Study Of Combustion And Pyrolysis Characteristics Of Torrefied Biomass

Biomass torrefaction is a promissing technic for improving fuel property.Torrefied biomass possesses a few advantages such as low moisture content,high energy density,enhanced hydrophobicity and grindability,and has attracted considerable attention from scientists and industires.However,for torrefied biomass,the combustion in practical fields remain remains rarely studied and so does the charring process,which is strongly related to the combustion.Hence,aiming to acquire deeper understanding to the thermal conversion behavior of torrefied biomass,this dissertation focus on the impacts of torrefaction on biomass high-temperature flame combustion and the pyrolysis char and vapors production.This dissertation strated with the flame combustion experiment of torrefied schima wood particle in a single particle reactor.The experiment found tht torrefaction shorten the ignition and devolatilization time of schima wood but extended the char combustion time as a result of more char produced from torrefied samples.A diffusion-control model was established to simulate the char combustion,and a well fitted result was achieved.Additionally potassium was found to favored char formation in devolitilization but the char combustion time was reduced for potassium also improve the char reactivity.Having decisive effect on overall combustion process,char is an important intermediate product in biomass combustion.Thereafter,this dissertation used step-wise pyrolysis to analyze the influence of torrefaction on char formation in high-temperature pyrolysis.Generally,with torrefaction,the shcima wood char yield was increased and the char reactivity was decreased.But this result was largely depended on the heating rate of the pyrolysis.Modelling compouds(cellulose,xylan,and lignin)were as well studied.Char yields of these compounds were increased by torrefaction yet the mechanisms behide them were different.Torrefaction reduced the char reactivities of cellulose and lignin but had no effect on xylan char.At last,this work compared the influences of dry and wet torrefaction on the pyrolysis vapors of biomass.The experiment found dried torrefied samples had less volatile content while wet torrefied samples had more volatile content.According to Py-GC/MS analysis,despite having different effects on the product distribution,both dry and wet torrefaction enhanced the property of pyrolysis vapors by reducing acid and nitrogen-containing heterocyclic compounds.To sum up,this dissertation contributes considerable meaningful basic research work to combustion and pyrolysis characteristics of torrefied biomass,especially on charring processes.It was for the first time found that the effect of torrefaction on char yield and char reactivity only existed when the pyrolysis heating rate and temperature reached a certain extent.