The Thermogravimetry Study Of Pyrolysis Kinetics And Fixed Bed Experimental Invesitigation Of Poplar Wood

The pyrolysis characteristics and kinetics of Poplar wood(Populus L.), klason lignin andcellulose(by nitric acid-alcohol methodology) were investigated by using TG and TG-FTIRtechniques. The effects of poplar pyrolysis conditions on characteristics of products (char, gas,liquid) were studied by bench-scale fixed bed reactor. The results showed as following:(1) The pyrolysis behaviors of Poplar wood, klason lignin and cellulose (by nitrate acid-ethanol methodology) were studied by using TG technique. The results showed that the processof poplar wood, klason lignin and cellulose (by nitrate acid-ethanol methodology) wereconsisted of drying stage, pyrolysis stage and carbonization stage. With the increasing ofheating rate, both points of maximum of mass loss rate in the TG/DTG curves shifted towordhigher temperature. All the temperature of drying stage took place at about100℃.Thetemperature of poplar wood pyrolysis stage occurred at200-500℃. The temperature ofmaximum weight loss was at350-390℃and the rate was ranging from9-43%/min. Thepyrolysis temperature interval of klason lignin was widest(start at250℃). And the temperatureof maximum weight loss was at365-416℃while the rate was ranging from3.73to19.24%/min. Cellulose (by nitrate acid-ethanol methodology) had the narrowest pyrolysis temperatureinterval, which was about350-450℃at the speed of24.21%/min to86.27%/min.The activation energies of the three materials were determined by Kissinger,Flynn-Wall-Ozawa, and atava-estak methods. The result showed that the activation energycalculated by Kissinger method was slightly lower than Flynn-Wall-Ozawa and atava-estakmethods as far as poplar wood and klason lignin. In the case of poplar wood and cellulose (bynitrate acid-ethanol methodology), the fitting degree which calculated by Kissinger method wasbetter than it did by Flynn-Wall-Ozawa and atava-estak method. The fluctuation of theactivation energy on conversion rate was observed both in Flynn-Wall-Ozawa method. Theresults showed that: with the increasing of conversing rate, activation energy of poplar woodand cellulose (by nitrate acid-ethanol methodology) were changing up and down. The activeenergy of klason lignin was smooth before rising abruptly.(2)The pyrolysis and combustion behaviors of volatile gases at20℃/min heating rate werestudied by using TG-FTIR technique. The results showed that in N2/air atmosphere, theappearance of absorbance peaks agreed well with the TG/DTG curves. In N2atmosphere, mostof the pyrolytic gases mainly produced at the temperature of200-450℃, such as CO2, CO, CH4,phenols and other alkanes. In air atmosphere, the generation of volatile gases mainlyconcentrated within the range of200-550℃. This combustion process was consisted of twostages. The first stage was the initial pyrolysis, and the second stage was the combustion stage.Volatiles like CO, CH4, ethers, aromatic species were mainly generated at the first stage. At the later stage, the main reactions taking place were the combustion of volatiles and charcoalbecause of the strong CO2peak on the infrared spectrum.(3) The effects of Poplar wood pyrolysis behavior was studied on a bench-scale fixed bedby changing the heating rate (5-30℃/min), terminal pyrolysis temperature (400-700℃) andparticle size (0.125-0.850mm). The results showed that: the pyrolysis gases of Poplar woodmainly included CO2, H2, CH4, CO (about70-90%of gases). It also contained a small amountof C2H6, C2H4, C3H8, C3H6and other lightweight carbon hydrocarbon compounds (about1-3%of gases). Under the same conditions, with the increasing of heating rate,, the surface area ofchar showed a downward trend after the first rise. Higher pyrolysis temperature made thepyrolysis reaction more completely. It resulted in more fixed carbon, less volatile and largersurface area. With the increasing of particle size, the surface area of char showed a downwardtrend after the first rise. Under the paricles between0.250mm and0.425mm, the surface areaof char achieved the maximum value. The LHV of the pyrolysis gases realeased from poplarwood was about9-11MJ/Nm3.The specific surface area of char was about200-550m2/g. Themoisture of liquid product was76.51%, pH value was between2.0-3.5, and the kinematicviscosity was1.24mm2/s. After dehydration, the C content of the liquid was about50-70%,and H content was6-7%.