Effect Of Temperature Oscillation On Torrefaction And Pyrolysis Of Biomass

Biomass as an important carbon containing renewable energy,its full utilization can greatly alleviate energy and environmental pressure.Pyrolysis technology has been widely studied because of its ability to degrade biomass into char,bio-oil and bio-gas for utilization.However,direct pyrolysis of biomass will result in low quality products.As an effective pretreatment method,torrefaction has been proved to be very helpful to improve the quality of biomass pyrolysis products.Because torrefaction requires extra energy to provide energy,this is also the main reason restricting the efficient utilization of biomass as an energy source.The industrial waste heat flue gas between 200 and 300℃can meet the torrefaction needs,but due to the instability of waste heat flue gas,the temperature will change.Therefore,in this paper,elm and poplar were taken as the research objects,and torrefaction experiments were conducted to simulate temperature oscillation with residence time of 30min at 220,250 and 280℃in vertical furnace,and then pyrolysis experiments were conducted on thermogravimetric analyzer with target temperature of 900℃.The influence of temperature oscillation on the physicochemical properties and subsequent pyrolysis of biomass after torrefaction was also concluded.Through the torrefaction experiment in vertical oven,it was concluded that when the oscillation range of torrefaction temperature is small(T_0.5),the relative content of O in elm and poplar was reduced by torrefaction,and the content of O showed a decreasing trend with the increase of torrefaction temperature.The H content of PT_0.5220 in Poplar is 5.80%,which is slightly higher than the original.However,with the increase of torrefaction temperature,the H content showed a decreasing trend,and the energy yield of elm showed an increasing trend,while that of poplar is opposite.When torrefaction temperature oscillated in a wide range（T₁）,the relative contents of O and H in elm and poplar decreased,and the content of O decreased with the increase of torrefaction temperature.The relative content of element H in elm decreased with the increase of torrefaction temperature,while the content of element H in poplar increased first and then decreased with the increase of torrefaction temperature.The energy yield of elm and poplar decreased with torrefaction temperature increasing.TG-DSC-MS was used to study the pyrolysis characteristics and the release characteristics of main volatile products of elm and poplar before and after torrefaction.The results showed that torrefaction improved the pyrolysis reaction performance of elm and poplar at T_0.5,and with the increase of torrefaction temperature,the pyrolysis reaction performance of elm first increased and then decreased,while poplar always showed an upward trend.Torrefaction increased the activation energy of elm and poplar,and the higher the torrefaction temperature,the higher the activation energy.Torrefaction promoted the release of H₂in elm and poplar,among which ET_0.5250released the largest H₂volume flow in elm,while PT_0.5280 in poplar.At T₁,the pyrolysis reactivity of elm and poplar increased firstly and then decreased with the increase of torrefaction temperature.Torrefaction increased the pyrolysis activation energy of elm and poplar,and with the increase of torrefaction temperature,the activation energy of elm showed an increasing trend,while the activation energy of poplar first increased and then decreased.The release of H₂in elm and poplar was increased by torrefaction,among which the release of H₂in ET₁280 sample of elm was the highest,while that in poplar was PT₁250.The co-pyrolysis characteristics of elm and poplar before and after torrefaction were studied by TG-DSC-MS.The results showed that there was an interaction during biomass co-pyrolysis,and the temperature oscillation also had an effect on co-pyrolysis.At T_0.5,the weight loss rate of elm and poplar was inhibited at all torrefaction temperatures,and the activation energy increased firstly and then decreased with the increase of torrefaction temperature,among which HT_0.5250 had the highest activation energy（69.14k J/mol）.Co-pyrolysis promoted the release of H₂at different torrefaction temperatures.At T₁,the weight loss rate was also inhibited during the co-pyrolysis of elm and poplar,and the activation energy showed an increasing trend with the increase of torrefaction temperature.The effect on volatile products was the same as that at T_0.5.