Influence And Its Control Of Reusing High Saline Wastewater Into Desulfurization System

The promulgation of"Water pollution control action plan"and the increasingly stringent water pollution control standards,has pushed power plants to find out routes for water conservation and treatment.In many power plants,various types of wastewater has been reused in the desulfurization system but the effect of the ions in reused wastewater on desulfurization system performance is not clear.Therefore,it is necessary to explore the effect of reused waste water on the performance of desulfurization system.The components of reused water in a power plant was analyzed.NaCl,MgCl₂,NaF,and other salt contained in the reused water was added in to simulated limestone slurry,to explore the effect of various ions on desulfurization efficiency.The inhibition effect of Cl^-on desulfurization efficiency is not significant before the concentration has reached the critical concentration,2 mol/L（71000 ppm）and the critical concentration of nitrate was 3.12 mol/L（193440 ppm）.The experiment results show that the chloride ions at high concentration have negative effect on the dissociation efficiency of limestone.To ensure the high dissociation efficiency of limestone,the concentration of chloride ions in the solution should be controlled below 1.23 mol/L.After field test in a power plant,the main factors affecting desulfurization efficiency were figured out and their influences were ranked.It was found that the Mg²⁺concentration and the conductivity had a great influence on the desulfurization efficiency,CaCO₃ content in gypsum,and gypsum purity.Mg²⁺at high concentration no only reduced the desulfurization efficiency,but also caused the problems of gypsum dehydration and the deterioration of gypsum quality.The slurry density and conductivity are also important factors affecting desulfurization efficiency.According to the field test results,the corresponding solutions and control measures were put forward.In view the calcium and magnesium at high concentration in desulfurization wastewater which bring problems to the subsequent treatments,the technical routes of using CO₂ in flue gas for desulfurization waste water softening and calcium and magnesium recovery were explored.The three-step softening method is proposed.First,the pH of the wastewater is adjusted to 9 by adding calcium hydroxide.The heavy metal is precipitated and separated,and then the CO₂ is bubbled in to reduce the pH to 7.The calcium carbonate is separated and returned to the desulfurization system.Finally,sodium hydroxide is added to adjust the pH of the solution to 10,and the magnesium hydroxide is precipitated and separated for recovery.The purity of magnesium hydroxide can reach more than 85%,which can basically meet the industrial requirements.To sum up,the influence of salt water on the desulfurization system was clarified;experiments were carried out,to ensure the economic and safe operation of the desulfurization system while conserving water in the power plant.The technical basis was put forward for the enterprise optimizing the operation of the high salt water treatment and desulfurization system.