Effect Of Zero Discharge Of Waste Water From Whole Plant On Gypsum Crystallization

With the improvement of people’s awareness of environmental protection.the society is paying more and more attention to the discharge of industrial wastewater.As a large industrial wastewater discharge,thermal power plants will become the focus of people’s attention.Therefore,it is the general trend to improve the discharge of wastewater from the whole plant.Cascade utilization at present,the coal-fired power plant are advocating wastewater,improve plant wastewater powerusageeffectiveness back,eventually reduce wastewater emissions,by evaporation crystallization realizing wastewater zero emissions,but the desulfurization system as the end of the waste water cascade utilization,all kinds of high salt waste water into the impurities will be under the plant,these impurities will lower the quality of slurry,affect desulfurization process,the stable operation of the desulfurization system bring hidden trouble.In this paper,the gypsum crystal experimental platform was set up in the laboratory to control the addition of elements in the reactor to simulate the desulfurization system gypsum crystal,and the laser particle size and SEM analysis of gypsum crystal were carried out.The results show that with the increase of chloride ion,a large amount of calcium chloride hexahydrate is formed in the reactor,which reduces the supersaturation of the solution and prolongs the crystallization induction time.With the increase of sulfate ion concentration,the calcium sulfate superssaturation in the reaction solution was effectively increased,and the crystallization induction time was greatly advanced.High concentration sulfate ion effectively promoted the growth of gypsum crystal in the B-axis direction,and made the gypsum crystal grow from plate-like to columnar,and the crystal size increased.The addition of metal cations such as Fe³⁺,Al³⁺,Mn²⁺,Zn²⁺ and Ni²⁺ into the reaction solution has no effect on the crystallization induction time,but metal ions can attach to the surface of crystal nucleus or replace calcium ions to embed into gypsum crystal,affecting the growth of subsequent crystals in this direction,making crystal morphology acicular and particle size significantly reduced.Secondly,the effects of the addition of crystal seeds and organic acids on the gypsum crystal were analyzed.The results showed that after the addition of crystal seeds,calcium ions and calcium sulfate ions in the reaction solution were more likely to grow on the surface of crystal seeds.Therefore,the number of crystal nuclei formed was significantly reduced,which effectively promoted the growth of crystal size.The crystal particle size was increased by 17～19μm by adding organic acids in addition to crystal seed,especially citric acid and trisodium citrate.Organic acids contain a large number of hydroxyl groups,which improves the adsorption probability of calcium ions on organic acids,thus promoting crystal distortion and facilitating the formation of large grain crystals.Finally,combined with the above experimental conclusions,the desulfurization system of a plant was optimized after the modification of wastewater discharge.By desulfurization water balance calculation,and combined with the plant salt and water balance report,quantitative analysis of high salt waste water into the impurity in the desulfurization system,optimize the water supply,improve the quality of the limestone,strengthen the operation parameters optimization,add the appropriate seed and organic acid and guarantee the reliability of the desulphurization gypsum crystallization process,avoid the serous problem such as diarrhea,dehydration difficult.