitates have the potential value of industrial salt.