Study On Fine Particle Emission From Coal Fired Circulating Fluidized Bed With Chemical Agglomeration

PM2.5 refers to the particle matters whose aerodynamic equivalent diameter are less than or equal to 2.5?m,and it is also called inhalable particles.Large amounts of PM2.5 emissions endanger human health and environment.It is urgent to do further research on the formation and emission control strategies of PM2.5.Chemical agglomeration is a technique that uses solid adsorbent or solutions to increase the particle size of PM2.5,which is favorable for PM2.5 capture in dust removal equipment.Attapulgite is available for PM2.5 emission control due to its special physical and chemical properties,such as great surface area,layer-chain structure and needle-like crystal.The study aims to figure out the influence of attapulgite on PM2.5 emission characteristics.Firstly,the effect of different kinds of coal and Ca/S on PM2.5 emission was investigated in a circulating fluidized bed.The results show that the distribution of number density and mass concentration of PM2.5 produced by different coal is not the same.The adding of CaO can decrease the number density and mass concentration of PM1 and PM2.5;the higher the Ca/S molar ratio is,the less the number density and mass concentration of PM1 and PM2.5 is.The number density and mass concentration of PM2.5 emission was investigated in a circulating fluidized bed.The effect of amount of attapulgite addition,flow rate of attapulgite suspension,different kinds of coal and Ca/S molar ratio were studied.The results show that the attapulgite added during coal combustion can effectively reduce the number density and mass concentration of PM2.5 emission,and the appropriate addition amount of attapulgite is no more than 6 wt.%.Spraying attapulgite suspension into dilute phase region or dense phase region can effectively decrease PM2.5 emission,and the capture efficiency is higher than the situation of adding attapulgite in bed.Attapulgite suspension shows no selectivity for kinds of coal.With the increase of flow rate of attapulgite suspension,the number density and mass concentration of PM2.5 emission decreases;however,when flow rate is over 38ml/min,the negative effect seems stronger than the positive one especially in the situation of spraying suspension into dilute phase region.When spraying attapulgite suspension,the increase of Ca/S can further improve PM2.5 capture efficiency.The effect of agglomeratin room which is set at the end of circulating fluidized bed on PM2.5 emission was investigated.The effect of the type of attapulgite,particle size of attapulgite,the attapulgite mass fraction,the flow rate of attapulgite suspension and the aggregation temperature on PM2.5 emission was investigated.The results show that the PM2.5 capture efficiency of Gaonian attapulgite is higher than Dabai attapulgite.The smaller the particle size of attapulgite is,the higher the PM2.5 capture efficiency is.With the increase of attapulgite mass fraction and flow rate of attapulgite suspension,the number density and mass concentration of PM2.5 decreases;however,it is not economical by relying on too high attapulgite mass fraction and flow rate of attapulgite suspension.The increase of agglomeratin temperature is unfavorable to PM2.5 capture efficiency.