The Effect Of Three Constituents Of Biomass On The Ignition Behavior Of Biomass In A Drop Tube Furnace

Due to the amount of CO₂ emitted during conversion process equals CO₂ which was assimilated into the plants during the process of their growth and very low emissions of pollutants such as SO₂ and NO_X,biomass is considered to be an environment-friendly clean renewable energy source with great application prospects.Combustion is an important utilization of biomass energy,therefore a lot of research on the ignition and combustion behavior of biomass has been reported.However,the effect of three constituents of biomass on the ignition behavior of biomass at high heating rates has not been reported so far.In this paper,the ignition and combustion characteristics of three constituents of cellulose,hemicellulose and lignin and seven kinds of biomass including rice straw,soybeen stalk,corn stalk,peanut shell,chestnut shell,bamboo and sawdust were studied.The experiments were carried out in a drop tube furnace with a wall temperature of 1273K under air atmosphere,and the combustion processes were recorded by a high-speed camera.The three components were sieved to 74-150μm and all of the biomass samples were ground and sieved to 500-700μm.The radiant energy analysis technology was used to obtain the temperature distribution of particles during the combustion process,and the effect of three constituents of biomass on ignition mechanism and combustion characteristics was investigated.The experiments of cellulose,hemicellulose and lignin show that the ignition mechanism of cellulose and hemicellulose is hetero-homogeneous ignition while lignin is homogeneous ignition under air atmosphere.The burning time of cellulose and hemicellulose is very short,and the burning time of lignin is longer.After homogeneous ignition of lignin,there is a period of volatile combustion process in which the temperature increases slowly.Once char ignites,the temperature increases sharply.The temperature of cellulose and hemicellulose increases dramatically afer ignition.The experiments of seven kinds of biomass show that the ignition mechanism of biomass particles mainly depends on the content of lignin in the biomass particles.The extremely low lignin content of rice straw is hetero-homogeneous ignition while the other six kinds of biomass are homogeneous ignition under air atmosphere.For the six types of biomass with homogeneous ignition mechanism,the temperature rise rate in the initial stage（6-7 ms）after ignition is closely related to the lignin content.The higher the lignin content in biomass,the faster the temperature rise rate in the initial stage after ignition.The combustion of biomass char lead to a rapid increase in the combustion temperature of biomass particles.The higher the lignin content,the sooner the biomass char is ignited.Biomass with moderate lignin content（10%-30%）takes much longer time from homogeneous ignition to the highest temperature level than biomass with high lignin content（>30%）from homogeneous ignition to the highest temperature.