| The growth of global energy consumption and unscientific use of fossil fuels has brought about negative impact on natural and ecological environment,which made more attention have been paid on renewable energy.Pyrolysis is one of the important ways in biomass energy conversion and utilization.Biomass carbon,biomass oil and combustible gas can be obtained by biomass pyrolysis technology,and bio-oil after refinement can be used as a substitute for fossil fuel,but at present the complex organic components has imposed restrictions to large-scale application of bio-oil.Focusing on the above problems,fractional condensation technology of biomass continuous pyrolysis volatiles and the characteristics of pyrolysis products were analyzed in-depth in this thesis,which can provide the theoretical support for large-scale application of biooil.The research contents are as follows:?1?Biomass continuous pyrolysis system was set up using two levels of feed system and flexible transmission technology,and continuous pyrolysis experiments taking pine nut shell,camellia shell,rice husk,and sawdust as raw material were carried out.The experimental results showed that the anaerobic and sealed technological conditions necessary for continuous pyrolysis process was achieved,stable transmission of raw materials and smooth discharge of pyrolysis volatiles was realized,which was adaptable to various raw material materials.Online primary fraction of liquid bio-oil product was achieved by fractional condensation and the influence of various experimental factors such as raw material,pyrolysis temperature,feed speed,condensation temperature,condensation heat transfer area on fractional condensation was discussed.The experimental results showed that as the pyrolysis temperature increasing,fractional bio-oil yield decreased significantly.When the temperature was more than 500 ?,the downwardtrend was larger gradually.The fractional bio-oil yield obtained from different materials was distinct obiviously.Increasing the condensation heat transfer area enabled the yield of fractional bio-oil increase.Decreasing feed speed made the yield of fractional bio-oil increase slightly.Decreasing condensation temperature made the yield of fractional bio-oil increase significantly,and so the condensation temperature was the most significant factors affecting biooil yield.?2?The impact of continuous pyrolysis and fractional condensation on physical and chemical characteristics of bio-oil was analyzed,including calorific value,p H value,density and viscosity,and the results showed that moisture content of fractional bio-oil from pine nut shell is low.Calorific value increased with pyrolysis temperature increasing,and calorific value of 1-level bio-oil was higher than 2-level bio-oil.After increasing heat transfer area,the change of moisture content of fractional bio-oil with pyrolysis temperature is not obvious,calorific value increased with pyrolysis temperature increasing,at 450 ? calorific value of 2-level bio-oil was lowest?26.194 MJ·kg-1?.Decreasing feed speed had not great impact on moisture content of 1-level biooil,but greatly affected the moisture content of 2-level bio-oil,and calorific value had little change.Decreasing condensation temperature enabled the moisture content of 1-level and 2-level bio-oil increase significantly,among which 2 levels of bio-oil increased to 38.73wt%,calorific value of 1-level bio-oil decreased obviously.The difference of moisture content from different raw material were little,the values of moisture content were at a lower level,calorific values were relatively high.pH value of fractional bio-oil samples with strong acidity were among 2.68 to 4.55.Pyrolysis temperature rose from 450? to 500?,the density of bio-oil has increased greatly,but from 500 ? to 550 ?,the density was slightly smaller,and the density of 1-level bio-oil was greater than 2 levels of bio-oil.Decreasing feed speed virtually had little impact on bio-oil density.Decreasing condensation temperature made bio-oil density decrease largely.Bio-oil density of different materials were large,among which pine nut shell is the largest,1.255 g/ml,the volume energy density reached 96.85% of diesel.With pyrolysis temperature increasing,bio-oil viscosity increased.After pyrolysis temperature exceeded 550 ?,liquidity of bio-oil under normal temperature was poor,and the viscosity of 1-level bio-oil was higher than 2-evel bio-oil.High fitting degree was justified using the experimental data into Andrade viscosity-temperature equation.?3?Using GC-MS analysis technology,the composition and distribution rule of bio-oil was analyzed.The main components were hydrocarbons and phenols.Hydrocarbons mainly include aliphatic hydrocarbons which carbon atom number are among 11-30.As the pyrolysis temperature increasing,carbon atom number in hydrocarbons increased gradually,aliphatic hydrocarbons and aromatic hydrocarbonsconverted intoeach other.At 550 ?,the proportions of aromatic hydrocarbons in 1-level and 2-level bio-oil were 32.61% and 20.13% respectively.Phenols mainly include unit phenol which accounts for over 60% of the total,carbon atom number are among 6-9,the main type is simple ring of phenol.Hydrocarbons in camellia shell consists maily of aliphatic hydrocarbon which carbon atom number are among 11-30,but at 600 ?,aromatic hydrocarbons which carbon atom number are among 7-9 was overwhelming.Phenols mainly include unit phenol which accounts for over 95% of the total.Decreasing feed speed made hydrocarbons content increased by 3%,phenols content decreased 8%.As the time of pyrolysis was extended,secondary reaction of pyrolysis volatiles aggravates,long chain hydrocarbons converts into short chain hydrocarbon,polyphenol converts into unit of phenol,hydrocarbon carbon atom number decreases from 20-30 to 11-20,phenolic hydroxyl groups decrease,carbon atom number maintained among7-9.As the condensation temperature increasing,hydrocarbons and phenolics in the main product were separated effectively,phenolics entered into 2-level condensation system,while the hydrocarbons remained in 1-level condensation system.The composition of raw material has adirect effect on bio-oil composition.The three major components had complexinteractions,cellulose and hemicellulose mainly converted into hydrocarbons,lignin mainly converted into phenols.Goodseparationperformances were justified in pine nut shell and camellia shell,separation effect of rice husk and sawdust were bad.Selection appropriate continuous pyrolysis according to different raw materials is necessary.?4?Pyrolysis and combustion characteristics of bio-oil was analyzed by TG-DSC coupling technique.Research results had showed that pyrolysis process of bio-oil can be roughly divided into three reaction stages,including evaporation of moisture and light components of low-boiling point,pyrolysis of medium and heavy components of and slow precipitation of a small amount of volatiles within bio-oil.Compared with pyrolysis process,combustion process of bio-oil can be divided into four stages,including evaporation of moisture and light components,decomposition of medium and heavy components,slow combustion of volatiles,carbon residue blazing.In the stage of slow combustion of volatiles,thermogravimetric curve of samples under air atmosphere is distinct from the nitrogen atmosphere,a significant reduction in the DSC curve indicated that heat release increased gradually and bio-oil began to burn.In the stage of carbon residue combustion,combustion temperature range of pyrolysis bio-oil under high temperature is large,compared with1-level bio-oi,2-level bio-oi advanced burning start time and had low heat release,carbon residue combustion was weaker,the influence of pyrolysis temperature was slight.As condensation heat transfer area increasing,combustion temperature range of fractional bio-oil deviated to low temperature zone,complete combustion time of 1-level bio-oi advanced.As the feed speed decreasing,combustion temperature range of 1-level bio-oil deviated to low temperature zone,maximum weight loss rate in the stage of carbon residue combustion increased,burning interval of2-level bio-oi extended.As the condensation temperature decreasing,ignition temperature of 1-level bio-oi advanced,maximum weight loss rate in the stage of carbon residue combustion decreased,combustion performance became poor,ignition temperature of 2-level bio-oil became higher,complete combustion time advanced.For other raw materials,performance of 1-level biooil from camellia shell was better than rice husk and sawdust.As heating rate increasing,the peak of maximum weight loss in DTG curves increased and the corresponding temperature rose,combustion reaction gradually intensified,combustion interval backward-shift,complete combustion time postponed.When heating rate was 30 K/min,the 6.41%,and 5.80% carbon residue had not burned in 1-level and 2-levels bio-oil respectively.Heating rate has distinct influence on bio-oil combustion.In this thesis,combustion performance of fractional bio-oil product was described using a variety of combustion characteristic index.For bio-oil from pine nut shell,at 500?,combustible indexes?7.424×10-6 K-2min-1?and comprehensive combustion characteristic index(12.282×10-9K-3min-2)of 1-level bio-oil reached the maximum,combustible indexes?5.671×10-6 K-2min-1?and comprehensive combustion characteristic index of 2-level bio-oil(6.519 × 10-9 K-3min-2)reached the minimum,difference between 1-level bio-oil and 2-level bio-oil was significant.As the feedspeed decreasing,combustible indexes,burnout characteristics index,and comprehensive combustion characteristic index increased.As condensation temperature decreasing,combustion characteristic index of bio-oil decreased,comprehensive combustion characteristic index of 2-level bio-oil reduced to 3.36 × 10-9 K-3min-2.For the other raw materials,combustible index and comprehensive combustion characteristic index of 1-level bio-oil from camellia shell was higher than rice huskand sawdust,among which combustible index?5.903 × 10-6 K-2min-1?and comprehensive combustion characteristic index(7.55 × 10-9 K-3min-2)of 1-level bio-oil from sawdust were the minimum.For 2-level bio-oil,combustion performance of rice husk was relatively preferable.Burnout characteristics index of overall samples had slight difference.Comprehensive combustion characteristic index of bio-oil samples obtained by fractional condensation were significantly superior than the raw material.?5?The influence of synthetic non-condensable gas generated in pyrolysis process and CO2 on condensation characteristics of simulant bio-oil.When the proportion of non-condensable gas in the mixture was constant,local heat flux density and convective heat transfer coefficient decreased with axial distance of condensing pipeline increasing.With the increase of noncondensable gas content in the mixture,local heat flux density and heat transfer coefficient decreased,and the proportion of non-condensable gas in the mixture has significant influence on the condensation performance.Taken synthetic pyrolytic gas as non-condensable gas,ahead of0.35 m axial distance of concentration pipe,local convective heat transfer coefficient significantly decreased with the concentration of non-condensable gas increasing.Taken CO2 as noncondensable gas,ahead of 0.25 m axial distance of concentration pipe,local convective heat transfer coefficient significantly decreased with the concentration of non-condensable gas increasing,then the coefficient was tend to stable on a very low level.Compared the experimental results with the conclusions of fractional condensation experiment,the remarkable influence of non-condensable gas on fractional condensation was justified further,which provides reference for discussing condensation characteristics of pyrolysis volatiles and designing efficient fractional condenser. |
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