Study On The Desulfurization Wastewater Evaporation And The Synergetic Removal Of The Flue Gas Pollutants Through Adjusting The Desulfurization Water PH Value

At present,the main technical means used to control the emission of SO₂ in coal-fired power plants in China is Wet Flue Gas Desulfurization（"Wet FGD"）,which will produce plenty of the "desulfurization waste water"（"DWW"）containing heavy metal ions and chlorine ions during the process.With complex constituents and high handling challenge in the DWW,the traditional wastewater treatment technology（chemical precipitation method）is not able to remove the enriched Cl^-and the requirements for zero discharge of the DWW,thus restricts the recycle of DWW.Flue evaporation technology,however,can meet the requirement of zero discharge of desulfurization wastewater,but it also brings problems such as corrosion,fouling,and clogging of the flue drying section.To solve the above problem,in this paper it is proposed the simultaneous removal technology of flue gas pollutants with the thermal evaporation of the DWW,which conducts the spray drying treatment on the DWW with partial thermal flue gas（medium temperature flue gas）extracted from air pre-heater by establishing the drying tower and the simultaneous removal of SO₂ and NO_x through the thermal evaporation of the DWW.On the basis of theoretical analysis and experimental requirements,the spray drying pilot test system of the DWW as well as the experimental system of the spray drying simultaneous pollutant removal mechanism are designed and established respectively.Besides,the drying characteristics of the DWW,its solid-phase and dried products’ characteristics as well as the rules of Cl^-precipitation,and that of the simultaneous removal of SO₂ and NO_x during the drying process of the DWW are studied so as to provide theoretical and data support for the promotion and application of the new wastewater treatment technology.Firstly,by research on the drying characteristics as well as solid-phase drying characteristics with the spray drying pilot test system of the DWW,it is found that:（1）compared with low temperature flue gas,it is more flexible to control the exit temperature and make the temperature changes during drying process more smooth under the medium temperature as well as strengthen the drying speed and the reliance;（2）the main drying products of the DWW are MgSO₄·H₂O,CaSO₄·0.5H₂O and NaCl,which had rough,multihole or incomplete hollow spheres on the surface,and the average particle’s diameter is longer than that of coal ash;（3）when added the drying products of the DWW,the coal ash has a specific resistance rising firstly and reducing and increasing slightly with the change of temperature while there is little obvious difference with the original coal ash in 120 ℃;（4）the chain-shaped,spherical or irregular clustered aggregate formed by the collision between the waste droplet and the coal ash particle enlarge the particles and facilitate the effective collection of electrostatic precipitator.Secondly,by research on the rules of Cl^-precipitation during the drying process of the DWW with the experimental system of the spray drying simultaneous pollutant removal mechanism,it is found that:（1）the precipitation amount and ratio of Cl^-rose firstly and then reduced slightly with the increase of the flue gas temperature;（2）the precipitation amount and ratio of Cl^-rose gradually with the increase of the spraying water amount;（3）with the increase of the concentration of Cl^-,its precipitation amount rose gradually while its ratio reduced gradually;and（4）with the increase of the value of PH,both the precipitation amount and ratio of Cl^-reduced gradually.The influence of Cl^-on metal corrosion can be reduced through conducting spray drying after thermal alkalinization on the DWW.Additionally,by research on the simultaneous removal of SO₂ and NO_x during the drying process of the DWW,it was found that:（1）the removal efficiency of SO₂ and NO₂ reduced with the increase of the flue gas temperature;（2）the removal efficiency of SO₂ and NO₂ rose gradually with the increase of the spraying water amount;（3）with the increase of the concentration of Cl^-the removal efficiency of SO₂rose gradually while that of NO₂ reduced gradually;（4）with the increase of molar ratio of OH^-/S,both the removal efficiency of SO₂ and NO₂ rose gradually;（5）with the increase of the inlet content of SO₂,both the removal efficiency of SO₂ and NO₂ reduced gradually;（6）with the increase of the inlet content of NO₂,both the removal efficiency of SO₂ and NO₂ reduced gradually.The removal of SO₂ and NO_x can be realized with the spray drying process of alkaline DWW.Additionally,the higher the value of PH is,the greater the removal efficiency will be.This research indicates that the simultaneous removal technology of flue gas pollutant with the thermal evaporation of the DWW can realize the goal of zero emission of the DWW,as well as the removal of some pollutants from the flue gas,which is significant for the wastewater treatment and ultra-clean discharge of SO₂ in practice and research.