Study On Thermal Treatment Technology And Optimization Of Desulfurization Wastewater

In view of the characteristics of high chlorine ion and COD content and hardness of desulfurization wastewater,reliable desulfurization wastewater evaporation concentration experiments and flue gas bypass spray drying technology are studied to find the best evaporation and drying parameters,which is certain engineering guidance significance for zero discharge of desulfurization wastewater.The effects of steam temperature,vacuum degree,rotating speed of evaporator and pH of desulfurization wastewater are analyzed on chloride ion,ammonia nitrogen,pH,COD and turbidity of condensate water,as well as on evaporation rate,energy consumption ratio and comprehensive evaluation parameter F of water quality.The results show that:With the increase of steam temperature,the hydrogen ion,chloride ion,ammonia nitrogen,COD,turbidity and evaporation rate of condensed water increase obviously,and the energy consumption ratio decreases continuously.When the steam temperature increases from 110℃to 130℃,the evaporation rate increases by about 25%,and the energy consumption ratio decreases by about 7%.When the steam temperature exceeds 120℃,the concentration of hydrogen ion,chloride ion,ammonia nitrogen and COD of the condensate rises sharply.In order to obtain better water quality of the condensate,the steam temperature should be controlled within 120℃.With the increase of vacuum degree,the chloride ion,ammonia nitrogen,COD,turbidity and evaporation rate of condensate gradually increase,and the energy consumption ratio gradually decreases.When the vacuum degree increases from 0.03Mpa to 0.08Mpa,the evaporation rate increases by about 11%and the energy consumption ratio decreases by about 7%.When the vacuum degree increase from 0.03Mpa to 0.08Mpa,the pH of condensate decrease from 8.75 to 5.72,the contents of chloride ion,ammonia nitrogen,COD and turbidity increased by 5.2 times,17.5%,146.1%and 203.7%respectively.With the increase of the evaporator speed,the evaporation rate shows an upward trend,the energy consumption ratio increases slightly at first and then decreases sharply,and the chloride ion,ammonia nitrogen,COD and turbidity in the condensate water show a slow upward trend.When the pH of desulfurization wastewater increases from 3 to 11,the content of chloride ion in the coagulative water decreases by 91.2%,and the ammonia nitrogen and turbidity increase by 6.77 and 3.43 times,respectively.When pH is close to 7,the evaporation rate is the minimum and the energy consumption ratio is the maximum.When pH is 3,the energy consumption ratio is minimum.On this basis,response surface methodology is used to study the main factors affecting evaporation rate,energy consumption ratio and water quality comprehensive evaluation parameter F are steam temperature and vacuum degree,and the secondary factors are evaporator speed and pH of desulfurization wastewater.Taking low F value,energy consumption ratio and high evaporation rate as target values,the optimal evaporation process conditions are as follows:vacuum degree is 0.063MPa,pH of desulfurization wastewater is 6.5,evaporator speed is 6.7 rpm,evaporation temperature is 118.4℃.Aiming at theΦ4×26.5m desulfurization wastewater spray tower in industrial application,the physical and mathematical models of spray drying numerical simulation are established.In the Fluent numerical simulation,the three-layer porous airflow uniformly distributed plate set at the flue gas inlet is treated as the porous medium model,and the nozzle type is air-blast-Atomizer.The particle type is set as droplet,and the standard k-εturbulence model is adopted.The temperature field and flow field obtained by simulation are less than 2.8%compared with the measured values in actual engineering,which shows a good coincidence.The evaluation indexes of particle adhesion and drying effect are put forward,and the effects of nozzle center distance,flue gas velocity,spray volume,inlet flue gas temperature,atomization angle and atomization particle size on the uniformity of particle adhesion and outlet temperature and water content of drying tower are studied by using the verified numerical simulation method.The results show that:The influencing factors on the adhesion and drying effect are atomized particle size,gas flow rate,nozzle center distance,nozzle atomization Angle.Taking the maximum moisture content of wall particles W_i,maxless than 5%,and the minimum moisture content index C_Wand flue gas temperature index C_Tof outlet section as target values,the drying conditions are optimized and screened by Design Expert10.0.7,and the optimal drying parameters are obtained as follows:The center distance of the nozzle is 1.18m,the flow rate of flue gas is 1.03m/s,the atomization Angle of the nozzle is 41.43°,and the atomization particle size is 125μm.TheΦ4×26.5m desulfurization wastewater spray tower is modified according to the optimal parameters.After the modification,the wall water content decreases by 4.36%on average from top to bottom,and the average and maximum particle water content at the outlet decreased by 4.5%and 3.9%,respectively,which prolong the continuous operation time of the actual project.Based on the optimization results of three-effect evaporation and spray drying experiments and numerical simulation,the thermal treatment project of desulfurization wastewater of 15m³/h for 1000MW unit is designed and successfully passed 168h trial operation.The results show that:The system runs stably and the treatment capacity meets the design requirements.The spray drying tower does not stick to the wall during operation,and the waste water particles are dried well.The indexes of the three-effect evaporative and coagulated water meet the water quality standard of circulating cooling water for urban Sewage Regeneration and Utilization（GB/T19923-2005）,which can be used for recycling.The research results of this paper are valuable for the engineering design and optimization operation of desulfurization wastewater evaporation and drying.