Coupling Study Of Seawater Decalcification And Carbon Fixation By Bipolar Membrane Electrodialysis

At present,the shortage of water resources and greenhouse effect have seriously restricted the development of human society.In order to solve the two major environmental problems,the research group carried out the research of chemical seawater decalcification and carbon fixation in the early stage,but it has the disadvantages of introducing extraneous alkali source and higher cost.On this basis,the subject developed a bipolar membrane electrodialysis seawater decalcification and carbon fixation process,respectively explored the ion transport law and process optimization conditions of the single membrane group,and conducted economic analysis of the continuous operation of this process to achieve bipolar Membrane electrodialysis decalcification and carbon fixation of seawater.The ion migration rate determines the ion concentration,reaction rate,and membrane fouling rate in the salt chamber.Therefore,first,the possible migration of ions under the system from the alkali chamber to the salt chamber in the electrodialysis system was explored to determine the process feasibility.By investigating the influence of the current density of the bipolar membrane,after determining the operating current of the experiment,the migration rate of single ions(OH^-,CO₃^2-,HCO₃^-)and the double ions(CO₃^2-and HCO₃^-,OH^-and CO₃^2-)Competitive migration rate.In addition to the traditional ion migration in this ion system,there are also complex ion reactions.Through screening and comparison,the reaction and migration rate of OH^-and HCO₃^-ions are the key factors,and the relative migration rate between the two is determined.It is speculated that the relative concentration between OH^-and HCO₃^-ions can be controlled by controlling the rate of bipolar membrane electrolysis and the hydrolysis rate of carbon dioxide,thereby inhibiting the scaling of the ion exchange membrane surface caused by OH^-.After determining the feasibility of the process,the coupling process was optimized.First,by adjusting the aeration device,the carbon fixation rate is improved.Then,using the parameters of carbon fixation rate,decalcification rate,energy consumption per unit of seawater treatment,energy consumption for decalcification,carbon fixation energy consumption and other parameters as indicators,the current density,CO₂ flux,gas-liquid contact method and the initial solution of the alkali chamber were investigated Process conditions such as p H.In order to further reduce the energy consumption of the experiment,the effects of stirring,temperature and solutions with different initial decalcification rates on the decalcification rate in the solution during crystal growth equilibrium were investigated.The optimized process of migration+reaction+crystallization was proposed,which could shorten the operation time of the electrodialysis system and reduce the energy consumption cost.Under optimal conditions,the seawater decalcification rate is over 90%,and the carbon sequestration rate is close to 100%.The seawater treatment energy consumption,decalcification energy consumption,and carbon sequestration energy consumption are 1.85k Wh/(t seawater)and 1.97 k Wh/(kg Ca CO₃),0.87 k Wh/(kg CO₂).Based on the process feasibility study and process optimization,the continuous operation study of bipolar membrane electrodialysis was finally carried out.And preliminary estimate the total process cost of small-scale experimental research,the results show that the cost of processing per ton of seawater is about 1.84?,and can obtain 0.9225 kg Ca CO₃ by-product,fixed 0.64 m³ CO₂.After the subsequent expansion of the experiment or even industrialization,the actual energy consumption and total production cost will be much lower than the energy consumption and total production cost calculated in this work,which initially verifies that the method is economically feasible and has the potential for industrialization.