Experimental Study And Numerical Modeling Of The Low-NO_x Grate Combustion For Biomass Pellets

In order to control the haze weather in our country recently,the ways of biomass pellets burning in coal-fired industrial boilers are more common.However,the arches of the existing biomass grate boilers in our country still follow the design concepts of the traditional coal-fired traveling grate boilers,which cause the problems of high NO_x and CO emisiions in operation.So aiming at the structural characteristics of the exisiting biomass grate boilers in our country,providing suitable technologies iproved has the urgent pratical significance.This paper systematically tidies the existing theories of the biomass grate combustion and the generation and control of NO_x,also summarizes and analyzes the foreign advanced furnace design concepts.Aiming at the biomass pellets with large particle characteristics,pyrolysis experiments were carried out in TA and large particle thermogravimetric reactors,results show that the particle morphology has a significant effect on the heat transfer and the secondary reaction,so the pyrolysis kinetic parameters should be obtained in the large particle thermogravimetric reacor.Next,the experiments of NO conversion in biomass char oxidation and NO heterogeneous reduction by char were conducted in the tube and fixed bed furnace,getting the influence rules of reaction temperature and fuel types on char-N to NO conversion ratio,and getting the kinetic parameters of heterogeneous reduction.Then,experiments under different air speeds and bed thickness were conducted in the unit furnace bed to analyze the generation and transformation of NO in grate combustion,getting the influence of char layer thickness on the NO reduction.After that,according to the characteristics of the biomass pellets in grate combustion,the biomass pellets grate combustion and NO_x model combined with experiments results of the pyrolysis and NO reduction by char was established,and verified with the unit furnace experiments.Finally,through the numerical simulation analysis,it is pointed out that the“chimney flow”characteristic of open-type arch boilers in our country is the root of high concentration of NO_x and CO,the“zigzag”arch scheme combined with air staging were carried out.