NO Reduction By Pyrolysis Tar Of Coal And Biomass

Nitrogen oxide(NOx),as one of the major serious atmospheric pollutants emitting from fuel combustion,causes harmful environmental pollutions including the acid rain,photochemical smog and many others.It impacts also human health.The reduction of NOx emission becomes thus an important subject of preserving global environment.This thesis mainly investigates the characteristics of NO reduction by pyrolysis tar in a lab-scale drop-tube reactor to deepen the understanding of the NO reduction by pyrolysis tar.The NO reduction capabilities of pyrolysis chars and tars of Sawdust(SD)and Xianfeng(XF)coal were firstly investigated and compared with the results realized by tar of Distilled Spirit Lees(DSL)in our previous work under the similar conditions.The stoichiometry ratio(SR)and temperature are considered as the key factors affecting the NO reduction by tar as well char which both showed considerable capability in reducing NO.Their realized NO reduction efficiencies increased with elevating temperature from 800? to 1000?.Under the similar conditions,Sawdust tar(SD tar)exhibited the best NO reduction efficiency among other tested agents.Furthermore,tars exhibited the higher NO reduction efficiencies than those realized by char under the same mass feeding rate(0.15 g/min)of reagent.Also,the maximal reduction efficiency was obtained at SR values of 0.6-0.9,which was similar to the optimal SR obtained for the circulating fluidized bed decoupling combustion(CFBDC)system.The NO reductions by major tar components were further evaluated to figure out their contributions to the capability of NO reduction by a tar.The used model compounds included benzene,phenol,aliphatic,acid and ester.Testing their NO reductions revealed that phenol enabled the best NO reduction capability among all tested model compounds at the same mass feeding rate of reagent(0.15 g/min).Therefore,phenol plays an important role to the NO reduction capabilities of both SD tar and DSL tar,indicating that the major contributor for reducing NO in biomass tar is phenols,while in coal tar this becomes aromatic or aliphatic compounds.Also because of this,biomass tar allowed the higher NO reduction efficiency than coal tar did.Nonetheless,more studies are needed to clarify the potential synergistic effects of tar components on NO reduction.In addition,the work examined the influences of major parameters of reburning process including the stoichiometry ratio(SR),reaction temperature,residence time(?)and initial NO concentration on the NO reduction efficiency by tar.All tested parameters significantly influenced the NO reduction efficiency by tar.With increasing the SR from 0.4 to 1.3,the realized NO reduction efficiency for both SD tar and XF coal tar first increased and then decreased,and the maximal NO reduction efficiency appeared at SRs of 0.6-0.7.This verified that the amount of O2 fed to the system plays an important role in NO conversion.Under the fuel-rich condition such as at SR=0.6,the realized NO reduction efficiency of tar obviously increased with elevating temperature in 800-1000?,indicating that a higher temperature is beneficial to the NO reduction efficiency at this kind of SRs.Also,the longer reaction time enhanced the reactions between reductant and NO to improve the NO reduction efficiency.Moreover,the increase of initial NO concentration in reburning process was found to facilitate the contact of NO with reductant,thus raising the realized NO reduction efficiency.