Experimental Study Of Lignite Conversion For Various Products Based On Vacuum Pyrolysis

Lignite is a kind of low rank and quality coal with the shortcomings of high moisture,volatiles and oxygen content,low heating value,poor thermal stability and inconvenience for storage and remote transportation,which makes it inefficient during direct combustion.China has abundant lignite.Developing high efficient lignite conversion technology for high quality energy or chemical products is significant for utilizing resource efficiently and relieving energy shortage pressure.This thesis carried out a series of experiments producing various products based on lignite vacuum pyrolysis and discussed related mechanismVacuum and atmospheric pyrolysis experiments for lignite char production were implemented between 300-900?.The results showed that lignite char yields during vacuum pyrolysis were obviously higher than those of atmospheric pyrolysis,approximately 4.4%-34.7%.Vacuum lignite chars have higher fixed carbon content,heating value and energy density.Specific surface areas and pore volumes of vacuum lignite chars were also dramatically higher than those of atmospheric lignite chars,and vacuum lignite chars' micro pore ratios were 2-8 times more than atmospheric lignite chars.Vacuum lignite chars showed better combustion performance with better combustible index Sw and comprehensive combustion characteristic index S.Tars were gained form lignite vacuum pyrolysis at the range of 400-900?.Vacuum pyrolysis significantly improved the tar yields when compared with atmospheric pyrolysis.Tar yield reached the peak at 600? with 0.24g/g,about 2 times of other references' results.Tar releasing mechanism was discussed as well.Different vacuum lignite chars,derived at 300?,600? and 900?,were gasified with steam for syngas production between 700-1000?.The influences of chars,gasification temperature and H₂O/char ratio on syngas yield,purity and H₂/CO ratio were researched and analyzed.Best gasification conditions were verified based on different controlling targets,and related mechanism was also discussed.Lignite and renewable energy resources,biomass and sewage sludge,were co-pyrolyzed in a vacuum reactor.Synergetic effects were obviously observed and verified when comparing results of co-pyrolysis,parent pyrolysis and calculated values involving yield distribution,char characteristics,tar and gas components.This thesis verified the significant advantage of vacuum pyrolysis for lignite conversion,and provided a promising new method for lignite conversion.