低温热提质褐煤的理化结构演化及燃烧特性

Physical / chemical structure evolution and combustion characteristics of mild thermally upgraded lignite

选取胜利褐煤在流化床台架上进行不同温度(200~500℃)和气氛(氮气、模拟烟气和有机气氛)的温和热解提质实验,采用热重分析仪研究提质煤的燃烧特性,分别使用傅里叶转换红外光谱(FTIR)和氮气等温吸附方法研究提质前、后煤的化学和物理结构的变化规律。结果表明:热解过程提高了褐煤的发热量,降低了水分和自燃倾向。模拟烟气增加了提质煤的热值损失率,而有机气氛降低了热值损失率。煤中的含氧官能团和脂肪烃结构随着热解温度的升高而逐渐分解,挥发分的析出和热变形导致了提质褐煤平均孔径的减小和比表面积的增大。500℃模拟烟气气氛下煤的理化结构变化最为显著。褐煤提质后物理化学结构的变化使得提质煤燃烧热稳定性增强,自燃倾向降低,而提质气氛对煤的燃烧特性影响较小。

A Shengli lignite was thermally upgraded in a fluidized-bed reactor at temperatures of 200-500 ℃ under N2,or simulated flue gas(SFG),or organic(ORG) atmosphere.The combustion characteristics of the raw and upgraded lignite were characterized by thermogravimetric analyzer.The chemical and physical structures of the raw and upgraded lignite were studied by using fourier transform infrared spectroscopy(FTIR),and N2 adsorption isotherm,respectively.The results indicate that the upgraded lignite has higher heating value,lower moisture content and lower spontaneous combustion tendencies compared to raw lignite.The upgraded lignite under SFG shows the highest thermal energy loss,while those under ORG shows the lowest thermal energy loss.The oxygen-containing groups and aliphatic hydrogen in the lignite decompose with the increase of temperature as a result of oxygen removal and aromatization of the lignite.The average pore diameter of the upgraded lignite decreases with the increase of temperature,while the surface area increases,which are caused by the volatile matter release and thermal deformation of the lignite.Significant changes in the chemical and physical structures of the upgraded lignite obtained under SFG atmosphere are observed when the upgrading temperature is 500 ℃.The spontaneous combustion tendency to the lignite is reduced and the combustion stability is improved after the thermal upgrading,which is resulted from the chemical and physical structurechanges of the lignite.The upgrading atmosphere slightly affects the combustion characteristics.