| The development of biomass energy would effectively reduce carbon emissions and remarkably contribute to achieving the ambition of "peak carbon dioxide emissions and carbon neutrality".As a technology with abundant products for developing biomass energy,the pyrolysis and liquefaction technology could convert lignocellulosic biomass into liquid fuel,char and combustible gas.The main liquid product bio-oil contained a variety of high value-added components and meanwhile had a relatively high energy density,but the bio-oil from the traditional pyrolysis and liquefaction also presented the disadvantages of high moisture,strong acidity,low heating value,poor stability and high componential complexity,which led to the low competitiveness in comparison with gasoline and diesel.According to the difference in condensing abilities between condensable components in pyrolysis vapors,the selective condensation technology would separate the bio-oil composition online through setting multi-staged condensers,which was universally applied in the large-scale platforms of biomass pyrolysis and liquefaction.However,the effectiveness of the existing selective technology was not enough to achieve the ideal separation of complex components in bio-oil due to the unknown mechanism of selective condensation.The condensation of biomass pyrolysis vapors involved the multi-component vapor-liquid phase transition as well as chemical reactions,and thereby the computational fluid dynamics and other numerical simulation methods were difficult to accurately understand this complex process due to the lack of comprehensive pyrolysis product composition and relative parameters.Therefore,the effective method for studying the condensing evolution mechanism of biomass pyrolysis vapors,and the effect of condensing conditions on the liquefaction and recovery of pyrolysis vapors and the separation and enrichment of bio-oil components,were the key to improving the separation and enrichment accuracy of selective condensation and preparing multi-purpose bio-oil.1.The experimental research method for the condensing evolution of biomass pyrolysis vapors was proposed based on bio-oil composition inversion and function fitting.The fast pyrolysis vapors of walnut shells were segmentally recovered in the top,middle and bottom of condensing field through developing a vertical tubular condenser with two flumes on the inner wall.The bio-oil composition was detected by Elemental analyzer,Kari Fischer micro moisture titrator and gas chromatography-hydrogen ion flame detector(GC-FID).The mass contents of water,acetic acid,furfural,methyl cyclopentenol ketone(MCP),phenol,catechol,guaiacol and its derivatives were quantified,which were inverted into the proportions of vaporous representative components at the set positions.The mathematical relationship between the proportions of vapor components and the positions of condensing field was fitted by functions,and the evolution curves and heat maps of representative condensable components in pyrolysis vapors were obtained along the condensing field.Three lengths of vertical tubular condensers were set,and the matching and prediction accuracy of linear function and Slogistic function was investigated.As the short length of condensing field was selected,the componential vapor evolution curves fitted by linear function exhibited higher effectiveness;as the long length was selected,the curves fitted by linear function deviated far from the actual results in the top of condensing field.Linear function showed great predictive precisions for water,acetic acid,furfural and other components with weak condensing abilities,and those predictive precisions were over 0.90.The difference in the top narrowed between the curves fitted by Slogistic function and the actual results but the R2 values of Slogistic fitting were generally lower than those of linear fitting.Slogistic function showed higher descriptive and predictive precisions for phenolic compounds and other components with strong condensing abilities,and those predictive precisions were over 0.85.2.The regulation mechanism of water bath temperature and sweeping gas flow rate on the condensing evolution of biomass pyrolysis vapors was studied.The regulation effect of the water bath at 273 K,313 K and 353 K and the sweeping gas at 100 mL/min,300 mL/min and 500 mL/min on the condensing evolution of walnut shell pyrolysis vapors was analyzed in the vertical tubular condensing field with 285 mm length.The inhibition effect of water bath temperature on the heat exchange of biomass pyrolysis vapors exhibited a non-linear upward tendency with increasing water bath temperature.The inhibition effect of water bath temperature below 313 K was negligible whereas the effect of the temperature close to 373 K was the strongest.Water and other components with weak condensing abilities had swift responses to the inhibition of increasing water bath temperature,and the water recovered by the condenser at 353 K high temperature water bath was less than 20%of the total condensable water under traditional condensation.But the inhibition of low temperature water bath showed no significant effect on phenols and other components with strong condensing abilities,and the recovery proportion of phenols at 353 K still reached 70%of the total condensable phenols.Furthermore,the whole recovery effect of condenser was inhibited by increasing sweeping gas flow rate.As sweeping gas increased from 100 mL/min to 300 mL/min,the recovery effect of each representative component decreased,but when the sweeping gas further increased to 500 mL/min,the increasing flow field disturbance of biomass pyrolysis vapors improved the recovery of the components with stronger condensing abilities than water.Compared with the results at 300 mL/min,the recovery proportions of acetic acid and guaiacols increased by 5%and 25%.At the same time,the liquefaction and recovery of one component would significantly increase when its solubility was improved,and the recovery of one component would vary with the condensing ability of azeotrope when it formed an azeotrope with other components.Moreover,the continuous evolution mechanism of condensable components in walnut shell pyrolysis vapors was analyzed with the whole water bath temperature adjustment of four-staged condensers through the modified experimental method based on bio-oil composition inversion and function fitting.As the whole water bath temperature decreased,the recovery effect of Condenser Ⅰincreased and that of Condenser Ⅱ remained stable but that of Condenser Ⅲ decreased.Under the whole high temperature of water bath,the recovery proportions of water,acetic acid and furfural were less than 5%,whereas the minimal recovery proportion of MCP or phenols was over 20%and the maximal recovery proportion was’ more than 50%.Under the whole low temperature of water bath,Condenser Ⅰ fully collected the oligomers in pyrolysis vapors and meanwhile about 20～40%of detectable components remained vapor and entered subsequent condensers,and the contents of representative components in the bio-oil recovered by Condenser Ⅱ were constant with the traditional contents except water and acetic acid.3.The comprehensive influence of adjusting condensing parameters on the separation and enrichment of bio-oil components was studied.According to the regulation mechanism of water bath temperature on the condensing evolution of walnut shell pyrolysis vapors,a 10 K temperature interval was selected to analyze the effect of 273～373 K water bath temperatures on the separation and enrichment of walnut shell bio-oil components.As water bath temperature increased,bio-oil moisture exhibited an S-type downward tendency,and the moisture at 353 K decreased by 70%compared with the traditional moisture.The contents of organic components with higher boiling points than water remained stable at first and then increased and finally decreased.The incremental content was determined by componential condensing ability,and the content of guaiacol and its derivatives increased by 230%at 363 K compared with their traditional contents.According to the regulation mechanism of water bath temperature and sweeping gas flow rate on the condensing evolution,10 K temperature interval and 300 mL/min flow rate interval were selected to analyze the coupling effect of 323～363 K water bath and 300～1500 mL/min sweeping gas on the separation and enrichment of walnut shell bio-oil components.As the water bath temperature and sweeping gas flow rate increased,biooil moisture always decreased and the decline scope was small at low or high water bath temperature but the decline scope was broadened at middle water bath temperature.The contents of MCP and guaiacols always increased with increasing temperature and flow rate,whereas the contents of acetic acid,furfural and phenol at low water bath temperature increased with increasing flow rate but those contents at high water bath temperature decreased with increasing flow rate.Under the coupling effect of 363 K water bath and 900 mL/min sweeping gas,the content of guaiacol and its derivatives increased by 400%compared with the traditional content,and the enrichment degree was nearly double the optimal result from the single effect of water bath temperature.4.The selective condensation technology was applied in the preparation of richphenol bio-oil and multi-purpose bio-oil.Based on the results of selective condensation by adjusting water bath temperature,323～363 K water bath(10 K temperature interval)was combined with 200℃,250℃and 300℃ torrefaction to conduct the preparation of rich-phenol bio-oil through the pyrolysis and liquefaction of walnut shells.The kinetic properties and surface functional groups of non-torrefied and torrefied walnut shells were analyzed using thermogravimetric analyzer and Fourier transform infrared spectrometer.With increasing torrefaction temperature,the activation energy of walnut shells increased and the stretch of-OH,-CH2-,C=O gradually decreased but the stretch of C=C remained stable.The bio-char yield remarkably increased after the walnut shells were torrefied and the growing bio-char improved the secondary reaction frequency of pyrolysis vapors in the horizontal fixed bed reactor,leading to the increasing proportion of water in the condensable components.The contents of detectable phenols increased from 2.70 wt.%to 3.20 wt.%under the single effect of torrefaction pretreatment whereas these contents considerably increased to 13.30 wt.%under the combining effect of torrefaction pretreatment and selective condensation.Based on the regulation mechanism of water bath temperature on the evolution of walnut shell pyrolysis vapors in the multi-staged condensers,the selective condensation condition was designed for the preparation of walnut shell multi-purpose bio-oil in the pilot-scale fluidized bed pyrolysis reactor with fractional condensation.The variations of moisture,pH,heat conductivity coefficient,specific heat capacity and viscosity in multi-purpose bio-oil were investigated during the natural storage for 75 days.The central pyrolysis temperature of the fluidized bed reactor was 773 K,and the temperature of the vapors entering the condensing field was 593 K.The temperatures of the vapors at the end of the four-staged condensers were set at 423 K,363 K,318 K and 300 K,respectively.The heavy bio-oil with 10 wt.%yield and 24 MJ/kg heating value was prepared in Condenser Ⅰ that was suitable for boiler combustion,and the flowable bio-oil with 16.5 wt.%yield and 22 MJ/kg heating value was prepared in Condenser Ⅱ and Ⅳ that could be utilized for atomizing combustion.The minimal proportion of phenols in all multi-purpose bio-oil was 42%,which indicated that the multi-purpose bio-oil could be used as the input materials for the extraction of high value-added phenolic products.During storage,the moisture,acidity and viscosity in the bio-oil from Condenser Ⅱ exhibited relatively small increase because of the lower frequency of aging reactions. |
PDF Full Text Request