Release Characteristics Of Volatiles From Rapid Pyrolysis Of Solid Fuels Based On LIBS

Coal and biomass are the main energy sources in national production at present,and pyrolysis is one of the important forms of solid fuel thermal conversion.The release characteristics of volatiles and tar during pyrolysis are affected by many factors such as heating power,temperature and alkali metals.At present,most of the relevant studies on the pyrolysis process of solid fuels are based on obtaining the types,yields and time characteristics of pyrolysis products off-line,rather than obtaining the product distribution information on the fuel surface during pyrolysis in situ.Therefore,it is necessary to deeply study the spatial and temporal distribution of the products around the particles in the pyrolysis process of solid fuels under different influencing factors,reveal the volatilization characteristics in the pyrolysis process,and lay a foundation for further study of the volatilization release mechanism in the pyrolysis process of solid fuels and the establishment of the corresponding kinetic model.In this paper,the CO₂ laser was used as the heating source,and the rapid pyrolysis process of solid fuel(coal and eucalyptus)particles under inert atmosphere was taken as the research object.An experimental platform for the study of volatile release characteristics based on laser-induced breakdown spectroscopy(LIBS)was established.First direct acquisition of different solid fuel use fiber optic spectrometer(eucalyptus and coal)the LIBS spectra of fast pyrolysis process,the different fuel pyrolysis process of volatile release process real-time information,the research analyzes the different atoms and molecules in the pyrolysis products(including C,H,O,CN,C₂)characteristic spectrum of time and space distribution characteristics.The experimental results show that the pyrolysis process of coal and eucalyptus presents two stages:dehydration and desorption stage and macromolecular decomposition stage.During the dehydration and desorption stage,the carbon and nitrogen components precipitated by the pyrolysis of eucalyptus were obviously more than that of coal.In the macromolecular decomposition stage,the peak time of each element precipitation from eucalyptus was obviously later than that from coal.Meanwhile,the proportion of H and O in volatile components precipitated from eucalyptus was larger,while the proportion of CN and C₂ in volatile components precipitated from coal was larger.In addition,the residual energy after laser breakdown was collected in the experiment,and the temporal and spatial distribution of the residual energy and H/C showed a good consistency,which proved that the distribution of macromolecular components such as tar was closer to the fuel surface,and the concentration of small molecular gas components increased with the increase of the height.On the one hand,increasing the heating power will increase the yield and precipitation rate of total volatiles,and on the other hand,it will make the volatiles precipitated secondary reaction.Then,in order to analyze the influence of different forms of alkali metals on the volatiles release during the rapid pyrolysis process of solid fuel,the coal and eucalyptus samples were mixed with different forms of potassium salts(KCl and K₂CO₃),and the adding ratios of potassium were 0,1%,3%,6%,respectively.Libs spectra of volatiles during the pyrolysis process were collected by optical fiber spectrometer.The results showed that the K and Na precipitated from coal and eucalyptus showed a good consistency during pyrolysis.At the same time,compared with eucalyptus,the precipitation rate of K and Na during coal pyrolysis is faster,and the pyrolysis duration is shorter.The addition of K₂CO₃ will increase the peak concentration of volatiles in the pyrolysis process of coal and eucalyptus,but there is an optimal proportion of the added content.When the optimal proportion is exceeded,K₂CO₃ may inhibit the pyrolysis process.When KCl was added,the promotion effect was not as obvious as that of K₂CO₃,and increasing the amount of KCl could even inhibit the volatiles release during the pyrolysis of coal and eucalyptus.