Emission Characteristics Of Contaminants During Oxy-fuel Combustion Of Torrefied Straw With Coal

Oxy-fuel co-combustion of biomass and coal can not only promote the reduction of CO2 emission,suppress the emission of gaseous pollutants such as SO2 and NO2,but also significantly improve the ignition performance and combustion characteristics of the fuel.However,due to the inherent drawbacks of biomass,there are still some problems in the combustion process,such as poor stability and high storage cost.Torrefaction pretreatment is an effective way to upgrade the physicochemical properties of biomass,but the traditional method is limited by many conditions,resulting in its low economic feasibility and practical operability.Therefore,in order to promote the large-scale and industrial application of cocombustion of torrefied biomass with coal and torrefaction pretreatment,this paper puts forward the idea of oxy-fuel co-combustion of biomass with coal,and using the recycled flue gas of oxy-fuel combustion to prepare torrefied biomass,which is intended to explore a more relaxed working condition of torrefaction pretreatment and study the contaminant emission behavior during the oxy-fuel co-combustion of torrefied biomass with coal.First,by simulating the flue gas atmosphere of oxy-fuel combustion,the effect of torrefaction temperature（200-300℃）and oxygen concentration（0-10%）on the physicochemical properties of rice straw under flue gas conditions were analyzed;Then,the effects of torrefaction temperature and oxygen concentration on the combustion characteristics of torrefied rice straw in the subsequent process of oxy-fuel co-combustion with coal and the emission behavior of main gas products were investigated by TG-MS platform;Finally,the oxy-fuel co-combustion experiment of torrefied rice straw and coal was carried out in a drop tube furnace to explore the effects of torrefaction temperature and mass ratio of rice straw on the formation characteristics of particulate matter,and the inorganic composition of particulate matter was analyzed.The main conclusions are as follows:（1）Compared with oxygen concentration,the effect of torrefaction temperature on physicochemical properties of rice straw was more significant.The torrafaction reaction takes place at temperatures above 250℃ and the oxidation reaction was obvious when the oxygen concentration was more than 6%.Compared with high oxygen concentration,the oxidative torrefaction degree of rice straw was higher under high torrefaction temperature.The relative content and release ratio of chlorine and potassium in torrefied rice straw increased with the increase of torrefaction temperature and oxygen concentration.（2）The release curves of NO2 and CO2 in the process of oxy-fuel co-combustion are similar to the DTG curves,and the gas release peak corresponds to the weightlessness peak in the DTG curve.The increase of torrefaction temperature and oxygen concentration can inhibit the release of NO2,SO2 and CO2 in the subsequent co-combustion,and SO2 is significantly lower than coal combustion.Compared with the increase of oxygen concentration,the increase of torrefaction temperature has more obvious effect on the release of NO2,SO2 and CO2.（3）Increasing oxidative torrefaction temperature can promote the emission of PM1-10,while increasing the mass ratio of rice straw can promote the emission of PM0.1-1.PM0.1-1 produced by co-combustion of raw rice straw with coal was mainly composed of Cl and K,and the total content is more than 82%,while the contents of Si and Mg in PM0.1-1 produced by cocombustion of torrefied rice straw with coal increased significantly.PM1-10 produced by cocombustion of torrefied rice straw with coal is mainly composed of Si,Mg,Ca,and K,in which the sum of Ca and Si is more than 60%.