Release Characteristics Of High Sodium Coal Combustion Pollutants

Xinjiang zhundong coal reserves rich,can satisfy our country long time energy demand.However,zhundong coal generally has high sodium contents.It is easy to stain the heat exchange surface of the boiler in the process of coal-fired power generation.The reason for the contamination of high sodium coal is that the melting point of sodium compounds produced during the combustion process is low(except for sodium aluminosilicate),compounds will be vaporized in the gas phase at the normal combustion temperature of the boiler,cool and condense of vaporized sodium compounds is the main cause of contamination.By adding a substance with high content of Si and Al mixed firing,such as kaolin,active alumina,diatomite,etc,the sodium element may combine with these additives,producing high melting point sodium aluminosilicate to reduce the vaporization of sodium compounds,which caused the deposited on the heater transfer tubes.Considering the content of Si and Al elements in the high sodium coal ash itself is also high,thus,the high sodium coal ash was used as an additive,mixed firing with the high sodium coal to see whether the mixed burning can make more sodium run into the ash.Mixed burning different proportions of high sodium coal ash and high sodium coal respectively,and mixed burning mechanically ground high sodium coal ash and high sodium coal.The results indicated that the additional ash(whether or not grinding)makes more sodium run into ash than high sodium coal combustion alone,the more sodium in the ash also found with the increase of the proportion of addition.Under the same addition proportion,adding grind ash mixed firing will bring more sodium elements into the ash than adding non grind ash mixed firing.It shows that adding ash combustion can inhibit the vaporization of sodium elements,the higher the proportion of adding,the stronger the inhibition effects.Under the same addition proportion,adding grind ash is more effective than that adding non grind ash to inhibit the vaporization of sodium elements.It is proved indirectly that adding ash combustion can slow down the deposits on the heat transfer surface,the higher the proportion of adding,the better the effect of slowing down the contamination of the heat exchange surface.Under the same addition proportion,adding grind ash has better effect of slowing down the contamination of the heat transfer surface than adding non grind ash.Due to there is large number of high sodium coal ash on site,using high sodium coal ash as an additive,can save the cost of purchased additives and the cost of transportation,has great practical and economic significance for the utilization of high sodium coal.In addition,Coal will produce dust,SO2,NOx and heavy metal pollutants such as Hg,As,Pb,Cd and Cr in the process of combustion.Currently,there is little research on the features of zhundong coal combustion heavy metal emissions,this study select typical zhundong wucaiwan coal and jingyu bituminous coal,test its heavy metals Hg?As?Pb?Cr emission after combustion in drop tube furnace.The test results show that the content of four kinds of heavy metals in wucaiwan coal is lower than that in jingyu coal,in particular,As and Pb is very low compared with jingyu coal.There are little difference in the concentration of four heavy metals in the fly ash and the bottom ash of wucaiwan coal and jingyu coal.The concentration of Hg,As and Pb in flue gas wucaiwan coal is lower than that in jingyu coal combustion.The concentration of Hg0+ which is difficult to remove in wucaiwan coal gas is much lower than that in jingyu coal combustion.The concentration of As and Pb in wucaiwan coal combustion is very low,so that the detection device can't detect the value,but the concentration of Cr in wucaiwan coal gas is slightly higher that in jingyu coal gas.Thus,it can be seen that,wucaiwan coal can also have less emissions of Hg,As and Pb to the atmosphere.There is no significant difference between two coals in the case of emission of Cr.