| In order to deal with the world energy crisis and greenhouse gas emissions,biomass energy,as a kind of abundant,widely distributed,renewable and carbon dioxide neutral energy,is considered as an ideal substitute of fossil fuels.Biomass is mainly composed of three conponents-cellulose,hemicellulose and lignin,which will affect the pyrolysis and combustion behaviors of biomass.Oxygen-enchanced combustion is a combustion technology with low nitrogen and carbon dioxide emission.In addition,it can enhance the combustion stability of biomass fuel.Biomass oxygen-enchanced combustion combines the advantages of biomass and oxygen-enchanced combustion,thus it is a promising technology.In this paper,the ignition and combustion behaviors of cellulose,hemicellulose and lignin under diferent O2concentrations（in O2/N2 atmospheres）were studied for the first time with the drop tube furnace（DTF）and image processing technology.Meanwhile,The combustion behaviors of rice husk,bamboo and soybean stalk with the particle size of 500～700μm under oxygen-enchanced atmosphere were studied.First of all,the ignition and combustion experiments of single particle cellulose,hemicellulose and lignin were carry out under O2/N2 atmosphere with different oxygen concentration in DTF,and the ignition and combustion behaviors of cellulose,hemicellulose and lignin particles in oxygen-enchanced combustion were analyzed respectively.The experimental results show that oxygen concentration affects the ignition mechanism of the three components,the ignition mechanism of cellulose and hemicellulose change from hetero-homogeneous ignition to heterogeneous ignition when the oxygen concentration increases to50%and 70%respectively.The ignition mechanism of lignin changes from homogeneous ignition to heterogeneous ignition when the oxygen concentration increases to 50%.With the increase of oxygen concentration,the probability of oxygen molecules diffusing to the surface of biomass particles increases,leading to the increase of heterogeneous reaction rate,which is the main reason for the change of ignition mechanism.When the lignin ignites homogeneously,the burnout time of lignin decreases significantly with the oxygen concentration increases.However,when the oxygen concentration is higher than 50%,lignin ignites heterogeneously,and the influence of increasing oxygen concentration on the burnout time of lignin is no longer obvious.Cellulose and hemicellulose ignites hetero-homogeneously or heterogeneously,so the burnout time decreases slowly with the increase of oxygen concentration.Then,the ignition and combustion experiments of single particle rice husk,bamboo and soybean stalk were carry out under O2/N2 atmosphere with different oxygen concentration in DTF,and the ignition and combustion behaviors the three kinds of biomass in oxygen-enchanced combustion were analyzed respectively.Also,the influence of oxygen concentration and the three components on the ignition and combustion behaviors was analyzed.The experimental results show that the ignition mechanism of rice husk,bamboo and soybean stalk changes from homogeneous ignition to heterogeneous ignition with the increase of oxygen concentration.This is mainly due to the change of lignin ignition mechanism.In the air atmosphere,the three kinds of biomass all ignited homogeneously.Due to the highest lignin content,the ignition mechanism of soybean stalk changes to heterogeneous ignition when the oxygen concentration is 30%.Because of the lowest lignin content,the ignition mechanism of rice husk keeps unchanged until the oxygen concentration reaches 100%,its ignition mechanism changes to heterogeneous ignition.The lignin content of bamboo is between soybean stalk and rice husk,and the ignition mechanism of bamboo changes to heterogeneous ignition mechanism when the oxygen concentration is 70%.The ignition distance of rice husk,bamboo and soybean stalk decreases with the increase of oxygen concentration.And the influence of oxygen concentration on the ignition distance of biomass particles decreases with the increase of oxygen concentration.Due to the lowest lignin content,the ignition distance of rice husk is the shortest of the three kinds of biomass under the same atmosphere.The increase of oxygen concentration results in the decrease of burnout time of rice husk,bamboo and soybean stalk.The burnout time of soybean stalk is the shortest under the same atmosphere due to the highest lignin content and moisture content.Although the moisture content of bamboo and rice husk is close,the lignin content of bamboo is higher than rice hulk,as a result,the burnout time of bamboo is longer than that of rice husk. |
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