Scavenging Effects of Kaolin on Fine Ash Formation during Zhundong Coal Combustion

The previous work found that the additive kaolin could scavenge not only sodium(Na)but also calcium(Ca)and magnesium(Mg),which is the important ash fluxing agents in low rank coal combustion.Such scavenging effects of kaolin on fine ash formation were studied in the present work.A typical Zhundong coal and its blends with kaolin at dosages of 1,2 and 4 wt%were combusted in an electrically heated drop tube furnace(DTF)at 1300℃.The fine ashes generated were collected and size segregated by a low pressure impactor(LPI).The morphology and chemical composition of fine ash were analyzed by scanning electron microscopy equipped with an energydispersive spectrometer(SEM-EDS).In addition,char/ash particles were sampled at various positions of DTF to elucidate how kaolin additive affected the fine ash formation process.The results further showed that apart from the scavenging of volatile Na,kaolin additive could also strongly scavenge the refractory Ca,Mg and Fe in the fine ash during Zhundong coal combustion,which transformed the sintered particles with irregular shape into melted spherical particles,and finally resulted in the considerable decrease of these elements in both PM_(0.4)and PM_(0.4-10)by melting and agglomeration.The close contacts between kaolin particles and coal resulted from physically mixing were a key factor responsible for the reaction of kaolin with the refractory Ca,Mg and Fe.

Impacts of Torrefaction on PM_(10) Emissions from Biomass Combustion

Typical biomass torrefaction is a mild pyrolysis process under conditions of ordinary pressure,low temperature(200–300°C)and inert atmosphere.Torrefaction is considered to be a competitive technology for biomass pretreatment,but its impacts on the emissions of particulate matter from biomass combustion are worthy of further study.In this paper,three kinds of biomass,i.e.,bagasse,wheat straw and sawdust were selected for torrefaction pretreatment and the impacts of torrefaction on the emission characteristics of PM_(10) from biomass combustion were investigated.The combustion experiments were carried out on a drop tube furnace.The combustion-generated particulate and bulk ash samples were collected and subjected to analyses by various techniques.The results show that torrefaction tends to result in a reduction of PM_(1)(particulates with an aerodynamic diameter less than 1μm)emissions from combustion,but the extent of reduction is dependent on biomass type.The reduction of PM_(1) from the combustion of torrefied biomass is mainly because that the torrefaction process removes some Cl and S from the biomass,thereby suppressing the release of alkali metals and the emissions of PM_(1) during the combustion process.As for PM_(1–10)(particulates with an aerodynamic diameter within 1–10μm),its emissions from combustion of torrefied biomasses are consistently reduced,compared with their untreated counterparts.This observation is primarily accounted for the enhanced particle coalescence/agglomeration in combustion of torrefied biomasses,which reduces the emissions of PM_(1–10).