Study On Low Temperature Upgrading And Kinetics Of Lignite

With the rapid development of economy in China, energy shortage is increasingly prominent. Our country began to pay attention to the exploitation and utilization of lignite resources, but its high moisture content, low calorific value, fragile and self-ignition, was not conducive to the direct combustion and transport. Therefore, it is necessary to upgrade lignite before using it. Most of the current process is high temperature upgrading, not only a waste of energy will lead to lignite explosion. So, low temperature upgrading of lignite is an important task of lignite utilization. In this paper, different moisture content lignite was chosen as object of study. The drying and pyrolysis characteristics of the lignite were studied through the low temperature drying and pyrolysis experiments combined with kinetic analysis.Low temperature drying experiments were conducted at air temperature of 90-160? with different kinds and thicknesses of lignite. The experimental data and the nine different thin-layer drying models for multiple non-linear regression analysis, using Fick's law of diffusion combined with the Arrhenius equation to calculate the moisture diffusion coefficient and the activation energy. The results show that two kinds of lignite are mainly in the falling rate drying. The drying rate increases with drying air temperature but decreases with layer thickness.1# lignite is in conformity with Page model while 2# lignite is in conformity with Midilli-Kucuk model. The activation energy of 1# lignite is 13.98-34.29kJ/mol and 2# lignite is 13.35-18.44kJ/mol.The experiments of moisture re-absorption and calorific value test and FTIR were investigated on dried lignite. The results show that the final moisture content increases with layer thickness but decreases with drying air temperature, and lignite calorific value increases with air temperature. Lignite structure changes after drying, and >C=O, -O-,-COOH reduce during drying process.The pyrolysis of different kinds of lignite were carried out using STA409PC, under dynamic conditions at heating rates of 10?30? range from room temperature to 500 ?. The experimental data were sorted out by Li Chung-Hsiung approximate expression, combined with thirty-four kinetic mechanism functions to calculate the activation energy and pre-exponential factor. To verify the mechanism function selected by Malek method and the kinetic compensation effect. The results show that 1# lignite is in conformity with cylindrically symmetric three-dimensional diffusion mechanism, and 2# lignite is in conformity with one dimensional mechanism. The activation energy of 1# lignite is 70.75-113.62kJ/mol and 2# lignite is 76.17?101.38kJ/mol.