Investigation Of Reducing Ultrafine Particulate Matter Formation By Adding Modified Diatomite And Montmorillonite During Coal Combustion

Coal is the most important primary energy in China and coal combustion contributes a lot to the air pollution.Nearly all coal-fired power plants have installed dust removal equipment,especially electrostatic precipitators(ESP).However most dust removal equipment could not remove ultra-fine particulate matter(PM)due to their working characteristics.Ultra-fine PM could be easily enriched with heavy metal elements and organic pollutant because of the high surface activity.It is a good way to control the emission of ultra-fine PM by adding sorbents during coal combustion and could cover the shortage of ESP.There are a lot of sorbents used to reduce emission of PM during coal combustion.However,these sorbents are all nature minerals and the research of using modified sorbents is rare.The physical and chemical properties of sorbents would be greatly improved after modification treatment.The modification methods include hydrochloric acid and sodium hydroxide.The co-combustion experiment of coal and modified sorbents were performed on a drop tube furnace(DTF).Finally,combustion experiment of raw/modified diatomite and sodium acetate was performed in the same DTF to study the emission mechanism of modified diatomite.The results indicate that acid treatment could improve the effect of ultra-fine PM emission but sodium hydroxide treatment would resist effect of ultra-fine PM emission.The surface characteristic of diatomite has been improved after modification by HCl and the basic structure was unchanged.Its capture ability to alkali metal did not improve obviously.So the physical adsorption property of diatomite has been optimized after treated by HCl.Besides,the reaction activity of diatomite would decresed due to that sodium hydroxide treatment destroy the structure of diatomite seriously.So sodium hydroxide treatment would resist effect of ultra-fine PM emission.HCl and polyhydroxyl aluminum were then used to modify montmorillonite and the combustion experiment was performed in DTF as mentioned above.The results indicate that modification treatment could improve the effect of ultra-fine PM emission effect.Besides montmorillonite could capture more alkali metal element after modification treatment.A special quartz reactor with three small extended tubes at different position along the vertical direction was used to collect the reaction products.The characterization results indicate that the modification process could improve the physical and chemical properties of montmorillonite.Further,there were more free active sites which have high efficiency to capture Na due to the broken or formation of some bonds.So modified montmorillonite shows better performance on controlling formation of ultra-fine PM.