Fundamental Study On The Recycle Of Absorption Liquor From FGD Via Cation-Exchange Membrane Electrolysis

A large amount of SO2 discharged without control has caused serious air pollution and resulted in the loss of huge amount of money. Therefore, it is necessary to control the discharge. However, owing to high cost of investment and operation, and lack of technical support, development of desulphurization techniques badly lagged behind. Therefore, a new technology of lower cost and easier operation is urgently required.The technique of recycling Natrium-alkali FGD fertile liquor by low electrovalent membrane electrolysis has many advantages comparing to traditional techniques. Thus it is important to learn and understand the behaviors of membrane electrolysis. The rule for regeneration of absorption liquor from FGD was studied in this paper. Sodium bisulfite and sodium sulfite were dissolved in water according to certain proportion to simulate the liquor, and a two-compartment electrolysis cell equipped with a cation-exchange membrane was used. Through unilateral and circular flow regeneration experiments, the effect of main operating parameters has been systematically studied.The results showed that solution flux in cathode cell has an important effect on current density and current efficiency than that in anode cell. Composition of liquid in anodic cell would affect the parameters such as pH, temperature and current density during electrolysis. Sodium sulfite solution used in anodic cell would have of better benefit to regeneration than sodium sulfate or sodium hydroxide solution. If the liquor volume in anodic cell increased, better regeneration efficiency would be obtained. The negative ion osmosis experiments indicated the osmosis phenomena of negative ion were not evident; on the contrary, the water molecule obviously penetrated the membrane and accordingly the volume variation reached to 1.5%, that is to say, the osmosis of one mol Na ion would lead 0.40 liter solution to penetrate the membrane.Experiments showed that when total concentration of natrium ion was 1.0 mol/L, voltage 4.0V, flow rate 5.56cm/min, initial pH =6.5,and the electrolyte volume in cathode cell and in anode cell were 4.0L and 12.0L respectively, after electrolyzing for 1.5h, pH in cathode cell was 7.0 and in anode cell would reduce to 2.0~5.0, transfer ratio of natrium ion was over 15%, and current efficiency up to 89.6%.