Zero Discharge Technology Of Two-stage Under Saturated Flue Gas Concentration Crystallization Desulfurization Wastewater

The wet limestone gypsum FGD technology has a good desulfurization effect,but it produces a large number of desulfurization wastewater.The water quality of desulfurization wastewater is complex and difficult to treat.In this paper,a zero discharge technology of desulfurized wastewater is proposed.The technology is to concentrate the desulfurized wastewater with the low temperature flue gas of about 110?from the dust remover.The desulfurized wastewater after concentration and reduction enters the crystallization tower,and a small amount of high temperature flue gas in front of the air preheater is extracted to evaporate the concentrated desulfurized wastewater and make it evaporate dry and crystallize.In this paper,CFD is used to simulate the evaporation process of desulfurization wastewater in the crystallizer,and the system and design of the test bench are optimized through the simulation results.In this paper,the grid is divided by ICEM,and the numerical simulation of the desulfurization wastewater evaporation process is carried out by using CFD simulation software FLUENT.The influence of flue gas flow,flue gas temperature and droplet size of desulfurization wastewater on the desulfurization wastewater evaporation process is explored.The results show that the increase of flue gas flow,the decrease of initial particle size and the increase of flue gas temperature have significant effect on the improvement of evaporation rate.According to the numerical simulation results of CFD,the initial tower height and diameter of the Crystal Tower in the pilot test platform are set as 5M and 80cm respectively.The evaporation test of desulfurized wastewater was carried out by using the established evaporation test-bed.In this paper,XRF,atomic absorption spectrophotometer and ion meter are used to analyze the concentrated liquid,gaseous evaporation products and precipitates of the products after flue evaporation of desulfurization wastewater.The results show that with the evaporation and concentration of wastewater,chromium,separator,zinc,copper and other heavy metal ions mainly exist in the concentrated wastewater after evaporation,and the above heavy metal ions are not detected in the condensate of gaseous evaporation,indicating that their ions do not migrate during the evaporation of wastewater.Calcium ion and magnesium ion will stay in the original liquid part to form precipitation with the evaporation process;fluorine ion and chlorine ion can be observed in the condensate of concentrated wastewater and gas evaporation,indicating that fluorine ion and chlorine ion have partial migration in the middle of the evaporation process of desulfurization wastewater.The corrosion characteristics of desulfurized wastewater on different metal materials were studied by immersion experiment.The corrosion experiment showed that the desulfurized wastewater had no effect on 304 stainless steel and 316 stainless steel.A pilot test bench was set up to test five kinds of nozzles and their positions in the crystallizer.The rotating single fluid atomizing nozzle is not easy to block,but when the pressure is small,the atomized particles are large,which is easy to cause the droplets to stick to the wall.The single fluid solid cone nozzle is similar to the fan-shaped nozzle,and the water flow rate is small,so it can get a good physical and chemical effect under a strong low pressure,but the nozzle layout is difficult and easy to block.The atomization effect of two fluid nozzles is better,and the phenomenon of sticking to the wall is lighter.However,external air compressor and corresponding supporting facilities are needed to increase the floor area of the equipment.In view of the serious coking in the pilot test-bed,the crystallizer with a diameter of 800mm and a height of 5000mm was transformed into a crystallizer with a diameter of 1600mm and a height of 6000mm.At the same time,a small amount of secondary air is introduced at the bottom to reduce the accumulation of fly ash at the bottomAfter the commissioning of the pilot test bench,the evaporation capacity of desulfurization wastewater is about 1171-1430 kg/h under the condition that the flue gas inlet temperature of the concentration tower is about 118-120? and the flue gas flow is 42100-53700 m3/h.However,the operation of crystallization tower is affected by the boiler load.The flue gas temperature at the inlet is between 300?320?,and the outlet temperature is not less than 180?,which can meet the evaporation capacity of 200kg/h.