Investigation On Co-pyrolysis Interactions Between Naomaohu Coal And Cedar

Co-pyrolysis is a promosing process to realize clean and efficient co-utilization of coal and biomass energy.However,the lack of co-pyrolysis interactions greatly restricted their industrial application.Thus,this dissertation started with unstanding the individual pyrolysis behaviors of coal and biomass.Firstly,a fixed-bed reactor was used to detect the effect of process parameters on products distribution and tar compositions.Furthermore,a self-designed novel pyrolysis time-of-flight mass spectrometry equipped with electron impact/vacuum ultraviolet photoionization（Py-EI/VUVPI-TOFMS）was employed to systematically investigate the formation and secondary evolution behaviors of primary volatiles from coal and biomass pyrolysis.In addition,the biomass basic components of lignin,cellulose and hemicellulose were applied to deeply reveal the interaction mechanisms during biomass pyrolysis.Based on these results,an infrared quick heating technique was used to enhance the synchronization and synergies of volatiles from coal and biomass,and investigate the effects of process parameters and inherent AAEMs on the co-pyrolysis products distribution and tar compositions.Finally,the co-pyrolysis interaction mechanisms were revealed by comparing the individual pyrolysis and co-pyrolysis results.The main results are as follows:Cedar sawdust（CS）was selected as the biomass pyrolysis material,and an infrared heating fixed-bed reactor was used to explore the effects of heating rate and pyrolysis temperature on the products distribution and tar compositions.The results show the heating rate can significantly influence the pyrolysis products distribution,and high heating rate is helpful to inhibit the secondary reactions of pyrolysis volatiles and enhance the tar yield,while high temperature results in the tar cracking and reduces the tar yield,and the G-type guaiacols in tar were converted into the mono-and bi-phenols.To reveal the formation and secondary evolution behaviors of primary volatiles during CS pyrolysis,the Py-EI/VUVPI-TOFMS was adopted to detect the primary volatiles from CS pyrolysis,and then,the inert quartz sand（QS）with varied amount was filled into the reactor to regulate the secondary reactions of primary volatiles.Finally,the information of secondary reactions was obtained combined with the EPR analysis of coke on the QS surface.It was found that the primary volatiles from CS pyrolysis mainly consist of aliphatic chains and its radicals,furans,phenols,G-type guaiacols and polycyclics.With the regulation of QS,the G-type guaiacols undergo the demethylation,demethoxy and polycondensation reactions to form phenols and coke,respectively;while the aliphatic radicals undergo the recombination and cyclization to form furan.To deeply understand the pyrolysis behaviors of biomass,the lignin,as the main component of CS,was used to explore the breaking mechaniasms of chemical bonds during CS pyrolysis combined with the analyses of Py-EI/VUVPI-TOFMS,EPR and FT-IR.The results show that the R-O-R lingkages（β-O-4 andα-O-4）in lignin break at<300oC to form the G-type guaiacols and o-methoxy and hydroxyl substituted phenoxy radicals-containing residue.With the increase of pyrolysis temperature,the G-type guaiacols further undergo the demethylation,demethoxy and cyclization to form mono-,bi-phenols and quinones.When the temperature increases to 500oC,the mono-and bi-phenols undergo the dehydroxylation to form benzenes and H₂O,and the aromatic radicals in residue are converted into 1～5 ring aromatic radicals via polycondensation.To reveal the interactions during biomass pyrolysis,the biomass basic components of lignin,cellulose and hemicellulose（xylan）were used and the Py-EI/VUVPI-TOFMS was adopted to investigate the primary volatiles from these components.Thereafter,the mechanical mixing method was used to conduct the co-pyrolysis tests.It was found that the lignin volatiles promote the formation of polycyclics during biomass pyrolysis.In detail,the G-type guaiacols and S-type compounds from lignin can interact with the aliphatic radicals from cellulose（or xylan）to form the polycyclic volatiles.Additionally,the volatiles from cellulose and xylan are also involved in obvious interactions,resulting in the formation of long aliphatic chains,furans and aliphatic radicals-containing char.Low-rank Naomaohu coal（NMH）was selected as the coal pyrolysis material,and the Py-EI/VUVPI-TOFMS was adopted to detect the primary volatiles from NMH,and then,the QS was also used to regulate the secondary evolution of primary volatiles,and the secondary reactions during NMH pyrolysis were obtained combined with the structural analysis of coke.The results show that the primary volatiles from NMH pyrolysis mainly consist of benzenes,mono-and bi-phenols,2～4 ring aromatic compounds,C₃～C₆ and C₁₄～C₂₁ aliphatic shains.With the regulation of QS,the mono-,bi-phenols and 3～4 ring aromatic compounds undergo the polycondensation reaction to form the 1～5 ring aromatic radicals-and quinone radicals-containing coke,while the C₁₄～C₂₁ long aliphatic shains were converted into the C₃～C₆ short ones via C-C cleavage,as well as the aromatic compounds via dehydrocyclization.An infrared fast heating fixed-bed reactor was applied to investigate the effects of process parameters（including pyrolysis temperature,mixing ratio and mixing mode）and inherent AAEMs on the products distribution and tar compositions during co-pyrolysis of CS and NMH combined with the analyses of simulated distillation,GC-MS and EPR,and the co-pyrolysis interactions were obtained by comparing the individual pyrolysis results of NMH and CS.The results show that there are obvious interactions between NMH and CS during co-pyrolysis,and they were significantly affected by the process parameters and inherent AAEMs.High pyrolysis temperatue is helpful for the formation of gases,but helpless for the char,and increasing the mixing ratio of CS in blends can inhibit the NMH pyrolysis.Samely,the mixing mode is also the key parameter for the co-pyrolysis process.In detail,the mechanical mixing mode is not good for the interactions between the CS and NMH volatiles,resulting in the decrease of tar yield and increase of char yield.While the layered mixing mode can provide the effective space for the volatile-volatile interactions,and the CS volatiles（such as·OH and·CH₃）can serve as the hydrogen donor to improve the co-pyrolysis process,and enhance the tar yield.In addition,these interactions promote the formation of 3～4 ring aromatic compounds in tar.Both mechanical mixing mode and layered mixing mode can promote the·CH₃ from CS to interact with the 2-ring aromatic compounds from NMH to form methyl-contained naphthalenes.As for the AAEMs in NMH and CS,the removal of AAEMs can inhibit the volatiles polycondensation during pyrolysis,and further enhance the volatile-volatile interactions,increasing the tar yield and decrsesing the gas yield.Simultaneously,1-and 2-ring aromatic compounds in tar increase and the 3～4 ring aromatic compounds decrease.