Pyrolysis Characteristics Of Lignite For Adopting Fluidized Bed Two-stage Gasification Process

At present,producing industrial gas is mainly based on fixed-bed gasification technology in Chinese industry,but there are some limitations such as difficulty in amplification,high cost of raw material,poor applicability to crushed coal,and high tar content.It is urgent to develop a technology that can handle cheap and abundant low-rank coal,expand Large-scale gasification technology,and decrease tar content in gas.For this reasons,the Institute of Process Engineering of the Chinese Academy of Sciences proposed a fluidized bed two-stage gasification technology to decouple the coal gasification process into two sub-processes of coal pyrolysis and char gasification,respectively,in fluidized bed pyrolyzers and transport beds.It can be realized in the gasifier,and the hot char particles ean be used to strengthen the cracking of tar and catalytically remove the tar at high temperature.This paper systematically studied the product distribution of the upper coal pyrolysis process by two different vapor modes for the first time.The thermogravimetric-mass spectrometer was used to investigate the performance of char to remove tar.The reorganization mechanism has established for the optimal operating conditions of the fluidized bed two-stage gasification process-providing theoretical data to support the amplification and industrialization of this process technology.The main research contents and results of this paper are as follows:(1)Basic research on pyrolysis of Xiaolongtan lignite in fluidized bed.The effects of pyrolysis temperature,simulated moisture and inherent moisture on the distribution of pyrolysis products in Xiaolongtan lignite in fluidized bed were researched.In the N2 atmosphere,with the increases of pyrolysis temperature,the gas yield increased significantly,the char and tar yield decrease;the two different vapor modes further reduce the char and tar yield,especially the gas yield and the H2 yield was significantly increased.For wet coal samples,the char yield reached the bottom at Rw/c=19.9%at any temperature.Compared with dry coal in N2,both inherent moisture and simulated moisture conditions could strongly promote the rising in tar yield below 700?.For the case of 4%,the tar yield of coal under the inherent moisture was lower than that under the simulated moisture at 600?.As the pyrolysis temperature increases,the difference became smaller.At the high water content of 14%,especially at 700-800?,the tar yield of the coal under the inherent moisture was much higher than that under simulated moisture.(2)The char gasification characteristic is closely related to the surface area.The gasification activity of generating char at lower temperature conditions was lower,and the char activity generated under simulated vapor atmosphere was the highest.Compared with the tar produced by coal pyrolysis in pure N2 atmosphere,especially at higher moisture content,both inherent moisture and simulated moisture can promote the production of aromatic hydrocarbons and heterocyclic compounds with a low boiling point fraction and a ring number lower than 2.The effect of inherent moisture on heavy component tar reforming was greater than that of simulated moisture.The heavy components of tar produced by watery coal samples decreased along with increasing water content,resulting in more light eomponents and micromolecular compounds,and better thermal cracking activity..(3)Basic research on tar cracking characteristics and char removal of tar.The effects of heating rate,reaction atmosphere,primary char and ash removal char on the removal of tar from pyrolysis of fluidized bed were investigated in TG-MS.The results showed that char catalytic reforming was effective to remove the tar and increase the effective gas contents.By comparing the ash removal char with the original char,it was found that the content of S?Cl and metal elements contained in the original char is good for the tar removal.