Effects Of Additives On The Migration And Transformation Of Heavy Metals And Fine Particles In Sludge Incineration Flue Gas

Sludge is the main by-product of urban sewage treatment.At present,with the continuous acceleration of urbanization and the improvement of sewage treatment standards,the sludge output keeps increasing.Therefore,it is particularly important to find a reasonable optimal sludge treatment and disposal method under the increasingly strict sewage treatment standards.Incineration has become a research hotspot because of its many advantages such as reduction,innocency and resource utilization.However,secondary pollutants such as heavy metals and fine particles produced in the incineration process have become a major difficulty in limiting sludge incineration.Heavy metal pollution and fine particulate matter is closely related to the burning process of heavy metal enrichment on fine particle gasification or precipitation in the form of gas,but the interaction between the two is not clear.Based on the sludge fluidized bed combustion as the breakthrough point,firstly,explores the incineration temperature and different additives on the influence of fine particulate matter and heavy metal interaction;Secondly,the thermodynamic software Fact Sage was used to simulate the morphological transformation of heavy metals in the whole incineration process.Finally,the adsorption of heavy metals by mineral fine particles at different temperatures was investigated by using the components of incinerated fine particles as the reference model compound,and the interaction with fine particles and the competitive adsorption of heavy metals were investigated by using modified boron nitride as the control adsorbent.The results showed that potassium chloride?KCl?inhibited the accumulation of heavy metals in fly ash,while ammonium chloride?NH₄Cl?promoted the accumulation.NH₄Cl has a more prominent inhibitory effect on the accumulation of heavy metals in fine particles than potassium chloride.In addition,heavy metals Cr,Mn and Ni are mainly entrainment into fly ash,while heavy metals Pb,Cu and Zn are mainly accumulated in fine particles by evaporation,condensation and adsorption.When the temperature is 850? and the addition amount of NH₄Cl is 3%,the content of heavy metal Cu in fly ash is 40.58mg/g.The relative proportion of heavy metal Pb in fine particles was 42.15%.Both NH₄Cl and KCl can reduce the number and concentration of particles,but KCl has a better effect.NH₄Cl will reduce the peak of coarse modal particles in the bimodal distribution of particle number concentration.The micromorphology of the model compounds was consistent with that of incinerated fine particles at different temperatures.The increase of temperature from750? to 950? has little influence on the contents of heavy metals Cd,Cr and Ni,while the contents of heavy metals Cu and Zn vary greatly.The adsorption of Cu is inhibited at high temperature,and the adsorption of Zn increases with the increase of temperature,from 11.5 mg/g to 15.8 mg/g.Modified boron nitride has certain inhibition on fine particulate intermediates and can reduce the formation and emission of fine particulate to some extent.The results of thermodynamic simulation show that Cr,Mn and Ni are relatively stable,and their forms of existence do not change with the change of temperature and kinds of additives.Cd and Si O₂ readily form stable solid oxides at high temperatures.The presence of Cl^-has a great influence on the morphology of Zn.High concentration of chlorine promotes the formation of gaseous zinc chloride at lower temperature.The existence of K exerts different influences on the migration and transformation of Pb and Cu.K inhibits the formation of gaseous chloride of Pb and promotes the formation of gaseous chloride of Cu at high temperature.In summary,the interaction between heavy metals and fine particles in fluidized bed incineration process of sludge is very different.In practical application,suitable additives and operating conditions should be selected according to emission requirements.