Investigation Of Simultaneously Reducing The Emission Of Ultrafine Pm And Heavy Metals By Adding Modified Kaolin And Modified Attapulgite During Pulverized Coal Combustion

The coal burning process creates serious particulate and heavy metals contamination problems.Ultrafine PM is a critical part of PM_2.5 and is of increasing concerns due to its toxicity and controlling difficulty.In the coal-fired power stations,devices such as electrostatic precipitators are widely used reduce the PM emission;however,they can not effectively capture the ultrafine PM.So,an in-furnace PM reduction technology has been proposed,which is supposed to reduce the formation of ultrafine during the coal combustion process by adding additives into the furnace.But the efficiency of natural minerals is limited,and their emission reduction efficiency needs to be improved.Therefore,this paper explores whether it is possible to improve the emission reduction efficiency of mineral additive?kaolin and attapulgite?for PM_0.2 and heavy metals Pb and V by modification treatment.Two kinds of typical modification methods were selected to modify kaolin,namely,the hydrochloric acid modification and the calcium acetate modification.Then,pulverized coal was burned with raw and modified kaolin separately in an electrical heated drop-tube furnace,and the mass yield of PM_0.2,Pb and V were obtained.The results indicate that,compared with raw kaolin,the modified kaolin can reduce the mass yield of PM_0.2 and heavy metals in PM_0.2.It is found that the modification by hydrochloric acid can increase the specific surface area and pore volume of kaolin,and provide more active sites to capture alkali and heavy metals.The kaolin modified by calcium acetate enhances reaction between kaolin and metals;at the same time,the kaolin particles can partially react with calcium acetate at high temperature to generate molten particles,which promotes the liquid phase capture process.Hydrochloric acid modification and calcium chloride modification were selected to modify attapulgite.Then,pulverized coal was burned with raw and modified attapulgite separately in an electrical heated drop-tube furnace,and the mass size distribution of the fly ash particulate and the mass yield of Pb and V were obtained.The results indicate that,the PM_0.2.2 reduction by adding raw attapulgite and modified attapulgite were 28.5%,44.1%and37.9%.Compared with raw attapulgite,the modified attapulgite can reduce the mass yield of Pb and V in PM_0.2.It is found that the modification by hydrochloric acid can remove carbonate in the attapulgite,H⁺replaced the original metal ions between the layers,and the modification also increased the content of free SiO₂ and Si-OH.After the calcium chloride modification,ion exchange occurs between the Ca²⁺and the original metal ions in the attapulgite layer,and Ca²⁺enters the interlayer,which improves the ion exchange property and causes unbalanced charge of the attapulgite.