Study On The Purifying Methods Of Water Quality Of Desulfurization Absorption Liquid Before Membrane Electrolysis Regeneration

Nowadays, wet desulfurization is the main way in FGD (Flue Gas Desulfurization) and especially calcium method is widely applied, but there are many problems, such as scaling, corrosion, blocking and so on. The technique, sodium alkali FGD and membrane electrolysis, has fully utilized the advantage that SO2 is efficiently absorbed by sodium alkali absorbent and has realized that effective use of the absorbent by means of circulation of membrane electrolysis regeneration. So in the thesis the purifying method of water quality of desulfurization absorption liquid before entering into membrane electrolysis device was investigated by both theory and experiment.Desulfurization absorption liquid always possesses strong acidity, many impurities and high content suspended substance which seriously affect the operation of membrane electrolysis. Thus, this work investigate the removal effect of natural sedimentation and centrifugal sedimentation on suspension in absorption liquid and the influence of settling time and centrifugal speed on the settlement effect. The results indicated that while the natural settlement time was 30min, the solid concentration decreased from 300mg/L to 112mg/L, and the removing rate of SS reached 62.6%; while centrifugal speed was 1500r/min, that is, separation factor was 272.5, centrifugal settlement time was 15min, and the removing rate of SS reached 98.9%.After sedimentation the top water was filtered by sand filter. The experiment investigates the effect of granule diameter and filtration bed thickness on the removal of suspension impurity. Under the average particle size of 0.8mm, filtration bed height of 70cm and filtering velocity of 10m/h, the turbidity of effluent can decrease to 2.22NTU, about 2.48mg/L.There are a large number of ions in absorption liquid, resulting in polarization and scaling during the membrane electrolysis. The adsorption of Al³⁺ and Fe³⁺ in absorption liquid by powdered activated carbon was discussed. The results indicated that approximately 30% of Al³⁺ and Fe³⁺ are absorbed by activated carbon, and Fe³⁺ was more easily absorbed than Al³⁺. In addition, scaling experiments of Ca²⁺ and Mg²⁺ were conducted by changing pH and temperature. The results showed that because of lower concentration of Ca²⁺ and Mg²⁺ in absorption liquid, as long as the concentration of SO42- was less than 0.47mol/L and pH was less 9, the scaling of CaSO4 and Mg(OH)2 cannot occur.The study in this thesis investigates the removal methods of suspension and related ions, as well as optimizes the operation parameters, explaining the mechanism of removal, and provides the design basis and theoretical guidance for sodium alkali FGD and membrane electrolysis regeneration technology design and operation.