Study On The Pyrolysis And Oxygen-fuel Combustion Characteristics Of Lignite Using Flue Gas Dried

Lignite has not been used effectively due to its high-volatile, high water content, high ash, low heating value, low ash and melting point. Therefore, it has great significance to enhance the utilization of lignite to relieve the pressure of energy and reduce the pollution of environment.In this thesis, Hai laer（HLE） lignite was chosen as the sample and it was dried by using simulated flue gas from oxygen fuel combustion. In the fluidized-bed, the moisture content of coal sample reached 5%, 10% and 15%, respectively by drying at 150 °C. In addition, the coal sample with 15% moisture content was prepared at 100 °C and 200 °C. Pyrolysis experiment of dried coal sample with different moisture content in the fixed-bed was systematically studied. The effects of drying atmosphere, moisture and pyrolysis temperature on yield of lignite pyrolysed product were also systematically studied. The product char were characterized using fourier transform infrared spectroscopy（FTIR） after pyrolysis, the composition and content of gas were analyzed by gas chromatography（GC）, the compositions and content of tar were detected by gas chromatography–mass spectrometry（GC–MS）. Oxygen fuel combustion of dried coal sample and char were studied using thermogravimetri（STA）. Effects of drying temperature, atmosphere and oxygen concentration on combustion characteristics of coal sample and char were also studied.As moisture content in the lignite char was decreasing, the yield of char increased, the yield of gas decreased and the yield of tar had no significant change. The compositions of the gas were different with various pyrolysis atmosphere and drying conditions. Pyrolysis gas were composed of CO, H₂, CH₄, N₂, CO₂ and C₂H₆. CO, H₂ and CH₄ had the highest content. The tar was mainly composed of alkanes, olefins, benzene and its derivatives, phenols and their derivatives etc. The functional group of lignite sample was affected under the condition of different pyrolysis and drying temperature. Drying atmosphere and pyrolysis temperature had different impact on C=C vibration peak,-COOH functional group and C-H vibration peak of aromatic nucleus and mineral substance. Flammability index, burnout index and combustion synthesis index of lignite after drying were higher than in raw coal.