Research On The Partial Hydropyrolysis Of East Yunnan Lignite In Fluidized Bed

The second largest lignite reserves were found in Yunnan, China. However, their high-effective utilization is limited. To explore the behavior of these Yunnan lignite coals, a technology of fluidized-bed pyrolysis with heated char as solid heat carrier was developed. The systematically researches on the pyrolysis and partial hydropyrolysis characteristics of East Yunnan lignite were conducted in this thesis.First of all, seven kinds of lignite coals, from East Yunnan region, were selected to study the structure and pyrolysis characteristics. And then, ShuiCheng lignite was chosen as the main research object to investigate its non-isothermal, isothermal pyrolysis and hydropyrolysis characteristics on different thermogravimetric analyzers and relevant kinetic models were built. After that, the effects of pyrolysis temperature and particle size on the distribution and composition of ShuiCheng lignite’s pyrolysis products were studied in a fluidized bed reactor, and a mathematical model was also developed based on coal pyrolysis and heat transfer inside a coal particle. Finally, the effects of low hydrogen concentration and simulated pyrolysis gas on the distribution and composition of pyrolysis products were clarified.The analysis of Fourier transform infrared spectra of seven lignite coals showed that the hydroxyl, aliphatic and oxygen-containing parts of infrared spectrums were well fitted with six, six and eighteen Gaussian peaks, respectively. The results of tests in the thermogravimetric-mass spectrometry(TG-MS) system showed the temperature of initial thermal decomposition differed from 253 to 270 ℃, the temperature with the maximum mass loss rate occurred in the range from 421 to 453 ℃, and the most prominent peaks of gaseous products were within the scope of 400-700 ℃. They suggested that the lignite coals in East Yunnan were suitable for low-temperature pyrolysis.Based on finite parallel reactions model, multi-pseudo-component pyrolysis model was set up by four reactions for the temperature programmed pyrolysis of ShuiCheng lignite, and the activation energies were 39.25-83.59 k J/mol. The final volatile yield at different temperatures of isothermal pyrolysis could be estimated by the empirical formula:0.9 6 201.7 7() e x p [ 0.9 4 7 1 0(()) ]d a fV V R T T￥ ￥= - ′ -. Distributed activation energy model(DAEM) using the Miura’s Integration Method was set up to describe the hydropyrolysis behavior, and the activation energies were 18.53-114.54 k J/mol.The results of fluidized-bed pyrolysis of ShuiCheng lignite showed that the tar yield reached a maximum at 600 ℃. Above 600 ℃, the secondary reactions occurred at a significant rate, and the tar yield decreased. For the pyrolysis of large coal particles at the same temperature, the tar yield decreased with increasing particle size, but not significantly. However, for specific product of the gaseous product, the pyrolysis yield did not increase or decrease monotonically.The results of partial hydropyrolysis of ShuiCheng lignite, which were conducted at 600 ℃ under low hydrogen concentration(<15vol%) and simulated pyrolysis gas atmosphere in a fluidized bed reactor, indicated that within the concentration range studied, the coal conversion increased and tar yield decreased with increasing hydrogen concentration. However, the relative content of phenolic compounds in tar was improved under the conditions of hydrogen existence. The tar yield in simulated pyrolysis gas was lower than that in N2 atmosphere, but higher than that in the 15vol% hydrogen. It suggested that although the CO2 reforming of CH4 improved the tar yield to some extent, H2 still played the leading role in the simulated pyrolysis gas.