Experimental Study On The Characteristics Of Lignite Pyrolysis In The Fixed-bed Reactor

Lignite resources are one of the most abundant energy resources in China,especially in Inner Mongolia region. The lignite has some disadvantages such as lowcalorific value, high moisture, easy weathering and spontaneous combustion and poorthermal stability. These issues have limited the application of lignite resources.However, lignite also has some advantages such as high volatile matter, high reactionactivity and high H/C ratio. These unique features make lignite extremely suitable forpyrolysis applications. Lignite pyrolysis is one of the important ways of clean andefficient utilization of lignite.In this paper, fixed-bed pyrolysis of three types of lignites from Inner Mogoliahas been studied. The effect of pyrolysis parameters such as temperature andresistance time on product distribution and yield has been investigated. The changesin chemical structure of raw coal and chars were studied by using FT-IR. The evolvedgas composition was analyzed by gas chromatographer (GC). The composition of tarwas studied by GC-MS.Lignite fixed-bed pyrolysis experiments has proved:(1) With the increasing oftemperature, the char and tar yields decreased accompanied by the increase in gasyield. Increasing the pyrolysis temperature also increased the yields of H2and CO anddecreased the CO2and CH4yields for the three kinds of lignites. The intensity of thearomatic bands C=C,–COOH, C–O, aliphatic ethers and alcohols, and aromatic C–Hbands decreased with increasing pyrolysis temperature.(2) Increasing the residencetime did not have any significant effect on char yield, however the gas yield increasemonotonically accompanied by a decrease in tar content. With increasing theresidence time, the yields of H2, CH4and CO decreased progressively, accompaniedby the increase in CO2evolution for all three types of lignite. The residence time has alittle effect on the functional groups of chars.(3) The tar was mainly composed ofbenzene and derivatives, phenol and derivatives, naphthalene and derivatives, indeneand derivatives, benzofuran, alkanes and small amounts of ketones, aldehydes,fluorine, anthracene and phenanthrene. With the increase of temperature, the contentof phenol and derivatives decreased. The residence time has almost no effection onthe composition of tar.Furthermore, the effect of heating rate on the lignite pyrolysis and thecombustion characteristics of char were studied by using the thermogravimetricanalysis (TGA).The results also proved:(1) The heating rate affected the lignite pyrolysis. The initial temperature of the volatile release increased and the position of DTG peakshifts to higher temperature. The intensity of maximum weight loss peak (DTGmax)increased with increasing the heating rate accompanied by a decrease in finalpyrolysis temperature.(2) The pyrolyzed chars showed increased ignition temperatureand lower combustion reactivity indicating higher thermal stability of char. Pyrolysisof lignite can effectively inhibit the spontaneous combustion of lignite.