Rapid Pyrolysis Characteristics Of Cohesive Coal By Infrared Heating Method

With respect to the difficulty in treating low-grade cohesive coal and the low utilization efficiency,an external heating fixed bed pyrolysis process with internals has been proposed to obtain the high-quality tar and char.To probe the pyrolysis property,a fixed bed reactor heated by a gold furnace was employed in this study firstly.By loading the massive coal sample,the characteristics of product distribution,pyrolysis gas content and tar component from coal pyrolysis were examined.The results shows that during low-temperature pyrolysis,the yields of tar and pyrolysis gas was very low,while the char particles were cohered together.Then,an infrared fast pyrolysis experimental device with high heating rate was used to pyrolyze the cohesive coal at different reaction temperature(600-1000 oC).Moreover,to suppress the secondary pyrolysis reaction,a kind of compressed thin-layer coal sample was adopted by varing the thickness from 1 mm to 5 mm.The main experimental results and conclusion are as follows:1.Compared to the gold furnace pyrolysis,the coal pyrolysis in the infrared equipment had more distinct advantages.the product distribution characteristics from infrared pyrolysis equipment was much better.At the final temperature of 700 oC,the pyrolysis tar yield from the gold furnace pyrolysis reached its maximum value of 7.4%,110.45% as the tar yield from G-K assay.While for the fast pyrolysis from infrared equipment,the yields of pyrolysis gas and tar were higher.For example,at 700 oC,the tar yield reaches a value of 8.06%,120.3% as the value form G-K assay;2.During the pyrolysis experiment,compared to the packed coal samples,the secondary reaction in the compressed thin-layer(3 mm)coal sample with the same mass of 3 g was significantly suppressed,releasing more volatiles and producing more tar;3.To minimize the secondary reaction,the effect of thickness and number of the thin-layer coal sample on pyrolysis behavior was further investigated.The thickness of thin-layer played an important role during the cohesive coal pyrolysis.The research results show that the secondary reaction of the coal pyrolysis process was well suppressed by reducing the thickness and number of thin-layer coal.The tar yield increased sharply,reaching a maximum of 9.96% at 1000 oC,which was 150% as G-K assay.This realized the synchronous increase of tar and pyrolysis gas;4.The simulated distillation analysis found that the tars produced by the common pyrolysis of coal mainly included asphaltenes,while the tars prepared by the rapid pyrolysis of thin-layer coal contained a large amount of light oil,phenol oil,naphthalene oil,washing oil and anthracene.GC-MS and FTIR analysis showed that as the thickness and the number of coal layer decreased,the composition and content of tar compounds increased,and the strength of aromatic hydrocarbons and oxygen-containing functional groups increased,further illustrating the rapid coal pyrolysis of thin-layer coal influenced the tar yield and quality.This also revealed the high temperature primary reaction characteristics of coal after the coal tableting method sufficiently by inhibiting the secondary reaction;5.During the experiment,the reaction conditions were continuously optimized,by changing the structure of the reactor and the porosity of gas distribution plate.This will decrease the gas residence time of volatile matter not only in gas phase but also in gas distribution plate.All of these operation facilitated the suppression of secondary reaction and thus realized a good understanding on primary reaction behavior of cohesive coal.